Spectrometric analysis of the influence of metal substrates on the color of metal-ceramic restorations.

The development and use of ceramic alloys have created the potential for variation in the color of dental porcelain. In order to define the nature of the alterations, it is necessary to examine quantitatively the color of dental porcelain baked onto ceramic alloys. The purpose of this study was to examine spectrometrically where color differences occur in the fabrication process. One shade of Vita porcelain was baked onto coupons of three ceramic alloys (high gold, palladium-silver, base metal). Eight replications were made in each alloy at seven fabrication steps: prepared metal, oxide, first opaque, second opaque, first dentin, second dentin, and glaze. Spectrometric analyses were performed for each replication at each step. Data were tabulated every 10 nm over the recorded 380-750-nm range, for conversion to the CIE color measurement system. Tristimulus values X, Y, and Z and chromaticity coordinates x and y were calculated. Differences from spectrographic inspection were seen among the metal substrate series. The greatest variation appeared at the first dentin step between the palladium-silver and high-gold alloys and between the palladium-silver and base metal alloys. Mean tristimulus values were significantly different (p less than 0.0001) for all steps and alloys. The distribution of plotted values followed the same pattern of spectral changes throughout the seven fabrication steps. Analysis of these data shows that color differences of metal-ceramic coupons based on dissimilar metal substrates can be quantified, and that spectral reflectance values can be converted to CIE notation. As depicted spectrally, notable color differences appeared with the first dentin porcelain layer.

Dimensions of effective preclinical teaching.

The purpose of this study was to identify the factors underlying dental students' evaluations of preclinical instruction. Ninety sophomore students in academic year 1979-80 and 74 sophomore students in academic year 1980-81 rated five preclinical instructors in a fixed prosthodontic technique course. At the end of the course, prior to final examinations, students received a 24-item evaluation instrument designed to assess preclinical teaching behavior. All items were rated on a 5-point scale, with response options ranging from no agreement to strong agreement. Factor analytic techniques were used to identify common sources of variation among items. Results indicate that 22 of the 24 items correspond to two underlying, stable dimensions that summarize preclinical teaching effectiveness, teaching style, and orientation toward students. The discussion compares teaching effectiveness dimensions identified in dental education studies with dimensions identified in studies of college instruction.

Safety and efficacy of a novel nasal spray for maxillary dental anesthesia.

This study examines the efficacy, safety, and tolerability of a nasal spray to induce anesthesia of maxillary teeth. Forty-five healthy adults requiring restoration of one maxillary tooth were randomized in a 1:2 ratio to receive (1) an intra-oral lidocaine-epinephrine injection with buffered saline nasal spray bilaterally, or (2) a tetracaine hydrochloride-oxymetazoline hydrochloride nasal spray bilaterally with sham injection. Primary endpoints were use of rescue anesthesia and patient global pain assessment. Secondary outcomes included vital sign changes, soft-tissue anesthesia, and treatment-emergent adverse events. In intent-to-treat analysis, 25 of 30 patients given nasal spray (83.3%) did not require rescue anesthesia. Proportion of anesthesia successes for nasal spray was significantly different from the hypothesized placebo anesthesia success of 30% (one-sided p value < .0001 by exact binomial test). Mean duration of soft-tissue anesthesia did not differ significantly by treatment for 3 of 4 sites assessed. No serious adverse events or systemic effects were observed. Tetracaine hydrochloride-oxymetazoline nasal spray appears to provide adequate and safe anesthesia for the majority of maxillary dental procedures. Based on the results from this Phase 2 study, pivotal trials are warranted to validate these findings in an expanded patient population.

Influence of tooth contact on the path of condylar movements.

The correlation between condylar inclination and tooth guidance was tested by comparison of recordings of condylar movement in right and left parasagittal planes during lateral excursion, opening, and protrusive movements in 13 subjects with temporomandibular joint (TMJ) clicks and 15 subjects without TMJ clicks. The characteristic tracing of mandibular movements at the condyle with tooth-guided versus non-tooth-guided conditions were investigated by use of a computerized Axiograph graph. The generated tracings of each subject were graphed and analyzed to calculate the horizontal condylar inclinations as related to the axis orbital reference plane. Information from a standardized questionnaire provided evidence of a definite correlation between the presence of TMJ clicking and a specific prior medical event (tonsillectomy). The data from computerized tracings of all subjects revealed no significant difference (p 0.05) in the mean angles of condylar guidance at any of the millimeter intervals examined regardless of whether the craniomandibular contact was an articulation of natural teeth or an articulation of maxillary natural teeth against a tray clutch. These results do not suggest that dynamic interarch tooth guidance or the change in vertical dimension reflect a significant alteration in the recordings of condylar guidance in clicking or nonclicking groups.

Social and economic factors in prosthodontic practice and education.

Prosthodontics represents a highly developed body of knowledge and skill that spans multiple disciplines. Numerous studies can be cited that address biologic, mechanical, or materials science factors that influence decisions about patient care. On a daily basis as clinicians, teachers, or patients, we experience an interplay of social, economic, and psychologic conditions that similarly influence treatment decisions. This article explored a rationale for including a clear, explicit emphasis on knowledge and skill development for prosthodontic practice and education related to social, psychologic, and economic factors.

Spectrophotometric analysis of a nongreening, metal-fusing porcelain.

Spectrometric analysis has been used previously to examine color differences among various porcelains and metal ceramic systems. This study determined whether nongreening porcelain of a single shade fused to high-gold and palladium-silver alloys results in the same final color. Both conventional (VMK-68) and nongreening (VMK-68N) porcelains were fused to metal coupons of high gold (Will-Ceram Y) and palladium-silver (Will-Ceram W-1) to make up four groups. CIELAB colorimetric data were collected at each of seven fabrication steps to define color differences between steps for each alloy-porcelain group as well as between groups at each step. For the shade tested, perceptible color differences between high-gold/conventional porcelain and palladium-silver/nongreening porcelain coupons did not support manufacturers' claims.

Clinical discrimination between autoglazed and polished porcelain surfaces.

Precementation refinements of porcelain-fused-to-metal crowns often require reglazing or polishing of the porcelain surface. This study was done to determine whether visual inspection differences exist between glazed and polished porcelain surfaces. Prosthodontists, general dentists, and students (six in each group) rated esthetic properties of 12 porcelain-fused-to-metal crowns. All crowns were initially autoglazed. For phase 1 observations, six crowns were air abraded and polished and six retained their glazed surface. For phase 2 observations, the surface treatments were reversed. At both observations, crowns were rated on 5-point Likert scales for outline form, porosity, smoothness, reflectance, texture, dullness, defects, and general esthetic appearances. Phase 1 polished and glazed crowns had different means for outline form sharpness, porosity, reflectance, dullness, and general esthetic appearance. Phase 2 crowns were different for dullness. Polished and glazed crowns alike were more dull at phase 1 than at phase 2. Glazed crowns were different between phases for reflectance and general esthetic appearance. All reported differences were significant at p less than .01. Significant differences occurred among raters with polished and glazed crowns for several variables.

The relationship between condylar guidance and temporomandibular joint clicking.

The association between condylar inclination and temporomandibular joint (TMJ) clicking was tested by measuring the angles of condylar guidance in the sagittal plane during opening and closing movements in 12 subjects with temporomandibular joint clicks and 16 subjects without TMJ clicks. Each subject had tracings made by using a customized functional clutch. All subjects had full dentition and were without symptomatic mandibular dysfunction. Condylar inclinations were measured in parasagittal tracing planes. The travel path of the hinge axis of the condyle's movements was recorded, directly formed, and compared with a four-component axiograph recording that used the axis-orbital plane as a reference for the subjects. The measurements of angles along several distances (millimeters) of condylar guidance from the axis-orbital plane were obtained and evaluated. The measurements were made in the sagittal plane and through opening-closing movements starting from the actual occlusal vertical dimension of each subject. The results do not support the hypothesis that mean angles of the condylar guidance are significantly different in the group with TMJ clicking compared with the group without TMJ clicking.

Procedure for a simplified collarless metal-ceramic restoration using gold powder.

This technique describes a simple and practical approach to the fabrication of collarless metal-ceramic restorations. Instead of making a duplicate die from the master die, this technique conserves time by blocking out the undercut using impression modeling compound on the master die. The use of gold powder does not require special equipment and produces a precise porcelain abutted margin on the shoulder. Excluding the labial gold collar from the shoulder enhances the esthetic appearance of the restoration. This approach is effective with gold-based and silver-palladium alloys as materials for the metal-ceramic framework. The marginal fit of 10 collarless meta-ceramic crowns cemented on silver plated dies were evaluated by measuring sectioned specimens with a scanning electron microscope. The average gap at the porcelain butt margin was observed to be 30 to 50 mu (Fig. 10).