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In Vitro Effect of Mastication on the Retention and Wear of Locator Attachments in a Flat Mandibular Ridge Model

PURPOSE
The effect of masticatory loads on the retention of overdenture attachments is poorly documented. The aim of this in vitro study is to assess the effect of simulated mastication on the retentive properties and dimensions of Locator inserts.


MATERIALS AND METHODS
30 specimens simulating nonanatomic edentulous flat ridges with two implant replicas each were fabricated. Overdenture units were connected to the implants with Locator attachments and 3 types of inserts: transparent (Group T; n = 10 pairs), pink (Group P; n = 10 pairs), and blue (Group B; n = 10 pairs). The overdenture units were subjected to simulated bi-axial masticatory loads of 68.6 N. Locator retention was assessed using axial dislodging forces at baseline (T0) and following 100,000 (T1) and 200,000 (T2) masticatory cycles. The inner diameter of the insert (XY) and the diameter of the central core (AB) were measured under stereomicroscope at T0 and T2. Retention changes and dimensional variations of the inserts were statistically analyzed.


RESULTS
The 3 groups showed significantly different retentions with the highest values recorded for group T followed by group P, and finally group B at T0, T1, and T2. Groups T and P were not affected by loading while group B showed a significant mean retention loss from T0 to T1. XY and AB were significantly different between the 3 color-coded inserts at baseline and at T2. No correlation could be established between retention changes and dimensional variations of the 3 types of inserts.


CONCLUSIONS
Within the limitations of this in vitro study, simulated mastication seems to significantly affect the extra-light blue Locator inserts but not the more-retentive ones. The transparent and pink inserts may require less frequent replacements and could therefore be recommended under clinical conditions.