Journal of Prosthetic Dentistry最新文献

Statement of problem: Denture teeth have traditionally been made from polymethyl methacrylate (PMMA) material. The introduction of subtractive manufacturing enabled the milling of denture teeth, and the advent of additive manufacturing (AM) enabled the 3-dimensional (3D) printing of denture teeth. However, the wear resistance of 3D printed denture teeth is unknown.

Purpose: The purpose of this in vitro study was to compare the linear and volumetric wear of AM resins of different compositions with conventional double cross-linked (DCL) PMMA denture teeth and natural enamel.

Material and methods: DCL PMMA second mandibular premolar denture teeth (Ivoclar Ortholingual conventional DCL PMMA resin teeth) and natural human enamel specimens were used as controls (n=8). The DCL teeth were scanned and printed in 3 different AM resin materials. The specimens DCL PMMA resin teeth (DCL), natural human enamel (enamel), VarseoSmile Crown Plus (AM-CFH), DENTCA Denture Teeth (AM-MPR), a diurethane dimethacrylate (DUDMA) photopolymerizable resin, and OnX Tough (AM-NCH), labeled a hybrid ceramic resin, underwent mastication simulation in a biaxial fatigue testing machine. The mastication simulator was set at 1.53 Hz, thermocycling between 5 °C and 55 °C, and 49 N against a Ø6-mm steatite antagonist following the International Organization for Standardization Technical Specification (ISO/TS) 14569-2. After 250 000 cycles, the linear and volumetric changes on the occlusal surfaces of the specimens were analyzed with a 2-way analysis of variance (ANOVA), followed by a Tukey comparison test (α=.05).

Results: A statistically significant difference in linear and volumetric wear was found between enamel, DCL, and AM denture teeth (P<.001). Enamel had the lowest mean values for linear (0.183 mm) and volumetric wear (0.224 mm³). Within AM materials, AM-CFH linear wear (0.265 mm) did not significantly differ from that of DCL (P=.707). AM-NCH resulted in the highest linear wear (0.515 mm) and largest wear volume (1.841 mm³).

Conclusions: AM denture teeth exhibited varying degrees of wear resistance. The wear rate was contingent upon the material, with AM-CFH resin and increased filler content exhibiting wear comparable with that of DCL denture teeth. Both types of denture teeth had a higher rate of wear than enamel.

Statement of problem: The accuracy of intraoral scanning is crucial for the long-term survival of indirect restorations. It remains unclear if preparation protocols, surface characteristics, and humidity play a role in the quality of an intraoral scan.

Purpose: The purpose of this in vitro study was to assess the impact of margin preparation on both dentin and enamel using different finishing protocols. These assessments were conducted on specimens stored in both dry and wet environments, with a specific focus on evaluating their influence on the accuracy of intraoral scans.

Material and methods: Six maxillary canines were prepared using three different sequences. In the first sequence, a coarse diamond rotary instrument (DC) was used. In the second, DC was followed by a fine grit diamond rotary instrument (DCDF). In the third, the DC was followed by a tungsten carbide rotary instrument. Margins were scanned 10 times using an intraoral scanner (TRIOS 3; 3Shape A/S) compared to a laboratory scanner (D2000; 3Shape A/S). Accuracy was determined by measuring precision and trueness (Geomagic Control; Hexagon). To assess the impact of 3-dimensional (3D) topography on accuracy, roughness was measured using a laser microscope (Lext OLS 4000; Olympus). The data were analyzed using the Levene test, followed by a 3-way ANOVA with Bonferroni post hoc testing to assess the effects and interactions of surface finish, environment, and tissue on the outcomes (α=.05).

Results: Improved precision was observed in enamel (15.7 µm) compared to dentin (24.3 µm) specimens (P<.001). Furthermore, the environment had a significant impact on accuracy (P<.001). Higher precision and trueness (P<.001) were observed for dentin in dry (18.3 µm) compared to wet (37.3 µm) conditions. The use of fine grit diamond rotary instruments improved precision and trueness for dry dentin (DC/DCDF P=.017; DC/DCCF P=.005; DCDF/DCCF P>.999), while no difference was detected for dry enamel (DC/DCDF P=.966; DC/DCCF P=.822; DCDF/DCCF P=.519). The use of a second finishing rotary instrument decreased Sa (µm) for dentin (DC/DCDF/DCCF) (7.11/5.63/4.53), whereas enamel values were similar (7.94/8.53/9.97).

Conclusions: Surface roughness, tooth substrate, and scanning environment (or humidity conditions) were found to influence the accuracy of intraoral scans.

Various methods have been described for fabricating standard or milled bars for implant overdentures. A challenge when using a digital workflow is the deviation of implant positions during intraoral scanner (IOS) data acquisition in edentulous arches, compromising passivity. Verifying implant positions digitally or conventionally is essential. This article presents a step-by-step protocol for digitally producing a maxillary bar-retained implant overdenture by scanning a duplicate of an adequate removable complete prosthesis or a new interim denture with scan analogs and using a reverse scanning technique to fabricate the definitive bar overdenture with a computer-aided design and computer-aided manufacturing (CAD-CAM) software program.

Statement of problem: A meta-analysis of the efficacy of autogenous tooth graft (ATG) for alveolar ridge preservation is still lacking given that earlier articles did not present a quantified synthesis or have a control group in their evaluation of the performance of ATG in comparison with other available materials.

Purpose: The purpose of this systematic review and meta-analysis was to critically assess the existing literature on the efficacy of ATG for alveolar ridge preservation.

Material and methods: The Scopus, MEDLINE/PubMed, and Cochrane Library databases were searched, with additional searches in the nonpeer-reviewed literature, screening for clinical studies that compared ATG with empty sockets or other materials and reported results on alveolar ridge dimensional changes or bone formation. A meta-analysis was performed using the standardized mean difference for the comparisons of alveolar ridge changes and the mean difference for bone formation. The random-effect model was implemented in all analyses.

Results: Fourteen studies were included. Regarding ridge width, a significant difference was noted between the ATG and empty sockets (SMD=1.60, 95% CI=0.53 to 2.66, P=.003). No significant difference was recorded compared with other grafts. As for ridge height, the results revealed no significant difference between the ATG and empty sockets and other grafts (P>.05). Moreover, no difference in bone formation between the ATG and empty sockets was seen (P>.05), while ATG demonstrated a higher percentage of bone formation than other grafts (MD=12.01, 95% CI=3.86 to 20.15, P=.004). Based on the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system, the evidence on ridge width and bone formation was moderate, while the ridge height outcome was of a low level.

Conclusions: Most of the studies included had a small sample size with potential risk of bias. Within these limitations, ATG could be an alternative for alveolar ridge preservation, as it demonstrates the ability to preserve volume and regenerate new bone in the grafted area.

Removing a fractured implant screw, though a relatively rare occurrence, presents a significant challenge for clinicians. Protecting the internal surface of the implant from damage during the retrieval of the fractured fragment is critical to avoid additional complications. A novel, cost-effective, and conservative technique for retrieving fractured implant screws using a small-diameter dental prophylactic brush is described.

Statement of problem: Screw loosening is a common mechanical complication that can compromise the long-term success of implant-supported restorations. Implant-abutment connection design and cyclic loading influence load transfer, preload retention, and joint stability; however, their specific contributions to screw loosening under functional conditions remain unclear.

Purpose: The purpose of this systematic review and meta-analysis was to evaluate the effect of implant-abutment connection geometry on abutment screw stability under cyclic mechanical loading.

Material and methods: This manuscript followed the Preferred Reporting Items for the Systematic Review and Meta-Analyses (PRISMA) statement. Electronic searches were conducted in the PubMed, Scopus, and Web of Science databases for in vitro studies assessing screw loosening after cyclic loading. Studies that evaluated implant-abutment assemblies with clearly specified connection designs using commercially available implants were included. Two reviewers independently screened and extracted data and assessed methodological quality. Random-effects meta-analyses were performed to estimate the mean removal torque loss ratio for each connection type. Meta-regression explored potential sources of heterogeneity. Designs not suitable for meta-analysis were evaluated qualitatively.

Results: A total of 21 in vitro studies met the inclusion criteria. Most applied cyclic loading ranging from 50 000 to 3 000 000 cycles, with forces between 100 and 300 N. Meta-analysis of studies on external hexagon connections revealed a significant pooled torque loss of 23.9% (P=.016) with high heterogeneity (I²=87.6%). The pooled torque loss was 19.2% for the internal hexagon (P=.074), 16.6% for Morse taper (P=.057), and 16.0% for conical connections (P>.05). Narrative synthesis indicated that hybrid conical connections retained preload more effectively than conventional internal hexagon designs. Angled abutments increased torque loss, and Morse taper hybrids generally showed superior stability.

Conclusions: All connection types experienced preload loss under cyclic loading, with external hexagon systems showing the greatest average loss. Conical and Morse taper designs preserved preload better than flat-to-flat hexagon connections. Mechanical stability was affected by connection geometry, abutment angulation, and screw material.

Statement of problem: An efficient protocol for removing stains from 3-dimensionally (3D) printed artificial teeth must also preserve their surface properties.

Purpose: The purpose of this in vitro study was to evaluate methods of removing stains from a 3D printed resin (Bio Crown) for artificial teeth submitted to immersion in coffee by using spectrophotometric analysis (CIEDE2000) and analyzing surface roughness with a profilometer and topography with a scanning electron microscope (SEM).

Material and methods: Disks (Ø10×1.2 mm) were 3D printed and stained in instant coffee simulating 1 year of consumption. Color data (L*, a*, b*) and roughness (Ra, µm) were obtained at T0 (baseline, before staining), T1 (after staining), and T2 (after each stain removal protocol, n=12). The stain removal groups used sodium perborate (SP), 0.25% sodium hypochlorite (SH), conventional polishing with brush and pumice stone + felt wheels and universal paste (CP), and polishing with 3-abrasive tip kit (AP); the control was storage in distilled water (DW). Mixed 2-way ANOVA followed by the Bonferroni test was performed to statistically analyzing data with α=.05.

Results: Roughness increased in all groups between T1 and T2 (P<.05), except for SH. The AP (0.64 ±0.12 µm) and CP (0.52 ±0.17 µm) groups showed similar roughness and higher roughness compared with the other groups (SP 0.40 ±0.22 µm, SH 0.31 ±0.12 µm, and DW 0.34 ±0.11 µm). A significant color difference (ΔE₀₀) was observed between T0 (1.03 ±0.49) and T1 (1.36 ±0.77), (P<.001), and the color remained statistically similar between T1 and T2 (1.48 ±1.02).

Conclusions: No method was effective in removing coffee stains. The polishing methods resulted in greater roughness, followed by sodium perborate. The only protocol that did not increase the roughness of the 3D printed resin for artificial teeth was 0.25% sodium hypochlorite. Longer application periods of the staining removal protocols are suggested for future studies.

This report describes the prosthodontic rehabilitation of a 79-year-old woman with severe microstomia following surgical management of facial burns. The limited oral opening was addressed by using a digital workflow to design a sectional maxillary complete denture incorporating a segmented cobalt chromium base with Novaloc attachments for intraoral assembly.

Statement of problem: The staining and discoloration of computer-aided design and computer-aided manufacture (CAD-CAM) and heat-polymerized denture base resins caused by cleaners and liquids influence material selection and patient instructions; systematic reviews, however, are lacking.

Purpose: The purpose of this systematic review was to evaluate whether CAD-CAM denture base resins exhibit more staining and discoloration compared with heat-polymerized resins after immersion in liquids and cleaners.

Material and methods: This review followed the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. Searches were conducted in the PubMed, Scopus, Web of Science, Embase, Google Scholar databases, and from the reference lists of articles found. The articles were screened by title and abstract, followed by full-text evaluation. Studies assessing the color change of milled or printed resins compared with heat-polymerized resins after immersion in liquids or cleaners were included. The risk of bias was evaluated using the Joanna Briggs Institute tool for quasi-experimental studies.

Results: Of the 1183 articles identified, 15 were included in this review. Printed resins showed higher staining and discoloration after immersion in cleaners and liquids, followed by heat-polymerized and milled resins.

Conclusions: Printed CAD-CAM resins showed more staining and discoloration, and milled resins showed lower stainability after immersion in liquids and cleaners when compared with heat-polymerized resins.