Prevalence of mandibular dysfunction in young adults.

A sample of students (739) were questioned and examined for symptoms and signs associated with mandibular dysfunction. The most frequently mentioned symptoms were headache, TMJ sounds, and pain in the face or neck. No significant differences were found between men and women with symptoms other than headache. The most common dysfunctional signs were dull occlusal sounds on repeated, firm closure of the teeth, tenderness of muscles in the jaw or head, and sounds on condylar movement. Women had a higher prevalence of these signs. Subjects who were aware of bruxism (7.9%) were more likely to have tenderness of the masseter muscle and limited mouth opening. Limited mouth opening was associated with dull occlusal sounds, pain on opening the mouth, and sounds in TMJs. Headaches were associated with tenderness in muscles and joints. Subclinical signs associated with dysfunction occurred more frequently than did awareness of symptoms.     

Volume changes in human masticatory muscles between jaw closing and opening

Most jaw muscles are complex, multipennate with multiple components. The morphologic heterogeneity of masticatory muscles reflects their functions. We hypothesized that the volume of masticatory muscles changes between jaw closing and opening, and that there is a difference in the volume change among the muscles. Magnetic resonance images of the entire head were obtained in ten normal young adult subjects before and after maximum jaw opening. The volume changes of the masseter, medial, and lateral pterygoid muscles were measured. Only slight changes were seen in the masseter and medial pterygoid muscles. The lateral pterygoid muscle, however, significantly decreased its volume during jaw opening. The results provide normative values of muscle volume in living subjects, and suggest that the volume changes differ among jaw muscles.     

Soft occlusal splint therapy in the management of myofascial pain dysfunction syndrome: A follow-up study

Background and Objectives: Myofascial Pain Dysfunction Syndrome (MPDS) has been recognized as the most common, nontooth-related chronic orofacial pain condition that confronts dentists. A variety of therapies has been described in literature for its management. The present study is a prospective study carried out to evaluate the efficacy of occlusal splint therapy and compare it with pharmacotherapy (using analgesics and muscle relaxants) in the management of Myofascial Pain Dysfunction Syndrome. Materials and Methods: Forty patients in the age range of 17-55 years were included in the study and randomly assigned to one of two equally sized groups, A and B. Group A patients received a combination of muscle relaxants and analgesics while Group B patients received soft occlusal splint therapy. All the patients were evaluated for GPI, VAS, maximum comfortable mouth opening, TMJ clicking and tenderness during rest and movement as well as for the number of tender muscles at the time of diagnosis, after the 1 st week of initiation of therapy and every month for three months of follow-up. Results: There was a progressive decrease in GPI scores, number of tender muscles, TMJ clicking and tenderness with various jaw movements and significant improvement in mouth opening in patients on occlusal splint therapy during the follow-up period as compared to the pharmacotherapy group. Conclusion: Occlusal splint therapy has better long-term results in reducing the symptoms of MPDS. It has better patient compliance, fewer side effects, and is more cost-effective than pharmacotherapy; hence, it can be chosen for the treatment of patients with MPDS.     

Temporomandibular disorders. Part III: Occlusal and articular factors associated with muscle tenderness

Two complete classes of freshman dental and dental hygiene students, 120 men and 102 women (mean age 23.9 years), were assessed for the presence of masticatory pain or dysfunction by questionnaire, clinical examination, and evaluation of dental casts. The purpose of these examinations was to determine potential relationships between clinical muscle tenderness, occlusal relationships, and signs of TMJ dysfunction. Awareness of muscle tenderness increased with the number of muscle sites involved (p less than or equal to .025) but 80% of clinically tender subjects were unaware of any tenderness (p less than or equal to .01). In comparison, subjects with generalized clinical muscle tenderness more often reported TMJ clicking that was not verified at the time of clinical examination (p less than or equal to .001). Occlusal factors, except in highly selective categories, were not associated with muscle tenderness. All subjects with moderate or severe TMJ tenderness had clinically tender muscle sites, whereas subjects with generalized muscle tenderness (greater than or equal to 4 sites) had more severe TMJ tenderness (p less than or equal to .01). Subjects with localized (p less than .05) or generalized muscle tenderness (p less than .05) had more TMJ clicking than those without muscle tenderness. TMJ clicking was reported more commonly than muscle pain among subjects who were clinically determined to have both muscle tenderness and TMJ clicking (p less than or equal to .001). TMJ dysfunction was verified more often in subjects with more localized muscle tenderness (p less than or equal to .025). Although occlusal factors were not good predictors of muscle tenderness, intracapsular signs of TMJ disorders and muscle tenderness were often associated.     

Dynamic simulation of muscle and articular properties during human wide jaw opening

Human mandibular function is determined in part by masticatory muscle tensions and morphological restraints within the craniomandibular system. As only limited information about their interactions can be obtained in vivo, mathematical modeling is a useful alternative. It allows simulation of causal relations between structure and function and the demonstration of hypothetical events in functional or dysfunctional systems. Here, the external force required to reach maximum jaw gape was determined in five relaxed participants, and this information used, with other musculoskeletal data, to construct a dynamic, muscle-driven, three-dimensional mathematical model of the craniomandibular system. The model was programmed to express relations between muscle tensions and articular morphology during wide jaw opening. It was found that a downward force of 5 N could produce wide gape in vivo. When the model's passive jaw-closing muscle tensions were adjusted to permit this, the jaw's resting posture was lower than that normally observed in alert individuals, and low-level active tone was needed in the closer muscles to maintain a typical rest position. Plausible jaw opening to wide gape was possible when activity in the opener muscles increased incrementally over time. When the model was altered structurally by decreasing its angles of condylar guidance, jaw opening required less activity in these muscles. Plausible asymmetrical jaw opening occurred with deactivation of the ipsilateral lateral pterygoid actuator. The model's lateral deviation was limited by passive tensions in the ipsilateral medial pterygoid, which forced the jaw to return towards the midline as opening continued. For all motions, the temporomandibular joint (TMJ) components were maintained in continual apposition and displayed stable pathways despite the absence of constraining ligaments. Compressive TMJ forces were presented in all the cases and increased to maximum at wide gape. Dynamic mathematical modeling appears a useful way to study such events, which as yet are unrecordable in the human craniomandibular system.     

Non-surgical treatment of sports-related temporomandibular joint disorders in basketball players

Abstract –  In this study, 18 basketball players (11 female, seven male; age range 14–32 years) with temporomandibular joint (TMJ) problems who had a history of sport injuries related to head or jaw region were evaluated and the results of the treatment were presented. A standardized functional examination of the masticatory system was performed including measurement of maximal jaw movements, recording of joint sounds, pain on movement of the jaw as well as tenderness to palpation of the both TMJ or masticatory muscles. Patients were also evaluated periodontally. Diagnosis was made according the criteria, described by Okeson, and appropriate treatment was applied using different kind of splints. At the end of treatment only one patient continued with right TMJ reduction with slight pain. Except for that patient, none of the patients had pain after treatment. The maximum opening of the jaws and the maximal jaw movements were statistically increased after treatment. Patients with TMJ problems also showed periodontal problems, most likely due to inadequate oral hygiene because of the limited jaw movements and pain. Periodontal parameters including probing depth (PD), Plaque index (PI), and Sulcus Bleeding Index (SBI) improved after treatment. Sports-related TMJ injuries may result in complex problems such as pain, TMJ sounds, limitation in maximal jaw movements and maximum opening of the mouth, difficulty in chewing. With the appropriate diagnosis this could be treated non-surgically in 6–8 months. This study also showed that the TMJ disorders may cause periodontal problems, which may affect all teeth and also the general health of the athlete.     

Prevalence of temporomandibular dysfunction in Turkish children with mixed and permanent dentition

This study was carried out to determine the prevalence of temporomandibular joint (TMJ) dysfunction in mixed and permanent dentition and to evaluate the sex distribution in Turkish children. One hundred and eighty-two children with mixed dentition and 212 with permanent dentition were selected for the study, which used a questionnaire and clinical examination. Children with one or more signs (TMJ sounds, TMJ tenderness, muscle tenderness, restricted mouth opening) and/or symptoms (TMJ pain during mastication and mouth opening, restriction of the jaw opening and TMJ sounds) met the criterion of TMJ dysfunction. The total prevalence of signs and symptoms of TMJ dysfunction in the studied population was 68% (68% in girls and 68% in boys) in mixed dentition and 58% (61% in girls and 56% in boys) in permanent dentition. The Z-test and analysis of variance (ANOVA) were used for statistical analysis of the difference between the results. The total prevalence of signs and symptoms of TMJ dysfunction in mixed dentition was found to be higher than in permanent dentition (P < 0.05). No statistically significant difference was found in the total prevalence of TMJ dysfunction between girls and boys.     

Myosin isoform composition of the human medial and lateral pterygoid muscles

The medial and lateral pterygoid muscles are different in structure as well as in function. The medial pterygoid muscle is concentrically active during jaw closing, and the superior head of the lateral pterygoid muscle is eccentrically active during jaw closing, while its inferior head is concentrically active during jaw opening. Architecturally, the medial pterygoid can deliver higher forces than the lateral pterygoid. We investigated whether these differences are reflected in the myosin heavy-chain (MyHC) composition and the fiber cross-sectional area (f-csa) of these muscles. The pterygoid muscles from eight cadavers were investigated by means of monoclonal antibodies against different isoforms of MyHC. The proportions of pure MyHC type I fibers did not differ significantly among the muscles (32% in medial pterygoid, 34% in superior head, and 36% in the inferior head of the lateral pterygoid), nor did the total proportions of pure MyHC type IIA and IIX fibers (16% in medial pterygoid, 26% in the superior head, and 19% in the inferior head of the lateral pterygoid). The mean f-csa of type I fibers was 1315 microm2, which did not differ significantly among the muscles, and was significantly larger than the f-csa of type IIA fibers. The relative proportions of hybrid fibers, which expressed more than one MyHC isoform, were 52% in the medial pterygoid, 40% in the superior head, and 45% in the inferior head of the lateral pterygoid and did not differ significantly among the muscles. The most abundant hybrid fiber types found were fibers expressing MyHCs-cardiac alpha+IIA and MyHCs-cardiac alpha+I+IIA. Significant regional differences were found in the proportions of MyHC type I fibers in the medial pterygoid and in the inferior head of the lateral pterygoid. Although the form and function of the muscles are different, we conclude that this is not reflected in their myosin isoform composition.     

Jaw function status in an elderly community sample

Abstract The purpose of this study was to assess jaw function status and disability in an elderly population. The sample consisted of 429 Medicare recipients dwelling in the community (mean age = 74.4±5 yr; 58% female and 42% male) who were enrolled in an HCFA-sponsored prevention demonstration project. An evaluation of TMJ and jaw muscle status was conducted at the completion of a general dental examination. This included assessment of joint sounds (clicking or crepitus), joint and jaw muscle tenderness to palpation, and measurement of maximum opening. Pain or disability during jaw use and history of TMD problems were assessed by self-report. The prevalence of TMJ clicking was 16%, crepitus 19%, TMJ tenderness 8%, jaw muscle tenderness 13%, and opening < 40 mm 22% Pain on jaw use was reported by 6.5%, and 12% reported a history of TMD problems. There was no significant relationship between TMD signs and symptoms and dental status. The lack of consistent relationship between TMD signs and symptoms and health status measures suggests that TMD is a localized disease process and not an extension of a general condition such as arthritis or depression, nor does it have major impact on activities of daily living. Examiner referral for treatment was low (1%) indicating that TMD was not a significant treatment concern in this sample of the elderly.     

Tenderness on palpation and occlusal abnormalities in temporomandibular dysfunction

Tenderness on palpation indicates objective painful symptoms. This study investigated the tenderness of the temporomandibular joint, muscles and their relation to occlusion in patients with temporomandibular dysfunction. Two hundred ten patients were examined; 96% had tenderness and 80% of cases of tenderness were diagnosed as occlusally related. The average number of tender areas was 5.4 per patient, despite the contribution of occlusion. Tenderness was observed most frequently in the lateral pterygoid muscle, followed by the insertion of temporal muscle. There was no correlation of temporomandibular joint tenderness to muscle tenderness, while tenderness of certain muscles to each other was correlated. Differences were related to the state of occlusion in the number of tender areas, to the ratio to tenderness of elevator muscles to horizontally acting muscles, and to the frequency of unilateral tenderness. The association of muscle tenderness and occlusion was suggested.     

Prevalence of symptoms of functional disturbances of the masticatory system in Swedish men

Subjective and clinical symptoms of mandibular dysfunction and cuspal interferences were studied in 389 Swedish men (median age 32 years). Impaired chewing function was noted in about 10%, different types of parafunction in 26%, frequent headaches in 5 %, TMJ or muscle pain in 3 % and difficulties in mouth opening in 10% of the men. Locking or luxation of the mandible was the most prevalent clinical symptom (24%), followed by reduced movement capacity and deviation on opening of the mandible, TMJ-sounds and muscle tenderness. Sixty per cent of the men had one or more clinical symptoms of dysfunction. Subjective symptoms of dysfunction were positively correlated with reduced movement capacity of the mandible and tenderness of the masticatory muscles and temporomandibular joints upon palpation. Positive correlations were found between subjective symptoms of dysfunction and non-working side interference as well as single tooth contact on the working side. Locking or luxation of the mandible and TMJ-sounds were positively correlated with single tooth contact on the working side and TMJ-sounds and muscle tenderness with interferences in the retruded position of the mandible.     

Correlation between oral parafunction and temporomandibular disorders and emotional status among saudi children.

Studies on association between temporomandibular disorders and oral parafunction in preschool children are few. The aim of the present study is to investigate the relationship between the subjective and objective signs and symptoms of temporomandibular disorders (TMD), oral parafunction and emotional status in preschool children. The study is based on a clinical examination and questionnaire. Five hundred and two Saudi children aged 3 to 7 years were examined for different signs and symptoms of TMD. In addition, the parents of the children were given a questionnaire to investigate the existence of oral parafunction and evaluate the emotional status of children. The results of the study showed significant association between attrition and temporomandibular joint (TMJ) pain, muscle tenderness and restricted opening, (P Values were 0.008, 0.019, 0.037 respectively). Significant association was found between habit of grinding and pain, while eating or opening the mouth (P<0.012). Significant association was found between emotional status and multiple signs and symptoms of TMJ tenderness, TMJ pain and muscle tenderness (P<0.042). Significant association was found between emotional status and pain, while eating or opening of the mouth (P<0.048). Close to positive association was found between oral parafunction and jaw lock. The association between TMD and oral parafunction as well as emotional status should direct the attention of the dentist to the importance of considering the emotional status, oral parafunction and TMD when examining and formulating treatment plan for the child patient.     

Electromyographic analysis of the functional components of the lateral pterygoid muscle in the rhesus monkey (Macaca mulatta)

Electromyographic recordings (EMG) obtained from intramuscular electrodes inserted in the lateral pterygoid muscle (lat. pt.) of 29 juvenile and adolescent monkeys were assessed in relation to the recorded activity of three jaw elevating muscles, temporalis, masseter and medial pterygoid, and a jaw muscle depressor, the geniohyoid. The lat. pt. was recruited in one of three patterns: (1) only during mandibular depression, (2) during both depression and elevation, or (3) only during elevation of the jaw. The discharge of fibres in the lat. pt. during closing movements occurred bilaterally in 9 of 21 recordings. Simultaneous recordings from the anterior temporalis, medial pterygoid and the ipsilateral lat. pt. indicated completely different discharge patterns of the three muscles. In 9 recording sessions, two pairs of electrodes were placed in the same lat. pt. The discharge patterns from the two pairs were different in 5 of the recordings. In one region, the fibres were active only during depression, whereas in the other region fibres discharged only during elevation of the mandible. The data support the concept of two groups of fibres with separate functions within the lat. pt. and suggest that adaptation to oral respiration utilizes the two groups in distinctive patterns.     

The treatment of temporomandibular disorders with stabilizing splints in general dental practice: one-year follow-up

BACKGROUND: The authors evaluated temporomandibular disorder (TMD) outcomes in general dental practice one year after treatment with stabilizing splints (SS) or nonoccluding control splints (CS). METHODS: Seventy-two randomly allocated subjects completed initial treatment. The outcomes measures were a pain visual analog scale (VAS), muscle tenderness, temporomandibular joint (TMJ) tenderness, interincisal opening, TMJ clicks and headaches. After initial treatment, 81 percent of the subjects were found to have been treated satisfactorily. The dentists referred the remaining subjects to a dental hospital. At one year, the authors recalled 52 of the original subjects for evaluation. RESULTS: Improvements after initial treatment were maintained at one year for all outcomes, except for TMJ clicking, which returned to pretreatment levels. Eighty-one percent of the subjects rated their treatment as either good or excellent in reducing jaw pain. The authors found that subjects were aware of more of their TMJ clicks than dentists observed at the one-year clinical examination, but most subjects thought their clicking or the associated pain had been reduced. Fifty-five percent subjects had used their splints in the previous six months, but only 31 percent of these had done so daily. There were no significant differences between splint groups. CONCLUSION: At one year, a good response to TMD treatment in general practice had been maintained, but many subjects still had clicking TMJs. CLINICAL IMPLICATIONS: Trained dentists can manage TMD satisfactorily, with only a small proportion of patients needing specialist attention.     

Morphological and positional assessments of TMJ components and lateral pterygoid muscle in relation to symptoms and occlusion of patients with temporomandibular disorders

Disc displacement is accepted as one of major findings in temporomandibular disorders (TMD). However, the associations of disc positions with morphological and positional changes of temporomandibular joint (TMJ) components and lateral pterygoid (LP), TMD clinical symptoms, and occlusion have rarely been discussed quantitatively. In this study, the morphological and positional changes of TMJ components and LP were assessed by means of magnetic resonance imaging (MRI) and tomography of the TMJ in 41 TMD and nine control (CN) subjects. Disc positions in TMD subjects were divided into normal position (NP) and anterior displacement with and without reduction (ADR+ and ADR-, respectively). From MRI scans and tomograms, the morphological and positional changes of TMJ components and LP were measured and compared among CN, NP, ADR+ and ADR- groups. Correlations between these measurements and the scored clinical symptoms and occlusal factors were analysed in TMD subjects. The results indicated that: (1) TMJ osseous structures and LP showed no significant difference among CN and the three TMD groups, except for a posterior seat of condyle and shorter/steeper condylar movement during jaw opening; (2) disc length and inclination were significantly shorter and steeper, respectively, in ADR+ and ADR-; (3) disc positions were not specified by clinical symptoms and occlusal factors, except for the dominant TMJ sounds in ADR+; (4) an uncoordinated movement of the condyle/disc complex was found in ADR+ and/or ADR-; (5) TMJ osseous structures and the disc were weakly associated with clinical symptoms and occlusal factors. However, the LP showed negative associations with palpable pain for both the TMJ and jaw muscles and the static occlusal factors. These findings suggest that TMJ internal derangements are more related to the positional changes or spatial relationships of TMJ components but less to the individual morphologies of TMJ osseous structures, disc and LP, as well as specific clinical symptoms and occlusal factors, which might be in disagreement with a large body of previous statements.     

Sex differences in signs and symptoms from masticatory and other muscles in 19-year-old individuals

Pain and tenderness of masticatory muscles are often related to muscle tenderness elsewhere in the body. It has been shown that women are more prone to musculoskeletal disorders than men. We sought to determine whether sex differences of muscular symptoms were established by the age of 19. The subjects comprised 51 boys and girls who received a questionnaire regarding the function of their masticatory system, frequency of headache, and neck, shoulder and low back pain. Their masticatory system was examined, and neck and shoulders were palpated. For all variables in the questionnaire girls reported symptoms more often than the boys. Of the subjects 50% had tender chewing muscles upon palpation. Again the girls had the most. There was good correlation between reports of pain in one area as compared to others. The number of clinically tender neck and shoulder muscles correlated with the number of tender masticatory muscles. It was concluded that girls presented more muscular symptoms than boys.     

The association of occlusal factors with masticatory muscle tenderness in 10- to 19-year old Turkish subjects

The aims of this study were (1) to investigate the relationship between occlusal factors and masticatory muscle tenderness among 10- to 19-year-old (mean 14 years eight months) Turkish subjects and (2) to identify possible sex differences between them. The sample consisted of 716 individuals (355 male and 361 female subjects). Tenderness with palpation of masseter and temporalis muscles and functional manipulation of lateral and medial pterygoid muscles was registered. The examiners recorded the Angle classification bilaterally for molars, presence of anterior and posterior crossbites, excessive overjet, open and deep bites, functional shift, and severity of anterior crowding. Associations between the occlusal factors and muscle tenderness according to sex were evaluated with chi-square analysis. Statistically significant associations were found between masticatory muscle tenderness and all the investigated occlusal factors except posterior crossbite and functional shift. Masseter, medial, and lateral pterygoid muscle tenderness was higher in female subjects. Medial and lateral pterygoid muscle tenderness in Class I cases and masseter and medial pterygoid muscle tenderness in Class II, division 1 malocclusion cases were higher in female subjects (P < .05). In open-bite cases, medial pterygoid muscle tenderness (P < .05), in deep-bite cases, masseter (P < .01) and medial pterygoid (P < .05) muscle tenderness, and in excessive overjet cases, masseter muscle tenderness (P < .05) were also higher in female subjects. These results suggest that greater masticatory muscle tenderness in female subjects may contribute to the greater prevalence of temporomandibular disorders in them.     

The effect of the local anesthesia to the posterior ramus of the mandible in patients with temporomandibular joint problems

Some clinicians in North America use anesthetic injections to differentiate the symptoms such as pain and stiffness in the facial area and neck in patients with TMJ problems. However, the effects and area which is influenced have not been studied. The purpose of this study was to study procedures and changes following administration of local anesthesia to the posterior ramus of the mandible. Twenty four patients with TMJ problems were used in this study. 0.5ml of 2% Lidocaine (epirenamine included) was injected into the most painful site upon palpation. The pain upon palpation test (following Krogh-Poulsen's method) was compared before and after 50 minutes. Results of this experiment were: 1) decrease of pain upon palpation was found not only in the site. In many cases subjective pain in the head and neck area was also reduced. 2) A significant reduction was found in the pain upon palpation test in the neck area. A highly significant reduction was seen in the Sterunoclydmastoid muscle only in the injected side. In the masticatory muscles. Also, reduction of pain upon palpation was seen in both lateral, medial pterygoid and digastric muscles in the injected side. 3) Contra side lateral pterygoid muscle and trapezius muscle also registered decreased pain upon palpation. 4) The mean values for the injected site were 5.7mm (S.D. 5.9) below the earlobe and the mean depth from the skin surface to the bony surface were 16.6 mm (S.D. 2.7mm). 5) The peak of the subjective effect were seen in one group in 20 minute later injection (early type) and in the 2nd group the peak were seen after 40 minutes (slowly type). 6) We did not experienced any paralysis of the facial nerve in this study.     

Botulinum toxin for the treatment of temporomandibular joint disk disfigurement: clinical experience

Type A botulinum toxin was used for the treatment of symptoms of 26 patients (40 joints) with temporomandibular joint disk disfigurement. In all patients, 0.5 ml (12.5 U) was injected into the lateral pterygoid muscle. The temporalis, medial pterygoid, and masseter muscles were injected if severe tenderness was noted. The data were compared using the Wilcoxon signed rank test and the McNemar test. With the exception of clicking of the right joint, all mean outcome measures showed a significant difference between the preinjection and postinjection assessments. There was a significant difference between the preinjection and postinjection pain scores of the right joint (P=0.0019) and the left joint (P=0.000). Postinjection values of the mouth opening (P=0.002), subjective functional dysfunction (P=0.065), and clicking of the left joint (P=0.001) also showed a statistically significant difference from the preinjection values. In addition, the severity and frequency of headache were reduced after botulinum toxin-A injection into the lateral pterygoid muscle.     

Growth patterns of the rabbit masticatory muscles

The post-natal growth of the masticatory muscles in the rabbit was examined. By means of anatomical dissection and measurement, total muscle length, muscle fiber length, and muscle weight were determined in animals varying in age between one week and 36 months and exhibiting a 50-fold weight increase. Growth data were fitted by linear regression models with facial skull length used as the independent variable. Many deviations occur from size-dependent isometric growth. The muscles can be divided into three groups, according to their pattern of weight increase: The jaw openers grow negatively allometrically, and their contribution to total muscle weight decreases with time; the temporal muscle grows negatively allometrically, but its relative weight proportion remains about the same; the masseter and medial pterygoid muscles have positively allometric growth, and their contribution to total muscle weight increases strongly. Generally, the length of the muscles and of their fibers increases at lower rates than does the length of the facial skull. After weaning, the rate of longitudinal growth drops steeply in some muscles. Total fiber area or physiological cross-section (PCS) of muscles is computed from weight and fiber length. It increases positively allometrically in the jaw closers and negatively allometrically in the jaw openers. In the lateral pterygoid muscle, the increase of PCS changes from negatively- to positively-allometric growth after weaning. The study demonstrates that individual oral muscles follow different patterns of longitudinal and cross-sectional growth, so that their functional capacities (force, range of contraction) and mutual functional relationships are age-dependent.