Purpose:In recent years, various complicated cases of implant treatment have increasingly been reported. Especially, it is often difficult to decide whether to remove an implant with bone resorption caused by peri-implantitis. The aim of this study was to establish implant removal criteria with a biomechanical analysis of a bone resorption model simulating peri-implantitis by the 3D-finite element method.
Material and Methods:The bone resorption model simulating peri-implantitis was a simplified mandibular segment with a cancellous core surrounded by a 1.5 mm thick cortical layer. A cylindrical implant was designed with a 4.0 mm diameter and three implant lengths (7.0, 10.0, and 13.0 mm). The superstructure had a height of 7.5 mm and head diameter of 7.0 mm. Four types of bone (Ⅰ to Ⅳ) were modeled by varying the elastic modulus for cancellous bone (9500, 5500, 1300, 690 MPa). We set the bone resorption per 0.5 mm from the alveolar crest, and osseointegration with the cancellous bone was kept by the bone resorption of 1.5 mm clinically. A vertical and an oblique load of 100 N were applied on the superstructure. The compressive and allowable stress in the bone around the neck of the implant were analyzed.
Results:Under all bone densities and loading conditions, the intraosseous compressive stress of the 7.0 mm implant was increased by bone resorption at first. Subsequently, the stress was increased in order of the 10.0 mm and 13.0 mm implants.
The clinical crown/implant ratio (CC/I ratio) of intraosseous stress exceeding the allowable stress in type Ⅰ bone was 3.8 for the 7.0 mm implant, 2.2 for the 10.0 mm implant, and 1.6 for the 13.0 mm implant. Similarly, the CC/I ratios for the 7.0 mm, 10.0 mm, and 13.0 mm implants were 2.2, 1.7, and 1.4 in type Ⅱ bone, 1.6, 1.1, and 0.8 in type Ⅲ bone, and 1.4, 1.1, and 0.8 in type Ⅳ bone.
Conclusion:This study suggested that the destruction of cancellous bone was caused by a short implant length and low bone density at an early stage when the bone resorption had progressed by peri-implantitis. Moreover, we showed that it is necessary to choose the timing of removing an implant with peri-implantitis based on the CC/I ratio under each condition of bone density and implant length.

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Poly(ethylene terephthalate) sheet coated with a double layer of gelatin and readily soluble calcium phosphate (CaP) has been proposed as a non-resorbable membrane in guided bone regeneration(GBR). This material promoted the proliferation and differentiation of MC3T3-E1 cells in vitro, which was attributed to the readily soluble nature of the CaP layer providing Ca^2＋ ions to the MC3T3-E1 cells. On the other hand, the migration of endothelial cells is also known to be promoted by Ca^2＋ ion supply, which implies that the material may also promote the migration of endothelial cells. The present study investigated the effect of the CaP layer on the migration and extension of human umbilical vein endothelial cells (HUVEC), which are responsible for angiogenesis. The experimental results showed that the CaP layer significantly promoted the migration and extension of HUVEC cells.

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Purpose:To assess quantitative changes in bone width before and after bone grafting in cases of veneer grafting to the maxillary ridge with block bone harvested from the mandible and to measure the width of the labial/buccal bones of implant bodies 5 years or more after superstructure placement.
Materials and Methods:We assessed 14 sites in 11 cases. The ridge bone width was measured at the time of veneer grafting as well as upon implant placement (four to six months later). The measurement sites were the 5-, 10-, and 15-mm horizontal bone widths at 5-mm intervals going vertically toward the floor of the nasal cavity, with the references points of the crest of the alveolar process. For cases in which five or more years had elapsed since the superstructure placement, 21 sites where implant bodies were placed were imaged by conebeam computed tomography(CT) , and the widths of the labial/buccal bone of the implant body were measured and assessed.
Results:The ridge bone width at the time of veneer grafting was 2.3±0.8 mm at the 5-mm position, 3.7±1.4 mm at the 10-mm position, and 5.3±1.8 mm at the 15-mm position going toward the floor of the nasal cavity from the crest of the alveolar process. The bone widths of the same sites again upon implant placement were 6.6±0.7 mm at the 5-mm position, 8.0±1.3 mm at the 10-mm position, and 8.7±1.4 mm at the 15-mm position. The diameter width measurements of the labial/buccal bone of the implants in 15 out of 21 sites where five or more years had elapsed since the superstructure placement and visualization with cone-beam CT was possible were 1.8±0.6 mm at the 5-mm position and 2.3±0.6 mm at the 10-mm position from the platform.
Conclusion:Veneer grafting with block bone harvested from the mandible to the maxillary alveolar process resulted in the ability to acquire the necessary horizontal bone mass for implant placement. Even when five years had elapsed since the superstructure placement, the labial/buccal bone of the implant body had maintained a thickness of 1.5 mm or greater, suggesting that this state will continue to be maintained.

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Nihon University School of Dentistry Dental Hospital adopted program 1 and program 2 as a dental training program in 2013. All dental trainees are given training by cooperating facilities determined by matching a group at program 1 or management-type facilities, program 2. Every year, they have implant placement training with a jaw bone model at the end of the program. The aim of this study is an investigation of their training environment, or consciousness about implant therapeutics.
Dental trainees have certain opportunities to experience implant treatments at either the cooperating or management-type facilities. Moreover, since they have therapeutic experience during the programs, implant placement training made them fully understood the steps of implant therapy.

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Objective: Extensive jawbone-supported devices were newly covered by health insurance from April 1, 2012. Therefore, we evaluated the cases of advanced medical treatment involving dental implant prosthesis performed at our hospital, and report the results.
Subjects and Methods:The subjects included in this review were 34 patients who had received advanced treatment involving implant dentures at our hospital between January 22, 2003 and March 31, 2012. The study considered the following factors:sex, age, primary ailment, patient-referral route, surgical treatment history of tumor patients, morphological defects, area of implantation and number of implants, anesthetic methods used during implantation and combined surgical methods, types of final prosthesis, and post-operative outcomes.
Results: The subjects consisted of 18 males and 16 females. The age range was from 18 years to 82 years, with a median age of 68 years. The primary ailments were malignant tumors (n=22), a highly-resorbed alveolar ridge (n=4), and congenital tooth defect (n=1) . Regarding patient-referral route, the largest percentage (n=19) directly approached our hospital. As for the surgical treatment history of tumor patients, soft-tissue surgery consisted of resection of the tongue and mouth floor in the largest percentage (n=9), and 12 patients had jawbone surgery. Concerning morphological defects, the largest percentage (n=24) of patients were edentulous. The total number of implanted fixtures was 112. During implantation, general anesthesia was administered to 20 patients, local anesthesia with intravenous sedation was chosen for 7 patients, and local anesthesia alone was administered to 7 patients. In cases where combined surgical procedures were used, guided bone regeneration (GBR) was performed on 4 patients, the inferior alveolar nerve was moved in 3 patients, elevation of the maxillary sinus floor was performed on 2 patients, and the debulking of skin flaps was conducted on 2 patients. Regarding the types of final prosthesis used, attachment dentures were fixed in 21 patients. Concerning post-operative outcomes, implants were functioning without problems in 18 patients.
Discussion and Conclusions: It had been considered that patients who had received advanced medical treatment involving implant dentures at our hospital in the past achieved favorable functional recovery. At present, it is considered that extensive jawbone-supported devices introduced under health insurance coverage are useful for functional recovery and improvement of patients' quality of life.

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Although the alteration of bone level and density around functional dental implants was well documented, there was little information about their alteration in dental implants procedures.
The aim of the present study was to evaluate the postsurgical bone level around the submerged dental implants before the secondary operation. The digital intraoral radiographs taken for 52 implants were used in this study. The digital radiographs were obtained at the time immediately after the first surgery, and at 3 and 6 months after the surgery, but before the second surgery, by a digital intraoral radiography system. The digital images were manipulated by EMAGO, and then linear and logarithmic digital subtraction images were produced. The subtraction images were analyzed by ImageJ. The data was analyzed using one-way ANOVA, and a p-value of less than 0.05 was considered statistically significant.
As for the results, regarding the bone losses around the implants, the bone losses around the implants of 3.75 mm diameter were significantly higher than those around the implants of 5.0 mm diameter, both at 3 and 6 months after the first surgery (p＜0.05). The bone losses around the implants of twist types were significantly higher than those around the implants of cylinder type (p＜0.05). The bone losses in mandible were significantly higher than those in maxilla (p＜0.05). The bone losses in women were significantly higher than those in men (p＜0.05).
The results suggested that the alteration of bone level around the implants was dependent on the diameter and shape of the implants, the distinction between the maxilla and mandible, and gender. Therefore, these factors should be considered in the planning of dental implant procedures.

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Peri-implantitis is defined as an inflammation with bone loss after achievement of osseointegration. Especially in cases where there is severe bone loss, peri-implantitis causes mobility of the implant and deteriorates the localized environment. The incidence of peri-implantitis varies depending on the criteria of diagnosis but it is generally accepted that the rate of occurrence increases year after year. Currently, several surgical treatment strategies are in use for peri-implantitis including Er:YAG laser, mechanical cleaning by air powder abrasion, or titanium scaler, and chemical cleaning by local administration of gluconate chlorhexidine. However, it has not yet been defined which strategy provides the most optimal efficiency.
In this study, we investigated visually the effects of various mechanical cleaning methods on hydroxyapatite (HA) coated implants with different types of shapes (cylinder and screw).
HA coated samples were selected as a means of simulating calculus attachment to the implant surface and were subjected to mechanical removal by Er:YAG laser (Er), titanium brush (Ti) and air-powder abrasion with β-TCP (β). The efficiency of mechanically removing the HA coating was calculated based on observation under a light microscope.
Following the debridement procedures, a larger amount of remnants of HA coating on the screw-type implant was observed compared to the cylindrical sample. After mechanical treatment, the order of the amount of HA remnants on the cylindrical and the screw-type sample were β=β＋Ti＜Ti＜Er (p＜0.05) and β＋Ti＜β＜Ti=Er (p＜0.05), respectively.
Based on these findings, it seemed to be more difficult to decontaminate screw-type implants compared with cylindrical types. In addition, the most effective method of mechanical removal was using β＋Ti and where the use of Er:YAG laser produced the lowest removal rate. The various forms of bone defect caused by peri-implantitis could prohibit the access of instruments, and that may limit the type of treatment materials available to the clinician. To provide optimal care for patients with peri-implantitis, several crucial factors must be considered, including accessibility of instruments, the texture of biofilm attached to the implant surface and design and characteristic of the implant surface.

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