Introduction

The enamel defect characterised as “molar incisor hypomineralisation” (MIH) seems to be common among children in Europe [3.58–21.8 % (Kukleva et al. 2008; Jälevik 2010; Lygidakis et al. 2010; Garcia-Margarit et al. 2014)]. This qualitative defect appears in the first permanent molars and frequently in incisors (Weerheijm et al. 2001; Chawla et al. 2008). The clinical characteristics can differ between the teeth of the same patient (Weerheijm et al. 2003; Lygidakis et al. 2010). Although the clinical findings also differ substantially between patients, most of the MIH studies show no gender-related distribution differences (Jälevik et al. 2001; Leppäniemi et al. 2001; Behrendt et al. 2004; Calderara et al. 2005; Fteita et al. 2006; Muratbegovic et al. 2007; Preusser et al. 2007; Martínez Gómez et al. 2012; Jasulaityte et al. 2007).

According to the EAPD criteria (Weerheijm et al. 2003), MIH teeth present demarcated opacities, post-eruptive breakdown and atypical restorations or may fail to erupt. In some severe cases, MIH molars might also need to be extracted. Although there is a lack of detailed information regarding the distribution of MIH defects between the different surfaces of affected teeth, the occlusal and the buccal surfaces are reported to be the most commonly hypomineralised areas in the first permanent molars and incisors (Muratbegovic et al. 2007; Preusser et al. 2007; da Costa-Silva et al. 2010).

The through mineral content in defective enamel (Chawla et al. 2008) and it's breakdown leads to hypersensitivity, e.g. when tooth brushing (Lygidakis et al. 2010). This favours rapid caries development. Thus, some studies have shown statistically significantly higher DMFT values in children with MIH (Behrendt et al. 2004; Preusser et al. 2007), although this has not been the case in other studies (Dietrich et al. 2003; Heitmüller et al. 2013). The necessity of caries prevention in MIH teeth beginning from the early stage of eruption has been strongly reinforced in order to eliminate caries progression and reduce future restorative treatment needs (Lygidakis et al. 2010). Though the knowledge of the intra-oral distribution and severity of MIH findings is helpful for assessing the treatment needs (Oliver et al. 2014), an association with severity has been proven at tooth level, since more severe cases present with more affected teeth (Jasulaityte et al. 2007; Ghanim et al. 2011; Heitmüller et al. 2013).

Thus, the aim of this study was to determine the distribution as well as severity and other clinical characteristics of MIH-affected teeth at surface level in a cohort of children who had been diagnosed with MIH.

Methods

Ethical approval

The data had been recorded during an epidemiological MIH study from February 2011 till March 2012 (Petrou et al. 2014) following an approval by the Greifswald University’s ethic commission council (BB 66/10). The school principals were also informed and approved all the necessary procedures as school oral examinations in Germany are compulsory with teachers coordinating these surveys.

Materials and methods

During the compulsory dental examinations of 20 German primary schools in four cities of Germany (West: Düsseldorf, East: Greifswald, North: Hamburg, South: Heidelberg), 242 children (10.1 %), out of 2395 examined, attending the second to fourth grade (128 boys, 114 girls), aged 7–10 years (mean 8.1 ± 0.8), were diagnosed with MIH according to the EAPD criteria (Weerheijm et al. 2003; Lygidakis et al. 2010). After tooth brushing, the teeth were examined using a portable light source, mirrors and cotton rolls.

All MIH defects >1 mm in diameter were registered. According to the recent EAPD criteria, defect types and severity (mild, severe) were recorded (Lygidakis et al. 2010). In addition to the clinical examination, standardised questions were asked of each child regarding any history of tooth hypersensitivity in order to evaluate the severity of the alteration at child level (Lygidakis et al. 2010). The questions referred to any experience of hypersensitivity/pain during daily activities (e.g. tooth brushing/eating).

Prior to the dental examinations, the five examiners had been trained and calibrated by using a group of pictures demonstrating different kinds of enamel defects. Repetitive diagnostics with these clinical pictures resulted in excellent intra- and interexaminer reliability (kappa = 0.9). Additionally, the senior investigator (MP) was present during the first examinations performed by each examiner in all the selected cities.

Data were recorded in Excel tables, coded and statistically analysed using the program SPSS® for Windows, version 18.0 (SPSS Inc., Chicago, IL, USA). The statistical MIH characteristic evaluation was performed with descriptive statistics. Any possible associations of the number of affected teeth and surfaces with the severity of the defects were statistically analysed with χ2 test and Spearman’s correlation.

Results

Defect distribution in the index teeth

The frequency of MIH teeth differed between the four quadrants in the mouth (Fig. 1). The differences between the mean number of affected teeth in the maxilla (1.56 ± 1.21) and mandible (1.25 ± 0.99) were statistically significant (p < 0.001) and determined by the affected incisors. As shown in Fig. 1, the most frequently affected teeth were the mandibular first permanent molars (n = 244) followed by the maxillary molars (n = 232) and to lesser extent the maxillary permanent central incisors (n = 107). All MIH-affected children had at least one hypomineralised molar, the mean number being 2.0 ± 1.1, while 39.2 % of the children presented with one affected molar, 33.5 % with two, 12.0 % with three and 15.3 % with four affected molars. The mean number of affected incisors was 0.8 ± 1.2; however, 57.8 % of the children with hypomineralised molars had no signs of MIH in their incisors and 19.1 % presented only one affected incisor. The mean number of affected teeth per child was 2.8 ± 1.7.

Fig. 1
figure 1

Distribution of hypomineralised teeth (first permanent molars and maxillary incisors) in children (n = 242) with MIH (%)

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Defect types in the index teeth

The majority of the affected teeth presented with demarcated opacities (82.8 %, molars 77.7 %, n = 380; incisors 95.9 % n = 188), whereas 10.3 % (molars 12.7 %, n = 62; incisors 4.1 %, n = 8) had post-eruptive breakdown and 6.9 % (only molars 9.6 %, n = 47) had atypical restorations. One first permanent molar was missing in a nine-year-old child. The reason remains unknown, but the child was diagnosed with MIH affecting other teeth and had no caries experience or restorations in the permanent dentition, and the other index teeth were completely erupted.

Combinations of defect types in the index teeth

Ninety-two of the total 490 hypomineralised first permanent molars (18.8 %) exhibited various combinations of MIH defects. Among them, 55.4 % (n = 51) molars demonstrated demarcated opacities and post-eruptive breakdown, 14.2 % (n = 13) demarcated opacities and atypical restorations, 8.7 % (n = 8) demarcated opacities, post-eruptive breakdown and atypical restoration, whereas 21.7 % (n = 20) had post-eruptive breakdown and atypical restoration. Only 1.5 % (n = 3) of the hypomineralised incisors showed demarcated opacities with post-eruptive breakdown affecting different surfaces.

Defect distribution at surface level

The mean number of affected surfaces per child was 4.5 ± 3.8. The most common defects were demarcated opacities, while the most affected surface in molars was the occlusal (72.4 %, n = 353) and in the incisors the buccal (73.5 %, n = 144) surface. Buccal surfaces were the second most commonly affected surfaces on MIH molars (57.7 %, n = 283) followed by the lingual/palatal surfaces (32.6 %, n = 160). The surfaces affected the least were the mesial in both the molars and the incisors (Table 1).

Table 1 Distribution of MIH defects among surfaces of MIH teeth (490 molars and 196 incisors) in a population of German children
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Sensitivity and severity of the enamel defects

Seventy-four out of the 242 (31 %) MIH-affected children presented with hypersensitivity of at least one of their hypomineralised teeth during daily activities (e.g. tooth brushing/eating). In addition 17.8 % (n = 117) of the MIH teeth presented with clinically detected surface breakdown and/or atypical restorations.

Correlation of the MIH severity and number of affected surfaces

There was a statistically significant correlation between the number of affected molar surfaces per child and the occurrence of severe forms of MIH (χ 2 test p < 0.001; Spearman’s correlation r = 0.366; p < 0.001; Fig. 2). A further statistically significant correlation was revealed between the number of all affected surfaces (including incisors) and the occurrence of severe forms of MIH (Spearman’s correlation, r = 0.321, p < 0.001).

Fig. 2
figure 2

Number of affected molar surfaces in a group of German children with mild or severe forms of MIH

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Discussion

The present study is among the first ones providing detailed information about the distribution of MIH at surface level, as well as reporting findings of MIH characteristics in the same tooth. Although Koch et al. (1987) in their early epidemiological study classified the characteristics of hypomineralised first permanent molars and incisors with respect to surface units, the prevalence of defective surfaces has rarely been examined in the past. In contrast to the criteria used in that study (Koch et al. 1987), the present examination included the fissure systems as part of the molars’ occlusal surfaces. Additionally the molars’ smooth surfaces were divided into mesial, distal, buccal and lingual surfaces in order to simplify the examination procedure. Although the diagnosis of MIH defects, exhibited on the distal, mesial or occlusal surfaces under preventive fissure sealants could be a challenging task, the inspection around the contact surface with the primary molar and margins of any fissure sealants could be revealed. The most frequently affected surfaces, the occlusal ones in the molars and the buccal ones in the incisors, in addition to the most common type of defects (demarcated opacities) were observed in the present study. This finding was in agreement with previous studies (Lygidakis et al. 2008; Wogelius et al. 2008; Ghanim et al. 2011; Mittal et al. 2014). Furthermore, similar mean numbers of affected surfaces (4.5 ± 3.8) have been reported in a recent study from India (4.99 ± 2.9; Mittal et al. 2014).

The results of the present study regarding the defect characteristics and severity highlight the need for further research on this subject, since the increase in affected surface numbers is apparently related to the severity of MIH. Similar findings were reported in the study of Mittal et al. (2014). Additionally, Oliver et al. (2014) judged the treatment needs of hypomineralised teeth based on the defects’ clinical appearance. Those authors suggested that the location of the most severe MIH defects combined with other clinical characteristics (e.g. prior restoration, sensitivity, etc.) and could be the basis for a new MIH severity index. However, as the molar characteristics are related to other tooth surfaces than in the present study (cuspal, occlusal and smooth), a direct comparison with our results would not be reliable. The heterogeneity of the tooth surfaces as examined for MIH emphases the need for clear MIH guidelines.

Regarding the distribution of MIH defects at the tooth level, the results of the present study are in agreement with the other German (Dietrich et al. 2003; Heitmüller et al. 2013) and international studies (Jälevik et al. 2001; Jasulaityte et al. 2007; Lygidakis et al. 2008; Ghanim et al. 2011). Demarcated opacities comprised by far the commonest of MIH defects (82.2 %; Jasulaityte et al. 2007; Ghanim et al. 2011; Heitmüller et al. 2013), as well as the upper central incisors, are more frequently affected (22.3–21.9 %) than the lateral (7.0–5.0 %) and mandibular incisors (9.1–2.5 %) (Lygidakis et al. 2008). The mean number of affected molars per child was also consistent with the previous reports (Jälevik et al. 2001; Dietrich et al. 2003). Severe defects with post-eruptive breakdown or atypical restorations have been less common among the affected teeth (Ghanim et al. 2011; Heitmüller et al. 2013), whereas Lygidakis et al. (2008) reported higher prevalences of these defect types among children with MIH. However, our findings that nearly one-fifth of all MIH teeth exhibit more severe characteristics and the frequent prevalence of teeth with combinations of different MIH defect types support recommendations of previous investigations for early diagnosis of MIH, in order to prevent more severe defects, more complicated treatments and higher treatment costs (Jasulaityte et al. 2008; Lygidakis et al. 2010; Oliver et al. 2014). This recommendation has an additional implications as multiple treatment sessions reduce patients’ collaboration even in adolescence and adulthood (Jälevik and Klingberg 2012). Eighteen-year-old MIH patients tend to show the same dental fear and anxiety during dental treatment as in their childhood (Jälevik and Klingberg 2002, 2012).

In cases where MIH is diagnosed later, the condition of the affected teeth might significantly deteriorate as avoidance of brushing the hypersensitive defective teeth may result in rapid caries development (Leppäniemi et al. 2001; Weerheijm 2003, 2004). Hence, information regarding MIH, the importance of tooth brushing and of regular dental examinations as well as early treatment, has to be emphasised to the public and, especially, to parents.

Conclusion

Almost one-fifth of teeth diagnosed with MIH exhibit severe defects. The MIH alterations are concentrated mostly at specific tooth surfaces, and there was a risk of having more severe lesions with an increasing number of affected surfaces per child. Detailed knowledge of the intra-oral distribution of MIH at the tooth surface level would be beneficial in assessing appropriate treatment approaches. Further epidemiological studies concerning MIH should consider the prevalence of MIH as well as the distribution of hypominaeralisations at the tooth surface level.