Brittleness index and its relationship with materials mechanical properties: Influence on the machinability of CAD/CAM materials

Abstract

The aim of this study is to evaluate the machinability of four CAD/CAM materials (n = 13) assessed by brittleness index, Vickers hardness, and fracture toughness and interaction among such mechanical properties. The materials selected in this in vitro study are Feldspathic ceramic [FC], Lithium-disilicate glass ceramic [LD], leucite-reinforced glass ceramic [LR], and nanofilled resin material [RN]. Slices were made from the blocks following original dimensions 14 x 12 x 3 mm (L x W x H), using a precision slow-speed saw device and then surfaces were regularized through a polishing device. Brittleness index and fracture toughness were calculated by the use of specific equations for each one of the properties. The Vickers hardness was calculated automated software in the microhardness device. One-way Anova and Pearson's correlation were applied to data evaluation. LD obtained the highest values for brittleness index and was not significantly different from FC. LR presented statistically significant difference compared with RN, which had the lowest mean. Vickers hardness showed LD with the highest average, and no statistical difference was found between FC and LR. RN presented the lowest average. Fracture toughness showed FC and LR not statistically different from each other, likewise LD and RN. The brittleness index, considered also as the machinability of a material, showed within this study as positively dependent on Vickers hardness, which leads to conclusion that hardness of ceramics is related to its milling capacity. In addition, fracture toughness of pre-sintered ceramics is compared to polymer-based materials.

In Vitro Evaluation of Translucency and Color Stability of CAD/CAM Polymer‐Infiltrated Ceramic Materials after Accelerated Aging

“…The ceramic and polymer materials currently used in dentistry for crowns and multiple‐unit FPDs have different material properties, not all of which are favorable. Ceramics are brittle, which increases the risk of marginal chipping and fracture, and delamination 5‐7 . Similarly, poor fracture toughness of glass ceramics has led to the development of a range of ceramic materials with a high crystalline content to withstand the mechanical stresses of occlusal forces 8 .…”

Overview of Several Typical Ceramic Materials for Restorative Dentistry

“…In addition, inlay and onlay restorations made of leucite-reinforced glass ceramic have shown satisfactory clinical results with a failure rate of about 16% after 12 years and no secondary caries observed [ 25 ]. However, due to the nature and machinability of leucite-reinforced glass ceramic, some studies still do not recommend its use in posterior dental crowns and fixed dentures [ 7 , 26 , 27 ]. There are various factors that affect the life of ceramic restorations.…”

“…Additionally, in cases where the use of feldspar porcelain materials in the posterior area of the mouth is not recommended, lithium disilicate ceramics have shown excellent and long-term success in the anterior region and posterior region of the oral cavity, such as extended veneers (as shown in Figure 6 ) [ 33 ]. Therefore, the excellent mechanical properties, high flexural strength, and esthetic properties of lithium disilicate ceramics make it the first choice for the overall restoration of the posterior oral area and gradually become one of the most popular all-ceramic restoration materials [ 7 , 11 , 13 , 26 ].…”

Development of silicon nitride ceramic for CAD/CAM restoration

“…In addition, machinability of new CAD/CAM material is a very important. The mechanical tests related to machinability, such as brittleness index and hardness, necessary to considered of patiallysintered CAD/CAM Si 3N4 block 21) .…”