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Purpose: The inter-relationships between various implant and bone parameters were evaluated for their influence on the von Mises stress distribution within the mandible using the finite element procedure. The maximum compressive stresses in cancellous and cortical bone were compared to the published stress-strain data to determine bone fracturing status when the maximum (traumatic) loading is applied., Materials and Methods: Parameters considered herein include the implant diameter and length. Also considered are Young's modulus of cancellous bone and that of cortical bone, along with its thickness. The implant-bone system was modeled using two-dimensional plane strain elements, 50% osseointegration between implant and cancellous bone was assumed, and linear relationships were assumed between the stress value and Young's modulus of both cancellous and cortical bone at any specific point within the mandible., Results: Implant length was more influential than implant diameter within cancellous bone, whereas implant diameter was more influential in cortical bone. A ranking of all the parameters indicated that the applied masticatory force had a more significant influence on the stress difference, in both cancellous and cortical bone, than all other parameters. Young's modulus of cortical bone and implant length were least influential in cancellous and cortical bone, respectively. Under traumatic loading, cancellous bone fractured for all parameter combinations. When all parameters were set to their average values, the cortical bone did not fracture under traumatic loading. However, it fractured if all the parameters were all set to the minimum values., Conclusion: Quantitative evaluation and ranking of the major implant and bone parameters will help provide practical guidelines that are useful for the design and testing of dental implants. The study may also be of interest to dental professionals in evaluating possible implant placement options under various clinical scenarios.

How 'control' characteristics of masticatory jaw movement, such as skilfulness of the movement, change after alteration in occlusion remains uncertain. For each of 10 healthy adults with good occlusion, an occlusal interference with artificial 'tooth-cusp' was introduced to the crown of the upper molar tooth on the non-working side of unilateral chewing. Mandibular incisor-point movements were then recorded by a 3D tracking device. The introduction of the occlusal interference induced a remarkable increase in the normalized jerk-cost (NJC), prolonged duration of the decelerative phase and lowered peak velocity for jaw closing movement during chewing. Overall, the NJC and velocity profile showed significant recoveries during the course of about 90 repetitive chewing cycles performed under the altered occlusal condition. These findings suggest that acute adaptive changes of jaw motion after introduction of occlusal interference might be characterized as the recovery process of movement skilfulness in terms of movement smoothness and velocity profile.

Associations between articulatory speech disorders and mandibular movement capacity, as well as between malocclusions and jaw movements, were examined in two groups of adolescents, i.e. 52 individuals with and 45 without misarticulations of speech. The mean age of the whole sample was 19.2 years. Articulatory speech disorders and functioning of the speech articulators were diagnosed by a phoniatrician. Mandibular movement capacity, malocclusions, occlusal interferences, and signs of temporomandibular dysfunction were recorded by an orthodontist. Multiple regression analyses showed that subjects with articulatory speech disorders were likely to have smaller opening capacity than subjects with a correct speech articulation. Excessive overjet, lateral cross bite, and a tendency to anterior open bite were associated with large movements of the jaw. These results suggest that in young adulthood mandibular movement capacity seems to vary depending on occlusion and is related to misarticulations of speech.

Frontal plane mandibular rotations and corresponding hemimandibular translations were studied in vitro by using direct observations of a human cadaver mandible and in vivo by using the indirect observations of rotational electrognathography. A comparison between the two methods showed that rotational electrognathography erred in measuring the clinically relevant hemimandibular translations resulting from mandibular rotations having a unilateral molar point (simulated occlusal interference) as the pivot of frontal plane torque. In vitro frontal plane rotations about a unilateral mandibular molar tooth (simulated occlusal interference) suggested that the resulting hemimandibular upward translations of the lateral portion of the mandibular condyle, contralateral to the molar tooth, would cause considerable compressive loading of the temporomandibular joint disc.

A rigid intercuspal interference (minimum mean height of 0.24 mm) was placed on either the right or left mandibular second premolar and first molar of 12 subjects. During brisk and forceful biting on the interference, rotational electrognathography measured maximum torque of the right and left mandibular condyles in the frontal and horizontal planes of orientation. All subjects showed frontal plan upward rotation (mean of 0.7 degrees) of the mandibular condyle contralateral to the interference. In 33% of the subjects there was no horizontal plane backward rotation. In 58% of the subjects there was horizontal plane backward rotation (mean of 0.5 degrees) of the mandibular condyle ipsilateral to the interference, and in one subject (8%) there was backward horizontal plane rotation (0.1 degree) of the mandibular condyle contralateral to the interference. It was inferred that the masseter muscle, ipsilateral to the interference, generated negative work in order to decelerate frontal plane 'unseating' of the mandibular condyle ipsilateral to the interference. It was inferred that the masseter muscle, contralateral to the interference, produced positive work in order to accelerate frontal plane 'seating' of the mandibular condyle contralateral to the interference. Finally, it was speculated that the impact forces of frontal plane 'seating' of the mandibular condyle, contralateral to the interference, might lead to 'vacuum sticking' of the temporomandibular joint disc because of the formation of negative hydrostatic pressures.

Mandibular jaw opening was related with general joint mobility in a non-patient adolescent group. The angular rotation of the mandible at maximum jaw opening was slightly larger in females than in males and significantly larger in hypermobile individuals. No significant relationship between linear measuring of maximal mandibular opening capacity and peripheral joint mobility was found either at active (AROM) or at passive range of mandibular opening (PROM). PROM was strongly correlated to the mandibular length. Clinical signs in the great jaw closer muscles could not be associated to decreased AROM. The mean value of the difference between PROM-AROM (DPA) was 1.2 mm. Frequent clenching and/or grinding was correlated to increased DPA only in hypermobile adolescents (r = 0.49***). Those with DPA exceeding 5mm had all reciprocal clicking.

The effects of occlusal interference on masticatory cycles have been studied in twenty nine volunteers with complete natural dentition, using an electromagnetic pantograph (Sirognatograph, Siemens A.G.). After a one week recall, a decrease in speed motion was noted and the range of cycles in the horizontal plane had been altered.

Open-close-clench cycles have been studied in 12 children with a lateral forced bite in order to investigate how the neuromuscular system of the mandible adapts itself in the presence of occlusal interferences. The mandibular movements were registered in a frontal plane at the central incisors with an opto-electronic registration technique. Series of 35 cycles were recorded to intercuspal position, against flat occlusal splints constructed in intercuspal raised and retruded positions, and against splints with occlusal stops in a retruded position. Average lateral displacements of the mandible during cycle series against flat occlusal splints were measured relative to cycle series to intercuspal position and relative to series against splints with occlusal stops in the retruded position. The lateral mandibular displacements were registered at maximal tooth-tooth or tooth-splint contact and at 7, 14, and 21 mm mouth-opening. It was found that the mandible in the subjects investigated is displaced to the forced bite side both during cycle series into intercuspal position as well as when occlusal contacts are eliminated by the use of flat occlusal splints.

The character of the occlusal surfaces of teeth programs the functions of muscles that move the mandible and imposes specifications upon the dentist within which he must work in manipulating the patient's mandible. If he exceeds those specifications, protective responses that inhibit his efforts are elicited in the patient's musculature. A knowledge of the laws governing functions of the muscles that move the mandible enables the dentist to acquire mandibular-manipulation skills necessary for diagnosis and effective occlusal treatment. A model in which the dentist visualizes the patient, the patient's protective reflexes, the components of the patient's gnathostomatic system, and himself as four independent personalities participating in the jaw manipulation is a useful tool in acquiring mandibular-manipulation skills. This article is Part III of a series presented in four parts on the "Biologic Laws Governing Functions of Muscles That Move the Mandible."

Lateral displacement of the mandible was induced experimentally in five adult male Rhesus monkeys. Following from 2 1/2 weeks to 19 months, the animals were sacrificed and examined histologically. Two of the monkeys received H3 proline 4 months prior to sacrifice and radioautographs were prepared. The lateral displacement apparently caused great discomfort because the monkeys refused to eat and lost weight rapidly for a few months. After about 12 months, the monkeys could again eat their normal diet to the extent they started to gain weight slowly. The histological and radio-autographic findings indicated almost no changes of the articular surfaces of the temporomandibular joints. However, extensive reorganization of the neck of the condyles was observed. Severe periodontal trauma and extensive movements of the teeth occurred in spite of the fact that the teeth in each jaw were splinted firmly together.

An experimental short term study on the effect of an occlusal interference on the path of closure of the mandible was carried out on 8 persons. The interference consisted of a gold inlay placed unilaterally in one of the mandibular first molars. Clinical and electromyographic studies revealed functional disturbances or pain in all subjects. The masticatory musculature was tender to palpation and showed coordinational disturbances; the TMJ showed tenderness to palpation, clicking and irregular movements and the interfering teeth periodontal tenderness.

The effect of four different occlusal situations (group function, canine guidance, working side occlusal interference, and hyperbalancing occlusal interference) on EMG activity in jaw elevator muscles and related mandibular movement was investigated on 12 subjects. With a computer-based system, EMG and displacement signals were collected simultaneously during specific functional (unilateral chewing) and parafunctional tasks (mandibular gliding movements and various tooth clenching efforts) and analyzed quantitatively. When a naturally acquired group function was temporarily and artificially changed into a dominant canine guidance, a significant general reduction of elevator muscle activity was observed when subjects exerted full isometric tooth-clenching efforts in a lateral mandibular position. The original muscular coordination pattern (relative contraction from muscle to muscle) remained unaltered during this test. With respect to unilateral chewing, no significant alterations in the activity or coordination of the muscles occurred when an artificial canine guidance was introduced. Introduction of a hyperbalancing occlusal contact caused significant alterations in muscle activity and coordination during maximal tooth clenching in a lateral mandibular position. A marked shift of temporal muscle EMG activity toward the side of the interference and unchanged bilateral activity of the two masseter muscles were observed. The results suggest that canine-protected occlusions do not significantly alter muscle activity during mastication but significantly reduce muscle activity during parafunctional clenching. They also suggest that non-working side contacts dramatically alter the distribution of muscle activity during parafunctional clenching, and that this redistribution may affect the nature of reaction forces at the temporomandibular joints.

Accurate diagnosis and treatment of the gnathostomatic system require an understanding of both its biomechanics and its physiology. Clinically, the treatment consists of modifying the existing occlusal program to relieve stress from distressed tissues. The objective of treatment is to effect a neuromuscular release of the mandible. This may be accomplished by (1) equilibration of the natural occlusion, (2) orthodontics, (3) restorative procedures, or (4) surgery. Most frequently, however, the treatment entails some combination of these procedures. The criteria for success of treatment are not determined by the method or technique employed but by the neuromuscular response that the treatment produces. The purpose of this article is not to suggest which occlusal scheme produces the most favorable muscle response in the gnathostomatic tissues. Neither is an objective of this article to teach the mandible-manipulation techniques that are needed to identify occlusal irritants, perform occlusal equilibrations, or obtain accurate centric relation recores. The objective of this article is to emphasize that there are definite principles by which the muscles respond to occlusal contacts. Occlusal contacts can excite bruxism and the sequelae to bruxism. Knowledge of the laws which govern functions of the muscles that move the mandible enables the dentist to acquire the mandibular-manipulation skills that are necessary for the effective diagnosis and treatment of occlusal conditions.

The prevalence of craniomandibular disorders was studied in 285 17-year-old adolescents with the aid of a questionnaire and a functional examination of the masticatory system including evaluation of TMJs, masticatory muscles, mandibular mobility, and occlusion. The adolescents were followed up longitudinally two more subsequent years. Totally 27 subjects dropped out, leaving 258 for the longitudinal intraindividual comparisons. At the age of 17 a fifth of the subjects reported some symptoms involving the masticatory system, of which most were mild, according to the anamnestic index (Ai) used. Oral parafunctions were commonly reported of which nail-biting dominated. Grinding and clenching of teeth were reported by 8% and 11% respectively. Signs of mandibular dysfunction were found in 56% of the adolescents and were mostly mild according to the dysfunction index (Di) used. Girls more often had signs of mandibular dysfunction than boys. Morphologic malocclusion was recorded in 35%, unilateral contact in RP in 77%, lateral shift between RP and IP greater than or equal to 0.5 mm in 19% and mediotrusion interferences in 30% among the 17-year-olds. No significant difference between sexes was found. Of the sample 62% had either some sign or symptom of dysfunction and there was a positive relationship between the dysfunction indices used. Neither morphologic nor functional malocclusions were related to the Ai. TMJ sounds were related to palpation tenderness in the lateral pterygoid muscle and impaired mobility of the mandible. The number of masticatory muscles tender to palpation was related to reports of fatigue in the jaw, TMJ tenderness, and mediotrusion interferences. Recurrent headache was reported by about 18% of the girls and by almost 6% of the boys. Fatigue in the jaws and difficulties in chewing were commoner in those with frequent and more intensive headache. Tenderness to palpation of the masticatory muscles and impaired mandibular mobility were significantly commoner findings among those with recurrent headaches and those with more intense headache. Tooth-grinding and clenching were related to frequency but not to intensity of headache. Reports of TMJ sounds increased with age for girls who also more frequently reported recurrent headaches than boys. The prevalence of symptoms of mandibular dysfunction was about 20% each year, but there was no general increase of frequency and severity of symptoms during the observation period in spite of an incidence of 8%. The prevalence was, according to the Ai, significantly higher for 18- and 19-year-old girls than for boys. Most symptoms were mild and fluctuated longitudinally.(ABSTRACT TRUNCATED AT 400 WORDS)

Oral behavioural patterns have received limited empirical support for their causal role in the development of head and facial pain. The present study was designed to assess electromyographic (EMG) variations in six muscle groups (i.e., bilateral masseter, temporalis and orbicularis oris) as a function of various oral behavioural patterns. A second purpose was to determine whether mandibular movement patterns and specific oral behaviours could be predicted by EMG patterns. Eleven non-pain subjects followed each of twenty oral behavioural patterns while EMG was recorded. Electromyographic change scores were computed for each behaviour relative to baseline measures. Initial analyses were performed using factorial repeated measures ANOVAS. Using post hoc analyses as general guides, specific EMG criteria were developed for classifying mandibular movements. For most subjects, EMG patterns accurately classified teeth clenching, protrusive/retrusive movements, right movements, left movements and lip movement patterns. Wide individual variations were found among muscle groups for identical behaviours. The association between particular oral behaviours and EMG patterns may explain 'sinus' headaches and certain types of facial pain.