Anterior disc displacement and the superior head of lateral pterygoid muscle: a case-control study / Desplazamiento discal anterior y la cabeza superior del músculo pterigoideo lateral: un estudio caso-control

The objective of this study was to assess the association between an increase in the proportion of the superior head of the lateral pterygoid muscle (SHLP) inserted into the temporomandibular joint (TMJ) disc and the presence of anterior disc displacement diagnosed by using MRI. We analyzed 75 images of patients with anterior displacement and 75 controls with normal relationship between the mandibular head and the articular tubercle also diagnosed by MRI. Levels of insertion were measured. Descriptive and analytic statistics were calculated. Analyses of differences were made by Fischer's exact test and also were calculated clinical significance (OR, CI = 95 percent). The average insertion of SHLP was 71.14 percent (SD 14.13) in controls and 67.80 percent (SD.16.23) in cases group. The only relationship that presented a significant association (OR 5.61) was found when comparing subjects with a percentage of inserting the disc into the SHLP at 50 percent with those who had higher levels of insertion (50 percent). Our results suggest that the highest percentage of insertion serves as a protective factor for anterior disc displacement, probably due to greater control of neuromuscular activity.

El objetivo de este estudio fue evaluar la asociación entre el aumento de la proporción de la cabeza superior del músculo pterigoideo lateral (CSPT) insertado en la articulación temporomandibular (ATM) y la presencia de desplazamiento discal anterior diagnosticado mediante resonancia magnética. Se analizaron 75 imágenes de pacientes con desplazamiento discal anterior y 75 controles con una relación normal entre la cabeza de la mandíbula y el tubérculo articular, también diagnosticada por resonancia magnética. Los niveles de inserción fueron medidos. La estadística descriptiva y analítica fueron calculadas. Los análisis de las diferencias se hicieron por la prueba exacta de Fischer, y también se calculó la significancia clínica (OR, IC=95 por ciento). La inserción media de la CSPT fue 71,14 por ciento (DS 14,13) en los controles y 67,80 por ciento (SD 16,23) en los casos de grupo. La única relación que presentó una asociación significativa (OR 5,61) se encontró al comparar los sujetos con un porcentaje de inserción en la CSPT 50 por ciento con aquellos que tenían niveles más altos de inserción (50 por ciento). Nuestros resultados sugieren que el mayor porcentaje de inserción sirve como un factor de protección para el desplazamiento discal anterior, probablemente debido a un mayor control de la actividad neuromuscular.

Superior head of the lateral pterygoid muscle inserting in asymptomatictemporomandibular joints / Inserción de la cabeza superior del músculo pterigoideo lateral enarticulaciones temporomandibulares asintomáticas

The constitution and shape of superior head of the lateral pterygoid muscle (SHLP) inserts remains a topic of interest in the literature. The purpose of this study was to analyze by magnetic resonance imaging (MRI) the temporomandibular joint (TMJ) of individuals without signs of temporomandibular dysfunction. One hundred seventy-eight MRI images of one hundred and three patients were utilized, and the surface and percentage of the SHLP insert into the articular disc and condilar process was determined. In women, the average insertion into the disc was found to be between 5.7–5.5mm (SD 1.5–1.3), corresponding to 69.8–70.7 percent of the SHLP. In men, the average insertion into the disc was between 6.2–6.12mm (SD 1.8–1.9), or 68.9–74.2 percent. There were no differences in terms of the sex of the patients or the side of the joint. We found a significant percentage of SHLP fibers embedded in the disc of asymptomatic TMJs, and its role in theanterior disc displacement and the development of the temporomandibular dysfunction should be revised.

La constitución y la forma de inserción de la cabeza superior del músculo pterigoideo lateral (CSMPL) sigue siendo un tema de interés en la literatura. El objetivo de este estudio fue analizar mediante resonancia nuclear magnética (RNM) la articulación temporomandibular (ATM) de individuos sin signos de disfunción temporomandibular. Fueron utilizadas 178 imágenes de RNM pertenecientes a 103 pacientes. Se determinó la superficie y porcentaje de la inserción de la CSMPL en el disco y proceso condilar. En mujeres, la media de inserción en el disco estuvo entre 5,7-5,5 mm (SD 1,5- 1,3) correspondiente al 69,8-70,7 por ciento de la CSMPL. En hombres, la media de inserción en el disco estuvo entre 6,2-6,12mm (SD 1,8-1,9) correspondiente al 68,9-74,2 por ciento de la CSMPL. No hubo diferencias en cuanto al sexo de los pacientes o lado de la articulación. Hemos encontrado un porcentaje significativo de las fibras de la CSMPL insertadas en el disco de ATMs asintomáticas, y su papel en el desplazamiento anterior del disco y el desarrollo de disfunción temporomandibular debe ser revisado.

Prevalence of the third head of the lateral pterygoid muscle: a magnetic resonance image study / Prevalencia de la tercera cabeza del músculo pterigoideo lateral: estudio con imaenes de resonancia magnética

The lateral pterygoid muscle (LPM) is important in the physiology and dysfunction of the temporomandibular joint (TMJ), which has described the presence of a third head in the lateral pterygoid muscle (THLPM). The purpose of this study was to evaluate the prevalence of THLPM and its relationship with the TMJ disc through magnetic resonance imaging (MRI). It was evaluated 178 MRI of the TMJ of healthy individuals, in images that presented THLPM, and these were defined and measured at the surface inserted into the disc. The prevalence of THLPM was 20.22 percent (n = 36). Insertion of THLPM was made entirely on the TMJ disc, the average area of insertion was 4.14mm (SD 1.35) in women and 4.67 (SD 2.68) in men, but these differences were not significant. We concluded that the LPM has a complex structure, and that a THLPM could contribute in the development of TMJ disc function alterations and anterior disc displacement.

El músculo pterigoideo lateral (MPL) tiene importancia en la fisiología y en la disfunción de la articulación temporomandibular (ATM), se ha descrito la presencia de una tercera cabeza en el músculo pterigoideo lateral (TCPL). El propósito de este estudio fue evaluar mediante resonancia nuclear magnética (RNM) la prevalencia de la TCPL y su relación con el disco de la ATM. Se evaluaron 178 RNM de ATM de individuos sanos. En las imágenes que presentaron TCPL éstos fueron delimitados y se midió la superficie inserta en el disco. La prevalencia de la TCPL fue del 20,22 por ciento (n=36). La inserción de la TCPL se realizó completamente en el disco de la ATM, la media del área de inserción fue de 4,14mm (DS. 1,35) en mujeres y 4,67 (DS. 2,68) en hombres, estas diferencias no resultaron significativas. Concluimos que el MPL presenta una estructura compleja y que una TCPL podría participar en el desarrollo de alteraciones en la función discal y en la presencia de desplazamiento anterior del disco.

Avaliação da assimetria facial em indivíduos com mordida cruzada posterior por meio de fotografias frontais / Evaluation of face asymetry in individuals with posterior crossbite through frontal photographs

O objetivo deste trabalho foi avaliar assimetria facial em indivíduos com mordida cruzada posterior através de fotografias frontais, correlacionando-a aos tipos de mordida cruzada e características individuais do grupo estudado. Foram avaliados 44 indivíduos na fase da dentição mista, sendo: Grupo 1 - 22 indivíduos com oclusão normal no sentido transversal, e Grupo 2 - 22 indivíduos com mordida cruzada posterior. Verificou-se freqüência de mordida cruzada, tipos, associação com etnia e gênero, fraturas faciais, tipos de parto, infecção na região do ouvido e habito de dormir com a mão sob o rosto em ambos os grupos. Realizou-se fotografias frontais a fim de verificar se havia diferença entre estes dois grupos através de traçados do plano dos olhos (interpupilar) e do plano da boca (linha da comissura), e mensurar estes ângulos em relação a linha média facial. No Grupo 2 verificou-se uma maior incidência de mordida cruzada unilateral (77,2%) do que bilateral (22,7%) e funcional (72,2%) do que verdadeira (27,8%). Quanto a análise frontal de fotografias verificou-se que existe maior correlação entre o ângulo do olho e da boca (r=0,7450n)o s indivíduos do Grupo I do que do Grupo 2 (r=0, 5260), apesar de não ter sido detectado nenhuma diferença estatística entre a média do ângulo do olho e da boca na face dos indivíduos do Grupo 2 com relação aos do Grupo 1 (p=20,05). Concluiu-se que a assimetria facial não está correlacionada com mordida cruzada posterior, independente do tipo e características do indivíduo.

The objective of this study was to evaluate facial asymmetry with posterior crossbite through frontal pictures, correlating it to the kinds of crossbites and individual characteristics of the group studied. 44 individuals in the mixed dentition phase were evaluated: Group 1-22 - individuals with normal occlusion in the transveral direction and Group 2-22 - individuals with posterior crossbite. It was verified the frequency of crossbite, types, association with ethnicity and gender, face fractures, labor types, infection in the ear area and the habit of sleeping with the hand on the face in both groups. Frontal photographs were performed to verify if there was any difference between these two groups through marks on the level of the eyes (interpupil) and on the level of the mouth (commisure line), and measure these angles in relation to the middle-line of the face. In Group 2, it was verified a higher incidence of unilateral crossbite (77%) than bilateral (22,7%), and functional(72,2%) than !rue (27,8%). As to the frontal analysis of photographs, it was verified that there is a higher correlation between the angle of the eye and the mouth (r=O, 7450) in the individuals of Group I than of Group 2 (r=0,5260), although no statistical differentiation was detected between the average of the angle of the eye and the mouth in the faces of the individuals of Group 2 in relation to the ones of Group I (p 0,05). It was concluded that the face asymmetry is not related with posterior crossbite and no relation is there to the types and characteristics of the individuals.