The inorganic component of bone is not hydroxyapatite but carbonate apatite. Living organisms originated in the sea and formed exoskeletons with calcium carbonate which can be extracted from sea water. On the other hand, the energy of living organisms comes from phosphates such as adenosine triphosphate. Increased mobility, and movement away from the sea, which contains trace amounts of phosphoric acid, to the land (where phosphoric acid does not exist in the air), led vertebrates to store phosphoric acid in their bones. As a result, the skeletal composition of vertebrates became carbonate apatite, which is calcium carbonate with phosphoric acid added.

Carbonate apatite bone substitute can be prepared by adding phosphate salts to calcium carbonate, inspired by the evolution of the aforementioned organisms. 100％ chemically synthesized carbonate apatite is resorbed by osteoclasts, similar to bones. Due to intercellular information transmission, osteoblasts are activated, demonstrating overwhelming bone conductivity.

The effectiveness of carbonate apatite has been proven in multi-center trials to be 100％. As a result, carbonate apatite artifical bone substitute has been approved by the PMDA in Japan as the first artifical bone substitute without application restrictions, and is being clinically applied in both Japan and the United States. It holds the top market share in Japan.

Apatite is essential as a medical device. However, hydroxyapatite is not part of the inorganic composition of bones. For the perspective of treatment effectiveness, there is an urgent need to reconstruct hydroxyapatite-related medical materials with carbonate apatite.

Octacalcium phosphate (OCP) is known to be formed prior to the formation of hydroxyapatite (HA) from aqueous solutions and has a structural similarity with HA. It has been suggested that OCP is a precursor for biological apatite crystals in bone and teeth. OCP shows higher osteoconductivity than HA and higher resorbability than β-tricalcium phosphate (β-TCP), a typical biodegradable calcium phosphate material. OCP is a metastable phase under physiological pH and in fact tends to progressively hydrolyze in vivo, resulting in the formation of an apatitic phase, Ca-deficient HA (CDHA). OCP interacts with the surrounding environment in various ways through structural changes and exhibits osteoconductive capacity. In vitro cell culture analyses have revealed that OCP enhances osteoblastic differentiation, osteoclast formation and other bone tissue-related cellular activities. When mesenchymal stem cells (MSCs) are cultured in coexistence with OCP and autologous bone, the presence of OCP further enhances osteoblastic differentiation of MSCs. A composite form consists of OCP granules and atelocollagen (Col) derived from porcine dermis (OCP/Col) has been confirmed to exhibit bone regenerative capacity in preclinical and clinical studies. OCP/Col is now used as a bone substitute material with dental implant placement. This article explains the properties of OCP as a biomaterial and the bone regenerative capacity of OCP/Col that we have reported so far.

Novel bioabsorbable materials have hardly progressed to clinical application ; collagen, hyaluronic acid, polyglycolic acid, and polylactic acid are still the mainstream. These bioabsorbable materials do not adhere to biological tissues. If bioabsorbable materials could be given the ability to adhere to biological tissues, the implantation of artificial bones and other mixtures into the affected area could be ensured. We have developed phosphorylated pullulan based on the tooth adhesive theory, which is the first non-animal-derived bioabsorbable material that adheres to bone and tooth. Phosphorylated pullulan is the only product selected for “Strategy of SAKIGAKE” by the Ministry of Health, Labour and Welfare in the dental field. We are planning to start an investigator-initiated clinical trial using phosphorylated pullulan as a class Ⅳ medical device in 2024. The mixture of phosphorylated pullulan and β-TCP has been reported to be useful as a putty-like bone replacement material for bone defects around dental implants. Practical applications are also being promoted outside the dental field. A submucosal injection material “enRise” used for endoscopic resection of gastric cancer, etc. has already received pharmaceutical approval. Phosphorylated pullulan has received various large amounts of support for research and development, probably because we have been focusing on introducing the new material from Japan to the world for the phosphorylated pullulan project. Other than the dental field, phosphorylated pullulan is expected to be used for scaffolds and carriers using drug delivery systems for various organs. Phosphorylated pullulan will be developed for a wide range of applications as new bioabsorbable materials instead of existing products.

To achieve successful implant surgery, it is imperative to prevent injury to adjacent tissues, such as blood vessels, nerves, mucosa, and muscles, by meticulously assessing the structures within the jawbone. This study examined anatomical specimens of the maxillary sinus and maxillary tuberosity and underscored the significance of risk management in implant therapy in the maxillary molar area.

Tooth loss leads to alveolar bone resorption, significant alveolar bone loss, and descent of the maxillary sinus floor. By utilizing anatomical images from cadaver specimens, we showed a case wherein implant base perforation occurred into the maxillary sinus. It is crucial to consider the course and distribution of the posterior maxillary alveolar artery, which is a branch of the maxillary artery, and the posterior maxillary alveolar nerve branch, which is a branch of the maxillary nerve, from the posterior maxillary tubercle to the maxillary sinus during implant therapy.

From an anatomical perspective, the following three implant therapy approaches for the maxillary molar region are delineated, encompassing scenarios with limited vertical bone volume and presence of the maxillary sinus.

1. Inclined implant placement within existing bone : When conventional implant placement is challenging, utilizing existing bone to position implants at an intentional angle proves effective. Nonetheless, cautious maneuvering is imperative to prevent harm to adjacent blood vessels and nerves.

2. Bone augmentation : In instances of reduced alveolar bone height, bone augmentation is used. Autogenous bone or bone graft materials are employed, necessitating meticulous monitoring of postoperative soft tissue closure.

3. Sinus floor elevation : For cases with limited vertical bone volume, sinus floor elevation is a viable surgical option. Both the lateral and alveolar crest approaches are utilized, demanding careful attention to prevent injury to the intra-maxillary sinus mucosa.

Dental implants have a long history, and dentists have developed and provided implants based on anatomical knowledge without cone-beam computed tomography (CBCT). Recently, implant dentistry entered a new era with CBCT technology, and the small bony structures have become visible. The anatomy of the mandibular canal is now completely understood. However, the present author believes that classic anatomy research on the mandibular canal needs to be remembered, considered, and even revisited. This article revisits the classic anatomy of the mandibular canal in old literature and reviews newly published research to discuss the significance of the mandibular canal anatomy in implant dentistry. The course of the mandibular canal, bifid mandibular canal and retromolar canal, macroscopic and microscopic anatomy of the mandibular canal, and mandibular canal morphology on CBCT and superposition with old anatomy research will lead to a better understanding of the clinical anatomy of the mandibular canal.

Purpose : Although implant therapy is now widely used, there have been many reports on biological complications such as peri-implantitis. Thorough plaque control before implant placement is important to improve the survival rate of implants. The purpose of this study was to compare the rate of reduction of O'Leary's plaque control record (PCR) in patients seeking implant treatment, by distinguishing between a group using a manual mirror (group T) and a group using an intraoral scanner (group I) after staining.

Materials and Methods : Forty patients seeking implant treatment underwent staining and oral hygiene instruction at 1, 2, and 3 months after tooth extraction. PCR at 1 month and 3 months after tooth extraction were denoted by P1 and P2,respectively. The target areas were the entire dentition, and the entire dentition was divided into six blocks : maxillary right molars, maxillary anterior teeth, maxillary left molars, mandibular right molars, mandibular anterior teeth, and mandibular left molars. Gender, buccolingual and lingual-palatal were also differentiated, and the PCR reduction rates were compared.

Results : The overall reduction rate of the oral cavity in group T was 14.8±7.3％, while that in group I was 26.5±13.5％, showing a significant difference between the two groups. Significant differences were observed in the maxillary left molars, mandibular right molars, mandibular anterior teeth, and mandibular left molars. There was no significant difference between the two groups in the rate of decrease by gender, but there was a significant difference in the rate of decrease by lingual-palatal.

Conclusions : The results of this study suggest the usefulness of the intraoral scanner in plaque control instruction. This may lead to a good oral environment and prevention of peri-implantitis.

Purpose : We attempted to immobilize cell-adhesive proteins onto zirconia surfaces using the tresyl chloride-activated method and evaluated the bone response towards cell-adhesive protein-immobilized zirconia using an animal implantation experiment.

Methods : Fibronectin (Fn) was immobilized onto yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) using a tresyl chloride-activated method. The surface morphologies of the Y-TZP and Fn-immobilized zirconia specimens (Fn/Y-TZP) were observed using an atomic force microscope (AFM), the average arithmetic roughness of the three-dimensional surface (Sa) was obtained, and the contact angles of the Y-TZP and Fn/Y-TZP surface concerning double-distilled water were measured. The immobilization of Fn was confirmed using fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Moreover, Y-TZP and Fn/Y-TZP implants were placed in the femur bone defects of rats. The bone response around the implants was observed 2 weeks after implantation. The bone-to-implant contact (BIC) ratio and bone mass (BM) around the implant in the cortical bone and bone marrow were measured.

Results : The AFM images of Y-TZP and Fn/Y-TZP displayed clearer surface protrusions on Fn/Y-TZP than on Y-TZP. Significant differences have been observed between Y-TZP and Fn/Y-TZP in terms of the surface roughness and contact angles (p＜0.05). Additionally, the FT-IR spectrum displayed the presence of a carbonyl group in the amide group of Fn, and the XPS spectrum of Fn/Y-TZP identified N1s and O1s peaks of immobilized Fn. The histological appearances around the Y-TZP and Fn/Y-TZP implants 2 weeks after implantation displayed new bone formation around the implants in both the cortical bone and bone marrow. The BIC ratio of Fn/Y-TZP was significantly higher than that of Y-TZP in the bone marrow. However, no significant differences were observed in the BIC ratio of the cortical bone area between Y-TZP and Fn/Y-TZP. Furthermore, no significant differences in bone mass were observed between the Y-TZP and Fn/Y-TZP.

Conclusion : In the present study, Fn was immobilized onto zirconia using the tresyl chloride-activated method. The study revealed that immobilization of Fn onto zirconia was effective in enhancing the bone response in the bone marrow area but not in the cortical bone area.

Purpose : This study examined the effects of implant connection design and inclination angle on bending load.

Materials and Methods : Experimental implants were manufactured using a type 4 titanium cementable abutment (TP), straight abutment type (IA) and an inclination of 5° type (IB) with internal taper joint. Bending load and deflection amount were measured for five implants each, using a universal testing machine, at inclination angles of 10°, 20°, and 30°. An analysis of variance was performed to compare significant differences among several groups and Tukeyʼs multiple comparison test (critical rate : 5％). After measurement, each specimen was observed by CT.

Results : The approximate bending load at an inclination angle of 10° was 5,060 N for TP, 3,850 N for IB, and 3,030 N for IA, which was the smallest, with significant differences (p＜0.001) observed among the implants. At an inclination angle of 20°, the approximate bending load was 1,640 N for TP, and those for IA and IB were 1,420 N, with significant differences observed between TP-IA (p＜0.001) and TP-IB (p＜0.001), respectively. The approximate bending load at an inclination angle of 30° was 910 N for TP, 870 N for IA, and 840 N for IB, with significant differences observed between TP-IA (p＜0.001), IA-IB (p＜0.001), and IA-IB (p＝0.008), respectively. The deflection value was 0.49-0.68 mm at an inclination angle of 10°, with significant differences observed between TP-IA (p＜0.001) and IA-IB (p＜0.001), respectively. At an inclination angle of 20°, the deflection value was 0.56-0.61 mm with no significant difference observed, and at an inclination angle of 30°, it was 0.70-0.84 mm with significant differences observed between TP-IA (p＝0.004) and TP-IB (p＜0.001), respectively. CT observations showed gaps between the abutment and collar part at inclination angles of 20° and 30° in each specimen.

Conclusion : It was revealed that the connection method and angle of inclination affected bending load, amount of deflection, and the formation of gaps in the connecting parts.

Objective : To measure the fatigue strength of commercially available implants by subjecting three different implant abutment connections to cyclic loading tests.

Methods : The three connection mechanisms used were the external joint (EXT), internal joint (INT), and taper joint (TAPER) systems. In addition, two types of commercially pure titanium (ASTM Grade 4) one-piece implants were prepared and used as controls ; the first was a solid type (Cont.) and the second, a hollow structure with a φ2.24 mm central axis (Cont. H).

The test specimens were mounted on a 30° inclined block and then placed in a fatigue testing machine. Cyclic sinusoidal loads were applied at 10 Hz, and the load and deformation of the test specimens were measured for each load cycle. The cyclic loading continued until the test specimen failed or reached five million cycles. If a test specimen failed, another specimen was retested using a 100 Nmm lower bending moment. The maximum load value achieved in five million cycles was considered the maximum fatigue load.

Results : The results of the cyclic loading test showed that the maximum fatigue loads for Cont., Cont. H, EXT, INT, and TAPER were 164, 55, 200, 237, and 291 N, respectively. The corresponding bending moments were 900, 300, 1,100, 1,300, and 1,600 Nmm.

Conclusion : The results of the fatigue tests of cyclic loading showed that INT had approximately 18％ higher fatigue strength than EXT, while TAPER had about 45％ higher fatigue strength than EXT. While these results may not be universally applicable to all implant systems, they suggest that the type of connection mechanism is an important factor for selecting implant systems from the perspective of preventing fatigue fractures.

When implant placement in the existing bone is not possible, bone regeneration is an essential procedure for long-term functional and esthetic stability of the implant. This clinical report describes implant treatment using a bone graft and implant overdenture (IOD) for a severe bone defect.

The patient was a 25-year-old man with the chief complaint of swelling of the left buccal region. CT images showed a unilocular radiolucent lesion extending from the maxillary anterior region to the maxillary sinus. The lesion included an impacted tooth and root resorption of 21 to 24 was observed. A biopsy suggested that it was a glandular odontogenic cyst (GOC). Cystectomy was performed with root canal filling and apicoectomy of 21 to 24. Nine months later, tooth extraction of 21 to 24 was performed because of increased mobility, and an immediate denture was inserted. Reconstruction of the alveolar ridge using particulate cancellous bone and marrow (PCBM) was carried out with a titanium mesh tray. Nine months after the PCBM graft, 3 dental implants were placed into the reconstructed bone. After confirming the osseointegration, an implant-supported prosthesis was fabricated. A telescopic system was selected as the retainer for cleanability. The patientʼs satisfaction was improved by the IOD. As of 6 years after IOD placement, implant loss, bone resorption, decrease of retention force, and denture breakage have not been observed.

We report the case of a patient with periodontal disease who had dental implants and was receiving bone resorption inhibitors due to multiple myeloma. Due to recurrence of periodontal disease, all remaining teeth were extracted, and the patient underwent a transition to an implant overdenture (IOD) to prevent medication-related osteonecrosis of the jaw (MRONJ). The patient was a 64-year-old man who had initially presented with tooth mobility in 2010. After periodontal treatment, dental implants were placed in 32 and 42, and the patient transitioned to maintenance therapy in 2012 with good outcomes.

In 2018, the patient required additional treatment for multiple myeloma. In March 2019, combination therapy with lenalidomide and dexamethasone was started, along with denosumab. Ten months later, the remaining teeth showed signs of periodontal disease recurrence. Given the risk of MRONJ due to the progression of multiple myeloma, decreased activities of daily living, and exacerbation of periodontal disease, it was decided that the risk of MRONJ outweighed the risk of tooth extraction. The patientʼs physician was consulted, and denosumab administration was stopped before tooth extraction.

The dental implants showed no signs of inflammation and were preserved, and the prosthodontic device was changed to an IOD. Three years later, MRONJ had not occurred. There was no change in OHIP-14 scores before and after re-intervention.

The decision to extract the teeth was considered based on a comprehensive assessment of the trade-offs among the risk of MRONJ after extraction, MRONJ risk due to residual infection within the jawbone, quality of life, life expectancy, and patient preferences. Preserving the implants proved effective in maintaining a minimum quality of life for this patient.

The material used for bone augmentation in implant treatment may be either artificial bone or autologous bone. Autologous block bone grafts are considered the best choice for the augmentation of extensive lateral bone defects, and the ilium is often chosen as the donor site. In this procedure, the bone block is normally harvested from the iliac crest, but this not infrequently results in morphological or functional issues after the procedure.

We harvested a bone block from the medial plate of the ilium and used it for bone augmentation of a severely resorbed maxillary defect. An implant was inserted at this site 8 months later, followed by secondary surgery 7 months after implant insertion. Two months later, a provisional restoration was made and occlusal loading on the implant was started. Five years and 3 months later, the grafted bone is stable, and there have been no problems with the implant.

It is generally easier to achieve favorable primary stability in mandibular dental implant cases than in maxillary cases because the mandibular bone is harder. Nevertheless, we have experienced two cases of dental implants that were displaced into the mandibular bone. We present these two cases and describe their removal and the clinical consequences.

Case 1 : A 52-year-old female patient. The implant body was displaced into the mandibular bone during placement of the implant. The displaced implant was removed with a long guide pin from the hole made during implant surgery.

Case 2 : A 35-year-old female patient. The implant body was displaced into the mandibular bone during placement of the implant using a torque wrench. In this case, a 3-D model was prepared using computed tomographic (CT) data to simulate the surgery to remove the implant body. Buccal cortical bone was cut out and the implant body was safely removed. In both cases, no sequelae such as nerve paralysis were reported.

It is widely known that the information from panoramic and CT images is important. However, it should be emphasized that the surgeonʼs own tactile sensation during preparation of the implant bed is also important. It is recommended to decide the drilling and placement protocol based on feel during the implant surgery.

A displaced implant can be removed using either a crestal approach or a lateral approach. It is important to remove the displaced implants with appropriate surgical planning using CT data at an early timing.