Several indices have been utilized to record DDE, the most popular being a descriptive index, the Developmental Defects of Enamel (DDE) index which does not attempt to identify the etiology [8]. There have been several modifications of this index, including simplified versions that can be applied for screening purposes. Many authors use the simplified modifications of the index to record DDE in the primary dentition for practical reasons [8]. Variations in prevalence of DDE reported in different populations are likely to be the result of differing criteria being used to define enamel defects. In addition, there are population variations resulting from differences in general health, and background fluoride exposure levels may also contribute to differences in the reported prevalence of DDE. Furthermore, in many studies, the recording of DDE in primary teeth several years post-eruption may be complicated by difficulties in diagnosing DDE once the lesions have become carious or have been restored [12]. Finally, differing field conditions during examination for DDE, such as variations in lighting and whether the teeth are dried prior to recording of the defects, may also contribute to differences in reported prevalence.

As there are few high-quality studies, the true prevalence of DDE in the primary dentition is unclear. Most prevalence studies on the primary dentition have been based on convenient samples from the general or special population groups such as medically compromised children. Table 1.2 lists selected reports of prevalence of DDE in the primary dentition published since 1996. There are significant variations in prevalence rates among different countries and population groups. A Chinese study showed that primary teeth with defective enamel were seen in 24 % of children, with opacities contributing 2 % and enamel hypoplasia 22 % [13]. In the USA, the study of Slayton and co-workers [14] reported a total prevalence of DDE in the primary dentition of 33 %, with 6 % of healthy children having at least one tooth with enamel hypoplasia and 27 % having enamel opacities [14]. In another USA study, Montero and co-workers reported an overall prevalence of DDE in the primary dentition of 49 % [15], while in Mexico, a DDE prevalence of only 10 % was found [20]. In Australia, the prevalence of DDE was reported to be 25 % in a primary school cohort [21], compared with a rate of approximately 24–44 % in Brazil [16, 17, 22]. In Holland, the prevalence of hypomineralized second primary molars was reported at 5 % and 4 % at the child and tooth level, respectively, with the majority of DDE being demarcated opacities [18]. More recently, a study in Iraq reported that 7 % of children had hypomineralization defects in at least one second primary molar [24]. In Tanzania, the prevalence of enamel defects was 33 %, with diffuse opacities constituting the most common defects (23 %), followed by hypoplasia (8 %) and demarcated opacities (5 %). In that study, the most frequently affected teeth were the primary central incisors (approximately 30 %), whereas lower central incisors (4–5 %) were least frequently affected [23]. Many indigenous communities, for example, in Australia, Canada, and the USA are reported to have higher rates of DDE, probably due to increased risks for poorer general health compared to other communities [25].

In a study of over 3,200 primary teeth, 5 % of primary teeth had some form of DDE, and the most prevalent defects were found, in descending order, in the mandibular second molar, maxillary second molar, mandibular canine, mandibular first molar, maxillary first molar, maxillary lateral and central incisors, and maxillary canine [21]. Only a very small percentage of the mandibular central and lateral incisors exhibited DDE, and these were mainly enamel opacities [21]. In addition, the most common type of DDE found in the primary dentition was the demarcated opacity, followed, in turn, by diffuse opacity and enamel hypoplasia. In another study, the maxillary primary central and lateral incisors were affected by enamel hypoplasia at the highest frequencies (41 % and 39 %), followed by the maxillary canines (26 %), maxillary first molars (22 %), and mandibular first molars (19 %) [13].

Table 1.3 shows the plethora of conditions that have been associated with DDE in primary teeth. Hereditary conditions such as amelogenesis imperfecta are caused by abnormalities in genes involved in enamel formation [26]. Other forms of DDE that may be inherited include those that are inherited as familial disorders or dysmorphic syndromes that show enamel defects [27]. Acquired systemic conditions that can cause DDE may be encountered perinatally, neonatally, or postnatally and include conditions such as birth trauma, metabolic conditions, and infections. Adverse conditions experienced by the mother during pregnancy that may cause DDE in the child include severe maternal vitamin D deficiency [28] and infection with syphilis [29]. Local factors impacting on the oral cavity, such as trauma and radiation, can also cause many DDE in the primary dentition. However, evidence for the associations between many of the acquired systemic conditions and DDE are based mainly on clinical studies and case reports. There are only a few instances such as the use of tetracyclines where direct causal links have been demonstrated between an individual adverse condition and enamel changes in primary teeth [30].