Recently, digital technologies have been widely available in dentistry. Especially, CAD/CAM has now become available in the field of dental laboratory technology to fabricate prostheses with glass ceramics and zirconia based fine ceramics. Moreover, the development of oral scanners for digital impression taking has made a series of digital prosthodontics practical, starting as it did from impression taking and moving into model preparation and laboratory work. Digital prosthodontics is expected to attract patients as a result of low intervention, reduction of treating time, improvement of clinical outcome, and reduction also of medical costs.
A lot of all-ceramic restorations are now being used in clinical situations. After the dental CAD/CAM system was introduced, the laboratory procedures for ceramic forming became greatly mechanized. The development of high-strength ceramic materials, including zirconia, also promotes the spread of all-ceramic restorations. In these days, digital technology became popular in the field of dentistry, and a digital impression technique using CCD cameras was introduced as a substitute of a mechanical impression. The purpose of this paper is to explain the basics of all-ceramic restorations by using CAD/CAM and digital technology, and to introduce a digital impression technique using the intra-oral scanner.
Recently, simulation software has been developed to import X-ray CT data for reconstruction into 3-dimensional images. Using these images, we have been able to perform reliable and safe minimally invasive implant treatment, such as inclined or short implant placement and/or flapless surgery. Moreover, the 3-dimensional finite element analysis based on CT data will be useful for preoperative simulations corresponding to individual cases. The purposes of this review are to discuss the importance of 3-D simulation using CT data for implant longevity and to providing possible solutions to manage complications related to parafunctions. This paper summarizes the lecture presented at the JPS 2011 meeting in Hiroshima.
The coexistence of an excellent prognosis and aesthetics in prosthodontic treatment has been easily accomplished by innovations of surgical and prosthodontic techniques. Esthetics should be established after recovery of the continuity of dentition and the approach to the stomatognathic function. It is a well-known fact that surgical techniques and choices and the superiorities of prosthodontic treatment have been improved by remarkable developments of new dental materials. Especially, the applications of esthetic restoration and dental implant prostheses have expanded as a result of CAD/CAM progression. Amid this continuing progress, however, in this article I will consider the possibility that at least one field of such original patient-oriented dental care still remains to be exploited. I will focus on zirconia as the new material and introduce its characteristics of strength, light permeability, and tissue compatibility. Furthermore, I would like to explain techniques to bring out the maximal characteristics of zirconia frameworks, along with the many available clinical applications and the important notices, including dental implant treatments. I find it important to clarify the role allotment of laboratory and clinical work and to cope with the one patient and his model and to maintain the same consciousness for dentists and dental technicians. I wish to show the necessary points to examine, diagnose, and make treatment plans, to recover the aesthetics and function, and to establish the maintainability I mentioned.
Assessments of the partially edentulous arch are conducted the grasp of the overviewof clinical case, the predictions of the effect and risk factors of prosthesis and the prognostic factor on the basis of the examination of the dento-occlusal triangula relationship, Eichner classification, receiving factor and pressure factor. However, there are clinical cases that the above-mentioned assessments are not connected with the treatment plan, even if the partially edentulous arches are the same cases. Thus, the balance of occlusal force as the assessment indicator for the partially edentulous arch is useful in addition to the above-mentioned assessments.
The influence of risk factors during the course of tooth loss widely varies in stages ranging from the initial loss to extensive edentulous dental arch. Therefore it is necessary to consider the weight of risk factors when the design of prostheses is determined. On the occasion to investigate what kind of factors are related to the course of tooth loss when faced with individual cases, a total evaluation involving all risk factors and pliable consideration is required. When the hypotheses are verified, however, it would be appropriate to focus on individual problems. The author has performed analyses of factors for the course of tooth loss and their trends. This paper demonstrates some examples of clinical data analyses of risk profiles on a partially edentulous dental arch.
The developments in regard to dental implants have recently been remarkable, and the survival rate has also become markedly higher. For cases with minor teeth missing, a dental implant is applied instead of the fixed partial denture. But a dental implant can now also be applied even in cases with major teeth missing, fabricated by removal of the partial denture. Therefore any case of missing teeth can be successfully treated by application of the crown and a fixed partial denture. Dental caries and periodontitis are chronic diseases. Generally, the treatment plan and prognosis are intensely affected by individuation of the patient's oral health status. In the same way, it is hard to select a uniform and permanent treatment plan for patients; therefore the removal of a partial denture might be made considering a further image. In other words, the treatment plan might be added in correspondence to the body changing with age. Three cases, whose status in the dento-occlusal triangula relationship is the third area, are shown in this section. I would then like to inspect whether these cases are really difficult, considering individuation of the patients. Also, I would like to investigate the possibility and the limits of the application of the removal partial denture.
Among other objectives, the preservation of remaining teeth and supporting tissues are very important in treating partially edentulous patients. To achieve this goal, we found that several strategic measures should be applied. In the design and fabrication of prostheses, fit, outline, occlusion and rigidity were carefully considered after preprosthetic treatments, including perio-, endo-, ortho- and surgical treatments. Roots were preserved as much as possible by using overdenture abutments and reestablishing occlusal support with implants. Periodic maintenance of periodontal tissues, as well as the fitness of dentures, has been executed every 3 or 6 months by the author after the above-mentioned treatments. To examine the efficacy of these strategies, we analyzed 110 partial edentulous cases (50 males, 60 females, average age 54.9 years) with at least 5 years (maximum 25, average 11.2). During the maintenance period, patients in 53 cases (48%) lost no teeth, 20 (18%) lost 1 tooth each, 18 (17%) lost 2 teeth each, and 19 (17%) lost more than 3 teeth each. The observation revealed that patients who had lost more than 3 teeth were involved either with severe periodontal disease initially, or with sudden major changes in systemic conditions. However, the speed of tooth loss becomes slower as the patient age increases in general. In conclusion, it is possible to preserve the remaining teeth and supporting tissues of partially edentulous patients usually by applying strategic measures and continuing regular maintenance.
Purpose: In recent years, the prosthetic clinical application of the non-clasp denture (NCD) has commonly expanded. However, the mechanical effects of the NCD on the living body during function have been unclear. In this study, we measured the load exerted on the abutment teeth and the residual ridge under the denture base when the NCD was functioning, and we aimed to examine the characteristics of these loads. Methods: The intermediated missing teeth model was developed to assume the mandibular second premolar and the first molar which were missing. The piezo-electric transducers for load measurement were contained in the abutment teeth, the first premolar and the second molar. The tactile sensor sheet was set on the residual ridge area of the model. Four kinds of experimental partial dentures for each were made of polyamide-nylon resin (PA-NCD), polycarbonate resin (PC-NCD), polycarbonate resin with a metal frame (mPC-NCD), and common acrylic resin (PMMA-CD). These were all examined. Static loads that were increased in stages (10, 30, 50, and 100 N) were applied to the artificial teeth area of the experimental dentures. The loads exerted on the abutment teeth and the load exerted on the residual ridge were examined by comparing these loads among the experimental dentures. Results: The axial component of the load exerted on the abutment teeth with PMMA-CD was larger than that with PA-NCD and PC-NCD when the amounts of 50 and 100 N loads were applied. The load exerted on the residual ridge with PA-NCD was larger than that with mPC-NCD and PMMA-CD when the amounts of 50 and 100 N loads were applied. Conclusions: The load exerted on the residual ridge with NCD has been shown to be potentially more excessive than that with the conventional removable partial denture.
Purpose: Nonmetal clasp dentures have been used recently in dental treatment because thermoplastic resins have particular elasticity that allows them to be retained without metal clasps. These nonmetal clasp dentures have often been designed to be especially aesthetic by using only thermoplastic resins without occlusal rests. The purpose of this study was to examine the influence of metal rests in nonmetal clasp dentures on the pressure distribution to the soft tissue. Methods: Three pressure sensors were seated on a model simulating mandibular unilateral bounded saddles. Three types of experimental dentures were fabricated on a simulation model: a nonmetal clasp denture with a metal rest, a nonmetal clasp denture with a thermoplastic resin rest, a nonmetal clasp denture without a rest, and two types of control dentures (acrylic resin denture with a metal rest and metal structural denture with a metal rest). Silicone impression material was injected to simulate soft tissue; the pressure distribution during displacement of the soft tissue by the denture was measured using 49.0 N loading. The data obtained (n = 5) were analyzed by one-way ANOVA and Tukey's multiple comparisonstest (α = 0.01). Results: Statistically significant differences were noted among the five types of dentures. The pressure distribution of the metal structural denture was the lowest, and the pressure distribution of the nonmetal clasp denture with a thermoplastic resin rest was highest. By using a metal rest, we found that pressure was reduced in the nonmetal clasp dentures (p < 0.01). Conclusions: The above findings indicated that a metal rest should be used for nonmetal clasp dentures to increase pressure on the soft tissue.
Purpose: The purpose of this study is to develop a new method for microwave resin polymerization in which the polymerization temperature is controlled by direct and accurate measurement of the temperature and subsequent feedback to the microwave source. Methods: In this newly developed resin polymerization method (feedback polymerization method), the microwave output is controlled by feedback of the measured temperature during polymerization. A fluorescence fiber thermometer is used as the sensor. To evaluate the proposed method, we compared feedback polymerization for 3 min at 500 W with thermal polymerization for 40 min at 60°C and 100°C, and low-temperature long-duration polymerization for 24 h at 70°C. The resulting polymer samples were then evaluated in terms of their conformance and other properties. Results: Accuracy results of the adaptation test, the three-point bending test, and the Vickers hardness test were comparable or better for the feedback polymerization method than for other methods tested. On the other hand, the feedback polymerization method showed the second-inferior results after the low-temperature long-duration polymerization method in both the residual monomer test and the cytotoxicity test. Conclusions: It was clarified that the feedback polymerization method was highly suitable for producing polymers with good adaptation and other mechanical properties, and except for a few results, it was comparable or superior to other polymerization methods.
Patient: A 51-year-old female presented with the chief complaint being discomfort at the marginal gingiva in relation to the left mandibular premolar region and difficulty in mastication resulting from missing teeth in the left mandibular molars. After treating the gingiva around the remaining teeth, we placed a partial denture using the milling technique to restore the occlusion. Discussion: Four years after the partial denture was placed, root fracture of the abutment tooth was observed. The damage may have occurred because of the high functional force exerted on this tooth. However, an objective evaluation indicated positive results with respect to quality of life, and we concluded that the treatment plan had been appropriate for this patient. Conclusion: Because the patient had lost a molar on one side, the milling technique employed to suppress movement of the denture when functioning was effective in restoring masticatory function and improving quality of life.
Patient: A 60-year-old male diabetic patient presented with tooth mobility and masticatory problems caused by chronic periodontitis in the maxillary right lateral incisor region. The tooth was extracted because of its poor prognosis. A resin-bonded fixed partial denture (RB-FPD) was fabricated and placed. Additionally, posterior edentulous space was also recovered for functional disorders. Discussion: Treatment with RB-FPDs required adequate occlusal relationships and adjustments. The design and materials contributed to the retention of the RB-FPDs, which functioned favorably for more than 3 years. The long-term stability of the RB-FPDs may be attributed to the appropriate selection of the adhesive system, a certain procedure, and the choice of a design that allowed for easy cleaning. Conclusion: Treatment with RB-FPDs in a case involving a diabetic patient with chronic periodontitis proved satisfactory. There were long-term functional results with low strain.
Patient: The patient was a 20-year-old female suffering from dental malocclusion in the left lower quadrant. Occlusion could not be achieved on the left side, though orthodontic treatment was conducted twice. The final restoration was performed using resin-bonded porcelain veneer crowns with metal substructure reinforcement to achieve occlusal support on the left side including the missing areas. Discussion:The patient's quality of life with regard to mastication improved because this procedure allowed her to masticate bilaterally. It was also effective in reducing the burden on her right teeth by eliminating the balancing occlusal contact and allowing bilateral mastication, maintaining the symmetry of features by preventing masticatory muscle hypertrophy, and reducing the risk of temporomandibular joint disorder. Conclusion:The masticatory dysfunction of the patient with congenital malocclusion improved using a maxillomandibular fixed prosthesis, and a good outcome was achieved.