A laboratory Study to compare modified replica technique and replica technique used to measure the marginal fit of zirconium posterior bridges CAD\CAM

Replica technique remain most commonly used technique for measuring the marginal fit in the medical literature, the silicone rubber addition is considered most accurate and least changing dimensions. Aim of study to compare the accuracy and simplicity of traditional replica technique and modified replica technique to measure marginal fit of zirconium posterior bridges manufactured by CAD\CAM. After removal of first lower molar from TYPODENT (Frasco, Tettnang, Germany), the second lower molar and premolar neighboring were prepared commensurate with full ceramic restoration. Final impression of this bridge was taken by silicone rubber addition (Zhermack Elite HD+) with the aid of custom tray. The impression was condensed with amalgam to make the main metal cast. Fifteen custom acrylic resin trays were used for fabricate fifteen impressions of main metal cast that were used for fabricate 15 zirconium bridges by CAD\CAM technique According to the manufacturer's instructions. Tow rubber thicknesses were taken for the marginal fit of each bridge over its cast gypsum by used light silicone rubber addition. Then the first rubber thickness was treated by developed replica technique to form the Group (A) of the study and the second rubber thickness was treated by replica technique to form the group (B) of the study. Depending on T-test, no significant difference between two techniques was detected. We conclude that developed replica technique reliable technique to study and measure the marginal gap of bridge and crown, and it is statistically more accurate than the traditional technique.

دراسة مخبريّة للانطباق الحفافيّ لطريقتي صنع الجسور الزيركونيّة CAD\CAM و Slip-Casting

Recent development in dental materials had led to the fabrication of metal free fixed prosthodontics to improve the mechanical and aesthetic properties to restore posterior teeth depending on many techniques, therefore came the propose of this study to compare the marginal fit of Zirconia bridges made by CAD/CAM and Slip-Cast techniques. 30 Bridges were fabricated to restore missing first lower molar, they were divided into two groups (15 CAD\CAM, 15 Slip-Cast). The marginal fit was evaluated by measuring the thickness of light body silicone that made using Replica technique. Depending on T-test, the mean marginal discrepancy for CAD/CAM groups was 13.92μ and 11.30μ for Slip-Cast techniques. Therefore, it was concluded that the marginal fit of Slip-Cast techniques was significantly better than CAD/CAM techniques.