Effects of acid hydrolysis and mechanical polishing on surface residual stresses of low-fusing dental ceramics

Abstract 

Statement of problem

Cracks may arise in a ceramic restorative material over time, resulting in sudden fractures at stresses well below the yield stress.

Purpose

This study evaluated by means of indentation technique the effects of acid hydrolysis and mechanical polishing on the surface residual stresses of low-fusing ceramic materials.

Material and methods

A total of 64 ceramic bars were formed to produce 4 groups of 16 bars each for 4 ceramic materials (Duceram-LFC Dentin, Duceram-LFC Enamel, Finesse Dentin, and Finesse Enamel). Four surface-treatment groups (n=4) were then formed for each of the 4 materials. The 4 surface treatments were control (autoglaze), hydrolysis, glaze/polish, and polish/glaze. A Vickers indenter contacted the Duceram-LFC specimens with a 5-N load and the Finesse specimens with a 3-N load for 10 seconds. Scanning electron microscope (SEM) was used to study surface texture before and after hydrolysis and polishing. Differences in mean crack lengths were analyzed with 1-way analysis of variance and least significant difference test (α=.05.)

Results

SEM showed obvious surface flaws as a result of hydrolysis on Duceram-LFC Enamel and Dentin specimens. However, statistical analysis of the resulting crack lengths revealed no significant differences between values for the control groups (58.16 ± 3.88) (53.53 ± 2.67) and hydrolysis groups (57.11 ± 4.09) (54.54 ± 3.15) for Enamel (P=.081) and Dentin (P=.093) respectively. When comparing polished groups and nonpolished groups, the mean crack lengths were significantly shorter for polished specimens of Duceram-LFC Enamel (53.76 ± 3.17), Finesse Enamel (40.56 ± 3.31), and Finesse Dentin (39.76 ± 3.81) porcelains compared with their control groups (58.16 ± 3.88) (43.54 ± 4.12) (41.19 ± 3.47), respectively (P<.0001). The mean crack lengths were significantly longer for polished specimens of Duceram-LFC Dentin (59.16 ± 3.52) porcelain compared with the control group (53.53 ± 2.67) (P<.0001).

Conclusion

Within the limitations of this study, hydrolysis did not improve surface residual stresses of Duceram-LFC and Finesse ceramic materials. Mechanical polishing improved surface residual stresses of all materials tested, except Duceram-LFC Dentin porcelain.