International Journal of Prosthodontics最新文献

Purpose: To determine the effect of scanning protocol, number of implants, and implant splinting on the accuracy of digital scanning in the edentulous arch.

Materials and methods: A resin-based model of an edentulous mandible with six implants was scanned with a coordinate measurement machine as a reference and then with two intraoral scanner (IOS) systems (Trios 3 and Primescan). Ten scans were taken per IOS for three experiments, and each scan was compared to the reference data to evaluate trueness and precision. Analysis involved measurement of linear and angular discrepanices using engineering software. In experiment 1, three scanning protocols were compared (curvilinear, zigzag, and half-arch). In experiment 2, three clinical situations were simulated (6 implants, 4 implants-short arch, and 4 implants-long arch). In experiment 3, the effect of implant splinting with a suture thread was measured. Normal distribution of data was examined with Shapiro-Wilk test. Levene test was used for equality of variance (α = .05). Statistical differences in distance and angular deviations were analyzed using Student t test or ANOVA with post hoc Tukey test (α = .05).

Results: The best results in terms of trueness and precision were obtained with a linear scanning protocol and six implants. The results were as follows: Trios 3: trueness = 52 μm/0.42 degrees, precision = 40 μm/0.26 degrees; Primescan: trueness = 24 μm/0.28 degrees, precision = 18 μm/0.27 degrees. The scanning protocol did not significantly affect distance or angular deviation accuracy. Trueness and precision significantly decreased with four implants using Primescan and TRIOS 3. Splinting implants negatively affected accuracy with both IOS devices.

Conclusion: Both IOS devices achieved clinically satisfying accuracy for distance (< 100 μm) and angular (< 0.5 degrees) deviations with six implants and a linear scanning protocol. With four implants, angular deviations sometimes differed between implants within the same group depending on the IOS and the clinical situation. Int J Prosthodont 2023;36:219-227. doi: 10.11607/ijp.7332.

Purpose: To comparatively evaluate the amount of wear of natural enamel against a glazed full coverage monolithic zirconia crown and a polished monolithic zirconia crown at 6 and 12 months.

Materials and methods: Thirty subjects within the age range of 18 to 35 years participated in this study. The subjects received a total of 60 single crowns, which were divided into two groups: (1) 30 glazed monolithic zirconia crowns opposed by natural enamel (group A); and (2) 30 polished monolithic zirconia crowns opposed by natural enamel (group B). Each subject received a crown from both groups, placed bilaterally in endodontically treated maxillary or mandibular first molars. An impression was made of the opposing arch at 24 hours, 6 months, and 12 months. The resulting casts were scanned with a 3D optical scanner. The recall scans were superimposed and compared to baseline scans using 3D AutoCAD software. A control group was included to compare the wear values to natural enamel against natural enamel.

Results: No significant difference (P = .855) was found in enamel wear between groups A (42.80 μm) and B (42.50 μm) after 6 months of use. However, a significant difference (P < .05) in enamel wear was found between group A (81.87 μm) and group B (71.43 μm) after 12 months of use.

Conclusion: Glazed monolithic zirconia crowns cause more wear to the opposing enamel than polished monolithic zirconia crowns after 12 months of clinical use.

Purpose: To evaluate the stress distribution in endocrowns and post-and-core crowns used as abutments for a Kennedy Class I removable partial denture constructed with different framework materials.

Materials and methods: 3D models of a Kennedy Class I mandible were constructed. Cobalt-chromium (Co-Cr) and polyether ether ketone (PEEK) frameworks were simulated for Models 1 and 2, respectively. An endocrown and a fiber post-and-core crown for the mandibular left and right second premolar abutments, respectively, were simulated for both models. Lithium disilicate porcelain was defined for the crowns. A 200-N occlusal force was applied in the vertical and 30-degree oblique directions.

Results: The von Mises stresses were evaluated for the abutments and prostheses, and the principal stresses for the cortical bone under vertical and oblique loading. Endocrowns showed lower stress values than post-and-core crowns in both models. Post-and-core crowns generated the highest stress in Model 2 under vertical loading. The PEEK framework caused higher stress values on the abutments than Co-Cr. Compressive stresses were higher than tensile stresses in cortical bone. The highest compressive stress was observed around the left premolar cortical bone area in Model 1 under oblique loading. Oblique loading caused lower stress values than vertical loading, except for on the minor connectors and cortical bone.

Conclusion: From a biomechanical perspective, endocrowns may be more advantageous than post-and-core crowns when used as abutments for a Kennedy Class I removable partial denture. In addition, Co-Cr frameworks showed more favorable stress distribution on abutments than PEEK frameworks. Int J Prosthodont 2023;36:203-215. doi: 10.11607/ijp.7269.

Purpose: To compare the mechanical behavior (stress load dissipation and/or concentration) of posterior crowns made from Lava Ultimate (LU; 3M ESPE) and IPS e.max CAD (LD; Ivoclar Vivadent) using finite element analysis (FEA).

Materials and methods: A 3D model of a mandibular first molar was prepared by reducing the occlusal surface by 1 or 2 mm (according to group), the axial walls by 1.5 mm, and using a 0.8-mm-deep shoulder margin as a finish line. A convergence of 6 degrees between opposing walls was set. Subsequently, four 3D crown models were created according to two test groups with two different occlusal thicknesses: (1) LD with 1.0 mm (LD1); (2) LD with 2.0 mm (LD2); (3) LU with 1.0 mm (LU1); and (4) LU with 2.0 mm (LU2). FEA models were constructed using the software Femap (Siemens). A load of 200 N was applied in the axial and oblique (20 degrees) directions for each group, and stress dissipation was viewed using the NEi Nastran software.

Results: FEA results demonstrated that the LU crowns dissipated the occlusal load to the tooth structure, whereas the LD material concentrated the load inside the crowns. For the LU material, the lower the occlusal thickness, the higher the stress concentration inside the crown became, and the 2.0-mm occlusal thickness transferred lower stress to the tooth structure. The oblique, rather than the vertical, load caused an increase in the maximum stress concentration at the shoulder margin and axial walls.

Conclusion: The higher the Young's Modulus mismatch between the crown material and substrate, the higher the load stress concentration inside the material became. The 2-mm occlusal thickness acted by decreasing the load stress to the tooth substrate. Finally, the axial load delivered more favorable stress transmission to the tooth substrate. The crown material and the occlusal thickness appear to be two factors that affect the mechanical behavior of stress dissipation to the tooth structure.

Purpose: To evaluate changes in the periodontium of teeth restored with ultrathin (0.2 to 0.39 mm) ceramic laminate veneers (CLVs) placed subgingivally without a finish line compared to the same teeth before restorative treatment and to nonrestored antagonist teeth in healthy periodontium patients. Materials and Methods: A total of 73 CLVs were bonded onto the enamel surface of teeth without a finish line and with the cervical margin placed about 0.5 mm subgingivally. The gingival crevicular fluid was collected before bonding (baseline) and at 7, 180, and 365 days after bonding to quantify S mitis, P intermedia, and P gingivalis by quantitative polymerase chain reaction analysis. Visible plaque index (VPI), bleeding on probing (BOP), probing depth (PD), clinical attachment loss (CAL), gingival recession (GR), and marginal adaptation were evaluated from baseline to 365 days in both groups. Results: No statistically significant differences were observed in VPI, PD, or BOP at any time point in the intragroup or intergroup comparisons (P > .05). All restorations obtained the alpha concept for marginal adaptation (ie, the restoration margin remained ideal at all time points). There was a statistically significant difference for S mitis between 180 and 365 days (P = .03). No statistically significant difference was observed for P gingivalis at any time point (P > .05). Conclusion: The periodontium in the restored group showed a clinical behavior similar to baseline. Overcontouring of the ultrathin (up to 0.39 mm) CLV, similar to the cementoenamel junction convexity, did not contribute to plaque accumulation or changes in the oral microbiota of patients with a healthy periodontium and proper oral hygiene instruction.

Purpose: To compare the morphologic trueness of provisional and definitive restorations constructed with conventional custom impression techniques to those constructed with intra- and extraoral scanning (IEOS), which can digitally transfer the subgingival morphology of the provisional restoration to the definitive restoration.

Materials and methods: Provisional restorations were fabricated on typodonts in which implants were placed. In the conventional method, a customized impression coping was produced by using polymethyl methacrylate resin to transfer the subgingival contour of the provisional restoration. Impressions were taken with silicone impression material, and definitive restorations were made by CAM. The IEOS technique was performed as previously reported. In brief, three individually scanned stereolithography (STL) files were superimposed in CAD software to transfer the morphology of the provisional restoration to the definitive restoration. Definitive restorations were then made by CAM. The provisional and definitive restorations were both scanned by IOS. Scanned data files were superimposed with morphometry software, and the distortions were measured. Student t test was used for statistical analysis.

Results: The subgingival morphologies of definitive restorations prepared by the conventional method showed significant negative distortions compared to definitive restorations prepared by the IEOS technique.

Conclusion: The IEOS technique can more accurately transfer the subgingival contour of provisional restorations to definitive restorations compared to the conventional customized impression coping technique.

Purpose: To investigate if and how the positions of condyles in centric relation (CR) varied from each other using different CR records.

Materials and methods: Condylar positions in CR were repeatedly recorded by four licensed clinicians in 81 stomatognathically healthy, fully dentate subjects with six different types of CR records. The maxillary casts were mounted in articulators after individual facebow transfer, and the mandibular casts were mounted with a central bearing point (CBP) registration on the tip of the Gothic arch. Mean values from three registrations of the centric condylar positions with each of the six methods were calculated, and comparative calculations were made.

Results: The median spatial distances of the condylar positions between the CBP and all other CR records was 0.73 ± 0.24 mm (0 to 3.19 mm). The median spatial values between the condylar positions of the different CR records ranged from 0.48 to 0.79 mm. Statistically, the positions of almost all types of registration were slightly different from each other.

Conclusion: Different CR records reproduce slightly different positions of the mandible, which is especially true for CBP registration, whereas reproducibilities and SDs between registrations are similar. Unrefined wax-wafer registrations using bimanual manipulation have proven particularly successful with regard to precision and time requirements, as has CBP registration with regard to condylar position.

Purpose: To evaluate the extent to which dentists elaborate removable partial denture (RPD) design themselves and what they leave to the dental laboratory, as well as to assess the quality of information transferred to the technicians.

Materials and methods: Data were collected using a questionnaire, and the responses of 211 dentists were analyzed. The categorized variables were analyzed using chi-square test and Fisher exact test. The significance level was considered as the standard P < .05.

Results: More than half (59.0%) of the dentists reported making an accurate, clear design for the dental technician before fabrication of the metal-framework RPD; 191 dentists (91.0%) specified the abutment teeth, 70.8% chose the type of clasps, and 60.7% gave instructions for the major connectors. The respondents largely took into account periodontal hygiene considerations (82.4%), and about one-third (37.7%) reported they were sending clear, precise instructions to the lab. The denture design was sent to the technician mainly (65.0%) in both drawing and text form. About half of the dentists (55.6%) gave only guidelines and left more details to be defined by the dental technician. Most dentists took responsibility in case of esthetic problems, irrespective of whether the dentist or technician prepared the denture design.

Conclusion: Everyday practice concerning RPD design is far from the professional, legal, and ethical guidelines and rules relating to the duties and responsibilities of the dentist in relation to RPD design, and the situation therefore needs to be improved. Int J Prosthodont 2022;36:131-137. doi: 10.11607/ijp.7523.

Purpose: To compare the feasibility and accuracy of using intraoral scanners to digitize a maxillary defect model simulating various trismus conditions.

Materials and methods: Four intraoral scanners were used to digitize a maxillary defect model simulating four different degrees of trismus (mouth opening = 10, 20, 30, and 40 mm), and the scanned areas were compared. The scans were also superimposed on each other for precision analysis and on reference data for trueness analysis using 3D evaluation software. Two-way ANOVA was used to compare area, precision, and trueness among scanners and among conditions.

Results: The surface area for which 3D data were obtained by the intraoral scanners ranged from 2,672 to 6,613 mm². Significant differences were observed between the scanners (P < .001) and between the trismus conditions (P < .001), with a smaller scanned surface area in severe trismus (10 mm). Trueness ranged from 0.033 to 0.301 mm, and precision from 0.022 to 0.397 mm. Significant differences in trueness and precision values were found among the scanners (P = .001 and P = .001, respectively), but not the trismus conditions (P = .260 and P = .075, respectively).

Conclusion: Although trueness and precision differed between intraoral scanners, digitization of the maxillectomy model simulating various trismus conditions appears to be feasible from the perspective of accuracy with all of the scanners used. The smaller scanned surface area in the severe trismus condition was due to lack of data on the defect site in that condition.

Purpose: To assess excess cement removal after cementation of implant-supported cementretained restorations using different cements.

Materials and methods: A dental model with soft tissue imitation, 20 individual zirconium oxide abutments, and 20 zirconium oxide crowns were fabricated. Half of the restorations were cemented using resin cement (RX) and the other half with resin-modified glass-ionomer cement (GC). After cement cleaning, each crown-abutment unit was removed from the model, photographed, and analyzed from 4 surfaces, resulting in a final sample size of 80 measurements. Radiographic examination and the computerized planimetric method in Adobe Photoshop were used to determine the amount of the cement left and to evaluate the ratio between the area of cement residue and the whole crown-abutment surface. The significance was set to .05.

Results: GC resulted in 7.4% more cement residue on all surfaces (P < .05) than RX. The P value on three of the surfaces (all except mesial) was < .05, meaning that the data were statistically significantly different between groups and surfaces. Absolute removal of the cement was impossible in all cases (100%), and in 95% of the cases, cement remnants could not be detected radiographically.

Conclusion: More undetected cement remains when using resin-modified glass-ionomer cement. It was impossible to remove excess of both types of cements completely. Most of the cement remains on the distal surface. Radiographic examination could not be considered as a reliable method to identify excess cement.