Influence of linear expansion of two different non metallic core materials upon cervical marginal accuracy of full veneer crowns

ABSTRACT

The effect of water sorption and linear expansion of two different non metallic core materials 1] Composite and 2] Reinforced glass ionomer on the cervical marginal seating of cast metal crowns was investigated in this study. Thirty freshly extracted sound mandibular molar teeth were used in this study. The teeth were machined cut to simulate average dimensions of a prepared lower second premolar tooth with chamfer finish line. The teeth were decoronated 2 mm above the finish line then specially prepared to receive equal volumes of either pin retained composite or pin retained reinforced glass ionomer. The teeth after that were restored with full coverage metal crowns. Ten of each type of core samples were immersed in 37 degree normal saline while the remaining samples were maintained dry [control]. The vertical cervical marginal accuracy of the crowns were microscopically measured with 1 micron accuracy before immersion and after 6, 12 hours and every day of the following ten days of saline immersion. The statistical analysis of the results revealed that composite core immersed in saline solution at 37 degree possessed dimensional instability with the maximum linear change between the first and the second day. Also the reinforced glass ionomer core showed no effect upon the certical marginal seating of the overlying full coverage cast metal crown