Effect of pH on element release from dental casting alloys

Statement of problem. Dental casting alloys are subjected to transient acidity in the oral environment, yet most studies have not investigated the effects of these transient environments on elemental release from alloys. Elemental release is important because it plays a significant role in alloy biocompatibility. Purpose. It was hypothesized that acidic environments would increase elemental release from dental alloys during exposure and after the acidic environment was removed. This hypothesis was based on the known increase in release of nickel from nickel-based alloys in an acidic environment. Material and methods. High-noble, noble, and base metal casting alloys were exposed for 30 minutes to solutions with pH ranging from 1 to 7. Elemental release of representative elements was measured by means of atomic absorption spectrometry during the exposure and in the week after the exposure. This release was compared with elemental release in the week before the exposure. Results. High-noble and noble alloys were resistant to acidic environments. A pH of 4 did not increase elemental release during or after exposure. A pH 1 environment slightly elevated release of Ag, Cu, and Pd in some alloys. However, a Ni-based alloy released large amounts of Ni during the acidic exposure of pH 1 or 4, and more importantly, in the week after the exposure as well. Increased time of exposure to acid did not alter elemental release from noble or high-noble alloys, but markedly increased release from the Ni-based alloy. Conclusions. Transient exposure of casting alloys to an acidic oral environment is likely to significantly increase elemental release from Ni-based alloys, but not from high-noble or noble alloys. (J Prosthet Dent 1998;80:691-8.)     

Porcelain-Fused-to-Metal Pontics for Improved Removable Partial Denture Esthetics

A removable partial denture fabrication technique that uses custom-constructed porcelain fused-to-metal (PFM) pontics is described. PFM pontics enhance the dentist's shade matching effort in esthetically demanding situations.     

Cephalometric errors: A comparison between repeat measurements and retaken radiographs

This study compares landmark location errors in cephalometric radiography (when re-measuring radiographs) and radiographic errors (when retaking the radiograph). The samples comprised 32 remeasured and re-digitized radiographs and a further series of 22 retaken radiographs drawn from the same overall sample of 12-year-old Chinese children in Hong Kong. All radiographs were recorded in natural head posture with the lips in light contact. The relative size of the errors were assessed by calculating the 'error percentage' for both selected dento-skeletal and soft tissue profile measures. It is suggested that this index is clinically more meaningful than the usually used 'method error'. It expresses the variance of the method error (me2) as a percentage of the variance of the measurement under study (standard deviation2). This error percentage was found to be doubled, on average, for measurements on the retaken radiographs. In general, measures with most landmarks in the mid-sagittal plane showed the least increase in percentage error. The results suggest that errors arising from retaking cephalometric radiographs may effectively be greater than those usually reported. The Frankfort plane, the functional occlusal plane and the incisor long axes displayed poor reproducibility. For the soft tissues the lips served as poor angular landmarks and relatively acute angles with short 'arms' also displayed large errors.     

One clinical visit for a multiple implant restoration master cast fabrication

The making of a one-piece, long-span, implant-supported prosthesis with conventional procedures frequently has difficulties associated with the accuracy of fit. This article presents a clinical and laboratory procedure for making an accurate implant working cast that facilitates fabrication of the casting on the master cast. The procedure demonstrates the process of sectioning and rejoining of the resin between the transfer copings and then pouring the impression by first joining the analogs alone with impression plaster, sectioning it, and rejoining it again to stabilize the analogs, and finally, using dental stone to pour the impression. Clinical, radiographic, and laboratory (optical microscope) measurements for one clinical implant restoration confirm the accuracy of fit of this one prosthesis made with this procedure. Its advantage is that it can allow fabrication of the final casting on the cast, thereby eliminating the clinical time necessary to obtain repetitive solder indexes, and thus minimizing inconvenience to the patient. (J Prosthet Dent 1997;78:550-3.)     

Surface Quality and Long-term Dimensional Stability of Current Elastomeric Impression Materials after Disinfection

PURPOSE: The objectives of this investigation were to evaluate the effect of disinfection on surface quality and dimensional stability of more recent, reformulated vinylpolysiloxane (VPS) and polyether (PE) materials. METHODS: Using ANSI/American Dental Association (ADA) specification 19 protocols, 50 impressions of stainless steel dies were made with each material. Ten impressions of each material were randomly assigned to a treatment group: (1) no disinfectant; (2) 10-minute dual phenol immersion; (3) 1-hour dual phenol; (4) 10-minute sodium hypochlorite (NaOCl); and (5) 1-hour NaOCl. Impression surface quality immediately after disinfection was categorized as smooth/shiny, matte, or wrinkled/sticky. Dimensional stability was evaluated by measuring dimensional accuracy according to specification 19 after 24-hour, 1-week, and 2-week storage at ambient laboratory conditions. RESULTS: The PE material surface quality was significantly affected (Pearson Chi-square, p相似文献   

Comparison of Dentists'' Treatment and Management of Normal and Handicapped Patients

Forty-eight of 120 dentists (40%) responded to a survey using a two-questionnaire time-series design. Responding dentists with a median age of 36 years and 9.5 years in practice had received education in care of the handicapped mainly in dental school (42%) and continuing education (40%). They were asked to make the same treatment and practice management decisions for both normal and handicapped patients. No significant differences were found between normal and handicapped patients in the amount of time dentists spend on diagnosis, treatment, planning, or recall (p less than 0.05). For both normal and handicapped patients, the dentists as a group always chose the same option as treatment of choice for both normal and handicapped patients most frequently from a list of treatment or management options. Individual dentist consistency between normal and handicapped patients in treatment and management was good, with four out of five dentists choosing the same first treatment of choice for both normal and handicapped patients for similar circumstances. Only about one out of six dentists maintained a consistent priority sequence for both normal and handicapped patients when asked to rank a list of four or five possible treatment or management choices.     

A comparative analysis of the accuracy of implant transfer techniques

Four different implant transfer techniques using two master cast systems (solid cast and Zeiser system) were evaluated and compared with respect to the accuracy with which abutment positions were reproduced. A stainless steel experimental analogue with two anterior and two posterior fixtures and abutments was fabricated. Polyether impressions (14 each) were made by use of four techniques, (I) nonsplinted, (II) splinted with dental floss and acrylic resin, (III) splinted with orthodontic wire and acrylic resin, and (IV) splinted with acrylic resin alone. The fourteen impressions of each technique were divided into two equal groups: group 1, solid cast system, and group 2, Zeiser system. The abutments of each master cast were measured vertically and horizontally with a profile projector. Statistical analysis indicated no significant difference between the splinted and nonsplinted techniques. The Zeiser system provided more accurate interabutment relationships for the posterior region than the solid cast system.