Smoothness of chewing jaw movements in adults with mandibular prognathism

Hemodynamic Changes in the Masseter and Superior Orbicularis Oris Muscles before and after Exercise Load: A Comparison between Young Adult Women and Middle-Aged to Old Adult Women

Background

The vascularity index (VI) is useful for measuring the hemodynamics on ultrasound imaging. However, there are no reports concerning the application of the VI to facial muscles.

Objective

The aim of this study was (1) to establish a method of measuring the hemodynamics in facial muscles in a constant way and (2) to evaluate the hemodynamic changes in the masseter and superior orbicularis oris muscles (SOOMs) before and after exercise load in two subject groups of females of different ages.

Methods

(1) The VI in the SOOM was calculated, and the test-retest reliability was assessed in seven healthy adults. (2) The VIs in the left-side masseter and SOOM were calculated in 3 sessions: before exercise loading (T0), immediately after loading (T1), and 5 minutes after T1 (T2) for the young adult group (YAG, n = 20; age range, 20–35 years) and the middle-aged to old group (MOG, n = 20; age range, 50–70 years). Tasks were gum chewing for the masseter muscle and lip sealing for the SOOM. The differences in the mean peak flows between two sessions were examined.

Results

(1) Significant differences were not noted for the repeatedly measured average volumes of blood flow with good test-retest agreement (intraclass correlation coefficient = 0.81). (2) In both muscles of the YAG, there were a significant increase in T1 compared with T0 and a significant decrease in T2 compared with T1 (all p < 0.05). In both muscles of the MOG, no significant differences were noted in either comparison.

Conclusions

A method of measuring the hemodynamics in facial muscles was developed and showed good reliability. Changes in the blood flow after exercise load in these muscles may vary with age in women.

Population affinity and variation of sexual dimorphism in three-dimensional facial forms: comparisons between Turkish and Japanese populations

Examining the extent to which sex differences in three-dimensional (3D) facial soft tissue configurations are similar across diverse populations could suggest the source of the indirect evolutionary benefits of facial sexual dimorphism traits. To explore this idea, we selected two geographically distinct populations. Three-dimensional model faces were derived from 272 Turkish and Japanese men and women; their facial morphologies were evaluated using landmark and surface-based analyses. We found four common facial features related to sexual dimorphism. Both Turkish and Japanese females had a shorter lower face height, a flatter forehead, greater sagittal cheek protrusion in the infraorbital region but less prominence of the cheek in the parotid-masseteric region, and an antero-posteriorly smaller nose when compared with their male counterparts. The results indicated the possible phylogenetic contribution of the masticatory organ function and morphogenesis on sexual dimorphism of the human face in addition to previously reported biological and psychological characteristics, including sexual maturity, reproductive potential, mating success, general health, immune response, age, and personality.

Extraction treatment of a class II division 2 malocclusion with mandibular posterior discrepancy and changes in stomatognathic function

This case report describes the successful extraction treatment of a Class II division 2 malocclusion with mandibular posterior discrepancy and a congenitally missing maxillary lateral incisor on the left side. The posterior space in the mandibular arch was small, and the mandibular second molars were impacted, with distal tipping. The discrepancies in the maxillary and mandibular arches were resolved by extraction of the maxillary lateral incisor on the right side and the mandibular second premolars on both sides. The mesial movement of the mandibular first molars occurred appropriately, with the second molars moving into an upright position. A lip bumper was used with a preadjusted edgewise appliance in the maxillary dentition to reinforce molar anchorage and labial movement of the retroclined incisors. Despite the extraction treatment, a deep bite could be corrected without aggravation as a result of the lip bumper and utility arch in the mandibular dentition. Thus, an Angle Class I molar relationship and an ideal overbite were achieved. The occlusal contact area and masticatory muscle activities during maximum clenching increased after treatment. The maximum closing velocity and the maximum gape during chewing increased, and the chewing pattern changed from the chopping to grinding type. The findings in the present case suggest that the correction of a deep bite might be effective for improving stomatognathic function.

Smoothness of molar movement during gum chewing in children with primary dentition

The purpose of this study was to test the null hypothesis that molar movement during gum chewing in children with primary dentition is as smooth as in adults. Twenty-two healthy children with primary dentition and 23 healthy adult females participated in this study. Mandibular movement during gum chewing was recorded using an optoelectronic analysis system with six degrees-of-freedom at 100 Hz, and 10 cycles were selected for analysis. Normalized jerk cost (NJC) at the incisors and working and balancing molars were calculated in each phase (i.e., opening, closing and occlusal level phases) for each chewing cycle. The NJC of the working side molar in children was larger than in adults in both the opening and occlusal phases. Inter-individual variances of the NJC in each phase in children and adults were smaller than corresponding intra-individual variances, except for the NJC during the occlusal phase of adults for the working and balancing side molars. The inter- and intra-individual variances of the NJC during the closing phase were the smallest in each phase for both children and adults. This indicates that the jaw movements of children with primary dentition are more variable, less smooth, and faster than that of adults.

Analysis of temporal variation in human masticatory cycles during gum chewing

OBJECTIVE

The study investigated modulation of fast and slow opening (FO, SO) and closing (FC, SC) chewing cycle phases using gum-chewing sequences in humans.

DESIGN

Twenty-two healthy adult subjects participated by chewing gum for at least 20s on the right side and at least 20s on the left side while jaw movements were tracked with a 3D motion analysis system. Jaw movement data were digitized, and chewing cycle phases were identified and analysed for all chewing cycles in a complete sequence.

RESULTS

All four chewing cycle phase durations were more variant than total cycle durations, a result found in other non-human primates. Significant negative correlations existed between the opening phases, SO and FO, and between the closing phases, SC and FC; however, there was less consistency in terms of which phases were negatively correlated both between subjects, and between chewing sides within subjects, compared with results reported in other species.

CONCLUSIONS

The coordination of intra-cycle phases appears to be flexible and to follow complex rules during gum-chewing in humans. Alternatively, the observed intra-cycle phase relationships could simply reflect: (1) variation in jaw kinematics due to variation in how gum was handled by the tongue on a chew-by-chew basis in our experimental design or (2) by variation due to data sampling noise and/or how phases were defined and identified.

Improvements in smoothness of chewing cycles in adults with mandibular prognathism after surgery: a longitudinal study

Although adults with mandibular prognathism are known to show impaired smoothness of masticatory jaw movements, it remains uncertain whether/how the surgical-orthodontic treatment is effective to improve masticatory jaw movements. The aims of this study were (i) to verify whether the surgical-orthodontic treatment of patients with mandibular prognathism improve smoothness of the chewing jaw movements post-operatively and, if so, (ii) to examine whether the improved parameters show similar quantities as those of the control subjects. The chewing jaw movements for 13 patients with mandibular prognathism were recorded at pre- and post-treatment stages. The patient group was divided into two groups: Class III(closed) showed full occlusal contact at the habitual intercuspal position, whereas Class III(open) showed inability of occlusal contact between the upper and lower anterior teeth. The control group (CG) consisted of 52 subjects having acceptably good occlusion. The normalised jerk cost (NJC), movement duration and peak velocity in jaw closing were compared. For both Class III(open) and Class III(closed) groups, statistical comparisons revealed that the NJC and movement duration were decreased after the treatment, whereas the peak velocity was increased (all P < 0·01). For the Class III(open), these quantities at the post-treatment stage did not show any significant differences compared with those for the CG. It is concluded that the smoothness of chewing jaw movements for patient with mandibular prognathism were improved after treatment, and for the patients with anterior open bite at pre-treatment, the post-operatively achieved smoothness of jaw-closing movements did not differ from those of the CG.

Reverse cycle chewing before and after orthodontic-surgical correction in class III patients

OBJECTIVE

The aim of this study was to investigate the prevalence of reverse-sequence chewing cycles in skeletal class III patients before and after orthodontic-surgical therapy to evaluate whether the occlusal and skeletal correction is followed by a functional improvement.

STUDY DESIGN

Twenty skeletal class III patients (11 males and 9 females, 22.7 ± 3.0 years old) were recruited for this study. All patients received orthodontic and surgical treatment. Chewing cycles were recorded with a kinesiograph before (T0) and after (T1) therapy.

RESULTS

A significant decrease in the number of reverse chewing cycles after surgical correction was exhibited in all recordings, when chewing either soft or hard boluses, on both the right and the left side.

CONCLUSIONS

Evaluation of the prevalence of reverse chewing cycles could be considered an indicator of functional adaptation after therapy and a method for the early detection of nonresponding patients who may require further consideration using a different approach.