Debbie Chachra

The Long-term Effects of Water Fluoridation on the Human Skeleton:

Municipal water fluoridation has notably reduced the incidence of dental caries and is widely considered a public health success. However, ingested fluoride is sequestered into bone, as well as teeth, and data on the long-term effect of exposure to these very low doses of fluoride remain inconclusive. Epidemiological studies suggest that effects of fluoride on bone are minimal. We hypothesized that the direct measurement of bone tissue from individuals residing in municipalities with and without fluoridated water would reveal a relationship between fluoride content and structural or mechanical properties of bone. However, consonant with the epidemiological data, only a weak relationship among fluoride exposure, accumulated fluoride, and the physical characteristics of bone was observed. Analysis of our data suggests that the variability in heterogenous urban populations may be too high for the effects, if any, of low-level fluoride administration on skeletal tissue to be discerned.

A new tool to assess the mechanical properties of bone due to collagen degradation.

Current clinical tools for evaluating fracture risk focus only on the mineral phase of bone. However, changes in the collagen matrix may affect bone mechanical properties, increasing fracture risk while remaining undetected by conventional screening methods such as dual energy x-ray absorptiometry (DXA) and quantitative ultrasound (QUS). The mechanical response tissue analyzer (MRTA) is a non-invasive, radiation-free potential clinical tool for evaluating fracture risk. The objectives of this study were two-fold: to investigate the ability of the MRTA to detect changes in mechanical properties of bone as a result of treatment with 1 M potassium hydroxide (KOH) and to evaluate the differences between male and female bone in an emu model. DXA, QUS, MRTA and three-point bending measurements were performed on ex vivo emu tibiae before and after KOH treatment. Male and female emu tibiae were endocortically treated with 1 M KOH solution for 1-14 days, resulting in negligible collagen loss (0.05%; by hydroxyproline assay) and overall mass loss (0.5%). Three-point bending and MRTA detected significant changes in modulus between days 1 and 14 of KOH treatment (-18%) while all values measured by DXA and QUS varied by less than 2%. This close correlation between MRTA and three-point bending results support the utility of the MRTA as a clinical tool to predict fracture risk. In addition, the significant reduction in modulus contrasted with the negligible amount of collagen removal from the bone after KOH exposure. As such, the significant changes in bone mechanical properties may be due to partial debonding between the mineral and organic matrix or in situ collagen degradation rather than collagen removal. In terms of sex differences, male emu tibiae had significantly decreased failure stress and increased failure strain and toughness compared to female tibiae with increasing KOH treatment time.

Outside the classroom: Gender differences in extracurricular activities of engineering students

Data from the Academic Pathways Study, a component of the NSF-funded Center for the Advancement of Engineering Education, were used to investigate engineering student involvement in extracurricular activities. The study design used a variety of methods: the results presented here are from longitudinal and cross-sectional surveys of engineering students as well as interviews with graduating seniors. Quantitative data from both surveys suggest that women place higher importance on extracurricular activities than their male counterparts, as well as reporting higher participation in both engineering-related and non-engineering-related extracurricular activities. In addition, the importance of non-engineering extracurricular activities and the level of involvement of engineering-related extracurricular activities increases over four years of engineering education for women. For men, an increase with time was only observed for involvement in engineering-related activities. Results from the interviews corroborate the quantitative findings as well as suggesting some intriguing differences between genders: for example, that women may be more likely to take on leadership roles and men more likely to be involved in activities which involve design or ‘handson’ work.

Self-efficacy and task orientation in first-year engineering design courses

Many engineering programs are implementing hands-on engineering experiences early in the curriculum, typically in the form of a project-based course in which students design and build a prototype as a team. However, research on these courses suggests that task orientation is correlated with gender, as are the increases in self-efficacy observed. As engineering self-efficacy is a critical determinant of persistence in engineering, particularly for underrepresented groups, this suggests that these courses may be reinforcing existing differences in self-efficacy by failing to provide mastery experiences to those with low engineering self-efficacy at the start. This work-in-progress presents some preliminary research on investigating the relationship between self-efficacy, tasks undertaken in courses of this nature, and other factors including demographics and teaming experiences. The goal of this work is to enable educators to design team-based engineering courses that allow all students to have equal access to both technical and professional tasks, both to develop their skills and to increase engineering self-efficacy.

Drowning in method, thirsty for values: A call for cultural inquiry

A decade or more has passed since publication of most calls for reform in engineering education. In the ensuing time, there has been significant work on the design, implementation, and transferability of appropriate methods and techniques - accompanied by, in most cases, little discussion of the values and beliefs of the people involved. But many theories of change rely on a fundamental shift in human beliefs and values, and purport that institutionalization of methods is impossible without this shift. Given this, now may be a reasonable time to re-visit the questions: What are the values of people involved in engineering education, and are our educational reform efforts considering these values throughout the curriculum design process? In this paper, we examine several models for engineering educational reform, with a particular focus on the role of individual values in determining responses to change. We highlight the importance of developing understandings of individual perspectives and social context. We contrast a user-oriented approach to curriculum design with common scenarios of curriculum design practice, and we argue that, in many cases, successes in curricular change can be traced to employment of user-centered approaches.

Task choice, group dynamics and learning goals: Understanding student activities in teams

In this work-in-progress research paper, we explore the task choice of students in first-year, team-based engineering design project courses, with the goal of gaining insight on how to best structure and scaffold team projects so that all students have a positive, effective experience. What factors affect student task choice? Do students select tasks that they feel the most confident about completing, or do they challenge themselves to learn new skills? Do gender or team dynamics or self-imposed roles affect how students participate? If students are asked to develop individual learning goals for the project, does that influence the activities that they engage in, and does articulating learning goals lead to a more beneficial project experience? We are using a mixed-methods approach to investigate the experiences of a small cohort of students engaged in a first-year design project, in order to better understand how students choose to undertake different tasks in team projects.

Response to Letter to the Editor, “The Long-term Effects of Water Fluoridation on the Human Skeleton”

Thank you for allowing us the opportunity to respond to the Letter to the Editor submitted by Phillips et al. in response to our paper in this journal, “The Long-term Effects of Water Fluoridation on the Human Skeleton” (Chachra et al., 2010). We appreciate the points that they raise regarding the confounding effects of age, gender, and disease states on the effect of fluoride on bone quality. In fact, we explicitly address the interaction effect of age and fluoride, under the heading “Variability in the Data” (p. 1221). The reference cited there is the doctoral thesis of the first author (Chachra, 2001), from which the data presented in this paper are excerpted. That thesis includes a detailed analysis of the data by age, gender, and disease state, which were collected for each patient and are presented in Table 1 (p. 1220). These analyses are outside the scope of the work presented here, but briefly, there was no evidence of a gender-specific relationship between the mechanical properties and the fluoride content. The relationship between the ultimate compressive stress and the fluoride content was slightly weaker when the osteoporotic samples were excluded, suggesting that both disease states have a similar effect on mechanical strength of bone. As for the inclusion/exclusion criteria of patients: We apologize, since it was not clear from the brief text that all patients undergoing primary total hip arthroplasties under the care of our collaborating orthopedic surgeons were approached to participate in this study. No other criteria were applied. Finally, we agree with Phillips et al. that the work presented here does not conclusively address the effects of long-term administration of environmental levels of fluoride on the mechanical properties of bone. To do that, we would need to track not only the duration of exposure to fluoridated water, as they point out, but also factors such as diet (Singer et al., 1985) and use of fluoride-containing oral care products and fluoride supplements (Ismail, 1994; Whitford, 1994). Gathering these kinds of detailed data retroactively for the requisite period of many decades is prohibitive. As well, beverages and foods are increasingly prepared with fluoridated water (Clovis and Hargreaves, 1988), so living in a non-fluoridated area does not guarantee the absence of exposure to environmental fluoride. This inability to measure the exposure accurately was the rationale for the comparison of mechanical properties with the fluoride content of the bone tissue, measured directly. Fig. 2 (p. 1222) displays the wide variation in response to fluoride, since only about 5% of the variability in the data could be explained by the fluoride content. As we pointed out, this is consistent with many decades of epidemiological studies that have failed to find a relationship between fluoride exposure and bone quality (McDonagh et al., 2000). In agreement with Phillips et al., we wrote in the conclusions of our paper (p. 1222) that we cannot rule out subtle effects of long-term ingestion of fluoride on the mechanical properties of bone, especially in the case of susceptible individuals. However, at the population level, there is no substantive evidence that fluoridated drinking water alone has an effect on bone quality.

Work in progress - a provisional competency assessment system

Over the last two years Olin College has been defining and implementing a provisional system to develop and assess student competency levels. The system particularly emphasizes the importance of creating a community of practice that includes not only faculty but also staff and students. In this paper we provide an overview of the design process, and comment on the results of our first year of implementing the system

An interactive exploration of gender and computing: unpacking the student experience

Being a computer science and engineering student is experienced differently by male and female students; gendered interactions affect the development of academic and professional role confidence as well as professional identity. In this hands-on special session, participants explore concepts of gender schemas, privilege, and identity using a range of interactive activities. We have found these concepts useful in framing discussion with our students and in understanding and improving student experiences. The session introduces and obtains feedback on a Gender and Engineering Exploration Kit, which the participants are encouraged to review, use, and share at their home institutions.

Special session: An interactive exploration of Gender and engineering: Unpacking the experience

The engineering student experience is understood to differ for male and female students; gendered interactions affect the development of academic and professional role confidence, as well as engineering identity. The purpose of this session is twofold. First, we aim to introduce participants to concepts of gender schemas, privilege, and identity using a range of interactive activities, including brainstorming and structured discussion. Second, we intend to share information about and obtain feedback on a Gender Discussion Exploration Kit, which the participants will be encouraged to review, use, and share at their home institutions.