Dentinogenesis Imperfecta Type I - A Case report with literature review on nomenclature system.. by Dr. Devaraju .D

Abstract: Significant hereditary anomalies have been diagnosed over the years, among which Dentinogenesis Imperfecta (DI) stands out. DI is an inherited disorder affecting dentin. Defective dentin formation results in discoloured teeth that are prone to attrition and fracture. Till date, mutation in Dentinsialophosphoprotein (DSPP) has been found to cause the dentin disorders DI- I and II (shields II & III). Early diagnosis and treatment are therefore fundamental, aiming at obtaining a favourable prognosis, since late intervention makes treatment even more complex. Here reporting a case with characteristic clinical, radiological and histological features of DI-I. The aetiology and classification followed in literature is confusing since Dentinoenamel junction (DEJ) in DI seems to be structurally and functionally normal and DI is clearly a disorder distinct from Osteogenesis Imperfecta, but we still relate aetiology of DI to DEJ and follow shields classification. So we have briefly reviewed aetiology and nomenclature system of DI.

Key-words: dentin, dentinsialophosphoprotein, osteogenesis imperfecta, tooth anomaly.

Key Messages: Dentinogenesis imperfecta is an autosomal dominant disorder of tooth development characterized by the presence of opalescent dentin, resulting in a dusky blue to brownish discoloration of the teeth.

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Introduction:

Dentinogenesis imperfecta was first reported by Tolbot as an autosomal dominant trait. While Hodge and his co-workers suggested the term hereditary opalescent dentin in 1936, Roberts and Schour proposed DI in 1939.¹ DI is described as a localized form of mesodermal dysplasia, observed in histodifferentiation, and which corresponds to a congenital hereditary change, involving deciduous and permanent teeth.

DI-I (shields type II) is transmitted as an autosomal dominant trait, with almost 100% penetrance and an incidence of 1:8000 births.² The defect has been reported to occur widely in the Caucasian race. In Type I, primary and secondary dentitions have typical amber like translucency against reflected light varying from grayish purple to purple brown or yellowish brown and there is often rapid attrition of the teeth. Radiographic features of DI include bulbous crowns with constricted short roots, progressive obliteration of the pulp chambers and periapical radiolucent areas may be noted. Histologically dentinal tubules are irregular and are bigger in diameter and areas of uncalcified matrix are seen.

Case History:

An 18 year old female patient reported with a complaint of pain in her lower right back region of the jaw since 2 months and discoloured teeth. Pain was intermittent and throbbing in nature, non- radiating and aggravated on consuming hot and cold food items. Sleep was disturbed due to pain. Patient’s mother gave a history of discoloured primary teeth and chipping of enamel. She was born from a second degree consanguineous marriage. She has one elder brother, who is not affected and none of the family members have similar complaint. (Figure-1)

The lower facial height was decreased due to severe attrition of maxillary and mandibular teeth and loss of molars (Figure-2). The oral findings include generalized brownish discoloration of teeth with loss of enamel and generalized attrition till the gingival margin. Multiple mobile teeth were present with an intra-oral draining sinus in relation to attached Gingiva of 22 (Figure- 3, 4, 5). Dental caries cannot develop in these cases owing to the absence of dentinal tubules and inability of caries to develop on a surface, where enamel is rapidly being lost due to abrasion and fracture. The case presented here confirms this with the absence of carious lesions.

Full mouth Periapical radiographs and panoramic radiograph showed narrowing of pulp chamber. Periapical radiolucencies in maxillary teeth and mandibular laterals are seen. Enamel of unerupted 38 is normal (Figure-6&7). Electric and Thermal Vitality test revealed non vital maxillary teeth and 42, 32. Ground sectioning of 42 showed dentinal tubules irregular in shape, size and course, increased hypo mineralized interglobular dentin and obliterated pulp chamber (Figure-8, 9&10). Based on the clinical, radiographic and histopathologic features, the case was diagnosed as DI-I.

Emergency treatment involves Endodontic access opening. The treatment carried out was oral prophylaxis; extraction of 12, 16, 22, 42, 46, and 47, followed by endodontic therapy. An over denture is planned, since efficacy of fixed partial denture is less.³

Discussion:

Dentin, the most abundant tissue in teeth, is produced by odontoblasts, which differentiate from mesenchymal cells of the dental papilla. DI is an inherited mesodermal condition affecting the primary and permanent dentition, but is more severe in the primary dentition. Inheritance of dentin defects is typically autosomal dominant, although autosomal recessive and X-linked cases of dentin defects associated with syndromes are reported. Dentin defects occur as a feature in a number of syndromes, including Osteogenesis Imperfecta, Ehlers-Danlos syndrome (EDS), Tumoral calcinosis and Hypophosphatemic rickets.⁴

DI is an inherited disorder affecting dentin. Mutation in Dentinsialophosphoprotein (DSPP) is the cause for this defect. The DSPP gene is located at 4q21.3 in a cluster of dentin and bone matrix genes (Table-II). DSPP encodes both dentin sialoprotein (DSP) and dentin phosphoprotein (DPP) as one precursor protein that is cleaved before secretion. DSP and DPP have different roles in dentinogenesis. DPP serves as a nucleator of mineralization and induces apatite formation.⁵

DI is classified under two systems, one by Witkop and the other by Shields. (Table-II)

These systems are well accepted but not totally satisfactory. The best nomenclature system was suggested by Levin. Extensive pedigrees of individuals with DI have been studied, and none have exhibited other changes suggestive of Osteogenesis Imperfecta (OI). Therefore, DI is clearly a disorder distinct from OI.⁶ So far, no definitive relation between the type of OI and the dental involvement can be established. Familial occurrence of DI with OI cannot be comprehensively explained by mutations in type I collagen genes.⁷ There is no substitute in the present classification for the category designated as DI-I of shields classification. So in present classification there are only two types, Type I - Dentinogenesis Imperfecta without OI & Type II – Brandywine Type with shell tooth. The Diagnosis of DI should be reserved for defective dentin formation with opalescent teeth in the absence of systemic disease. Appropriately, dentin defects associated with the systemic bone disease are termed OI with opalescent teeth.  Some authors classify these disorders as DSPP associated dentin defects, with dentin dysplasia type II representing the mild end of the phenotypic spectrum and DI- II representing the severe end.⁴

         Table – I: Genes underlying dentin defects.

Disorder	location	Gene
DI- I	4q21.3	DSPP
DI- II	4q21.3	DSPP

        Table – II: Various classifications of DI.

Shields8	Witkop9	REvised6,10	Clinical presentation
DI -I	DI	No substitute	Osteogensis Imperfecta with opalescent teeth
DI -II	Hereditary Opalescent Teeth	DI-I	Isolated opalescent teeth
DI -III	Brandywine isolate – found only in a population of southern Maryland(USA)	DI-II	Isolated opalescent teeth

DI-I Clinical presents with amber-brown or blue-grey coloration of teeth with opalescence. The opalescence colour is due not to the pulp showing through but to the collagen structural defect within the dentin, which may reflect either a bluish light through the enamel or a brown color. The enamel tends to chip away from the incisal rim of the anterior teeth and from the occlusal surface of posterior teeth. Originally it was thought that a defective DEJ was resulting in chipping of enamel, but scanning electron microschopic studies have disclosed a normal junction.¹¹ The enamel does not actually fall off the DEJ, as some believe; the DEJ in DI seems to be structurally and functionally normal (Figure-11).

It needs to be appreciated that odontoblasts differentiate in the pre-existing ground substance of the dental papilla and that into this ground substance the first dentin collagen is deposited.¹² Odontoblast differentiation follows three steps a) induction, b) competence and c) terminal differention.¹³ In the first formed dentin (mantle dentin), some of the matrix components are contributed by dental pulp cells beneath the odontoblasts. The odontoblasts are still undergoing the late stage of differentiation as the first layer of dentin matrix is being deposited.¹⁴ The need for an alternate mechanism of mineralization during mantle dentin formation may relate to the fact that odontoblasts are still completing their terminal differentiation at this stage and may not be able to fully exhibit the odontoblast phenotype in terms of expression of dentin specific matrix components.¹³The result is a near normal DEJ because of the less affected mantle dentin. Imperfect primary dentin in DI is because of matrix components which are completely formed by defective odontoblasts. They secrete an abnormal collagen, which is undermineralized and fails to form odontoblastic tubules.

 Some amount of enamel wears off excessively because of hypoplastic hypocalcified areas within the enamel rods. This is presumably due to the fact that the cells of the internal dental epithelium were needed to induce odontoblast and their product, dentin, becomes the initiator for further differentiation of the internal dental epithelial cells in a process of reciprocal induction.¹² The abnormality in dentin formation results secondarily in enamel that is also microscopically somewhat defective.³ The exposed dentin, which is soft, undergoes quick attrition, to such an extent that the dentin becomes smooth and continuous with the gingival tissue

Radiographic feature include bulbous crown with short root, obliteration of pulp chamber and multiple Pseudo periapical radiolucencies with the absence of pulpal exposure or pulpal necrosis. Although the pulp is usually obliterated by excess dentin production, some teeth may show normal sized pulp or pulp enlargement.  Cementum and alveolar bone are normal.²

The histological features include complete absence or reduction in the number of Dentinal tubules. They are irregular in shape, size and course. Hypo mineralized interglobular dentin is increased and cementum is normal. Odontoblasts entrapment may be seen within the dentinal matrix. Large areas of unmineralized dentin and irregular border between the unmineralized and mineralized dentin is seen. The enamel appears defective with subtle hypocalcification defects in the enamel rods just above the DEJ. The DEJ appears flattened although the DEJ appears qualitatively normal.

DI should be differentiated from amelogenesis imperfecta (AI), fluorosis & dentin dysplasia. AI can be recognized by its more clinically apparent enamel defect. AI and fluorosis are associated with normal pulp chambers. Dentin dysplasia type I, has normal coloration of both the primary and permanent dentition, although their pulps are almost completely obliterated. Unlike DI, it almost manifests with extremely short roots and periapical radiolucencies. Type-II does cause a discoloured opalescent primary dentition with obliterated pulp chambers. But the permanent dentition is of normal colour and the pulp chambers are enlarged.³

The goal of the treatment is to establish a more favourable prognosis for such a complex anomaly, and to insure the integrity of the erupting dentition. The treatment should aim to prevent the abrasion of the erupted teeth and to establish the proper vertical dimension. Prosthetic treatment using an overdenture seemed to be preferable in young patients. Once the skeletal development is complete permanent prosthesis is done.¹Contradictory statements were found in the literatures regarding the need for treatment of asymptomatic periapical rarefaction, or whether these are the regions of non infected hypocalcified bone only. In present case the endodontic treatment was carried out for the periapical rarefactions as they were symptomatic. The great challenge to the dentists facing such an anomaly is adequate treatment to achieve functional and aesthetic restoration, thus improving the self esteem and quality of life for these individuals.

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