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The third molars or wisdom teeth generally erupt between the ages of 18 to 24 years.

However, sometimes they fail to erupt because they are either absent or impacted. An

impacted third molar tooth that fails to attain a functional position can cause infection,

unrestorable caries, periodontal diseases, cysts, or tumors.

The impacted third molar tooth can be managed conservatively, or alternatively, removed

by surgical extraction, a common oral surgical procedure and other procedures such as

operculectomy, which can be considered in carefully selected cases with the provision

that subsequent removal of the tooth may be required. Surgical exposure or surgical

reimplantation/ transplantation may be appropriate treatment in selected cases.

Several factors have been found to be important in causing third molar problems and

malocclusion. The most important factor is probably diet. But the influence of other

factors including mutations needs to be examined more fully to understand why wisdom

teeth are more often a problem today. The once common belief that wisdom teeth

problems are related to putative evolution modifications has now been discredited.

Mac Gregor concluded following an extensive study that the increase of brain size at the

expense of jaw size evolutionary view is invalid. The evidence derived from

paleontology, anthropology, and other studies indicates very convincingly that a

reduction in jaw size has occurred due to civilization. The main associated factor appears

to be the virtual absence of inter proximal attrition, but initial tooth size may have some

effect.

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Jaw size and dental attrition are related and they have both decreased with modern diet.

Jaws were thought to be reduced in size in the course of evolution but close examination

reveals that within the species Homo sapiens, this may not have occurred.

Hence, it can be concluded that the problems associated with wisdom teeth in modern

society are not due to evolution or mutation effect but largely to changes in diet, namely

to softer, less abrasive processed foods which do not give the teeth the workout which

they require to ensure proper relationship in the jaw.

The removal of third molars is not indicated if they are asymptomatic and free of any

pathology as long as good oral hygiene is maintained. The possible outcomes of surgery

may be worse than that of non-treatment; the risk of an impacted third molar developing

pathology being small compared to the risks of surgical intervention. Conservative

treatment has also been found to be more cost-effective. Late anterior crowding related to

impacted third molars cannot be accurately predicted and hence the removal of third

molars to prevent crowding may be unjustified. Conservative treatment is also advised

for medically compromised patients when the risk to the patients overall health

outweighs the benefits of surgery.

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CLASSIFICATION OF IMPACTED MANDIBULAR THRID MOLARS

A classification system based on clinical and radiographic findings becomes a tool for

predicting the difficulty of removal. A classification system is useful to categorize the

degree of impaction and to plan a surgical approach that facilitates removal and

minimizes morbidity , hence the classification is necessary to :

1. To know the Pathology precisely2. To assess the difficulty3. To anticipate complications

To draw a suitable treatment plan

Winters classification : It is based on the position of the long axis of the impacted tooth

in relation to the long axis of second molar.

A.MesioangularB.HorizontalC.VerticalD.DistoangularE.Bucco - versionF.LinguoversionG.Inverted

The mesioangular impaction, accounts for approximately 43% of all mandibular

impacted third molars. It is the one in which the third molar is mesially tilted toward the

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second molar . Such impactions are generally considered the least difficult to remove

(Fig. 1A). An exaggerated mesial inclination results in a horizontal impaction (Fig. 1B),

which is considered more difficult to remove than a coventional mesioangular impaction

and accounts for approximately 3% of all mandibular impactions . The vertical

impaction, in which the long axis of the impacted tooth runs parallel to the long axis of

the second molar, is seen in approximately 38% of all mandibular impactions (Fig. 1C) .

It is considered more difficult than a mesioangular or horizontal impaction. The

distoangular impaction, in which the long axis of the impacted tooth is inclined distally

(Fig. 1D), occurs uncommonly and accounts for approximately 6% of mandibular

impactions but is considered the most difficult impaction to remove. The path of removal

of this tooth is into the ramus and requires more extensive bone removal for its successful

delivery.

Impacted mandibular third molars may be in buccal version (Fig.1 E), Most mandibular

third molars are also angled toward the lingual (in lingual version) because the lingual

cortical plate progressively thins from anterior to posterior (Fig.1 F) however, and rarely

in inverted position (Fig. 1G) .

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The Pell and Gregory classification relates the position of the impacted mandibular

third molar to the ramus of the mandible in an anterio-posterior direction. When the

mesiodistal diameter of the third molar crown is completely anterior to the anterior

border of the ramus, it is considered a class I relationship (Fig. 2A). Such a tooth can be

angled in a mesial, distal, or vertical direction. The likelihood for normal eruption is best

for a class I tooth with a vertical angulation.

In a Pell and Gregory class II relationship, approximately one half the mesiodistal

diameter of the mandibular third molar is covered by the ramus of the mandible (Fig.

2B). The distal aspect of the crown of teeth in this position is covered by bone and soft

tissue. Teeth so positioned are particularly susceptible to caries and pericoronitis.

A Pell and Gregory class III relationship involves an impacted mandibular third molar

that is located completely within the ramus (Fig. 2C). The accessibility of a class III

impaction is such that it should be considered the most difficult tooth to remove.

Fig. 2. Pell and Gregory classification based on relationship to the anterior border of the

ramus. (A) Class I impaction,in which mandibular third molar has sufficient room

anterior to the anterior border of the ramus to erupt. (B) Class II, in which half of the

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impacted third molar is covered by the ramus. (C) Class III, in which the impacted third

molar is completely embedded in the ramus of the mandible.

The vertical relationship of the occlusal surface of the impacted mandibular third

molar to the occlusal plane of the second molar tooth is also described by the Pell and

Gregory classificationiii

. In a class A impaction, the occlusal surface of the third molar is

at the same level as the occlusal plane of the second molar (Fig. 3A).

In a class B impaction, the occlusal plane of the impacted tooth is between the occlusal

plane and the cervical line of the second molar (Fig. 3B).

A class C impaction results when the occlusal surface of the impacted third molar is

below the cervical line of the second molar (Fig. 3C).

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Fig. 3. Pell and Gregory classification based on relationship to the occlusal plane. (A)

Class A impaction, in which the occlusal plane of the impacted tooth is the same as the

second molar. (B) Class B, in which the occlusal plane of the impacted third molar is

between the occlusal plane and the cervical line of the second molar. (C) Class C, in

which the occlusal plane of the impacted third molar is below the cervical line of the

second molar.

Garcia et al in their study of 166 extractions of impacted lower third molars, all vertical

and all extracted by the same surgeon. Each tooth was classified according to the Pell

Gregory scales of position for the occlusal plane (scale AC) and the ascending ramus of

the mandible (scale 13). The extraction was subsequently rated as easy or difficult.

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Taking PellGregory class C as a predictor of a difficult extraction, specificity was 88%

but sensitivity was low at 15%. Taking PellGregory class 3 as an indicator of difficult,

sensitivity was somewhat better (50%), but at the expense of specificity (62%).

Likelihood ratios for the individual classes also indicated that the scales are of little value

for predicting a difficult extraction.

They concluded that the PellGregory classification is not a reliable predictor of surgical

difficulty in the extraction of vertical impacted lower third molars. Their findings, and the

fact that more than half (55%) of the patients who consulted them had non-vertical

molars (which are difficult to classify on the PellGregory scales), suggest that this

classification is of little value in clinical practice.

Sequelae of Impaction

The most common condition which occurs as sequelae of impaction is pericoronitis. It

arises as a result of infection and sometimes by the impingement of cusp of upper third

molar on the soft tissue operculum around the lower wisdom tooth. However, some

people have partially erupted lower third molars which have remained dormant and

symptomless for many years. The conditions which occur are:

1. Pericoronitis2. Caries3. Periodontal problems4. Root resorption of second molar

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5. Abscess formation6. Orthodontic problems7. Pathologic lesions (biological behaviour unpredictable)8. Pathological lesions predispose to fracture of jaw.9. Pain, Paresthesia, Anesthesia, Reffered pain to ear & neck region.

RADIOGRAPHIC EVALUATION

The assessment of third molar is incomplete without radiological evaluation. The portion

of the impacted third molar which is inside the bone and not visible needs to be

visualized as it is also to be removed. The radiograph provides vital information about

the roots, bone, presence of any pathologies with the tooth and the relation of the

impacted tooth with adjacent vital structures. It also helps in predicting difficulty and

facilitates treatment planning82.

An ideal radiograph should visualize the following things:

1. The entire outline of impacted tooth, with complete visualization of the roots.2. Outline of follicular sac3. More than 2mm of healthy cancellous bone around the folloicular sac and

impacted root outline.

4. Proximity wit adjacent tooth and vital structures

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The radiographs are required to know:

1. Relation to anterior border of ramus of mandible2. Relation to adjacent tooth3. Angulation and position of tooth4. Quality of surrounding bone5. Root morphology: Number / size / shape /Fused / Divergent / dilacerated /

bulbous/ hypercementosed roots.

6. Relation to inferior alveolar canal7. Associated pathology, if any

Panoramic radiograph ( Orthopantomogram)

Displays the entire dentoalveolar complex and adjacent anatomy. They are excellent for

imaging many impacted teeth. Impacted 3rd

molar in all 4 quadrants can be imaged on

one radiograph. These are a necessity if periapical or other intra oral films are inadequate

to display an entire impacted tooth or its associated pathology83

.

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Use of panographs in the diagnosis and treatment planning of third molars

1. Identify the presence of third molars2. Locate unusual position3. Facilitate establishing their angulation4. Show the vertical relationship to the second molar,5. Identify caries and dentoalveolar bone loss6. Detect the location of the inferior canal7. Detect bone pathology8.

Establish the height of the mandible

9. Show the relationship of upper third molars and the maxillary sinus10.Identify the structural stability of the second molar11.Locate the relationship of root apices with dense bone12.Detect dilacerated roots

Panoramic films lack the image definition seen on intra oral films. The maximum

achievable resolution on panoramic film is 8 line pairs per millimeter, whereas it is the

range of 20 line pairs per millimeter for intra oral film. This lack of image definition may

create problems in imaging areas with resorption of adjacent teeth or early cystic

degeneration of an impacted dental follicle. It does provide a coronal view of the third

molar area.

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Fig. panoramic radiograph

RADIOLOGICAL RELATIONSHIP OF THE IMPACTED 3rd MOLAR TO THE

INFERIOR ALVEOLAR CANAL:

The criteria used for the radiographic analysis of the relationship between the roots of 3rd

molar and inferior alveolar canal is radiographic shadow of inferior alveolar canal, the

proximity of root tips and upper border of canal is noted, when no distance exists

between two, the case is classified as encroachment. All such cases showing

encroachment were further categorized into7 signs ( J P Rood Criteria)84

:

1. Darkening of the roots - When there is impingement of the canal on the toothroot, there is loss of density of the root, the root appears darker (Howe and

Poyton, Main) , Darkening of root is attributed to the decreased amount of tooth

substance or loss of cortical lining of the canal between the source of x ray and

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the film. It is the most dangerous sign, which indicate increased chances of IAN

damage.

2. Deflection of roots ((Stockdale,Waggener)85,86 - There is abrupt deviation ofthe root when it reaches the inferior alveolar canal, the root may be deflected to

the buccal or lingual side or to both side so that it may completely surround the

canal or it may be deflected to mesial or distal aspect.

3. Narrowing of the rootSeward (1960)87 stated, if there is narrowing of theroot where the canal crosses it, it implies that the greatest diameter of the root has

been involved by the canal or that there is deep grooving or perforation of the

root.

4. Dark and bifid root XVIII - This sign appears when the root crosses the apexand is identified by the double periodontal membrane shadow of the bifid apex.

5. Interruption of the white line - The white lines are two radio opaque lines thatconstitute the roof and floor of the inferior alveolar canal. These lines appear dark

on the radiograph due to dense structure of the canal. The white line is considered

to be interrupted if it disappears immediately before it reaches the tooth structure,

either one or both lines may be involved (Kipp 1980, Rood 1983)84

. The

interruption of the white line is considered to indicate deep grooving of the root if

it appears with the narrowing of the inferior alveolar canal (Howe 1985)88

. The

interruption is considered one of the most reliable sign of nerve injury.

6. Diversion of inferior alveolar canal - The inferior alveolar canal is considered tobe diverted, if it changes its direction. When it crosses the mandibular 3rd molar

Seward (1963) attributed an upward displacement of the inferior alveolar canal to

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the contents of passing through the root and hence during eruption of 3rd molar,

the contents are dragged upward with it.

7. Narrowing of inferior alveolar canal - It occurs when, while crossing the rootof the mandibular 3rd molar, there is reduction of its diameter (Poyton 1982). The

narrowing could be due to the downward displacement of upper border of the

canal (Rud 1983) or the displacement of upper and lower border towards each

other with the hourglass appearance, it indicated a partial encirclement of the

canal or a complete encirclement or it may mean either of these alternative.

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The darkening of the roots, diversion of the inferior alveolar canal and interruption of

white line are the most dangerous signs indicating the increased chances of IAN injury.

Darkening of roots is the most dangerous sign.

LOCAUZATION OF MANDIBULAR CANAL IN RELATION TO THE APICES

OF THE OWER THIRD MOLAR:

As a means of locating this canal, Frank suggests that a modification of the 'Tube shift'

method can be used to determine whether the mandibular canal is medial to, lateral to or

below an impacted mandibular 3rd molar. This technique was first described by Richards.

Frank's technique follows

"By placing two films in identical positions in the mouth, when x raying a lower

impacted third molar and changing the position of the x ray tube, we can determine

whether the canal lies lingually or buccally to the impaction, or in the same plane as the

tooth".

To accomplish this the x ray angle must be shifted 25 upwards and this second film

compared to the film taken with the x ray tube parallel to the occlusal plane of the teeth".

"In the mouth an x ray taken from 25 below the plane of occlusion will make a distant

object move downward in relation to an object in the foreground, i.e. if mandibular canal

lies lingual to impaction, it will move downward in relation to the roots of the 3rd molar.

Conversely a canal on the buccal side of root will appear to move upward on the roots. If

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the canal remains in the same position, it is directed below the roots or passes between

the roots, or is in a groove in the root substance apically, lingually or buccally.

Pedersons difficulty index for removal of impacted 3rd molar :

DIFFICULTY RATING SCORE

Inclination of the longitudinal axis of the molar

Great difficulty 7

Moderate difficulty 5 to 6

Little difficulty 3 to 4

Mesioangular 1

Horizontal/transverse 2

Vertical 3

Distoangular 4

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Depth (with respect to occlusal plane)

Level A 1

Level B 2

Level C 3

Available space (with respect to ascending mandibular ramus)

Class I 1

Class II 2

Class III 3

Pedersen difficulty index is widely cited in oral and maxillofacial surgical texts as a

useful way of predicting the difficulty of extraction of impacted lower third molars but

are not universally accepted as predictors of third molar surgical 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 .

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WHARFE ASSESSMENT CRITERIA

6 factors were choosen for WHARFE assessment scoring criteria

1. Winters classification

2. Height of mandible

3. Angulation of II molar

4. Root shape

5. Follicle

6. Path of exist of tooth during removal

CATEGORY SCORE

1. Winters classificationHorizontal 3

Distonangular 2

Mesioangular 1

Vertical 0

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5. FolliclesNormal 0

Possibly enlarged 1

Enlarged 2

6. Path of exitSpace available 0

Distal cusps covered 1

Mesial cusp also covered 2

Both covered 3

TOTAL 33