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OBJECTIVES: This study aimed to evaluate the shear bond strength and failure behavior between cobalt-chromium (Co-Cr) alloy and different types of denture base resins (DBRs) over time. METHODS: Seventy-two disk-shaped specimens (8 mm in diameter and 2 mm in thickness) were manufactured using a selective laser melting technology-based metal 3D printer. Three types of DBRs were used: heat-cure (HEA group), cold-cure (COL group), and 3D-printable (TDP group) DBRs (n = 12 per group). Each DBR specimen was fabricated as a 5 mm × 5 mm × 5 mm cube model. The specimens of the TDP group were manufactured using a digital light processing technology-based 3D printer. Half of the DBRs were stored in distilled water at 37 °C for 24 h, whereas the remaining half underwent thermocycling for 10,000 cycles. Shear bond strength was measured using a universal testing machine; failure modes were observed, and metal surfaces were evaluated using energy dispersive spectrometry. RESULTS: The shear bond strength did not differ between the DBR types within the non-thermocycled groups. Contrarily, the TDP group exhibited inferior strength compared to the HEA group (P = 0.008) after thermocycling. All three types of DBRs exhibited a significant decrease in the shear bond strength and an increased tendency toward adhesive failure after thermocycling. CONCLUSIONS: The bond strength between 3D-printable DBRs and Co-Cr alloy was comparable to that of heat-and cold-cure DBRs before thermocycling. However, it exhibited a considerable weakening in comparison to heat-cure DBRs after simulated short-term use. CLINICAL SIGNIFICANCE: The application of 3D-printable DBR in metal framework-incorporated removable partial dentures may be feasible during the early phase of the treatment. However, its application is currently limited because the bond strength between the 3D-printable DBR and metal may weaken after short-term use. Further studies on methods to increase the bond strength between these heterogeneous materials are required.
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PURPOSE: To develop the most compatible cementation protocol for ensuring minimal residual cement and optimal retention of cement-retained implant-supported fixed dental prostheses. MATERIALS AND METHODS: Thirty custom implant abutments and zirconia crowns with bilateral wings were prepared. Three cement types were used for cementation: non-eugenol resin cement (Premier Implant Cement; Group IC), dual-polymerizing self-adhesive resin cement (SmartCem 2; Group SC), and zinc oxide eugenol cement (Temp-Bond; Group TB) (n=30 per group). Three cementation methods were applied for each cement type and the samples were divided into subgroups: 1) cement was injected using a graduated syringe (IC-N, SC-N, and TB-N); 2) a cementation jig made with a silicone impression material and temporary resin material was used (IC-CJ, SC-CJ, and TB-CJ); 3) three dimensionally (3D) printed abutments were used as replicas for cementation (IC-3DP, SC-3DP, and TB-3DP). The amount of cement injected, surface area of the residual cement, and retentive strength were measured. Kruskal-Wallis and post-hoc Mann-Whitney tests were used for statistical analyses. RESULTS: Excess cement was not observed when cementation jig or 3D-printed replicas were used. For IC and SC subgroups, non-use of these auxiliary tools resulted in significantly higher amounts of injected cement. The retentive strength differed significantly among the IC subgroups, but not among the SC subgroups. The retentive strength of subgroups TB-N and TB-CJ was significantly higher than that of subgroup TB-3DP. CONCLUSIONS: To prolong the main purpose of each cement type, a cementation jig or 3D-printed replica is highly recommended regardless of the cement type. Int J Prosthodont 2023. doi: 10.11607/ijp.8344.
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Evaluating tooth mobility is clinically significant, not only for diagnosing periodontal tissues but also in determining the overall periodontal treatment plan. Numerous studies related to tooth mobility have been conducted over the years, including the proposal of various classifications as well as the development of electronic devices for objective measurement. However, there is still no consensus on the measurement methods and criteria for assessing tooth mobility. In this study, we provide a comprehensive review of past and current tooth mobility classification and measurement methods. In order to propose a new method to intuitively evaluate tooth mobility based on previous studies, a digital approach capable of recording tooth micromovements induced by dynamic load should be considered.
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STATEMENT OF PROBLEM: Clinical trials comparing outcomes associated with digital complete dentures (CDs) fabricated from intraoral scan data with those of CDs fabricated by using the conventional workflow are lacking. PURPOSE: The purpose of this randomized clinical trial was to evaluate the clinical performance of and patient satisfaction associated with digitally versus conventionally fabricated CDs. MATERIAL AND METHODS: Eight participants requiring CDs were enrolled in this study. Two sets of CDs were fabricated for each participant. One set was fabricated by using a digital workflow, which involved digital scanning with an intraoral scanner, whereas the other set was made by using the conventional workflow. The participants were given 1 set of CDs for 1 month and another set for the next month. The order of placing CDs was randomly selected for each participant. The internal adaptation, masticatory force, and masticatory efficiency of the CDs in each group were evaluated for objective analysis. Additionally, a questionnaire was provided to the participants, and the responses were evaluated for subjective satisfaction analysis. All parameters were analyzed by using t tests (α=.05). RESULTS: The internal adaptation did not statistically significantly differ between the conventional and digital CDs with regard to the maxillary arches (P=.406) and mandibular arches (P=.412). The average masticatory force (P=.051) and maximum masticatory force (P=.110) likewise did not statistically significantly differ between the 2 types of CDs. Masticatory efficiency, expressed via the mixing ability index, was statistically better for conventional CDs than the digital CDs (P=.009). No statistically significant differences were observed between the 2 types of CDs in terms of overall patient satisfaction as assessed by using the study questionnaire (P=.172 for maxillary CD and P=.161 for mandibular CD). However, the conventional CDs were statistically significantly better than the digital CDs with regard to subjective satisfaction with pronunciation ability (P=.006). CONCLUSIONS: The digital CDs were inferior to the conventional CDs in terms of masticatory efficiency and pronunciation. However, internal adaptation and overall patient satisfaction were comparable between conventional and digital CDs. This finding suggests that intraoral scanning and additively manufactured CDs may be suitable for edentulous patients, at least for interim use.
