The effect varied scanning electron microscopy desiccation techniques has on demineralized dentin.

The study objective was to assess (a) the effect of a rubbing-application of ethylenediaminetetraacetic acid (EDTA) or citric acid (CA) has on the ultrastructure of surface dentin and (b) the effect of two scanning electron microscopy (SEM) desiccation preparation techniques have on the collagen surface produced. Treatment regions on proximal root surfaces of extracted human teeth were root planned to expose dentin. Cotton pellets soaked in either 30% CA or 24% EDTA solution were rubbed on the treatment region then processed for SEM using one of two desiccation techniques, that is, (a) critically point dried from liquid CO2 (control) or (b) air-dried from tetramethylsilane (experimental). Specimens were coated with gold/palladium and viewed/photographed with an SEM. Specimens of the control groups displayed tufted fibrils (CA > EDTA) with many dentin tubules being partially obscured by overhanging fibrils. Air-dried specimens of both treatment groups displayed a flat intact monolayer devoid of a matted meshwork of fibrous collagen. Discrete fibril "sprigs," emanating from the surface monolayer, were characteristic of the EDTA group only. The rubbing-application of EDTA on dentin produces a tufted fibril surface somewhat similar to that produced by CA. Air-drying desiccation of both resulted in marked distortion with fibril collapse/coalescence of the tufted collagen matrix.

Facilitating improvements in laboratory report writing skills with less grading: a laboratory report peer-review process.

Incorporating peer-review steps in the laboratory report writing process provides benefits to students, but it also can create additional work for laboratory instructors. The laboratory report writing process described here allows the instructor to grade only one lab report for every two to four students, while giving the students the benefits of peer review and prompt feedback on their laboratory reports. Here we present the application of this process to a sophomore level genetics course and a freshman level cellular biology course, including information regarding class time spent on student preparation activities, instructor preparation, prerequisite student knowledge, suggested learning outcomes, procedure, materials, student instructions, faculty instructions, assessment tools, and sample data. T-tests comparing individual and group grading of the introductory cell biology lab reports yielded average scores that were not significantly different from each other (p = 0.13, n = 23 for individual grading, n = 6 for group grading). T-tests also demonstrated that average laboratory report grades of students using the peer-review process were not significantly different from those of students working alone (p = 0.98, n = 9 for individual grading, n = 6 for pair grading). While the grading process described here does not lead to statistically significant gains (or reductions) in student learning, it allows student learning to be maintained while decreasing instructor workload. This reduction in workload could allow the instructor time to pursue other high-impact practices that have been shown to increase student learning. Finally, we suggest possible modifications to the procedure for application in a variety of settings.

The effects of scanning electron microscopy desiccation preparation on demineralized dentin surfaces.

This study assessed the effect various scanning electron microscopy (SEM) desiccation preparation techniques have on a tufted collagen surface produced using an acid-burnished (rubbed) demineralization application technique. Citric acid- soaked cotton pellets (30%) were burnished on the dentin treatment region, rinsed in water, and then fixed. Four SEM desiccation preparation techniques were employed: (1) air-dried from glutaraldehyde; (2) air-dried from ethanol; (3) critical point dried from liquid carbon dioxide (control); or (4) air-dried from tetramethylsilane. Control specimens all displayed a characteristic tufted fibril surface. In all experimental groups, fibrils collapsed, forming an intact, undulating nondescript surface monolayer. All air-drying SEM desiccation preparation procedures appear to cause artifactual distortion of a tufted dentin collagen surface.