Does Alveolar bone changes following molar protraction?

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Mandibular first molar is the first permanent tooth to erupt and it is easily affected by dental
caries or periodontitis, which results in most frequently missing tooth due to extraction
(Meskin et al). Also, the mandibular second premolar is one of the most frequently
congenitally missing teeth excluding the third molars (Polder et al). The treatment options for
management of missing teeth is either by uprighting and space opening by distalization or
space closure by protraction of molars. Molar protraction could be a challenging task for
clinicians, but with the help of Temporary Anchorage Devices (TADs), protracting molars to
close the spaces can become easier. Following molar protraction and increase in available
posterior space, the impacted third molars may spontaneously erupt and mesialize to attain
posterior occlusion. When molars are protracted into the edentulous alveolar ridge of an
edentulous area, the periodontal health of the protracted tooth might be a concern. Kim et al
in 2015 reported a mean of 0.56 ±0.70 mm mesial alveolar bone resorption as a result of
molar protraction whereas Baik et al in 2019 reported that alveolar bone loss was distal to the
protracted molar. A cone-beam computed tomography (CBCT) study by Santos et al in 2017
on the alveolar bone level of protracted molars showed slight bone dehiscence at the lingual
and buccal alveolar bone crest, compared with those who had space reopening followed by
prosthodontic treatment. However, only buccal and lingual bone levels at a cross section
passing through the center of the teeth were assessed.

The article of our interest in the blog is the first study to assess the alveolar bone changes
following molar protraction at six levels using CBCT.

Alveolar bone changes after molar protraction in young adults with missing mandibular
second premolars or first molars
Baik UB, Jung JY, Jung HJ, Kim YJ, Chae HS, Park KS, Vaid NR, Nanda R. Alveolar bone
changes after molar protraction in young adults with missing mandibular second premolars or
first molars. Angle Orthod. 2022 Jan 1;92(1):64-72.

What did this paper assess?
This study evaluated the alveolar bone level of mandibular second molars at the buccal,
lingual, mesial, and distal areas and factors associated with alveolar bone changes as a result
of second molar protraction

What was the protocol?
A retrospective study consisting of 29 patients who had missing mandibular first molar or
mandibular premolars where space closure was done by molar protraction with the use of
TADs.
CBCTs were taken at two time periods

  • T0 – Pretreatment
  • T1 – Full eruption and alignment of third molars following second molar protraction.

Measurements
Amount of protraction and Change in angulation-
CBCTs superimposed at the lower cortical border of the mandible. Amount of protraction
was measured as distance between second molar root furcation at T0 and T1.Change in
angulation was measured along long axis of the second molar to the line connecting the
central fossa and the root furcation from T0 to T1

Alveolar bone level
CBCTs superimposed along the posterior occlusal plane and the long axis of the second
molar. The sagittal reference plane was defined as the plane passing through the mesial and
distal points of the second molar crown and the root furcation. Bone levels were measured at
six points on the second molar: buccal, lingual, mesiobuccal (MB), mesiolingual (ML),
distobuccal (DB), distolingual (DL)
Ridge thickness was measured in a plane parallel to the occlusal plane and passing through
the second molar root furcation at the center of the missing space. Angulations of the second
and third molars were measured relative to the mandibular plane at T0.

What did their results show?
The second molar was protracted by 7.8 ± 3.8 mm as measured at the furcation. The mean
angulation change of the second molar was 3.78 ± 9.68, with positive values indicating
uprighting. The alveolar bone changes observed at the lingual, DB, DL, and ML of the
second molar were significant.

Univariate analysis
Third molar impaction, angulation and Nolla stage at T0 were significantly associated with
the changes in alveolar bone level. Patients with impacted third molars with mesial
angulation at T0 and those at lower Nolla stage were likely to have less alveolar bone
resorption at the distal of the second molars as a result of protraction. Age, sex, missing tooth
(L-6 or L-E), second molar angulation at T0, treatment duration, and ridge thickness were not
significant as predictors of distal alveolar bone changes

Multivariable analysis
Third molar angulation and Nolla stages were the only significant predictors. Treatment
duration was the only significant factor in predicting alveolar bone changes at ML and MB of
the second molar; a longer treatment time was associated with less alveolar bone resorption

Critical appraisal
It is appreciable that this is the first study to assess the alveolar bone changes following molar
protraction at six levels using CBCT. The authors intended to evaluate the alveolar bone
levels of mandibular second molars and the factors associated with alveolar bone changes as
a result of second molar protraction and have successfully achieved it.
One of the first limitation is that, it is a retrospective study design, therefore factors
associated with oral hygiene and periodontal indices that could affect the alveolar bone level
could not be gathered. The effects of periodontal care on alveolar bone changes as a result of
molar protraction could be assessed by conducting a prospective study. Also the factors
related to the levelling of the adjacent teeth may have affected the outcome of the study.
CBCTs were taken before and after treatment in addition to the panoramic radiographs.

Conclusion and scope for future studies:
This study suggest that molar protraction to close an edentulous posterior space leads to
changes in the alveolar bone level that are clinically acceptable and it can be considered as
an alternative treatment approach for missing second premolars or first molars in young
adults. Various risk factors which can lead to alveolar bone loss in the mesial and distal
alveolar bone should be considered.
Future studies can be carried out with a prospective study design and also considering the
periodontal health following molar protraction.

Contributors: Dr.M.Dilip kumar, Dr.Haritha PS