Marginal Accuracy of CAD/CAM Fabricated Monolithic All-Ceramic Crowns As A function of Digital Scanning Techniques

Purpose : The aim of this study was to evaluate the influence of intraoral and extraoral scanning techniques on the vertical marginal gap distance of two types of computer aided designing/computer aided manufacturing (CAD/CAM) fabricated all-ceramic monolithic crowns.
Materials and methods: Maxillary and mandibular typodont models were used in this study in which a standardized all-ceramic preparation of lower first molar tooth was carried out. These typodont models with the prepared tooth were representing the patient’s mouth. Thirty all-ceramic crowns were fabricated by CAD/CAM technique and divided into three groups(10 crowns each) according to their scanning technique; Group I: scanning of the typodont models by intraoral scanner. Group II: scanning of silicon impressions by extraoral scanner. Group III : scanning of stone casts by extraoral scanner. Each group was further sub-divided into 2 sub-groups (5 crowns each) according to the type of crown material. Sub-group(A): zirconia(BruxZir) crowns and
Sub-group (B): hybrid ceramic(Vita Enamic) crowns. The vertical marginal gap distance between each crown margin and finish line of the prepared tooth was measured using a Digital microscope of 40X at 16 points / crown. Data were collected, tabulated and statistically analyzed using Tukey’s post-hoc and Two-way ANOVA tests (P< 0.05). Results: Different scanning techniques as well as crown materials had a statistically significant effect on vertical marginal gap distance (µm) at P-value 0.026. The intraoral scanning technique recorded the lowest statistically significant vertical marginal gap distance mean values for both crown materials among the three scanning techniques. Regarding the crown material, hybrid ceramic Vita Enamic crowns had a lower statistically significant vertical marginal gap distance values than zirconia BruxZir crowns with all the tested scanning techniques. Conclusion: The vertical marginal gap distance of monolithic crowns was significantly affected by the scanning techniques and crown materials with the superiority of the intraoral scanning technique. Vita Enamic crowns had lower vertical marginal gap distance than BruxZir crowns with different scanning techniques. All the tested monolithic crowns had vertical marginal gap distance values within the clinically acceptable levels.
Key words: intraoral scanner, extraoral scanner, vertical marginal gap distance, monolithic, hybrid ceramics, Vita Enamic, zirconia, BruxZir.