Implant Over Dentures: A Concise Review Of The Factors Influencing The Choice Of The Attachment Systems

Haroon Rashid ¹                                              BDS, MDSc

Ayesha Hanif ²                                                 BDS

Fahim Vohra ³                                                 BDS, MFDS, M.Clin.Dent, MRDRCS

Zeeshan Sheikh ⁴                                            BDS, MSc, PhD

INTRODUCTION

Over-dentures are defined as,”removable dental prosthesis that cover and rests on one or more remaining natural teeth, the roots of natural teeth, and/or dental implants”^[1]. It may also be termed as an overlay denture, overlay prosthesis, superimposed prosthesis, hybrid prosthesis, a crown and sleeve prosthesis, superimposing denture and a biological denture¹.

The concept of retaining teeth/roots of the terminal dentition for the provision of an overdenture dates back to more than 100 years^[2],[3]. It was first described in 1950’s that the residual alveolar bone undergoes resorption which continues to progress after tooth extraction compromising support for a conventional dentures to be provided. The analysis of several longitudinal studies confirmed that the resorption was progressive, irrevocable and

continuous^[4],5. The rate of resorption is the greatest in the first six months after tooth extraction however; it slows down due to several biological and mechanical factors⁴. Overdenture abutments, whether a retained root or an implant, have shown to preserve alveolar bone height^7,8 and stabilize dentures, particularly the mandibular ones⁹. Retained roots are cost effective than implants, with no requisite of an invasive therapy, and therefore should be considered by general practitioners as a useful platform for over dentures, particularly for older individuals¹⁰. From physiological viewpoint, the roots provide not only a periodontal ligament to support the teeth, but also directional sensitivity, tactile sensitivity to load, dimensional discrimination,^7,11,12 and gives an individual a sense of not being edentulous¹³. Dental implants provide adequate retention and stability for overlying prosthesis however; the individual is deprived of tactile sensitivity¹⁴.

Dental implant therapy is considered the treatment of choice for edentulous patients¹⁰. IODs have gained worldwide acceptance and improve the quality of life for edentulous patients. IODs although retentive and stable,require good maintenance of the prosthesis and implant retentive components⁶.  Continued research related to IODs has resulted in multiple options and combinations for IOD attachment systems with varying success. The aim of the current paper is to briefly review the attachment systems used for IODs and the factors influencing their selection. Chair-side pickup Impression technique for mandibular implant over-denture is also briefly described. The treatment of the patient described in the current paper was carried out at the department of prosthodontics, college of dentistry,Ziauddin University, Karachi.

OVERDENTURE ABUTMENTS

In the early days, only bare teeth with questionable prognosis as a whole were used as abutments for over dentures. Recently, the use of implant abutments for overdenture use has increased. The use of sub-mucosal roots with magnets is also still in use ^15,16.

When using naturally retained bare teeth, it is aimed that canines and second premolars are preserved on both sides of the arches. Teeth are prepared in a dome shape, 2-3 mm above the gingival level, with the dome converging occlusally. To cope up with certain disadvantages of bare teeth such as caries progression, attrition of the abutment teeth, metal copings (short and long) were used over the dome shaped prepared teeth. Sub-mucosal root retention helps to reduce the possible oral hygiene obligations for the patients but delays residual ridge resorption. Being submerged, they escape the sequelae of poor oral hygiene by being isolated from the oral cavity.

With advancements in implant dentistry, implant supported over-dentures are gaining wide popularity. Along with implant abutments, sub-mucosal vital tooth retention and use of magnets are also commonly used. For many years, osseointegrated implant-supported overdentures have been used in the rehabilitation of the edentulous jaws particularly the lower ones, offering promising results ^17,18,19.

Literature states that the IODs should become the first choice of care for the edentate mandibles^20,21. This is a lucrative option but simultaneously, has been questioned for the fact that wide number of the edentate patients are poor and cannot afford the cost of implant therapy 22,23.

ATTACHMENT SYSTEMS FOR IODs

IODs come with a variety of attachment systems including the bar and clip attachment systems or a range of individual, abutment-based attachments called stud attachments (ball, magnets, and resilient stud attachments such as Locators [Zest Anchors], ERA [Sterngold], and non resilient stud attachments such as Ankylos Syncone [DENTSPLY Implants])^{24,25,26,27,28}. Fabrication of an IOD over these systems is costly; require clinical expertise and signification chair-side time¹⁸.

FACTORS INFLUENCING SELECTION OF THE ATTACHMENT SYSTEMS

Selecting the most apposite system for an individual is dependent on a variety of factors²⁹. These factors are identified during the treatment and planning phase of the therapy. Following are the factors that influence the selection:

a) Implant site:

The location of the placed implant in reference to the bone and the pontics will guide the selection of the type of attachments. However; the selection should ideally be decided during the phase of treatment planning. For ample retention, it is highly recommended that the implants are placed as parallel as possible^30,31,32.  Where parallelism cannot be achieved, a bar designed is favored. Bar design is also preferred in cases where the unfavorable location of the anatomic structures such as, prominent mental foramen or the knife-edge ridge, precludes the ideal placement of the implants^33,34,35,36.

b) Cross arch stabilization:

Bars are indicated in patients with shallow vestibules and resorbed ridges. The bar helps to resist the lateral loading and provides stabilization³⁷. The stability of the prosthesis is also improved and cantilever design may be provided with one to two teeth distal to the most posteriorly placed implant³⁸. The cases where denture stability is not a concern and retention is the only requirement, individual attachments should be used which offer promising results.

c) Prosthesis extent:

When the patient demands the prosthesis to be of the minimal size, custom designed milled bars is the attachment system of choice³⁹.  These types of restorations require ideal implant placement. The size of the prosthesis may be limited while keeping in mind the principles of anterior-posterior spread and cross arch stabilization. This also minimizes the lateral loads on the implants³⁸. Fabricating a denture using the neutral zone technique will also determine the horizontal space availability for the prosthesis³⁹. Neutral zone is the area of the minimal conflict i.e. the potential denture space; “that space in the edentulous mouth vacated by the natural dentition and dental supporting tissues and bound by the tongue medially, and the lips and cheeks laterally”^40,41,42 .

d) Sore spots:

It is established that the patients who are prone to soft-tissue sore spots, for instance xerostomic patients, are reportedly more comfortable with a bar, since the denture can rest entirely on the bar without impingement of the soft tissues⁴³. With individual attachments, the denture is supported by the mucosa and the compressive forces acting on the mucosa cause may cause soreness in patients who are prone to it⁴⁴.

e) Patient’s Oral Hygiene:

Dentures retained over bars are capable of gathering more debris and hence make such patients more susceptible to mucosal inflammation and peri-implantitis 44,45,46,47,48,49,50,51. Unless the patient commits to the meticulous oral hygiene measures⁵², the bar attachments should be denied in patients with poor oral hygiene.

f) Treatment Costs:

Bar attachments are costly as compared to the stud abutments in most of the scenarios^35,53. Cost is one of the major decisive factors in the selection of the attachment system. Patients may be upgraded to the bars and a new over denture may be fabricated if the financial condition of the patient has improved and other factors are considered. Yet, in every case, the selective treatment option must follow the appropriate guidelines maximizing the welfare of the patient and the options should never be merely dependent on patient’s finances.

g) The Restorative Space:

Restorative space is the space which is available for prosthesis restoration. In general, this space is bounded by the planned occlusal plane, the denture bearing tissues, facial tissues i.e. the lips, cheeks and the tongue⁵⁴. When planning an implant overdenture, considerations should be given to the adequate space available for the denture base, denture teeth, and the attachment system of the implant. The freeway space, phonetics and aesthetics must also be considered. The minimum space requirement for implant supported over-dentures with Locator attachment system is 8.5mm of vertical space and 9 mm of horizontal space⁵⁵. Ideally, for maxillary implant over-dentures, 13-14mm of vertical space is required for dentures which are supported by bars and 10-12mm for the over-dentures supported with individual attachments⁵⁶.

h) The Aesthetic Space:

This is defined as “the space between the ridge crest and the corresponding lips at rest”²⁹. Prosthesis supported by the individual attachment systems will require less aesthetic space compared o the bar counterparts. The measurement of the aesthetic space helps the dentist in determining the space allowed for a particular type of the attachment system of an over-denture.

i) Ease of Fabrication and Repair:

Bar supported removable prosthesis require manual dexterity for the fabrication and repair compared with the removable prosthesis supported by individual studs ^{24,57,58,59,60}. Many a times, the attachment systems are chosen without the proper consideration given to the aforementioned factors. This eventually leads to a failed prosthesis with patient dissatisfaction.

j) Resilience Difference:

Another factor documented that influences the selection of the attachment system for implant-retained over-dentures, is the difference of resilience between the implant and the oral mucosa^61,62. Furthermore, this difference should be considered while taking the impression of the implant and tissue retained over-dentures.

k) The Attachment System:

IODs supported with bars or balls offer good survival rates and patient’s appreciation levels with a denture retained with implants are better as compared to a conventional complete denture⁶³. The use of magnets for retaining over-dentures is also described in the literature however; their success rates have been limited⁶⁴. The limited success of magnets is mainly due to corrosion of the magnets caused by saliva and partly because of less retentive forces achieved as compared to other attachment systems. Bar and ball attachment systems offer better mechanical retention and have many differences between them. Table 1 outlines the differences between

the attributes of bar and ball attachment systems ^{65,45,66,49,67}.

CHAIR SIDE “PICK-UP” IMPRESSION TECHNIQUE FOR IODs

The selected attachment can be incorporated into the denture either chair-side or in the laboratory. Chair-side pick-up technique allows for passive in-vivo pick up of the attachment, furthermore, attachments are picked-up under mucosal compression allowing for even load distribution during function^68,69. The technique requires manual dexterity but simultaneously provides the incorporation of the attachments into a pre-fabricated denture. Direct chair-side attachment incorporation also avoids laboratory cost and a further denture delivery visit. Usually resilient, non-splinted, prefabricated attachments are utilized.

Abutments are selected with an appropriate gingival height (Figure 1), which is obtained by measuring the vertical distance from the implant collar to the highest

point of soft tissue circumferentially. Another important factor for abutment selection is the available space in occlusion in the denture. The suitable abutments are torqued at 25Ncm and housings are placed over the overdenture abutments after placing a spacer to avoid acrylic block-out (Figure 2, Figure 3). The prefabricated complete denture prosthesis is hollowed at the location of abutments for the housing to be incorporated, (Figure 4) and is checked intra-orally.  The denture preparation results in two open windows lingual to the mandibular anterior denture teeth. The abutment housings are placed on to verify and check the full seating of the final prosthesis and ensure there is not interference either from the

attachments or the housings. Auto-cure denture base acrylic resin is mixed and placed into the housing space and the denture is seated in position. The patient is made to bite in centric occlusion and the acrylic resin excess

on the polished surface of the denture is cleared. On complete setting of acrylic resin, the prosthesis is removed and any defect in the reline/pick up, is filled extra-orally using the auto cure acrylic (Figure 5). The prosthesis after the final finishing and polishing is ready to be delivered (Figure 6).

REFERENCES

1. Glossary of Prosthodontic terms. J Prosthet Dent 2005.
2. Ledger, R. On Preparing the Mouth for the Reception of a Full Set of Artificial Teeth: Br J Dent Sci 1856; 1:90.
3. Atkinson WH. Plate over Fangs. Dent Reg. 1861; 15: 213-216.
4. Tallgren A. The Effect of Denture Wearing on Facial Morphology-a 7-Year Longitudinal Study. Acta Odontol Scand 1967; 25: 563 -592.
5. Atwood DA, Coy WA. Clinical, Cephalometric and Densitometric Study of Reduction of Residual Ridges. J Prosthet Dent 1971; 26: 280 – 295.
6. Shah DS, Vaishnav K, Matani HP, Patel P. Overdenture: conventional to contemporary: A review. J Res adv Dent 2013;291):24-30.
7. Brewer A. A. And Morrow R. M. Overdentures. 1st Ed. The C.V. Mosby Company, SAINT LOUIS; 1975 8. Prince IB. Conservation of the supporting mechanism. J Prosthet Dent 1965;15:237.
8. Prince IB. Conservation of the supporting mechanism. J Prosthet Dent 1965;15:237.
9. Rissin L, House JE, Manly RS, Kapur KK. Clinical Comparison of Masticatory Performance and Electromyographic Activity of Patients with Composite Dentures. Overdentures and Natural Teeth. J Prosthet Dent 1978; 39: 508 -511.
10. Ettinger RL. Do Root Supported Overdentures Have a Good Prognosis in General Dental Practice?Oral health group. March 2014 http://www.oralhealthgroup.com Accessed on 12.03.2015.
11. Kay WD, Abes MS. Sensory Perception in Overdenture Patients. J Prosthet Dent 1976; 35: 615 619
12. Toolson BL, Smith DE. A Five-Year Longitudinal Study of Patients Treated with Overdentures. J Prosthet Dent 1983; 49: 749 – 56.
13. Guerra, Luis R. DDS, MS; Finger, Israel M. BDS, MSc, MEd, DDS; Stock, Michael S. DMD, Tissue supported implant overdentures. Implant Dent 1992; 1: 69-77.
14. Garver D. G., Fenster R. K., Baker R. D. and Johnson D. L. Vital root retention in humans: A preliminary study J Prosthet Dent. 1978; 40:23- 28.
15. Welker W. A., Jividen G. J. and Kramer D. C. Preventive Prosthodontics-mucosal coverage of roots. J Prosthet Dent. 1978; 40:619-621.
16. Park J. Rehabilitation of the edentulous mandible with implant-supported overdenture using ball attachments and healing abutments: A case report. Saudi Dent J. 2009;21:139-142.
17. Bergendal T, Engquist B. Implant-supported overdentures: a longitudinal prospective study. Int J Oral Maxillofac Implants. 1998; 13: 253 -262.
18. Feine JS, Carlsson GE, eds. Implant overdentures. The standard of care for edentulous patients. Chicago; Quintessence; 2003.
19. Ercruyssen M, Marcelis K, Coucke W, Naert I, Quirynen M. Long-term, retrospective evaluation (implant and patient- centred outcome) of the two-implantssupported overdenture in the mandible. Part 1: survival rate. Clin Oral Implants Res 2010; 21 : 357-365.
20. Feine JS, Carlsson GE, Awad MA, Chehade A, Duncan WJ, Gizani S, et. al. The McGill Consensus Statement on Overdentures. Montreal, Quebec, Canada. May 2425, 2002. Int J Prosthodont 2002; 15 : 413-414.
21. Thomason JM, Kelly SA, Bendkowski A, Ellis JS. Two implant retained overdentures-a review of the literature supporting the McGill and York consensus statements. J Dent 2012; 40: 22-34.
22. Carlsson GE, Omar R. The future of complete dentures in oral rehabilitation. A critical review. J Oral Rehabil 2010; 37: 143-156.
23. Owen PC. Appropriatech: prosthodontics for the many, not just for the few. Int J Prosthodont 2004; 17 : 261262.
24. Gotfredsen K, Holm B. Implant-supported mandibular overdentures retained with ball or bar attachments: a randomized prospective 5-year study. Int J Prosthodont. 2000; 13: 125 – 130.
25. Naert I, Gizani S, Vuylsteke M, et al. A 5-year prospective randomized clinical trial on the influence of splinted and unsplinted oral implants retaining a mandibular overdenture: prosthetic aspects and patient satisfaction. J Oral Rehabil1999;26:195 – 202 .
26. Walton JN, MacEntee MI. A prospective study on the maintenance of implant prostheses in private practice. Int J Prosthodont. 1997; 10: 453 – 458.
27. Zarb GA, Jansson T, Jemt T. Other prosthodontic applications. In: Brånemark PI, Zarb GA, Albrektsson T, eds. Tissue-Integrated Prostheses: Osseointegration in Clinical Dentistry. 3rd ed. Chicago, IL: Quintessence Publishing; 1985: 283 – 292.
28. Morrow, R. M., et al. Tooth-supported complete dentures: An approach to preventive prosthodontics. J Prosthet Dent 1969 21:513-552
29. Joseph J. Massad, DDS; Swati Ahuja, BDS, MDS; and Dave Cagna, DMD, MS. Implant Overdentures: Selection for attachment systems. Dentistry Today. 2013,14:47
30. Banton B, Henry MD. Overdenture retention and stabilization with ball-and-socket attachments: principles and technique.J Dent Technol. 1997;14:14-20.
31. Chung KH, Chung CY, Cagna DR, et al. Retention characteristics of attachment systems for implant overdentures. J Prosthodont. 2004;13:221-226.
32. Preiskel HW. Overdentures Made Easy: A Guide to Implant and Root Supported Prostheses. Chicago, IL: Quintessence Publishing; 1996:212-232.
33. Asvanund C, Morgano SM. Restoration of unfavorably positioned implants for a partially edentulous patient by using an overdenture retained with a milled bar and attachments: a clinical report. J Prosthet Dent. 2004;91:610
34. Taylor TD, Agar JR. Twenty years of progress in implant prosthodontics. J Prosthet Dent. 2002;88:89-95.
35. Khadivi V. Correcting a nonparallel implant abutment for a mandibular overdenture retained by two implants: a clinical report. J Prosthet Dent. 2004;92:216-219.
36. Walton JN, MacEntee MI. A retrospective study on the maintenance and repair of implant-supported prostheses. Int J Prosthodont. 1993;6:451-455
37. Kurtzman GM. The locator attachment: free-standing versus bar-overdentures. Dental Labor International Plus. 2009;1:20-23.
38. English CE. Critical A-P spread. Implant Soc. 1990;1:2-3
39. Moeller MS, Duff RE, Razzoog ME. Rehabilitation of malpositioned implants with a CAD/CAM milled implant overdenture: a clinical report. J Prosthet Dent. 2011;105:143-146.
40. Cagna DR, Massad JJ, Schiesser FJ. The neutral zone revisited: from historical concepts to modern application. J Prosthet Dent. 2009;101:405-412.
41. Beresin VE, Schiesser FJ, eds. Neutral Zone in Complete and Partial Dentures. 2nd ed. St. Louis, MO: Mosby; 1979:15, 73-108, 158-183.
42. Beresin VE, Schiesser FJ. The neutral zone in complete dentures. J Prosthet Dent. 1976;36:356-367.
43. DeBoer J. Edentulous implants: overdenture versus fixed. J Prosthet Dent. 1993;69:386-390.
44. Naert I, Quirynen M, Theuniers G, et al. Prosthetic aspects of osseointegrated fixtures supporting overdentures. A 4-year report. J Prosthet Dent. 1991;65:671-680.
45. Cune MS, de Putter C, Hoogstraten J. Treatment outcome with implant-retained overdentures: Part II. Patient satisfaction and predictability of subjective treatment outcome. J Prosthet Dent. 1994;72:152-158.
46. Ekfeldt A, Johansson LA, Isaksson S. Implantsupported overdenture therapy: a retrospective study. Int J Prosthodont. 1997;10:366-374.
47. Engquist B, Bergendal T, Kallus T, et al. A retrospective multicenter evaluation of osseointegrated implants supporting overdentures. Int J Oral Maxillofac Implants. 1988;3:129-134.
48. Parel SM. Implants and overdentures: the osseointegrated approach with conventional and compromised applications. Int J Oral Maxillofac Implants. 1986;1:93-99.
49. Krennmair G, Ulm C. The symphyseal single-tooth implant for anchorage of a mandibular complete denture in geriatric patients: a clinical report. Int J Oral Maxillofac Implants. 2001;16:98-104.
50. Watson RM, Jemt T, Chai J, et al. Prosthodontic treatment, patient response, and the need for maintenance of complete implant-supported overdentures: an appraisal of 5 years of prospective study. Int J Prosthodont. 1997;10:345-354.
51. Widbom C, Söderfeldt B, Kronström M. A retrospective evaluation of treatments with implantsupported maxillary overdentures. Clin Implant Dent Relat Res. 2005;7:166-172.
52. Cagna DR, Massad JJ, Daher T. Use of a powered toothbrush for hygiene of edentulous implant-supported prostheses. Compend Contin Educ Dent. 2011;32:84-88.
53. Sadowsky SJ. The implant-supported prosthesis for the edentulous arch: design considerations. J Prosthet Dent. 1997;78:28-33.
54. Ahuja S, Cagna DR. Classification and management of restorative space in edentulous implant overdenture patients. J Prosthet Dent. 2011;105:332-337.
55. Lee CK, Agar JR. Surgical and prosthetic planning for a two-implant-retained mandibular overdenture: a clinical report. J Prosthet Dent. 2006;95:102-105.
56. Sadowsky SJ. Treatment considerations for maxillary implant overdentures: a systematic review. J Prosthet Dent. 2007;97:340-348.
57. Ahuja S, Cagna DR. Defining available restorative space for implant overdentures. J Prosthet Dent. 2010;104:133-136.
58. Behr M, Lang R, Leibrock A, et al. Complication rate with prosthodontic reconstructions on ITI and IMZ dental implants. Internationales Team für Implantologie. Clin Oral Implants Res. 1998;9:51-58.
59. Mericske-Stern RD, Taylor TD, Belser U.Management of the edentulous patient. Clin Oral Implants Res. 2000;11(suppl 1):108-125.
60. Payne AG, Solomons YF. The prosthodontic maintenance requirements of mandibular mucosa- and implant-supported overdentures: a review of the literature. Int J Prosthodont. 2000;13:238-243.
61. Schmitt A, Zarb GA. The notion of implant-supported overdentures. J Prosthet Dent. 1998;79:60-65.
62. Ichikawa T, Horiuchi M, Wigianto R, Matsumoto N. In vitro study of mandibular implant-retained overdentures: the influence of stud attachments on load transfer to the implant and soft tissue. Int J Prosthodont. 1996;9:394-399.
63. Cune M, Burgers M, van Kampen F, de Putter C, van der Bilt A. Mandibular overdentures retained by two implants: 10-year results from a crossover clinical trial comparing ball-socket and bar-clip attachments. Int J Prosthodont. 2010; 23:310-317.
64. Ceruti P1, Bryant SR, Lee JH, MacEntee MI. Magnetretained implant-supported overdentures: review and 1year clinical report.  J Can Dent Assoc. 2010 ; 76:a52.
65. Naert, I., Quirynen, M., Theuniers, G., and van Steenberghe, D.Prosthetic aspects of osseointegrated fixtures supporting overdentures. A 4-year report. J. Prosthet. Dent. 1991; 65: 671-680
66. Schmitt, A. and Zarb, G.A. The notion of implantsupported overdentures. J. Prosthet. Dent. 1998; 79: 6065
67. Tokuhisa, M., Matsushita, Y., and Koyano, K. In vitro study of a mandibular implant overdenture retained with ball, magnet, or bar attachments: comparison of load transfer and denture stability. Int. J. Prosthodont. 2003; 16: 128-134.
68. Sadowsky SJ. Mandibular implant-retained overdentures: a literature review. J Prosthet Dent. 2001;86:468-473.
69. Robert C. Vogel, Implant Overdentures: A New Standard of Care for Edentulous Patients- Current Concepts and Techniques. Compendium. June 2008Volume 29, Number 5.
    

    ---

    1.Assistant Professor, Department of Prosthodontics,Ziauddin College of Dentistry, Karachi, Pakistan.

    2.Clinical Lecturer, Department of Prosthodontics, Ziauddin College of Dentistry, Karachi, Pakistan.

    3.Assistant Professor, Department of Prosthetic Dental Science, King Saud University, Riyadh, Saudi Arabia.

    4.Post-doctoral Fellow, Faculty of Dentistry, University of Toronto, Ontario, Canada.

    Corresponding author: “Dr Haroon Rashid ” < drh.rashid@hotmail.com >