Analysing the effect of sodium bicarbonate and glycine air polishing on tooth surfaces with two different imaging methods.

The aim of this study was to compare two different imaging methods by assessing changes caused by sodium bicarbonate and glycine air polishing on the tooth surfaces. Fourteen single root teeth with exposed root surfaces were included into the study. The teeth were randomly divided into two groups: sodium bicarbonate and glycine group. Samples were scanned in a micro-computed tomography (micro-CT) and CAD/CAM (computer-aided design/computer-aided manufacturing) at baseline and then after air-polishing powder applications, the defect volume values were evaluated. There was a statistically significant difference between mean defect volume values that occurred after glycine and sodium bicarbonate air polishing evaluated with micro-CT and CAD/CAM (p < 0.05). After sodium bicarbonate air polishing, defect volume on enamel surface at maximum power and defect volume on the exposed root surface at medium power values calculated with CAD/CAM were higher. After glycine air polishing, defect volume values on both surfaces at medium power setting calculated with CAD/CAM were lower. Defect volume values on enamel surface at maximum power setting calculated with CAD/CAM were higher than calculated with micro-CT. We concluded that CAD/CAM cannot provide as accurate results as micro-CT. Glycine-based powder is less abrasive than sodium bicarbonate, especially on enamel surface. Lay Description: Micro-CT is a non-destructive imaging method with high resolution and allows to examine all tooth structures individually. CAD/CAM are systems that are widely used in dentistry today. Access to the device is easier than micro-CT. Intraoral scanners in CAD/CAM systems also provide non-destructive image scanning. The aim of this study was to compare two different imaging methods by assessing changes caused by sodium bicarbonate and glycine air polishing on the tooth surfaces. The results showed that because of the analyses made with CAD/CAM, similar results could not be obtained with micro-CT and cannot be used to evaluate the changes that occur after air polishing.

Fracture Resistance of Esthetic Prefabricated and Custom-Made Crowns for Primary Molars After Artificial Aging.

Purpose: The purpose of this in vitro study was to compare the fracture resistance and survival of various esthetic crowns for primary molars after artificial aging via chewing simulation. Methods: A typodont tooth (mandibular primary second molar) was prepared to receive five different types of crowns as follows (n equals 10): prefabricated fiberglass (PF); CAD/CAM zirconia (CZ); CAD/CAM resin-ceramic (CR); composite- strip (CS); and prefabricated zirconia (PZ) as control. All specimens were subjected to 750,000 cycles of thermomechanical loading to artificially simulate three years of clinical service. None of the crowns from the CS group survived artificial aging. Surviving crowns were evaluated via micro-CT considering microcrack formation, and a load-to-fracture test was applied. Data were analyzed using one-way analysis of variance followed by the Duncan test. Results: Group PZ (557.4±170.1 N) and CR (669.6±255.2) were found to have comparable results (P >0.05), which were lower than the other groups (P<0.05). Group CZ resulted in the highest mean load-to-fracture value (1126.2±180.6; P <0.05). At the end of three years of artificial aging, microcracks were observed for only CS and PF groups. Conclusions: These in vitro data suggest that all tested crowns, except CS crowns, survived three years of artificial aging; however, CAD/CAM zirconia crowns may provide longer service, as they showed the highest fracture resistance with no microcrack formation.

Comparative Evaluation of Adaptation of Esthetic Prefabricated Fiberglass and CAD/CAM Crowns for Primary Teeth: Microcomputed Tomography Analysis.

Adaptation is an important factor for the clinical success of restorations. However, no studies are available evaluating the adaptation of primary crowns. The aim of this study was to compare the adaptation of crowns fabricated by CAD/CAM technology versus prefabricated fiberglass primary crowns. Typodont maxillary central, canine, and mandibular molar teeth were prepared to serve as master dies after the size of Figaro crowns was determined (n = 10). Master dies were scanned with an intraoral scanner, and 10 identical CAD/CAM crowns were fabricated from resin-ceramic blocks. Figaro and CAD/CAM crowns were placed on the corresponding master dies and scanned via micro-CT. Three-dimensional volumetric gap measurements were performed to evaluate the overall adaptation. A total of 255 location-based linear measurements were allocated into 4 categories: marginal, cervical-axial, middle-axial, and occlusal. Statistical analyses were performed with factorial ANOVA, repeated measure ANOVA, and LSD tests (α = 0.05). CAD/CAM crowns showed significantly lower overall and location-based gap measurements than Figaro crowns regardless of tooth number (p < 0.05). For all groups, mean marginal discrepancies were lower than occlusal measurements (p < 0.05). Both crown types showed higher marginal gaps for molar teeth than for canine and central incisors with no significant difference between them (p > 0.05). CAD/CAM-fabricated crowns showed better marginal and internal adaptation than prefabricated Figaro crowns.

Evaluation of Denture Base Adaptation Fabricated Using Conventional, Subtractive, and Additive Technologies: A Volumetric Micro-Computed Tomography Analysis.

PURPOSE: An in vitro study to compare the adaptation of denture bases fabricated with 4 different techniques using volumetric 3-dimentional (3D) analysis. MATERIAL AND METHODS: Edentulous maxillary and mandibular casts were scanned, and standardized denture bases were designed using CAD design software. The same standard tessellation language (STL) data were used to produce the denture bases with 4 different fabrication methods: compression molding (CM), injection molding (IM), PMMA milling (PM), and 3D printing (3D) (n = 11/group). Milled wax denture bases were used to fabricate CM and IM groups. Denture bases placed on edentulous casts were scanned using micro-computed tomography (micro-CT). Volumetric gap between denture base and cast was calculated from 6 locations for maxilla (anterior ridge crest, posterior ridge crest, labial vestibule, buccal vestibule, palate, and posterior palatal seal) and 3 locations for mandible (intermolar, molar, and retromolar) in addition to overall gap measurements for edentulous arches. The data were analyzed with factorial analysis of variance (ANOVA), 1-way ANOVA, and post-hoc Duncan tests. Reproducibility of fabrication methods with regard to each location was assessed using Z test (α = 0.05). RESULTS: In the maxilla, the highest and lowest palatal gap measurements were recorded for CM (898.44 ± 87.73 mm3 ) and PM (357.16 ± 57.68 mm3 ) (p = 0.05). The highest gap measurements for CM and 3D were at palate and, for IM and PM were at posterior ridge crest. In mandible, the volumetric gap measurements for CM were the highest and for PM were the lowest irrespective of location (p = 0.05). PM group showed the best reproducibility and adaptation with the lowest overall mean gaps for both edentulous arches (p = 0.05). CONCLUSIONS: Denture bases milled from PMMA blocks showed better adaptation than 3D printed, or wax milled and conventionally fabricated denture bases for both maxillary and mandibular arches. PMMA milling is a reproducible technique that enables the construction of accurate dentures. Clinicians should be cautious about the palatal gap when the compression molding technique is used. Micro-CT is a valid technique for evaluating the denture base adaptation.

Marginal and internal fit of feldspathic ceramic CAD/CAM crowns fabricated via different extraoral digitization methods: a micro-computed tomography analysis.

The aim of this study was to compare the fit of feldspathic ceramic crowns fabricated via 3 different extraoral digitizing methods. Twelve maxillary first premolars were prepared and 36 single crowns were fabricated via 3 extraoral digitizing methods using a laboratory scanner (n = 12): (1) scanning the typodont (ST [control] group); (2) scanning the impression (SI group); (3) scanning the stone cast (SC group). Micro-computed tomography was used to calculate two-dimensional marginal-internal gap and the three-dimensional volumetric gap between the crowns and their corresponding dies. The measured gaps were divided into 6 location categories as follows: marginal gap (MG), finish line gap (FLG), axial wall gap (AWG), cuspal gap (CG), proximal transition gap (PTG), and central fossa gap (CFG). The correlation between each of the 3 extraoral digitizing methods and the adaptation status of the crown margins were also evaluated. The Wilcoxon signed-rank test, Spearman's rank test, and Chi-square test were used for data analysis (α = 0.05). The marginal gaps in the ST, SI, and SC groups differed significantly (24, 198 and 117.6 µm, respectively) (p < 0.05). Significant differences were found between the groups with regard to internal gap measurements, with SI representing higher gap measurements at FLG, PTG and CFG locations (p < 0.05). 3D volumetric gap measurements did not differ significantly (p > 0.05). Under-extended margins observed in the SI and SC groups were correlated with the digitizing method (Cramer's V-square: 0.14). When performing extraoral digitalization, clinicians should choose to scan the stone cast as scanning the stone cast resulted in better internal and marginal fit compared to scanning the impression.

Impact of multiple firings and resin cement type on shear bond strength between zirconia and resin cements.

PURPOSE: The aim of this study was to evaluate the effect of multiple firings on the bond strength between yttria-tetragonal zirconia polycrystals (Y-TZP) and 2 types of resin cements. MATERIALS AND METHODS: Sixty 3Y-TZP specimens (LAVA Frame Multi) were divided into 3 groups depending on the following firing procedures: (1) 2-firing cycles, (2) 5-firing cycles, (3) 10-firing cycles. Two samples from each group were investigated by using SEM to determine the morphological changes. All specimens were treated with 125 µm airborne-particle abrasion and the surface roughness of each specimen was measured. The specimens from each firing group were then further divided into 2 subgroups (n = 9) to apply 2 types of resin cement (MDP-free resin cement: RelyX Unicem-RU, and MDP containing resin cement: Panavia F 2.0-PA). The shear bond strength (SBS) test was performed and failure types of all the debonded specimens were classified by using a stereomicroscope as adhesive, cohesive, and mixed. The statistical analysis of surface roughness and SBS data were performed by using 1-way ANOVA and 2-way ANOVA followed by Tukey-HSD tests (α=.05). Failure modes were calculated as a percentage for each group. RESULTS: The bond strength of RU and PA to the specimens obtained with 2 firings were not statistically different from each other (P=.1). However, the SBS values of PA were found to be significantly higher than RU for the specimens obtained with 5 and 10 firing cycles (P=.001 and P=.02, respectively). Surface roughness analysis revealed no statistical difference between groups (P=.2). The SEM analysis of samples fired 5- and 10- times showed irregularities and boundary loss in zirconia grains, and empty spaces between zirconia grains. CONCLUSION: The bond strength of PA cement was higher than that of RU to the zirconia subjected to repeated firings (5 and 10 firing cycles). When zirconia is subjected to multiple firings, using MDP-containing resin cement can be recommended.

Effect of endodontic access simulation on the fracture strength of lithium-disilicate and resin-matrix ceramic CAD-CAM crowns.

OBJECTIVES: The purpose of this in vitro study was to compare the effect of simulated endodontic access preparation on the failure loads of lithium disilicate crowns and resin-matrix ceramic (RMC) crowns. MATERIALS AND METHODS: Eighty maxillary first premolar crowns were manufactured by using four different CAD/CAM blocks (n = 20): lithium disilicate (LD; IPS e.max CAD), resin nanoceramic (RNC; Lava Ultimate), flexible nanaoceramic (FNC; GC Cerasmart), and polymer-infiltrated ceramic (PIC; VITA Enamic). Half of each group was accessed and repaired to simulate endodontic treatment. After cyclic loading, all specimens were loaded to failure. Data were analyzed with two-way ANOVA followed by Tukey-HSD test (α = .05). RESULTS: The load to failure results showed significant differences for material types (P < .001), but not for endodontic access simulation (P = .09). The highest and lowest mean failure loads were obtained for LD (1546 N) and PIC (843 N), respectively. CONCLUSION: The endodontic access preparation was not found to affect the fracture strength of LD and RMC crowns. The LD showed higher fracture strength than RMC crowns. Even though significant differences were noted for failure loads regarding different crown materials, all could reasonably withstand masticatory forces. CLINICAL SIGNIFICANCE: The endodontic access preparation through a restoration is known to be a common challenge in clinical practice. Maintaining a repaired LD or RMC crown is feasible and replacement may not be necessary.

Effect of various polymerization protocols on the cytotoxicity of conventional and self-adhesive resin-based luting cements.

OBJECTIVES: This study evaluated the cytotoxicity of resin-based luting cements on fibroblast cells using different polymerization protocols. MATERIALS AND METHODS: Two conventional dual-polymerized (RelyX ARC, VariolinkN) and two self-adhesive resin cements (RelyX Unicem, Multilink Speed) specimens were polymerized using four different polymerization protocols: (a) photo-polymerization with direct light application, (b) photo-polymerization over ceramic and (c) resin nano-ceramic discs and (d) auto-polymerization. The specimens were then assigned to four groups to test cytotoxicity at 0, 1, 2 and 7 preincubation days (n = 5). MTT test was performed using NIH/3T3 fibroblast cells. Data were analysed using three- and one-way ANOVA. Multiple comparisons were made using Bonferroni post hoc test (p < 0.05). RESULTS: The highest cytotoxic values were recorded at day 2 for conventional resin cements and at day 0 for self-adhesive resin cements. Self-adhesive resin cements showed the most cytotoxic effect at the second day, while conventional resin cements presented immediate cytotoxicity. Auto-polymerized resin specimens and especially Multilink Speed demonstrated the most cytotoxic effect regardless of the preincubation time. Cytotoxicity of cements tested reached the lowest level at day 7. Interposition of ceramic or nano-ceramic restorative material did not significantly affect the cytotoxicity of tested luting cements (p > 0.05). CONCLUSIONS: Cytotoxicity of dual-polymerized resin cements was material-dependent and decreased gradually up to 7 days. Photo-polymerization plays an important role in reducing the cytotoxic effects. CLINICAL RELEVANCE: When luting ceramic or resin nano-ceramic restorations of which thickness does not exceed 2 mm, the level of cytotoxicity with the tested materials is not significant. Luting of restorative materials that do not allow for light transmission such as metal-fused porcelain, clinicians should be cautious in the use of dual-polymerized conventional resin cements as only auto-polymerization of resin cements takes place under such materials.

Comparative analysis of denture base adaptation performance between pour and other conventional fabrication techniques.

STATEMENT OF PROBLEM: Studies assessing the comparative denture base adaptation performance of the pour technique for various palatal vault depths are sparse. PURPOSE: The purpose of this in vitro study was to investigate the denture base adaptation performance of the pour technique compared with other conventional fabrication techniques (light-polymerization, injection, compression molding) for shallow and deep palatal vault depths. MATERIAL AND METHODS: Edentulous maxillary study models with 2 palatal vault depths were prepared. Based on the power analysis, the sample size of each conventional fabrication technique was 12 (N=96). After denture bases for each technique had been fabricated on the casts according to the manufacturers' recommendations, the casts and the intaglio surfaces of the denture bases were scanned by using a laboratory scanner (InEos X5). The standard tessellation language (STL) files of the casts and the intaglio surfaces of acrylic resin bases were transferred into a software program (Romexis, version 5.0), and the software superimposed each cast and its corresponding denture base scan with the reference pyramids semi-automatically. After superimposition, the mean gap distances (mm) were calculated by using the software and recorded from the identified 4 specific regions (denture border apex, palate, ridge crest, and posterior palatal seal). A statistical analysis was performed by using the 3-factor factorial ANOVA. Post hoc comparisons among the subgroups were performed by using the Tukey HSD test. RESULTS: Two- and 3-way interactions among palatal vault depth, polymerization technique, and location variables were statistically significant (P<.05). For shallow palatal vault depth, injection and pour polymerization techniques demonstrated similar mean gap distances irrespective of location (P>.05). The light-polymerization technique showed the highest mean gap distances among the tested polymerization techniques in all regions except for the posterior palatal seal area (P<.05). CONCLUSIONS: The pour technique showed similar denture base adaptation to compression molding and injection. Light-polymerization exhibited the highest mean gap distance between the denture base and the cast for both palatal vault depths for most of the locations. A deep palatal vault depth led to inferior denture base adaptation performance for light-polymerization in the ridge crest and compression molding in the posterior palatal seal location.