The International Journal of Prosthodontics, 03/2001

Purpose: It was the aim of this study to investigate the long-term success of a telescopic crown system that can be used for both rigid and resilient support and to evaluate by means of a literature review whether the use of resilient support may be advantageous compared to other double crown systems when the restoration is placed on only a few remaining teeth. Materials and Methods: Patient records were used to evaluate 125 dentures (with 460 abutment teeth) based on the Marburg double crown system. The loss of abutment teeth, endodontic treatment, and fracture of the metallic framework were investigated with regard to the different types of denture support. Results: The probability that a patient would have kept all abutment teeth was 84% after 5 years and 66% after 10 years. No significant differences were found for the two groups esilient support ( three abutment teeth) and igid support ( four abutment teeth). For abutment teeth with a double crown with clearance fit, the risk of loss was 4% after 5 years and 15% after 10 years for rigid support, and 10% and 24%, respectively, for resilient support. The risk of endodontic treatment was 7% after 5 years and 9% after 10 years for rigid support, and 3% and 7%, respectively, for resilient support. None of the denture frameworks showed a fracture during the observation period. Conclusion: Removable partial dentures retained by double crowns with clearance fit and constructed without major or minor connectors provide good clinical longevity. The survival rates of abutment teeth were comparable to those reported in the literature for other double crown systems. There was no significant increase of the risk of abutment loss when the restoration was placed on three or fewer remaining teeth and the concept of resilient support was applied.

Purpose: The impact strength and the flexural properties of denture base materials are of importance in predicting their clinical performance upon sudden loading. This study compares the impact and transverse strengths and the flexural modulus of three denture base polymers. Materials and Methods: The investigation included a relatively new microwave-polymerized polyurethane-based denture material processed by an injection-molding technique, a conventional microwave-polymerized denture material, and a heat-polymerized compression-molded poly(methyl methacrylate) (PMMA) denture material. Impact strength was determined using a Charpy-type impact tester. The transverse strength and the flexural modulus were assessed with a three-point bending test. The results were subjected to statistical analysis using a one-way analysis of variance and the Scheffé test for comparison. Results: The impact strength of the microwave-polymerized injection-molded polymer was 6.3 kJ/m2, while its flexural strength was 66.2 MPa. These values were lower than those shown by the two compression-molded PMMA-based polymers. The differences were statistically significant. The flexural modulus of the new denture material was 2,832 MPa, which was higher than the conventional heat-polymerized polymer but was comparable to the other microwave-polymerized PMMA-based polymer. The difference in the flexural modulus was statistically significant. Conclusion: In terms of the impact and flexural strengths, the new microwave-polymerized, injection-molded, polyurethane-based polymer offered no advantage over the existing heat- and microwave-polymerized PMMA-based denture base polymers. However, it has a rigidity comparable to that of the microwave-polymerized PMMA polymer.

Purpose: The aim of this study was to evaluate clinical usefulness and durability of continuous glass-fiber reinforcement in repair of acrylic resin removable dentures. Materials and Methods: Fractured removable dentures without reinforcement, with conventional metal-wire reinforcement, or with mesh reinforcement were collected from two dental schools in Finland. The total number of dentures was 51 and the number of patients was 48. During the repair, the dentures were reinforced with a polymer-preimpregnated E-glass fiber at the region of the fracture. The fibers were used as partial fiber reinforcement, ie, only the weakest part of the denture was reinforced. Follow-up time varied from 4 months to 4.1 years. After the follow-up period, possible fractures and discoloring were visually inspected. Possible irritation of oral mucosa by glass fibers and the general shape of the denture were also evaluated. Results: In 88 % of the cases, there was no need for adjustment at the region of partial fiber reinforcement, and the clinical condition of the dentures was good. Glass fibers did not irritate the oral mucosa. In the case of refracture or hairline fracture, positioning of the partial fiber reinforcement was incorrect or the reinforcement had been used incorrectly (the wetting of the reinforcement with denture base resin was inadequate). Conclusion: Polymer-preimpregnated partial fiber reinforcement seems to be useful in eliminating fractures of acrylic resin removable dentures. However, this study emphasizes the importance of correct positioning and accurate laboratory technique when partial fiber reinforcement is used.

Purpose: The purpose of this study was to investigate the effect of priming time on bovine enamel and dentin adhesion promoted by self-etching primer systems. Materials and Methods: Two commercial self-etching primer systems, Clearfil SE Bond (SE) and Unifil Bond (UB), were used. Bovine enamel and dentin were treated with each system with various priming times (5, 20, and 60 seconds), and the tensile bond strength was measured. Scanning electron microscopic (SEM) observation was also performed to examine the effect of priming time on the morphology of the resin-tooth interface. Results: The tensile bond strength to enamel ranged from 10.6 to 14.3 MPa, and no statistically significant difference was detected among products or priming times. To dentin, UB showed the statistically significantly lowest tensile bond strength when primed for 5 seconds, 6.9 ± 1.1 MPa, but there was no significant difference between the groups primed for 20 and 60 seconds, 13.5 ± 4.1 MPa and 13.8 ± 4.6 MPa, respectively. SE created tensile bond strengths ranging from 13.9 to 15.7 MPa and showed no effect of priming time on dentin adhesion. SEM observation revealed that resin penetrated into both enamel and dentin more deeply with extension of priming time. Conclusion: Priming times longer than those recommended by the manufacturers did not influence the tensile bond strength to enamel and dentin when using two commercial self-etching primers. In contrast, a shortened priming time, 5 seconds, carried a risk of decreasing dentin adhesion, although it had no adverse effect on enamel adhesion.

Purpose: The purpose of this study was to determine the fracture resistance of three-unit fixed partial dentures (FPD) made of new core ceramics. Materials and Methods: A base metal three-unit master FPD model with a maxillary premolar and molar abutment was made. Tooth preparation showed 0.8-mm circumferential and 1.5-mm occlusal reduction and a chamfer margin design. FPDs were constructed with a uniform 0.8-mm-thick core ceramic and a porcelain veneer layer. In-Ceram Alumina, In-Ceram Zirconia, and DC-Zirkon core ceramics were machined by a computer-aided design/manufacturing system, whereas IPS Empress 2 core ceramic was indirectly built up using the fabrication technology of waxing and heat pressing. FPDs of IPS Empress were heat pressed as complete restorations without core material. To ensure standardized dimensions, the FPDs were controlled at different points. All FPDs were cemented with ZnPO4 on the master model and loaded on a universal testing machine until failure. The failure load and mode of failure were recorded. Results: The highest failure loads, exceeding 2,000 N, were associated with FPDs of DC-Zirkon. FPDs of IPS Empress and In-Ceram Alumina showed the lowest failure loads, below 1,000 N, whereas intermediate values were observed for FPDs of IPS Empress 2 and In-Ceram Zirconia. Differences in mean values were statistically significant. Conclusion: The high fracture resistance evaluated for FPDs made of DC-Zirkon underscores the remarkable mechanical properties of high-performance ceramic, which could be useful for highly loaded all-ceramic restorations, especially in the molar region.

Purpose: This research investigated the effect of surface treatment on the fatigue life of metal-ceramic postsoldering. Materials and Methods: Twenty cylindric specimens were cast in a metal-ceramic alloy. All specimens received appropriate heat treatment simulating ceramic application, although no porcelain was applied. Each specimen was cut in half to form two half specimens. The 40 half specimens were randomly assigned to one of the four treatment groups, which differed in the type of surface treatment performed on one end of each half specimen (joint surface) prior to soldering: (1) aluminous oxide pink stone; (2) 50-ìm aluminum oxide sandblasting; (3) brown rubber point; and (4) gray silicone wheel followed by pink silicone wheel. All surface treatments were performed for 30 seconds. The half specimens were then steam cleaned, aligned, indexed, and oven soldered with #650 postceramic solder. The soldering of two half specimens formed a complete test specimen, and a total of 20 postceramic soldered specimens were prepared. Following soldering, a 241.1 MPa fatigue stress was applied to each solder joint during specimen testing. The test variable was the number of stress cycles required to fail each specimen. Results: All specimens failed adhesively at the joint interface between the solder and parent metal. There were significant differences in the number of stress cycles to failure between groups 1 and 2, groups 1 and 4, and between groups 2 and 3. Conclusion: The load cycle to failure for postceramic soldered joints was affected by the metal surface treatment.

Purpose: The main aim was to investigate the current opinions among general dental practitioners and board-certified prosthodontists in Sweden on how to restore root-filled teeth. Materials and Methods: A questionnaire containing 31 multiple-choice questions was mailed to 892 general practitioners and 150 board-certified prosthodontists in Sweden. The questions asked for information on when the clinicians used posts in endodontically treated teeth and what kind of clinical procedure they used. They were also asked if they believed that a post strengthened a root-filled tooth. Results: Sixty percent of the general practitioners and 67% of the prosthodontists returned the questionnaire. Twenty-nine percent of the responding general practitioners and 17% of the prosthodontists were of the opinion that a post reinforces a root-filled tooth. Only a few clinicians used posts always or most of the time when restoring endodontically treated teeth with fillings, while the vast majority used posts when restoring such teeth with crowns or fixed partial dentures. In both groups of dentists, cast posts were most commonly used. Despite the present knowledge that parallel-sided posts have a significantly higher success rate than tapered cast posts, only a minority of Swedish dentists use parallel-sided posts. Conclusion: In contrast to the results of several current studies, a high proportion of both general practitioners and prosthodontists believe that a post reinforces an endodontically treated tooth. This is one probable explanation for the almost ubiquitous application of posts when teeth are restored with crowns or fixed partial dentures.

Purpose: Wetting characteristics of denture lining materials indicate the degree of salivary lubricating effect, which promotes denture retention and patient comfort. This in vitro study investigated the wettability of ten commercially available visible light-cured denture lining materials. Materials and Methods: Ten soft and hard visible light-curing materials, one autopolymerized hard lining material, and one autopolymerized denture base material were evaluated for wettability. Wettability was estimated by measuring the equilibrium and hysteresis contact angles using the dynamic contact angle analysis, or Wilhelmy, technique. Results: The equilibrium contact angle ranged from 59.9 to 77.3 degrees, and contact angle hysteresis ranged from 14.7 to 30.6 degrees. Conclusion: Visible light-curing lining materials exhibit wetting properties similar to the conventional hard lining and denture base materials.

Purpose: Interchangeability between articulators allows mounted casts to be transferred accurately from one articulator to another. The purpose of this study was to evaluate the interchangeability of 109 new, unused interchangeable articulators in the centric position. Materials and Methods: The interchangeability of 38 unused Whip Mix model #2240 and 71 unused model #3040 semiadjustable articulators was evaluated using the Whip Mix #2245 check system as the standard. Vertical discrepancies between the check system cylinders were also measured. Results: Within the standard for interchangeability established by the Whip Mix #2245 check system ( 94 µm horizontal discrepancy), 101 (93%) of 109 articulators were interchangeable (34 were model #2240 and 67 were model #3040). Overall, the amount of vertical space between the check system cylinders was 52 µm in 99.4% of the model #2240 articulators and 99.7% of the #3040 articulators. Conclusion: New, unused Whip Mix model #2240 and #3040 articulators are potentially interchangeable in the centric position.

Purpose: Because of existing controversy, the present study investigated the individual and combined effects of endodontic treatment and porcelain veneer restoration on the fracture behavior of human mandibular incisors. Materials and Methods: Forty extracted intact human mandibular incisors were assigned to four groups of ten with a similar range of labiolingual widths at the cementoenamel junctions. Group A consisted of intact teeth; group B consisted of endodontically treated teeth; group C teeth were restored with labial porcelain veneers; and those of group D were endodontically treated and had labial porcelain veneers. All teeth were subjected to a slow continuous loading test at 30 degrees to the long axis of the teeth and 1 mm below the incisal edge on the labial side. Results: Fracture forces were 415 ± 220 N, 370 ± 89 N, 420 ± 128 N, and 448 ± 156 N for groups A, B, C, and D, respectively. Root fracture was the most common mode of failure. There were no statistically significant differences between the groups in terms of fracture forces and modes of failure. Conclusion: Human mandibular incisors with endodontic treatment and/or porcelain veneer restorations were able to withstand the same magnitude of oblique loading as intact teeth. Endodontic treatment and/or porcelain veneer restoration did not affect the mode of failure of mandibular incisors.

Purpose: The aim of this report was to study the ability of examiners to measure reliably the clinical signs of temporomandibular disorders (TMD). Four examiners participated in this study of 11 TMD patients and 25 nonpatients. Materials and Methods: Vertical and lateral excursions of the jaw were measured using a millimeter ruler. Joint sounds during vertical jaw movements were assessed using digital palpation. The reliability of delivering appropriate degrees of digital pressure to assess masticatory muscle pain was assessed using a manometer after training examiners to exert specified pressures. Results: Intraclass correlation coefficients for the measurement of vertical and protrusive jaw movements were >= 0.87, which was considered excellent. The intraclass correlation coefficient for measurements of left and right lateral jaw excursions varied between 0.73 and 0.85, which was considered acceptable. The interobserver agreement for detecting the joint sounds showed overall agreement across examiners of 78%. Kappa for every possible pair of examiners varied between .52 and .86 (median .75, interquartile range .18). Reliability for diagnostic categories from the Helkimo index and Research Diagnostic Criteria for Temporomandibular Disorders involving joint noises showed modest reliability. Conclusion: Point estimates and measures of spread for reliability measures of single clinical TMD signs as well as combinations of signs into diagnostic categories from the Helkimo index and Research Diagnostic Criteria for Temporomandibular Disorders involving joint noises were sufficient in a group of four examiners.

Purpose: This study was undertaken to characterize the shear bond strength established between four denture base polymers and four denture reline polymers. Materials and Methods: Cylindric columns of denture reline polymers were bonded to columns of denture base polymers. Specimens were immersed in water for 4 months and then thermocycled. The strength at which the bond failed under shear stress was recorded. Results: Significant differences in bond strength existed among the specimens because of the denture base polymer variable, the denture reline polymer variable, and their interaction (P .05). A light-activated denture base polymer (Triad) bonded adequately with a light-activated reline polymer (Triad) but less well with the other reline polymers tested. The bond strength established between some denture base polymers and a different light-activated reline polymer (Rebaron LC) was relatively low. Conclusion: The type of denture base polymer and denture reline polymer affected the shear bond strength between them.

Purpose: This study was initiated with the purpose of developing and evaluating a system for measuring the magnitude of the variation between a computer-aided design (CAD) object created on the computer screen and a replicated object produced by computer-aided manufacturing (CAM). Materials and Methods: Controlled geometric forms, a square and a cone, were designed in a CAD program, and measuring distances were selected. The CAD data were transmitted to CAM data, and objects were produced. The CAD/CAM process was the Procera system, and the holder system permitted the objects to be ground into cross sections, similar to the visualization in the CAD program. Five objects of each shape were produced and measured by two operators two times. Three operators measured one of the objects 30 times. Results: Observed values were greater than the true value. For all objects, the systematic error was at most 15.5 µm. Interoperator difference was small. The variation because of measurement error was greater for the square object compared to the cone. However, the variation because of object was higher for the cone object than for the square. The total standard deviation was 7.7 µm. Thus, the total random error caused by object variation and measurement error was in approximately 95% of all measurements less than 15 µm. Conclusion: There are no differences in the measurement data derived from this method and actual measurement data from an object created by the computer-aided dental design program. The method has high validity and reliability, ie, high accuracy.

Purpose: The increased demand for tooth-colored restorations has prompted the use of ceramics in areas that are subject to masticatory stresses. To maximize the strength of these restorations, manufacturers and clinicians advocate placement of core materials in lieu of veneering materials in areas that are more susceptible to fracture. The objectives of this study were to determine the: resistance to staining of three core porcelains used for all-ceramic restorations, Procera, IPS Empress, and In-Ceram, through the use of colorimetry and visual observation; flexural strength of these porcelains under a three-point bend test; and chemical solubility in a controlled environment. Materials and Methods: L*a*b* values were obtained for each specimen before and after immersion in a saturated solution of methylene blue in ethanol for 24 hours. Visual observation was also performed to ascertain color differences before and after staining. A three-point bend test was used to determine flexural strength. A reflux-condenser type, three-piece extraction apparatus was used with 4% acetic acid solution for 16 hours to determine solubility. Each sample was weighed before and after the reflux procedure to ascertain percentage weight loss. Results: The mean DE obtained for IPS Empress was 14.5; In-Ceram was 9.2, and Procera was 9.0. Flexural strength obtained for IPS Empress, In-Ceram, and Procera was 176.9 MPa, 323.4 MPa, and 464.3 MPa, respectively. Weight loss of IPS Empress, In-Ceram, and Procera was 0.056%, 0.734%, and 0.003%, respectively. Conclusion: IPS Empress showed the least resistance to staining. IPS Empress had the lowest flexural strength, while Procera had the highest. In-Ceram demonstrated the highest chemical solubility.