"Avaliação da retenção de coroas metálicas fundidas em função dos tipos de agentes cimentantes e das ciclagens térmica e mecânica"

Abstract

The aim of this study was to evaluate the retention of NiCr cast metal crowns fixed with two different lutting agents after thermocycling and mechanical load. The nature of the cement failure was evaluated too. Twenty natural human molar teeth extracted were selected (Banco de Dentes Permanentes Humanos da Faculdade de Odontologia da Universidade de São Paulo-SP). They were prepared at 4mm height, 8mm diameter and 20º of convergence. The cast crowns were lutted with zinc phosphate cement (n=10) and resin cement (n=10) and stored in water at 37ºC for 24 hours. Randomly the half of the specimens of each cement were thermal (5ºC and 55ºC for 700 cycles) and load cycled (2 Hz, 141 N load for 200.000 cycles). The control group did not perform the thermal or fatigue tests. The pull-out test was performed and the results showed a significant (confidence interval 95%) superior retentive strength for Panavia F resin cement (mean value 569,43 N) when compared with zinc phosphate (mean value 350 N). The aging tests were significant (p<0,001) about their influence over the retention of the crowns. They was no significant difference between control and cycled group for crowns lutted with phosphate cement (p>0,05). Adhesive failure of the cements was observed for all subjects.