Faisal Moeen.
Effect of varying height and taper on the fatigue performance of full-coverage Tesceraatl ceromer crowns.
J Pak Dent Assoc Jan ;14(3):163-70.

OBJECTIVE: This study assessed the effects of varying crown preparation heights and tapers on the fatigue performance of full-coverage TESCERAATL ceromer crowns. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

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