Biomedical subjects

G Göller

Publications and source records attributed to G Göller.

3 recordsLinked to original sources

PubMed2000

Shear bond strength of resin luting cement to glass-infiltrated porous aluminum oxide cores.

STATEMENT OF PROBLEM: Resin bonding surface treatment methods for conventional silica-based dental ceramics are not reliable for glass infiltrated high alumina content In-Ceram ceramics. PURPOSE: This study developed an alternative surface treatment to improve resin bonding of glass-infiltrated aluminum oxide ceramic blasting with diamond particles and then observed the efficiency of this treatment. Material and methods. In-Ceram test specimens were prepared and divided into 2 groups. All specimens were sandblasted with Al(2)O(3), and blasted with diamond particles and 2 adhesive resins were applied. After bonding and storage in humid conditions, shear bond strength values were measured with a universal testing machine. Surface roughness and fracture interfaces were determined with a perthometer and a SEM. RESULTS: The highest bond strength was obtained on the samples blasted with diamond particles (group II). The differences between the 2 groups and the 2 adhesive resin cements were both statistically significant. CONCLUSION: Panavia-Ex cement exhibited higher bond strength than Super-Bond cement. This higher bond strength was attributed to ceramic oxide and ester bond and the mechanical properties of Panavia-Ex cement.

Aluminum Oxide↗

PubMed1998

Resampling methods in sparse sampling situations in preclinical pharmacokinetic studies.

Toxicokinetic studies often require destructive sampling and the determination of drug concentrations in the various organs. Classically, the corresponding information is summarized in one mean concentration-time profile, which is regarded as representative for the animal population. On the basis of a mean profile, only estimates of the secondary pharmacokinetic parameters (for example AUC, t1/2) but no variability measures may be obtained. In this paper two resampling techniques are contrasted to Bailer's approach. The results obtained show that the resampling techniques can be considered a reliable alternative to Bailer's approach for the estimation of the standard error of the AUC t(k)0 in the case of normally distributed concentration data. They can be extended to the estimation of a variety of other secondary pharmacokinetic parameters and their respective standard deviations. One disadvantage with Bailer's method is its restriction to linear functions of the concentrations. On the other hand, using the population approach, prior knowledge of the underlying pharmacokinetic model is necessary. The resampling techniques discussed here, the "pseudoprofile-based bootstrap" (PpbB) and the "pooled data bootstrap" (PDB), are noncompartmental approaches. They are applicable under nonnormal data constellations and permit the estimation of the usual secondary pharmacokinetic parameters along with their standard deviations, standard errors, and other statistical measures. To assess the accuracy, precision, and robustness of the resampling estimators, theoretical data from three different pharmacokinetic models with different add-on errors (up to 100% variability) were analyzed. Even for the data sets with high variability, the parameters calculated with resampling techniques differ not more than 10% from the true values. Thus, in the case of data that are not normally distributed or when additional secondary pharmacokinetic parameters and their variability are to be estimated, the resampling methods are powerful tools in the safety assessment in preclinical pharmacokinetics and in toxicokinetics where generally sparse data situations are given.

Area Under Curve↗

PubMedDate not supplied

Analysis of pseudo-profiles in organ pharmacokinetics and toxicokinetics.

In general, the pharmacokinetic model parameters, like rate constants, area under the curve (AUC) etc. are estimated via a two-stage procedure, where the values obtained from concentration-time relationships within one subject (experimental unit) are considered to be functionally related to the drug concentrations measured. In many cases 'mean' estimators and their respective standard errors are calculated afterwards. The determination of drug concentrations in organs as well as in the serum of small animals (mice, rats) in dependence of the time after administration often does not permit the establishment of reasonable profiles within one subject suited for conventional pharmacokinetic analyses and tolerability studies. Frequently, only one experimental value per organ or animal is recorded. The consequence is that most pharmacokinetic parameters are to be estimated on the basis of the mean concentrations rather than via the mean of individual parameter estimates. In all cases of a non-linear relationship between a target item and the concentration, the mean-concentration based estimators and the two-stage profile based estimators need not coincide. In addition, in the former case variance estimators may be either difficult to obtain or not deducible. In order to get variance estimators as well as to enable comparisons between different treatment regimens, in addition to bioequivalence testing as a step towards human dose finding studies, various resampling techniques (parametric and non-parametric bootstrap) were applied to generate pseudo-profiles from independent measurements and compared to their more conventional counterparts where applicable. Simulation studies based on different predefined pharmacokinetic models (first-order elimination after i.v. bolus, first-order elimination after first-order absorption, simple capacity-limited kinetics) revealed that even the non-parametric pseudo-profile stratified 'bootstrap' (resampling with replacement per time point) performs quite satisfactorily.

Administration, Oral↗