Effect of Model Resin and Shaft Taper on the Trueness and Fit of Additively Manufactured Removable Dies in Narrow Ridge Models.

Effect of model resin and shaft taper angle on the trueness and fit of additively manufactured removable dies in narrow ridge casts Purpose. To evaluate how model resin and shaft taper affect the trueness and fit of additively manufactured removable dies in narrow ridge casts. MATERIAL AND METHODS: A typodont model with a prepared mandibular molar was scanned to design virtual dies with different shaft tapers (0-degree (straight), 5-degree, and 10-degree tapered). Fifteen dies and one hollowed cast per taper were additively manufactured from two resins (G-PRINT 3D Model, GP and DentaMODEL, DM). Dies and casts were digitized to evaluate their trueness (root mean square (RMS)). The fit of the dies was evaluated with crown portion's RMS when seated in the cast and with distance deviations. Kruskal-Wallis and Mann-Whitney U tests were used to analyze data (α =.05). RESULTS: GP dies had lower overall, root, and base RMS, while DM dies had lower crown RMS (P≤.016). Straight dies had the highest overall, root, and base RMS within GP (P≤.030). Ten-degree dies had the lowest overall and base RMS, lower crown RMS than straight, and lower root RMS than 5-degree dies within DM (P≤.047). When the dies were seated, GP had lower crown portion RMS within 5- and 10-degree dies, and 5-degree dies had the highest RMS within DM (P≤.003). GP had lower distance deviations within 5- and 10-degree dies. Five-degree dies had the highest deviations within DM (P≤.049). CONCLUSIONS: GP dies mostly had higher trueness and better fit. Straight dies mostly had lower trueness within GP. Ten-degree taper mostly led to higher trueness within DM. The shaft taper affected DM dies' fit.

Fatigue behavior of implant-supported cantilevered prostheses in recently introduced CAD-CAM polymers: An in vitro study.

STATEMENT OF PROBLEM: Cantilevered complete arch implant-supported prostheses are commonly fabricated from zirconia and more recently from strength gradient zirconia. Different polymer-based materials indicated for definitive fixed prostheses that could be used with additive or subtractive manufacturing have also been marketed recently. However, knowledge on the long-term fatigue behavior of cantilevered implant-supported prostheses made from these polymer-based materials and strength gradient zirconia is lacking. PURPOSE: The purpose of this in vitro study was to evaluate the fatigue behavior of implant-supported cantilevered prostheses of recently introduced computer-aided design and computer-aided manufacturing polymers and zirconia. MATERIAL AND METHODS: A master standard tessellation language file of a 9×11×20-mm specimen with a titanium base (Ti-base) space that represented an implant-supported cantilevered prosthesis was used to fabricate specimens from additively manufactured interim resin (AM), polymethyl methacrylate (SM-PM), nanographene-reinforced polymethyl methacrylate (SM-GR), high-impact polymer composite resin (SM-CR), and strength gradient zirconia (SM-ZR) (n=10). Each specimen was prepared by following the respective manufacturer's recommendations, and Ti-base abutments were cemented with an autopolymerizing luting composite resin. After cementation, the specimens were mounted in a mastication simulator and subjected to 1.2 million loading cycles under 100 N at 1.5 Hz; surviving specimens were subjected to another 1.2 million loading cycles under 200 N at 1.5 Hz. The load was applied to the cantilever extension, 12-mm from the clamp of the mastication simulator. The Kaplan-Meier survival analysis and Cox proportional hazards model were used to evaluate the data (α=.05). RESULTS: Significant differences in survival rate and hazard ratio were observed among materials (P<.001). Among tested materials, SM-ZR had the highest and AM had the lowest survival rate (P≤.031). All materials had a significantly higher hazard ratio than SM-ZR (P≤.011) in the increasing order of SM-GR, SM-PM, SM-CR, and AM. CONCLUSIONS: SM-ZR had the highest survival rate with no failed specimens. Even though most of the tested polymer-based materials failed during cyclic loading, these failures were commonly observed during the second 1.2 million loading cycles with 200 N. All materials had a higher hazard ratio than SM-ZR.

Validation of the pink esthetic score/white esthetic score at single tooth-supported prostheses in the esthetic zone: A randomized clinical trial.

OBJECTIVES: To validate the reproducibility and inter/intra-observer variability of the Pink Esthetic Score/White Esthetic Score (PES/WES) of single tooth-supported prostheses in the maxillary esthetic zone (13-23). MATERIALS AND METHODS: Forty-five patients were randomly assigned to one of the three treatment options (15 patients per group) receiving each one a different crown type: Porcelain fused to metal (PFM), monolithic zirconia, and lithium disilicate. Eight observers from each of four different specialties (Prosthodontists, Orthodontists, Periodontists, and Oral Surgeons) were recruited and assessed twice and four weeks apart (i.e., T1 and T2) 45 photographs of the single tooth-supported prosthesis using PES/WES and compared them with contralateral teeth. RESULTS: According to the ANOVA and post hoc tests, the zirconia crown type obtained the highest mean score by all observers, with a mean value of 16.70 ± 2.94. The prosthodontists and oral surgeons assigned the lowest mean score to PFM crowns, 13.03 ± 3.47 and 13.80 ± 3.17, respectively. Notably, the prosthodontists awarded the highest scores, specifically 17.50 ± 2.81 for the zirconia crowns. Intraobserver agreement was calculated utilizing the paired t-test. Pairwise comparisons between observers of different specialties revealed significant intraobserver agreement. Interclass correlation coefficient (ICC) scores were statistically significant among four specialties. No difference was detected concerning the interobserver agreement. CONCLUSIONS: The PES/WES index remains consistent across various observers from different specializations, yielding uniform results in the overall esthetic evaluation. Consequently, in light of the presented preliminary positive results, its use might also be considered for the esthetic assessment of single-tooth-supported prostheses. CLINICAL SIGNIFICANCE: The PES/WES index may be employed clinically to evaluate single tooth-supported prostheses as it emerged as a reproducible esthetic scoring system.

Fabrication trueness and marginal quality of additively manufactured resin-based definitive laminate veneers with different restoration thicknesses.

OBJECTIVES: To evaluate how restoration thickness (0.5 mm and 0.7 mm) affects the fabrication trueness of additively manufactured definitive resin-based laminate veneers, and to analyze the effect of restoration thickness and margin location on margin quality. METHODS: Two maxillary central incisors were prepared either for a 0.5 mm- or 0.7 mm-thick laminate veneer. After acquiring the partial-arch scans of each preparation, laminate veneers were designed and stored as reference data. By using these reference data, a total of 30 resin-based laminate veneers were additively manufactured (n = 15 per thickness). All veneers were digitized and stored as test data. The reference and test data were superimposed to calculate the root mean square values at overall, external, intaglio, and marginal surfaces. The margin quality at labial, incisal, mesial, and distal surfaces was evaluated. Fabrication trueness at each surface was analyzed with independent t-tests, while 2-way analysis of variance was used to analyze the effect of thickness and margin location on margin quality (α = 0.05). RESULTS: Regardless of the evaluated surface, 0.7 mm-thick veneers had lower deviations (P < 0.001). Only the margin location (P < 0.001) affected the margin quality as labial margins had the lowest quality (P < 0.001). CONCLUSION: Restoration thickness affected the fabrication trueness of resin-based laminate veneers as 0.7 mm-thick veneers had significantly higher trueness. However, restoration thickness did not affect the margin quality and labial margins had the lowest quality. CLINICAL SIGNIFICANCE: Laminate veneers fabricated by using tested urethane-based acrylic resin may require less adjustment when fabricated in 0.7 mm thickness. However, marginal integrity issues may be encountered at the labial surface.

Impact of the superimposition methods and the designated comparison area on accuracy analyses in dentate models.

OBJECTIVES: To measure the impact of superimposition methods and the designated comparison area on accuracy analyses of dentate models using an ISO-recommended 3-dimensional (3D) metrology-grade inspection software (Geomagic Control X; 3D Systems; Rock Hill, South Carolina; USA). MATERIALS AND METHODS: A dentate maxillary typodont scanned with a desktop scanner (E4; 3 Shape; Copenhagen; Denmark) and an intraoral scanner (Trios 4; 3 Shape; Copenhagen; Denmark) was used as reference. Eight groups were created based on the core features of each superimposition method: landmark-based alignment (G1); partial area-based alignment (G2); entire tooth area-based alignment (G3); double alignment combining landmark-based alignment with entire tooth area-based alignment (G4); double alignment combining partial area-based alignment with entire tooth area-based alignment (G5); initial automated quick pre-alignment (G6); initial automated precise pre-alignment (G7); and entire model area-based alignment (G8). Diverse variations of each alignment and two regions for accuracy analyses (teeth surface or full model surface) were tested, resulting in a total of thirty-two subgroups (n = 18). The alignment accuracy between experimental and reference meshes was quantified using root mean square (RMS) error as trueness and its repeatability as precision. The descriptive statistics, a factorial repeated measures analysis of variance (ANOVA) and a post hoc Tuckey multiple comparison tests were used to analyze the trueness, and precision (α = 0.05). RESULTS: A total of 576 superimpositions were performed. The unique partial area-based superimposition method demonstrated the least precise alignment and was the sole group to exhibit a significant difference (p<.001). Automated initial pre-alignments demonstrated similar accuracy to other superimposition methods (p>.05). Double alignments did not result in accuracy improvement (p>.05). The designated comparison area displayed differences in both trueness (p<.001) and precision (p<.001), leading to an overall discrepancy of 8 ± 4 µm between selecting the teeth surface or full model surface. CONCLUSIONS: The superimposition method choice within the tested software did not impact accuracy analyses, except when the alignment relies on a unique and reduced area, such as the palatal rugae, a single tooth, or three adjacent teeth on one side. CLINICAL SIGNIFICANCE: The superimposition method choice within the tested ISO-recommended 3D inspection software did not impact accuracy analyses.

Effect of Hydrothermal Aging on the Flexural Strength and Microhardness of Materials Used for Additive or Subtractive Manufacturing of Definitive Restorations.

PURPOSE: To evaluate the flexural strength (FS) and microhardness of various CAD/CAM restorative materials intended for definitive use. The effect of hydrothermal aging on the mechanical properties of these materials was also investigated. MATERIALS AND METHODS: A total of 210 bar-shaped specimens (17 × 4 × 1.5 mm ± 0.02 mm) were fabricated via either subtractive manufacturing (SM) methods-reinforced composite resin (SM-CR), polymer-infiltrated ceramic network (SM-PICN), fine-structured feldspathic ceramic (SMFC), nanographene-reinforced polymethyl methacrylate (PMMA; SM-GPMMA), PMMAbased resin (SM-PMMA)-or additive manufacturing (AM) methods with urethane acrylate-based resins (AM-UA1 and AM-UA2). Specimens were then divided into two subgroups (nonaged or hydrothermal aging; n = 15). A three-point flexural strength test was performed, and five specimens from the nonaged group were submitted to microhardness testing. Specimens were subjected to 10,000 thermal cycles, and the measurements were repeated. RESULTS: Regardless of aging, SM-CR had the highest FS (P < .001), followed by SM-GPMMA (P ≤ .042). In nonaged groups, AM-UA2 had a lower FS than all other materials except SM-FC (P = 1.000). In hydrothermal aging groups, AM specimens had lower FS values than other materials, except SM-PMMA. With regard to microhardness, there was no significant difference found between any of the tested materials (P ≥ .945) in the nonaged and hydrothermal aging groups. CONCLUSIONS: The effect of hydrothermal aging on FS varied depending on the type of restorative material. Regardless of aging condition, SM-CR showed the highest FS values, whereas SM-FC had the highest microhardness. Hydrothermal aging had no significant influence on the microhardness of the tested materials.

Dimensional Stability of Additively Manufactured Diagnostic Maxillary Casts Fabricated with Different Model Resins.

PURPOSE: To evaluate the effect of model resin type and time interval on the dimensional stability of additively manufactured diagnostic casts. MATERIALS AND METHODS: Ten irreversible hydrocolloid impressions and 10 impressions from an intraoral scanner were made from a reference maxillary stone cast, which was also digitized with a laboratory scanner. Conventional impressions were poured in type III stone (SC), while digital impressions were used to additively manufacture casts with a nanographene-reinforced model resin (GP) or a model resin (DM). All casts were digitized with the same laboratory scanner 1 day (T0), 1 week (T1), 2 weeks (T2), 3 weeks (T3), and 4 weeks (T4) after fabrication. Cast scans were superimposed over the reference cast scan to evaluate dimensional stability. Data were analyzed with Bonferroni-corrected repeated measures ANOVA (α = .05). RESULTS: The interaction between the main factors (material type and time interval) affected anterior teeth deviations, while the individual main factors affected anterior teeth and entire-cast deviations (P ≤ .008). Within anterior teeth, DM had the lowest deviations at T3, and GP mostly had lower values at T2 and lower deviations at T3 than at T0 (P ≤ .041). SC had the highest pooled anterior teeth deviations, and GP had the highest pooled entire cast deviations (P < .001). T3 had lower pooled anterior teeth deviations than at T0, T1, and T4, and higher pooled entire cast deviations than T1 were demonstrated (P ≤ .027). CONCLUSIONS: The trueness of nanographene-reinforced casts was either similar to or higher than that of other casts. Dimensional changes were acceptable during the course of 1 month.

Effect of Polymerization Unit, Polishing, and Coffee Thermocycling on the Color and Translucency of Additively Manufactured Resins Used for Definitive Prostheses.

PURPOSE: To evaluate the effect of polymerization unit, polishing, and coffee thermocycling on the color and translucency of additively manufactured polyurethane-based resins with different viscosities. In addition, their color behavior was compared with the color of the shade tab throughout the fabrication steps and aging. MATERIALS AND METHODS: Disk-shaped specimens (Ø10 × 2 mm) were fabricated from polyurethane-based resins with different viscosities (Tera Harz TC-80DP and C&B permanent; n = 30 per material). Baseline color coordinates were measured after cleaning. The specimens in each resin group were divided into three subgroups (n = 10 per subgroup) to be polymerized with different polymerization units (Otoflash G171 [FLN], Wash and Cure 2.0 [CLED1], and P Cure [CLED2]), polished, and subjected to coffee thermocycling. Color coordinates were remeasured after each process. Color differences (ΔE00) and relative translucency parameter (RTP) values were calculated. Data were statistically analyzed (α = .05). RESULTS: Time points and polymerization units affected the ΔE00 for each material (P ≤ .049). ΔE00 of each polymerization unit pair had significant differences within and among different time points within each material (P ≤ .024). ΔE00 (when compared with the shade tab) and RTP were mostly affected by polymerization units and time points within both materials (P ≤ .042). CONCLUSIONS: Tested polymerization units, polishing, and coffee thermocycling affected the color difference and translucency of tested resins. Color differences ranged from moderately unacceptable to extremely unacceptable, and the differences in translucency values mostly ranged from perceptible to unacceptable, according to previous thresholds. In addition, tested resin-polymerization unit pairs had unacceptable color differences when compared to the shade tab. CLED1 may enable higher color stability for tested resins.

Implementation of triple-scan protocol to evaluate the fit of complete-arch implant-supported fixed prostheses.

Passive fit is essential for multiple-unit implant-supported prostheses. Conventional methods to assess the passivity of complete-arch implant-supported prostheses do not allow 3-dimensional (3D) visualization and quantification of misfit. This report describes the marginal and internal fit evaluation of a complete-arch implant-supported prosthesis by using the triple-scan protocol involving a scanner and a 3D analysis freeware. This technique allows researchers, clinicians, or dental technicians to detect and quantify 3D prosthetic misfit, which may facilitate the preparation for dental appointments and objective measurement of misfit for research studies.

Tooth morphology, internal fit, occlusion and proximal contacts of dental crowns designed by deep learning-based dental software: A comparative study.

OBJECTIVES: This study compared the tooth morphology, internal fit, occlusion, and proximal contacts of dental crowns automatically generated via two deep learning (DL)-based dental software systems with those manually designed by an experienced dental technician using conventional software. METHODS: Thirty partial arch scans of prepared posterior teeth were used. The crowns were designed using two DL-based methods (AA and AD) and a technician-based method (NC). The crown design outcomes were three-dimensionally compared, focusing on tooth morphology, internal fit, occlusion, and proximal contacts, by calculating the geometric relationship. Statistical analysis utilized the independent t-test, Mann-Whitney test, one-way ANOVA, and Kruskal-Wallis test with post hoc pairwise comparisons (α = 0.05). RESULTS: The AA and AD groups, with the NC group as a reference, exhibited no significant tooth morphology discrepancies across entire external or occlusal surfaces. The AD group exhibited higher root mean square and positive average values on the axial surface (P < .05). The AD and NC groups exhibited a better internal fit than the AA group (P < .001). The cusp angles were similar across all groups (P = .065). The NC group yielded more occlusal contact points than the AD group (P = .006). Occlusal and proximal contact intensities varied among the groups (both P < .001). CONCLUSIONS: Crowns designed by using both DL-based software programs exhibited similar morphologies on the occlusal and axial surfaces; however, they differed in internal fit, occlusion, and proximal contacts. Their overall performance was clinically comparable to that of the technician-based method in terms of the internal fit and number of occlusal contact points. CLINICAL SIGNIFICANCE: DL-based dental software for crown design can streamline the digital workflow in restorative dentistry, ensuring clinically-acceptable outcomes on tooth morphology, internal fit, occlusion, and proximal contacts. It can minimize the necessity of additional design optimization by dental technician.

Effect of coffee thermocycling on the surface roughness and stainability of denture base materials with different chemical compositions manufactured with additive and subtractive technologies.

OBJECTIVE: To evaluate the effect of coffee thermocycling (CTC) on the surface roughness (Ra ) and stainability of denture base materials with different chemical compositions fabricated by using additive and subtractive manufacturing. MATERIALS AND METHODS: Disk-shaped specimens were additively (FREEPRINT denture, AM) or subtractively (G-CAM, GSM and M-PM, SM) fabricated from three pink denture base materials in different chemical compositions (n = 10). Ra was measured before and after polishing, while color coordinates were measured after polishing. Specimens were subjected to CTC (5000 cycles) and measurements were repeated. Color differences (ΔE00 ) after CTC were calculated. Ra among different time intervals within materials was evaluated by using repeated measures analysis of variance (ANOVA), while 1-way ANOVA was used to evaluate the Ra of different materials within each time interval and the ΔE00 values. Color coordinates within each material were compared by using paired samples t-tests (α = 0.05). RESULTS: Ra before polishing was the highest for all materials (p < 0.001), while SM had its lowest Ra after CTC and AM had its lowest Ra after polishing (p ≤ 0.008). Before polishing, AM had the highest Ra among the materials (p < 0.001). After polishing, SM had higher Ra than AM (p < 0.001). After CTC, GSM had the lowest Ra (p ≤ 0.048). SM had the lowest (p ≤ 0.031) and AM had the highest (p < 0.001) ΔE00 . CTC decreased the a* and b* values of SM and AM (p ≤ 0.017), and increased the L* values of AM (p < 0.001). CONCLUSIONS: Polishing significantly reduced the surface roughness of all materials. CTC did not increase the surface roughness of materials above the clinically acceptable threshold. Only AM had perceptible color change when previously reported threshold values for denture base materials were considered. CLINICAL SIGNIFICANCE: Tested denture base materials may have similar surface stability after coffee thermocycling. However, subtractively manufactured denture base materials may have improved color stability when subjected to long-term coffee consumption.

Effect of Material Thickness and Coffee Thermocycling on the Color Stability and Translucency of Additively and Subtractively Manufactured Resin-Based Materials for Definitive Restorations.

PURPOSE: To evaluate the effect of material thickness and coffee thermocycling on the optical properties of definitive resin-based materials created via additive manufacturing (AM) and subtractive manufacturing (SM). MATERIALS AND METHODS: Specimens were prepared in three thicknesses (1, 1.5, and 2 mm) from three AM (3D-CB, 3D-TH, and 3D-CT) and two SM (G-CAM and VE) resin-based materials (n = 15 per material and thickness combination). Color coordinates of each specimen were measured after polishing and after 10,000 cycles of coffee thermocycling. Color differences (ΔE00s) and relative translucency parameter (RTP) values were calculated. After logarithmic transformation, ΔE00 values were analyzed with two-way ANOVA, while RTP values were analyzed with generalized linear model test (α = .05). RESULTS: 3D-TH had the highest pooled ΔE00 and G-CAM had the lowest (P ≤ .004). 3D-CB had higher pooled ΔE00 than VE and 3D-CT (P ≤ .002). For the SM group, the 1.5-mm and 2-mm 3DCT specimens and 1-mm 3D-TH specimens had lower ΔE00 than 1.5-mm and 2-mm 3D-TH specimens (P ≤ .036). Most of the AM specimens and 1-mm VE specimens had higher ΔE00 than 2-mm G-CAM specimens (P ≤ .029). Further, most AM specimens had higher ΔE00 than 1.5-mm G-CAM specimens (P ≤ .006). RTP values increased in order of 3D-CT, G-CAM, VE, 3D-CB, and 3D-TH specimens (P < .001). Increased thickness and coffee thermocycling mostly reduced RTP (P < .001). CONCLUSIONS: 3D-TH typically had higher color change values than SM specimens, while G-CAM typically had lower color change values than AM specimens. Only the 1.5-mm and 2-mm 3D-TH specimens had unacceptable color changes. Thickness and coffee thermocycling mostly reduced the translucency.

Fabrication Trueness, Intaglio Surface Adaptation, and Marginal Integrity of Resin-Based Onlay Restorations Fabricated by Additive and Subtractive Manufacturing.

PURPOSE: To evaluate the fabrication trueness, intaglio surface adaptation, and marginal integrity of resin-based onlay restorations made via additive manufacturing (AM) or subtractive manufacturing (SM). MATERIALS AND METHODS: An onlay restoration was designed (DentalCAD Galway 3.0) and saved as an STL file to generate a design STL file (DO-STL). Using this design, 45 onlays were fabricated either with AM (3D-printed resin for definitive [AM-D; Tera Harz TC-80DP] and interim [AM-I; Freeprint temp] restorations) or SM (composite resin, Tetric CAD) technologies. Onlays were scanned with an intraoral scanner (CEREC Primescan SW 5.2), and the scans were saved as test STL files (TO-STLs). For trueness evaluation, TO-STLs were superimposed over the DO-STL, and root mean square (RMS) values of overall and intaglio surfaces were measured (Geomagic Control X). For the intaglio surface adaptation and marginal integrity, a triple-scan protocol was performed. Kolmogorov-Smirnov, one-way ANOVA, and post-hoc Tukey honestly significant difference tests were used to analyze data (α = .05). RESULTS: RMS values of intaglio and overall surfaces, intaglio adaptation, and marginal integrity varied among test groups (P < .001). AM-D had the greatest overall surface RMS (P < .001), while SM had the greatest intaglio surface RMS (P < .001). SM had the highest average distance deviations for intaglio surface adaptation and marginal integrity, whereas AM-D had the lowest (P < .001). CONCLUSIONS: AM-D onlays showed lower overall trueness than AM-I onlays and SM definitive onlays. However, AM-D onlays presented high intaglio surface trueness, intaglio surface adaptation, and marginal integrity.

Influence of intraoral scanner and finish line location on the fabrication trueness and margin quality of additively manufactured laminate veneers fabricated with a completely digital workflow.

STATEMENT OF PROBLEM: Knowledge of the fabrication trueness and margin quality of additively manufactured (AM) laminate veneers (LVs) when different intraoral scanners (IOSs) and finish line locations are used is limited. PURPOSE: The purpose of this in vitro study was to evaluate the fabrication trueness and margin quality of AM LVs with different finish line locations digitized by using different IOSs. MATERIAL AND METHODS: An LV preparation with a subgingival (sub), equigingival (equi), or supragingival (supra) finish line was performed on 3 identical maxillary right central incisor typodont teeth. Each preparation was digitized by using 2 IOSs, (CEREC Primescan [PS] and TRIOS 3 [TS]), and a reference LV for each finish line-IOS pair (n=6) was designed. A total of 90 LVs were fabricated by using these files and urethane acrylate-based definitive resin (Tera Harz TC-80DP) (n=15). Each LV was then digitized by using PS to evaluate fabrication trueness (overall, external, intaglio, and marginal surfaces). Each LV was also qualitatively evaluated under a stereomicroscope (×60), and the cervical and incisal margin quality was graded. Fabrication trueness and cervical margin quality were evaluated by using 2-way analysis of variance, while Kruskal-Wallis and Mann Whitney-U tests were used to evaluate incisal margin quality (α=.05). RESULTS: The interaction between the IOS type and the finish line location affected measured deviations at each surface (P≤.020). PS-sub and TS-supra had higher overall trueness than their counterparts. and the subgingival finish line resulted in the lowest trueness (P≤.005). PS and the subgingival finish line led to the lowest trueness of the external surface (P≤.001). TS-sub had the lowest intaglio surface trueness among the TS subgroups, and PS-sub had higher trueness than TS-sub (P<.001). PS-sub and PS-supra had higher marginal surface trueness than their TS counterparts (P<.001). TS resulted in higher cervical margin quality (P=.001). CONCLUSIONS: Regardless of the IOS tested, subgingival finish lines resulted in the lowest trueness. The effect of IOS on the measured deviations varied according to the surface evaluated and finish line location. The cervical margin quality of AM LVs was higher when TS was used.

Stainability and translucency of potassium aluminum sulfate applied computer-aided design and computer-aided manufacturing materials after coffee thermocycling.

OBJECTIVE: The purpose of this in vitro study was to evaluate the effect of potassium aluminum sulfate (alum) application on the stainability and translucency of computer-aided design and computer-aided manufacturing (CAD-CAM) materials after coffee thermocycling (CTC). MATERIALS AND METHODS: Disk-shaped specimens (Ø10 × 1 mm; N = 200) were fabricated by using additively (Crowntec [CT] and Varseo Smile Crown Plus [VS]) and subtractively manufactured (Brilliant Crios [RCR], CEREC Block [FC], and Vita Enamic [VE]) CAD-CAM materials and polished. All specimens were randomly divided into two groups as alum applied and control (n = 10). All specimens were then subjected to CTC (10,000 cycles at 5-55°C) and color coordinates were measured at each time interval. Color differences (ΔE00 ) and relative translucency parameters (RTPs) were calculated and the data were statistically analyzed (a = 0.05). RESULTS: Among tested time intervals, alum applied specimens had their lowest ΔE00 after alum application (p ≤ 0.006), except for FC (p = 0.177). In addition, alum applied RCR had lower ΔE00 values than its control specimens (p = 0.029). Alum applied specimens had their lowest RTP after CTC (p < 0.001) and alum application decreased the RTP of CT (p = 0.010). CTC reduced the RTP of all materials in control groups (p < 0.001). Alum applied CT had higher RTP than its control specimens (p = 0.049). CONCLUSIONS: Alum application's effect on color change varied depending on the material and alum mostly resulted in clinically acceptable changes in translucency. CTC led to unacceptable color and translucency changes based on previously reported threshold values. CLINICAL SIGNIFICANCE: Optical properties of CAD-CAM materials and the sustainability of these properties over time is critical for longevity. Alum may improve the color stability of reinforced composite resin when subjected to long-term coffee consumption.

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.

Surface roughness, optical properties, and microhardness of additively and subtractively manufactured CAD-CAM materials after brushing and coffee thermal cycling.

PURPOSE: To evaluate the surface roughness, optical properties, and microhardness of additively or subtractively manufactured CAD-CAM materials after simulated brushing and coffee thermal cycling. MATERIAL AND METHODS: Two additively manufactured resins (Crowntec, CT and VarseoSmile Crown Plus, VS) and 3 subtractively manufactured materials (a reinforced composite (Brilliant Crios, BC), a polymer-infiltrated ceramic network (Enamic, VE), and a feldspathic ceramic (Mark II, VM)) were used to fabricate disk-shaped specimens (Ø10×1-mm) (n = 10). Surface roughness, Vickers microhardness, and color coordinates were measured after polishing, while surface roughness was also measured before polishing. Specimens were then subjected to 25000 cycles of brushing and 10000 cycles of coffee thermal cycling, and measurements were repeated after each time interval. Color difference (ΔE00 ) and relative translucency parameter (RTP) were calculated. Robust analysis of variance test was used to evaluate surface roughness, ΔE00 , and RTP data, while generalized linear model analysis was used for microhardness data (α = 0.05). RESULTS: Material type and time interval interaction affected tested parameters (p ≤ 0.002). In addition, material type affected all parameters (p < 0.001) other than surface roughness (p = 0.051), and time interval affected surface roughness and microhardness values (p < 0.001). Tested materials mostly had their highest surface roughness before polishing (p ≤ 0.026); however, there was no clear trend regarding the roughness of materials within different time intervals along with ΔE00 and RTP values within materials or time intervals. VS and CT had the lowest microhardness regardless of the time interval, while the remaining materials were listed as VM, VE, and BC in decreasing order (p < 0.001). Coffee thermal cycling only reduced the microhardness of VM (p < 0.001). CONCLUSIONS: Tested additively manufactured resins can be considered more susceptible to simulated brushing and coffee thermal cycling than the other materials, given the fact that their surface roughness and ΔE00 values were higher than previously reported acceptability thresholds and because they had the lowest microhardness after all procedures were complete.

Effect of coffee thermal cycling on the surface properties and stainability of additively manufactured denture base resins in different layer thicknesses.

PURPOSE: To compare the effect of coffee thermal cycling on surface roughness (Ra), Vickers microhardness (MH), and stainability of denture base resins additively manufactured in different layer thicknesses with those of subtractively manufactured denture base materials. MATERIALS AND METHODS: Eighty disk-shaped specimens (Ø10×2 mm) were fabricated from two subtractively (Merz M-PM [SM-M] and G-CAM [SM-G]) and three additively (NextDent 3D+ [50 µm, AM-N-50; 100 µm, AM-N-100], FREEPRINT Denture [50 µm, AM-F-50; 100 µm, AM-F-100], and Denturetec [50 µm, AM-S-50; 100 µm, AM-S-100]) manufactured denture base materials (n = 10). Ra measurements were performed before and after polishing by using a non-contact optical profilometer, while MH values and color coordinates were measured after polishing. Specimens were then subjected to 5000 cycles of coffee thermal cycling, all measurements were repeated, and color differences (ΔE00) were calculated. A linear mixed effect model was used to analyze Ra and MH data, while one-way analysis of variance was used to analyze ΔE00 data (α = 0.05). Ra values were further evaluated according to a clinically acceptable threshold of 0.2 µm, while ΔE00 values were evaluated according to perceptibility (1.72 units) and acceptability (4.08 units) thresholds. The interaction between the material type and the time interval affected both Ra and MH (p ≤ 0.001). Tested materials had their highest Ra before polishing (p ≤ 0.029). Before polishing, AM-F-100 had the highest, and SM-M and SM-G had the lowest Ra (p < 0.001). After polishing and after coffee thermal cycling, SM-G mostly had lower Ra than those of other materials (p ≤ 0.036). SM-G mostly had higher MH than that of other materials before and after coffee thermal cycling (p ≤ 0.025). Coffee thermal cycling reduced the MH of SM-M and increased that of AM-S-100 (p ≤ 0.024). AM-N-100 had higher ΔE00 than AM-F, AM-S-100, and SM-G (p ≤ 0.009), while AM-F and SM-G had lower ΔE00 than AM-S-50 and AM-N-50 (p ≤ 0.024). CONCLUSIONS: Polishing reduced the surface roughness of all materials, whereas the effect of coffee thermal cycling was nonsignificant. Most of the tested materials had acceptable surface roughness after polishing and after coffee thermal cycling according to the reported threshold. Layer thickness only affected the microhardness of tested additively manufactured resins, which was material-dependent. Subtractively manufactured specimens mostly had high microhardness and that of nonreinforced subtractively manufactured resin decreased after coffee thermal cycling. When reported color thresholds are considered, all materials had acceptable color stability.

Effect of polymerization unit, polishing, and coffee thermocycling on the color and translucency of additively manufactured resins used for definitive prostheses.

PURPOSE: To evaluate the effect of polymerization unit, polishing, and coffee thermocycling on the color and translucency of additively manufactured polyurethane-based resins with different viscosities. In addition, their color behavior was compared with the color of the shade tab throughout the fabrication steps and aging. MATERIALS AND METHODS: Disk-shaped specimens (Ø10x2 mm) were fabricated from polyurethane-based resins with different viscosities (Tera Harz TC-80DP and C&B permanent) (N=30). Baseline color coordinates were measured after cleaning. The specimens were divided into 3 to be polymerized with different polymerization units (Otoflash G171, FLN; Wash and Cure 2.0, CLED1; CARES P Cure, CLED2) (n=10), polished, and subjected to coffee thermocycling. Color coordinates were remeasured after each process. Color differences (ΔE00) and relative translucency parameter (RTP) values were calculated. Data were statistically analyzed (α=.05). RESULTS: Time points and polymerization units affected the ΔE00 for each material (P≤.049). ΔE00 of each polymerization unit pair had significant differences within and among different time points within each material (P≤.024). ΔE00, when compared with the shade tab, and RTP were mostly affected by polymerization units and time points within both materials (P≤.042). CONCLUSION: Tested polymerization units, polishing, and coffee thermocycling affected the color difference and translucency of tested resins. Color differences ranged from moderately unacceptable to extremely unacceptable and the differences in translucency values mostly ranged from perceptible to unacceptable according to previous thresholds. In addition, tested resin-polymerization unit pairs had unacceptable color differences when compared to the shade tab. CLED1 may enable higher color stability for tested resins.

Effect of scan powder and scanning technology on measured deviations of complete-arch implant supported frameworks digitized with industrial and intraoral scanners.

OBJECTIVES: To evaluate the suitability of intraoral scanners (IOSs) to analyze the fabrication trueness of titanium complete-arch implant-supported frameworks by comparing with an industrial-grade scanner and investigate how anti-reflective scan powder affects measured deviations. METHODS: Ten titanium complete-arch implant-supported frameworks were milled from a reference standard tessellation language (STL) file. An industrial-grade blue light scanner (ATOS Core 80 (AT)) and three IOSs (Primescan (PS), TRIOS T3 (T3), and TRIOS T4 (T4)) with (PS-P, T3-P, and T4-P) or without (PS, T3, and T4) anti-reflective scan powder application were used to generate test STL (TSTL) files of the frameworks. Reference STL and TSTLs were imported into a metrology-grade analysis software (Geomagic Control X) and whole surface root mean square (RMS) values were calculated. Another software (Medit Link v 2.4.4) was used to virtually isolate marginal surfaces of all STL files and marginal RMS values were calculated by using the same metrology-grade analysis software. A linear mixed effects model was used to compare the transformed deviations of the scans performed by using each IOS (with or without powder) with the deviations of those performed by using the reference AT scanner within each surface, where a Box-Cox type transformation was used for variance stability. Bonferroni corrected post-hoc tests were used to compare conditions within each IOS (α=0.05). RESULTS: All IOSs had significantly higher whole surface and marginal RMS values than AT, regardless of the condition (P≤.002). However, scan powder application did not affect the whole surface and marginal RMS values in scans of tested IOSs (P≥.054). CONCLUSION: Measured whole surface and marginal deviations in all IOS scans performed with or without the use of scan powder were higher than those in AT scans. The application of anti-reflective scan powder did not affect the deviations in scans of tested IOSs. CLINICAL SIGNIFICANCE: Even though deviations measured in the scans of tested scanners were significantly different than those in the reference scanner, the maximum raw mean difference was 37.33 µm and the maximum raw confidence interval value of estimated differences was 47.88 µm, which can be considered clinically small taking into account the size of the frameworks tested. Therefore, tested intraoral scanners may be feasible to scan prostheses similar to or smaller than tested frameworks for fabrication trueness analysis, which may facilitate potential clinical adjustments.