Volumetric and dimensional accuracy assessment of CAD-CAM-manufactured dental prostheses from different materials.

STATEMENT OF PROBLEM: In computer-aided design and computer-aided manufacturing (CAD-CAM) dentistry, the CAD of the prosthesis represents the clinical prerequisite design to restore the treated tooth. However, how closely the CAM prosthesis shape matches the CAD, particularly in relation to different materials, is unclear. PURPOSE: The purpose of this in vitro study was to evaluate onlays designed and manufactured with the same CAD-CAM system but manufactured with different materials. MATERIAL AND METHODS: A single standard tessellation language (STL) model was used to produce 6 composite resin onlays, 6 leucite glass-ceramic onlays, and 6 lithium disilicate glass-ceramic onlays. The onlays were digitized by using an X-ray microtomographic protocol with a metrological calibration. The CAD model was then compared with the scans of the different onlays. An analysis by region of interest was then carried out to assess the accuracy and reliability of the dimensional accuracy. RESULTS: The composite resin and the lithium disilicate glass-ceramic had the best dimensional accuracy. The leucite glass-ceramic exhibited a lack of trueness linked to consistent overmilling. The composite resin had less peripheral chipping than the glass-ceramics. CONCLUSIONS: The composite resin and the lithium disilicate glass-ceramic material exhibited satisfactory dimensional accuracy. Milling the glass-ceramic before crystallization considerably improved dimensional accuracy.

Accuracy of Additively Manufactured and Milled Interim 3-Unit Fixed Dental Prostheses.

PURPOSE: To investigate the accuracy of additive manufacturing (AM) by means of internal fit of fixed dental prostheses (FDPs) fabricated with two AM technologies using different resins and printing modes (validated vs nonvalidated) compared to milling and direct manual methods. MATERIAL AND METHODS: Sixty 3-unit interim FDPs replacing the first mandibular molar were divided into 6 groups (n = 10): manual (Protemp 4), milled (Telio-CAD), and AM groups were subdivided based on AM technology (direct light processing (Rapidshape P30 [RS]) and stereolithography (FormLabs 2 [FL])) and the polymer type (P-Pro-C&B [St] and SHERAprint-cb [Sh]) (RS-St, RS-Sh, FL-St, FL-Sh). Validated (RS-Sh and RS-St) or nonvalidated (FL-St and FL-Sh) modes were adopted for AM. The specimens were scanned to 3D align (GOM inspect) according to the triple scan method. The internal space between the FDPs and preparation surfaces in four sites (marginal, axial, occlusal, and total) was measured using equidistant surface points (GOM Inspect). Statistical analysis was done using Kruskal Wallis and Dunn post-hoc tests. (α = 0.05). RESULTS: One AM group (FL-Sh) and milling exhibited better adaptation compared to manual and RS-St at molar site (p < 0.05). FDPs with St resin (FL-St and RS-St) displayed bigger marginal space than milled, FL-Sh, and RS-Sh. The nonvalidated printing mode showed better mean space results (p < 0.05) with higher predictability and repeatability (p < 0.001). CONCLUSIONS: The AM interim FDPs tested provided valid alternatives to the milled ones in regard to their accuracy results. The printing mode, resin, and the AM technology used significantly influenced the manufacturing accuracy of interim FDPs, particularly at the marginal area. The nonvalidated printing mode with lower-cost 3D printers is a promising solution for clinical applications.

Evaluation of the dimensional accuracy of a manufactured dental prosthesis in relation to its computer-aided model.

AIM: Currently, there is no reliable methodology to evaluate the dimensional conformity of dental prostheses manufactured through a digital shaping process. In the CAD/CAM method, the digital design of the prosthesis is considered as a reference, and it is crucial to reproduce it perfectly during the manufacturing process. Therefore, the aim of this study was to offer a comparison between a CAM prosthesis and its design model by superimposing the CAD model with the digitization of the manufactured prosthesis. MATERIALS AND METHODS: The metrological inspection developed in this study and presented in this article involved a comparison of the points cloud obtained by micro-computed tomography (micro-CT) and the CAD model of the prosthesis. First, an estimation of all inspection-method induced measurement errors was carried out, in which the measurement errors were assessed by proceeding to the dimensional inspection of a reference object of known dimensions. Then, the metrological inspection was extrapolated to a dental prosthesis. RESULTS: The estimation of measurement errors presented satisfying results compared with the usual metrological protocols developed by the dentistry research community. The dimensional deviation was estimated at 0.31% and the form deviation at 0.165 µm between the Gaussian sphere and the certified ball. The inspection of the manufactured surfaces revealed under-milled areas on the occlusal face, particularly on the anatomical fossae, and an irregular margin limit compared with its smooth design. CONCLUSION: A reliable micro-CT evaluation of the dimensional accuracy of a manufactured dental prosthesis compared with the CAD model demonstrated the performance level of CAD/CAM systems. The evaluation reliability was confirmed by the estimation of prior measurement errors. This estimation is essential for the metrological analysis.

Contemporary management of minimal invasive aesthetic treatment of dentition affected by erosion: case report.

BACKGROUND: The paradigm shift obtained with new dental materials permits minimally invasive dentistry, by following a biomimetic approach. Erosion increasingly affects the adult population through dental substance loss by acid attack. Oral rehabilitation is often extensive and requires careful mouth examination and treatments codified in the literature. CASE PRESENTATION: This clinical report proposes a reasoned approach to erosion treatment for a 39-year-old male patient presenting several old fixed prostheses. These old restorations are all of correct quality and are retained. The temporomandibular joint was free from disorder. Only defective reconstructions are remade together with eroded teeth, according to a three-step technical protocol. In the first step, mock-up manufacturing is performed which occlusal vertical dimension increased to 1 mm provoking passive dental overeruption to the second and third molars. In all, one ceramic crown was remade, and two ceramic onlays and a resin composite were integrated on the posterior teeth. The last step consisted of palatal veneers on the maxillary incisor and canine, and an aesthetic resin composite on the incisor edge. After these treatments, regular assessments were carried out at 4 months then at 6 months with visual, photographic and radiographic examinations. CONCLUSION: The present dental care philosophy is to preserve dental tissue as much as possible, even in large erosion cases, and to respond to the aesthetic and functional expectations of the patient. This methodology requires a thorough evaluation phase, compliance with the protocol and regular patient follow-up.

Evaluation of the marginal fit of CAD-CAM zirconia copings: Comparison of 2D and 3D measurement methods.

PURPOSE: The purpose of this in vitro study was to compare the marginal fit of zirconia copings by using 2 different measurement methods: a triple optical scan method and a silicone replica method. MATERIAL AND METHODS: Sixty zirconia copings fabricated by computer-aided design and computer-aided manufacture (CAD-CAM) systems were studied for the marginal fit. For the replica method, the thickness of the light-body silicone layer of the discrepancy was assessed using light microscopy and image analysis software. The triple-scan optical method was performed to obtain a digital three-dimensional map of the marginal fit and analyzed marginal fit measurement values. For each method, the reliability of the measurement was tested, and a nonparametric analysis was then performed to compare the marginal fit values as measured by the 2 evaluation methods (α=.05). RESULTS: Intraclass correlation coefficients and repeatability coefficients revealed good repeatability for both of the evaluation methods. However, the triple-scan method produced a smaller marginal fit than the replica method (P<.001) for the entire group studied. CONCLUSIONS: Although both methods showed good repeatability, the triple-scan method was more reliable.

3D fitting accuracy evaluation of CAD/CAM copings - comparison with spacer design settings.

OBJECTIVES: The accuracy of computer-aided design/computer- aided manufacturing (CAD/CAM) systems is linked to their technical characteristics and reliability for manufacturing the restoration designed. The aim of this study was to compare the accuracy of fit of zirconia copings manufactured with different CAD/CAM systems and their capacity to conform to pre-established spacer design settings. METHODS: Sixty zirconia copings were manufactured by three CAD/CAM systems, with their spacers set as recommended by their manufacturer on occlusal, axial, and marginal surfaces. The 3D triple-scan optical technique was used to obtain a fit mapping and to analyze the marginal and axial accuracy of fit. The reliability of the 3D measurement method was estimated using intraclass correlation and repeatability coefficients. The preparation coping interface width results were statistically analyzed using non-parametric analysis (Kruskal-Wallis, one-way ANOVA, and Wilcoxon signedrank tests) (P < 0.05). RESULTS: The repeatability coefficient was 6, 8, and 15 µm for axial, marginal, and occlusal interface width measurements, respectively. For the three systems tested, no differences were found in the marginal area of the copings studied, with a mean fitting accuracy ranging from 54.3 to 66.6 µm interface width. Statistically significant differences between groups were observed for the fitting accuracy measured in axial and occlusal areas. With the spacers set in the different areas, mean fit measurements of the zirconia copings were significantly larger, with an increased fit width ranging from 30 to 73 µm. SIGNIFICANCE: The three CAD/CAM systems evaluated allowed similar marginal accuracy but failed to reproduce the pre-established spacer parameters, with larger spacing showing throughout.