The International Journal of Prosthodontics, 04/1998

Purpose: A more precise and up-to-date definition of prosthetic dentistry is warranted. The aim of the present review is to present a new core definition of the discipline on the basis of a discussion of existing definitions. Materials and Methods: Clinical textbooks in prosthetic dentistry and dental implantology, as well as medical and dental glossaries were reviewed. Results: Two main categories of definitions of prosthetic dentistry were identified: first, definitions that emphasized the technologic aspects of the discipline, ie, the fabrication of prostheses; and second, definitions that incorporated some reference to the objectives or aims of prosthetic treatment, ie, the restoration of one or more apsects of oral function. Slightly more than half of the citations contained such aim-related references, and this aspect tended to be most pronounced in recent publications. Conclusion: The following definition is ventured: prosthodontics is the discipline of dentistry concerned with the consequences of congenital absence or acquried loss of oral tissues and with the methods for and assessment whether more good than harm is done by inserting artificial devices made from alloplastic materials

Purpose: The purpose of this study was to investigate the distribution of shades selected for metal ceramic crowns provided at a dental teaching hospital. Materials and Methods: Data on the selection of shade for 2,500 metal ceramic crown units, placed over a 5-year period at the University Dental Hospital of Manchester, were collected and analyzed. Only those crowns placed adjacent to minimally restored vital teeth were included in the study. Results: The results indicate that the most frequently chosen shades were in the mid-range of reddish-brown hue. Furthermore, shades in the reddish-grey range of hue were rarely chosen. The selection of more than one shade for a crown ( mixed shades ) was generally restricted to the maxillary anterior teeth. Conclusion: Knowledge of the distribution of shades selected for permanently luted metal ceramic crowns may be a useful adjunct in shade selection, particularly for the inexperienced operator.

Purpose: The aims of the study were to evaluate the postinsertion care needed by patients treated with four implants to retain mandibular overdentures and to compare two types of superstructures. Materials and Methods: The study consisted of 54 patients who had been treated with conventional maxillary dentures and mandibular overdentures retained by four implants and a triple-bar superstructure with cantilever extensions (28 patients) or without cantilever extensions (26 patients). Differences between both groups with regard to age, gender, length, and diameter of the implants and preoperative mandibular bone height were tested by means of Student's t and chi-square tests with a probability level of 0.05. No significant differences were found. Both groups were retrospectively compared on adjustments and complications. The follow-up period after insertion of the dentures was 2 years. Results: During the 2-year follow-up, 17 patients of the cantilever-extension group and 20 patients of the group without cantilever extensions needed adjustments, and 17 patients of the cantilever group and 12 patients of the group without cantilever extensions had to be treated because of complications. Significantly more (P 0.05, chi-square test) superstructure fractures were present in the cantilever group (14 occasions in 7 patients) than in the group without cantilever extensions (1 occasion). All superstructure fractures in the cantilever group involved the cantilever extensions. Conclusion: This study demonstrated a considerable need for postinsertion care, confirming the necessity of routine follow-up services for patients restored with implant-retained overdentures. Furthermore, the results of this study suggest restriction of the use of cantilever extensions.

Purpose: The aim of this study was to describe an alternative technique to fabricate single-implant restorations by using adjustable titanium abutments with porcelain applied directly to the abutment, and to follow an early group of patients treated with these crowns. Materials and Methods: Seventeen randomly selected single crowns were consecutively placed in 14 patients and then followed for 2 years. A protocol of using healing abutments, implant impressions, and adjustement of the final abutment in the laboratory was used to fabricate the crowns. Results: The clinical result revealed few clinical problems, and the mean marginal bone loss was 0.4 mm (standard deviation ± 0.57 mm) after 1 year in function. Conclusion: The conclusion drawn, based im part on published literature, was that occurrence of mucosal inflammation and marginal bone loss was not related to the use of the present protocol.

Purpose: Recent research revealed that races of single posterior reference points can depend on the location of the monitored point. The aim of this study was to quantify this dependence and to point our its consequences for clinical application of condylar path registrations. Materials and Methods: In 60 asymptomatic volunteers, mandibular motion was recorded during protrusion, lateral excursion, and opening-closing of the jaw. Simultaneous trace-patterns of 10 condylar points including the hinge-axis point and the kinematic-axis point were compared with respect to length, inclination angles, coordination, and shape. Results: In protrusion, traces of the difference condylar points were equal and independent of the location of the monitored point. Bennett angles depended on the sagittal position of the reference point and varied by 0.8 degrees per 1 mm change of location. Opening-closing traces differed considerably. Their lengths varied by up to 9 mm and inclination angles varied by 40 degrees. Opening-closing patterns also shoed irregularities like those observed in temporomandibular disorders. Irregularities were minor for the hinge-axis point and least for the kinematic-axis point. Conclusion: In tooth-guided movements condyle motion is repr esented by the traces of any point near the condyle. In opening-closing, however, the trajectory of a single condylar point will not reliably represent condylar motion. For articulator adjustment, condylar angles must not be taken from opening-closing, but only from protrusion. In diagnostic applications, one has to be aware that irregular traces may not only result from dysfunction, but may as well be a result of the choice of reference point.

Purpose: The present study tested the hypothesis that metal ceramic crowns with a varying axial height are moer susceptible to marginal distortion during mechanical and thermal processing treatments than crowns with a uniform axial height. Materials and Methods: Copings of Pd-Cu-Ga alloy with buccal margin extensions of 0, 1.5, and 3.0 mm were prepared. Oxidized copings were veneered with experimental opaque porcelain with a mean thermal contraction coefficient (25 degrees C to 500 degrees C) that was either 2.1 ppm/degrees C below (a = + 2.1 ppm/degrees C) or 0. 1 ppm/degrees C above (a = - 0.1 ppm/degrees C) that of the alloy. Nine groups of six specimens each were prepared for analysis. Eighteen copings from these 54 specimens were used as porcelain-free controls. All specimens were subjected to a 10-step procedure including grinding, oxidation, firing of four opaque porcelain layers (O1: 0.15 mm; O2: 0.15 mm; O3: 0.5 mm; O4: 0.5 mm), glazing, abrasive blasting for 15 seconds, removal of ceramic by dissolution in hydrogen fluoride, and a postannealing treatment. The control specimens were also subjected to this procedure with the exception of the firing of four layers of porcelain, which were not applied. Marginal gap width was determined using a measuring microscope at a magnification of 30X. Results: Analysis of variance revealed a significant difference in mean gap width as a function of axial length. Th e largest gap change was associated with a 3.0-mm buccal extension and the negative mismatch condition (a 0). Conclusion: Marginal distortion of crowns decreases as the axial length becomes more uniform. Analysis of crown distortion based on differences in the mean contraction coefficients of metal and porcelain alone is not recommended because it ignores the effects of metal grinding, metal sandblasting, and transient stress.

Purpose: Computer-aided design/computer-integrated machining (CAD/CAM) allows defect-oriented custom-shaping of the inside surfaces of all-ceramic crowns. The urpose of this study was to examine the effect of inside crown form on fracture strength of cemented and bonded crowns. Materials and Methods: Four preparation types were used: (1) classic with a butt should of 1.2 mm, abutment height of 4 mm, and 6-degree convergence, (2) like type 1 with mesio-occlusodistal cavity, (3) like type 1 with height reduced by 50%, and (4) like type 1 with abutment reduced by 100% plus a pulp chamber cavity. Crowns were CAD desgined on preparations 1 to 4 using identical outside morphology. Machined crowns were placed on abutments (a) without any media as controls (n = 15), (b) ceme nted (n = 15), and (c) bonded (n = 15), and wre loaded until fracture. Results: Zinc phosphate-cemented crowns (1b, 2b, 3b, and 4b) showed significant (P 0.001) increase of fracture load values compared to uncemented control crowns (1a, 2a, 3a, 4a). Fracture load values of bonded crowns (1c, 2c, 3c) were significantly (P 0.001) higher than those for cemented crowns. Bonded crowns with thick occlusal dimensions (3c and 4c) showed the highest fracture load values. Conclusion: Bonded all-ceramic CAD/CIM crowns with defect-oriented inside morphology and increased occlusal dimensions showed high fracture load values.

Purpose: The aim of this study was to determine the effect of water on the flexural properties of fiber-reinforced denture base polymers. Materials and Methods: Continuos woven silanized electrical glass, or E-glass, fibers and woven silica fibers were used to reinforce heat-cured and autopolymerized denture base polymers. Fibers were oriented at a 45-degree angle to the long axis of the test specimens. Control specimens were unreinforced. Dry test specimens and those stored in water for up to 48 weeks were tested with a three-point loading apparatus. The surface of the fibers of the test specimens stored dry or 48 weeks in water were analyzed with a scanning electron microscope to evaluate the degree of adhesion between fibers and polymer matrix. Results: The ultimate transverse strength of unreinforced and reinforced denture base polymers decreased during 48 weeks' storage in water (P 0.05, one-way analysis of variance, n = 5), and most of this reduction occurred during the first 4 weeks of storage in water. The flexural modulus of the unreinforced test specimens decreased significantly (P 0.001), whereas there was less, if any, change in the flexural modulus of the fiber-reinforced test specimens. Scanning electron microscopic examination revealed no differences in adhesion of E-glass fibers to the polymer matrix when the specimens stored in water wre compared with those stored dry. Reduced adhesion between the silica fibers and matrix was observed after 48 weeks' storage in water. Conclusion: The results of this study suggest that the ultimate transverse strength of the E-glass fiber-reinforced test specimens decreased 14% and that of the silica fiber-reinforced test speicmens decreased 36% after 48 weeks of storage in water.

Purpose: The aim of this 5-year prospective study was to compare the results of single-tooth implant treatments planned and performed at four general practitioners' offices with the results from a specialist clinic. Materials and Methods: The group comprised 38 patients. Nineteen patients, with 19 implants/crowns, were planned and treated by four general practitioners, and the outcome was compared to a matched group of patients from a specialist clinic. Results: Three patients did not complete the study. None of th e implants failed; one crown failed. This was a very positive result, as the single failure, a crown at the specialist clinic, was caused by an extraordinary trauma and was not related to a common cause such as bite forces or fatigue. No significant differences were observed between the groups when the radiographic findings were compared. Some minor differences, for bleeding and the position of the mucosal level around implants and adjacent teeth, were observed between the two groups. Conclusion: The small discrepancies that were observed between treatment performed by the four general practitioners at their own offices and treatment performed at the specialist clinic were not regarded to be of any clinical importance. This indicates that complete single-tooth implant treatment may be performed for many patients by general practitioners who have received adequate training, allowing the possibility of referring complicated treatments to specialists and other treatments to general practitioners.

Purpose: The ultimate goal in modern esthetic dentistry is the restoration of lost hard and soft tissues by imitating nature as closely as possible. With the increasing esthetic awareness of patients, surgical and technical develop ments, and dentists' enhanced skills and knowledge, op timal function and esthetics are achievable even with implant-supported restorations in molar regins. Anatomic and morphologic factors and poor bone quantity and quality might reduce success rates of dental implants in the posterior jaw. Today, there are two options to replace a single missing molar by an implant-supported crown: the single wide-diameter implant or two standard-diameter implants. These two approaches are described and their advantages and disadvantages discussed in two exemplary clinical cases. Materials and Methods: In one case, the edentulous ridge in the area of the mandibular right first molar (FDI tooth 46) provided sufficient mesiodistal space to restore tooth 46 with a porcelain-fused-to-metal crowns on wide-diameter implants. Results: It can be concluded that both options to replace a single molar provide more surface area and better biomechanical properties than one standard implant. Conclusion: Long-term data are needed before these treatment modalities can be recommended for the private practitioner.