Background: This paper focuses on the additional time and effort associated with placing a problem based learning (PBL) case within a learning management system (LMS) and reporting on both student LMS utilization and course satisfaction data. Methods: The study involved 13 PBL students who volunteered to participate in one of two 9 week long PBL courses (6 or 7 students in each course). The LMS selected for utilization in this experiment was Moodle version #1.9.5. A questionnaire assessed the students’ attitudes about the hybrid PBL-LMS system. Time-effort data, collected prospectively, were divided into faculty tasks that: occur during a typical PBL case; involved preparing and presenting several lectures as part of an expert resource session(s); and were associated solely with the LMS creating and posting process. Results: The total time in each course was 119.5 hours and the LMS related tasks involved 25.5 hours or 21.3% of the total course time. While opinions will vary on this issue, this extra time is probably outweighed by the advantages a LMS offers. For example, by placing a PBL course inside a LMS tracking and comparing the performance of multiple simultaneous PBL groups and tutors for consistency can be readily accomplished. Conclusions: A majority of the students (72.7%) agreed that the various materials contained on the website (e.g. videos and supplemental materials) were very helpful and 54.5% agreed that all future PBL courses should have a web-based component.
This study was aimed to observe the fracture surfaces of dentin specimen after the fatigue test to be taken into account for teeth fracture. Radicular dentin from bovine lower central incisors was used. Dentin slabs of 1 mm thickness were trimmed into dumbbell-shaped specimens along the tooth axis, then, fatigue tests were performed. The staircase method was employed to determine fatigue strength and its standard deviation. Thereafter, the fractured surfaces of the specimens were coated using an ion sputtering machine and examined by scanning electron microscopy. Observations of the dentin fatigue specimens using the scanning electron microscopy showed that the fatigue striations were almost aligned perpendicularly to dentinal tubules. Moreover, fatigue striations spaced approximately 3 to 10 μm apart from fracture surfaces of intertubular dentin. Additionally, a porous fibrous reticulate texture can be seen in the intertubular dentin. On the other hand, a thin peritubular collar can be seen lining the tubules in dentin. However, some of the peritubuler cuffs in the dentin appeared debonded from the surrounding intertubular dentin and partially fractured. In addition, it was also confirmed that there was no distinction between the peritubular dentin and the intertubular dentin in fracture surfaces. The peritubular and intertubular dentin differ in fracture and fatigue crack propagations.