Manifestation of hemispheric laterality in chewing side preference and handedness

The relationship between facial directional asymmetry, handedness, chewing side preference, and eyedness

We aimed to describe facial directional asymmetry (DA) in individuals with different manifestations of laterality. Due to the overlap between brain and face development, a relationship between the manifestation of brain laterality and DA is hypothesised. These findings could clarify the relationship between the brain and facial phenotype and help to plan facial or oral motor rehabilitation. The DA of 163 healthy individuals was assessed by two complementary 3D methods: landmark and polygonal surface analysis using colour-coded maps. Handedness was assessed using the Edinburgh Handedness Inventory, while chewing side and eye preferences were self-reported. The results showed a similar DA pattern regardless of sex and laterality (the right-sided protrusion of the forehead, nose, lips, and chin) and a slightly curved C-shape of the midline in landmark analysis. A relationship between lateralized behaviours and DA was found only in males, in females the DA pattern was more homogenous. Right-handed individuals and right-side chewers showed a protrusion of the right hemiface. Males, left-handed and left-side chewers, manifested a protrusion of the left lateral hemiface. We suggest that these specific differences in males may be due to their typically higher level of brain asymmetry. No apparent relationship was found between eyedness and DA.

Masticatory habits of the adult Neanderthal individual BD 1 from La Chaise-de-Vouthon (France)

OBJECTIVES

The analysis of dental wear provides a useful approach for dietary and cultural habit reconstructions of past human populations. The analysis of macrowear patterns can also be used to better understand the individual chewing behavior and to investigate the biomechanical responses during different biting scenarios. The aim of this study is to evaluate the diet and chewing performance of the adult Neanderthal Bourgeois-Delaunay 1 (BD 1) and to investigate the relationship between wear and cementum deposition under mechanical demands.

MATERIALS AND METHODS

The macrowear pattern of BD 1 was analyzed using the occlusal fingerprint analysis method. We propose a new method for the bilateral measurement of the cementum volume along both buccal and lingual sides of the molar root.

RESULTS

BD 1's anterior dentition is more affected by wear compared to the posterior one. The macrowear pattern suggest a normal chewing behavior and a mixed-diet coming from temperate environments. The teeth on the left side of the mandible display greater levels of wear, as well as the buccal side of the molar crowns. The cementum analysis shows higher buccal volume along the molar roots.

DISCUSSION

BD1 could have been preferably chewing on the left side of the mandible. The exploitation of various food resources suggested by the macrowear analysis is compatible with the environmental reconstructions. Finally, the greater wear on the buccal side of the molar occlusal surface and the greater volume of cementum in that side of the molar roots offers a preliminary understanding about the potential correlation between dental wear and cementum deposition.

Modifications of the articular eminence inclination in association with the loss of occlusal support in the molar area. A cone-beam computed tomography study

The articular eminence (AE) is part of the temporal component of the temporomandibular joint (TMJ). The inclination of the AE (AEI) has an important role in TMJ biodynamics, influencing the path of movement of the disc-condyle complex. Although AEI values might change due to tooth loss, little is known about what effect could have the loss of occlusal support in the molar area on AE morphology. AEI was measured on cone-beam computed tomography (CBCT) images of 41 patients (82 TMJs) with or without occlusal support in the molar region. The patients included in this study were divided into four groups: (1) patients with maintained occlusal support in the molar areas on both sides (right and left side) (MM); (2) patients with loss of occlusal support in the molar areas on both sides (right and left side) (LL); (3) patients with loss of occlusal support in the molar area only on the right side, but with maintained occlusal support on the left molar area (LM); (4) patients with loss of occlusal support in the molar area only on the left side, but with maintained occlusal support in the right molar area (ML). AEI values were higher in the TMJs on the side with maintained occlusal support in the molar area (M) than the AEI values measured in TMJs from the side with loss of occlusal support in the molar area (L). AEI values on the right side were higher in the MM patients in comparison to the AEI values on the right side of LL patients. The loss of occlusal support in the molar areas changes the mandibular biodynamics, which might be reflected in the morphological changes at the AE level, where it might cause flattening of the articular slope predominantly on the right side.

Comparative evaluation of hemispheric and masticatory laterality in complete dentures with two occlusal schemes - A prospective cohort study

Purpose

The lateralization can influence the choice of occlusion scheme, patient comfort and success of the prosthesis. The existence of favored masticatory side in complete denture patients and its influence with various occlusal schemes is less analyzed in the literature. The study objective was to compare the masticatory and hemispheric laterality in complete denture subjects rehabilitated with 2 different occlusal schemes at different time intervals.

Methodology

The cohort study recruited 26 patients in each group of balanced and non-balanced occlusion with definitive criteria. Conventional procedures were followed in denture fabrication. The hemispheric and masticatory laterality for all participants were established at 0,1,3- and 6-month intervals. The laterality was categorized as preferred chewing side (CPCS), predominant preferred chewing side (PPCS) and observed preferred chewing side (OPCS). The data on chewing side preference was analyzed by chi square test. (α = 0.05).

Results

Right side preference was predominant in 86.1% of non-balanced and 60.1% of balanced occlusion participants. The side preference among the 2 laterality and across time interval decreased in masticatory laterality of balanced occlusion participants (P < .05) when compared to non-balanced occlusion. (P > .05).

Conclusion

The balanced occlusion dentures had lesser masticatory side preference when compared to non-balanced occlusion complete denture.

Does Orthodontic Treatment Change the Preferred Chewing Side of Patients with Malocclusion?

Whether orthodontic treatment can change the preferred chewing side (PCS) is unknown. This study examined (1) if the PCS changes after orthodontic treatment and (2) which factors contribute to this change. Two hundred fifty patients who visited the orthodontic clinic at Tokyo Medical and Dental University Hospital between 2017 and 2020 were included in the study. Mandibular kinesiograph (MKG) was taken at pre- and post-treatment, and PCS was determined. Patients who showed a change in PCS to the opposite side and those who showed no change in PCS at post-treatment were pooled into the PCS-changed and PCS-unchanged groups, respectively. The demographic, clinical, and cephalometric parameters were compared between the groups. Significant factors associated with changes in were of age < 20 years at the beginning of orthodontic treatment (odds ratio (OR), 2.00), maximum lateral mandibular movement to PCS ≥ 10.0 mm at pre-treatment (OR, 6.51), and change in occlusal canting of ≥1.0° (OR, 2.72). The predicted probability of change in PCS was 13.2%, 36.0%, and 67.5% for no factor, one factor, and two factors associated with PCS change, respectively. Orthodontic treatment may change PCS due to patient age, maximum lateral mandibular movement to PCS, and change in occlusal canting.

Effect of Electro-Acupuncture on Lateralization of the Human Swallowing Motor Cortex Excitability by Navigation-Transcranial Magnetic Stimulation-Electromyography

Background

The use of transcranial magnetic stimulation combined with electromyography for the functional evaluation of the cerebral cortex in both clinical and non-clinical populations is becoming increasingly common. Numerous studies have shown that electro-acupuncture (EA) can regulate cerebral cortical excitability. However, the effect of EA on the lateralization of the human swallowing motor cortex excitability is not yet fully understood.

Objective

The aim of this study was to assess whether lateralization is present in the swallowing motor cortex of healthy subjects, and to investigate the impact of EA at Lianquan (CV23) and Fengfu (GV16) on lateralization.

Methods

Forty subjects were randomized 1:1 into the EA group and the sham-EA group. The bilateral swallowing motor cortices was located by a neuroimaging navigation system. Then, the resting motor threshold (RMT) and motor evoked potential (MEP) of the mylohyoid of healthy subjects were recorded while applying combined transcranial magnetic stimulation and electromyography before and after EA or sham-EA.

Results

First, the RMT and MEP latency of the contralateral mylohyoid innervated by the right swallowing cortex (71.50 ± 1.67%, 8.30 ± 0.06 ms) were lower than those innervated by the left (79.38 ± 1.27%, 8.40 ± 0.06 ms). Second, EA at CV23 and GV16 reduced the bilateral RMT and enhanced the bilateral MEP latency and amplitude (P = 0.005, P < 0.001; P = 0.002, P = 0.001; P = 0.002, P = 0.009), while sham-EA did not (P > 0.05). Third, EA had an effect on the RMT and MEP latency in terms of lateralization changes, but this was not significant (P = 0.067, P = 0.156).

Conclusion

The right swallowing motor cortex of healthy subjects is more excitable than that of the left at resting state. Thus, we found that lateralization is present in the swallowing motor cortex of healthy people, which might indicate a hemispheric dominance of swallowing predominates in the right swallowing motor cortex. In addition, EA at CV23 and GV16 can instantly promote the excitability of the bilateral swallowing motor cortices. But there was no significant difference in EA stimulation in terms of lateralization.