Fabricating Low-Fusing Metal Casts for More Accurate Implant Prosthodontics

An important factor that affects the clinical success of dental implants is the way stresses are transferred to the bone via the implant framework and fixture. An ill-fitting implant framework will contribute to these stresses and may result in catastrophic failure of the prosthesis or one of the components and/or fixtures, in addition to possible alveolar bone loss. Many factors may contribute to the difficulty of achieving a passive fit on a complete-arch implant framework. A technique for producing an accurate master cast by using a low-fusing metal is described. The low-fusing metal is dimensionally more accurate than conventional gypsum products. The technique does not require a significant change from conventional chairside and laboratory procedures for complete-arch master cast impressions, and should result in a more passively fitting framework.     

Accuracy and pourability of gypsum preweighed packages

PURPOSE: The purpose of this study was to determine the amount of gypsum provided by the manufacturers in their preweighed packages and to determine the amount of gypsum dispensed from the packages as a function of the method used. MATERIALS AND METHODS: One hundred twenty unopened packages from 8 manufacturers were weighed. Ten packages from each manufacturer were opened with the contents completely removed by tapping the packages, and the contents were weighed (thorough method). The other 5 packages from each manufacturer were opened, quickly poured, and the contents weighed (quick method). All packages were then slit open on all sides and completely cleaned. The cleaned packages were then weighed. Calculations were made to determine (1) the amount of gypsum that was "supplied" by the manufacturer and (2) the amount removed from the packages using the "quick" and "thorough" methods. The raw data was normalized to percentage of stated weight. A Welch analysis of variance was used to evaluate the heteroscedastic data at a 95% confidence level. Thereafter, a post hoc Student t test was used to determine if the percentages of stated weight for (1) supplied, (2) thorough, and (3) quick were significantly different from 100%. RESULTS: A statistically significant difference was found for the amount of gypsum supplied by the manufacturers (p <.001) and the amount of material removed from the packages via the 2 different methods used (p <.001). Seven of the 8 manufacturers' preweighed packages were remarkably close to their stated weight for amounts "supplied" and the "thorough" method. High standard deviations from the mean were found for the "quick" method of gypsum removal. CONCLUSION: Within the limits of this study, results indicate that the use of a "thorough" method to remove gypsum from preweighed packages was important. Ideally, gypsum supplied in preweighed packages should be weighed initially to ensure an optimal water/powder ratio.     

An attractive solution to unerupted teeth

A user- and patient-friendly method of treating unerupted teeth is described. A neodymium iron boron magnet is attached to the unerupted tooth, and a second, larger magnet is incorporated in a removable appliance. The resulting forces provide a friction-free system, requiring little or no adjustment, which rapidly encourages the unerupted tooth into a position in which it may be bonded and thereby aligned by more conventional methods.     

Aetiology and diagnosis of clinically evident jaw trismus

Trismus is a common problem presenting to the dental practitioner. It is usually of a benign nature; however a number of types can have serious implications. This review outlines the aetiology and diagnosis of clinically evident jaw trismus.     

Evaluation of the pH of a new carbonated soft drink beverage: An in vivo investigation

PURPOSE: Recently, a modified version of a successful soft drink has been developed that aims to reduce the potential for dental erosion in consumers. The aim of this investigation was to compare the effect of the modified and original formula soft drink on the pH at various tooth surfaces during and after ingestion in subjects without erosion. MATERIALS AND METHODS: Fifteen subjects (10 female and 5 male) without dental erosion drank both a modified and an unmodified beverage for over 5 minutes in a randomized order. Oral pH was measured with antimony electrodes positioned on the labial and palatal surfaces of an incisor and premolar and held in place by a close-fitting vacuum-formed appliance. The results were compared (using the Wilcoxon signed rank test, with matched pairs) for the percentage and total time that pH fell below 4, 5, and 5.5. RESULTS: The percentage and total time that pH fell below 4 was significantly different between the drinks (P <0.02), but the total time that pH fell below 5 and 5.5 was not. The time taken for subjects to return to pre-exposure pH levels in the mouth showed considerable variation between individuals. CONCLUSIONS: The modified-formula drink appeared to have less erosive potential than the original formula when assessed by measuring pH at the tooth surface. Although the erosive potential has been reduced by modifying the soft drink, it has not been eliminated.     

The Wetting of Surface-Treated Silicone Impression Materials by Gypsum Mixes Containing Disinfectants and Modifiers

PURPOSE: This work evaluated wettability of silicone impression surfaces by gypsum mixes containing disinfectants. MATERIALS AND METHODS: Two types of dental stone were modified by mixing with aqueous solutions of either sodium hypochlorite or povidone iodine. These materials were subjected to further modification by adding a mixture of 1% gum arabic and 0.132% calcium hydroxide to reduce the water requirement of the hemihydrate. Mix consistency tests were carried out to determine the effect of the disinfectants and the modifying additives on the mix fluidity. Contact angles of the mixed materials were measured when they were poured against a polyvinylsiloxane impression material that had undergone the following treatments (1) no treatment (control), (2) surfactant treated, (3) disinfectant treated, and (4) treated with both surfactant and disinfectant. One-way analysis of variance (ANOVA) was carried out using Dunnett's method to determine if experimental groups were significantly different from the control. RESULTS: Gypsum mix consistency was reduced by the presence of combined gum arabic and calcium hydroxide additives. Contact angle data showed that the additives and disinfectants incorporated into the gypsum had, in general, no beneficial effect on the wetting of an untreated silicone surface, or a surface treated with surfactant. In some instances, better wetting was obtained with disinfectant-treated surfaces, and surfaces that had been disinfected and treated with surfactant. CONCLUSIONS: Fluidity of the mixed gypsum was affected by the modifying additives. Chemical disinfectants incorporated in gypsum have little effect on the wetting behavior of dental gypsum. Modifying dental stone powders with gum arabic and calcium hydroxide additives (before mixing at the manufacturers' recommended liquid/powder ratios), improved the wetting behavior of the mixed materials in some cases, but results were not consistent.     

The evolution of chewing: A dentist''s view of palaeontology

The vast majority of animals have dentitions in which the upper and lower teeth cannot be occluded. Only in mammals are the teeth used to process, as opposed merely to collect, food. The evolution of this processing of food by teeth is considered, together with the ways in which teeth work. These considerations suggest that artificial molar teeth could usefully be constructed of two substances of different hardness.     

Ectopic eruption of transposed mandibular permanent lateral incisors beneath primary first molars. Case report

Mandibular permanent lateral incisors showing bilateral transposition and ectopic eruption were seen beneath primary first molars on bitewing radiographs in a female aged 9 years. This report chronicles management of the case during the mixed dentition period. Appropriate space maintenance after extraction of mandibular primary first molars, cuspids and lateral incisors on both sides facilitated eruption and repositioning of the permanent lateral incisors without the need to sever supracrestal gingival fibres.     

The use of role-play and psychodrama in the education of the dental undergraduate

The delivery of effective information flow through self learning, critical thinking and problem solving is one of the objectives of current curriculum development within the Dental Faculty of the University of Hong Kong. These objectives reflect a desire to encourage skills related to 'comprehension learning' and 'meaning orientation' rather than 'rote' learning and 'surface' approaches. This paper explains the way in which role-play and psychodrama are used in an effort to achieve these objectives.