Optimization of milling condition of composite resin blocks for CAD/CAM to improve surface roughness and flexural strength

Abstract

This study aims to elucidate the relationships between the flexural strength and surface topography of composite resin blocks, utilized for the CAD/CAM system, after milling in various step-over amounts. The rectangular specimens were milled from CAD/ CAM blocks with step-over amount 0.01, 0.02, 0.05, 0.1, and 0.2 mm; further, a three-point bending test was conducted to reveal the flexural strength. The surface morphology after milling was assessed by a 3D laser microscope. The surface roughness significantly decreased by reducing the step-over amount. Although there was significant association between the surface roughness and flexural strength by the Pearson correlation, the 95% confidence intervals of the flexural strength were between the mirror-polished and sand-blasted groups. These results suggest that a precise step-over amount enables us to obtain a smooth surface. Furthermore, the flexural strength of the rough surface milled by a large step-over amount caused no damage to the composite resin for CAD/CAM crown.

Effect of Spindle Speed and Feed Rate on Surface Roughness and Milling Duration in the Fabrication of Milled Complete Dentures: An In Vitro Study

“…The sample size was calculated using an analysis software program (G*Power 3.1.9.7; Kiel University, Kiel, Germany). Based on a previous study [16], the sample size required to investigate the accuracy and milling duration for one combination of spindle speed and feed rate was determined to be six. Three specimens are aligned with eight supports.…”

“…The surface roughness of a composite resin block improves the bonding strength and is influenced by the milling conditions [16]. A previous study measured the milling duration; however, it did not discuss the relationship between the milling duration and the milling conditions.…”

Effect of air abrasion pressure and CAD/CAM milling on microtensile bond strength of reinforced composite inlays to immediately sealed dentin: An invitro comparative study

“…7 Furthermore, CAD/CAM milling procedures are well known to significantly increase the surface roughness of ceramics and composite materials. 8,9 However, the effect of such roughness solely on the restoration bond strength is not fully understood.…”