Evaluation of the presence of the third head on the lateral pterygoid muscle in adult individuals

Abstract

SUMMARY: The lateral pterygoid muscle (LPM) is one of the muscles involved in jaw movements, and is therefore of great importance in the physiology of the temporomandibular joint. This muscle has classically been considered to have two heads, superior and inferior, however previous studies have indicated the presence of a third head (TH). The object of this research was therefore to evaluate, through a study in cadavers, the presence of the third head of the LPM and its relation with the joint disc of the TMJ in adult individuals. The study used 30 half-skulls of adult individuals, 11 right side and 19 left side. The number of heads on each LPM was analysed, with the length and thickness of each. The Chi-squared, Mann-Whitney U, Kruskall-Wallis and Spearman's correlation coefficient tests were applied, with a significance threshold of 5 %. The TH of the LPM was present in 20 % of the samples. Statistically significant differences were found in the thickness of the superior head (SH) vs. the inferior head (IH) (p<0.001) and between TH vs. SH and TH vs. IH (p=0.010). No correlation was found between the thickness of the heads or in their lengths. The LPM most frequently presents two heads, superior and inferior. The TH is an anatomical variation that may be present in 20 % of cases. The IH usually presents the greatest thickness. The use of cadavers is a good method for analysing the presence of the TH and the morphometry of the various heads of the LPM.