J.J. ten Bosch

A comparison of new and conventional methods for quantification of tooth color

Tooth color is caused by volume reflection, that is, passage of incident light through the tooth followed by backward emergence. This passage is concurrent with sideward displacement of photons that, in effect, influences the result of usual instrumental methods of determining tooth color. This problem is overcome by the use of large-field illumination and small-field observation. A fiber-optics colorimeter based on this principle is described. The color observed through two holes in a double box was visually matched by subtractive adjustment of the illuminating color in one box, whereas the other box showed the central part of the tooth diffusely illuminated by illuminant C light. This colorimeter was tested on wet, extracted human incisors in the tooth arch of a phantom-head. Results were compared with a visual standard-strip method described previously and with a conventional spectrophotometer. It was concluded that the fiber-optics colorimeter is a promising instrument, although technical improvement is necessary.

Tooth Color and Reflectance as Related to Light Scattering and Enamel Hardness

Tooth color is determined by the paths of light inside the tooth and absorption along these paths. This paper tests the hypothesis that, since the paths are determined by scattering, a relation between color and scattering coefficients exists. One hundred and two extracted incisors were fixed in formalin, mounted in a standardized position in brass holders, and pumiced. A facet was prepared near the incisal edge on the labial plane to allow for Knoop hardness measurements with a 500-gram load. Light scattering by the enamel was measured in a 45°/0° geometry; light scattering by both enamel and dentin was measured in a 0°/0° geometry. The reflection spectrum of the tooth was measured from the labial plane with a spectroradiometer in a 45°/0° geometry, with standard illuminant A and standard illuminant D65. To include all volume-reflected light, we used entire-tooth illumination and small-area measurement. CIELAB color coordinates were calculated from the spectra. Neither spectra nor coordinates showed evidence of a contribution of fluorescence to tooth color. Averaged values and standard deviations for L*,a*,b* were 69.9 (4.1), 1.22 (1.4), and 17.9 (2.9), respectively. Both scattering coefficients averaged to 0.6 (0.4) mm-1; Knoop hardness number was, on average, 271 (39) kg/mm 2. L* correlated with a* (r = -0.51), with the enamel scattering coefficient (r = 0.60), and slightly with hardness (r = 0.17, p = 0.03). The colors of 28 teeth from which the enamel was removed correlated strongly with the colors of the complete tooth. This study quantitatively confirms that tooth color is determined mainly by dentin, with enamel playing only a minor role through scattering at wavelengths in the blue range.

FORCES ACTING ON THE MANDIBLE DURING BILATERAL STATIC BITE AT DIFFERENT BITE FORCE LEVELS

Abstract A mathematical model based on an assumed linear relationship between the forces exerted by a muscle and its integrated electromyogram is presented for calculating muscle forces and joint forces acting on the human mandible during static bite situations. Full data from one of 7 male subjects are included as an example of the approach and to illustrate the relevance of the mechanical model for calculating these forces. Under the assumption that the maximum muscle tension (Γ), expressed in N/m2 (kg/cm2) is equal for all muscles, a value of this quantity can be calculated for any bite in any of three bite positions. It appears to be dependent upon the test person only. Alinearity between EMGI and bite force is caused by alinear behavior of muscle force and bite force and is not due to alinearity between EMGI and muscle force. The ratios between muscle force values are dependent on the location of the bite force. Forces in the lateral pterygoid muscles and in the temporomandibular joints increase nearly linearly with increasing bite forces. Reduced data on bite forces, forces in jaw muscles and in temporomandibular joints found from all subjects are presented. Data on maximum bite forces are higher than those found in the literature. Highest bite forces and muscle forces are exerted most often when biting takes place in the region of the first molar. The loading of the temporomandibular joints is highest when biting in the region of the first premolar. Muscle activity may be inhibited in this situation. Forces in all muscles are dependent on the location of the bite force, most clearly demonstrated in the temporal muscles. Joint forces are higher when the bite force is applied more ventrally and may initiate an inhibition when biting in position P1. In position M2 all forces are considerably lower than expected on the basis of the mechanical model only.

Clinical consequences of complaints and complications after removal of the mandibular third molar

Quantitative data on postoperative complaints and complications after removal of the mandibular third molar, especially in relation to the different methods of treatment, are scarce. Mostly an objective approach is lacking. The present study attempts to provide such data and their clinical consequences. Within 1 year, 932 mandibular third molars were removed; 430 extractions served as a control group for 502 surgical removals. The procedure was fully standardized and all measurements objectively obtained. A computer was used for statistical evaluation. It appeared from this study that the possibility of postoperative complaints and complications will be smaller if the wound is not packed, if tight suturing is not done and if reflection of the mucoperiosteum is avoided. If reflection is inevitable the oblique vertical relaxing incision is preferred. Prophylactic administration of antibiotics is rejected.

Influence of window size in small-window colour measurement, particularly of teeth

Tooth colour is often measured with a small window for illumination and measurement. This causes edge loss of the light, resulting in systematic errors in colour coordinates. This paper gives a quantification of the edge losses, and explains their cause. We measured reflectance spectra for 27 Formalin fixated extracted incisors using a small-window reflectance spectrophotometer equipped with external diaphragms of 3, 4, and 5 mm diameter, and using a spectroradiometer. We calculated the colour coordinates L*a*b* from these spectra. Finally, 16 randomly chosen teeth were illuminated with a pencil beam (lambda = 543 nm, and lambda = 633 nm) while the emerging light was measured as a function of distance from the illuminated spot using a CCD detector. These data were used to calculate small-window edge losses, and thus to predict the small-window reflectance factors relative to spectroradiometrically determined reflectance, at both 543 nm and 633 nm. In all instruments the same spot on the tooth was illuminated and measured, and the teeth were always wet. Colour coordinates for the small-window colour measurements deviate significantly from those determined using the spectroradiometer. These deviations can be explained from the wavelength-dependant edge loss that arises in small-window colour measurement.

The absorption and scattering of light in bovine and human dental enamel

The reflectance and transmission of thin slabs of dental enamel has been measured at all wavelengths between 220 and 700 nm by means of an integrating sphere. From the results the true scattering and absorption coefficients have been computed. The theoretical model used is an extended two-flux model, which is presented and discussed. The absorption spectrum of the dissolved organic component of enamel was also determined. An absorption peak at 270 nm is common to all the spectra. This peak in the bovine enamel spectrum is about three times as high as in the spectrum of human enamel. The peak of the dissolved material is about as high as the peak of the corresponding enamel. Hence it is concluded that the organic component, presumably aromatic amino acids, is responsible for most or all of the observed optical absorption.

Optical Methods for the Detection and Quantification of Caries

The commonly used clinical methods are inadequate for reliable diagnosis of caries lesions until demineralization is established. By the time a reliable diagnosis can be made, the damage is often irreversible, and restorative methods may be necessary to prevent further progress of the lesions. Early detection of the caries lesion would enable the dentist, by using effective prophylactic measures, to provide remineralization and conservation of the tooth substance rather than restoration of the dentition. Attempts to improve traditional methods or to develop new methods of detecting caries lesions have been numerous. Most of the presently used diagnostic methods require visual observation of an optical signal. Reflected light is used tc detect changes in color, texture, and translucency of the tooth substance. The tools required are a bright light source and a mouth mirror. With special methods utilizing drying, magnification, and photography, the sensitivity of the method can be increased. Various optical methods for the detection and quantification of caries will be discussed - for example, fiber optic transillumination, ultraviolet illumination, the use of various dyes, and fluorescent or non-fluorescent substances to enhance the contrast between the carious and the sound enamel. This presentation will focus on the following two methods: (1) a method that uses visible laser light within the blue-green region as the light source to improve signal-to-noise ratio and increase sensitivity for detection of early caries lesions, and (2) a recently developed quantitative method based on the scattering of light by enamel crystals in relation to their surrounding environment. The possibilities and limitations of the different methods will be critically evaluated. In the near future, optical methods for the detection and quantification of early caries lesions will provide efficient tools for reliable evaluation of caries-preventive measures.

Invited Review: A Review of Quantitative Methods for Studies of Mineral Content of Intra-oral Incipient Caries Lesions

Modern prospective caries studies require the measurement of small changes in tooth mineral content. Quantitative measurements of changes in mineral content in a single caries lesion is desirable. Quantitative methods can be either destructive or non-destructive. The latter type permits longitudinal studies to be conducted. Various methods available for the analysis of lesion parameters are reviewed. The basic principle of each method is summarized, and its characteristics are discussed. For each method, the correlation between the measured parameter and mineral loss, the useful range of mineral loss, the discrimination threshold, and the repeatability, are presented. Where such quantities were not available in the original papers, they were calculated from literature data. A comprehensive table of specifications of all methods is given.

SCATTERING AND ABSORPTION OF TURBID MATERIALS DETERMINED FROM REFLECTION MEASUREMENTS .2. MEASURING METHOD AND CALIBRATION

A new experimental method has been developed to determine the scattering and absorption characteristics of a turbid material. Existing methods usually require transmission and reflection measurements carried out on a thin slab of the material under study; this method is based on reflection measurements carried out on bulk material. This will be of great advantage in many applications. This paper describes the measuring system and indicates the area of application of the method. Calibration measurements have been carried out to substantiate the approach.

Jaw muscle EMG-activity and static loading of the mandible

Abstract A method is described to relate jaw muscle EMG-activity to static bite forces. Bite forces are measured bilaterally in several reproducible positions on the human dentition by means of small wedge shaped transducers. Electromyographic methods are used to derive a relative measure of the activity in the opener and closer muscles. Visual feedback methods are used to obtain bite recordings at various levels of bite force and muscle activity. There is no reason to doubt the linear relationship between integrated EMG-activity and the force exerted by individual muscles in isometric conditions. The anterior and posterior parts of the temporal muscle show a different functional behaviour. The role of the opener muscles as antagonists is of such importance, that it should not be neglected in a muscle force analysis.