Classification of impacted 3rd molars is often an attempt in
defining the degree of difficulty of removal; this is generally
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.
The Pederson scale is used in prediction of pre-operative
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 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.
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