Staining- and aging-dependent changes in color and translucency of 3D-printed resin-modified ceramics.

PURPOSE: To evaluate staining- and aging-dependent changes in the color and translucency of 3D-printed resin-modified ceramics (RMC). METHODS: Specimens (n= 5 per condition and material) were fabricated from test materials: Permanent Crown Resin (PCR), Crowntec (CT), Vita Enamic (VE) and Tetric CAD (TC). Specimens were stained in wine, coffee, tea, and water (control) and exposed to artificial accelerated aging (AAA). Color measurements were obtained using a spectrophotometer at baseline (T0) and at 3.5 (T1) and 7 (T2) days after immersion. For AAA, measurements were obtained at baseline (T0) and after exposure to controlled irradiance of 150 kJ/m² (T1) and 300 kJ/m² (T2). Mean and standard deviations were calculated on CIEDE2000 color differences (ΔE00), translucency parameter (TP00) and treatment-dependent changes in the translucency parameter (ΔTP0 0). Differences between materials and test conditions were tested by one-way ANOVA (α= 0.05). Results were additionally interpreted using visual color difference thresholds in dentistry ΔE00= 0.8 for the 50:50 perceptibility threshold (PT) and ΔE00= 1.8 for the 50:50 acceptability threshold (AT). ΔTP00 values were interpreted using 5058;50 TPT00= 0.6 and 50:0% TAT00= 2.6. RESULTS: Statistically significant differences were found among the materials when exposed to the different test conditions. At the T0-T1 time interval, the highest color difference was found with wine (0.1-2.2) on all materials except CT, which showed the highest ΔE00 with AAA (2.5). The second highest color differences were obtained upon exposure to AAA (0.2-2.5) and tea (0.5-1.1). The TP00 at baseline ranged from 5.1 to 9.8. Significant differences in ΔTP00 were found among the tested materials and staining/aging conditions, but no significant differences were found among the staining/aging intervals (T0-T1, T0-T2 and T1-T2). CLINICAL SIGNIFICANCE: Staining- and artificial aging-dependent changes of 3D-printed and milled resin modified ceramics used for definitive restorations could represent a challenge in terms of restoration acceptability or dissatisfaction. Staining and aging conditions produced significant color changes, while translucency changes were not significant.

Wear Resistance of 3D Printed and Prefabricated Denture Teeth Opposing Zirconia.

PURPOSE: To evaluate the wear resistance of a recently developed three-dimensional (3D) printed denture teeth resin compared to three commercially available prefabricated denture teeth. MATERIALS AND METHODS: A total of 88 maxillary first molar denture teeth were evaluated: C (Classic; Dentsply Sirona, York, PA), DCL (SR Postaris DCL; Ivoclar Vivadent, Schaan, Liechtenstein), IPN (Portrait IPN; Dentsply Sirona, York, PA), and F (Denture Teeth A2 Resin 1 L; Formlabs, Somerville, MA). The 3D printed denture tooth specimens were fabricated from a methacrylate-based photopolymerizing resin using stereolithography (SLA). Denture teeth were subjected to a three-body wear test with a poly(methylmethacrylate) (PMMA) abrasive slurry. A Leinfelder-style four station wear apparatus with custom bullet-shaped milled zirconia styli was utilized with a load force of 36-40 N at 1.7 Hz for 200,000 cycles. Maximum depth of wear was measured using a lab grade scanner and analyzing software program. Data were analyzed using a one-way ANOVA followed by the Tukey's Multiple Comparisons post hoc test (α = 0.05). RESULTS: A statistically significant difference in depth of wear was found between denture tooth materials (p < 0.001). The mean vertical depth of wear for the 3D printed denture teeth (0.016 ± 0.010 mm) was statistically significantly less than the prefabricated denture teeth. The highly cross-linked denture teeth, DCL (0.036 ± 0.011 mm) and IPN (0.035 ± 0.014 mm), exhibited statistically significantly less wear than the conventional acrylic denture teeth. The conventional acrylic denture teeth demonstrated the greatest wear (0.058 ± 0.014 mm). No significant difference in depth of wear was found between DCL and IPN (p > 0.001). CONCLUSIONS: Denture tooth material significantly influences the depth of wear. The 3D printed denture teeth demonstrated superior wear resistance compared to the commercially available prefabricated denture teeth when opposed to zirconia. Denture teeth fabricated with SLA technology may have a promising future in prosthetic dentistry.

Referral patterns of pediatric dentists and general practitioners to orthodontists based on case complexity.

OBJECTIVE: The objectives of this research were to investigate and compare general and pediatric dentists' subjective judgments of orthodontic case complexity and to determine how their perceptions of case complexity influence their decisions to refer the patient to an orthodontist. METHODS: Twenty pediatric dentists and 21 general dentists participated in the study. Pretreatment orthodontic records of 20 patients with a variety of malocclusions and a range of American Board of Orthodontics Discrepancy Index (DI) scores were used. Respondents were asked about their background and training in orthodontics. They were also asked to identify the subjective complexity of each case with the use of a 100-point visual analog scale (VAS) and whether they would refer the patient to an orthodontic specialist. A mixed-model multivariate data analysis was used to evaluate the subjective case complexity with the use of fixed factors such as DI score, type of panel member, experience, annual continuing education rate, and gender. Generalized linear mixed models were used to investigate the referral patterns of the general dentists and pediatric dentists. Level of significance was set at P < 0.05 for all statistical analyses. RESULTS: General dentists appeared to provide more overall orthodontic treatment than pediatric dentists; many general dentists provide limited orthodontic treatment and clear aligner therapy (P < 0.05). The perceived complexity score for cases was not significantly different between the 2 groups (P = 0.82). The association between DI score and perceived complexity was similar in both groups (P = 0.183) and there was a high correlation between DI and VAS score in the sample (r = 0.71; 95% Cl 0.38-0.87). Pediatric dentists had higher referral rates for cases with DI scores both below and above 20. Significant differences were noted between the pediatric and general dentists in the individual case referral decision as evaluated by the DI (P < 0.037) and VAS (P < 0.042) scores. CONCLUSIONS: General dentists provided more orthodontic care than the pediatric dentists. Both groups identified case complexity similarly, with only minor differences, but pediatric dentists had higher referral rates to orthodontic specialists regardless of the initial case complexity.

Gloss and Surface Roughness of Anterior Pediatric Zirconia Crowns.

PURPOSE: The purpose of this study was to determine gloss and surface roughness (Ra) of pediatric anterior zirconia crowns. METHODS: Gloss of labial and lingual surfaces of pediatric anterior zirconia crowns from three manufacturers was measured on 20 specimens using a small area gloss meter on each. Ra (µm) was measured using a contact-type surface profilometer. Data were evaluated by analysis of variance and pair-wise comparison at the 0.05 level of significance. RESULTS: There were statistically significant interactions between surface location and crown type for both gloss and Ra scores. NuSmile had higher mean gloss scores and lower mean Ra scores than both Kinder Krowns and EZCrowns. Kinder Krowns showed lower mean gloss scores and higher Ra scores than other crown groups. CONCLUSION: Among all crowns, there was a trend of higher mean gloss paired with lower mean surface roughness, and lower mean gloss paired with higher mean Ra. Hand smoothed followed by mechanically polished zirconia crowns (NuSmile) displayed the highest mean gloss and lowest mean Ra compared to hybrid polishedglazed zirconia crowns (Kinder Krowns, EZCrowns). Of the hybrid polished-glazed zirconia crowns, Kinder Krowns displayed the lowest mean gloss and highest mean Ra.

Impact of Technique-Specific Operative Videos on First-Year Dental Students' Performance of Restorative Procedures.

The aim of this study was to examine the impact of psychomotor operative video demonstrations on first-year dental students who are performing specific procedures for the first time in a preclinical setting. The class was randomly divided into two groups, and three restorative procedures were selected. On the date on which each procedure was to be performed in the preclinical laboratory for the first time, one group (experimental, n=50) was shown a technique video for that specific procedure immediately before commencing the exercise; the control cohort (n=50) did not view the video. Technical performance on procedures was evaluated by students and two calibrated and blinded examiners. The students' perceptions of the experience were also collected in a survey. All first-year students participated in the study, for a 100% response rate. A Mann-Whitney U test did not show any group differences in technical performance (mean values on preparation: 77.1 vs. 77.8; amalgam: 82.7 vs. 82.8; composite: 79.7 vs. 78.0). A Spearman rho test revealed a significantly higher correlation in 13 out of 25 evaluation categories between student self-assessment and blinded examiner assessment for the experimental group. A chi-square test of questionnaire responses revealed a positive student perception of administering these videos for the preparation (X(2)=4.8, p<0.03), the amalgam restoration (X(2)=12.4, p<0.001), and the composite restoration (X(2)=11.3, p<0.001). The psychomotor video demonstrations did not immediately improve student performance on preclinical operative procedures, but they were well received by students and augmented self-assessment ability. These findings suggest that videos can be a useful teaching aid in a preclinical environment, especially regarding comprehension of concepts.

Utilization of iTero digital impression unit for resin composite inlay.

Historically, traditional elastomeric impression techniques for indirect fixed procedures have presented challenges for the operator, laboratory, and patient. Recent digital impression unit technology offers a compelling alternative to elastomeric impressions. The iTero system applies parallel confocal imaging to create a virtual impression that can be easily captured, edited, and uploaded electronically to the dental laboratory. Computer-aided design/computer-aided manufacturing technology is applied to the virtual impression to create an unlimited number of identical polyurethane models. This case report is presented from the perspectives of the clinicians and the laboratory technician using an iTero system to treat a left mandibular second premolar with a resin composite inlay.

Latex and non-latex orthodontic elastic force loss due to cyclic temperature.

UNLABELLED: The purpose of this study was to compare the force loss of 1/4 inch (6.35mm) 3.5oz (99g) medium latex elastics from Ormco Corp. to non-latex elastics from ClassOne Orthodontics and Phoenix after being cycled between different temperatures. Elastics were stretched to 1.57 inches (40mm) on jigs and cycled in water baths for 4 minutes at 5 degrees C and 37 degrees C, 21 degrees C and 37 degrees C, 5 degrees C and 50 degrees C, 37 degrees C and 50 degrees C, and a control group was held at 3 degrees 7 degrees C. The force produced by new elastics and elastics after incubation was measured using a Mini 44 Instron. RESULTS: All elastics experienced increased force loss that correlated with increased temperatures with the exception of Ormco latex elastics. The latex elastics had the greatest force loss upon cycling between 5 degrees C and 50 degrees C while the non-latex elastics had the greatest force loss while cycling between 37 degrees C and 50 degrees C. All elastics were strongest when cycled between 5 degrees C and 37 degrees C. CONCLUSION: This study suggests that hot liquids reduce the force of latex and non-latex elastics even when cycled between hot temperatures for brief periods of time.

Bond strength comparison of color change adhesives for orthodontic bonding.

This study investigated whether three different color change light-cured orthodontic bonding adhesives have comparable shear bond strengths to a conventional light-cured orthodontic bonding adhesive. The sample of 240 bovine incisors was divided into four groups of 60 each. Each group tested one of four orthodontic bonding adhesives: 3M Unitek Transbond PLUS, Ormco Gréngloo, Ormco Blúgloo, and 3M Unitek Transbond XT (control). The four groups were further divided into two subgroups of 30 with shear bond strength tested at two different times (15 minutes and 24 hours) post-bond. The shear bond strength was measured on a universal testing machine. The data were analyzed by two-way analysis of variance and post-hoc comparisons (Fisher's PLSD) at the 0.05 level of significance. The average shear bond strength was greater at 24 hours than at 15 minutes for Transbond PLUS, Blúgloo, and Transbond XT. For Gréngloo, the average shear bond strength was greater at 15 minutes than at 24 hours. Gréngloo tested at 15 minutes had the highest average shear bond strength. Gréngloo tested at 24 hours had the lowest average shear bond strength. All four orthodontic bonding adhesives demonstrated bond strengths considered to be clinically acceptable for orthodontic purposes.

Bond strength comparison of color-change adhesives for orthodontic bonding using a self-etching primer.

BACKGROUND: The purpose of this study was to compare the shear bond strengths of two color-change adhesives with a commonly used conventional light-cure adhesive while using a self-etching primer, and to compare any changes in shear bond strengths over time. METHODS: One hundred and eighty extracted bovine incisors were randomly divided into nine groups of 20 teeth each. The teeth were prepared with a self-etching primer (Transbond™ Plus) Metal lower incisor brackets were bonded directly to each tooth with two different color-change adhesives (TransbondPlus and Grengloo™) and a control (Transbond XT). The teeth were debonded at three different time points (15 minutes, 24 hours, 1 week) using an Instron at 1.0 mm/min. The teeth that were to be debonded at 24 hours and 1 week were stored in distilled water at 37°C to simulate the oral environment. The data were analyzed by two-way analysis of variance and with Fisher's protected least-significant difference multiple comparisons test at the P < 0.05 level of significance. Adhesive remnant index (ARI) scores were calculated for each debonded tooth. RESULTS: Transbond Plus at 1 week had the highest mean shear bond strength (14.7 mPa). Grengloo tested at 24 hours had the lowest mean shear bond strength (11.3 mPa). The mean shear bond strengths for the remaining seven groups had a range of 12-14.5 mPa. Grengloo had >80% samples presenting with an ARI score of 1 at all times. Interestingly, both Transbond groups had ARI scores of 3 in more than 50% of their samples. CONCLUSION: Time had no significant effect on the mean shear bond strength of Transbond XT, Grengloo, or Transbond Plus adhesive.

Retention of gold alloy crowns cemented with traditional and resin cements.

The aim of this study was to measure in vitro retention of cast gold crowns cemented with traditional and resin cements. Forty-eight human molars were prepared on a lathe to produce complete crown preparations with a consistent taper and split into six groups, eight crowns in each group. Crowns were cast in a high-gold alloy and then cemented. After 24 hours, the retention force (N) was recorded and mean values were analyzed by one-way analysis of variance and the Fisher post-hoc least significant difference (PLSD) multiple comparisons test (a = .05). Failure sites were examined under 3100 magnification and recorded. Mean values (SD) for each group in increasing order of retention force were: Harvard Cement: 43 N (27), TempoCem: 59 N (16), PermaCem Dual: 130 N (42), RelyX Luting Cement: 279 N (26), Contax and PermaCem Dual: 286 N (38), and TempoCem with Contax and PermaCem Dual: 340 N (14). The Fisher PLSD interval (P = .05) for comparing cements was 29 N. Zinc-phosphate cement and provisional resin cements had the lowest retention forces. Resin cement with a bonding agent and the hybrid-ionomer cement had similar retention forces. Resin cement with a bonding agent applied after use of a provisional resin cement had a significantly higher retention force than the other cements tested.

A comparison of shear bond strengths among different self-etching primers.

By the 1980's, bonding of orthodontic brackets had become the routine technique for attaching fixed appliances to teeth, replacing the need to fit and cement bands on each tooth (1). This modification in appliance attachment revolutionized orthodontics. Before, each tooth required a band. This meant a band must be fitted, have a bracket welded to it, and be cemented onto each tooth. Not only was this process time consuming and frustrating, but it meant 4 to 6 millimeters of space per arch was needed to seat the bands. Many cases that perhaps could have been treated without tooth extraction ended up needing extractions to accommodate the band space.