| Abstract|| |
Dental fusion is a rare developmental anomaly, which is included in the anomalies of tooth morphology or shape. Fusion can occur at the level of enamel or enamel and dentin, which results in the formation of a single tooth with enlarged clinical crown. Fusion is more common in deciduous dentition. Incisors are reported to be fused in primary and permanent dentition, but bilateral fusion is a rare occurrence. The prevalence of bilateral fusion in the permanent dentition is less frequent than unilateral fusion and is reported to be around 0.05%. The authors report a case of a 20-year-old male with bilateral fusion of maxillary central and lateral incisors. Multi-disciplinary treatment approach is essential to get the desired esthetic result. The best way to manage these difficult cases depends on a number of factors including the knowledge and technical skills of the practitioner.
Keywords: Anomaly, bilateral, deciduous, teeth, fusion
|How to cite this article:|
Hans MK, Shetty S, Chopra H. Bilateral fusion of permanent maxillary incisors. Indian J Dent Res 2011;22:603-5
A fused tooth can be defined as a single enlarged or joined tooth in which the tooth count reveals a missing tooth when the anomalous tooth is counted as one.  Its occurrence is more in the primary dentition (0.5%) compared to the permanent dentition (0.1%).  The prevalence of bilateral fusion in the permanent dentition is less frequent than unilateral fusion and is reported to be around 0.05%.  Fusion may be complete or incomplete depending on the developmental stage of the teeth at which it occurs. If it occurs before the beginning of calcification the union will be complete with the formation of a single large tooth.  Complete fusion may be characterized by a single pulp chamber and a single root canal or a single pulp chamber and two separate root canals or a separate pulp chamber as well as root canals. , If the contact of teeth occurs later, when a portion of the tooth crown has completed its formation, there may be union of the roots only. The tooth may have separate or fused root canals. The dentin, however, is always confluent in cases of true fusion. 
The etiology of fusion is not yet clear. The most common belief is of some physical force or pressure causing contact of the developing tooth germ.  Other investigators consider a viral infection during pregnancy and use of thalidomide as the possible cause of the anomaly.  An animal study has found hypervitaminosis A as the cause of fusion.  Still others have considered the role of heredity in this condition. ,
| Case Report|| |
A 20-year-old male patient reported to dental out-patient department with chief complaint of large front teeth. The patient's medical history was non-contributory. Additionally, there was no history of orofacial trauma. Patient did not complain of pain in the maxillary anterior teeth. Clinical examination revealed large maxillary left and right central incisors with a vertical groove [Figure 1] on facial aspect. Poor oral hygiene with abundance of plaque and calculus was noted. When anomalous teeth were counted as one unit, there was decrease in number of teeth by two. Both maxillary lateral incisors were not present clinically. Intraoral periapical radiographs revealed two separate pulp chambers with a wide single canal in both teeth [Figure 2] and [Figure 3]. Orthopantomogram (OPG) [Figure 4] also showed fusion of maxillary incisors on both sides and absence of both maxillary lateral incisors. Hence this was a case of true fusion of all four maxillary incisors. Both fused teeth elicited positive response on both electric and thermal pulp testing. Family history was non-contributory. Other findings noticed in the OPG were generalized horizontal and vertical bone loss. Therefore, a diagnosis of chronic generalized periodontitis was formulated. Treatment plan involving oral prophylaxis, comprehensive periodontal therapy, endodontic treatment and prosthodontic rehabilitation of fused teeth was made. Unfortunately patient was lost in the follow-up.
|Figure 1: Clinical image showing bilateral fusion of maxillary central and lateral incisors|
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|Figure 2: Intraoral periapical radiograph showing fusion of right maxillary central and lateral incisors|
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|Figure 3: Intraoral periapical radiograph showing fusion of left maxillary central and lateral incisors|
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|Figure 4: Panoramic radiograph showing fusion of maxillary incisors on both sides and absence of both maxillary lateral incisors|
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| Discussion|| |
Fusion and gemination are developmental anomalies with inherently unusual anatomy. These anomalies may develop during tooth bud morpho-differentiation as a result of a developmental aberration of both the ectoderm and mesoderm.  Brook and Winter elucidated the difficulty of deciding whether a tooth is fused or geminated, and proposed that these anomalies be referred to in a neutral term, such as "double teeth".  Definite categorization of joined teeth as either gemination or fusion, however, is often difficult. 
Several clinical and radiographic criteria are used to distinguish fusion from gemination. Fusion is the incomplete attempt of two tooth buds to fuse into one, whereas gemination is the incomplete attempt of one tooth bud to divide into two. Clinically when the joined teeth are counted as one, a full complement of teeth usually means that the phenomenon represents gemination; less than full complement of teeth usually indicates fusion. In our case when the total number of teeth was counted in the maxillary arch it was found to be 14 due to the absence of both maxillary lateral incisors.
According to reviewed literature for bilateral fusion for permanent dentition, only two cases of complete fusion of incisors were reported , and one was of incomplete fusion.  Teeth with this abnormality are unesthetic due to their irregular morphology. They also present a high predisposition to caries and periodontal disease, and spacing problems. The main periodontal complication in fusion cases occurs due to the presence of fissures or grooves in the union between the teeth involved. If these defects are very deep and extend subgingivally, the possibility of bacterial plaque accumulation in this area is quite high. Strict oral hygiene is imperative to maintain periodontal health. Furthermore, fusion may have an adverse effect on occlusion, causing deviation and, sometimes, delaying the eruption of other teeth.
In the literature many different multidisciplinary approaches in the therapy of fused incisors were suggested depending on whether there are independent pulp chambers and canals or one pulp chamber and two canals. The aesthetic criterion is the determining factor when choosing therapy.
| Conclusion|| |
Efforts must be directed to understand the root canal anatomy in order to avoid treatment complications. Despite the fact that surgical therapy may be necessary in some cases, a thorough knowledge of the complexity of root canal morphology in addition to adequate operative procedures appear to be the main requirements for successful endodontic treatment of these dental abnormalities. Difficult cases include a wide spectrum of problems. After successful endodontic treatment, these fused teeth should be separated and recountered to obtain the desired esthetics. The best way to manage these difficult cases depends on a number of factors including the knowledge and technical skills of the practitioner.
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Manoj Kumar Hans
Department of Conservative Dentistry and Endodontics, K.D. Dental College and Hospital, Mathura, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4]