Effect of thermal cycling on the flexure strength of CAD-CAM denture base materials: An in vitro study.

STATEMENT OF PROBLEM: The impact of thermal cycling on the flexure strength of contemporary denture base materials remains inadequately understood despite its crucial role in determining the long-term performance of complete dentures. PURPOSE: The purpose of this in vitro study was to evaluate the flexural strength of different CAD-CAM denture base materials and the effects of thermal cycling. MATERIAL AND METHODS: A total of 120 rectangular specimens were fabricated from 6 denture base materials according to the International Organization for Standardization (ISO) 20795-1:2013 standard: a heat-compressed PMMA ([Lucitone 199 [C-L199]), 2 brands of milled material (Ivotion Base [M-IB] and Lucitone Digital Fit [M-LDF]), and 3 types of 3- dimensionally (3D) printed material (Lucitone Digital Print [P-LDP], Flexcera Base [P-FB], and FotoDent Dentures [P-FD]). Specimens were divided into 2 subgroups of 10; half underwent thermocycling, half did not. Thermally cycled specimens were immersed in distilled water at 37 °C for 2 days, followed by 5000 thermal cycles at 5 and 55 ºC, with a dwell time of 30 seconds. They were then subjected to a 3-point flexural strength test. Two-way ANOVA, followed by post hoc Tukey multiple comparison tests were used to assess the effect of material type and the thermal cycling process on the flexural strength of denture base materials (α=.05). RESULTS: All materials met the ISO standard of 65 MPa flexural strength, except for thermal cycled P-FB. A significant difference (P<.05) in flexure strength value was found among various denture base materials without thermal cycling (M-LDF>M-IB≈P-FD≈P-LDP>C-L199≈ P-FB) and with thermal cycling (M-LDF> M-IB≈P-FD>P-LDP≈C-L199>P-FB). The flexural strength of tested materials was reduced significantly (P<.05) with thermal cycling. CONCLUSIONS: Three-dimensionally printed denture base materials have a flexural strength value similar to or less than that of milled denture base materials. Thermal cycling impacts the flexural strength of denture base materials.

Maximum Fracture Load of Interim Crowns Fabricated by Additive and Subtractive Techniques.

PURPOSE: To evaluate fracture load values of five types of interim CAD/CAM crowns with and without thermocycling. MATERIALS AND METHODS: A complete coverage crown was designed on a mandibular first molar with a uniform 1.5-mm axial and occlusal reduction, and the STL file was exported to manufacture 100 crowns using five materials (20 crowns per material): ZCAD Temp Esthetic (SM-ZCAD; Harvest Dental); Telio CAD (SM-TCAD); P pro Crown and Bridge (AM-PPRO); E-Dent 400 C&B MHF (AM-EDENT); and DENTCA Crown & Bridge (AM-DENTCA). Each group was then divided into two subgroups: before and after thermocycling (10 cornws per subgroup). The STL file of the mandibular first molar die was used to manufacture 100 resin dies. Each die was assigned to one interim crown. Interim crowns were then luted to their assigned die using a temporary luting agent. The fracture strength of crowns was then assessed using a universal testing machine at a crosshead speed of 2 mm/minute. Two-way ANOVA followed by Tukey multiple comparations post-hoc tests were used to assess the effect of material choice and thermocycling process on the fracture strength of interim crowns (α = .05). RESULTS: Material choice and the thermocycling process exerted a significant (P < .001) impact on the fracture strength of interim crowns. However, the interaction between these two factors did not yield a statistically significant effect (P = .176). CONCLUSIONS: Within the limitations of this study, the type of interim materials and thermocycling process have a significant impact on the fracture strength of interim crowns.

Fracture resistance of chairside CAD-CAM lithium disilicate occlusal veneer with various designs after mechanical aging.

PURPOSE: This study evaluated the fracture resistance of chairside computer-aided design and computer-aided manufacturing (CAD-CAM) lithium disilicate crown, onlay, and non-anatomical occlusal veneer (A-OV) with and without margin fabricated. MATERIALS AND METHODS: Sixty-four CAD-CAM lithium disilicate restorations were designed as (1) complete coverage crown (CCC); (2) A-OV with margin; (3) non-A-OV with margin (NA-OV-M); and (4) non-A-OV without margin (NA-OV-NM), 16 of each. Restorations were crystallized and adhesively luted to resin dies using resin cement. Specimens were then subjected to 400,000 cycles of chewing in a mastication simulator. A universal testing machine was used to apply a compressive load at a crosshead speed of 1 mm/min to the long axis of the tooth with a stainless-steel sphere until fracture occurred. One-way ANOVA followed by post hoc tests were used to assess the impact of preparation design on the fracture load of CAD-CAM lithium disilicate restorations. RESULTS: The highest fracture load was recorded for CAD-CAM lithium disilicate indirect restorations for non-A-OVs preparation with margin (2549 ± 428 N) and onlay (2549 ± 293 N) and the lowest fracture load was recorded for CCCs (2389 ± 428 N); however, there was no significant (p = 0.640) between groups. CONCLUSIONS: CAD-CAM lithium disilicate restorations fabricated for anatomical and non-A-OV preparation display a fracture resistance similar to CCCs. Conservative partial coverage restorations may be considered an acceptable approach for posterior teeth.

Fracture resistance of cement-retained lithium disilicate implant-supported crowns: Effect of material used for two-piece abutments.

PURPOSE: This study compared the fracture strength of single lithium disilicate implant-supported crowns fabricated on two-piece abutments with various materials: ceramic-reinforced PEEK, zirconia, and lithium disilicate. MATERIALS AND METHODS: Thirty-six implants were embedded in acrylic cylinders. A two-piece abutment and a crown were designed following a pre-operation scan for a maxillary left central incisor. The designed crown was used to fabricate 36 lithium disilicate crowns. The designed abutment was used to manufacture 36 abutments from 3 materials, 12 each: (A) zirconia; (B) lithium disilicate; and (C) ceramic-reinforced PEEK. Abutments were surface treated and bonded on the titanium base abutments with resin cement. Then, lithium disilicate crowns were bonded on the assigned abutments. Specimens were then subjected to dynamic loading for 1,200,000 cycles. The fracture strength (N) of the assembly was assessed using a universal testing machine. One-way ANOVA followed by multiple comparison tests was used to evaluate the effect of abutment material on the fracture strength of single implant-supported restorations at a significance of .05. RESULTS: The average fracture strength for the groups with zirconia, PEEK, and lithium disilicate two-piece abutments were 1362N ± 218N, 1235N ± 115N, and 1472N ± 171N, respectively. There was a significant (p < 0.05) difference in fracture strength among the groups. The lithium disilicate group had significantly higher fracture strength (p = 0.0058) than the group with PEEK; however, there was no significant (p > 0.05) difference between the other groups. CONCLUSIONS: Two-piece abutments restored with lithium disilicate crowns investigated in the study have the potential to withstand the average physiological occlusal forces in the anterior region.

Shade match comparison of CAD-CAM single crowns to a lithium disilicate crown.

PURPOSE: To assess the shade match ability of four varieties of all-ceramic crowns to a neighboring bilayered lithium disilicate crown. MATERIAL AND METHODS: A dentiform was used to fabricate a bilayered lithium disilicate crown on the maxillary right central incisor, following the anatomy and shade of a selected natural tooth. Two crowns (one full-contour, one cutback) were then designed on a prepared maxillary left central incisor, following the contour of the neighboring crown. The designed crowns were used to manufacture monolithic lithium disilicate, bilayered lithium disilicate, bilayered zirconia, and monolithic zirconia crowns, 10 each. An intraoral scanner and a spectrophotometer were used to assess the frequency of matched shades and to calculate the color difference (ΔE) between the two central incisors at the incisal, middle, and cervical thirds. Kruskal-Wallis and two-way ANOVA were used to compare the frequency of matched shades and ΔE values, respectively (α = 0.05). RESULTS: There was no significant (p > 0.05) difference in frequencies of matched shades for each group at the three sites; except bilayered lithium disilicate crowns. Bilayered lithium disilicate crowns had significantly (p < 0.05) higher match frequency than monolithic zirconia at the middle third. The ΔE value was not significantly (p > 0.05) different among the groups at the cervical third. However, monolithic zirconia had significantly (p < 0.05) higher ΔE values than bilayered lithium disilicate and zirconia at the incisal and middle thirds. CONCLUSIONS: Bilayered lithium disilicate and zirconia appeared to most closely match the shade of an existing bilayered lithium disilicate crown.

Fracture strength of screw-retained zirconia crowns assembled on zirconia and titanium implants.

PURPOSE: This in vitro study evaluated the fracture strength of screw-retained zirconia crowns connected to zirconia (Zr) and titanium (Ti) implants after undergoing a simulation of 5 years of clinical use. MATERIALS AND METHODS: Forty-eight screw-retained zirconia crowns were fabricated and assembled on four implant systems, with 12 in each group: (1) Zr implant (pure ceramic; Straumann AG) (PZr); (2) Zr implant (NobelPearl; Nobel Biocare) (NPZr); (3) Ti-Zr implant (Bone Level Roxolid; Straumann AG) (RSTiZr); (4) Ti implant (Conical Connection PMC; Nobel Biocare) (NRTi). Crowns were luted to their associated abutments using resin cement and then torqued to their assigned implants at the recommended torque value. Specimens were subjected to dynamic loading for 1,200,000 loading cycles. Fracture strength, measured in Newtons (N), was tested under static compression load using a universal testing machine at an angle of 30°. One-way ANOVA and Tukey's multiple comparisons post hoc test were used to compare the mean fracture values between the groups at a significance level of 0.05. RESULTS: The average fracture strengths for the RSTiZr and NRTi groups were 1207 ± 202 and 1073 ± 217 N, respectively, which was significantly (p < 0.0001) higher than the PZr and NPZr groups (712 ± 76 and 571.6 ± 167 N, respectively). However, no significant difference was found between the fracture strength value of RSTiZr and NRTi (p = 0.260) or PZr and NPZr (p = 0.256) groups. CONCLUSIONS: Zirconia crowns connected to Zr implants have the potential to withstand the average physiological occlusal forces which occur in the anterior and premolar regions.

Effect of incisal preparation design on the fracture strength of monolithic zirconia-reinforced lithium silicate laminate veneers.

PURPOSE: This study aimed to assess the fracture resistance of monolithic zirconia-reinforced lithium silicate laminate veneers (LVs) fabricated on various incisal preparation designs. MATERIALS AND METHODS: Sixty maxillary central incisors with various preparation designs were 3D-printed, 15 each, including preparation for: (1) LV with feathered-edge design; (2) LV with butt-joint design; (3) LV with palatal chamfer; and (4) full-coverage crown. Restorations were then designed and manufactured from zirconia-reinforced lithium silicate (ZLS) following the contour of a pre-operation scan. Restorations were bonded to the assigned preparation using resin cement and following the manufacturer's instructions. Specimens were then subjected to 10,000 thermocycles at 5 to 55°C with a dwell time of 30 s. The fracture strength of specimens was then assessed using a universal testing machine at a crosshead speed of 1.0 mm/min. One-way ANOVA and Bonferroni correction multiple comparisons were used to assess the fracture strength differences between the test groups (α = 0.001). Descriptive fractographic analysis of specimens was carried out with scanning electron microscopy images. RESULTS: Complete coverage crown and LV with palatal chamfer design had the highest fracture resistance values (781.4 ± 151.4 and 618.2 ± 112.6 N, respectively). Single crown and LV with palatal chamfer had no significant difference in fracture strength (p > 05). LV with feathered-edge and butt-joint designs provided significantly (p < 05) lower fracture resistance than complete coverage crown and LV with palatal chamfer design. CONCLUSION: The fracture resistance of chairside milled ZLS veneers was significantly influenced by the incisal preparation designs tested. Within the limitation of this study, when excessive occlusal forces are expected, LV with palatal chamfer display is the most conservative method of fabricating an indirect restoration.

Flexural strength, surface roughness, and biofilm formation of ceramic-reinforced PEEK: An in vitro comparative study.

PURPOSE: This in vitro study aimed to compare flexural strength, surface roughness, and biofilm formation of ceramic-reinforced polyetheretherketone (PEEK) with conventionally heat-compressed and milled polymethylmethacrylate (PMMA) denture base materials. MATERIALS AND METHODS: Thirty strips (6.4 mm × 10 mm × 3 mm) and 30 discs (10 mm × 1 mm) were fabricated from a heat-compressed PMMA, milled PMMA, and ceramic-reinforced PEEK, 10 each. One surface of each sample was polished to mimic the laboratory procedure for denture base materials. Strips were then subjected to a three-point bend test using a universal testing machine at a crosshead speed of 5.0 mm/min. An optical profilometer was used to assess the Ra value (mm) of the discs on polished and unpolished sides. Biofilm formation behavior was analyzed by measuring the colony-forming unit (CFU)/mL of Candida albicans on the unpolished surface of the discs. One-way ANOVA followed by Tukey multiple comparison tests were used to compare the flexural strength, Ra value, and biofilm formation of the studied materials (a = 0.05). RESULTS: Ceramic-reinforced PEEK showed significantly higher flexural strength (178.2 ± 3.2 MPa) than milled PMMA (89.6 ± 0.8 MPa; p < 0.001) and heat-compressed PMMA (67.3 ± 5.3 MPa; p < 0.001). Ceramic-reinforced PEEK exhibited a significantly higher Ra value than the other groups on unpolished sides; however, the polishing process significantly reduced the Ra values of all studied groups (p < 0.05). There was no significant difference in C. albicans adhesion among the groups (p < 0.05). CONCLUSION: The flexural strength of tested materials was within acceptable limits for clinical use as a denture base material. Ceramic-reinforced PEEK had the highest surface roughness; however, its similarity in biofilm formation to other groups indicates its clinical acceptability as denture base material.

Effect of mastication load on retention force of custom-made LOCATOR abutments manufactured for angled implants: An in vitro study.

STATEMENT OF PROBLEM: Custom-made angled LOCATOR abutments have been used to compensate for the angulation of implants placed to support removable prostheses; however, their retention forces and the impact of mastication loading on retention have yet to be well addressed. PURPOSE: The purpose of this in vitro study was to evaluate the retention force of custom-made LOCATOR abutments for implants placed at 0-, 15-, and 30-degree angulations with prefabricated abutments and to investigate the effect of mastication load on retention. MATERIAL AND METHODS: Implant analogs were placed at the first molars of 40 maxillary typodonts, and 40 LOCATOR abutments were fabricated. Twenty implant analogs were placed at 0 degrees, 10 of which received prefabricated LOCATOR abutments and 10 of which received custom abutments. The remaining 20 implant analogs were placed at 15- and 30-degree angulations (n=10), and custom LOCATOR abutments were fabricated on them. A denture analog was digitally designed and manufactured from polymethyl methacrylate (PMMA) billets. Metal housings were then picked up using PMMA. The specimens were subjected to 2 rounds of 120 000 cycles of mastication loading. Retention force was assessed before and after each round of mastication loading using a universal testing machine. The wear of nylon inserts before and after mastication loading was accessed with a digital stereomicroscope. A 2-way ANOVA followed by the Tukey HSD test was used to determine the impacts of LOCATOR abutment type and times of mastication loading on the retention forces of the denture base (α=.05). RESULTS: No significant difference in retention forces was found between prefabricated LOCATOR and custom abutments (placed at 0-, 15-, and 30-degree angulations) regardless of mastication loading (P>.05). The retentive force values of all groups increased significantly after the first round of mastication loading and decreased significantly to the initial level after the second round of mastication loading (P<.05). CONCLUSIONS: Mastication loading impacted the retention force of both prefabricated and custom LOCATOR abutments; however, no significant difference in retention forces was found among various types of abutments.

A survey on utilization and barriers of digital removable prostheses in the US dental education.

PURPOSE: Gaining knowledge on the extent of digital technology implementation in dental education and the barriers to it will help inform future directions to promote the use of such technology and will enhance dental education. This study aimed to investigate the utilization of digitally fabricated removable prostheses and the potential obstacles to implementing such technology in US dental schools. METHODS: A survey was developed and distributed to the restorative dentistry department chairs and postdoctoral prosthodontic program directors. The survey delivery protocol included follow-up emails 1 week, 3 weeks, and 4 weeks after the initial email. The collected data were analyzed descriptively. RESULTS: The response rate was 85% and 45% for predoctoral and postdoctoral prosthodontic programs, respectively. The results showed that 88.06% of the predoctoral programs and 95.65% of the postdoctoral prosthodontic programs implement digital complete dentures in the curriculum; however, the digital removable partial dentures implementation rate was recorded at 70.77% in predoctoral programs and 61.9% in postdoctoral prosthodontic programs. CONCLUSIONS: Dental schools are challenged by cost, design software limitations, IT and laboratory support, and faculty training. Multifaceted support is instrumental in further implementing digital removable prosthodontics into dental education.

Effect of adding a hard-reline material on the flexural strength of conventional, 3D-printed, and milled denture base materials.

STATEMENT OF PROBLEM: Novel 3-dimensionally printed resin and milled polymethyl methacrylate materials have been marketed for computer-aided design and computer-aided manufacturing (CAD-CAM) denture base fabrication. However, information on the flexural strength of digitally fabricated denture base material is limited, and little is known about how they are affected by a hard-reline procedure. PURPOSE: The purpose of this in vitro study was to assess the flexural strength of 6 digitally manufactured denture base materials and to assess the effect of a hard-reline procedure on their flexural strength. MATERIAL AND METHODS: A total of 140 strips of denture base material were fabricated from a conventional heat-polymerized polymethyl methacrylate (L199), 3 brands of milled polymethyl methacrylate (IBC, DSL, and ADH), and 3 brands of 3D-printed resin (DFD, ADB, and DrFD) (n=20). Ten specimens in each group did not receive any treatment, and 10 were relined with a hard-reline material (ProBase Cold Trial Kit). Specimens were then subjected to a 3-point flexural strength test using a universal testing machine at a crosshead speed of 5.0 mm/min. A 1-way ANOVA test followed by the Tukey multiple comparison test was used to detect the difference in flexural strength and the strain at fracture of the different types of denture base materials (α=.05). The comparison of flexural strength between with and without hard-reline was analyzed using an unpaired t test (α=.05). RESULTS: All materials, with or without the hard-reline, met the International Organization for Standardization (ISO) 20 795-1:2013 standard for flexural strength (65 MPa). The milled materials (DSL>IBC≈ADH) showed higher flexural strength than the 3D-printed or conventional materials (DrFD>DFD≈ADB≈L199) without a hard-reline. No statistical difference in flexural strength was found among the hard-relined denture base materials (P=.164). All 3 milled materials showed reduced flexural strength after relining, while the relined conventional (L199) and 3D-printed materials (DFD and ADB) showed notably higher flexural strength; printed DrFD showed no significant difference (P=.066). In terms of strain at fracture, the milled materials displayed higher values than those of the conventional or 3D-printed materials (P<.05). CONCLUSIONS: All digitally fabricated denture base materials were within acceptable limits for clinical use, even after hard relining. Flexural strength was highly dependent on the type of material. Hard relining affected the flexural strength of most of the digitally fabricated denture base materials.

Adopting artificial intelligence in dental education: A model for academic leadership and innovation.

INTRODUCTION: The continual evolution of dental education, dental practice and the delivery of optimal oral health care is rooted in the practice of leadership. This paper explores opportunities and challenges facing dental education with a specific focus on incorporating the use of artificial intelligence (AI). METHODS: Using the model in Bolman and Deal's Reframing Organizations, the Four Frames model serves as a road map for building infrastructure within dental schools for the adoption of AI. CONCLUSION: AI can complement and boost human tasks and have a far-reaching impact in academia and health care. Its adoption could enhance educational experiences and the delivery of care, and support current functions and future innovation. The framework suggested in this paper, while specific to AI, could be adapted and applied to a myriad of innovations and new organizational ideals and goals within institutions of dental education.

Rehabilitating simulated worn dentition by using a complete digital workflow and five anatomic guidelines.

This report describes the rehabilitation of worn dentition by using a complete digital workflow on a nonhinged simulated patient. A dentiform was used to represent an individual with loss of occlusal vertical dimension. Interim restorations were designed following the simulated patient's midline, interpupillary line, and ala-tragus line and a defined central incisal edge position, posterior maxillary teeth central groove, and buccal cusp position of posterior maxillary teeth. The definitive restorations were then designed and fabricated by following the contour of the interim restorations.

Assessment of Tooth Preparations Submitted to Dental Laboratories for Fabrication of Monolithic Zirconia Crowns.

PURPOSE: The objective of this study was to assess the quality of posterior teeth prepared for monolithic zirconia crowns. MATERIALS AND METHODS: A total of 392 STL-files of posterior preparations for monolithic zirconia crowns were evaluated in this study. Three-dimensional (3D) images were evaluated using a software (3D Viewer; 3Shape A/S, Copenhagen, Denmark) for finish line design, finish line width, occluso-cervical dimension, total occlusal convergence (TOC), intercuspal angulation, finish line quality, line angle form, and presence or absence of undercut at the axial wall and unsupported lip of enamel. The assessment was performed by two calibrated evaluators. Then, data were descriptively analyzed. Data for occluso-cervical dimension and TOC were descriptively analyzed according to their location. RESULTS: Thirty-nine percent of premolars, 77% of first molars, and 91% of second molars had an average occluso-cervical dimension of less than 3 mm (premolars) and 4 mm (molars), with most of the preparations having a TOC of more than 20 degrees. More than 50% of preparations had undercut, unsupported enamel and/or unacceptable finish line quality. CONCLUSIONS: The quality of tooth preparation including finish line quality, absence of unsupported enamel and undercut at the axial wall should be evaluated when preparing monolithic zirconia crowns.

Students' perception of 3D video microscope use in preclinical fixed prosthodontics: A comparative study.

OBJECTIVES: The purpose of this study was to determine how students perceived the use of a 3D video microscope (3D VM), in comparison to conventional methods, for providing instruction on fixed prosthodontics procedures and issuing feedback on student performance. METHODS: From May until December of 2020, University at Buffalo School of Dental Medicine's second-year students were introduced to fixed prosthodontics. During May and June, a 3D VM was used to live-stream psychomotor skill demonstrations via a web-based software. After each procedure, students were asked to complete a short survey regarding their experience with the training. From August until December 2020, students received feedback via: 1. The conventional method, in which faculty use magnification loupes to assess student's perfromance. 2. A 3D VM. Irrespective of the method used, feedback was given following the same defined rubrics. At the conclusion of the semester, students completed a survey comparing their experiences in receiving instruction and feedback. The data were gathered and analyzed descriptively. The chi-square test (α = .05) was used to gauge if students' gender had an impact on their perception of feedback methods. RESULTS: More than 94% of students participated in the surveys. The majority of students had a positive reaction toward the use of the 3D VM for live web-based training. In regard to receiving feedback, 63% opined that the 3D VM was more effective than the conventional method. Additionally, 80% of students felt that the 3D VM was effective in maintaining physical distance during skill evaluations. CONCLUSION: This study examined the use of a 3D VM for teaching psychomotor skills and providing student feedback and compared it to the conventional method. It was found that the use of the 3D VM was perceived positively by students. Gender had no significant impact on students' attitudes toward the teaching and feedback methods.

Fracture Strength of Interim CAD/CAM and Conventional Partial Fixed Dental Prostheses.

PURPOSE:  To compare the fracture strength of three-unit provisional partial fixed dental prostheses (FDPs) fabricated by an indirect-direct technique from poly(methylmethacrylate) (PMMA) through digital and conventional workflows, and FDPs fabricated by a direct technique using Bisacryl (BisA) and externally reinforced BisA. MATERIALS AND METHODS:  Forty partially edentulous typodonts with a missing mandibular left first molar and standard preparations on mandibular left second premolar and molar were used to fabricate three-unit provisional FDPs. Two materials and two techniques were used to fabricate a total of forty provisional FDPs: (1) BisA; (2) BisA reinforced with glass fiber strips [BisA-GFR]; (3) conventionally fabricated PMMA shell relined with PMMA [C-PMMA]; (4) CAD/CAM fabricated PMMA shell relined with PMMA [CAD/CAM-PMMA]. Provisional FDPs were then luted onto the preparations using a temporary cement. Specimens were mounted onto a chewing simulator; 20,000 cycles of 70 N forces were applied under 25°C distilled water. Specimens were then loaded to fracture using a universal testing machine (The Dillion Quantrol TC2i; Mecmesin) with a crosshead speed of 2 mm/min. One-way ANOVA, followed by Tukey post hoc test, was used to assess the effect of production technique on the fracture strength of the provisional FPDs (α = 0.5). RESULTS:  Mean fracture strengths recorded for the CAD/CAM-PMMA, C-PMMA, BisA, and BisA-GFR groups were 520 N, 448 N, 245 N, and 169 N, respectively. PMMA groups had significantly (p < 0.0001; F = 24.40) higher fracture strength compared to Bisacryl groups. CONCLUSION:  When high occlusal forces are expected, provisional FDPs fabricated with PMMA using the indirect-direct technique are recommended, irrespective of CAD/CAM or conventional workflow.

Audience and Presenter Comparison of Live Web-Based Lectures and Traditional Classroom Lectures During the COVID-19 Pandemic.

PURPOSE: The purpose of the study was to assess participants' and presenters' perceptions of a live web-based lecture series in comparison to traditional in-person lectures. MATERIALS AND METHODS: A virtual lecture series was organized by the---from March 25th until June 3rd of 2020. Twenty-five postgraduate prosthodontics programs and 81 presenters participated. Two surveys were developed and distributed to the audience (N = 330) and the presenters (N = 81). Follow-up emails were sent one week, three weeks, and four weeks after the initial email survey to encourage its completion. The data were analyzed descriptively. One-way ANOVA (p = 0.05), followed by a post hoc test, were used to compare the response percentages among the different generations of presenters and participants. RESULTS: Fifty-two percent of participants, and 65% of presenters, completed the survey. More than 96% of participants and presenters were satisfied with the lecture series. Seventy-nine percent of audience members felt that the live web-based lectures were as effective as traditional classroom lectures, or more effective; 32% of presenters agreed. Millennial audience members had significantly (p = 0.0028) more negative responses than the other generations. CONCLUSION: Participants have more positive perceptions of web-based lectures than presenters.

Effect of zirconia etching solution on the shear bond strength between zirconia and resin cement.

STATEMENT OF PROBLEM: The bond between resin cement and zirconia is essential to the long-term retention of a zirconia crown. However, it is unclear if the existing methods provide a long-term bond between resin cement and zirconia. PURPOSE: The purpose of this in vitro study was to evaluate the effects of a zirconia etching solution on the shear bond strength between zirconia and resin cement. MATERIAL AND METHODS: Sixty yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) disks (Ø8×5 mm) were divided into 4 groups (n=15). Each group was then treated with 1 of the following methods: airborne-particle abraded with 50-µm Al2O3 (AA); etched with zirconia etching solution (ZES); airborne-particle abraded with 50-µm Al2O3 and then etched with ZES (AA-ZES); etched with ZES and then airborne-particle abraded with 50-µm Al2O3 (ZES-AA). Sixty composite resin cylinders (Ø2.3×2.4 mm) were luted to the zirconia disks with a self-adhesive resin cement under constant load and then light-polymerized for 40 seconds. Specimens were stored in a 37 °C incubator in distilled water for 24 hours and then thermocycled for 1000 cycles between 5 °C and 55 °C. A universal testing machine with a crosshead speed of 0.5 mm/min was used to measure the shear force (N). The shear bond strength (MPa) was then calculated. One-way ANOVA was used to compare the mean shear bond strength among the groups (α=.05). The failure mode was evaluated by using light microscopy at ×90 magnification and categorized as an adhesive, cohesive, or mixed failure. RESULTS: Mean ±standard deviation shear bond strength for AA, ZES, AA-ZES, and ZES-AA groups were 9.9 ±2.6, 8.9 ±2.9, 9.6 ±3.9, and 11.0 ±2.3 MPa, respectively. There was no significant difference among the treatment groups (P>.05). CONCLUSIONS: A zirconia etching solution did not significantly improve the shear bond strength between zirconia and resin cement compared with airborne-particle abrasion with Al2O3.

Comparative Analysis of Biofilm Formation on Materials Used for the Fabrication of Implant-Supported Prostheses.

The purpose of this study was to compare biofilm formation on materials used for the fabrication of implant-supported dental prostheses. Twenty discs (D=15 mm, H=3 mm) were fabricated from one of the following restorative materials: yttria tetragonal zirconia polycrystal (Y-TZP); commercially pure titanium (CP-Ti); or heat-cured polymethyl methacrylate (PMMA). Specimens were polished following standard protocols. A non-contact profilometer (NPFLEX, Bruker, UK) was used to assess the surface roughness of each disk; results were reported as Ra (µm). Five strains of Gram-negative bacteria frequently associated with peri-implantitis, Aggregatibacter actinomycetemcomitans, Candida. albicans, Porphyromonas gingivalis, Prevotella intermedia, and Tannerella forsythia, were cultured on hand-polished discs fabricated from heat-cured PMMA, Y-TZP, or CP-Ti to compare biofilm formation on each type of material. The results were reported as colony-forming units per milliliter (CFU/mL). One-way ANOVA and post hoc tests were used to compare surface roughness and bacterial colonization on the respective materials. Statistical significance was set at a = 0.05. Discs fabricated from Y-TZP had a significantly higher Ra value (350 ± 30 µm) than either PMMA, or CP-Ti discs. Discs fabricated from either Y-TZP and CP-Ti may exhibit less colonization by bacteria associated with peri-mucositis and peri-implantitis. Y-TZP and CP-Ti are suggested materials for fabrication of implant-supported prostheses, considering biofilm formation.