Chewing Side Research Articles

ANALYSIS OF THE IMPACT OF THE BIOMECHANICAL PROPERTIES OF THE MASTICATORY, TEMPORAL, LATERAL, AND MEDIAL PTERYGOID MUSCLES ON THE ONSET AND PROGRESSION OF GENERALIZED INCREASED TOOTH WEARING

Increased wear of dental hard tissues is a longstanding and pressing issue that has become widespread among populations across different regions, with prevalence ranging from 3% to 83.2%. The influence of the muscles responsible for lifting, extending, and moving the lower jaw on the pathogenesis of generalized increased tooth wear has been studied, but the biomechanical components of “speed” and “force” in these muscles have not been fully clarified. Objective. Using D. Bernoulli's principle, this study aims to investigate the impact of the biomechanical properties—specifically "speed" and "force"—of the masticatory, temporal, medial, and lateral pterygoid muscles on the side of priority and secondary importance for chewing, and their role in the development of increased wear of tooth hard tissues. The tasks of the study is to determine the length, width, and thickness of the masticatory, temporalis, and pterygoid muscles on the primary and secondary chewing sides in patients with increased attrition of tooth hard tissues, as well as in individuals without signs of increased attrition; using D. Bernoulli’s principle, to calculate a dimensionless coefficient for each muscle, and compare the biomechanical properties of “speed” and “force” of the studied muscles to determine their impact on the development of increased wear of tooth hard tissues. Discussion of Results. As the severity of increased tooth wear progresses, the temporal and masticatory muscles exhibit the physical property of “strength”, while the pterygoid muscles demonstrate “speed”. A greater acquisition of “strength” by the temporal and masticatory muscles, coupled with increased "speed" in the pterygoid muscles, leads to heightened friction between the occlusal surfaces of the teeth. Conclusion. The imbalance between the physical properties of “strength” and “speed” in the masticatory, temporal, and pterygoid muscles contributes to the development of increased wear of hard dental tissues.

Pathology of the temporomandibular joint in dental diseases

Temporomandibular joint diseases (TMJ) significantly reduce the quality of life, causing such unpleasant symptoms as orofacial pain, joint sound, limited mouth opening, tinnitus, insomnia. TMJ pathology can be a consequence of both the dental interventions themselves and diseases of the oral cavity, including complete or partial edentia, malocclusion, dominance of one chewing side, periodontitis, etc. The purpose of this review was to study, based on literature data, possible disorders in the temporomandibular joint (TMJ) in dental pathology. The risk factors for the development of TMJ, the most common symptoms, clinical picture, features of differential diagnostics, the relationship with the use of general anesthesia, age-related changes are considered. The relationship of TMJ with dental diseases is considered in detail. The mutual influence of changes in the TMJ and the dentition has been confirmed. A conclusion has been made about the need for constant attention to the pathology of the TMJ in dental diseases.

Possible link between the preferential unilateral chewing side and eruptive guidance of the maxillary canine germ : Cross-sectional study on panoramic radiographs.

To determine whether unilateral preferent chewing (UPC) affects the position and angulation of the permanent maxillary canine germ on the preferred side. In aretrospective cross-sectional study, medical records from children 7.91(± 0.8) years old with unilateral preferred chewing side and unilateral posterior crossbite were selected. The position of the maxillary canines was analysed by measuring the following angles and distances: the angles formed between the canine axis and the midline (PS; potential impact range > 15°), and that between the canine axis and the bicondylar line (W; potential impact range < 75°). In addition, the canine's position with respect to the lateral incisor (EK; potential impact range > II) and the distance between the canine cusp and the occlusal plane (CCOP potential impact range > 10 mm) were measured. The final sample consisted of 106 radiographs; thus, atotal of 212 maxillary canines were analysed. Tooth angulation on the preferred chewing side was higher for the angle PS with an average angle of 13.88° (± 7.56) and its position was more frequently found in sectorII (49.1%), according to the EK analysis, compared to its contralateral that had an average of 11.75° (± 10.13) for the PS angle and afrequency of 67% in the sectorI (p < 0.05 in both analyses). The data obtained for the angleW resulted in an average of 76.12° (± 9.09), while on the contralateral side it was 77.16° (± 12.56; p = 0.012). Lastly, according to the CCOP analysis, the preferred chewing side measured on average 15.3 mm (± 2.4), while on the nonpreferred side it was 15.19 mm (± 2.43; p = 0.143). Based on this research, UPC seems to have acertain unfavourable influence on canine position and angulation. Thus, this is another factor to consider in decision-making regarding early treatment of this development disorder.

Unilateral molar Incisor hypomineralization influences the chewing side? an observational study in children.

The aim of this observational study was to compare the chewing patterns of children with unilateral Molar Incisor Hypomineralization (MIH) to those of children without MIH and to assess how the MIH severity influences the risk of chewing deviation. The hypothesis was that children with unilateral MIH would prefer to chew on the side opposite the defect. A total of 121 children were included in this investigation and evaluated for their preferred chewing side (PCS). This study population comprised 45 children with unilateral mild MIH (G1), 42 with unilateral severe MIH (G2), and 34 children in the control group (CG) who had no MIH but presented with unilateral chewing complaints. The PCS pattern differed among the groups, with 31% of the children with MIH and 55.9% of the CG showing bilateral chewing. The chewing deviation prevalence was 24% in the CG and 52% in G2 (χ2 test; p = 0.03). Binomial logistic regression analysis revealed that both severities of MIH influenced the likelihood of chewing deviation (χ2 = 7.33, p = 0.026). Children with unilateral severe MIH were 3.57 times more likely to exhibit chewing deviation than were those without MIH. The null hypothesis was rejected, indicating that unilateral MIH affects children's masticatory patterns, increasing the risk of chewing deviation. Unilateral chewing may be associated with various health issues, such as temporomandibular disorders (TMDs), decreased hearing, and vision problems. Unilateral MIH is a potential risk factor for unilateral chewing.

Ultrasonographic Evaluation of the Masseter Muscle in Skeletal Malocclusions (Class I, II, and III).

There is limited research on the sonographic view of people with skeletal malocclusions. Therefore, this study aimed to evaluate the sonographic findings of the masseter muscle in patients with skeletal malocclusions. In this descriptive study, 48 patients aged 15-20 years with skeletal class I, II, and III malocclusions (n = 16) who were referred to Mashhad Dental School for treatment were selected. The masseter muscle was evaluated by ultrasound, including transverse and longitudinal scans on both sides of the face in resting and contraction states. The age, gender, muscle thickness, muscle pattern (Malocclusion were classified based on A-point, nasion, B-point (ANB): 0< ANB <4 as class I, ANB > 4 as class II, ANB < 0 as class III), side of chewing, and body mass index (BMI) parameters were measured for each patient. Paired t-tests compared masseter muscle states; ANOVA assessed differences among malocclusion groups. The most commonly observed pattern in the masseter muscle of patients with class III skeletal malocclusions was type II, and in people with class II malocclusions was type I. There was a positive and significant correlation between the thickness of masseter muscle and BMI in each group separately (P < 0.001). However, the masseter muscle pattern did not show a significant correlation with BMI, gender, and age. A significant difference was observed between the thickness of the masseter muscle in the resting and contracted states in each group (P < 0.001). This study showed that skeletal malocclusions can affect the pattern and internal structure of the masseter muscle in the anterior-posterior dimension of the face. Ultrasound can be a suitable diagnostic tool for these patients.

Mandible Position and Chewing Preference Side Do Not Alter Plantar Support in Children Aged 4-11 Years.

Mandible positioning can cause global postural adaptations. Physiotherapists and dentists try to relate the mandible position and chewing side to plantar support; however, this indication is uncertain. To check the existence of a relationship between mandible position, preferred chewing side, age, and plantar support in children. This is a cross-sectional study with 93 children, aged between 4 and 11 years. Photogrammetry was used to confirm the mandibular positions (centralized, to the right, and to the left), and baropodometry was used to measure plantar support. The mandibular displacement distance to the right and left was evaluated, and the plantar support in the three mandibular positions was compared as a function of age (4-7 and 8-11 years) and preferred chewing side. There was greater mandibular displacement in left laterality [13 (9-19) cm] compared to right laterality [7 (3.50-12.00) cm] (p < 0.01). Mandibular position did not alter mean pressure, maximum pressure, or plantar support surface (p > 0.05). With the mandible centralized, higher mean pressure, maximum pressure, and surface area were observed in the left foot (p < 0.01). Older children showed greater mandibular displacement to the left (p < 0.01). No differences were observed for the variables of plantar support as a function of age (p > 0.05) and chewing side (p > 0.05). There was a moderate to strong correlation between age, body mass, height, and plantar surface area (0.63 < r < 0.83; p < 0.05) and between mean and maximum pressures of plantar support (0.58 < r < 0.89; p < 0.05). Mandibular position, age, and preferred chewing side do not influence plantar support in children. Bittar KCB, Zamboti CL, Macedo CSG. Mandible Position and Chewing Preference Side Do Not Alter Plantar Support in Children Aged 4-11 Years. Int J Clin Pediatr Dent 2024;17(6):658-664.

Mandibular overdenture with a single implant in the canine region (c-SIMO): a feasibility study

ObjectivesThe aim of this multi-center pilot study was to assess the viability and feasibility of a novel treatment concept – the canine-positioned single implant mandibular overdenture (c-SIMO), with the single implant placed on the patient's preferred chewing side instead of the midline.Materials and methodsParticipants received a single implant in the canine region of their preferred chewing side, based on an Asymmetry Index observed during mastication. The pre-existing mandibular denture was transformed into a c-SIMO on a spherical attachment. The primary outcome was oral health-related quality of life (OHRQoL), measured with GOHAI and OHIP-EDENT. Secondary outcomes included denture satisfaction index (DSI), chewing efficiency (CE), maximum bite force (MBF), implant survival and success, and prosthetic maintenance. Data analysis included descriptive statistics and bivariate comparison tests.ResultsFifteen participants received the c-SIMO treatment (mean age: 69.9 ± 7.0). Implant success and survival rates were 100% at 1 year. Patient-reported outcome measures improved significantly compared to pre-treatment values (OHIP-EDENT: p = 0.001; DSI: p = 0.001; GOHAI: p = 0.002). Masticatory outcomes also improved significantly (CE: p = 0.001; overall MBF: p = 0.005). Post-implant, MBF was significantly higher in the ipsilateral side compared to the contralateral side at 2 weeks (p = 0.019) and 3 months (p = 0.015), but no longer at T3 (p = 0.730). Common prosthodontic events included denture base adjustments (n = 17) and matrix activation (n = 9).ConclusionsThis pilot study concludes that c-SIMO is a promising treatment option, and a potential alternative to the single midline implant overdenture.Clinical relevanceThe novel treatment concept of a canine-positioned single implant mandibular overdenture could be a viable treatment alternative to the midline positioning.

Prolonged use of a soft diet during early growth and development alters feeding behavior and chewing kinematics in a young animal model.

In infants and children with feeding and swallowing issues, modifying solid foods to form a liquid or puree is used to ensure adequate growth and nutrition. However, the behavioral and neurophysiological effects of prolonged use of this intervention during critical periods of postnatal oral skill development have not been systematically examined, although substantial anecdotal evidence suggests that it negatively impacts downstream feeding motor and coordination skills, possibly due to immature sensorimotor development. Using an established animal model for infant and juvenile feeding physiology, we leverage X-ray reconstruction of moving morphology to compare feeding behavior and kinematics between 12-week-old pigs reared on solid chow (control) and an age- and sex-matched cohort raised on the same chow softened to a liquid. When feeding on two novel foods, almond and apple, maintenance on a soft diet decreases gape cycle duration, resulting in a higher chewing frequency. When feeding on almonds, pigs in this group spent less time ingesting foods compared to controls, and chewing cycles were characterized by less jaw rotation about a dorsoventral axis (yaw) necessary for food reduction. There was also a reduced tendency to alternate chewing side with every chew during almond chewing, a behavioral pattern typical of pigs. These more pronounced impacts on behavior and kinematics during feeding on almonds, a tougher and stiffer food than apples, suggest that food properties mediate the behavioral and physiological impacts of early texture modificationand that the ability to adapt to different food properties may be underdeveloped. In contrast, the limited effects of food texture modification on apple chewing indicate that such intervention/treatment does not alter feeding behavior of less challenging foods. Observed differences cannot be attributed to morphology because texture modification over the treatment period had limited impact on craniodental growth. Short-term impacts of soft-texture modification during postweaning development on feeding dynamics should be considered as potential negative outcomes of this treatment strategy.

Contributions of Alveolar Bone Density and Habitual Chewing Side to the Unilateral Failure of Orthodontic Mini-Screws: A Cross-Sectional Study

This study aimed to analyze the relationship between bone density, habitual chewing side (HCS), and mini-screw stability to investigate the intra-individual factors contributing to mini-screw failure. This retrospective study included 86 sides in 43 adults, who underwent bilateral maxillary mini-screw placement with subsequent unilateral failure of the mini-screw. Pre-treatment cone-beam computed tomography was used to measure the buccal cortical bone thickness and bone density on the failed and successful sides. Pre-treatment mandibular kinesiographic records were used to determine the HCS. Paired t-tests, one-proportion z-tests, and multivariable multilevel Poisson regression were used to examine the statistical significance. The buccal cortical bone thicknesses were 0.93 ± 0.27 mm (unsuccessful side) and 1.01 ± 0.27 mm (successful side), with no significant difference. The bone density on the unsuccessful side (1059.64 ± 202.64 mg/cm3) was significantly lower than the success side (1317.89 ± 332.23 mg/cm3). Regarding HCS, 27.9% of failures occurred on the preferred side, and 62.8% occurred on the non-preferred side. After adjusting for all factors, the non-preferred side showed a 2.22 times higher prevalence ratio for mini-screw failure than the preferred side. HCS is significantly related to mini-screw stability, while the cortical bone thickness, bone density, and site of mini-screw implantation were not correlated.

ELECTROMYOGRAPHY AS A METHOD FOR ASSESSING THE EFFECTIVENESS OF ORTHOPEDIC TREATMENT OF PATHOLOGICAL ABRASION OF HARD TISSUES OF TEETH

The combination of pathological wear of the teeth with defects of the dental rows causes significant changes in the maxillofacial complex, which leads to substantial morphofunctional disorders and creates difficulties in the orthopedic rehabilitation of such patients.&#x0D; The combination of pathological tooth wear and defects of the dental rows causes significant changes in the maxillofacial complex, which leads to substantial morphofunctional disorders and creates difficulties in the orthopedic rehabilitation of such patients.&#x0D; Thirty four persons aged from 35 to 60 years with a generalized form of pathological wear of grades I-II, in combination with defects of dentition of classes I, II and III according to Kennedy, were treated. The examination has included the data of the anamnesis, general clinical examination, measuring interalveolar height, study of diagnostic models, X-ray examination, and EMG of the masticatory muscles.&#x0D; The results. The EMG data of the research groups before treatment showed a different degree of the rhythm of chewing movements, a clear alternation of the phases of activity and rest, uneven inclusion of motor units in the contraction process compared to healthy patients, the habitual side of chewing was determined, as a result of which an extension of chewing time, a decrease in its rhythm and chewing efficiency.&#x0D; Thirty days after the appropriate treatment, the electromyographic study showed morphological and functional changes in the maxillofacial apparatus of the patients of the experimental groups, which were reflected in the quantitative indicators of the EMG of the masticatory muscles. In the I group, the EMG parameters significantly approached those in the control group, and in the II group, a tendency to approach the norm was determined.&#x0D; Appropriate orthopedic treatment of pathological attrition, complicated by existing dentition defects, various structures contributed to the emergence of new myotatic reflexes, the creation of a new chewing stereotype.&#x0D; A positive change in EMG indicators, especially the "K" coefficient, and their approach to the indicators of the control group indicates the appropriate choice of the prosthetic method, which will contribute to the process of adaptation to the orthopedic structure and improve the psycho-somatic condition of patients in general.&#x0D; Conclusions. Analyzing the variance in biopotentials of the masticatory muscles enables the evaluation of both the extent and the characteristics of existing disorders in patients with pathological attrition.&#x0D; The positive dynamics of electromyography indicators in the treatment of patients with a generalized form of pathological wear, complicated by defects of the dental rows, indicates the quality of the treatment, the feasibility of choosing an orthopedic structure, and the smoothness of the process of adaptation to it.&#x0D; The future research involves continued monitoring of long-term treatment outcomes, including the potential for determining the duration required for complete adaptation to the orthopedic prosthesis.

The biomechanical effects of bimaxillary osteotomies to the patients with mandibular retraction under incisal clenching.

The purpose of this study is to investigate the biomechanical effect of bimaxillary osteotomies on patients with mandibular retraction. Mandibular retraction, as a typical maxillofacial deformity, and has great adverse effects on TMJ. Bimaxillary osteotomies are widely used to correct symptoms of mandibular retraction. It is necessary to understand the effect of surgery on temporomandibular disc (TMJ). Five patients with mandibular retraction and 10 asymptomatic subjects were involved in this study. Finite element models of preoperative, postoperative and control group were constructed based on the CT data. Nine sets of concentrated forces were used to simulate the muscle effect and contact method was used to simulate the interaction within the TMJs and dentitions. The results showed that bimaxillary osteotomies could effectively improve the maxillofacial morphology and alleviate the overload in TMJ. The facial asymmetry and right chewing side preference could cause imbalanced stress distributions in the TMJs and interfere the surgical treatment.

Chewing Side Preference Related to Food Texture and Occlusal Contact Area.

To determine whether food texture affects chewing side preference (CSP) and to investigate the relationship between CSP and masticatory factors, such as occlusal contact area, bite force, and masticatory performance. Forty-seven adults (20 women and 27 men; mean age: 24 years) participated in this study. Three types of food (chewing gum, beef jerky, and peanuts) were provided to assess CSP. Occlusal contact area was measured at various ranges of interocclusal distance, and the bite force was measured. Masticatory performance was assessed according to the median particle size. Asymmetry indices of each measurement were calculated and analyzed using Pearson correlation coefficient (α &#61; .05). The CSP for beef jerky and peanuts were significantly correlated with each other, whereas the CSP for chewing gum was not correlated with other food. The proportion of participants who chewed equally on both sides was higher for chewing gum than for beef jerky. There was a significant correlation between the CSP for beef jerky and occlusal contact area, especially at interocclusal distance ranges of 0 to 89 μm and 0 to 109 μm (r &#61; 0.41). Bite force and masticatory performance were not significantly correlated with CSP. Food texture seemed to affect CSP, and masticatory laterality was greater for tough foods. Moreover, CSP for tough food was closely related to the occlusal contact area at an interocclusal distance level of about 0.1 mm.

Relationships between maxillofacial morphology and oral function on the habitual and non-habitual chewing sides.

This study aimed to investigate the relationships between reference planes and oral functions on the habitual and non-habitual chewing sides. Thirty-four subjects with no abnormalities in the maxillofacial region and oral functions were enrolled in this study. Relationships between angles between the reference plane (Frankfort horizontal plane, Camper's plane, and occlusal plane) and masticatory performance, occlusal force, and occlusal contact area by chewing side were examined. Regarding the measurement of reference planes, a creatively modified three-plane measuring device was used to measure angles between the reference planes. Images were taken from the right and left sides and angles between reference planes were measured. Masticatory performance was examined by measuring the amount of glucose extracted from a gummy jelly on the habitual and non-habitual chewing sides separately. Occlusal force and occlusal contact area were measured by occluding against pressure-sensitive film, and values on the habitual and non-habitual chewing sides were calculated and analyzed. The angle between Camper's plane and the occlusal plane correlated with masticatory performance on both the habitual chewing side (r = 0.47, P < .01) and the non-habitual chewing side (r = 0.36, P < .05). A correlation was observed between masticatory performance and occlusal force on the habitual chewing side (r = 0.46, P < .01). Masticatory performance became higher as occlusal plane inclination increased. This result represents essential knowledge for prosthetic treatment.

Визначення схильності до прогресування дисфункції скронево-нижньощелепного суглоба на підставі морфометрії

Actuality. The temporomandibular joint diagnosis includes the computer tomography analysis. This research method is extremely common, and as a rule, it is used during the stages of orthodontic treatment of gnathological patients and is actually more accessible in comparison with magnetic resonance imaging (MRI). The information obtained during the TMJ computer tomograms analysis, while making up an orthodontic plan, orthopedic treatment, can affect the sequence of occlusal rehabilitation stages. The aim. To determine the morphometric parameters of the TMJ structure in which dysfunction accompanied by limited opening of the mouth occurs most often by means of analysing computer tomograms. Materials and methods. The width of the glenoid fossa and condylar head inclination were measured on computer tomograms in 91 subjects with limited mouth opening due to temporomandibular joint dysfunction. A general clinical examination was carried out, which included identification of the dominant side of chewing, previously existing clicking in the temporomandibular joint, which was revealed during the interview. Results. The largest number of examinees with temporomandibular joint dysfunction due to the limited mouth opening, had a width of the condylar head from 3.5–4.4 mm to 7.5–8.4 mm condylar head inclination angle from 53 to 72° (47.2%), and the smallest from 4.5–5.4 mm to 11.5–12.4 mm at an condylar head inclination angle from 85 to 93° (18.6%). Unilateral type of chewing was found in 41 (45%) of the examined, and clicking in the temporomandibular joint, which existed before the appearance of jamming, was confirmed by interviewing of 39 (42.8%) patients. Conclusions. The maximum width of temporomandibular joint, at which the condylar head inclination angle from 53 to 72° is detected on TMJ computer tomograms is 8.4 mm within patients with temporomandibular joint dysfunction, which is determined by the presence of limited opening of the mouth. Keywords: limited mouth opening, temporomandibular joint, computer tomography.

MATHEMATICAL SUBSTANTIATION OF BIOMECHANICAL BASES OF PATHOLOGICAL WEAR OF HARD TISSUES OF TEETH

Using the Bernoulli principle, the muscles that raise, laterally shift, and advance the mandible were studied. The biomechanical component of the pathogenesis of pathological tooth abrasion was revealed. The role of "fast" and "strong" muscles in the process of excessive abrasion of hard tissues is revealed. Applying the Bernoulli principle to the study of muscles, the ratio of muscle length to its cross-sectional area was expressed mathematically in terms of coefficients. The average values of the coefficients of the same muscles in the control group on the priority and secondary sides differ insignificantly, which indicates a balanced work: the muscles are equally "fast" and equally "strong". Compared to the control group, the first group of patients showed a tendency to a more pronounced difference in the physical qualities of the muscles: strength begins to prevail in some, and speed in others. Clinically, this is manifested at the initial stage of abrasion of hard tooth tissues. A decrease in the temporalis and masseter muscle coefficients in the second group compared to the control group indicates a decrease in muscle length. The gradual increase in the ratios of the wing-shaped lateral muscle from the first to the second group on both the priority and secondary sides of chewing indicates its greater length relative to the cross-sectional area, and therefore, the acquisition of the quality of "speed". In patients of the third group, the difference in the ratio coefficients with the control group and between the priority and balancing sides is more pronounced. Increasingly, the temporalis and masseter muscles acquire the physical quality of "strength", and the wing-like muscles "speed". It is noteworthy that the coefficients of the wing-shaped muscles in patients of the second and third groups on the secondary side are increased compared to the priority side of chewing. Violation of the balance between the physical qualities of the muscles "strength" and "speed" affects the development of pathological tooth abrasion.

Is There A Relationship Between Chewing Side Preference and Brain Laterality in Bruxers and Non-Bruxers?

Objective: There is no consensus on the etiology of unilateral mastication. While some studies argue that environmental factors such as missing teeth, teeth with restoration, pain, dental caries and temporomandibular disorder affect chewing side preference, others claim that brain laterality associated with hand, foot, ear and eye preferences also influences a chewing side preference. The aim of this study was to evaluate the relationship between the direction of unilateral chewing preference and brain laterality in fully dentate bruxers and non-bruxers (fully dentate or with missing and/or restored teeth).&#x0D; Methods: Brain laterality of the subjects (n=132) was determined based on responses to questions about extremity and sensory preferences. The reliable visual analogue scale (VAS), Kazazoglu’s method and the sunflower seed shell cracking test were used to determine chewing side preference (CSP).&#x0D; Results: CSP as determined by VAS was not associated with brain laterality. While extremity and sensory preferences were predominantly right-sided (dominant left hemisphere) in all groups, the frequency of the left-side chewing was found to be high only among bruxers (p&gt;0.05). No significant association was found between the results of VAS and other techniques (p&gt;0.05). &#x0D; Conclusion: The left-side CSP is observed more commonly in bruxers, suggesting that different central and peripheral mechanisms may be involved in bruxers.

Three tests to determine a preferred chewing side in partially edentulous patients: A pilot study

Determining the preferred chewing side may be an important factor in prosthetic treatment planning, especially where additional support for a removable dental prosthesis can be provided by implants. The purpose of this clinical study was to investigate the validity and reproducibility of 3 different tests to determine the preferred chewing side. A total of 82 partial denture wearers, with an average age of 70 years, were enrolled in this study. The first test (CG) evaluated the left or right position of a piece of chewing gum after spontaneous mouth opening during mastication. A second test (ASI) videotaped 30 seconds of mastication and analyzed the distribution of masticatory cycles by means of an asymmetry index. For the third test (VAS), participants were asked to mark their subjective perception of their preferred chewing side on a visual analog scale representing the right and left sides. All the tests were performed and repeated in a randomized sequence. The reproducibility of the tests was first evaluated. The mean values of the ASI and VAS tests were calculated, and the results were compared with the second series of the CG test. The Pearson correlation test was used to associate ASI and VAS, and the Cohen kappa agreement was used for the inter-reliability of CG (α=.01). The results indicated fair to almost perfect reproducibility for the 3 tests. Kappa values were.37 (P<.01) for the CG,.47 (P<.01) for the ASI and.91 (P<.01) for the VAS. Correlation coefficients resulted in rho=.86 (P<.01) for the ASI and rho=.97 (P<.01) for the VAS. The correlation between ASI and VAS was excellent, with rho=.85 (P<.010). CG and ASI (test kappa=.36, P<.010) and CG and VAS (test kappa=.39, P<.010) showed fair agreement. ASI and VAS seem more reliable than CG to determine a patient's preferred chewing side and might be helpful within the context of prosthetic treatment planning, where additional support may improve denture function.

Synchronous Muscle Synergy Evaluation of Jaw Muscle Activities during Chewing at Different Speeds, a Preliminary Study.

Human mastication is a complex and rhythmic biomechanical process regulated by the central nervous system (CNS). Muscle synergies are a group of motor primitives that the CNS may combine to simplify motor control in human movement. This study aimed to apply the non-negative matrix factorization approach to examine the coordination of the masticatory muscles on both sides during chewing. Ten healthy individuals were asked to chew gum at different speeds while their muscle activity was measured using surface electromyography of the right and left masseter and temporalis muscles. Regardless of the chewing speed, two main muscle synergies explained most of the muscle activity variation, accounting for over 98% of the changes in muscle patterns (variance accounted for >98%). The first synergy contained the chewing side masseter muscle information, and the second synergy provided information on bilateral temporalis muscles during the jaw closing. Furthermore, there was robust consistency and high degrees of similarity among the sets of muscle synergy information across different rate conditions and participants. These novel findings in healthy participants supported the hypothesis that all participants in various chewing speed conditions apply the same motor control strategies for chewing. Furthermore, these outcomes can be utilized to design rehabilitation approaches such as biofeedback therapy for mastication disorders.

Trigeminal Stimulation and Visuospatial Performance: The Struggle between Chewing and Trigeminal Asymmetries.

Chewing improves visuospatial performance through locus coeruleus (LC) activation. The effects of bilateral and unilateral mastication were investigated in subjects showing different degrees of asymmetry in masseter electromyographic (EMG) activity during clenching and in pupil size at rest (anisocoria), which is a proxy of LC imbalance. Correlations between performance changes and asymmetry values were found in males, but not in females. Among males, subjects with low asymmetry values (balanced-BAL) were more sensitive than those with high asymmetry values (imbalanced-IMB) to bilateral and unilateral chewing on the side with higher EMG activity (hypertonic). The opposite was true for hypotonic side chewing. BAL subjects were sensitive to unilateral chewing on both sides, while in IMB subjects, hypertonic side chewing did not influence performance in either males or females. Bilateral chewing elicited larger effects in BAL subjects than in IMB subjects, exceeding the values predicted from unilateral chewing in both groups. Finally, pupil size and anisocoria changes elicited by chewing were correlated with asymmetry values, independent of sex. Data confirmed the facilitation of visuospatial performance exerted by chewing. Trigeminal asymmetries modulate the chewing effects, making occlusal rebalancing an appropriate strategy to improve performance.

The Effect of Asymmetrical Occlusion on Surface Electromyographic Activity in Subjects with a Chewing Side Preference: A Preliminary Study.

The relationship between asymmetrical occlusion and surface electromyographic activity (sEMG) in people with different chewing preferences is not clear. In this study, the 5 s sEMG changes in the masseter muscle (MM), sternocleidomastoid (SCM), lateral (LGA), and medial (MGA) gastrocnemius muscles were recorded in controls, and subjects with chewing side preference (CSP) during clench with bilateral (BCR), left (LCR), and right (RCR) posterior teeth placement of cotton rolls. The images of the middle 3 s were selected and expressed as the root mean square (unit: μV/s). The EMG waves of bilateral muscles were compared by computing the percentage overlapping coefficient (POC). Only the POCMM of the CSP showed gender differences at BCR and RCR. Between the control group and the CSP group, there were significant differences in the POCMM and the POCLGA at BCR. In addition, there was a significant difference in POCMM and POCSCM between the two populations in different occlusal positions. The change in the POCSCM correlated with the change in the POCMM (r = 0.415, p = 0.018). The experiment-induced asymmetrical occlusion showed that the altered symmetry of the MM correlated with the altered symmetry of the SCM. Long-term asymmetrical occlusion (i.e., CSP) not only affects MM but also has potential effects on other superficial muscles (e.g., LGA).