This article was written based on a special lecture presented by the author at the 41st annual academic meeting of the Tohoku-Hokkaido branch of the Japanese Society of Oral Implantology. The main theme of this academic meeting was “Towards the changing society and coming new era” ; both the special lecture and this article have the same title. Although various topics involved in this theme were presented in the special lecture, only two topics are discussed in this article : dental implant treatment in the ultra-aged society, and the strategy of dental implant treatment from the viewpoint of long-term prognosis.

There are three major problems regarding dental implant treatment in the ultra-aged society in Japan today : 1) problems regarding implant treatment for elderly patients, 2) problems arising a long time after implant treatment when patients become elderly, and 3) problems occurring after patients start requiring nursing care a long time after receiving implant treatment when they were younger and in good physical condition.

In the ultra-aged society, it is important to maintain masticatory function for as long as possible. The key for this is to establish stable and firm occlusal support by dental treatment, and then to maintain the established occlusal support for a long period. Dental implants are very effective as well as a useful treatment for this purpose.

In order to accomplish this goal, dentists should foresee the risk factors for the long-term success of dental implant treatment at the time of treatment planning, then implement the treatment in accordance with the plan and observe the patients in line with those factors.

Implant dentistry has developed based on clinical science, while periodontics provides clinical treatments with an emphasis on basic medicine. Therefore, when peri-implantitis occurs, a knowledge of periodontitis is required because the pathological signs of pocket formation and bone resorption are very similar in the two inflammations. This knowledge is also useful in the treatment and prevention of peri-implantitis.

The pathogenesis of periodontitis and peri-implantitis is caused by a disruption of the bacterial flora (dysbiosis) of the biofilm in the pocket. In the chronic process, pathogen-associated molecular patterns (PAMPs) and danger- or damage-associated molecular patterns (DAMPs) react with TLRs (Toll-like receptors) of macrophages and fibroblasts. As a result, inflammatory cytokines (IL-1β, TNF-α, IL-6, IL-17, etc.) and PGE₂ are produced. These cytokines differentiate and activate osteoclasts via a RANKL-RANK dependent signaling. In diabetes mellitus with periodontitis, advanced glycation end-products (AGEs) react with RAGE (receptor of AGEs), and inflammatory cytokines are excessively released, resulting in sterile inflammation with bone resorption. Periodontitis and peri-implantitis as well as diabetes are also chronic inflammations that trigger systemic diseases, therefore, two-way treatments are important.

In terms of treatment, ridge defects on the alveolar bone are classified as periodontal disease, so bone grafting is an essential technique for treatment. Especially in the case of implant reconstruction of extensive defects, due to restrictions on the use of GBR, extensive surgery such as iliac bone grafting or distraction osteogenesis is necessary. In this sense, education and practice from periodontal surgery to alveolar surgery are important. However, one should not simply insert implants after a strategic tooth extraction without prioritizing periodontal disease treatment. Periodontal treatment should be prioritized under strict diagnostic criteria before treating implants.

The RTB classification was proposed as a simplified classification of implants. R stands for rehabilitation, which is the purpose of implant treatment. R1 is for restoration of chewing function, R2 for esthetic function, and R3 for denture function. T stands for time, the number of years since implant treatment, where T1＜10 years, 10≤T2＜20 years, and T3≥20 years. B stands for bone, indicating bone resorption around the implant, and was evaluated in three groups : B1 : no resorption, B2＜3 mm, and B3≥3 mm. To determine the validity of the RTB classification, 1,463 implants and 294 patients were studied at two institutions over a 30-year period from 1990 to 2019. Bone resorption was determined from dental X-rays. Of the 1,463 implants, 110 implants were dropped or removed. This was 7.52％ of the total number of implants, and the simple survival rate was 92.48％. The results showed that items R and B of the RTB classification were predominantly associated with the removal ratio. B3 (bone resorption ≥3 mm) had a significantly higher removal ratio than B1 (no bone resorption) and B2 (bone resorption＜3 mm) (p＜0.01). These results suggest that examination items B1 to B3, which indicate the degree of bone resorption in the RTB classification, are effective indicators for determining the prognosis of implants. In addition to the RTB classification of R, T, and B, the presence or absence of bone construction during implant surgery, probing pocket depth (PPD), and bleeding on probing (BOP) during maintenance were also investigated as additional items. The classification was as follows : stage Ⅰ : PPD＜6 mm & BOP (－), Ⅱ : PPD＜6 mm & BOP (＋), Ⅲ : PPD≥6 mm & BOP (－), Ⅳ : PPD≥6 mm & BOP (＋).

The results showed that the bone construction group was significantly more likely to be classified as B2 or B3 than the group without bone construction (p＜0.01). Stage Ⅲ and Ⅳ had a significantly higher removal ratio than stage Ⅰ and Ⅱ (p＜0.01), and the percentage of B3 was also significantly higher (p＜0.01). The RTB classification is characterized by its simplicity and can be determined only by 1) medical interview, 2) intraoral examination, and 3) dental X-ray examination, enabling even dentists who do not perform implant treatment or who have just graduated from dental school to classify the implants.

In Japan, oral surgeons, prosthodontists, or periodontists are often in charge of implant treatment. Therefore, it is thought that a method to accurately determine the difficulty level of implant treatment, especially for treatment in areas other than

their own main field, would help to provide safe and secure implant treatment.

Currently, several tools for determining the difficulty level of implant treatment have been proposed, but there are some problems that cannot be well expressed by the various classification methods that have been used so far. For example, a single tooth defect in a mandibular molar with no problems in bone quality or quantity and no occlusal problems may be considered to be an easy case, but for an inexperienced dentist, drilling the bone itself may seem difficult. Thus, whether a case is easy or difficult depends greatly on the operator's perception and experience. Apart from such kinds of technical difficulty, which is perceived differently by different operators, there is another level of difficulty based on the general condition, the treatment site, and the individuality of the patient, and so on. High-quality evidence generally shows that the success rate of implant treatment decreases when there are problems with these items.

The Research Promotion Committee of the Japanese Society of Oral Implantology is attempting to classify the difficulty level of implant treatment, which can be called an Evidence-Based Difficulty Assessment Tool, independent of the surgeon's experience. This paper presents a trial proposal.

Dental implant bodies, abutments, and ready-made superstructures (e.g. abutment cylinders) are medical devices, and are regulated by the Pharmaceutical and Medical Devices Act.

On the other hand, custom-made superstructures (e.g. implant prostheses) made by dental technicians are not medical devices, but the materials and instruments used by dental technicians are medical devices. Dental technicians and the process of making custom-made products are regulated by the Dental Technicians Act.

Each Act targets different products. But, in dental implant surgery, both medical devices and custom-made prostheses are used in combination. Moreover, some of the abutments are approved as devices which can be customized for patients.

This article explains the Japanese regulation of medical devices, especially those used for dental implant surgery, in order to clarify the confusion about medical devices and custom-made products made by dental technicians, and to understand the

proper use of medical devices.

The Japan Association of Dental Implant Suppliers is an industry group that aims to promote the sound development of the dental implant equipment industry by providing excellent dental implant equipment and information. It is composed of 23 companies that market dental implants or related equipment, or provide related services in Japan.

Medical device manufacturers have a responsibility not only to ensure the quality, effectiveness and safety of their products, but also to provide medical personnel with the information necessary for proper use of medical devices. Furthermore, the revised PMD Act, which came into effect in August 2021, requires even greater legal compliance.

With the rapid progress of digitalization in the dental industry, guided surgery and CAD/CAM prostheses are becoming more common in dental implants, and new technologies and products are increasing the choice of treatment options. On the other hand, when these are viewed as medical devices, some concerns remain.

This article describes, from the standpoint of the industry group, the points that require attention for safe and secure treatment when using dental implants and materials.

The purpose of this study was to compare the masticatory ability and subjective satisfaction with the oral function of elderly recall maintenance patients treated with implants and prosthodontics based on Eichner's classification and type of prosthetic treatment. One hundred and thirty-six patients (55 males and 81 females) aged 65 years or older who visited the dental clinic for recall maintenance between January and April 2019 were included in the study. Their masticatory ability was measured using the Gluco Sensor GS-Ⅱ^® device and their subjective satisfaction with oral function in daily life was evaluated. We found that masticatory ability was greater in the implant treatment group than in the denture treatment group, and was similar to that of the group with natural teeth and the group with crowns and bridges. Subjective satisfaction ratings were also greater than for those with other prosthetic treatments, suggesting that implant treatment may improve oral awareness in the elderly.

Purpose : When dental implants made of titanium or titanium alloy are implanted in the oral cavity, there is a concern that discoloration or corrosion may occur due to exposure to fluoride. This study aimed to compare the discoloration and ion release behavior of commercially pure titanium and titanium alloys in fluoride-containing solutions and to clarify the mechanism by which titanium is corroded by fluoride using surface analysis.

Method : As specimens, commercially pure titanium (TI), Ti-6Al-4V (TAV), and Ti-7Nb-6Al (TNB) were mirror-polished. The polished specimens were immersed in saline solutions with or without sodium fluoride (NAF and SAL). Corrosion was evaluated based on the color difference (ΔE^＊ab), reduction of glossiness (Gs (20°)), and concentration of metal ions released into the NAF and SAL solutions. In addition, surface analysis was performed on certain specimens using X-ray photoelectron spectroscopy (XPS).

Results : There was no indication of corrosion on the specimens immersed in SAL from the ΔE^＊ab value, Gs (20°) decrease, and concentration of released metal ions. TAV and TNB immersed in NAF showed larger ΔE^＊ab and concentration of released metal ions than TI. The XPS analysis revealed that oxidation progressed in all specimens immersed in NAF. In addition, TiO₂ and V₂O₅ were detected on TAV, and TiO₂ and Nb₂O₅ were detected on TNB. Al was not detected on the surfaces of either TAV or TNB.

Conclusion : TI, TAV, and TNB specimens showed superior corrosion resistance in SAL but low resistance in NAF. TAV and TNB showed lower corrosion resistance to fluoride than TI in NAF. After immersion in NAF, passive films covered the surfaces of TAV and TNB but no Al₂O₃ was detected.

Purpose : A dynamic navigation system specifically for implant placement surgery has been introduced in Japan. Unlike conventional guided surgery, a new surgical procedure is required for implant surgery using this system. The purpose of this study was to investigate whether past implant placement experience affects placement accuracy during implant surgery using a dynamic navigation system.

Methods : The subjects were divided into a group with abundant implant placement experience (n＝5) and an inexperienced group (n＝20). Implant placement surgery was performed on a mandibular demonstration model using X-Guide^®. After placement, the difference between the setting position and the actual placement position (starting point, tip position, embedding depth, embedding angle) was examined using the double scan method.

Results : Comparisons were made between the two groups with different implant placement experience for each endpoint, but the errors in all measurement points were not significantly different between the two groups. Furthermore, the subjects were divided by length of career working as a dentist into those with less than 10 years (n＝15) and 10 years or more (n＝10), and the same examination was conducted. Again, there was no significant difference between the two groups in all the measurement points. A similar comparative study was performed by age bracket of the surgeon, but there was no significant difference in the error values in any of the four measurement points.

Conclusion : The placement accuracy of the dynamic navigation system was not correlated with age, length of career as a dentist, or implant placement experience. Therefore, it is suggested that sufficient training is required when using this system regardless of experience with implants.

Objective : This study aimed to clarify the influence of the thickness of the implant collar part and cantilever on the maxi mum bending load, deformation, and strain of the collar.

Materials and Methods : The superstructure was prepared by simulating the mesiodistal width (12 mm) of the lower first molar. To apply a load, 3.25 mm was added to both ends, resulting in a full length of 18.5 mm (using JIS SK4 steel). The thickness of the collar part was changed to 0.7 (T07), 0.8 (T08), or 0.9 (T09) mm (using JIS 4 type titanium). The angle of inclination of the implant was set to 30°, and the maximum bending load, deformation, and strain were measured. The inner region was observed using CT.

Results and Discussion : The maximum bending load was 387.3, 402.9, and 414.5 N for T07, T08, and T09, respectively ; thus, the maximum bending load increased as the implant collar became thicker (p＜0.05). The measured deformation was 1.86, 1.82, and 1.52 mm for T07, T08, and T09, respectively ; thus, T09 had the least deformation (p＜0.05). Strain of 0.1% was caused by a 150 N load in both T07 and T08, and by a 200 N load in T09. Strain of 0.3% was caused by a 350 N load in both T07 and T08. The strain caused by a 400 N load in T09 was less than 0.3% (p＜0.05). Computed tomography (CT) imaging further revealed that a portion of the abutment of each implant had deformed and invaded into the chip evacuation hole. There was a gap between the tip of the collar and abutment that fit the collar, and the gap was the greatest for T07.

Conclusion : Using implants with a cantilever, we demonstrated that the thickness of the collar affected the degree of strain. This indicated that the biting force at the site of an implant should be carefully considered.

Partial and subtotal maxillectomies are frequently indicated as surgical procedures for hard palate cancer, often with defects of the alveolar ridge. Here, we report a case of hard palate cancer treated from the nasal cavity side by tumor resection using Le Fort I osteotomy. Furthermore, bilateral maxillary sinus floor elevation was performed to achieve good results by implanting a dental implant. The patient was a 64-year-old man, who had become aware of pain in the palatal region while eating and underwent a biopsy in November 2015, resulting in the diagnosis of squamous cell carcinoma (SCC). He underwent tumor resection approaching from the nasal cavity side with Le Fort I osteotomy in January 2016 for the diagnosis of hard palate cancer. Maxillary sinus floor elevation was performed in July 2019 using an implant-retained obturator prosthesis, and implant surgery was performed in May 2020. Four implants of bilateral maxillary molars obtained sufficient initial fixation with buried torques of 30 to 35 Ncm. Healing abutments were mounted half a year after the primary implantation surgery. As of 2021, fixation has been uneventful.

Purpose : Most mechanical failures in implant treatment are screw breakage or loosening. One cause is excessive or insufficient screw tightening torque, so it is essential to use a torque wrench to provide an accurate tightening torque. However, the detailed characteristics of torque wrench are still unknown. The purpose of the present study was to clarify the accuracy and reproducibility of typical torque wrenches.

Materials and methods : Torque values of torque wrenches of 12 manufacturers (8 beam type, 2 preset type, and 2 digital type wrenches) were measured with a torque gauge. One examiner applied the recommended torque value of each manufacturer's screws five times clockwise. Average measured torque, standard deviation, bias, and coefficient of variation were calculated. The statistical method used was the Tukey method with the target torque value as the factor and the difference between the measured torque value and the target torque value as the dependent variable.

Results : The torque wrench used in this study showed a maximum value of 10% and a minimum value of －8% when the target torque value was about 10 Ncm. When the target torque value was about 25 Ncm, the maximum value was 0.6% and the minimum value was －2.3%. The maximum and minimum values were 2.4% and －7.2%, respectively, when the target torque value was about 50 Ncm.

Conclusion : The accuracy and reproducibility of the torque wrench depended on the manufacturer. It was revealed that a smaller target torque value had poorer accuracy and reproducibility, suggesting that prosthetic screws should be tightened carefully to about 10 to 15 Ncm.