[in Japanese]

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Some dogmas that lack support of good evidence still lurk in the clinical procedures of complete dentures. However, such dogmas that waste costs of many kinds are not permitted to exist in our country, which face very high-aged society. The impression technique using custom tray and border molding with impression compounds has been adopted at many universities. However, this technique is difficult to master because extensive training is necessary to accomplish the required skills to effectively use this technique. In current educational environments in which educational time for technological training has been remarkably reduced, it is doubtful whether enough training is now available. Moreover, reports claim that poor correlation results between a dentist's assessment of denture quality and the patient's satisfaction with the treatment. We should elaborately reexamine current production methods and an educational techniques, and then educate by a truly appropriate technique.

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It is well recognized that most diagnostic and treatment procedures daily performed by dentists include a dental occlusion. Therefore it is possible to consider that clinical dental practice cannot be discussed without the concept of occlusion. Although multiple concepts of "ideal occlusion" have been proposed and argued about for more than a century, a clear answer has yet to be found. Furthermore, even though additional topics are now present, such as a relationship between dental occlusion and temporomandibular disorders, the ideal occlusions of dental implants have recently become involved, and heated controversies on this subject continue.
In this situation, the authors had an opportunity to discuss with Dr. Gunnar E. Carlsson, who is the expert of clinical evidence of prosthodontics, to clarify and eliminate dogmas related to dental occlusion at the 120th Memorial Meeting of the Japan Prosthodontic Society. Based on this discussion, we wrote this article to obtain the current consensus on dental occlusion, especially therapeutic occlusion.

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A 2010 statement by the American Association for Dental Research in regard to temporomandibular disorders (TMDs) strongly recommended that the treatment of TMD patients should initially be based on the use of conservative, reversible, and evidence-based therapeutic modalities. However, we often see a full-mouth prosthesis with too much crown height, which will cause the wrong setting of vertical dimension, or too much occlusal equilibration. So we asked why this confusion (dogma) in relation between TMD and occlusion still continues. And the following questions and answers were presented. Question 1: What is your opinion about the problem still believed to remain in the causal relation between TMDs and occlusion? Answer 1: Better information. Question 2: How should we manage TMD patients with an occlusal splint? Answer 2: It is effective, but not always necessary. Question 3: What do you think about prosthodontic intervention after the disappearance of TMD symptoms? Answer 3: It is, of course, OK to improve the occlusion.

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Purpose: The aim of this study is to observe the bonding interface in veneering porcelain bonded to two kinds of zirconia (yttria-stabilized zirconia and ceria-stabilization zirconia/alumina nanocomposite) and to examine its integrated state.
Methods: Two kinds of zirconia plates of this finished size, 20.0 (L) × 4.0 (W) × 0.4 (T) mm, were prepared. Some were pretreated by sandblast, some by heat, and some not at all. Porcelain was fired to zirconia plate with or without opaque porcelain and finished thickness of 1.6 mm. The specimen was tested by 3-point flexural testing. The fractured specimen was observed with an electron microscope to confirm the exfoliation of porcelain from the zirconia. The bonding interfaces were analyzed with an electron probe microanalyzer.
Results: The results of 3-point flexural testing were not significantly different under any condition, but the existence of exfoliation revealed a significant difference between the two kinds of zirconia (P < 0.01). The electron microscope image revealed a minute particulate change near the interface of the ceria-stabilization zirconia/alumina nanocomposite. As for element analysis at the bonding interface, no diffusion of the main ingredient elements was observed, but a diffusion-like change with oxygen was noticed.
Conclusions: As for the zirconia/porcelain composite, no difference of strength was observed under any condition. It was clear, however, that the destruction of yttria-stabilized zirconia was accompanied by exfoliation. An electron microscope image and ultimate analysis suggested the possibility of a chemical bond between porcelain and zirconia.

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Purpose: The effectiveness of a mouthguard used after stomatognathic injury related to sports depends on what the guard is made of and its thickness. The aim of this study was to investigate the thickness of a mouthguard after formation from the mouthguard sheet.
Methods: Three mouthguard sheet materials were compared. They were EVA: the material being ethylene-vinyl acetate copolymer; OL: olefin copolymer; and OS: polyolefin-polystyrene copolymer. Cross-stripes (10 × 10 mm) were printed on mouthguard sheets. The thickness of each cross-stripe area was measured by a measuring device. The working model was trimmed to a height of 20 mm at the incisal edge of the upper central incisor, and to 15 mm at the medial buccal cusp of the upper first molar. The sheets were heated by vacuum former until they sagged 15 mm from the baseline. The differences in the ratio of thickness change of the three mouthguard sheet materials after forming was analyzed by one-way ANOVA and Tukey test.
Results: The thickness of the sheet fitted to the anterior teeth, palate, and posterior teeth of OL sheet was thinnest, and that of OS sheet was thickest.
Conclusions: This study suggests that the thickness of the sheet after vacuum forming was affected by the mouthguard sheet materials, and that the polyolefin-polystyrene copolymer sheet could secure the thickness of the mouthguard.

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Purpose: The prevalence and etiology of bruxism in patients who are unaware of this condition are unclear. Therefore we investigated the relationship between the consciousness of bruxism and temporomandibular disorders (TMDs) in dental students.
Method: A total of 256 students from the Department of Dentistry at Iwate Medical University who had no pre-existing medical conditions or history of TMDs were included in the study. First-grade students were given a questionnaire to complete and underwent clinical examinations of the mandibular function. This was repeated after 2.5 years (fourth-grade students) and again at five years (sixth-grade students).
Results: Of the initial 256 students, 90 were investigated over a 5-year period. During this period, an awareness of bruxism was reported in 32.1% of the sixth graders as teeth being "clenched", in 20.5% of fourth graders, and in 14.2% of first graders. The feguency of this awareness increased as the students grew older. Moreover, the consciousness of "ground teeth" also rose similarly. The sixth-grade students were more aware of a relationship between bruxism and TMDs.
Conclusion: The results of the study suggest that most people are unlikely to be conscious of bruxism, and that only by clinical investigation and use of a questionnaire is bruxism diagnosed. The results are important because bruxism is thought to be a contributing factor to TMDs.

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Purpose: Considerations of healthcare economics make it important to clarify the time required for each type of dental treatment. In this study, we conducted a survey of dentists' estimates of the time that would be required to treat certain patients after reading the clinical information about their particular cases. The purpose of this paper was to elucidate the relationship between the actual chair time and the estimated chair time from the patient's information.
Method: Three patients with edentulous jaws requiring treatment of varying degrees of difficulty were treated by a specialist with 14 years of clinical experience, and the time required to perform each treatment was recorded. The information on the three patients was presented to 20 dentists of our department. We asked them to make estimates of the time each treatment step would take and the frequency of performance of these steps. At a later date, they were again asked to give their estimates of the chair time, after we had shared with them knowledge of survey results prepared by grouping the dentists surveyed by their extent of clinical experience (Delphi technique).
Results: The actual chair time and the estimations made by our department dentists were not different on average. For those treatment steps upon which the skill of the practitioner has a considerable impact, both the actual chair time required for those steps and our dentists' estimations became longer as the degree of difficulty of the treatment steps became greater.
Conclusion: Actual chair time might be estimated only the patient's information. The time study was able to be established without doing actual treatment, by conducting various surveys of dentists' opinions about chair times under varying clinical conditions.

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Patient: A 64-year-old woman visited our hospital with her chief complaint being difficulty in mouth opening and chewing. Physical therapy was initiated to alleviate the temporomandibular dysfunction, and treatment dentures were applied to improve the ridge mucosa and chewing function. The occlusal form of the treatment dentures was switched to the final dentures when the temporomandibular joint symptoms and chewing function were improved. This resulted in improved mouth opening and the introduction of complete dentures with satisfactory chewing function.
Discussion: Appropriate control of the load to the temporomandibular joint is known to be important for treating temporomandibular arthrosis. In the present case, use of the treatment dentures allowed the load to be controlled, and it improved mucosa under the dentures, resulting in satisfactory clinical results.
Conclusion: The use of treatment dentures improved both the temporomandibular and chewing functions.

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Patient: A 54-year-old male patient presented with difficulties in opening his mouth and also with masticatory dysfunction. A splint was prepared to improve his ability to open his mouth and to chew. To ensure that there were no functional problems, we added provisional restoration work that involved elevating the anterior jaw position by approximately 3 mm for final restoration of the crown and a partial denture.
Discussion: The splint is a reversible method of treatment that provides recovery of adequate occlusal vertical dimension. The increase in the occlusal area is very likely to relieve the disorder.
Conclusion: For patients with temporomandibular disorders caused by occlusion, using a splint to reconstruct the maxillomandibular relationship is recommended.

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Patient: The patient, a 68-year-old male, arrived at our clinic with the chief complaint being an esthetic impairment as a result of tooth attrition. To rectify the esthetic impairment and the decreased occlusal diameter that occurred because of extensive defects in tooth quality, which were brought about by significant tooth attrition, we reconstructed the occlusion with prosthetic treatment.
Discussion: We used a provisional splint restoration to set the jaw position and achieved a favorable outcome because the prosthetic device was constructed after a long-term follow-up observation.
Conclusion: In cases of esthetic impairment occurring because of substantial defects in tooth quality, a result of tooth attrition, it is essential to repair tooth crown morphology and occlusal diameter, and also to construct prosthetic devices, after identifying an appropriate occlusal diameter and performing reversible safety checks before starting treatment.

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Patient: A 63-year-old male presented with masticatory dysfunction in his maxillary anterior teeth with malocclusion. He had severe maxillary protrusion and deep overbite. Orthodontic treatment was not advised, and the patient's chief complaint has been improved by prosthetic therapy. After provisional restorations of the maxillary anterior teeth were performed, a fixed partial denture was inserted.
Discussion: It was thought that the main complaint of mandibular position was resolved after the removable occlusal splint and provisional restorations were set.
Conclusion: Prosthetic therapy with setting of the removable occlusal splint and provisional restorations provided a highly satisfactory improvement of maxillary protrusion and deep overbite.

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Patient: A 48-year-old male patient complained of snoring, sleep disorders, and arousal that were characterized by obstructive sleep apnea syndrome (OSAS). Oral appliance (OA) therapy provided an important treatment choice and was also the preferred initial treatment, but two types of OAs made the patient uncomfortable. Therefore treatment was subsituted with an anterior repositioning splint (ARS) for OA. The effect of the ARS was evaluated with polysomnography, and the influence on platelet activation regarding OSAS was investigated by conducting a platelet aggregation test (PAT).
Discussion: The use of an ARS put the patient's jaw in a protrusive mandibular position and secured the airway, resulting in a reduction of the apnea hypopnea index.
Conclusion: The use of an ARS reduced the chief complaint regarding OSAS, and the PAT test produced a negative reaction. Nevertheless, the patient should be reevaluated post-treatment and followed-up closely by a physician on a long-term basis.

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Patient: A 71-year-old female complained of masticatory disturbance resulting from the unconformity of her upper and lower removable partial dentures (RPDs). Non-vertical stop occlusion was observed, and her RPDs were functionally unstable because of the deflected mandibular position including the low occlusal vertical dimension and the inadequate design of the RPDs. The mandibular position was recovered using the treatment RPDs, and de.nitive RPDs were set after reassessment of her oral condition
s. Discussion: The proper mandibular position, the proper distribution of occlusal force on her occlusal arches by the relevant occlusal contacts and the rigid support design as a result of the proper supporting and bracing elements of the RPDs were fundamental for RPD stability in a case of non-vertical stop occlusion.
Conclusion: This case with non-vertical stop occlusion was successfully rehabilitated using the RPDs supplying relevant occlusal force distribution and function stability.

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Patient: A 72-year-old man was referred to our department because of mandibular denture instability. The diagnosis revealed an instability of both the maxillary and mandibular dentures resulting from periodontal disease of the remaining upper teeth and a marked reduction in the residual ridge dimensions. A maxillary overdenture utilizing crown and sleeve-coping retainers and a mandibular complete denture were applied to the patient as .nal prostheses in terms of rehabilitating a stable occlusal relationship.
Discussion: During the observation period, the stability of dentures, the periodontal tissue condition, and an occlusal relationship were maintained. A rehabilitation of the stable occlusal relationship had thus seemed to be accomplished.
Conclusion: For a patient with few remaining teeth affected with periodontal disease, the preservation of these teeth and a rehabilitation of stable occlusal relationship were successfully conducted by the use of an overdenture utilizing crown and sleeve-coping retainers.

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Patient: A 68-year-old female presented with the chief complaints being unstable occlusion and masticatory disturbance induced by an open bite. The occlusion was stabilized using acrylic resin provisional restorations in the maxillary and mandibular molars. Crowns or a fixed partial denture was replaced to the provisional restorations, after restorative treatment, root canal treatment, or extraction. A removable partial denture was also fabricated for mandibular missing teeth.
Discussion: With focus on the horizontal- and vertical-occlusal positions, the use of a provisional restoration to establish occlusal stabilization for a long period after examination is recommended.
Conclusion: This report describes the fabrication of occlusal support by focusing on the vertical dimension of the unstabilized occlusion and masticatory dysfunction. Appropriate occlusal support provided satisfactory function.

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Patient: The patient was a 62-year-old woman with severe periodontitis associated with insufficient occlusal support and temporomandibular disorders (TMD). Following initial treatment with an occlusal sprint, a fixed prosthesis and rigid support removable denture with metal base were fabricated to connect mobile teeth and to recover occlusal support.
Discussion: Besides periodontal treatment, the dental prosthesis improved teeth mobility and provided sound occlusal function. Because the attrition of artificial teeth caused a relapse of TMD problems, maintenance of suffficient occlusal support was indispensable for this patient.
Conclusion: In cases of severe periodontal problems, the maintenance of occlusal functions with dental prosthesis should be considered as an important part of periodontal treatment.

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Patient: The patient was a 57-year-old male with doubts about the treatment plan for attrition at a dental office. Occlusal vertical dimension was increased before placement of prosthesis, and the function and shape of the tooth were restored satisfactorily.
Discussion: As a result of the examination, bruxism was suspected to be a major contributing factor to attrition. Therefore a splint was used to determine the permissible distance of the occlusal vertical dimension. The diagnostic waxing up was then transferred to provisional restorations and observed for four months. Long-term observation seemed useful for successful results.
Conclusion: The bite raising led to improvement of the esthetical and functional problems. Occlusal vertical dimension is retained without severe attrition or temporomandibular arthralgia.

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