368
Australian Dental Journal, December, 1975 Volume 20, No. 6
Oral surgery in general dental practice. Assessment of lower third molars. L. Summers, M.D.S., F.D.S.R.C.S.
Senior Lecturer in Oral Medicine and Oral Surgery, University of Western Australia
ABsTmm-Methods of pre-operative assessment of impacted lower third molar teeth are discussed and the main diagnostic features are stressed in order to ensure that the practitioner fully comprehends the nature and difficulty of the procedure. (Received for publication September, 1973. Revised February, 1975)
PART VII Introduction
The literature is rich in methods of removing these teeth. However, most practitioners find the most difficulty in determining those cases which can be treated in the dental surgery, those which should be referred to an oral surgeon and those for which no treatment is necessary. Generally, all surgery accomplished under local anaesthesia should be aimed at completion within half an hour. If it is anticipated that surgery will exceed this time, then the patient is best referred to a specialist oral surgeon for treatment. Thus, the most important aspect is how does one assess these teeth prior to surgery.
Assessment It is a sine qua non that it is impossible to assess cases without a good radiograph. The film
of choice is a periapical film and this should show the whole of the crown and roots of the third molar, the position of the second molar and its roots, and the position of the inferior alveolar canal. There must be no overlapping or distortion on the film as this renders accurate assessment impossible. The following are the important features to note: (1) The position and depth of the tooth
This is determined from the radiograph by means of Winter’s lines. Experienced surgeons do not use this technique routinely but relatively inexperienced operators would d o better if they always used these lines to assess individual cases. These imaginary lines are described as white, amber and red, and it is understood that impactions may be either vertical, mesio-angular
369
Australian Dental Journal, December, 1975
or disto-angular. p h e horizontal impaction is merely an extreme variety of the mesio-angular impaction.) The white line connects the occlusal surfaces of the first and second molar teeth and is extended backwards over the third molar. The occlusal surface of a vertically impacted tooth is
Fig. l.-Dist+angular impacted third molar. Continuous line dsnoru the white line. Note the difimca in the
external oblique ridge should be differentiated from the shadow of the alveolar bone (Fig. 1). The red line is a perpendicular dropped from the amber line to the point of application and measures the depth of an impacted tooth (Fig. 3). This point of application is the mesial aspect of
Fig. 2.-The
a m k line drawn w a film of a muioangular impaction.
Fig. 3.-The
w h i k amber and red linw marked on
amount of intn-aptal bone between the first and sccoad
molars, and between the second and third molars. The shadow of tbs cxtcmal oblic,ue ridge is denoted by a broken line. Also note the adverse root pattern of the third molar.
parallel with the white line. Where a distoangular impaction is present the white line and the occlusal surface of the third molar meet or converge in the anterior aspect of the third molar (Fig. 1). It is most important to distinguish a vertical impaction from a disto-angular impaction as the latter is generally the most difficult of all and the one most likely to lead to fracture of the mandible if not diagnodd and treated properly. This is because the path of withdrawal of a disto-angular impaction is backwards against the ascending ramus. Therefore, space must either be present or created to move such a tooth distally. A further diagnostic point is that the amount of interseptal bone between a distoangular third molar and the second molar is less than the amount of interseptal bone between the first and second molars (Fig. 1). The amber line is drawn to connect the crest of the interdental septum between the first and second molars to the crest of the interdental septum between the second and third molars, and extended backwards to the surface of the bone distal to the third molar (Fig. 2). This line indicates the amount of bone encompassing the crown of the third molar. All tooth tissue superficial to the amber line will be seen on reflecting the flap. It is important that the shadow of the
the film of a mesib-angular impaction. The point of application of the elevator is the mwial aspect of the
amdo-cementa1 junction. The exteanal oblique ridge is denoted by the upper broken line.
the amelo-cementa1 junction for all impactions other than disto-angular impactions when the point is the distal aspect of the amelo-cementa1 junction (Fig. 3). The red line is perhaps the most important line when assessing wisdom teeth and for every increase of 1 mm in length, the extraction becomes three times more difficult. As a rule of thumb, impactions less than 5 mm may be treated under local analgesia, whilst impactions over 5 mm are best treated under general anaesthesia. (2) Position and pattern of roots
These reasons:-
factors
are
important
for
several
370 (a) each root may have a conflicting line of withdrawal which will render surgery more difficult, because the roots will require division (Fig. 1); (b) the presence of multiple roots will obviously lead to greater surgical difficulties than a single conical root; (c) the position of the root in relation to the inferior alveolar canal is important as failure to recognise a true relationship may result in trauma to the nerve and consequent paraesthesia of the lip. The canal is often seen on radiographs as two radio-opaque parallel lines crossing the roots of the third molar. Usually this appearance is caused by imposition of these structures. The danger signs of a true relationship are:6) where the continuity of one or both of the radio-opaque lines crossing the root is interrupted. This may indicate grooving of the root by the neuro-vascular bundle; (ii) where the neuro-vascular bundle assumes an increase in radio-lucency in its relationship to the apex of a third molar. This is usually indicative of grooving of the third moIar by the inferior alveolar canal; (iii) where a distinct narrowing of the canal is apparent there is every chance that it perforates the tooth.
(3) The density of bone In older patients bone generally is more sclerosed, and hence less elastic. Surgery is easier
Australian Dental Journal, December, 1975 on bone which is more elastic, such as in patients under the age of thirty years. Thus a 5 mm impacted wisdom tooth is much more difficult to remove at 55 years of age than at 25 years of age. (4) The second molar
The shape of the second molar is important. Although an adjacent tooth should never be used as a fulcrum, all too often it is. In the event of the second molar having a single conical root, force applied to elevate a third molar might well displace the second molar from its socket. Removal of wisdom teeth is further complicated when the external oblique ridge approaches the vertical when there is then decreased access to the site. When the external oblique ridge is more obtuse in angulation, access is facilitated.
To summarise, the main points to assess third molars are:(a) position and depth of the tooth; (b) position and pattern of the roots; (c) the relationship of the neuro-vascular bundle to the tooth; (d) the shape of the second molar; (e) the degree of access to the site. Department of Oral Medicine and Oral Surgery, University of Western Australia, 179 Wellington Street, Perth, W.A. 6000.
Australian Dental Journal, December, 1975 Volume 20, No. 6
Oral surgery in general dental practice. Assessment of lower third molars. L. Summers, M.D.S., F.D.S.R.C.S.
Senior Lecturer in Oral Medicine and Oral Surgery, University of Western Australia
ABsTmm-Methods of pre-operative assessment of impacted lower third molar teeth are discussed and the main diagnostic features are stressed in order to ensure that the practitioner fully comprehends the nature and difficulty of the procedure. (Received for publication September, 1973. Revised February, 1975)
PART VII Introduction
The literature is rich in methods of removing these teeth. However, most practitioners find the most difficulty in determining those cases which can be treated in the dental surgery, those which should be referred to an oral surgeon and those for which no treatment is necessary. Generally, all surgery accomplished under local anaesthesia should be aimed at completion within half an hour. If it is anticipated that surgery will exceed this time, then the patient is best referred to a specialist oral surgeon for treatment. Thus, the most important aspect is how does one assess these teeth prior to surgery.
Assessment It is a sine qua non that it is impossible to assess cases without a good radiograph. The film
of choice is a periapical film and this should show the whole of the crown and roots of the third molar, the position of the second molar and its roots, and the position of the inferior alveolar canal. There must be no overlapping or distortion on the film as this renders accurate assessment impossible. The following are the important features to note: (1) The position and depth of the tooth
This is determined from the radiograph by means of Winter’s lines. Experienced surgeons do not use this technique routinely but relatively inexperienced operators would d o better if they always used these lines to assess individual cases. These imaginary lines are described as white, amber and red, and it is understood that impactions may be either vertical, mesio-angular
369
Australian Dental Journal, December, 1975
or disto-angular. p h e horizontal impaction is merely an extreme variety of the mesio-angular impaction.) The white line connects the occlusal surfaces of the first and second molar teeth and is extended backwards over the third molar. The occlusal surface of a vertically impacted tooth is
Fig. l.-Dist+angular impacted third molar. Continuous line dsnoru the white line. Note the difimca in the
external oblique ridge should be differentiated from the shadow of the alveolar bone (Fig. 1). The red line is a perpendicular dropped from the amber line to the point of application and measures the depth of an impacted tooth (Fig. 3). This point of application is the mesial aspect of
Fig. 2.-The
a m k line drawn w a film of a muioangular impaction.
Fig. 3.-The
w h i k amber and red linw marked on
amount of intn-aptal bone between the first and sccoad
molars, and between the second and third molars. The shadow of tbs cxtcmal oblic,ue ridge is denoted by a broken line. Also note the adverse root pattern of the third molar.
parallel with the white line. Where a distoangular impaction is present the white line and the occlusal surface of the third molar meet or converge in the anterior aspect of the third molar (Fig. 1). It is most important to distinguish a vertical impaction from a disto-angular impaction as the latter is generally the most difficult of all and the one most likely to lead to fracture of the mandible if not diagnodd and treated properly. This is because the path of withdrawal of a disto-angular impaction is backwards against the ascending ramus. Therefore, space must either be present or created to move such a tooth distally. A further diagnostic point is that the amount of interseptal bone between a distoangular third molar and the second molar is less than the amount of interseptal bone between the first and second molars (Fig. 1). The amber line is drawn to connect the crest of the interdental septum between the first and second molars to the crest of the interdental septum between the second and third molars, and extended backwards to the surface of the bone distal to the third molar (Fig. 2). This line indicates the amount of bone encompassing the crown of the third molar. All tooth tissue superficial to the amber line will be seen on reflecting the flap. It is important that the shadow of the
the film of a mesib-angular impaction. The point of application of the elevator is the mwial aspect of the
amdo-cementa1 junction. The exteanal oblique ridge is denoted by the upper broken line.
the amelo-cementa1 junction for all impactions other than disto-angular impactions when the point is the distal aspect of the amelo-cementa1 junction (Fig. 3). The red line is perhaps the most important line when assessing wisdom teeth and for every increase of 1 mm in length, the extraction becomes three times more difficult. As a rule of thumb, impactions less than 5 mm may be treated under local analgesia, whilst impactions over 5 mm are best treated under general anaesthesia. (2) Position and pattern of roots
These reasons:-
factors
are
important
for
several
370 (a) each root may have a conflicting line of withdrawal which will render surgery more difficult, because the roots will require division (Fig. 1); (b) the presence of multiple roots will obviously lead to greater surgical difficulties than a single conical root; (c) the position of the root in relation to the inferior alveolar canal is important as failure to recognise a true relationship may result in trauma to the nerve and consequent paraesthesia of the lip. The canal is often seen on radiographs as two radio-opaque parallel lines crossing the roots of the third molar. Usually this appearance is caused by imposition of these structures. The danger signs of a true relationship are:6) where the continuity of one or both of the radio-opaque lines crossing the root is interrupted. This may indicate grooving of the root by the neuro-vascular bundle; (ii) where the neuro-vascular bundle assumes an increase in radio-lucency in its relationship to the apex of a third molar. This is usually indicative of grooving of the third moIar by the inferior alveolar canal; (iii) where a distinct narrowing of the canal is apparent there is every chance that it perforates the tooth.
(3) The density of bone In older patients bone generally is more sclerosed, and hence less elastic. Surgery is easier
Australian Dental Journal, December, 1975 on bone which is more elastic, such as in patients under the age of thirty years. Thus a 5 mm impacted wisdom tooth is much more difficult to remove at 55 years of age than at 25 years of age. (4) The second molar
The shape of the second molar is important. Although an adjacent tooth should never be used as a fulcrum, all too often it is. In the event of the second molar having a single conical root, force applied to elevate a third molar might well displace the second molar from its socket. Removal of wisdom teeth is further complicated when the external oblique ridge approaches the vertical when there is then decreased access to the site. When the external oblique ridge is more obtuse in angulation, access is facilitated.
To summarise, the main points to assess third molars are:(a) position and depth of the tooth; (b) position and pattern of the roots; (c) the relationship of the neuro-vascular bundle to the tooth; (d) the shape of the second molar; (e) the degree of access to the site. Department of Oral Medicine and Oral Surgery, University of Western Australia, 179 Wellington Street, Perth, W.A. 6000.
