Few reports describe the functional superiority of full balanced occlusion to that of lingualized occlusion. Recently, a bilateral balanced scheme has been much more generally applied than a unilateral balanced scheme in lingualized occlusion as well as in full balanced occlusion. Occlusal contacts on the non-chewing side occur earlier than on the chewing side; in the order of second molar, first molar, and then premolars. The contact on the balancing side contributes to the prevention of denture dislocation and guidance from eccentric positions to the centric occlusal position during mastication. Therefore, bilateral balanced occlusion was shown to be effective for denture stability during mastication with complete dentures. Today's typical edentulous patients have greater mean age than in the past, and thus are seen with severe alveolar bone resorption, thin mucosa and sometimes abnormalities of the maxillomandibular relation. Their occlusal positions are often unstable and changeable after insertion of complete dentures. Because lingualized occlusion allows for easier accommodation and correction, lingualized occlusion is more suitable for such cases than full balanced occlusion, which requires a strict occlusal relationship. In light of the standard Japanese diet, there is some doubt about why lingualized occlusion might be suitable for Japanese edentulous patients in terms of the sense of mastication. A method of evaluating the sense of mastication needs to be established.

View full abstract

In case of making complete dentures, we have to consider not only denture stability but also the restoration of aesthetics and function such as mastication and speech. However these are contradictory theoretically from the point of view of denture stability, and it is very difficult to satisfy both requirements in the case of a patient who has poor upper and lower alveolar ridges. We investigated the effect of artificial posterior teeth form and occlusal scheme on the distribution of pressure on supporting structures under complete dentures during mastication with upper and lower edentulous simulators. In this report, a guideline for the selection of occlusal scheme for complete dentures, based on our previous investigations, is described. The occlusal scheme remakably affected the distribution of pressure under simulated complete dentures, as shown by comparing the distribution of pressure using two different occlusal schemes: fully balanced occlusion and lingualized occlusion. However other factors such as posterior teeth form and position affect the distribution of pressure as well, and are related to each other. Therefore, not only occlusal scheme but also posterior artificial teeth form has to be considered, and the form of posterior teeth should be carefully and comprehensively decided when making complete dentures.

View full abstract

The characteristics of full balanced occlusion (FBO) and lingualized occlusion (LO), which are occlusions that make up removable dentures, were investigated from the standpoint of masticatory function, and an attempt was made to clarify criteria for selecting and configuring occlusions to suit individual cases. Since there have been few studies that have quantitatively compared FBO and LO from the aspect of masticatory function, we decided to organize and present thecharacteristics of both in this paper based on our findings from studies carried out in our department.We found that LO offered a higher ability of food crushing, showed higher masticatory performance in the case of hard foods, displayed faster as well as smoother masticatory movement, and showed chewing patterns that were closer to the chopper type compared with FBO. Moreover, subjective evaluation by subjects indicated that “it was easier to eat and the food tasted better” with the LO compared with the FBO in the case of general foods. Furthermore, a comparison of anatomical form and bladed form of upper lingual cusps in the case of LO showed no difference between the anatomical form and the bladed form in terms of masticatory performance in the case of any of the test foods, but the bladed form offered a higher ability of food crushing, displayed faster and smoother masticatory movement, and showed chewing patterns that were closer to the chopper type. In addition, subjective evaluation by subjects showed that it was easier for them to eat raw carrots and pickled radish, whichare hard foods generally thought to be difficult to eat with dentures, with the bladed form compared with the anatomical form.

View full abstract

Lingualized occlusion is applied to patients with alveolar ridge resorption, and it is considered that this occlusion is functionally useful and should be applied to cases with alveolar ridge resorption. However, selection criteria supported by evidence for what conditions of the alveolar ridge lingualized occlusion should be selected do not exist. For that reason, we conducted an investigation on choosing lingualized occlusion. As a result, no differences were noted in subjects with a good alveolar ridge condition while a sufficient lingualized occlusion effect was obtained in subjects with a poor alveolar ridge condition, suggesting that efficient mastication could be attained. The following indexes were examined as the criteria for applying lingualized occlusion: The ratio of the residual alveolar ridge should be less than approximately 0.5, in which the distance between the inferior border of the mental foramen and the superior border of the mandibular bone shold be less than half the distance between the inferior border of the mental foramen and the inferior border of the mandibular bone. The supporting area of the denture base should be less than approximately 2, 000 mm². Though the effect can be expected when applying lingualized occlusion under these criteria, they are one standard, and cannot be applied in all cases. In clinical cases, it is important to grasp thelocal and the whole-body conditions of the patient in order to choose denture occlusion.

View full abstract

Purpose: In recent years, aesthetic appearance and function are called for and all-ceramic crowns are spreading. By choosing an all-ceramic crown, the problem of metal ceramics is avoided. There are difficulties of color tone reproducibility of cervical margin, and darkness of gingival margin. We examined IPS Empress also in various all-ceramic crowns. IPS Empress has high permeability, a ceramic ingot of various color tones, and excellent color tone reproducibility of natural teeth. Generally, a layering technique is used for an anterior tooth, and the staining technique is used for a molar. However, the details are unknown. We examined how differences of manufacturing method and cement affect the color tone of all ceramics clinically.
Methods: Two kinds of Empress crown were fabricated for a 27-year-old woman's upper left-side central incisors: the staining technique of IPS Empress, and the layering technique of IPS Empress II. Various try-in pastes (transparent, opaque white, white and yellow) of Variolink II of the IPS Empress System were used for cementing. Color was measured using a spectrophotometer CMS-35 FS. The L^*a^*b^* color system was used for showing a color. The right-side central incisors on the opposite side of the same name teeth were used for comparison.
Results: We analyzed the color difference (ΔE^* ab) with a natural tooth. Consequently, when it had no cement of staining technique and was tranceparent, small values were obtained.
Conclusions: It is considered that the color tone can be adjusted by color cement. It is effective to use the staining technique for an anterior tooth crown depending on the case. The crown manufactured using the layering technique is not easily influenced by cement. The crown manufactured by the staining technique tends to be influenced by cement.

View full abstract

Purpose: The purpose of this study was to determine the frequency of human papillomavirus (HPV) infections in the oral cavity of middle-aged and elderly dental patients with dentures.
Methods: In this study, 47 patients (20 men and 27 women), aged from 50 to 78 years, were randomly selected from the patients in the Department of Prosthodontics, Aichi-Gakuin University Affiliated Dental Hospital. Oral squamous cells were collected from swabs of the buccal mucosa. For this procedure, informed consent was obtained. Extracted DNA was evaluated for HPV infections by PCR methods, using consensus and specific primers, and direct DNA sequencing analysis.
Results: Twenty-four of 47 specimens (51.1%) were positive for HPV DNA. A statistically significant association was not found in the HPV positivity between men and women. The high rate of infection was recognized from 60 or more years old. A statistically significant association wasfound in the HPV positivity between non-denture wearers and denture wearers. Frequent HPV types in the specimens of all were HPV 11, 4 and 16. Frequent HPV types in the specimens of non-denture wearers and denture wearers were HPV 4, 11 and HPV 11, 16 and 4, respectively.
Conclusions: The results of the present investigation indicate that HPV is present in the oral cavity, especially those of denture wearers, of middle-aged and elderly patients. It is suggested, therefore, that the oral cavity of middle-aged and elderly patients with dentures is a reservoir of HPVs where later HPV-associated diseases, such as oral cancer and other oral lesions, may develop.

View full abstract

Purpose: To apply salivary proteins to the diagnosis of periodontal disease in partial denture supporting teeth, total protein concentrations and protein fractions in whole saliva were compared among dentulous subjects, edentulous subjects and periodontitis patients.
Materials and Methods: Eighty-five subjects/patients in total were studied, who consisted of 52 dentulous subjects with diagnosed normal periodontal tissue, 18 edentulous subjects using complete dentures and 15 patients with diagnosed periodontal disease. Total protein concentration in whole saliva was measured using dot blotting-silver staining, and protein fractions were analyzed using cellulose acetate membrane electrophoresis and silver staining. Based on the results obtained and some oral cavity examination items, the correlation between the periodontal pocket depth and the number of residual teeth was studied.
Results: Total protein concentration was highest in the group of periodontal disease patients and significantly different from that in the group of dentulous subjects (p<0.01). The percentage area and concentrations of albumin fraction were largest in periodontal patients, followed by dentulous subjects and edentulous subjects in this order. A significant difference (p<0.01) was observed in albumin concentration between periodontal patients and edentulous or dentulous subjects. Concentrations of immunoglobulin A and γ-globulin were significantly higher in periodontal patients than in dentulous subjects (p<0.01). In addition, among oral cavity examination items, the total periodontal pocket depth, the number of residual teeth and the number of teeth with periodontal pocket depth of over 4mm were significantly correlated with the percentage area of albumin fraction or albumin concentration.
Conclusions: Albumin concentration in whole saliva was suggested to be most effective for diagnosing periodontal disease in supporting teeth.

View full abstract

Purpose: This study investigated the hypothesis of a direct association between the shift of incisal point and the diameter of the oropharynx space, and nocturnal oximetry with and without prosthodontic mandibular advancement (PMA) which is one type of oral appliance used to treat obstructive sleep apnea syndrome (OSAS), and to indicate the effects of PMA.
Methods: A total of 19 patients with OSAS were subjected to finger pulse oximetry recording and lateral cephalometric radiography: with and without PMA. The distance of the oropharynx space (PNS-AS, SPAS, MAS, and IAS) and the shift of incisal point with PMA were measured. The oxygen desaturation index (ODI4%) and the cumulative percentages of time spent at saturations below 90%(CT₉₀) during sleeping were calculated. Spearman's rank correlation test was used to measure the relationship between the increase of the velopharyngeal space and the distance of the mandible. The ODI4%, CT₉₀ and distance of the velopharyngeal space were compared for all subjects with and without PMA by Wilcoxon's linking test.
Results: There was a strong relationship between the increase of the lower part (IAS) and the distance of anterior shift of incisal point (r=0.61, p=0.01). ODI4% and CT90 significantly decreased (p<0.01) and the three liners of the oropharynx (SPAS, MAS, IAS) significantly increased with PMA (p<0.01).
Conclusions: It was shown that prosthodontic mandibular advancement could reduce the ODI4% and CT₉₀ value in patients with OSAS, by enlarging the oropharynx space.

View full abstract

Purpose: Various methods have been used for observation of mandibular movement. However, many methods disturb physiological movement as the subject must wear a sensor. Therefore, to predict mandibular movement from the motion of facial skin, the correlation between the movements of mandibular incisor-tooth point and facial skin markers was evaluated by multiple regression analysis.
Methods: Nine retro-reflective markers were placed on the lower facial skin of 8 dentulous subjects and three markers on the wire frame attached to the mandibular tooth, respectively. Movement of markers was repeatedly recorded by 6 video cameras from centric occlusion to maximal opening position. Data was analyzed and the movements were constructed in 3D. In order to predict movement (opening, vertical, anterior-posterior) at an incisor-tooth point, multiple regression analysis was performed by making the 27 amounts of 3D movements (X, Y, Z components) of nine facial skin markers as explanatory variables. The difference between the actual value and the predicted value by multiple regressions was calculated, and compared in the 5 ranges of analysis (0-5 mm, 0-10 mm, 0-15 mm, 5-10 mm, 10-15 mm).
Results: The movements of mouth opening and vertical direction could be predicted with the accuracy of 0.76 mm (3.7%) and 0.69 mm (4.9%) in the range of 0-15 mm with nine variables, respectively. However, the accuracy of movements in the anterior-posterior direction was 0.40 mm (9.7%) with ten variables. The ratio was larger than these in the movements of mouth opening and vertical direction.
Conclusions: It was suggested that movement of mandibular incisor-tooth point in mouth opening and vertical direction to 15 mm could be predicted from the facial skin markers.

View full abstract

Purpose: The purpose of this experiment was to construct a system of waxing pattern using virtual reality in the odontological field. The success of operation with feedback on the maniphalanx sense of waxing is reported.
Methods: The constructed device was a system based on PHANToM DESKTOP®(SensAble Technologies Inc.). This device includes six-degrees-of-freedom input and reproduction of the sense of touch by anti-power feedback. The software which controls this device enables four operations such as “Cutting down”, “Piling up”, “Melting”, and “Finishing” to be applied to the virtual waxing pattern by virtual reality. Finally, the virtual waxing was examined by applying this system to a virtual abutment tooth.
Results: With six-degrees-of-freedom input and anti-power feedback, a virtual waxing and the designer's highly developed designs were successfully expressed regardless of the virtual space. Conclusions: 1. The virtual waxing up could be done by six-degrees-of-freedom input with the stylus in a virtual space. 2. The time laken for all these numerical values of corresponding rate of volume, occlusal, mesio-distal and bucco-lingual views to reach 100±5% ranged from 50 to 75 minutes, with an average of 63 minutes. 3. The virtual wax improvement showed the tendency to trace the passage of first arranging the volume, and straightening the outlook on the occlusal view at the end. 4. This system, which prorides an interface between man machines, six-degrees-of-freedom input and antipower feedback, has much in common with the existing waxing up and crafting. The demand for special technologies by technical persons and engineers can be kept to a minimum and application of the method can be expanded into education and to objective evaluations.

View full abstract

Purpose: The 4-dimensional human body model that combines reconstructed 3-dimensional image data (CT and MRI) and exercise data of the human body is widely applied in the medical field. We have applied this technique to assess mandibular movement, particularly in dentistry, and developed a 4-dimensional system of analyzing mandibular movement. The aim of this study was to determine the accuracy of this analysis system.
Methods: A dry skull mandible was fixed at several mandibular positions and the skull-mandible relationship was measured at each position by two procedures: CT scanning was performed and a 3-dimensional image was reconstructed from image data that were regarded as true values; then, optical measurement markers attached to the dental arch were measured 3-dimensionally and calculated as positional measurement values. The measurement values were compared with the corresponding true values to identify measurement errors of the analysis system.
Results: The root-mean-square (RMS) errors of the 4-dimensional analysis system of mandibular movement were, on average, 0.41mm and 0.43 degrees.
Conclusions: These findings suggest that our 4-dimensional analysis system has sufficient measurement accuracy for mandibular movements.

View full abstract

Purpose: There are no reports on numerical investigation of suitable shapes of restoration.This study examines the relationship between gingival cone and marginal gingiva in natural dentition, and discusses the standard angles for giving a suitable shape at the gingival cone of restoration.
Methods: Twenty dental casts of healthy subjects with normal dentition were examined. The angles between gingival cone and marginal gingiva (CG angle), and the angles between gingival cone and the long axis of the tooth crown (CA angle) were measured.
Results: The mean CG angles of each site were measured between 96.7 degrees (palatal surface of the upper first molar) and 123.9 degrees (labial surface of the lower central incisor). Within the same kind of teeth, lower significant differences were observed among upper and lower, or buccal and lingual surfaces. The CG angles of anterior teeth were 9.5 to 19.2 degrees larger than those of posterior teeth. The CA angles of anterior teeth were negative, and the apex of gingival cone of anterior teeth was directed toward the incisal edge. Conversely, the CA angles of posterior teeth were positive, and the apex was directed toward the root apex. Significant negative correlation was found between CA angle and CG angle (p<0.001).
Conclusions: These results suggested that the relationship between gingival cone and marginal gingiva is fairly constant throughout their angles, and that the cervical shape could affect the shape of marginal gingiva.

View full abstract

Purpose: This study evaluated the effect of woven glass fiber reinforced composite (FRC) on transverse strength of denture base materials.
Methods: Three denture base resins (heat-activated resin, autopolymerizing resin and microwaveactivated resin) and FRC (Vectris Frame, Ivoclar-Vivadent) were selected for the study. The FRC was light-cured and sandwiched in the middle of denture base resin and then the specimen was polymerized according to manufacturers' instructions in a gypsum mold with a cavity of 65mm×10mm×2.5mm. Each specimen was immersed in 37°C distilled water for 50 hours. The control group was without FRC. Ten specimens were fabricated for each group. The transverse strength test was performed on a universal testing machine at a crosshead speed of 5mm/min.
Results: The transverse strengths of all denture base resins reinforced with FRC were significantly higher than that of denture base resin bulk.
Conclusions: Within the limitation of the current study, the FRC has an effect upon reinforcement of denture base resin.

View full abstract

Purpose: We investigated the durability of the cutting tool (bar) that is used when creating a dental crown by using the CAD/CAM system of a computer-assisted NC machine tool.
Methods: We used the chamfer type as the shape of the dental cervical margin of the support tooth model. We also used a mold model whose shaft surfaces on both sides had an 8-degree taper. We used the CAD/CAM system of DENTAL Cadim (Advance Inc.). First, we manufactured a nonocclusion dental crown of the resin-pattern on top of the support dental model, and measured its 3-dimensional shape. Upon measuring the 3-dimensional shape, we created a pure-titanium block by using cutting bars continuously for rough processing and for finishing processing separately. Upon completion of the pure-titanium block, we measured the time required for each processing and measured the surface roughness after each processing.
Results: The surface roughness Ra of the rough processing became significantly worse after the fifth processing (p<0.01). Rmax became significantly worse after the sixth processing (p<0.05) and after the seventh processing (p<0.01). The surface roughness of both Ra and Rmax of the finishing processing became significantly worse after the fifth processing (p<0.05) and after the seventh processing (p<0.01).
Conclusions: From the viewpoint of quality of the crown's finished surface and compatibility fitness, the number of cuttings, the number of rough processing and the number of finishing processing using the same cutting tool for making a full crown of a molar tooth should be limited to four times.

View full abstract

Purpose: This study investigated the effect of a cavity lining on marginal leakage of a cast restoration.
Methods: MOD cavities were prepared on human extracted upper third molars. Additional hemispherical cavities (1.6mm diameter), simulating deep caries, were prepared on axial walls, and they were restored with lining materials including a glass-ionomer, a resin-modified glass-ionomer, and a low viscosity composite for a lined group. Metal inlays were cast with a 12% Au-Ag-Pd alloy and luted with four luting agents including a zinc phosphate (HZ), a conventional glass ionomer (FI), a resin-modified glass ionomer (VL), and an adhesive resin (SB). The specimens were stored in 37°C distilled water for 24 hours and subjected to 5, 000 thermo-cycles, and then, dye penetration was evaluated after 24 hr immersion in 2% erythrosine solution.Metal disks were luted to dentin disks, which have the same-sized spherical cavities in the central area, with the same luting agents. Shea bond strengths were evaluated for both lined and non-lined specimens after the same storing and thermo-cycle processes.
Results: The inlay specimens luted with SB exhibited no dye penetration, while the specimens luted with HZ presented dye penetration reaching to the pulp chamber. The specimens luted with FI and VL showed moderate dye penetration and the values of dye penetration for the cavity-lined group were significantly less compared to those for the lined group (p<0.05). The shear bond strength of the specimens luted with SB and VL was significantly affected by the lining material. The shear bond strength of the specimens luted with HZ or FI was 0 MPa.
Conclusions: The marginal leakage of a cast restoration is affected by the cavity lining but can be improved by using adhesive resin.

View full abstract

Patient: A 55-year-old patient with left maxillary defect was referred to the clinic in 1987, and an obturator prosthesis was made, but frequent denture base fracture occurred. In 1998, she came to the clinic complaining of unfitted obturator. A metal framework obturator prosthesis was constructed for her maxillofacial rehabilitation. Since delivery of the prosthesis, normal masticatory and speechfunction and appearance were successfully achieved.
Discussion: Oral functions were improved by the obturator prosthesis, but the remaining part of the obturator was broken and caries of the remaining teeth were observed after 3 years. It was considered that frequent recalls were necessary to keep the remaining teeth and obturator prosthesis in good conditions.
Conclusion: This article describes the prosthetic rehabilitation of left maxillary defect. The metal framework obturator improved function and esthetics.

View full abstract

Patients: A man (68 years total edentulous) visited us because of masticatory soreness around the mandible. He also suffered from frequent fracture of the dentures.As the poor fitting and severe absorption of the mandible area was considered to be the main cause of the trouble, soft denture lining materials were used. After trying different types of soft denture liners over the new acrylic base dentures, the dentures were finally relined with fluoroelastomer.
Discussion: The condition was good and the patient was very satisfied with the lined dentures.The soft liner contributed to the improvement of the QOL of the edentulous patient.
Conclusion: The use of soft liner was effective for this difficult edentulous case. This case concerns the guideline for the relining of soft liners.

View full abstract

Patient: This case report describes a treatment method for a 68-year-old female with reciprocal clicking on her left temporomandibular joint. Wearing complete dentures for a long time and her unilateral habitual mastication caused this condition. As a countermeasure, an interocclusal record was taken at a position without clicking and a new complete denture set was fabricated.
Discussion: In such a case, we usually expect to adopt a new jaw position by adjusting the old dentures. If the degree of disc displacement or transformation of the disc is severe, mandibular repositioning may be difficult. Furthermore, many aged patients have limitated ability to adapt to a new mandibular position. In this case, the degree of disc displacement was slight, so the patient could accept a new position.
Conclusion: After wearing the new dentures, her clicking disappeared and MRI showed reduction of the disc. She was able to accept the new position.

View full abstract

Patient: 65 years old, female. Chief complaint: Esthetic problem of upper right incisor because of labial displacement. After initial periodontal therapy, a hawley bite plane was inserted to reposition the mandible and retract the anterior teeth. The anterior teeth were stabilized with pin ledge materials.
Discussion: For a patient with severe chronic periodontitis, it is difficult to decide whether to replace or retain the remaining teeth.The hawley bite plane is effective in these cases in order to control occlusal trauma, to reposition the mandible, and to reduce teeth movements.
Conclusion: It is critical to evaluate the prognosis of each tooth through initial periodontal diagnostics in cases of severe chronic periodontitis. A treatment plan can then be created which will address all known etiologic factors.

View full abstract