Impact of tooth structure and fatigue cycles on the fracture strength of glass-ceramic onlays in the elderly

Abstract

Objective To investigate the impact of tooth structure and fatigue cycles on the fracture strength of glass-ceramic onlays for molar restoration in the elderly. Methods A total of 72 extracted molars due to periodontitis from people aged 60 years or over were selected and flattened to different levels of the occlusal surface.The percentage of enamel was calculated.Two groups with different percentages of enamel were selected from 72 molars, one group with(80±10)% enamel or the E group and the other group with (20±10)% enamel or the D group, with 12 samples in each group.IPS e. max CAD discs(diameter=9 mm, thickness=1.3 mm)were cemented to the prepared sample surface by using Variolink N resin cement system.Furthermore, three subgroups were formed randomly from each group(n=4, in each group). Subgroups were treated with 5, 100 000 and 1000 000 fatigue cycles, respectively, with the same load(180 N, 1.5 Hz)in water, following thermal cycling(5~55 ℃ for 1 500 cycles), and then fracture strength was tested. Results The fracture strength was(2 761.8±477.2)N in the E group and(1 100.1±216.9)N in the D group.The two-factor analysis of variance indicated that tooth structure had a significant influence on fracture strength(F=98.51, P 0.05). Enamel percentage had a positive linear correlation with fracture strength(r=0.915, =10.66, P<0.05). Conclusions Enamel percentage has a positive correlation with fracture strength of glass-ceramic onlays.For elderly people who have severe tooth wear, preserving more enamel within the adhesive area can increase the fracture strength of ceramic onlays for an extended period of time. Key words: Dental porcelain; Dental enamel