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Biomedical subjects

H F Kappert

Publications and source records attributed to H F Kappert.

At least 19 recordsLinked to original sources
PubMed1991

[Integrated and frequency spectra of the electromyograms in patients with temporomandibular symptoms].

With the aid of bipolar surface electrodes, the electromyographic activity of the anterior temporal and the superficial masseter muscles were recorded bilaterally and evaluated by counting the integrated potentials and mean power frequency using Fourier's analysis. A comparison between 17 patients with myofacial pain dysfunction (average age 21.3 years) and a group of 20 controls (average age 20.5 years) revealed a significantly greater activity in patients with pain syndrome, while no significant inter-group difference in mean power frequency was seen. The differences in the level of activity between the right and left sides in the control group were significantly smaller than in patients with pain dysfunction. An investigation of measures aimed at reducing the right/left asymmetry in a further 14 patients with pain dysfunction revealed the practice of "maximum occlusion with feedback" to be the most effective measure.

Adolescent↗
PubMed1991

[Strength of the In-Ceram system under mechanical loads and thermocycling in artificial saliva].

The mechanical strength of the new oxide ceramic system In-Ceram introduced by Vita (Bad Säckingen, Germany) was investigated by an in-vitro study for its mechanical strength and suitabilities for use as posterior three-unit bridges. The transverse strength value measured by a three-point bending test (DIN 13,927) is 320 MPa and the maximum vertical load on three-unit bridges until brittle failure occurs is in the range of 1000 to 1350 N. This is up to four times higher than corresponding values of other ceramics, e.g. Dicor (Dentsply) or Optec (Jeneric). The dental bridges were luted to metallic pontics, and a layer of silicon rubber simulating the periodontal membrane, separated the pontic from a resin base in the testing machine. Life value tests were performed before and after 10 days of thermocycling at temperatures alternating between 5 and 55 degrees C in artificial saliva. Although the pontics had a much higher mobility than normal teeth, the fatigue limit was found to be above 600 N which is much higher than the average biting forces acting on the first and second molars.

Aluminum Oxide↗
PubMed1991

[Field study on the accuracy of fit and the marginal seal of In-Ceram crowns and bridges].

It was the objective of this in-vitro field study to evaluate the marginal fit of the In-Ceram system (Vita). All the materials applied in this system were compared with each other under the aspect of their dimensional behavior to determine the influence of this factor on die adaptation. The mean value of the marginal fit of the In-Ceram restorations on the master models was 12 (+/- 10) microns. The PFM bridges showed marginal openings of 9 (+/- 10) microns. The values on the patient models were 38 (+/- 12) microns for In-Ceram, and 44 (+/- 19) microns for PFM. This increase had been anticipated because of the grain size of the Harvard Cement. The dimensional changes of the materials involved were in great harmony. At least one coat of die spacer is necessary to compensate for the contraction of the ceramic and the expansion of the special plaster. Two paints are recommended for crowns and three for bridges. Careful shoulder or chamber preparation is required to create smooth surfaces.

Aluminum Oxide↗
PubMed1991

[Texture formation of the dental ceramic core material In-Ceram and thermal expansion of its individual components].

Electron microscopic investigations of the core material In-Ceram show how its texture is formed. While these are processed the Al2O3 crystallites turn idiomorphic. Etching the material with sulphuric acid selectively dissolves the glassy phase and reveals the crystallites. The chemical composition of the two components of the core material is determined by microprobe analysis. While the crystallites are pure Al2O3, the glass consists of La2O3, SiO2, Al2O3 and CaO. Measurements of the thermal expansions of the glass and the Al2O3 frame show the value for the glass to be 5.1% lower than that of the Al2O3 frame. This results in internal pressure and contributes to the high strength of the material.

Aluminum Oxide↗
PubMed1989

[Determining the threshold level for sensibility responses to galvanic potentials in the oral cavity].

The presence of different alloys in the oral cavity may produce potential differences of up to 900 mV. In the majority of the patients this phenomenon presents no problems. Occasionally, however, disturbing sensations, such as "metallic taste", "twinging or stabbing" and "minute electric shock" are reported. In finding out on the threshold level for discomforting sensations due to galvanic potentials in different probands, a special battery operated device was developed. Using a pair of electrodes connected to metallic restorations in the mouth, this device enabled the application and adjustment of direct current voltage and a superimposed pulse spectrum to evoke sensible reactions. The trials were conducted with 102 probands. The mean value for the threshold of sensation was above 1000 mV. In solitary cases, however, the threshold level was as low as 250 mV. This method may be used as a diagnostic aid to the objective assessment of complaints due to galvanic effects in the oral cavity and for the selection of a suitable metal in sensitive patients.

Dental Alloys↗
PubMed1989

[Qualitative studies on the surface crystallization of dental glass ceramics (Dicor)].

The crystallization of enstatite at the surface of Dicor glass during 'ceramization' is proved by electron microscopy and x-ray diffraction. Microprobe measurements demonstrate a loss of potassium and an uptake of calcium in the outer region of the glass-ceramic after ceramization due to an ion exchange between glass and ceramization investment. This investment consists of gypsum and leucite. A thermal analysis reveals the decomposition of gypsum in the range of the ceramization temperature. Calcium diffuses into the surface of the glass while simultaneously potassium leaves the glass. The altered composition allows the crystallization of enstatite.

Ceramics↗
PubMed1989

[Effects of the mode of ceramization on the compressive strength of Dicor crowns. A laboratory study].

The critical compressive strength of cast glass-ceramic samples with a standardised shape was evaluated as a function of the ceramization temperature. The maximum critical compressive stress was obtained under conditions prescribed by the manufacturer. After under- and overceramization by only 6 degrees C, as well as after repeated ceramization, the critical compressive strength was decreased significantly (p less than or equal to 0.05) by about 13-24%.

Ceramics↗
PubMed1989

[Frequency spectrum and integral value of electromyographic recordings of the masseter and temporal muscles in correlation with muscle length].

In 15 children and 15 adults the influence of muscle length on the EMG-recordings of the anterior temporal and superficial masseter muscles was investigated. Myoelectric activity was measured by surface electromyography during maximal clenching in habitual occlusion. The quantitative EMG analysis was performed by means of a computer program which allowed calculation of a) the integrated value and b) the mean frequency of the power spectrum (MPF) from the raw signal after Fourier transformation. Muscle length was determined with the aid of lateral cephalometric films. Using a correlation analysis this investigation revealed the following results: Under standardized functional conditions short muscles work with a higher activity and a higher MPF than long muscles. In children as well as in adults muscle activity and MPF show close negative correlations with the parameter "muscle length". These relations are directly proportional.

Adult↗
PubMed1989

[Testing metal/acrylic bonds for shear strength, axial tensile strength and maximum bending stress].

The effects of thermocycling and water penetration on the bond strength of resin-metal-systems and improvements using bonding agents have been tested by shear, bending and tensile tests. After 10,000 cycles within 10 days in different water-baths with 5-37-55 degrees C, there is a decrease in bond strength by 40 to 60%. The use of bonding agents increases the adhesion of the resin to the metal by more than 100%. No significant differences were found between the three bonding agents Silicoater, Sebond MKV and OVS.

Acrylic Resins↗