Showing papers in "Journal of Prosthodontics in 1999"

Classification system for complete edentulism

Abstract: The American College of Prosthodontists has developed a classification system for complete edentulism based on diagnostic findings. These guidelines may help practitioners determine appropriate treatments for their patients. Four categories are defined, ranging from Class I to Class IV, with Class I representing an uncomplicated clinical situation and a Class IV patient representing the most complex and higher-risk situation. Each class is differentiated by specific diagnostic criteria. This system is designed for use by dental professionals who are involved in the diagnosis of patients requiring treatment for complete edentulism. Potential benefits of the system include: 1) better patient care, 2) improved professional communication, 3) more appropriate insurance reimbursement, 4) a better screening tool to assist dental school admission clinics, and 5) standardized criteria for outcomes assessment.

Dental implant materials: commercially pure titanium and titanium alloys.

Abstract: Manufacturers use six different titanium-based biomaterials to fabricate dental implants. Each of these materials, including four grades of commercially pure titanium and two titanium alloys, has distinct mechanical and physical properties. Clinicians should recognize these differences for optimal treatment planning and patient care.

Flexural Properties and Surface Finishing of Acetal Resin Denture Clasps

Abstract: Purpose: This study examined flexural properties of acetal resin to determine the appropriate design for an acetal resin removable partial denture clasp. The effectiveness of various acetal resin polishing procedures was also evaluated using scanning electron microscopy. Materials and Methods: Loads of up to 1,500 g were applied to cylindrical acetal resin specimen lengths of 5, 10, and 15 mm, and the degree of deflection of the specimen tip was measured. Specimens were 2 mm and 1.5 mm in diameter with a round cross-section (R2 and R1.5, respectively), as well as 2 mm in diameter and half-round in cross-section. Half-round specimens were loaded with their flat surface vertical and then horizontal (HRV and HRH, respectively). Contour plots showing load and deflection for varying lengths of resin were developed for each cross-sectional type based on specimen length, and the stiffness was calculated. Additional acetal resin specimens underwent polishing techniques including tungsten carbide burs, aluminium oxide stones, abrasive impregnated rubber points, and "Polish-D." Polished specimens were examined with scanning electron microscopy to compare surface roughness. Results: For the 5-mm-length specimens, the median stiffness values decreased in the following order: R2 > HRV > HRH > R1.5. The median stiffness values for the 10-mm and 15-mm lengths followed a similar trend. At each length, the R2 specimen was generally at least twice as stiff as other designs. Regarding polishing, the smoothest surface was seen on the specimen that was polished with the rubber point followed by "Polish-D." Conclusions: To have stiffness similar to a cast cobalt-chromium clasp 15 mm long and 1 mm in diameter, a suitable acetal resin clasp must be shorter (approximately 5 mm) with greater cross-sectional diameter (approximately 1.4 mm). To obtain a smooth surface, the acetal resin clasp should be polished with a rubber point followed by a material such as "Polish-D." Copyright © 1999 by The American College of Prosthodontists.

Current methods of finish-line exposure by practicing prosthodontists.

Abstract: Purpose The purpose of this study was to survey members of The American College of Prosthodontists to evaluate current methods of finish-line exposure. In addition, frequency of use of epinephrine compounds and observed side effects were assessed. Materials and Methods A questionnaire was mailed to the 2,436 members of The American College of Prosthodontists. Group differences were evaluated using x2 analysis. Results Completed questionnaires were returned by 1,246 prosthodontists, which is a return rate of 51%. Ninety-eight percent of respondent prosthodontists use retraction cord, and 48% use a double-cord technique. Plain cord is the most commonly used cord (44%), followed by aluminum chloride-impregnated cord (18%), and epinephrine-impregnated cord (14%). Nine hundred one respondents (81%) soak the cord before placing it in the gingival sulcus. The most common medicament for soaking the cords is buffered aluminum chloride (55%). Side effects to epinephrine were reported by 387 respondents (33%), with the most common side effect reported being increased pulse rate, followed by anxiety. Approximately one quarter (24%) of the prosthodontists surveyed had observed side effects to chemical agents other than epinephrine. Conclusions Prosthodontists throughout the country use many different techniques and agents to expose finish lines. No statistically significant differences (p > .05) were found between year of specialty training completion groups with respect to retraction cord use. Copper bands are used significantly more frequently (p < .05) in the northwest region of the United States than elsewhere.

Dental cutting with diamond burs: heavy-handed or light-touch?

Abstract: Purpose The cutting efficiency of diamond dental burs using different handpiece loads was evaluated against simulated enamel, a machinable glass ceramic (Macor). Materials and Methods An ultra-high-speed dental handpiece was mounted in a frictionless bearing so that the pressure applied at the contact interface between the dental bur and the cutting substrate was controlled. One type of coarse- and two types of medium-grit diamond burs were studied. Handpiece loads of 44,91.5, and 183 g were applied at the bur/Macor interface, and cutting efficiency was determined as the amount of Macor removed in ten 30-second-duration cuts that were 4 mm in length. The data were analyzed by one-way ANOVA and a post-hoc Scheffe test at an a priori α= 0.05. Results Cutting efficiency depended on both the diamond grit of the bur and the load applied to the handpiece. Conclusion The pressure used by most dentists, about 100 g at the bur tip, appears to be optimal for medium-grit burs. If the pressure applied to the handpiece is markedly increased, there was no increase in cutting efficiency for medium-grit burs. In contrast, an increased handpiece pressure raises the cutting efficiency of coarse-grit burs but the effect of this enhanced rate of cutting on the pulpal tissues is uncertain. Cutting efficiency also appeared to be dependent on debris accumulation between the diamond chips.

Distortion of Three-Unit Implant Frameworks During Casting, Soldering, and Simulated Porcelain Firings

Abstract: PURPOSE: The aim of this study was to assess distortion inherent in casting, soldering, and simulated porcelain firings of screw-retained, implant-supported three-unit fixed partial dentures (FPDs). MATERIALS AND METHODS: Ten wax patterns were fabricated on a die-stone cast containing two implants, 20 mm apart from center to center. Five specimens were cast in a high-palladium alloy, exposed to simulated porcelain firings, sectioned, and then soldered with low-fusing solder. Five specimens were cast, sectioned, soldered with high-fusing solder, and then exposed to simulated porcelain firings. For each specimen, two horizontal and six vertical distances between appropriately scribed reference points were measured with a traveling microscope. Comparisons were made among the various measurements taken after wax-pattern fabrication, casting, high- and low-fusing soldering, and each porcelain firing. Data were analyzed using a repeated-measures factorial ANOVA (alpha = 0.05). RESULTS: Significant difference was detected in the amount of horizontal distortion during casting (53 +/- 24 microns) and high-fusing soldering (-49 +/- 50 microns), as well as in the amount of horizontal distortion during high-fusing soldering (-49 +/- 50 microns) and low-fusing soldering (17 +/- 26 microns). However, no clinically significant difference was found in the amount of horizontal distortion during casting, low-fusing, and high-fusing soldering. The greatest amount of distortion during the simulated porcelain firings took place during the oxidizing cycle. CONCLUSIONS: Soldering did not improve the casting misfit of a three-unit implant-retained FPD model. Metal-ceramic implant frameworks should be oxidized before intraoral fit evaluation.

Effective taper criterion for the full veneer crown preparation in preclinical prosthodontics.

Abstract: PURPOSE: Effective taper criteria must define a realistic, measurable goal that the student can visualize and achieve. Six degrees is widely accepted as the taper criterion for the full veneer crown preparation. However, studies show the actual taper of most preparations to be greater than 12 degrees. The purpose of this study was to determine whether 12 degrees is an effective taper criterion for the full veneer crown preparation in preclinical prosthodontics instruction. MATERIALS AND METHODS: A group of 191 full veneer crown preparations with 6 degrees as the taper criterion, and a group of 130 full veneer crown preparations with 12 degrees as the taper criterion were evaluated. All preparations were accomplished by preclinical dental students working on typodonts under examination conditions. RESULTS: The overall mean taper for each group exceeded the targeted criterion. The overall mean taper for the 6 degrees group was 14,490. When 12 degrees was the criterion, the overall mean taper was 15,580. The t test results indicate significant differences (p < .0001) between the targeted criterion and the actual preparation mean taper in all samples except one: the faciolingual measurements in the 12 degrees group. The faciolingual measurement of 12,920 was not statistically significantly different (.0542) from the targeted criterion of 12 degrees. CONCLUSION: The use of a 12 degrees taper criterion did not result in preclinical students achieving the goal of a 12 degrees taper. However, a 12 degrees criterion is more realistic than a 6 degrees criterion for full veneer crown preparations.

The Esthetic Width in Fixed Prosthodontics

Abstract: With the evolution of adhesive dentistry and the increasing use of porcelain veneers, single-unit crowns generally are restricted to the replacement of pre-existing full-coverage crowns and the restoration of nonvital and/or severely damaged teeth. Porcelain-fused-to-metal restorations are still widely used to generate single-unit crowns and fixed partial dentures. Collarless metal-ceramic restorations represent the most successful evolution among efforts to meet maximum esthetic requirements using porcelain-fused-to-metal restorations. Extended metal frameworks and opaque aluminous ceramic cores are associated with unpleasant optical effects in the soft tissues surrounding such restorations. This problem is particularly evident in the presence of the upper lip, which can generate an "umbrella effect" characterized by gray marginal gingivae and dark interdental papillae. Based on the concept of the biologic width, a systematic approach is proposed for the elaboration of an "esthetic width," including: 1) positioning of preparation margins; 2) reduction of the metal framework; and (c) appropriate marginal design of porcelain-fused-to-metal restorations. Strategic features of pontics and a specific interdental design are suggested to compensate for deficient anatomical features of the soft tissue and the edentulous ridge.

A technique for border molding edentulous impressions using vinyl polysiloxane material.

Abstract: A technique for making selective tissue placement final impressions for complete dentures using vinyl polysiloxane and custom trays with peripheral relief is presented. This technique is an alternative to the conventional method of border molding using modeling plastic impression compound.

Vertical Height Loss: An Investigation of Four Restorative Materials Opposing Enamel

Abstract: Purpose The objective of this in vitro investigation was to compare the vertical wear produced by cone-shaped styli of three ceramic restorative materials and a Type III gold alloy opposing flattened human enamel. Vertical wear was measured as enamel height loss, material stylus height loss, and total vertical height loss (the sum of the enamel height loss and the restorative material height loss). Materials and Methods Ten cone-shaped styli were fabricated from each of four restorative materials, which included two machined ceramics, a pressed ceramic, and a Type III gold alloy. To maintain the standardized shape, styli were not polished or glazed. Specimens were subjected to wear in the presence of water for 100,000 cycles at 1.2 Hz under a load of 75 N using a wear simulation device. Enamel wear was evaluated by profilometry, and stylus wear was evaluated by computer imaging. Vertical wear was reported as enamel height loss, material stylus height loss, and total vertical height loss (the sum of the enamel height loss and material height loss). Data were compared using one-way analysis of variance and Scheffe's analysis (α= 0.05). Results Significant differences existed among materials based on material height loss (p= .0001), enamel height loss (p= .0001), and total vertical height loss (p= .0118). No significant difference among the three ceramics was found in mean total height loss, which ranged from 0.280 to 0.305 mm. However, the Type III gold exhibited less mean total wear (0.231 ± 0.082) than the pressed and one machineable ceramic. This machined ceramic exhibited the most material height loss (0.249 ± 0.044 mm). With the other ceramics, mean enamel wear was significantly more (0.211 and 0.216 mm, respectively). Conclusions During wear simulation, pressed or machineable ceramics opposing flattened enamel exhibited a similar degree of total vertical height loss. One machined ceramic material wore significantly more than the other materials. The other machineable ceramic and the pressed ceramic wore the opposing enamel significantly more.

Reinforcement of denture base resin with glass fillers.

Abstract: Purpose This study evaluated the effect of short glass fibers on the transverse strength of a heat-polymerized acrylic resin denture base material. Materials and Methods Four groups of specimens (n = 10) were fabricated according to the ISO standard for the transverse strength test. E-glass fibers were triturated to produce short fibers of different lengths. Specimens for Group 1 (control) were made of unfilled polymethylmethacrylate (PMMA). For group 2, the PMMA powder was modified with 0.1 g of dry glass fibers. For group 3, the PMMA powder was modified with 0.1 g of silanized glass fibers. For group 4, the PMMA powder was modified with 0.2 g of silanized glass fibers. A three-point loading test was used to determine the transverse strength of the tested specimens. The fracture surface of each specimen was evaluated using SEM. Results The addition of untreated glass fibers increased the transverse strength by 11% but produced some porosity in the polymeric matrix. The addition of silane-treated glass fibers increased the transverse strength of PMMA by 28% for group 3 and by 26% for group 4, and produced a dense structure for the polymer-fiber composite. Conclusion The transverse strength of PMMA can be slightly increased by the addition of short glass fibers.

Oral rehabilitation of a child with primary failure of tooth eruption.

Abstract: This article describes the prosthetic evaluation and treatment of a 10-year-old female patient with primary failure of tooth eruption. This case is unique in that the failure of eruption affected both the deciduous and permanent dentition in all quadrants, in the absence of any other systemic abnormalities. After diagnostic articulation and a thorough discussion of the treatment with the patient and her parents, complete maxillary and mandibular overdentures were fabricated. The process followed with this preadolescent patient to ensure maximum compliance, success, and encouragement toward a positive attitude in wearing complete dentures is reported.

Evaluation of a Computer‐Aided Learning Program in Removable Partial Denture Framework Designing

Abstract: Assessment of a computer-assisted learning (CAL) program dealing with designing removable partial dentures was performed as both formative and summative evaluation. Formative evaluation was obtained through open-ended questions in a written questionnaire administered to 60 junior students from two Australian Dental Schools and through observation of four groups of these students as they worked through the program. Formative evaluation, fundamental to completion of the program, led to several changes and additions. Observation of the students using the program during its final stages of development was one of the most informative and helpful parts of the evaluation. It allowed nuances of expression and body language to be noted that would not have been apparent in written or numerical data. Summative evaluation was obtained through structured questions in the questionnaire and through a post-CAL test under examination conditions. Summative assessment showed that students could attain a desired standard of knowledge if a lecture series was replaced by the CAL program; that the program was user-friendly, even for students with little or no computer experience; and that most students considered it to be a useful learning resource. More than half the students were concerned about using CAL to replace human instruction. It is significant that students were particularly impressed by aspects of the program that could not be duplicated by a book; the interactive nature of the learning process and the ability to rotate the diagnostic casts. This highlights the need for CAL programs to use the full potential of computer capability, rather than merely replicate a textbook on a screen.

Effect of toothbrushing on elemental release from dental casting alloys.

Abstract: Purpose This study assessed the effect of toothbrushing on the elemental release from common dental casting alloys. Materials and Methods A Au-Pt high-noble alloy, a Au-Pd high-noble alloy, a Pd-Cu-Ga noble alloy, and a Ni-Cr base-metal alloy were placed into a biological medium for 1 week to allow equilibration of elemental release, then brushed for 30 minutes at 90 strokes/min under 200 g of force with a soft toothbrush. The brushing was performed in neutral saline or lactic acid at pH 4 with or without toothpaste. The alloys were then transferred back into a biological medium for 1 week. Atomic absorption spectroscopy was used to measure the mass lost from each alloy during and in the week after brushing. Mass loss was expressed as micrograms per square centimeter of alloy surface, and the various brushing conditions were compared by analysis of variance and Tukey multiple comparison intervals (α= 0.05). Results During brushing, element release increased significantly over nonbrushed controls for all alloys except the Ni-Cr. Toothpastes, acidic solutions, or combinations of these conditions with toothbrushing further enhanced elemental release, but Ni release from the Ni-Cr alloy increased the most (30-fold). In the week after brushing, brushing alone increased elemental release only from the Ni-Cr alloy. However, toothpastes and acidic solutions increased elemental release for all alloys significantly, except for the Au-Pd alloy. In general, elemental release during brushing was far greater than in the week after brushing. Conclusions Under the conditions of this study, toothbrushing increased the elemental release from dental casting alloys.

Compressive and tensile zones in the cement interface of full crowns: a technical note on the concept of resistance.

Abstract: Purpose The objectives of the study were: 1) to map the stresses acting on the cement interface of crown and abutment analogs during loading; and 2) to provide a theoretical basis for the hypothesis that resistance to lateral dislodgment is a function of the distribution of compressive force vectors acting on the cement lute. Materials and Methods Three-dimensional finite element (FE) meshes of crown and abutment analogs were constructed and loaded in a direction perpendicular to the axes of symmetry of the abutments. Three parameters were investigated: taper (10° and 20° of convergence), abutment substrate (Ni-Cr alloy and dentin), and type of cement (zinc oxide eugenol, zinc phosphate, glass ionomer, and composite resin). The tensile and compressive components of the resulting force systems were plotted along two axes (z: parallel to the axis of symmetry of the crown/abutment complex; and y: perpendicular to z, ie, parallel to the direction of loading). Von Mises stresses were also generated. Results First, it was shown that the restoration's axis of rotation was located inside the abutment cone and was perpendicular to and intersected the axis of symmetry of the crown/abutment complex. Second, stress distribution was dependent on the three parameters investigated. Varying taper led to shifts due mainly to alterations in specimen geometry, whereas the abutment substrate and the cement type had a bearing on the level of the axis of rotation. The smaller the modulus of elasticity of the abutment substrate or the cement lute, the farther apical the location of the axis of rotation. Conclusions Conventional schemes for explaining crown dislodgment in which the restoration rotates around an axis located at the preparation margin should be reassessed. The results of the FE analysis are compatible with the hypothesis that resistance to lateral dislodgment is a function of the distribution of compressive force vectors acting on the cement interface.

Comparison of sectioning rates among carbide and diamond burs using three casting alloys.

Abstract: Purpose This study compared the sectioning rates of commercially available high noble, noble, and base metal casting alloys using two new cross-cut tungsten carbides specifically manufactured for alloy sectioning and two medium grit diamond burs. Materials and Methods Rectangular bars cast from a base metal alloy (Ni-Cr-Mo-Be), a noble alloy (Pd-Cu-Au), and a high noble alloy (Au-Ag-Cu-Pd) were sectioned under controlled conditions. Two types of cross-cut tungsten carbide and two types of medium grit diamond burs were tested using a high-speed handpiece under a coolant flow rate of 20 mL/min and an applied load at the bur tip of 0.9 N (91.5 g). Three 4-mm cuts were made through the alloy specimens using six burs of each type. The time required for Cuts 1, 2, and 3 was recorded, and sectioning rates in millimeters per minute were calculated as a relative measure of cutting efficiency. For each alloy, the total time required for the three cuts was analyzed using one-way analysis of variance (one-way ANOVA) and Scheffe tests (α= 0.05) to determine differences in sectioning rate among bur types. Results In general, mean sectioning rate for Cut 1 through Cut 3 decreased with longer use of the bur. Regarding total sectioning times, the carbide burs sectioned the base metal alloy significantly faster (P < .001) than the diamond burs. However, diamond burs sectioned the high noble alloy significantly faster (P < .001) than the carbide burs. Diamond burs also sectioned the noble alloy more quickly than the carbide burs, but the difference was not statistically significant. Conclusions The cross-cut tungsten carbide burs should be used to section the base metal alloy but the medium grit diamond burs should be used to section the high noble alloy.

Fabrication of complete denture bases reinforced with polyethylene woven fabric.

Abstract: Incorporation of 5 layers of woven, high-modulus polyethylene fiber into acrylic resin denture bases produces substantial improvements in mechanical properties and dimensional changes. A modified split-pack technique has been developed using conventional dental-laboratory compression molding to accommodate multiple layers of woven fabric in complete denture bases. A recess formed in the resin by a spacer allows the reinforcement to be embedded in the denture base without exposing the fibers. Embedded fibers do not compromise the esthetics of complete dentures.

Dental burs--what bur for which application? A survey of dental schools

Abstract: Purpose The purpose of this study was to survey North American dental schools regarding recommendations for rotary instrumentation for fixed prosthodontic and operative procedures at the predoctoral and postgraduate level. Materials and Methods A 25-question survey was sent to 64 North American dental schools, of which 15 questions specifically related to rotary instrument recommendations. One questionnaire was addressed to the individual at each school having administrative responsibility for teaching tooth preparation techniques. A high response rate was assured by follow-up telephone calls and faxes. The distributions of bur recommendations for both predoctoral and advanced prosthodontic programs were analyzed by chi-squared tests at an a priori α= 0.05. Results Completed surveys were received from 58 of 64 dental schools, a response rate >90%. Medium grit burs predominate in predoctoral education for gross tooth reduction for fixed prosthodontics, whereas coarse grit burs predominate at the graduate level (p .05) and were principally tungsten carbide (WC) burs. Carbide burs are the instrument of choice for internal walls, but the WC bur alone or in combination with diamond burs is preferred for refining composite margins (p < .05). Conclusions There is a broad consensus within North American dental schools on rotary instrumentation used by dental students. There is a greater use of coarser grit burs for gross tooth reduction in fixed prosthodontics at the postgraduate than predoctoral level.

Physical‐Property Comparison of a Chairside‐ or Laboratory‐Polymerized Permanent Soft‐Liner During 1 Year

Abstract: PURPOSE This investigation examined the influence of polymerization mode and water storage duration on the Shore A hardness, water sorption, resin solubility, and glass transition temperature of Permasoft, a commercial soft denture liner that is polymerized either chairside or in the laboratory. MATERIALS AND METHODS Specimen disks (31-mm diameter x 10 mm thick) and bars (44 x 8.5 x 1.2 mm) were polymerized following manufacturer's recommendations. The chairside polymerization process was simulated by pouring the mixed components into a mold and processing at 70 degrees C for 15 minutes under 2-psi pressure. Laboratory-polymerized specimens of the same dimensions were fabricated by processing under 500-psi pressure at 100 degrees C for 45 minutes. Specimens were stored in distilled water at 37 degrees C for 1, 7, and 30 days, and 6 and 12 months. Specimens were tested for Shore A hardness, water sorption, resin solubility, and glass transition temperature after the prescribed interval. To determine the effects of polymerization mode and storage time on material properties, a repeated-measures ANOVA (hardness data) and a two-way ANOVA (sorption and solubility data) with appropriate post-hoc tests were used. RESULTS Shore A hardness values increased from a low of 9.4 (+/- 0.5) units immediately after fabrication to a maximum of 15.9 (+/- 1.1) units after 1 year. Mode of polymerization did not influence hardness (p = .9851). Water-sorption values ranged from 4.2 (+/- 0.2%) of dry weight to 14.7 (+/- 2.5%) after 1 year. Resin solubility varied from 10.3 (+/- 0.6%) of preimmersion weight to 15.4 (+/- 1.1%), and immersion duration had no effect on solubility. In addition, after 1 year of storage, no difference in resin solubility or water sorption was found with respect to cure mode. The glass transition temperature for chairside-polymerized samples approximated -10 degrees C, while that for labpolymerized samples approximated -15 degrees C. CONCLUSIONS With regard to the material properties evaluated in this study, clinically processed Permasoft liner was equivalent to the laboratory-processed material.

A technique to create appropriate abutment tooth contours for removable partial dentures.

Abstract: A technique is presented for using light-cured composite resin to create desirable contours on abutment teeth for the retention and support of removable partial dentures. The desired tooth shape is created on a diagnostic cast, captured in a clear temporary splint material, and formed in resin on the abutment teeth with the splint acting as a matrix.

A Pilot Study to Evaluate Different Palate Materials for Maxillary Complete Dentures with Xerostomic Patients

Abstract: Purpose The hypothesis tested in this pilot study was that materials used for the palatal region of a maxillary denture affect the comfort of the maxillary denture in xerostomic patients. Materials and Methods Xerostomic complete denture wearers were selected to test three different maxillary dentures that were made with different palatal materials. Each denture was worn for a period of 2 weeks. The Kapur Index was used to measure retention. The Oral Health Index Profile (OHIP) was used to determine the patient's perception of each denture after the 2-week period. At the end of the study, the patients were asked to select which of the three dentures they would like as their primary denture. Results All participants chose the metal-palate dentures, and 4 of 5 selected the titanium-palate denture as their primary denture. Statistical analysis of the OHIP demonstrated that the metalpalate dentures were perceived as being more comfortable than the acrylic-resin dentures. Conclusion This pilot study suggests that for xerostomic patients who have worn complete dentures, their selection of a metal-palate denture as their primary prosthesis strongly suggests that these dentures have properties that make them more comfortable to the patient than acrylic dentures. Subjective patient measurements supported this conclusion that the metal-palate dentures were preferable, while the evaluation method available to the clinician failed to discriminate among the prostheses.

A technique to replicate soft tissues around fixed restoration pontics on working casts.

Abstract: When missing maxillary incisors are replaced, the patient's primary concern is usually esthetics. Depending on the patient's smile line and the display of the incisors, the esthetic zone may extend to the entire clinical crown and include the surrounding soft tissue. For these patients, the appearance and form of the soft tissue at the base of the pontics is as critical as the esthetics of the incisal edges of the restoration. A technique is presented to precisely transfer the soft tissue morphology of the pontic area to the working cast. This modified master cast allows the laboratory technician to fabricate restorations that will harmonize precisely with the soft tissues of the patient.

Centric relation registration using an anterior deprogrammer in dentate patients.

Abstract: A technique is described for registering centric relation in dentate patients using an anterior deprogrammer to prevent muscle splinting. Properly executed, the patient is able to close into centric relation unassisted, eliminating the possibility of operator-induced error associated with commonly accepted manipulative techniques. Verification is possible visually when articulating casts by confirming the precise alignment of the mandibular incisors with occlusal markings on the deprogrammer attached to the maxillary cast.

Long-term reliability of semiadjustable articulator interchangeability.

Abstract: PURPOSE Interchangeability between articulators allows mounted casts to be accurately transferred from one articulator to another. The purpose of this study was to evaluate the interchangeability of Whip-Mix model #2240 articulators (Whip-Mix Corporation, Louisville, KY) that had been in clinical use for between 1 and 6 years. MATERIALS AND METHODS Forty-six Whip-Mix model #2240 articulators that had been in clinical use by students, practitioners, or laboratory technicians for between 1 and 6 years were evaluated for interchangeability using the Whip-Mix #2245 check system. The horizontal tolerance of the check system was 94 microns. The articulators were also evaluated in the vertical dimension at four locations around the check system cylinders using 26-micron shimstock. Vertical discrepancies between the cylinders were recorded as the thickness of 0, 1, 2, or more than 2 pieces of shimstock. RESULTS Thirty-eight of the articulators (83%) passed the test for interchangeability. These articulators were interchangeable with other Whip-Mix model #2240 articulators fabricated over a 5 1/2-year period (December 1990 to August 1996). In the vertical dimension, most articulators had discrepancies < or = 26 microns. Three articulators (6.5%) had vertical discrepancies greater than 52 microns. CONCLUSIONS (1) Eighty-three percent of Whip-Mix model #2240 articulators that had been in clinical use for between 1 and 6 years remained interchangeable within a tolerance of 94 microns in the horizontal dimension. (2) Only three articulators in this study (6.5%) had a vertical discrepancy at any location between the cylinders greater than 52 microns. (3) The model #2240 articulator has the potential to remain interchangeable during clinical use.

Use of a Surgical Template for Autologous Bone Grafting of Alveolar Defects

Abstract: This article describes the fabrication of a surgical template for planning and performing the harvest and placement of autologous bone grafts for the reconstruction of alveolar defects before implant placement. A diagnostic cast is altered to replicate the anticipated bone anatomy. The ideal bony contours for implant placement are then created on the cast to form the template. This template may then be used for treatment-planning donor sites for the harvest of corticocancellous bone grafts. The template is sterilized and used by the surgeon in procuring and placing the bone graft. This template allows communication of the prosthetic requirements of the ridge augmentation, as well as ensuring adequate volume and proper positioning of the block graft for eventual implant placement.

Comparison of perceptions of computer-animated left- and right-facing profiles.

Abstract: Purpose Although scientific publications differ in displaying left- or right-facing profiles, there are few systematic studies of the possible effects of directional biases and laterality on patients' and clinicians' perceptions of treatment need, outcomes, and satisfaction. As part of a research program to quantitate the physical bases of the perceived zone of acceptability and most-pleasing facial profiles, responses to computer-animated left- and right-facing soft-tissue profile images were compared and related to eye and hand preference. Materials and Methods Standardized left-facing, soft-tissue profile images were captured in color and digitized. The right-facing profile was created by reversing the left profile image to display a mirror image. Using imaging and customized morphing software, retrusive and protrusive extremes were created, from which transitional frames were developed to display five features of the soft-tissue profile: upper lip, chin, bimaxillary position, lower face height, and mandible. One left- and one right-facing profile for a Class II division 1 female, and Class III male were randomly presented to 24 subjects who were asked to indicate: 1) acceptability by pressing a mouse button and releasing the button when the images were no longer acceptable; and 2) most-pleasing image by pressing the mouse button once. Results No differences were found between left- and right-profile images for zone of acceptability, midpoint of the zone of acceptability, or most pleasing; nor was there any relation to laterality measures. However, consistently higher intercorrelations among the features for the zone of acceptability were found for the left- than for the right-facing profiles for retrusive to protrusive and protrusive to retrusive excursions measured in millimeters (p < .001). The bimaxillary position accounted for most of the variance in judgments of acceptability with greater influence on the left than on the right profile. Conclusion With the increasing use of computer-imaging in dental practices, the influence of psychophysical and other environmental variables on perception must be considered.

Infrared gold alloy brazing on titanium and Ti-6Al-4V alloy surfaces and its application to removable prosthodontics.

Abstract: Purpose: This study investigated the area size of the flow of a gold braze alloy on commercially pure titanium and Ti-6AI-4V alloy plates, and elemental composition at the interface was determined. In the second part of this study, the tensile strengths of titanium plates brazed using a gold alloy were investigated. Materials and Methods: Chips of Type IV gold alloy and silver braze alloys were melted onto commercially pure titanium and li-6AI-4V surfaces in a dental infrared radiation unit. Flow area of each braze alloy was measured using a digital image analyzer. Tensile specimens (n = 5) were also prepared by infrared brazing using the braze alloys. Five specimens for each combination of thetwo titanium plates and the two braze alloys were subjected to tensile loading using a Universal testing machine. Electronprobe microanalysis of x-rays at cross-section of the brazed joints to determine elemental composition across the interface, as well as scanning electron microscopic observation at the fracture surfaces, were also conducted. Resu1ts:The braze alloys flowed well and spread over the Ti and Ti-6AI-4V plates. Braze alloy type significantly influenced flow, and the gold alloy flowed less on the titanium materials. The mean tensile strengths of Ti and Tii-6AI-4V plates brazed using the gold braze alloy were 219 MPa and 417 MPa, respectively. The fracture surfaces of Ti-6AI-4V specimens with the gold braze alloy exhibited typical ductile behavior. Ti with the same braze alloy showed brittle surfaces. A greater concentration of Cu was found at the Ti with gold braze interface. Conc1usion:The flow and the tensile strength of the gold alloy coating on titanium surface by means of an infrared brazing is adequate for dental use. J Prosthod 1999;8:180-187. Copyright 0 1999 by The American College of Prosthodontists. INDEX WORDS: infrared brazing, titanium, T-6AI-4V alloy, removable partial denture, gold alloy clasp

Silicone thermoplastic sheeting for treatment of facial scars: an improved technique.

Abstract: Silicone thermoplastic sheeting has been used successfully in the management of hypertrophic and keloid scars resulting from thermal burn injuries. A technique is described that incorporates silicone thermoplastic sheeting for fabrication of a compression face mask. This technique combines the moldability of thermoplastic splinting materials with the therapeutic surface of silicone, yielding the advantages of both in a one-step process.