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Biomedical subjects

S F Rosenstiel

Publications and source records attributed to S F Rosenstiel.

At least 19 recordsLinked to original sources
PubMed2001

Clinical diagnosis of dental caries: a North American perspective.

This paper summarizes current trends in the clinical diagnosis of occlusal caries in response to the RTI/UNC review and reflects the dilemma felt by many dentists who understand the difficulty in accurately assessing the extent and activity of pit and fissure caries in many of their patients. They are unsure if they should be aggressive in instrumenting suspicious lesions and provide small restorations, some of which may not be indicated. Alternatively, should they wait until signs are more clear-cut and provide larger restorations? Discussed here is the advantage of practicing dentists who obtain immediate false-positive feedback when they instrument a tooth with no clinical caries and false-negative feedback when a recall patient exhibits progression of an equivocal lesion. They should be encouraged to use this feedback as part of their diagnostic procedure and explain to their patients the difficulty of providing an accurate and precise diagnosis with existing tests.

Decision Trees↗
PubMed2000

Dentists' preferences of anterior tooth proportion--a web-based study.

PURPOSE: This study aimed to determine dentists' esthetic preferences of the maxillary anterior teeth as influenced by different proportions. The goal was to link choices to demographic data as to the experience, gender, and training of the dentist. METHOD AND MATERIALS: Computer-manipulated images of the 6 maxillary anterior teeth were generated from a single image and assigned to 5 tooth-height groups (very short, short, normal height, tall, and very tall). For each group, 4 images were generated by manipulating the relative proportion of the central incisors, lateral incisors, and canines according to the proportions 62% (or "golden proportion"), 70%, 80%, and "normal" or not further altered. The images were randomly ordered on a web page that contained a form asking for demographic data and fields asking for a ranking of the images. Dentists were asked via e-mail to visit the web page and complete the survey. The responses were tabulated and analyzed with repeated measures logistic regression with the alpha at 0.05. A subset of North American respondents was chosen for further analysis. RESULTS: A total of 549 valid responses were received and analyzed from dentists in 38 countries. There were statistically significant differences in all groups for the variables of proportion, group (tooth height), and their interaction. The 80% proportion was judged best for the Very Short and Short groups. Three of the choices were almost equally picked for the Normal Height and Tall groups, and the golden proportion was judged best for the Very Tall group. The variables of year of graduation, gender, professional activity, generalist or specialist, or number of patients were not significantly correlated with the choices for the North American respondents. CONCLUSIONS: Dentists preferred the 80 percent proportion when viewing short or very short teeth and the golden proportion when viewing very tall teeth. Golden proportion was worst for normal height or shorter teeth and the 80% proportion for tall or very tall teeth. They picked no clear-cut best for normal height or tall teeth, and their choices could not be predicted based on gender, specialist training, experience, or patient load.

Attitude of Health Personnel↗
PubMed1998

Crystallization kinetics of a low-expansion feldspar glass for dental applications.

Previous studies have shown that the crystallization of glasses in the system K2O-Al2O3-SiO2, in the primary field of leucite, is not possible without modification of the composition. Leucite (KAlSi2O6) is used as a reinforcing phase in some compositions for all-ceramic dental restorations. However, because of their higher coefficient of thermal expansion, these materials cannot be veneered with conventional metal-ceramic porcelains. The purposes of this study were to investigate the crystallization behavior of a glass in the system K2O-Al2O3-SiO2 and to evaluate the effect of heat treatment on the crystal size, percent crystallinity, and coefficient of thermal expansion of the material. Ion-exchanged glass powder was prepared by mixing the glass with rubidium nitrate and heat-treating at 450 degrees C for 4, 8, 24, or 48 h. Bars were made from these powders and baked under vacuum at 1038 degrees C for 2 min. The bars made from the powder ion-exchanged for 48 h were further heat-treated for 4 h at either 800 degrees C, 850 degrees C, 900 degrees C, 950 degrees C, or 1038 degrees C. X-ray diffraction analyses showed cubic leucite was the only crystalline phase in the specimens made from the powders ion-exchanged for 4, 8, 24, or 48 h and baked at 1038 degrees C for 2 min. Further heat treatment for 4 h at either 800 degrees C, 850 degrees C, 900 degrees C, 950 degrees C, or 1038 degrees C promoted the growth of cubic leucite. In addition, a second phase identified as tetragonal rubidium-leucite was present in the specimens heat-treated for 4 h at 1038 degrees C. SEM observations showed that all specimens made from the powders ion-exchanged for 48 h exhibited small spherical crystals dispersed in a glassy matrix. The percent crystallinity ranged from 18.9% to 42.9% and the average particle size was between 0.64 to 1.18 microns. The coefficients of thermal expansion ranged between 8.076 and 8.788 x 10(-6)/degree C.

Aluminum Silicates↗
PubMed1998

Dental luting agents: A review of the current literature.

STATEMENT OF PROBLEM: The practice of fixed prosthodontic has changed dramatically with the introduction of innovative techniques and materials. Adhesive resin systems are examples of these changes that have led to the popularity of bonded ceramics and resin-retained fixed partial dentures. Today's dentist has the choice of a water-based luting agent (zinc phosphate, zinc polycarboxylate, glass ionomer, or reinforced zinc oxide-eugenol) or a resin system with or without an adhesive. Recent formulations of glass ionomer luting agents include resin components (resin-modified glass ionomers), which are increasingly popular in clinical practice. PURPOSE: This review summarizes the research on these systems with the goal of providing information that will help the reader choose the most suitable material. MATERIAL: The scientific studies have been evaluated in relation to the following categories: (1) biocompatibility, (2) caries or plaque inhibition, (3) microleakage, (4) strength and other mechanical properties, (5) solubility, (6) water sorption, (7) adhesion, (8) setting stresses, (9) wear resistance, (10) color stability, (11) radiopacity, (12) film thickness or viscosity, and (13) working and setting times. In addition, guidelines on luting-agent manipulation are related to available literature and include: (1) temporary cement removal, (2) smear layer removal, (3) powder/liquid ratio, (4) mixing temperature and speed, (5) seating force and vibration, and (6) moisture control. Tables of available products and their properties are also presented together with current recommendations by the authors with a rationale.

Dental Cements↗
PubMed1998

Handpiece degradation associated with performance testing of diamond rotary cutting instruments.

Reliable standardized testing of dental rotary cutting instruments remains a problem because of the many significant parameters that require identifying and quantifying. In a previous study, handpiece wear or degradation was identified as a potentially significant confounding variable leading to the suggestion that the use of industrial handpieces might be necessary. Therefore, the objective of this investigation was to measure and compare industrial and dental air rotor degradation during a simulated diamond rotary cutting instrument test. Two dental and two industrial products were tested in a random sequence using three replicate samples of each air rotor. The simulated test consisted of 10 diamond instruments each making 90 passes through a float glass substrate. The testing apparatus comprised a computer-interfaced device that controlled the contact force between the cutting diamond and the substrate. Air rotor performance was based on the time required to cut a standardized path through the substrate. The performance change that occurred from diamond instrument to instrument during the simulated test was attributed to air rotor degradation. Multiple regression analyses showed significant differences between replicate samples of the same type and between regression intercepts for different air rotor types. Surprisingly, four air rotors exhibited improving performance during the simulated test. Changing air rotor performance must be considered to achieve reliability for the testing of diamond rotary cutting instruments.

Air↗
PubMed1998

Effect of ion exchange on the microstructure, strength, and thermal expansion behavior of a leucite-reinforced porcelain.

Leucite (KAlSi2O6) is used as a reinforcing agent in some porcelains for all-ceramic restorations; however, it increases their coefficients of thermal expansion, imposing constraints on the processing of the material. The potassium ions in leucite are exchangeable for rubidium or cesium ions, leading to rubidium leucite or cesium leucite (pollucite). Both rubidium leucite and pollucite exhibit a lower coefficient of thermal expansion and inversion temperature than leucite. The purpose of this study was to evaluate the effects of rubidium and cesium leucites on thermal expansion, microstructure, crack deflection patterns, and flexural strength of a leucite-reinforced porcelain. A dental porcelain powder was mixed with rubidium or cesium nitrate and heat-treated. Porcelain bars (n = 3) and discs (n = 15) were made with the exchanged powders. X-ray diffraction analyses were performed before and after bars were fired. Controls were made of untreated Optec HSP porcelain powder, formed into bars and disks, and baked following manufacturer's recommendations. The density of all specimens was determined by Archimedes' method. The thermal expansion behavior of the materials was measured by dilatometry. The microstructure and Vickers indentation crack patterns were investigated by scanning electron microscopy. X-ray diffraction showed that after ion-exchange and firing, leucite transformed into either tetragonal rubidium leucite or cubic cesium leucite. The mean coefficient of thermal contraction (550 to 50 degrees C) was significantly (p < 0.003) greater for the control material, followed by the rubidium-exchanged material, and lowest for the cesium-exchanged material. Crack pattern analyses revealed that the cesium-exchanged material exhibited a significantly lower number of crack deflections compared with those in the two other materials (p < 0.001). The microstructure of the two exchanged porcelain materials was dense, with well-dispersed small crystals as well as larger rubidium or cesium leucite crystals. The mean flexural strength of the rubidium-exchanged material was significantly higher than those of the other materials, which were not significantly different. It was concluded that the thermal expansion of leucite-reinforced porcelain can be lowered by ion-exchange, which also modifies the microstructure, crack deflection patterns, and flexural strength of the material.

Aluminum Silicates↗
PubMed1997

Influence of tooth surface roughness and type of cement on retention of complete cast crowns.

STATEMENT OF PROBLEM: Bond strength of luting cements to dentin is a critical consideration for success of cast restorations. PURPOSE OF STUDY: This study determined the relationship between surface characteristics of teeth prepared for complete cast crowns and retention of respective cemented restorations. MATERIAL AND METHODS: Ninety artificial crowns were cast for standardized complete crown tooth preparations accomplished with the use of a milling machine on extracted human teeth. Diamond, tungsten carbide finishing, and cross-cut carbide burs of similar shape were used. The crowns in each group were randomly subdivided into three subgroups of 10 for the three luting cements selected for this study: zinc phosphate cement (Fleck's), glass ionomer cement (Ketac-Cem), and adhesive resin cement (Panavia-EX). Retention was evaluated by measuring the tensile load required to dislodge the artificial crowns from tooth preparations with an Instron testing machine. RESULTS: Analysis of forces with parametric analysis of variance and Tukey's Studentized Range (HSD) disclosed a statistically significant difference for both luting cement and finishing burs (p < 0.001). A statistically significant interaction effect (p < 0.001) was also found. The greatest retention value (372.9 N) was for tooth preparations refined with carbide burs and cemented with Panavia-EX cement. However, the least retention value (201.6 N) was for tooth preparations completed with finishing burs and luted with zinc phosphate cement. CONCLUSIONS: Significant differences were found among all three cements for finishing burs. However, there was a difference only between Panavia-EX cement and the other two cements for tungsten carbide burs. For diamond rotary instruments, zinc phosphate cement was significantly different from glass ionomer and Panavia-EX cements.

Analysis of Variance↗
PubMed1997

Custom-cast post fabrication with a thermoplastic material.

Problems associated with fabrication of custom-cast posts with a plastic rod and autopolymerizing resin include voids in the pattern, locking of the pattern into undercuts, and resin fracture during removal of the pattern. This article describes a system for fabricating custom-cast posts with a thermoplastic resin to address these problems. The system consists of a plastic support rod and a thermoplastic resin. A custom post pattern can be quickly and easily produced by trimming the plastic rod, heating the resin either over a direct flame or in a low-temperature glue gun and seating it into a lubricated prepared canal. The resin flows well and thereby reduces voids. The resin is elastic enough to be removed from small undercuts without locking into the canal or fracturing.

Dental Casting Technique↗
PubMed1996

Surface roughness of dentin after tooth preparation with different rotary instrumentation.

Although surface finish can be a critical variable in clinical performance, there is a dearth of information regarding surface characteristics of teeth prepared for artificial crowns. This study characterized teeth prepared for complete cast restorations using three representative types of rotary instruments. One hundred and five standardized tooth preparations for complete crowns were performed using a modified milling machine on extracted human teeth with diamond, tungsten carbide, and tungsten carbide finishing burs of similar shape (n = 35). The prepared dentin was analyzed with a surface profilometer and a scanning electron microscope (SEM). Differences between rotary instrument groups were determined with parametric ANOVA and Tukey's Studentized Range (HSD). Statistically significant differences in the surface topography of prepared teeth were open. Mean surface roughnesses (Ra) were 8.6 and 6.8 mum for teeth prepared with diamond and tungsten carbide burs. Teeth completed with finishing burs appeared to result in a smoother surface (1.2 mum).

Analysis of Variance↗
PubMed1996

A pilot study of lactic acid as an enamel and dentin conditioner for dentin-bonding agent development.

The purpose of this pilot study was to determine how lactic acid solution at various concentrations and etching times affected prepared human enamel and dentin surfaces and to assess whether it could be used in place of phosphoric or maleic acid as an etchant. The occlusal surfaces of extracted molar teeth were ground wet with 600-grit silicon carbide paper and treated with various aqueous solutions of lactic acid. Random samples were prepared for observation by scanning electron microscopy. The rest were used to determine shear bond strength of bonded dental composite cylinders. The micrographs revealed that lactic acid dissolved the smear layer with various degrees of etching and demineralization. The degree of smear layer and matrix removal was proportional to the concentration of the acid and the length of application time. A 20% lactic acid concentration applied for 10 seconds produced a clearly etched surface with minimal demineralization. A 30% concentration not only removed the smear layer and enlarged the dentin tubule orifices but also appeared to affect the collagen matrix. The shear bond strength to enamel treated with 50% lactic acid (17.5 +/- 1.5 MPa) and All-Bond 2 etchant (18.9 +/- 1.3 MPa) were not significantly different (p > 0.05). However, mean dentin bond strengths for all groups of lactic acid etchant and All-Etch etchant (10% phosphoric acid) were statistically similar.

Acid Etching, Dental↗
PubMed1996

Effect of cubic leucite stabilization on the flexural strength of feldspathic dental porcelain.

Previous studies (Mackert and Evans, 1993) have shown that, when feldspathic dental porcelain is cooled, leucite undergoes a transformation from cubic to tetragonal, associated with a 1.2% volume contraction. This contraction leads to the formation of microcracks in and around the crystals and the development of tangential compressive stresses around the crystals. Our aim was to stabilize increasing amounts of the cubic form of leucite in a leucitereinforced dental porcelain, evaluate its effect on the flexural strength, and characterize its microstructure. The hypothesis was that in the absence of crystallographic transformation, the contraction of the leucite crystals would be lower, thereby limiting the formation of microcracks and minimizing the development of tangential compressive stresses around the leucite particles. We prepared 8 porcelain compositions by mixing increasing amounts of either leucite (KAlSi2O6) or pollucite (CsAlSi2O6) with Optec HSP porcelain (Jeneric/Pentron Inc., Wallingford, CT). Porcelain disks were made from each composition (n = 10 per group). X-ray diffraction analyses showed that the amount of stabilized leucite increased with the amount of pollucite added. The microstructure of the specimens containing tetragonal leucite was characterized by twinned leucite crystals, whereas no twinning was observed in the specimens containing cubic leucite. The evaluation of crack deflection showed that significantly less deflection occurred in the specimens containing cubic leucite. The mean biaxial flexural strength for the group corresponding to 22.2 wt% added pollucite, fired at 1038 degrees C, was significantly lower than that for the control group. The group corresponding to 22.2 wt% added leucite fired at 1150 degrees C exhibited a mean biaxial flexural strength significantly higher than that of all other groups that were not significantly different from the control group. Overall, the stabilization of cubic leucite reduced the flexural strength and the number of crack deflections in leucite-reinforced porcelain. Apparently, the development of tangential compressive stresses around the leucite crystals when cooled is responsible for a significant amount of strengthening of feldspathic dental porcelain.

Aluminum Silicates↗
PubMed1996

Randomized clinical trial of the efficacy and safety of a home bleaching procedure.

The safety and efficacy of a home-use carbamide peroxide tooth-whitening procedure were evaluated in a double-blind experimental design. Fifty-two adults were randomly assigned to experimental and control (placebo gel) groups. The products were applied in a custom-fitted tray and used for 5 consecutive nights in accordance with the manufacturer's recommendations. Tooth color changes from baseline were measured with a small-area colorimeter. Concurrently, electric pulp test and periodontal indices were measured. At the end of 6 months, the teeth in the active group had a statistically significant greater mean color change that did the placebo controls. The mean color change differed significantly by tooth type. No statistically significant changes in vitality, sulcus depth, or Gingival Index were found in the treatment group.

Adult↗
PubMed1995

Relative fracture toughness and hardness of new dental ceramics.

Dental ceramics can fail through growth of microscopic surface flaws that form during processing or from surface impact during service. New restorative dental ceramic materials have been developed to improve resistance to crack propagation. Eleven of these improved materials with the common feature of a considerable amount of crystalline phase in the glassy matrix were evaluated. The ceramic materials studied included fluormica-, leucite-, alumina-, and zirconia-reinforced glasses. The relative hardness and fracture toughness were determined by indentation technique. Alumina-reinforced materials resulted in the highest fracture toughness values, whereas the fluormica- and leucite-reinfoced materials showed more moderate but statistically significant greater values compared with those of control materials. The hardness values of ceramic materials with improved fracture toughness were both substantially higher or lower than those of the control groups and suggested a lack of direct correlation between these two properties. Selection of appropriate restorative materials depends on clinical application and requires consideration of several physical properties including fracture toughness.

Aluminum Oxide↗
PubMed1994

Disturbance of the dentinal smear layer by acidic hemostatic agents.

The pH of nine commonly used hemostatic agents was measured. Three measurements were recorded for each solution, and values ranged from 0.7 to 2.0. The effect of exposure to one hemostatic material, ferric sulfate solution (Fe2(SO4)3), on the dentinal smear layer was investigated. Prepared extracted teeth were exposed for periods ranging from 30 seconds to 5 minutes to an acidic ferric sulfate-based hemostatic agent. A smear layer was clearly demonstrated on a control specimen; however, the dentinal smear layer was rapidly removed by exposure to the hemostatic agent, and peritubular dentin was lost after prolonged exposure.

Acid Etching, Dental↗
PubMed1993

Fluoroalkylethyl silane coating as a moisture barrier for dental ceramics.

The performance of dental ceramics is reduced in wet environments due to stress-corrosion limiting restoration lifetime. As analysis suggests that fracture is typically initiated from the internal surface, placement of a thin coating before a restoration is cemented to place may prevent fracture if it acts as a moisture barrier. Of coatings we tested, a fluoroalkylethyl silane (du Pont MPD-7680) showed promise. This study aimed to test a range of concentrations on glass and to determine any strength improvement on dental ceramics. Glass slides (n = 8-9) were indented (29-N load) stored 24 h, etched, coated with 100, 50, and 25% fluorosilane in isopropyl alcohol, and air-cured for 24 h. The slides were fractured on a biaxial fixture in water at 0.5 mm/min and maximum stresses calculated. Uncoated controls were tested in water and liquid N2 to determine the inert strength without stress-corrosion. Results showed increasing mean strength from uncoated (53.6 MPa) to 100% (68.0 MPa) which compared to the 80.4 MPa inert strength. ANOVA showed P < .05. Subsequently the experiment was repeated on discs of three dental ceramics (n = 7-10): feldspathic (Ceramco), glass-ceramic (Dicor MGC), high-leucite (Optec) with the 100% solution only. Mean strength was significantly (P < .01) enhanced in the feldspathic (56.2 MPa, untreated, 70.7 MPa, treated) but not the high-leucite (83.1, 83.0) or the glass-ceramic (283.9, 271.4). Fluoroalkylethyl silane coating reduced stress-corrosion in glass and feldspathic porcelain. It may be a practical approach to reducing fracture of ceramic restorations.

Ceramics↗
PubMed1993

Strength of a dental glass-ceramic after surface coating.

Clinical evidence suggests that using a resin luting agent rather than a traditional cement reduces the fracture incidence of glass-ceramic crowns. There is some evidence from stress analysis and fractography to indicate that fracture failure is typically initiated from their internal surface. The objective of this study was to determine if surface treatments and cement coatings of the fracture-initiating surface affected fracture stresses of ceramic discs in vitro. Glass-ceramic discs were cast, crystallized, and given various treatments. The discs were fractured with a ball-on-ring of balls biaxial fixture in air. The maximum stresses at the ceramic-coating interface were calculated using the bi-layer material equations. ANOVA and Tukey's multiple range test revealed that resin coating the fracture-initiating surface increased the biaxial fracture strength of the glass-ceramic discs by 33%. The effect was not reduced by short-term water storage. Etching alone did not significantly alter strength. The results suggest that crack-bridging is the most likely mechanism for the strengthening. Selecting techniques and materials that are likely to enhance crack-bridging may be a practical method of improving the performance of ceramic dental restorations.

Acid Etching, Dental↗
PubMed1993

Flexural strength and fracture toughness of Dicor glass-ceramic after embedment modification.

Previous studies on the surface properties of Dicor castable glass-ceramic have shown the formation of a specific crystalline phase at the glass-ceramic/embedment interface. If this phase is not removed by grinding, it leads to an undesirable strength decrease. The aims of this study were: (1) to determine the nature of this surface layer, (2) to promote the formation of a different crystalline phase at the surface with the intention of improving the properties of the glass-ceramic, by modification of the composition of the Dicor ceramming embedment, and (3) to evaluate the fracture toughness and flexural strength of Dicor glass-ceramic after embedment modification. Modifications were made to the embedment by incorporation of 2.5 wt% of lithium fluoride and ceramming at various temperatures. X-ray diffraction was used to determine the crystalline nature of the surface layer. Fracture toughness was investigated by the indentation technique. The maximum bi-axial stresses were calculated after the samples were fractured in water on a ball-on-ring fixture at 0.5 mm/min. With the recommended embedment and ceramming cycle, the crystalline phase constituting the ceram layer was a calcium magnesium silicate CaMg(SiO3)2 (diopside). The crystalline composition of the ceram layer was successfully modified by addition of 2.5 wt% lithium fluoride to the embedment. This promoted the crystallization of mica in the ceram layer and increased the fracture toughness of the glass-ceramic when the ceramming temperature was 950 or 975 degrees C. The flexural strength was significantly increased when the ceramming temperature was 1000 degrees C.

Aluminum↗