While there is a definitive consensus on 2-IOD for edentulous mandible patients, there is still no definitive consensus on implant overdentures for edentulous maxillary patients. There have been very few clinical studies on maxillary IODs, but early publications from 1997 to 2009 show a trend of low survival rates, ranging from 61 to 84％. Since 2013, RCT studies have started to be published, and there have been reports of RCT studies comparing 4-IOD and 6-IOD. However, there were no significant differences in outcomes. Since 2019, clinical study reports have also been published that compared connected implants and unconnected implants, but again, no significant differences were reported. Therefore, it is considered that four standard implants are the standard for maxillary IODs, and that although there is no significant difference between connected and unconnected implants in the case of upper and lower edentulous jaws, it is more likely that connected implants are preferable when the opposite teeth are natural or in a fixed prosthesis. Further evidence for maxillary IARPD needs to be accumulated.

When the number of teeth decreases with aging, there are cases where the speed of maxillary tooth loss is faster than that of mandibular teeth. Even with treatment intervention for such cases, it is sometimes impossible to stop the reduction of maxillary teeth, leading to occlusal collapse. For such cases, called “maxillary arches with rapid tooth-loss,” more thorough treatment intervention is necessary, focusing mainly on molar occlusal reconstruction and reinforcement of maxillary anterior teeth. One possible method of molar occlusal reconstruction that may be considered is implant placement under the maxillary denture base, known as IARPD.

In most clinical cases, maxillary implant overdentures (IOD) are indicated in patients with functional disorders, such as chewing difficulty, unstable artificial dentures, and dissatisfaction with prosthetics due to poor adhesion. Following the loss of teeth, the maxillary alveolar crest resorbs inward, and the dental arch tends to become smaller, resulting in worsened interarch relationships, instability of the upper complete denture, and mechanical issues. In addition, many cases demonstrate a severely atrophic edentulous alveolar ridge in the anterior maxilla with insufficient height, width, and angulation issues. We documented a case with postoperative complications due to compromised quality and quantity of bone in maxillary IOD. Therefore, it is crucial to rehabilitate partially edentulous patients to overcome the issue of maxillary bone loss in complete edentulism. We present a clinical case describing the fabrication of an implant-assisted removable partial denture supported by several implants.

Magnetic resonance imaging (MRI) is a technique based on nuclear magnetic resonance. In clinical MRI, the hydrogen nucleus, which consists of a single, positively charged proton, is the object of imaging. This allows the various signals from hydrogen nuclei in different tissues to be visualized. There is no risk of exposure to radiation during an MRI examination because ionizing radiation is not used. In addition, compared to computed tomography (CT), MRI has superior contrast resolution of soft tissues. Therefore, MRI is widely used as a non-invasive imaging method that produces excellent soft tissue contrast, and the number of MRI examinations is increasing year by year.

However, because MRI uses powerful magnetic fields, there have been numerous cases in which ferromagnetic materials, which are attracted to the magnetic fields, have led to medical accidents. Therefore, great care must be taken not to bring ferromagnetic materials into the exam room, and metals on or inside the body must always be checked for compatibility with MRI before the examination.

Recently, the use of cardiac pacemakers and defibrillators that are compatible with MRI examinations under certain conditions has been increasing. Since MRI is the most useful imaging method for the diagnosis of oral lesions such as oral tumors, salivary gland diseases, and temporomandibular joint disorders, it is desirable to use MRI-compatible materials in dental treatment. This review outlines the principles and features of MRI.

Magnetic resonance imaging(MRI) is a non-invasive diagnostic technique that utilizes magnetic fields to obtain cross-sectional images of living organisms. However, a phenomenon called artifacts can lead to the detection of erroneous signals. The primary artifacts include motion artifacts, partial volume effects, and susceptibility artifacts.

Motion artifacts are the phenomenon whereby patient movement causes image blurring, necessitating head fixation during examinations. Partial volume effects occur when the averaging of MRI data results in signals being visualized in varying states. Although reducing the slice thickness can suppress this effect, it causes the problem of decreasing the signal-to-noise ratio (S/N ratio). Susceptibility artifacts arise in regions with significant differences in susceptibility within the body, with highly susceptible materials being the primary cause. In dentistry, oral prosthetics are often the source of these artifacts, with particular attention required for orthodontic wires and magnetic attachments.

By understanding and addressing these artifacts appropriately, it is possible to effectively utilize MRI, leading to accurate diagnoses.

In Magnetic resonance imaging （MRI）, the dental region and oral cavity area is a region where image deterioration is observed due to metal artifacts associated with restorative prostheses.

A metal artifact is one of the magnetic susceptibility artifacts in MRI.

MRI images of patients wearing metal objects, especially ferromagnetic materials such as those containing iron, cobalt, and nickel, suffer from significant distortion. The effects of magnetic metals are not limited to image distortion; the heat generated by the metal itself and changes in the position of the magnetic material due to magnetic force pose problems for the human body.

On the other hand, among metals, non-magnetic metals（titanium, gold, silver, palladium, etc.） that do not become magnetized even when exposed to a magnetic field are considered safe metals for MRI examinations.

All dental magnetic metals, including magnetic attachments, vary in magnetic content and nature, but MRI distortion from the base of the skull to the pharyngeal region is basically observed due to magnetic metals. Regarding the problem of metal heat generation, experiments and literature indicate that there is almost no possibility of burning the oral mucosa with magnetic dental metals. However, another problem is that the keeper deviates from the abutment tooth due to deterioration of the resin cement that fixes the magnetic material such as the keeper, which becomes a problem in long-term use. When a magnetic material is adhered, it is desirable to re-adhere it in about 3-4 years considering deterioration over time.

Increasing the static magnetic field strength of clinical MR equipment from 1.5 T （Tesla） to 3.0 T does not change the above observations and knowledge.

Purpose： This study aimed to create experimental implants using JIS grade 4 titanium and titanium subjected to severe plastic deformation and compare their mechanical properties along with the strain in the collar portion.

Materials and Methods： An experiment that involved processing a 0.7 mm-thick collar portion (CFT) using the severe plastic deformation of titanium was conducted. In addition, processing was performed on a 0.7 mm-thick collar portion (T7S)and 0.9 mm-thick collar portion (T9S) using JIS grade 4 titanium. The bending load, deformation, and strain in the collar were measured with each implant fixed to a jig at an inclination angle of 30°. Each implant was observed by X-ray CT.

Results： CFT exhibited the highest bending load (1,124.6±6.3 N) followed by T9S (957.8±24.4 N) and T7S (878.9±17.1 N)：a significant difference(p＜0.001). CFT of deformation exhibited the largest value, and a significant difference (T7S-CFT：p＝0.0141；T9S-CFT：p＜0.001) was found between CFT and T7S／T9S, but not between T7S and T9S. Regarding the strain in the collar portion for loads of up to 550 N, no significance difference was found between T7S, T9S and CFT. However, for loads of 600-700 N, a significant difference (at 600 N, T7S-CFT：p＝0.0351；at 650 N, T7S-T9S：p＝0.0227, T7S-CFT：p＝0.0430；at 700 N, T7S-T9S and T7S-CFT：p＜0.001, respectively) was found：T7S exhibited a much higher strain than T9S and CFT.

Meanwhile, no significant difference between the amount of strain for T9S and CFT was found. CT observations at a load of 600 N identified a gap in the connection part of T7S. For loads exceeding 700 N, a gap was found in the connection part of all test pieces.

Conclusion： Implants fabricated using the severe plastic deformation of titanium demonstrated superior mechanical properties compared to those fabricated using JIS grade 4 titanium. Furthermore, the amount of strain in the collar portion was lower, suggesting that the severe plastic deformation of titanium is effective in preventing accidental symptoms.

Dental implant treatment for congenitally missing teeth in patients with cleft lip and palate is often performed after cleft bone grafting. We report the case of a cleft lip and palate patient with jaw deformity who underwent dental implant treatment combined with alveolar osteotomy, resulting in good functional and esthetic recovery.

The patient was a 38-year-old woman. She had undergone lip and palatoplasty after birth for cleft lip and palate, and at age 18 underwent a sagittal split ramus osteotomy. However, she had not received treatment for the cleft jaw. She was referred to our department in September 2016 for dental implant treatment for the cleft jaw. Due to the diagnosis of left-sided cleft jaw and maxillary retroversion, an alveolar osteotomy of the left first premolar was performed during the preoperative orthodontic period to close the cleft jaw and to secure space for placing the dental implant. The dental implant was placed in the space secured by the bone distraction, and Le Fort I osteotomy was performed after preoperative orthodontic treatment. In April 2019, after postoperative orthodontic correction, the final superstructure was placed. In April 2022, the jaw position was stable, the lateral view was improved, and the dental implant was in good condition.

The use of temporary bone lengthening after alveolar osteotomy to close the cleft jaw and to secure the dental implant placement space is useful. Soft tissue formed around the temporary bone distraction area and good cleanability of the dental implants was established.

Currently, implant treatment is regarded as a prosthetic for defects, and has good predictability and stability. However, peri-implantitis may be a complication after implant placement. We report on non-surgical debridement using air-powder abrasion (APA), which was performed in two patients with peri-implantitis due to interruption of maintenance for oral implant hygiene after implant placement, and that appropriate maintenance was resumed.