PHYSIOLOGICAL RECALCIFICATION OF CARIOUS DENTIN

In order to confirm the ability of physiological recalcification of the human carious dentin, the first layer of carious dentin was removed from the symmetric cavities of bilateral pairs of human teeth, disclosing it by 0.5% basic fuchsin-propylene glycol solution staining. One of the pair teeth was immediately extracted and the other was left in the mouth after filling the cavity with polycarboxylate cement. The Ca content and hardness of the remaining second layer immediately and three months after the operation were compared by an electron probe microanalyzer and microhardness tester. They increased markedly after three months returning to the normal level from inside, proving physiological recalcification. A similar experiment was performed by using bilateral pairs of dog teeth with cavities having artificially decalcified dentin floor. After removing the fuchsin-stainable first layer, one of the pair was immediately extracted and the other was left in the mouth for three months after exposing or filling the cavity with various cements. As the Ca content was compared, a marked recalcification of the second layer of softened dentin was observed after three months returning to the normal level from the inside. The effect of different cavity treatments was slight

MARGINAL CLOSURE OF NON-γ2 AMALGAM

In order to investigate the effect of burnishing on the marginal closure of non-γ2 amalgam restorations, a single-composition high-copper alloy (Indiloy), a conventional lathe-cut alloy (Lunargent Alloy), and a conventional spherical alloy (Shofu Spherical) were each mixed with mercury and filled in transparent plastic cavities. Half of the specimens were burnished along the cavity margins immediately after packing and again after carving. The remainder was unburnished. A dye was sprayed on their occlusal surfaces after 24 hr and leakage indicated by the dye penetration was observed through the plastic walls, and following facts were found: 1. Burnishing markedly decreased the leakage of all type alloy amalgams. 2. When burnished, the marginal leakage with the high-copper alloy was remarkably less than that with the conventional spherical alloy but slightly more than that with the lathe-cut alloy. 3. The difference in the marginal leakage and in the effect of burnishing among the three amalgams was apparently related to their setting dimensional change curves

STRUCTURE AND HARDNESS OF FOUR TYPES OF AMALGAM

Three non-γ2 and one conventional amalgams were compared for their structure and hardness. The Ag-Cu dispersants hardened the amalgam by generating hard Cu-Sn halos and diminishing the γ2 phase. The Ag-Sn-Cu-In single composition alloy produced the hardest amalgam by its high hardness and the Cu-Sn reaction phase scattered as minute granules

TAGS PENETRATING DENTIN OF A NEW ADHESIVE RESIN

The change of the dentinal tubules by acid-etching and the morphology and the adhering state of new adhesive composite resin tags penetrating the tubules were obse1ved by SEM, comparing with the representative conventional composite resin. When the fractured surfaces of the unetched floor dentin were observed, all tubule entrances were closed by blocking with cutting debris up to 10 to 20 µm depth. Etching opened them by dissolving the debris and further widened the tubule entrances up to 10 to 20 µm depth by dissolving the peritubular dentin near the apertures. Resin tags penetrated 10 to 20 µm in vital teeth, 60 to 100 µm in freshly extracted teeth and several hundred µm in old extracted teeth. The tags of the new resin penetrating the tubules copied exactly the shape of the tubule walls, producing hollow depressions at the ends, indicating that the resin polymerized, adhering tightly to the walls, while those of the conventional resin produced highly tapered side walls with pointed ends, indicating that the resin shrank separating from the tubule walls on polymerization. The new resin did not produce any gap at the resin-dentin interface unlike the conventional resm