Guillermo Pradíes

Evaluation of the absolute marginal discrepancy of zirconia-based ceramic copings.

STATEMENT OF PROBLEM Marginal fit is an important factor for the long-term success of ceramic restorations; however, it is difficult to compare results from studies on marginal accuracy of zirconium oxide-based restorations that used various computer-assisted systems, because different methods were used to obtain the data. PURPOSE The purpose of this study was to analyze the effect of different manufacturing techniques on the marginal adaptation of zirconia ceramic copings. MATERIAL AND METHODS An extracted mandibular first premolar was prepared for a complete coverage restoration and subsequently duplicated 40 times in a liquid crystal polymer (LCP). Ceramic copings (n=10) were fabricated on the LCP models using the following systems: glass-infiltrated zirconia-toughened alumina (In-Ceram Zirconia) and yttrium cation-doped tetragonal zirconia polycrystals (In-Ceram YZ, Cercon, and Procera Zirconia). The absolute marginal discrepancy of the cores was assessed by using an image analysis system. The data were analyzed using 1-way ANOVA and Scheffés test (α=.05). RESULTS The mean marginal openings were 29.98 ± 3.97 μm for the In-Ceram Zirconia group, 12.24 ± 3.08 μm for the In-Ceram YZ group, 13.15 ± 3.01 μm for the Cercon group, and 8.67 ± 3.96 μm for the Procera group. Significant differences were found among the 4 systems (P<.05). CONCLUSIONS The marginal accuracy achieved for the 4 zirconia-based ceramic crown systems analyzed was within the range of clinical acceptance (120 μm).

Clinical evaluation comparing the fit of all-ceramic crowns obtained from silicone and digital intraoral impressions based on wavefront sampling technology

OBJECTIVE The aim of this study was to compare the fit of ceramic crowns fabricated from conventional silicone impressions with the fit of ceramic crowns fabricated from intraoral digital impressions. METHODS Twenty-five participants with 30 posterior teeth with a prosthetic demand were selected for the study. Two crowns were made for each preparation. One crown was fabricated from an intraoral digital impression system (IDI group) and the other crown was fabricated from a conventional two-step silicone impression (CI group). To replicate the interface between the crown and the preparation, each crown was cemented on its corresponding clinical preparation with ultra-flow silicone. Each crown was embedded in acrylic resin to stabilise the registered interface and then cut in 2mm thick slices in a buco-lingual orientation. The internal gap was determined as the vertical distance from the internal surface of the crown to the prepared tooth surface at four points (marginal gap, axial gap, crest gap, and occlusal fossa gap) using stereomicroscopy with a magnification of 40×. Data was analysed by using Wilcoxon signed rank test (α=0.05). RESULTS Internal adaptation values were significantly affected by the impression technique (p=0.001). Mean marginal gap was 76.33 ± 65.32 μm for the crowns of the IDI group and 91.46 ± 72.17 μm for the CI group. CONCLUSION All-ceramic crowns fabricated from intraoral digital impressions with wavefront sampling technology demonstrated better internal fit than crowns manufactured from silicone impressions. CLINICAL SIGNIFICANCE Impressions obtained from an intraoral digital scanner based on wavefront sampling technology can be used for manufacturing ceramic crowns in the normal clinical practice with better results than conventional impressions with elastomers.

Conventional and adhesive luting cements.

Abstract. Luting materials for fixed prosthesis must fulfill special requirements in order to retain indirect restorations and fully maintain the integrity of abutments. The main requirements (inhibition of plaque accumulation, sealing of interface, possible antibacterial effects, acceptable solubility, wear, mechanical properties, adhesion, radiopacity, film thickness, type of curing, esthetics, storage, and cost) are reviewed to update clinical criteria on the selection of suitable materials. It can be concluded that there is no ideal luting material on the market. Alleged improvements in the physical data of newer materials do not necessarily result in better clinical performance. Only clinical trials can confirm the assumed benefits of materials.

Accuracy of a digital impression system based on active wavefront sampling technology for implants considering operator experience, implant angulation, and depth.

BACKGROUND There is a scarce knowledge on the accuracy of intraoral digital impression systems for dental implants. PURPOSE The purpose of this study is to evaluate the accuracy of a digital impression system considering clinical parameters. MATERIALS AND METHODS A master model with six implants (27, 25, 22, 12, 15, 17) was fitted with polyether ether ketone scan bodies. Implant no. 25 was placed with 30° mesial angulation in relation to the vertical plane (y axis), and implant no. 15 was positioned with 30° distal angulation. Implant no. 22 was placed 2 mm and no. 12, 4 mm below the gingiva. Experienced (n = 2) and inexperienced operators (n = 2) performed scanning (Lava Chairside Oral Scanner; 3 M ESPE, St Paul, MN, USA) at standard and high accuracy mode. Measurements involved five distances (27-25, 27-22, 27-12, 27-15, 27-17). Measurements with high accuracy three-dimensional coordinated measuring machine (CMM) of the master model acted as the true values. The data obtained were subtracted from those of the CMM values. RESULTS Experience of the operator significantly influenced the results (p = .000). Angulation (p = .195) and depth of implant (p = .399) did not show significant deviation from the true values. The mean difference between standard and high accuracy mode was 90 μm. CONCLUSIONS With the active wavefront sampling, technology-based digital impression system training seems to be compulsory. Impressions of angulated implants may diminish the accuracy of the impression, yet the results were not significant.

Marginal discrepancy of monolithic and veneered all-ceramic crowns on titanium and zirconia implant abutments before and after adhesive cementation: a scanning electron microscopy analysis.

PURPOSE To evaluate the marginal discrepancy of monolithic and veneered all-ceramic crown systems cemented on titanium (Ti) and zirconia implant abutments. MATERIAL AND METHODS Sixty customized implant abutments for a maxillary right central incisor were fabricated of Ti and zirconia (n = 30 of each) for an internal-connection implant system. All-ceramic crowns were fabricated using the following systems (n = 10 per group): monolithic with computer-aided design/computer-assisted manufacture (CAD/CAM) lithium disilicate (MLD), pressed lithium disilicate (PLD), or CAD yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP). The frameworks of the PLD and Y-TZP systems were manually veneered with a fluorapatite-based ceramic. The crowns were cemented to their implant abutments, and the absolute marginal discrepancy of the gap was measured before and after cementation. Data were analyzed statistically. RESULTS Marginal discrepancies were significantly influenced by the crown system and by cementation, but the material did not significantly affect the results. Interaction terms were not significant. Y-TZP crowns on both Ti and zirconia abutments presented the smallest mean marginal discrepancies before (52.1 ± 17 μm and 56.2 ± 11 μm, respectively) and after cementation (98.7 ± 17 μm and 101.8 ± 16 μm, respectively). Before cementation, MLD crowns showed significantly larger mean marginal openings than PLD crowns on both Ti and zirconia abutments (75.2 ± 12 and 77.5 ± 13 μm for MLD, 52.1 ± 17 μm and 69.7 ± 8 μm for PLD, respectively). After cementation, both Ti and zirconia abutments with MLD crowns (113.5 ± 12 μm and 118.3 ± 14 μm, respectively) showed significantly larger values than with PLD crowns (98.7 ± 17 μm and 109.4 ± 9 μm, respectively). CONCLUSIONS Manually veneered Y-TZP crowns demonstrated more favorable marginal fit on both Ti and zirconia implant abutments before and after cementation compared to those of MLD and PLD.

Comparison of a conventional and virtual occlusal record

STATEMENT OF PROBLEM Conventional methods associated with many processes in dentistry are being replaced by methods that use digital technology. One of these processes is the making of occlusal records for the positioning of casts in a virtual articulator. Conventional interocclusal records and the articulator are being replaced by the virtual occlusal record and the virtual articulator. PURPOSE The purpose of this study was to validate a virtual procedure to locate the mandibular cast in a 3-dimensional (3D) spatial position and to verify the occlusal contact points in reference to the corresponding maxillary cast on a virtual articulator. MATERIAL AND METHODS The conventional procedure was carried out by locating 6 sets of casts in maximal intercuspal position without any interocclusal record. Then, the occlusal contacts were determined with articulating paper. Subsequently, the occlusal relationships and stone cast were digitized with a 3D scanner. The occlusal contacts were compared with photographs and by superimposing these on screenshots of the software. Finally, the deviation of discrete points on the mandibular cast was calculated, and all the points of the occlusal surface were compared point by point. RESULTS This study analyzed the main variables of the virtual occlusal record by using 3 current reverse engineering software packages. The results show a mean deviation of 0.069 mm from the virtual occlusion procedure and a mean standard deviation of 0.011 mm from all the points of the occlusal surface. CONCLUSIONS The main conclusion of this study was that the accuracy provided by a virtual occlusion procedure is greater than that of the traditional physical interocclusal record. Additionally, knowing the deviation of each alignment (best-fit operation or algorithm) is useful.

Accuracy of a Digital Impression System Based on Active Triangulation Technology With Blue Light for Implants: Effect of Clinically Relevant Parameters.

Purpose:To evaluate the accuracy of a digital impression system considering clinical parameters. Materials and Methods:A master model with 6 implants (27, 25, 22, 12, 15, and 17) was fitted with polyether ether ketone scan bodies. Implant no. 25 was placed with 30° mesial angulation and no. 15 with 30° distal angulation in relation to the vertical plane (y axis). Implant no. 22 was placed at 2 mm and no. 12 placed 4 mm below the gingiva. Experienced (n = 2) and inexperienced (n = 2) operators performed the scanning (CEREC system). Measurements involved 5 distances (27–25, 27–22, 27–12, 27–15, 27–17). Measurements with coordinated measuring machine of the master model acted as the true values. Results:The experience of the operator affected the accuracy. Operator 3 (inexperienced) performed better than the rest. Angulation and implant depth did not affect the accuracy results. The position of the camera affected the accuracy of the system. The first scanned quadrant had significantly smaller error, −17 ± 26.3 &mgr;m, than the second quadrant, −116 ± 103 &mgr;m. Conclusions:Digital impressions with CEREC Bluecam system can be a feasible alternative for challenging cases where angulation and depth of the implants are present. The accuracy of the CEREC system for the first scanned quadrant is high, and it decreases when completing a full arch.

Accuracy of two digital implant impression systems based on confocal microscopy with variations in customized software and clinical parameters.

PURPOSE To evaluate the accuracy of two digital impression systems based on the same technology but different postprocessing correction modes of customized software, with consideration of several clinical parameters. MATERIALS AND METHODS A maxillary master model with six implants located in the second molar, second premolar, and lateral incisor positions was fitted with six cylindrical scan bodies. Scan bodies were placed at different angulations or depths apical to the gingiva. Two experienced and two inexperienced operators performed scans with either 3D Progress (MHT) or ZFX Intrascan (Zimmer Dental). Five different distances between implants (scan bodies) were measured, yielding five data points per impression and 100 per impression system. Measurements made with a high-accuracy three-dimensional coordinate measuring machine (CMM) of the master model acted as the true values. The values obtained from the digital impressions were subtracted from the CMM values to identify the deviations. The differences between experienced and inexperienced operators and implant angulation and depth were compared statistically. RESULTS Experience of the operator, implant angulation, and implant depth were not associated with significant differences in deviation from the true values with both 3D Progress and ZFX Intrascan. Accuracy in the first scanned quadrant was significantly better with 3D Progress, but ZFX Intrascan presented better accuracy in the full arch. CONCLUSION Neither of the two systems tested would be suitable for digital impression of multiple-implant prostheses. Because of the errors, further development of both systems is required.

A clinical protocol for intraoral digital impression of screw-retained CAD/CAM framework on multiple implants based on wavefront sampling technology.

Purpose:To obtain an accurate CAD/CAM metal framework over 6 implants using a Chairside Intraoral Scanner based on the principle of active (optical) wavefront sampling. Material and Methods:Six prototype cylindrical scan bodies screwed in the implants were used to obtain an intraoral digital impression. A conventional resin tooth try-in was fabricated and digitized with an extraoral scanner, and this dataset was merged to the digital data obtained from the intraoral impression to calculate the best framework design with advanced CAD software. The framework was fabricated with a 5-axis computer numerical control milling unit. Three clinical tests (saliva intrusion, Sheffield test, and screw resistance test) were performed to assess the fit of the framework. Results:Under 3 clinical tests, an accurate fit was observed. Conclusion:The case presented in this report proposes a new clinical protocol for obtaining accurate digital impressions of multiple implants.

Accuracy of Definitive Casts Using 4 Implant-Level Impression Techniques in a Scenario of Multi-Implant System With Different Implant Angulations and Subgingival Alignment Levels

Purpose: To evaluate the effect of various implant-level impression techniques on the accuracy of definitive casts for a multiple internal connection implant system with different implant angulations and subgingival depths. Material and Methods: Six tapered Screw-Vent implants were placed in a reference model with different angles (0, 15, and 30 degrees) and subgingival positions (0, 1, and 3 mm). Twenty medium-consistency polyether impressions of this model were made with 4 techniques (n = 5 per group): (1) indirect technique, (2) unsplinted direct technique, (3) acrylic resin-splinted direct technique, and (4) metal-splinted direct technique. Impressions were poured with type IV dental stone. The interimplant distances were measured for casts using a coordinate measuring machine and the deviations compared with the reference model were calculated. Data were analyzed using intraclass correlation coefficient, ANOVA and Bonferroni test (&agr; = 0.05). Results: Four impression procedures showed significant differences (P = 0.0001). Only group 4 casts showed no significant differences in comparison with the reference model (P = 0.666) (ANOVA repeated measures). Conclusions: The impression procedure affected the accuracy of definitive casts. The metal-splinted direct technique produced the most accurate casts, followed by acrylic resin-splinted direct, indirect, and unsplinted direct techniques.