Ectopic eruption of first permanent molars: a preliminary report of presenting features and associations.
Aim: To investigate presenting features of ectopically erupting first permanent molars and associations with other dental anomalies. Study Design: Prospective convenience study. Methods: 28 panoral radiographs were collected, over a 24-month period, of 7-11 year-old children with radiographic evidence of ectopic eruption of first permanent molars who presented to a Dental Teaching Hospital in England. A further 20 radiographs were collected of matched patients with no evidence of ectopic molar eruption. All radiographs were analysed under standard conditions to record the distribution and type of ectopic eruption (if present). In addition, the presence of the following dental anomalies was noted: cleft lip and/or palate; supernumerary teeth; hypodontia, and infraocclusion of primary molars. Chi-squared analysis was performed to determine any significant differences in the frequency of these dental anomalies between ectopic molar and control groups. Results: For patients with ectopic molar eruption, the majority demonstrated ectopic eruption of either one or two first permanent molars (32% and 57% of subjects respectively). There were a similar proportion of 'jumps' and 'holds'. 92% of these were maxillary teeth and there was equal left and right distribution. Interestingly, a positive record of ectopic eruption was only documented in the dental records of 35% of these subjects. Children with ectopic eruption were significantly more likely to have at least one additional dental anomaly than was the case for the control group (60% versus 25%). Notably, primary molar infraocclusion and cleft lip/palate were significantly more frequent in the ectopic group. Conclusions: This study, the first in a British population, identified a significant association between ectopic eruption of first permanent molars and other dental anomalies. A multifactorial aetiology is thus supported and clinicians should be alert to the co-existence of ectopic eruption and other dental anomalies.
Key words: Ectopic eruption, first permanent molar, dental anomalies, cleft lip and palate.
Ectopic eruption of first permanent molars (FPM) represents an interesting local disturbance in eruptive behaviour. These teeth appear to deviate from normal eruptive pathways and become 'locked' behind the distal aspect of the second primary molar. Distal resorption of the second primary molar is a common sequelae. There are two types of ectopic eruption: reversible and irreversible. In the reversible type, a FPM eventually succeeds in erupting into the arch. Conversely, in the irreversible type, a FPM remains locked until either the premature exfoliation or extraction of the second primary molar. The terms 'jump' and 'hold' were introduced by Young  to respectively describe these patterns of reversible and irreversible ectopic eruption.
Previous studies have reported that, in cases of reversible ectopic eruption, the majority of FPMs will usually have disimpacted themselves by the time a patient is 7 or 8 years old. It is therefore considered that should a molar fail to erupt then a diagnosis of irreversible ectopic eruption can normally be made by this age [Bjerklin and Kurol, 1981, 1983].
Ectopic eruption of the maxillary FPM molar has a reported prevalence of between 1.8% and 6% [Young, 1957; Pulver, 1968; Bjerklin and Kurol, 1981; Wackerle-Heporauta, 1981; Kimmel et al., 1982; Canut and Raga, 1983; Rinderer, 1984]. The largest study, conducted by Kimmel and co-workers , found maxillary molar ectopic eruption in 3.8% of a sample of 5,277 children. Involvement of the mandibular FPM, which is less well reported, appears to be much less common, with Young  finding only three occurrences in a total of 78 ectopic eruptions. Conversely, a much more recent study reported similar prevalences for maxillary and mandibular teeth [Chintakanon and Boonpinon, 1998]. A number of studies have also identified a higher prevalence of ectopic first molar eruption in children with other disturbances of oro-facial or dental development. Notably, children with a cleft lip and/or palate may demonstrate a 2026% prevalence of ectopic FPM eruption [Carr and Mink, 1965; Ranalli et al., 1986; Bjerklin et al., 1993; Silva Filho et al., 1996].
Other investigators have reported an association between ectopic eruption and dental anomalies such as infraocclusion of primary molars [Bjerklin et al., 1992]. Pulver  noted the presence of several related conditions including congenitally missing teeth, supernumerary teeth and tooth size anomalies. Recently, it has been found that ectopic eruptions demonstrate significant associations with aplasia of the second premolars, reduced size of maxillary lateral incisors, infraocclusion of primary molars, and enamel hypoplasia [Baccetti, 1998a].
The aetiology for ectopic first molar eruption remains unclear with likely involvement of both genetic and environmental factors. The prevalence is increased in siblings suggesting a hereditary component [Kurol and Bjerklin, 1982]. The phenomenon is considered multifactorial with a number of purported risk factors including: increased tooth size, a small maxilla, posterior position of the maxilla, abnormal angulation of eruption of the FPM, and in some cases, delayed calcification of these teeth [Pulver, 1968; Canut and Raga, 1983]. Bjerklin and Kurol  identified both an increased mesial angle and mesio-distal dimension of the FPM in ectopic eruption cases.
A diagnosis of ectopic eruption is usually made on the basis of combined clinical and radiographic findings. A clinical suspicion of ectopic eruption is usually raised if there is a delay (greater than 6 months) or asymmetry in the eruption of one or more FPM compared with the other FPMs.
Evidence of ectopic eruption may also present as an incidental finding following radiographic investigation of a different dental complaint.
To date, there have been no studies relating to ectopic first molar eruption in a British population. The aim of this study therefore was to investigate the presenting features of ectopically erupting FPM and associations with other dental anomalies in children seen within a British Dental Hospital. A subsidiary aim was to determine the level of reporting of ectopic eruption by the dental profession.
Materials and Methods
Radiographs. The experimental material comprised 28 panoral radiographs each taken from 28 different children with radiographic evidence of ectopic eruption of one or more FPMs. A further 20 control radiographs were collected with no evidence of ectopic eruption and were matched for age and gender. The radiographs were collected prospectively over a 24-month period and had been taken as part of each child's routine assessment and diagnosis within the Charles Clifford Dental Hospital, Sheffield, UK. Ethical approval was granted for the study by the South Yorkshire Research Ethics Committee.
Dental records were reviewed to ascertain age at radiographic examination, gender, ethnic group, and the presence of any craniofacial abnormality. In addition, the notes were systematically checked to determine whether the radiographic finding of ectopic eruption had been documented by the clinician who had originally requested the radiographic assessment.
All radiographs were taken and processed within the Department of Radiography. Each radiograph was then examined under standardised viewing conditions by two examiners (GCM and AGM). Standard criteria were employed to clarify the type of ectopic eruption seen radiographically [Bjerklin and Kurol, 1981; Silva Filho et al., 1996]. Ectopic eruption was recorded as 'irreversible' if the first permanent molar remained impacted against the distal aspect of the second primary molar (see figs 1 and 2) and 'reversible' if the first permanent molar had erupted into its normal position (see figs 3 and 4). The findings were recorded for each individual patient and for each quadrant. A quadrant was excluded if the radiograph was of poor quality, or the FMP or the primary second molar was missing, or if there was distal caries in the primary molar. In addition, the presence of the following dental anomalies was recorded for both the ectopic molar and control subgroups: infraocclusion of primary molars; supernumerary teeth; hypodontia (excluding missing third permanent molars), and the presence of a cleft lip and/or palate. To determine the inter- and intra-investigator reproducibility of the exercise, 10% of the radiographs were reanalysed four weeks after the initial assessment.
Statistical Methods. Results were coded and analysed using Microsoft Statistical Package for Social Sciences v12. Chi-squared analysis was undertaken to determine whether there were any significant differences in the presence of additional dental anomalies between the ectopic eruption and control subgroups. Significance levels were set at P<0.05. Levels of agreement for inter- and intra-investigator agreement were determined using the Kappa coefficient (I), where a finding of 1.0 indicates perfect agreement [Altman, 1991].
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Subjects. The mean age of the 48 children, when subject to panoral radiographic examination, was 8.5 years (SD=1.2, range=7.0-11.4). There were 28 (58%) females and 20 (42%) males and the majority of children (n=43; 89.6%) were of White (Caucasian) Northern European descent.
Findings in relation to ectopic eruption. Data were pooled for the 28 children with ectopic eruption as there were no significant differences in the number of affected molars or the specific type of ectopic eruption according to gender (P>0.05, chi-squared analysis). As can be seen from (table 1), exactly half of the subjects demonstrated ectopic eruption of two of their FPMs. Only one child was found to have abnormal FPM eruption in all four quadrants (Fig. 1) In 11 (39.3%) patients, a 'jump' type of molar eruption was seen, 13 (46.4%) patients demonstrated a 'hold' type of eruption, and four (14.3%) patients demonstrated both types of abnormal eruption within different quadrants.
Data were further analysed according to quadrant rather than individual. However, 11 from a maximum of 112 quadrants (9.8%) were excluded from this analysis due to the absence of the second primary molar in this region. Of the remaining 101 quadrants, 49 molars (48.5%) were recorded as having ectopic eruption. The distribution and type of ectopic eruption recorded for these 49 teeth is presented in (table 2). It can be seen that that ectopic eruption was much commoner in maxillary teeth (n=45; 91.8%) than in mandibular teeth (n=4; 8.2%) and there was an almost equal distribution between left and right quadrants. There was also a very similar number of 'jumps' and 'holds'. The case notes actually documented the ectopic eruption of a FPM in only ten (35.7%) of the affected individuals
Findings in relation to other dental anomalies. A total of 17 (60.7%) patients with ectopic eruption were also found to have radiographic evidence of one or more dental anomalies. In contrast, only 5 (25%) of the control group were seen to have a dental anomaly, which was a statistically significant difference (P=0.01, chi-squared analysis). Table 3 provides further details of the individual anomalies. It can be seen that for children with ectopic molar eruption, the most frequently occurring other anomaly was primary molar infraocclusion (n=9; 32.1%) (Fig 2), followed by hypodontia (n=8; 28.6%) (Figs 1-3), cleft lip and/or palate (n=7; 25%) (Fig 3) and supernumerary teeth (n=5; 17.9%) (Fig 4) For the non-ectopic eruption group, only one subject (5%) demonstrated infraocclusion of a primary molar, three children (15%) had hypodontia, one (5%) had a supernumerary tooth and no child had a cleft lip/palate.
Statistical analysis. This revealed that, overall, children with ectopic eruption had a significantly higher frequency of primary molar infraocclusion and cleft lip/palate than the control group (P<0.05, chi-squared analysis). However, no significant differences were found between the two groups in relation to hypodontia or supernumerary teeth (P>0.05, chi-squared analysis).
Repeatability. Good to very good intra- and inter-investigator agreement was found for all parameters. The kappa value for the classification of type and distribution of ectopic eruption ranged between 0.76 and 1.0. There was perfect agreement (I=1.0) in relation to identification of other dental anomalies.
The study group comprised a greater proportion of girls than boys. However, due to the method of recruitment, it cannot be concluded that this finding truly reflects a higher prevalence of ectopic molar eruption in British females than males. Interestingly previous studies have reported conflicting gender distributions with most studies finding equal male and female prevalence [Pulver 1968; Kimmel, 1982; Chintakanon and Boonpinon, 1998; Barberia-Leache et al, 2005].
The present study found no significant difference between the distributions of 'hold' versus 'jumps' which is in agreement with Pulver . Interestingly, a number of other studies have reported a higher prevalence of jumps [Young, 1957; Bjerklin and Kurol, 1981; Barberia-Leache et al., 2005]. However as these studies did not clearly state whether there was actually a significant difference in the frequency of 'jumps' versus 'holds', it is difficult to draw any firm conclusions.
The majority of subjects in the present study were of White Northern European Caucasian descent. Thus no analyses could be undertaken according to ethnic group. However, there would appear to be no conclusive racial differences in the prevalence of ectopic eruptions of first molars [Kimmel et al., 1982].
A number of findings from the present study are consistent with those of previous investigations including: the low occurrence of ectopic eruptions in mandibular molars [Cheyne and Wessels, 1947; Young, 1957] and an equal left and right distribution [Bjerklin and Kurol, 1981]. The present study also confirmed previous reports of strong associations between ectopic eruption and other dental anomalies. In the present study, about 60% of children with ectopic molar eruption were also seen to have at least one other of the four selected dental anomalies. It was speculated that this figure may have been even greater, if other dental anomalies, such as tooth size, structure and morphology, had been taken into consideration. Additionally the study did not find any significant association with ectopic eruption of FPMs and palatal displacement of canines which is in agreement with previous data [Baccetti, 1998b]. This was in contrast to the findings of a Swedish study [Bjerklin et al., 1992] which found a significantly higher prevalence of ectopic eruption of maxillary canines in children with a primary diagnosis of ectopic eruption of maxillary FPM. However, a limitation of this present study was that data were only obtained from panoral radiographs, thus without clinical examination and other radiographic investigation, diagnosis of these additional anomalies could not be certain. In addition, it is acknowledged that investigations on selected dental groups (in this case a hospital population) are not likely to be representative of the 'normal' population. It is very likely that this subgroup will have a greater prevalence of dental anomalies than a non-hospital patient group. Additionally, it is recognised that the inclusion of subjects with a cleft lip and/or palate may have resulted in a higher overall frequency of ectopic eruption in the experimental group due to the higher prevalence of dental anomalies seen in cleft patients. Conversely, the exclusion of patients with missing second primary molars or distal caries may have actually resulted in under reporting. Nonetheless, the association of ectopic molar eruption and other anomalies strongly points towards a shared, and most likely hereditary, aetiology. Larger scale studies would allow regression analysis to determine the actual risk of each specific dental anomaly with ectopic molar eruption and vice versa, thus giving greater insight into the complex interactions of dental development.
A concern arising from the study was the low level of reporting of ectopic molar eruption by clinicians who had initially made a request for the radiograph for other diagnostic purposes. This was surprising, particularly in view of the fact that patients were under the care of a number of specialists. However, it is not known whether this simply reflects poor documentation or stems from a failure to actually identify the presence of ectopic molar eruption as an incidental radiographic finding.
Early diagnosis of ectopic molar eruption is of clinical importance as intervention is usually recommended. Failure to provide appropriate treatment may result in premature loss of the second primary molar, resultant mesial shift of the FPM and potential impaction of the second premolar [Kimmel et al., 1982]. There are two treatment strategies: the first option is to release the FPM from the second primary molar and distally move the permanent molar to normal inclination and occlusion. Alternatively the second primary molar may be extracted and space can be regained or maintained as appropriate [Bjerklin, 1994]. If the treatment is directed towards releasing the FPM and gaining distal movement, a brass wire ligature [Braden, 1964; Kennedy and Turley, 1987], separating spring [Kurol and Bjerklin 1986] or separating elastics [Hartmann, 1984] can be employed. Alternatively, to facilitate the eruption of the FPM, the distal surface of the second primary molar can be reduced [Kurol, 2002]. However, if an affected FPM is tipped mesially any reduction of the distal surface of the adjacent primary molar is likely to result in further space loss for the permanent second premolar. It has been suggested that placing a preformed metal crown or band on the second primary molar may create an inclined plane for an ectopic FPM to erupt against with a resultant degree of up righting [Roberts, 1986]. A variety of orthodontic appliances have also been proposed to achieve molar eruption [Humphrey, 1962]. If resorption extends into the pulp chamber of the second primary molar, pulpal necrosis may ensue and extraction may be indicated. However, most teeth survive until the expected time of exfoliation. [Kurol and Bjerklin, 1982; Kennedy and Turley, 1987].
This first British study, has identified a significant association between ectopic eruption of first permanent molars and a number of dental anomalies. A multifactorial aetiology is thus supported and clinicians should be alert to the co-existence of ectopic eruption and other anomalies. Greater awareness of this condition and its implications would seem to be indicated in view of the poor level of reporting indicated in this study.
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GC. Mooney, AG. Morgan, HD. Rodd, S. North
Dept Paediatric Dentistry, Charles Clifford Dental Hospital, Sheffield, England.
Postal address: Dr. G Mooney: Charles Clifford Dental Hospital, Wellesley Road, Sheffield, UK, S10 2SZ
Table 1. Number and type of ectopic first permanent molar eruption recorded for 28 individual patients. Variable Number (%) of patients Number of teeth affected One 11 (39.3) Two 14 (50.0) Three 2 (7.1) Four 1 (3.6) Type of abnormal eruption 'Jump' 11 (39.3) 'Hold' 11 (39.3) 'Jump and hold' 4 (14.3) Table 2. Distribution and type of ectopic first permanent molar eruption according to individual quadrants Variable Number (%) of quadrants Quadrant affected Maxilla right 22 (44.9) Maxilla left 23 (46.9) Mandible left 2 (4.1) Mandible right 2 (4.1) Type of abnormal eruption 'Jump' 24 (49) 'Hold' 25 (51) Table 3. Presence of additional dental anomalies in children with ectopic first permanent molar eruption (n=28) and normal eruption (n=20). Number (%) of patients Dental anomaly Ectopic Normal Infraocclusion 9 (32.1) 1 (5.0) * Hypodontia 8 (28.6) 3 (15.0) Cleft lip/palate 7 (25.0) 0 (0.0) * Supernumerary 5 (17.9) 1 (5.0) * significant difference between groups, P<0.05 chi-squared analysis.
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|Author:||Mooney, G.C.; Morgan, A.G.; Rodd, H.D.; North, S.|
|Publication:||European Archives of Paediatric Dentistry|
|Article Type:||Clinical report|
|Date:||Sep 1, 2007|
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