Failure rate is noticeably high in dental bioceramics for restorations even though progress has been made in reinforcement of the materials. One of the major causes of failures is due to surface and subsurface damage induced in intraoral adjustments. This process is a routine clinical procedure for marginal and occlusal fit using high-speed dental handpieces and diamond burs. Material removal using the diamond burs easily produce surface and subsurface damage in ceramic prostheses. Therefore, it is essential to minimize the surface damage in clinical dentistry. In this paper, we investigated the effect of diamond burs with coarse, medium and fine grit sizes on the degrees of subsurface damage in in vitro dental adjustments via numerical modeling. Finite element analysis was applied to model the dental adjusting processes and to predict the degrees of subsurface damage using different grit sizes of diamond burs.