Frederik Bosman

Stress distribution around dental implants: Influence of superstructure, length of implants, and height of mandible

The stress distribution around dental implants was investigated by use of a two-dimensional model of the mandible with two implants. A vertical load of 100 N was imposed on abutments or the bar connection. The stress was calculated for a number of superstructures under different loading conditions with the help of the finite element method. The length of the implants and the height of the mandible were also varied. A model with solitary abutments showed a more uniform distribution of the stress when compared with a model with connected abutments. The largest compressive stress was also less in the model without the bar. Using shorter implants did not have a large influence on the stress around the implants. When the height of the mandible was reduced, a substantially larger stress was found in the bone around the implants because of a larger overall deformation of the lower jaw.

Force-deformation properties of artificial and natural foods for testing chewing efficiency

The force-deformation characteristics of two artificial test foods (Optosil and Optocal) for measurements of food comminution during mastication were investigated in a bite simulator and compared with those of carrots and peanuts. The influence of cusp geometry was evaluated by use of a flat plate and three cusp forms. The forces at the yield point were lower for Optocal than for Optosil artificial test food. The forces needed for Optocal overlapped those needed for carrots and peanuts. The natural foods showed more variation in the force and percentage of deformation at the yield point than the artificial foods. The artificial foods reflected the differences in cusp form better than did the natural foods. The use of artificial foods fulfills a need for standardization and warrants consideration in studies of mastication.

STANDARDIZED RADIOGRAPHS OF THE ALVEOLAR CREST AROUND IMPLANTS IN THE MANDIBLE

The techniques currently used for standardized longitudinal radiographic evaluation of the supporting bone around dental implants are not suitable for general application. An aiming device is described for intraoral radiography used to evaluate the crestal bone height around dental implants used as retention for overdentures. This aiming device has been tested on four different implant systems by four dentists. Error analysis of serial radiographs indicates small deviations in reproducibility. It is concluded that this method is suitable for routine evaluation of dental implants.

Information on infraorbital nerve damage from multitesting of sensory function

Sensory disturbance following orbitozygomatic complex fractures was studied in 65 patients from 4 treatment groups which represented potentially varying degrees of sensory disturbance. The fracture-type-dependent treatments were: no surgical intervention (n = 20), closed reduction with or without wire fixation (n = 17), open reduction with miniplate fixation (n = 15) and/or reconstruction of the orbital floor (n = 13). In order to assess the sensory function of different classes of afferent fibres, several methods of sensory testing were applied. On average 6.3 months after treatment, the patients report was obtained, and tests regarding touch, two methods of two-point discrimination, and cold were applied on the cheek and upper lip. The degree of sensory disturbance was method-dependent. In patients who underwent closed reduction, pronounced levels of positive correlation occurred between results from different tests or from both test sites. The levels of these correlations were, in general, low for all other treatments. These findings suggest that afferent fibres of both large and small diameter tended to be permanently damaged in the patient group with closed reduction. In contrast, the types of sensory afferent fibres that were involved in the trauma and/or their recovery were highly variable within patients and sites for all other treatment groups.

Maximal bite force and surface EMG in patients with myasthenia gravis

Masticatory muscle strength was quantified in patients with bulbar myasthenia gravis and compared with that of patients with ocular myasthenia gravis, patients in clinical remission (whether or not pharmacological) who previously suffered from bulbar myasthenia gravis, and healthy subjects. Maximal bite force and maximal activity of the masseter and temporalis muscles and of the submental muscle complex were measured. Bite force was decreased in the patients with bulbar myasthenia gravis, but was normal in the patients in the clinical remission group and in the ocular group. These findings were consistent with the results of electromyographic data. Although subjective reports of masticatory muscle weakness provide valuable information, quantitative measurements provide more information about the degree of muscle weakness of individual muscles. This is especially important for longitudinal evaluation of therapy in individual patients and for pharmacotherapeutic research.

A selection model to estimate the interaction between food particles and the post-canine teeth in human mastication

Food comminution during chewing is the composite result of selection and breakage. In the selection process, every food particle has a chance of being placed between the antagonistic post-canine teeth and being subjected to subsequent breakage. The selection chance, being the ratio between the number of selected and offered particles, has been mathematically described as a function of the number of particles offered, in terms of the number of breakage sites available on the teeth and particle affinity, i.e. the fraction of breakage sites occupied by one particle. The assumption has been made that particles are successively selected during a jaw-closing phase and that the selection chance of subsequent particles having the opportunity to occupy a breakage site proportionally decreases with the unoccupied fraction of the breakage sites left. The number of selected particles of a single size then asymptotically approaches the total number of breakage sites available for that size, when the number of particles offered increases. The critical particle number, derived from the measure of particle affinity, indicates the number of particles by which the breakage sites become saturated. The selection model for single particle sizes has been successfully applied to describe one-chew experiments, using various numbers and sizes of particles made of a silicone-rubber. After pseudo-chewing movements the subjects were unexpectedly instructed to carry out a real chew on particles (half-cubes). Undamaged, hence non-selected half-cubes could afterwards be distinguished from broken particles. The model has been extended to a particle mixture to describe the selection of particles of a certain size while other particles of different sizes are present. If a two-way competition between smaller and larger particles is assumed, the model predicts that the ratios of the selection chances between different particle sizes do not depend upon the numbers of the particles in the mixture.

Orthopedic diagnostic tests for temporomandibular and cervical spine disorders.

The interexaminer reliability of six orthopedic tests, applied to the masticatory system, was determined in a group of 79 patients with signs and/or symptoms of TMD. Multitest Scores were composed for each test and combinations of tests for the three main symptoms of TMD, namely, pain, joint sounds, and restriction of movement. Although the tests showed different reliability scores, the reliability of detecting these three main symptoms of TMD was satisfactory. All the tests contributed to the diagnostic process, with active movements being the most powerful test. The combination of active movements, passive movements, and palpation provided valuable diagnostic information. Other tests could be used for specific diagnostic problems. The scores of the orthopedic tests applied to the neck show that extension and flexion can be evaluated most reliably with active movements and by assessing end feel. The interexaminer agreement for recording pain was also satisfactory for flexion and extension. The interexaminer reliability of the tests recording pain and end feel in the shoulder girdle was moderate for anteflexion.