This article reviews epidemiologic studies and basic researches concerning the mechanical risk factors that cause overload in implant occlusion.
When natural teeth are adjacent to an implant, occlusal contact on the implant prosthesis requires a reduced initial mechanical load on the implant. This is called the implant-protected occlusion concept. However, few studies support this concept, and several researchers are concerned about the influence on the temporomandibular joint and the adjacent teeth when using this occlusal concept. It is thought that the same initial mechanical load on the implant and adjacent teeth does not result in an overload on the implant itself.
The influence of a non-axial load, large cantilevers, and offset loading with a large occlusal table is greater than that of the axial load because of the bending moment. However, no epidemiologic study supports the biological influences of overloading. Meta-analysis of the connection of natural teeth and implants shows the biological and prosthetical risks.

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On prosthodontic treatment with dental implants, we have refered to crown restorations similar to natural teeth and recostructed so far. Therefore differences between implants and teeth have happened many problems. Especially, for we harmonize occlusion for implant restoration with supporting tissue, superstructure of implant prosthesis, muscles surrounding the jaw and temporomandibular joint, how should we compensate for differences between implants and teeth, and observe occlusal shift and symptom in postoperative progress? It seems that there is little evidence on the relation between implant and occulusion.
While, it is necessary for examination of the problem on occlusion for implant restoration to consider mechanically risk and character of dentition. It is essential to reveal that the cause of happened problems is whether trouble of implant or risk of dentition. There has not been the consensus between parafunction and practice in prothodontics in natural dentition yet. How do implants harmonize with nonfunctional and nonphysiological force? We cannot overlook problems that the factor of surplus force affects implant restorations.
In the symposium, I propounded some problems through clinical cases.

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A firmly established theory on occlusion, even with natural teeth, has been all but absent throughout history. It is even more difficult to find an evidence-based concept of occlusion for the relatively new field of implantology.
Since I harbored doubts on initial gnathological theories of occlusion four decades ago, my work in treating occlusion in patients with temporomandibular arthrosis has brought me to the realization that the diagnosis and adjustment of the alignment or misalignment of the light guide tapping position (LGTP) and clenching position (CLP) in the stable condylar position are important focal points for clinical occlusion. I have therefore striven for the seamless incorporation of the prosthodontic techniques of maintaining, correcting, and restoring occlusion into my day to day clinical practice, which includes periodontal treatment and orthodontics. Implantology has now been added to this context, and I feel there is no need to take a drastically different approach to implant occlusion versus occlusion with natural teeth in considering the stability of implants, which includes the stability of natural teeth.
In this paper, I wish to discuss my approach to creating and adjusting implant occlusion. I will present actual case reports and postoperative observations of patients who received implant therapy in our clinic.

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It is believed that one of the potential risk factors for peri-implant bone loss and failure of the implant/implant prosthesis may be occlusal overloading. Overloading factors, e.g. parafunctions, may negatively influence on implant longevity, however, It must be emphasized that currently there is little evidence regarding implant failure caused by overloading. The purposes of this paper are to discuss the importance of implant occlusion for implant longevity and to provide possible solutions managing complications related to parafunctions. This paper summarizes the lecture presented at the International Congress of Prosthodontics 2007 in Kobe.

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Clinical practice guidelines are the supporting tool for decision-making in medical and dental practice. It is a duty of the academic societies of medicine and dentistry, including Japan Prosthodontic Society, to establish and publish the evidenced-based clinical practice guidelines.. This article deals with the essential knowledge of the clinical practices guideline and the desirable methods of making the guideline for preparing the high- quality clinical practice guideline for prosthodontics.

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In recent years “practice guidelines” based on EBM techniques have even been attracting attention at a societal level, and guidelines modeled after the procedure for preparing practice guideline (described at http://www.niph.go.jp/glgl-4.3rev.htm) have begun to be drafted and made public.
With the aim of ensuring the quality and presenting the basic concepts of prosthodontic therapy, the Japan Prosthodontic Society, which bears a great obligation and responsibility toward society and the Japanese public, has decided to undertake the formulation of guidelines related to prosthodontic therapy, and decided to first undertake the formulation of “Practice guideline for denture relining and rebasing”, and to prepare a guideline model.
We tried to prepare the guidelines according to the “Procedure for preparing practice guidelines”, but because of the scientific uniqueness of prosthodontic treatment and dentistry, research to elucidate the basis of treatment has been insufficient, and we ultimately reconfirmed the current state of affairs in which it is difficult to perform. We therefore prepared the guidelines based on the limited evidence obtained in a search of the scientific literature and on the consensus of experts.
The Japan Prosthodontic Society has investigated and prepared a Society guideline “model” to the extent possible at the present time, and it has prepared “Guidelines for adhesion bridge” and “Practice guidelines for denture prosthodontics” based on it. Nevertheless, the fact of the matter is that we are faced with numerous problems, and we think that in the future new bases and clinical knowledge will be accumulated by promoting scientific clinical research, and that the guidelines should be revised regularly based on them.

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Purpose : The aim of this study was to determine the adaptability of fracture toughness evaluation and the relationship between three testing methods: single-edge notched beam fracture toughness test (SENB), indentation fracture toughness test (IF), and notchless triangular prism fracture toughness test (NTP).
Methods : Two types of indirect composite, Ceramage and Estenia C&B, were used. Four types of experimental specimens were prepared under two curing conditions for each composite resin. One curing condition was only light curing and the other was heat curing after light curing. The fracture toughness value (K_Ic) of the experimental specimens was measured by each of the three fracture toughness tests. K_Ic of each test was compared by ANOVA and Tukey's multiple comparison test for the adaptability of fracture toughness evaluation. Then the correlation of two tests was evaluated by a simple linear regression analysis.
Results : Evaluation of the load-strain curve (or load-deflection curve) and fracture surface observation of SEM suggested the plane strain fracture phenomenon. K_Ic values obtained by the three testing methods were significantly different (p<0.01). SENB could separate significantly these experimental specimens into four groups. IF could separate them into two groups. NTP could separate them into three groups. The fracture toughness evaluation of NTP was almost the same as that of SENB. The relationship between SENB and NTP showed a significant correlation (R²=99.7%) and its equation was NTP (K_Ic)=0.82 SENB(K_Ic)+1.05. IF did not show a significant correlation.
Conclusion : These indirect composites tested exhibited different fracture toughnesses. This difference occurred due to the contents and curing conditions. The adaptability of fracture toughness evaluation showed different values depending on the testing method. The relationship of SENB and NTP showed a significant correlation.

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Purpose : Little information is available on the mandibular protrusion with oral appliances (OA) for the treatment of obstructive sleep apnea syndrome (OSAS) to have no negative effect on the stomatognathic system. The purpose of the current study was to assess the influence of mandibular protrusion on occlusion to fabricate the appropriate OA.
Methods : Twelve healthy adults were selected. With the OA in position, the mandible was advanced 0, 45, 60, 75% of maximum protrusion capacity ; bite raising distance between the first molars was 5mm (OA5-0, 45, 60 and 75). The occlusal force, occlusal contact area and occlusal load center following maximum voluntary clenching for 5 seconds were investigated as follows : after wearing the OA for 1, 3 and 6 hours (Stage A1, A3 and A6) and 1 hour after removal (Stage R1). These data were compared with before wearing (Stage B).
Results : Occlusal force has significant decrement at Stages A1, A3 and A6 after wearing OA5-75, at Stages A3 and A6 after wearing OA5-60, and at Stage A6 after wearing OA5-0. Occlusal contact area has significant decrement at Stages A1, A3 and A6 after wearing OA5-75, and at Stage A6 after wearing OA5-60. Occlusal load center has significant forward displacement at Stages A3 and A6 after wearing OA5-75, and at Stage A6 after wearing OA5-60.
Conclusion : To fabricate the appropriate OA in occlusal perspective, it is preferable to set the mandibular position at 45% advancement of maximum protrusion capacity of condyle head in terms of the mandibular positions used in this study.

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Purpose : The aim of this study was to evaluate the variation of thickness discrimination by wearing an upper removable partial denture. We investigated the thickness discrimination by changing the covered area and the food-recognizing area of the palate. We also evaluated the variation of thickness discrimination after two weeks of wearing the plate which covered the anterior area of the palate.
Methods : Four kinds of experimental palatal plate, which covered the anterior, middle, posterior and whole area of the palate, were used. Five kinds of test pieces were used for the thickness discrimination test. The same test pieces coated with a fit checking material for removable dentures were used to detect the food-recognizing area. The thickness discrimination test was done after two weeks by the same method mentioned above.
Results : The food-recognizing area was the anterior part of the plate regardless of with or without the experimental palatal plate. Although the thickness discriminative ability was the worst when wearing the plate that covered the anterior part of the palate, the ability improved by wearing the plate for two weeks.
Conclusion : These results suggest that the removable partial denture covering the anterior part of the palate decreased the food discrimination, but it improved by wearing for two weeks.

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Purpose : The Preparation of rest seat and guiding plane is an essential part of the prosthetic restoration for partial denture treatments. Although these preparations are confined within the outer enamel surface, cut surfaces are left exposed after completion, which involve potential risks of caries. This study observed the morphological change of the cut surface of the enamel in vivo.
Methods : The prominent areas of bucco-lingual surfaces of the volunteers' third molars to be extracted, were cut with a dental turbin. The prepared tooth was then left for while (3, 6 months) in the oral cavity, and subsequently extracted. Either cut and non-cut surface were observed by SEM, TEM, HRTEM. In addition, salivary buffer test and cariostat test were introduced.
Results : In most subjects, salivary buffer test showed “middlespillage” with “high buffer”, and cariostat test showed “attention area”. The observation of SEM showed that the enamel prism was not broken although cut and non-cut surface of the enamel were covered with bacterial flora. The observation of TEM and HRTEM revealed that the apatite crystal had dissolution and broken in both cut and non-cut area.
Conclusion : Comparative study of cut and non-cut surface of the enamel showed that the apatite crystal had dissolution and broken in two stages.

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Patient : The patient presented with skeletal class III malocclusion and posterior edentulism. The patient had difficulty in chewing and wanted to improve his chewing ability.
Discussion : Implant-supported prostheses lack periodontal mechanoreceptors and therefore tend to be subjected to excess lateral force, which may cause clinical complications. To minimize heavy lateral force the implants were placed so that they could be vertically loaded. To achieve this, a cross-bite was established in the posterior. Occlusal adjustment was performed carefully to guide the chewing force to the axis of the prosthesis.
Conclusion : In a case of skeletal class III malocclusion, the establishment of a cross-bite using implants is biomechanically rational and therefore produces a predictable outcome.

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Patient : A 36-year-old male is reported. He visited the clinic complaining of discomfort of the tongue due to an attached prosthesis and dysmasesis by mandibular deviation. The occlusion was reconstructed for the original mandibular position to improve the oral environment.
Discussion : Muscle tone was relieved, and the mandible was guided below. As a result, an adequate occlusal relationship could be established in the original mandibular position. Tongue habits were eliminated, and the patient was satisfied both functionally and aesthetically, suggesting that a stable condition had been maintained for a long period.
Conclusion : In this case, the long-term follow-up through reversible treatment with a splint corrected the mandibular position and improved the tongue habit, resulting in reconfiguration of occlusion in the whole jaw. No significant problem has occurred for three years after the treatment.

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