2. can this problem be detected early, and what should be
done in the mixed dentition to facilitate future peri-
odontal and restorative treatment?
The orthodontist must remember that the crowns of
the primary molars are naturally shorter than those of
the adjacent permanent first molar. Therefore, a step in
the occlusal plane does not indicate that a primary
molar is ankylosed. Certain methods of detection, such
as tapping the tooth to determine a difference in sound,
generally do not predict ankylosis. The best method to
determine true ankylosis of the primary molar is by
evaluating the interproximal bone level on a bitewing
radiograph. If the interproximal bone level is flat, the
tooth is probably erupting at the same rate as the
adjacent permanent tooth. If the radiograph shows a
developing vertical defect between the primary and the
permanent teeth, then the tooth is ankylosed and may
need to be extracted before the defect worsens. Unfor-
tunately, extracting an ankylosed primary molar is
often a difficult procedure that might require a flap as
well as bone removal. The ultimate result could be a
narrow ridge buccolingually that requires future bone
grafting to achieve successful implant placement.
Age, gender, and presence of a permanent successor
ultimately influence the decision to extract an ankylo-
sed primary molar. What if a 14-year-old girl has a
submerged primary second molar, and the succedane-
ous second premolar is congenitally absent? Should the
primary tooth be extracted? This decision should be
based on the patient’s remaining facial growth. As a
child grows, the rami lengthen; this causes the posterior
teeth to erupt to maintain occlusion.1
This affects a
14-year-old boy more than a girl, because boys gener-
ally continue to grow until they are 18 years or older.
Therefore, ankylosis in a 14-year-old girl with little
remaining facial growth will have minimal effect on the
occlusion. The primary tooth can be maintained but
will most likely need to be reduced mesiodistally and
temporarily restored into a more ideal occlusion.
A 14-year-old boy with an ankylosed primary
second molar and no permanent second premolar will
require extraction of the primary tooth because he will
continue to grow throughout adolescence. This will
allow the edentulous alveolar ridge to move occlusally
as the adjacent teeth erupt.3
Donnelly and Swoope4
showed that as the periosteum is stretched over the
edentulous ridge, osteoblastic activity is stimulated to
lay down bone and promote alveolar ridge develop-
ment.
What if the succedaneous second premolar is
present? Should an ankylosed primary molar be ex-
tracted? This depends on age as well as location and
stage of root development of the premolar. A-9-year-
old with an ankylosed and submerged primary second
molar and a premolar with one-third root formation
might eventually experience a significant effect on the
occlusion because of the ankylosed tooth. Therefore, it
might be better to extract the tooth and maintain the
space until the premolar root development is complete
and the tooth erupts naturally. An 11-year-old with
initial radiographic evidence of ankylosis will exhibit
further root formation and significant root resorption of
the primary tooth. In this instance, the orthodontist
might choose to wait until the ankylosed tooth exfoli-
ates by normal eruption of the premolar.5
Orthodontists commonly encounter patients with
congenitally missing maxillary lateral incisors and
ankylosed mandibular primary second molars. Treat-
ment decisions must be based on eruption pattern, age,
gender, and presence of a permanent tooth. If the
patient is missing the maxillary lateral incisors, guided
eruption and ridge development are critical. Early
diagnosis and treatment of ankylosed primary second
molars also might be important to the future periodontal
and restorative treatment of the adolescent. Therefore,
monitoring these patients in the mixed dentition is
essential to preserve various treatment options in the
future.
REFERENCES
1. Kokich VG. Managing orthodontic–restorative treatment for the
adolescent patient. In: McNamara JA, Brudon WL, editors.
Orthodontics and dentofacial orthopedics. Ann Arbor (Mich):
Needham Press; 2001. p. 423-52.
2. Atherton JD. The gingival response to orthodontic tooth move-
ment. Am J Orthod 1970;58:179-86.
3. Ostler MS, Kokich VG. Alveolar ridge changes in patients
congenitally missing mandibular second premolars. J Prosthet
Dent 1994;71:144-9.
4. Donnelly MW, Swoope CC. Periosteal tension in the stimulation
of bone growth in the mandible [thesis]. Seattle: University of
Washington; 1973.
5. Kurol J, Olson L. Ankylosis of primary molars: a future periodon-
tal threat to the first permanent molars? Eur J Orthod 1991;13:
404-9.
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 121, Number 6
Kokich 595