The influence of framework design on internal and marginal gap width of anatomic and nonanatomic metal copings fabricated by selective laser sintering

In spite the fact that conventional slip-cast crowns are still largely used in everyday practice, and these techniques had shown their efficiency, selective laser sintering is a new technology which arouse more and more interest in prosthetic dentistry. One of the key factor which determines clinical success is the marginal and internal fit of fixed dental prostheses who influences the long-term survival and clinical outcomes. Selective laser sintering is a rapid prototyping technology used to produce accurate complex-shaped metal objects directly using a three dimensional computer model obtained by computer-aided design. Pieces are automatically fabricated, layer-by-layer by selective superficial melting of metallic powder, these metallic particles fusing together. Being a relatively new technology in this field, it requires further evaluation before embracing it and use it on a large scale as a current procedure. The aim of the study was to evaluate the effect of geometry of tooth preparation and copings design on marginal and internal gap of laser-sintered frameworks. Two maxillary first molars where prepared with two different kind of marginal limits. Two different framework designs were conceived for each: model 1 – a coping with a constant framework thickness of 0.6 mm and model 2 an anatomically modified shaped cusp supporting framework with a constant veneering thickness. Marginal fit was evaluated with silicone replica technique. Specimens were analyzed by light microscopy at X4 magnification, digital photos were taken and a digital measurement program.The mean marginal gap values were between 37 and 95 μm, the means for the axial region were between 47 and 70 μm and for the occlusal region between 67 and 147 μm. Copings produced by selective laser sintering using CAD/CAM technologies demonstrate acceptable marginal and internal fit in the range of 47 to 120 μm, with better results in case of anatomically-reduced frameworks. Key-Words: rapid prototyping, selective laser sintering, marginal and internal fit, CAD/CAM system, cobaltchromium alloy, metal-ceramic crowns