The results show that there is a notable disparity between different clinicians’ treatment choices. On a newly erupted permanent first molar with moderate hypomineralization and no disintegration of the surface enamel, the majority of the respondents (51.2 %) preferred treatment with fluoride varnish. On a severely damaged first permanent molar in a 6-year-old child, more than half of the respondents (53.7 %), would place a conventional glass ionomer restoration. In a severely damaged permanent first molar in a nine year old child, only 21.0 % would remove all affected enamel and leave the cavity margins in sound enamel, which may reflect a preference for adhesive techniques. Of those who preferred cavity design C, 32.2 % chose glass ionomer cement and 67.7 % resin composite as restorative material.
Patient Case 1 (Fig.
1) showed a newly erupted permanent first molar with moderate hypomineralizations and no disintegration of the surface enamel. The tooth was newly erupted and belonged to a 6 year old child indicating that there is a need for a decision on how to follow-up. In this case, 35 % of the dentists would choose to treat the tooth with fissure sealants (either glass ionomer or resin based materials). Fluoride varnish, which was chosen by more than 50 %, may reduce sensitivity [
24] and possibly reduces the caries risk observed in MIH patients [
25]. Almost 8 % of the dentists would do nothing. There are a few studies indicating that there is some potential for mineralisation of the porous MIH affected enamel or reduced hypersensitivity using CPP-ACFP (casein phosphopeptide - amorphous calcium fluoride phosphate) solution [
24,
26], but so far more research is needed before this can be advocated on more general basis. In the authors’ opinion, a fissure sealant would be appropriate and probably a GIC based product would be preferable in the short run if moisture control could be difficult because an operculum covers the most distal part of the fissure.
Patient Case 2 (Fig.
2) showed a severely damaged FPM with post-eruptive breakdown in a 6 year old patient with a newly erupted, sensible first permanent molar. The case was supposed to reflect an unclear situation where dentists should consider a temporary, pain-relieving solution until the prognosis of the tooth becomes more certain or extract the tooth. In this patient case, almost 54 % of respondents chose to restore the affected areas with GIC. It may be questioned whether GIC has sufficient mechanical properties in stress bearing areas in MIH molars [
6,
9], but as a temporary restoration, with fluoride release, dentists may consider GIC a “forgiving” material. The fluoride release may prevent both secondary caries and development of caries on the surface of the adjacent tooth. According to Lygidakis et al. [
9], a conventional resin composite restoration or a SSC should be placed once breakdown has occurred depending of the severity of the hypomineralization. These are good alternatives in this case, since it was given that the child cooperated well. Only 19.1 % chose resin composite restoration and 9.8 % chose SSC in this patient case. If only two or three of the total five surfaces are affected, resin composite restorations show adequate long term performance and may be an alternative treatment to SSCs [
27]. However, Mejàre et al. [
6] found that conservative restorative treatment resulted in a need for additional retreatment in approximately half of the patients before reaching the age of eighteen. The median longevity of all kind of restorations in molars was 5.2 years. GIC had the lowest and resin composite the highest success rate. In
Patient Case 2 only 5.0 % of dentists chose extraction as the preferred treatment. Extraction of one or more molars has been claimed to be a good alternative in cases with heavily destroyed FPM [
28]. Spontaneous space reduction and favourable development of the permanent dentition can be expected when extracting a severely damaged FPM before the eruption of the second permanent molar. Mejàre et al. [
6] also found that extraction of molars with severe enamel defects gave good or acceptable results in most patients. Guidelines for such treatment are available [
29]. The fact that Norwegian dentists did not use SSCs much could be due to little training in placing SSCs as students, partly due to low caries prevalence. Crombie et al. [
5] found in their survey that SSCs were used significantly more by paediatric dentists (97 %) and postgraduate students in paediatric dentistry (100 %) compared with non-paediatric dentists (58 %). In our study, we did not distinguish between specialists in paediatric dentistry and non-paediatric dentists, because the number of practising specialists in Norway is very low. In the authors’ opinion, extraction might be considered as first choice. However, if the tooth should be kept for a shorter or longer period a SSC would be indicated. In
Patient Case 3 (Fig.
3) the dentists were asked to choose how much enamel they would remove based on three different situations. The patient was 9 year old and this illustrates a situation about three years after the molar eruption and that there is no acute symptoms and treatment needs. With respect to placement of preparation margin, only 21% would remove all affected enamel (cavity design C). In the authors’ opinion, this is the best treatment choice if a resin composite restoration is to be made. In the long term could an inlay or onlay be indicated if the composite needs revision, but this was not an option when the immediate treatment was to be decided. All other options than resin composite must be considered temporary solutions, since the etch pattern requires good retention and a tight seal [
12‐
17]. Of the dentists who preferred cavity design C, 67.7 % would place a resin composite restoration and 32.2 % a GIC restoration. The latter may be considered a semi-permanent choice since the longevity of a GIC restoration in such a large cavity normally will be limited. Thus, in fact only 86 dentists (14.2 %) chose what the authors consider the best treatment alternative in this patient case. Most dentists chose cavity design A or B. Norwegian dentists are reluctant to remove tooth substance in general [
11]. The concept of minimally invasive dentistry has been widely adopted by Norwegian dentists and it is likely that many dentists use this approach regularly even in cases where a more invasive approach could be beneficial, such as treatment of MIH. Another explanation could be that dentists find the patient group so challenging to treat that they limit tooth substance removal. Children with MIH-affected teeth show behavioural management problems (BMP) more often than other children [
30]. It has been shown that MIH patients receive more restorations than do controls and they also get more caries [
30,
31]. Even at the age of 18-years, MIH patients need more restorative dentistry [
32]. One reason for the development of BMP could be difficulties in achieving adequate anaesthesia and the frequent dental treatments these children undergo. There is some evidence that the increased pain associated with MIH teeth has a biological explanation due to increased expression of a noxious heat receptor (TRPV1) in the pulp [
33]. This emphasises the importance of using sedation with benzodiazepines, nitrous oxide or in severe cases general anaesthesia, when treating this patient group, both to be able to perform optimal treatment and to prevent the development of BMP. The hatched preparation border in cavity design C (Fig.
3) was supposed to illustrate that the preparation border was in healthy enamel. However, it is not easy to define the borderline between healthy and hypomineralized enamel. Fearne et al. [
34] reported in one study that even visually normal enamel in these teeth was 5 % less mineralised than truly unaffected enamel. This five per cent deficit has been reported to result in dramatic reduction in the mechanical properties of hypomineralized teeth [
35]. This could be one reason why these teeth frequently need retreatment after receiving restorations. In addition, the prismatic morphology in the porous enamel is altered, making bonding less effective [
13].