Effect of Preventive Dental Products on Bonding Force: An in vitro Study.

Aim: Testing the effect of Fluoride, chlorhexidine, and molecular iodine applications on the mean micro-shear bond strength (SBS) of enamel in an attempt to preserve enamel integrity during the bonding process. Materials and Methods: The study was an observational case-control one in which 150 human teeth were classified into 10 groups according to the product kind and the prescribed treatment. Each group consisted of 15 teeth. Group C was the control group. Groups FP, FV, and OS utilized products that could be utilized in a professional dental setting. Group FP was treated with 1.23% NaF prophy paste, Group FV was treated with 5% NaF varnish, and Group OS was treated with Opal® Seal Fluoride releasing primer and sealant. Groups L, LF, CHX, and I were treated with mouth rinses. Group L was treated with Listerine Zero Fluoride-Free Mouthwash, Group LF with Listerine Zero 0.02% NaF Mouth Rinse, Group CHX with 0.12% chlorhexidine gluconate, and Group I with ioRinse RTU 100 ppm molecular iodine rinse. Groups TP and G utilized alternative remineralization products. Group TP was treated with Fluoro Calcium Phosphosilicate bioglass containing toothpaste, and Group G was treated with Curodont Protect remineralizing tooth gel. One-way ANOVA test was utilized to perform all statistical analysis in this study. Results: For mean micro-SBS, no significant difference (P > 0.05) between any of the experimental groups was observed when compared to the control group. There was a significant difference (P < 0.05) between Opal Seal versus Listerine Total, Opal Seal versus Peridex, Listerine versus Listerine Total, and Listerine versus Peridex. All other experimental group comparisons revealed a nonsignificant difference (P > 0.05). Conclusions: As the null hypothesis (H0) assumes that changes observed in an experiment are due to chance, hence, the outcomes of this study are coherent with (H0) since the aforementioned application methods did not significantly impact the SBS of orthodontic resin cement to enamel.

Clinical wear of different types of denture teeth after one year in service: A clinical study.

STATEMENT OF PROBLEM: Worn denture teeth are a common reason for replacing complete dentures. However, clinical studies on the amount of denture tooth wear are lacking. PURPOSE: The purpose of this clinical study was to compare the clinical wear of denture teeth made from double cross-linked (DCL) versus highly cross-linked (HCL) materials after 1 year in service. MATERIAL AND METHODS: Fourteen participants received maxillary and mandibular removable complete dentures (RCDs). The participants randomly received either DCL or HCL teeth. Each RCD was scanned with an intraoral scanner 1 week after finishing any occlusal adjustment and after 1 year. Occlusal contact marks were recorded using articulating paper, and photographs were made in centric and eccentric movements. The generated 1-week and 1-year standard tessellation language (STL) files of the scans were obtained and trimmed using the Geomagic X software program. After merging the files, the depth of the wear facets was measured using the software program tool that measures the vertical gap distance in micrometers at 100 points distributed on the contact areas. These areas were identified by using the segment tools in the software program. Repeated measures ANOVA was used to analyze the differences between the collected data (α=.05). RESULTS: The DCL had higher mean ±standard deviation wear (62.7 ±40 µm) than the HCL (37 ±31 µm) after 1 year in service (P<.001). CONCLUSIONS: Both DCL and HCL denture teeth showed acceptable clinical wear after 1 year of clinical use. HCL denture teeth showed more resistance to occlusal wear than DCL denture teeth.

Novel methodology for measuring intraoral wear in enamel and dental restorative materials.

OBJECTIVES: To test the hypotheses that (a) the chairside/handheld dental scanner combined with a metrology software will measure clinical wear in vivo in agreement with measurements from X-ray computed microtomography and; (b) polished monolithic zirconia does not cause accelerated wear of opposing enamel. MATERIALS AND METHODS: Thirty single crowns were randomized to receive a monolithic zirconia or metal-ceramic crown. Two non-restored opposing teeth in the same quadrants were identified to serve as enamel controls. After cementation, quadrants were scanned using an intraoral dental scanner. Patients were recalled at 6-months and 1-year for re-scanning. Scanned images were compared using a metrology software to determine maximum vertical wear of teeth. The accuracy of the scanning measurements from this new method was compared with X-ray computed microtomography (micro-CT) measurements. Statistical analysis was performed using Mann-Whitney U test to determine significant differences between wear of enamel against zirconia, metal-ceramic or enamel. Linear regression analysis determined agreement between measurements obtained using intraoral scanning and micro-CT. RESULTS: Regression analysis demonstrated that there is a quantitative agreement between depth and volume measurements produced using intraoral scanning and the micro-CT methodologies. There was no significant difference between the wear of enamel against polished monolithic zirconia crowns and enamel against enamel. CONCLUSIONS: Intraoral scanning combined with a matching software can accurately quantify clinical wear to verify that monolithic zirconia exhibited comparable wear of enamel compared with metal-ceramic crowns and control enamel. Agreement between the intraoral scanner and the micro-CT was 99.8%. Clinical Trials.gov NCT02289781.

In vitro wear of dual-cured bulkfill composites and flowable bulkfill composites.

OBJECTIVES: The objective of this study is to test the wear of dual-cured bulkfill and flowable bulkfill composites. MATERIALS AND METHODS: Six dual-cured bulkfill composites, Cention, Cention-Exp, Activa, Fill-up, Hyperfil Injectafill, and two flowable bulkfill composites Tetric Evoflow BulkFill and G-aenial Universal Flo were tested in this study (n = 8). Each composite was applied into an aluminum sample holder and cured with a Valo Grand (1230 mW/cm2 ) or self-cured according to manufacturer's recommendations, and stored in water for 3 weeks. The samples were subjected to 120 000 load cycles of 49 N (CS-4) against spherical steatite antagonists and simultaneously subjected to 4440 thermocycles (5°C-55°C). At intervals between load cycles, polyvinyl siloxane impressions were taken and scanned with a True Definition Laser Scanner. The volumetric wear was calculated using image software (Geomagic). Microscopic images of selected wear facets and their corresponding worn antagonists were obtained using SEM. All data were analyzed using analysis of variance (ANOVA) and Tukey post hoc test for multiple comparison (α = .05; ß = .2). RESULTS: The load cycles volumetric wear-increase was linear. Two-way ANOVA showed significant main effects (material and light-cured) and significant interactions. Self-cured materials (mean = 0.38 mm3 ) showed more wear than light-cured materials (mean = 0.35mm3 ). CONCLUSIONS: The bioactive materials except Activa light-cured showed significantly more wear than the flowable composites. CLINICAL SIGNIFICANCE: This study demonstrated that most of the dual-cured composites, if light-cured, showed the same wear as the flowable composites used as control. Therefore, to obtain adequate wear resistance the dual-cured composites should be routinely light-cured.

Quantitative fractography as a novel approach to measure fracture toughness of direct resin composites.

Dental resin composites generally fail from small cracks. Large crack techniques are not representative of in vivo failures. Quantitative fractography relies on the observation of small "natural flaws". This study investigates the effect of flaws that occur from fabrication and handling on the measurement of fracture toughness for four different direct resin composites. Microtensile dog-bone shaped specimens for each of four composites were fractured to measure the strength. In addition, we measured crack sizes of the fracture initiating cracks and determined the fracture toughness from these measurements using quantitative fractographic analysis on selected specimens. The characteristic strengths (28-51 MPa) and Weibull moduli (4.9-7.8) were also determined and related to the toughness values (0.5-0.9 MPa m1/2) obtained. The elastic moduli (5-10 GPa) were measured using an indentation technique that has not been used before for direct resin composites. The indentation technique offers an alternative method for small specimens. Quantitative fractographic analysis offers a useful technique to assess fracture toughness of resin composites from cracks of the same size as observed in practice. The toughness of the direct resin composites results from a balance between the size, number and shape of filler particles and the viscosity of the resin matrix.

Effect of Thickness of Ceramic Veneers on Color Stability and Bond Strength of Resin Luting Cements Containing Alternative Photoinitiators.

PURPOSE: To evaluate the light transmittance of ceramic veneers of different thicknesses and verify their influence on the degree of conversion, color stability, and dentin bond strength of light-curing resin cements containing different photoinitiator systems. MATERIALS AND METHODS: Experimental resin cements were fabricated containing camphorquinone and amine (CQ-amine), TPO, Ivocerin (IVO), or TPO and Ivocerin (TPO-IVO). All photoinitiators were characterized by UV-Vis spectrophotometry. Disk-shaped lithium disilicate ceramic specimens that were 0.4, 0.7, and 1.5 mm in thickness were prepared using IPS e.max Press (Ivoclar Vivadent, shade LT/A2). Light transmittance through each specimen was measured using spectrophotometry. Specimens of each cement (n = 10) were made in a custom-designed mold and were light cured through each glass-ceramic disk using a multiwave LED (Bluephase G2, Ivoclar Vivadent). CS was evaluated using spectrophotometry before and after artificial aging with UV light. DC was evaluated using FTIR-spectroscopy. Dentin µSBS was evaluated using 0.75-mm-thick specimens that were light cured under the same protocol (n = 10). All data were submitted to two-way ANOVA and Tukey's test (α = 0.05; ß = 0.2). RESULTS: CQ-amine cements showed the highest color changes (p < 0.05) due to increased yellowing when compared to the amine-free cements (p < 0.05). However, all cements showed a significant color change after aging when cured through ceramics up to 1.5 mm thick (p < 0.05). The TPO-IVO cement showed the highest DC and the IVO cement showed a similar DC when compared to the CQ-amine cement. The TPO cement presented the lowest DC (p = 0.0377). No differences in mean dentin µSBS were found among the cements, except for the TPO cement, which presented a lower mean dentin µSBS (p = 0.0277). CONCLUSION: Amine-free cements containing Ivocerin and TPO seem to be a better alternative to CQ-amine cements, while not reducing either DC or dentin µSBS of amine-free cements. However, CQ-amine and amine-free cements still seem to change color over time.

Comprehensive analysis of laserscanner validity used for measurement of wear.

OBJECTIVES: The aims of this study were to test the hypotheses that (a) a laserscanner used for measuring maximum depth and volume loss will yield the same results as a surface profilometer; (b) the surface roughness will affect the maximum depth and volume loss measured with the laserscanner; (c) analytical results using the laserscanner from multiple operators have no more than 10% inter-rater difference and; (d) replicating samples using either stone or impression material is an accurate method for measuring wear using the laserscanner. MATERIALS AND METHODS: The volume and maximum depth of indentations from fine, medium and rough burs on glass-ceramic disks were measured using two devices, a surface profilometer (Dektak II, Veeco) and a 3D Laserscanner (LAS-20, SD Mechatronik). Replicates of the indentations made from polyvinysiloxane impression material and gypsum were also measured. RESULTS: Comparison of profilometer and laserscanner readings using ceramic disks demonstrated a mean error of 13.61% for depth and 25.32% for volume. Replication errors were minimal (2.6% for impression, 2.5% for stone). Surface profilometer data for volume measurements revealed a difference of 6.1% for impression and 6.5% for stone compared with ceramics. However, when measurements for replicates were compared between laserscanner and surface profilometer, depth had a mean error of 74% for impression and 51% for stone. Volume differences of 78% for impression and 44% for stone were recorded. CONCLUSION: This work demonstrated that the laserscanner was a convenient device for measuring wear but there is a need to validate the accuracy of the measurements.

Acrylic Reinforcement with Off the Shelf Perforated Metal Plates.

To evaluate the effect of Dentaurum Grid Strengthener on flexural strength and modulus of two types of PMMA, 24 beams (75 mm x 10 mm x 2.5 mm) containing bonded and flattened Grid Strengthener and 24 beams without Grid Strengthener were subjected to a 3-point bending test at 5 mm/min. Flexural strength and modulus were calculated. Data were analyzed with a 2-way ANOVA. The highest mean strength and flexural modulus was measured for reinforced high impact resin (96.2±14.3 MPa and 3425±779 MPa, respectively). For flexural strength and modulus, resin and reinforcement had a significant effect. CLINICAL RELEVANCE: Independent of the resin used, the incorporation of a grid strengthener increases the strength and modulus, thus the fracture probability of dentures is reduced.