PubMed Health⌕ Search

Biomedical subjects

A G Gegauff

Publications and source records attributed to A G Gegauff.

17 recordsLinked to original sources
PubMed2000

Effect of crown lengthening and ferrule placement on static load failure of cemented cast post-cores and crowns.

STATEMENT OF PROBLEM: Restoration of mandibular second premolars with completely missing clinical crowns in the Kennedy Class I and II arches is costly and the risk of failure is high. Should the dentist choose crown-lengthening to allow the addition of a ferrule, despite incurring the disadvantage of an increased crown/root ratio? PURPOSE: This in vitro study determined the combined effect of crown lengthening and placement of a ferrule on the failure resistance to static load of decoronated and restored mandibular second premolar analog teeth. MATERIAL AND METHODS: An extracted mandibular second premolar of average dimensions was selected to form molded composite root analogs and metal crowns. Ten specimens prepared with no-ferrule root and negligible axial wall lengths and 10 specimens with ferrule root, apically repositioned finish lines, were made. Cast gold alloy post and cores and complete crowns were made and cemented. Each root was placed in bone-simulating resin located 3 mm from the finish line. Crown lengthened/ferrule and no-crown lengthened/no-ferrule groups were equally subdivided, whereby 5 crowns were compressively loaded on the buccal cusp tip and 5 were compressively loaded on the mesial marginal ridge. A testing machine applied force until failure occurred. Failure loads were examined with 2-way ANOVA. Significant differences were accepted at P </=.05. RESULTS: Mean failure loads for the crown lengthened/ferrule and no-crown lengthened/no-ferrule groups were as follows: buccal load, 0.61 kN (SD +/- 0.11) and 0.83 kN (SD +/- 0.08); mesial load, 0.70 kN (SD +/- 0.08) and 1.00 kN (SD +/- 0.15), respectively. Crown lengthened/ferrule and no-crown lengthened/no-ferrule groups were significantly different (P <.001). CONCLUSION: The combination of simulated surgical crown-lengthening and more apical crown margin placement to provide a 2-mm crown ferrule on a decoronated mandibular second premolar analog resulted in a reduction of static load failure for the restored analog tooth.

Analysis of Variance↗
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↗
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↗
PubMed1993

Evaluating tooth color change from carbamide peroxide gel.

A double-blind experiment assessed the efficacy, longevity and safety of a tooth whitener in young adults. Significant color changes occurred after active treatment but were substantially reversed after one week. No permanent changes were found in either pulpal or gingival health.

Adult↗
PubMed1991

Duration of tooth color change after bleaching.

Tooth color change was monitored after a single, in-office bleaching technique using a colorimeter. Twenty young adults participated in the double-blind study at The Ohio State University College of Dentistry. Half of the participants had their maxillary anterior teeth bleached and half were controls. By one month, the large initial color change was considerably reversed and only noticed by one subject. After six months, the effect of bleaching was small, but still measurable.

Adult↗
PubMed1991

In vitro tooth color change with repeated bleaching.

The interest of patients in vital tooth bleaching has created a demand for treatment. However, few objective data are available to help determine the number of bleaching appointments necessary and the lightening that can be expected. The purpose of this study was to measure color changes in bleached extracted teeth and compare these to control groups. Group A was etched and bleached with 35% stabilized hydrogen peroxide. Group B was treated the same as group A, but the bleaching solution was replaced with distilled water. Group C was not treated, but was stored in water. Mean color difference after one treatment was 3.33 for group A, 1.67 for group B, and 0.48 for group C. After six treatments, the overall color difference was 3.82, 2.41, and 1.38 for groups A, B, and C, respectively (P less than .01). Color changes beyond those found after the first treatment were small, suggesting that there was little benefit in repeated bleachings under the conditions of this study.

Acid Etching, Dental↗
PubMed1990

A potential MRI hazard: forces on dental magnet keepers.

The objective of this study was to determine the forces on dental prosthetic magnet keepers, with a view to assessing the potential for patient injury during magnetic resonance imaging (MRI). Four pre-formed keepers and one castable keeper alloy were tested. Magnetizations and high field susceptibilities were determined for each of the five specimens using data from a vibrating sample magnetometer. The magnetic field intensity with respect to distance from the main magnet coil was obtained from the manufacturer (1-5 tesla General Electric Signa Imaging System). A plot of force versus distance from the main coil and the maximum force at the magnet portal was determined for each specimen. The maximum forces ranged from 0.12-0.24 N for the pre-formed keepers and 3.67 MNm-3 for the castable alloy. It was concluded that the risk of patient injury by displacement is minimal, if the keepers are properly attached to supporting structures.

Dental Alloys↗
PubMed1989

The seating of one-piece and soldered fixed partial dentures.

This laboratory study compared the seating of one-piece castings with that of soldered fixed partial dentures. Two investments were investigated, five American Dental Association type III and five metal ceramic alloy fixed partial dentures were made by using the conventional indirect technique. The investing and casting protocol was designed to produce an ideal fit of the individual complete crown abutments, not the fixed partial denture. Independent seating of each retainer provided a baseline measurement for complete seating and was compared with fixed partial denture seating. Fixed partial dentures were then sectioned and reassembled by soldering twice, using a low- and high-expansion investment. Statistical evaluation identified significant differences between the metals and the techniques. Marginal discrepancies with one-piece casting and lower (0.6%) thermal-expansion soldering were clinically unacceptable. A clinically acceptable fit was obtained with the higher (1%) thermal-expansion soldering investment.

Dental Abutments↗
PubMed1989

Magnetic resonance image degradation from prosthetic magnet keepers.

Eight types of prosthetic magnet keepers were imaged in a water phantom and a living human subject by a 1.5 T magnetic resonance device. Image artifacts were present for all eight samples and ranged from 160 mm to greater than 280 mm in diameter. These artifacts obliterate vital craniocervical areas making their examination by magnetic resonance impossible. Patients with magnetic keepers requiring comprehensive magnetic resonance imaging of the head and neck region must have them removed.

Denture Design↗
PubMed1989

Reassessment of die-spacer with dynamic loading during cementation.

The authors previously reported a reduction in crown seating discrepancies of approximately 200 microns resulting from the application of dynamic forces during cementation. Previous in vitro die-spacer studies used static loads with large seating discrepancies unrepresentative of clinical practice. This investigation reassessed paint-on die-spacer for its effect on completeness of seating and retention when dynamic seating was used. A series of seven complete crowns was made for each of three extracted human teeth by using 0 to 6 coats of spacer. Index marks were used to measure crown position before and after cementation. Mean seating discrepancies indicated complete seating for all groups of crowns irrespective of the number of coats of die-spacer. An analysis of variance demonstrated no significant differences in the degree of seating. However, crowns made from dies without spacer were significantly more retentive (p less than 0.05) than those made from spaced dies.

Cementation↗
PubMed1988

Improving the cementation of complete cast crowns: a comparison of static and dynamic seating methods.

This study measured the effect of static and dynamic forces, during cementation, on the retention and seating of complete cast crowns made for extracted human teeth prepared with a diamond bur. Under a static load, the castings failed to seat by a mean value of 203 micron. When dynamically loaded, the castings seated an average of 14 micron beyond the point of precementation measurement. No statistically significant differences were found in the retention of the crowns cemented by the two different methods.

Cementation↗
PubMed1987

Fracture toughness of provisional resins for fixed prosthodontics.

Six resins for treatment restorations were tested to determine fracture resistance. The resins were broadly categorized chemically as: one epimine, two poly(methyl methacrylate)s, one composite, and two poly (R' methacrylate)s. Miniature compact tension specimens were molded and then cured for 5 minutes at atmospheric pressure or at an additional pressure of approximately 0.14 MPa. A commercially available pressure vessel was used for curing. The epimine and two poly(methyl methacrylate) resins demonstrated the greatest fracture toughness whereas poly (R' methacrylate) had the lowest. The composite, representing a new class of provisional material, recorded an intermediate fracture toughness. The use of a pressure vessel during polymerization did not significantly increase the fracture toughness of the six resins. There was minimal effect of pressure on the surface of the specimens but it reduced the internal porosity evident in the atmospheric pressure-cured specimens.

Composite Resins↗
PubMedDate not supplied

Mixing variables of zinc phosphate cement and their influence on the seating and retention of complete crowns.

Variations in the powder/liquid ratio, mixing time, and temperature of zinc phosphate cement were studied to determine their effect on the seating and retention of complete cast crowns. The crowns were made for extracted human molar teeth machined to an 8-degree convergence using a diamond instrument. Seating measurements were made between four pairs of marks using a machinist's microscope. A servohydraulic testing machine was used to measure retention values. A dynamic seating method allowed essentially complete seating of the castings in all groups. No statistically significant differences in retention between the groups were found.

Adhesiveness↗
PubMedDate not supplied

Fracture toughness testing of visible light- and chemical-initiated provisional restoration resins.

This in vitro study determined the fracture toughness of four classes of resin using wet and dry test environments, following 48 hours of wet storage. Two of the resins were light initiated, while the other two were chemically initiated. No significant difference in fracture toughness was detected for the wet and dry test environments using miniature compact tension specimens. The light-initiated, urethane dimethacrylate resin demonstrated a significantly higher fracture toughness than the poly(methyl methacrylate) resin.

Acrylic Resins↗