Takao Fusayama

Bovine Teeth as Possible Substitutes in the Adhesion Test

In order to find a substitute for human teeth in the adhesion test, the adhesive strength to bovine teeth was compared with that to human teeth using five dental cements and two composite resins. The adhesion to enamel and the superficial layer of dentin showed no statistically significant difference between human and bovine teeth, although the mean values were always slightly lower with bovine teeth. Adhesion to bovine dentin decreased considerably with the depth of dentin.

Non-Pressure Adhesion of a New Adhesive Restorative Resin

Non-pressure adhesion of a new adhesive restorative resin was investigated employing a new tensile test. The material was adhesive to both enamel and dentin as well as to carious dentin and showed strong adhesion to all substrates tested. Etching further increased the adhesion even to dentin.

Relationship between Hardness, Discoloration, and Microbial Invasion in Carious Dentin

SYNOPSIS IN INTERLINGUA LE RELATION INTER LE DURITATE, LE DISCOLORATION, E LE INVASION MICROBIAL IN DENTINA CARIOSE.-Frescamente extrahite dentes con carie esseva dissecate verticalmente. In un del partes le superficie sectional esseva examinate pro duritate secundo Knoop e discoloration. Sectiones histologic del altere parte esseva usate pro le detection de evidentia microbiotic. Le resultatos esseva le sequentes: In dentina cariose, mollification precedeva in omne casos le discoloration, e invasion microbial esseva semper le tertie stadio. Le duritate de dentina in le fronte discolorate o microbial esseva inferior in casos acute e superior in casos chronic. Le distantia inter ille frontes e le fronte de mollification esseva plus grande in casos acute e plus micre in casos chronic.

The Ultrastructure and Hardness of the Transparent of Human Carious Dentin

The ultrastructure of the transparent layer of carious dentin was investigated in relation to hardness. This layer was the deeper part of the intermediately-softened inner carious dentin. Intratubular deposition of fine crystals was initially observed at the uppermost layer of normal dentin, increased in the subtransparent layer, and gradually shifted to deposition of rhomboid-shaped crystals in the transparent layer. Crystals were not seen in the tubules in the overlying discolored layer. Softening, due to demineralization of the intertubular and peritubular dentin, started at the bottom of the subtransparent layer and increased in the outward direction.

Collagen Biochemistry of the two Layers of Carious Dentin

Carious dentin consists of a superficial first layer and a deeper second layer. Chromatographically compared with sound dentin, the second layer showed a change in the cross-linkage of collagen with cross links partly shifting to precursors. In contrast, the first layer showed virtual disappearance of cross links indicating irreversible denaturation of collagen.

Relief of resistance of cement of full cast crowns

T HE RESISTANCE OF cementing materials is a factor that prevents cast restorations from being seated correctly. Such a failure in seating restorations, if slight, can be compensated by malleting or burnishing their margins. However, the margins of full crowns are difficult to mallet or burnish in the mouth. In a previous study,l the thickness of the film of cement of Class I, II, and MOD inlays, and full crowns was determined on their cross sections. The best adaptation of full crowns was obtained when they were made by a combination of an alginate indirect method as described by Fusayama,2p” and the improved thermal expansion technique. 3,4 These crowns generally exhibited more than 90 p thickness of cement on their occlusal floors unless some special means were used to relieve the heavy resistance of the cementing substance. Many means have been suggested5-8 for relieving the resistance of cement for the placement of full crowns. Perforation of the center of the occlusal surfaces of crowns to provide an outflow for the cement has been reported as the most effective method.9-11 However, this technique is not convenient because the perforations must be sealed later with gold foils or inlays. Another technique requires relief spaces inside of cast crowns such as reduced inside surfaces by means of dental burs. However, in this procedure the advantage of cast crowns is reduced by the irregular loss of bulk. In this study, the influences of the cementing load, the taper and height of preparations, and relief spaces inside crowns were investigated as they related to the adaptation of full cast crowns during cementation.

Electron Microscopic Structure of the Two Layers of Carious Dentin

Two layers of carious dentin from extracted human teeth were observed with an electron microscope. The first layer, which is superficial and fuchsin-stainable, showed degenerated collagen fibers and granular or leaflike inorganic crystals irregularly scattered. The second layer, which is profound and fuchsinunstainable, showed expanded odontoblastic processes, sound collagen fibers, and apatite crystcls bound to the fibers like fringes.

Relation of finish to discoloration of composite resins

3. Popovich, F. and Thompson G. W.: Maxillary diastema: Indications for treatment. Am J Orthod 75:399, 1979. 4. Keene, H. J.: Distribution of diastema in the dentition of man. Am ,J Phys Anthropol 21:437, 1963. 5. Becker, A.: The median diastema. Dent Glin North Am 22:685, 1978. 6. Lindsey, D.: The upper midline space and its relation to the labial frenum in children and adults. Br Dent J 143:327, 1977. 7. Hornwitz, H. S.: A study of occlusal relations in 10 to 12 year old Caucasian and Negro children. Int Dent J 20:593, 1970. 8. Becker, A.: The median maxillary distema: A review of its etiology. Israel J Dent Med 26:21, 1977. 9. Lavelle, C. L. B.: Distribution of diastema in different human population sample. Scand J Dent Res 78:530, 1970.

Factors and technique of precision casting part I

Abstract 1. The effect of surface roughness on the fit of castings was approximately 5 μ using regular inlay gold alloys and modern investments of fine particle size. It was constant with a given metal, alloy, and investment. The softer metals produced less effect of roughness than the harder alloys. 2. The casting shrinkages of pure gold and four alloys of various forms and normal inlay size were determined. The variation of the shrinkage by varying pattern forms was greater in harder gold alloys and the Cu-Ni-Zn alloy than in softer gold alloys. The representative casting shrinkages of regular gold inlays were 2.1 per cent in simple inlays, 2.0 per cent for crowns, and 1.9 per cent for MOD inlays. 3. The desired dimensional changes of castings are +(0.1 ~ 0.5) per cent in the insides of external restorations such as crowns and MOD inlays and −(0.3 ~ 1.2) per cent in the outside of internal inlays. 4. The desired investment expansions were determined for various types of restorations. The ideal total expansion of investment for universal use is 2.0 per cent, in which the ideal thermal expansion is 1.95 per cent since the ideal setting expansion is 0.05 per cent. However, such a large thermal expansion is difficult in commercial production. Two possible modified means were suggested. One method for compensating for the lack of thermal expansion is by a slight increase of the setting expansion. Another technique is by means of a large expansion of indirect dies using alginate and a high expanding hydrocal. 5. Using an investment having 0.2 per cent setting and 1.8 per cent thermal expansions, a new system of precision dental casting restoration was developed. This technique produced consistently successful results on various types of preparations made in extracted teeth with no distortion or inconsistency. The investment can be used universally in the indirect technique for external inlays and both the direct and indirect techniques for internal inlays.

The addition of an adhesive composite resin to the same material: Bond strength and clinical techniques

The addition of a chemically adhesive composite resin to a restoration of the same material may be evaluated by the bond strength. This was determined after no contamination and after momentary (30 seconds), short-term (7 days), and long-term (3 months) contamination under various conditions. The momentary contamination was not removed by spray-washing the glossy surface that set under a matrix. Removing the glossy surface reduced the bond. The momentary contamination was removed by the etchant whereas the longer contamination was removed only by surface reduction. The application of etchant and bonding agents significantly strengthened the bond to the reduced surface. According to the directives drawn from this investigation, the clinical techniques were illustrated for a large restoration, a subgingival proximal restoration, repair of an open proximal contact, and repair of a worn restoration.