Flexural strength of repaired denture base materials manufactured for the CAD-CAM technique

PURPOSE

To evaluate the flexural properties of repaired poly(methylmethacrylate) (PMMA) denture base materials for computer-aided design/computer-aided manufacturing (CAD-CAM) and to compare them with heat-activated polymerized PMMA.

METHODS

A total of 288 specimens (65 × 10 × 2.5 mm) were prepared using both CAD-CAM and conventional blocks and repaired using autopolymerizing and visible-light polymerizing (VLC) materials. Microwave energy, water storage and hydroflask polymerization were applied as additional post-polymerization cycles after the repair process. The flexural strength (FS) of the specimens was evaluated using the three-point bending test. Data were evaluated statistically using 2-way ANOVA followed by Bonferroni's correction to determine the significance of differences between the groups (P ≤ 0.05).

RESULTS

The FS of the denture base materials for CAD-CAM was significantly higher than that for the heat-activated group (P ≤ 0.05). The FS was significantly highest when microwave energy was used for the post-polymerization cycle. The FS values for all groups repaired with VLC resin were significantly lower than for the autopolymerization group (P ≤ 0.05).

CONCLUSION

The flexural properties of denture base materials for CAD-CAM repaired using autopolymerizing acrylic resins can recover by 50-70%. Additional post-polymerization cycles for autopolymerizing repair resin can be suggested to improve the clinical service properties of repaired dentures.

Effect of Surface Textures and Fabrication Methods on Shear Bond Strength Between Titanium Framework and Auto-Polymerizing Acrylic Repair Resin

The aim of the study was to evaluate the effect of airborne particle abrasion (using different sizes of alumina particles) on the shear bond strength (SBS) between cast and milled titanium metal frameworks and auto-polymerizing acrylic repair resin. Forty flat cylindrical titanium disks were divided into two main divisions: cast and milled titanium. The two divisions were further subdivided into four groups based on metal surface treatment. Three particle sizes of aluminum oxide air abrasive powders (50µm, 110µm, and 250µm) were used for metal surface treatment by airborne particle abrasion. One group was the control group with no surface treatment. Auto-polymerizing acrylic repair resin was applied to all titanium disks. The specimens were subjected to SBS testing using a universal testing machine (Instron Corporation, Norwood, Massachusetts, United States). Surface evaluation was performed using a scanning electron microscope. One-way ANOVA was used for statistical analysis. The results showed a significant increase in SBS after airborne particle abrasion of both milled and cast titanium groups (p<0.001). The SBS was directly proportional to the size of the aluminum oxide particles. The milled titanium group showed higher SBS values than the cast group when the surface was not treated with alumina particles (p < 0.001) and when the surface was treated with the smaller particle sizes of 50 µm, whereas the cast group demonstrated higher SBS values than the milled group (p < 0.01) when the particle size was increased to 110 µm and 250 µm. It could be concluded that SBS between titanium metal frameworks and auto-polymerizing repair acrylic resin was directly related to the size of the alumina airborne particle abrasives. The fabrication method of the titanium framework also influenced the SBS as the untreated milled frameworks demonstrated favorable SBS values compared to the untreated cast frameworks.