Definition: Ectopic eruption is a developmental
disturbance in the eruption pattern of the permanent dentition.1
Impaction of the first permanent molar is often diagnosed as ectopic eruption.
The molar erupts at a mesial angle to the normal path of eruption. This
results in a cessation of eruption and atypical resorption of the neighboring
primary molar. The permanent tooth may get locked in this position or correct
itself without treatment and erupt into a normal position. These two types
are classified as reversible or irreversible ectopic eruption ("hold" and
"jump" cases).2
Fig 1. Ectopic eruption of both maxillary first permanent molars and lower right first permanent molar. Upper left molar #14 has self corrected, #3 required active therapy.
Prevalence: The first written reference to ectopic eruption is found in 1923.3 The author mentions that the abnormality had been discussed at dental meetings prior to that time. Cheyne and Wessels (1947) reported ectopically erupting permanent first molars in 1.8% (nine out of approximately 500 children) of their study group.4 This study only included those teeth that were actually locked apical of the distal aspect of the second primary molar at the time of examination. Young (1957) introduced the terms "jump" and "hold" to further classify the abnormality.2 She found a prevalence of 3.2% children with one or more ectopically erupting first molars. 66% of the cases were classified as self-correcting "jump" cases. Bjerklin and Kurol (1982) reported a prevalence of 4.3%.5 Almost 60% of these were reversible ectopic eruptions. All authors agree that ectopic eruption is mostly seen in the maxilla, it can be unilateral or bilateral. Reports about sex correlation are not consistent in results.1,2,3,4,5 Kimmel et al. (1982) could not identify significant differences between different racial groups, but he confirmed the prevalence of an approximate 4% rate.1
Carr observed a more frequent occurrence in cleft lip and palate patients (29% girls, 22.9% boys).6
Etiology: The etiology of first molar ectopic eruption is not completely understood. Pulver (1968) examined lateral cephalograms and study casts from 46 children.7 He could not find one specific factor that was common to all cases, but he suggested that a combination of factors contributes to the ectopic eruption of the maxillary first molar. (1) larger than normal mean sizes of all maxillary primary and permanent teeth; (2) larger affected first permanent and second primary molars; (3) smaller maxillae; (4) posterior position of the maxilla in relation to the cranial base; (5) abnormal angulation of eruption of the maxillary first permanent molar; (6) delayed calcification of some affected first permanent molars. Bjerklin and Kurol (1983) tried to further analyze these etiologic factors.8 Their investigation could only identify two factors that definitely cause ectopic eruption of the first permanent molar: The mesial angle of the first permanent molar was clearly increased in cases of ectopic eruption. Extraction of the second deciduous molar had no influence on the angulation. The cause of this pronounced mesial inclination could not be established. The second factor was increased width of the first permanent molar compared to children with normal eruption. The size of the central incisors cannot be used to predict ectopic molar eruption.
Clinical implications: Christensen and Fields recommend a three to six month observation period if the resorption on the primary molar is not too severe.9 Bjerklin and Kurol (1983) report that those cases that self correct usually correct before 7 years of age.8 They conclude that the type of ectopic eruption can be reliably predicted at ages between 7 and 8. Kurol and Bjerklin (1982) followed and evaluated the prognosis for atypically resorbed second primary molars after reversible ectopic eruption of the maxillary first molar.10 Most of their sample teeth showed severe resorption, but only two out of ninety-two were lost prematurely. Only 14% showed further resorption. In the rest of the material arrest of resorption could be demonstrated clinically and histologically.
The treatment goals for irreversible ectopic eruption are movement of the permanent molar distally in order to regain space and correction of the mesial tipping of the permanent molar to allow normal eruption.11 Cross-arch anchorage may be necessary to prevent loss of leeway space.12 Moyers feels that distal slicing of the primary molar is not indicated because it will result in space loss and the permanent molar will erupt in a tipped position that will favor the development of malocclusion.13
Numerous simple techniques, such as brass ligatures, separating elastics, springs, band and spring have been described.9,12,14,15,16
Careful supervision of these techniques is important. Apical dislodgment of separators and placement of brass ligatures may induce infection and early loss of the primary molar.9,10
Space loss after premature exfoliation of the primary second molar can be prevented with adequate space maintainers (Nance, distal shoe, etc.). If necessary a space regaining appliance needs to be fabricated. Garcia-Godoy performed successful treatment with a band and spring appliance placed on the first primary molar.16 The most favorable time for treatment with extraoral cervical traction is close to eruption of the second premolar.11 Cephalometric diagnosis is strongly recommended. The cervical traction leads possibly to decreased sagittal maxillary growth.
References
1. Kimmel NA, Gellin ME, Bohannan HM, and Kaplan AL: Ectopic eruption of maxillary first permanent molars in different areas of the United States. J Dent Child 49: 294-299, 1982
2. Young DH: Ectopic eruption of the first permanent molar. J Dent Child 24: 153-162, 1957
3. Chapman H: First upper permanent molars partially impacted against second deciduous molars. Int J Orthodont, Oral Surg, Radiog 9:339-345, 1923
4. Cheyne VD, Wessels KE: Impaction of permanent first molar with resorption and space loss in the region of the deciduous second molar. J Am Dent Assoc 35:774, December, 1947
5. Bjerklin K, Kurol J: Prevalence of ectopic eruption of the maxillary first permanent molar. Swed Dent J 5:29-34, 1982
6. Carr GE: Ectopic eruption of the first permanent maxillary molar in cleft lip and cleft palate children. J Dent Child 32:179-188, 1965
7. Pulver F: The etiology and prevalence of etopic eruption of the maxillary first permanent molar, J Dent Child 35:138-146, 1968
8. Bjerklin K, Kurol J: Ectopic eruption of the maxillary first permanent molar: etiologic factors. Am J Orthod 84:147-155, 1983
9. Pinkham JR: Pediatric dentistry: infancy through adolescence, 2nd ed. WB Saunders Co, 1994
10. Kurol J, Bjerklin K: Resorption of maxillary second primary molars caused by ectopic eruption of the maxillary first permanent molar: a longitudinal and histological study. J Dent Child 49:273-279, 1982
11. Bjerklin K, Kurol J: Treatment of children with ectopic eruption of the maxillary first permanent molar by cervical traction. Am J Orthod 86:483-492, 1984
12. McDonald RE: Dentistry for the child and adolescent, 6th ed. Mosby 1994
13. Moyers RE: Handbook of orthodontics, 3rd ed. Year Book Medical Publishers 1973
14. Humphrey WP: A simple technique for correcting an ectopically erupting first permanent molar. J Dent Child 29:176-178, 1962
15. Levitas TC: A simple technique for correcting an ectopically erupting first permanent molar. J Dent Child 31:16-18, 1964
16. Garcia-Godoy F:Correction of ectopically erupting maxillary permanent first molars. J Am Dent Assoc 105:244-246, 1982
