Does the timing of premolar extraction have an influence on the rate of orthodontic space closure?

Posted on by

The duration of orthodontic space closure can be influenced by a number of factors such as the
severity of malocclusion, extraction or nonextraction treatment plan, and patient compliance during
treatment. The average duration of orthodontic treatment with fixed appliance is 18-24 months
where the core time consuming process is extraction space closure. Therefore, acceleration of
orthodontic treatment is of interest to both the patient and the orthodontist. Over the years various
surgical as well as non-surgical methods have been proposed for acceleration of tooth movement
and one such method is retraction of teeth into a recent extraction site compared to a healed socket
thus taking advantage of the regional accelerated phenomenon (RAP). There are limited articles in
literature that have studied this phenomenon and all the literature available is based on the rate of
canine retraction in the maxilla.

The following is the first article that compares the rate of canine retraction in the mandibular arch
towards a recent vs healed extracted sockets.

‘A comparative assessment of the amount and rate of orthodontic space closure toward a healed vs recent lower premolar extraction site:A split-mouth randomized clinical trial’

Abu Alhaija ES, Al Shayeb RA, Al-Khateeb S, Daher HO, Daher SO. A comparative assessment of the amount and rate of
orthodontic space closure toward a healed vs recent lower premolar extraction site: A split-mouth randomized clinical trial.
The Angle Orthodontist. 2022.

What did this paper assess?
This study compared orthodontic retraction of lower canines toward recent vs healed extracted sockets.

The objectives of the current study were to investigate and compare:

  • width of the extraction space
  • rate of space closure and
  • adjacent tooth tipping

during orthodontic space closure toward a recent vs healed lower first premolar extraction site using
0.019 × 0.025-inch stainless-steel archwires (SSAW) at different time points.

What was the protocol?

This study was a randomized controlled clinical trial with a split-mouth design. A total of 28 subjects
who fulfilled the inclusion criteria were included in the study. All patients were treated by first
premolar extractions (only the lower arch was included in this study).

Randomization protocol

The intervention was randomly allocated using the permuted random block size of 2 with 1:1
allocation ratio. The random sequence for the intervention was concealed in opaque envelopes.
Each patient was asked to pick a sealed envelope to assign the intervention to either the right or left
side.

Blinding

It was not possible to blind the patient nor the clinician during treatment. The measurements were
performed by a blinded research assistant.

Interventions

All patients were treated by the same orthodontist using a fixed pre-adjusted edgewise appliance,
after the extraction of one lower first premolar (based on the allocated intervention). All lower teeth
were included in the appliance. After reaching 0.019 × 0.025-inch SSAW patients were subdivided
into two groups based on the random allocation

Group 1: Lower first premolar was extracted before orthodontic treatment (1 week before strap-up)

Group 2: Lower first premolar was extracted when 0.019 × 0.025-inch SSAW was reached,
immediately before space closure.

Elastomeric power chain from second molar to second molar was used to close lower extraction
spaces. The patients were followed up monthly, at which time the elastomeric power chain was
replaced and alginate impressions were taken.

Outcome assessment

A digital calliper was used to measure the width of extraction space on each follow-up model.
Coronally, space width was measured between two points at the maximum convexity of the lower
canine and second premolar. Gingivally, space width was measured between two points on the
gingival margin of the canine and second premolar.

Amount of space closure was calculated by subtracting values at each time point. The rate of space
closure was calculated as space closure achieved in mm/month (3 months). The following time
points were defined to measure the amount of space closure.

T1: When reaching 0.019X0.025-inch SSAW and just before space closure.
T2: First follow-up (1 month from T1).
T3: Second follow-up (2 months from T1).
T4: Third follow-up (3 months from T1).

What did their results show?
During the analysis stage, there were complete records for 23 patients due to attrition

  • During the first month (T1–T2), a significantly greater amount of space closure was
    measured in group 2 compared to group 1.
  • Subsequently (T2–T3 and T3–T4), the amount of space closure was similar between the two groups (P > .05).
  • Tipping of teeth was detected in both groups (P > .05).

Critical appraisal

The efforts made by the author to assess whether the teeth have tipped into the extraction space is
appreciated. However, the method of retraction was by the application of an elastomeric chain from
second molar to second molar where the force application is away from the center of resistance
which in turn would result in tipping. The timing of start of retraction in the upper arch and the type
of anchorage preparation has not been mentioned. Moreover, the measurements were made on a
dental cast obtained through alginate impression and the distortion of the impression could affect
the results obtained. The measurements on the dental cast were made Coronally- between two
points at the maximum convexity of the lower canine and second premolar and gingivally- between
two points on the gingival margin of the canine and second premolar both of which are not stable
landmarks. Lastly, the force decay of the E-chain is 3 weeks and the reason for selecting four-week
activation is not mentioned.

Contributors:
Dr.Mrithulaa.M.V.
Dr.Venkateshwaran