ABSTRACT
OBJECTIVE: This study was performed to investigate an appropriate degree of prestretch for orthodontic synthetic elastomeric chains focusing on time-dependent viscoelastic properties. METHODS: Orthodontic synthetic elastomeric chains of two brands were prestretched to 50, 100, 150, and 200% of the original length in one and three cycles, and the hysteresis areas of the obtained stress-strain curves were determined. Acrylic plates were employed to maintain constant strain during the experiment. A total of 180 samples were classified into nine groups according to brand, and their stresses and permanent deformations were measured immediately after prestretch (0 hour), after 1 hour and 24 hours, and after 1, 2, 3, 4, 5, 6, 7, and 8 weeks. The relationship between stress relaxation and permanent deformation was investigated for various degrees of prestretch, and the estimated stress resulting from tooth movement was calculated. RESULTS: The degree of prestretch and the stress relaxation ratio exhibited a strong negative correlation, whereas no correlation was found between the degree of prestretch and the average normalized permanent strain. The maximal estimated stress was observed when prestretch was performed in three cycles to 200% of the original length. CONCLUSIONS: Although prestretch benefited residual stress, it did not exhibit negative effects such as permanent deformation. The maximal estimated stress was observed at the maximal prestretch, but the difference between prestretch and control groups decreased with time. In general, higher residual stresses were observed for product B than for product A, but this difference was not clinically significant.
Subject(s)
Elastomers , Relaxation , Tooth Movement TechniquesABSTRACT
OBJECTIVE: To investigate a potential relationship between degree of stretching and resulting permanent deformation of elastomeric chains (ECs) as well as whether or not stretching time has any bearing on the degree of permanent deformation. METHODS: Five-module segments of closed elastomeric chains manufactured by 3M Unitek were stretched to 10-100% of their original length in devices especially designed for this purpose, remaining submerged in artificial saliva at 37 ± 1° C and were removed sequentially after 1, 2, 3 and 4 weeks. Upon removal, each segment was measured and, once recorded the values, were statistically analyzed with the purpose of assessing the degree of permanent deformation. CONCLUSIONS: It was concluded that permanent deformation is directly proportional to the degree of stretching of the ECs assessed. The mean percentages found were 8.4% to 10% of stretching, and exceeding 20% (21.3%) when stretched by 40%, and reaching 56.6% permanent deformation when stretched 100% of their original length. Finally, the highest percentage of permanent deformation occurred during the first week and was not statistically significant after this period.
OBJETIVO: verificar a possível relação entre o grau de estiramento e a consequente deformação permanente dos elásticos em cadeia, bem como se o fator tempo de estiramento tem influência sobre o grau de deformação permanente. MÉTODOS: segmentos de 5 elos de elásticos em cadeia curta da Unitek/3M foram estirados em de 10 a 100% de seu comprimento original, em dispositivos especialmente idealizados para essa finalidade, permanecendo submersos em saliva artificial a 37 ± 1°C e removidos, sequencialmente, após uma, duas, três e quatro semanas. Quando de sua remoção, para se avaliar o grau de deformação permanente, cada segmento era medido e os valores registrados submetidos à análise estatística. CONCLUSÃO: pode-se concluir que a deformação permanente foi diretamente proporcional ao grau de estiramento dos elásticos em cadeia avaliados, onde os percentuais médios encontrados foram de 8,4% com 10% de estiramento, ultrapassando o percentual de 20% (21,3%) quando distendidos em 40%, chegando a 56,6% de deformação permanente se estirados em 100% de seu comprimento original. Por fim, o maior percentual de deformação permanente ocorreu durante a primeira semana, não sendo estatisticamente significativo após esse período.
Subject(s)
Humans , Elastomers , Orthodontic Appliances , Stress, Mechanical , Biotransformation , Dental Stress Analysis , Elasticity , Mechanical Phenomena , Microscopy, Electron, Scanning , Saliva, Artificial/chemistry , Tensile StrengthABSTRACT
La propuesta de este estudio fue analizar el efecto de la pigmentación y de la desinfección química sobre la deformación inicial y permanente de dos siliconas (Silved Selant y Brascoved) utilizadas en la confección de prótesis faciales. Las muestras para los analisis de deformación inicial y permanente (20 mm × 12,5 mm) fueron confeccionadas de acuerdo con las instrucciones del fabricante. Para cada silicona (n= 40), diez muestras fueron pigmentadas con polvo de maquillaje, diez con óxido de hierro, diez con polvo de cerámica y diez sin pigmentación. Cinco muestras de cada grupo fueron sometidas a desinfección química, con clorhexidina al 2 por ciento por aspersión. Todas las muestras fueron inmersas en suero fisiológico y almacenado en estufa a 35 º ± 1 ºC. Después de 90 días, las muestras fueron sometidas a los exámenes de deformación inicial y permanente. Para ambas propiedades, los datos fueron analizados por el test de Tukey (a= 0,05). Los resultados mostraron que todos los materiales presentaron deformación inicial y permanente independiente de la desinfección química y pigmentación. Los grupos pigmentados con óxido de hierro fueron los que presentaron menor deformación, inicial y permanente, cuando fueron sometidos a desinfección química, independientemente de la silicona usada(AU)
The purpose of present study was to analyze the effect of pigmentation and chemical disinfection on the initial and the permanent deformation of two silicones (Silved Selant and Brascoved) for facial prosthesis. Initial and permanent deformation tests samples (20 mm × 12.5 mm) were made following the manufacturer's instructions. For each silicone (n= 40), ten samples were used for pigmentation with make up power, ten with iron oxide, ten with ceramics power and tem were tested without pigmentation. Five samples of each group were submitted to chemical disinfection using a 2 percent Chlorhexidine spray. All samples were immersed in physiological saline and stored in an oven at 35 º ± 1 ºC. After 90 days, the samples were submitted to initial and permanent deformation tests using a dial indicator. For both properties, data were analyzed by Tukey's test (a= 0.05). The results showed that all the materials had initial and permanent deformation regardless of pigmentation and chemical disinfection. The groups were used for pigmentation with iron oxide showed less initial and permanent deformation when were submitted to the chemical disinfection regardless the silicone used(AU)