Comparison of Polishing and Overglazing Effect on Fracture Load of Machinable Feldespathic Ceramics (Vita Mark II)

Nowadays, there is little information about the effect of surface polishing and glazing on the fracture strength of ceramic restorations made with CAD/CAM. Also, due to the contradictions in the available information and the shortcomings in previous studies in this field, this research aims to compare the fracture load of ceramic restorations made of CAD/CAM blocks (vita Mark II) after overglazing and polishing. The purpose of this study is to compare the effects of polishing and overglazing on the fracture load of Vita Mark II machinable feldspathic porcelain. The prepared model was scanned by a laboratory scanner, and 20 composite resin dies were made from it by CAD/CAM. 20 feldspathic crowns were made for the dies by the CAD/CAM system. The crowns were divided into two groups. One group was polished, and the other was overglazed. The cemented crowns were kept for 1 week in normal saline, and their breaking force was measured and statistically analyzed. The findings were analyzed by a T-test. A distinct difference was observed between the studied groups (P = 0.004). According to the T-test, the fracture force of the polished group was significantly higher than that of the overglazed group. Based on the results of this study, polished coatings had higher fracture resistance than overglazed coatings. Although the overglazed surface was smoother than the polished one, its strength was lower, which indicated that the fracture resistance was dependent on the internal structure of the material.