A case-based learning model in orthodontics.

This report describes a case-based, student-centered instructional model designed to mimic orthodontic problem-solving and decision-making in dental general practice. Groups of about ten junior students meet in a series of one-hour seminars. One week prior to each seminar, a set of diagnostic data is distributed to every student and instructor for advance preparation. A list of questions is included to guide students through the analytical process and they record their diagnosis and treatment plan on a form. At each seminar two preassigned students lead the discussion, and others are randomly selected to answer the programmed questions. Instructors serve as facilitators and evaluators. To ensure consistency of evaluations and feedback, instructors are provided all the expected responses in advance, which they discuss in a pre-seminar meeting. Both students and instructors rated the seminars positively. Students reported significantly higher (p < 0.01) levels of confidence after the seminars for each of seven reasoning skills. This teaching method can be applied to other dental areas to better develop the clinical reasoning skills of future dentists.

Nodule formation and calcification of mandibular condylar cartilage cell cultures mimic in vivo ultrastructure.

Mandibular condylar cartilage (MCC) of growing mammals contains four layers of cells which display a series of increasingly differentiated phenotypes and which culminate in a terminally differentiated cell that produces a calcified matrix. In this study, MCC cells were placed into culture in Dulbecco's modified Eagle's medium containing 10% fetal bovine serum and 50 micrograms/ml ascorbic acid. After 12 h in culture, transmission electron microscopy revealed the presence of multiple cell types that underwent differentiation with additional time in culture. By 7 days, fusiform-shaped cells were seen that contained numerous actin-like cytofilaments and micropinocytotic vesicles characteristic of myofibroblasts. Chondroblast-like cells were also observed. By 10 days, without addition of beta-glycerophosphate or dexamethasone, these cellular events culminated in the formation of mineralized nodules containing matrix vesicles. The nodular surface at day 13 consisted of two or more layers of myofibroblast-like cells, while the deeper zones of the nodule contained cells displaying a morphology typical of calcified hypertrophic chondroblasts. These ultrastructural observations are consistent with the hypothesis that cells from the MCC are capable of recapitulating in culture the maturational events seen in vivo. This cell culture model may be useful for investigating cell-mediated cartilage calcification without the addition of exogenous phosphate or other regulatory factors.

Phenotypic changes of rabbit mandibular condylar cartilage cells in culture.

The present study describes the behavior of mandibular condylar cartilage (MCC) cells as a function of time in primary culture, since it is not yet clear whether these cells maintain their phenotype in culture. MCC cells from New Zealand white rabbits were seeded at high density and cultured in DMEM containing 50 micrograms/mL ascorbic acid and 10% fetal bovine serum. These cells appeared as a heterogeneous population and changed their shape, size, and refractivity as cultures aged. Cartilage-like cells, which always dominated the culture, were infiltrated with a minority of fibroblast-like cells. Cell number increased progressively, and cultures reached confluence at nine days. Antibody activity for cartilage-specific glycosaminoglycan was determined by ELISA assay. This reaction reached a maximum at six days and decreased thereafter. Cultures stained with Alcian blue (pH 1.0) supported these results. Cytoplasmic mRNA analysis indicated that the transcription of type II collagen gene was present at all time points. Type I collagen and alkaline phosphatase mRNA levels showed progressive increases from 12 h to nine days, with significantly higher values in cells cultured for six, nine, and 12 days than in cells collected from earlier time points. These results suggest that in our present culture system, MCC cells undergo phenotypic changes that resemble their maturation processes in vivo.

Cephalometric superimposition on the cranial base: a review and a comparison of four methods.

Spatial change in the jaws of growing persons is often evaluated by superimposing cephalometric tracings made at different points in time. Methods of superimposition vary according to structures used as references within the skull. This study compares four different superimposition methods. The sample consisted of 26 patients (13 boys, 13 girls) treated for Class II, Division 1 malocclusions with extraction of the four first premolars. Tracings of pretreatment (average age for boys, 12.5 years; for girls, 12.2 years) and posttreatment (average age for boys, 15.4 years; for girls, 14.9 years) cephalograms were superimposed according to the following methods: (1) best fit of anterior cranial base anatomy, (2) superimposition on SN line, registered at S, (3) superimposition on registration point R with Bolton-nasion planes parallel, and (4) superimposition on basion-nasion (Ricketts), registered at point CC (4) and point N (4a). Differences in amount of change among the superimposition methods were assessed independently for each of the following landmarks: PNS, ANS, A, B, Pog, Gon. On each patient and for each landmark, ten distances--the paired differences of five posttreatment positions obtained by methods 1, 2, 3, 4, and 4a--were evaluated. Two methods were compared at a time. A t test examined the average difference for each comparison. Because all differences between all paired methods were significant (P less than 0.01), t tests were then viewed under the hypothesis that a difference less than or equal to 1 mm was insignificant clinically. Clinically-statistically significant differences were found only for boys and for the total sample between methods 4a and each of methods 1, 2, and 3. As method 4a is advocated to assess changes of point A (Ricketts), this method gives, for the same person, an interpretation of anterior maxillary change in position different from the other methods. Conclusions about facial changes may be made only in reference to the superimposition method.