ABSTRACT
ABSTRACT Objectives: Assess the stability of three different mini-implants, based on thread shape factor (TSF), and evaluate stresses at the mini-implant site and surrounding cortical bone on application of retraction force, at two different insertion angles. Methods: Mini-implants of three different diameters (M1 - Orthoimplant, 1.8mm), (M2 - Tomas, 1.6mm) and (M3 - Vector TAS, 1.4mm) and length of 8mm were used. Using scanning electronic microscopy, the mean thread depth, pitch and relationship between the two (TSF) were calculated. The mini-implants were loaded into a synthetic bone block and the pull-out strength was tested. One way ANOVA and Tukey post-hoc tests were used to compare the pull-out strength of mini-implants. P values < 0.05 were considered statistically significant. Finite element models (FEM) were constructed with insertion angulation at 90° and 60°, with retraction force of 150 g. The results were analyzed using ANSYS software. Results: Statistically significant difference was found among all the three mini-implants for thread depth and pitch (< 0.001). Statistically significant higher pull-out force value was seen for Orthoimplant. The stress distribution level in mini-implant and surrounding bone was observed to be smaller for Orthoimplant. Conclusion: Orthoimplant mini-implants have more favorable geometric characteristics among the three types, and less stress with 90°angulation.
RESUMO Objetivos: Avaliar a estabilidade de três diferentes tipos de mini-implantes, com base no fator formato da rosca (thread shape factor, TSF), e avaliar a tensão no local de inserção e no osso cortical ao redor dos mini-implantes inseridos com dois ângulos diferentes, durante a aplicação de força para retração. Métodos: Foram usados três diferentes diâmetros de mini-implantes, sendo eles 1,8 mm (M1, ORTHO Implant), 1,6 mm (M2, Tomas) e 1,4 mm (M3, Vector TAS), todos com comprimento de 8 mm. Por meio da microscopia eletrônica de varredura, foram calculados a profundidade da rosca, o passo da rosca (distância entre os filetes da rosca) e a relação entre os dois (TSF). Para realização do teste de tração (pull-out), os mini-implantes foram inseridos em um bloco de osso sintético. Os testes ANOVA de uma via e post-hoc de Tukey foram usados para comparar as forças de resistência à tração dos mini-implantes, considerando-se estatisticamente significativos valores de p< 0,05. Modelos de elementos finitos (MEF) foram gerados com ângulos de inserção dos mini-implantes a 90° e 60°, com força de retração em 150g. Os resultados foram analisados usando-se o software ANSYS. Resultados: Diferenças estatisticamente significativas foram encontradas entre os três mini-implantes quanto à profundidade da rosca e o passo da rosca (p< 0,001). O ORTHO Implant apresentou a maior força de resistência à tração, com significância estatística. O nível de distribuição das tensões no mini-implante e no osso circundante também foi menor para o ORTHO Implant. Resultados: Entre os diferentes tipos de mini-implantes analisados, o ORTHO Implant apresentou as características geométricas mais favoráveis e a menor tensão com o ângulo de inserção de 90°.
Subject(s)
Dental Implants , Dental Stress Analysis , Stress, Mechanical , Software , Finite Element AnalysisABSTRACT
?AlM: To observe the changes of corneal topography and astigmatism et al with various duration of closing eyes and sleep;and study the impact of closing eye and sleep causing physiological hypoxia on corneal topography. ? METHODS: Sixteen volunteers were selected ( 32 eyes), 22-33 (26. 19 ± 3. 95) years old, without refractive errors and other eye diseases, as well as never wearing corneal contact lens, including 10 male eyes and 22 female eyes. The main parameters received corneal simulation K value, corneal astigmatism, corneal irregular measure ( ClM ) and the shape factor ( SF ) by Zeiss corneal topographer. They were measured before and after closed eyes 10, 20, 30, 60, 120min; before sleep and after over 6h sleep, they were detected immediately as soon as they opened eyes after 10, 20, 60, 120min. ? RESULTS: During closing eyes, there were no statistical significance on the changes of corneal topography, corneal astigmatism, and SF. After opening eyes and over 6h sleep, there were no statistical significance on the changes of corneal topography, corneal astigmatism, ClM, and SF. ?CONCLUSlON:Closing eyes and sleep don’t injure the cornea substantially, so corneal topography and corneal astigmatism don’t mainly change.
ABSTRACT
PURPOSE: To provide fundamental data for screening for prior refractive surgery in donor cornea. METHODS: The corneal curvature map and pachymetric measurements were analyzed in 68 eyes that had undergone corneal refractive surgery. Differences in the corneal curvature of the center and periphery, differences in the corneal thickness of the center and periphery, and the shape factor on the curvature map in postoperative eyes were compared with preoperative measurements. RESULTS: Measurement of the central corneal curvature subtracted from the peripheral corneal curvature was -1.64 +/- 0.71D in the preoperative eyes and 3.10 +/- 1.68D in the postoperative eyes. With a criterion of -0.23D, the sensitivity and specificity were 100% and 98.5%, respectively. The shape factor was 0.24 +/- 0.09 in the preoperative eyes and -0.82 +/- 0.45 in the postoperative eyes. With a criterion of 0.058, the sensitivity and specificity were both 100%. Measurement of the central corneal thickness subtracted from the peripheral corneal thickness was 97.60 +/- 25.42 micrometer in the preoperative eyes and 163.47 +/- 38.5 micrometer in the postoperative eyes. With a criterion of 123.0 micrometer, the sensitivity and specificity were 89.7% and 88.4%, respectively. CONCLUSIONS: Regional differences in corneal curvature and shape factor may be very useful parameters in screening for prior refractive surgery in donor cornea. The difference in corneal thickness may also be a useful parameter.