A possible association between early apical resorption of primary teeth and ectodermal characteristics of the permanent dentition
Department of Orthodontics, School of Dentistry, University of Copenhagen, Denmark
Address for correspondence Professor I. Kjær, Department of Orthodontics, School of Dentistry, University of Copenhagen, 20 Nørre Allé, DK 2200 Copenhagen N, Denmark, E-mail: ik{at}odont.ku.dk
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The hypothesis of this study is that children with unexpected early apical resorption of the primary teeth are also predisposed to resorption in the permanent dentition. Accordingly, the aim was to perform a longitudinal study focussing on the permanent teeth in children with unexpected early apical resorption in the primary dentition.
Panoramic radiographs of 12 children (7 boys and 5 girls) aged 6 years 4 months to 8 years 9 months with unexpected early apical resorption of primary teeth were identified from a dental archive of 588 patients. After written request, follow-up radiographs were obtained (2–15 year interval between early and follow-up radiographs). The radiographs were examined in order to verify the abnormal resorption pattern of the primary teeth and dental deviations in the permanent teeth, known to predispose for root resorption (i.e. invaginations, narrow crowns, abrupt root deflections, slender roots, short roots, taurodontia, agenesis, deviant pattern of eruption).
Primary dentition: Two phenotypically different resorption groups were identified: group I, eight patients (resorption of the roots only), and group II, four patients (resorption of root and crown). Permanent dentition: In all 12 children, dental deviations in the permanent dentition were observed. Additionally, idiopathic external apical resorption of the permanent teeth was seen in three children, two of whom had received orthodontic treatment.
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Introduction |
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During orthodontic treatment, root resorption can be a complication. It is generally agreed that a tendency to root resorption is dependent on treatment factors and the patient's individual susceptibility (Brezniak and Wasserstein, 1993
; Hartsfield et al., 2004). Previous research has revealed that dentitions exhibiting certain morphological characteristics are predisposed to root resorption during orthodontic treatment (Kjær, 1995; Levander and Malmgren, 1988; Thongudomporn and Freer, 1998; Nishioka et al., 2006). In other studies, this association between resorption tendency and dental morphology was not observed (Lee et al., 1999; Kook et al., 2003; Mavragani et al., 2006).
A link has been demonstrated between resorption of the permanent teeth during orthodontic treatment and deviant resorption of primary teeth due to ectopic eruption of a permanent tooth and atypical external collum resorption (Kjær, 1995).
Kjær (1995) also showed a relationship between root resorption during orthodontic treatment and certain morphological characteristics and dental anomalies in the permanent dentition, such as invaginations, narrow crowns, short roots, slender roots, pipette-shaped roots, abrupt root deflections, taurodontia, agenesis, and ectopia.
Additionally, an association was seen between root resorption and anterior open bites as well as between root resorption and condylar changes such as flattening of the cranial contour of the mandibular condyle (Kjær, 1995).
The normal correlation between maturity stages of the permanent teeth and resorption stages of the corresponding primary teeth has been described by Haavikko (1973). Two abnormal apical resorption patterns in the primary dentitions have recently been described in 14 children (Bille et al., 2007). The abnormal resorption pattern was designated ‘unexpected early apical resorption’, and the subjects were divided into two groups according to phenotype. Group I was characterized by resorption of the roots only and group II by resorption of the entire root complex and partial resorption of the crown (Bille et al., 2007). The resorption pattern of group II was designated as teeth with a ‘shell appearance’.
In the present study, it was hypothesized that this recently described unexpected early apical resorption of the primary teeth observed in the presence of permanent successors also predisposes to root resorption of the permanent teeth during orthodontic treatment. The aim therefore was to determine whether children with unexpected early apical root resorption of the primary teeth in the later stage of dental development had deviations in the permanent dentition previously shown to be connected with root resorption (Kjær, 1995).
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Material |
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Dental pantomograms of the early mixed dentitions for evaluating mainly the primary dentition
Dental pantomograms of 12 children (7 boys and 5 girls, aged from 6 years 4 months to 8 years 9 months) in the early mixed dentition were identified in an archive of dental radiographs. The archive consisted of radiographic material from 588 patients forwarded since 1995 from Danish municipal clinics to the Department of Orthodontics, Copenhagen School of Dentistry, for diagnostic guidance and treatment planning.
The criterion for identifying radiographs for the present study was the occurrence of a subjective estimate of unexpected early apical resorption of several primary teeth in regions with a permanent successor. In no case could the early resorption of several primary teeth be explained by caries, apical infection, or ectopic eruption of the permanent successor.
Follow-up radiographs for evaluating the permanent dentition
After a written request, follow-up radiographs were obtained (Table 1). These follow-up radiographs were taken 2–15 years after the radiographs of the early mixed dentition. Two of the 12 children had received orthodontic treatment during the follow-up period.
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The radiographs were examined by two independent observers in order to verify the abnormal resorption pattern of the primary teeth and to divide the material into group I (abnormal root resorption only) and group II (abnormal root and crown resorption). Only radiographs with agreement between the observers were included. In the permanent dentition, dental deviations known to predispose for root resorption were registered, i.e. invaginations, narrow crowns, screwdriver-shape, abrupt root deflections, slender roots, short roots, taurodontia, agenesis, and deviant pattern of eruption (Kjær, 1995
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Invagination was defined as teeth with radiographically distinct enamel notching (a distinct cingulum dentis) according to Kjær (1995). A crown was defined as narrow when the diameter of the crown was no wider than the collum of the root. A root was defined as short if the root had the same size or appeared shorter than the crown, and a tooth was defined as taurodontic if the part of the tooth between the enamel dentine junction and the furcation was enlarged (Shaw, 1928).
Additionally, deviations from the normal eruption pattern of permanent teeth were noted, and resorption of permanent teeth was registered.
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Results |
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Primary teeth
Two phenotypically different groups of resorption were identified according to Bille et al. (2007). Eight children (four boys and four girls) belonged to group I (Figure 1) and four children (three boys and one girl) to group II (Figure 2).
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Morphological characteristics of the permanent teeth
Dental deviations of the permanent teeth previously described by Kjær (1995) as associated with to root resorption during orthodontic treatment were seen in all 12 patients with unexpected early resorption of the primary teeth.
The following morphological characteristics and dental anomalies were seen in the subjects: invaginations in five (Figure 1), a narrow crown of the maxillary central or lateral incisors in one (not shown), abrupt root deflection of a maxillary incisor in one (Figure 3), slender or tapered roots in six (Figure 3), short roots in three (Figures 1 and 3), taurodontia in six (Figures 2 and 3), and agenesis in three (Figures 1 and 2). Pipette-shaped teeth were not registered.
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Additional findings
Deviant eruption pattern of the permanent teeth. Premature eruption of lower incisors was presumed in two subjects. Resorption of a neighbouring primary tooth during eruption of a permanent tooth was seen in six subjects, with resorption of a primary maxillary canine during eruption of a permanent maxillary lateral incisor as the most common type of deviant eruption pattern (Figure 1).
Resorption of permanent teeth. Resorption of the permanent teeth was seen in four subjects. These resorptions were as follows: ongoing idiopathic external apical resorption of the mandibular first molars with the most pronounced resorption of the distal roots, seen in one patient who had not received orthodontic treatment (Figure 4); one case of internal crown resorption of a permanent molar; external apical resorption of molars, incisors, and lower canines, seen in two subjects who had received orthodontic treatment (Figure 5).
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The distribution of dental deviations between the groups and genders is listed in Table 1.
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Discussion |
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This longitudinal study examined the morphology of the permanent teeth on the radiographs of a sample of patients with unexpected early apical resorption of the primary teeth.
In the present study, the association between morphological deviations in the permanent teeth known to be of ectodermal origin and unexpected early apical resorption is described. This is the first communication suggesting that there is a connection between unexpected early apical resorption of the primary teeth and root resorption tendency of the permanent teeth, but further investigations as well as a longer follow-up period are needed in order to document this association.
The material in the present study was forwarded from different municipal dental clinics in Denmark. Although the radiographs varied in contrast and sharpness, they were considered suitable for the present investigation.
Two independent observers were used in this study in order to control and discuss the subjective evaluation of unexpected early apical resorption and morphological characteristics of permanent teeth. Although a subjective evaluation of tooth morphology on radiographs is not precise, it is a simple method that can easily be applied in dental practice with the purpose of identifying patients with root resorption tendencies.
The findings indicate that it is possible even in the early mixed dentition to identify patients particularly disposed to resorption of the permanent teeth. Very few studies have focussed on connections between resorption in the primary and the permanent dentitions (Kjær, 1995).
Several authors have shown a relationship between resorption of the permanent teeth and deviant morphology of the permanent teeth (Kjær, 1995; Levander and Malmgren, 1988; Thongudomporn and Freer, 1998; Nishioka et al., 2006), while others did not find an association (Lee et al., 1999; Kook et al., 2003; Mavragani et al., 2006). Such disagreement might be due partly to different study designs as well as varied definitions of the morphological characteristics. For example, Thongudomporn and Freer (1998) did not find a connection between root resorption and taurodontia. In several studies, taurodontia is defined as the size and dimensions of the pulp chamber, which is often clearly visible on the radiographs (Shifman and Chanannel, 1978; Ruprecht et al., 1987). The problem is that the absence of a large pulp chamber does not prove the absence of taurodontia since the size of the pulp chamber in taurodontic teeth as well as in non-taurodontic teeth is gradually reduced with age and influenced by external stimuli. Other definitions of taurodontia exist based on different external measurements.
The main problem with regard to root resorption is that the mechanism initiating and controlling root resorption is not known. Recent studies of tooth resorption and tooth eruption have focussed on the cellular regulation of resorption processes. Especially RANK, RANKL, and OPG have been demonstrated in the roots of human primary teeth undergoing resorption (Lossdörfer et al., 2002) as well as in the permanent crown follicles of rats (Wise et al., 2002).
The present findings indicate that the molecular genetic factors responsible for resorption of the primary tooth roots are the same as those responsible for resorption of the permanent tooth roots at a later stage in development. This link between resorption in the primary and permanent dentition requires further elaboration.
In addition, the relationship between the resorption process and the ectodermal deviation in tooth morphology described in a previous study (Kjær, 1995) needs further elaboration. The connection between resorption and ectodermally derived deviations in morphology can only be understood if the resorption process is also dependent on ectodermal tissue. In a recent study, the epithelial rests of Malassez of ectodermal origin were documented as a continuous cell layer in the periodontal membrane (Becktor et al., 2007). If this ectodermal cell layer influences the resistance of the tooth root against resorption or the susceptibility to resorption, the relationship between morphology and resorption becomes understandable. Future studies will focus on the role of this epithelial cell layer of the periodontium during the resorption process.
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Conclusions |
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Two types of unexpected early apical root resorption in the primary teeth were demonstrated in this study. In one type, the root was completely (severely) or partially (less severely) resorbed. The distinction between normal conditions and less severe resorption is difficult to define. In the other type of unexpected primary apical resorption, the root was completely resorbed and the crown partially resorbed. The present research did not comprise sufficient material to decide whether these two different phenotypic patterns of resorption are associated with different types of dental deviations in the permanent dentition. This is a condition that should be examined more closely as it is likely that the genetic causes for the two types of resorption could be different. Any gender differences should also be examined.
Once the different patterns and associations of root resorption are revealed at a macroscopic level, precautions can be taken to avoid resorption during orthodontic treatment and more systematic and goal-orientated research on the aetiology of resorption at a cellular and genetic level can be applied.
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References |
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