Developmental defects of enamel (DDE) can be detected and studied using microscopic and macroscopic methods. Macroscopic methods are especially important in epidemiological studies. Direct clinical examination is the most widely used method for detecting enamel defects, while photographic and replication methods are of special interest because of their suggested advantages over direct clinical examination. None of these methods are fully standardized as no single detailed method is used by many researchers. The replication method used by some dental anatomists, archaeologists and anthropologists is not used by epidemiologists. The significance of digital technologies, which have opened up new horizons in almost all aspects of science, has been relatively neglected in epidemiological studies of DDE. Digital photography, which has been shown to have high levels of success in caries detection , has only been used in a few DDE studies.
Direct clinical examination is fast and cheap and all surfaces of teeth can be examined. However, it has many disadvantages such as observer bias and effects of visual problems related to fatigue of the examiner. Accuracy is highly dependent on cooperation of subjects [2, 3]. Direct examination was unreliable when multiple indices were used or compared . Direct visual examination of enamel can be done with or without tactile examination of the enamel surface with a probe . Examination may be conducted under natural light, avoiding direct sunshine. When natural light is not strong enough or when posterior teeth are being examined, a fibre optic light may be used . Teeth may be cleaned before the examination [7, 8]. Polarizing filters may be used to overcome the burn outs from strong flashlight and to enhance the visual details of enamel defects, especially when the extent of defects is more important than their colour .
Photography has been used in some studies of tooth and enamel defects [3, 4, 9–14]. Assessing photographs is more objective than direct clinical examination. With photography it is possible for all cases (even from different geographic areas or examined at different times) to be assessed under standard conditions by one person or one group of examiners . Photography facilitates randomization and blinding, so observer bias can be avoided. Photographs can be kept for future reassessment or application of different approaches or indices [3, 12]. On the other hand, the disadvantages of photography are cost, technical sensitivity and inability to use tactility. Furthermore, with single photographs only labial surfaces of incisors are recorded. Multiple views are needed to view more teeth and/or more surfaces . Some surfaces or parts of a surface may be missed even in multiple views. Some researchers have preferred to use conventional photography with 35 mm film [3, 4, 13]. However, digital photography provides better conditions to record developmental defects of enamel. Digital photography is cheaper and independent of developing negatives and printing or projection. Most importantly, it gives the photographer the opportunity to view each image immediately and repeat it in case there is any problem with the image, such as a burn-out caused by flash; or to take several photos and choose the best one later .
Replicas of teeth may be used in both macroscopic and microscopic studies of enamel defects. In this method the whole cast is in one colour, so changes in colour of enamel are not shown. But a replica of teeth gives the observer better visibility to investigate hypoplasia, including small changes in the enamel surface . This method also enables researchers to spend as much time as needed and provides a dry specimen that can be studied easily from different perspectives without worrying about adjacent structures. Disadvantages of the replication method are cost, time needed to make replicas, and its sensitivity to technical methods. Even under the best conditions some proximal surfaces may not be well recorded. And, as stated above, it only displays hypoplastic defects.
As the three methods differ in sensitivity in detecting DDE, it is surprising that very few studies have compared them [3, 4, 14]. No published epidemiological study has compared the results of detecting DDE using the replication method with the direct examination on a population basis. Wong et al. (2005) used the Modified DDE Index to compare the photographic and direct examination methods and found kappa agreement values from 0.79 to 0.85 between them for detecting subjects with any DDE. They used one-view, three-view and five-view photographic methods. The highest prevalence of subjects with DDE (36.6%) was, surprisingly, obtained from their one-view method. It was close to the prevalence obtained by the direct clinical method (33.9%). The intra-examiner reliability of the photographic method (k = 0.81 to 0.88) was also close to the direct examination method (k = 0.82) . Ellwood et al. (1996) used the TF (Thylstrup and Fejerskov) Index  for their comparison and found a substantial agreement between the two methods at subject level (k = 0.63). At subject level, the prevalence obtained by photographic method (44.9%) was close to that obtained by the direct examination (41.4%) . Sabieha and Rock (1998) used both the Modified DDE Index and TF Index and reported almost perfect agreement between the direct examination and the photographic methods for both indices (k = 0.91 and 0.83 respectively). They only assessed maxillary central incisors .
Several clinical indices have been developed to categorize enamel defects based on their nature, appearance, microscopic features or their cause. Some indices, such as the TF Index , were introduced specifically for fluorosis. Other indices are descriptive and include all kinds of enamel defects including fluorosis. The Modified DDE Index  is a descriptive index derived from the original Developmental Defects of Enamel Index . It covers all defects based on their macroscopic appearance. However, the criteria for classification are closely related with histo-pathological changes . The Modified DDE index was claimed to be a more practical and comparable index in epidemiological studies. Its extensive use and its high degree of validity and reliability support that claim [6, 20–22].
As there are few epidemiological studies comparing the three methods of detecting DDE, the objective of this study was to compare the ability of the digital photographic and replication methods with the direct clinical examination method to detect DDE in children's permanent incisors.