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Dentinogenesis Imperfecta


Treatments for Dentinogenesis Imperfecta

Evaluating the Patient:  The oral health care provider called upon to manage the patient with DI should first ascertain which type they are dealing with. Severe cases of dentin malformation associated osteogenesis imperfecta or other syndromnes can present significant medical management problems. Careful review of the patient's medical history will provide clues as to the severity of bone fragility based on the number of previous fractures and which bones were involved. The dentist must be extremely cautious in those individuals prone to fractures when performing any surgical procedures or treatment that could involve forces that will be transmitted to the jaws due to the increased risk of fracturing the jaw. Physical restraint is contraindicated in those patients with a predisposition to frequent bone fractures. The presence of spontaneous cases of DI where there is no family history is likely the first presenting feature of an autosomal recessive or new autosomal dominant mutation of OI and requires further medical and genetic evaluation. Children with unexplained bone fracturing should be evaluated for DI as a possible indicator of an undiagnosed case of OI. This can help explain bone fractures and be important in helping delineate child abuse from mild or undiagnosed OI [57].
Providing optimal oral health treatment for DI frequently includes preventing severe attrition associated with enamel loss and rapid wear of the poorly mineralized dentin, rehabilitating dentitions that have undergone severe wear, optimizing esthetics,and preventing the common dental problems associated with caries (which is reportedly low in people with DI) and periodontal disease.  The dental approach for managing DI will vary depending on the severity of the clinical expression.

Treatment of mild to moderate DI severity or in those patients not exhibiting enamel fracturing and rapid wear of the dental crown, routine restorative techniques can often be used effectively. 

Becuase the permanent dentintion is frequently less severely affected than the primary dentition these treatments are more commonly applied to the permanent teeth.  For example, intra-coronal restorations (i.e., amalgams and composites) will typically be adequately retained in individuals not suffering from enamel fracturing and attrition but are contraindicated in cases of enamel loss with attrition. Bonding of veneers can be used to improve the esthetics and mask the opalescent blue gray discoloration of the anterior teeth.  Bleaching has been reported to lighten the color of DI teeth with some success, however, becasuse the tooth discoloration is caused primarily by the yellow-brown underlying dentin, bleaching alone is unlikley to produce a normal tooth coloration in cases with significant discoloration.

In more severe cases where there is significant enamel fracturing and rapid dental wear, the treatment of choice is full coverage crowns. Intra-coronal restorations, such as amalgams and composites, are not well retained in patients having severe attrition. In these individuals the tooth structure tends to wear and break away from the restoration ultimately resulting in restorative failure. Stainless steel crowns will be the treatment of choice for cases in the primary dentition with excessive tooth wear. Stainless steel crowns with open face composite restorations or composite crowns can be used for a more esthetic result when crowning anterior teeth. Management of permanent DI teeth with fracturing and excessive wear can be treated with porcelain fused to metal crowns.

Ideally restorative stabilization of the dentition will be completed before excessive wear and loss of vertical dimension. Cases with significant loss of vertical dimension will benefit from re-establishing a more normal vertical dimension during the restorative treatment. Obtaining an appropriate vertical dimension and providing soft tissue support from restoration of the patient's dentition will return the individual's facial profile to a more normal appearance. Cases having severe loss of coronal tooth structure and vertical dimension maybe considered candidates for overdenture therapy.

Before

After

Some cases of dentinogenesis imperfecta will suffer from multiple periapicle abscesses apparently resulting from pulpal strangulation that occurs secondarily to pulpal obliteration or from pulp exposure due to extensive coronal wear. The potential for developing periapicle abscesses is another indication for performing thorough periodic radiographic surveys on all individuals with DI. Since these cases have pulpal obliteration and the dentist will rarely be able to negotiate the canal, apical surgery may be required to maintain the abscessed teeth. Attempting to negotiate and instrument obliterated canals in DI teeth can easily result in lateral perforation due to the poorly mineralized dentin.

What is Dentin Dysplasia

Two types of dentin dysplasia are recognized. Dentin dysplasia type I (OMIM# 125400) is a rare dentin defect that appears to be inherited as an autosomal dominant condition with a reported frequency of 1:100,000 persons. Clinically the dental crowns appear normal while radiographically, the teeth are characterized by pulpal obliteration and short blunted roots [54]. The teeth are generally mobile, frequently abscess and can be lost prematurely. There is no known specific treatment approach for DD type I although effort to keep occlussal forces to a minimum and avoiding orthodontic treatment for the malaligned teeth may increase the longevity of the dentition [54]. The genetic defect for DD type I remains unknown.

The affected dentin has a unique cascading waterfall appearance apparently due to a cyclical developmental process of premature odontoblast death, new odontoblast recruitment, dentin deposition and odontoblast death. The molecular defect in DD type I is unknown.


Dentin Dysplasia Type 1
Dentin dysplasia type II (OMIM# 125420) is also inherited as an autosomal dominant trait. Dentin dysplasia type II appears virtually identical to dentinogenesis imperfecta (DI) type II in the primary dentition with yellow-brown to blue-gray discoloration of the teeth and pulpal obliteration. However, in DD II the permanent dentition is normal in color or minimally discolored, but displays abnormal pulpal morphology that can appear shaped like a thistle tube in the anterior teeth [55]. Pulp stones also are common in the permanent teeth. Due to the similar phenotype of the primary teeth and known similar gene loci DD type II and DI type II it was speculated that DD type II could be an allelic mutation of the gene responsible for DI type II [56]. Indeed studies now show that in at least some families DD type II is caused by mutations in the DSPP gene which is associated with DI type II.

Genes and Dentin Formation

Dentin is the most abundant dental tissue and largely determines the size and shape of teeth. Dentin is formed by odontoblast cells. The unique structure and composition of dentin allow it to function as the substructure for the rigid enamel tissue, thereby imparting teeth with the ability to flex and absorb tremendous functional loads without fracturing. Dentin contains about 60% mineral by weight and, unlike enamel, has a substantial organic component (20%). Dentin contains a complex organization of tubules (Figure 22) that are approximately 1um in diameter, filled with fluid and/or the cellular processes of the odontoblasts and are thought to play a role in the neurosensory function of teeth [58]. Additional dentin can be deposited along the tubule (sclerotic dentin) or the pulpal wall in a reparative or protective mode in response to environmental stimuli such as trauma, tooth wear, or dental caries.

Figure 22

Dentin formation involves numeorus genes that produce a complex extracellular matrix that is highly organized, is processed, sand that eventually mineralizes in a highly controlled fashion.   Type I collagen (product of COL1A1 and COL1A2 genes) is the most abundant dentin protein [58]. This complex molecule has the structure of a heterotrimer and forms the foundation for several mineralized tissues including bone and dentin. The collagen molecules interact with a variety of non-collagenous proteins to help initiate and regulate the mineralization process in these tissues.  Interestingly, mutations in either type I collagen or proteins that interact with it can cause the DI dental phenotype.   There are known to be hundreds of different mutations in these two genes that are associated with osteogenesis imperfecta, a group of hereditary defects associated with bone fragility. Interestingly only some of the collagen mutations result in the dental manifestations of dentinogenesis imperfecta.

There are numerous non-collagenous proteins present in dentin, some of which interact with collagen to initiate and/or regulate mineralization [59]. The most abundant non-collagenous protein, dentin sialophosphoprotein (product of DSPP gene) is a highly phosphorylated protein.  That attaches to the type 1 collagen fibril helping regulate mineralization at specific sites within the collagen.  Mutations in either type 1 collagen or DSPP can alter this interaction resulting in abnormal mineralization and a DI dental phenotype.

For additional information on dentinogenesis see the following reviews: [58, 59]

Dental Pulp
The dental pulp is a specialized tissue comprised of a layer of odontoblasts, fibroblasts, blood vessels, nerves and a complex extracellular matrix. The pulp provides the reparative potential of teeth and neurosensory function.[60] The dental pulp can increase production of dentin (reparative dentin) in an attempt to protect and wall off the vital pulp tissue from the injury or noxious stimuli.[61] Prompt treatment of dental trauma and dental caries are critical steps towards maintaining a healthy vital pulp and allowing an injured or diseased tooth to retain a vital pulp. The pulp will continue to lay down small amounts of dentin throughout the life of a tooth as part of the normal pulp physiology.[62] This process ultimately results in a smaller pulp chamber in people as they age and is part of the reason teeth continue to become more yellow in color with age. It is especially critical to maintain a healthy dental pulp until the root is fully formed and its walls are of adequate thickness to maintain the tremendous forces transmitted from the crown during function. If the pulp becomes non-vital in a young tooth that lacks complete root formation, it is much more difficult to complete endodontic treatment successfully and the prognosis for retaining the tooth is diminished.

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

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