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Rapid Responses: Rapid Responses published:
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Breadsticks are a worthy study model as well
- Karl A Grindulis (21 December 2007)
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poor camparisons
- R. A. Evans (22 December 2007)
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Accuracy of T score determination for Choc Bars
- John J. Brand (22 December 2007)
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How old was your chocolate?
- Susan M Ott (30 December 2007)
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A fallen engineer writes...
- John Shaw (9 January 2008)
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Karl A Grindulis, Consultant Rheumatologist Sandwell General Hospital, West Bromwich, B71 4HJ
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When discussing bones and osteoporosis with students, GP's and lay public, I often snap a breadstick to demonstrate that bones have a hard shell and softer centre. Differences in the pressure needed to snap a breadstick, their appearance in cross-section and the number and size of crumbs at the bottom of laptop and brief cases from fragility fractures in transit caused me to consider their relative fracture risk. Unfortunately, I don't have access to a physics laboratory but, over the last 10 years, experience suggests that there are differences in fracture resistance. With the strongest first, I'd suggest M&S, Sainsbury's, Waitrose and Tesco's. Their order in terms of pallatability may, of course, be quite different but this has not been tested. I'd be interested to hear from those with equipment to test this more thoroughly if my impression is correct. Competing interests: None declared |
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R. A. Evans, Sitting down, Cruchie eater Home, SY23 3HF
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The comparison of two bars of varying throws the results into question. 1 Cruchie bars are uniform in shape, Areos are not - they are designed to break at specific point which are made thinner hence the picture of the bar broken in half! 2. Crunchies are brittle toffee with a chocolate coating, Areos are chocolate throughout (well chocolate ones are), a fairer comparison would have been to use mint Aeros which have a chocolate outer and a candy inner - more comparable in structure to a Crunchie. Suggest further tests are carried out to test mint Aeros if the budget will allow, if not Santa might bring some if you ask nicely! Competing interests: None declared |
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John J. Brand, Sessional GP PO12 2JS
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Perhaps a more relevant measure of the T score for both bars could be made by reference to young healthy specimens of the same gender and not to a 50 year old woman. Cf. WHO Osteoporosis Foundation recommendations. Yours etc. John Brand Competing interests: None declared |
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Susan M Ott, physician University of Washington 98112
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I was puzzled by the statement that both T and Z scores were referenced to a 50-year-old woman. When the T-score and Z-score are the same, then the age would have to be the age of peak bone mass, which is generally considered to be age 25 years. A 50-year-old woman would have T-score that is lower than her Z-score, because the average bone density of 50- year- old women is lower than of those at peak bone mass. The whole body bone density for a 25-year-old white female is 1.095 ± .087 g/cm2 (reference from Hologic as printed in the appendix of the ASBMR Primer); thus a T-score of -9 would correspond to a density of 0.312 g/cm2. According to a recent reference database for children (Kalkwarf, J Clin Endocrin Metab, 2007;92:2087) the median bone density for a 7-year-old black female is 0.753 g/cm2, with standard deviation of 0.062. Thus, a bar with a density of 0.312 g/cm2 would have a z-score of about -7. I'm not sure how old the chocolate bars were in this study, but I used the data from the 7-year-old because it was the youngest one in the database. If the bars were only a few weeks old, then the z-scores would be closer to zero. Competing interests: None declared |
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John Shaw, FY1 Doctor St Helier Hospital, SM5 1AA
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As a former chartered Engineer who has turned his hand to medicine late in life (well, aged 39), I was very interested to read your article. It took me back to my PhD on Preparation and Characterisation of Porous Hydroxyapatite (University of London, 1996), in which I spent 3 long years firstly using Aero as my dream model structure for a porous bone substitute, and secondly demonstrating that it does not really matter what shape of hole you put in a brittle material, it is the overall percentage porosity which determines its strength. A few minor observations. As has been pointed out by other correspondents, standard sized test pieces would have helped to layer up the cloak of credibility surrounding your analysis. You note improved elastic stress properties in the Aero - I think that plastic strain is more likely to be the clincher. Finally, I think that there is definitely some potential for fracture toughness studies in your work, but that may be a job for next year. I for one would enjoy seeing a standard sized hammer being swung through a hundred or so standard sized Nestle and Cadbury products. For an old classic, have a look at Behiri and Bonfield, Fracture Mechanics of Bone, J Biomechanics 1984; 17: 25-34. Competing interests: None declared |
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