dens invaginatus ( di ) is a developmental anomaly that results in a deepening or invagination of the enamel organ into the dental papilla prior to calcification of the dental tissues .
this type of malformation was first described by ploquet in 1794 in a whale 's tooth .
di was first described as a  tooth within a tooth  by salter in 1855 while socrates in 1856 reported the first case of di in a human tooth .
commonly , this anomaly occurs in the permanent maxillary lateral incisors followed by the maxillary central incisors , premolars , canines , and less often in the molars .
the etiology of this anomaly is controversial and remains unclear ; however , most authors conclude that di results from an infolding of the papilla during tooth development .
radiographically , di presents as a radiopaque invagination , equal in density to enamel , which extends from the cingulum into the root canal .
oehlers classification categorizes invaginations into three classes as determined by how far they extend radiographically from the crown into the root : type i : an enamel - lined minor form occurs within the crown of the tooth and does not extend beyond the cementoenamel junction .
type ii : an enamel - lined form that invades the root as a blind sac and may communicate with the dental pulp .
type iiia : the invagination extends through the root and communicates laterally with the periodontal ligament space through a pseudo - foramen .
there is usually no communication with the pulp , which lies compressed within the root .
type iiib : the invagination extends through the root and communicates with the periodontal ligament at the apical foramen .
the invagination allows entry of irritants into an area that is separated from the pulpal tissue by only a thin layer of enamel and dentin and is a predisposing factor for the development of dental caries . in some cases
, the enamel - lining may be incomplete , and channels may exist between the invagination and the pulp , allowing bacteria and their products to gain access to the pulp . therefore , pulp necrosis often occurs at an early stage , usually within a few years of eruption , and sometimes even before root - end closure .
this article describes a rare case report of bilateral di in the mandibular second premolars that were treated nonsurgically .
a 25-year - old male patient reported to the department of conservative dentistry and endodontics of our institution with a chief complaint of bilateral swellings in relation to the lower right and left posterior teeth since the last 2 months .
the patient gave a history of an occasional dull aching pain in relation to the swellings .
clinical examination revealed draining sinuses in relation to noncarious 35 and 45 [ figure 1 ] .
both the teeth were tender to percussion and failed to respond to thermal and electrical pulp testing .
radiographic examination of both 35 and 45 revealed an oehlers type i di , with incomplete root - end formation and a periapical radiolucent lesion .
incidentally , an oehlers type i di was also noted in relation to 34 and 44 [ figures 2 and 3 ] .
however , both 34 and 44 were nontender and showed a positive response to pulp testing . to obtain a detailed understanding of the root canal morphology and evaluate the type of invagination , a spiral computed tomography ( ct ) scan was done with a multi - detector ct scanner ( 16 slices / s ) , as per the recommendations given by christoph et al . to reduce the radiation dosage ( collimation : 1 mm ; pitch : 2 ; tube voltage , 80 kv ; tube current , 40 ma ) .
axial images were transmitted to a commercially available dental program ( denta scan , advantage windows ; general electric , buc , france ) to reformat panoramic and cross - sectional images in all three planes [ figures 46 ] .
( a ) right mandibular second premolar region , ( b ) left mandibular second premolar region preoperative intra - oral periapical radiographs .
( a ) right mandibular premolars , ( b ) left mandibular premolars panoramic radiograph ( preoperative ) spiral computed tomography scan ( sagittal view ) of right mandibular second premolar spiral computed tomography scan ( sagittal view ) of left mandibular second premolar spiral computed tomography scan ( reformatted panoramic view ) a clinical diagnosis of pulp necrosis and chronic periapical abscess in relation to 35 and 45 was made .
the canal was enlarged , and central hard tissue was removed using h - files and gates glidden drills with copious irrigation using 5.2% sodium hypochlorite .
apical closure was done using mineral trioxide aggregate ( mta ) , and the teeth were obturated by the thermoplasticized technique using obtura ii ( obtura spartan co. , fenton , mo , usa ) with vertical compaction using finger pluggers .
there was no evidence of any pathology in relation to 34 and 44 and hence no treatment was needed for these teeth .
( a ) right mandibular premolars , ( b ) left mandibular premolars postoperative clinical and radiographic examination after 6 months showed satisfactory healing of the draining sinus and periapical lesion in relation to 35 and 45 [ figures 810 ] .
( a ) right mandibular second premolar region , ( b ) left mandibular second premolar region postoperative intra - oral periapical radiographs showing healing of the periapical lesion .
( a ) right mandibular premolars , ( b ) left mandibular premolars panoramic radiograph ( postoperative )
di is thought to affect usually the permanent maxillary lateral incisors , with the posterior teeth less likely to be affected .
while cases of di in the mandibular teeth have also been reported , only a few cases have been shown to involve the mandibular second premolars .
the present case showed bilateral di in both the first and second mandibular premolars . according to hlsmann , if there is no evidence of an entrance to the invagination and no signs of pathosis are visible clinically and radiographically , no treatment is necessary , but strict observation is recommended . in our case , both the mandibular first premolars did not show any clinical or radiographic signs of pathology .
hence , no treatment was carried out for these teeth , and the patient was advised to report regularly for follow - up . since both the mandibular second premolars were nonvital and showed periapical lesions , they were endodontically treated .
endodontic treatment of di constitutes a challenge due to the complicated root canal anatomy of the affected teeth .
nonsurgical endodontic treatment should be attempted first regardless of the size of the periapical lesion .
the successful management of the present case indicates that the size of the periapical lesion does not influence the treatment procedure to be performed or its outcome .
however , a major concern with the use of a ct scan is its high radiation dosage . in the present case , guidelines proposed by christoph et al .
were used , and the effective radiation dosage produced by this method was 0.56  0.06 mgy , which is roughly equivalent to that of a standard panoramic radiograph .
the prognosis of nonsurgical endodontic treatment depends on a number of factors like the extent of the invaginated central mass in relation to the pulp space , continuous drainage of fluid from the canal during treatment which prevents dryness of the canals , and an open apex which may negate apical seal of the root canal filling .
mechanical debridement of the canal is difficult in many cases , but the combination of chemo - mechanical instrumentation and the use of calcium hydroxide may be sufficient without resorting to surgery .
the use of mta as an apical seal for immature roots allows the immediate rehabilitation of the crown , thus increasing the resistance to fracture and enhancing the esthetic result .
the present case showed the occurrence of type i di in relation to 35 and 45 with periapical lesions , which was successfully treated nonsurgically .
this case illustrates that even in cases with bilateral di , open apices and an associated periapical lesion , use of nonsurgical endodontic treatment can result in satisfactory peri - radicular healing .
although di is a relatively common anomaly , it may be easily overlooked due to the absence of any significant clinical signs .
this is unfortunate as the presence of an invagination is thought to increase the risk of dental caries , pulpal involvement , and periodontal inflammation .
also , the variable nature of the invagination can often mean that any required endodontic treatment may be complicated .
careful radiographic examination and knowledge of the variations in morphology of the internal anatomy of teeth are thus necessary for a successful treatment outcome .
 dens invaginatus ( di ) is a developmental anomaly that results from an infolding of the dental papilla during tooth development and simulates the appearance of a tooth within another tooth . 
 it shows a wide spectrum of variations in morphology and usually affects the maxillary lateral incisors . 
 this study presents an unusual case of an oehlers type i di involving the bilateral mandibular first and second premolars , which presented as an incidental radiographic finding in the first premolars and was associated with a periapical lesion in the second premolars which was successfully treated using nonsurgical endodontics . 