Changes In Masticatory Function Research Articles

Masticatory function and three-dimensional facial morphology of soft tissues: One year after orthognathic surgery

ObjectiveDentofacial deformities (DFD) require orthodontic treatment, orthognathic surgery, and speech therapy for aesthetic and functional problems. This longitudinal study analyzed changes in masticatory function and three-dimensional (3D) facial soft tissue in patients with Class II and Class III DFD after orthognathic surgery. In addition, the study investigated the relationship between facial measurements, maximum bite force (MBF), and orofacial myofunctional status (OMS). DesignThe sample consisted of 46 participants, including 10 patients with Class II DFD, and 11 patients with Class III DFD. These groups were assessed before (T0) and 6 months (T1) after surgery. Twelve patients who completed the treatment protocol were evaluated 12 months post-surgery (T2). The patient groups were compared with each other and with a control group (CG) of 25 healthy subjects. The participants underwent MBF and clinical evaluation of OMS, including masticatory behavior, using a validated protocol. The 3D facial soft tissue was assessed using laser scanning. ResultsCompared to the CG, DFD patients showed reduced MBF, masticatory behavior, and OMS scores at T0. At T2, there was an improvement in MBF, masticatory, and OMS scores, but differences were observed compared to the CG. Changes in facial soft tissue followed the underlying hard tissue movement resulting from surgery, and reduction of vertical measurements contributed to improvements in masticatory function. ConclusionThese findings indicated that combined surgery, orthodontic treatment, and speech therapy can lead to a significant improvement in masticatory function and facial soft tissue in DFD patients, although not completely 12 months post-surgery.

Structural brain feature is associated with changes of masticatory performance in healthy elderly people: Evidence from longitudinal neuroimaging research over two years.

Human neuroimaging studies have revealed the association between brain structure and masticatory function. However, the majority of the studies adopted a cross-sectional design, which hardly reveals the change in masticatory function and brain structure between different timepoints, and the dynamical association between changes in masticatory function and changes in brain structure has not been elucidated. With a longitudinal design, we assessed the association between changes in masticatory performance (MP) and regional brain volume. Twenty-two elderly participants received assessments of the number of missing teeth and MP (via colour-changeable chewing gum) when they entered the study (i.e. the initial stage, T0 ), approximately 6 months later (T0.5 ), and approximately 1-2 years later (T1 ). Difficulty of food intake was assessed using a questionnaire. The participants received magnetic resonance imaging (MRI) at T0 and T1 . The brain volume of the motor-related area was estimated using FreeSurfer for MRI data. The associations between different stages were analysed using Spearman's rho correlation coefficients. (1) Individually, a smaller volume of right primary motor cortex at T0 was associated with increased MP from T0 to T1 , suggesting the brain's role in changing oral functions; (2) higher MP at T0 was associated with an increased volume of the left superior frontal cortex from T0 to T1 p, suggesting a potential effect on brain plasticity, and (3) increased difficulty to eat was associated with decrease MP but not brain volume of motor-related area. The preliminary findings revealed a complicated pattern of structural brain features and masticatory function in elderly people, and either the hypothesis that the brain predisposes masticatory function or the hypothesis that mastication reshapes the brain is oversimplified.

Short-term and long-term outcomes of zirconium dioxidebased dental restorations, and it effects on masticatory function

Purpose: To investigate the short- and long-term outcomes of zirconium dioxide-based restorations (ZDBR), and changes in masticatory function (MF).Methods: One hundred and two (102) patients who received restorative dentistry procedures were divided into two groups using random number method: control group (CG, n = 52, alloy-based restorations) and study group (SG, n = 50, zirconium dioxide restorations). Treatment efficacy, quality, levels of IL-8 and IL-6 in gingival sulcus fluid, and satisfaction scores were compared.Results: The SG showed better outcomes and restoration quality than CG. After restoration, SG showed greater decrease in IL-8 and IL-6 levels than CG (p < 0.05), while IL-8 and IL-6 levels were higher in SG and CG than those before restoration (p < 0.05). After 1 and 6 months of restoration, SG showed increased dental appearance satisfaction and a higher success rate than CG (p < 0.05). Occlusal force and MF were significantly improved in both groups (p < 0.05). Gingival index, bleeding index, plaque index, and tooth looseness after restoration significantly improved in both groups, but were lower in SG than in CG (p < 0.05).Conclusion: In oral restorations, ZDBR is more effective in terms of short-term and long-term outcomes. Patients' occlusal force and MF are better restored, and patients' quality of life is also significantly improved. Therefore, ZDBR in oral restorations is feasible but further clinical trials are required.

Evaluation of masticatory behavior and taste sensitivity after pacifier removal in preschool children: a 1-year follow-up.

The aim was to investigate the influence of pacifier removal on the development of masticatory function and taste sensitivity in preschool children. Sixty children (mean age 48.2months) were divided into two groups: pacifier group (n = 28) and a control group (n = 32), which were evaluated and followed up for a period of 12months (at baseline, 6months, and 1year). Masticatory and swallowing functions were assessed using the Mastication Observation and Evaluation (MOE) protocol and Orofacial Myofunctional Rating (MBGR), respectively. Detection thresholds for sucrose and urea were measured by the staircase method. The two-way ANOVA mixed model was used for time*group interaction analysis. MOE scores improved significantly over time in both groups, although a significant difference between groups persisted after 1year. On the other hand, swallowing scores were significantly different at baseline, but within 1year, the scores were no longer different between groups. Chewing time and the number of cycles were not different between groups and both decreased after 1year. Sucrose sensitivity was significantly greater in the control group at baseline and changed over time (p < 0.05), being no longer different between groups after 6months. Bitter sensitivity did not differ over time nor between groups. Detection threshold for sucrose differed significantly between children with and without pacifier habit at a mean age of 42months. Total masticatory function did not self-correct after sucking habit removal within a 1-year period. Children with pacifier habit showed important changes in masticatory function that did not self-correct 1year after cessation of the habit, highlighting the need for prevention and habit interruption as early as possible.

The Impact of Masticatory Function on Cognitive Impairment in Older Patients: A Population-Based Matched Case-Control Study.

PurposeThe aim of this study was to investigate the association between the changes in masticatory function and cognitive impairment by analyzing longitudinal data of older Korean patients.Materials and MethodsPatients aged over 60 years with dental records between 2005 to 2010 (baseline; T1) and 2014 to 2020 (follow-up; T2) were selected in a single medical center. Based on the dementia diagnosis after T2, the cohort was classified into two groups, the dementia group (n=122) and the control group (n=366). Changes in masticatory function were calculated using the total functional tooth unit (T-FTU) in both groups. The incidence of tooth extraction (%) and the subsequent rehabilitation during the observation period were also evaluated.ResultsIn the dementia group, T-FTU significantly decreased from T1 to T2 (9.81±2.78 to 9.11±3.16, respectively, p=0.008), while no significant change was observed in the control group. During the mean observation period of 9 years, significantly more teeth were extracted and neglected to be prosthetically restored in the dementia group than in the control group. Regression analysis revealed that the number of missing teeth neglected [odds ratio (OR)=1.195, 95% confidence interval (CI)=1.025–1.393, p=0.023] and previous alcohol consumption (OR=4.445, 95% CI=1.831–1.795, p=0.001) were the most significant risk factors of dementia.ConclusionThere might be a causative relationship between the neglected missing dentition and the onset of dementia.

Masticatory function after comprehensive dental treatment in children with severe early childhood caries.

Parents are frequently concerned that their child's mastication may be compromised after comprehensive dental treatment. To evaluate changes in masticatory function and food preferences after dental treatment in children with early childhood caries. This prospective study assessed masticatory function with the (1) mixing ability test using duo-coloured chewing gum and (2) the number of chews/g and time taken to eat six food items before and 3months after dental treatment. A dental examination and a food preference questionnaire were also completed. Twenty-five children (age: 4.9±0.5years, baseline dmft/child: 11.4±4.9) completed the study. The mean number of restorations/child, total extractions/child, and posterior extractions/child was 5.1±2.9, 6.4±5.2, and 3.6±2.3, respectively. The number of chews/g of cereal (p=.014) and popcorn (p=.003) significantly increased after dental treatment. The number of chews/g and duration taken for cereal (chews/g: r=0.795, p=.000, duration: r=0.794, p=.000) and peanuts (chews/g: r=0.459, p=.032) were significantly associated with more extractions. There was no change in mastication function for the other foods, mixing ability score, and child's food preferences after dental treatment. An increased number of chews/g is needed for certain hard foods after dental treatment, which was associated with an increased number of total and posterior extractions.

Masticatory function and oral health-related quality of life of patients with atrophic and non-atrophic mandibles using implant-retained mandibular overdentures: 3-year results of a prospective clinical study.

Long-term changes in masticatory function, oral health-related quality of life (OHRQoL) and prosthetic complications in implant-retained mandibular overdenture (IMO) wearers as a function of bone atrophy require detailed investigations. Investigating the evolution of masticatory function, OHRQoL and prosthetic occurrences of IMO wearers according to mandibular bone atrophy over 3years of usage. This study evaluated 26 IMO wearers after 2 and 3years of IMO loading categorised according to mandibular resorption degree into atrophic mandible (AM) and a non-atrophic mandible (NAM) group. Masticatory function was assessed by the Masticatory Performance (MP) and Swallowing Threshold (ST) tests; OHRQoL and satisfaction via the Dental Impact on Daily Living (DIDL) questionnaire; and the prosthetic maintenance requirements and complications were monitored. After the second year, the AM Group performed 32% more cycles (P=.047) than the NAM Group during the ST test. The DIDL questionnaire showed no significant difference for all domains, except for a moderate effect size in the General Performance domain after the third year. AM Group had more prosthetic occurrences (n=109) than NAM Group (n=60) in the first year, mainly due to Equator attachment dislodgment. During the third year, NAM Group presented a greater number of events (n=45) than AM Group (n=21) due to the greater number of O-ring exchanges. Masticatory function and OHRQoL are not related to mandibular bone atrophy until 3years after IMO rehabilitation. The prosthetic complications profile differs between groups, mainly in the first year.

Assessment of masticatory function of mandibular implant-supported overdenture wearers: A 3-year prospective study

Statement of problemWearers of mandibular complete dentures (CDs) often complain of retention and stability problems resulting in poor masticatory function. Evidence suggests that a mandibular overdenture (MOD) stabilized by 2 implants represents the treatment of choice to improve stability and masticatory function. Measurements are needed of the improvement in masticatory function after providing mandibular implant-stabilized overdentures. PurposeThe purpose of this prospective clinical study was to evaluate the changes in masticatory function from baseline (T0) to 3 months (T1) and 3 years (T2) in participants with MODs and to assess the effect of baseline mandibular bone height and volume on masticatory function after 3 years. Material and methodsParticipants were assessed for masticatory function by using masticatory performance involving paraffin wax cubes as an objective measure and by using masticatory ability involving a questionnaire as a subjective measure. Edentulous individuals presenting for replacement dentures were provided with conventional mucosa-supported prostheses and evaluated for masticatory function after a 3-month settling-in period (baseline measure). Before implant placement, baseline measures of bone height and volume were recorded from cone beam computed tomography (CBCT) images. The prostheses were then converted to implant-stabilized mandibular overdentures while any maxillary prostheses remained supported by the mucosa. Masticatory function was reassessed at 3 months and 3 years after insertion of the mandibular overdentures, and the mean changes from baseline were analyzed with the Wilcoxon signed-rank test. The effect of variables on masticatory function was determined by using multivariate linear regression analyses. ResultsA total of 23 participants were included in the study, with only 1 participant not completing the 3-year assessment. Significant improvement was observed in the masticatory performance (mixing ability index) (P<.01) and masticatory ability score (P<.001) from baseline to 3 months and baseline to 3 years. Bone height and volume had no significant effect on the improvement of masticatory function after conversion to an implant-stabilized mandibular overdenture. ConclusionsMasticatory function significantly improved after 3 months and was maintained over 3 years in participants with implant-stabilized mandibular overdentures. However, baseline bone height and volume had no significant effect on these changes in masticatory function after 3 years

Congenital muscle dystrophy and diet consistency affect mouse skull shape differently.

The bones of the mammalian skull respond plastically to changes in masticatory function. However, the extent to which muscle function affects the growth and development of the skull, whose regions have different maturity patterns, remains unclear. Using muscle dissection and 3D landmark-based geometric morphometrics we investigated the effect of changes in muscle function established either before or after weaning, on skull shape and muscle mass in adult mice. We compared temporalis and masseter mass and skull shape in mice with a congenital muscle dystrophy (mdx) and wild type (wt) mice fed on either a hard or a soft diet. We found that dystrophy and diet have distinct effects on the morphology of the skull and the masticatory muscles. Mdx mice show a flattened neurocranium with a more dorsally displaced foramen magnum and an anteriorly placed mandibular condyle compared with wt mice. Compared with hard diet mice, soft diet mice had lower masseter mass and a face with more gracile features as well as labially inclined incisors, suggesting reduced bite strength. Thus, while the early-maturing neurocranium and the posterior portion of the mandible are affected by the congenital dystrophy, the late-maturing face including the anterior part of the mandible responds to dietary differences irrespective of the mdx mutation. Our study confirms a hierarchical, tripartite organisation of the skull (comprising neurocranium, face and mandible) with a modular division based on development and function. Moreover, we provide further experimental evidence that masticatory loading is one of the main environmental stimuli that generate craniofacial variation.

Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry

This study aimed to evaluate the postoperative changes in masticatory function in patients with jaw deformities with or without asymmetry treated by orthognathic surgery. Thirty female patients who underwent a Le Fort I osteotomy with sagittal split ramus osteotomy (SSRO) were enrolled. The patients were divided into symmetry and asymmetry groups. The bite force, occlusal contact area, and bite force balance were measured before and at 1, 3, and 6 months and 1 year after surgery; these measurements were compared statistically within and between the two groups. In the symmetry group, there was a significant difference in the preoperative bite force and the 1 month postoperative bite force (P=0.0033). In the asymmetry group, the bite force before surgery was significantly different from that at 1 month (P=0.0375) and at 1 year (P=0.0353) after surgery. Significant differences in the bite force were also observed between the following time points: 1 month and 1 year (P=0.0003), 3 months and 1 year (P=0.0034), and 1 month and 6 months (P=0.0486). The occlusal contact area, bite force, and occlusal balance tended to change after Le Fort I osteotomy with SSRO, with a significantly improved bite force in patients with asymmetry before surgery.

Changes in masticatory function after injection of botulinum toxin type A to masticatory muscles

This study examined changes in masticatory function after botulinum toxin type A (BTX-A) injection using objective and subjective tests during 12weeks. Also, we compared differences in masticatory function between group in which only masseter muscle (M group) was injected and group in which masseter and temporal muscle (M-T group) were injected. Forty subjects were assigned into two groups; M group (n=20) and the M-T group (n=20). The Meditoxin(®) was used as BTX-A injection. The mixing ability index (MAI) was used as the objective indicator, and visual analogue scale (VAS) and food intake ability (FIA) index were used as subjective indicators. Overall, the masticatory function drastically declined after 4weeks and gradually recovered with time. Compared with the pre-injection state, the masticatory function decreased by 89·2% (MAI), 12·2% (FIA) and 32·2% (VAS) 4weeks after the injection (P<0·05). When the results between M group and M-T group were compared, scores of VAS and FIA were significantly different 4weeks after the injection (P<0·05), but the MAI score showed no significant difference between two groups. In conclusion, this study showed that masticatory function was significantly decreased after BTX-A injection into the masticatory muscle after 4 and 8weeks from injection. However, masticatory efficiency measured using MAI could completely recover after 12weeks. Furthermore, after 8weeks from the injection, the masticatory function measured after injection into only the masseter muscle was similar to that measured after injection into both masseter and temporal muscle.

Comparative Feeding Biomechanics of Lystrosaurus and the Generalized Dicynodont Oudenodon

Differences in cranial morphology among the Dicynodontia have been correlated with changes in masticatory function, and hence, dietary preference. Although the derived masticatory apparatus of dicynodonts allowed propaliny, it has previously been hypothesized that Lystrosaurus primarily utilized powerful orthal jaw movements to process fibrous vegetation. Cranial specializations of Lystrosaurus, such as shortened and deepened cranium and a mobile premaxilla-nasal suture, are thought to have increased the efficiency of its masticatory system compared with generalized Permian dicynodonts. Here we aim to test this assertion using biomechanical modeling techniques. We use finite element analysis (FEA) and a study of cranial functional morphology to compare the biomechanical performance of the crania of Lystrosaurus and Oudenodon, a generalized dicynodont, during orthal bite simulations. Muscle forces were estimated for each dicynodont using the dry skull method and applied to each cranium to produce a reaction force at a bite point. Patterns and average magnitude of Von Mises stress in each dicynodont cranium and in segmented regions of interest were assessed. During orthal bite simulations, higher stress occurs throughout the Oudenodon cranium, indicating that the cranium of Lystrosaurus is more resistant to normal, static feeding loads. Despite this difference in stress magnitude, patterns of stress are similar within both taxa. The FE-stress results, along with mechanical advantage of adductor musculature, a broad symphyseal contact, and other cranial features suggest that Lystrosaurus may have used a snapping bite to cope with tough fibrous vegetation.

Effect of implant-supported or retained dentures on masticatory performance: A systematic review

While subjective patient-based measures have been increasingly recognized as critical outcomes for prosthodontic treatment, there continues to be a need to validate for patients what changes in masticatory function can be expected with the provision of new implant-supported or retained dentures. The purpose of this review was to evaluate the critical factors impacting change in masticatory performance following the provision of new implant-supported or retained dentures. Information retrieval followed a systematic approach using PubMed and the Cochrane Library. English articles published from 1966 to June 2007, in which the masticatory performance of subjects with implant-supported or retained dentures was assessed by objective methods and compared to performance with conventional dentures, were included. Ratings of the evidence provided in each article followed United States Agency for Healthcare Research and Quality recommendations. From 281 articles identified, 18 peer-reviewed articles met prespecified criteria for inclusion. Specific outcomes of significance identified by these articles rated as level II are: (1) fixed implant-supported partial dentures do not provide significant improvement in masticatory performance compared to conventional removable partial dentures for Kennedy Class I and II partially edentulous mandibles; (2) the combination of a mandibular implant-supported or retained overdenture (IOD) and maxillary conventional complete denture (CD) provides significant improvement in masticatory performance compared to CDs in both the mandible and maxilla for a limited population having persistent functional problems with an existing mandibular CD due to severely resorbed mandible; and (3) the type of implant and attachment system for mandibular IODs has a limited impact. Specific outcomes of significance identified by articles rated as having a moderate level of evidence (level III) are: (1) mandibular fixed implant-supported complete dentures provide significant improvement in masticatory performance compared to mandibular CDs in subjects dissatisfied with their CDs; and (2) implant-supported mandibular resection dentures have an advantage over conventional dentures in masticatory performance on the defect side of the mouth. Objective benefits in masticatory performance of implant-supported or retained dentures compared to conventional dentures are limited to a mandibular IOD in edentulous patients with a resorbed mandible and/or difficulty adapting to CDs.

Poster 199: Changes in Masticatory Function After Surgical Orthognathic Treatment in Patients With Jaw Deformities: Efficay of Masticatory Exercise Using Chewing Gum

Recovery of masticatory function is one of the important objectives of orthognathic surgery. In the present study, changes of masticatory function after surgery and efficacy of masticatory exercise were evaluated longitudinally in 41 patients in whom jaw deformities were surgically corrected and masticatory exercise using chewing gum were conducted for five minutes two times a day for 90 days. The findings of masticatory function were compared with those of 20 control subjects with normal occlusion and those of 15 patients in whom jaw deformities were surgically corrected and masticatory exercise were not conducted. Masticatory efficiency was measured using ATP granules, and the number and area of occlusal contacts and maximum occlusal force were evaluated by Occlusal Prescale, and subjective feeding abilities were evaluated by questionnaires.Measurements were performed three times, namely before surgery, and six months and one year after surgery. The mean masticatory efficiency in the patients with high executing rates of masticatory exercise was increased postoperatively to the same level as control group, but that in the patients with low executing rates of masticatory exercise was low and at the same level as the patients without masticatory exercise. On the other hand, improvement rates of the number and area of occlusal contacts were not correlated with executing rate of masticatory exercise. Subjective feeding abilities were considerably improved postoperatively in all patients. In conclusion, it is considered that masticatory exercise using chewing gum after orthognathic surgery is effective to improve maximum occlusal force and masticatory efficiency in the patient with jaw deformity and should be integrated into the treatment.

Changes in masticatory function after orthognathic treatment in patients with mandibular prognathism

Changes in masticatory function were measured in 27 patients in whom mandibular prognathism was corrected surgically. The mean value of masticatory efficiency before treatment was 46% of that of control subjects with normal occlusion. It improved, but remained at 60% of the control value postoperatively. Similar changes were seen in the number and area of occlusal contacts and the integrated muscle activities of the masseter and temporalis on the chewing side, but the postoperative improvement in masticatory efficiency was mainly the result of improvement in masseter activity. The mean values of masticatory cycle variables in the patient group did not differ significantly from those of the controls. Their preoperative mean coefficients of variation, which were significantly higher than those of the controls, decreased significantly postoperatively. These results suggest that the stability of masticatory rhythm was improved by orthognathic surgery.

A clinical and physiological evaluation of the unilateral occlusal deficit and its RPD treatment--a four-year follow-up study

The aim of this study was to evaluate the longitudinal clinical and physiological changes in masticatory function for unilateral shortened arch, partially edentate patients by treatment with removable partial denture prostheses from the denture insertion over approximately four years of observation. The present follow-up study was conducted using objective findings and standpoints of unilateral occlusal deficit case, especially the clinical and physiological relation between musculature activity and changes of load center location periodically. The changes in masticatory functions by the muscle activity observed in EMG, and the occlusal loads and distributions throughout the arc, were surveyed by the modified Prescale system. The findings were statistically analyzed by using a sophisticated computer system that was developed by our research institute. The results were as follows: i) The functional musculature of unilateral shortened arc patients was clearly activated by using the unilateral RPD, and the improvements continued for four years after initial denture insertion. ii) The activation of masticatory muscle by denture-wearing over time, was in edentate side masseter, although the amplification of anterior temporal muscle was distinct in mandibular cases. iii) The muscle activity during rhythmical motion, such as tapping with denture-wearing, increased about two times than that of two and three years from the starting edentate value similarly to the clenching values within the measured period. iv) The masticatory efficacy of unilateral free end saddle prosthodontics was estimated using the changes in I-EMG values during peanut mastication. These findings suggested that the use of RPD accomplished an arc form and improved masticatory function for agglomeration of foods and masticatory efficiency over time.

Changes in masticatory mandibular movements in growing individuals: a six-year follow-up

The pattern of mandibular movement during chewing is influenced by several central and peripheral factors. The aim of the present study was to determine whether changes in masticatory function, characterized by mandibular velocity and displacement, occurred during individuals' normal growth. Forty-seven children, 9-15 years of age, were followed over a 6-year period. All had an Angle Class I occlusion with no obvious orthodontic problems. Oral motor function with respect to mandibular displacement, duration, and velocity was monitored 3-dimensionally with an opto-electronic method. The chewing cycle was divided into an opening, closing, and occlusal phase. Total body height was measured. During the follow-up period, all masticatory variables except the 3-dimensional opening distance showed significant changes. The total chewing cycle duration, the opening and occlusal time of the chewing cycle, and the 3-dimensional closing distance increased during the growth period, while the closing time of the chewing cycle, the 2-dimensional lateral and vertical distances and both the opening and closing velocity decreased. The children who grew proportionally most in height during the 6-year period, i.e. the youngest children in the group studied, showed a significantly larger decrease in the opening velocity. From this study it becomes evident that the variables of the chewing cycle undergo a continuous process of change during growth. This is possibly a reflection of anatomical changes, maturation of the central nervous system, and altered functional demands.

Human mastication modulated by experimental trigeminal and extra‐trigeminal painful stimuli

summary This paper describes the modulation of human deliberately unilateral mastication by trigeminal and extra‐trigeminal standardized painful stimuli. Series with 15 s of gum‐chewing before induction of pain, during pain and after pain were quantitatively assessed by jaw‐closing muscle electromyography (EMG) and kinematics of the lower jaw. Four different painful stimuli were used: cold stimulation of the frontal region, cold stimulation of the dominant hand, capsaicin stimulation of the hard palate, and pressure painm stimulation of the temporomandibular joint (TMJ). Intensity and quality of perceived pain were rated on visual analogue scales (VAS) and McGill's Pain Questionnaires (MPQ). Analysis of the data showed that frontal cold stimulation was the least painful test and was associated with the fewest changes in masticatory function. Cold stimulation of the hand and palatal capsaicin stimulation caused significant increases in peak amplitudes of EMG bursts from all jaw‐closing muscles and faster jaw movements whereas TMJ pressure pain produced significantly lower peak EMG amplitudes. The present results suggest that nociceptive input from different tissues and even extra‐trigeminal regions may modulate trigeminal motor function in selective ways. Thus, clinical observations of changes in masticatory function may not always be due to pain in the orofacial region and therefore do not necessitate orofacial treatment.

Human mastication modulated by experimental trigeminal and extra-trigeminal painful stimuli.

This paper describes the modulation of human deliberately unilateral mastication by trigeminal and extra-trigeminal standardized painful stimuli. Series with 15 s of gum-chewing before induction of pain, during pain and after pain were quantitatively assessed by jaw-closing muscle electromyography (EMG) and kinematics of the lower jaw. Four different painful stimuli were used: cold stimulation of the frontal region, cold stimulation of the dominant hand, capsaicin stimulation of the hard palate, and pressure pain stimulation of the temporomandibular joint (TMJ). Intensity and quality of perceived pain were rated on visual analogue scales (VAS) and McGill's Pain Questionnaires (MPQ). Analysis of the data showed that frontal cold stimulation was the least painful test and was associated with the fewest changes in masticatory function. Cold stimulation of the hand and palatal capsaicin stimulation caused significant increases in peak amplitudes of EMG bursts from all jaw-closing muscles and faster jaw movements whereas TMJ pressure pain produced significantly lower peak EMG amplitudes. The present results suggest that nociceptive input from different tissues and even extra-trigeminal regions may modulate trigeminal motor function in selective ways. Thus, clinical observations of changes in masticatory function may not always be due to pain in the orofacial region and therefore do not necessitate orofacial treatment.

Jaw morphology and function in living and fossil old world monkeys

This allometric investigation on a sample of 29 cercopithecine and 22 colobine taxa augments the data and implications of prior work on subfamilial variation in mandibular form and function in recent Cercopithecidae. To increase the size range encompassed by living cercopithecines and colobines, I included many of the larger-bodied fossil specimens. These analyses serve to fill a gap in our understanding of size-related changes in masticatory function and symphyseal morphology and curvature in extant and extinct Old World monkeys. Results of subfamilial scaling comparisons indicate that for a given jaw length, colobines possess significantly more robust corpora and symphyses than those of cercopithecines, especially at smaller sizes. Following from previous work, the most plausible explanation for why the subfamilies differ in relative corporeal and symphyseal dimensions is that colobine mandibles experience elevated loads and greater repetitive loading during mastication due, on average, to processing a diet of tough leaves and/or seeds. Although colobines have relatively larger symphyses, subfamilial analyses of symphyseal curvature demonstrate that they evince less symphyseal curvature vis-a-vis cercopithecines of a common size. Moreover, both subfamilies exhibit similar allometric changes in the degree of curvature, such that larger-bodied Old World monkeys have more curved symphyses than those of smaller taxa. Subfamilial scaling analyses also indicate that colobines possess a shorter M2 bite-point length relative to masseter lever-arm length, but not versus temporalis lever-arm length. Thus, as compared to cercopithecines, colobines can recruit less masseter-muscle force to produce similar bite forces during mastication. In both clades, M2 bite-point length scales with positive allometry relative to masseter lever-arm length, such that larger species are less efficient at generating molar bite forces. This seems especially important due to the lack of subfamily difference in M2 bite-point:temporalis lever-arm scaling (which is isometric across cercopithecids). A consideration of extinct cercopithecids indicates that many of the large-bodied papionins have more robust corpora, due perhaps to a diet which was of similar toughness to that of extant and extinct colobines. However, the biomechanical arrangements of the masseter and temporalis in all but one fossil cercopithecine and all of the fossil colobine specimens are much as predicted for a subfamilial member of its skull size. That most large-bodied papionins with tougher diets nonetheless maintain a less efficient jaw-muscle configuration may be due to stronger offsetting selection for increased relative canine size and gape.