Marginal Chipping Of Three Different CAD/CAM Ceramic Veneering Materials As Influenced By Machinability

Statement of the problem: The curiosity of many prosthodontists was attracted towards CAD/CAM technology combined with the newly specifically designed ceramic materials to achieve superb esthetic restorations for their patients. The new ceramic materials with their different mechanical properties might have an impact on their machinability particularly for producing thin esthetic restorations.
Purpose: The purpose of this investigation was to evaluate the marginal quality of three different ceramic veneers: Leucite reinforced, hybrid and lithium di-silicate in terms of edge chipping and chipping factor using different machining protocols.
Materials and methods: In order to achieve the purpose of this study, a maxillary central incisor of a Typodont was prepared for a feather edge veneer preparation to receive forty five ceramic veneers that were milled from three different materials using the Cerec CAD/CAM system. The three tested materials were leucite-reinforced glass ceramic (IPS Empress CAD), hybrid ceramic (Vita Enamic), and lithium di-silicate glass ceramic (IPS e.max CAD). The forty five veneers were classified into three groups according to the type of the material fifteen each, that were further divided into three subgroups of five specimens each according to the three tested machining speeds: normal, fast, and two-step. A digital camera was used for taking top images for the tested veneer margins that were imported into image analysis software to measure the peripheral veneer circumference (P). A stereomicroscope was used to measure the amount of marginal chipping of each veneer in microns (L). The chipping factor (CF) was calculated using the following equation: CF= L/P x 100, where (L) is the amount of marginal chipping and (P) is the marginal circumference of each veneer. The data of the chipping factor of each veneer margins were recorded and tabulated to be statistically analyzed in order to detect the influence of either the ceramic material or the machining protocol on the quality of the veneer margins in terms of edge chipping.
Results: Effect of ceramic type regardless of machining protocol: The statistical analysis of the obtained data revealed that e.max CAD (LD) showed the statistically significant highest mean chipping factor value (7.25 ± 2.56) followed by IPS Empress CAD (LR) (4.01 ± 0.83), and the least mean value was obtained with Vita Enamic (HC) (2.83 ± 1.56). Effect of machining protocol regardless of ceramic type: there was a statistically significant difference between the three milling techniques, where fast milling showed the highest mean chipping factor value (6.30±2.97), followed by normal milling (4.89±2.22) where the least chipping factor mean value (2.90±1.60) was obtained with the two-step milling.
Conclusions:
The edge quality of thin ceramic CAD/CAM restorations proved to be material dependent.
The machinability for producing thin CAD/CAM ceramic restorations influenced significantly their marginal quality.
The prosthodontist should be aware and knowledgeable about the mechanical properties of the recent CAD/CAM ceramic materials in order to choose the optimum one with the convenient milling protocol during the treatment planning to get the best clinical performance.