The International Journal of Prosthodontics, 06/2020

The world has been suffering incredible loss due to a pandemic caused by a novel coronavirus called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; 2019-nCoV). The disease was later named the coronavirus disease-19 (COVID-19). The transmission routes of COVID-19 include respiratory transmission, aerosol transmission, and contact transmission. Many dental diagnosis and treatment procedures generate droplets and aerosols, and thus both dental staff and patients are at a high risk of becoming infected and transmitting COVID-19 to others. Shanghai Ninth People’s Hospital is a comprehensive hospital with 18 craniofacial-/dental-related departments. During the outbreak of COVID-19 and up to the present date, there have been no confirmed cases of COVID-19 in this hospital thanks to strict protocols for infection prevention and control. In this communication, we would like to share with the prosthodontic community our experience in the prevention and control of COVID-19 in our dental departments and hope it will contribute to the worldwide efforts to overcome the global COVID-19 pandemic.

Purpose: To test the applicability of coded healing abutments, intraoral scanners, and monolithic zirconia for the fabrication of three-unit fixed dental prostheses (FDPs) on two dental implants. Materials and Methods: Patients with three missing teeth in the posterior region of either the maxilla or mandible received two dental implants. After healing, coded healing abutments were placed. Full-arch intraoral scans were made to produce individual titanium abutments and a three-unit FDP. Peri-implant tissues were assessed 2 weeks after placement of the FDP and again after 1 year. Patient-reported outcome measures were registered prior to treatment and after 1 year. The quality of the FDPs was assessed using modified United States Public Health Service criteria after 1 year of service. Results: A total of 54 patients were treated with 60 restorations, and 51 patients with 56 restorations were available at the 1-year follow-up. Implant survival was 99.1%, and prosthesis survival was 100%. The peri-implant tissues remained healthy, and patient satisfaction was high. However, the USPHS evaluation showed that some prostheses exhibited fit or color issues that needed to be addressed, although most were rated as successful (80.4%). Conclusion: The use of coded healing abutments and intraoral scanners to produce full-zirconia three-unit FDPs on two dental implants proved to be a feasible technique, with promising objective and subjective results. However, technical challenges still impacted the treatment results, resulting in a number of restorations having clinical or radiographic marginal gaps or reduced color match.

Purpose: To evaluate the effectiveness of liquid disinfectant soaps for the reduction of microorganisms present on maxillary complete dentures. Materials and Methods: The selected patients (N = 28) were randomly divided into four groups (n = 7), and each group underwent all four disinfection treatments in a different order. The disinfection treatments evaluated were: 0.5% sodium hypochlorite (positive control); Dettol liquid soap; Lifebuoy liquid soap; and phosphate-buffered saline solution (negative control). The patients were instructed to immerse their maxillary dentures in the disinfectant solution for 8 hours (overnight) for 7 days, with the solutions in a randomized sequence with a washout period of 1 week between solutions. Biofilm samples of the dental prostheses were obtained before and after each treatment with a sterile swab, and the microbiologic material was diluted and plated in selective media for Candida spp. Colony-forming unit count (CFU/mL) was performed in each group. One-way ANOVA with Welch correction was used for analysis, with Games-Howell post hoc test with a significance level of .05. Results: A 3-log reduction in microorganisms was considered effective compared to baseline. The highest incidence observed was for Candida albicans, which presented with a frequency between 66% and 92%, followed by C tropicalis, with a frequency between 7% and 33%, in all experimental groups. Sodium hypochlorite was able to reduce more than 3 log10 of microorganisms for all patients, showing high antifungal effectiveness for both C albicans and C tropicalis species. Regarding the experimental groups, both liquid soaps (Dettol and Lifebuoy) were effective in reducing the two types of microorganisms. Conclusion: Liquid soaps were effective at reducing biofilm and may be an alternative for disinfection of removable partial dentures or complete dentures.

Purpose: To assess the effect of extraoral polishing of the crown-abutment interface on the marginal fit of implant-supported screw- and cement-retained prostheses (SCRPs). Materials and Methods: In 31 patients, the marginal gap of an SCRP was measured using a stereomicroscope before and after polishing of the crown-abutment interface, and the paired data were compared. Results: The marginal gap was significantly decreased after surface polishing regardless of the prosthesis material (P < .001). Conclusion: Extraoral polishing of the crown-abutment interface could improve the marginal fit of SCRPs.

Purpose: To investigate the influence of different postpolymerization strategies and artificial aging periods on the Martens hardness parameters of 3D-printed resin materials indicated for temporary use. Materials and Methods: Disks made of four 3D-printed resin materials (n = 30 each) were additively manufactured and postpolymerized with three different postpolymerization devices (n = 10 specimens of each material per device). Disks cut from a prefabricated milling material served as a control. The Martens parameters (ie, Martens hardness [HM] and indentation modulus [EIT]) were measured initially and after 14- and 28-day storage periods in 37°C distilled water. The data were statistically analyzed using univariate analysis, Kolmogorov Smirnov test, and nonparametric tests, including Kruskal-Wallis, Mann-Whitney U, and Wilcoxon tests (α = .05). Results: The highest impact on the Martens parameters was exerted by material (HM: ηP ² = 0.957, EIT: ηp ² = 0.967, P < .001), followed by postpolymerization device (HM: ηP ² = 0.557, EIT: ηP ² = 0.496, P < .001) and duration of water storage (HM: ηP ²= 0.068, EIT: ηP ²= 0.038, P < .001). The values for HM ranged between 108 and 282 N/mm², and for EIT between 2.89 and 7.73 kN/mm². The materials 3Delta Etemp and Temp PRINT showed the highest HM and EIT values regardless of the postpolymerization device and water storage duration (P < .001). In contrast, NextDent C&B, followed by Freeprint Temp, showed the lowest HM and EIT values (P < .001). The milled control group Telio CAD ranged between the two lower groups. Conclusion: Postpolymerization strategy has a high impact on the mechanical properties of 3D-printed resin materials. Materials with a higher filler content showed better results regarding the Martens parameters. Such materials might be an alternative to conventional materials for the milling procedure.

fabricated with different workflows using a combination of the silicone replica technique and microcomputed tomography (μCT). Materials and Methods: Thirty abutments were fabricated to restore internalconnection implants and were divided into three groups according to fabrication method: (1) full digital (abutment machined using CAD/CAM system); (2) Ti-Base (prefabricated standard Ti-Base abutments); and (3) UCLA (UCLA-type abutments) (n = 10/group). Linear and volume measurements were performed to assess the internal misfit using a silicone replica of the implant-abutment interface misfit area, which was three-dimensionally reconstructed after μCT. The internal discrepancies in three different regions of interest (Gap_superior, Gap_marginal, and Gap_center) were assessed. Data were statistically evaluated using ANOVA and Tukey test (P < .05). Results: Ti-Base and UCLA abutments presented significantly lower misfit volume (0.49 mm3, 95% CI: ± 0.045 mm3 and 0.48 mm3, 95% CI: ± 0.045 mm3, respectively) and mean internal gap (25.20 μm, 95% CI: ± 3.14 μm and 27.97 μm, 95% CI: ± 3.14 μm, respectively) than the full digital group (0.70 mm3, 95% CI: ± 0.045 mm3; 34.90 μm, 95% CI: ± 3.14 μm) (P < .001), but did not differ from each other (P = .825). While Gap_center was significantly higher in the full digital group (P < .001), Gap_superior and Gap_marginal did not demonstrate significant differences among groups. All regions were statistically similar within groups, except for Gap_center in the full digital group, which exhibited higher mean values compared to the other regions (P = .000). The 3D measurements for quantification of internal discrepancy were strongly associated with the 2D measurements. Conclusion: Ti-Base and UCLA abutments exhibited better internal fit at the implant-abutment interfaces compared to a fully digitalized workflow (CAD/CAM custom abutments).

Purpose: To determine the influence of thermal and mechanical cycling on fracture load and fracture pattern of resin nanoceramic crowns and polymer-infiltrated ceramic-network (PICN) crowns, both fabricated with CAD/CAM technology. Materials and Methods: A total of 90 premolar crowns bonded to titanium abutments were divided into three groups of 30 crowns each: 30 resin nanoceramic crowns (LU); 30 PICN crowns (VE); and 30 metal-ceramic crowns (MC). The 30 specimens of each group were further divided into three subgroups of 10 each that underwent (1) no treatment, (2) thermocycling (2,000 cycles, 5°C to 55°C), and (3) thermocycling with subsequent mechanical cycling (120,000 cycles, 80 N, 2 Hz). The specimens were loaded to failure, and two-way ANOVA and chi-square test were used to determine differences in fracture resistance and pattern. Results: Mechanical and thermal cycling significantly influenced the critical load to failure of the three materials; however, no significant differences were observed between the thermocycled materials and the materials that were thermocycled with subsequent mechanical cycling. The MC specimens experienced significantly higher fracture loads than those of the LU and VE specimens, which showed no differences from each other in fracture resistance. The fracture patterns showed chipping in MC crowns and partial or complete fracture in LU and VE crowns. The fracture pattern depended on the material and was unrelated to the type of treatment it underwent. Conclusion: All crowns showed adequate resistance to normal masticatory forces in the premolar area. The cyclic fatigue load negatively influenced all three materials.

Purpose: To investigate the effect of aging on the morphology of the interface between monolithic implant crowns and standardized titanium base abutments. Materials and Methods: Four groups of hybrid abutment crowns differing in restorative material (lithium disilicate [LD] or polymer-infiltrated ceramic network [PICN]) and in fabrication procedure of the interfacial zone for luting to a titanium abutment (milled during CAD/ CAM procedure [M] or prefabricated [P]) were formed: LDS-M, LDS-P, PICN-M, and PICN-P (n = 10 each). The morphology of the crown-abutment interface was examined before and after artificial aging using scanning electron microscopy. The total gap length per specimen was measured at both time points, and intergroup (Kruskal-Wallis [KW]) plus pairwise (Wilcoxon Mann-Whitney [WMW]) comparisons were performed (α = .05). Results: Before aging, statistically significant differences in gap length were identified among groups (KW: P = .0369) for PICN-P > LDS-P (WMW: P = .0496) and LDS-M > LDS-P (WMW: P = .0060). The effect of aging among the groups, expressed as an increment of total gap length, was 50% in LDS-M, 30% in LDS-P, 20% in PICN-M, and 30% in PICN-P. After aging, the statistically significant differences in gap length identified among groups (KW: P = .0048) were for PICN-P > LDS-P (WMW: P = .0134); LDS-M > PICN-M (WMW: P = .0204); PICN-P > PICN-M (WMW: P = .0486); and LDS-M > LDS-P (P = .0022). However, comparison of the difference in gap length from before to after aging among the groups was not statistically significant (KW: P = .3549). Conclusion: The cementation interfaces of CAD/CAM crowns on standardized titanium base abutments demonstrated a high percentage of gaps before and after thermomechanical loading. The composition of the restorative material and the nature of the interface influenced the interfacial gap dimension.

Purpose: To investigate the overeruption of unopposed molars and the adaptation of alveolar bone height in young and adult rats. Materials and Methods: A total of 56 4-week-old (young) and 26-week-old (adult) male Wistar rats were followed up longitudinally. In each age group (n = 28), 16 rats were included in the experimental subgroup, in which all the maxillary right molars were extracted, and 12 rats were included in the control subgroup. All rats were scanned at regular intervals with in vivo microcomputed tomography for a 12-week period, and the eruption rate of the mandibular first molars and the surrounding bone were measured, with the reference point at the mandibular canal. The molar categories were unopposed right molars and overloaded left molars in the experimental group and control molars in the control group. Results: The young unopposed molars had the highest mean eruption rate (172 ± 67 μm/day). The overeruption was most marked during the first 3 weeks postextraction, thereafter gradually returning to a level comparable to controls (12.9 ± 6.8 μm/day). The overloaded adult molars did not erupt during the experimental period. Alveolar bone height also increased in young unopposed molars, but at a slower pace than overeruption, causing an increase in clinical crown height. Conclusion: Unopposed young molars overerupt at a higher pace than adult molars during the first weeks postextraction. The alveolar bone grows in response to the tooth eruption but to a lesser extent, which leads to a constant increase in clinical crown height at the same rate in young and adult rats. The increase of clinical crown height was 4.5-fold higher in young unopposed molars compared to control molars.

Purpose: To undertake a scoping review of the available research on the application of polyetheretherketone (PEEK) in implant prosthodontics, map the available literature in order to highlight possible gaps in knowledge and, if possible, extract clinical guidelines. Materials and Methods: The literature on PEEK in implant prosthodontics published through August 2018 was identified with an online search of MEDLINE (via PubMed), Science Direct, Embase (via Ovid), and Google Scholar databases. Qualitative and quantitative syntheses were carried out for original research studies. Results: The amount of published original researcah studies was found to be limited. PEEK was found to be applied as a material in the fabrication of implantsupported fixed dental prosthesis (IFDP) frameworks (43%), prosthetic implant abutments (35%), implant abutment screws (15%), and retention clips on implant bars (7%). Only 38% of the studies were clinical studies, while 15% were observational and 47% were in vitro. The studies identified did not permit the estimation of long-term survival nor success rates for any of the prosthetic components. The results only allowed a preliminary short-term assessment of PEEK IFDP frameworks, which presented satisfactory survival but alarming success rates over the first year of service. Conclusion: In light of the paucity of evidence on the viability of PEEK as an implant-prosthodontic material, its use cannot yet be endorsed. Clinicians should heed the suggested protocols to improve mechanical performance and lower the incidence of prosthetic complications. Further high-quality research is needed for an enhanced understanding of the material’s viability.

Purpose: To introduce an augmented reality (AR) application for students, patients, and practitioners to use to visualize a maxillectomy defect, the associated obturator prosthesis, and the eventual effects on the patient’s facial appearance. Materials and Methods: Various 3D virtual models related to maxillectomy defects and their prosthetic rehabilitations were used to illustrate the handheld AR application. The AR “scene” was created using Vuforia and Unity3D software. Within this scene, 3D virtual models were linked to the target image by detecting a symbol track marker. The final file was saved as an installable application and exported for Android smart devices. Results: The target image containing the maxillectomy defect and the prosthetic rehabilitation were successfully visualized interactively in 3D mode using the handheld AR maxillofacial prosthetic application. Conclusion: An AR application for visualizing maxillofacial prosthetic data could interestingly be developed as a pedagogic tool to explain prosthetic treatments.

The restoration of severely damaged teeth challenges dental practitioners because defects are often located at the subcrestal level. In these cases, surgical crown lengthening or orthodontic extrusion procedures are deemed necessary to maintain the biologic width and respect a sufficient ferrule design after preparation. Considering the negative effects of invasive surgical therapy—such as the reduction of alveolar bone support of the neighboring teeth—forced extrusion might be a valid therapeutic alternative. This clinical case report illustrates forced orthodontic extrusion with a minimally invasive appliance that is applicable in daily clinical routine.