Comparison Of Retention Forces Of Three Locator Retentive Male Attachments Retaining Mandibular Overdenture

INTRODUCTION

Retention is a key element in removable prosthodontics. There is strong evidence that retention is of great importance for patients’ satisfaction. Burns et al. found a strong patient preference for overdenture attachments with superior retention.1 The lower retention of mandibular overdenture and the lower resistance against horizontal movements may lead to less denture stability during chewing and thus to a reduced masticatory performance.2 Although many factors such as proper border extensions, adhesion, cohesion, neuromuscular control etc. contribute to the retention of complete dentures, mechanical attachments play a chief role in enhancing the retention of the prosthesis especially that of mandibular overdentures. Among all implant restorations; loosening of overdenture retentive mechanisms were identified as the most common (33%) prosthodontic complication3, therefore, routine maintenance is required to ensure successful long-term outcomes.4 Fatigue or failure of overdenture attachments adversely affects function, maintenance aspects, and patient satisfaction.5

The aim of the present in vitro study is to compare the retention strength of three LOCTOR Male Attachments on an implant-retained overdenture model.

METHODOLOGY

Three pairs of LOCATOR Male Attachments (Zest Anchors, Escondido, CA, USA), namely, blue, pink and clear were tested. Each pair was subjected tovertical dislodgment forces.

The Test Model:

The experimental model representing a two implantretained mandibular overdenture was fabricated as follows:

A mandibular test model was poured in clear acrylic resin. Two 3.5 x 11 mm titanium implants (Astra Osseo SpeedTM (3.5 — 11 mm, Astra Tech, Mlndal, Sweden) were impeded in the anterior area of the mandible. A cast metal cobalt-chromium framework was fabricated and used to reinforce the experimental acrylic overdenture. The framework had four withdrawal loops, two in the anterior region and two in the molar regions of the mandible to be used during pull-off testing. Four stainless steel nuts (3 mm in diameter) were soldered to the most anterior area of the framework: two nuts soldered labial

to the implants and two nuts soldered lingual to the implants. The nuts were used to fasten and secure a lightcured acrylic resin housing (Triad, Dentsply International, Inc., York, PA) confining the two implants anteriorly (Fig 1).

Fig 1: Mandibular test model

The female compartments of the LOCATOR Attachment were screwed into the implants and the metal housings of the LOCATOR males were picked up in the acrylic housing with auto-polymerized acrylic resin. The different male pairs were interchanged within the metal housings.

Materials Testing:

Retentive force for each pair of the Locator males was tested using the series 5500 Instron Materials Testing Machine (Instron, Canton, MA) with a computer interface. The force was exerted at a crosshead speed of 50.8 mm/min, which has been reported to approximate the removal force of the denture from the edentulous ridge during mastication. Metallic chains with S hooks connected the framework to the universal testing machine at the withdrawal loops.

Dislodging tensile forces were applied in a vertical direction to measure the peak or maximum load- the maximum force developed before separation of the attachment components.

The one-way analysis of variance was performed for each of the four measurements. The three male compartments were compared using the .05 level of significance.

RESULTS

Results with statistical analysis are presented in Tables 1 & 2 and in Fig.2. The peak load-to-dislodgement for all retentive males ranged from 11.86 +-2.52 N to 39.11+-3.24 N.

Retention force of Locator LR white showed the greatest retention, with a peak load-to-dislodgement of 35.49+-3.24 N. The Locator LR blue took the second place with a retention force of 19.02 ± 5.32 N which is higher than that of the Locator LR pink (15.5 ± 2.52 N).

The statistical measures (Minimum,maximum, Standard deviation) for the peak load-to-dislodgement for the three colors and the Anova test results are shown in tables1 and 2:

Descriptive Statistics

Table 1. Peak load to dislodgement measures for the three male attachements.

ANOVA

Table 2. Anova test results comparing the retention forces of the three male attachemnts

Fig 2. Graphical representation of the retention forces for the three male attachments, white, pink and blue.

DISCUSSION

A minimum of 20 N has been suggested for optimum overdenture retention. Chung et al compared the retention forces of different attachments. Among those was Locator white and Locator pink nylon attachments (28.95 &12.33 N; respectively).

Several studies compared the retention of locator attachments and ball attachment. Sadiq studied two models designs based on number & location of the implants.

He found that the retention force of locator attachments (31.30 +- 0.12 N)was more than that of the ball attachments. Also, Alsabeeha et al. found that Locator attachments had more retention force than ball attachments. The values of his findings for Locator white & pink were 28.95 N & 12.33, respectively. The results found in our study for Locator white and pink attachments are close to these findings (35.49 & 15.5 N; respectively). Hence, Locator white could be recommended in cases of severely resorbed mandible where other anatomical and biological factors are limited to aid in the retention of mandibular overdentures. However, our results are in disagreement with the findings of Ahmadzadeh who found that Locator pink had a retention force of 20.90 += 3.74 N which is greater than the findings of this study (15.51 +- 2.52N).

Both the white and the blue attachments have retention forces that are within the optimum retention value for overdenture retention while the pink male attachment showed a retention force that is below the required optimum value to retain a mandibular overdenture.

CONCLUSIONS

Within the limitations of this study, it was found that:

• Locator white male attachment shows the highestretention force.
• The retention force values of the Locator pink areless than that of the Locator blue attachment.
• The Locator blue retention force found to be veryclose to the value for optimum overdenture retention, which can be used, in average cases where all other biological factors are favorable.
• The Locator pink found to have a retention forcevalue that is lower than the required optimum value for overdenture retention. It can be used in cases of wellformed residual ridges with minimal bone resorption.

Author Contribution: Both MF and SOB have significant contribution in conceiving and designing the study, and recording, analysis and interpretation of data; have written or critically reviewed the manuscript, have approved the final version and have agreed to be responsible for accuracy of results and integrity of the research Potential Conflict of Interest: Authors have no potential conflict of interest, have no source of funding for the research project and have access to the study data and are responsible about integrity and accuracy of data analysis.

 Disclosure: None disclosed

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