Properties of Nanohybrid Dental Composites-A Comparative In Vitro Study.

(1) Background: the current study investigated three nanohybrid composites: two commercial products ClearfilMajestyTM (CM) and HarmonizeTM (HU), compared with an experimental product PS2. (2) Methods: Two sample types were molded using Teflon dies. The first sample type was represented by standard discs (20 mm diameter and 2 mm thickness) (n = 60, 20/each material), used for surface conditioning investigation, specifically roughness monitoring and color stability analysis using AFM and the CIELab test, respectively. The second sample type was a standard cylindrical specimen (4 mm diameter and 6 mm height) for compression testing (n = 60, 20/each material). After complete polymerization, the samples were ground with sandpaper and further polished. The filler size and distribution in the polymer matrix were investigated with SEM. Data were statistically analyzed using the Anova Test followed by Tukey's post hoc test on the Origin Lab 2019 software produced by OriginLab Corporation, Northampton, MA, USA. (3) Results: A mono-disperse system was identified in HU samples, while CM and PS2 revealed both nano- and microfiller particles. The samples' observation after immersion in coffee and tea indicated that a lower roughness combined with optimal filler lamination within the polymer matrix assured the best color preservation. The compression strength was lower for the HU sample, while higher values were obtained for the complex filler systems within CM and PS2. (4) Conclusions: the behavior of the investigated nanohybrid composites strongly depends on the microstructural features.

Polymer Mixtures for Experimental Self-Limited Dental Burs Development-A Preliminary Approach (Part 1).

Alternative techniques have been investigated for effectiveness in caries removal because conventional metallic dental burs can lead to an excessive loss of sound tissue. The aim of the present study is to realize a preliminary approach in obtaining effective polymer mixtures for polymeric bur development, capable of removing primary dental caries using combinations of polymers to ensure the requirements for such instruments, but also a greater compatibility with the teeth structure. This study assessed the main mechanical properties, water sorption, solubility and microscopic structure of four new polymer mixture recipes to provide essential features in obtaining experimental self-limited dental burs. Two mixtures have in their composition polymer mixtures of Bis-phenol A diglycidyl ether dimethacrylate/Triethylene glycol dimethacrylate/Urethane dimethacrylates (R1, R2), and two other mixtures have Bis-phenol A diglycidyl ether dimethacrylate/Polymethyl methacrylate/Methyl methacrylates (R3, R4). The incorporation of nanoparticles into the polymer matrix has become essential due to the need of polymer biocompatibility increasing along with teeth surface remineralization, so that the powder charge was added to four recipes, such as 5% glass with BaF2 and 0.5% graphene with silver particles. All data sets were analyzed using the One-Way ANOVA test. R3, R4 showed higher compressive strength and diametrical compression values; these values increased when glass and graphene were added. Moreover, the addition of glass particles lead to an increase in flexural strength. Regarding the sorption, sample R3 had the most significant differences between day 69 and the rest of the investigation days, while the solubility varied at different intervals. From the mechanical evaluation, we could conclude that the Bis-GMA/PMMA/MMA mixtures fit the mechanical characteristics supported by polymer burs, following future studies regarding their use on the affected dentin.

Surface Characteristics, Fluoride Release and Bond Strength Evaluation of Four Orthodontic Adhesives.

Orthodontic adhesives have similar properties in terms of fluoride release, roughness, shear bond strength or cement debris for specific clinical conditions. Three commercial consecrated orthodontic adhesives (Opal Seal®, Blugloo®, Light Bond®) were compared with an experimental orthodontic material (C1). Brackets were bonded to enamel using a self-etch technique followed by adhesive application and then de-bonded 60 days later. Share bond strength evaluation, scanning electron microscopy, atomic force microscopy and fluoride release analysis were performed. The highest amount of daily and cumulative fluoride release was obtained for the experimental material, while the lowest value was observed for Opal Seal®. The materials evaluated in the current study presented adequate shear bond strength, with the experimental material having a mean value higher than Opal Seal and Blugloo. The atomic force microscopy measurements indicated that the smoothest initial sample is Opal Seal® followed by Light Bond®. Scanning electron microscopy evaluation indicated different aspects of cement debris on the enamel and/or bracket surface, according to the type of adhesive. The experimental material C1 presented adequate properties in terms of shear bond strength, fluoride release, roughness and enamel characteristics after de-bonding, compared to the commercial materials. Under these circumstances, it can be considered for clinical testing.

Comparative apical sealing evaluation of two bioceramic endodontic sealers.

AIM: The current study aims to evaluate, using scanning electronic microscopy, the sealing ability of two bioceramic endodontic sealers, one consecrated and one experimental. METHODS: Twenty monoradicular teeth were included in the study. The teeth were endodontically prepared at the working length. The shaping and cleaning involved the use of chelating gel MM EDTA 19% and continuous irrigation with sodium hypochlorite 2.5%. The radicular filling was performed using gutta-percha in association with a sealer. Ten teeth were filled with consecrated endodontic filling material and the others ten with the experimental bioceramic based sealer. RESULTS: The evaluation of the sealers using SEM analysis allowed the identification and the measurement of gaps on the radicular dentin/sealer interface and the degree of apical sealing ability. No significant statistical difference was observed between the gap dimensions in the three areas for the tested bioceramic materials (p<0.005). In the apical region a homogenous layer with extensions intersecting the hybrid layer was observed when the experimental bioceramic sealer was used. In case of teeth filled with commercial sealer, peripheral hybrid extended areas were identified. CONCLUSIONS: The two bioceramic sealers presented similar apical sealing. Gaps were identified in both sealers but also the presence of hybrid layer was identified.

In vitro evaluation of root canal preparation with two rotary instrument systems - Pro Taper and Hero Shaper.

BACKGROUND AND AIMS: The purpose of this study was to compare several parameters of root canal preparation using two different rotary Nickel-Titanium instruments: Pro-Taper (Dentsply Maillefer, Ballagigues, Switzerland) and Hero-Shaper (Micro Mega, Besancon, France). METHODS: Twelve extracted maxillary premolars were randomly divided into two groups and embedded into a muffle system. All root canals were prepared to size 25 using Pro-Taper or Hero-Shaper rotary instruments. The following parameters were evaluated: root canal form, centering capacity of the instrument, the presence of residual dentinal debris and smear layer on the root canal walls, working time and the occurrence of intraoperative accidents. Statistical analysis was performed using the chi(2) test (p=0.05). RESULTS: The majority of the root canals prepared with Hero Shaper (88.89%) and ProTaper (77.78%) showed a round or oval cross-section postoperatively. Superposition of pre- and postoperative photographs of the cross-sections showed that for the coronal third of the root canals the Hero Shaper performed in a superior manner, while for the apical third better results were obtained with the Pro Taper system. Cleanliness of the root canal walls was investigated under the SEM, in the middle third of the canal, using a five-score system for debris and smear layer. For debris Hero Shaper and Pro Taper rotary systems achieved 66.67% and 50% scores of 1 or 2, respectively. The results for the smear layer were similar: cleaner root canal walls were found after preparation with Hero Shaper (66.67% scores 1, 2), followed by Pro Taper (50%). Mean working time was shorter for Hero Shaper (124s) than for Pro Taper (184s); the difference was not significant. CONCLUSIONS: Within the limits of this study, both systems had almost the same cleaning ability and excellent centering capacity.