Journal ofNeurology, Neurosurgery, and Psychiatry 1996;60:41-50 41 Jaw movement dysfunction related to Parkinson's J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.60.1.41 on 1 January 1996. Downloaded from disease and partially modified by levodopa Lee T Robertson, John P Hammerstad Abstract also have difficulties in the production of clear Objectives-To test the hypotheses that speech5 and with the automatic clearing of the Parkinson's disease can differentially throat or swallowing.3 Although the same produce deficits in voluntary and rhyth- peripheral structures are involved in various mic jaw movements, which involve differ- oral motor acts, such as speaking, swallowing, ent neuronal circuits, and that levodopa or chewing, distinct basal ganglia circuits may treatment improves specific components be used to generate the various motor pat- of the motor deficit. terns.6 The neural circuits involved in volun- Methods-Patients with idiopathic tary movement of the mandible may be Parkinson's disease and control subjects different from those used for force production were tested on a series of jaw motor tasks whereas those circuits regulating chewing may that included simple voluntary move- include portions of circuits for voluntary ment, isometric clenching, and natural movement and force as well as additional cir- and paced rhythmic movements. Jaw cuits to process specific sensory input. A major movements were measured by changes in basal ganglia circuit is the projection from the electromagnetic fields and EMG activity. globus pallidus and substantia nigra reticulata, Patients with Parkinson's disease with via the thalamus, to the primary motor cortex, fluctuations in motor responses to lev- the supplementary motor cortex, and the pre- odopa were tested while off and on. motor area. Animal studies suggest that these Results-During the off state, patients cortical areas help to control the initiation, with Parkinson's disease were signifi- direction, force, and internal guidance of vol- cantly worse than the control subjects on untary movements.68 A circuit that may influ- most tasks. The deficits included a ence rhythmic jaw movements is a small direct decrease in amplitude and velocity during projection from the substantia nigra reticulata jaw opening and closing, aberrant pat- to brain stem neurons, which have connec- terns and low amplitude of EMG activity tions with the trigeminal motor complex.9 10 during clenching, and low vertical ampli- Little information is available on how tude and prolonged durations of occlusion Parkinson's disease affects the motor control during rhythmic movements. No decre- of the jaw. Connor and Abbs" showed that ments were found in the amplitude of patients with Parkinson's disease had http://jnnp.bmj.com/ voluntary lateral jaw movements or the decreased peak velocities and increased dura- frequency of rhythmic movements. tions in a visually guided vertical jaw move- During the on state, improvements ment task. Abbs and associates3 reported that occurred in the patterns and level ofEMG patients with Parkinson's disease were unable activity during clenching and in the verti- to sustain a steady four to five second isometric cal amplitude and duration of occlusion force using jaw closing muscles. However, the during rhythmic movements, although a changes in velocity and force occurred in Department of significant decrement occurred in the lat- patients receiving dopamine replacement, on October 2, 2021 by guest. Protected copyright. Biological Structure eral excursion ofthe jaw. which may have produced a motor deficit and Function, School Conclusions-Parkinson's disease affects of Dentistry, Oregon because of dyskinesia.4 Karlsson and cowork- Health Sciences the central programming of functionally ers'2 studied patients both on and off levodopa University, Pordand, related muscles involved in voluntary and treatment and showed that levodopa increased OR, USA rhythmic jaw movements and levodopa the duration of the chewing cycle and the L T Robertson replacement influences only certain opening and closing velocities during Department of peanut Neurology, School of aspects of jaw movement, most likely chewing. Medicine, Oregon those requiring sensory feedback. The present study examines the effects of Health Sciences Parkinson's disease and the effect of dopamine University, Portland, CT Neurol Neurosurg OR, USA Psychiatry 1996;60:41-50) replacement on voluntary jaw movements, jaw J P Hammerstad clenching, and rhythmic jaw movements. A Correspondence to: battery of jaw motor tasks was used to discern Dr Lee Robertson, Keywords: mastication; Parkinson's disease; levodopa Department of Biological possible involvement of different neural cir- Structure and Function, cuits (for example, voluntary jaw movements Oregon Health Sciences Orofacial motor abnormalities have long been that likely involve University, 611 S W Campus connections with the motor Drive, Portland, OR 97201, recognised in Parkinson's disease. -3 Included cortical areas versus rhythmic movements that USA. in most textbook descriptions of Parkinson's may include connections with brain stem neu- Received 30 March 1995 disease is hypokinesia of the muscles of facial rons), differences and in revised form among various variables of 28 June 1995 expression and a reduced eye blink rate, movement (for example, velocity, amplitude, Accepted 7 September 1995 resulting in a mask-like face.4 Many patients or force), and differences between internal and 42 Robertson, Hammerstad external signals to organise rhythmic jaw small magnet was glued to a point below the J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.60.1.41 on 1 January 1996. Downloaded from movements. By testing patients with lower central incisors and changes in the elec- Parkinson's disease with major fluctuations in tromagnetic fields were detected by magne- their motor response to levodopa (the on-off tometers mounted on a lightweight set of phenomenon), we could determine whether eyeglass frames worn by the subject. The kine- Parkinson's disease, as manifested during the siograph was interfaced with a microcomputer off state, affects particular types of jaw motor for data display and analyses. control and whether acute levodopa treat- Recordings of the EMG activity of the right ment, during the on state, is useful for all types and left temporalis and masseter muscles were or only specific classes of jaw motor deficits. obtained with bipolar, silver-silver chloride EMG electrodes placed in standardised posi- tions on the skin over each pair of muscles. Subjects and methods For the jaw clenching task, the EMG activity SUBJECTS was differentially amplified, bandpass filtered We tested eight patients (six men and two (30 to 500 Hz), and full wave rectified. women with a mean age of 53-7 years) with idiopathic Parkinson's disease (average dura- EXPERIMENTAL DESIGN AND PROCEDURES tion nine years) and 11 control subjects (nine Patients with Parkinson's disease were evalu- men and two women with a mean age of 54-4 ated in two one-hour test sessions. The first years) who were free of signs of neurological test session was done while the patients were disease. Routine examinations of the orofacial in the off state and the second test session region were made and included an examina- began one hour after the patients took their tion of intraoral structures; palpation of the usual oral dose of carbidopa-levodopa (the on temporomandibular joints, muscles of mastica- state). A single test session was used for most tion, and associated muscles and tissues; and control subjects because no difference was an assessment of the range of movement of the found between the first and second test session mandible and any accompanying pain or joint for three subjects who were tested in two one- sounds. All subjects had most of their normal hour sessions with an hour of rest between ses- dentition and no signs of malocclusion. Two sions and because the performance of the controls and two patients with Parkinson's dis- control subjects was not significantly different ease had condyle displacement during the from the results of a pilot study, which showed opening phase of the movement, but no evi- no difference between two separate one-hour dence of pain and tenderness in the region of sessions. the jaw muscles and joints. All patients with The jaw motor tasks were performed while Parkinson's disease showed some reduction in the subject sat upright on a chair. Three types the range of normal jaw movement. of jaw motor tasks were given simple volun- Patients were specifically selected because tary jaw movements, brief isometric molar they displayed an on-off oscillating clinical clenching, and natural and paced rhythmic response to levodopa and did not show signs of movements and were done in the same oral-buccal-lingual dyskinesia. For the data col- sequence for all subjects. All tasks began and lection, the patients with Parkinson's disease ended with intercuspal contact. The subjects had refrained from all medication for 10 to 12 were given simple verbal instructions and hours and showed posture and locomotion dis- allowed to practice the tasks two to three http://jnnp.bmj.com/ turbances when they entered the laboratory. times. Each task involved several trials with During their off state, the patients with about 30 to 60 seconds of rest between trials; Parkinson's disease reported that they had con- no information was given to the subject siderable difficulty with activities of daily living, regarding their performance. were unable or barely able to walk, and several The voluntary jaw movements included reported having difficulty chewing or eating an normal vertical opening and closing of the entire meal. Their motor disability during the mouth, opening the mouth as wide as possible, on October 2, 2021 by guest. Protected copyright. off state ranged from stage 2 5 to 5 0 on the vertically opening and closing the mouth as Hoehn and Yahr scale.'3 After being tested in fast as possible, and right to left horizontal jaw the off state, the patients took their usual morn- movements.