Abstract : This study investigated the biocompatibility and reparative dentinogenic potential of mineral trioxide aggregate (MTA). Tissue reactions were examined under light and electron microscopes at 1, 5, and 10 days after MTA application to exposed pulp tissue in rat incisors. At 1 day after pulp capping, slight inflammatory reaction, including neutrophilic leukocyte infiltration, was seen in the vicinity of the exposed region. At 5 days, a newly formed matrix layer was in direct contact with the capping material, and disaggregated MTA particles were surrounded by this matrix tissue. At 10 days, the exposed area was covered with thick reparative dentine composed of a fibrodentinal matrix and true dentine with tubular form. Ultrastructural examination at day 5 showed collagenous fibrils to be densely present between disaggregated MTA particles and pulp cells containing well-developed rough-surfaced endoplasmic reticulum.

 These results suggest that MTA possesses good tissue compatibility and high reparative dentinogenic potential, indicating its potential for use as a direct pulp-capping material.

Abstract : Generally, the form of a root canal on cross section at the coronal side and/or the middle 1/3 shows an ovoid type, except for the upper central incisor and the palatal root of the upper first molar in the medio-distal view. Recently, Ni-Ti files were developed for speedy and safe root canal shaping. When using Ni-Ti files, a low-speed rotary engine is used in the clinic. It is useful for shaping a circle-type root canal on cross section. However, they cannot shape an ovoid-type root canal on cross section, completely. We developed a new root canal shaping system using 4 and 6% tapered stainless steel H-files (NHF) with a vertical stroke motion and a Ni-Ti file (GT Rotary) with rotary motion. With use of a GT Rotary, insufficient shaping or non-shaping parts have been found at the coronal side of a root canal, because the root canal cuts to a circle using a GT Rotary. However, it was clarified that the root canal system was securely shaped with combined use of NHF and a GT Rotary.

Abstract : In this study, we observed the smear layer on root canal dentin after using the following hand instruments : a stainless steel K-file, an H-file, trial-manufactured H-files, and a trial-manufactured K-file, by SEM, and we also observed after application of 10% polyacrylic acid to those smear layers. With application of 10% polyacrylic acid for 20 seconds to those smear layers, dentinal plugs were not observed by SEM, except with use of a K-file and a trial-manufactured K-file. Therefore, it is considered that the H-file and the trial-manufactured H-file hardly created dentinal plugs in root canal shaping. It is suggested that EDTA is necessary to remove the smear layer and dentinal plug created using a K-file ; however, application of 10% polyacrylic acid for 20 seconds is sufficient to remove the smear layer created by an H-file or a trial-manufactured H-file.

Abstract : This article describes that great care is needed to treat mandibular premolars endodontically. The patient was a 9-year-old Japanese boy who had incompletely formed roots of the permanent mandibular left second premolar with a central cusp-like structure (dens evaginatus). The tooth had radiographically two well-differentiated roots (1 mesial and 1 distal). Clinical and radiographic examinations of the tooth revealed an acute periapical abscessed lesion and blunderbuss canals with resultant pulp necrosis. Pain was both spontaneous and severe, as well as long-lasting for a few days. The tooth and the adjacent molars were tender to touch.

 At the first visit to our university hospital clinic, pain, swelling, and other symptoms had almost disappeared. The canal space had been opened without anesthesia by another dentist. In the canals, a cotton pellet moistened with Calvital had been sealed into the pulp chamber with zinc oxide eugenol cement. Routine apexification procedures with calcium hydroxide were used for the tooth.

 The patient has done well for three years. Although the radicular pulp did not maintain vitality, apical closure occurred almost normally at approximately two years after the root canal treatment. A calcified barrier that formed across the open apices of the three root canals was detected by careful examination by touch, use of a surgical microscope, measuremet of impedance, and replica technique. The end of the roots seemed to have increased a few millimeters in length.

 We have the view that once the environment of the periapex has been improved, even where little pulp tissue remains, a Hertwig’s epithelial root sheath can continue to function with subsequent root maturation.