It is unfortunately not uncommon to encounter cases of tooth fracture with difficulty preserving teeth in clinical practice. The mesio-distal root coalesces to the mandibular second molar on the cheek side, whereas they do not coalesce on the lingual side, and with high probability, manifest C-shaped roots with deep grooves. Therefore, we conducted a structural analysis of this typical C-shaped root using frames in order to clarify the appearance of fracture. Frame is just a stress calculation for a cross section indicating only the tendency of fracture. By applying this frame model and more precisely calculating the risk by taking into account the actual dentin thickness or by subdividing the calculation and examining the detailed stress distribution, we can not only obtain figures other than those obtained from image data such as CBCT, but also prevent root breakage by root canal enlargement during treatment while considering the influence of force directionality.

This study described a method for membrane perforation repair during sinus lift using platelet-rich fibrin (PRF) and autologous fibrin glue (AFG). It also highlighted the importance of using a microscope during surgery. PRF promotes wound healing and tissue regeneration. AFG forms sticky bone when mixed with bone material on a glass dish, which accelerates tissue healing and minimizes bone loss during healing.

A large perforation was created in the Schneiderian membrane at the peak of the septum after opening the lateral window, during lateral wall sinus elevation in a 43-year-old woman. PRF was placed at the perforation site, which prevented bone material from entering the sinus cavity, followed by the placement of sticky bone. The implant was placed 7 months after the sinus lift. Computed tomography (CT) revealed stable bone-like structures around the implant.

PRF was used to repair the perforated Schneiderian membrane during transcrestal sinus lift in a 38-year-old woman as the sole filling material. Implant placement was followed by placement of bone material in the gap. CT revealed a bone-like structure around the implant after 6 months.

The use of PRF and AFG under microscopy simplifies membrane perforation repair, as they use minimally invasive techniques, without additional surgery.

An important point for disinfection of the root canal system is root canal preparation following the original canal. Negotiating and cleaning the original canal can prove difficult when the canal has been altered in previous treatments. In retreatment cases, dentists need so long time to negotiate the original canal by hand files. In this case report, the rotary device (TriAuto ZX2) was used to negotiate the original canal in the ledged canal. This step of negotiation was performed entirely under microscope, to minimize treatment time. This technique appears useful for root canal treatment.

This is a report of a patient referred to Isozaki Dental Clinic for removal of a broken instrument in the mandibular central incisor. In addition to the fact that removal of a broken instrument from the root canal is difficult even under microscopy, difficult conditions were present in this case. The tooth concerned was the mandibular central incisor. Use of a dental mirror in the mandible under a dental microscope is generally considered difficult. The 5-mm-long broken instrument was located at the apex of the root canal, so the head of the broken instrument could not be identified under direct view. Despite these difficult conditions, the instrument was successfully removed from the root canal by assuming an ergonomically optimal posture with the finger rest placed close to the operating point, and using a modified ultrasonic tip to enable precision work.

Single-file enlarging and shaping of curved root canals was performed using RECIPROC, a Ni-Ti rotary file with reciprocating motion imparted by a special-purpose motor, and using the RECIPROC direct handpiece designed especially for the RECIPROC and linkable to a dental unit, with comparisons between the two systems of operating time, forces, shaping regions, and transportation amounts, at a rotary speed setting of 15,000 rpm. The results showed no significant differences in total enlargement and shaping time, pulling force average, average values for shaping amounts of inside or outside curvature region after root canal enlargement and shaping, or root canal transportation. The average pushing force was significantly higher with RECIPROC direct. With use of RECIPROC with the torque control function of its special-purpose motor, the operator can lessen the force setting with a warning alarm on reaching the torque limit, but no warning alarm is issued by RECIPROC direct, and this may be the reason for the significant difference found in pushing force. With either system, however, no file fracture, step formation, or other complication, and no file deformation were found. These results show that proper root canal enlargement and shaping similar to that of RECIPROC attached to the special-purpose motor can be obtained with RECIPROC direct at a speed setting of 15,000 rpm, provided care is used to avoid excessive force application.