Deutsche zahnarztliche Zeitschrift最新文献

In a clinical study the accuracy of fit of 82 crowns manufactured with the Procera-system (duplication milling/spark erosion) was investigated. The average marginal space width was 71 microns. Roughness of eroded surfaces was found to be similar to that of coarsely ground metal. Below the eroded areas a zone of increased hardness with a width of approximately 20 microns was demonstrated.

Six methods of assessing the resting position were evaluated in this study of 22 patients with teeth and 10 edentulous patients. None of these methods yielded reproducible results. The resting position is not a fixed, constant value, but depends on the method used. As could be shown by means of the standard deviation the method used to determine the resting position has a considerable influence on the distribution, and hence on the margin of error when the vertical relation is being determined. Small ranges of distribution were achieved: a) by means of the closest speaking distance when the patient spoke the numbers from 60 to 70 in a natural voice, b) after prompt relaxation of the lower jaw when the patients were asked to relax their jaws, c) when the interocclusal distance was measured after the mouth had been opened a little and the lips subsequently touched again lightly. Since there is little difference in the values with any one patient the three methods can be recommended for practical use.

Chewing forces were measured in a needle point tracing while the patients could view their actual and the proposed chewing forces (5 N, 10 N and 30 N) on a computer screen (biofeedback). Most probands used less than the proposed forces in the experiments. All probands approached the proposed level of force step by step. Fatigue of the chewing muscles led to a change in the Fourier-transformation of the recorded samples: An increase in short-waved components (frequencies of approximately 1 Hz) was found.

Acrylic, plaster and polyether were evaluated for their accuracy in indexing needle point registration. Additionally, a new experimental system was tested, that permits the dentist do immediately verify the accuracy of the recording. Best results were obtained when the indexes were not removed from the occlusal plane plates. When the indexes were dislodged, acrylic and plaster demonstrated the most accurate results in repositioning the occlusal plane plates. The experimental system demonstrated comparable accuracy to both, acrylic and plaster.

The titanium casting system Cyclarc (Morita) was examined for its suitability for the fabrication of dense, fitting restorations. The investment material Titavest CB exhibited no setting expansion. Instead, thermal expansion, highly dependent on the liquid/power ratio and the temperature during preheating, was observed. The castability of unalloyed titanium is fully acceptable for the fabrication of prosthetic restorations. Single crowns showed a high accuracy of fit, if an optimal liquid/power ratio was used for investment.

Difference reflectometry is a new method for assessing material surfaces by measuring the relative amount of light reflected within a range of 300-720 nm. The in vivo and in vitro results of the present study indicate that it is possible to transfer this measuring principle to dental applications. Reflexion measurements allow the detection of hard tooth structures and their pathologic alterations with adequate exactness. With the aid of this method it is possible to differentiate between carious hard tissues and clinically healthy tissues by color and surface structure during excavation. It also allows a reliable demarcation from oral soft tissues. Due to its high measuring frequency it may be used as on-line process control. In contrast to other spectrometric methods it requires a minimum of equipment and is easy to handle.

Electrical resistance measurements may be used to determine the situation of the pulp horn tips of teeth prepared for crown restorations. The resistance value recorded for these sites of minimum dentin thickness depends on the thickness of the dentin layer and the degree of tooth development. A resistance value of 25 k omega revealed dentin thickness of 0.7-1.45 mm. The teeth of younger patients had thicker dentin layers than those of older patients.

This study reports the clinical success rates of 6 different implant types inserted with defined clinical indications. The criterium used was implant loss. The survival periods of a total of 1723 implants were statistically evaluated according to Kaplan and Meier's method in relation to the type of implant used and the indication chosen.

With the aid of a photoelastic model it was possible to visualize the transmission of forces from four different types of attachment (parallel bar, round bar, RS- and O-ring attachment) onto IMZ implants. The parallel bar produced the highest stresses between the implants. By contrast, the round bar mainly transmitted transverse forces. RS- and O-ring attachments transmitted the least forces onto the implants. The retentive power of the attachments has also been measured. The round bar proved to be almost twice as retentive as the RS attachment and nearly three times as retentive as the O-ring.

17 distal extension cases were treated with IMZ implants supporting a fixed-removable bridge connected to a natural tooth abutment with a precision attachment. Instead of the polyoxmethylene internal shock absorber an identically dimensioned titanium element was incorporated in the implants of every second patient. Patients were monitored on a recall schedule. Implant and tooth mobility, pocket probing depth, and bone loss were the parameters evaluated. The results after a mean incorporation time of 16.5 months indicate that, at least during this initial time of function, there are no differences between a mobile and rigid bedding of the superstructure on the implants.