Simultaneous occurrence of triple teeth and double teeth in primary dentition: A rare case report and review of the literature

Abstract This paper reports the case of a 3‐year‐old male patient with triple teeth in the right maxillary incisor region and double teeth in the left mandibular incisor region. He had pre‐existing medical conditions. The triple teeth were extracted and examined using micro‐computed tomography. A literature review was performed to discuss this abnormality.

"triplication" are used and have the advantage of covering all types of unions. 3 In fact, the clinical aspect of fusion or gemination of normal or supernumerary teeth is similar.
The prevalence of triple teeth in primary dentition is rare (0.02%) 4 and shows a predilection for the male sex and Asian populations. 5 It occurs more frequently in the upper arch than in the lower arch. A number of etiological hypothesis have been suggested: Close developing tooth buds, insufficient space in the dental arch, and physical pressure or trauma can cause contact between tooth germs 6 that results in necrosis of the epithelial tissue that separates tooth germs and leads to fusion; genetic factors (dominant autosomal heredity) 7 ; and disturbances in the prenatal period or environmental factors such as viral infection during pregnancy, intake of thalidomide, and lack of vitamins. 8 However, none of them proved satisfactory.
Shilpa and Nuvvula classified triple teeth into two types and subtypes. 9 Type I corresponds to fusion with three pulp chambers and three root canals, which includes type Ia: fusion of two normal teeth with a supernumerary tooth and type Ib: fusion of three normal teeth. Type II corresponds to fusion with two pulp chambers and two root canals, which includes type IIa: combination of one geminated tooth and a supernumerary tooth, and type IIb: combination of one geminated tooth and a normal tooth. However, it is difficult to determine the type even with intraoral radiography.
This paper aimed to report a rare case of a young patient presenting large triple teeth in the right maxillary incisor region and double teeth in the left mandibular incisal region, which has not been reported in the literature before, and further discuss it by a comprehensive literature search on triple teeth.

| CASE PRESENTATION
A 3-year-old male patient of Cambodian origin was referred for extraction of an unusual right maxillary incisor after a traumatic injury. According to his mother, there were no such anomalies in the other family members. The anamnesis revealed that the child was born premature and actually presented with delayed growth, hyperlaxity, and cerebellar atrophy. Moreover, his built was small for his age. These symptoms led to genetic exploration of syndromic diseases, but with no remarkable findings.
The extraoral examination did not show any alterations. Intraoral examination revealed a gingival laceration next to a decayed triple tooth, in which was a double crown in place of the maxillary central incisor fused with the lateral incisor ( Figure 1). These triple teeth were affected by a large carious lesion at the junction between the double crown and an incipient carious lesion in the groove between the double crown and the lateral incisor crown. These teeth presented no mobility or fracture. In the region of the right central incisor, a submucosal abscess was observed, suggesting infected pulp necrosis. Moreover, the left mandibular central and lateral incisors appeared fused, with a unique but larger crown ( Figure 2). No other findings were reported.
An intraoral periapical radiograph of the triple teeth revealed two distinct structures, an upper right incisor with a possibly unique pulp chamber (difficult to confirm because of the carious lesion) and a large root canal (possibly dividing into two canals in the middle-third), and a lateral incisor with separate pulp chamber and separate root canal ( Figure 3). It also showed a radiolucent area around the apex of the large central incisor, but the lateral incisor seemed unaffected. It was not possible to take a radiograph of the double teeth due to noncompliance of the patient.
The diagnosis was gingival laceration due to trauma and abscess on the triple teeth due to an advanced carious lesion. Because of the difficulty in performing root canal treatment in such teeth and the poor cooperation of the young patient, extraction of the triple teeth was planned. Due to the difficulty in extracting such teeth and for the patient's comfort, this procedure was performed under nitrous oxide/oxygen inhalation. To prevent functional, esthetic, and phonetic problems, the missing teeth should have been replaced with a transitional partial denture. However, the replacement was not possible at this stage due to insufficient cooperation by the patient. A 1-year follow-up showed good healing ( Figure 4). It was however not possible to perform a radiograph to check the underlying tooth germs, because of insufficient cooperation.
The extracted teeth had three separate crowns and roots conjoined from the crown to the apex and possibly from the incisal edge to the apex in the large central incisor ( Figure 5). Macroscopically, almost no root resorption was detected. The teeth were analyzed using micro-computed tomography to obtain a three-dimensional model and a two-dimensional cross-sectional slice ( Figure 6). It showed two separate pulp chambers in the large central incisor, which were joined together at the cervical area, and one root canal. The lateral incisor presented separate pulp chamber and root canal, but its root canal was connected to the root canal of the large central incisor. These observations suggested gemination of the central incisor fused with the lateral incisor (type IIb of the classification by Shilpa and Nuvvula).

| DISCUSSION
To our knowledge, coexistence of triple teeth and double teeth in two different arches has never been reported. To address this issue, an extensive literature review was conducted to identify all reported cases of triple teeth in the English language. A search was performed on the PubMed database using keywords related to triple teeth and primary dentition according to the following equation search: (triplication OR "triple teeth" OR "triple tooth" OR "three teeth" OR triplicated OR "three tooth fusion") AND (primary OR decidual OR deciduous OR temporary). It was manually completed with the references of the selected articles and a search on Google Scholar in order to find nonindexed publications. Inclusion criteria were all types of articles reporting or discussing triple teeth in primary dentition, written in English language, published up to December 2019, and availability of the full text. A table was created to collect details regarding age and sex of patients, teeth implicated, patient origin, familial history, medical context, diagnostic tools, radiographic interpretation, resorption trouble/delay of eruption, absence of successional tooth, other dental anomalies, and treatment performed.
All the articles are listed in Table 1.
Our compilation corroborates with the literature data that females are less commonly affected (seven cases), and the maxillary and left side of the arch are more commonly affected. 9 Fusion of three normal teeth is rare (two cases), 13,26 with only one case showing affected teeth on both right and left sides. 26 All other cases showed fusion with a supernumerary tooth or gemination. In addition, the association of triple teeth with double teeth is also rare (three cases) with respect to the same arch. 13,21,27 Ours is the first case showing triple teeth associated with double teeth in two different arches.
It has been suggested that triple or double teeth are more frequent in Mongolian or Asian populations. 5 Our search reported more than half of the cases were of probable Indian origin, 9,[12][13][14][15][16][17][18][19][20]22,25,29 that is, cases reported by Indian authors. However, there is a bias in the publications selection. In fact, Indian authors are better in writing English as compared to Japanese or Korean authors for examples. However, it should be noted that few European or American authors have reported such cases. In addition, one third of these cases 3,12,13,[15][16][17][18]20,29,31 included children aged > 6 years, indicating a late screening of triple teeth.
Familial or medical history is not often reported. Only three cases reported familial history 25,27,30 and three cases reported medical history. 13,17,27 However, the number of cases reporting familial history may be lower than the actual number, because familial history relies on the memory of parents or other family members. Even if these may not be common etiologies, they could be possible aggravating factors. 13 In fact, the only patient who reported a premature birth was one of the two cases showing triple teeth and double teeth, similar to our patient. Thus, premature birth could be an aggravating factor. Moreover, one of these two cases combined familial and medical history. 27 Most studies only use intraoral periapical or occlusal radiographs, limiting the distinction between fusion and gemination as well as the relationship and proximity between the triple teeth and adjacent and underlying teeth. Panoramic radiographs help in better examination of the entire dental situation, especially to detect potential agenesis of underlying permanent teeth. In fact, 10 cases 9,11,13,17,19,20,[23][24][25]31 reported missing successional teeth and one case reported presence of two mesiodens. 11 The cone beam computed tomography (CBCT) avoids image distortions and superimpositions, allowing easy observation of root canal and precise determination of resorption areas. However, it is difficult to perform panoramic radiography in very young patients and CBCT is irradiating. Only three cases underwent panoramic radiography, 10,25,26 while CBCT was used in two cases. 10,14 Furthermore, several cases reported crossbite or malalignment, 12,[16][17][18]29,31 underlying the importance to monitor tooth resorption and its timely exfoliation.
In most cases, monitoring was implemented 3,9,10,13,15,19,26,28 or extraction was indicated, 11,12,14,[16][17][18]20,[22][23][24]27,[29][30][31] as in our case. Only three cases had undergone restoration procedure 11,25,27 and one case underwent pulpotomy. 11 Because of the complexity of the root canal system, reliable root canal treatment is almost impossible; thus, all efforts should be made to avoid carious lesions. Sealants should be placed in the grooves of the occlusal surfaces, followed by regular monitoring. Only two cases reported sealing of the grooves, 25,26 whereas 10 cases were monitored. In cases of deep pulpal involvement or periapical lesions, extraction is inevitable. In cases of delayed exfoliation, extraction is also recommended to avert malocclusion.

| CONCLUSION
Fused teeth are initially asymptomatic and rarely seen in children. Aside from esthetic concerns, they can develop carious