the dentigerous cyst is the most common type of noninflammatory odontogenic cyst and the most common cause of a pericoronal area of lucency associated with an impacted tooth . the dentigerous cyst develops around an unerupted tooth by accumulation of fluid between the reduced enamel epithelium and the enamel . it has been suggested that the pressure exerted by a potentially erupting tooth on an impacted follicle obstructs the venous outflow and there by induces rapid transudation of serum capillary walls . the increased hydrostatic pressure of this pooling fluid separates the follicle from the crown with or without reduced enamel epithelium . dentigerous cysts by far the most common lesion that often exhibits marked displacement of the unerupted tooth within the jaw . with the pressure of enlarging cyst , the unerupted tooth can be pushed away from its direction of eruption . here , we present a rare case report of a dentigerous cyst in an 80-year - old male in the anterior mandible crossing the midline . this rare case is reported because of its unusual presentation at such a location , its occurrence at this age and most importantly it is unique case because it is a single dentigerous cyst crossing midline , which is not reported in any of the literature available . an 80-year - old man , reported to the department of oral medicine and radiology with the chief complaint of pus discharge from the left lower front region of face since 2 years . extra - oral view showing fibrosed sinus opening in the parasymphyseal region in the lower border of the mandible on examination , extra - orally a fibrosed sinus opening was present on the left parasymphyseal region . on palpation , sinus opening was non - tender and fixed to the underlying bone with no frank discharge but a single , non - tender , movable left submandibular lymph node was palpable . root stump in relation to 17 , 21 , 22 , 27 , 46 were present and 26 , 34 , 35 , 43 were missing . iopa in relation to 35 , 36 , 37 revealed radiolucency in the periapical region of 36 not contacting the teeth . mandibular cross - sectional occlusal radiograph showed diffuse radiolucency extending from 34 to 44 region , latero - medially and from periapex to lower border of mandible superior - inferiorly . mandibular cross - sectional radiograph revealing radiolucent area from 34 to 44 region latero - medially and from periapex to lower border of mandible superior - inferiorly opg showed a unilocular well - defined radiolucency extending lateromedially from the distal root of 36 to the mesial root of 47 and superior - inferiorly from the furcation area of the teeth to the lower border of the mandible . a well - defined radio - opacity is seen at the lower border of the mandible on the right side in the periapex of 44 , which was identified as impacted canine ( 43 ) [ figure 3 ] . opg showing a unilocular well defined radiolucency with scalloped margins associated with impacted canine on the basis of history , clinical and radiological examination , a provisional diagnosis of odontogenic keratocyst was given . enucleation of the cyst with chemical cauterization was done conserving the impacted canine to avoid fracture of lower border of the mandible . histopathological examination revealed cystic epithelium comprising of 2 - 3 layers of non - keratinized stratified squamous epithelium . photomicrograph revealed-3 layers of non - keratinized stratified squamous epithelium with fibrous connective tissue and inflammatory cell infiltrate healing was uneventful and 1 week after the surgery , the surgical site showed good healing and the sutures were removed . the patient was recalled for follow - up every week and iodoform dressing was given . the post - operative opg taken after 2 weeks revealed healing by secondary intention [ figure 5 ] . iopa in relation to 35 , 36 , 37 revealed radiolucency in the periapical region of 36 not contacting the teeth . mandibular cross - sectional occlusal radiograph showed diffuse radiolucency extending from 34 to 44 region , latero - medially and from periapex to lower border of mandible superior - inferiorly . mandibular cross - sectional radiograph revealing radiolucent area from 34 to 44 region latero - medially and from periapex to lower border of mandible superior - inferiorly opg showed a unilocular well - defined radiolucency extending lateromedially from the distal root of 36 to the mesial root of 47 and superior - inferiorly from the furcation area of the teeth to the lower border of the mandible . a well - defined radio - opacity is seen at the lower border of the mandible on the right side in the periapex of 44 , which was identified as impacted canine ( 43 ) [ figure 3 ] . opg showing a unilocular well defined radiolucency with scalloped margins associated with impacted canine on the basis of history , clinical and radiological examination , a provisional diagnosis of odontogenic keratocyst was given . enucleation of the cyst with chemical cauterization was done conserving the impacted canine to avoid fracture of lower border of the mandible . histopathological examination revealed cystic epithelium comprising of 2 - 3 layers of non - keratinized stratified squamous epithelium . photomicrograph revealed-3 layers of non - keratinized stratified squamous epithelium with fibrous connective tissue and inflammatory cell infiltrate healing was uneventful and 1 week after the surgery , the surgical site showed good healing and the sutures were removed . the patient was recalled for follow - up every week and iodoform dressing was given . the post - operative opg taken after 2 weeks revealed healing by secondary intention [ figure 5 ] . dentigerous cyst accounts for more than 24% of jaw cysts and it is the most common developmental cyst of oral region . the dentigerous cyst occurs most commonly in second and third decade . koseoglu et al . in their study , stated that dentigerous cysts occur over a wide age range age from 15 years to 65 years . as evident from literature dentigerous cyst is twice as often in males than females and is 10 times more likely to occur in the lower - jaw than in the upper - jaw . the present case seems to support the age and sex pre - dilection given by other authors . a study reported by mourshed state that 1.44 per cent of impacted teeth may undergo dentigerous cyst transformation . as was found in our case report . stated that dentigerous cysts are frequently associated with impacted teeth and its occurrence in association with canines is frequent as the canines are the commonly impacted anterior teeth as was found in our case report . there is no evidence of dentigerous cyst crossing the midline in the literature in various search engines like medline , cochrane and pubmed apart from a case report by gonzalez et al . ( 2011 ) who reported a dentigerous cyst encompassing the right and left impacted mandibular canines and crossing the midline . hence , we are reporting this case , which is unique in its own kind as dentigerous cyst has never been found to cross midline . this will be a great break - through in the classification of midline crossing cysts . the authors also stated that as dentigerous cyst enlarges , it displaces the affected tooth or teeth apically , which was found in accordance to our case report . this new case presentation shows that a dentigerous cyst might also cross the midline . as dentigerous cysts are asymptomatic , they can attain considerable size without the notice of the patient and this warrants an early clinical and radiographic detection of the cyst so that early treatment strategies will prevent or decrease the morbidity associated with the same .