Ability of human subjects to discriminate forces applied to certain teeth

Occlusal Concepts and Considerations in Fixed Prosthodontics

The UK has an increasingly ageing population, many of whom are retaining more of their own teeth. This has led to an increase in the prevalence of tooth wear and the need to replace pre-existing failing restorations. In many cases this will be achieved by fixed prosthodontics. This paper provides a brief overview of important occlusal concepts that should be considered when providing non-implant fixed prosthodontics using either a conformative or reorganised approach. The aim is to give general dental practitioners the confidence to provide these types of restorations in primary care. Clinical cases demonstrate how the occlusion can be controlled to optimise clinical outcomes.

Discrimination of hardness by human teeth apparently not involving periodontal receptors

Periodontal receptors are generally thought to provide the input used to detect the hardness of food. Whether hardness can be sensed by teeth without periodontal assistance was tested here. A bite-force transducer was sandwiched between a hard acrylic strip on one side and rubber on the other side, both sides being covered with masking tape to prevent participants from sensing a difference in touch. Participants were asked to increase the bite force on the sandwich until, and if, they could detect which material, hard acrylic or rubber, was on the upper side. The positions of acrylic and rubber were randomly chosen. Fifteen participants each undertook three separate experiments each involving 10 tests using (1) bare incisors, (2) incisors capped with acrylic and (3) bare molars. The accuracy of responses and the direction and magnitude of bite forces were recorded. Participants most correctly detected the surfaces with bare incisors (91% correct, SD = 11%). Performance was significantly worse with capped incisors (79%, SD = 19%) (p < 0.01) and worse still with molars (57%, SD = 24%) (p < 0.001). The detection threshold using bare incisors was increased in 14 out of the 15 participants when the incisors were capped, but the increase was statistically significant (0.002 < p < 0.01) in only six of them. The molar threshold was significantly increased (0.002 < p < 0.01) in comparison with the bare incisor threshold in 12 of 15 participants. There was no correlation between bite direction and the position of the rubber. Because in each trial the upper and lower periodontal input was the same whether the rubber was on the top or on the bottom, it was concluded that the periodontal ligament was not involved. The observed discrimination was probably based on a difference in the pressure on the upper and lower teeth. Incisal edges sank more deeply into the rubber and reduced the pressure (force/unit area) on a tooth crown.

Bite force displayed during assessment of hardness in various texture contexts

The relationship between mastication pattern, mechanical properties of the food bolus and texture perception are not fully understood, though the mastication process is known to adjust to different textural properties of foods. This study investigated the role of the bite force as one major aspect in hardness assessment of materials exhibiting simple mechanical properties over a wide hardness range. Elastic, plastic and brittle materials (silicone elastomers, waxes and pharmaceutical tablets, respectively) were tested. The rheological characteristics of these products were measured. For each product, one to four differential thresholds were determined at different points on a hardness scale by 10 individuals free of dental pathology. Bite forces were recorded by placing a small intraoral load cell under each sample. To assess the influence of the nature of the applied force, bites were made either directly on to the sample or on a metal disc placed between the teeth and the sample. As the individuals had to break the brittle products to perceive any hardness difference, bite forces were very closely correlated with the hardness of the products (r = 0.99). For plastic products, bite forces again correlated with the hardness (r = 0.96), even though individuals could stop biting at any time during the plastic deformation. Hardness perception of brittle and plastic products depends directly on sensory information about the bite force. However, hardness assessment of elastic products was obtained under constant bite force; here, the resulting deformation may provide sensory information about hardness.

Discrimination ability in patients with extensive fixed partial dentures on mandibular canine teeth

To study discrimination ability under different test situations, a psychophysiologic test was performed in a group of patients with 12-unit mandibular fixed partial dentures supported on the 2 canines. The cantilever segments were exchangeable. Analyses of discrimination ability were performed with regard to periodontal and endodontic status of the abutment teeth and to type of mucosal contact in cantilever regions. Discrimination ability was markedly reduced with a strongly reduced periodontal bone contact area. The endodontic status did not affect discrimination ability. A tendency towards better discrimination ability was seen when the cantilever sections without mucosal contacts were compared with those with mucosal contacts through pontics or saddles.

Human bite force discrimination using specific maxillary and mandibular teeth

The purpose of this study was to determine whether performance differences existed in subjects' self-generated bite force discrimination ability using maxillary and mandibular central incisors, canines, premolars and first molars. Two separate studies were conducted: (i) to assess whether performance differences existed in subjects' bite force discrimination ability using central incisors and premolars; (ii) to compare subjects' performance on bite force discrimination using central incisors, canines and first molars. Assessment of bite force was measured using a specially designed strain gauge scale allowing subjects to visually monitor when their biting force equalled a preset resistance. Resistance forces of 500, 1000 and 3000 g were selected as standards. Subjects were presented with a series of paired resistance settings, one at a time, the first of each pair being the standard and the second being the comparator setting of a predetermined amount. This paired-comparisons procedure was continued until the subjects' difference limen (DL) value (the threshold of discrimination between two forces) could be established. The first study revealed no significant (P greater than 0.05) overall difference in subjects' bite force discrimination ability relative to specific teeth. In contrast, in the second study a significant difference (P less than 0.05) was identified in subjects' performance relative to specific teeth; subjects' performed better using central incisors compared to first molars. In both studies, subjects' performance was significantly better (P less than 0.05) using the 500 g standard compared to the 3000 g standard in the first study, and compared to the 1000 g standard in the second study. No significant differences (P greater than 0.05) were observed between the performance of males and females in either study.

The effect of experimental anesthetization of the temporomandibular joint superior cavity on bite force discrimination

The purpose of this study was to determine whether bilateral experimental sensory impairment of the temporomandibular joints (TMJs), as induced by injecting 1.5 ml of two percent mepivacaine into the superior cavity of the TMJs would alter the subject's ability to discriminate among differences in their bite force. Assessment of bite force was measured isometrically, using the strain gauge scale, and isotonically, using the mechanical swing beam scale. Resistance forces of 500 and 1000 gms were selected as standards. For each task, subjects were given a series of paired resistance settings, one at a time, the first of each pair being the standard resistance and the second being a comparator resistance of some greater amount. Subjects reported whether biting against the comparator resistance was equal to, greater than, or less than the standard resistance. This procedure of paired comparisons was continued until the subject's threshold of discrimination (difference limen value) between two biting forces was established. The results revealed that the subject's ability to discriminate differences in their bite force, either isometrically or isotonically, was not significantly (p greater than 0.05) affected following anesthetization of the superior cavity of the TMJs. These findings suggest that the sensory receptors within the TMJ capsules are not significantly involved in the detection of forces that play a role in monitoring biting force.

The effect of periodontal bone loss on bite force discrimination

This study compared bite force discrimination between 14 treated periodontal patients with significant bone resorption and 14 control subjects who were free of periodontal disease. Bite force was measured using a strain gauge scale which permitted subjects to visually monitor when their bite force equaled a preset resistance. A bite force of 500 gm was selected as the standard. Subjects were presented with a series of paired resistance settings, one at a time, the first of each pair being the standard and the second being the comparator setting of some predetermined different amount. This procedure was continued until the subject's difference limen (DL) value, the threshold of discrimination between two bite forces, was established. The periodontal patients required an average of 334 additional grams of resistance over the standard before they could detect a difference, whereas the control subjects required only 201 additional grams. These group means were significantly different (P less than 0.01). The results of this study suggest that the periodontal ligament provides sensory feedback relative to bite force discrimination.

Bite force discrimination by individuals with complete dentures

The purpose of this study was to determine whether differences existed in interincisor bite force discrimination between a group of subjects wearing complete dentures and a group of dentate individuals. It was hypothesized that biting force is monitored at least in part by the sensory mechanism within the PDL and that the absence of the PDL would result in reduced bite force discrimination. A specially designed strain gauge scale was constructed for the measurement of bite force. Bite force discrimination was assessed at three different standards including 500, 1000, and 3000 gm. Data analysis revealed that, overall, bite force discrimination was not significantly different for the two groups. However, at the lightest standard of 500 gm, the dentate group performed significantly better (p less than .05) than the denture wearers. It is concluded that the sensory system within the PDL plays a role in monitoring bite force discrimination.

Human discrimination of different bite forces

Twenty young adult subjects were selected to determine normal baseline data of dynamic interdental bite force discrimination by use of a specially designed strain gauge instrument. The data may aid in defining the role of the periodontal ligament, temporomandibular joint and muscles of mastication in the regulation of interincisor bite force.

Magnetic retention units for overdentures

Mechanical attachments used to improve retention of overdentures have their limitations. With the recent development of the cobalt-samarium magnet an alternative method of achieving increased overdenture retention is offered. The most suitable form of magnet appears to be of a reverse split pole design with a ferromagnetic disc or keeper which will ensure a closed magnetic field. Clinical techniques involve conventional endodontic therapy, and the basic method of overdenture construction can be followed with only minor modification.

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.

Tooth loading and cuspal guidance in canine and group-function occlusions

(1) Tooth loading with cuspal guidance in canine and group-function occlusions has been discussed. (2) Canine guidance and group-function guidance occlusions are considered normal; the latter occurs naturally due to occlusal wear. (3) When an entire occlusion is to be restored, either occlusal scheme will serve adequately. (4) Where only a portion of the occlusion is to be restored, the restoration must be consistent with the existing occlusal scheme. (5) Regardless of which occlusal scheme is used, the dentist must maintain it during regular postoperative appointments.

Reflex control of the jaw muscles by stimuli from receptors in the periodontal membrane

In the opinion of a number of investigators, the only function of the mechano-receptors in the periodontal membrane is to inhibit closure of the jaws via a reflex pathway when a predetermined pressure on the teeth has been exceeded. In our opinion, the receptor system in the periodontal membrane may also play a role in a complex regulatory system which controls the movements of the lower jaw during chewing. In order to test this hypothesis a study was made of the changes occurring in the contraction pattern of three masticatory muscles of the cat, when the cuspids in the upper jaw were displaced in various directions. In all the experimental animals used, electromyographic changes in the three muscles investigated, could be recorded as a result of displacement of the cuspids. The results obtained suggest, at least in the case of the temporal and pterygoid muscles, that there are specific reflexogenic zones in the periodontal membrane, These results support the previously suggested hypothesis that a number of the pressure-sensitive receptors in the periodontal membrane play a role in a regulatory system which controls the movements of the lower jaw--as during chewing--by exerting a reflex influence on the degree of contraction of the masticatory muscles. In the discussion this hypothesis is worked out in more detail and the extent to which the results fit the chewing pattern of the cat is examined. In the conclusion, the author asks whether the finding of a regulatory system in the cat may also be applied to man.

Occlusal force discrimination by denture patients

A study was conducted on subjects with conventional dentures and with overlay dentures to compare their abilities to discriminate between occlusal forces. Perpendicular forces were applied to the dynamic center of the occlusal table of the mandibular denture. Each subject's ability to distinguish differences in values of force was observed and recorded. All subjects with dentures showed sensory threshold values close to those reported for natural teeth. A graphic plotting showed that the responses of subjects with overlay-type dentures were more closely correlated with the psychophysical law as expressed by Stevens as a power function. Since this phenomenon holds true for natural teeth, the overlay denture more closely resembles natural teeth in this type of sensory function than does the conventional denture. In addition to recognized advantages, such as preservation of the ridge and improved retention and stability, the overlay denture provides more typical sensory function than is provided by the conventional denture. This advantage should further motivate dentists and patients to consider the retention and utilization of at least two suitable teeth in an overlay-type denture service.