P.C.F. Borsboom

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.

A NEW METHOD FOR MATCHING TOOTH COLORS WITH COLOR STANDARDS

A new method for quantitative intra-oral tooth color determination is presented. Basically, the tooth color is assessed by visual comparison with opaque color standards, which are logically arranged according to three visual color dimensions. The standards were analyzed spectrophotometrically, and the C.I.E. color coordinates were computed. Illumination and observation were standardized during the matching procedure. Two distinct situations, method 1 and method 2, were investigated. The situation in method 1 is to be considered as large window illumination and small window collection of the reflected light. For method 2, the same small window was used for both illumination and observation. Using both methods, the color of a tooth could be quantified into three separate color dimensions. Using method 1, the consistency among 25 examiners was high in determining the color of ten teeth; using method 2, the inter-examiner agreement was low. For the same tooth, different color standards were selected with method 1 or method 2. The standard selected with method 2 often appeared to be in disagreement within clinical expectations. The differences in results between method 1 and method 2 are explained by the optical properties of the translucent dental enamel (e.g., volume reflection). Method 1 allows for reproducible quantification of clinical tooth discoloration according to C.I.E. color specifications and can possibly be applied in prosthetic dentistry.

Measurement of bone displacement in a macerated human skull induced by orthodontic forces; a holographic study.

Abstract A macerated human skull was subjected to orthodontic forces from 6.25 to 7.0 N per side. Double-exposure holographic interferograms (5 mW HeNe laser) were made frontally and oblique laterally. These were complemented with observations from a real time holographic interferogram. The displacements of the maxilla and the zygomatic bone were quantified. Special attention was paid to the reaction of the zygomaticomaxillary suture.

Measurement of the uniaxial elasticity of oral mucosa in vivo after CO2-laser evaporation and surgical excision

The stress-strain relation of oral mucosa of dogs was measured before and 6 weeks after surgical removal of mucosa. Both CO2-laser evaporation and excision were employed. Measurements were done with a miniature tensile tester, especially developed for this purpose. The load-strain ratio of the healed mucosa was proportional to the histologically determined thickness of the healed epithelium and scar tissue together. Laser evaporation caused a 75% increase, excision almost a threefold increase of the load-strain ratio compared with untreated tissue.

A Nondestructive Method for Monitoring De- and Remineralization of Enamel

The scattering of white light by bulk dental enamel and artificial lesions was studied with light incident under an angle of 45 ° and observed perpendicularly to the surface. The frames of illuminatio

Fiber Optic Scattering Monitor For Application On Bulk Biological Tissue, Paper, And Plastic

A method and apparatus is described to monitor non-destructively the turbidity of near white materials based on edge-losses from a small illuminated area. Measurements will be shown on paper and plastic; on teeth during carious demineralization; on the whiteness of the human eyeball and on milk, changing the fat concentration.

A Non-Destructive Optical Method to Study De- and Remineralization of Enamel

The absorption and scattering of light in dental enamel or in a carious lesion have been studied quantitatively by using thin slabsl. The method thus required destructive preparation techniques. In this paper we describe how the scattering by a bulk sample can be used to obtain semi-quantitative information.

An Instrument To Measure The Color-Determining Properties Of Bulk Translucent Materials

A pencil beam incident on a translucent material causes a luminous circular spot of volume-reflected light. Its spectral radiance L (r) decreases with radius r. Lc, the value close to the centre is mainly determined by the scattering parameter s(1-g) of material. Le, the value at the edge of the spot, is determined by s(1-g) and the absorption coefficient a. The instrument (the CTM) employs three fibre bundles to measure Lc and Le, both as a function of λ (400-700 nm). A central bundle (2 mm p) of - 1300 fibres each of 50 um g is randomly divided in a bundle for illumination and a bundle for measurement of Lc. A concentric ring (i.d. 4 mm, o.d. 5 mm) of - 2500 fibres is used to measure Le. This instrument was tested with aqueous suspensions of latex and a dissolved, non-latex adsorbing, red dye. Thus s(1-g) (scattering) and a (absorption) could be independently varied. For a=0, both Lc and Le increased with s(1-g), reached a maximum and decreased. The maxima for Lc and Le were at s(1 g) = 1 and 0.06 mm -1, respectively. At a constant scattering, increase of absorption decreased Le much stronger than it did Lc. This absorption-caused decrease depended only weakly on the scattering coefficient: a variation of scattering of a factor 20 caused only a few percent change in absorption-caused decrease of Lc and only a factor 2 in absorption-caused decrease of Le. At s(1-g) = 0.3 mm-1, Le depended much more strongly on a than did the overall regular reflection spectrum of the suspension as measured with a Hunter spectrophotometer under 0°/45° geometry. The readings of Lc and Le with this instrument can be used to determine s(1-g) and a and the reflection spectrum. Only small samples are needed in comparison to the regular reflection spectrometry. To obtain absolute values the instrument has to be calibrated on the specific type of material under investigation.