Occlusal caries: Evaluation of direct microscopy versus digital imaging used for two histological classification systems
Introduction
In vitro studies commonly establish the validity of a detection system by using a “gold standard” against which the sensitivity and specificity of the diagnostic method can be calculated. The most common gold standard used for occlusal caries lesions is the histological evaluation of hard tissue sections.1 There are large variations on this theme and at its simplest the teeth are hemisected at the place to be examined, or hard tissue sections are prepared whose thickness can vary considerably (250–1000 μm).2 In these cases, there is danger that a proportion of the tooth area under investigation is missed, thus the true depth of the caries cannot be confidently ascertained.
There are a number of shortcomings in histological methods, many of which are operator errors. For instance there may be section damage during preparation of samples and the section might not relate to the actual investigation site in question. In addition, assessment of lesion depth from a section is also difficult as it is often unclear where caries affected tissues end and pulp–dentine complex reactions begin. There is therefore scope for error in making this subjective decision. It is therefore important to have a meticulous histologic methodology and more than one validator which pose a problem in large multi-national studies.
In order to evaluate serial sections histologically, elaborate equipment is required. It takes considerable time and equipment to judge hard tissue sections directly under the microscope and in nation-wide or international research this poses a problem if histological specimens are to be examined by more than one examiner in one or more institutes. There is danger that sections may be damaged during transport or handling, or may simply be lost.
To reduce these potential pitfalls it is possible to simply take magnified digital photographs of hard tissue sections and evaluate these. Photography has been used previously to assist in diagnosing or assessing plaque and gingivitis3, 4, 5, 6 and in assessing the prevalence of developmental defects in enamel including enamel fluorosis.7, 8, 9, 10
Two histological classification systems have been used to determine the depth of a carious lesion.1, 11 Using these, the main aim of this study was to evaluate the relationship between the depth of occlusal caries in the enamel and dentine of serial sections of extracted teeth as determined by directly viewing the sections with the aid of a microscope and indirectly using digital photographic images of sections. In addition, we intended to determine the intra- and inter-examiner reproducibility of the two viewing techniques and the two histological classification systems.
Section snippets
Sample selection
One hundred unrestored molar (n = 85) and premolar (n = 15) teeth were selected from a group of extracted teeth collected at Dundee and Marburg Dental Schools. These were cleaned thoroughly and stored in water. The teeth were collected and used in accordance with the appropriate legislation and regulations in place in the UK and Germany predating September 2006. The teeth used in this study were the same as those used in a previously published study by the same authors.12
Prior to the visual
Results
A total of 339 sections were examined from 166 investigation sites in 96 teeth.
For both viewing techniques intra-examiner reproducibility for the Downer histological scoring system was 0.77–0.90 (weighted kappa) (Table 1). Inter-examiner reproducibility between the reference examiner (Examiner 1) and Examiners 2–4 was 0.72–0.83 (weighted kappa). When comparing the kappa values for the microscopy and viewing digital images all effect sizes except for one were <0.20 indicating no effect for the
Discussion
Numerous techniques have been used to validate the presence and extent of caries from hard tissue sections and all have advantages and disadvantages which need to be balanced according to the research question being asked. For example confocal microscopy, polarised microscopy and microradiography have been used to name but a few for small lesions.18, 19, 20 However the latter two techniques require thin sections which result in loss of extensive tooth tissue and possibly the area of interest
Conclusion
This study has shown that viewing histological sections on a computer screen leads to comparable results to viewing hard tissue sections under a microscope using two histological classification systems. This has potential benefits for multi-centre studies where images could be used and transferred electronically and the results from this study have been used successfully to validate the ICDAS-II visual classification system.12
Conflict of interest
None.
Acknowledgments
The authors thank the Medical Hospital Laboratory for fine Mechanics for preparing the embedding forms and further Mrs. U. Schaefer for executing the cutting and photo-reproduction tasks. All the equipments which were used and mentioned in the study were property of and supported financially by the Medical Faculty, Philipps University-Marburg. No further external funding was obtained for the study.
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