Duration of the electromyographic silent period following the jaw-jerk reflex in human subjects.

During voluntary jaw clenching, a sharp tap to the menton of the mandible resulted in a transitory silent period (pause) in the electromyographic activity of the masseter and anterior temporalis muscles. Factors that could influence the duration of the silent period were studied, including direction and magnitude of the stimulus applied by the operator, the amount of muscular effort exerted by the subjects, and varying occlusal vertical dimensions. Decreased isometric muscle force resulted in statistically significant increases in silent period durations.

Factors related to success and failure rates at 3-year follow-up in a multicenter study of overdentures supported by Brånemark implants.

An international prospective study of Brånemark implants retaining overdentures was conducted at nine clinical centers. One hundred thirty-three subjects were recruited in a 12-month period and provided with 510 implants, 117 of which were in maxillae and 393 were in mandibles. This study reports the 3-year follow-up status of 120 overdentures and 444 implants. There were 11 overdenture failures (9.2%). Maxillary overdenture failure rates (27.6%) were nearly nine times greater than mandibular overdenture failure rates (3.3%). Maxillary overdenture treatment was less successful than previously reported fixed implant-supported restorations. However, their mandibular counterparts had success rates slightly higher than those reported for fixed implant-supported restorations. At 3 years, 150 implants remained submerged and 66 implants had been withdrawn because the subjects discontinued study participation. Eleven mandibular and 29 maxillary implants had failed and had been removed from 21 subjects. Logistic regression with forward model selection indicated that one two-way interaction was significantly related to implant failure. At highest risk were the subjects who possessed dental arches with bone quantity E and bone quality 4. Subjects with one implant failure were likely to have more than one failure. The Generalized Estimating Equation was used to adjust for the cluster effect in this population because multiple implants (2 to 6) were placed and evaluated in each of the 133 subjects.

A multicenter study of overdentures supported by Brånemark implants.

Nine clinical centers participated in a prospective study of overdentures supported by Brånemark implants in the maxilla or mandible. The study initially comprised 133 patients provided with 117 implants placed in the maxilla and 393 implants placed in the mandible. The preliminary results indicate a success rate in the mandible comparable with the reports on fixed prostheses. Conversely, overdenture treatment in the maxilla seems to be less favorable than previous reports of fixed restorations. The differences between the fixed and the present overdentures in the maxilla were mainly based on differences in patient selection and bone quality. A total of 32 implants was mobile and removed and another 29 implants were lost to follow-up because of patient dropout up to the first annual checkup after denture placement. A higher implant failure rate occurred in the maxilla. Mucosal reactions were also more unfavorable around implants placed in the maxilla.

A 5-year prospective multicenter follow-up report on overdentures supported by osseointegrated implants.

This report presents the results of a 5-year prospective multicenter study including nine centers worldwide. A total of 30 patients received 117 Brånemark implants in the maxillae, and 103 patients received 393 implants in the mandibles. According to the protocol, all integrated maxillary implants were to be loaded; however, only two of four mandibular implants were planned for support of the overdentures, leaving the remaining implants covered by mucosa as backup for possible implant failures. Thirty-five patients (26.3%) who were provided with 127 implants (24.9%) were withdrawn from the study. Six patients treated in the maxilla lost all their implants and resumed wearing complete dentures. The cumulative success rates for implants and for overdentures supported by two implants in the edentulous mandible were 94.5% and 100%, respectively. The corresponding cumulative success rates for implants and for overdentures supported by an optimal number of implants in the maxilla were 72.4% and 77.9%, respectively. Significantly better jawbone characteristics at the time of implant surgery were considered to contribute to the better cumulative success rates in the mandibles. Mean marginal bone loss was 0.8 mm (SD 0.8) and 0.5 mm (SD 0.8) for loaded implants during a 5-year period of time in the maxillae and mandibles, respectively. Measurements of the clinical height of the abutment cylinders indicated a mean recession (0.2 mm) of peri-implant mucosa during the follow-up period in the mandibles. Conversely, hyperplasia was observed in the maxillae.

Pathophysiology of occlusal balance.

Functional disturbances of the masticatory system reflect a failure in the adaptive capacity of the individual to excessive structural and functional demands. Formerly, a particular type of articulation, balanced occlusion, was thought necessary for maintaining the health of the dental apparatus. Over the years the concept of stability of occlusion has evolved, however controversy still exists as to where stable tooth contact is made, centric occlusion of centric jaw relation. In order to express biological adaptability within the normal masticatory system, harmony at the anatomical median occlusal position is suggested as the prerequisite of a physiologically balanced occlusion.

Examination, diagnosis and treatment of occlusal pain-dysfunction.

The complaint of chronic oro-facial pain is common, and this often presents as a frsutrating diagnostic problem. Conventional efforts at dental management of chronic pain-dysfunction in the occlusal components, tend to be unrewarding when the tissue degeneration is advanced. However, early treatment and prevention of the signs and symptoms are in the realm of every-day general practice.

Endurance of jaw elevator muscles during cementation of a single molar crown.

Muscle activity of four jaw-closing muscles was monitored in 19 healthy subjects by EMG, under conditions associated with cementation of a crown restoration. Each subject performed two maximum voluntary contractions (MVC), each of two minutes duration, separated by a thirty-minute time interval. There was no visual feedback of muscle activity. Local analgesia, psychologic reinforcement and actual cementation were other conditions tested. All muscles fatigued as a function of time. For this experimental procedure the ipselateral muscles demonstrated less endurance than contralateral muscles. Psychologic reinforcement did not alter muscle activity. The effect of local analgesia was inconclusive and requires further investigation.

Efficacy of arthroscopic surgery and midlaser treatments for chronic temporomandibular joint articular disc derangement following motor vehicle accident.

As a result of motor vehicle accident soft-tissue injury, temporomandibular joint articular disc derangement may develop and persist despite symptomatic treatment and medication. This study reports the effectiveness of management directed at controlling the TMJ and masticatory neuromuscular pain dysfunction with a TMJ/interocclusal stabilization appliance, specific biofeedback and ultrasound therapy. Following these conservative measures residual articular disc derangement was present in some subjects who were offered arthroscopic surgery and infrared midlaser with TMJ/occlusal stabilization. Twenty subjects with residual disc derangement were randomly selected into two groups with and without arthroscopic surgery, and analyses of variance made before treatment, 12 months after conservative procedures, 3 months following arthroscopic surgery and midlaser therapy and 3 years since commencement of management. Dependent variables compared were pain-discomfort, Clinical Dysfunction Index, articular disc derangement and maximal voluntary jaw opening. Conservative management alone provided significant reduction of pain-discomfort and clinical dysfunction, while arthroscopic surgery resulted in significant reduction in articular disc derangement. The midlaser with TMJ/occlusal stabilization maintained significant improvement in the variables (p < 0.01) for both groups. The common articular deviations in form found at arthroscopy were soft tissue alteration with hyperaemia, synovitis, synovial membrane and posterior attachment folding with connective tissue hyperplasia, and disc displacement with fibrous adhesions. The Global Status Score of pain behaviour compared with residual function, confirmed the presence of greater pain before treatment commenced.

Occlusal adjustment for a physiologically balanced occlusion.

An investigation of the neuromuscular effects of dental contact at the physiologic median occlusal position was conducted before and after occlusal adjustments. Eighteen patients with histories of functional disturbances of the masticatory system, but whose painful symptoms had subsided, were analyzed before and after occlusal adjustments. Nine of the patients with missing teeth received fixed partial dentures and occlusal adjustments. Another group of nine subjects with normal occlusions were used as controls. Electromyographic recordings of the bilateral temporal and masseter muscles enabled quantification of two reflex parameters, the EMG silent period duration, and the mechanical latency of the jaw-opening reflex. Phase-plane traces of jaw-closing velocity as a function of position displayed the repeatability of the median occlusal position. The statistical analysis disclosed that the mean duration of EMG silent periods and latency of the jaw-opening reflex were significantly reduced following the treatment procedures. Within the limits of this study it was concluded that the described occlusal adjustments will reduce the masticatory reflexes evoked at median occlusal position to within the range of normal subjects. Furthermore these changes can be monitored by electrophysical methods.

The clinical significance of median occlusal position.

The harmony of the occlusal components of the teeth, mandibular joint and muscles, were investigated in 180 human subjects by clinical, dental articulator, radiographic and electrodiagnostic methods. Significant correlations were found between disharmony of these components at median occlusal position (MOP), and with pain-dysfunction of the masticatory system. Using the standardized stimuli of opening the jaw wide and snapping it shut automatically into MOP, temporalis and masseter muscle co-ordination and somesthetic reflex effects were quantified. The interval from tooth contact (s) to reinstitution of EMG activity (x), and the EMG silent-period duration (SP), were prolonged in the patients but returned to within the control range with elimination of the pain-dysfunction. Muscle incoordination with mandibular dysfunction was prevalent in the patients, and the incidence of osteoarthritis was greatest in those with persistent symptoms. The hypothesis was supported that disharmony of MOP exists in pain-dysfunction patients--while successful occlusal therapy leads to the restoration of the harmony within the biologic range. This implies physiological significance to this hitherto clinically neglected occlusal position.

The effect of the bite plane splint on the electromyographic silent period duration.

An electromyographic study of the masseter and anterior part of the temporalis muscles was performed on ten patients presenting temporomandibular joint dysfunction symptoms. The EMG silent periods (SP) produced in the open-close-clench cycle and jaw-jerk reflex were compared for duration before and after treatment with an occlusal bite splint. Following use of the splint, there was a shortening of SP indicating the possible use of the duration of SP as a diagnostic measurement, and also as an indication of treatment effectiveness.

Prosthodontic treatment, patient response, and the need for maintenance of complete implant-supported overdentures: an appraisal of 5 years of prospective study.

The prosthodontic methods and outcomes of treating 127 patients in nine centres over a period of 5 years is described. The benefits perceived by patients and the changes induced in the denture-bearing tissues and temporomandibular joints are reported. To sustain effective treatment outcomes, the levels of maintenance needed by the overdentures are contrasted for restoration of the edentulous mandibles and maxillae.