<b>Histological and morphological evaluation of condylar cartilage of young rats in response to stimulation of mandibular protrusion

Abstract

ABSTRACT. The aim of this study was to evaluate the histogical and morphological aspects of the condyle in response to mandibular protrusion induced by composite resin occlusal planes. Thirty fiveweek-old male Wistar rats were selected and randomly divided in two groups. One group received a composite resin type of oclusal plane that induced mandibular protrusion, and the other was the control group, without treatment. Animals were euthanized after experimental time intervals of 7, 21 and 30 days. For histological analysis, thickness of the proliferative, serial and hypertrophic layers was measured, as well as each layer separately. The highest difference in cartilage thickness was observed at day 21, showing a significant increase of the proliferative layer. There were also other histomorphological changes related to occlusal plane interference. Condylar forward repositioning induced by composite occlusal planes influenced the endochondral ossification, increasing the proliferative layer.Keywords: articular cartilage, mandibular condyle, angle class II malocclusion.Avaliação histológica e morfológica da cartilagem condilar de ratos frente a estímulos de protrusão mandibular RESUMO. Este estudo teve como objetivo avaliar os aspectos histológicos e morfológicos do côndilo mandibular diante da protrusão induzida por um plano inclinado fixo de resina. Para tanto, trinta ratos Wistar machos com cinco semanas de vida foram divididos aleatoriamente em dois grupos. Um grupo experimental (E) recebeu o plano inclinado fixo de resina, que induziu a mandíbula à protrusão, e o outro consistiu no grupo controle (C), sem tratamento. Os animais foram eutanasiados após 7, 21 e 30 dias de experimento. Para análise histológica, foi realizada a mensuração da espessura condilar total, incluindo as camadas proliferativa, seriada e hipertrófica, assim como cada camada separadamente. A maior espessura da cartilagem foi observada em 21 dias no grupo E, com significante aumento da camada proliferativa. Também foram verificados níveis de histodiferenciação nos demais períodos, caracterizando interferência do plano inclinado. Concluiu-se que a indução do posicionamento condilar em avanço por meio do plano inclinado fixo interferiu no processo de ossificação endocondral, aumentando a atividade da camada proliferativa.Palavras-chave: cartilagem articular, côndilo mandibular, má-oclusão de angle classe II.

Mandibular condylar process remodeling in rats with different bite-altering devices

“…Nevertheless, despite this variability, the aluminum splint was still able to create an observable amount of condylar process remodeling in at least half of the animals. The joints remodeled in a different manner compared to the RM group, probably owing to the fact that the aluminum splints used were thin anterior-posteriorly, so that the lower incisor teeth moved outside the occlusion plane of the splint during mastication and the incisor teeth were pushed protrusively or intrusively by the splints, similar to the setup in other studies ( Farias-Neto et al , 2012 ; Sá et al , 2017 ). This could be why there was a minimal amount of remodeling observed in two of the rats with aluminum splints, at least at the site analyzed, if the changes were primarily manifest in the anterior/posterior region.…”

“…However, there was no assessment of the joint contralateral to the splint in these studies, despite the possibility that bilateral changes that might be more reflective of the human condition. As for incisor splints, studies also have shown an impact on condylar process remodeling ( Farias-Neto et al , 2012 ; Ghafari and Degroote, 1986 ; Guo et al , 2020 ; Sá et al , 2017 ; Wang et al , 2018b ; Watanabe et al , 2008 ), but the effects observed were the same on both condylar processes. Therefore, the objective of this study was to compare the impact between different splint methods (incisor and molar) and materials (resin, aluminum, stainless steel) for altering the bite on the gross and histological appearance of the mandibular condylar processes of Sprague Dawley rats.…”

“…However, there is inconsistency in the literature as to the extent and nature of the remodeling observed following abnormal loading of the joint. This is likely due to differences in splinting techniques, as they can be placed on the incisor teeth ( Farias-Neto et al , 2012 ; Ghafari and Degroote, 1986 ; Guo et al , 2020 ; Sá et al , 2017 ; Wang et al , 2018b ; Watanabe et al , 2008 ) or the molar teeth, and if on the molar teeth the splints can be unilateral ( Abdalla et al , 2019 ; Gazit et al , 1987 ; Mao et al , 1998 ) or bilateral ( Buchner, 1982 ; Li et al , 2010 ; Long et al , 2019 ). Furthermore, the splints can be placed on the maxillary ( Gazit et al , 1987 ; Li et al , 2010 ; Long et al , 2019 ; Mao et al , 1998 ) or mandibular molar teeth ( Abdalla et al , 2019 ; El-Bialy et al , 2015 ).…”

Histological Evaluation of Mandibular Condyle after Jaw Protrusive Stimulation in Rats

“…The literature points out that the condylar region may be subject to remodeling to the detriment of external stimuli due to the high adaptive capacity of the cartilaginous zones, which would result in the potential to manipulate the growth of the mandible [8][9][10][11][12]. Many studies have evaluated skeletal and dentoalveolar changes during mandibular advancement therapies for the treatment of Class II malocclusions due to mandibular deficiency [13][14][15][16][17][18][19] with the use of fixed and removable functional orthopedic devices due to their ability to stimulate the growth of the mandible, especially in the region of the condyle and the mandibular fossa, restricting the anterior displacement of the maxilla, in addition, to generate dentoalveolar effects [20][21][22][23][24].…”

“…Animal studies show that the anterior repositioning of the mandible can accelerate the maturation of chondrocytes in young animals [9,10,37,38] and reactivate chondrogenesis at rest in adult animals [10,39,40], inducing morphological and histological changes in the anterior and posterior region of the condyle, formation of cartilaginous matrix and consequent increase in endochondral ossification. However, there are divergences especially concerning the age limit of response to orthopedic-functional therapies [8,9,41].…”