STUMBLING BLOCKS TO THE ACCEPTANCE OF IDEAS: BONE MINERAL AS A CASE STUDY

Science progresses as ideas are tested and as analyses confirm or refute specific statements and interpretations. Scientists typically assume that, through these means, the incorrect and the unsound are culled out, so as to bring the actual facts to light. In some cases, however, an observation that is irrefutably correct and also significant to a particular group of scientists is overlooked or not accepted by them. Not only is such an error irksome at the practical level to those in that field, but it also causes concern to the broader scientific community that wishes to avoid such systemic errors in judgment. Analysis of such mistakes may reveal flaws in the approach taken, and future errors can be avoided. The case study here concerns the mineral component of bone, which is a nanocrystalline form of hydroxylapatite [Ca₁₀(PO₄)₆(OH)₂] in which several weight percent carbonate substitute for the phosphate ion. The history of the discovery of the chemical composition and later the mineral structure of the inorganic salt in bone follows, as expected, the historic development of the field of chemistry. Interwoven with this story of increasing sophistication in determining the presence and stoichiometric proportions of elements in bone apatite, however, is a tale of the often-overlooked component water, H₂O. The presence of structurally incorporated water in bone apatite, in addition to even greater amounts of simply adsorbed water, was documented 140 years ago. Over the intervening decades, repeated studies by researchers in such fields as inorganic chemistry, industrial synthesis, mineralogy, dental science, and spectroscopy further documented the presence of water within the structure of carbonated apatites produced at low temperature, including those that form bone. Yet, even today, there is no widely recognized review article on bone or its mineral component that lists water as a structural component of bone apatite. Among the possible reasons for this extreme example of oversight are (1) although it is medical researchers who typically investigate bone, the pertinent data in this bone issue came dominantly from non-medical researchers, and (2) medical scientists became lulled by the simple formula of the mineral hydroxylapatite, relying too heavily on the anhydrous nature of what was only the "model" mineral.