Musculoaponeurotic architecture of the human masseter muscle: an in vivo ultrasonographic study of architectural changes during mandibular protrusion and lateral excursions.

OBJECTIVE: The present study evaluated the in vivo musculoaponeurotic architecture of the superficial head (SH) of the masseter muscle (MM) of asymptomatic participants in excursive mandibular movements compared to the relaxed state as examined with ultrasonography. It was hypothesized that the mean fiber bundle length (FBL) and mean height of the aponeurosis (HA) of the laminae of the SH would differ significantly between the relaxed state and protrusion, ipsilateral excursion, and contralateral excursion. STUDY DESIGN: The MM was studied volumetrically in 12 female and 12 male asymptomatic participants bilaterally by using ultrasound imaging. Mean FBL and HA in protrusion and ipsilateral and contralateral excursion were compared to these values in the relaxed state using paired t tests (P < .05). The intraclass correlation coefficient was used to assess intraexaminer reliability. RESULTS: The SH exhibited multiple laminae. Fiber bundles were found to attach to bone and the superior and inferior aponeuroses. Mean FBL was significantly shorter and mean HA significantly longer in protrusion and the excursions than in the relaxed state although the pattern of altered laminae and aponeuroses differed among the mandibular movements. Intraexaminer reliability was excellent. CONCLUSION: Specific changes in mean FBL and mean HA suggest differential contraction of the SH of the MM based on laminar morphology. These findings provide a baseline to investigate musculoaponeurotic changes in patients with myogenic masseter muscle pain.

Lobodontia in the primary and permanent dentition: a condition requiring individualized care.

Lobodontia is a rarely documented dental condition associated with pointed or conical cusps on premolars and canines, multitubercular occlusal surfaces on molar teeth, and irregularly shaped incisors. Information on this uncommon condition continues to be scarce, with particularly little information available on the primary dentition. The purpose of this article is to describe 6 cases of lobodontia and discuss the variability in presentation and management. Previously unreported manifestations in the primary dentition are included. The cases described in the current study demonstrate the spectrum of clinical and radiographic features of the condition, and show that a varied, individualized approach to treatment is necessary.

La lobodontie est une affection dentaire rarement documentée liée à des cuspides pointues ou coniques sur les prémolaires et les canines, à des molaires ayant des surfaces occlusales multituberculées et à des incisives de forme irrégulière. Les informations sur cette affection peu courante continuent à être rares, notamment en ce qui concerne la dentition primaire. L'objectif de cet article est de décrire 6 cas de lobodontie et de discuter de la variabilité en matière de présentation et de gestion. Des manifestations de la dentition primaire qui n'avaient pas été déclarées auparavant sont incluses. Les cas décrits dans la présente étude illustrent le spectre des caractéristiques cliniques et radiographiques de cette affection et montrent que le traitement nécessite une approche variée et personnalisée.

A dynamic ultrasonographic in vivo study of the musculoaponeurotic architecture of the human masseter muscle.

OBJECTIVE: In the present study, we sought to investigate the in vivo musculoaponeurotic architecture of the masseter muscle (MM) volumetrically with ultrasound in asymptomatic participants. It was hypothesized that the mean fiber bundle length (FBL) and mean aponeurotic height of laminae of the MM differ significantly between the relaxed state and maximally contracted state upon elevation of the mandible. STUDY DESIGN: The MM was investigated volumetrically in 12 male and 12 female asymptomatic participants (mean age, 25.8 ± 4.1 years) using ultrasound. The mean FBL and mean height of aponeuroses in the relaxed and maximally contracted states were compared using paired t tests, with significance established at P ≤ .05. Intrarater reliability was assessed using the intraclass correlation coefficient (ICC). RESULTS: The MM consisted of the superficial head (SH) and deep head, each arranged in multiple laminae. Fiber bundles extended between superior and inferior aponeuroses and/or bone. Statistically significant differences (P ≤ .05) were observed in mean FBL and in mean height of aponeuroses between the relaxed and contracted states only in superficial laminae of the SH. CONCLUSIONS: These results suggest there is differential contraction of the laminae of the MM in the transition from relaxed to contracted states. Future comparison with pathologic patients can be made on the basis of an established normative database.