Gregório Antônio Soares Martins

Fracture Strength of Implant-Supported Ceramic Crowns with Customized Zirconia Abutments: Screw Retained vs. Cement Retained

PURPOSE To compare the fracture resistance before and after cyclic fatigue assays of ceramic crowns with customized zirconia abutments when screw retained and cemented onto implants. MATERIALS AND METHODS The sample of this study consisted of 40 ceramic crowns with zirconia infrastructure fixed onto external hexagonal implants. The crowns were distributed into two groups (n = 20): Screw-retained and cemented crowns. Half the crowns of each group (n = 10) underwent compression until fracture and the other half (n = 10) underwent cyclic fatigue and subsequent compression until fracture. The cyclic fatigue test was carried out using an electromechanical fatigue device (loads from 0 to 100 N, 2 Hz frequency, in distilled water, at 37 °C for a period of 1 million cycles). The compression test was carried out using a universal testing machine with a 0.5 mm/min speed and 5 KN load cell. After fracture, the crowns were classified according to the type of fracture. Students t test (p < 0.05) was used for statistical analysis. RESULTS The cyclic fatigue altered neither the mean fracture resistance of the screw-retained crowns (before = 1068.31 N, after = 891.49 N; p > 0.05) nor that of the cemented crowns (before = 2117.78 N; after = 2094.81 N; p > 0.05); however, the mean fracture resistance of the cemented crowns was higher than that of the screw-retained crowns both before (p < 0.001) and after (p < 0.001) the cyclic fatigue. Fractures occurred most frequently in the ceramic veneer, followed by fracture of some of the copings. CONCLUSION The ceramic crowns cemented onto the customized zirconia abutments offered greater fracture resistance than ceramic crowns with customized zirconia abutments screw retained onto implants. The cyclic fatigue did not seem to influence the fracture resistance of these crowns, whether cemented or screw retained onto implants. Fracture of the veneering ceramic was the predominant failure in this study.

Disinfection of irreversible hydrocolloid impressions with sodium hypochlorite steam: Assessment of surface roughness and dimensions of gypsum models

PURPOSE: To evaluate the surface roughness and dimensional stability of types III and IV gypsum models, obtained from irreversible hydrocolloid impressions after disinfection with 5.25% sodium hypochlorite steam. METHODS: The impressions to obtain type III and type IV gypsum models were divided into 3 groups: Group 1 (disinfection with 5.25% sodium hypochlorite steam for 10 minutes); Group 2 (simulated disinfection with distilled water steam) and Group 3 (no treatment). To measure the dimensional changes with a digital caliper, 36 models (18 for each type of gypsum) were cast according to a stainless steel master model with four pillars. For the surface roughness measurement, 36 gypsum models were cast from the impressions of the polished stainless steel platform. The data were analyzed using ANOVA and Tukeys test (α=1%). RESULTS: There was no statistically significant difference in linear dimensions or surface roughness when the different disinfection treatments were compared (Groups 1, 2 and 3), for all types of gypsum. CONCLUSION: The disinfection treatments with sodium hypochlorite steam and distilled water steam for irreversible hydrocolloid impressions did not significantly affect the dimensional stability and surface roughness of the types III and IV gypsum dental models.

Conducts of disinfection, pouring and storage of irreversible hydrocolloid impressions by undergraduate students

Introducao A obtencao de modelos odontologicos que representam com precisao os tecidos moldados requer do profissional muita atencao, principalmente quando se utiliza o hidrocoloide irreversivel como material de moldagem. Objetivo Avaliar as condutas dos alunos de graduacao em Odontologia em diferentes estagios sobre os procedimentos de desinfeccao de moldes de hidrocoloide irreversivel, vazamento e acondicionamento dos modelos odontologicos. Material e metodo Trata-se de um estudo observacional, transversal e descritivo, com amostra censitaria constituida por 89 alunos matriculados nos estagios supervisionados I, II, III e IV. A coleta de dados foi realizada por meio de um formulario estruturado contendo 8 questoes. Os dados foram analisados com nivel de significância de 5%. Resultado A maioria dos graduandos (88,8%) realizavam o procedimento de desinfeccao, sendo o metodo de desinfeccao mais utilizado (64,6%) o spray de hipoclorito de sodio a 1% acondicionado em recipiente fechado. O tempo de desinfecao por 10 minutos foi o mais relatado (86,1%). Os alunos dos estagios iniciais apresentaram melhores condutas referente a proporcao agua/gesso, quando comparados com os alunos dos estagios finais. Em todos os estagios as condutas de vazamento e acondicionamento do conjunto molde e modelo durante a reacao de presa foram negligenciadas. Verificou-se associacao estatisticamente significativa entre o estagio cursado e o metodo de desinfeccao, proporcao agua/po e metodo de vazamento dos moldes (p<0,05). Conclusao Os alunos apresentam condutas adequadas de desinfecao, no entanto devem ser estimulados a utilizar a pratica clinica baseada em evidencias a fim de melhorar as condutas de vazamento e acondicionamento dos moldes de hidrocoloide irreversivel.

Disinfection of irreversible hydrocolloid impressions with sodium hypochlorite steam: Assessment of antimicrobial efficacy

Purpose: To evaluate the antimicrobial effectiveness of 2.5% and 5.25% sodium hypochlorite steam to disinfect an irreversible hydrocolloid impressions in Humidifier and Nebulizer Boxes. Methods: The study used a total of 80 quadrant impressions of patients, divided into 4 experimental groups of 20 samples each, with respective controls. The impressions were placed in an atmosphere of sodium hypochlorite with 100% relative humidity for 10 min. After disinfection, each impression was immersed in saline solution that was ultrasonically vibrated. Microbiological analysis of the solution was carried out by counting colonies grown in BHI-agar culture medium after 24 hours in an incubator at 37 oC. The data were analyzed using Wilcoxon’s t test. Results: In all groups, it was found that the mean number of colonies in control groups was higher then in the experimental groups (P 0.01). Conclusion: Sodium hypochlorite at 5.25% can be used for disinfection in the Humidifier Box and Nebulizer Box methods. However, at a 2.5% concentration it is only effective in the Nebulizer box method.