The International Journal of Prosthodontics, 03/2023

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 analyze the clinical performance of two-wing–retained resin-bonded fixed dental prostheses (RBFDPs) after 5 years of clinical use with respect to technical and biologic complications, as well as survival and success rates. Materials and Methods: RBFDPs were fabricated from 3Y-TZP zirconia layered by hand (Lava Frame veneered with Lava Ceram; 3M ESPE) or metal (Remanium Star, Dentaurum; layered with Reflex, Wieland). The primary endpoints were debonding and fracture. The secondary endpoints (marginal integrity, marginal discoloration, abrasion of antagonist dentition, patient satisfaction, Gingival Index, and side effects) were evaluated at baseline and after 5 years. Survival and success rates were calculated using the Kaplan- Meier method. Log-rank test was used to compare the survival and success rates of the different materials. Results: The mean observation time was 6 years and 10 months. The estimated cumulative success rate after 5 years was 88.9% ± 10% for metal-supported and 33% ± 16% for all-ceramic two-wing RBFDPs. After conversion into one-wing RBFDPs, the survival rate was 100% in both groups. Debonding of one of the two wings was the major complication. One zirconia framework fracture occurred. Metal-based twowing RBFDPs showed a significantly higher success rate, but lower esthetic evaluation. Conclusion: Due to a reduction in technical complication rate and less invasiveness, one-wing RBFDPs should be preferred over two-wing RBFDPs whenever possible.

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 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 1-year survival and success rates of 6-mm short implants placed in mandibular molar sites with two different abutments (dome/ball) retaining existing removable partial dentures (RPDs). Materials and Methods: In 19 patients, 38 implants of 6-mm length were placed bilaterally. After 4 months, each participant received the dome abutment, which 2 months later was exchanged with the ball abutment. Clinical data were recorded at abutment connection (4 months postsurgery) and at 6 and 12 months postsurgery, including probing depth, bleeding on probing, presence of plaque, and standardized radiographs. Implant success was assessed using the following criteria: presence of pain, mobility, radiographic bone loss, probing depth, and the presence of exudate. For descriptive analyses, mean and SD values were calculated. Paired sample t tests and linear regressions with a significance level of α < .05 were applied to analyze the evolution of peri-implant parameters and the influence of implant placement depth. Results: The overall mean marginal bone level alteration (DMBL) was 1.05 ± 0.69 mm. A statistically significant marginal bone loss over time was observed at the mesial and distal aspects of all implants (P < .05). The implant survival rate was 100%. No implants showed pain, exudate, mobility, or probing depth > 7 mm. Three implants were classified as having satisfactory survival due to a DMBL > 2 mm (resulting success rate: 92.1%). No influence of implant placement depth was found. Conclusion: These short-term results suggest that short implants can be used in mandibular molar sites for additional posterior support of free-end RPDs. However, in individual cases, DMBL > 2 mm may occur.

Purpose: This in vitro study was conducted to evaluate the marginal accuracy of all-ceramic onlay restorations and prototypes fabricated using additive and subtractive methods. Materials and Methods: Ten typodont first molars were prepared and scanned two times using two different scanners: ARCTICA AutoScan (KaVo Dental) and CEREC Omnicam (Dentsply Sirona). The two groups of virtual models were used to design two groups of virtual onlay restorations using two different CAD software (n = 10 each group) and exported in STL files. Each group of STL files was converted to physical onlay restorations and prototypes by using three different methods; these included two additive manufacturing techniques, stereolithography apparatus (SLA) and digital light processing (DLP), and one subtractive technique, e.max milling using the KaVo Everest system and the Dentsply Sirona inLab MC X5. A digital microscope was used to evaluate the marginal fit around the onlay restorations or prototypes on the typodont teeth. Results: All evaluated groups showed mean marginal gaps between 59 and 84 μm. No statistically significant differences were found when comparing the marginal accuracy of onlay restorations fabricated by the subtractive method and onlay prototypes from the two additive methods, SLA (P = .70) and DLP (P = .21). Conclusion: All the models evaluated produced marginal gaps within the reported acceptable clinical range. Thus, these subtractive and additive methods may be considered suitable for onlay restoration production.

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 with 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 Femap software (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 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 LU material, the lower the occlusal thickness, the higher the stress concentration inside the crown, 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 modulus mismatch between the crown material and substrate, the higher the load stress concentration inside the material. 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. Crown material and occlusal thickness both affect the mechanical behavior of stress dissipation to the tooth structure.

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 assess excess cement removal after cementation of implant-supported cement-retained restorations with different cements. Material and Methods: A dental model with imitation soft tissue, 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 abutment-crown unit was removed from the model, photographed, and analyzed on four 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 cement left and evaluate the ratio between the area of cement residue and all abutment-crown surfaces. 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 surfaces (all except the mesial) was < .05, indicating that the data were statistically significantly different between groups and surfaces. Complete removal of the cement was impossible in all cases (100%), but in 95% of cases, cement remnants could not be detected radiographically. Conclusions: More undetected cement remains when using GC. It was impossible to remove excess of both types of cement completely. Most of the cement remnants were located on the distal surface. Radiographic examination could not be considered as a reliable method to identify excess cement.

Purpose: To compare the effect of office, home, and internal bleaching on the shear bond strength (SBS) of enamel to porcelain laminate veneers. Materials and Methods: A total of 36 extracted maxillary central incisors were randomly assigned to four groups: (1) no bleaching (control); (2) office bleaching with 40% hydrogen peroxide (HP); (3) home bleaching with 15% carbamide peroxide; and (4) intracoronal bleaching with sodium perborate (SP) using the walking bleaching technique. All teeth were separately immersed in artificial saliva for 14 days. The enamel surface was then reduced by 0.5 mm, and IPS e.max Press ceramic discs were bonded using a resin cement. After 24 hours, all specimens were thermocycled (5,000 cycles, 5°C to 55°C). The SBS was measured using a universal testing machine, and the failure mode was determined using a stereomicroscope. One-way ANOVA and Tukey honest significant difference tests were used for data analysis (P < .05). Results: A significant difference was noted among the groups (P < .001). The highest SBS was noted in the control group (15.71 ± 5.39 MPa). The mean SBS in the office bleaching group (12.30 ± 4.64 MPa) was almost the same as the control. The lowest mean SBS belonged to the home bleaching group (5.39 ± 3.99 MPa). The mode of failure was adhesive in all four groups. Conclusion: If bleaching is intended to be followed by porcelain veneers, the office bleaching technique with 40% HP is recommended. Delaying the bonding procedure for 2 weeks does not appear to be effective with home or intracoronal bleaching.

Purpose: To determine and compare the accuracy and reliability of shade matching using the conventional and smartphone virtual methods. Materials and Methods: A phantom head with both maxillary central incisors removed was set up. A central incisor of various standard shades was inserted into the phantom head. Five undergraduate and five postgraduate students were asked to select the closest shade to match the central incisor using the Vita Classic shade guide. The procedure was then repeated using images taken by a smartphone. Each technique was repeated three times. Differences in accuracy of shade matching between the two techniques for every shade tab and between undergraduate and postgraduate dental students were compared using chi-square statistical analysis. The P value was set at .001. Differences in intrarater and inter-rater reliability between the two techniques and among the three sessions were compared using paired t test and analysis of variance (ANOVA), respectively, with a P value of .05. The reliability of both techniques was further measured using Cohen kappa statistical test. Results: The smartphone virtual shade-matching technique showed significantly higher accuracy in shade matching with most of the tested shade tabs than the conventional method (P < .001), irrespective of observers’ clinical experience. Higher repeatability was found in the virtual technique than the conventional technique, with higher intra-rater and inter-rater reliability observed. Conclusion: Smartphone virtual shade matching showed better accuracy and reliability than the conventional method and could be used as an alternative shade-matching method.

Purpose: To compare the production efficiency of selective laser sintering (SLS) to traditional casting for the fabrication of metal prosthodontic frameworks in a prospective pilot evaluation in a hospital prosthodontic laboratory setting. Materials and Methods: The time taken to complete each of the identified stages in the production of 50 removable partial denture frameworks made using either SLS (n = 25) or casting (n = 25) workflows was measured. The mean time for production was calculated for each workflow, and the difference was tested for statistical significance. Results/Conclusion: The results indicate that an SLS workflow may be more time-efficient, and further cost-effectiveness research is indicated.

Purpose: To investigate the fracture loads of differently veneered and monolithic single-unit fixed dental prostheses (FDPs) made of a novel potential framework material, polyphenylene sulfone (PPSU). Materials and Methods: The fracture loads of four PPSU frameworks with different veneers (manual polymer veneer with Ceramage Body A3B; prefabricated polymer veneer with Novo.lign; digital polymer veneer with Telio CAD; digital ceramic veneer with IPS Empress CAD) and a monolithic control group (PPSU, Gehr) were examined initially and after 1,200,000 masticatory (50 N, 1.3 Hz) and 6,000 thermal cycles (5°C/55°C). Fracture analysis was performed using light microscope imaging. Fracture types were classified, and relative frequencies were determined. Univariate analysis of variance, post hoc Scheffé, partial eta squared (ηp 2), Kruskal-Wallis test, and Weibull moduli using the maximum likelihood estimation method were calculated. The defined level of significance was adjusted by Bonferroni correction (P < .005). Results: Aging did not affect the fracture load values. Single-unit FDPs with a digital ceramic veneer showed lower values than monolithic and manual polymer veneer specimens. Single-unit FDPs with a prefabricated and digital polymer veneer were in the same value range as specimens with a manual polymer and digital ceramic veneer. No differences were observed between manual polymer veneer and monolithic single-unit FDPs. All veneered specimens showed a fracture of the veneer. For monolithic single-unit FDPs, plastic deformation was observed. Conclusion: Veneered and monolithic PPSU showed sufficient fracture load values to indicate successful clinical use in single-unit FDPs. The choice of veneering method and material may play a minor role.

Purpose: To compare the clinical outcomes of metal-ceramic vs metal–acrylic resin implant-supported fixed complete denture prostheses (IFCDPs). Materials and Methods: An electronic literature database search was conducted in the CINAHL, EMBASE, PubMed, and Web of Science databases. A manual search of the literature was also performed. Studies conducted in edentulous human subjects comparing clinical outcomes of metalacrylic IFCDPs to metal-ceramic IFCDPs were included if quantitative outcomes for the following variables were reported: implant failure, prosthetic failure, incidence of peri-implantitis, incidence of peri-implant mucositis, incidence of peri-implant mucosal recession, prosthetic complications, and/or patient-centered outcomes. Data from included studies were pooled to estimate effect size. Results: Five studies met the inclusion criteria. A quantitative analysis was possible for risk of implant failure, prosthetic failure, and incidence of peri-implantitis. Meta-analysis showed no statistically significant differences in the risk of implant and prosthetic failure between the two groups. However, a meta-analysis showed a significantly greater risk of developing peri-implantitis at the implant level in the metal-acrylic group when compared to the metal-ceramic group (risk difference = 0.069; 95% CI = 0.028 to 0.06; P = .001; fixed-effects model). Furthermore, descriptive analysis of the literature indicated a higher incidence of other biologic complications (such as peri-implant mucositis and peri-implant mucosal recession) and prosthetic complications (such as abrasion and veneer fracture) in metal-acrylic IFCDPs compared to metal-ceramic IFCDPs. Conclusion: The available evidence suggests that higher incidence of biologic and prosthetic complications, including a higher risk of peri-implantitis, present with metal-acrylic IFCDPs compared to metal-ceramic IFCDPs.

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.

Patients with a facial malformation due to a cleft lip and palate (CLP) usually suffer from a reduced ability to function normally associated with a poor oral health–related quality of life. This condition often requires multiple significant surgical interventions, and the prosthetic restoration, when needed, is not always included in the initial treatment plan. In order to obtain the highest possible degree of functional, occlusal, and phonetic performance, as well as esthetics, a facially guided prosthodontic treatment sequence should be established. The case presented in this publication shows a multidisciplinary approach for reconstruction of a compromised maxilla with an implant-supported prosthesis via a minimally invasive, digitalized approach.