Dentist's preferences on vital and nonvital tooth bleaching: findings from a Guatemalan survey

Aim: The present study aimed to investigate if the Guatemalan dentist's options on tooth bleaching could be influenced by their time in clinical practice, the level of specialization or their working place. Methods: A representative sample of dentists working in clinical practice in Guatemala was selected. Data were collected using a self-administered questionnaire with information related to gender, professional characteristics (time since graduation in years and working place) and preferences regarding vital (at-home or in-office; type and concentration of bleaching agent) and the nonvital tooth bleaching (bleaching agent used). The analysis was performed and the association between preference for bleaching technique and independent variables were investigated using Fisher's exact test. Results: 200 dentists were interviewed. More than half of dentists were male (57.0%) with time since graduation between 11 and 20 years (n= 64; 32.3%). Dentists mostly (60.5%) preferred in-office technique for vital bleaching, with 10-20% Carbamide peroxide (CP) as the preferred agent (50%). For nonvital teeth, the preferred agent (46.8%) was 37% Hydrogen Peroxide (HP). About the associations, younger dentists (< 20 years of graduation) selected mostly in-office technique, while those with more than 20 years indicated more the at-home technique. Also, the dentists working in private practice chose more frequently in-office technique. Thus, the in-office technique was more popular among Guatemalan dentists, with 10-20% CP and 37% HP selected as favorite bleaching agents for vital and nonvital techniques, respectively. Conclusion: The time of clinical practice and working place influenced some choices

Effects of alternatively used thermal treatments on the mechanical and fracture behavior of dental resin composites with varying filler content.

The purpose of this study was two-fold: (i) to investigate whether the thermal treatment of direct dental resin composites (RCs) using microwave or autoclave heating cycles would modify the materials' strength as compared to the protocol without heating (control); and (ii) to compare the mechanical performance of direct and indirect RCs. Three RCs (from 3M ESPE) were tested: one indirect (Sinfony); and two direct materials (microhybrid - Filtek Z250; and nanofilled - Filtek Z350). Specimens from the direct RCs were prepared and randomly allocated into three groups according to the thermal treatment (n = 10): Control - no thermal treatment was performed; Microwave - the wet heating was performed using a microwave oven; and Autoclave - the wet heating was performed in an autoclave oven. The indirect RC was prepared following the instructions of the manufacturer. All materials were tested using flexural strength, elastic modulus, work of fracture (Wf), microhardness, and scanning electron microscopy (SEM) analyses. Data were analyzed with ANOVA and Tukey as well as Weibull analysis (α = 0.05). The thermal treatments tended to produce slight changes in the topography of direct RCs, especially by the autoclave' wet heating. Overall, the physico-mechanical properties changed after thermal treatment, although this effect was dependent on the type of RC and on the heating protocol. Sinfony showed the lowest modulus and hardness of the study, although it was the most compliant system (higher work of fracture). The load-deflection ability was also greater for the indirect RC. Reliability of the tested materials was similar among each other (p > 0.05). In conclusion, the alternative thermal treatments suggested here may significantly influence some aspects of the mechanical behavior of dental resin composites, with negative effects relying on both the chemical composition of the restorative material as well as on the wet heating protocol used. Clinicians should be aware of the possible effects that additional wet heating of direct resin composites using microwave or autoclave thermal protocols as performed here could have on the overall fracture and mechanical responses during loading circumstances.

Cytotoxicity of contemporary resin-based dental materials in contact with dentin.

In this study, the cytotoxicity of different combinations of contemporary resin-based restoratives (adhesives, composites, luting agents) against human keratinocytes (HaCaT) was evaluated under two conditions, whether materials were applied to dentin or not. Adhesives (3-step etch-and-rinse/3ER: OptiBond FL; 2-step self-etch/2SE Clearfil SE Bond; Single Bond Universal/UNI), composites (conventional composite resin/CCR: Filtek Z350XT; flowable/FCR: Filtek Z350XT Flow; self-adhesive composite resin/SACR: Dyad Flow), and luting agents (conventional luting agent/CLA: Variolink-II; self-adhesive luting agent/SLA: RelyXU200) were combined according to their clinical use. Eluates from polymerized specimens applied to dentin were placed in contact with cells grown for 1 and 7 d. The controls were defined by cells without material contact. Cell viability was determined using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)] assay. C=C conversion was investigated using Fourier-transform infrared spectroscopy. After 1 d of incubation, when dentin was not present, 2SE yielded the highest cell viability, whereas 3ER, UNI, and SACR showed higher cell viability in the presence of dentin. After 7 d, when dentin was absent, 2SE and CLA achieved significantly higher cell viability. The presence of dentin resulted in a drastically higher cell viability for all materials, except 2SE and CLA. UNI had the lowest C=C conversion. The presence of dentin was a significant factor, which resulted in higher cell viability than what was seen for the material specimens per se. All materials resulted in a lower viability of HaCaT than what was seen under the no-material control conditions, with effects mainly limited to the first 24 h.

A new method for evaluating the retentive efficacy of different denture adhesives

Aim: The aim of this study was to evaluate a new method for measuring the retention values of different denture adhesives. Methods: The adhesive strength values of three different commercial denture adhesives (Corega powder, Corega adhesive tape and Ultra Corega cream) were evaluated using three different moisturizing agents (distilled water, artificial saliva and natural saliva). The adhesive test was performed on a universal testing machine, after applying the adhesive products to acrylic resin specimens, under two different test conditions (wetting or dipping). Tensile bond strength values in MPa were obtained for each denture adhesive presentation and test condition. Viscosity of the denture adhesives mixed with the different moisturizing agents was determined using a rotary rheometer. Maximum viscosity values were analyzed using the one-way ANOVA test. Tensile bond strength data was analyzed using Kruskal-Wallis and the Tukey's test. Pooled data of each denture adhesive presentations for all test conditions was also carried out. Correlation between viscosity and pooled tensile strength values was analyzed through linear regression analysis. A significance level of α=0.05 was set for all analyses. Results: Results showed that statistically higher adhesion strength was obtained with tape and cream adhesives when using natural saliva as moisturizing agents (p<0.05). The adhesive strength values obtained with the dipping method were similar to those obtained with the conventional wetting method. The denture retention strength was influenced by both the denture adhesive type and moisturizing agent used. Conclusion: The dipping method showed to be a reliable test capable to simulate the oral conditions and should be better explored in further studies