ABSTRACT
This study aims at revising the biomechanical principles of the segmented archwire technique as well as describing the clinical conditions in which the rational use of scientific biomechanics is essential to optimize orthodontic treatment and reduce the side effects produced by the straight wire technique.
O objetivo desse trabalho é revisar os princípios biomecânicos da técnica do arco segmentado, bem como descrever situações clínicas onde o uso racional da biomecânica científica é fundamental na otimização do tratamento ortodôntico e eliminação dos efeitos colaterais da abordagem com arco contínuo.
Subject(s)
Humans , Orthodontic Appliance Design , Orthodontic Wires , Tooth Movement Techniques/instrumentation , Biomechanical Phenomena , Cuspid/physiology , Elasticity , Incisor/physiology , Molar/physiology , Orthodontic Extrusion/instrumentation , Overbite/therapy , Patient Care Planning , Rotation , Stress, Mechanical , Torque , Tooth Crown/physiology , Tooth Movement Techniques/methods , Tooth Root/physiologyABSTRACT
This study evaluated the fracture strength of teeth restored with bonded ceramic inlays and overlays compared to sound teeth. Thirty sound human maxillary premolars were assigned to 3 groups: 1- sound/unprepared (control); 2- inlays and 3- overlays. The inlay cavity design was Class II MOD preparation with an occlusal width of 1/2 of the intercuspal distance. The overlay cavity design was similar to that of the inlay group, except for buccal and palatal cusp coverage The inlay and overlay groups were restored with feldspathic porcelain bonded with adhesive cement. The specimens were subjected to a compressive load until fracture. Data were analyzed statistically by the Kruskal-Wallis test at 5 percent significance level. The fracture strength means (KN) were: Sound/unprepared group = 1.17, Inlay group= 1.17, and Overlay group = 1.14. There were no statistically significant differences (p>0.05) among the groups. For inlays and overlays, the predominant fracture mode involved fragments of one cusp (70 percent of simple fractures). The fracture strength of teeth restored with inlay and overlay ceramics with cusp coverage was similar to that of intact teeth.
Este estudo avaliou a resistência à fratura de dentes restaurados com inlays e overlays de cerâmicas comparadas a dentes íntegros. Trinta pré-molares humanos íntegros foram divididos em 3 grupos: 1-Dentes sem preparo cavitário (controle), 2-Inlays e 3-Overlays. O preparo para as inlays apresentava uma cavidade de Classe II MOD tendo caixa oclusal com largura de metade da distância intercuspídica. O preparo para as overlays era semelhante ao das inlays; porém com cobertura das cúspides vestibular e palatina. Os grupos 2 e 3 foram restaurados com porcelanas feldspáticas fixadas com cimento resinoso. As amostras foram submetidas à compressão até a fratura. Os valores médios de fratura (KN) foram: grupo 1 = 1,17, grupo 2 = 1,17 e grupo 3 = 1,14. O teste de Kruskal-Wallis não revelou diferença estatisticamente significante entre os 3 grupos (p>0,05). Para as inlays e overlays, a predominância das fraturas envolveu fragmentos de uma das cúspides (70 por cento de fraturas simples). Concluiu-se que os dentes restaurados com inlays e overlays apresentaram resistência da cúspide comparável aos dentes intactos.