Water sorption, solubility, and tensile bond strength of resilient denture lining materials polymerized by different methods after thermal cycling.

STATEMENT OF PROBLEM

The clinical properties of resilient denture lining materials may be influenced by the methods used to polymerize them.

PURPOSE

This study evaluated and compared water sorption, solubility, and tensile bond strength of 2 resilient liner materials polymerized by different methods after being thermal cycled.

MATERIAL AND METHODS

Two acrylic resin-based resilient liner materials were evaluated: 1 (Light Liner) polymerized by visible light, and 1 (Ever-Soft) processed by 2 different methods: hot water bath and microwave energy. To evaluate water sorption and solubility, 10 disc-shaped specimens (50 x 0.5 mm) were fabricated for each polymerization method, using acetate matrices. The specimens were dried and thermal cycled (2000 cycles) between baths of 5 degrees C and 55 degrees C. After thermal cycling, the specimens were weighed, dried, and weighed again to calculate the water sorption values and solubility. For tensile bond strength assessment, 12 rectangular specimens measuring 83 mm in total length and with a cross-sectional area of 10 x 10 mm were fabricated using each polymerization method. The specimens were also thermal cycled (2000 cycles) and, afterwards, tested in a universal testing machine at a crosshead speed of 6 mm/min with 100 Kg load cell. The type of failure was determined by use of stereoscopic microscopy. The data (for water sorption and solubility, n = 30, and for tensile bond strength, n = 36) were submitted to 1-way analysis of variance. The means were compared using the Bonferroni test (alpha=.05).

RESULTS

For water sorption the results showed no significant differences among the polymerization methods. Light Liner showed the lowest solubility values (5.3% +/- 0.3%) when compared to Ever-Soft (hot water bath: 7.3% +/- 1.1% and microwave energy: 7.8 +/- 0.9%). For tensile bond strength, Ever-Soft polymerized by microwave energy (0.7 +/- 0.0 MPa) showed the greatest and most significant ( P <.05) value when compared to Ever-Soft polymerized by hot water bath (0.5 +/- 0.1 MPa) and Light Liner polymerized by visible light (0.5 +/- 0.0 MPa). Most Ever-Soft specimens polymerized by microwave energy and Light Liner specimens showed adhesive/cohesive failures. However, Ever-Soft polymerized by hot water bath showed 50% adhesive/cohesive and 50% adhesive failures. The results at the reline material-resin bond interface showed the absence of cohesive failures.

CONCLUSION

Within the limitations of this study, Light Liner showed the lowest solubility values. Ever-Soft should be polymerized by microwave energy to obtain the greatest tensile bond strength values. Materials polymerized by microwave energy and visible light showed predominantly adhesive/cohesive failures.