Conventionalplastic teeth (CV teeth) are inferior to porcelain teeth in maintaining an adequate esthetic appearance with wear and discoloration, and thus have a shorter period of durability.Recently, high-strength plastic teeth (HS teeth) have been developed and applied to overcome the wear problems of CV teeth. Since HS teeth made of hard resin are still susceptible to staining with pigments, it has been observed that the esthetics of removable partial dentures made from such plastic teeth are gradually impaired in many patients.To investigate the susceptibility of HS teeth to pigments, we conducted an in vitro study by immersing three types of artificial teeth in three coloring liquids.It was found that the HS teeth tended to be less susceptible to the test pigments than the CV teeth to various degrees. In contrast, they showed markedly stronger susceptibility to the pigments than porcelain teeth. For all three artificial tooth types, daily tooth cleaning with an ultrasonic vibrator had a tendency to reduce the coloration in comparison with their counterparts without ultrasonic cleaning.

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Purpose: To determine whether prilocaine, a local anesthetic, induces apoptosis in osteoblastic cells. Methods: After reaching subconfluence, human osteoblastic Saos-2 and HG63 cells and mouse osteoblastic MC3T3-E I cells were exposed for 48 hr to varying concentrations of prilocaine up to I 0 mM and the cytotoxicity of the cells was analyzed by phase-contrast microscopy and WST-I assay. Saos-2 cells treated for 48 hr with 5 mM prilocaine were stained with Hoechst 33342 and nuclear fragmentation was examined under a fluorescence microscope. DNA was extracted from the cells treated with 5 mM prilocaine and DNA ladder formation (a hallmark of apoptosis) was analyzed by agarose gel electrophoresis. Rr.s~t: Prilocaine induced cell death in Saos-2 cells in a dose-and time-dependent manner up to the concentration of 10 mM. Marked nuclear condensation and fragmentation of chromatin were observed in the prilocainetreated cells. DNA ladder formation also was induced by prilocaine treatment, Prilocaine-induced DNA ladder formation was dose-dependent with maximal effect at a concentration of 5 mM and was time-dependent from 12 to 48 hr. DNA ladder formation was also induced by prilocaine treatment in human osteoblastic MG63 cells and mouse osteoblastic MC3T3-EI cells. Cycloheximide prevented prilocaine-induced apoptosis in Saos-2 cells in a dose-dependent fashion up to 20/IM as determined by WST-I assay and DNA ladder formation in agarose gel electrophoresis. ConckLsion: Osteoblastic cells treated with prilocaine exhibit both morphological and biochemical features indicative of apoptosis. The apoptotic mechanisms involve transcriptional regulation of specific proteins or protein synthesis.Objectif: D&errniner si la prilocaYne, un anesth&ique local, a induit rapoptose de cellules ost~oblastiques. M~.thode : Apt& avoir atteint le stade de sous-confluence, des cellules ostEoblastiques humaines Saos-2 et MG63 et ost~oblastiques de souris HC3T3-E I ont &~ expos~es pendant 48 h ~ des concentrations variables de prilocaYne allant jusqu'~ I0 mM et la cytotoxicit~ des cellules a &~ analys~e par microscopie en contraste de phase et par dosage WST-I. Les cellules Saos-2 traitEes pendant 48 h avec 5 mM de prilocaYne ont Et~ color~es avec le Hoechst 33342 et la fragmentation nuclEaire a Et~ examinee sous microscopie en fluorescence. I'ADN a ~t~ extrait et la formation if&helle d'ADN (signe cardinal de l'apoptose) a EtE analys~e par Electrophor&e sur gel d'agarose. ]~.~talm 9 La prilocaine a induit la mort des cellules Saos-2 d'une mani&e d~pendante de la dose et du temps jusqu'~ une concentration de I0 mM. En effet, la prilocaYne a induit dans les cellules trait&s une condensation nucl~aire marquee et la fragmentation de chromatine de m~me que la formation if&helle d'ADN. La formation d'ADN, d~pendante de la dose, a connu son effet maximal avec une concentration de 5 mH et ~tait d~pendante du temps entre 12 et 48 h. La formation d'ADN a Et~ aussi induite par la prilocaYne clans les cellules humaines MG63 et dans les cellules de souris ...

High-strength denture teeth (HS teeth) were developed in order to improve the hardness and wear resistance of conventional plastic denture teeth (PL teeth), while retaining their feature of easy occlusal adjustment.The objective of this study was to evaluate the abrasive wear resistance of HS teeth. We conducted wear tests and measured surface roughness using six types of anterior artificial teeth, i.e., three types of HS teeth and three types of PL teeth, the latter serving as the control.The results of the toothbrush abrasion test revealed that the HS teeth had about 5 times greater wear resistance than the PL teeth. It was also found that the type of artificial teeth and the number of abrasive wear-testing strokes had a significant (P<0.05) influence on the surface roughness of artificial teeth.

The aim of this research was to examine the effects of metals used in dentistry upon magnetic resonance imaging (MRI). Ten disk-shaped samples of metals have been used in this study. Each sample has been set into a volunteer who had produced a normal MR image when tested. The subject was imaged in the sagittal, frontal and coronal plane with a 0.1 T MRI device and results examined for MR defects. Au, Ag, Au-Ag-Pd and amalgam produced no defect. Ni-Cr, Co-Cr and SUS304 expressed small amounts of MR defects, but SUS405, Pd-Co-Ni and Sm-Co expressed large defects. Those metals which create MR image degradation must not be used for fixed prosthesis or orthodontic devices both of which could easily be made from other metals. If the MR image degrading metals are to be used in dentistry, their application should be restricted to removable prosthesis.