Developmental dental disorders may be due to abnormalities in the differentiation of the dental lamina and the toothgerms (anomalies in number, size, shape) or to abnormalities in the formation of the dental hard tissues (anomalies in structure). In some, both stages of differentiation are abnormal. Developmental dental disturbances may be inherited, acquired, or idiopathic. Not all developmental dental disorders are congenital.
1. VARIATIONS IN TOOTH NUMBER
1.A. Decrease in Number: Anodontia, Oligodontia and Hypodontia
Anodontia (congenital absence of teeth) and oligodontia (only a few teeth present) are rare conditions, often associated with generalised disorders. Hypodontia (one or a few teeth missing) is a common condition.
Hereditary factors are often involved in the congenital absence of teeth. Teeth can also be missing as a result of disturbances (e.g., trauma, infection, chemical irritation) during initial development.(1)
Hypodontia in the permanent dentition is more frequent than in the primary dentition. When a primary tooth is congenitally missing, its permanent successor is often missing too, though not necessarily.(2) Premolars and incisors are the most frequently affected teeth.
Some systemic disorders are connected with hypodontia/oligodontia in the permanent dentition: e.g. ectodermal dysplasia in the hairless breeds.(3)
Radiography is essential to differentiate missing teeth from impacted and embedded teeth.
Clinical importance: In hypodontia mainly cosmetic, differentiation between possible hereditary and proven traumatic causes is important for breeding dogs.
1.B. Increase in Number: Supernumerary Teeth (Hyperdontia)
This can occur in primary and/or permanent dentition. Supernumerary teeth may be inherited, but can also be caused by disturbances during tooth development.(1) Most supernumerary teeth are incisors or premolars. They can, but do not necessarily, have a normal shape and size.
Clinical importance: Supernumerary teeth may cause disturbances in eruption, crowding, and deviation of teeth. In that case, extraction needs to be considered. Most of the time, we choose the tooth most deviate in size, shape, or position. Again, radiographs are mandatory. When these teeth don’t cause clinical problems, they should not be extracted. The owner needs to be advised of the possible inheritability of the disorder.
1.C. Impacted and Embedded Teeth
An impacted tooth results from failure of the tooth to erupt into its normal position because of some physical barrier in the eruption path.(4) Generally this is an acquired condition but it can be genetic. Impaction can be caused by trauma or simply because of the tooth’s position in the alveolus so that it is not capable to erupt into its normal position. Embedded teeth are teeth that are unerupted, usually because of a lack of eruptive force.(4)
Clinical importance: Impacted and embedded teeth need to be differentiated from missing teeth. Radiographs are therefore indicated. Impacted teeth should be removed or at least monitored on a regular basis. Impacted teeth may cause resorption of the roots of adjacent teeth. In man, periodic pain due to tooth impaction had been described. A dentigerous cyst may develop around the coronal portion of the tooth. Furthermore, cases of ameloblastoma have been reported to develop in the wall of such a cyst.(4)
2. ALTERATIONS IN SIZE
Alterations in size are of limited clinical importance in dogs and cats. Teeth that are smaller than normal are microdont. When they are larger than normal they are referred to as macrodont. Teeth present in dogs with ectodermal dysplasia often are too small and of simple conical shape.(5) Sometimes supernumerary teeth are smaller than normal.
Clinical importance: Mainly cosmetic, although a macrodont tooth may need to be extracted because of interference with comfortable occlusion.
3. ALTERATIONS IN SHAPE
3.A. Gemination, Fusion and Concrescence
Gemination. Gemination is defined as an attempt to make two teeth from one enamel organ. This results in a structure with two completely or incompletely separated crowns with a single root and root canal. Occasionally we see complete cleavage or twinning (two teeth from one enamel organ). The etiology is unknown, but trauma has been suggested as a possible cause, though a familial tendency has been suggested too.(5,6) Gemination is seen in the deciduous as well as in the permanent dentition.
Clinical importance: Radiography is essential before extraction or endodontic treatment.
Fusion. Fusion is the joining of two tooth germs, resulting in a single large tooth. Fusion may involve the entire length of the teeth, or only the roots, depending on the stage of development of the teeth at the time of the union. The root canal can be shared or separate. The etiology is unknown, but trauma and a familial tendency both have been suggested as a possible cause.(5,6) Fusion is seen in the deciduous as well as in the permanent dentition. It may be difficult or even impossible to differentiate fusion of supernumerary teeth from gemination.
Clinical importance: Radiography is essential before extraction or endodontic treatment.
Concrescence. Concrescence is the fusion of adjacent already-formed teeth by cementum. It may take place before or after eruption. It is a form of fusion where the teeth are united by cementum only. It is thought to arise from trauma or crowding of teeth.(5)
Clinical importance: This condition is insignificant unless one tries to extract one of the teeth involved. Again, before doing any extraction at all, radiography is mandatory!
Dilaceration refers to a sharp bend or curve or angulation in the root or crown of a tooth. The cause is usually acute mechanical trauma during the development of the tooth such that the position of the calcified portion of the tooth is changed and the remainder is formed at an angle. The curve or bend may occur anywhere along the length of the tooth. Hereditary factors are supposed to be involved only in a small number of cases.(4)
Clinical significance: A dilacerated crown may be an esthetic problem. Extraction or endodontic treatment may be difficult in case of a dilacerated root. Severely dilacerated teeth may be unable to erupt.
3.C. Dens Invaginatus, Dens in Dente, “Tooth within a Tooth”
This is an uncommon tooth anomaly, with only a few cases described in the veterinary literature.(7) It represents an invagination of enamel and dentin towards the pulp of the tooth. It can be superficial (crown) to deep (crown and root). The etiology of the condition is unknown. In humans the mild form is fairly common (up to 5%).(4)
Clinical significance: Depends on the severity of the lesion (varying from higher caries susceptibility to pulpal necrosis and periapical inflammation).
3.D. Supernumerary Roots
Accessory roots can be seen in dogs and cats. Most commonly involved are the upper third premolar in the dog and the upper second (9%) and third premolar (10%) in the cat.(8)
Clinical significance: Radiographic recognition of supernumerary roots is very important when endodontic treatment or extraction of the involved tooth is necessary.
3.E. Enamel Pearls, Enamel Drops
An enamel pearl is a small, focal excessive mass of enamel on the surface of the tooth. It occurs most frequently in the bifurcation or trifurcation of the tooth. Occasionally the enamel pearl is supported by dentin; very rarely a pulp horn extends into it. Enamel pearls have been described in the dog.(9)
Clinical significance: Clinically, they are only significant when located in a periodontally diseased area, since there is no periodontal attachment to enamel pearls.
3.F. Other Defects
Other defects with no specific name can be seen regularly. Clinical importance varies from insignificant and mainly cosmetic, to extremely significant and leading to pulp necrosis and tooth abscess.
4. STRUCTURAL DEFECTS
Amelogenesis imperfecta, a hereditary form of enamel defects, affects both dentitions. The incidence in dogs and cats is unknown.(1) Three types are described in human medicine: enamel hypoplasia, enamel hypocalcification, and enamel hypomaturation.
Environmental enamel hypoplasia is a common structural defect seen in dog’s teeth. Enamel develops in two stages: a secretory stage (matrix production and early mineralization) and a maturation stage (increase in mineral content by withdrawal of water and protein). The enamel can be quantitatively defective (normal hardness = enamel hypoplasia) or qualitatively defective (normal amount, hypomineralized = enamel hypocalcification).(5) Some disturbances affect both matrix formation and mineralization. Enamel defects occur with injury during the formative stage of enamel development; once the enamel has calcified, no such defect can be produced.(4)
Etiologic factors may occur locally or systemically. Examples of etiologic factors include: vitamin deficiencies (rickets), epitheliotropic viruses, hypocalcemia, excessive fluoride ingestion, local infection, or trauma. Sometimes, no apparent cause can be identified (idiopathic). The extent of the defect(s) depends on the intensity of the etiologic factor, the duration of the factor’s presence and the time at which the factor occurs during tooth development.(5) , Since the ameloblasts are one of the most sensitive cells in the body in terms of metabolic requirements, any serious nutritional deficiency or systemic disease is potentially capable of producing enamel hypoplasia.
4.B. Other Structural Defects
Very few reports exist in veterinary literature regarding dentin defects. Described in human literature are the inherited conditions dentinogenesis imperfecta (hereditary opalescent dentin) and dentinal dysplasia. Dentin hypocalcification has the same causes as environmental enamel defects and can only be detected by histological examination.(4)
Regional odontodysplasia affects both dentin and enamel. One or several teeth in a localized area are affected and are described as “ghost teeth” (teeth with abnormal shape, very thin enamel and dentin, defective mineralization). The cause is unknown, though numerous etiologic factors have been suggested.(5) Because of the poor quality of affected teeth, extraction is the treatment of choice.
1. Harvey CE, Emily PE. Occlusion, occlusive abnormalities, and orthodontic treatment. In: Small Animal Dentistry. St.Louis: Mosby Year Book: 266-296, 1993
2. Nik Noriah Nik-Hussein, Zubaidah Abdul Majid. Dental anomalies in the primary dentition: distribution and correlation with the permanent dentition. Journal of Clinical Pediatric Dentistry 21(1): 15-19, 1996.
3. Foil C. In: Hoskins JD, ed. Veterinary Pediatrics. Philadelphia: WB Saunders: 366, 1993.
4. Shafer WG, Hine MK, Levy BM. Developmental disturbances of Oral and Paraoral structures. In: A textbook of Oral Pathology, 3rd ed. Philadelphia: WB Saunders: 2-80, 1974.
5. Regezi JA, Sciubba J. Abnormalities of teeth. In: Oral Pathology: Clinical-Pathologic correlations. Philadelphia: WB Saunders: 494-501, 1993
6. Wiggs RB, Lobprise HB. Developmental Pathology. In:Veterinary Dentistry: Principles and practice. Philadelphia: LippincottRaven: 105-112, 1997
7. DeForge DH. Dens in Dente in a six year old Doberman Pinscher. JVetDent 9(3): 9, 1992
8. Verstraete FJM, Terpak CH. Anatomical variations in the dentition of the domestic cat. JVetDent 14(4):137-140, 1997
9. Verstraete FJM. Dental disease and microbiology. In: Textbook of Small Animal Surgery, 2nd ed. Slatter D, ed. Philadelphia: WB Saunders: 2316-2326, 1993