The International Journal of Prosthodontics, 04/1997

Pure elemental titanium was alloyed with cobalt and chromium in dilutions of 4%, 5%, and 6% to evaluate the suitability of the resulting alloy for removable partial denture frameworks. The physical properties of the Co-Cr-Ti alloy were compared to the properties of a commercial pure titanium and Vitallium. Clasp replicas were cast in Co-Cr-Ti and Vitallium and subjected to cyclic deflection. Representative specimens from the fatigue f ailure tests were then evaluated using scanning electron microscopy and analyzed for elemental content. The 5% titanium dilution of cobalt-chromium proved to have the best physcial properties and was used for comparison with the pure titanium and Vitallum. The Co-Cr-5% Ti had significantly better physical properties than pure titanium and a greater flexure fatigue limit than the Vitallium alloy.

This study presents the outcome of single-tooth restorations supported by Astra Tech single-tooth implants followed for 2 years. Forty-seven implants were placed in the same number of patients. Forty-three patients attended the second recall visit, and none of the evaluated implants have been removed. The mean marginal bone loss after 2 years of service was 0.31 (SD = 0.48) mm. Overall, few complications were recorded during the 2-year period, the most frequent of which were loos crowns (7).

This article is the initial report of a 10-year study of all fixed prosthodontic treatment preformed in a specialist prosthodontic practice between January 1983 and December 1992. A set management protocol was maintained throughout the study. Three hundred forty-four patients who underwent 411 treatment episodes involving 768 crowns and 346 fixed partial dentures (786 abutments, 599 pontics) were recalled between July and December 1993. A classification system detailing outcome with well-defined parameters and including repair requriements was developed. This report limits discussion to the study parameters and patient profile. Of the total treatment episodes, 8.5% required some form of retreatment over the survey period. Of these, 5.5% involved prostheses that had failed, and 3.0% involved prostheses that had been repaired. Females sought fixed prosthodontic treatment more than males in a ratio of 2:1. Aesthetic considerations were the most common reasons for patients seeking crowns, while replacement of failed prostheses was the predominant reason for patients seeking fixed partial dentures.

This study investigated fractures of the cement layer between a crown and a die. Model crowns were luted on dies with zinc phosphate cement and various magnitudes of load were applied. Surface strain on the crown was measured using strain gauges. Seal was evaluated using dye penetration and tensile tests. Results showed that cement frac ture affected surface strain behavior on the crown and was detected using the surface strain measurement. The dye penetration test and the tensile test could not be used to detect the cement fracture. It is suggested that the three-dimensional realtive positioning between the crown and the die affected the development of the cement fracture.

This study evaluated the influence of varying the cement thickness upon the tensile strength of nickel-chromium specimen cylinders cemented with Panavia Ex or Panavia 21 resin cements. A decrease in mean tensile strength of the resin-nickel-chromium alloy composite structure was recorded with an increasing cement thickness for both resin cements. Panavia 21 exhibited a significantly greater mean tensile strength than Panavia Ex at all cement thicknesses tested (P < .01).

The prosthodontic methods and outcomes of treating 127 patients in nine centres over a period of 5 years is described. The benfits perceived by patients and the changes induced in the denture-bearing tissues and temporomandibular joints are reported. To sustain effective treatment outcomes, the levels of maintenance needed by the overdentures are contrasted for restoration of the edentulous mandibles and maxillae.

Cross-sectional and longitudinal studies have identified that persons wearing overdentures require regular care and maintenance of their dentures and their remaining dentition. This paper reports on a longitudinal study of the denture treatment needs of 284 dentures placed in 254 patients seen over a period of 12 years. At placement of the overdentures, baseline measurements and photographs were made by a single examiner. These measurements included evaluation of the restorations, abutment height above the gingival margin, periodontal probing depths, and oral hygiene. Denture status was evaluated by examining stability, retention, the integrity of the denture bases, and the relationship of the teeth in centric occlusion. Denture hygiene was also assessed. Based upon this examination, the subjects; denture treatment needs were determined. The majority of overdentures were well tolerated, and in general the patients were satisfied with their dentures. The most common denture treatment need was cle aning, followed by adjustment of the denture bases. Relaining was a more common problem in the mandibular arch than in the maxillae. The need for occlusal adjustment did not seem to be a problem after the fifth year, but this might have been because of replacement of worn teeth or dentures. The majority of denture repairs were necessitated before the sixth year. Patients who received immediate dentures did not have greater treatment needs. Looseness of the dentures was the primary complaint, followed by sore teeth and denture-bearing tissues. In spite of their complaints, the great majority of the patients were satisfied with their overdentures.a

All patients (n = 46) treated with implant-supported overdentures at the Department of Prosthetic Dentistry, Dental and Medical Health Centre, Halmstad, Sweden, from 1986 to 1993 were studied. The clinical examination was completed in 1994. The material was divided into two subgroups : Group A had been initially treatment planned for an implant-supported overdenture, and Group B had been planned for fixed prostheses but because of loss of implants before loading, treatment with a fixed prosthesis was not possible. The authors present their experience and patient reactions to overdenture therapy in two defined groups of patients. The implant failure rate before loading for Group A _n = 12) was 15% (six implants out of 39), and the rate before loading for Group B (n = 29) was 43.6% (68 implants out of 156). After prosthodontic treatment in Group A, the implant success rate after loading 87.9%, and the overdenture stability was 84.6%. In group B, 17 implants placed in the maxillae were lost after overdenture therapy, which resulted in an implant success rate of 79.3%. A total of eight overdentures, all of which had been placed in the maxillae, were lost, resulting in an overdenture stability of 73.3%. In this study change of retentive clips was the predominant prosthodontic complication related to the overdentures, especially in Group B. Most of these complications (62%) occurred in patients with clinical signs of bruxism. Patient reactions to treatment with an overdenture were positive regarding esthetics for both groups. More negative views were recorded in Group B than in Group A in response to function and retention of the overdenture.

This study evaluated dilatometric data for predicting ceramic-ceramic compatibility for porcelains fied on central incisor copings (n = 72) of high expansion colored IPS-Empress porcelain. Nine body porcelains (leucite 0 wt% to 51 wt%) were each fired onto eight copings. Cracks were detected at 10 x magnification using transilluminating light. Failure was defined as the rpesence of at least one crack and probability of failure (Pf) as the ratio of failed to total crowns. Thermal contraction coefficients (a) were determined using four bars of each porcelain followin g the protocol of ISO 9693. Absolute differences in thermal contraction, [ a], between core and test porcelains were plotted against Pf and curve fit. Significant differences in a were found among the porcelains tested (ANOVA, 95% Tukey); the a values ranged from 7.92 to 17.83 x 10 to the negative sixth power/degrees C; Pf ranged from 0 to 1. Compatible porcelains (no cracks during any firing of all eight crowns) had [ a] values less than 1 x 10 to the negative sixth power/degrees C. Absolute values ([ a]) were surprisingly predtive of Pf given the very different cooling rates (dilatometry versus dental lab) and the relatively complex crown shape. Standard dialtometry may be useful for predicting the compatibility of ceramic-ceramic systems. Three porcelains, IPS-Empress dentin, Duceram, and Will-Ceram were successfully used for veneering IPS Empress cores.

Osteoporosis has been suggested to contribute to the edentulous condition. However, studies specifically designed to examine the relationship between tooth loss and osteoporosis are scarce, and reported results have been mixed. This study investigated the correlation between tooth loss and spinal bone density in a nonHispanic white female population. Forty-four subjects were recruited and divided into high and low spinal bone density groups based on whether the bone density was higher or lower than the age-adjusted population mean bone density. Missing teeth and periodontal status in these groups were assessed and analyzed. Tooth loss was not significantly different between subjects with low spinal bone density (4.90 =- 0.89 teeth) and high spinal bone density (3.81 ± 0.90 teeth). Tooth loss did not differ after age and periodontal adjustment. However, the loss of attachment levels (relative to the cementoenamel junction) was greater in the low spinal bone density subjects (3.42 ± 0.30 mm) than in the high spinal bone density subjects (2.37 ± 0.26 mm) (P < .05). The difference may have resulted from gingival recession (P < .05), because the gingival pocket depths were not significantly different between the two groups. In this study, total tooth loss was not directly associated with systemic bone density. However, periodontal disease was negatively associated with spinal bone density. Whether periodontal disease will ultimately lead to greater tooth loss in low spinal bone density group merits further investigation.

This study evaluated the efficacy of a new occlusal analysis sytem (Dental Prescale System) composed o pressure-sensitive sheets and a computer for analysis for complete denture wearers. In the laboratory portion of the study, the system registered values that were greater than the actual applied loads (mean 6.3 ± 10.6 N). Clinical measurements of five parameters related to the analysis of occlusion were made using two groups: 50 wearers of nonadjusted complete dentures and 50 wearers of adjusted prostheses. An error discrimination rate of 16% resulted between the two groups. This system is capable of measuring occlusal pressure at every contact point and can be considered a useful method for occlusal analysis and patient screening.