Indices of Difficulty in Removing of 3rd Molars (Wisdom Teeth)
Classification of impacted 3rd molars is often an attempt, 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

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
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.

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

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-
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 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

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

JOMS 2007.  Assessment of Factors associated with Surgical Difficulty in Impacted Mandibular Third Molar Extraction

JOMS 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.

JOMS 2008.  Frequency Estimates & Risk Factors for Postoperative Morbidity After Third Molar Removal - A Prospective
Cohort Study

Head & Face Med 2011.  Effect of Age, Impaction Types & Operative Time on Inflammatory Tissue Reactions following
Lower Third Molar Surgery

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

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

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

J Maxillofac Oral Surg 2013.  Is Pederson Index a True Predictive Difficulty Index for Impacted Mandibular Third Molar
Surgery - A Meta-analysis

J Kathmandu Med Coll 2014.  Difficulty Index in Extraction of Impacted 3rd Molars& their Post-operative Complications

J Oral Dis 2014.  Reliability of Pederson Scale in Surgical Extraction of Impacted Lower Third Molars - Proposal of New

Health Renaissance 2015.  Tooth impaction - A new variable in difficulty index of third molar extraction

J Korean Assoc Oral Maxillofac Surg 2016.  Which factors are associated with difficult surgical extraction of impacted lower
third molars

JOMS 2016.  Difficulty of Impacted Mandibular Third Molar Tooth Removal - Predictive Ability of Senior Surgeons &

Med Oral Patol Oral Cir Bucal. 2017.  Evaluation of Kharma scale as a predictor of lower third molar extraction difficulty
Last Updated 1st February 2020