Amelogenesis Imperfecta
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Treatments for Amelogenesis Imperfecta

Treatment of the different amelogenesis imperfecta types depends on the specific AI type and the character of the affected enamel. Treatments range from preventive care using sealants and bonding for esthetics to extensive removable and fixed prosthetic reconstruction. The treatment approach should ideally be developed considering the specific AI type and underlying defect. For example, while bonding may be very effective for restoring teeth with hypoplastic types of AI, the forms with hypomineralization and weak enamel (hypocalcification, hypomaturation) may not be amenable to procedures relying on bonding to the enamel as the sole source of retention.

Before figure16a

After figure16b

AI types with hypomineralized enamel are prone to enamel fracturing and rapid wear making them poor candidates for conservative restorative approaches or bonding procedures. Extreme dental sensitivity to thermal, chemical, and mechanical stimuli, commonly seen with hypocalcified and hypomaturation AI, may require early treatment with full dental coverage so the individual can masticate and perform appropriate oral hygiene procedures adequately.

Treatment in AI types with severely affected enamel will typically require multiple phases to maintain form, function and esthetics in the primary dentition (2-6 year olds), early mixed dentition (6-11 year olds) and permanent dentition (11 and older). Initial restorative care in severe forms of AI should begin in the early primary dentition to prevent excessive sensitivity, protect the dentition, and allow for maintenance of a functional occlusion. Consideration must be given to the dental, esthetic, psychological, skeletal, and functional factors when developing a treatment approach.

Correction of the diverse dental and skeletal manifestations associated with the different AI types can require intervention from multiple dental disciplines. For example, the general or pediatric dentist may be involved with restorative therapies in the early primary dentition and early mixed dentitions while complex restorative therapies in the adolescent or adult will often be best accomplished by a general dentist or prosthodontist. Although many malocclusions may be managed by orthodontics alone, the severe skeletal open bites often associated with AI may require both surgical and orthodontic intervention. Active dental intervention of the complex AI patient may, therefore, span several decades including both the primary and permanent dentition and may involve numerous dental specialties.

Treatment of Hypoplastic AI Types


Figure 13a

Figure 13b
Therapy for the hypoplastic AI types typically involves the use of bonding procedures to protect the malformed teeth from caries and improve esthetics. Hypoplastic teeth usually have reasonably well mineralized enamel, albeit thin and/or pitted, making them suitable for restorative therapies involving bonding to the enamel (Figure 13a and 13b). Composite resin or porcelain veneers can be bonded to the anterior teeth when the incisor shape, size and/or color requires modification. Orthodontic therapy may be used to partially close the interdental spaces (space between teeth) prior to restoration in those individuals having small square shaped incisors (due to the thin enamel) and interdental spacing that is too excessive to close with restorative therapy alone. Individuals with hypoplastic AI often can retain intracoronal restorations such as amalgams (silver fillings) and composite resins (tooth colored fillings), however, if the enamel is extremely thin and malformed the teeth can require full dental coverage with crowns.

Treatment of Hypomaturation and Hypocalcified AI Types

The hypomaturation and hypocalcified AI types can be restored with conventional approaches if the enamel is not severely involved. Bonded restorations may be successful in some cases depending on the enamel mineral content and strength. In hypocalcified and hypomaturation AI types where the enamel is severely hypomineralized and of insufficient strength to retain bonded or intracoronal restorations, full coverage restorations should be placed. In cases of severely hypomineralized enamel, stainless steel crowns are indicated in the primary and early permanent dentitions.

Esthetic anterior restorations can be made using a variety of techniques. Open face stainless steel crowns with composite inserts (Figure 14) or composite crowns (Figure 15a and 15b) that are retained both by mechanical undercuts and bonding can greatly reduce tooth sensitivity and provide reasonable esthetics. The dentist should not rely on retention from bonding alone in those cases with very weak and poorly mineralized enamel. Resin crowns can be placed on permanent incisors soon after they begin to erupt during the mixed dentition (about age 7 – 10 years). As the gingival margin becomes exposed during continued tooth erupt the resins are easily modified by adding resin to the gingival margin of the tooth.

Ultimately, porcelain fused to metal or other custom fabricated crowns can be placed on the dentition. This may be delayed until late adolescence or early adulthood when all the teeth are present, the teeth are fully erupted, and the gingival height around the teeth has stabilized. While costly, these types of restorations can allow even severely affected dentitions to be treated and achieve excellent function and esthetics. The severely afftected individual shown in Figures 16a and 16b had AR Hypomaturation AI and was treated over several years with stainless steel crowns, orthodontics, orthognathic surgery and eventually porcelain fused to metal crowns to achieve this excellent result.

figure16b

figure14

figure15a

figure15b

figure16a

 

Treatment of Dental Malocclusions

Malocclusions can be managed using a variety of techniques depending on the character and severity of the problem. The prevalence of skeletal open bites ranges from about 25-35% of people [16-19] with AI (Figure 17). It appears to occur more commonly with the hypomaturation and hypocalcified AI types [18]. It is variable in affected individuals even within the same family having the same type of AI. The cause of skeletal open bites in AI has been proposed to result secondarily to the severe sensitivity and jaw posturing or due to affects of the mutant gene in tissues other than the ameloblasts. The reason skeletal open bite occurrs with an increased frequency in people with AI compared with the general population remains unknown.

Treatment of malocclusions will typically involve traditional orthodontic treatment using “braces”. Braces are most often placed using bonding. However, in AI cases where all the teeth are covered with crowns, the orthodontic brackets can still be placed using orthodontic bands. In severe cases of skeletal open bite, orthognatic surgery (jaw surgery) can be required to achieve a more optimal alignment of the jaws and teeth [20, 21]. This treatment is usually not performed until the child has completed growing (late adolescence). The young lady in Figure 18 is seen before and after orthognathic surgery showing the excellent result that can be achieved using this procedure.

figure18

Gingival Health Management in AI

Excessive calculus formation occurs in some AI types and is most severe in the hypocalcified and hypomaturation types (see Figure 16a). Calculus deposits may be extensive and grow to such proportions on the anterior teeth so as to obscure the dentition and produce tremendous soft tissue inflammation. The factors contributing to the development of these calculus deposits can include a rough enamel surface prone to deposits, altered salivary flow rate and/or composition, decreased oral hygiene abilities due to dental sensitivity, and altered oral microflora. Regardless of etiology these deposits form very rapidly on some restorative materials, such as composite or stainless steel, but appear to have a lower affinity for glazed porcelain. Individuals with rapid calculus formation may require more frequent recall appointments and professional scaling to control these deposits and maintain gingival health. Dentifrices developed to assist in controlling calculus formation could prove beneficial in AI patients with excessive calculus formation although this has not been clinically evaluated.

Prior to restorative treatment it is important to have optimal gingival health. Gingivitis and bleeding gums makes placement of bonded and esthetic restorations extremely difficult. Preventive interventions, such as professional cleaning, the use of antimicrobial oral rinses (e.g. chlorhexidene), and excellent oral hygiene, help to achieve healthy soft tissue prior to and after restorative care.

Genes and Enamel Formation

Enamel is the hardest, most mineralized tissue in the human body. Enamel is made up of very small mineralized crystallites (small crystals) that are oriented in a specific pattern to form enamel prisms (Figure 19). The prisms are organized in an interlocking pattern adding to the enamel’s fracture and wear resistance. Human enamel is approximately 97% mineral by weight with approximately 1% protein and 2% water. The enamel mineral is composed of a carbonate substituted hydroxyapatite mineral that has varying concentrations of trace elements such as fluoride, chloride, sodium and magnesium. The enamel on a human tooth takes years to form and involves a complex and highly orchestrated process of laying down a protein matrix, processing

Figure 19

this matrix in a controlled fashion and regulating the ion concentration of the mineralizing environment. Many of these processes are controlled directly by the ameloblasts, the cells that produce enamel. There are many excellent reviews written on enamel formation for those seeking further information on this topic [22-25]

There are thousands, to potentially over 10,000 genes involved in the formation of human enamel. We estimate from our research on forming teeth using microarrays that the number is 10,000 or more genes are involved in tooth formation. Many of the genes known to be involved in tooth formation can be reviewed at (http://bite-it.helsinki.fi/).

Genes involved in enamel formation are expressed in a highly regulated fashion at specific times and locations. Genes produce proteins that regulate gene expression, cell function and can be secreted from the enamel forming cells (ameloblasts) to form the matrix or template for the developing enamel. Some of the proteins secreted from ameloblasts regulate the size, shape and orientation of the growing enamel crystallites and thus contribute to the ultimate structure and composition of the enamel. Several genes and gene products that are either known to be associated with AI or are thought to be likely candidate genes for AI types where the associated gene remains to be identified are briefly reviewed in the following sections.

Amelogenin: (product of AMELX and AMELY genes located on the X and Y chromosomes) is the most abundant protein in developing enamel [26, 27]. While its exact role in enamel formation is not fully understood, it is thought to be crucial for regulating the size and shape of the mineralizing enamel crystallites. Multiple human mutations in the AMELX gene are associated with different AI types. There are no known AMELY mutations and it is thought that only about 10% of amelogenin mRNA transcripts comes from the AMELY gene. A transgenic mouse lacking expression of the AMELX gene has only a very thin covering of enamel that lacks a prismatic structure that is similar in appearance to some humans having AMELX mutations[28].

Ameloblastin: (product of AMBN gene located on chromosome 4) is another enamel associated protein that appears to be the second most abundant enamel matrix protein [29]. The function of this protein is unknown but it is considered a likely candidate for being associated with some AI types.

Enamelin: (product of ENAM gene located on chromosome 4) is secreted by amelobasts in relatively low amounts [30, 31]. It has been speculated that this protein could interact with amelogenin or other enamel matrix proteins and be important in determining growth of the length of enamel crystallites. Multiple mutations ENAM gene mutations are associated with different autosomally inherited AI types.

Enamelysin: (MMP20 gene located on chromosome 11) is a proteinase that cleaves amelogenin and is thought to be the major proteinase involved in processing the enamel matrix proteins [32, 33]. The enamelysin knockout mouse has a reduced enamel thickness, poorly mineralized enamel and the enamel lacks a prismatic structure.

Kalikryn 4: (KLK4 gene located on chromosome 19) is a proteinase that is secreted predominantly during the maturation stage of enamel development [34]. This aggressive proteinase could be responsible for processing any proteins not cleaved by enamelysin. Removal of this protein during maturation is critical to allow the enamel crystallites to grow and mature fully and the enamel to mineralize completely. Mutation of KLK4 is associated with autosomal recessive hypomaturation AI that is characterized by poorly mineralized enamel.

There are other enamel related genes, such as tuftelin, that have been proposed as candidate genes for AI [35]. It is highly probable that genes not yet even known to be important in enamel formation are associated with one or more of the AI types where the molecular defect is not yet known.

FAM83H: (Product of FAM83H gene located on chromosome 8q24). FAM83H is the first ameloblast associated protein to be identified that is not secreted into the extracellular matrix and is causative of AI. The are several potential functions of this gene including Phospholipase D (PLD)activity due to the genes similarities to the PLD gene. Mutations in this gene can cause a severe disturbance in the enamel mineralization (autosomal dominant hypocalcified AI - ADHCAI). The actual function of this gene remains unknown at this time.

For more information on genes in teeth link to http://bite-it.helsinki.fi/.

 

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