Scanning electron microscopy reveals severe external root resorption in the large periapical lesion.

The present study was designed to investigate the relationships between clinicopathological findings and the resorptive conditions of root apices of teeth with periodontitis. The samples included 21 root apices with large periapical radiolucent lesions. The preoperative computed tomography (CT) and intraoperative findings were correlated with the presence, extension, and the progression pattern of periapical resorption using a scanning electron microscope. The subjects' age, gender, chief complaint, type of tooth, percussion test results, size of periapical lesion using CT, and intraoperative findings were recorded. All apicoectomies were performed under an operative microscope for endodontic microsurgery. A significant large size was observed in cystic lesions compared with granulomatous lesions. The cementum surface at the periphery of the lesion was covered with globular structures (2-3 µm in diameter). Cementum resorption started as small defect formations at the surface. As the defect formation progressed, a lamellar structure appeared at the resorption area, and the size of globular structures became smaller than that of globules at the surface. Further resorption produced typical lacuna formation, which was particularly observed in fracture cases. The most morphologically severe destructive pattern of dentin resorption was observed in large cystic lesions. This study is the first report to elucidate the relationships between three clinical types of undesirable periapical lesions: (1) undertreatment, (2) periapical fracture, (3) macro-level resorption, and the microstructure of external root resorption including from small defects at the cementum surface to a significant destructive pattern inside the dentin. Microsc. Res. Tech. 79:495-500, 2016. © 2016 Wiley Periodicals, Inc.

Timing for composite resin placement on mineral trioxide aggregate.

INTRODUCTION: The aim of this study was to investigate the proper time to restore composite resin over mineral trioxide aggregate (MTA). METHODS: Thirty-five samples of MTA blocks were divided into 7 groups with 3 different times (10 minutes, 1 day, and 7 days) selected for restoring the composite resin over MTA with and without bonding resin, and a control group was included for comparison. After 21 days, the distances between MTA and the composite resin or between MTA and the bonding agent on sectioned planes along the long axis were measured using a scanning electron microscope (×2,000 magnification). The hardness of the MTA near the composite resin was presented as the Vickers microhardness. RESULTS: There were no gaps at the interface in the 10-minute groups, the 1-day group with a bonding agent, and the 7-day group with a bonding agent. The groups without a bonding agent at 1 and 7 days presented a separation or gap at the interface. The value of the Vickers microhardness in the 1-day groups was significantly decreased compared with those of the other groups regardless of the presence or absence of a bonding agent. CONCLUSIONS: These findings suggest that composite resin with a bonding agent over MTA can be restored almost immediately after MTA mixing during a single visit.

Surface changes of mineral trioxide aggregate after the application of bleaching agents: electron microscopy and an energy-dispersive X-ray microanalysis.

INTRODUCTION: The aim of this study was to investigate the changes in the surface structure and chemical composition after applying bleaching agents to completely hardened mineral trioxide aggregate. METHODS: A total of 12 samples of MTA blocks were divided into three groups, two different bleaching agents, and a control group. The surface structure was observed using a scanning electron microscope. The changes in elemental composition were analyzed by an energy-dispersive x-ray microanalysis (EDX) system. RESULTS: The surface of the MTA covered with each bleaching agent changed in terms of both color and structure compared with the control. EDX showed that both bleaching agents affected the elemental distribution. A decrease in Ca and an increase in Si were shown, and this tendency was especially pronounced in the higher hydrogen peroxide concentration group. CONCLUSIONS: The acidic conditions induced by bleaching agents brought about the deterioration of the MTA surface. These findings suggest that MTA is an insufficient barrier against tooth bleaching.

Analysis of arsenic in gray and white mineral trioxide aggregates by using atomic absorption spectrometry.

INTRODUCTION: The aim of the present study was to investigate whether the concentration of arsenic (As) released from gray or white mineral trioxide aggregates (MTAs) met the requirement of the International Standards Organization (ISO) for dental cements. METHODS: Sample preparations were carried out according to the ISO methods. After centrifugation of dissolved samples, As (III) concentration in the final supernatant was analyzed by a high-performance atomic absorption spectrophotometer. RESULTS: As (III) concentration from both MTAs was much less than the required value (2 ppm) for dental cements regulated by the ISO. An experiment simulating pulp capping by using MTA revealed that As concentration was also below the standard value of the ISO. The As concentration in white MTA was lower than the value (10 ppb) recommended for tap water and environmental standards. CONCLUSIONS: The present in vitro studies demonstrated that there is no threat to patient health in using commercially available brands of MTA for endodontic practices.