Non-invasive endodontic management of fused mandibular second molar and a paramolar, using cone beam computed tomography as an adjunctive diagnostic aid: A case report.

Tooth fusion is a developmental anomaly characterized by the union between the dentin and/or enamel of at least two separately developing teeth. Fusion is a rare occurrence, with overall prevalence to be approximately 0.5% in deciduous teeth and 0.1% in permanent dentition. The significance of this particular case was that the unilateral fusion occurred in a permanent mandibular second molar with a paramolar and successful endodontic management was done. The rarity with which this entity appears, along with its complex characteristics, often makes it difficult to treat. In this case, a new advanced three-dimensional imaging Cone Beam Computed Tomography (CBCT) was used as an adjunctive diagnostic aid to differentiate between fusion occurred before or after root formation and help to reach the correct diagnosis.

INTRODUCTION

Teeth with morphoanatomic changes pose a challenge in endodontic therapy. It is imperative that aberrant anatomy is identified before and during root canal treatment of such teeth. Morphoanatomic changes in teeth may be divided according to the site of their occurrence, that is, tooth crown, roots, and root canals.[1] Fusion is a developmental anomaly, which occurs due to union of one or more adjacent teeth during morphodifferentiation of the dental germs.[2] Pindborg defined fusion as the union between dentin and/or enamel of two or more separate developing teeth.[3] Fused teeth may contain separate or share a common pulp chamber and root canals depends on the stage of tooth development at the time of union.[4]

Fusion is more prevalent in primary dentition (0.5%) than in permanent dentition (0.1%). The prevalence of fusion is higher in the anterior region than in posterior.[1] Fusion may occur between two normal teeth or between a normal tooth and a supernumerary tooth.

Supernumerary teeth are defined as those in addition to the normal series of deciduous or permanent dentition. Supernumerary teeth might occur as single or fused to their normal counterpart. The prevalence of supernumerary teeth varies between 0.1% and 3.8% and are common in permanent dentition.[56] The incidence is considerably higher in the maxillary incisor region followed by maxillary third molar and mandibular molar, premolar, canine, and lateral incisors.[7] Males are affected approximately twice than females in the permanent dentition.[8] When supernumerary tooth erupts distal to the molar, it is called distomolar and when it erupts buccal or lingual to the molar, it is called a paramolar.[2]

Fused teeth showed an abnormal morphology and excessive width, which may create crowding, malalignment, and malocclusion. These teeth are predisposed to caries and periodontal disease.[9]

The purpose of this article is to present the non-invasive endodontic management of mandibular second molar fused to paramolar with the use of radiography and Cone Beam Computed Tomography (CBCT), helped to confirm the radiographic diagnosis and accuracy of endodontic treatment.

CASE REPORT

A 21-year-old female patient presented to the Department of Conservative Dentistry and Endodontics with chief complaint of continuous pain in the right mandibular posterior region. There was no dental history of trauma or any hereditary conditions. Medical history was non-contributory.

On clinical oral examination, the right mandibular second molar had deep occlusal caries exhibited abnormal crown morphology with a paramolar on the mesiobuccal aspect of the crown [Figure 1a]. Distinct developmental occlusogingival grooves between the paramolar and its normal counterpart were noticed. However, the probing depth was within the normal limits, that is, between 1 and 3 mm. Despite the presence of the grooves, there was no discernible separation between the two teeth. The fused teeth showed increased buccolingual width with a wide distinct crown. The right mandibular first molar also showed the deep carious lesion adjacent to fused tooth. Other oral examinations revealed absence of both right and left mandibular third molars and had no history of extraction.

Figure 1

(a) Preoperative clinical picture of 47 fused to a paramolar (b) Preoperative IOPAR of mandibular right quadrant showing 47 with extra cusp as well as canal (c) Rubber dam isolation with three canals in molar and separate single canal in fused paramolar (d) Confirmatory working length radiograph (e) Immediate postoperative radiograph (f) Postoperative clinical image of restored 46,47 (g) CBCT image obtained by curved slicing (h) Occlusal view, by CBCT (i) Buccal view (j) 1year follow-up radiograph

On electric pulp testing, right mandibular second molar showed delayed response compared with adjacent teeth and was tender on percussion. Preoperative radiographs taken at different angulations revealed union between the right mandibular second molar and the paramolar [Figure 1b]. Based on clinical and radiographic examinations, a diagnosis of irreversible pulpitis with acute apical periodontitis was made.

Local anesthesia was administered and endodontic access cavity preparation was done under rubber dam isolation [Figure 1c]. The prongs of the rubber dam retainer had to be trimmed to accommodate the unusual anatomy of the tooth. The pulp chamber of second molar was large with visible dentinal map, whereas the pulp chamber of paramolar was small with a round orifice. The second molar had three separate mesiobuccal (MB), mesiolingual (ML), and distal (D) canals. The paramolar had a single canal located mesiobuccally to the MB canal of the second molar. Working lengths were measured with electronic apex locator (DentaPort ZX, J Morita, USA) and confirmed by radiograph [Figure 1d]. However, by exploring the canal of paramolar and MB canal of second molar by using two separate K-files combined with an apex locator provided evidence of communication between the two pulp canal systems. Cleaning and shaping of the root canal system was completed using ProTaper rotary system (Dentsply Maillefer, Switzerland). Canals were copiously irrigated with sodium hypochlorite (2.5%), followed by normal saline. The canals were dried with sterile paper points, calcium hydroxide was placed in the root canal, and the access cavity was temporized with Cavitemp (Ammdent, India). The patient was recalled after 1 week for obturation.

After a week, the tooth was asymptomatic, and the root canal was obturated using single cone technique with AH Plus (Dentsply Maillefer, Switzerland) as a sealer [Figure 1e]. Both the access cavities and mandibular first molar were restored permanently with a universal composite resin restorative material (Z250; 3M, ESPE, Germany) [Figure 1f].

Informed consent from the patient was obtained, and a CBCT of the right mandibular region was performed. The involved tooth was focused and CBCT gave a three-dimensional view of fused teeth [Figure 1h and i], as well as all the root canals in transverse, axial, and sagittal sections. The CBCT images revealed an example of fusion before root formation between MB root and paramolar [Figure 2]. There was connection between the paramolar and MB canal of second molar in the middle third region of root and exhibited a Type II canal configuration (according to Vertucci's configuration) with a thin lip of dentin separating both the canals [Figure 1g]. After 1-year follow-up, there were no clinical symptoms, and the recall radiograph appeared normal [Figure 1j].

Figure 2

CBCT image by custom slicing showed fusion of mesiobuccal root canal with single root canal of paramolar, clearly showing an example of true fusion and not concrescence

DISCUSSION

Fusion is a developmental anomaly with inherently unusual and bizarre anatomy. The complexity of root canal system of fused teeth depends on their developmental stage at the time of union. When fusion occurs at an early stage, the root canal system of the two teeth will merge resulting in a complicated morphology. However, fusion in the final stages results in two separate root canal systems.[1011] In this case, the fusion occurred before the complete root formation, thus the root canals merge in the radicular area as similarly reported by Ballal et al.[12]

Fusion between a paramolar and the permanent teeth occurs less frequently compared with fusion between other teeth, and such a fused tooth is known as “double tooth”.[4] As far as etiology for fusion is concerned, many theories have been proposed, such as the phylogenetic theory,[13] the dichotomy theory,[14] occurrence due to hyperactive dental lamina,[15] combination of genetic and environmental factors,[16] local metabolic interference during tooth bud differentiation, traumatic or inflammatory causes, and lack of space.[117] But still the etiology of fusion is an enigma. Shafer et al.,[9] speculated that pressure produced by some physical force prolongs the contact of the developing teeth causing fusion.

Endodontic treatment is usually problematic, owing to the complex anatomy, tooth positioning and difficulty in rubber dam isolation. In this case, the prongs of the rubber dam retainer were trimmed to properly seat it on the tooth. A prerequisite for endodontic treatment of anomalous teeth is careful examination of radiographs from various angles. Radiographic examination is an essential component in the management of endodontic problems. However, the conventional intraoral periapical views produce only a two-dimensional image of a three-dimensional object, resulting in superimposition of structures.[5] In these areas, CBCT has proved to be a useful diagnostic tool with three-dimensional imaging.

CBCT technology provides the clinician with an unparalleled visualization of the often complex relationships and boundaries between teeth and their associated pathology and anatomic features within the alveolus.[18] Although the use of CBCT involves less radiation than conventional CT, it is still higher than required by regular conventional intraoral radiographs.[19] At this point of time, CBCT is limited to major metropolitan areas and is expensive. Methods and training to improve accessibility and affordability of CBCT should be explored.

CONCLUSION

Any abnormality in a tooth's external morphology during examination should direct the clinician to the possibility of abnormal internal anatomy. Fusion in posterior permanent dentition is an uncommon condition and is extremely rare; however, it is a developmental anomaly that could affect any tooth in mouth. During the management of fused teeth, the clinician faces multiple problems due to intricate and unpredictable anatomy that require greater skill. Clinical identification and radiographic evaluation of such condition is mandatory before the treatment for successful outcome. A successful nonsurgical endodontic management of fused mandibular molar and paramolar was presented in this case study. Introduction of new advanced imaging techniques in dentistry such as CBCT helped us to reach the correct diagnosis and gave us three-dimensional images of complicated root canal systems. Proper diagnosis and treatment planning for endodontic management of fused teeth by using CBCT can ensure predictable and successful results.