Transmission electron microscope characterisation of molar-incisor-hypomineralisation

Molar-incisor-hypomineralisation (MIH), one of the major developmental defects in dental enamel, is presenting challenge to clinicians due, in part, to the limited understanding of microstructural changes in affected teeth. Difficulties in the preparation of site-specific transmission electron microscope (TEM) specimens are partly responsible for this deficit. In this study, a dual-beam field emission scanning electron microscope (FESEM)/focused ion beam (FIB) milling instrument was used to prepare electron transparent specimens of sound and hypomineralised enamel. Microstructural analysis revealed that the hypomineralised areas in enamel were associated with marked changes in microstructure; loosely packed apatite crystals within prisms and wider sheath regions were identified. Microstructural changes appear to occur during enamel maturation and may be responsible for the dramatic reduction in mechanical properties of the affected regions. An enhanced knowledge of the degradation of structural integrity in hypomineralised enamel could shed light on more appropriate management strategies for these developmental defects.

Enamel hypoplasia in coeliac children: a potential clinical marker of early diagnosis

AIM

To assess at the scansion electron microscope (SEM) the structural aspects of enamel hypoplasia (EH) in coeliac disease (CD) with the aim to investigate our hypothesis of a possible significant difference between structural characteristics of EH in CD affected patients and EH of non-coeliac patients. If the presence of specific features of the EH associated with CD were demonstrated, these findings would represent for the dentist early non-invasive clinical markers of diagnosis of CD in case of suspected disease.

METHODS

We analysed at SEM two samples of enamel fragments from hypoplasic teeth, both deciduous and permanent, harvested from 10 coeliac children (18 permanent teeth, 6 deciduous teeth; study group) and 10 non-coeliac children (16 permanent teeth, 4 deciduous teeth; control group) treated for dental caries, dental extractions for extensive caries lesions or deciduous teeth exfoliation.

RESULTS

Significant structural differences were noted between EH of non-coeliac patients and same dental ? lesion in the group with CD. In the study group, EH defects were predominantly located on the central and lateral incisors, upper and lower, both deciduous and permanent, and on the first permanent molars, and were always simmetrical. EH of permanent teeth of CD affected patients was characterised by prisms more irregularly distributed with irregular margins and less interprismatic substance than observed in non-coeliac EH. The deciduous teeth of the study group showed shorter enamel prisms with a non-parallel direction up to convergence and less interprismatic substance than observed in the control group.

CONCLUSION

This morphological analysis at SEM of the hypoplasic enamel defects of a group of coeliac children, the first published in literature, demonstrates that the EH of deciduous and permanent teeth in CD is highly hypomineralised with shorter prisms, more irregularly distributed and less interprismatic substance than observed in the non-coeliac EH. More data are needed to validate the significance OF our observations with the aim to assess if this simple, non-invasive microscopic analysis can be considered effective for the early identification of silent cases of CD that otherwise would not be diagnosed in the paediatric age.

Health of infants in an Imperial Roman skeletal sample: Perspective from dental microstructure

This study examines general health in the first year of life of a population of 127 subadults from the Imperial Roman necropolis of Isola Sacra (2nd-3rd century ACE). Health status was determined by analyzing 274 deciduous teeth from these children for Wilson bands (also known as accentuated striae), microscopic defects caused by a disruption to normal enamel development arising from some generalized external stressor. While macroscopic enamel defects, or hypoplasias, have long been used as proxies of general population health, we believe that this is the first population-wide study of microscopic defects in deciduous teeth. We used microstructural markers of enamel to attach very precise chronologies to Wilson band formation that allowed us to calculate maximum prevalence (MAP) and smoothed maximum prevalence (SMAP) distributions to portray what we believe to be a realistic risk profile for a past population of children. There appear to be two periods of high prevalence, the first beginning around age 2 months and continuing through month 5, and the second higher period beginning around month 6 and continuing through month 9. These results are discussed in light of historical records of Roman childhood rearing practices.

Acid-etching effects in hypomineralized amelogenesis imperfecta. A microscopic and microanalytical study

OBJECTIVES

The purpose of this study was to use quantitative x-ray microprobe analysis with scanning electron microscopy to define the morphostructural and calcification patterns in the enamel of teeth with the hypomineralized variant of amelogenesis imperfecta.

STUDY DESIGN

We compared 5 fragments of permanent human canines from patients with clinically diagnosed hypomineralized amelogenesis imperfecta and 5 normal permanent canines from subjects without amelogenesis imperfecta. All specimens were etched with phosphoric acid for morphological and microanalytical examination.

RESULTS

Two types of etching patterns were found; in addition, islets of pattern I were seen within areas of pattern II. Microanalysis detected no significant differences in calcium concentration between specimens with amelogenesis imperfecta and normal control specimens after acid etching. Pattern III was not observed.

CONCLUSIONS

The changes and their distribution in the enamel structure after 30 s of acid etching are described in teeth with this rare disorder. Although these data seem to coincide with alterations in prism development, no alterations in calcium concentration were found.

A study of primary dental enamel from preterm and full-term children using light and scanning electron microscopy

PURPOSE

The aim of this study was to examine the enamel thickness of the maxillary primary incisors of preterm children with very low birth weight (< 1,500 g) compared to full-term children with normal birth weight.

METHODS

A total of 90 exfoliated maxillary primary central incisors were investigated using light microscopy and scanning electron microscopy (SEM). Three serial buccolingual ground sections of each tooth were examined under light microscopy, and maximum dimensions of the prenatally and postnatally formed enamel were measured.

RESULTS

The enamel of preterm teeth was approximately 20% thinner than that for full-term teeth. Most of the reduction was observed in the prenatally formed enamel. This was 5 to 13 times thinner than that for full-term children (P<.001). The "catch-up" thickness of postnatally formed enamel did not compensate fully for the decrease in prenatal enamel (P<.001). Although none of the teeth used in this study had enamel defects visible to the naked eye, 52% of preterm teeth showed enamel hypoplasia under SEM, compared with only 16% found on full-term teeth (P<.001). These defects were present as pits or irregular, shallow areas of missing enamel.

CONCLUSIONS

Preterm primary dental enamel is abnormal in surface quality, and is significantly thinner compared to full-term enamel. The thinner enamel is due mainly to reduced prenatal growth and results in smaller dimensions of the primary dentition.

Scanning electron micrograph analysis of hypomineralized enamel in permanent first molars

First molars with cream- to yellow-coloured demarcated opacities of the enamel, often in combination with severe loss of substance, are common in many child populations. The aetiology is obscure.

AIM AND METHOD

The aim of this study was to study the ultrastructure of the enamel of 10 affected teeth by means of scanning electron microscopy (SEM) in order to gain a better understanding of the clinical appearance and treatment problems of this condition, and to find some clues to its aetiology.

RESULTS

The basic enamel structure with enamel rods and interrod zones was found in porous parts of the enamel, as well as in normal parts, but the packing of the hydroxylapatite crystals seemed to be looser and less well organized in the porous parts. The border between normal and hypomineralized enamel was usually distinct, and followed the direction of the rods. The preserved basic structure indicates normal function of the ameloblasts during their secretion phase, but impaired function during their maturation stage.

CONCLUSION

Considering the poor etch profile, it seems reasonable to recommend removal of all affected enamel surrounding the cavity, if possible, and to use a glass ionomer filling with its chemical bonding to tooth substrate, when restoring first molars with remaining affected enamel.

Ultrastructure of dental enamel afflicted with hypoplasia: an atomic force microscopic study

The ultrastructure of the human tooth enamel from a patient diagnosed with hypoplasia (HYP) was investigated using atomic force microscopy (AFM) and compared with the surface of normal human tooth enamel. Hypoplasia is a hereditary defect of dental enamel in which the enamel is deficient in either quality or quantity. AFM results presented for the HYP tooth enamel clearly demonstrate that the apatite crystal morphology in hypoplasia tooth enamel is perturbed in the diseased state which could result from a defective synthesis of the extracellular matrix proteins, e.g., amelogenin, by the ameloblasts. HYP enamel consisting of loosely packed, very small grains does not present a tendency for association, as in the case of the normal healthy tooth. Indeed, the enamel surface affected by HYP is porous and is made of much smaller grains. In some samples, the HYP part of enamel surface appeared in the form of a point-defect, which we believe may be associated with the early stages of the HYP deformation.

The small bovine amelogenin LRAP fails to rescue the amelogenin null phenotype

Amelogenins are the most abundant secreted proteins in developing dental enamel. These evolutionarily-conserved proteins have important roles in enamel mineral formation, as mutations within the amelogenin gene coding region lead to defects in enamel thickness or mineral structure. Because of extensive alternative splicing of the primary RNA transcript and proteolytic processing of the secreted proteins, it has been difficult to assign functions to individual amelogenins. To address the function of one of the amelogenins, we have created a transgenic mouse that expresses bovine leucine-rich amelogenin peptide (LRAP) in the enamel-secreting ameloblast cells of the dental organ. Our strategy was to breed this transgenic mouse with the recently generated amelogenin knockout mouse, which makes none of the amelogenin proteins and has a severe hypoplastic and disorganized enamel phenotype. It was found that LRAP does not rescue the enamel defect in amelogenin null mice, and enamel remains hypoplastic and disorganized in the presence of this small amelogenin. In addition, LRAP overexpression in the transgenic mouse (wildtype background) leads to pitting in the enamel surface, which may result from excess protein production or altered protein processing due to minor differences between the amino acid compositions of murine and bovine LRAP. Since introduction of bovine LRAP into the amelogenin null mouse does not restore normal enamel structure, it is concluded that other amelogenin proteins are essential for normal appearance and function.