Análisis In vitro de yesos dentales de alta resistencia y baja expansión disponibles en Perú / In vitro analysis of high resistance and low expansion dental plasters available in Peru

Objetivo. Comparar la dureza, estabilidad dimensional y resistencia a la compresión de los yesos dentales de alta resistencia y baja expansión disponibles en el Perú. Métodos. Se realizó un estudio descriptivo, observacional y transversal. Se confeccionaron muestras de forma cilíndrica (8) y rectangular (8), de siete yesos dentales de alta resistencia y baja expansión. Se evaluó la dureza utilizando el Durómetro Universal Identec, la estabilidad dimensional con un calibrador digital y la resistencia a compresión con la Máquina de Ensayo Universal. Para determinar si hay diferencia en cada una de estas propiedades se empleó el análisis de varianza, la prueba F y la prueba de Duncan. Además, se empleó la prueba de comparación de medias, t de Student, para evaluar si difieren con los valores de la ADA (Asociación Dental Americana). Resultados. La dureza, estabilidad dimen-sional y resistencia a la compresión promedio de los yesos dentales presentó diferencias significativas (p<0.05) entre cada uno con los promedios estándares establecidos por la ADA. Conclusiones. En relación resistencia a la compresión el 100% de los yesos analizados cumplen con los parámetros establecidos por la ADA, en relación estabilidad dimensional solo el 28.6% y el 100% no alcanzan los estándares de dureza promedio establecidos por la ADA.

Objective. To compare the hardness, dimensional stability, and compressive strength of high-strength, low-expansion dental plasters available in Peru, according to ADA criteria. Methods. A descriptive, observational and cross-sectional study was developed. A selection of 8 cylindrical-shaped samples and 8 rectangular- shaped ones, from seven high-resistance, low-expansion dental plasters were fabricated. The hardness was evaluated using the Identec Universal Durometer. Dimensional stability was evaluated with a digital caliper and compressive strength was evaluated with the Instron Universal Testing Machine. To determine if there is a difference in each of these properties, the analysis of variance, F test, and the Duncan's test were used. In addition, to assess whether these values differ from those of the ADA, the mean comparison test, student's t table, were used. Results. The hardness, dimensional stability and average compressive strength of the high-strength, low-expansion dental plasters showed that there are significant di-fferences (p<0.05) between each of the dental plasters and with the standard averages established by the American Dental Association. (ADA). Conclusions. 100% of the high-strength, low-expansion dental casts meet the parameters established by the ADA in terms of their compressive strength, only 28.6% of these comply with the ADA in terms of dimensional stability and that 100% of these do not meet the average hardness standards established by the ADA.

The Effect of Different Additives on the Hydration and Gelation Properties of Composite Dental Gypsum.

Dental mold gypsum materials require fine powder, appropriate liquidity, fast curing, and easy-to-perform clinical operations. They require low linear expansion coefficient and high strength, reflecting the master model and facilitating demolding. In this article, the suitable accelerators and reinforcing agents were selected as additives to modify dental gypsum. The main experimental methods used were to compare the trends of linear expansion coefficients of several commercially available dental gypsum products over 72 h and to observe the cross-sectional microstructure of cured bodies before and after dental gypsum modification using scanning electron microscopy. By adjusting the application of additives, the linear expansion coefficient of dental gypsum decreased from 0.26% to 0.06%, while the flexural strength increased from 6.7 MPa to 7.4 MPa at 2 h. Formulated samples showed good stability and gelation properties with linear expansion completed within 12 h. It is indicated that the performance of dental gypsum materials can be improved by adding additives and nanomaterials, which provided a good reference for clinical preparation of high-precision dental prosthesis.

Evaluation of the mechanical properties and biocompatibility of gypsum-containing calcium silicate cements.

Mineral trioxide aggregate (MTA) cement is widely used in the field of endodontic treatment. We herein synthesized calcium silicates from calcium carbonate and silicon dioxide, with the aim of reducing the cost associated with the MTA. Additionally, we prepared gypsum-containing calcium silicate cement to reduce the setting time while enhancing the mechanical strength. We evaluated the physical properties of this cement and investigated the response of human dental pulp stem cells (hDPSCs) grown in culture media containing cement eluate. Our results revealed that calcium silicates could be easily synthesized in lab-scale. Furthermore, we demonstrate that gypsum addition helps shorten the setting time while increasing the compressive strength of dental cements. The synthesized gypsum-containing calcium silicate cement showed minimal cytotoxicity and did not inhibit the proliferation of hDPSCs. These results suggested that the newly developed calcium silicate material could be a promising pulp capping material.

Accuracy and reproducibility of 3D digital tooth preparations made by gypsum materials of various colors.

PURPOSE: The study aimed to identify the accuracy and reproducibility of preparations made by gypsum materials of various colors using quantitative and semi-quantitative three-dimensional (3D) approach. MATERIALS AND METHODS: A titanium maxillary first molar preparation was created as reference dataset (REF). Silicone impressions were duplicated from REF and randomized into 6 groups (n=8). Gypsum preparations were formed and grouped according to the color of gypsum materials, and light-scanned to obtain prepared datasets (PRE). Then, in terms of accuracy, PRE were superimposed on REF using the best-fit-algorithm and PRE underwent intragroup pairwise best-fit alignment for assessing reproducibility. Root mean square deviation (RMSD) and degrees of similarity (DS) were computed and analyzed with SPSS 20.0 statistical software (α=.05). RESULTS: In terms of accuracy, PREs in 3D directions were increased in the 6 color groups (from 19.38 to 20.88 µm), of which the marginal and internal variations ranged 51.36 - 58.26 µm and 18.33 - 20.04 µm, respectively. On the other hand, RMSD value and DS-scores did not show significant differences among groups. Regarding reproducibility, both RMSD and DS-scores showed statistically significant differences among groups, while RMSD values of the 6 color groups were less than 5 µm, of which blue color group was the smallest (3.27 ± 0.24 µm) and white color group was the largest (4.24 ± 0.36 µm). These results were consistent with the DS data. CONCLUSION: The 3D volume of the PREs was predisposed towards an increase during digitalization, which was unaffected by gypsum color. Furthermore, the reproducibility of digitalizing scanning differed negligibly among different gypsum colors, especially in comparison to clinically observed discrepancies.

Accuracy and reproducibility of 3D digital tooth preparations made by gypsum materials of various colors

PURPOSE: The study aimed to identify the accuracy and reproducibility of preparations made by gypsum materials of various colors using quantitative and semi-quantitative three-dimensional (3D) approach. MATERIALS AND METHODS: A titanium maxillary first molar preparation was created as reference dataset (REF). Silicone impressions were duplicated from REF and randomized into 6 groups (n=8). Gypsum preparations were formed and grouped according to the color of gypsum materials, and light-scanned to obtain prepared datasets (PRE). Then, in terms of accuracy, PRE were superimposed on REF using the best-fit-algorithm and PRE underwent intragroup pairwise best-fit alignment for assessing reproducibility. Root mean square deviation (RMSD) and degrees of similarity (DS) were computed and analyzed with SPSS 20.0 statistical software (α=.05). RESULTS: In terms of accuracy, PREs in 3D directions were increased in the 6 color groups (from 19.38 to 20.88 µm), of which the marginal and internal variations ranged 51.36 – 58.26 µm and 18.33 – 20.04 µm, respectively. On the other hand, RMSD value and DS-scores did not show significant differences among groups. Regarding reproducibility, both RMSD and DS-scores showed statistically significant differences among groups, while RMSD values of the 6 color groups were less than 5 µm, of which blue color group was the smallest (3.27 ± 0.24 µm) and white color group was the largest (4.24 ± 0.36 µm). These results were consistent with the DS data. CONCLUSION: The 3D volume of the PREs was predisposed towards an increase during digitalization, which was unaffected by gypsum color. Furthermore, the reproducibility of digitalizing scanning differed negligibly among different gypsum colors, especially in comparison to clinically observed discrepancies.

Efficacy of Disinfection of Dental Stone Casts: Virkon versus Sodium Hypochlorite.

OBJECTIVES: The purpose of this experimental study was to compare the disinfection efficacy of sodium hypochlorite and peroxygenic acid (Virkon) solutions for dental stone casts contaminated with microbial strains. MATERIALS AND METHODS: A total of 960 spherical stone beads with a diameter of 10 mm were prepared and used as carriers of bacterial inoculums. They were individually inoculated by soaking in broth culture media containing each of the four understudy microorganisms. Different concentrations of Virkon and hypochlorite solutions were prepared using distilled water and then were sprayed on the surfaces of dental casts contaminated with Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus subtilis and Candida albicans. The pour plate technique was used to evaluate the antimicrobial efficacy of each solution. Microbicidal effect (ME) was calculated according to the log10 of control colony counts minus the log10 of the remaining colony counts after the antimicrobial procedure. Statistical difference was assessed using the Kruskal Wallis and the Man Whitney U tests with a significance of 95%. RESULTS: We observed different bactericidal effects of Virkon at various concentrations; 1% Virkon killed S. aureus, P aeruginosa, and Candida albicans, while 3% Virkon solution was required to kill B. subtilis. For S. aureus, P. aeruginosa, and C. albicans, no significant difference was observed between 1% Virkon and 0.525% sodium hypochlorite (P >0.05). For B. subtilis, the efficacy of 3% Virkon and 0.525% sodium hypochlorite was not significantly different (P >0.999). CONCLUSION: According to the obtained results for Virkon and based on its low toxicity and good environmental compatibility, it may be recommended as an antimicrobial disinfectant for dental stone casts as non-critical items.

Evaluation of efficacy of microwave irradiation in disinfecting dental gypsum casts: an ex vivo study.

The aim of this study is to assess the efficacy of microwave irradiation in disinfecting gypsum casts and also to compare its efficacy with validated method of chemical disinfection. The present study is an ex vivo study conducted on a sample of five irreversible hydrocolloid impressions in vitro and on ten patients gypsum casts in vivo following standard impression techniques to check the efficacy of microwave oven irradiation and compare its efficacy with standard chemical method of disinfection. Results were analysed using Mann-Whitney test and Wilcoxon signed rank test. Untreated gypsum casts showed cfu/ml counts with a median log value of 6, while microwave-irradiated ones had median cfu/ml counts of 0. Casts poured from chemically disinfected impressions demonstrated cfu/ml counts with a median log value of 5. Microwave irradiation was found to be effective in disinfecting gypsum casts when compared to chemical disinfectant in disinfecting dental impressions.

Evaluation and comparison of high-level microwave oven disinfection with chemical disinfection of dental gypsum casts.

BACKGROUND: The aim of this study was to evaluate and compare microwave disinfection with chemical disinfection of dental gypsum casts. MATERIALS AND METHODS: A total of 120 casts were prepared from a silicone mold using Type III dental stone. Of the 120 casts, 60 casts were contaminated with 1 ml suspension of Staphylococcus aureus and 60 casts were contaminated with 1 ml suspension of Pseudomonas aeruginosa. Then, the casts were disinfected with microwave irradiation and chemical disinfection using the microwave oven and 0.5% sodium hypochlorite. Bacteriologic procedures were performed; the cfu/ml for each cast was calculated as a weighted mean. The results were analyzed using Kruskal-Wallis test and Mann-Whitney test. RESULTS: The untreated casts showed Brain heart infusion broth counts of 106 log cfu/ml compared to irradiated and chemically disinfected casts, in which 105 log reduction of cfu/ml was seen. These results satisfied the requirements of current infection control guidelines for the dental laboratory. The results obtained for chemical disinfection were in equivalence with microwave disinfection. CONCLUSIONS: Within the limitation of this in vitro study, it was found that microwave disinfection of casts for 5 min at 900 W gives high-level disinfection that complies with the current infection control guidelines for the dental laboratory and microwave disinfection method is an effective and validated method as chemical disinfection. How to cite the article: Meghashri K, Kumar P, Prasad DK, Hegde R. Evaluation and comparison of high-level microwave oven disinfection with chemical disinfection of dental gypsum casts. J Int Oral Health 2014;6(3):56-60 .

Avaliação e comparação de propriedades físicas e mecânicas de materiais de moldagem experimentais / Assessment and comparison of mechanical and physical properties of commercial and experimental gypsums

OBJETIVO: O objetivo deste estudo foi avaliar e comparar in vitro propriedades fisicas e mecanicas (resistencias a compressao e a tracao diametral, tempo de presa, fidelidade de copia e dureza) de gessos comerciais, cujas composicoes foram alteradas. MATERIAL E METODO: Foram confeccionados 40 corpos-de-prova para cada tipo de gesso e submetidos aos testes citados (n=10). Os corpos-de-prova obtidos para verificacao da resistencia a tracao foram antes submetidos a analise de dureza. Os tempos de presa foram analisados imediatamente apos a manipulacao dos materiais e os demais ensaios propostos foram realizados apos 7 dias da obtencao das amostras. RESULTADOS: Os valores obtidos nos testes foram analisados estatisticamente (1-way ANOVA, Tukey, p<0.05); observou-se que Exp1 apresentou melhor reproducao de detalhes e Exp2 o menor tempo de presa em relacao aos materiais comerciais (p<0.05). Nas demais propriedades, os gessos experimentais apresentaram comportamentos semelhantes aos comerciais. CONCLUSOES: Concluiu-se que as alteracoes na composicao dos gessos contribuiram para a melhoria na reproducao de detalhes no grupo Exp1, e diminuicao no tempo de presa no grupo Exp2.

OBJECTIVE: The purpose of this study was to evaluate and to compare in vitro mechanical and physical properties (compression and diametral tensile strength, setting time, loyalty to copy and hardness) of commercial and experimental gypsums (Exp1 and Exp2), whose compositions were altered. MATERIAL AND METHOD: Forty specimens were obtained for each type of gypsum (n=10). The specimens obtained to verify tensile strength were submitted to hardness analysis before. The setting time were analysed immediately after the manipulation of materials and the other tests were conducted 7 days after the specimens were obtained. RESULTS: The values were analyzed statistically (1-way ANOVA, Tukey, p <0.05) and it was observed that Exp1 showed better reproduction of details and Exp2 presented lesser setting time than commercial materials (p <0.05). As regards to other properties, experimental gypsums showed similar behavior to commercial gypsums. CONCLUSION: It was concluded that alterations in gypsum composition contributed to the improvement in reproduction of details in Exp1 group, and promoted a decrease in setting time in Exp2.