Repair strength of autopolymerizing, microwave, and conventional heat-polymerized acrylic resins☆

Abstract 

Statement of problem

Acrylic resin dentures are susceptible to fracture after clinical use. The repair procedure should be time saving, strong, and should not affect dimensional accuracy.

Purpose

This study evaluated the transverse repair strength of a conventional heat-polymerized (Lucitone 199, “L”) and a microwave-polymerized (Acron MC, “A”) acrylic resin that were repaired with these same resins and with an autopolymerizing acrylic resin (Acron MC/R, “AR”).

Material and methods

Twenty-four rectangular specimens (65.0 × 10.0 × 3.3 mm) of L or A and 6 of AR were manufactured according to ISO/FDI 1567 and stored in distilled water at 37°C for 7 days. Eighteen specimens of L or A were selected randomly. Six specimens of each material remained intact (control), each 6 were sectioned in the middle to create a 10-mm gap and repaired with the materials L, A, or AR. After an additional 7 days of storage at 37°C, the transverse strength (MPa) of the repaired and intact specimens was measured using a 3-point bending test. A 2-way ANOVA and a Tukey HSD test were performed to identify significant differences (α=.05). The nature of the failure was noted as adhesive, cohesive, or mixed.

Results

The intact and repaired specimens showed similar transverse strength values (MPa), except for A-intact (80.6 ± 2.9), which was significantly stronger (P<.05) than the other materials tested as well as the repaired groups (P<.05). No differences were detected among the repaired groups. Repaired specimens exhibited 3 types of failures: adhesive (interface), cohesive (only in the repair material), and mixed (interface and repair material), with incidences of 2.8, 25, and 72.2%, respectively.

Conclusion

The autopolymerizing resin exhibited a repair strength similar to those found for the conventional heat- and microwave-polymerized materials.