The International Journal of Prosthodontics, 06/2000

Purpose: The aim of this study was to propose a new clincial diagnostic rating index for secondary caries lesions at crown margins and to correlate this index with histologic evaluations. Materials and Methods: Based on criteria for the evaluation of root caries, a modification for secondary caries lesions at the crown margin (SC index) was applied; the lesion characteristics were described as SCO to SC4. A total of 16 crowned teeth exhibiting secondary caries were randomly selected. The teeth were rated and grouped according to their clinical SC grades (SC1 to SC4). After embedding in Technovit, the teeth were serially sectioned and histologic caries scores were given for each section. Results: Fifty-two percent of the prepared margins were in cementum/dentin. Crown margins with no caries lesions were mainly found in teeth clinically rated as SC1 and exhibiting localized discolorations, whereas deep lesions were found histologically at teeth rated SC4. The nonparametric test according to Spearman's rank correlation coefficient (rho) confirmed a highly significant correlation between the clinical SC index and the histologic evaluation (rho = 0.87, 95% confidence interval = 0.67 to 0.96, P 0.01). SC1 discolorations overestimate caries lesions, whereas SC2 and SC4 lesions are well correlated to the percentage of histologically evaluated caries extension into all sections of a tooth. Lesions rated SC3 demonstrated a high variability of caries penetration into the dentin. Conclusion: The depth of discolorations and circular lesions is clinically not well predictable. Clinical diagnosis for localized superficial caries and deep caries lesions at the crown margin correlated well with the histologic caries rating.

Purpose: Resin-bonded fixed partial dentures (RBFPD) have been in our profession for over 20 years. The aim of this work was to provide some background about their development and the factors that influence their clinical longevity. Materials and Methods: A recent literature search conducted using MEDLINE along with analysis of bibliographies of published papers revealed a considerable number of publications on RBFPDs since their first introduction in the mid-1970s. Critical analysis of these publications revealed some important and interesting key facts. These were divided into sections about developments in the treatment of the fit surface of the casting, bonding systems, and prosthesis design. A separate section about factors that affect the longevity of RBFPDs is included, along with a detailed description of preparation designs of an anterior and a posterior RBFPD. Results: The typical design of RBFPDs is characterized by a high degree of conservation of tooth structure of abutments compared with designs of conventional fixed prostheses. While the early RBFPDs were associated with a high fequency of premature failure-mostly because of debonding-developments in preparation design and bonding techniques as well as better understanding of the appropriate type of metal alloy to be used and the best preparation method for enhanced bonding have led to significant improvements in their long-term survival. Conclusion: RBFPDs should be considered viable treatment options for those clinical situations that are best suited for their use. Preparation design, cement type, and casting alloy type as well as surface treatment are among the most important factors that influence longevity of RBFPDs.

Purpose: This investigation was designed to determine whether heat pressing and/or simulated heat treatments affect the flexure strength and microstructure of the lithium disilicate glass-ceramic of the IPS Empress 2 system. Materials and Methods: Four groups of the lithium disilicate glass-ceramic were prepared as follows: group 1 = as-received material; group 2 = heat-pressed material; group 3 = heat-pressed and simulated initial heat-treated material; and group 4 = heat-pressed and simulated heat-treated material with full firings for a final restoration. Three-point bending tests and scanning electron microscopy (SEM) analysis were conducted. Results: The flexure strength of group 2 was significantly higher than that of group 1. However, there were no significant differences in strength among groups 2, 3, and 4, or between groups 1 and 4. The SEM micrographs of the lithium disilicate glass-ceramic showed a closely packed, multidirectionally interlocking microstructure of numerous lithium disilicate crystals protruding from the glass matrix. The crystals in the glass matrix of the heat-pressed materials (groups 2, 3, and 4) were a little more homogeneous and about 2 times bigger than those of the asreceived material (group 1). These changes of the microstructure were greatest between groups 1 and 2. However, there were no marked differences among groups 2, 3, and 4. Conclusion: Although there were significant increases in the strength and some changes of the microstructure after the heat-pressing operation, the combination of heat pressing and simulated subsequent heat treatments did not produce an increase of strength of IPS Empress 2 glass-ceramic.

Purpose: Although dental composites are excellent for restoring the appearance of natural tooth tissues, their relatively poor resistance to wear, especially in approximal and occlusal contact areas, is still a major source of concern. The aim of this research was to study a basic wear mechanism, under 2-body wear conditions, that may be integrated into our understanding of the in vitro and in vivo wear behavior of dental composites. Materials and Methods: An in vitro 2-body wear test was conducted on 2 selected ultrafine compact-filled dental composites under different magnitudes of sinusoidal cyclic load. The wear surfaces and cross sections of the wear layers were assessed using scanning electron microscopy (SEM) to explore the nature of the wear pattern of the dental composites under cyclic loading conditions. Results: The wear losses of both composites increased with load. SEM analysis of wear surfaces and subsurface sections indicated that the composites tested displayed different wear mechanisms from low to high loads. An explanation for the wear pattern is proposed based on the observed wear behavior. Conclusion: The in vitro wear pattern of the ultrafine compact-filled dental composites tested is closely related to the applied load. Although the wear loss increased in a roughly linear relationship with applied load, the underlying wear mechanism involved may experience a significant change from low to high load conditions during wear.

Purpose: There has been a general belief that permanent teeth without antagonists overerupt, creating, after some time, considerable clinical problems. However, very few studies in the literature support this statement. The purpose of this investigation was to examine the position of molars that had been unopposed for a long period and to test the hypothesis that overeruption does affect every tooth without an antagonist. Materials and Methods: Fifty-three individuals were examined clinically, and dental casts were taken to evaluate the position of unopposed molars. There were 84 molars (61 in the maxilla and 23 in the mandible) with a documented period of at least 10 years without antagonists. Among these teeth, 25 molars had neither an antagonist nor a mesially adjacent tooth. A qualitative method was used to evaluate the position of the molars in the vertical direction: (1) teeth with no sign of overeruption, (2) teeth with slight overeruption ( 2 mm), and (3) teeth with moderate to severe overeruption (! 2 mm). Results: Of the 84 molars examined, 15 teeth (18%) revealed no signs of overeruption, 49 teeth (58%) displayed overeruption of less than 2 mm, and 20 teeth (24%) showed moderate to severe overeruption. Individuals with molars that had lost their antagonists in adult age had a lower risk for overeruption than the other subjects examined. The existence of adjacent teeth was important for the position of the unopposed molar in a mesiodistal or buccolingual direction. Molar rotation was more frequent in the maxilla, whereas tipping was more common in the mandible. Conclusion: It is concluded that not all molars without antagonists overerupt, not even in a long-term perspective.

Purpose: The aim of this study was to determine the dimensional accuracy and water sorption of a denture base polymer that was reinforced with glass fibers in continuous unidirectional and woven form in different weight fractions. Materials and Methods: Ten rhombic brass plates were prepared with reference points, and 70 heat-cured denture base polymer specimens were produced using these brass models. Ten of 70 were used for controls, and 60 were reinforced with glass fibers in continuous parallel and woven form. The dimensional changes of polymer and fiber-reinforced composite specimens after processing, drying for 4 days at 37°C, and storage in 37°C water for 90 days were calculated by the change of the distance vector. The measurements were made between the reference points on the specimens and were compared with those on the brass model at 4 different stages. The water sorption calculations were made at 10 different time intervals on 70 specimens, which were immersed in a 37°C distilled water bath and weighed. Results: The polymerization shrinkage and water sorption of denture base polymers is lower when the specimens are reinforced with glass fibers in continuous unidirectional and woven form. The highest fiber content showed the smallest dimensional change (0.069 mm, or 0.25%), and the unreinforced group showed the largest change (0.139 mm, or 0.54%). Water sorption occurred mainly during the first 14 days. Conclusion: As the fiber content increases, the dimensional change and water sorption decrease.

Purpose: To stabilize overdentures, a wide range of attachments to implants is suggested. Although there is evidence that denture stability is an important factor for patient satisfaction, there are no data on how these attachments may reduce denture mobility. It was the purpose of this study to compare the effects of different types of attachments on the mobility of implant-stabilized overdentures in vitro, designing a measurement device that could also be used in vivo. Materials and Methods: On an acrylic model with 2 implants in the canine areas, magnets were fixed to one of the implant abutments. Four Hall-effect devices were attached to the denture opposite the magnet, which allowed contact-free measurements of denture movements. Results: In vitro experiments loading an overdenture showed very small, largely insignificant differences in denture mobility when different bar or ball attachments were used. Geometric aspects of load application were more important than the choice of attachment. Conclusion: The measurements gave no guide to the choice of an attachment. The similarity of the attachments must be confirmed by in vivo measurements.

Purpose: The aim of this study was to investigate the effect of experimental alterations of nonworking-side occlusal contacts on jaw-elevator muscle activity. Materials and Methods: Individual devices were fabricated to simulate various lateral occlusal relationships. Twelve human subjects were asked to carry out submaximal lateral clenching, and electromyographic (EMG) activity of the masseter and anterior and posterior temporalis muscles was measured. Results: Clenching in a lateral mandibular position under natural conditions induced an activity pattern with a clear dominance of the anterior and posterior temporalis muscles on the working side. Working-side dominance in the anterior temporalis was reduced moderately when an experimental nonworking-side occlusal contact was added. Dominance decreased dramatically when an experimental nonworking-side interference was added. The working-side activity in the posterior temporalis was also reduced dramatically by an experimental nonworking-side interference, but not by a nonworking-side occlusal contact. None of the experimental contact patterns had a significant effect on the masseter activity. Conclusion: These results suggest that the nonworking-side occlusal contacts have a significant effect on clenchinginduced temporalis muscle activity.

Purpose: This study described and explored verbal communication during prosthodontic treatment. Materials and Methods: Sixty-one patients and 15 dentists participated. Sixtyone prosthetic treatment periods, during which fixed tooth- or implant-supported prostheses were placed, were followed. One visit during each treatment period was audio recorded. The recorded verbal communication was analyzed with the Roter Interaction Analysis System-dental. The inter-rater reliability was 95% to 97% for utterance classification and κ = 0.71 to 0.78 for categorization definition. Results: There were 43,663 utterances available for analysis. Of those, 59% was dentist communication, 28% was patient communication, and 10% was dental nurse communication. Other persons, eg, dental technicians, contributed with 3%. The dentist-patient communication contained more task-focused than socioemotional behaviors. Female patients used socioemotional talk to a greater extent than did the male patients. Dentists and patients of different genders communicated more overall, especially male dentists with female patients. The age difference between dentist and patient had no effect on the amount or type of communication. The dental nurse talked slightly more with male patients. Conclusion: When different genders met there was more communication, and the talk was more socioemotional when the patient was female.

Purpose: The purpose of this study was to measure medial convergence, dorsoventral shear, and corporal rotation in the human mandible. Materials and Methods: Measurements were made using custom-fabricated strain gauge displacement transducers in 6 edentulous subjects who had been treated with mandibular endosseous dental implants. These were mounted on the most distal of the mandibular implants on each side, and measurements were made in real time using a multichannel analogue/digital converter and a personal computer for data storage and analysis. Measurements were made while the implants were loaded, and the subjects opened and closed their mouths and made lateral mandibular excursions. Medial convergence was measured as a linear change at the site of the most distal implant. Dorsoventral shear was expressed as a relative rotation of the right and left mandibular bodies projected onto the median sagittal plane, and corporal rotation was expressed as the relative rotation of the most distal implant. Results: Jaw deformation was found to occur immediately on opening and was related to closing forces and jaw position. Medial convergence of up to 41 µm was observed, with values for corporal rotation of up to 6 degrees and dorsoventral shear of up to 19 degrees. Conclusion: The study demonstrated clinically for the first time 3 different and simultaneous patterns of functional mandibular deformation.

Purpose: The purpose of this study was to evaluate the curing efficiency of 8 light- and dual-cured denture reliners. Materials and Methods: The curing efficiency was measured with Fourier infrared micromultiple internal reflectance spectroscopy, calculating the percentage of remaining carbon double bonds on the top and bottom surfaces of each specimen immediately after exposure to the extraoral light-curing unit according to the manufacturer's instructions and after 1 week of storage in dark and dry conditions. Another group of specimens was photopolymerized initially through a denture base resin prior to the extraoral light-curing polymerization. Five specimens of each reliner were tested. Results: The dual-cured reliners showed no statistically significant differences (P > 0.05) between top and bottom surfaces after immediate exposure to the light-curing unit. On the contrary, light-cured reliners revealed significant differences. The majority of the reliners showed reduction of the percentage of remaining carbon double bonds at both surfaces after 1 week of storage in dark and dry conditions. Photopolymerization of lightcured reliners through a denture base resin induced an increased amount of remaining carbon double bonds, whereas no effect was observed in dual-cured materials. Conclusion: Dual-cured denture liners exhibited distinct advantages over light-cured ones concerning the curing efficiency.

Purpose: The aim of this study was to examine the interfacial region of poly(methyl methacrylate) (PMMA) reinforced with untreated and surface-treated PMMA fibers in both chopped and continuous form using scanning electron and atomic force microscopy. Materials and Methods: Acrylic resin specimens incorporating untreated and surfacetreated (with butadiene styrene latex emulsion) PMMA fibers were examined using a scanning electron microscope and an atomic force microscope. Results: There was evidence of random arrangement of untreated and surface-treated chopped fibers throughout specimens with areas of dense fiber aggregation and other areas containing few or no fibers. For the untreated and surface-treated fibers in continuous forms (a single and 2 unidirectional layers), there was evidence of fiber displacement and buckling, together with variation in interfiber spacing. For the specimens containing surface-treated continuous fibers in a cross-ply arrangement that had demonstrated a substantial improvement in the modulus of rupture, there was no evidence of fiber buckling, and the layer of butadiene styrene was consistently thin and even in comparison to weaker specimens. Conclusion: The thickness of the rubber layer and the fiber arrangement (in terms of fiber displacement and interfiber spacing) may be important factors in the success of the reinforcement.