Movement in Maxillary Third Molar Resulting in Open Proximal Contact Between First & Second Molar: A Case report

 

Aiman Sheikh1                         BDS

Farhan Raza Khan2                 BDS, MS, PhD, MCPS, FCPS

ABSTRACT:

 Proximal contact area is the part of the tooth which touches the adjacent tooth in the same arch. Untreated open proximal contact between posterior teeth is very cumbersome for the patient as it allows food stagnation between teeth leading to caries and crestal bone loss. Dental caries and periodontal disease are the common cause of open contacts between posterior teeth. This report demonstrates an unusual cause of bilateral open proximal contacts i.e. movement in the maxillary third molars. Third molars sometimes exert unwanted force at the radicular part of the adjacent second molars which result in an orthodontic tipping movement of the second molar in the distal direction. This leads to creation of an open contact distal to the first molar. The present case was managed with the extraction of the third molars followed by direct amalgam restorations in the first and second molars. At one-year follow up, the patient remained asymptomatic.

KEY WORDS: Proximal contacts; tooth movement: impacted teeth

HOW TO CITE: Sheikh A, Khan FR. Movement in Maxillary Third Molar Resulting in Open Proximal Contact Between First & Second Molar: A Case report. J Pak Dent Assoc 2018;27(1):43-45.

DOI: https://doi.org/10.25301/JPDA.271.43

Received: 17 December 2017, Accepted: 17 January 2018

INTRODUCTION

Proximal contact area is the part of the tooth which touches the adjacent tooth in the same arch.1 Their function is to maintain normal mesio-distal relationship of teeth and to preserve the stability and integrity of the dental arch. An anatomically correct proximal contact allows normal healthy interdental papilla to fill in the interdental space, protects the interproximal tissues from periodontal disease and prevents food impaction.2,3 An open proximal contact is a condition where adjacent teeth fail to make correct contact with each other. It may be due to a non-ideal occlusion, tooth loss, faulty restoration, drifting of teeth, oral diseases or oral habits. An untreated open contact area initially causes discomfort due to impaction of food and accumulation of bacterial plaque and eventually leads to proximal caries (class II carious lesions on proximal surfaces) and periodontal disease resulting from interdental crestal bone loss. Therefore, reproduction of the contact size and location of the contact area to imitate the natural dentition is essential for the success of the operative dental procedure. Proximal restorations that have correct anatomy, contour, location and configuration are imperative to maintain the adjacent soft tissues from future insults. Inability of dentist to develop the physiologic contact area and contours in the proximal restorations results in the failure of restorative work.4
Third molar is the most commonly impacted tooth in the human dentition. Completely Impacted or partially impacted third molar can result in pain, damage to the other teeth, malocclusion.5 But in the present case, third molars have resulted in the tipping movement of the adjacent second molar, creating an open proximal contact between first and second molars.

CASE REPORT

A 30 year-old male presented for consultation at the Operative Dentistry clinic of the Aga Khan University Hospital, Karachi in 2016 with the chief complaint of bilateral food impaction between maxillary first and second molars (figure 1 a and b). The patient’s medical history was noncontributory. Clinical examination revealed bilateral open proximal contacts between first and second molars but no caries. On probing with a University of Michigan graduated periodontal probe (Williams’s probe), the probing depth for both teeth was within normal limits. The peri-apical radiographs were taken which revealed erupted maxillary third molars. Panoramic radiograph was then offered which showed that the crowns of both partially impacted maxillary third molars were pressing on the second molars and causing

Fig 1a & b. Pre-operative Intra-oral photograph of right and left sides

 

Fig 2. Pre operative Radiograph

an unwanted tipping movement as a result of which the crown of second molars had move distally; creating an open contact between 1st and 2nd molars (figure 2). Diagnosis of unwanted orthodontic movement by maxillary 3rd molar leading to proximal open contact between first and second molar was made. The patient was informed of the diagnosis and treatment plan. Both maxillary third molar teeth were extracted within an interval of two weeks under local infiltration anesthesia employing two cartridges of 1.8ml each of 2% Xylestesin (Lidocaine) with 1:80,000 epinephrine (3M-ESPE, USA) in each exodontia. Then a waiting period of two months was observed to explore if the second molars would spontaneously drift back to their actual position.
However, no change was observed, therefore, an operative management was planned. A class II cavity preparation was made using high and low speed dental drills in the mesial surface of maxillary 2nd molars and distal aspect of the maxillary 1st molars that were later refined with hand

Fig 3. Post op Intra-oral photograph

 

Fig 4a & b. Post-operative radiograph of right and left sides

instruments. Two circumferential Automatrix bands (Dentsply, USA) were simultaneously placed on the adjacent molars secured with wooden wedges. Admixed particles amalgam restoration (Tytin FC, Kerr Dental, USA) was in the cavity preparations using standard incremental method (figure 3). The patient was kept on regular follow-ups. At one year follow-up, the patient remained asymptomatic. Both the proximal contacts were free of food stagnation and patient could easily pass in the floss with a little physiologic resistance. Figures 4 a & b show the periapical radiographs at one year follow-up.

DISCUSSION

Food impaction between teeth is a prevalent clinical condition among all populations.6 Food stagnates in the interproximal space, mainly by a vertical plunger effect of the antagonist tooth from the occlusal direction.7 Alternatively, food particles also enter in the proximal space from the lateral (horizontal) side owing to receded interdental papillae.
In clinical practice, an open proximal contact in absence of caries or periodontal disease is observed when the adjacent marginal ridges heights are uneven and the opposing tooth centric holding cusp plunges the fibrous food particles between the teeth in question.8
Food impaction from vertical aspect is mostly iatrogenic in nature caused by an improper Class II restoration or fabrication of a faulty indirect restoration.9
In our case, patient’s periodontal status was satisfactory and he had no restorations placed in the posterior teeth. After clinical and radiographic investigation, we inferred that the mesio-buccal cusp of the third molars have caused distal tipping movement; creating an open proximal contact between first and second molar. After elimination of the cause of the open contact i.e. the extraction of right and left maxillary third molars, the possible management options were:

  1. Keep the open proximal area clean by meticulous flossing
  2. Orthodontics to tip back the second molars and resume tight contacts
  3. Place direct restorations in one or two teeth
  4. Place indirect restorations such as crowns Flossing cannot be considered as an ultimate treatment option as compliance is a challenge. Orthodontic treatment was not only time consuming but appeared as an overtreatment for a localized problem. Crowns were not preferred as it involved substantial tooth substance cutting and potentially detrimental to vitality of teeth. Therefore, we opted for directly placed Class II amalgam restorations in teeth # 16, 17 and 26, 27. It was not only cost-effective but time saving with predictable outcome. Amalgam was preferred over composite restorations because it provides tighter proximal contacts with less wear, decreased marginal leakage and extended longevity.10,11 The patient was satisfied with the restorations as his food catching problem was predictably resolved in a single visit.

CONFLICT OF INTEREST

None declared

REFERENCES

  1. Stappert CF, Tarnow DP, Tan JH, Chu SJ. Proximal contact areas of the maxillary anterior dentition. Int J Periodontics Restorative Dent. 2010;30(5):471-7.
  2. Jernberg GR, Bakdash MB, Keenan KM. Relationship between proximal tooth open contacts and periodontal disease. J Periodontol. 1983;54(9):529-33. https://doi.org/10.1902/jop.1983.54.9.529
  3. Allison PJ, Schwartz S. Interproximal contact points and proximal caries in posterior primary teeth. Pediatr Dent. 2003;25(4):334-40.
  4. Khan FR, Umer F, Rahman M. Comparison of proximal contact and contours of premolars restored with composite restoration using circumferential matrix band with and without separation ring: A randomized clinical trial. Int J Prosthodont Restor Dent. 2013;3(1):7-13. https://doi.org/10.5005/jp-journals-10019-1068
  5. Ventä I, Ylipaavalniemi P, Turtola L. Clinical outcome of third molars in adults followed during 18 years. J Oral Maxillofac Surg. 2004;62(2):182-5. https://doi.org/10.1016/j.joms.2003.04.011
  6. Newell DH, John V, Kim SJ. A technique of occlusal adjustment for food impaction in the presence of tight proximal contacts. Oper Dent. 2002;27(1):95-100.
  7. Nagarsekar A, Gaunkar R, Aras M. Knowledge, attitude, and practice of dental professionals regarding the effect and management of food impaction associated with fixed partial denture prostheses:A survey. J Indian Prosthodont Soc. 2016;16(4):372-9.
    https://doi.org/10.4103/0972-4052.191286
  8. Gokhale S, Padmaja K. Food Impaction after Crown Placements. J Adv Med Dent Scie Res. 2014;2(4):162-5.
  9. Khairnar M. Classification of food impaction-revisited and its management. Indian J Dent Adv. 2013; 5(1):1113-
    9.
  10. El-Badrawy WA, Leung BW, El-Mowafy O, Rubo JH, Rubo MH. Evaluation of proximal contacts of posterior composite restorations with 4 placement techniques. J Can Dent Assoc. 2003;69(3):162-7.
  11. Sachdeo A1, Gray GB, Sulieman MA, Jagger DC. Comparison of wear and clinical performance between amalgam, composite and open sandwich restorations: 2- year results. Eur J Prosthodont Restor Dent. 2004;12(1):15- 20

1. Karachi Medical & Dental College, Karachi, Pakistan.
2. Associate Professor & Head of Dental Section, Aga Khan University Hospital, Karachi, Pakistan.
Corresponding author: “Dr. Farhan Raza Khan ” < farhan.raza@aku.edu >

Movement in Maxillary Third Molar Resulting in Open Proximal Contact Between First & Second Molar: A Case report

 

Aiman Sheikh                         BDS

Farhan Raza Khan                 BDS, MS, PhD, MCPS, FCPS

ABSTRACT:

 Proximal contact area is the part of the tooth which touches the adjacent tooth in the same arch. Untreated open proximal contact between posterior teeth is very cumbersome for the patient as it allows food stagnation between teeth leading to caries and crestal bone loss. Dental caries and periodontal disease are the common cause of open contacts between posterior teeth. This report demonstrates an unusual cause of bilateral open proximal contacts i.e. movement in the maxillary third molars. Third molars sometimes exert unwanted force at the radicular part of the adjacent second molars which result in an orthodontic tipping movement of the second molar in the distal direction. This leads to creation of an open contact distal to the first molar. The present case was managed with the extraction of the third molars followed by direct amalgam restorations in the first and second molars. At one-year follow up, the patient remained asymptomatic.

KEY WORDS: Proximal contacts; tooth movement: impacted teeth

HOW TO CITE: Sheikh A, Khan FR. Movement in Maxillary Third Molar Resulting in Open Proximal Contact Between First & Second Molar: A Case report. J Pak Dent Assoc 2018;27(1):43-45.

DOI: https://doi.org/10.25301/JPDA.271.43

Received: 17 December 2017, Accepted: 17 January 2018

Effect of Thyroid Hormone on the Histology of Rat Submandibular Salivary Gland During Postnatal Development

Shaher Bano1                         BDS

Sarah Ghafoor2                     BDS, PhD

Nadia Naseem3                     MBBS, PhD

OBJECTIVE:

 Salivary glands pass through various stages of prenatal and postnatal development. This process is a highly regulated event governed by signaling molecules, growth factors and hormones. Submandibular salivary gland is an excellent model to study salivary gland morphogenesis. It has been reported that alternations in endocrine hormones can affect morphological and functional states of salivary gland formation and for this purpose the current study was designed to investigate the effects of exogenous administration of T3 on the histology of the submandibular salivary gland during early postnatal development.

METHODOLOGY: Following ethical approval, twenty four healthy Wister rats were obtained. Twelve were taken at the age of three weeks and divided into control (A1) and experimental (B1) groups. Remaining twelve were taken at the age of seven weeks and divided into control (A2) and experimental (B2) groups. The experimental animals were administered 0.5 mg/kg body weight of T3 while controls were given normal saline. The animals of group A1 and B1 were sacrificed at week 5 and those of group A2 and B2 at week nine. The submandibular glands were dissected out and their morphological structure was observed. The combined weight and volume of submandibular and sublingual gland was taken. Hematoxylin and Eosin staining was performed to assess any histological changes in the parenchyma and stromal components of the submandibular salivary gland.

RESULTS: No significant gross and histological changes in parenchyma and stroma of submandibular salivary gland tissue were observed in control and experimental groups at week five and week nine. No statistically significant difference was found in the combined weight and volume of submandibular and sublingual glands through the independent sample t-test.

CONCLUSION: Exogenous administration of T3 at a lower dose did not cause significant changes in the postnatal development of the submandibular salivary gland.

KEY WORDS:  Submandibular salivary gland, development, thyroid hormone, postnatal

HOW TO CITE: Bano S, Ghafoor S, Naseem N. Effect of thyroid hormone on the histology of rat submandibular salivary gland during postnatal development. J Pak Dent Assoc 2018;27(1):37-42.

DOI: 2https://doi.org/10.25301/JPDA.271.37

Received: 11 January 2018, Accepted: 17 January 2018

INTRODUCTION

Salivary glands are exocrine glands that produce saliva. There are three pairs of major salivary glands and a large number of minor salivary glands that are present in various parts of the oral cavity.1 Two important structural components of salivary glands include the secretory portion (parenchyma) and the connective tissue (stroma).2 Salivary glands consist of a connective tissue capsule that surrounds the parenchyma and divides it into lobes and lobules. The parenchyma consists of secretory end-pieces known as the acini and a ductal system. The acini are more abundant as compared to the salivary ducts which include the intercalated, striated and excretory ducts.3

Unlike humans, in rats, in addition to these ducts, the ductal system also includes the granular convoluted tubules (GCT’s).4 GTC’s are an extension of the striated ducts. They are absent at birth5 and begin to develop as budding off from striated ducts during the second and third month of postnatal life.6 They lie between the intercalated and striated ducts.7,8 The granular convoluted tubules are named as they are highly convoluted due to the presence of a large number of secretary granules. Previous studies have shown that these granules contain a large number of biologically active peptides including nerve growth factor (NGF), hepatic growth factor (HGF), epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-α).5,9 These growth factors play essential roles in development proliferation, differentiation and functions of the salivary glands. The granular convoluted tubules are present only in the rat submandibular gland (SMG)10 but they can be induced in the parotid gland by administration of thyroid hormone11 as their development is under hormonal control.5 In rats, submandibular gland is the largest salivary gland12 and is used as an excellent model to study various aspects of growth and development of salivary glands.4
Thyroid hormone is a trophic hormone that is essential for growth and differentiation.13 It promotes postnatal growth and development of organisms.14,15 Previous studies have shown that development of rat submandibular glands is affected by many endocrine hormones like androgens, glucocorticoids, estrogens, progesterones, and corticosteroids including thyroid hormone.6,13,16,17
The metabolically active form of thyroid hormone is 3, 3, 5 tri-iodo-thyronine (T3) which induces cyto-differentiation of GCT’s precociously thus affecting postnatal development of submandibular salivary glands.5 As the rodent salivary glands complete their development postnatally, any alterations in hormones such as T3 can also have an influence on the normal completion of salivary gland development.18 Keeping in view the possible hormonal changes induced by T3 on differentiation of salivary GCT’s,5 the present study was designed to investigate the effects of exogenous administration of thyroid hormone on the histology of submandibular gland during postnatal development.

METHODOLOGY

Ethical Approval

This experimental study was conducted at the University of Health Sciences Lahore following ethical approval from the Institutional ethical review committee of the University of Health Sciences Lahore and all the experiments were conducted as per the guidelines set by the committee.

Calculation of sample size

The sample size was calculated by the following formula keeping the power of study equal to 90% and level of significance equal to 5%.10 Where, Z1-β at desired power of 90% = 1.28, Z1-α/2 at desired level of significance of 5%

=1.96, estimated mean of group A, µ1 = 13 and, estimated mean of group B, µ2 = 4, mean Difference (µ1- µ2) = 9, standard deviation of Group A (σ1) = 2, standard deviation of group B (σ2) = 1, calculated sample size in each group = 1. The sample size came out as one in each group however it was increased to six in each group according to previous published literature.8

Preparation of animals

A total of twenty four healthy male Wister (Rattus norvegicus) were obtained through non-purposive sampling from the colony maintained at the Experimental Research Laboratory at the University of Health Sciences, Lahore. The pups were reared from birth and were weaned off at day twenty one of age. The rats of age three weeks having weight approximately 50 grams and seven weeks having weight approximately 201-225 grams were used in this study. All animals were housed in a temperature controlled room (23± 2°C) and humidity (50±5%) was maintained. In order to maintain a stable biological rhythm, constant cycles of having 12-h light and 12-h darkness were applied. The animals
received standard rat diet and water ad libitum and were allowed to acclimatize for one week before starting the experiment. Female or pregnant rats and rats suffering from any illness were excluded from the study. Group allocation was done through balloting technique. Out of twenty four rats, twelve were taken at the age of three weeks and divided into control (A1) and experimental (B1) groups. Remaining twelve were taken at the age of seven weeks and divided into control (A2) and experimental (B2) groups. So each group comprised of six animals.

Administration of thyroid hormone

Freshly prepared 3, 3, 5 tri-iodo-thyronine (T3) (Sigma chemicals) at 0.3mg/ml in 0.005N NaOH in 0.9% NaCl was used. The dose for mice was 1mg/kg body weight11 which was adjusted as 0.5mg/kg body weight for rats 19 that was given subcutaneously on alternate basis for fourteen days.

Sample collection

The animals of group A1 and B1 were sacrificed at week five and those of group A2 and B2 at week nine. The animal to be sacrificed was transferred to a plastic jar having a cotton wool soaked in chloroform to euthanize it. The exposed submandibular glands were carefully dissected out, washed with normal saline, weighed together with the sublingual gland for analysis of combined weight and volume.

Tissue processing and histological staining

All the tissues were subjected to the automatic tissue processor (Microm STP-120) and passed through Xylene and graded concentration of Ethanol at 70%, 90% and 100%. After dehydration, paraffin-embedded wax blocks were obtained by placing in embedding center (Tissue Tek TECTM, Sakura). Sections were cut at a thickness of 6µm by rotary microtome (Leica RM 2125RT) and placed on the slides for Hematoxylin and Eosin staining. The slides were immersed twice in Xylene for five minutes. Rehydration was done by immersing the slides in 100% 90%, 70% Ethanol, washed with tap water and dipped in Hematoxylin solution for five minutes. This was followed by immersion in 1% acid alcohol and 0.2% ammonia water, until the desired blue color was obtained. The slides were then immersed in 1% eosin for few minutes and rehydrated by passing through graded series of 70%, 80%, 90% and 100% ethanol and xylene.20 They were dried at room temperature and mounted with DPX and cover-slipped. The stained sectioned were visualized under Olympus microscope (BX51TF) with camera (Infinity-1) under 10X and 40x magnification to observe any histological changes in response to administration of T3.

Statistical analysis

Statistical analysis was conducted using Statistical Package for Social Sciences Version 20 (SPSS-20). Comparison of difference between mean combined weight and volume of the salivary glands was done through the independent sample test. A p-value of <0.05 was taken as
statistically significant.

RESULTS

Macroscopic Examination of Submandibular gland The gross examination of submandibular (SMG) of both the control (A1, A2) and experimental groups (B1, B2)

Table No.1: Comparison the mean of combined weight and volume of SMG and SLG of control and experimental groups

The mean difference of combined weight and volumes of SMG (submandibular gland) and SLG (Sublingual gland) between both the control and experimental groups was found to be almost similar. Independent sample t-test suggested that there is a statistically non-significant difference between the combined weight and volume of SMG and SLG of both the control (A1 and A2) and experimental (B1 and B2).

showed that the glands were pink in color, smooth in texture and roughly ovoid in shape. The lobes of the glands were clearly visible and they were enclosed in a connective tissue capsule. There was no gross abnormality noted in all four groups.
Combined weight and volume of the salivary glands In the present study, combined weight of submandibular and sublingual glands was taken as both the glands were placed in the same connective tissue. No significant difference in the combined weight and volume of the glands was noted after T3 administration (Table 1)

Histological Examination of Submandibular salivary gland (SMG)

The histological analysis of submandibular glands of both the control and experimental (A1, A2) (B1, B2) groups was done at week five and week nine. The glands of both the experimental groups showed similar structure to that of control and hence are described together with details of parenchymal and stromal components.

a) Parenchymal components of SMG of control and experimental groups at week 5 and 9

The parenchymal components were categorized into lobe architecture, nature and nuclei of acini, ductal epithelium and nuclei and myoepithelial cells. The architecture of lobules of all submandibular salivary glands was completely preserved. Each lobe was observed having acini and completely surrounded by the connective tissue capsule (Fig 1). The serous acini were almost equal in size with pyramidal shaped cells and dense granular cytoplasm was observed.

Fig 1: Photomicrograph of Hematoxylin and Eosin stained histological section of SMG showing lobules with preserved architecture containing serous acini and ducts under 10x magnifications

They appeared to have a regular pattern. The serous acini had a rounded nucleus that was normochromatic (Fig 2). The striated and excretory ducts had simple columnar and pseudostratified columnar epithelium.

Fig 2: Photomicrograph of Hematoxylin and Eosin stained section of SMG showing pyramidal shaped cells of serous acini with rounded, normochromatic nuclei (yellow arrow), striated duct having simple columnar epithelium (blue arrow), a blood vessel having blood cells (green arrow) under 40x magnification.

The striated ducts were more numerous as compared to excretory ducts. The nuclei of various ducts appeared round or ovoid in shape and were normochromatic (Fig 2, 3). Myoepithelial cells appeared as flattened cells associated with the basement membrane of the serous acini. No difference in morphological histology was observed between both controls and experimental groups.

b) Stromal components of SMG of control and experimentalgroups at week 5 and 9

The stromal components comprised of connective tissue, adipose cells and the blood vessels. The inter-lobular (between two lobules) and intra-lobular (within the lobules) connective tissue was found to be normal and showed nuclei of the fibroblasts and connective tissue fibers.

Fig 3: Photomicrograph of SMG illustrating an excretory duct having a large lumen with pseudostratified columnar epithelium and goblet cells (red arrow), intra-lobular connective tissue with fibroblasts (blue arrow), blood vessel with blood cells (green arrow) under 40x magnification.
Fig 4: Photomicrograph of SMG showing adipocytes (black arrow) with empty appearing cytoplasm and nucleus pushed to one side giving signet ring appearance under 40x magnification.

No inflammatory changes were observed in both groups (Fig 3). Blood vessels associated with the ducts within the lobules were visible (Fig 2). They were also present between the lobes associated with the excretory ducts. They appeared normal, lined by single layer of endothelium and contained red blood cells in them (Fig 3). The clusters of adipocytes with clear cytoplasm having signet ring appearance were also observed in the submandibular salivary glands of both control and experimental groups and were found to be similar in appearance in both groups (Fig 4).

DISCUSSION

Submandibular gland is used as an excellent model to study various aspects of growth and development of salivary glands.4
How exogenous administration of T3 affects the morphological or histological development of rat SMG is currently unknown and may provide valuable insights into conditions of hypo- or hyperthyroidism. It has been reported that to function as a mature gland, the rat salivary glands complete their morphological development postnatally by 7 to 10 weeks 6,21 and during this period alteration in the
hormones such as thyroid, androgens and growth hormones also have an influence on the normal completion of salivary gland development.18 The gross examination of submandibular salivary glands showed no morphological changes in postnatal
development. Thyroid hormone administration to the animals did not affect the weight and volume of both the salivary glands suggesting that exogenous T3 administration did not have any significant morphological and histological changes in the submandibular salivary glands of both control and experimental animals. These findings are similar to another study on the parotid gland where the parenchymal and stromal elements of both the control and experimental groups were also found to be normal when thyroid hormone was administered at low dosage.22 This may also be possible as T3 was administered at a dose that was on alternate days and was kept within the physiological limits so it did not lead to any adverse effects. It may be interesting to investigate with higher doses of T3 and observe cytological changes. The GCT’s of submandibular gland are associated with production of various growth factors such as epidermal growth factor (EGF), nerve growth factor (NGF) and transforming growth factor alpha (TGF-α).5,9 These growth factors play essential roles during developmental processes
exhibited in salivary glands such as proliferation, differentiation and functions.10 We could not find any morphological differences in histology of SMG in both the experimental groups. It is likely that following T3 administration, compensatory regulation provided by other
growth factors involved in salivary gland development such as EGF signaling may also overcome the negative effects of exogenous T3 administration leading to an overall normal development of submandibular salivary glands.23

CONCLUSIONS

Exogenous administration of T3 at a dose of 0.5 mg/ kg did not cause any significant changes in the histology of the submandibular salivary gland.

CONFLICT OF INTEREST

The authors declare no conflict of interest

ACKNOWLEDGEMENTS

We would like to thank the animal care staff of the Experimental Research Laboratory at the University of Health Sciences Lahore (UHS) for their facilitation throughout study. We would also like to thank the Library department (UHS) regarding access to relevant books and publications. We thank the Higher Education Commission of Pakistan (HEC) for allowing our university access to the e-Library.

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  20. Harris H.F. On the rapid conversion of hematoxylin into haematein in staining reactions. J Appl Micros Lab Methods. 1900; 3(3): 777.
  21. Young WG, Ramirez-Ya-ez GO, Daley TJ, Smid JR, Coshigano KT, Kopchick JJ, Waters MJ. Growth hormone and epidermal growth factor in salivary glands of giant and dwarf transgenic mice. J Histochem Cytochem. 2004; 52(9):1191-7. https://doi.org/10.1369/jhc.4A6294.2004
  22. Ikeda R, Aiyama S, Redman RS. Effects of exogenous thyroid hormone on the postnatal morphogenesis of the rat parotid gland. Anat Rec. 2008; 291(1):94-104. https://doi.org/10.1002/ar.20620
  23. Kashimata, M. and Gresik, E.W. Epidermal growth factor system is a physiological regulator of development of the mouse fetal submandibular gland and regulates expression of the α6-integrin subunit. Dev. Dynam. 1997; 208(2): 149- 161. https://doi.org/10.1002/(SICI)10970177(199702)208:2<1 49::AID-AJA2>3.0.CO;2-I

1. M. Phil Scholar, Department of Oral Biology University of Health Sciences Lahore, Pakistan.
2. Assistant Professor. Department of Oral Biology University of Health Sciences Lahore, Pakistan.
3. Assistant Professor. Department of Morbid Anatomy & Histopathology, University of Health Sciences Lahore, Pakistan.
Corresponding author: “Dr. Sarah Ghafoor ” < sarahghafoor@uhs.edu.pk >

Effect of Thyroid Hormone on the Histology of Rat Submandibular Salivary Gland During Postnatal Development

Shaher Bano                         BDS

Sarah Ghafoor                    BDS, PhD

Nadia Naseem                     MBBS, PhD

OBJECTIVE:

 Salivary glands pass through various stages of prenatal and postnatal development. This process is a highly regulated event governed by signaling molecules, growth factors and hormones. Submandibular salivary gland is an excellent model to study salivary gland morphogenesis. It has been reported that alternations in endocrine hormones can affect morphological and functional states of salivary gland formation and for this purpose the current study was designed to investigate the effects of exogenous administration of T3 on the histology of the submandibular salivary gland during early postnatal development.

METHODOLOGY: Following ethical approval, twenty four healthy Wister rats were obtained. Twelve were taken at the age of three weeks and divided into control (A1) and experimental (B1) groups. Remaining twelve were taken at the age of seven weeks and divided into control (A2) and experimental (B2) groups. The experimental animals were administered 0.5 mg/kg body weight of T3 while controls were given normal saline. The animals of group A1 and B1 were sacrificed at week 5 and those of group A2 and B2 at week nine. The submandibular glands were dissected out and their morphological structure was observed. The combined weight and volume of submandibular and sublingual gland was taken. Hematoxylin and Eosin staining was performed to assess any histological changes in the parenchyma and stromal components of the submandibular salivary gland.

RESULTS: No significant gross and histological changes in parenchyma and stroma of submandibular salivary gland tissue were observed in control and experimental groups at week five and week nine. No statistically significant difference was found in the combined weight and volume of submandibular and sublingual glands through the independent sample t-test.

CONCLUSION: Exogenous administration of T3 at a lower dose did not cause significant changes in the postnatal development of the submandibular salivary gland.

KEY WORDS:  Submandibular salivary gland, development, thyroid hormone, postnatal

HOW TO CITE: Bano S, Ghafoor S, Naseem N. Effect of thyroid hormone on the histology of rat submandibular salivary gland during postnatal development. J Pak Dent Assoc 2018;27(1):37-42.

DOI: 2https://doi.org/10.25301/JPDA.271.37

Received: 11 January 2018, Accepted: 17 January 2018

Comparison of Surface Conditioning Protocols on The Shear Bond Strength of Metal Brackets Bonded To Amalgam Surface

Muhammad Azeem1            BDS, FCPS

Arfan Ul Haq2                       BDS, FCPS, MDS, MCPS

Samina Qadir3                     BDS, MDS

OBJECTIVE:

Orthodontists more often comes across amalgam restoration as a surface to bond brackets. The objective of current study was to compare the mean shear bond strength of orthodontic metal brackets bonded on sandblasted versus diamond bur roughened amalgam surfaces.

METHODOLOGY: Current In-vitro, comparative study was conducted at Orthodontic department of Faisalabad medical university from 17.2.2017 to 17.8.2017. Sixty extracted human maxillary molars were included in the study as per inclusion criteria. They were randomly divided into two groups. In group-A, metal brackets were bonded to amalgam using sandblasting with 50 ?m alumina particles. In group-B, brackets were bonded after roughening the amalgam surface with diamond bur. Shear bond strength (SB) was measured and compared using universal testing machine, in both the groups.

RESULTS: SB of metal brackets bonded with sandblasting (17.05±5.9 MPa) was significantly higher than diamond bur roughened group (11.08±4.0 MPa).

CONCLUSION: Amalgam surface treatment with sandblasting increased the shear bond strength of metal orthodontic brackets significantly higher than the diamond bur roughening.

KEY WORDS: Brackets; Amalgam; Sandblast; Shear bond strength.

HOW TO CITE: Azeem M, Haq AU, Qadir S. Comparison of Surface Conditioning Protocols on The Shear Bond Strength of Metal Brackets Bonded To Amalgam Surface. J Pak Dent Assoc 2018;27(1):32-36.

DOI: https://doi.org/10.25301/JPDA.271.32

Received: 16 October, 2017, Accepted: 06 December, 2017

INTRODUCTION

One third of the children population needs some sort of orthodontic treatment.1,2 The recent advancements in the area of orthodontic bonding have suggested the replacement of molar banding with bonding, as banding deteriorates the periodontal status of dentition.3,4 Successful orthodontic treatment should not only corrects the malocclusion but should also keep the attachment apparatus sound and healthy.5
Many patients undergoing orthodontic therapy have large amalgam restorations on their posterior teeth as amalgams are still preferred over composite restorations in teeth having large carious defects.6
This clinical predicament demand requirement of different techniques to improve the bonding between amalgam restoration and bracket surface by special surface preparation methods such as; sandblasting, diamond bur roughening, use of intermediate resins, and intraoral laser.7
Results from previous study showed that amalgam surfaces treated with laser produced higher shear bond strength (SB) compared to the sandblasting technique.8 Compared to the green stone, sandblasting resulted in 2- fold increase in the SB.9 4-META used as primer is also
found to increase the SB closer to etched enamel teeth with amalgam surfaces roughened with air-borne particle abrasion.10
Sandblasting is used successfully to bond metal brackets on porcelain surfaces being safer than hydrofluoric acid etching.11 Resin composite masking with sandblasting of amalgam surface, was found to provide the increased SB with value of 15.54/6.41 MPa. Bur roughened amalgam surface showed SB of 15.26/3.90 MPa.10 Insignificant difference was found when SB between sandblasted and diamond rough amalgam bonding surfaces were compared.12 In another study SB for diamond bur roughened group was 6.44 ± 0.12 MPa and for sandblasted group 6.01 ± 0.02 MPa.13
The variability in literature suggests the need to determine the best surface treatment method for amalgam surfaces to get maximum SB while orthodontic bonding.12 Results of present study will guide the orthodontists for successful orthodontic bonding with lesser bond failures on amalgam surfaces. Therefore the objective of our study was to compare the mean shear bond strength of metal brackets bonded on sandblasted versus diamond bur roughened amalgam surfaces. Our hypothesis was that the mean SB on amalgam surface is significantly higher with sand blasting than diamond bur roughening.

METHODOLOGY

Current In-vitro, comparative study was conducted after ethical board approval (110-D/2017) at Orthodontic department of Faisalabad medical university from 17.2.2017 to 17.8.2017. Sample size of 60 was estimated using 95% confidence level, 80% power of test.13
Selection criteria consisted of: (1): Extracted maxillary posteriors because of orthodontic reasons,(2): Intact buccal surfaces,(3): Extracted teeth with fracture, caries, enamel hypoplasia, etc were excluded.
According to the selection criteria, 60 extracted teeth were included from the Exodontia department and were kept in 0.1% (wt/vol) thymol solution, at room temperature for 24 h. Class V buccal amalgam restorations with axial wall depth of 2.0 mm, were prepared by one expert operator on all the selected premolar teeth. The shape of cavity was rectangular and preparations were extended beyond the dimensions of the orthodontic attachments. To increase the retention, undercuts were placed at the coronal and gingival walls of class V cavity with a No.35 diamond bur. The cavities were filled with the non- gamma 2 amalgam (Nordiska Dental AB, Angelholm, Sweden) and hand burnished. For standardization, each amalgam surface was polished with a green stone, after allowing amalgam 24 hours to set. Mixing time, condensation time, and force were carefully standardized to rule out any amalgam variation in all the samples. After polishing but before bonding brackets, all amalgam surfaces were cleaned with distilled water ultrasonically to dislodge any impurities and dried with the oil-free air.
Teeth were randomly allocated into the 2 groups following random number table method. Group A 30 teeth were sandblasted with 50 µm alumina particles at right angle from the distance of 10 mm for 3 s at the pressure of 90 psi using the microetcher model II (Danville Engenieering) and Group B 30 teeth were diamond bur roughened with medium grit (100 µm) cylindrical diamond bur ( Lemgo, Germany)
with their shafts parallel to the amalgam surfaces, in a highspeed hand piece at the speed of 40,000 rpm at the force of 1 N, under the water spray. In the present study, the rpm were calibrated with an optical tachometer mounted on the high speed hand piece head, while the bur force was standardized using an electric balance, adjusted using sash weights before each experiment. Metal brackets (Discovery, Dentaurum, Germany) with bracket base area of 10.3 mm2 were bonded as per manufacturer’s directions to each tooth buccal amalgam surface with adhesive (Transbond XT, 3M Unitek, Monrovia, USA) and 4-META metal primer, at a room temperature. Samples were stored in normal saline for 72 h at 37°C temperature. All amalgam surfaces were thermocycled (Thermocycler, Dorsa, Iran) 1000 cycles, between 5°C and 55°C in each bath, with an overall dwelling time of 30 s and transfer time of 10 s at room temperature.
The samples were removed and embedded in type III gypsum in a PVC ring. The mounted specimens were kept wet while gypsum was setting and then placed in a gypsumsaturated water bath at 37°C for 60 hours. The samples were removed from wet bath and mounted in a custom made holding jig fitted with the brackets positioned vertically.
The bonded teeth were then tested on a universal testing machine (Instron 5544, Instron Corp) at a cross head speed of 1mm/min and 50 kg load/tension cell. The force was placed to the bonding site while the bracket base was parallel to the direction of force. A mounted chisel-edge plunger with tip dimension of 1.0 mm was positioned so that the leading edge of the testing machine was aimed at the toothresin junction before being brought into the contact. The SB was measured in Newton’s and then converted in MPa using the formula: Shear strength (MPa) = Debonding force (N)/bracket base area (mm2) and 1 N/mm2. 1 2 Data collected was analyzed by using computer software SPSS version 20.0. The SB was presented in the form of mean, standard deviation and t-test was applied for comparison of SB between the two groups. Statistical significance was defined at <0.05.

RESULTS

The mean and standard deviation values for the SB of sandblasted and diamond bur roughened group are presented in the table 1 and 2.

Table 1: Descriptive statistics of shear bond strength of sandblasted group

The t-test comparison indicates that there was a significant difference between the two groups (P<0.05). The sandblasted group was having significantly higher SB (17.05±5.98 MPa) than the diamond bur roughened (11.08±4.02 MPa) group (Table 3)

Table 2: Descriptive statistics of shear bond strength of diamond bur roughened group
TABLE 3: Comparison of both the groups

DISCUSSION

This study was conducted to compare the shear bond strength of metal brackets on bonding to the amalgam surface treated with sandblasting or diamond bur roughening. The hypothesis was accepted as the SB of metal brackets bonded with sandblasting (17.0 MPa) was significantly higher than the diamond bur roughening (11.0 MPa). This can be linked to the fact that sandblasting produced higher surface roughness
than the diamond bur roughening and thus resulted in increased bonding surface area by creating the 3-dimensional micro-porous structure. The other mechanism behind increased SB obtained with sandblasting is the removal of unfavourable surface oxides and contaminants from the amalgam by sandblaster thus resulting in increased bonding surface area and mechanical retention of orthodontic brackets having adhesive.
Amalgam surfaces are treated with diamond bur roughening and sandblasting techniques to enhance the SB between metal brackets and amalgam surface. 14 Bourke et al. also suggested the use of 9.6% for 2 minutes hydrofluoric acid to increase the bond between porcelain and stainless steel bracket but use of such acids are not recommended for the amalgam surfaces. 15
The SB results in our study is comparable to the study by Machado et al.16 with sandblasted group showing 16.3 MPa of mean SB and diamond bur roughening showing 10.02 MPa, similarly in our study the sandblasted group was having 17.0 MPa and diamond bur roughened showed 11.0 MPa. However, SB in our study was measured through metal brackets rather than directly testing the amalgam-composite interface. Results are also in accordance with findings of other studies, where sandblasting was found to be superior method for surface treatment of amalgam surfaces when compared with other groups. 9,17
Our results are in contrast with Zachrisson et al, who suggested that SB on bonding to amalgam surface with sandblasting is insignificant and 6.8 MPa – 11 MPa less than the controls 16 MPa while in our study the sandblasted group was having SB of 17.0 MPa and diamond bur roughened showed SB of 11.0 MPa. 18 Jessup19in 1998 concluded that diamond bur roughening yielded more SB on repaired amalgam surfaces. The study results are opposed to our results probably different because of the primer that is used in current study that is 4-Meta metal primer. Lingual buttons bonded to the amalgam surfaces also found to yield the higher SB with several resin /conditioner combinations and sandblasting was also done prior to bonding lingual attachments. 20 These results are in agreement with current study as sandblasting and use of metal primer adhesive yielded positive effects. In 1981, Tanaka21 suggested use of 4-Meta metal primer for bonding adhesive resin to nickel chromium surface to produce superior SB, similarly in our study 4-Meta was used as a metal primer to bond brackets to amalgam surface to yield clinically predictable SB. In 2010, Katrina concluded that water storage has deleterious effects on mean values of shear bond strength.22
The samples in our study were stored in water after bonding for 72 hours that might have increased the results obtained in our study.
Although sandblasting got superior SB, but its disadvantages are high chair side cost, need proper isolation and training and difficult accessibility. 23,24 On the other hand, diamond bur is easily available in practice but got inferior SB values as inferred and supported by the results of current study.

There are certain shortcomings of present study. Current research compared only the mean shear bond strength of orthodontic metal brackets bonded on sandblasted versus diamond bur roughened amalgam surfaces, but it was also important to know the surface morphology of amalgam restoration in form of its cohesive or adhesive behaviour by using scanning electron microscope. Information about surface roughness produced with sandblasting and with burs is also missing. Furthermore, current study was conducted in-vitro environment and factors like temperature, stress, humidity, acidity and plaque may complicate assessment of best bonding protocol. Future in-vivo studies with larger sample size are suggested.

CONCLUSION

Amalgam surface treatment with sandblasting increased the shear bond strength of metal orthodontic brackets significantly higher than the diamond bur roughening.

CONFLICT OF INTEREST

None to declare.

REFERENCES

  1. Johnson EK, Fields HW, Beck FM, Firestone AR, Rosenstiel SF. Role of facial attractiveness in patients with slight-to-borderline treatment need according to the Aesthetic Component of the Index of Orthodontic Treatment Need as judged by eye tracking. Am J Orthod Dentofac Orthop. 2017;151(2):297-310. https://doi: 10.1016/j.ajodo.2016.06.037.
  2. Chestnutt IG, Burden DJ, Steele JG, Pitts NB, Nuttall NM, Morris AJ. The orthodontic condition of children in the United Kingdom, 2003. British dent J. 2006;200(11):609. https://doi.org/10.1038/sj.bdj.4813640
  3. Agrawal N, Kundu D, Agrawal K, Singhal A. Comparison of longitudinal changes in clinical periodontal parameters of canines and first molars treated with fixed orthodontic appliances. Am J Orthod Dentofac Orthop. 2016;149(3):325-30. https://doi.org/10.1016/j.ajodo.2015.07.041
  4. Al-Anezi SA. The effect of orthodontic bands or tubes upon periodontal status during the initial phase of orthodontic treatment. Saudi dent J. 2015;27(3):120-4. https://doi.org/10.1016/j.sdentj.2014.11.010
  5. Ghijselings E, Coucke W, Verdonck A, Teughels W, Quirynen M, Pauwels M, Carels C, Gastel JV. Long?term changes in microbiology and clinical periodontal variables after completion of fixed orthodontic appliances. Orthod craniofac res. 2014;17(1):49-59. https://doi.org/10.1111/ocr.12031
  6. Moraschini V, Fai CK, Alto RM, Dos Santos GO. Amalgam and resin composite longevity of posterior restorations: A systematic review and meta-analysis. J dent. 2015; 43(9):1043-50. https://doi.org/10.1016/j.jdent.2015.06.005
  7. Yetkiner E, Özcan M. Adhesive strength of metal brackets on existing composite, amalgam and restoration-enamel complex following air-abrasion protocols. Inter J Adhes Adhes. 2014;54:200-5. https://doi.org/10.1016/j.ijadhadh.2014.06.012
  8. Parnian-Alizadeh O, Mojgan K, Sahand R, Farzaneh F, Elmira-Jafari N. Effect of surface treatment with sandblasting and Er,Cr:YSGG laser on bonding of stainless steel orthodontic brackets to silver amalgam. Med Oral Patol Cir Bucal 2012;17:292-296. https://doi.org/10.4317/medoral.17473
  9. Portugal J, Marqes P, Jardim L, Leitcio J. Shear Bond Strength of Aged Dental Amalgam Repaired with Composite. Rev Port Estomatol Cir Maxilofac 2008;49:69-74. https://doi.org/10.1016/S1646-2890(08)70037-2
  10. Machado C, Sanchez E , Alapati S, Seghi R, Johnston W. Shear bond strength of amalgam-resin composite interface. Oper Dent 2007; 32:341-346. https://doi.org/10.2341/06-100
  11. Bach GK, Torrealba Y, Lagravere M. Orthodontic bonding to porcelain A systemic review . Angle Orthod 2013;0:00
  12. Germec D, Cakan U, Ozdemir FI, Arun T, Cakan M. Shear bond strength of brackets bonded to amalgam with different intermediate resins and adhesives. Eur J Orthod 2009; 31:207-212. https://doi.org/10.1093/ejo/cjn086
  13. Hammad SM, Banna MSE. Effect of surface loading on the shear bond strength of metal orthodontic brackets bonded to resin composite veneer surface using different conditioning protocols. Prog Orthod 2013; 14:14. https://doi.org/10.1186/2196-1042-14-14
  14. Kocadereli I, Canay S, Akca K. Tensile bond strength of ceramic orthodontic brackets bonded to porcelain surfaces. Am J Orthod Dentofacial Orthop. 2001; 119:617-620. https://doi.org/10.1067/mod.2001.113655
  15. Major PW, Koehler JR, Manning KE. 24-hour shear bond strength of metal orthodontic brackets bonded to porcelain using various adhesion promoters. Am J Orthod Dentofacial Orthop. 1995; 108:322-329. https://doi.org/10.1016/S0889-5406(95)70028-5
  16. Machado C, Sanchez E, Alapati S, Seghi R, Johnston W. Shear Bond Strength of the Amalgam-Resin Composite Interface. Opt Dent, 2007, 32-4, 341-346 https://doi.org/10.2341/06-100
  17. Skilton JW, Tyas MJ, Woods MG. Effect of surface treatment on orthodontic bonding to amalgam. Aus J Orthod 2006; 22:59-66.
  18. Buyukyilmaz T, Zachrisson BU. Improved orthodontic bonding to silver amalgam. Part 2. Lathe-cut, admixed and spherical amalgams with different intermediate resins. Angle Orthod 1998;68: 337-344
  19. Jessup JP, Vandewalle KS, Hermesch CB, Buikema DJ. Effects of surface treatments on amalgam repair. Opt dent.
    1998;23:15-20.
  20. Jost-Brinkmann PG1, Drost C, Can S.In-vitro study of the adhesive strengths of brackets on metals, ceramic and composite. Part 1: Bonding to precious metals and amalgam. J Orofac Orthop. 1996;57(2):76-87
  21. Shiba A, Hayashi T, Yoshida J, Tanaka O. Functionally generated amalgam paths for complete dentures. J prosth dent. 1981;46(5):494-7.
  22. Katrina J F, Mutlu OZ, Wendy J. Post Y R, Pieter UG. In-vitro orthodontic bond strength testing: A systematic review and meta-analysis. Am J Orthod dentofacial Orthop 2010;137:615-22 https://doi.org/10.1016/j.ajodo.2009.12.021
  23. Ülker M, Malkoç S, Ülker HE, Yalçin M, Malkoç M. Orthodontic bonding to high-copper amalgam with different adhesive cements. J Rest Dent. 2016;4(1):7. https://doi.org/10.4103/2321-4619.176015
  24. Naseh R, Rahnamoon N, Afshari M. Shear Bond Strength of Orthodontic Attachments to Amalgam Surfaces Using Assure Universal Bonding Resin after Different Surface Treatments. Iran J Orthod. 2016;11(2).

    1. Assistant Professor Orthodontics, Faisalabad Medical University, Pakistan.
    2. Dean of Dentistry, Professor & Head, Department of Orthodontics, Faisalabad Medical University.
    3. Assistant Professor Orthodontics, de’Montmorency college of dentistry, Lahore.
    Corresponding author: “Dr. Muhammad Azeem” < dental.concepts@hotmail.com

Comparison of Surface Conditioning Protocols on The Shear Bond Strength of Metal Brackets Bonded To Amalgam Surface

Muhammad Azeem            BDS, FCPS

Arfan Ul Haq                       BDS, FCPS, MDS, MCPS

Samina Qadir                     BDS, MDS

OBJECTIVE:

Orthodontists more often comes across amalgam restoration as a surface to bond brackets. The objective of current study was to compare the mean shear bond strength of orthodontic metal brackets bonded on sandblasted versus diamond bur roughened amalgam surfaces.

METHODOLOGY: Current In-vitro, comparative study was conducted at Orthodontic department of Faisalabad medical university from 17.2.2017 to 17.8.2017. Sixty extracted human maxillary molars were included in the study as per inclusion criteria. They were randomly divided into two groups. In group-A, metal brackets were bonded to amalgam using sandblasting with 50 ?m alumina particles. In group-B, brackets were bonded after roughening the amalgam surface with diamond bur. Shear bond strength (SB) was measured and compared using universal testing machine, in both the groups.

RESULTS: SB of metal brackets bonded with sandblasting (17.05±5.9 MPa) was significantly higher than diamond bur roughened group (11.08±4.0 MPa).

CONCLUSION: Amalgam surface treatment with sandblasting increased the shear bond strength of metal orthodontic brackets significantly higher than the diamond bur roughening.

KEY WORDS: Brackets; Amalgam; Sandblast; Shear bond strength.

HOW TO CITE: Azeem M, Haq AU, Qadir S. Comparison of Surface Conditioning Protocols on The Shear Bond Strength of Metal Brackets Bonded To Amalgam Surface. J Pak Dent Assoc 2018;27(1):32-36.

DOI: https://doi.org/10.25301/JPDA.271.32

Received: 16 October, 2017, Accepted: 06 December, 2017

Learning Style and Preferences Among Students and Dentists in Various Dental Colleges of Karachi

Farhan Butt1                            BDS, MAS, MDS

Marium Iqbal2                        BDS, FCPS

Khurram Khan3                     BDS, MSc

OBJECTIVE:

 To determine the learning style and learning preference of dental students and dentists in different dental colleges within Karachi.

METHODOLOGY: Total six hundred and four students and dentists participated in this study. Learning preferences were elicited using a Learning Style Questionnaire (LSQ) which consisted of eighty questions. It is based on four learning styles Activist, Theorist, Reflector and Pragmatist. Each of the learning style has twenty related questions in questionnaire. The result was analyzed using Excel software.

RESULTS: The overall response rate was 86.28%. The most preferred learning style was Reflector (39.73%) and Pragmatist (35.09%), while, the least preferred style was Theorist (19.86%) and Activist (17.71%). Majority of the students have developed preference for at least one learning style. Some students (20.52%) have developed equally strong preference for two learning styles. None of the students have developed equally strong preference for three or four learning styles.

CONCLUSION: A wide range of learning occurs in dental Colleges in Karachi. The result of this study can be used to teach students according to their preferred learning style or alternatively, students can be motivated or encouraged to learn in any situation.

KEY WORDS: Learning; learning style; learning preference

HOW TO CITE: Butt F, Iqbal M, Khan K. Learning style and preferences among students and dentists in various dental colleges of karachi. J Pak Dent Assoc 2018;27(1):27-31.

DOI: https://doi.org/10.25301/JPDA.271.27

Received: 05 November, 2017, Accepted: 04 January, 2018

INTRODUCTION

The concept of knowledge translation can be defined as “Learning that has occurred when students absorb new material, knowledge or the use of a new technique.1,2 It is an evolving lifetime process, best achieved through real life experiences. Knowledgeable teachers recognize that students react very differently from one another to the same learning experiences during their period of study in dental colleges. This phenomenon indicates dissimilarities in the students’ learning style, also known as “an individual’s characteristic”, but potentially flexible way of interacting with a learning environment.3 Recognizing students’ learning individualities may lead to improvement in areas such as designing of a course.4 An important strategy used to positively induce students’ performance and effective learning is by introducing mechanisms that support a variety of learning techniques.5

Advances in knowledge translation indicate that awareness of one’s own learning style, allows the individual to synthesize information more effectively.6 Over the years, adult learning patterns have shifted from a focus on teaching to a focus on learning as directed by educational institutions.7 Assessment policies, teaching methods and provisions as well as the practices of learning resources all make an impact on student learning.8 An optimum learning environment is produced when factors such as (assessment policies and teaching methods) are combined with different learning style preferences.9,10,11 There are a variety of different ways in which students learn. Some prefer presentations from the teacher and others prefer small group discussions.12 The ability of a student to learn in the classroom depends on the
student’s personal capability, preferred learning style and prior preparation, as well as adapting to the instructor’s teaching style.

The teaching-learning process is classified according to the various forms of receiving and providing knowledge. Learning style theory has already been utilized in a lot of fields such as business education and economics.14,15,16 Learning situations can be seen to differ across and within disciplines. Students themselves are unlike in relation to age, gender and phase of education.

Honey and Mumford’s Learning Style Questionnaire (LSQ) consists of 80 questions which are intended to measure preferences for learning styles. This questionnaire is built on the earlier work of David Kolb.6 This author stated that learning styles mature as a result of inborn factors, prior experiences, and requirements of the surroundings in which the person lives. The LSQ was made commercially available in 1986 for business purpose in the UK. It was later translated to Spanish and was finally adapted for educational purpose.17 The LSQ is designed to assess the relative strengths of four different learning styles: Activist, Reflector, Theorist, and Pragmatist.

The activist are those who are enthusiastic for current information, remain up to date, are good presenters and people who do not accept sitting still for a long time or listening to descriptions without interacting. Theorist are people interested in knowing the explanation behind everything. They like clearness in their goals. The reflective style prevails in people who prefer to collect comprehensive facts and information. Reflectors often tend to reproduce and observe upon their inferences before taking action. The pragmatic style is dominated by people who can discover techniques in their daily learning. Pragmatists are curious to discover fresh policies and determine whether these strategies are efficient and valid. Rationale: It is crucial to know the learning preferences of our learners to be able to decide on the teaching methodologies that we as educators plan for them. Although, it may be impossible to revise the whole curriculum it may still be possible to include a few more learning activities or to train the students to adopt new preferences. This can be especially beneficial for an otherwise struggling student who has preferences different from a larger group. Local literature, related to the learning preferences of our students, is deficient. Therefore, it seems appropriate to explore the learning preference of our students from first year through to final year and even after graduation.

METHODOLOGY

This is a cross-sectional study. Data was collected between 1st January, 2017 and 28th February, 2017 using Honey and Mumford’s Learning Style Questionnaire (LSQ). 700 questionnaires were distributed among various dental colleges in Karachi. Students were approached individually, and requested to complete the form. Six hundred and four completed questionnaires were eligible for this study and ninety six were discarded, due to incomplete answers or blank questionnaires. Questionnaires were distributed according to the availability of classes. Each class on average has 45 to 50 students. Students were briefed about the survey. Each student was requested to give consent before participating in this study. No attempt was made to follow up with those students who were absent. It took approximately 20 minutes for each student to complete the questionnaire.

Exclusion criteria includes those who did not want to participate in this study or those who were absent. Excel software was used to record and analyze each student’s response. Honey and Mumford’s scoring norm was used to interpret data from this study. This helped to categorize student’s learning preferences. Scoring criteria specially designed for LSQ research, which is available on its website were used for management of data (Table1). Filled questionnaires were kept in locker to which only the researcher had access.

Table 1: learning style interpretation table as presented by Honey and Mumford

RESULTS

The sample consisted of 604 respondents, out of which 482 were dental students (79.80%), 122 house officers (20.19%) and 23

Figure 1: Distribution as percentage of interpretation of the Activist, Reflector, Theorist and pragmatist learning styles among dental students at different dental colleges in Karachi.

demonstrators (3.80%), selected from various dental colleges in Karachi. The sample has 90 first year students (14 male; 76 female), 140 second year students (16 male; 124 female), 120 third year students (24 male; 96 female), 132 final year students (32 male; 100 female), 99 house officers (25 male; 74 female) and 23 demonstrators (6 male and 17 female).The demographic data shows that most of the respondents (69.5%) are between the age 18-21 years, while only 30.5% are between age of 22-33 years,

Table 2: showing number of male and female in study with their age

The most preferred learning style for first year dental students was pragmatist (41.11%), Table 3. The least preferred learning style for first year dental students was theorist. It is interesting to note that from second year till final year dental school as well as demonstrator level participants all preferred using the reflector learning style. Activist learning style remained the least preferred method from second year till house job. For demonstrators the least preferred learning style was theorist (13.04%).

In this study, a variety of learning style preferences was determined when considering individual student’s score. Majority of the students have already developed either very strong or strong preference for any one of the four learning styles, Fig. 2. Few students have moderate preference for either learning styles. However, it is interesting to note that only 15 students still have very low or low preference for a specific learning style. Most of the respondents have a preference for one type of learning style, however, out of total 604 respondents 124 (20.52%) respondents have developed equally strong preference for two learning styles.

Table 3: Descriptive statistics of all respondents of BDS
Figure 2: Showing change in percentage in learning styles from First year till Demonstrator
Table 4: Summary of learning style preferences for BDS students

While, none of the respondents have equally strong preference for more than two learning styles.

DISCUSSION

This research allows us to examine the learning styles of students and demonstrators in various Dental colleges in Karachi, Pakistan. Individuals have different preferences in the way they absorb and process information, which leads to different learning styles.

In our study the most preferred learning style was Reflector and least preferred was Activist. A similar study was conducted by Alexandra I et al., on students of pharmacy using the same LSQ questionnaire. He concluded that most participants preferred the pragmatist learning style, and the least preferred learning style was theorist.18 In another study conducted to see differences in learning style based on gender, it was found that, preferences for male and female students are not significantly different.19 Wilkinson conducted a study on first year medical and dental students and did not find any effect of student’s preferred learning style on their result/ scores.20 In another study it was found that those students who had a predominating “activist” learning style have showed weakest performance in the subject of anatomy.21

Moreover, the stability of learning style of student remains ambiguous during their learning period.15 Conflicting results have been found in research between years of study and learning style preferences. It is still unsure if the learning style/ preferences remain stable over a period of time and if it changes, which factors contribute to its change. Since some studies revealed that there was a change with time and yet others said that there was no change, so we need to explore it further In one of the study conducted by Randall LE found no relationship between years of study and learning style preference.22 While in another study, it was found that dissimilarities in learning style preference occur and that these preferences change over time, which may be linked to the personal maturing of students.23 Lecturers also differ in their methods, style of teaching and/or delivering lectures.

When the learning style of the student is not well-matched with the teaching style of the lecturer, difficulties in educational accomplishments may occur. Classroom conflicts may occur when teaching and assessment methods do not match the various learning styles of students. Factors such as classroom environment, past educational background, inspiration, gender and multiethnic issues additionally influence the learning process.17 Randall et al. in 1995 suggested an advantage in teaching styles which fit a broader range of students. Students may benefit by gradually introducing class activities that significantly expand their learning style preferences. In this way students can be assisted in broadening their abilities to accommodate greater variety.22 In another study conducted by Witkin et al. 1976 results suggest that, teachers recognized the various learning styles of students.23 This will provide a catalyst for appraising the learning situation and will ultimately result in improvements and success of learners through better matched learning activities. In another study conducted on dental students, the authors used a different learning style questionnaire based on sensory inputs. They have not introduced anything so far about the new strategies introduced.24

In students with same learning style, preference can still be found, which can be mild, moderate or strong. This explains the difference among students with similar learning styles. Some factors that differentiate individual learning styles include experience, skillfulness and knowledge.17 When students are familiar regarding their own learning style (most prevalent), then, they can also work to adapt to less prevalent learning styles.25 It can be concluded that, faculty should learn to apply various teaching strategies to reach more students in a
specified class, thus inspiring all the students to learn from teaching activities.23 However, the point is not to match the teachers teaching style with the student’s learning style, rather, to achieve a balance by confirming that each style is met at reasonable level as part of the teaching method.26,27

CONCLUSION

The overall findings suggests that teaching mechanisms used within Dental schools should support a broad range of learning styles. It is important for learners to practice a variety of learning styles because each style has its own strengths and weaknesses depending on the situation. Activist and theorist were the least preferred learning style, which indicates, the need for modification to teaching-learning process, so that the students can develop these processess more easily.

LIMITATIONS

Our study was cross-sectional, which prevents conclusion regarding changes in learning style over period of time. In future, more studies should be performed to identify students’ learning style at the time of entrance in Bachelor of Dental Surgery program, particularly longitudinal studies to observe changes in learning preferences over time.

CONFLICT OF INTEREST

None declard

REFERENCES

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  13. Marriott P. A longitudinal study of undergraduate accounting students’ learning style preferences at two UK universities. Account Educ. 2002 ; 11(1):43-62. https://doi.org/10.1080/09639280210153263
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  19. McKeachie WJ. Learning styles can become learning strategies. Natl Teach Learn Forum. 1995;4:1-3.
  20. Wilkinson T, Boohan M, Stevenson M. Does learning style influence academic performance in different forms of assessment?. J Anat. 2014;224(3):304-8. https://doi.org/10.1111/joa.12126
  21. O’Mahony SM, Sbayeh A, Horgan M, O’Flynn S, O’Tuathaigh CM. Association between learning style preferences and anatomy assessment outcomes in graduateentry and undergraduate medical students. Anat Sci Educ. 2016;9(4):391-9. https://doi.org/10.1002/ase.1600
  22. Randall LE. Learning Style Preferences of Physical Education Majors: Implications for Teaching and Learning. J Excell Coll Educ. 1995; 6(2):57-77.
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1. Assistant Professor and classified specialist in Periodontics Department, Armed foces institute of dentistry, Rawalpindi.
2. Professor HOD in Operative Dentistry, Endodontics and Paedodontics Department, Jinnah Medical and Dental College.
3. Senior Registrar in Paediatric Dentistry Department. Jinnah Medical and Dental College.
Corresponding author: “Dr. Farhan Butt ” < buttfarhan84@hotmail.com >

Learning Style and Preferences Among Students and Dentists in Various Dental Colleges of Karachi

Farhan Butt                            BDS, MAS, MDS

Marium Iqbal                        BDS, FCPS

Khurram Khan                     BDS, MSc

OBJECTIVE:

 To determine the learning style and learning preference of dental students and dentists in different dental colleges within Karachi.

METHODOLOGY: Total six hundred and four students and dentists participated in this study. Learning preferences were elicited using a Learning Style Questionnaire (LSQ) which consisted of eighty questions. It is based on four learning styles Activist, Theorist, Reflector and Pragmatist. Each of the learning style has twenty related questions in questionnaire. The result was analyzed using Excel software.

RESULTS: The overall response rate was 86.28%. The most preferred learning style was Reflector (39.73%) and Pragmatist (35.09%), while, the least preferred style was Theorist (19.86%) and Activist (17.71%). Majority of the students have developed preference for at least one learning style. Some students (20.52%) have developed equally strong preference for two learning styles. None of the students have developed equally strong preference for three or four learning styles.

CONCLUSION: A wide range of learning occurs in dental Colleges in Karachi. The result of this study can be used to teach students according to their preferred learning style or alternatively, students can be motivated or encouraged to learn in any situation.

KEY WORDS: Learning; learning style; learning preference

HOW TO CITE: Butt F, Iqbal M, Khan K. Learning style and preferences among students and dentists in various dental colleges of karachi. J Pak Dent Assoc 2018;27(1):27-31.

DOI: https://doi.org/10.25301/JPDA.271.27

Received: 05 November, 2017, Accepted: 04 January, 2018

Compressive Strength of Composite Resins at Different Exposure Time Using LED and Halogen Units

Hasham Aleem1                       BDS

Faiza Ameen2                           BDS, MDS

Abdur Rehman3                      BDS, MDS

OBJECTIVE:

To evaluate the compressive strength of resin composites cured with a QTH lamp & LED unit at different exposure time.

STUDY DESIGN: In Vitro Experimental study

METHODOLOGY: Two composite materials were used in this study. Filtek Z250, (3M ESPE Dental products) and Filtek P60 (3M ESPE Dental products). For each composite 114

Table 1: Composition of resin material tested
Table 2: Technical details of light curing units

disc shaped samples were prepared (5mm in diameter and 2mm in thickness) by using stainless steel mold. The mold was packed with the bulk of resin composite by incremental technique. Each sample was cured through the polyester strip with either QTH unit or LED unit depending on samples grouping. Samples were irradiated for 20, 30 and 40 seconds. Nineteen specimens were prepared for each experimental group. Specimens were placed in artificial saliva for 24 hours after curing. Compressive strength was then determined in universal Instron Testing Machine. Data was analyzed by factorial design by Three Way ANOVA and post hoc Tukeys HSD test. Units

RESULTS: Halogen light curing unit is more effective then LED unit in terms of compressive strength. Compressive strength was influenced by exposure time (20, 30 or 40 s) (p<0.001), by curing lights (QTH or LED) (p<0.001) and by resin composite (Filtek Z250 or ZP60) (p<0.001).

Table 3: Mean and standard deviation of compressive strength of Filtek Z250 cured by halogen and led curing light unit.
Table 4: Mean and standard deviation of compressive strength of Filtek P60 cured by halogen and led curing light unit.

CONCLUSIONS: The compressive strength of specimens cured with a QTH and a LED curing light was influenced by the curing unit and the chemical composition of the material. The study concluded that superiority of LEDs over halogen lamps is questionable with different composite resins.

KEY WORDS: Composite resins, compressive strength, artificial saliva.

HOW TO CITE: Aleem H, Ameen F, Rehman A. Compressive strength of composite resins at different exposure time using led and halogen units. J Pak Dent Assoc 2018;27(1):227-31.

DOI: https://doi.org/10.25301/JPDA.271.227

Received: 08 November, 2017, Accepted: 05 February, 2018

INTRODUCTION

An important milestone in the history of restorative dentistry is the development of light-cured composite resins.1 Before the advent of light cure technique, composites were cured by cold curing or chemical curing which were initiated by mixing two pastes.2 Blue light was first introduced in 1970s to overcome the complications of chemical curing dental composites.3 Improved physical properties, esthetics and operator’s control over the working time are the few advantages of light cured restorative materials as compared to the chemical cured materials.4 Most commonly used light polymerizable restorative materials are resin modified glass ionomers (RMGIC), compomer and composite resins.

Polymerization sources that have been developed till today are: argon-ion lasers, plasma-arc lamps, light emitting diodes (LED) units and quartz tungsten halogen (QTH) lamps.5 In daily clinical practice halogen lights and LED units are most frequently used.5 QTH light curing unit deliver the light with the light intensity of 400-900 mW/cm2. 6 Halogen lamps, despite having low cost and have broad emission spectrum which allows almost complete polymerization of resin composite materials. However, they have many disadvantages. They require filters because they have very low capability to convert electronic energy into light and most of the energy is transformed into heat.7 Because of the halogen bulb proximity and high temperature of light unit filters degrade with the passage of the time.8 Several studies have pointed out that there is a lack of maintenance of these halogen light which further restrict their use by clinicians.3 Average lifetime of Conventional halogen lamp is between 30-50 hours.9 These limitations could negatively affect the long term success of the restoration due to inadequate polymerization of the material.10 In 2001, to overcome the limitations of the quartz tungsten halogen light, the first LED curing units were introduced.9

The mechanism involved in the LED units is combination of two different doped semiconductors instead of a hot filament.11 RW Mills proposed that LED devices utilizes, Gallium Nitride blue light which produce narrow spectrum of light (400- 500nm).3 Polymerization of resin monomers is initiated by the Gallium Nitride blue light because of electroluminescence effect that falls closely within absorption range of camphorquinone.5 They convert most of their electronic energy into light and therefore, to produce blue light they do not require filters.12 LEDs have constant light output in spectra and power and have the lifetime of thousand of hours.13 Till now two generations of LEDs have been introduced. There were multiple LEDs in the first generation of LED curing units and had a comparatively low power output. According to author10 these units have irradiance values similar to those of conventional light sources. Whereas, a second-generation of LCUs has light emitting diodes with high-power. The second generation LEDs offer shorter curing times and perform better working operation as compared to the first generation.

Several studies have investigated the influence of LED light-curing and halogen on properties of light-cured composites. These properties are diametrical tensile strength,14 hardness,3,9,12,15,16 depth of cure,9,17,18flexural strength,19 abrasion resistance,20 degree of conversion21 and compressive strength.10 Both of these lights are capable of curing composite resins, however, in the performance of the cured resins some differences have been observed.9,17 Moreover, adequate association has been observed between the degree of polymerization and the composite materials and its curing time.9,17

Adequate polymerization of resin composites is essential for the ultimate success of the restorations. Polymerization effectiveness determined the materials color change, dimensional stability, mechanical properties, solubility, and biocompatibility. Materials which are generally brittle and weak in tension can best be evaluated by the compressive strength. The aim of the present study is therefore to assess the compressive strength of composite resins cured by different light curing units at different time exposures.

METHODOLOGY

Two resin composites, Filtek Z250, (3M ESPE Dental products) and Filtek P60 (3M ESPE Dental products) of A3 shade were used for this study. Table 1 showed the details of the materials. The two light curing units evaluated were the QTH lamp (682 Deepblue Technology Co LTD, 700 mW/cm2 ) and the LED light (Elipar free light (3M ESPE, 400 mW/cm2). Table 2 showed the technical details of both the curing lights. Sample preparation was carried out in Dow Dental College, Dow University of Health Sciences. Testing was carried out in Pakistan Council of Scientific Research (PCSIR). For each composite 114 samples which were disc in shaped were prepared (5mm in diameter and 2mm in thickness) by using stainless steel mould.22 The mould was packed with the bulk of resin composite by incremental technique. The resin composite was slightly overfilling the mould. After insertion of the last increment, the composite was covered with transparent polyester strip (20mm length and 6mm breadth) and 2.0- mm-thick glass plate was gently pressed to remove the excess material. Each sample was then irradiated through the polyester strip using QTH unit (682 Deepblue Technology Co LTD, 700 mW/cm2 ) or LED unit (Elipar free light (3M ESPE, 400 mW/cm2) depending on sample group. The curing time used for of each sample was 20, 30 and 40 seconds for both light curing units. After the curing, cellulose strip was removed; specimens were extruded from the mould. The samples were kept in artificial saliva for 48 hours at 37°C.

For each experimental group nineteen specimens were prepared. Digital calipers (Mitutoyo Co.) was used to measure the diameter of the prepared samples. Then evaluation of the specimens for the presence of any defects and air bubbles was carried out. Faulty specimens were excluded from the study. The samples were then randomly divided into three test groups, each group having 19 specimens.

Preparation of Artificial saliva

The specimens were immersed in 250 ml of artificial saliva solution at 37°C for 24 hours. The artificial saliva solution had an electrolyte composition similar to that of human saliva. It was composed of 4.3 g xylitol, 5 mg calcium chloride, 40 mg potassium phosphate, 1 mg potassium thiocyanate, 1 g sodium carboxymethylcellulose, 0.1 g potassium chloride, and 100 g distilled deionized water. After 24 hours the specimens were removed from the artificial saliva. The surfaces were rinsed with distilled water for 30 seconds and then dry the specimens.23

Compressive strength Measurements

After 48 hours of storage compressive strength of specimens were measured. Universal testing machine (Instron universal testing machine model static) at a crosshead speed of 0.5 cm/min and load cell of load cell 5KN was used to measure the compressive strength.(Figure 2) Specimens were positioned on base of the testing machine vertically and exposed to compressive load until fracture. The strength was expressed in MPa. Following formula was used to calculate the compressive strength.

Compressive strength = Load X10 (N)
                                             Area (mm2)

Factorial design three way analysis of variance (ANOVA) and Tukey’s HSD was used for each composite to evaluate the effects of light curing unit and exposure time on compressive strength (α=0.05).

RESULTS

Table3 and table 4 showed the mean values and standard deviations for both composites used in this study. The interaction between exposure time and light curing unit for both the composites were statistically significant.(p<0.001) Factorial design three way ANOVA showed that compressive strength was influenced by curing lights (QTH or LED) (p<0.05) by exposure time (20,30 or 40 s) (p<0.001) and by resin composite (Filtek Z250 or ZP60) (p<0.001).

DISCUSSION

This study evaluated the compressive strength of composite resins at different curing time using led and halogen units. Over the last few years LED polymerization of oral biomaterials has become a field of intensive scientific research and commercial product development. In restorative dentistry after the introduction of LED devices, researchers showed great interest in comparing their capability with halogen lamps. Material’s polymerization is greatly influence by the irradiance of curing light. Though, the degree of conversion is greatly depends on the energy dose of the light curing unit.24 For the successful outcome of the restorative material, it should have the mechanical properties
similar to that of tooth structure. Several of the masticatory forces are of compressive nature and therefore compressive strength is considered to play important role in the masticatory process. The compressive strength is calculated by the maximum force applied and the cross-sectional area of test specimens.25

In the present study Filtek Z250 has higher compressive strength at 40sec when cured with halogen light as compared with the specimens that were cured with led light. Similar results were found in the study conducted by Mousavinasab SM et al in which they demonstrated that the total irradiance of halogen light curing unit is 2.2 times greater than the irradiance of led light curing unit.26 It is therefore expected that the physical properties of composites cured with LED is inferior then the specimens cured with halogen light. However, this relationship can only be established when curing time and other parameters like spectrum of emitted light, material and tip diameter are kept constant.21 The present study showed that the compressive strength was increased further when cured at 30 sec and 40 sec with halogen light as compared to 20 sec whereas when the specimens were cured with led light markedly decrease in the compressive strength was observed at 30 and 40 sec for Filtek Z250 specimens. Similar results were obtained in a study conducted by Eduardo Batista Franco et al in which they concluded that better results were obtained with halogen light as compared to led light in term of strength of the material.24 Similar pattern were followed for the other material used in the study that is Filtek P60. However, when comparing the results of FiltekZ250 and Filtek P60 the compressive strength of P60 at 20 seconds was markedly increased when cured by halogen light. Critical variables for achievement of maximum curing are wavelength, light intensity, polymerization condition and exposure time. All these factors influence the mechanical properties of lightpolymerized dental materials.27 However, in a study conducted by Kumar CNV et al they found that both halogen light and led light produced similar compressive strength and no statistical difference was found among the two lights.28 The compressive strength is influenced by the output power density, used, light intensity and time.9 It was surprising that there were only minor differences in the composite’s mechanical performance when polymerized with one or the other LCU although the LED LCU had less than half of the halogen LCUs irradiance. Another study explained one possibility for the efficiency of LED LCU polymerization through the convolution of the absorption spectrum of the camphorquinone photoinitiator present in composites and the emission spectra of the LED LCUs.14 The same study showed in some cases that there was no statistically significant difference in the flexural strength and moduli of different composites when polymerized with either a commercial halogen LCU with an irradiance of 755 mW cm2 or an LED LCU with an irradiance of 350 mW cm2. 13 This study shows that compressive strength of the composites cured with either a halogen lamp or a LED source demonstrated different results. In summary, the impact of the light intensity, output power density of the LCUs, curing time and chemical composition of the materials, should be considered. More research is required to illuminate the mechanical properties of composites cured with LED curing units, to address the factors mentioned above.

CONCLUSION

Under the limitations of this study following conclusions can be drawn: Filtek Z250 has higher compressive strength at 40sec when cured with halogen light whereas Filtek Z250 has lower compressive strength at 40sec when cured with LED light. At 20 sec Filtek P60 has higher compressive strength when cured with halogen light. Filtek P60 has lower compressive strength at 40sec when cured with LED light.

Compressive strength was increased further when cured at 30 sec and 40 sec with halogen light as compared to 20 sec. When the specimens were cured with led light markedly decrease in the compressive strength was observed at 30 and 40 sec for Filtek Z250 specimens. Same sequence was followed for Filtek P60.

CONFLICT OF INTEREST

None declared

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1. Department of Science of Dental Materials. Dow University of Health Sciences
2. Associate Professor, Dept of Science and Dental Matrials. Dow University of Health Sciences
3. Assistant Professor, Dept of Science and Dental Matrials. Hamdard University
Corresponding author: “Dr. Hashim Aleem” < hasham_alim@hotmail.com >

Compressive Strength of Composite Resins at Different Exposure Time Using LED and Halogen Units

Hasham Aleem                       BDS

Faiza Ameen                           BDS, MDS

Abdur Rehman                      BDS, MDS

OBJECTIVE:

To evaluate the compressive strength of resin composites cured with a QTH lamp & LED unit at different exposure time.

STUDY DESIGN: In Vitro Experimental study

METHODOLOGY: Two composite materials were used in this study. Filtek Z250, (3M ESPE Dental products) and Filtek P60 (3M ESPE Dental products). For each composite 114 disc shaped samples were prepared (5mm in diameter and 2mm in thickness) by using stainless steel mold. The mold was packed with the bulk of resin composite by incremental technique. Each sample was cured through the polyester strip with either QTH unit or LED unit depending on samples grouping. Samples were irradiated for 20, 30 and 40 seconds. Nineteen specimens were prepared for each experimental group. Specimens were placed in artificial saliva for 24 hours after curing. Compressive strength was then determined in universal Instron Testing Machine. Data was analyzed by factorial design by Three Way ANOVA and post hoc Tukeys HSD test. Units

RESULTS: Halogen light curing unit is more effective then LED unit in terms of compressive strength. Compressive strength was influenced by exposure time (20, 30 or 40 s) (p<0.001), by curing lights (QTH or LED) (p<0.001) and by resin composite (Filtek Z250 or ZP60) (p<0.001).

CONCLUSIONS: The compressive strength of specimens cured with a QTH and a LED curing light was influenced by the curing unit and the chemical composition of the material. The study concluded that superiority of LEDs over halogen lamps is questionable with different composite resins.

KEY WORDS: Composite resins, compressive strength, artificial saliva.

HOW TO CITE: Aleem H, Ameen F, Rehman A. Compressive strength of composite resins at different exposure time using led and halogen units. J Pak Dent Assoc 2018;27(1):22-26.

DOI: https://doi.org/10.25301/JPDA.271.22

Received: 08 November, 2017, Accepted: 05 February, 2018