The Act on Securing Quality, Efficacy and Safety of Products Including Pharmaceuticals and Medical Devices (“PMD Act”) requires that medical devices to be used in dental practice be approved for manufacture and sales or otherwise certified. Dental practitioners are therefore obligated to use approved or certified medical devices. There are, however, many uncertainties concerning the pre-marketing approval/certification process, and the characteristics and features of dental medical devices examined during that process have not been made clear. These uncertainties seem especially evident in medical device programs or other similar programs that are now subject to the same rules and regulations of the PMD Act as conventional medical devices, and are likely to trouble not only companies in the dental field but also those aspiring to enter the field from other industries.

For medical devices to be approved, they must undergo an approval review process by the Pharmaceuticals and Medical Devices Agency (PMDA). During the review process, the efficacy, effectiveness, and other clinical benefits of the medical device in the treatment and diagnosis of patients are examined, along with its clinical safety, which is essential to justify their use in clinical settings. Understanding not only the regulations of the PMD Act governing medical devices but also the approval review process can be useful in deepening our understanding of the intended use and effectiveness of medical devices in daily clinical practice or other similar settings.

This article mainly describes the following : (i) the meaning of medical devices as defined by the PMD Act ; (ii) the classification of medical devices that takes into consideration their risks to safety ; (iii) an overview of the approval review or other similar process for medical devices ; (iv) a regulatory framework for quality and safety assurance ; and (v) how medical devices in the field of dental and oral care are reviewed and the association with other regulations concerning dental practice. It also presents prospects for the future of regulations governing medical devices, which have important implications for devices used in the field of dental and oral care.

Digital dentistry has fundamentally changed the quality and safety of dental care and the workflow of dental practice.

For implant treatments, digitalization has dramatically expanded the use of prior information and changed treatment protocols, shortening treatment times and reducing the number of surgeries, resulting in minimally invasive treatments. In the field of restorations and prosthetics, the advent of strong and highly aesthetic materials has reduced damages to healthy natural dentitions. In the field of orthodontic treatments, aligners are created using digital data from intraoral scanners. In addition, dentists are beginning to process the data and use it for making presentations to patients.

As digitalization advances further, dentists may rethink their own role.

With the development of digital devices in recent years, it has become possible to motivate patients with smile design (2D, 3D) when giving explanations, and thus obtain their approval for treatment. Then, in the examination and diagnosis, a threedimensional diagnosis of the jaw and skeletal system is made, such as by a temporomandibular joint examination based on the centric relation obtained from a CBCT and MRI and a skeletal examination (occlusal plane, occlusal dimension) using the lateral cephalogram. In conjunction with the medical examination, dental-related digital devices such as a CBCT, intraoral scanner, surgical guide system, and facial 3D camera will be used to formulate a plan for facially driven implant treatment, which has been a long-cherished wish of clinicians. This restoration treatment has shifted from conventional “bone driven” to “restoration driven” and more advanced “facially driven” treatment, and is considered to be a treatment method with good prognosis and high patient satisfaction.

Introduction : Although lateral sinus augmentation has been established as a highly predictable treatment method, there have been many reports of perforation of sinus mucosa during surgery and postoperative inflammation and onset sinusitis due to infection. In this study, we investigated the sinus mucosal thickness, which affects the indication for maxillary sinus elevation, intraoperative sinus membrane perforation, and sinus membrane perforation risk factors, which are frequent intraoperative complications, with cone beam computed tomography (CBCT).

Subjects and Methods : This retrospective clinical study included patients who underwent sinus augmentation with the lateral approach to the maxillary molar region between 2018 and 2020. We examined the relationship between sinus membrane thickness and age, smoking, nasal septum curvature, sex, healing period after tooth extraction, causes of tooth extraction, and residual bone height ; and the relationship between sinus membrane perforation and preoperative sinus mucosa thickness, smoking, sex, defect type, healing period after tooth extraction, and PNR angle.

Results : There were 31 patients (10 males and 21 females), 36 sinuses, and the average age was 59.2 years. The average residual bone height was 2.12 ± 1.03 mm. The mean sinus membrane thickness was 1.00 ± 1.23 mm, and the sinus mucosa thickness ＞ 2 mm ratio was 22.2%. As risk factors for increased sinus membrane thickness, males and period after tooth extraction ＜ 1 year were involved. As risk factors for sinus membrane perforation, residual bone height ＜ 1.5 mm, post-extraction period ＜ 6 months, and PNR angle ＜ 90° were involved.

Conclusion : When performing lateral sinus augmentation, it is necessary to pay attention to gender, period after tooth extraction, residual bone height, and PNR angle.

Introduction : The most serious complication of maxillary sinus floor augmentation is postoperative infection including max illary sinusitis. Maxillary sinusitis after implant surgery is associated with postoperative local inflammation, dysfunction of the maxillary sinus due to bacterial infection and obstruction of the ostium or ostiomeatal complex. Therefore, we examined the changes in the maxillary sinus mucosa before and after maxillary sinus floor augmentation and the factors affecting the post operative increase in maxillary sinus mucosal thickness.

Subjects and Methods : The subjects were patients who underwent maxillary sinus floor augmentation surgeries with the lateral approach to the maxillary molar defect. The changes in maxillary sinus mucosal thickness before and after surgery, and the factors affecting postoperative maxillary sinus mucosal thickness (preoperative maxillary sinus mucosal thickness, age, sex, presence of systemic disease, smoking, nasal septal deviation, residual bone height, defect type, operative procedure, maxillary sinus mucosal perforation, period from tooth extraction) were investigated.

Results : There were 28 patients (9 males and 19 females), 31 sinuses, and the average age was 59.5 years. The maxillary sinus mucosa had a mean thickness of 1.04 ± 1.17 mm preoperatively, 6.40 ± 3.90 mm within 7 days after surgery, and 6.96 ± 3.59 mm within 8 to 14 days after surgery. The results showed that the preoperative maxillary sinus mucosal thickness, age, nasal septum deviation and tooth extraction period were associated with the postoperative maxillary sinus mucosal thickness.

Conclusion : We conducted a CBCT study on the factors affecting the increase in postoperative maxillary sinus mucosal thickness after maxillary sinus floor augmentation using the lateral approach.

The following conclusions were obtained.

1. The postoperative maxillary sinus mucosal thickness tended to increase significantly within 7 days after surgery and 8 to 14 days after surgery compared with before surgery.

2. The postoperative maxillary sinus mucosal thickness is affected by the preoperative maxillary sinus mucosal thickness, age, period after tooth extraction, and nasal septal deviation.

When performing maxillary sinus floor augmentation surgery, it is necessary to consider not only the preoperative maxillary sinus mucosal thickness but also the period after tooth extraction and nasal septum deviation.

Introduction : The purpose of this study was to assess whether differences in the surface topography of implants affect the bone resorption of adjacent inter-implants.

Subjects and Methods : From the patients who underwent implant therapy at Meikai University PDI Tokyo Dental Clinic between 2004 and 2014, patients in which two or more implants with identical surface topography had been placed adjacently and who had the superstructure in place for 3 years or more were extracted. Subjects were divided into 2 groups according to the surface topography of the implants, and radiological measurements were performed. The different surface topographies that were compared were implants that were machined smooth for 3 mm from the platform and thereafter the surface was roughened as far as the tip (group A), and implants with a roughened surface all the way from the platform to the tip (group B). The inter-implant distance of the adjacent implants was also measured, and measurements were compared using Mann-Whitney U Test (p ＜ 0.01)

Results : Among subjects with an inter-implant distance of 3 mm or more the amount of horizontal bone resorption and vertical bone resorption tended to be smaller in the group B. However, no differences were found between the group A and the group B among subjects with an inter-implant distance less than 3 mm.

Discussion and Conclusion : In the present study, a statistically significant difference was found in the amount of bone resorption due to differences in implant surface topography. However, there were no effects due to differences in surface topography among subjects with an inter-implant distance less than 3 mm. Using implants which have the whole surface roughened and maintaining an appropriate distance between adjacent implants are likely to be useful in protecting against inter-implant bone resorption.

Purpose : The influence of the inclination angle of implants with a cantilever on the maximum bending load, amount of deformation, and strain of the collar part was investigated.

Methods : The superstructure was prepared simulating the mesiodistal width (12 mm) of the lower first molar, and to apply a load, 3.25 mm was added to both ends, resulting in a full length of 18.5 mm. Four angles of inclination were set : no inclination, 10, 20, and 30°. A deformation gauge was attached to the tip of the collar part of the fixture, a load was applied at 3.25 mm from the end surface of the superstructure, and each measurement was performed.

Results : When the implant was not inclined, the maximum bending load was about 609 N, and the strains at inclination angles of 10, 20, and 30° were about 18, 21.2, and 31％, respectively, being reduced compared with that of the implant with no inclination angle. The deformation amount increased as the inclination angle increased. Internal observation by CT was performed after measurement. The gap between the collar part and abutment tended to increase as the inclination angle increased. In addition, plastic deformation was noted in the upper part of the screw, but fracture was not observed. The strain of the implant collar region reached 0.1％ when the applied load was 150 N at both inclination angles of 20 and 30°. The strain of the collar part increased as the inclination angle increased, and the load at which the strain reached 0.1％ at all inclination angles was 250 N. No difference was noted in the strain of the collar part at an inclination angle of 0 or 10° at any load.

Conclusion : It was clarified that the limit of the inclination angle of the implant with a cantilever in this study was 10°, at which no difference was noted in strain from that in the preparation with no inclination.

Introduction : For patients with Kennedy Class I and II partially edentulous alveolar ridges, implant-supported prosthetic appliances (ISPAs) can achieve denture stability and help recover the masticatory function of patients better than conven tional removable partial dentures. In this paper, we report the clinical results for eleven patients with Kennedy Class I and II partially edentulous ridges treated with ISPAs, and also review the literature.

Case description : Eleven patients were treated with ISPAs. Their mean age was 64.5 years. The patients consisted of nine females and two males ; three were treated in the mandible and eight in the maxilla. The number of missing teeth ranged from 8 to 11. Thirty-three implants were placed in the 11 cases, and five types of attachment system were used (magnets : 3 cases, locator attachments : 2 cases, milled healing abutments : 2 cases, bar and clip attachments : 2 cases, and extra-crown attachments : 2 cases). Follow-up periods ranged from 41 to 183 months (mean 97 months). There were no failed implants and therefore the implant survival and prosthesis survival rates were 100％ for the 97-month mean observation period. Three cases had no prosthetic complications. Eight cases had problems, such as fracture of denture bases, wear of artificial teeth, and removal of magnets, and only two abutment teeth were extracted. However, both prosthetic complications could be re paired.

Conclusion : The results of this study suggested that ISPAs therapy is a predictable and minimally invasive treatment method for patients with multiple tooth loss.

The purpose of this study was to find a way to quickly remove the cement-fixed superstructure when it encounters a com plication. A zirconia superstructure and a titanium abutment were prepared from the CAD/CAM data used in clinical prac tice before, and an experiment was conducted with a gypsum model in which the implant body and the titanium abutment were fixed with a screw and the zirconia superstructure was fixed with cement on it. Regarding the method, the cement fixed zirconia superstructure and abutment were removed from the implant body as a mass using CAD data images, and the zirconia superstructure was removed from the titanium abutment using an auto furnace.

Resin-added glass ionomer cement or resin cement was used as the cement. Before the removal experiment, changes due to heat treatment of cement lumps were investigated. The temperature inside the auto furnace was set to 350 and 400℃ for the resin-added glass ionomer cement and to 400℃ for the resin cement, and the mooring times outside and inside the fur nace were set. After mooring in the furnace, the cement lumps were taken out, allowed to cool naturally, and pressed with how pliers. The state of the cement lumps at that time was classified into fine particles, crushed pieces, and impossible-to crush pieces.

The shortest mooring time (outside the furnace ＋ inside the furnace) for fine particles was 18 min (8 min ＋ 10 min) at 350℃, 6 min (0 min ＋ 6 min) at 400℃ for resin-added glass ionomer cement, and 10 min (0 min ＋ 10 min) at 400℃ for implant cement. In this shortest mooring time, the cement-fixed superstructure could be removed from the abutment, and suggesting that the removed superstructure and abutment could be reused.