Exodontia.Info
Indices of Difficulty in Removing of
3rd Molars
(Wisdom Teeth)
Classification of impacted 3rd molars is often an attempt in
based on 4 commonly used classifications of third molars,
which are defined by
angulation, impaction, application
depth
& eruption.

Assessment of difficulty of 3rd molar surgery is
fundamental to forming an optimal treatment plan in order
to minimise complications.

A compilation of both clinical and radiological information is
necessary to make an intelligent estimate of the time
required to remove a tooth and also whether the removal
should be done in the dental surgery or a more specialised
setting (such as a specialist clinic or hospital).  Leading on
from this is whether the tooth extraction would be better
done under
LA, LA Sedation or GA.

The various extraction difficulty indices include the following:

  • Pell–Gregory classification
  • Pederson scale
  • Parant scale
  • Winter's Lines (WAR)
  • WHARFE Scale
Various studies have shown that the Pell–Gregory scale,
which is widely cited in textbooks of oral surgery, is not
reliable for the prediction of operative difficulty.

Pederson proposed a modification of the Pell–Gregory
scale that included a 3rd factor, the angulation of the molar
(
mesio-angular, horizontal, vertical or disto-angular).  The
Pederson scale is designed for evaluation of dental X-rays
(such as
DPT's / OPG's).
Although the Pederson scale can be used for predicting
operative difficulty, it is not widely used because it does
not take various relevant factors into account, such as
bone density, flexibility of the cheek and buccal opening.
difficulties.  On the other hand, the modified Parant scale
was implemented to predict
post-operative difficulties.

Pre-operative
Pederson scale (easy, moderate or difficult)
and post-operative
Parant scale (easy [I or II] or difficult
[
III or IV]).


Winter's Lines (WAR)

The position & depth of the mandibular 3rd molar can be
determined using the
Winter’s Lines (WAR).  These are 3
imaginary lines (
red, amber & white) “drawn” on the dental
X-ray (these days, normally an
OPG / DPT).

White Line

The white line is drawn along the occlusal surfaces of the
erupted
mandibular molars & extended over the 3rd molar
posteriorly.  It indicates the difference in
occlusal level of
the 1st & 2nd molars & the 3rd molar.

Amber Line

The amber line represents the (height of the) bone level.  
The
amber line is drawn from the surface of the bone on
the
distal aspect of the 3rd molar (or from the ascending
ramus
) to the crest of the inter-dental septum twixt the 1st
& 2nd molars.  This line denotes the margin of the
alveolar
bone
covering the 3rd molar and gives some indication to
the amount of bone that will need to be removed for the
tooth to come out.

Red Line

The red line is an imaginary line drawn perpendicular from
the
amber line to an imaginary point of application of an
elevator.  Usually, this is the
cemento-enamel junction on
the
mesial aspect of the impacted tooth (unless, it is the
disto-angular impacted tooth where the application point
is the
distal cemento-enamel junction).  The red line
indicates the amount of bone that will have to be removed
before elevation of the tooth i.e. the depth of the tooth in
the jaw & the difficulty encountered in removing the tooth.

With each increase in length of the
red line by 1mm, the
impacted tooth becomes 3 x more difficult to remove (as
opined by
Howe).  If the red line is < 5mm, than the tooth
can be removed under just
LA; anything above, a GA or
LA Sedation would be more appropriate.
Where the various classifications are not used, the following observations are more
likely to be noted and acted upon.


Factors that Make Surgery Less Difficult

  • Mesio-angular impaction
  • Class 1 ramus
  • Class A depth
  • Roots 1/3 – 2/3 formed (present in the younger patient)
  • Fused conical roots
  • Wide periodontal ligament (present in the younger patient)
  • Large follicle (present in the younger patient)
  • Elastic bone (present in the younger patient)
  • Separated from 2nd molar
  • Separated from IDN
  • Soft tissue impaction


Factors that Make Surgery More Difficult

  • Disto-angular impaction
  • Class 3 ramus
  • Class C depth
  • Long thin roots (present in the older patient)
  • Divergent curved roots
  • Narrow periodontal ligament (present in the older patient)
  • Thin follicle (present in the older patient)
  • Dense, inelastic bone (present in the older patient)
  • Contact with 2nd molar
  • Close to IDN
  • Complete bony impaction
Another method of judging the depth of the 3rd molar is to divide the root of the
2nd molar into thirds.  A horizontal line is drawn from the
point of application for an
elevator to the 2nd molar.  If the
point of application is adjacent to the coronal,
middle or apical root third, then the tooth extraction is assessed as easy,
moderate or difficult respectively.
WHARFE Assessment

The six factors chosen for scoring are:

  • Winters classification
  • Height of the mandible
  • Angulation of the 2nd molar
  • Root shape & morphology
  • Follicle development
  • Path of Exit of the tooth during removal

The scoring by this system helps the beginners to anticipate problems and to avoid
difficult impactions.  Unfortunately, the disadvantage of this method is that it is
related only to radiological features alone; the details of the surgical procedures
are not considered.  The total scoring is directly related corresponding difficulties in
removing that impacted teeth.
Assessment of difficulty of third molar surgery is fundamental to forming an optimal
treatment plan in order to minimise complications.  A compilation of both clinical
and radiological information is necessary to make an intelligent estimate of the time
required to remove a tooth and whether it would be better done just under
LA or
under
LA Sedation or GA.

There are a number of classifications / scales that try to be predictive of the
extraction however each has its good and bad points.

There has been an attempt to computerise the assessment of impacted 3rd
molars.  However good this is though, there is still the problem of whether the
scale used is of any use or widely understood.

The acid test for any of these classifications / scales is whether they are actually
used in
OMFS Departments or dental surgeries.  From personal experience, they
are not.
Useful Articles:


BDJ 2001.  Factors predictive of difficulty of mandibular third molar surgery

BJOMS 2000.  Pell–Gregory classification is unreliable as a predictor of difficulty in
extracting impacted lower 3rd molars

BJOMS 2002.  Classification of Surgical Difficulty in Extracting Impacted 3rd Molars

JOMS 2004.  Risk Factors for 3rd Molar Extraction Difficulty

JOMS 2005. Estimating 3rd Molar Extraction Difficulty - A Comparison of
Subjective & Objective Factors

JOMS 2005. How Well Do Clinicians Estimate 3rd Molar Extraction Difficulty?

BJOMS 2007.  Pederson scale fails to predict how difficult it will be to extract
lower 3rd molars

J Oral Maxillofac Surg 2008.  Evaluation of intra-examiner and inter-examiner
agreement on classifying lower third molars according to the systems of Pell and
Gregory and of Winter.

J Oral Maxillofac Surg 2009.  Assessment of Difficulty in Third Molar Surgery — A
Systematic Review

JOMS 2011.  3-Dimensional Imaging for Lower 3rd Molars - Is There an
Implication for Surgical Removal?

Med Oral Patol Oral Cir Bucal 2011.  Validation of a computer-assisted system on
classifying lower third molars.

J Oral Maxillofac Surg 2011. Assessment of Factors associated with Surgical
Difficulty during Removal of Impacted Lower 3rd Molars
Last Updated 30th December 2011