Molar-incisor-hypomineralisation: a literature review

BACKGROUND

Molar-Incisor-Hypomineralisation (MIH) is a qualitative defect of 1-4 first permanent molars with or without the maxillary and mandibular permanent incisors. It seems to have been recognised first in the 1970s and prevalence varies between 2.8% and 25%, dependent upon the study.

METHODS

The dental literature was searched using a number of key terms entered into MEDLINE, the reference list of each paper as located was examined for further papers that had been missed in the initial search.

RESULTS

The review of the literature showed that teeth that are affected indicate a systemic cause at around the time of birth; investigators have put forward a number of possible causes; asthma, pneumonia, upper respiratory tract infections, otitis media, antibiotics, dioxins in mother's milk, tonsillitis and tonsillectomy and exanthamatous fevers of childhood. However, at the present time the aetiology remains unclear. Treatment of the affected permanent first molars can include restorations using adhesive intra-coronal restorations to extra-coronal restorations (e.g. preformed metal crowns). There is little evidence to support one option over another. In severe cases extraction at the optimum time may be the best option; allowing the permanent second molars to come forwards. There is little improvement in affected anterior teeth with microabrasion and direct or indirect composite resin restorations may be appropriate in some children. Ultrastructural and biochemical make up of MIH affected teeth seem to have been investigated less than other areas.

CONCLUSION

It is important that children with MIH are diagnosed as early as possible and managed appropriately; this will involve multidisciplinary input.

An X-Ray Microtomography Study on the Mineral Concentration of Carious Dentine Removed during Cavity Preparation in Deciduous Molars

Dentists use a number of criteria in order to assess when a cavity is caries free, amongst which hardness is probably the most widely used. However, the judgement is subjective. X-ray microtomography (XMT) is a non-destructive microscopic technique that allows in vitro specimens to be scanned, manipulated and then rescanned. In this study, a high-definition XMT scanner was used to determine the mineral distribution of carious dentine in 10 deciduous molars, and the extent of dentine removed by an experienced clinician was investigated. For each tooth, after an initial XMT scan, caries was removed using a steel bur in a slow hand-piece. The tooth was then repositioned and rescanned. Mineral concentrations were calculated from the linear attenuation coefficients assuming the mineral phase to be hydroxyapatite and the organic phase to be collagen. The volume of dentine tissues removed was calculated by subtracting data of the second scan from the first. The results showed that the mean modal mineral concentration for the 10 teeth was 1.42 g x cm(-3) for sound dentine. Because of uncertainty about collagen concentration in carious dentine, the mean modal mineral concentration for the carious dentine had a range of 0.37-0.5 g x cm(-3). It was found that the subjective criteria used by the operator could lead to inconsistency of cavity preparation. The cavities could be overprepared by 8.5-44.3% in volume. However, the overpreparation was not uniform throughout the cavity: residual demineralised dentine could still be detected in the postoperative scan in isolated regions.

Dentinal carious lesion in three dimensions

AIM

The aim of this study was to show the morphology of the carious lesion in dentine in three dimensions (3D).

DESIGN

A novel high-definition X-ray microtomography (XMT) scanner was used to scan 10 carious primary molars at a resolution of 15 x 15 x 15 microm3. A stack of approximately 640 XMT slices were recorded for each tooth. Using this data set and a volume rendering algorithm, each tooth was reconstructed in 3D. The VG Studio Max 1.0 visualization software package was used to make normal enamel and dentine transparent to show the carious lesions in 3D. A video film, comprised of the rendered images from 60 viewing angles rotating through 360 degrees , was produced to show the carious lesion and its relation to the pulp in a three-dimensional perspective (http://www.smd.qmul.ac.uk/dental/oralgrowdev/biophysics/xmt/images/carious.mpg).

RESULTS

These images showed that carious lesions in dentine were bowl-shaped. The pulp adjacent to the carious lesion was also observed to mimic the base of the bowl-shaped lesion.

CONCLUSIONS

It was concluded from the teeth studied that the shape at the base of the carious lesion in dentine is curved in 3D, rather than conical, as traditionally believed from two-dimensional image interpretation. Further 3D studies are needed to investigate whether the bowl-shaped carious lesions in dentine also apply to caries in other types of teeth.

The biodegradation of albumin microspheres used for regional chemotherapy in patients with colorectal liver metastases

The poor results of systemic chemotherapy for colorectal liver metastases have focussed attention on the use of regional chemotherapy. Embolizing, biodegradable particles can be coadministered with anticancer drugs to slow temporarily the arterial blood flow and increase drug uptake within the tumour-bearing liver. Alternatively, such microspheres can be loaded with cytotoxic agents and act as slow-release mechanisms following embolization. In both instances, size and rate of degradation are important. The aim of this study was to evaluate the biological degradation of albumin microspheres in the liver of patients with colorectal liver metastases. Seven patients with advanced liver metastases had a 200-250 mg bolus dose of customized albumin microspheres (diameter range: 20-40 microns), labelled throughout with covalently bound 131I, injected into the hepatic artery. The abdomen was imaged immediately before injection to give an estimation of background count rate, and daily after injection for five days. Activity-time curves were constructed for the liver region. The median biological half-time of the particles within the whole liver was 2.4 days (range: 1.5-11.7 days), but was longer in tumours than in normal liver in some patients. The rate of microsphere degradation within tumours may be an important factor in the efficacy of microsphere-based regional therapy, and can be studied accurately by the technique we have employed.