Korean J Dent Mater.  2022 Mar;49(1):14-26. 10.14815/kjdm.2022.49.1.14.

Machinability evaluation of ceramic blocks for CAM by merlon fracture test model

• Lee H
• Bae JM
• Oh S

• KMID: 2528136
• DOI: http://doi.org/10.14815/kjdm.2022.49.1.14

Abstract

In this study, the machinability of two silica-based and two zirconia-based ceramic blocks was evaluated by using the Merlon fracture test model in accordance with the International Standard “ISO/DIS 18675 Dentistry — Machinable ceramic blanks (2020)”. The two silica-based blocks of Vitablocs Mark II (VM) and IPS e.max CAD LT (IC) were machined with Cerec inLab MC ×5 (Dentsply Sirona, Bensheim, Germany), and the two zirconia-based blocks of Katana Zirconia HT (HT) and Katana Zirconia STML (ST) were machined with DWX-51D (Roland, Sydney, NSW, Australia). For the evaluation of the machinability of the prepared specimens, one Merlon wall was subdivided into 10, and the intact surface was counted among the ten divided surfaces. Each sample having four Merlon walls was rated out of 40. The surface roughness of the prepared specimens was measured using a surface probe microscope. The machinability of the prepared specimens in 0.4 mm group (32.00±3.82) showed the highest score values compared to other groups (P<0.05). Also, the machinability decreased in proportion to the machined thickness of the specimens. A comparative test of the machinability of silica-based and zirconia-based blocks showed that the machinability scores of two zirconia-based blocks were significantly higher than those of silica-based blocks (P<0.05). From the result of surface roughness measurement, two silica-based blocks (VM and IC) showed a rough surface in the bottom area and a smooth region in the Merlon area. On the contrary, two zirconia-based blocks (HT and ST) showed a smooth surface in the bottom area and a rough surface in the Merlon area. These results confirmed that the material for used for computer aided milling (CAM), the block pre-treatment process, and the insertion direction of the milling bur seemed to affect the machinability of the block for CAM. Therefore, within the limitation of this study, we can expect that additional research considering external factors such as various block materials, cutting machines, and milling burs would be necessary.

Keyword

Merlon fracture test; Ceramic block; Silica; Zirconia; Machinability; Surface roughness