Braz Dent J (1999) 10(2): 111-116  ISSN 0103-6440

| Introduction | Case report | Discussion | Acknowledgments | References |

Amelogenesis imperfecta (AI) is a heterogeneous genetic disorder which affects the dental enamel. It can have an autosomal dominant, autosomal recessive or X-linked pattern. The authors describe a case of a family with hypomaturation X-linked AI and discuss the clinical and histopathological aspects of this disorder.

Key Words: amelogenesis imperfecta, dental anomalies, malocclusion.

Introduction

Amelogenesis imperfecta (AI) is a group of hereditary defects of the enamel not associated with any other generalized defect. The prevalence of this condition is 1:718 to 1:14000, depending on the population studied (Seow, 1993). Its genetic inheritance pattern can be autosomal dominant, autosomal recessive or X-linked. It is an exclusively ectodermal disorder, because the mesodermic components of the teeth are not altered (Shafer et al., 1987). Its etiology is related to the alteration of genes involved in the process of formation and maturation of the enamel (Seow, 1993).
The genetic origin of the autosomal forms is still unknown, although the cause of X-linked amelogenesis imperfecta is definitely related to defects in the amelogenin gene, which is the principal protein related to the formation of human dental enamel (Line and Trevilato, 1996). The human amelogenin gene is in the distal region of the p 22.1 ® p 22.3 short arm of the X chromosome and in the pericentromeric region of the Y chromosome. The determination of the human amelogenin gene in the p 22 region of the X chromosome, together with the discovery of the locus of AI in the Xp22.2 region, support the association of this gene with the different AI phenotypes that have inheritance linked to this chromosome (Lau et al., 1990).
This genetic alteration can be divided into 3 main types: hypoplastic, hypocalcified and hypomaturation, according to the clinical characteristics of the enamel, which reflect the stage of formation at which the enamel was affected. Each type can be subdivided into subtypes depending on the mode of inheritance, as well as on the clinical and radiographic aspect of the enamel defect, although in some cases characteristics overlap, making classification difficult (Seow, 1995).
The hypoplastic types are characterized by a deficiency in the quantity of enamel, which can be expressed clinically through a fine enamel, or with grooves and pits on its surface. The hypocalcified types show an enamel that has low mineralization, manifested clinically by a pigmented, softened and easily detachable enamel. The hypomaturation types are associated with anomalies of the maturation stage during the formation of the enamel, resulting in an opaque and porous enamel (Shafer et al., 1987; Seow, 1993).
This article describes a case of a family with hypomaturation amelogenesis imperfecta, whose transmission pattern suggests X-linked inheritance.

Case report

A male patient (C.E.S.), leukoderma, 10 years and 3 months old, was seen at the Pediatric Dentistry Clinic of the School of Dentistry, Federal University of Rio de Janeiro because of the stained appearance of his teeth. The patient’s mother reported that, in the 1st 3 months of her pregnancy, she took an estrogen and progesterone-based medicine prescribed for amenorrhea, although the patient was born in a normal athermic delivery. At 10 months of age, he was hospitalized due to a urinary infection and subsequent pneumonia, when he took gentamicin and sulphamethoxazole associated with trimethoprime. He had always lived in a region where the water was fluoridated at suboptimum levels and took fluoride supplements at 2 years of age for 6 months. About 1 month before the exam, he was submitted to iron treatment due to slight anemia. On examination, he was in good general health.
Clinical examination showed a convex profile, a mouth-nasal breathing pattern, lack of lip sealing, short upper lip, Class II Division 1 occlusion and dental biprotrusion (4 mm overbite and 3 mm overjet). The teeth were opaque, pigmented and had no carious lesions. There were areas where the enamel was missing, similar to hypoplasias, although it was hardened and did not break loose when probed. In spite of the loss of dental structure, there was no reduction in the vertical dimension (Figure 1a-c). The radiographic examination showed thin enamel and radiopacity similar to dentin. The proximal contact surfaces were preserved (Figure 1d-f). Panoramic radiography showed a mixed dentition phase, compatible with the chronological patterns of normality and without any other pathological alteration (Figure 2).
The patient’s parents did not show enamel alterations similar to those noted in the patient. His 6-month-old brother had no erupted teeth. Nevertheless, when questioning about the existence of similar cases in the family, they reported that there were two cousins, sons of the patient’s mother’s sister, whose teeth had a similar appearance.
At the next appointment, these cousins came to the Pediatric Dentistry Clinic, where it was noted that they had a dental enamel pattern similar to that of the patient, although examination of the occlusion of the two brothers (A.C.A. 10 years, 10 months and M.C.A. 14 years, 11 months) revealed an anterior open bite without their mentioning any addictive habit as an etiological factor (Figures 3a-f). In addition, another cousin was examined (daughter of another maternal aunt of the patient) and also the maternal grandmother. The little girl did not show any clinically detectable alteration of the enamel and the grandmother was entirely toothless.
The heredogram gives information on the members of the family in which the alteration in question was observed (Figure 4).
None of the boys examined mentioned any symptoms of pain when mastigating or brushing, nor were there signs of sensitivity to heat stimuli.
In view of the clinical picture observed and the heredogram analysis, a diagnosis was made of hypomaturation AI with X-linked inheritance.

Discussion

The differential diagnosis of defects in the dental enamel must be based on clinical and, if possible, laboratory data. This diagnosis can be the key to discovering genetic and systemic diseases, and also local aggressor factors that occur during dental development (Seow, 1991).
Molecular and biochemical methods have shown differences in the proteic content and in the composition of the enamel in the various types of AI (Venezie et al., 1994). Although there may be true advances made in the diagnosis of this disorder, these sophisticated techniques are not routinely available. Diagnosis and subsequent classification are mainly based on their morphological characteristics and on family inheritance (Seow, 1993), making routine clinical observations extremely important.
The patients described showed general enamel defects, as much in their deciduous as in their permanent teeth, suggesting that this malformation did not occur due to aggressor agents during a certain period of formation of the dental germ. The clinical aspect was very suggestive of fluorosis, although the patient always lived in an area where the fluoride levels in the water supply were below optimum levels (< 0.7 ppm F) and his cousins did not live in the same area. Fluoride supplements were used in a period when the deciduous teeth were already mostly formed, so this was not the cause of the enamel alterations in these teeth. Furthermore, the patients did not show any systemic disease which could cause general enamel hypoplasia, such as renal or endocrine disturbances involving calcium metabolism (Seow, 1993).
The morphological pattern of the enamel and the family distribution characteristics are in keeping with the genetic anomaly known as hypomaturation AI. According to Seow (1993), this AI variant shows fine enamel of an opaque white coloring which can be detached. The interdental contacts are preserved and the radiographic image denotes thin enamel contrasting little with the underlying dentin.
The pattern shown in the heredogram of this family (Figure 4) strongly suggests an X-linked inheritance, where all the male children of affected mothers will be affected. Affected women have a 50% probability of transmitting this inherited trait to their female offspring. The phenotypic manifestation of the hypomaturation form can differ according to sex. Males have teeth that are normal in shape and size, with irregular opaque white pigmentation and females can show discreet vertical bands of pigmentation of the enamel, although transillumination is necessary for it to show up (Crawford and Aldred, 1992). A visual inspection did not reveal this banding pattern in the female patients examined, and the transillumination showed a different to normal pattern, although not characteristic of AI, as described in literature. Nonetheless, the possibility of this manifestation being very subtle and not detectable clinically should not be ruled out.
Although there are reports of a great tendency of AI patients to show impacting of permanent teeth and other anomalies associated to a delay in eruption, such as follicular cysts (Seow, 1995), the patient’s (C.E.S.) dentition radiography did not reveal any associated pathological alteration.
In studies made of the prevalence of anterior open bite in patients with amelogenesis imperfecta, it was noted that it occurred in 24% in the affected group compared with only 2% in the world population. The coexistence of the two conditions can be due to a pleiotropic action of the AI genes, influencing the growth of the craniofacial skeleton (Rowley et al., 1982). Disorders of the enamel epithelium also can cause alterations in the eruption mechanism, resulting in the anterior open bite (Persson and Sundell, 1982). However, Witkop and Sauk (1976) suggested that this malocclusion was of a dentoalveolar nature, due to the patient inserting his tongue in a reaction to protect against aggressor thermal stimuli, resulting in local interference that would prevent alveolar growth. The patients of this family who had AI and anterior open bite did not mention any sucking habit or complaints of pain, which would call for a reaction to protect through tongue intervention, nor did they show tongue intervention when in repose. This almost rules out the possibility of the malocculsion resulting from a local mechanical interference.
Comparing the cephalometric radiographs of AI patients with a control group, other discrepancies in the facial skeleton are found, such as a reduction in the angle of the mandibular plane, increased anterior facial height and a reduction in the posterior portion of the skull base, suggesting that the open bite may be of skeletal origin and not due to a disorder in the dental eruption mechanism (Persson and Sundell, 1982). Investigations into the embryonic development of the craniofacial complex suggest that this and the dental enamel have a common origin. In AI, therefore, it is possible that the gene acts in cells derived from the neural ridge, causing subsequent anomalies in the dental enamel and in the skull (Rowley et al., 1982).
According to Seow (1993), the main clinical problems of AI are esthetics, dental sensitivity, and loss of occlusal vertical dimensions. However, the severity of dental problems experienced by the patients varies with each type of AI.
Amelogenesis imperfecta represents a group of hereditary alterations in human dental enamel of particular interest to the pediatric dentist because, in addition to the clinical implications that may result from this pathology, these professionals usually have the first contact with the patient and the opportunity to establish their diagnosis, thereby allowing prompt preventive treatment to be given and intercepting any aggravation of the clinical manifestations of this disorder.

Acknowledgments

The authors sincerely thank Henrique Castilhos Ruschel, student of the Master’s Course in Pediatric Dentistry of the School of Dentistry of UFRJ, for taking the photographs.

References

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Line SRP, Trevilato PC: Amelogenina, amelogênese imperfecta e estrutura do esmalte dental. Revista da APCD 50: 32-35, 1996
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Correspondence: Dr. Ellen Rose Bundzman, Departamento de Odontopediatria e Ortodontia, Universidade Federal do Rio de Janeiro, Av. Brigadeiro Trompowsky, s/nº, Rio de Janeiro, RJ, Brasil. E-mail: uarlellen@highway.com.br

Accepted October 29, 1998
Eletronic publication: April, 2000