Removal of dentin by fuchsin staining.

A 0.5% basic fuchsin-propylene glycol solution was applied to the carious dentin of extracted and vital human teeth, and the depths of the fuchsin-stained dentin and the bacterial invasion were compared on histological sections. Excavation guided by this staining method was always deeper than the bacterial invasion, with differences between the depths being greater in acute decay than in chronic decay. This staining is considered to be a reliable clinical guide for the complete removal of deteriorated dentin without causing failure to remove the infection completely. The depths of the images of dentin caries on the radiographs before treatment and after excavation guided by the fuchsin staining method were also compared. The image on the radiograph was always shallower than the excavated cavity. Dentists must expect to excavate caries cavities somewhat deeper than radiographic images.

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 crystals bound to the fibers like fringes.

Effect of cyanoacrylate treatment of cavity walls.

Cyanoacrylate treatment of the cavity wall for composite resin restoration failed to keep adhesion when set, but the marginal closure improved markedly both in vivo and vitro, even when thermal-cycled. It irritated the pulp slightly only at the beginning. Ethylcyanoacrylate was superior to methylcyanoacrylate in regard to adhesion, leakage and pulp response.

Effect of moisture contamination on high-copper amalgam.

Moisture contamination caused delayed excessive expansion and deterioration of the physical properties only with the non-high-copper lathe-cut alloy amalgam containing zinc, but not with the new high-copper amalgam and the non-high-copper spherical alloy amalgam containing zinc. It affected the compressive strength and creep but not the hardness. The setting dimensional change of all amalgams containing zinc was slightly affected by it.

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.

Structure and effects of non-gamma-2 amalgam.

The metallurgical structure of a non-gamma-2 amalgam was investigated by using metallurgical microscopy, surface, point, and line analyses by an electron probe microanalyzer, and a microhardness test. Referring to these findings, their effects on clinical results were then discussed. Findings were as follows: The residual dispersant particle was less hard than the gamma 1 matrix, but the ring around it was much harder than the gamma 1 matrix or the residual gamma particle. The improved mechanical properties seem to be the result of the presence of this ring. The gamma 2 phase was absent in this amalgam. The absence of gamma 2 phase seems to improve chemical resistance, to prevent the deformation by mercuroscopic expansion of amalgam margins, and thus to decrease their fracture potential. The minute gamma 1 crystals found adjacent to the ring around the residual dispersant particle seem to indicate that they were late in crystallization, resulting in low early strength.

Collagen biochemistry of the two layers of carious dentin.

The amino acid composition and intermolecular cross links of collagen fibers in the two layers of carious dentin, differentiated by a 0.5% basic fuchsin-propylene glycol-stain, were biochemically investigated. No difference in the pattern of amino acid composition of collagen fibers was found between the first and second layers of carious dentin and the sound dentin. However, obvious differences in the intermolecular cross links of collagen fibers were found between the three layers. Namely, compared with the sound dentin, the second layer of carious dentin had decreased cross links and increased precursors. This change is considered to be reversible. Contrastingly, in the first layer, both the cross links and the precursors remarkably decreased. In addition, the hexitollysines (protein-saccharide compounds probably related to bacterial metabolism) were found and several peaks of unknown materials appeared. This indicates irreversible destruction of cross-linkage in the first layer of carious dentin.

Measurements of cervical undercuts of human tooth crowns.

The dimensional factors of the cervical undercut of the human teeth were measured. The facial and lingual undercuts showed considerable deviations in depth, width, and inclination to the crown axis and the food stream. The proximal undercuts showed a uniform depth of 1 +/- 0.3 mm with some deviations in width and inclination.

A laboratory report on vibration etching for fissure sealants.

We have developed a vibration etching technique in which occlusal pits and fissures are simultaneously cleansed and acid-etched using a fissure needle mounted on an electromagnetic vibrator. When tested on extracted teeth, the needle completely cleansed the fissures by removing the contents and the prismless enamel layer, and widened them to from 100 to 150 micrometers to the depth reached by the needle. The sealant penetrated readily and adhered to the reduced and etched fissure walls interlocking with resin tags.

Pulpal response to a new adhesive restorative resin.

The pulpal response to a new adhesive restorative resin was histopathologically investigated using dogs, and was compared with a representative conventional resin. When filled without etching and cavity wall lining, bacterial penetration and pulpal response were less with the new resin. Lining of dentin walls and total etching of cavity walls, including dentin, caused less pulpal response under the new resin. Cavities which were totally etched and filled with the new resin showed only a slight pulpal response and no bacterial penetration.

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.

The extent of the odontoblast process in normal and carious human dentin.

When observed by SEM, after being treated with the HCl-collagenase method, the odontoblast processes extended throughout the whole thickness of dentin in intact teeth and the whole thickness of normal and the inner carious dentin in carious teeth. Small holes and depressions were found on the processes in the transparent layer.

The ultrastructure and hardness of the transparent layer 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.

Mechanism of differential staining in carious dentin.

The caries detector, 1.0% acid red solution in propylene glycol, failed to stain EDTA-demineralized bovine dentin matrix, but stained the same matrix when treated by lactic acid in a concentration above 0.01 M. Thus, acid of bacterial origin could possibly be responsible for the stainability change of carious dentin in vivo.

Adhesive resin splint.

A technique to splint mobile anterior teeth with a chemically adhesive composite is presented.

The process and results of revolution in dental caries treatment.

The traditional system devised by G.V. Black for dental caries treatment has been fundamentally changed by the development of new knowledge about dental caries pathology and chemically adhesive resin composite. The scientific background is first discussed, together with the process of the development of new materials, following which the essence of the latest clinical techniques are described and illustrated. The system of minimal tissue reduction is extremely simple and painless, not requiring anaesthesia and is able to secure maximal longevity of restored teeth. The author describes his personal record in the development of acid etched dentine and composite restoration systems.

A tooth substance saving restorative technique.

The basic concept behind the Black system in the restoration of teeth is a mechanical one. It aims at the retention of restorations by perfect contact with, and the grip of, resilient sound dentinal cavity walls. This necessitates the cutting of sound dentin which is sometimes accompanied by pain and pulpal irritation. For the complete removal of infected carious dentin the conventional technique has depended upon the operator's perception of discoloured dentin and its changed hardness. It has been shown that carious dentin consists of two layers. Namely, a superficial layer which is infected, not remineralizable and necrotic, whereas the deeper layer is uninfected, remineralizable and vital. The first step in the tooth substance saving restorative technique is to use a dye to differentiate between the two layers. Pain on caries removal is virtually eliminated by the selective removal of the stained and necrotic superficial layer while assuring complete removal of all infected dentin. The second step is to use chemically adhesive composite resins which have been developed for both anterior and posterior use. They adhere to enamel and sound dentin and also to the deeper layer of carious dentin. Cutting painful tissue so as to provide the retention form of the classical technique is not required, nor is amalgam as a restorative material in operative dentistry.

The effect of etching on the dentin of the clinical cavity floor.

The most conservative cavity preparation, which takes full advantage of chemically adhesive composite resin, involves removal of only the infected outer carious dentin that is stainable by the caries detector. This preparation exposes in the cavity floor either the turbid layer at the top of the inner carious dentin or the underlying transparent layer. Examination by scanning electron microscope revealed that etching the cavity floor demineralized the intertubular dentinal surface slightly and produced tapered, cylindrical holes or ring-shaped holes at the dentinal tubule apertures of the turbid or transparent layer, respectively. The holes were blind with solid floors of intratubular crystal deposits of the transparent layer, suggesting that etching increases permeability little. Placement of the adhesive resin on the etched cavity floors produced a resin-impregnated dentinal layer and tapered, cylindrical or tubular-shaped resin tags, which apparently improved the bond and tubule aperture seal.