dens invaginatus ( di ) is referred to as a developmental anomaly that results from an infolding within the crown prior to calcification . according to the 0.04 to 10% frequency of dens invagination in the currently available literature ,
several hypotheses have been proposed concerning the etiology of invaginated teeth , including constriction of the dental arch on the enamel organ , decreased or increased growth rate of the internal enamel epithelium , distortion of the enamel organ during dental development or insufficient nutrition of a portion of a single tooth germ .
the epithelium forms a lining of enamel in a channel inside the dentin of the affected tooth .
following calcification of the enamel , it radiographically appears as parallel radiopaque lines within the less radiopaque dentin .
the enamel lining is sometimes imperfect and develops caries , which can lead to dentin or pulpal exposure and eventual pulpal pathosis .
maxillary lateral incisors are most commonly affected and bilateral occurrence is not uncommon , involving 43% of all cases [ 6 , 7 ] .
dens evagination ( de ) ( also known as talon cusp ) is a relatively infrequent developmental abnormality characterized by the existence of an accessory cusp - like structure projecting from the cingulum area or cemento - enamel junction ( cej ) of the maxillary or mandibular anterior teeth both in the primary and permanent dentition [ 810 ] .
de can occur in both sexes and the most commonly affected teeth are the permanent maxillary incisors , particularly the lateral .
although both di and de have been reported frequently in the literature , simultaneous occurrence of these two entities within a single tooth has been noticed only limitedly [ 1315 ] . to the best of our knowledge ,
co - existence of a de with two dis within a single tooth is considered a rarity and has not been encountered in the literature .
a 21-year - old girl came to the school of dentistry , kerman university of medical sciences for her regular dental follow - up visits and was advised to receive a full - mouth periapical radiographic evaluation .
intra - oral examination revealed several carious lesions , restorations and a mild periodontal disease .
presence of a de was noticeable in the patient s permanent right maxillary lateral incisor ( fig 1 ) .
the patient s maxillary left lateral incisor did not have any problem based on clinical and radiographic evaluations .
periapical radiographic evaluation showed co - existence of two dis with the aforementioned de ( fig 2 ) .
the tooth responded as vital on electrical and thermal pulp sensitivity tests and no periapical lesion was detected radiographically .
pits mesial and distal to the de were conservatively removed and restored by bonded restorations ( 3 m , espe , st paul , mn ) .
dens invaginatus is a relatively common dental anomaly . it has been stated that di affects maxillary lateral incisors in 0.25% to 5.1% of the population [ 16 , 17 ] .
however , double di in a single tooth has infrequently been reported [ 14 , 18 , 19 ] .
it is possible for dental caries to easily reach the pulp chamber in di cases . the patient is usually detected incidentally by intraoral periapical radiographs .
the reported patient did not have any complaint about the considered tooth and the problem was accidentally diagnosed on full - mouth radiographic examination . according to oehlers description of invagination , the case was categorized as  type i  because the invaginated cavities did not extend beyond the cemento - enamel junction .
it has been stated that the morphology of the tooth with di may undergo changes such as increased labio - lingual or mesio - distal dimension , incisal notching associated with a labial groove , a peg - shaped or conical morphology or the presence of an exaggerated palatal cingulum or 
talon cusp [ 21 , 22].simultaneous occurrence of two dis with one de in a single tooth has not been previously reported but separate conditions in different teeth have been reported exclusively in the literature . in other words
de is a rare dental anomaly occurring commonly on the lingual surface of primary or permanent teeth [ 23 , 24 ] .
usually , grooves or fissures can be found at the junction of the evagination with the lingual tooth surface , which often allows plaque retention , thereby causing caries and endodontic and periodontal inflammation .
the etiology of this condition is multifactorial with genetic and environmental factors playing significant roles .
it has also been reported that this anomaly is related to rubinstein - taybi , mohr , and sturge - weber syndromes and to anomalies including odontome , dens invaginatus , double tooth , supernumerary tooth , peg - shaped lateral incisors , agenesis of canines , mesiodens , megadont , and shovel - shaped incisors [ 8 , 12 , 24 , 25 , 27 , 28 ] .
although there is no strong correlation between the aforementioned syndromes and talon cusp , in a study by hennekam and van doorne   on 45 patients with rubinstein - taybi syndrome , 92% of these patients had talon cusps .
other signs of this syndrome such as mental and developmental retardation , thin upper lip , retrognathia , micrognathia and cleft palate were not evident in our patient , therefore the presence of this syndrome was ruled out .
talon cusp has a prevalence of 0.067.7 percent with a predominance in the male gender [ 12,23 , 30 , 31 ] .
although many authors have reported de in the primary dentition [ 8 , 25 ] , it is seen more frequently in permanent dentition .
talon cusp can cause problems for the patient including poor esthetics , caries , occlusal trauma , displacement of the involved tooth , irritation of the tongue during speech and mastication , periodontal problems , accidental cuspal fracture and attrition causing pulpal exposure or periapical pathosis [ 11 , 12 , 3234 ] .
the radiographic appearance of talon cusp resembles that of a supernumerary tooth or compound odontoma , consequently increasing the likelihood of misdiagnosis [ 11 , 12 , 32 ] . de can either be treated conservatively or radically , depending on the shape or size of the affected tooth [ 11 , 28 , 33 , 3537 ] .
treatment remedies may consist of gradual periodic cuspal reduction with fluoride as a desensitizing agent , one - visit reduction with or without endodontic therapy , application of sealants for developmental grooves and placement of esthetic restorations . in this case ,
simultaneous occurrence of two dis and one de was encountered in a permanent maxillary lateral incisor .
this patient represented positive responses to vitality tests without any radiographic signs of apical periodontitis . in such cases
, it is recommended that the susceptible parts should be sealed prophylactically using restorative materials in order to prevent formation of any communication pathways between the oral environment and pulpal space .
it has to be taken into consideration that ohlers classification is based on the presence of a single dens invagination ; whereas , this patient represented two invaginations simultaneously . according to similar reports in the literature [ 18 , 38 ] , this classification should be modified based on the presence of multiple defects .
 a case with two simultaneous dens invaginations ( dis ) and one dens evagination ( de ) in a permanent maxillary lateral incisor is reported for the first time in a 21-year - old girl.de known as talon cusp of the anterior teeth is a rare entity and its co - existence with di has been reported scarcely in the literature . 
 simultaneous occurrence of two dis with one de has not been reported elsewhere . 
 undoubtedly , familiarity with the internal anatomy of such a rare condition can help prevent pulpal disease while performing restorative procedures . 
INTRODUCTION
CASE REPORT
DISCUSSION