Elsevier

Micron

Volume 83, April 2016, Pages 48-53
Micron

Synchrotron X-ray diffraction and scanning electron microscopy to understand enamel affected by metabolic disorder mucopolysaccharidosis

https://doi.org/10.1016/j.micron.2016.01.001Get rights and content

Highlights

  • Mucopolysaccharidosis (MPS) is an inherited metabolic disorder.

  • Synchrotron X-ray diffraction and scanning electron microscopy have been used to study normal dental enamel and dental enamel affected by mucopolysaccharidosis (MPS).

  • Presence of a partially calcified layer between the enamel and dentine at the EDJ (Enamel Dentine Junction) in a MPS affected tooth can cause the tooth to become weak and fracture whereas scalloping of EDJ seen in a normal tooth allows the tooth structure to become more stable and resist fracture.

Abstract

Mucopolysaccharidosis (MPS) is an inherited metabolic disorder that can affect the tooth structure leading to defects. Synchrotron X-ray diffraction being a state of the art technique has been used to determine the enamel crystallite orientation in deciduous enamel affected by Mucopolysaccharidosis Type I and Mucopolysaccharidosis Type IVA and comparing these with that of healthy deciduous enamel. Using this technique it was observed that there is a loss of texture in deciduous enamel affected by Mucopolysaccharidosis Type I and Mucopolysaccharidosis Type IVA when compared to the healthy deciduous enamel. Generally it was observed that the incisal surface of the deciduous teeth possessed a higher texture or preferred orientation of enamel crystallites and on progression towards the cervical region there was a decrease in the texture or preferred orientation of enamel crystallites. Scanning electron microscopy showed that the presence of a poorly calcified layer between the enamel and dentine at the enamel–dentine junction (EDJ) in MPS affected samples was likely to be responsible for rendering the tooth structure weak and prone to fracture as is often the case in MPS affected deciduous enamel.

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.

References (18)

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