The International Journal of Prosthodontics, 01/2001

Purpose: The influence of different types of posts and cores on light transmission through all-ceramic crowns was assessed by spectrophotometric analysis and clinical evaluation. Materials and Methods: Three extracted natural teeth were replicated in acrylic resin, with roots prepared to receive standardized posts and cores. Using a silicone impression material as a template, various prosthodontic reconstructions were obtained by combining four types of posts and cores (polished and matte-finished gold alloy, all-ceramic, and ceramized metal alloy) and three types of all-ceramic crowns (IPS-Empress 2 surface-colored, IPS-Empress 2 stratified, and In-Ceram). The spectrophotometric analysis was performed in the dark at 25°C. The teeth were backlit with an incandescent lamp at the color temperature of A illuminant and shielded to avoid spurious light entering the spectrophotometer. The transmitted light was analyzed in terms of luminance at four points of the sample surface (cervical, middle, incisal, and proximal). Twelve measurements were performed for the natural teeth, and 144 were performed for the artificial teeth. Results: Natural teeth had the highest luminance. Among all-ceramic crowns, surface-colored IPS-Empress 2 had the highest luminance, and stratified IPS-Empress 2 had the lowest. Regarding posts and cores, the luminance was highest with the all ceramic, lower with the ceramized and the polished gold alloy (which had very similar luminance), and lowest with the matte-finished gold alloy. No significant difference among prosthodontic combinations was detected under clinical observation. Conclusion: The surface-colored glass ceramic (IPS-Empress 2) was the most translucent crown. At the standard crown thickness used, there were small, significant spectrophotometric, but not clinical, differences among the combinations tested. Thesefindings show no esthetic contraindications for the use of polished gold alloy posts and cores with all-ceramic crowns.

Purpose: The purpose of this study was to compare the electromyographic (EMG) activity level and signs and symptoms in patients with myogenous temporomandibular disorders (TMD) treated with two different types of occlusal devices. Materials and Methods: Eleven TMD patients were treated with maxillary occlusal devices. The first group received a flat-plane stabilization occlusal device, while the second group received an anatomic occlusal device that maintained the anatomy of the original occlusal surfaces. The severity of signs and symptoms and the masseter EMG activity were recorded and evaluated before treatment and at 72 hours, 2 weeks, and 4 weeks following the delivery of the occlusal device. EMG activity was measured during maximum clenching and during chewing on the right and left sides. The EMG was also recorded for seven normal subjects as a control group. Results: All patients showed reduction of reported and clinically found muscle pain, with no statistically significant differences between the two groups. A reduction in the EMG activity level at maximum clenching was seen in both patient groups, but was significant only with the anatomic occlusal device. Mean EMG activity during chewing was highly variable within and between groups. Conclusion: The subjective and objective improvements with both types of occlusal devices suggest that either type of occlusal device can be beneficial to TMD patients.

Purpose: The aim of this study was to measure the flexural properties of fiber-reinforced composite (FRC) used in frameworks of fixed partial dentures. In addition, the influence of water storage on the properties was determined. Materials and Methods: Rhombic test specimens for four groups were milled from bulk FRC material DC-Tell. The test specimens of the first group were stored and tested dry. In the second group, the test specimens were water stored for 3 months at 37 ± 1°C and tested in water. The specimens of the third group were also water stored, but they were tested dry at room temperature. Water-stored test specimens of the fourth group were dehydrated and tested dry at room temperature. A three-point bending test was used to measure the flexural properties. The quantity of glass fibers in the test specimens was determined by combustion analysis. Water uptake was calculated after 3 months of water immersion. The direction and length of fibers were examined, and elemental composition was determined. Results: Water storage decreased the flexural strength by 66% and flexural modulus by 60%. After dehydration, the flexural strength did not recover to the same level as the flexural strength of the dry-group specimens. The fiber content was 38% by volume. Water uptake was 3 wt%. The reinforcement of DC-Tell was short fibers in random orientation, and the elemental composition of fibers was similar to that of E-glass. Conclusion: Water storage decreases the flexural properties of the bulk fiber-reinforced composite DC-Tell. This may restrict the use of DC-Tell as a framework of crowns and bridges in the oral cavity in the long term.

Purpose: This article proposes a classification protocol for reporting the outcome of implant overdentures. Materials and Methods: Review of the literature pertaining to postinsertion prosthodontic procedures for maxillary and mandibular implant overdentures revealed a wide range in the terminology used and methods of reporting outcome, usually as a result of the use of varying designs among different implant systems. A need for comparative evaluation of the prosthodontic success of implant overdentures was identified. Results: An existing classification protocol for implant-fixed prostheses containing six objectively defined fields was modified for implant overdentures. This new protocol, which also uses the descriptive fields of success, survival, unknown, dead, and retreatment (repair or failure), provides a method whereby postinsertion prosthodontic procedures and subsequent time to retreatment can be quantified regardless of design, method of attachment, or implant system. A ratio method for identifying prosthodontic treatment cost effectiveness of implant overdentures is included. Conclusion: This protocol could assist clinicians in their choices of implant overdenture therapy by providing accurate comparisons of varying implant overdenture systems and designs, and by identifying prosthodontic treatment cost effectiveness.

Purpose: The aim of this study was to measure the flexural strength and the elastic modulus of composite resin with and without reinforcing fibers and to evaluate the reinforcing effect of various fibers. Materials and Methods: A polyethylene fiber (Ribbond), a polyaramid fiber (Fibreflex), and three glass fibers (FibreKor, GlasSpan, Vectris) were used to reinforce composite resins. The flexural strength and elastic modulus of specimens in the three-point bending mode were measured using a universal testing machine at a cross-head speed of 1 mm/min after storage in water at 37°C for 24 hours. All tests were carried out in a water bath at 37°C. The data were analyzed using analysis of variance and the Sheffé test at P = 0.05. After testing, the fractured surface was evaluated using a scanning electron microscope at 50X, 500X, and 3,000X magnifications. Results: Yield flexural strengths of nonreinforced resins were 48 to 56 MPa, and those of reinforced resins were 56 to 134 MPa. Ultimate flexural strengths of nonreinforced specimens were 96 to 119 MPa, and those of reinforced ones were 203 to 386 MPa. Elastic modulus of nonreinforced resin was 6 to 9 GPa, and fiber reinforcing increased the value to 9 to 15 GPa, while it had no effect in Ribbond. Conclusion: Most of the fibers used in this study increased both yield and ultimate flexural strengths of composite resins, with the exception of the yield strength of Vectris. GlasSpan, Fibreflex, and FibreKor were effective in reinforcing elastic modulus, while Ribbond had no effect on it. Unidirectional glass fibers and polyaramid fiber were effective in reinforcing both flexural strength and elastic modulus of composite resin.

Purpose: Microstructural analyses of commercially pure titanium (CpTi) are scarce. The present report presents the micrographs, fractographs, elemental characteristics, and hardness profiles of brazed joints and weldments using machined rods of CpTi. Materials and Methods: CpTi rods were joined using four techniques: laser welding, electric-arc welding, electron-beam welding, and gold- and Ti-filler brazing. The specimens were then subjected to tensile and fatigue loading. After sectioning and patterning, optical micrographs of intact joints were obtained. Fractured surfaces were investigated using scanning electron microscopy (SEM). The joints composition was determined by SEM-energy dispersive x-ray analysis. Hardness was determined at specific locations using a microindenter. Results: While laser welding left the parent metals equiaxed structure fairly intact, electric-arc welding, electron-beam welding, and brazing created a heat-affected zone in the vicinity of the joint. The extent and characteristics of the heat-affected zone depended on the amount of heat transferred to the specimens. In this respect, brazing essentially increased grain size and altered their shape. Electron-beam welding augmented this phenomenon, yielding grains that encompassed the full diameter of the joint. Electric-arc welding disrupted the granular pattern and generated highly lamellar/acicular structures. Conclusion: Hardness was not a good indicator of mechanical resistance, nor was the joints structural continuity with the parent substrate. Still, acicular microstructures were characterized by a peculiar behavior in that such joints were highly resistant to tensile stresses while their fatigue strength ranged among the lowest of the joints tested.

Purpose: Although denture adhesives are widely used by the elderly, it is unknown whether denture adhesives support microbial growth. Therefore, we investigated the growth of Candida species on six commercial denture adhesives. Materials and Methods: The growth of a single isolate of C albicans and C tropicalis on six commercial denture adhesives was investigated by monitoring pH changes in growth media. Results: In the preliminary study, the effect of each product on the pH value of the medium was examined; a single product itself significantly reduced the pH of medium below 5.0. When the yeast was grown on the materials, the pH changes in the media varied depending on the adhesive materials and, to a greater or lesser extent, on whether they showed antifungal activity. Two products (Cushion Collect and Collect Soft A) significantly suppressed C albicans growth (P 0.01), and one product (Collect Soft A) effectively reduced C tropicalis growth (P 0.01). Conclusion: Our results suggest that denture adhesives possess antifungal activity to a greater or lesser degree. However, one product caused the reduction of pH below 5.0. Thus, in the daily use of denture adhesives, attention should be paid to both the materials and their microbiologic properties.

This article is based on the thesis of A. J. Humplik, submitted to the School of Dental Science, The University of Melbourne, in partial fulfillment of the requirements for the degree of Master of Dental Science. Purpose: This study investigated the effects of low seating force (5 N) with and without oscillation on pulpward pressure transmission during crown cementation. Materials and Methods: Thirty human premolars received standardized complete-crown preparations. They were randomly allocated into three experimental groups of ten: group 1 = 100-N static load; group 2 = 5-N static load; and group 3 = 5-N load with oscillation. Crowns were constructed of base-metal alloy and attached to a purpose-built loading device. Pulpal pressures were recorded using a 0- to 104-kPa pressure transducer that was connected via the sectioned root of the premolar to the pulp chamber, which was perfused with saline driven by nitrogen gas at 83 kPa until a steady rate was achieved. The crowns were cemented using zinc phosphate cement, and postcementation elevations were measured with a linear variable differential transformer. An amalgam condenser provided oscillation for 1 minute. Results: The pulpal pressures were: group 1 = 455 Pa; group 2 = 26 Pa; and group 3 = 76 Pa. The postcementation crown elevations were: group 1 = -48 µm; group 2 = 362 µm; and group 3 = 26 µm. Conclusion: Acceptable crown seating can be obtained using low force (5 N) combined with oscillation, and lower pressure pulses are generated compared to using high force (100 N) alone.

Purpose: This study compares the survival rate and fracture strength of endodontically treated maxillary incisors with moderate coronal defects restored with different post-and-core systems after exposure to an artificial mouth. Materials and Methods: Sixty-four caries-free human maxillary central incisors were selected for standardized size and quality, endodontically treated, and decoronated 2 mm coronal to the cementoenamel junction. Group 1 was restored with titanium posts and composite cores, group 2 received zirconia posts and a composite core, and in group 3 zirconia posts with a heat-pressed ceramic core were used. Teeth restored with cast posts and cores served as controls. All teeth were prepared and restored with complete cast crowns. All samples were exposed to 1.2 million cycles in a computer-controlled chewing simulator with simultaneous thermocycling. In addition, the samples were loaded until fracture in a static testing device. Results: The survival rates of the different groups were: 94% for titanium/composite, 63% for zirconia/composite, 100% for the all-ceramic post and core, and 94% for the cast post and core. The following mean fracture strengths were obtained: titanium/composite = 425 ± 155 N, zirconia/composite = 202 ± 212 N, zirconia/ceramic = 378 ± 64 N, cast post and core = 426 ± 178 N. The lower fracture load in the group with zirconia posts and composite cores was statistically significant. The use of zirconia posts resulted in fewer oblique root fractures. Conclusion: Prefabricated titanium posts with composite cores, zirconia posts with heat-pressed ceramic cores, and cast posts and cores yield comparable survival rates and fracture strengths for the restoration of crowned maxillary incisors with moderate coronal defects. Survival rates and fracture strengths for zirconia posts with composite cores are significantly lower, so this combination cannot be recommended for clinical use.

Purpose: The objective of this study was to determine the severity, distribution, and correlates of tooth wear in a sample of Mexican-American and European-American adults drawn from a community-based longitudinal aging study on oral health. Materials and Methods: The maxillary teeth of 71 subjects enrolled in a longitudinal aging study were assessed using a previously introduced five-point (0 to 4) ordinal scoring system in which each tooth is given a score describing the severity of wear. The tooth wear scores were compared with data concerning demographic factors, functional/parafunctional habits, soft drink consumption, and bite force measurements to determine specific correlates of tooth wear. Results: The mean wear score for all teeth was 1.50 on the five-point scale. There was a significant difference between the mean wear score of anterior teeth (1.85) and posterior teeth (1.17). Bivariate analyses detected a moderate degree of correlation between maxillary tooth wear and age and bite force. Maxillary tooth wear was significantly greater in males and in subjects with reported teeth clenching/grinding. Multivariate analyses revealed that age, gender, bite force, self-reported teeth clenching/grinding, and number of daily meals/snacks had significant correlations with maxillary tooth wear. Conclusion: The overall severity of maxillary tooth wear in this sample of Mexican-American and European-American adults was low, with anterior teeth having a greater degree of wear than posterior teeth. Age, gender, bite force, teeth clenching/grinding, and number of daily meals/snacks are potential factors that may have contributed to tooth wear in the study sample.

Purpose: Major connectors must be rigid to perform their functions with maximum efficacy. This study investigated the deformation of four major connectors for maxillary Kennedy Class I removable partial dentures. Materials and Methods: The designs were palatal plate, U-shaped plate, palatal strap, and anteroposterior bar. The deformation properties of major connectors were comparatively analyzed by two methods. In the photogrammetric part, a stereometric camera, Avipan-100 glass films, and an analytic apparatus were used. A computerized hydraulic machine was programmed to load the eight test dentures at 4-Hz frequency under a vertical load of 100 kg and a maximum of 300,000 cycles. The fluorescence penetrant liquid inspection test was used to detect the surface microcracks. Results: The anteroposterior bar showed the least deformation. The other connectors, ranked in increasing order for the amount of deformation, were the U-shaped plate, the palatal strap, and the palatal plate. There were no microcracks in the U-shaped plate and the anteroposterior bar designs. Conclusion: Anteroposterior bar major connectors showed the least deformation among the maxillary major connector types tested. Microscopic cracks were seen in major connectors showing the highest degree of deformation and located at the depth of the hard palate.

Purpose: This study was done to clarify the correlation between the quality of life (QOL), defined as overall satisfaction with daily life, and denture satisfaction in elderly complete denture wearers. Materials and Methods: A new method for quantifying overall satisfaction with daily life (QOL) among 2,079 elderly people (age >= 65 years) was developed by evaluating the contribution of 13 factors (eating, health problems, daily exercise, fatigue, sleep quality, smooth communication, physical comfort, aging, loneliness, job and hobbies, meaningfulness, social life, and economic problems) to overall daily life satisfaction by a multiple regression analysis. Then, correlation between the QOL and denture satisfaction was analyzed by the regression model in 84 randomly selected complete denture wearers from the above population. Results: Quantification of the QOL was completed by converting category scores to integers between 0 and 100 for eight highly correlated factors (eating, smooth communication, physical comfort, loneliness, job and hobbies, meaningfulness, social life, and economic problems) to overall satisfaction with daily life (P 0.01). Significant positive correlation was found between the QOL score and denture satisfaction score (P 0.05). Conclusion: Edentulous elderly people who are well satisfied with their daily lives are also satisfied with their complete dentures.

Purpose: This prospective clinical trial evaluated the clinical acceptability of a new material, ceromer, used for inlay and onlay restorations in single- or multisurface cavities of posterior teeth. Materials and Methods: Forty-three Targis inlay and onlay restorations were placed in 25 patients and evaluated using the United States Public Health Service criteria. The laboratory work was conducted by three dental technicians according to the manufacturers recommendations. Twenty-five restorations were luted with Syntac bonding system and Variolink II, and 18 were luted with Scotchbond Multi Purpose and Opal Luting Composite. The recalls were done at 6, 12, and 18 months. Restorations were evaluated for six parameters and scored as ideal (A), clinically acceptable (B), or clinically unacceptable (C). Results: Indirect restorations received, after 18 months, scores of A at the following rates: color match 77%; marginal discoloration 93%; secondary caries 100%; anatomic form 93%; and marginal integrity 95%. For these parameters, statistical analysis indicated no significant differences at baseline and after 18 months. Postoperative hypersensitivity was reported by seven patients at baseline, but it decreased and there was no hypersensitivity at 12- and 18-month follow-ups. Conclusion: Over an 18-month period the Targis restorative system yielded good clinical service.