Artificial teeth: evaluation of wear resistance, microhardness and composition / Dentes artificiais: avaliação da resistência ao desgaste, microdureza e composição

Objective: To evaluate the Knoop hardness, composition, and wear resistance of acrylic-resin artificial teeth exposed to mechanical toothbrushing.Methods: Artificial teeth from three commercial brands - Biotone, Trilux, and Soluut PX - were used. From each brand, 10 teeth were selected for wear evaluation after mechanical brushing, 10 for microhardness testing, and 5 for composition analysis. Specimens underwent 55,000 brushing cycles, under a 200-g load and at a frequency of 250 cycles per minute, using a soft-bristled toothbrush (IndicatorPlus 30, Oral-B) soaked in a 1:1 toothpaste/water slurry (Oral B Pró Saúde). Microhardness testing was performed using a 25-g load for 15 seconds in an HMV-2 hardness tester (Shimadzu). The composition of teeth from different brands was determined by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS) (Jeol JSM 5800).Results: Wear results after mechanical brushing were compared by means of the paired t-test, whereas those obtained in microhardness testing were compared by ANOVA with Bonferroni correction. There was no statistically significant difference between brands in either trial.Conclusion: Composition analysis revealed that all of the artificial teeth analyzed contain carbon and oxygen. Trilux and Soluut PX brand teeth also contain silicon; however, the presence of filler particles did not result in increased resistance.

Objetivo: Avaliar a microdureza Knoop, composição e resistência ao desgaste de dentes artificiais de resina acrílica submetidos ao ensaio de escovação mecânica.Métodos: Foram selecionados 10 dentes para o ensaio de escovação mecânica, 10 para microdureza e 5 para determinação da composição, de três marcas comerciais: Biotone, Trilux e Soluut PX. As amostras foram submetidas a 55.000 ciclos de escovação, sob carga de 200g e frequência de 250 ciclos por minuto, utilizando escova dental macia (IndicatorPlus 30, Oral-b), imersas em solução de dentifrício/água destilada na proporção de 1:1(Oral B Pró Saúde). O ensaio de microdureza foi realizado sob carga de 25 gramas durante 15 segundos em microdurômetro (HMV-2, Shimadzu). A composição das diferentes marcas comerciais foi determinada em MEV 5800, utilizando EDS que permite a análise química por meio de raios-x.Resultados: Os resultados obtidos no ensaio de escovação mecânica foram submetidos ao teste t pareado e aqueles obtidos no ensaio de microdureza Knoop foram submetidos à Análise de Variância e teste de BONFERRONI. Não houve diferença estatisticamente significativa entre as marcas em ambos os ensaios.Conclusão: A análise da composição revelou que todos os dentes artificiais possuem carbono e oxigênio. Os dentes das marcas Trilux e Soluut PX apresentam também silício em sua composição, entretanto, a presença de partículas de carga não resultou em aumento da resistência.

Evaluation of retention forces and resistance to fatigue of attachment systems for overdentures: plastic and metal components.

PURPOSE: To compare retention forces of 3 overdenture attachment systems with metal and plastic components. MATERIALS AND METHODS: Four samples of each system evaluated (Ball-Attachment [metal]; O-Ring, and ERA [plastic]) were prepared and underwent fatigue and retention force in a universal testing machine. Maximum retention force (N) was measured at 6 time points (from 0 to 36 months-0.5 mm/min). Two-way analysis of variance and the Tukey test were used (α = 0.05). RESULTS: The Ball-Attachment group showed the highest retention values, statistically greater than the other systems, without differences during the trial (42.75-44.75). The ERA group had intermediate values and a statistically significant decrease during the trial (20.75-14). The lowest retention forces were found for the O-Ring group (13.75-11.75), with no statistical differences during the trial. CONCLUSION: Retention forces are significantly affected by abutment type because the metal retainer was more retentive than plastics, possibly providing better fixation of the prosthesis in position, and more difficult to remove. After 6 months of simulation, retentiveness of both plastic components was similar. There was no fracture of any component.

Cimentos usados em prótese fixa: uma pesquisa com especialistas em prótese de Porto Alegre / Cements used for fixed prosthodontics: a survey with Porto Alegre specialists

Actually, many dental cements are available to cement fixed prosthesis at dental clinical practice. The aim of this study was to evaluate the cements used to fixed prosthesis by specialists who work at city of Porto Alegre with a questionnaire. A questionnaire with 22 questions was elaborated and applied to professionals registered at Regional Dentistry Council (CRO). From the 225 electable subjects, 39 were excluded. The sample of 186 specialists, 72 weren´t interviewed. The 114 interviewed subjects represented a 61.29% of response rate. The graduate year of 52% of subjects was between 1981 and 2000, and 63% finished the post graduate course after 1991. To final cementation of fixed metal ceramic prosthesis, 65% used zinc phosphate cement. However, to cements metal free fixed prosthesis, 57% used resinous cement. With technological advances at rehabilitation materials, new materials and techniques were developed. However, the zinc phosphate cement is still the first choice to cement metal ceramic prosthesis to Porto Alegre specialists.

Atualmente, diversos cimentos são utilizados para cimentação de próteses fixas na prática clínica odontológica. Sendo assim, o objetivo do presente estudo foi avaliar o uso de cimentos para prótese fixa por especialistas em prótese dentária que atuam no município de Porto Alegre. Para isso, um questionário com 22 perguntas foi elaborado e aplicado a tais profissionais registrados no Conselho Regional de Odontologia. Dentre os 225 indivíduos elegíveis, 39 foram excluídos. Da amostra de 186 especialistas, 72 não foram entrevistados. Os 114 indivíduos entrevistados representaram uma taxa de resposta de 61,29%. O ano de graduação de 52% dos respondentes foi entre 1981 e 2000 e 63% concluíram o curso de pós-graduação após 1991. Para cimentação final de próteses fixas métalo-cerâmicas, 65% dos dentistas usavam cimento de fosfato de zinco. Entretanto, para prótese fixas livres de metal, 57% utilizavam cimento resinoso. Com o avanço da tecnologia em materiais reabilitadores, novos materiais e técnicas foram criados, no entanto, o cimento de fosfato de zinco segue como primeira escolha entre os especialistas para cimentação final de próteses métalo-cerâmicas.

Effects of thermocycling on the tensile bond strength of three permanent soft denture liners.

PURPOSE: This study investigated the effect of in vitro accelerated aging reproduced with thermocycling on the bond strength of three commercially available permanent denture soft liners (PermaSoft, Dentuflex, Ufi-gel) with one heat-polymerized polymethyl methacrylate resin denture base (QC-20) by tensile test. MATERIAL AND METHODS: Ten specimens were prepared for control and test groups of each material for a total of 60 specimens. All controls were stored in water (37 degrees C) for 24 hours before testing. All test groups received 3000 thermal cycles consisting of 1 minute at 5 degrees C and 1 minute at 65 degrees C. All specimens were submitted to a tensile test using a universal testing machine at a crosshead speed of 5 mm/min. Results were statistically analyzed (ANOVA, p < or = 0.05, Tukey's post-hoc test). RESULTS: The mean bond strength of control specimens was (MPa): 0.32 (Ufi-gel), 0.49 (PermaSoft), and 1.19 (Dentuflex). There was no statistical difference (p > 0.05) between Ufi-gel and PermaSoft, but both were statistically different (p < 0.05) when compared to Dentuflex. After thermocycling, the mean bond strength was (MPa): 0.18 (Ufi-gel), 0.81 (PermaSoft), and 3.32 (Dentuflex). All materials were statistically different (p < 0.05). Ufi-gel had the lowest value and Dentuflex the highest in both control and test groups. Dentuflex presented only adhesive failure; in the remaining groups, there was no predominant failure mode, except Ufi-gel control with no adhesive failure. CONCLUSIONS: Despite presenting greater bond strength, thermocycling had a deleterious effect in Dentuflex; Ufi-gel may be adequate for short-term use.

Polymerization time for a microwave-cured acrylic resin with multiple flasks.

This study aimed at establishing the polymerization time of a microwave-cured acrylic resin (AcronTM MC), simultaneously processing 2, 4, and 6 flasks. Required time was measured according to the parameters: monomer release in water, Knoop hardness, and porosity. Samples were made with AcronTM MC in different shapes: rectangular (32 x 10 x 2.5 mm) for monomer release and porosity; and half-disc (30 mm in diameter x 4 mm in height) for Knoop hardness. There were four experimental groups (n = 24 per group): G1) one flask (control); G2) two flasks; G3) four flasks, and G4) six flasks. At first, polymerization protocol was similar for all groups (3 min/450 W). Time was then adjusted for G2, G3, and G4, based on monomer release evaluation in the control group, obtained by spectrophotometer Beckman DU-70, with emitting wave of 206 nm. Knoop hardness test was performed using a Shimadzu HMV 2000 hardness tester, and 10 indentations were performed on each specimen's surface. Porosity was assessed after specimens were immersed in black ink and the pores counted in a microscope. Results showed that the complete polymerization of the resin occurred in 4.5 min for two flasks (G2); 8.5 min for four flasks (G3); and 13 min for six flasks (G4), all with 450 W. Statistical analysis revealed that the number of flasks does not interfere with polymerization, Knoop hardness, and porosity of the resin. Results showed that polymerization of microwave-curing resin with more than one flask is a viable procedure, as long as polymerization time is adjusted.

Polymerization time for a microwave-cured acrylic resin with multiple flasks

O objetivo deste estudo foi o de determinar os tempos necessários para a polimerização padrão de uma resina acrílica em microondas, utilizando várias muflas simultaneamente. Os tempos necessários foram aferidos por parâmetros como monômeros liberados em água, dureza Knoop e porosidade. As amostras, confeccionadas em resina AcronTM MC, apresentavam as seguintes dimensões: para os parâmetros monômero residual e porosidade, retângulos de 32 x 10 x 2,5 mm e, para dureza superficial Knoop, semidiscos de 30,0 mm de diâmetro e 4,0 mm de espessura. As mensurações foram realizadas em quatro grupos (24 amostras cada): G1 - uma mufla (controle); G2 - duas muflas; G3 - quatro muflas; e G4 - seis muflas no forno de microondas, respectivamente. Inicialmente, o mesmo protocolo de polimerização foi utilizado para todos os grupos: 3 minutos a 450 W. Em seguida, o tempo de polimerização foi ajustado para os grupos 2, 3 e 4, usando como padrão os resultados do grupo 1 obtidos na análise do monômero liberado em água em espectrofotômetro Beckman DU-70, com comprimento de onda de 206 nm. Para a determinação da dureza Knoop, 10 endentações foram realizadas em cada espécime, utilizando microdurômetro Shimadzu HMV-2000. A porosidade foi avaliada após a imersão das amostras em tinta nanquim preta, contando-se os poros em microscópio. Os tempos necessários para a polimerização da resina AcronTM MC foram: 4,5 minutos para duas muflas; 8,5 minutos para quatro muflas e 13 minutos para seis muflas. De acordo com os resultados, a polimerização de resina em microondas, utilizando mais de uma mufla no forno, é um procedimento viável, desde que os tempos de polimerização sejam ajustados.