Vertical Jaw Movements Research Articles

Canine Rise Method: A Conservative Approach for Worn Teeth Rehabilitation with Different Adhesive Restorative Materials

Background In this article, two cases with generalized dental wear and four cases with localized dental wear are reported. In some of the cases, the worn teeth were restored with direct composite techniques with no mock-up and articulator mounting according to the canine rise method. This method is used without any change in the intercuspation of posterior teeth without a muscle relaxation appliance. It introduces a stable occlusal condition that can alter neuromuscular reflex activity, leading to improvements in certain muscle pain disorders. It is also used to protect the teeth and supporting structures from abnormal forces that might create a further breakdown and/or tooth wear. Methods The first step of treatment in all the cases was a composite build-up for maxillary and mandibular canines to restrict and guide the horizontal and vertical jaw movements and create adequate space for restorations. The second step was the placement of direct or indirect restorations on upper and lower anterior teeth efficiently and accurately. Results This method enhanced the esthetic outcomes in a conservative approach with no reduction in tooth material or time-consuming treatments. Conclusions This technique can be suggested for the treatment of worn teeth in patients with Angle's Cl I and Cl II classifications of malocclusion based on the follow-up results. It is not applicable for the treatment of worn teeth in patients with Angle's class III because occlusion is reversed, and canine teeth do not have guidance role. Practical Implications. This method significantly reduces the overall treatment time, and additional steps are required to restore the worn-out teeth and/or occlusion using the canine rise method.

Development of the Sakiika transport test: A practical screening method for patients with oral-phase dysphagia.

This study aimed to develop a simple screening test for mastication, "the Sakiika (squid jerky) transport test (STT), which evaluates the vertical jaw movement coordinated with the lateral tongue movement during stage I transport, and investigate the possibility of its clinical application. The study included 73 people with dysphagia (mean age, 78.5 ± 7.8 years; median age, 79.0 years; interquartile range, 75.0-84.0). The STT evaluated the ability of a participant to transport a piece of squid jerky placed on the midline of the tongue to the molar region. The STT score was defined as the number of vertical jaw movements occurring as the tongue transported food to the molars. A cutoff value was set by comparing the STT scores with masticatory function evaluated via a videofluoroscopic swallowing study and with food texture evaluated using the Food Intake LEVEL Scale (FILS). The STT scores counted by the two examiners had a κ coefficient of 0.79, indicating good reliability. The STT score was significantly associated with both the presence of masticatory movement ( p = 0.019) and food texture classified by FILS ( p = 0.032) at cutoff value of "3" (3 vertical movements). The STT showed 62% sensitivity and 75% specificity for masticatory movements. The STT could be a useful screening test to assess the presence or absence of food transportation to the molars for mastication in older patients with dysphagia. In addition, the STT could be useful in identifying the need to modify food texture to meet functions.

Functional Analysis of Rhythmic Jaw Movements Evoked by Electrical Stimulation of the Cortical Masticatory Area During Low Occlusal Loading in Growing Rats.

The maturation of rhythmic jaw movements (RJMs) and related neuromuscular control has rarely been studied in animals, though this process is essential for regulating the development of stomatognathic functions. Previous studies have shown that occlusal hypofunction during growth alters masticatory performance. However, little is known about patterns of cortically-induced RJMs under conditions of soft-diet feeding during development. The aim of this study is to clarify the effect of low occlusal loading on the pattern of cortically induced RJMs and related neuromuscular responses in growing rats. Sixty-four 2-week-old male albino Wistar rats were randomly divided into two groups and fed on either a normal diet (control) or soft diet (experimental) soon after weaning. At 5, 7, 9, and 11 weeks of age, electromyographic (EMG) activity was recorded from the right masseter and anterior digastric muscles along with corresponding kinematic images in RJMs during repetitive intracortical microstimulation of the left cortical masticatory area (CMA). Rats in both groups showed an increase in gape size and lateral excursion until 9 weeks of age. The vertical jaw movement speed in both groups showed no significant difference between 5 and 7 weeks of age but increased with age from 9 to 11 weeks. Compared to the control group, the average gape size and vertical speed were significantly lower in the experimental group, and the pattern and rhythm of the jaw movement cycle were similar between both groups at each recording age. EMG recordings showed no age-related significant differences in onset latency, duration, and peak-to-peak amplitude. Moreover, we found significantly longer onset latency, smaller peak-to-peak amplitude, and greater drop-off mean and median frequencies in the experimental group than in the control group, while there was no significant difference in the duration between groups. These findings indicate that a lack of enough occlusal function in infancy impedes the development of patterns of RJMs and delays the neuromuscular response from specific stimulation of the CMA.

A salamander that chews using complex, three-dimensional mandible movements.

Most non-mammal tetrapods have a hinge-like jaw operation restricted to vertical opening and closing movements. Many mammal jaw joints, by contrast, operate in more complex, three-dimensional (3D) ways, involving not only vertical but also propalinal (rostro-caudal) and transverse (lateral) movements. Data on intraoral food processing in lissamphibians and sauropsids has prompted a generally accepted view that these groups mostly swallow food unreduced, and that in those cases where lissamphibians and sauropsids chew, they mostly use simple vertical jaw movements for food processing. The exception to this generally accepted view is the occurrence of some propalinal chewing in sauropsids. We combined 3D kinematics and morphological analyses from biplanar high-speed video fluoroscopy and micro-computed tomography to determine how the paedomorphic salamander Siren intermedia treats captured food. We discovered not only that S. intermedia uses intraoral food processing but also that the elaborated morphology of its jaw joint facilitates mandibular motions in all three planes, resulting in complex 3D chewing. Thus, our data challenge the commonly held view that complex 3D chewing movements are exclusive to mammals, by suggesting that such mechanisms might have evolved early in the tetrapod evolution.

Coordinative movement of articulators in bilabial stop /p/*

Speech articulators are coordinated for the purpose of segmental constriction in terms of a task. In particular, vertical jaw movements repeatedly contribute to consonantal as well as vocalic constriction. The current study explores vertical jaw movements in conjunction with bilabial constriction in bilabial stop /p/ in the context /a/-to-/a/. Revisiting kinematic data of /p/ collected using the electromagenetic midsagittal articulometer (EMMA) method from seven (four female and three male) speakers of Seoul Korean, we examined maximum vertical jaw position, its relative timing with respect to the upper and lower lips, and lip aperture minima. The results of those dependent variables are recapitulated in terms of linguistic (different word boundaries) and paralinguistic (different speech rates) factors as follows. Firstly, maximum jaw height was lower in the across-word boundary condition (across-word < within-word), but it did not differ as a function of different speech rates (comfortable = fast). Secondly, more reduction in the lip aperture (LA) gesture occurred in fast rate, while word-boundary effects were absent. Thirdly, jaw raising was still in progress after the lips’ positional extrema were achieved in the within-word condition, while the former was completed before the latter in the across-word condition. Lastly, relative temporal lags between the jaw and the lips (UL and LL) were more synchronous in fast rate, compared to comfortable rate. When these results are considered together, it is possible to posit that speakers are not tolerant of lenition to the extent that it is potentially realized as a labial approximant in either word-boundary condition while jaw height still manifested lower jaw position in the across-word boundary condition. Early termination of vertical jaw maxima before vertical lower lip maxima across-word condition may be partly responsible for the spatial reduction of jaw raising movements. This may come about as a consequence of an excessive number of factors (e.g., upper lip height (UH), lower lip height (LH), jaw angle (JA)) for the representation of a vector with two degrees of freedom (x, y) engaged in a gesture-based task (e.g., lip aperture (LA)). In the task-dynamic application toolkit, the jaw angle parameter can be assigned numerical values for greater weight in the across-word boundary condition, which in turn gives rise to lower jaw position. Speech rate-dependent spatial reduction in lip aperture may be able to be resolved by means of manipulating activation time of an active tract variable in the gestural score level.

Coordinative movement of articulators in bilabial stop /p/*

Speech articulators are coordinated for the purpose of segmental constriction in terms of a task. In particular, vertical jaw movements repeatedly contribute to consonantal as well as vocalic constriction. The current study explores vertical jaw movements in conjunction with bilabial constriction in bilabial stop /p/ in the context /a/-to-/a/. Revisiting kinematic data of /p/ collected using the electromagenetic midsagittal articulometer (EMMA) method from seven (four female and three male) speakers of Seoul Korean, we examined maximum vertical jaw position, its relative timing with respect to the upper and lower lips, and lip aperture minima. The results of those dependent variables are recapitulated in terms of linguistic (different word boundaries) and paralinguistic (different speech rates) factors as follows. Firstly, maximum jaw height was lower in the across-word boundary condition (across-word < within-word), but it did not differ as a function of different speech rates (comfortable = fast). Secondly, more reduction in the lip aperture (LA) gesture occurred in fast rate, while word-boundary effects were absent. Thirdly, jaw raising was still in progress after the lips’ positional extrema were achieved in the within-word condition, while the former was completed before the latter in the across-word condition. Lastly, relative temporal lags between the jaw and the lips (UL and LL) were more synchronous in fast rate, compared to comfortable rate. When these results are considered together, it is possible to posit that speakers are not tolerant of lenition to the extent that it is potentially realized as a labial approximant in either word-boundary condition while jaw height still manifested lower jaw position in the across-word boundary condition. Early termination of vertical jaw maxima before vertical lower lip maxima across-word condition may be partly responsible for the spatial reduction of jaw raising movements. This may come about as a consequence of an excessive number of factors (e.g., upper lip height (UH), lower lip height (LH), jaw angle (JA)) for the representation of a vector with two degrees of freedom (x, y) engaged in a gesture-based task (e.g., lip aperture (LA)). In the task-dynamic application toolkit, the jaw angle parameter can be assigned numerical values for greater weight in the across-word boundary condition, which in turn gives rise to lower jaw position. Speech rate-dependent spatial reduction in lip aperture may be able to be resolved by means of manipulating activation time of an active tract variable in the gestural score level.

Reliability of mandibular movement assessments depending on TMD

Objective: This study determines the effect of temporomandibular disorders (TMD) on the reliability of mandibular movement assessments.Methods: The vertical and horizontal jaw movements, as well as overjet and overbite, were measured twice in 56 consecutively recruited adult subjects with TMD according to the RDC/TMD and 29 controls without TMD diagnosis by experienced dentists utilizing a millimeter ruler. The reliability was determined by intraclass correlation coefficient (ICC).Results: Neither statistically nor clinically relevant differences in the repeatability between both subgroups could be detected (all p ≥ 0.077). The mouth opening and overjet proved an excellent reliability (ICC 0.85–0.92). Overbite and laterotrusion showed good to excellent reliable results (ICC 0.74–0.82). The second measurement of the vertical jaw movement resulted in systematically higher values (p < 0.003).Discussion: The assessment of the mandibular movement with a millimeter ruler is a reliable procedure irrespective of TMD. To decrease the variances in the mouth opening measurements, the patient should be asked beforehand to practice this movement.

Quantifying kinematic aspects of reduction in a contrasting rate production task

Electromagnetic articulometry (EMA) was used to record the 720 phonetically balanced Harvard sentences (IEEE, 1969) from multiple speakers at normal and fast production rates. Participants produced each sentence twice, first at their preferred “normal” speaking rate followed by a “fast” production (for a subset of the sentences two normal rate productions were elicited). They were instructed to produce the “fast” repetition as quickly as possible without making errors. EMA trajectories were obtained at 100 Hz from sensors placed on the tongue, lips, and mandible, corrected for head movement and aligned to the occlusal plane. Synchronized audio was recorded at 22050 Hz. Comparison of normal to fast acoustic durations for paired utterances showed a mean 67% length reduction, and assessed using Mermelstein's method (1975), two fewer syllables on average. A comparison of inflections in vertical jaw movement between paired utterances showed an average of 2.3 fewer syllables. Cross-recurrence analysis of distance maps computed on paired sensor trajectories comparing corresponding normal:normal to normal:fast utterances showed systematically lower determinism and entropy for the cross-rate comparisons, indicating that rate effects on articulator trajectories are not uniform. Examples of rate-related differences in gestural overlap that might account for these differences in predictability will be presented. [Work supported by NSF.]

Effects of short-term training on behavioral learning and skill acquisition during intraoral fine motor task

Sensory information from the orofacial mechanoreceptors are used by the nervous system to optimize the positioning of food, determine the force levels, and force vectors involved in biting of food morsels. Moreover, practice resulting from repetition could be a key to learning and acquiring a motor skill. Hence, the aim of the experiment was to test the hypothesis that repeated splitting of a food morsel during a short-term training with an oral fine motor task would result in increased performance and optimization of jaw movements, in terms of reduction in duration of various phases of the jaw movements. Thirty healthy volunteers were asked to intraorally manipulate and split a chocolate candy, into two equal halves. The participants performed three series (with 10 trials) of the task before and after a short-term (approximately 30min) training. The accuracy of the split and vertical jaw movement during the task were recorded. The precision of task performance improved significantly after training (22% mean deviation from ideal split after vs. 31% before; P<0.001). There was a significant decrease in the total duration of jaw movements during the task after the training (1.21 s total duration after vs. 1.56 s before; P<0.001). Further, when the jaw movements were divided into different phases, the jaw opening phase and contact phase were significantly shorter after training than before training (P=0.001, P=0.002). The results indicate that short-term training of an oral fine motor task induces behavior learning, skill acquisition and optimization of jaw movements in terms of better performance and reduction in the duration of jaw movements, during the task. The finding of the present study provides insights into how humans learn oral motor behaviors or the kind of adaptation that takes place after a successful prosthetic rehabilitation.

Phenotypic characterization of orofacial movement topography in mutants with disruption of amino acid mechanisms: Glutamate N2A/B/D [GluRε1/2/4] subtypes and the GABA synthesizing enzyme GAD65

To investigate the role of glutamate receptor subtypes and GABA in orofacial function, six individual topographies of orofacial movement, both spontaneous and induced by the dopamine D1-like receptor agonist [R/S]-3-methyl-6-chloro-7,8-dihydroxy-1-[3-methyl-phenyl]-2,3,4,5-tetrahydro-1H-3-benzazepine (SKF 83959), were quantified in mutant mice with deletion of (a) GluN2A, B or D receptors, and (b) the GABA synthesizing enzyme, 65-kD isoform of glutamate decarboxylase (GAD65). In GluN2A mutants, habituation of head movements was disrupted and vibrissae movements were reduced, with an overall increase in locomotion; responsivity to SKF 83959 was unaltered. In GluN2B mutants, vertical and horizontal jaw movements and incisor chattering were increased, with an overall decrease in locomotion; under challenge with SKF 83959, head and vibrissae movements were reduced. In GluN2D mutants, horizontal jaw movements, incisor chattering and vibrissae movements were increased, with reduced tongue protrusions and no overall change in locomotion; under challenge with SKF 83959, horizontal jaw movements were increased. In GAD65 mutants, vertical jaw movements were increased, with disruption to habituation of locomotion; under challenge with SKF 83959, vertical and horizontal jaw movements and incisor chattering were decreased. Effects on orofacial movements differed from their effects on regulation of overall locomotor behavior. These findings (a) indicate novel, differential roles for GluN2A, B and D receptors and for GAD65-mediated GABA in the regulation of individual topographies of orofacial movement and (b) reveal how these roles differ from and/or interact with the established role of D1-like receptors in pattern generators and effectors for such movements.

Alterations in intraoral manipulation and splitting of food by subjects with tooth‐ or implant‐supported fixed prostheses

Sensory information provided by the periodontal mechanoreceptors (PMRs) is used by the nervous system to optimize the positioning of food, force levels, and force vectors involved in biting. The aim of this study was to describe motor performance during a novel manipulation-and-split task and to assess the extent to which control of this performance involves information from the PMRs. A total of 10 subjects with natural teeth, 10 with bimaxillary tooth-supported fixed prostheses (TSP) and 10 with bimaxillary implant-supported fixed prostheses (ISP) (61-83 [mean 69] years of age) were asked to perform an intraoral manipulation-and-split task that involved positioning a spherical chocolate dragée between the front teeth and then splitting it into two parts of equal size. The vertical jaw movement, sound of food cracking and masseter muscle activity were monitored during this task and the accuracy of the split was evaluated. The group with natural teeth was significantly better than the other groups at splitting the candy with high precision. The jaw movements were similar between groups, but the contact phase prior to the split was significantly longer for those with natural dentition. The present findings support the conclusion that the nervous system collects rich information about contact between the teeth and food from the PMRs prior to powerful jaw action. Impairment (TSP) or absence (ISP) of this information alters motor behavior and impairs performance during the natural biting task employed here.

Constitutive and Conditional Mutant Mouse Models for Understanding Dopaminergic Regulation of Orofacial Movements: Emerging Insights and Challenges

Among numerous mechanisms implicated in the regulation of orofacial movements, dopamine-containing neurons have received the most extensive study. Here we review the effects of a) constitutive knockout of D1–5 dopamine receptors and b) conditional mutations with progressive ablation of D1 receptor–expressing cells, on the topography of spontaneous and D1-like agonist–induced orofacial movements. In constitutive knockouts, D1 and D2 exert primary roles in regulating horizontal and vertical jaw movements, respectively, in opposite directions; in contrast, both D1 and D2 receptors regulate tongue protrusions and incisor chattering, in the same direction. D3 and D5 receptors play more subtle roles in regulating orofacial movements, while D4 receptors do not play any material role. Progressive loss of forebrain D1 receptor–expressing cells in CamKIIa/Cre D1Tox mutants is associated primarily with decreases in head and vibrissae movements, while progressive loss of striatal D1 receptor–expressing cells in DARPP-32/Cre D1Tox mutants is associated primarily with reductions in jaw movements and tongue protrusions but increases in head and vibrissae movements. Further application of constitutive and particularly conditional mutants may clarify further not only dopaminergic regulation of orofacial movements but also the pathophysiology of orofacial dysfunction in Huntington’s disease and Parkinson’s disease.

Interpositional Arthroplasty in the Treatment of Temporomandibular Joint Ankylosis: A Review of Literature

We have reviewed the clinical and experimental reports regarding interpositional arthroplasty materials in the treatment of temporomandibular joint(TMJ) ankylosis. The aim of this review is to determine what constitutes an ideal interpositional material and whether any of the existing materials reported in the literature provide all requirements of an effective disc substitute following the surgical excision of ankylotic mass. We evaluated these reports in terms of the maximum mouth opening(MMO), aetiology, type of ankylosis, type of graft used, recurrence and other complications. Also we compared the results of the other experimental studies with those of our former experimental study. This was the first report that human amniotic membrane(HAM) had been used as an interposition material. The study has clearly demonstrated that HAM was superior to gap arthroplasty evidenced by vertical, left and right jaw movements in the rabbits clinically. This was supported by histological and radiological investigations, as well. However HAM had the inability to achieve the vertical height of the mandibular ramus, so that a total functional reconstruction was not obtained. In reviewing the literature, it is obvious that there is no ideal interpositional material that provides all the criteria for replacement of a missing articular disc following TMJ discectomy. Although HAM as an interpositional material in tmj ankylosis treatment has not yet been used in human beings, we consider HAM as an interface material with replacing the disc using a cartilage graft might be effective to prevent reankylosis method for treatment of type 1 and 2 of TMJ ankylosis.

Orofacial movements in phospholipase C‐related catalytically inactive protein‐1/2 double knockout mice: Effect of the GABAergic agent diazepam and the D1 dopamine receptor agonist SKF 83959

Orofacial movements are regulated by D(1)-like dopamine receptors interacting with additional mechanisms. Phospholipase C-related catalytically inactive protein (PRIP) regulates cell surface expression of GABA(A) receptors containing a gamma2 subunit. Mutant mice with double knockout of PRIP-1 and PRIP-2 were used to investigate aspects of GABAergic regulation of orofacial movements and interactions with D(1) mechanisms. Vertical jaw movements, tongue protrusions and movements of the head and vibrissae were reduced in PRIP-1/2 double knockouts. The GABA(A)ergic agent diazepam reduced movements of the head and vibrissae; these effects were unaltered in PRIP-1/2 double knockouts. The D(1)-like agonist SKF 83959 induced vertical jaw movements, incisor chattering, and movements of the head and vibrissae that were unaltered in PRIP-1/2 double knockouts. However, SKF 83959-induced tongue protrusions were reduced in PRIP-1/2 double knockouts. PRIP-mediated regulation of GABA(A)ergic receptor mechanisms influences topographically distinct aspects of orofacial movement and interacts with D(1) receptor systems.

Assessment of jaw movements by magnetic sensor in relation to topographies of orofacial behaviour in freely moving rats: Studies with the dopamine D 1-like receptor agonists SKF 83822 vs SKF 83959

This study applies new magnetic sensor-electromyographic technology for recording jaw movements in freely moving rats to analyse topographies of orofacial movement that occur in association with individual elements of behaviour under challenge with two dopamine D 1-like receptor agonists, SKF 83822 ([ R/S]-6-chloro-7, 8-dihydroxy-3-allyl-1-[3-methyl-phenyl]-2,3,4,5-tetrahydro-1 H-3-benzazepine) and SKF 83959([ R/S]-3-methyl-6-chloro-7, 8-dihydroxy-1-[3-methyl-phenyl]-2,3,4,5-tetrahydro-1 H-3-benzazepine). Grooming of the snout/face involved primarily dominant-mouth opening jaw movements with small activation of digastric muscles; subsequent grooming of the flank/trunk was characterised by repetitive, uniform jaw movements with small activation of digastric and masseter muscles. In contrast, grooming of the fingers and tail typically involved high-frequency jaw movements with variable vertical jaw movements and/or strong activation of masseter muscles. Vacuous chewing involved two distinct patterns of jaw movements: a dominant-closing pattern, with strong activation of masseter muscles, and a dominant-opening pattern, with slight activation of masseter muscles. SKF 83822 stimulates dopamine D 1-like receptors and activates adenylate cyclase but not phosphoinositide hydrolysis, while SKF 83959 stimulates dopamine D 1-like receptors and activates phosphoinositide hydrolysis but not adenylate cyclase. These agonists exerted differential effects on jaw movements, as SKF 83959 induced more jaw movements per episode of syntactic grooming than SKF 83822, while SKF 83822 induced more jaw movements during non-syntactic grooming than SKF 83959. Magnetic sensor technology in freely moving animals resolved distinct topographies of orofacial movement and informs on their relationship to other behaviours in the rodent repertoire and to dopamine D 1-like receptor function.

Phenotype of spontaneous orofacial dyskinesia in neuregulin-1 ‘knockout’ mice

Studies in antipsychotic-naïve patients with schizophrenia indicate a baseline level of spontaneous involuntary movements, particularly orofacial dyskinesia. Neuregulin-1 is associated with risk for schizophrenia and its functional role can be studied in ‘knockout’ mice. We have shown previously that neuregulin-1 ‘knockouts’ evidence disruption in social behaviour. Neuregulin-1 ‘knockouts’ were assessed for four topographies of orofacial movement, both spontaneously and under challenge with the D 1-like dopamine receptor agonist SKF 83959. Neuregulin-1 ‘knockouts’ evidenced an increase in spontaneous incisor chattering, particularly among males. SKF 83959 induced incisor chattering, vertical jaw movements and tongue protrusions; the level of horizontal jaw movements was increased and that of tongue protrusions decreased in neuregulin-1 ‘knockouts’. These findings indicate that the schizophrenia risk gene neuregulin-1 is involved in the regulation of not only social behaviour but also orofacial dyskinesia. Orofacial dyskinesia in neuregulin-1 mutants may indicate some modest genetic relationship between risk for schizophrenia and vulnerability to spontaneous movement disorder.

Patterns of variation across primates in jaw-muscle electromyography during mastication

Biologists that study mammals continue to discuss the evolution of and functional variation in jaw-muscle activity during chewing. A major barrier to addressing these issues is collecting sufficient in vivo data to adequately capture neuromuscular variation in a clade. We combine data on jaw-muscle electromyography (EMG) collected during mastication from 14 species of primates and one of treeshrews to assess patterns of neuromuscular variation in primates. All data were collected and analyzed using the same methods. We examine the variance components for EMG parameters using a nested ANOVA design across successive hierarchical factors from chewing cycle through species for eight locations in the masseter and temporalis muscles. Variation in jaw-muscle EMGs was not distributed equally across hierarchical levels. The timing of peak EMG activity showed the largest variance components among chewing cycles. Relative levels of recruitment of jaw muscles showed the largest variance components among chewing sequences and cycles. We attribute variation among chewing cycles to (1) changes in food properties throughout the chewing sequence, (2) variation in bite location, and (3) the multiple ways jaw muscles can produce submaximal bite forces. We hypothesize that variation among chewing sequences is primarily related to variation in properties of food. The significant proportion of variation in EMGs potentially linked to food properties suggests that experimental biologists must pay close attention to foods given to research subjects in laboratory-based studies of feeding. The jaw muscles exhibit markedly different variance components among species suggesting that primate jaw muscles have evolved as distinct functional units. The balancing-side deep masseter (BDM) exhibits the most variation among species. This observation supports previous hypotheses linking variation in the timing and activation of the BDM to symphyseal fusion in anthropoid primates and in strepsirrhines with robust symphyses. The working-side anterior temporalis shows a contrasting pattern with little variation in timing and relative activation across primates. The consistent recruitment of this muscle suggests that primates have maintained their ability to produce vertical jaw movements and force in contrast to the evolutionary changes in transverse occlusal forces driven by the varying patterns of activation in the BDM.

Differential involvement of cyclase- versus non-cyclase-coupled D 1-like dopamine receptors in orofacial movement topography in mice: Studies with SKF 83822

Though orofacial movements are fundamental motor patterns that are known to be regulated critically by D 1-like dopamine receptors, these processes remain poorly understood. This uncertainty is heightened by evidence for putative D 1-like receptors that are linked not only to adenylyl cyclase (AC) but also to phospholipase C (PLC). Using a new method, we have characterised four topographies of orofacial movement in the mouse using the novel D 1-like agonist SKF 83822, which stimulates AC but not PLC. These were compared with responses to SKF 83959, which stimulates PLC but not AC. Also, effects were characterised using the D 1-like antagonist SCH 23390 and the D 2-like antagonist YM 09151-2. SKF 83822 induced vertical jaw movements with incisor chattering but inhibited horizontal jaw movements; there was little effect on tongue protrusions. Vertical jaw movements induced by SKF 83822 were inhibited by SCH 23390 but uninfluenced by YM 09151-2, while YM 09151-2 released horizontal jaw movements; thus, D 1-like agonist-induced, AC-mediated vertical jaw movements constitute a ‘pure’ D 1-like-dependent process that does not involve D 1-like:D 2-like interactions, while horizontal jaw movements involve oppositional interactions. Orofacial movements in mice appear to consist of at least four phenomenologically dissociable topographies that are mechanistically distinct. They are regulated differentially by AC- and/or PLC-dependent processes and these processes involve distinct D 1-like:D 2-like interactions.

Disruption of orofacial movement topographies in congenic mutants with dopamine D 5 but not D 4 receptor or DARPP-32 transduction ‘knockout’

The role of D 1-like [D 1, D 5] and D 2-like [D 2, D 3, D 4] dopamine receptors and dopamine transduction via DARPP-32 in topographies of orofacial movement was assessed in restrained mice with congenic D 4 vs. D 5 receptor vs. DARPP-32 ‘knockout’. D 4 and DARPP-32 mutants evidenced no material phenotype; also, there were no alterations in topographical responsivity to either the selective D 2-like agonist RU 24213 or the selective D 1-like agonist SK and F 83959. In contrast, D 5 mutants evidenced an increase in spontaneous vertical jaw movements, which habituated more slowly than in wildtypes, and a decrease in horizontal jaw movements; topographical responsivity to SK and F 83959 and RU 24213 was unaltered. D 5 receptors regulate distinct topographies of vertical and horizontal jaw movement in an opposite manner. In assuming that the well-recognised role of the D 1-like family in regulating orofacial movements involves primarily D 1 receptors, a role for their D 5 counterparts may have been overlooked.

Topographical effects of D1-like dopamine receptor agonists on orofacial movements in mice and their differential regulation via oppositional versus synergistic D1-like: D2-like interactions: cautionary observations on SK&amp;F 82958 as an anomalous agent

Using a novel procedure, the regulation of individual topographies of orofacial movement in the mouse by oppositional versus cooperative/synergistic D1-like: D2-like dopamine receptor interactions was studied. The D1-like agonists SK&amp;F 38393 and SK&amp;F 83959 each induced vertical, but not horizontal, jaw movements, together with tongue protrusions and incisor chattering; however, SK&amp;F 82958 induced a different profile which, consistent with other neurochemical and neurophysiological studies, suggests that this agent shows anomalous properties relative to other D1-like agonists. When given alone, the D2-like agonist quinpirole reduced horizontal jaw movements and incisor chattering. On coadministration, both SK&amp;F 38393- and SK&amp;F 83959-induced vertical jaw movements and tongue protrusions were inhibited by quinpirole, while SK&amp;F 82958 again showed an anomalous profile. These findings indicate that, in the mouse, vertical jaw movements and tongue protrusions are regulated by oppositional D1-like: D2-like interactions, and appear to involve a D1-like receptor that is not coupled to adenylyl cyclase, whereas horizontal jaw movements are inhibited by D2-like receptors. Additionally, results obtained using SK&amp;F 82958 as a probe for D1-like mechanisms should be treated with considerable caution until they are confirmed using other D1-like agonists.