The diagnosis of dental arch defect has conventionally tended to be performed in order to serve as an index for prosthetic treatment rather than to grasp the affected state. Nevertheless, such a diagnosis has often failed to establish a distinct therapeutic strategy and thus seemed to have been so far used as a scale for determining the severity of disorder called “defect” and/or the degree of stability. In other word, this implies that the dental prosthesis per se plays a significant role in the rehabilitation for disorder called “defect”. On the other hand, it is hardly denied that the diagnosis of diseases which may result in a dental defect has been replaced by the diagnosis of caries or periodontal disease. In recent years, however, some clinicians began to have a common recognition on a case which is hardly explained by caries and/or periodontal disease alone, and a term of “occlusal force” or “force” is now widely added to the concept of its pathogenesis. Although no established consensus is not yet available in the definition of these terms, this third “force” gives an opportunity for re-examining the pathogenesis. When the pathogenesis is considered in relation to the time elapsed, caries and periodontal disease have been weighed on the so-called vector of the affected state including a general tendency produced by the progress or the patient's age at the time examined.
In the affected state due to occlusal habits or force for example, however, the total dose accumulated during the past years or even an organic defect may be required to consider depending on the case involved. In addition, a risk management for caries and periodontal disease by preventing exogenous bacterial infection is quite different from that for individual intrinsic neuromuscular system. A possible involvement of advanced age and/or general condition is naturally different and the accumulated period of disharmony may influence the speed of decay in some cases. In so-called intractable cases, a more deepened understanding seems to become frequently possible through the examination of self-uncontrollable excessive occlusal force or satisfaction but not through the diagnosis of static defect morphology.
We thus emphasize the necessity of diagnosing the occlusal force when the prosthetic treatment is started.

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Typical dental diseases are dental caries and periodontal disease. These dental diseases are considered to be the most serious risk factors for the encroachment and collapse of teeth. A matter of course, a missing tooth is deemed as causing a lost tooth. The causes of lost teeth vary with the patient, but it is very important to grasp the past tendency of disease for each patient that is suffering dental caries or periodontal disease in order to estimate recurrence after treatment. Therefore, the most important diagnostic point is to probe the cause of the lost tooth in prosthetics for a missing tooth. However, when we observed many long-term clinical cases, we found that the two dental diseases are not the only cause of lost teeth. On the other hand, the concept of healthy teeth has been believed by both dentists and patients to be that strong chewing power means healthy teeth. However, this concept has been misunderstood to mean that teeth can stand up to excessive occlusal pressure. I have experienced many clinical cases that suggested the existence of a sequential change in oral environment and overloaded occlusion or para-function that is weakened by collapsed prosthetics for missing teeth, increasing overloading of the abutment and the influences of the mechanical factors of the selected prosthetic retainer. These cases suggests that it is necessary to add the traumatic force factors, which means the factors for abutment teeth as causes of occlusal trauma, disharmonized occlusion, abnormal prosthetics pressure, destruction of alveolar bone and consequently, lost teeth. It is strongly considered that these various types of traumatic force factor may become high risk factors. For that reason, we must diagnosis the different pathological findings between clinical symptoms of traumatic force factors that significantly concern the beginning of missing dentition and after the life span of prosthetic appliances for missing teeth and dental caries or periodontal disease that occur due to bacterial infection.

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It is observed in most clinical cases that their condition changes in various ways after treatment even if their alignment of missing teeth or level of occlusive abnormality was similar among each case at the first medical examination. Missing teeth alignment develops into a pathological condition of chronic disease, which makes the factor of “time-line” quite significant. The time-line indicates speed, the change of pathological condition over time.
Patients are faced with various kinds and levels of risks. Furthermore, some risks are easy to control, while others are rather difficult. The level of alignment of missing teeth and causes of failure have been pointed out as typical examples of such risks. Therefore, the level of occlusion support that could not be changed with dentures was improved with implants and was evaluated. As a result, parafunction was regarded as one of the risks that is important in itself as well as difficult to control. Unfortunately, however, there are few strategies for this risk factor which is difficult to control.

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Purpose: The systematic review was conducted to answer the clinical questions as to 1) what are the risk factors for the failures of prostheses, 2) whether the influence of those risk factors on the longevity of prostheses can be compared.
Methods: In order to reveal the survival rates of crowns, fixed partial dentures (FPDs) and removable partial dentures (RPDs), and the risk factors of crown and FPD failures, the systematic review using computer online search was conducted.
Results: The complications rapidly increase 10 years after the crown and FPD placement. One-third and half of crowns and FPDs would lose their function in 15 and 20 years after placement, respectively. The survival rate of RPDs is obviously lower than crowns and FPDs and half of RPDs is replaced with a new one or not worn after 8 to10 years of insertion. Risk factors of crown and FPD failures are divided into four factors, i.e., patient-related, infection-related, load-related, and technique and design-related factors. Each factor is not independent and a combination of risk factors may be most detrimental for the survival of prostheses.
Conclusion: Each risk factors of prostheses failure should be quantitatively evaluated in each patient. The final prostheses should be designed and placed based on the risk evaluation. The consideration can contribute to extend the length of service of prostheses.

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In the impression procedures for removable partial dentures, it is important to consider the difference of properties between the hard and soft tissues. However, it is difficult to record both the anatomic form of the teeth and adjacent structures and, at the same time, the functional form of the edentulous ridge. In other words, the impression technique which is most commonly used requires, as a preliminary step, a difficult and complicated procedure: the border molding with a thermoplastic compound. Therefore, it is thought that this impression procedure should be separated into two stages to make the impression procedure easier and to provide more adequate support of the denture base. The first stage is the anatomic impression. For a successful anatomic impression, the preparation of the oral structures and the fabrication of a custom-made tray play an important role. The following are the main factors that should be noted to produce an accurate master cast: 1. Coexistence of hard and soft tissues ; 2. Sharp angles and corners of teeth; 3. Undercuts ; 4. Tooth mobility ; 5. Risk of impression material detachment from the tray ; 6. Proper intraoral positioning of the tray; and 7. Risk of breaking the master cast teeth during separation from the impression. The second stage is the functional impression. The functional impression procedure for the residual ridge, such as Applegate's “fluid-wax” impression method using Korecta-wax, assures the success of removable partial dentures. This functional impression provides denture stability and a reduction in occlusal load per unit surface area of the residual ridge. In addition, this accurate secondary impression will reduce the number of follow-up adjustments once the partial denture is delivered. This article reports on the Clinical Skill-up Seminar I in the 115th Scientific Meeting of the Japan Prosthodontic Society held in Sapporo in 2006.

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The objective in the treatment of patients with removable partial dentures is to establish good function and harmonious occlusion. Occlusal harmony between a partial denture and the remaining natural teeth is a major factor in preserving the health of their surrounding structures. Because of the wide variety of combinations of missing and remaining teeth, numerous types of prosthodontic service are available.
The establishment of a satisfactory occlusion for the removable partial denture should include the following: an analysis of the existing occlusion ; the correction of existing occlusal disharmony: the recording of centric relation or adjusted centric occlusion and so on. Therefore, the recording of occlusal relationship for the partially edentulous patient is an important clinical procedure for fabricating a removable partial denture.
Maxillomadibular relations can be recorded accurately only by using a stable record base and occlusion rim. It is essential that an accurate base with temporary clasp and rest be used to help support the occlusal relationship.
It is also important, when being obtained by using the recording base, that excessive pressure on the displaceable tissues of the denture-bearing area be avoided, because excessive pressure will depress the record base by displacing the underlying resilient mucosa.
This article deals with clinical methods of taking static jaw records for establishing the occlusion of removable partial dentures, and with the basic principles which underlie these procedures.

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Minimizing denture mobility is the first principle of partial denture design. This article summarizes the considerations necessary when designing distal extension partial dentures from the standpoint of minimum denture movement.
The border molding using an individual tray in impression making and setting mesial rest effectively restrain the displacement of residual mucose membrane that is closely related with denture mobility. An embrasure clasp is better than an Akers clasp or an RPI clasp as a direct retainer, and improvement of bracing by adding a distal guide plate and widening bracing arms is recommended. Displacement of abutment teeth is influenced by the mesiodistal inclination of the residual ridge. Distal movement of an abutment tooth easily occurs when the residual ridge is inclined distally. Covering the retromolar pad by the denture base and consideration of indirect retainers are important to reduce the displacement of abutment teeth.
Rehabilitation of function and its maintenance are needed to satisfy patients with removable partial dentures. Clinical and experimental data need to be accumulated for the development of partial denture design.

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Purpose: Although the paths of jaw movements differ between normal occlusion and malocclusion cases, head movements accompanied with mouth opening and closing movements are observed in persons with normal occlusion and patients with malocclusion. We tried to clarify the role of head movement during food ingestion employing two groups: a mandibular protrusive patient group and a control group.
Methods: The subjects were six patients with skeletal mandibular protrusion without abnormalities in the stomatognathic function, and 10 persons with individual normal occlusion. By using a 6-degrees-offreedom jaw movement tracking system, the distance of mouth opening, the amount of head movement, the amount of condylar movement, and the rotation angle of the mandible during food ingestion were analyzed.
Results: The class III group was classified into the class III A group in which the amount of condylar movements during mouth opening was similar to that in the normal occlusion group, and the class III B group in which the amount was smaller than that in the normal occlusion group. The amount of head movement in the class III A group was similar to that in the normal occlusion group, whereas the amount in the class III B group was larger than that in the normal occlusion group. Furthermore, the mandibular posterior space was larger in the class III B group than in the normal occlusion and class III A group on roentgenographic cephalometric analysis.
Conclusion: It was revealed that in the subjects with smaller amount of condylar movement, large mouth opening was performed using the mandibular posterior space and accompanying large head movement. Therefore, it was suggested that the size of the mandibular posterior space was a determinant of the amount of condylar movement.

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Purpose: With an increase in the aged population in Japan, clinicians are expected to provide high-quality treatment to improve patients' QOL. The purpose of this study was to evaluate the change of outcome before and after insertion of new dentures and clarify the causes.
Methods: Thirty-five patients wearing complete dentures were selected after obtaining informed consent. Chewing function score, satisfaction score and supporting tissue score were used the assessment factors. These were evaluated at three stages in complete denture treatment: before insertion of new dentures (old denture), first visit after insertion of new dentures (1st visit), and one month after insertion (1 month). Changes in scores were analyzed with ANOVA, t-test and correlation coefficient. Factors evaluating chewing function and satisfaction were analyzed in detail.
Results: In chewing function, when the score of “old denture” was high, the score after insertion decreased greatly. Satisfaction increased from old denture to lst visit, and increased further by 1 month. In addition, there were significant relationships between the changes in satisfaction and the satisfaction factor “fit of the maxillary denture” and “comfort of the mandibular denture”. There was also a significant correlation between the changes in chewing function and the changes in satisfaction.
Conclusion: The changes in outcome were evaluated before and after inserting new dentures and the causes were clarified. In case of the good outcome of old denture, the outcome of new denture tended to decrease. The satisfaction factor “fit of the maxillary denture” and “comfort of the mandibular denture”were suggested to be the key factor after insertion of new dentures.

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Purpose: A triangular gap between the keeper and magnetic assembly caused by the inclination might weaken the attractive force of the overdenture. Furthermore, the load supporting ability may be compromised with a change in the position of the fulcrum line when occlusal force is loaded on the outer side of the occlusal surface.
Therefore, in this study, the influence of a triangular gap in the magnetic attachment for implant-retained overdentures on load supporting ability was evaluated by tensile test and 3-D geometric analysis.
Methods: The inclined angle of the gap was set at 0 to 10.0 degrees with aluminum foil to measure the attractive force when triangular gaps existed, and the maximum tensile strength of magnetic attachment was measured. Based on these results, overdentures on four implants placed at bilateral first molar and canine regions on an edentulous model of the upper jaw were simulated, and the load supporting ability of implant-retained overdentures was calculated with 3-D geometric analysis.
Results: The attractive force decreased with an increase in the angle of inclination. The attractive force decreased remarkably from 0 to 1.0 degrees, and it was reduced to half at 2.0 degrees and showed a moderate decrease thereafter.
When there was a gap on the palatal side, the load supporting ability decreased depending on the inclined angle, however when the gap was on the buccal side, it decreased to 1/3 on incisor loading and 1/7 on molar loading compared to that with no gap.
Conclusion: Attractive force decreased significantly when a triangular gap existed in the magnetic attachment, and in particular, it clearly caused a large decrease of load supporting ability when the gap was on the buccal side.

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Purpose: Objective assessment of the hardness of the mucous membrane to assess the biomechanical characteristics of denture supporting tissues by subjective sensation at problem of reproducibility and universality is important in removable denture treatment. The purpose of this study was to establish an objective assessment of mucous membrane, to clarify the influence of the fixation method and contact angle of the tactile sensor probe on the measurement value and to grope for the correction method.
Methods: The elasticity of simulated mucosa made from four different kinds of materials was measured using a tactile sensor. A probe guide was fabricated in order to regulate the contact angle of the tactile sensor and to prevent the tip of the probe from slipping. The effects of the contact angle, fixation method and installation of probe guide were analyzed. In addition, the mucosal elasticity was measured in vivo. Results: The measurement results indicated that when inclined to 30°, the degree of elasticity was greater than that at 0°. The simulated mucosa, the contact angle, and the fixation method were all significant (P<0.01) from three-way ANOVA. The elasticity at different contact angles showed a straight line relationship. It was presumed the degree of elasticity of 0° from the degree of elasticity inclined to 30° because of the error margin within 16% by the regression analysis.
Conclusion: The influence of contact angle and fixation method of the tactile sensor probe was clarified. As for the correction by regression and calculation of the elasticity, the possibility of objectively appreciating the hardness of the mucous membrane that the denture supporting tissue was suggested.

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Purpose: For an appropriate diagnosis of removable denture patients, it is important to assess the biomechanical characteristics of denture supporting tissue. To establish a comprehensive assessment of biomechanical characteristics, the relationship between the elasticity and thickness of denture supporting tissue was examined.
Methods: Three parts of the hard palate of ten dentate subjects with healthy palatal mucosa were measured: lateral part of first molar, lateral part of palate, and median part of palate. The elasticity was measured with a tactile sensor and thickness with an ultrasonic thickness gage.
Results: Young's modulus was highest at the median part of the palate (2.4±0.8 MPa) and lowest at the lateral part of the palate (1.0±0.5 MPa). The thinnest part was the lateral part of the palate (1.2±0.3 mm) and the thickest part was the median part of the palate (2.8±0.7 mm). Young's modulus and the thickness of mucosa indicated a negative linear relation. However, values of Young's modulus were distributed widely where the mucosa is thin.
Conclusion: Values of Young's modulus were distributed widely where the mucosa is thin. Therefore Young's modulus cannot be estimated from only the thickness. To establish a comprehensive assessment of the biomechanical characteristics of denture supporting tissue, both elasticity and thickness should be evaluated simultaneously.

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Patient: The patient, a 69-year-old female, was missing her upper right and left molar teeth. An implant that had been at the lower right side premolar area was removed because of periimplantitis. Implant-supported fixed prostheses were placed on the upper right side molar and the lower right side molar areas.
Discussion: Implant-supported fixed prosthesis is a treatment option to restore missing teeth. A discussion of connecting implants to natural teeth is presented. In this case, it was necessary to connect implants to natural teeth. A rigid form was used to prevent tooth intrusion.
Conclusion: After 3 years and 11 months, a follow-up examination showed no complications. The patient expressed satisfaction with the fixed partial prostheses.

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Patient: Two females (Case A: 58 years old, Case B: 82 years old) visited us because of pain on the anterior residual ridge. They wore upper complete dentures. Case A had a very hard residual ridge, and Case B had flabby gums. We selected the bite pressure impression method for Case A, and selective pressure impression method for Case B.
Discussion: By selecting the optimal impression method for each case, we could fabricate complete dentures with good long-term prognosis.
Conclusion: It is important to consider each oral situation and select the optimal method for each case.

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Patient: The patient was a 69 year-old male who visited the dental hospital with the chief complaint of fallen facing crown with root fracture of anterior teeth. Full mouth restoration was done to correct the defect of occlusal support with sunk dentures and slight infraocclusion with occlusal wear. During 14 years of follow-up, only one tooth was extracted due to root fracture, thus the prognosis was considered stable.
Discussion: Occlusal reconstruction for decrease of occlusal support with active prosthesis is considered to prevent occlusal collapse in the long term.
Conclusion: Continuous regular follow-up and observation of occlusal condition is important to obtain a good prognosis for defective dentition.

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Patient: A 51-year-old woman visited the Department of Fixed Prosthodontics, Osaka University Dental Hospital with complaints of difficulty during mastication and esthetic dissatisfaction with a removable partial denture. In this case, restoration-driven implant treatment was applied for distal extension missing upper and lower molars.
Discussion: Implant placement surgery was performed at all missing tooth positions. Free gingival graft surgery was performed at the bilateral lower molar regions. Custom-made abutments were connected with all the implants and cement-retained metal-ceramic restorations were placed as the non-splinting implant superstructure. Soft tissue and surrounding bone around implants were stable after treatment.
Conclusion: The patient was followed for 3 years with no complications and she was very satisfied with mastication and esthetics. The implant treatment effectively improved mastication difficulty and esthetic dissatisfaction in free-end partially edentulous maxilla and mandible.

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Patient: The patient was a 76-year-old male with the complaint of temporo-mandibular disorders. He had severe deep bite and attrition of teeth. The diagnosis of the patient was TMD III a. Splint therapy using lower partial dentures was chosen. After the splint therapy, the symptoms of TMD disappeared. Crowns and removable partial dentures were fabricated.
Discussion: There has been no specific trouble on TMD, crowns or denture during 3 years of follow-up.
Conclusion: Splint therapy using lower partial dentures for improvement of vertical dimension was applied to the TMD patient. The patient was satisfied with moderate crowns and dentures.

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Case: Prosthetic treatment was provided for a partially edentulous female patient with cleft of lip, alveolus and plate. The chief complaint of the patient was aesthetic appreciation disorder by being unable to wear an upper partial denture because of its clasp failure. There were two prosthodontic problems in the case. One was the discrepancy in jaw size, and the other was pressure of the upper lip by scar contraction to the denture. For the former problem, edge to edge occlusion and arrangements of reverse articulation were adopted. For the latter point, magnetic attachments were applied to upper anterior tooth roots to act as anchors for the rotation of denture by lip pressure. In both the diagnostic dentures with interim denture and definitive denture, magnetic attachments were used as retainers.
Discussion: Magnetic attachments played an important role for denture retention and stability.
Conclusion: The patient was followed for 3 years with no surgical or prosthetic complications.

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Patient: A 70-year-old edentulous woman attended our hospital, complaining of pain on movement around the left TMJ and disturbance of mouth opening. She was diagnosed with osteoarthrosis of the left TMJ caused by a poor maxillomandibular relationship. After the mandible was repositioned with a treatment denture and manipulation, a new complete denture was fabricated using bladed artifical teeth. Symptoms of TMJ pain and disturbance of mouth opening disappeared as the treatment progressed.
Discussion: TMJ tomography, occlusal contact balance and gothic arch tracing were all improved by reducing the load on the TMJ by using a denture with bladed teeth which repositioned the mandible, and by mobilization of the TMJ by manipulation.
Conclusion: These results suggest that dysfunction of the TMJ caused by osteoarthrosis is improved by establishing an adequate maxillomandibular relationship by manipulation and reduction of the TMJ load by using bladed artifical teeth.

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Patient: A 66-year-old male complained of speech disturbance and dysmasesis. The case was diagnosed as decreasing occlusal vertical dimension and an inappropriate form of the polished denture surface on the palatal side of the upper complete denture. The occlusal vertical dimension was increased in new dentures, and the palatal form was determined using a static palatogram.
Discussion: The border movement of the mandible expanded on gothic arch tracing and the mandible position changed to the postero-inferio position compared with that before treatment as a result of the analysis of lateral cephalograms, due to the increase in occlusal vertical dimension. It was considered that speech disturbance was improved by correcting the palatal form.
Conclusion: In the present clinical case, speech disturbance was improved by changing to an appropriate occlusal vertical dimension and correcting the palatal form. Furthermore, stomatognathic function was examined before and after new denture insertion and objective evaluations were achieved.

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Patient: The pateient was a 17-year-old female adolescent whose chief complaints were deformation of the right side of her face and pain in the right maxilla region. The pathological diagnosis was myxoma. The right side of the maxilla (from the canine to the third molar), part of the top wall of the maxillary sinus, and part of the right nasal cavity were extirpated. Autogenous bone from the ilium was grafted five years after the extirpation. Three implants were inserted, and a four-unit fixed partial denture was set for use in reconstructing the missing part of the maxilla and the missing teeth.
Discussion: A complete bone graft was not done due to the possible recurrence of the myxoma. Although a removable partial denture supported by implants is the standard treatment, a fixed partial denture was used instead at the patient's request, and the right upper molar region was not reconstructed. Bone resorption was observed for two years after the denture was set. Although the resorption has become calm, continuous observation was naturally needed. While the occlusal contact pattern changed during the six months following denture setting, more significant changes were not observed.
Conclusion: Using an autogenous bone graft and dental implants to prosthetically reconstruct the maxillary defect following myxoma extirpation could provide both esthetic and social satisfaction for the patient as well as improve occlusal and masticatory functions.

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Patient: A 68-year-old male complained of masticatory disorders and temporomandibular disorders by edentulous posterior mandible.
The diagnosis was masticatory disorders and temporomandibular disorders of type I due to infraocclusion. I applied treatment denture, and provisional restoration and restored occlusal vertical dimension were performed for masticatory function without appealing for a muscle and temporomandibular joint abnormality.
Discussion: About 10mm bite raising does not produce a problem.
Conclusion: I restored the occlusal support, aesthetics by treatment denture and provisional restoration, and quick correspondence was possible. Masticatory function was restored by changing the vertical dimension.

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Patient: A 50-year-old woman presented with difficulty in chewing. The patient exhibited a “difficulty score for prosthodontic care” of 32, with the oral status of Level IV. Occlusal reconstruction was planned by fixed and removable dentures. The superplastic Ti-6Al-4V alloy for the maxillary framework, and cast commercially-pure titanium for the mandibular framework were used to construct the prostheses.
Discussion: Continued post-insertion observations have been carried out for 13 years. The patient is satisfied with the thin palatal coverage made by the superplastic forming. The occlusal rests and the connectors show acceptable fit to the abutments, enhancing the firm support and stability of the dentures, and thus contributing to the long-term preservation of the function.
Conclusion: The Ti-6Al-4V framework revealed its advantages, while continued maintenance of the periodontal tissues appeared to be essential for preservation of oral function.

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