Developmental Defects of the Dental Hard Tissues and their Treatment
Ivar Espelid, Dorte Haubek, and Birgitta Jälevik
This chapter focuses on the diagnostic process and classification of disturbances in the dental hard tissues. General treatment principles and treatment planning are discussed. Furthermore, different types of dental defects are described as localized and generalized dental defects including those of genetic origin. The most common and important diseases or conditions are given most attention in the chapter whereas many conditions with low prevalence are mentioned in the boxes.
Aspects related to tooth development
In contrast to bone, enamel and dentin are not remodeled. Therefore disturbances in the function of ameloblasts and/or odontoblasts during tooth development result in permanent defects. In contrast to the ameloblasts, odontoblasts are still functional in a fully formed tooth, capable of producing secondary and tertiary dentin. Irregularities in primary dentin will persist. The tissues under development and mineralization can be reduced in either quantity or quality or both. As the development of the first primary tooth begins in the fourth week in utero and the development of the roots of the third molars is completed around the age of 20 years, teeth serve a role similar to a “flight recorder” that covers a long time period. From this “record” the clinician can roughly judge when the disturbance occurred and the appearance of the defects may in some cases give clues as to the etiologic factor. But one major diagnostic challenge associated with developmental defects of teeth is that the etiologic factor(s) are rarely pathognomonic. The findings are often consistent with many possible etiologic factors and the anamnesis is of crucial importance to achieve the correct diagnosis. On the other hand, some clinical findings are pathognomonic or highly suggestive for a specific condition, such as dental changes due to tetracycline medication during tooth formation (Figure 20.12).
In the body, enamel is the only mineralized tissue of epithelial origin. Once formed, it loses contact with living cells. The basic unit of the enamel is the prism, each prism being the product of the activity of four ameloblasts. The prisms are bundles of crystallites which are much bigger and better organized than other mineralized tissues in the body. Enamel is formed at three stages: (a) deposition and (b) mineralization of the matrix occur simultaneously, and (c) maturation, involving final degradation and transport of the organic constituents, does not begin until the full thickness of enamel has been achieved at a given site. Amelogenins, constituting the major enamel matrix protein species during the secretory stage, are progressively degraded and lost.
The striae of Retzius are incremental growth lines seen in enamel. These striae are results of a halt or a slowing down in enamel growth and end on the enamel surface as perikymata. Microscopically, in cross‐sections, striae of Retzius appear as concentric rings or as a series of dark bands in longitudinal sections. These are incremental lines similar to the annual rings of a tree. The cross‐striations are created by the daily incremental enamel matrix production. The long‐period incremental growth lines are striae of Retzius. These lines are made with a periodicity of 6–11 days  (Figures 20.1 and 20.2). The neonatal line is an incremental line which is particularly pronounced due to the stress associated with birth and makes a distinction between the prenatal and postnatal enamel.
Dentin is mineralized connective tissue produced by odontoblasts, which are continually functional cells. The nonmineralized predentin, contiguous with the mineralized dentin, faces the coherent layer of odontoblasts located at the periphery of the pulp. Dentin is traversed by radial tubules, with each tubule housing an odontoblastic process. The main constituent of the organic dentin matrix is type I collagen.
Like dentin, cementum, which is formed by cementoblasts, is mesenchymal in origin. Morphologically, it is divided into the acellular cementum which covers the cervical portion of the root and the cellular cementum overlying the apical portion. Cellular cementum is slowly deposited throughout the life of the tooth.
Etiology of developmental dental defects
Developmental dental defects can be environmentally or genetically derived. Often the reason for the defect(s) in a given patient remains unknown. Genetic defects can be restricted to dental tissues or the dental defect can be a manifestation of generalized tissue/organ involvement. Environmental (also called acquired) dental defects can be divided into those caused by local factors and those caused by systemic factors. Typically, a local factor can be suspected when the enamel defect affects a single tooth or a group of neighboring teeth, or has an asymmetric distribution in the dentition. General symmetric defects are related to the timing of the insult and thus to the sequence of the development of the teeth. These defects are called chronological defects. The etiology of general defects not related to any particular time period during tooth formation is either genetic or due to nongenetic, longstanding environmental influence. Wright et al.  has recently reviewed the diverse genetic mechanisms related to hereditary enamel defects. The affected protein functions cover enzymes, regulatory proteins, extracellular matrix proteins, transcription factors, and transmembrane proteins. This diversity is in contrast to the genetically based dentin disturbances which seem to have a more uniform pattern related to fewer proteins.
Figure 20.3 gives a systematic approach to the collection and classification of findings. Boxes 20.4, 20.9, and 20.10 list a number of diseases and etiologic factors which can lead to developmental disturbances in the dental hard tissues.
Collection of information and treatment planning
The medical history is of utmost importance for disclosing the etiology of the dental aberration. Often, the nature of the symptoms is not specifically related to a certain cause and differential diagnostic considerations have to be made to form the final diagnosis. Keywords regarding history taking are mapping of family and childhood diseases, previous and current intake of medication, and environmental contamination level during childhood, fluoride exposure, dental history, and symptoms. A checklist of some important questions to ask is given in Box 20.1.
A brief examination of the features of the head and face is recommended to record indications of abnormal development (see also Chapter 24). Also, inspection of skin, hair, and nails may in some cases give useful information since they develop from the ectoderm‐like enamel.
Clinical characteristics of developmental dental defect
The classification of abnormalities of the dental hard tissues is governed by clinical characteristics of the affected tooth. However, with the expanding knowledge of the molecular basis of genetically determined dental defects, the need for classification relying on specific molecular defects has become increasingly evident. The most apparent defects are those seen in the enamel, namely enamel opacity and enamel hypoplasia (Figure 20.4). Since dentin is less available to inspection, the fact that dentin may also be involved is often unappreciated, and the dental defects are most often described and referred to as defects of the enamel (Box 20.2).
Enamel opacity results from incomplete mineralization and is a qualitative defect. Another term frequently used synonymously for this condition is enamel hypomineralization. Opacities are often divided into demarcated and diffuse lesions. Demarcated opacities have a clear and distinct boundary to the adjacent normal enamel and can be white, yellow, or brown in color. Diffuse opacities can have a linear, patchy, or contiguous distribution, but there is no clear boundary to the adjacent normal enamel . Some opacities have significant subsurface porosity which can lead to breakdown of the surface after the tooth has erupted. Tooth attrition and physical stress may result in such defects. These defects should be denoted posteruptive breakdown (Figure 20.4g) and not hypoplasia (Figure 20.4e,f).
Enamel hypoplasia is a consequence of deficient enamel matrix formation. It appears as a surface defect resulting from reduced enamel thickness. Hypoplasia can occur in the form of pits—single or multiple, shallow or deep, or scattered or arranged in horizontal rows; or grooves—single or multiple, narrow or wide, or evident as partial or complete absence of enamel over a considerable area of the tooth crown. The enamel of reduced thickness may be translucent or opaque when the hypoplasia is combined with hypomineralized enamel .
It should be noted that the same etiologic factor may cause an opacity or hypoplasia, depending on the timing, duration, and severity of the influence of the disturbing agent and the susceptibility of the individual.
To make a final diagnosis, it is necessary to combine the information from the patient history and medical record as well as clinical and radiographic findings from the dental examination. In some cases, it may be impossible to reach a final diagnosis or there is more than one likely diagnosis. For example, mild degrees of dental fluorosis and some cases of amelogenesis imperfecta (AI) have similar appearance.
Historically, symptoms and newly discovered diseases were named and more or less arbitrarily classified according to the current knowledge and beliefs. As medicine and dentistry progress continuously, more knowledge of the etiology and genetics is acquired. Classification of hereditary enamel and dentin diseases, primarily based on molecular etiology, will be an absolute necessity for genetic counseling, but so far not enough knowledge of the genetics for proposal of new classifications describing the relationship between genotype and phenotype is available [4–7].
A classification based primarily on the genetics and secondarily on phenotypic expression has been proposed . The first criterion is information on the defective gene locus and then the biochemical consequences of this failure. This systematic approach is more common in medicine; however, it may over time also lead to reclassification of hereditary dental defects as well.
For hereditary dentin defects, the classification of dentinogenesis imperfecta (DI) and dentin dysplasia (DD) by Shields et al. from 1973  is commonly used (Box 20.3). However, more recent studies indicate that the entities DI‐II and DI‐III are different phenotypic expressions of the same defect in the gene 4q13‐21. Similar gene defects are found in DD‐II, indicating that this is a similar entity. Another problem with Shields’ classification is the DI‐I diagnosis. This is based on dentin alterations in a syndrome while other syndromes, such as Ehlers–Danlos (EDS), are not included. EDS may have phenotypes with dysplastic dentin and obliterated pulp which can mimic DD‐I and DI‐II with variable expressivity, and similar findings may appear in some other syndromes as well .
All known diseases with a genetic component are catalogued and described in the electronic database Online Mendelian Inheritance in Man (OMIM). This can be accessed with the Entrez database searcher of the National Library of Medicine in the USA (www.ncbi.nlm.nih.gov/sites/entrez?db=OMIM). The database contains updated genetic information about all the hereditary diseases including those with dental implications.
General treatment principles
Patients with developmental disturbances of the teeth constitute a very heterogeneous group with respect to treatment needs. The opinions and instruction from general practitioners as to when and to what extent developmental defects of enamel need treatment vary considerably. The perception of dentists is influenced by type, size, and color of the defects, and in addition by dentist‐related factors . There is no common standard showing when it is correct to perform operative treatment. In relation to cases with mainly esthetic problems, the self‐perceived opinion of the patient is of paramount importance with respect to the treatment need.
The appearance of normal enamel may vary from one individual to another with respect to color, texture, and morphology. Teeth constitute an important part of an individual’s appearance and satisfaction with teeth contributes to well‐being for many people. As professional health workers it is important not to strengthen the tendency in society to judge people by the appearance of their teeth, and dentists should be aware that perceptions of desirable tooth color vary among parents, dentists and children . On the other hand, the dentist has to accept that the “owner” of the teeth has his or her right to dislike the appearance, but the task for the dentist is to decide whether it is within the ethics of the health profession to do the specific treatment considered. The concept of normality has a wide range also with respect to tooth color.
It is important to identify and address the particular needs of each individual patient. Rapport with parents and child is essential for establishing a long‐term relationship, particularly in cases with an extended treatment and follow‐up period. Systematic collection of clinical experience in relation to rare dental conditions can be made in larger, more specialized clinics in which dentists gain experience from treating a number of these patients. An example is the rare condition dentinogenesis imperfecta in which the dental treatment constitutes a clinical challenge. But there is also reason to claim that the general dental practitioner can do much of the treatment, but preferably under supervision in complex cases to ensure that the patient will receive proper treatment.
The period from diagnosis of the defect through childhood and adolescence can be divided into three phases: acute treatment, observational period and long‐term treatment.
In a child or adolescent with tooth disturbances this may affect the psychosocial health as in a patient with systemic health conditions . Some focus on the parents’ need for support and information is also required .
The treatment of teeth with developmental disturbances that cause pain, teeth with marked disintegration of enamel (chipping), exposed dentin, and/or extreme wear has to be taken care of as soon as possible after eruption. The overall goals of acute treatment are to relieve symptoms and prevent further disintegration of teeth and consequential problems. Diseases where such conditions can be encountered could be severe AI or DI, which as soon as the first tooth has erupted may have problems due to a heavily affected primary dentition. Exposed dentin should be protected to avoid pain and the choice of restorative materials differs with the type of dental problems. Temporary materials as intermediate restorative material (IRM) may be useful and both resin‐modified GICs (RMGIC) and high viscosity GICs may also be used as semi‐permanent restorations. It should also be kept in mind that uncured resin is a potential source for adverse reactions. The eruption of the permanent dentition starts at 5–7 years of age and introduces a new treatment period for the permanent first molar and the permanent front teeth in severe cases. Acute treatment will include handling of the extreme sensitivity of teeth and covering of the exposed dentin.
Young individuals who are severely affected with developmental disturbances are sometimes very sensitive to pain, and it is important to provide proper pain control which often is combined with sedation. Patients with extensive treatment need are in danger of developing dental fear . General analgesia is recommended when young patients have to undergo extensive treatment. A caring attitude with respect for the integrity of the child combined with good pain control and feeling of control will help in prevention of dental fear (see Chapters 6 and 9).
After the acute treatment is taken care of there is a transitional period when the permanent front teeth and permanent first molar should be kept under supervision and restorations are maintained according to the individual needs. In this period from about 7 to 11 years of age, the major lines in the final treatment are planned. In complicated cases it is necessary to have contributions from a multidisciplinary team of specialists. In addition to the pediatric dentist, the team may consist of an orthodontist, an oral surgeon, a prosthodontist, a maxillofacial radiologist or other specialists relevant for the specific condition. During the planning it is important to find the most appropriate time for various treatments, such as tooth extractions and prosthetic therapy.
In cases where the need for treatment is extensive and may result in partial or complete prosthetic reconstruction, the child may often go through a lot of early, intermediate treatment in the primary and young permanent dentition during childhood. This may include provisional or permanent fillings, microabrasion in an attempt to remove tooth discoloration, insertion of a partial denture or bridge work to replace teeth extracted early, or missing due to hypodontia, tooth retention or eruption disturbances. In many cases, there is no need for further treatment, but the teeth with disturbances have to be paid particular attention at the dental check‐ups due to increased risk for caries, chipping of enamel or attrition.
The long‐term treatment goals are a combination of a well‐functioning dentition, no pain or sensation from teeth and good esthetics. Prosthetic work has a limited durability and a lifelong period with regular dental check‐ups is needed. In cases with generalized severe disturbances full crown therapy as early as the teenage years may represent the optimal treatment. In patients with less severe tooth disturbances, a tooth‐saving philosophy using adhesive techniques may be the best option. A good relationship between the dentist and the patient is beneficial for the clinical results, and the pediatric dentist should put particular effort into the avoidance of dental fear in these patients. In cases with complicated and extensive treatment needs, it is important to be aware relative early on of the need to consult specialists within the field to obtain the best possible treatment outcome. In severe cases, it is beneficial to the patient to have dental treatment under general anesthesia .
Environmentally determined dental defects
Localized defects of the dental hard tissues
External damage to developing teeth
A common local trauma to the permanent tooth germ occurs often with avulsion or intrusive luxation in very young children when the primary incisor penetrates the unmineralized or still poorly mineralized permanent tooth (Figure 20.5). It is useful to think of the three‐dimensional localization of the primary teeth in relation to the permanent tooth buds. The root apices of the primary front teeth are placed in a more buccal position compared to the permanent teeth. A trauma to the primary teeth, which brings these into physical contact during trauma or creates an infection in the region, is likely to create some kind of damage to the permanent tooth. The severity may vary from a minor opacity to a hypoplasia with missing enamel and altered morphology of the crown and/or root. Another, local trauma to developing teeth may result from dental mutilation. Dental mutilation has long been an important cultural tradition in various ethnic groups around the world. Enucleation of the primary canine bud is reported among British‐born Somali children, raising important health issues . Removal of primary teeth or attempts to remove tooth germs from their follicles with improper instruments may often damage the developing teeth (Figure 20.6). In the study from the UK, 32% of the subjects showed dental features that could indicate previous removal of canine buds.
A long‐lasting periradicular infection of a primary molar may result in a range of developmental disturbances of the permanent successor (Figure 20.7). These vary from enamel opacities to enamel hypoplasia and to arrest of the development of the permanent tooth germ . Which of these possible and various changes in the permanent tooth occur is determined by the interaction of a number of factors, including the timing, severity and duration of the insult in relation to the development of the permanent tooth, and the susceptibility/resistance of the host. Other examples of possible disturbances of tooth development are therapeutic irradiation or high‐dose chemotherapy. These interventions can severely disturb dental development resulting in enamel defects, microdontia, arrested root development and agenesia of one or more teeth (Figure 20.8).
Generalized defects of the dental hard tissues
Disturbances in the development of the dental hard tissues of systemic origin can occur prenatally, perinatally, postnatally, during infancy or during early childhood. At birth, even the normal change from intrauterine to extrauterine life may have an adverse effect on amelogenesis and dentinogenesis as evidenced by the so‐called neonatal line (Figure 20.9). This pronounced incremental line is seen histologically in all primary teeth. Any stressful event during birth is likely to accentuate this line, resulting in clinically evident enamel defects.
Other factors associated with developmental defects include ingestion of chemicals (fluoride, tetracycline, thalidomide, aromatic hydrocarbons, such as polychlorinated biphenyls and dioxin); prematurity/low birth weight (Figure 20.10); severe malnutrition, neonatal hypocalcemia, vitamin D deficiency; bilirubinemia (Figure 20.11), thyroid and parathyroid disturbances; maternal diabetes; neonatal asphyxia; certain viral infections; and metabolic disorders.
This list by no means includes all the generalized environmental conditions that have been described as associated with developmental defects of the dental hard tissues. The resultant defect is generally not specific to the generalized environmental insult but depends, as with localized defects, on the timing, severity, and duration of the insult, the stage of development of the dentition and the susceptibility of the host; and the same insult may result in different responses in different individuals. However, there are a few exceptions and among those are discolorations of teeth caused by tetracycline given during the tooth‐forming period (Figure 20.12).
The presence of appropriate concentrations of fluorides in the oral environment, whether it originates from naturally occurring fluorides in the water supply or added as part of a public health program, or in oral hygiene products, e.g., toothpastes and mouthrinses, has contributed significantly to the major reduction in dental caries in industrialized countries over the past three decades. However, excess fluoride ingestion can result in enamel disturbances. Clinically, mild fluorosis appears as thin white lines following the perikymata (Figure 20.13). In more severe cases the enamel is chalky, stains easily and has areas of posteruptive breakdown due to the forces of abrasion or attrition (Figure 20.14). The teeth erupt with an intact surface. The breakdown is related to areas of subsurface porosity.
It has been suggested that fluoride outside the ameloblasts decreases the concentration of free calcium ions and thereby reduces the activity of the proteases. Thus, fluoride interferes with the degradation of amelogenin, which leads to a higher content of protein in the enamel .
Fluoride defects have been studied in areas with naturally occurring high concentrations of fluoride in the water supply. Children who swallowed fluoride toothpaste during early infancy, when the amelogenesis was still proceeding, may have enamel opacities. This is also seen in populations where fluoride tablets are used frequently. The differential diagnosis of these opacities can be difficult as some hypomaturation types of AI may clinically resemble fluorosis. Anamnestic information is crucial for a correct diagnosis.
Treatment of dental fluorosis
For mild and moderate cases, the main problem is poor esthetics affecting the incisors and canines, especially in the upper jaw. The mild opacities are confined to the superficial area of enamel. The appearance of these can be improved by the technique of microabrasion (Figure 20.15). More severe defects extend deeper and may require the use of restorations or veneers. Cases of severe fluorosis require extensive treatment comparable with the treatment of severe AI (Figure 20.16).
Tetracycline has a strong affinity to mineralized tissues, primarily to dentin and bone. Tetracycline oxidation occurs on exposure to light. Since dentin is not remodeled, the dentin defects are persistent. The discolored horizontal bands may appear gray or bluish when observed under ultraviolet light. In natural light the teeth may all have grayish appearance. The discolored enamel usually has some translucency left. The severity of the defect depends on the time of exposure in relation to the stage of tooth development, duration of exposure, dosage and the type of tetracycline preparation. Repeated exposure gives rise to series of bands of tetracycline bound to dentin and within the enamel (Figure 20.12). As tetracycline may cause discoloration of teeth these antibiotics should not be prescribed to children below the age of 8 years, pregnant women or lactating mothers.
Anti‐acne treatment with preparations containing tetracycline (typically minocycline) has been shown to cause discolored enamel if administered before crowns of third molars are completed at the age of 15 .
Treatment of discolored teeth due to tetracycline
Management of discolored teeth is difficult as much of the stain originates from dentin. In cases of moderate or severe discoloration, composite veneers may be used as temporary treatment. They may need to be replaced by porcelain veneers or jacket crowns at a later age. However, it has been shown that extended bleaching resulted in tooth whitening, which was stable over a period of 5 years .
Demarcated opacities in the permanent first molars are common in many child populations. Epidemiologic studies have found prevalence estimates up to 40%. The first permanent molars are particularly affected, but the permanent incisors are often also involved. In the literature, this condition has had many denominations as hypomineralized permanent first molars, idiopathic enamel hypomineralization, nonfluoride hypomineralization in permanent first molars, and cheese molars. In 2001, the term molar–incisor hypomineralization (MIH) was proposed  and is currently widely used, although the logic of the terminology of the condition may be disputed.
The enamel defects can be present in one to four first molars and one or more incisors are often also affected concomitantly. Similar lesions can be seen in the second deciduous molars, termed DMH (decidous molar hypomineralization) , and in the cuspal parts of the permanent canines, as these teeth are mineralizing in the same period of time as the permanent first molars and incisors. The degree of disturbance in the molars varies from creamy‐white opacities, with a hard, well‐mineralized surface, to yellowish‐brown discoloration and enamel disintegration. The defects in the incisors are described as creamy‐white, sometimes yellowish‐brown opacities. The number of affected teeth varies and the enamel spots do not always appear symmetrically (Figure 20.17). Histomorphological and micro‐CT studies of the enamel in affected permanent first molars reveal areas of porosity in the occlusal half of the crown of varying degrees (Figure 20.18). The enamel in the cervical half of the crown is most often well mineralized . The yellowish‐brown defects are more porous than the creamy‐white demarcated opacities and extend through the whole enamel layer, while creamy‐white demarcated opacities are situated in the inner parts of the enamel. Oral bacteria have been found in dentinal tubules beyond the porous enamel zones as well as inflammatory reactions in the pulp .
The most severely affected molars often show disintegration of the enamel in the occlusal parts (Figure 20.19). These teeth create problems for patients as well as for dentists. Children often report shooting pain when they are brushing their teeth or even breathing cold air, often shortly after the eruption of the affected teeth has started. At dental examination, these children most often open their mouth reluctantly, and react intensely to air blowing. The severely affected teeth are in need of restoration soon after eruption due to disintegrated enamel and the risk for subsequent caries development .
The etiology of MIH is not yet fully understood. There have been some suggestions of possible etiologic factors. The clinical appearance indicates some specific environmental influence on the development of enamel during a limited period of time. A systematic review of the literature dealing with etiology, concluded that childhood illness is likely to be associated with MIH. . There is some evidence that early childhood fever and respiratory disease may increase the odds of MIH. Asthma/allergy in early childhood is also associated with MIH in some studies. In the review the authors discuss possible biologic mechanisms which hampers the crystal growth of enamel. In addition possible effect of genetic predispositions and epigenetic influence is mentioned . However, a lot of high quality research is needed before any final conclusion can be drawn about MIH etiology.
Treatment of MIH‐affected teeth
The treatment rationale depends on the severity of the lesion. It varies from a small filling to extensive restoration, e.g., onlays and crowns, to more radical treatment as extraction of the affected molars.
When moderate or severe hypomineralized areas in the enamel have been diagnosed in a newly erupted tooth, frequent controls are of the utmost importance in order to determine the future fate of the tooth. Fluoride varnishing prevents caries and may also have some influence on preventing hypersensitivity.
The main clinical problems are the continuing enamel disintegration with subsequent caries and the frequently reported hypersensitivity of the affected tooth. When the lesions comprise large areas of the tooth surface, the filling often will be surrounded by opaque porous enamel. Then, depending on the degree of porosity and the size of the opacity, continuous disintegration of enamel may occur and repeated filling therapy may be needed. Occasionally, an affected tooth is extremely sensitive when it erupts, preventing the child from tooth‐brushing and eating cold food items, e.g., ice‐cream, while other teeth become more and more sensitive, in particular after repeated restorative treatment. It is a main treatment objective to cover exposed dentin to avoid sensitivity, caries development and damage to the pulp. In cases like these with highly sensitive teeth, dentists frequently report considerable difficulties in obtaining pain control. It is reported that increased TRPV1 expression is found within the pulps of hypomineralized teeth even with intact enamel surface . TRPV1 plays a role in signalling related to noxious heat stimuli. Malfunction may provide a major contribution to certain pain conditions. This can possibly also contribute to the understanding of the heat sensitivity experienced by some patients with MIH.
In filling therapy, GICs are the material of choice in the initial treatment, as microscopy studies of affected enamel indicate it is not suitable for etching and thus not composite bonding [26,27] (Figure 20.20). Resin‐modified GICs appear to work well. Pretreatment with sodium hypochlorite can be a good idea, as there is indication of retained organic substance in the porous enamel. In the long run, restorations of composite resins may be durable if the affected enamel is removed and the restoration is bonded to sound enamel. Painless treatment is important. In cases with poor effect of local analgesia, sedation with nitrous oxide or benzodiazepines may help. Use of preoperative analgesics may also be considered.
In cases with extensive disintegration, troublesome hypersensitivity, and/or increasing dental anxiety, crown therapy or extraction of the tooth must be considered. The choice of treatment alternative should be made in collaboration with both the child and the parents after the permanent dentition has been mapped and the development of occlusion analyzed. When crown therapy is preferred, a stainless‐steel crown can be used as a semipermanent restoration until the adjacent permanent teeth erupt to the occlusal plane, when it is replaced by a cast‐metal crown. However, in many cases extraction is to be preferred, when, for example, crowding is expected, or when the child is not able to manage crown therapy. One advantage of extraction is that the troublesome treatment‐consuming tooth is gone, since similar defects in the bicuspids or the second molars are rarely seen. Extraction of the permanent first molars generally presents no problems as regards the maxilla when performed prior to eruption of the second molar. In general, the best result was found when extractions were performed prior to eruption of the second permanent molar. Crowding in the relevant quadrant is also found to be favorable for a good orthodontic result as well as presence of the third molar. A careful follow‐up and easy access to orthodontic expertise are mandatory in all cases of extraction of permanent teeth due to developmental defects.
The age of the child, the cooperative skills, and “dental age” are some of the factors necessary to take into consideration before extensive preparation of the teeth. The exact age when it is possible to perform this type of treatment is difficult to establish on a general basis. In the treatment of young individuals the dentist may need to take intermediary types of treatment into consideration. Examples of this treatment plan could be the use of restorative materials and techniques requiring minimal preparation such as using an adhesive bonding technique (Figures 20.21, 20.22, and 20.23).
Inherited defects of the enamel
Amelogenesis imperfecta (AI) is a genetic disease characterized by clinical as well as genetic heterogeneity [2,5,6,28–30] (Figure 20.24). Crawford et al.  have defined the disease:
AI represents a group of conditions, genomic in origin, which affect the structure and clinical appearance of the enamel of all or nearly all the teeth in a more or less equal manner, and which may be associated with morphologic or biochemical changes elsewhere in the body. AI is a developmental condition of the dental enamel (characterized by hypoplasia and/or hypomineralization) that shows autosomal dominant, autosomal recessive, sex‐linked and sporadic inheritance patterns, as well as sporadic cases.
AI is caused by mutations in the genes controlling amelogenesis and follows patterns of autosomal dominant, autosomal recessive or X‐linked inheritance. Occasionally, new mutations occur in genes controlling amelogenesis. In such cases a family history or pattern of inheritance relevant to the disease may not be possible to identify. AI is seen in both the primary and the permanent dentition (Figures 20.24 and 20.25). The disease may be less clinically evident in the primary dentition in some AI phenotypes.
Different prevalence figures have been reported from different parts of the world, being from one in 14,000 in Michigan, to one in 700 in the north of Sweden. The majority of reports are descriptions of cases and only a few epidemiologic studies reporting prevalence data are available [31–33].
The clinical picture of AI is highly variable and numerous variants have been described . In the literature three main types have been focused on, one named hypoplastic type (Figure 20.24e‐g) and two hypomineralized types, called hypomaturated (Figure 20.24a‐c) and hypocalcified types (Figure 20.24d). Furthermore, a fourth type mixing hypoplastic and hypomaturated traits (Figure 20.24h) and, in addition, characterized by taurodontism has been described [34,35]. The characteristics of the three main types of AI are given in Boxes 20.5, 20.6 and 20.7. In the majority of teeth with AI the mineral content is lower than in unaffected teeth. Even in AI teeth with hypoplasia, various degrees of hypomineralization in areas of the enamel are found . As mentioned above, taurodontism may be a feature in some variants of AI. An association between AI and anterior open bite of skeletal origin is found, but no exact reason for this co‐occurrence has been reported. In some cases of AI delayed eruption and/or retention of teeth are seen (Box 20.7).