![]() Consequently, digital impressions of these preparations are obtained by capturing accurate 3D images to generate appropriate virtual models. Thus, the Planmeca PlanScan Intraoral Scanner (Planmeca OY, Helsinki, Finland), which is part of the Planmeca Romexis all-in-one dental software platform, is used to scan the tooth preparations. This allows clinics to produce restorations in a single patient’s visit. The Planmeca FIT ® system (Planmeca OY, Helsinki, Finland) is used, namely, the chairside CAD/CAM system that combines the entire restorative workflow, from scanning to designing and milling ( Figure 2). The designing and manufacturing processes of both types of veneers (i.e., CO and CR) are based on Computer-Aided-Design (CAD) and on Computer-Aided-Manufacturing (CAM). Therefore, this limit is considered in the present study as well. Although various studies showed controversial results concerning the clinically acceptable gap values, most of them agreed that a marginal and internal discrepancy between 100 and 120 μm appears to be in the range of clinical acceptance. A large cement thickness under the ceramic restoration especially causes mechanical failure because of the limited shear strength. On the other hand, the internal marginal gap is a direct measure of the cement film thickness underneath the restoration and is significantly influenced by the accuracy of the fabrication process. These may also produce microleakage, recurrent decay, discoloration of the tooth structure, and fracture of the veneers. The close proximity between the margin of restorations and the tooth structure protects the adhesive resin cement from excessive exposure to the oral cavity, which would eventually lead to the slow process of gradual decrease of its chemical, physical, and mechanical properties. Moreover, it has been demonstrated that increased marginal discrepancy values reduce the fracture resistance of the veneering ceramic. Therefore, it is important to minimize marginal gaps to decrease the incidence of associated complications. Marginal adaptation is one of the basic factors in the success of restorations a poor one may lead to cement dissolution, marginal discoloration or staining, microleakage, secondary cavities, restoration debonding, and, eventually, restoration fracture. The marginal gap (i.e., the perpendicular distance from the peripheral margins of the restoration to its finish line) should be small enough to prevent ingress of saliva and/or lactic acid, which is the byproduct of bacterial metabolism. The importance of the thickness/width of the marginal and internal gap of veneers for the clinical success of ceramic restorations has been emphasized in several clinical trials. ![]() Thus, it provides favorable premises for better clinical performances. Conclusion: The novel veneers design produces an improvement in the marginal and internal adaptation of the restorations to the prepared tooth surface. The characteristic functions obtained allow us to compare the volume of luting cement for the two types of veneers. Analytical modeling is achieved for internal gaps using the micro-CT results. Results: STATA and one-way ANOVA tests reveal significant differences between CO and CR veneers: (i) the marginal gap is smaller for CR (64 μm) than for CO veneers (236 μm) (ii) the internal adaptation is better for CR veneers: for a cement width of up to 120 μm, the covered surface for the CR group is 81.5%, while for the CO group it is 64.5% (iii) the mean of the porosities within the cement is not significantly different (3.4♱0 6 μm 3 for CO and 3.9♱0 6 μm 3 for CR veneers), with a higher standard deviation for the CO group. All samples are bonded to frontal teeth, and the adhesive interfaces are analyzed using two methods, optical microscopy and micro-Computed Tomography (CT): the former for the accuracy of the marginal gap and the latter for the internal gap (as well as for the homogeneity of the luting cement) of ceramic veneers. The samples are divided into two groups: 12 conventional (CO) veneers (i.e., with a linear marginal contour) and 12 crenelated (CR) veneers, the latter with the novel sinusoidal marginal design. Materials and Methods: Twenty-four lithium disilicate ceramic veneers are obtained using Computer-Aided-Design (CAD) and then milled using Computer-Aided-Manufacturing (CAM). The aim of this in vitro study is to assess the effect of a novel (patented) design of veneers compared to conventional ones on their marginal and internal gap to the prepared tooth surface. For long-term clinical success, the accurate marginal and internal adaptation of dental restorations are of paramount importance. Background and Objectives: Ceramic veneers represent the most appropriate treatment option for minimally invasive aesthetic rehabilitation.
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