Fifty-four years have passed since the clinical application of dental implants, and good results have been obtained with them as defect prostheses, but rapid population aging presents various issues for dental treatment in Japan. Therefore, we examined changes in the oral cavity among long-term cases of implant treatment, with the aim of planning for ultra-long-term treatment for the super-aging society.

Many long-term cases seem to be closely related to changes in the patient's age and oral cavity, but it is also true that such changes cannot generally be considered due to patient-specific risks. Therefore, we divided cases with long-term changes (about 20 years of change) into the following five groups, and considered cases 2), 3), and 5) characterized by the changes among them :

1) Cases with few major changes at a young age

2) Cases with moderate change in middle and high age

3) Cases with lost in perio or vital teeth in middle to high age

4) Cases with high age and high incidence of root caries

5) Other groups with high risk of occlusal force, immunity etc.

The long-term cases examined this time showed that the age of treatment start, the number of missing teeth, the form of the missing teeth, and the state of the remaining teeth greatly affect the long-term stability. Accordingly, it is important to consider a long-term treatment plan based on these findings.

What to expect from the long-term course of implant treatment :

1. If there are few missing teeth, the form of missing teeth is simple, and the remaining teeth are in good condition, there tend to be fewer problems.

2. If there are many missing teeth and the form of missing teeth is complicated, there tend to be many problems with the remaining teeth.

3. If the remaining teeth are in bad condition and the occlusal force is strong, there tend to be many problems with the remaining teeth and the implant part.

4. If there is a bad habit and the occlusal force is strong, implant treatment tends not to be an effective treatment.

However, because it is not possible to grasp everything when starting treatment, it is important to always predict changes in the oral cavity while grasping the health status even after implant treatment, and to respond to changes in the situation. An ultra-long-term treatment plan may be useful for the super-aging society.

It has long been discussed how dental therapies including implant treatment should be performed in older patients in Japan. However, definitive treatment guidelines and position papers have not been published due to the lack of clinical evidence for older patients. An appropriate dental implant treatment that resolves several problems due to aging of patients is required. However, which problems play an important role in such treatment remains unknown, since older people have many types of problems such as multiple diseases, polypharmacy, nutrition, age, cognitive function, frailty, sarcopenia, locomotive syndrome and oral frailty. Hence, dentists cannot perform dental implant treatment in older patients based on scientific evidence.

The aim of this study was to clarify the Japanese population, definition of older people, average lifetime and healthy lifespan, frailty, sarcopenia, locomotive syndrome, cognitive function and nutrition of older people, relationship between oral frailty and dental treatment, and useful and easy methods for evaluating risk factors regarding older people, in order to propose suitable dental implant treatment in older patients. This study may contribute to the establishment of clinical guidelines for dental implant treatment in older patients, although we cannot show definitive treatment strategies for older patients.

Oral function declines with age in line with the decline of whole body function. The presence of teeth and dental implants is effective for promoting health and preventing frailty. On the other hand, patients with diminished physical function tend to lose efficacy. In more serious care situations, the presence of teeth and dental implants can be a risk to the oral environment and life prognosis; oral management must be properly implemented at all stages so that the presence of teeth is not a risk. The present situation where sufficient oral care cannot be provided to elderly people who have lost independence is a dental problem that must be resolved at an early stage.

Preoperative examinations and installation protocols for dental implants are now being established. The current issues for dental implants are prediction and long-term prognosis. Bone classification based on bone mass and bone mineral density of alveolar bone at implant placement, namely bone quality, has been used in the dental community. On the other hand, bone quality in the orthopedic field is a factor affecting bone strength other than bone mineral density. Collagen crosslinks, one of the representative elements of bone quality, are inter-molecular crosslinks formed as a result of a series of post-translational modifications during the process of collagen biosynthesis. It is known that the amount and composition ratio of the collagen crosslinks contribute to the mechanical properties of the tissue. Recent studies have reported that collagen crosslinks in tissues control cellular activity, thus, collagen crosslinks in bone not only affect the mechanical strength of tissues but also control local bone metabolism. In this review, we introduce the new function of collagen crosslinks, and its clinical significance and future prospects in implant treatment.

Dental implant rehabilitation is an established treatment for edentulous patients. Recently, treatment procedures have changed from the original protocols, towards a shorter treatment time. The achievement of greater primary stability, which is one of the prerequisites for osseointegration, is demanded in clinical situations, since there is a trend to load the implant immediately or in the early stages after implant placement. With this aim, several modifications have been introduced, such as more aggressive implant design, modified surfaces, and novel surgical techniques. Undersized drilling osteotomy is one of the most commonly adopted procedures for implant surgery. This technique creates an osteotomy that is substantially smaller than the implant diameter, so that a tight interfacial contact and compression are created. This is perceived by the surgeon with an increase of the insertion torque value (ITV).

Albeit commonly performed in clinical situations, several aspects of undersized drilling are still not well investigated. It was hypothesized that large compression at implant placement would cause tissue damage and may trigger a negative bone response during the healing time. This could lead to impaired bone material properties, decreased stability, marginal bone loss, and in the worst case, implant loss. The aim of our research was to gain a more consistent understanding of the effects of an undersized drilling osteotomy.

Our studies suggested that undersized drilling osteotomy can cause negative effects in cortical bone. The literature indicated that the undersized drilling technique is effective for increasing the ITV in low-density bone. However, ITV is mostly influenced by bone quality rather than drilling protocol. Furthermore, high ITV can induce greater bone resorption in dense bone. On the other hand, cortical bone has the capability to maintain high levels of rotational stability at undersized sites in the early healing period, despite the great amount of micro-damage. From a biological point of view, this procedure causes a reduced apposition of newly formed bone at the implant surface and initiates an intense bone resorption activity in the surrounding tissue. This creates a temporary porosity into cortical bone, reducing the volume of peri-implant mineralized tissue. Intra-cortical resorption cavities caused an impairment of material properties and compromised mechanical behavior. The model with bone resorption cavities was more prone to micro-damage and delayed healing process. Therefore, it is recommended to avoid the early loading protocol. Further studies are needed to establish the protocol for immediate and early loading with undersized drilling osteotomy.

Many studies have suggested that peri-implantitis causes inflammation similar to periodontal disease due to the accumulation of plaque. Furthermore, the soft tissue around dental implants, with weak connective tissue sealing and epithelial adhesion and low resistance to infection, is different from that of natural teeth. To date, various clinical approaches for peri-implantitis have been reported, but no successful clinical application has been suggested. Under this situation, various basic studies have been conducted to obtain a long-term prognosis for implants, one of which is soft tissue sealing at the implant transmucosal area.

Since 2015, we have been conducting joint research with Harvard University School of Dentistry for the purpose of improving adhesion between titanium and oral epithelium. In our study, we have fixed peptide-conducting epithelial cells to pure titanium polished surfaces treated with PA linker and confirmed strong adhesion of epithelial cells. Through this study, we consider future research of soft tissue sealing.

In the super-aged society of Japan, the number of older people is expected to continue to increase. Accordingly, there is an urgent issue of how to control the growth of the number of older people requiring long-term care and to extend the healthy life expectancy in the future. One possible way is to prevent the incidence of frailty and sarcopenia. In addition, recent studies have shown that these pathological conditions are strongly associated with oral function. In order to enable older people to extend their healthy life expectancy, medical doctors and dentists need to work together to address this issue across Japan.

Purpose : Recently, it was estimated that there are more than 43 million patients with hypertension in Japan. Although hypertension is considered to have high prevalence among implant patients, the relevance of taking antihypertensive drugs and implant treatments has not been reported. Therefore, we clinically examined the effects of various antihypertensive medications on the clinical parameters of the peri-implant tissue. Materials and Methods : Patients who visited between November 2016 and April 2018 for implant maintenance were enrolled in this study. Clinical histories were reviewed and patients were classified into a healthy group (H : without systemic diseases or any medications) and an antihypertensive medication group (AH : those medicated with calcium antagonist or angiotensin II receptor blocker (ARB)). We excluded those patients who smoked or had a history of mild to severe periodiontitis. Those for whom 6 months or more had elapsed since setting of the superstructure were evaluated. Clinical parameters examined included probing pocket depth (PPD), bleeding on probing (BoP), and marginal bone loss (MBL). Statistical analyses were performed with the Mann-Whitney U-test and Spearman's rank correlation coefficient to determine significant differences between these parameters. Results : Seventy implants in 35 patients (male:10, female:25, mean maintenance period:5 years 6 months) were assessed. Fortysix implants in 25 patients were analyzed in the H group and 24 implants in 10 patients in the AH group. The prevalence of implant-based peri-implantitis was 5.7% of all the implants. Comparing the two groups, PPD and MBL were significantly larger in the AH group. Moreover, we found moderate positive correlations between BoP and MBL (r_s=0.461, p＜0.05) in the AH group. Conclusion : Our findings suggest that probing pocket depth is possibly deeper and bone resorption may be increased in patients taking calcium antagonist and ARB medications in medium-term maintenance therapy.

Collagen used clinically is generally derived from either cows or pigs, thus there is a risk of zoonosis. On the other hand, there is no danger of animal-to-human disease transmission with scale collagen derived from fish scales, a possible alternative to bovine or porcine collagen.

In the present study, fish scale collagen was applied using sponges to bone defects with a diameter of 8 mm and thickness of approximately 2 mm formed in the skullcaps of rats. Samples were obtained at 4 and 8 weeks postoperatively, and examined with micro-computed tomography. Using those images, we determined the ratio of new bone to bone defects, as well as bone volume, mineral content, and mineral density, and then compared the results with images from the control group.

New bone area ratio, bone volume, and bone mineral content tended to be greater in the experimental group. Bone mineral density showed an increasing tendency at 4 and 8 weeks postoperatively, with a significant difference noted between that at 4 and 8 weeks. Furthermore, bone mineral density in the experimental group was lower at 4 weeks than in the control group, while it reached nearly the same level at 8 weeks.

Fish scale collagen is thought to offer superior levels of cell proliferation, and initial differentiation and promotion of osteoblasts. We consider that the present findings may have been related to promotion of proliferation of cells involved in osteogenesis. Accordingly, fish scale collagen may be an effective alternative to conventional bovine and porcine collagen materials for promoting osteogenesis.

Purpose : Complications in mandibular implant treatment are rarely serious due to its specific histological and anatomical properties. On the other hand, complications are expected to decrease with the progress of diagnostic apparatus. However, few investigations on complications after recent changes in implant treatment techniques and environmental facilities have been reported. In this study, we performed a questionnaire survey to study the present situation of complications considering the changes in recent implant treatments. Materials and Methods : A questionnaire survey of complications in mandibular implant treatment and dental clinic systems was conducted, targeted 51 certifying and supervisory doctors of the Japanese Society of Oral Implantology in Hokkaido for three years (April 1, 2012 to the end of March, 2015). Results : The complica tion rate of inferior alveolar nerve injury was 22% in supervisory doctors and 21% in certifying doctors. The rate of lingual perforation was 22% in supervisory doctors and 10% in certifying doctors. Discussion and Conclusions : The results revealed that there are still a considerable number of complications despite the changes in implant treatment techniques and environ mental facilities. It is considered that in-office cooperation with co-dental staff and other medical institutions is crucial to pre vent complications.