Background
Amelogenesis imperfecta is a rare genetic disease affecting enamel. Primary and permanent teeth are concerned with almost the same severity. Differential diagnosis must be made with enamel developmental defects caused by environmental factors (fluoride, tetracycline???) [
1] or traumatic etiologies as they will only affect defined teeth and rarely both dentitions. For example, experimental studies showed that molar incisor hypoplasia (MIH), which only affects permanent incisors and first molars, might be caused by prenatal or early child exposure to endocrine disruptors [
2].
Amelogenesis imperfecta presents large variability in its clinical expression. Mutations have been reported in different genes. Some of them encode for enamel proteins, either structural (amelogenin, enamelin, ameloblastin, c4orf26) or enzymatic (kallikrein 4
, MMP20); some others encode for transcription factors (
MSX2, DLX3), cellular proteins (
WDR72, FAM83H, COL17A1), cellular receptor (
ITGB6) and calcium carrier (
SLC24A4) [
3]. Until today, no relation between genotype and phenotype has been established. Enamel may be modified in its width, microstructure or mineralization degree. Thus, clinical symptomatology goes from light discoloration to disintegration/breakdown of the enamel of the entire tooth. Witkop’s classification distinguished 4 different types: hypoplastic, hypomature, hypomineralized and hypomature with taurodontism forms, with 14 specific subtypes [
4]. Indeed we differentiate 3 clinical entities: hypoplastic, hypomature and hypomineralized AI.
-
Hypoplastic AIH (type I) consists of quantitative alteration of enamel with localized or generalized reduced thickness. Teeth are yellow to light brown, surface is rough with pits or larger area defects. Severe hypoplastic phenotype leads to morphological anomalies seen on radiographic examinations. No pain is associated with this AI, although some slight thermal sensitivity may sometimes be reported [
5].
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Hypomature AIH (type II) consists of a defect in matrix protein degradation. In enamel, which is the most calcified structure in the organism, proteins must be degraded and removed to achieve final crystal growth. In type II, enamel appears white or brown, without translucency. Hardness during probing and thickness of enamel layer are normal. However, enamel breakdown often occurs. On radiographs, enamel opacity is decreased especially near the enamel dentin junction. This type of AIH is the mildest form and frequently undiagnosed. Aesthetics is the first cause of consultation [
6].
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Hypomineralized AIH (type III) is the most severe AI form. Enamel mineral content is reduced causing pain while masticating, and brushing. Gingivitis and periodontal diseases have been described, with large amounts of dental calculus. Teeth are very sensitive to temperature and brushing. Enamel is dark yellow or brown. On radiographs, enamel and dentin may reach the same radiodensity [
7]. Anxiety has often been reported in these patients due to permanent dental pain [
8].
Other dental anomalies may be associated with AI [
9]: taurodontism [
10], pulp stones, delayed tooth eruption, anterior open bite or craniofacial anomaly [
11,
12]. Surprisingly, no increased incidence of caries has been reported.
Discussion and conclusion
Guidelines for AI treatment have been established by AAPD (American Academy of Pediatric Dentistry) [
15]. Factors such as age, socio-economic conditions, AI type and severity have to be taken into account in treatment planning. Patients’ first appointment usually corresponded to establishment determining the age of primary, mixed and permanent dentitions (that is 4, 8 and 13 year-old, respectively), and the two main demands were pain and aesthetics [
16]. These patients suffered from reduced quality of life, social integration difficulties and loss of self-esteem [
17]. Oral hygiene and rigorous follow-up are recommended. Hypomineralized enamel showed progress alteration with time because of its softness. Composite fillings can limit this degradation. Dental rehabilitation is still important to improve oral health in children. Rough enamel is associated with dental plaque retention, increasing gingival inflammation and pain. Hypomineralized enamel is the most severe form: once occlusion is established, teeth wear quickly inducing large tissue losses. Patients describe eating difficulties and pain when temperature changes. Thus, efficient tooth brushing cannot be achieved / tooth brushing cannot be effective. By contrast, hypoplastic AIs mainly present unsightly teeth complaints, while in hypomineralized type, local anesthesia is required for dental scaling.
Treatment should begin as soon as possible according to patient compliance in office dental care. For very young patients, general anesthesia may be necessary. Stainless steel crowns were indicated in primary teeth with hypoplastic or hypomineralized AI in order to reduce tooth sensitivity and restore enamel loss. Composite restorations were indicated for all primary teeth. Previous studies regarding bonding to AI enamel were contradictory and varied with AI types [
18,
19]. Some authors suggest complete enamel etching with sodium hypochlorite rinsing (5% during 1 min) in order to remove residual enamel proteins, especially in hypomature forms [
20‐
22]. In vitro studies showed a decrease in bonding strength [
23] while some others observed similar rupture strength values to healthy enamel ones. This latter may be explained by an increase of bonding area due to the microporosity of the affected enamel. Bonding on dentin is also different. Indeed, dentin in AI patients is more mineralized than usual, looking like reactional dentin with obliterated tubuli [
24].
In mixed dentition, rehabilitation must be done as soon as teeth erupt. Treatment main goals should be the preservation of tooth integrity and vitality [
25]. Paediatric crowns can be easily performed on first molars without tooth preparation, especially indicated when teeth are painful or hypoplastic. Orthodontic elastic spacer was used to separate teeth. In other cases, only prophylactic care may be enough. In hypomineralized forms, glass ionomer cements on occlusal surfaces were efficient in preventing pain and allowing temporizing until teeth eruption was achieved. Clinical follow ups should be planned every 6 months if new teeth erupt and every 9–12 months in stable periods. Orthodontic treatment is not contraindicated in AI patients. Brackets’ bonding can be made with glass ionomer cements. Open bite prevalence is increased in AI patients. Treatment is often long and might need orthognatic surgery. In mild AI forms (without any pain or important hypoplasia), definitive rehabilitation should be planned only at the end of the orthodontic treatment. In other cases, primary restoration could be done before orthodontic treatment and reassessed at the end of the treatment.
In permanent dentition, different treatments from restorative to prosthetic rehabilitation have been reported in the literature [
26] (Table
1). Nevertheless, no consensus between several case reports has been reached. Before adhesive dentistry and full ceramic material arrival, prosthetic treatment with ceramic crowns was done on all teeth. This kind of treatment is no longer recommended today for young adult. Most aesthetic results were obtained with fixed prosthodontics and all ceramic restorations showed good success rates [
27]. However, teeth, especially anterior teeth, have to be devitalized, which decreases their longevity. Veneers were also done on anterior teeth in order to preserve dental tissues [
28‐
32]. Their major disadvantage is their cost and the fact that their placement is time consuming [
30].
Table 1
Advantages and disadvantages of the therapeutic alternatives in AI dental treatment
Fixed Prosthodontics | Aesthetics Occlusion Mechanical properties | Invasive Long treatment Tooth vitality Cost | Robinson et al., 2006 [ 32] |
Removable Prosthodontics | Fast Occlusion Cost effective | Transitory Hygiene Retention issues | |
Resin Based Composites - Direct Restoration | Correct aesthetics Non invasive Cost effective | Mechanical properties Longevity? Occlusion regulation | |
Resin Based Composites-Indirect Restoration | Minimally Invasive Aesthetics (stratification, opacity) Mechanical properties Easy to repair Bite set up on simulator | Durability? Wear | Manhart J et al., 2000 [ 45] Koyuturk AE et al., 2013 [ 46] |
Resin Based Composites-Indirect Restoration CAD-CAM | Same as above Possibility to use new polymer infiltrated ceramic network materials single office appointment | Same as above Steep Learning curve Occlusion | Schlichting LH1 et al., 2011 [ 48] |
Some authors proposed overdenture treatments [
33]. In this case, occlusion and aesthetics were restored quickly. This kind of treatment is an option in mixed or young permanent dentition in order to wait for growth end. Still, overdentures should be transitory options since long term failures due to retention loss are frequent [
34].
Direct or indirect [
35‐
38] dental composites constitute other treatment options. These materials allow an aesthetic result with good long term outcomes and minimally invasive intervention [
39]. Clinical reports showed short term follow-ups. Only two articles presented data with a longer follow-up [
40]. Nevertheless in AI patients, the failure rate seemed to be increased compared to unaffected patients [
41] or to the other dental abnormalities (for example: oligodontia or palatal clefts [
42,
43]). This may be due to the less shear bond strength reported in AI teeth. A consensus protocol on AI enamel and dentin bonding is still to be decided.
AI is a rare inherited enamel disease, which explains the absence of evidence-based clinical recommendation and makes AI treatment challenging. Aesthetics, pain or tooth breakdown were the major patient complaints. Restorative to prosthodontic dentistry must be done in order to maintain oral function and growth preventing tooth loss and allowing oral hygiene maintenance. The first consultation must be as early as possible. Treatment alternatives deal with minimal invasive dentistry with the objective of maintaining tooth vitality as long as possible. The goal is to achieve therapeutic answer during the entire patient’s life. In this respect, establishing a good trust relationship between child and dentist is critical. Genetic and biological knowledge of AI physiopathology is also helpful in treatment plan decision.