Effect of varying height and taper on the fatigue performance of full-coverage TESCERA ATL ceromer crowns

ABSTRACT

This study assessed the effects of varying crown preparation heights and tapers on the fatigue performance of full-coverage TESCERAATL ceromer crowns. Seven cobalt-chromium dies were fabricated to receive full-coverage crowns. The first four dies had heights measured at 4.0, 3.5, 3.0 and 2.5 mm from the lingual wall, each with a 6° taper and assigned as groups 1 to 4 respectively. The last three dies had tapers measured as 14°, 18° and 22°, with heights fixed at 4 mm and assigned as groups 5 to 7 respectively. All other variables were kept constant. Ten full-coverage TESCERAATL crowns were fabricated for each of the 7 dies, All 70 crowns were cemented with zinc phosphate onto their respective cobalt-chromium dies and secured on a metal repositioning jig, which standardized the load application point. The assembled specimens were subjected to a unidirectional cyclic loading of 210 N at a frequency of 4 Hz sequentially from group I to 7. Number of cycles to failure for each specimen was recorded once catastrophic failure occurred. Two electrical resistance strain gauges were used to indicate preliminary failure. One-way Analysis of Variance [ANOVA] and post hoc Tukey tests were conducted for groups 1-4 and 5-7. There is a statistical difference between groups 1-4 and 5-7 [p<0.05]. The means and standard deviations for the first four groups were 4.255 x105 [ +/- 0.486], 4.295 x l 05 [ +/- 0.689], 4.264 x 105 [ +/- 0.567] and 2.406 x 105 [ +/- 0.656] cycles to failure respectively. The means and standard deviations of groups 5, 6 and 7 were 4.12 x105 [ +/- 0.401], 3.583 x105 [ +/- 0.352] and 3.016 x105 [ +/- 0.246] cycles to failure respectively. Fatigue performance remains unaffected by reductions in height up to a particular value [3.0mm] and then suddenly drops. Fatigue performance follows a linear relationship with changes in taper, with fatigue life gradually decreasing with an increase in taper