Essay examples --

Ceramics are used extensively in dental restorations because of their superior aesthetics and biocompatibility compared to metals (1). However, the brittleness of ceramics can initiate snap off propagation causing failure of the restoration (2). Resin cementums are used for cementing ceramic restorations because of their excellent aesthetics and mechanical properties. The cement penetrates any defects or irregularities on the ceramic surface thereby preventing propagation of cracks (3, 4, 5). Optimal clinical performance depends on sufficient rosin cement polymerisation. Degree of conversion (DC) is affected by the amount of light reaching the cement which in turn, is affected by the opacity and the midstness of the ceramic as well as the thickness of the resin cement layer. Insufficient polymerisation influences both mechanical properties and clinical performance of the restoration (2, 5). Aims of this study are to see how light transmission (LT) is affected by thickness or opac ity of a ceramic and how resin cements thickness affects DC. Hypotheses are (1) LT falls with increasing thickness or opacity (2) DC would decrease with thicker cement samples. Method Shade A1, A2, A3 and A3.5 of Base Dentine VN7 powder (Vita, Bad Sckingen, Germany) were used. Ceramic disc thicknesses tested (measured using digital calliper) were 1.40, 1.00 and 0.60mm.Specimen preparation 20 ceramics discs, five of each shade, were prepared by mixing 0.73g of powder with 0.29mL of Modelling Liquid (Vita, Bad Sckingen, Germany). The mixture was placed in a 1.60mm thick metal ring on a mould assembly and vibrated for 40 seconds. The surface was levelled using a razor blade before firing the discs in a furnace (Vita Vacumat 40, Bad Sckingen, Germ... ... the disc. LT through a ceramic disc would ultimately affect the polymerisation of resin cements. The second hypothesis that DC should decrease with increasing resin cement thickness layer is rejected as the graph showed that 1.00mm re sin cement thickness had the greatest DC. A higher DC was seen with thinner resin cement specimens because there would be more LT and the photoinitiator in resin cements needs light to initiate the polymerisation reaction. A thicker resin cement layer would allow less light to reach the bottom so there would be less monomer to polymer conversion and resultantly, lower DC. However, very thin specimens may experience light reflectance which may affect the DC results. ConclusionLT through ceramics was measured and LT decreased with increasing thickness or opacity. DC appeared to plus when thicker resin cement samples were tested.