The International Journal of Prosthodontics, 05/1995

A blunt-indentation fracture mechanics technique was used to investigate the response of a feldspathic dental porcelain to cyclic mechanical fatigue. The indentation stress -strain curve was determined first, which showed the critical pressure necessary for crack initiation. This research also demonstrated that pressures too small to cause immediate catastrophic failure can still cause irreversible damage. A second series of fatigue experiments, using pressure parameters chosen from the first project, investigated strength loss. These experiments showed that the porcelain was susceptible to cyclic mechanical fatigue, and the cyclic mechanical fatigue is different from quasistatic fatigue. Strength loss curves indicated that cyclic mechanical fatigue damage is cumulative and permitted quantification of the severity of accumulated damage.

A comparative evaluation of torque at the gold screw, abutment screw, and implant was calculated for cuspal inclination, implant inclination, and horizontal and vertical implant offset. The method of comparison as expressed as a percentage of change from ahypothetical standard maxillary implant/prosthesis configuration. These data facilitate rational clinical conclusions that cuspal inclination produces the most torque, followed by maxillary horizontal implant offset, while implant inclination and apical implant offset produce minimal torque. Although these data are not intended as a quantitative analysis, they nonetheless provide a practical guide to diagnosis and treatment planning.

Chemical cleansing has been suggested as one of the most effective methods for plaque control, particularly ffor resilient denture-lining materials. These materials are known to be easily colonized and infected by Candida albicans. Maintaining the cleanliness of such materials is difficult because of porosity and incompatibility with some types of denture cleasers. Therefore, denture cleansers used for soft liners must address both microbiologic and physical requirements. This study evaluated the antifungal efficacy of 11 commercial denture cleansers on C albicans biofilm, studied the compatibility of tissue conditioners with denture cleansers, and makes suggestions for the chemical cleansing of dentures lined with tissue conditioners.

This pilot study describes responses of Sprague Dawley rats to mandibular retrusion. Lingually overcontoured crowns were cemented onto maxillary incisors to produce 3.5 mm of autoretrusion. Monitoring data indicate that activity was suppressed and nutritional intake was reduced. Histologic evaluation of the 2-, 4-, 7-, and 59 day test specimens detected only a monocytic infiltrate response in the 4-day group.

This study evaluated the clinical quality of 62 Empress restorations placed for 18 patients. Patients were evaluated for caries and fracture by two investigators at 7 and 26 months using the CDA quality evaluation criteria in addition to periodontal criteria. The results indicated a large number of excellent ratings for color and surface, but lower ratings for anatomic form and marginal integrity. The study is ongoing.

This in vitro study compared the microleakage of Class 5 amalgam restorations placed in extracted human teeth lined with a 4-META liner (Amalgambond), with similar restorations lined with copal varnish (Copalite). The restored teeth were stored in saline for 1 week, 6 months, and 1 year, then thermocycled, stained with 5% methylene blue, sectioned, and viewed using a light microscope. It was found that at 1 week and 6 months the 4-META group leaked significanlty less than the copal resin group, but after 1 year there was no significant difference between groups.

A longitudinal electromyographic study of the swallowing activity of the anterior temporal and masseter muscles was performed on 21 subjects with complete dentures. In six patients, the lip activity was recorded. At the pretreatment stage, when the patients had a residual anterior dentition, the peak mean voltages of the elevators showed low values (range 18 to 30 uV), and after denture placement, the anterior temporal muscles showed a further decrease. After denture relining, slight increases in temporal activity were noted at the 1-year stage. During the second year, when no corrections of the dentures were made, the temporal activity decreased below the pretreatment level. The masseter activity showed no significant changes during the 2-year observation period. The mandibular lip showed significantly stronger swallowing activity than the maxillary lip. The mean durations of the swallows were markedly longer than values reported for subjects with a complete natural dentition.

The resistance to staining of two low-fusing porcelains (Procera and Duceratin) for use with titanium and one conventional feldspathic porcelain (Vita VMK 68) were examined visually according to a protocol similar to the ADA Specification No. 69. The color deviation was also quantified using a colorimeter. Forty samples of each produce were prepared using manufacturer's instructions and the samples divided into two groups of 20. The samples of one group were immersed in methylene blue, and the control group in distilled water. Of the twenty samples frome ach group, ten were ground to remove the glaze. The color values for each sample were recorded prior to and after immersion in the staining medium. The color deviation value , E, for each sample was calculated. Visually discernible stain was present on tht unglazed samples of all three porcelain products immersed in methylene blue. No stain was visually detectable on the glazed samples or the unglazed samples immersed in distilled water for all three porcelain products. The objective evaluation confirmed that the unglazed porcelain of all three porcelain products had statistically higher color deviation after immersion in methylene blue.

This study assessed the antifungal activity of seven commercial mouthrinses against Candida albicans, the organism often found in denture wearers with denture stomatitis. Screening for efficacy of growth inhibition found that five mouthrinses inhibited the growth of fungi, and their maximum inhibitory dilution values and the fungicidal activity were then determined. Two mouthrinses containing cetylpyridinium chloride were shown to be most effective after determination of the maximum inhibitory dilution and the test of fungicidal activity.

This study was conducted to measure the changes of pressure distribution over time on the denture-bearing mucosal surface resulting from relining the intaglio surface of dentures with tissue conditioners. Pressure sensors of electrostatic capacitance variation were used to detect changes on three models of different residual mandibular ridge height. It is suggested that the shrinkage of tissue conditioners influences the dimensional accuracy of a dynamic impression technique.