Differences of isolated dental stem cells dependent on donor age and consequences for autologous tooth replacement.

OBJECTIVE: Autologous therapy via stem cell-based tissue regeneration is an aim to rebuild natural teeth. One option is the use of adult stem cells from the dental pulp (DPSCs), which have been shown to differentiate into several types of tissue in vitro and in vivo, especially into tooth-like structures. DPSCs are mainly isolated from the dental pulp of third molars routinely extracted for orthodontic reasons. Due to the extraction of third molars at various phases of life, DPSCs are isolated at different developmental stages of the tooth. DESIGN: The present study addressed the question whether DPSCs from patients of different ages were similar in their growth characteristics with respect to the stage of tooth development. Therefore DPSCs from third molars of 12-30 year-old patients were extracted, and growth characteristics, e.g. doubling time and maximal cell division potential were analysed. In addition, pulp and hard dental material weight were recorded. RESULTS: Irrespective of the age of patients almost all isolated cells reached 40-60 generations with no correlation between maximal cell division potential and patient age. Cells from patients <22 years showed a significantly faster doubling time than the cells from patients ≥22 years. CONCLUSION: The age of patients at the time of stem cell isolation is not a crucial factor concerning maximal cell division potential, but does have an impact on the doubling time. However, differences in individuals regarding growth characteristics were more pronounced than age-dependent differences.

Low-temperature degradation of different zirconia ceramics for dental applications.

The aim of this investigation was to determine the influence of simulated ageing on the tetragonal-to-monoclinic phase transformation and on the flexural strength of a 3Y-TZP ceramic, compared to alumina toughened zirconia (ATZ) and ceria-stabilized zirconia (12Ce-TZP). Standardized disc specimens of each material were hydrothermally aged in steam at 134°C and 3bar for 0, 16, 32, 64 or 128h. The phase transformation was determined by X-ray diffraction (XRD) and atomic force microscopy. Scanning electron microscopy was performed to estimate the depth of the transformation zone. The flexural strength was investigated in a biaxial flexural test. XRD revealed a significant increase in the monoclinic phase content for 3Y-TZP and ATZ due to ageing, although this increase was less pronounced for ATZ. In contrast, the monoclinic phase content of 12Ce-TZP was not influenced. For 3Y-TZP and ATZ, a transformation zone was found of which the depth linearly correlated with ageing time, while for 12Ce-TZP no transformation zone could be observed. Changes in flexural strength after ageing were heterogeneous: while 3Y-TZP showed a significant decrease in strength - from 1740 to 1169 MPa - with ATZ there was a considerable increase - from 1093 to 1378 MPa. The flexural strength of 12Ce-TZP remained unaffected at the low level of about 500 MPa. These results indicate that both alumina and ceria, as stabilizing oxides, reduce the susceptibility of zirconia to hydrothermal degradation; the alternative use of these oxides may enhance the clinical long-term stability of dental zirconia restorations.

The effects of seasonal changes on temporomandibular disorders.

The aim of our study was the evaluation of seasonal influences on development and evolution of temporomandibular disorders (TMD). In a retrospective study based on data from 1997 and 1998, we analyzed the monthly number of patients at the Department of Prosthodontics. The total number of first time examinations during these two years was 11,747. Nine hundred and sixty-one (961) patients showed symptoms frequently found in TMD. These patients were submitted to a special TMD diagnosis based on the criteria of a validated craniomandibular index questionnaire. In 568 patients (group A1), a TMD was confirmed, in the other 393 patients (group A2), the disorder could not be confirmed. Dividing up the numbers of patients into summer and winter half years, we found statistically significant relationships between patient numbers and season in TMD patients (A1) as well as in all patients (group B). The distribution of the monthly numbers of TMD patients with its maximum in winter, however, was characteristically different from that of all patients with the maximum in summer. The number of TMD patients per month was significantly correlated to the mean daily sunshine duration per month. Parallels could be drawn to seasonal variations of symptoms in Seasonal Affective Disorders (SAD). As the mechanisms which influence the emergence of psychologically impacted disease in TMD patients might be comparable to SAD, we propose that a similar therapy may be applied.