Purpose: Slight disharmony of occlusion in implant prostheses may cause many problems because there is no periodontal membrane or nerve system as a stress breaker. However, much remains unclear regarding the optimum occlusal contacts of implant prostheses. The purpose of this study was to investigate variations of changes in occlusal load according to clenching strength of implant prostheses and occlusal gap for implants.
Method:The subjects consisted of 17 patients (59±16years old) with an implant for a single intermediate missing posterior tooth with satisfactory prognosis for more than two years. Electromyograms for maximum clenching at the intercuspal position were recorded as 100% MVC (maximum voluntary contraction). Subsequently, clenching at 20, 40, 60, and 80% MVC was instructed with visual feedback. Occlusal load was recorded with pressure-sensitive sheets. Occlusal contacts were recorded with a silicon occlusal contact checking material. The changes in occlusal load according to clenching strength for the implant and each adjacent tooth were examined. The occlusal gap for implants could be estimated from both the occlusal forces of implants and individual teeth and existing data on the degree of displacement.
Results: The subjects were classified into three groups: the WC (Weak clenching) group where occlusal load on implants was recorded from weak (20% MVC) clenching; the MC (Moderate clenching) group where load was recorded from moderate (40% MVC) clenching; and the SC (Strong clenching) group where load was recorded from strong (60% MVC) clenching. At maximum clenching, average loads on implants were 110 N (WC), 90 N (MC), and 123 N (SC), respectively. Average occlusal gaps for implants were less than 43μm (WC), more than 83 μm (MC), and more than 197μm (SC).
Conclusion:The occlusal gap for implants could be estimated with the newly developed method. Clinically, there were many kinds of occlusal situations between the implants and the natural teeth with satisfactory prognosis. These results suggest that the occlusal gap for implants might have some adequate range. However, a long-term study is needed to determine the functional aspects.
It is considered that work hardening can be present in titanium used for implants. In this study, to clarify the relationship between the heat treatment temperature and duration until fatigue failure, a constant strain was repetitively applied to titanium materials, the number of cycles to fatigue failure and hardness in areas near the fracture site were measured, and the fractograph and metallographic structures were observed. Furthermore, the bending strength, strain, and hardness of titanium materials before and after heat treatment were measured.
The bending strength and hardness of the specimens decreased after heat treatment. The crystal grains of specimens before heat treatment were fine, while those after heat treatment showed recrystallization with crystal growth. In the fractograph of the specimens after the fatigue failure test, striations and minute cracks were observed. The number of cycles to fatigue failure was greater in the specimens treated at 400℃ for 80 minutes, and at 450℃ for 40 minutes. It was considered that these heat treatments partially removed the work hardening.
Background: Guided bone regeneration (GBR) therapy using a titanium mesh (TM) is expected to be an effective bone regenerative technique capable of achieving a 3-dimensional massive bone augmentation with a solid, flat and regular cortical layer and, consequently, enhancing the indication of implant therapy and quality of clinical outcomes. Despite many clinical and animal observations indicating TMʼs favorable osteoblastic compatibility, the cell-biological advantages of TM as a GBR membrane are not fully addressed or understood.
Objectives: The purpose of this in vitro study is to examine whether cultured osteoblasts generate a mineralized matrix with superior structural and mechanical properties on a TM and to determine the biological advantages of the TM as a membrane material for use in bone regeneration therapy.
Methods: The surface roughness of a TM was measured using laser microscopy. Rat femoral bone marrow-derived osteoblasts were seeded on polystyrene (PS) which categorized into bioinert material as titanium, and on the TM. The surface morphology and development of calcifications of the cultured mineralized matrix at day 28 were qualitatively analyzed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The micro hardness and elastic modulus of the cultured mineralized matrix at day 28 were measured by nanoindentation.
Results:Ra, Ry and Sm values on the TMʼs surface were 0.10 ± 0.02μm, 0.7 ± 0.1μm and 4.4 ± 1.0μm, respectively. SEM observation revealed that the mineralized matrix at day 28 of the osteoblastic PS culture was porous and exposed a fibrous network and globular extracellular matrix. On the other hand, the mineralized matrix on the TM showed a dense and flattened lamellar structure without exposure of fibrous and globular components. An identical lamellar mineralized matrix was universally and evenly spread on the TM. The Ca/P atomic ratio in the matrix was 1.28 in contrast with 0.87 in the polystyrene culture. The mineralized matrix cultured on the TM for 28 days was four times harder and stiffer than that on the PS.
Conclusion:Rat femur bone marrow-derived cultured osteoblasts produced mineralized matrix with a denser structure and higher biomechanical strength on the micro-roughened surface of the TM than on the PS. This in vitro study helped to indicate the cell-biological mechanism underlying the excellent bone augmentation effects of TM.
The maxilla is generally known as a site where anatomical limitations make it difficult to obtain sufficient bone volume. A large amount of bone exists in the canine region between the anterior margin of the maxillary sinus and the piriform aperture margin. Although this region is crucial for implant treatments, there have not been any reports on morphological studies of the region. In this study, we investigated the morphology of the canine region based on CT, and also the morphology and position of the maxillary sinus located posterior to the canine region.
The results were as follows:
1. In the area above the anterior nasal spine, the higher the level, the smaller the mesio-distal length and the bucco-lingual width tended to become.
2. In the area above the anterior nasal spine, the mesio-distal length and the bucco-lingual width tended to be smaller in female patients than in male patients.
3. In the area above the anterior nasal spine, no significant differences in mesio-distal length and buccolingual width were observed between dentulous and edentulous jaws.
4.The morphology of the maxillary sinus was mainly of an inverse-trapezoidal, circular, or triangular form.
5.The position of the anterior wall of the maxillary sinus was most frequently found at the site corresponding to the second premolar.
Through this study, we have reconfirmed that the canine region is vital for implant treatments in the maxilla.
Objective: There are approximately 11 million osteoporosis patients in Japan today. Although osteoporosis is known as a risk factor for dental implant treatment, no studies have investigated how the pathogenesis of osteoporosis after implantation is related to dental implant failure. Bone metabolic markers are used to ascertain bone quality in orthopedics, and have been suggested to be indicators of osteoporosis. The aim of this pilot study was to investigate the ratio of patients with abnormal bone metabolic marker values to determine their suitability for use as indicators of the risk of implant failure.
Methods: Samples were obtained from 488 patients (men: 148, women: 340) visiting the Department of Oral and Maxillofacial Implantology, Tokyo Dental College Chiba Hospital between May 2005 and April 2008. Urinary deoxypyrinoline (DPD), urinary type I collagen N-telopeptide (NTx), bone specific alkaline phosphatase (BAP), osteocalcin (OC), parathyroid hormone (PTH), serum calcium (Ca) and inorganic phosphorus (P) were selected as biochemical markers of bone metabolism.
Results: Forty-seven percent showed abnormal values for the metabolic markers selected. Regarding parameters related to the pathogenesis of osteoporosis, low values for OC and BAP as osteogenesis markers and high values for NTx and DPD as bone resorption markers were recognized in 13.8%. The ratio of men with low osteogenesis markers was higher than that of women. On the other hand, the ratio of women with low bone resorption markers was higher.
Conclusion: Some implant patients have anomalous metabolic values, suggesting a risk of developing osteoporosis in the future. Based on these results, investigating the relationship between chronological changes in these parameters and the survival rate of implants would clarify the suitability of bone metabolic markers as indicators of the risk of implant failure.
Objective:This study investigated the morphological variance in the mandibular molar region using reconstructed helical computed tomographic (CT) images. In addition, we discuss the necessity of CT scanning as part of the preoperative assessment process for dental implantation, by comparing the results with the findings of panoramic radiography.
Materials and Methods:Sixty patients examined using CT as part of the preoperative assessment for dental implantation were analyzed. Reconstructed CT images were used to evaluate the bone quality and cross-sectional bone morphology of the mandibular molar region. The mandibular cortical index (MCI) and X-ray density ratio of this region were assessed using panoramic radiography in order to analyze the correlation between the findings of the CT images and panoramic radiography.
Results:CT images showed that there was a decrease in bone quality in cases with high MCI. Crosssectional CT images revealed that the undercuts on the lingual side in the highly radiolucent areas in the basal portion were more frequent than those in the alveolar portion.
Conclusion:This study showed that three-dimensional reconstructed CT images can help to detect variances in mandibular morphology that might be missed by panoramic radiography. In conclusion, it is suggested that CT should be included as an important examination tool before dental implantation.
We report a case of frequent premature ventricular contractions (PVC) occurring during intravenous sedation for dental implant surgery in an aged dental patient. The patient was a 75-year-old male whose properative electrocardiogram was normal. A dental anesthesiologist administered intravenous sedation with midazolam during surgery under vital sign monitoring. At 90 minutes after the start of surgery, however, PVC at a rate of 5 times a minute was noted. The operation was interrupted to investigate the cause of the PVC. The possibility that the frequent PVC was caused by adrenaline contained in the local analgesic could not be ruled out. This case suggests that intraoperative monitoring by a dental anesthesiologist is essential for reducing systemic complications in dental implant surgery. Further, we suggest the possibility that intraoperative complications which were not noted preoperatively may happen in aged patients.