Synchrotron X-ray diffraction and scanning electron microscopy to understand enamel affected by metabolic disorder mucopolysaccharidosis
Introduction
Enamel being a hard and mineralized tissue can undergo metabolic disturbances during developmental stages of the tooth that can lead to the disorientation of enamel crystallites and cause defects in the structure of enamel. One of the rare metabolic disorders affecting the enamel structure is mucopolysaccharidosis (MPS) which has been classified into seven types (James et al., 2011). This study focuses on two types of MPS known as MPS I (Hurler syndrome) and MPS IVA also known as Morquio’s syndrome. In both of these types of MPS, deficiency of an enzyme responsible for the breakdown of glyscosaminoglycans (GAGs) results in a build up of GAGs that affects the crystallite structure of enamel.
MPS I (Hurler syndrome) has a prevalence of 1 in 100,000 and is characterized by the deficiency of an enzyme known as Alpha-l-iduronidase which is responsible for the degradation of GAGs such as heparin sulphate and dermatan sulphate. The accumulation of GAGs due to the enzyme deficiency leads to among other things intellectual disability, joint disease and cardiomyopathy (Neufeld and Muenzer, 1995). On the other hand MPS IVA (Morquio A syndrome) is an autosomal recessive disorder with a prevalence of 1 in 170,000 live births (Meikle et al., 1999) and is caused by the deficiency of N-acetylgalactosamine 6 sulphatase (GALNS) (Baker et al., 1993, Masuno et al., 1993, Hendriksz et al., 2014, Leadley et al., 2014). MPS IVA is the only type of MPS that is known to be associated with defects in the enamel structure (Witkop and Sauk, 1976) although there is accumulation of GAGs in the dental follicle of developing teeth in the cases of MPS I (Hurler syndrome) and MPS II (Hunter syndrome) (Worth, 1966, Gardner, 1971). In MPS IVA significant malformations in the enamel structure are seen. The enamel is thin, pitted, dull grey in colour and has the tendency to flake off from the underlying dentine. The enamel being hypoplastic in nature has a normal radiodensity and hardness (Garn and Hurme, 1952, Rølling et al., 1999). This study, by making use of a combination of synchrotron X-ray diffraction and scanning electron microscopy, aims to determine the structure at multiple length-scales (from the crystallographic to the microstructure of the enamel deciduous teeth affected by the MPS I and MPS IVA and to compare these with healthy deciduous enamel).
Section snippets
Specimen preparation
The samples used in this study were deciduous maxillary central incisors which were collected from individuals affected by different types of mucopolysaccharidosis specifically MPS I and MPS IVA, and from healthy type-matched control individuals. The specimens were collected following ethical approval (UK National Research Ethics Service Reference 08/H1202/119) and consent at the Birmingham Children’s Hospital NHS Foundation Trust, Birmingham, United Kingdom. The extracted teeth were stored in
Results
Fig. 1 shows two scanning electron micrographs and a texture map taken from a healthy deciduous maxillary central incisor. Fig. 1a shows the texture map with a colour-scale for the FWHM values and schematic of the outline shape of the healthy maxillary central incisor. The incisal surface and the lingual aspect are represented by the two red arrows. The colour-scale for the FWHM values indicates the degree of preferred orientation or the texture of enamel. A high value of FWHM suggests that
Discussion
Our study shows that the incisal enamel surface of the healthy deciduous maxillary central incisor has higher texture or preferred orientation of enamel crystallites compared to the cervical region marked by a red box as shown in Fig. 1a, this finding is supported by the scanning electron micrographs as Fig. 1b shows that the enamel prisms at the incisal surface are well oriented and aligned indicative of a high enamel texture or preferred orientation whereas in Fig. 1c the cervical region has
Conclusion
Our study suggests that in health the enamel texture or preferred orientation of enamel crystallites in the incisal region is higher than in the cervical region and the regions away from the enamel surface. When it comes to comparison, healthy deciduous enamel has the highest enamel texture or preferred orientation overall whereas MPS I and MPS IVA affected deciduous enamel show low enamel texture or preferred orientation overall indicating that the GAGs play an important role in causing loss
Acknowledgements
This work was performed on the ESPRC-funded XMaS beamline at the ESRF, directed by M.J. Cooper, C.A Lucas and T.P.A Hase. We are grateful to the beamline team of S.D. Brown, O. Bikondoa, D. Wermeille, L. Bouchenoire and P. Thompson for their invaluable assistance and to S. Beaufoy and J. Kervin for additional support.
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