Short Root Anomaly (SRA)/Rhyzomicroly-Report of an Unusual Radicular Anomaly with Comprehensive Literature Review

Prevalence of SRA/Rhyzomicroly

Prevalence of SRA among different ethnic groups has been studied (Table 2). In Swedish children, Jacobson and Lind found 2.4% of SRA in maxillary central incisors. Ando, et al. [10] got 10% prevalence in maxillary central incisors of Japanese school children [11]. In Mongolian population, the reported prevalence was 10% [12] and in Caucasians it varies from 2.4 – 2.7% [13]. In Finnish population the reported prevalence was 1.3% [14, 15, 16]. All these studies have shown that it is three times more common in females compared to males. From Indian context there are no studies showing prevalence of SRA except for few case reports. Therefore, some more future studies investigating the prevalence of SRA in other population around the globe is required.

Clinical presentation of Rhyzomicroly/SRA

On clinical examination, rhyzomicroly affected teeth shows normal size and shape in morphology. Even surrounding tissues with these teeth appear normal and asymptomatic. It is more often diagnosed on routine radiographic examination, as a result, most of the time this condition remain un-diagnosed [1, 2, 3]. In addition to this, it is difficult to diagnose for teeth with short roots in the mixed dentition. However tooth mobility has been reported as a first clinical finding encountered in SRA cases [15]. Therefore proper meticulous early diagnosis of rhyzomicroly by ruling out presence of tooth mobility is very essential for successful management of these cases and from preventing these teeth from early tooth loss. In case of maxillary central incisors, peculiar characteristic root morphology like short roots with “lack of significant tapering towards the root apex” and round apices is been reported. In case of mandibular second premolars less round and blunted apices are noticed. Therefore careful examination is required for not misdiagnosing this clinical condition from root resorption. In all three cases presented here the crown morphology appeared normal except for presence of dental caries in second the third cases. Short roots were accidentally noticed on radiographic examination [6].

Radiographic Presentation of Rhyzomicroly/ SRA

Teeth with rhyzomicroly are accidentally diagnosed on routine radiographic examination as these clinically appear normal in morphology. Radiographically apart from short roots, the pulp chamber, root canals and periodontium appear normal except for few cases reported showing taurodontium [16]. In the cases presented here too the surrounding periodontal tissues and alveolar bone architecture appeared normal except for presence of periapical infection in the third case. The external root resorption arising from periapical infection was ruled out in this case. The resorption pattern in external root resorption exhibit a typical shape in the apical surface of the root compared with SRA. In external root resorption, the apical surface of the resorbed roots depicts irregular and gradual shortening compared to SRA which shows rounded and smooth roots without any resorption [1, 2, 3]. Therefore based on this finding the third case was diagnosed as SRA.

In a recent article published by Trimeridou, et al. [2] short roots were found generalized but surprisingly not involving molars in both maxillary and mandibular arch. Contrary to this in cases described here, the rhyzomicroly was observed only in mandibular molars. Although orthopantomograph was not taken to rule out generalized appearance, but second and premolars were absolutely normal on intraoral periapical radiograph. Therefore this is the unique case showing rhyzomicroly in the permanent mandibular molars.

Etiology

The exact etiology behind occurrence of rhyzomicroly is still not known. It is hypothesized towards idiopathic occurrence. However some authors have stated that this anomaly occurs as a result of impairment in the Hertwig’s epithelial root sheath and apical proliferation during root development of the involved tooth [1]. Root resorption or due to any systemic disorders is also not reported in the literature. However, familial occurrence of this condition in parents and children of the same family has been reported showing it as an autosomal dominance pattern of inheritance [17]. Apajalahti, et al. [17] extensively studied hereditary predisposition of SRA by collecting detailed family data. They finally concluded from their study that an apparent genetic heterogeneity of the pedigree did not reveal definitive conclusions towards mode of inheritance. However, autosomal dominant pattern was observed in 3/8 families. In 2/8 families the disorder was seen in siblings but not in parents. Hence these single cases of SRA indicate that this condition occurs due to fresh mutations [1, 2]. In addition to this an autosomal recessive pattern inheritance has also been reported.[2] Other etiologies like congenital or developmental origin, chemotherapy and radiotherapy and external influences like trauma, syndromes have also been reported [18].

Previous molecular studies show the fragmentation, activation and complex formation of the matrix metalloproteinase 9 (MMP-9) particularly in gingival crevicular fluid (GCF) of rhyzomicroly patients [19]. From this it is confirmed that compared to other MMPs, MMP- 9 has low collagenolytic resorptive activity thereby not causing severe root resorption. Whereas in patients with active periodontitis and gingivitis patients other MMPs present in GCF cause severe root resorption due to high collagenolytic activity [20]. Therefore it is speculated that the rhyzomicroly is a developmentally induced anomaly rather than due to root resorption. One more recent animal research also stated that deficiency of nuclear factor Ic (Nfic) gene causes the development of short and abnormal roots by disturbing odontoblast differentiation, because Nfic gene is significantly responsible for the odontoblast differentiation and for development of root formation [21, 22].

SRA in Association with other Anomalies

Literature shows an association of SRA with other dental abnormalities. There are case reports showing presence of hypodontia [17], obliterated pulp chambers, dens invaginatus and supernumerary teeth, generalized microdontia [15, 16, 17, 18]. Some authors have shown increased tendency of root resorption in SRA cases [20]. In 1999 research work, authors studied series of families for association of various dental anomalies like peg shaped lateral incisors, ectopic eruption, tooth agenesis, supernumerary teeth, taurodontism, dens invaginatus and tendency for root resorption [17]. Authors measured mesiodistal dimensions of the crown in teeth affected with SRA to evaluate any change in increase or decrease in dimensions. They found 46% of tooth agenesis and 33% of ectopic canines along with SRA. Authors have also stressed on the fact of not misdiagnosing this condition with root resorption. Yu, et al. [15] reported a case of generalized SRA in association with other dental anomalies like dens invaginatus and enamel hypoplasia. They also reported peculiar extra-oral finding like bridging of sella turcica. In sella turcica bridging, an excessive calcification of interclinoid ligaments of sella turcica which mostly caused by congenital defects is observed. This condition frequently seen associated with multiple dental anomalies which could be due to sharing of genes and neural crest cells, which are necessary for development and differentiation of both teeth and sella turcica. Leonardi, et al. [23] also reported that early diagnosis of sell turcica bridging in early age will help practitioners to identify possible occurrences of dental anomalies which form later.

Differential Diagnosis of SRA

Reports shows that short roots of teeth are seen in other conditions and hence rhyzomicroly should be carefully differentially diagnosed from other conditions. Short and tapered roots have been reported in those children who had received radiotherapy or chemotherapy for the cancer treatment (head-neck region/ total body) [24, 25, 26]. This may be due to arrested root development and premature apical closure or even complete absence of root development. The more severe developmental anomalies of the roots and teeth are seen in younger children with higher dose of the treatment received. One more clinical condition like dentin dysplasia type I (dd – I), the teeth appear normal in shape and color or opalescent, amber-colored crowns [27]. In patients with dd-I the roots of the teeth appear blunt and short. But the only distinguishing feature from SRA is the presence of obliterated pulp chambers in dd-I cases. In addition an apical radiolucency in absence of caries is also reported in dd-I. Moreover, dd-I is seen both in primary and permanent dentition, in contrast to rhyzomicroly which is reported only in permanent teeth [27]. Presence of previous trauma should also be differentiated from SRA. Mainly root shape should be considered. In traumatized teeth, short roots, thin radicular walls and wide open apex is seen which is due to disturbance and arrest of root growth. Molar incisor malformed hypoplastic teeth (MIMH), a newly researched dental abnormality mainly affects roots of permanent molars and crowns of incisors. This condition too should be differentiated from short roots [28]. In MIMH, affected molars typically exhibit thin, short and divergent hypoplastic roots with narrow slits in the pulp chamber. Clinical symptoms are usually absent in MIMH and a characteristic enamel notch at the cervical third of the tooth crown especially in incisors is seen [28].

SRA in Association with Other Disorders

Short roots are even reported in patients with short stature. Short roots are also reported in some metabolic disorders like Vitamin D-dependent rickets, pseudohypoparathyroidism and hypophosphatasia [29]. Patients with syndromes exhibiting short stature conditions such as Hallerman-Streiff syndrome, Schimcke immune- osseous dysplasia, Stevens-Johnson syndrome, Frazer

syndrome and Turner syndrome have shown short roots in multiple teeth [2, 3, 4, 5, 6, 7, 8, 9, 10]. In thalassemia major patients spiky- shaped short roots along with alveolar bone malformations have been reported [30]. In the three cases presented here, authors did not come across any of the above diseases or syndromic, or metabolic features and medical history in all three patients found uneventful. Moreover history of trauma was also ruled out. So by ruling out presence of all the above factors, the present case was diagnosed as non-syndromic idiopathic rhizomicroly or short root anomaly. Clinical Significance of SRA/Rhyzomicroly in Pediatric Dentistry It is a well-known fact that SRA is a poorly understood developmental radicular anomaly. As a result this disorder significantly affects dental treatment. The presence of SRA has various implications in orthodontics and orthognathic treatment.

a. Orthodontic Implications In patients going for orthodontic treatment the careful evaluation of crown-root ratio of each tooth is essential to rule out iatrogenic root resorption. Therefore use of pretreatment radiographs as baseline or reference points is of more advantageous to evaluate further decrease in root length due to resorption arising from inadvertent orthodontic forces [3]. Ponraj, et al. have advised for use of periodic radiographs mandatorily in every orthodontic patient with SRA to monitor the root resorption of the teeth. Moreover, judicious judgment of risks and benefits is thought before commencing orthodontic treatment as each case of SRA are challenging to an orthodontist. When mobility of the affected tooth or teeth is present, orthodontic treatment is absolutely contraindicated. It is also recommended that use of light forces throughout the treatment with longer intervals in each activations and appointments will definitely give better stability for these teeth with short roots. In cases when mobility is seen with short roots, authors have advised for the use of splints to stabilize the teeth (mainly for incisors) with mobility following an orthodontic treatment. Therefore increased awareness of rhyzomicroly is essential not only for orthodontist but also for oral and maxillofacial surgeons in order to reduce root resorption.

b. Orthognathic implications Both orthodontics and Orthognathic surgery is required for patients with a skeletal discrepancy to achieve best functional and esthetic outcome [3]. Although orthodontic treatment is the first phase of treatment in patients with skeletal discrepancy Orthognathic surgery is always required. Therefore meticulous diagnosis of short roots is not only important for planning of orthodontic treatment planning but also essential for success of Orthognathic surgery.

c. Prosthodontic Implications In patients with rhyzomicroly a fixed prosthesis is usually not recommended if the adjacent tooth with short roots is acting as an abutment [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18]. Such tooth may not withstand the occlusal forces. Rather a removable appliance can be given. Permanent prosthetic replacement with dental implants is of great option in SRA patients as the alveolar bone is absolutely normal. However, it is mandatory to consider the age of the patients before going for replacement of mobile tooth with short roots using implants.