| Summary: | 碩士 === 國立臺灣大學 === 臨床牙醫學研究所 === 95 === Under the exposure to ultraviolet, the natural teeth emit a light blue fluorescence, which may enhance the whiteness and brightness of teeth in daylight. Dental prostheses should present the fluorescence which can act as natural teeth in color and intensity under exposure of sunlight or artificial ultraviolet illumination. Since there is no guide for comparing restorative materials to natural teeth, people with anterior prostheses may present different fluorescence from their natural teeth when they go to nightclubs or discotheques with ultraviolet illuminations. According to the reviewed articles, the factors that would affect the fluorescence of dental porcelains are constituents of luminophores, shade difference, layer thicknesses, firing cycles and firing temperature. The fluorescent properties of commercial full ceramic systems for dental prosthesis were rarely reported and discussed in the previous researches. Human eye sensitivity to the intensity of fluorescence was also poorly investigated. The purposes of this experiment are to observe and analyze the fluorescence reaction of different systems of fired dental ceramic samples as well as the powders of dental ceramics, to study the sensitivity of human eyes to fluorescence of the different samples under ultraviolet illumination, then to discover the possible composition of luminophores and its influence to the fluorescence spectrum and to the visual observation, and to fabricate the guide of fluorescence comparison as well as to adjust the fluorescent intensity of dental ceramics.
The total 29 pieces of sample disks (1 mm in thickness and 1 cm in diameter; 5 systems --- Procera AllCeram, Cercon Zirconia, IPS Empress II, Noritake Ex-3 and Shofu Vintage; 2 shades --- A1 and B4; 3 layers --- enamel, body and opaque layer or core layer) were fabricated according to the manufacturers’ instructions of firing procedures. 1 ~ 2 g enamel powders of A1 shade of each system were also examined for observation of the change after firing sequence. The fluorescence of samples was observed under ultraviolet illumination. Then the excitation and the emission spectrum of the samples were recorded by using the spectrofluorometer. The samples of powders and their corresponding enamel disks were examined by an X-ray diffraction instrument to observe the crystal structure, to see if the firing procedures affect the crystal structure and the influence to the fluorescence. By using the SEM, the surface conformation and particle diameter of the powders were observed and recorded. Then the emission spectra of sample enamel disks were recorded by using spectrofluorometer with excitation light of wavelength of 365 nm. The subjects of human eye test were 20 dentists with experience of anterior prostheses fabrication and shade selection (average age --- 29.6 years old). The samples were put on the black background with ultraviolet illumination, and let the subjects rank the intensity of fluorescence. The order of ranking result was then compared with the order of intensity of emission spectra.
Experimental result and conclusion: (1) Most opaque and core layers were unable to present suitable fluorescence. In general, enamel and body layers presented similar pattern of emission spectra, but different intensity of fluorescence. CIE coordination of emission spectra were all located in the blue light scope. The manufacturers may utilized the same ingredient of activators to the body and the enamel layers, but different or no ingredient of activator was added into to opaque layer and core materials. (2) Firing procedures caused the change of emission spectrum mainly in the intensity of fluorescence. (3) Non-crystallization structure presented similar intensity of fluorescence to that of samples with the lattice structure. (4) After dividing the enamel samples into two groups, the subjects were able to make more consistent ranking, which result became more similar to the ranking of intensity of fluorescence obtained with the spectrofluorometer. This means that the brightness recognition and sensitivity of human eyes will be influenced under different color condition. The difference of fluorescence intensity is not large between the two samples of weakest brightness, but all subjects distinguished the difference. In contrast, human eyes hardly recognized the difference of intensity in brighter samples. It means human eye sensitivity to the dim light is higher than that to the brighter light.
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