Third Molars Flashcards
When do third molars erupt
18-24 years old
When do the upper third molar crowns begin calcification
7-9 years old
When do the lower third molars begin calcification
between 8-10 years old
When is root calcification of third molars complete
18-25
What is the prevelance of agenesis of third molars
25%
What is agenesis
where there is failure of development of the third molar
What jaw is agenesis more common in
upper
more common in females
What gene is 3rd molar agenesis linked to
PAX9
What age can we be confident that it is unlikely the third molars will develop
14
What does impacted mean
molar can’t erupt to the functional position
What is the most common reasons third molars fail to erupt
impaction
What are the third molars impacted against
adjacent teeth (usually the 7) but can also be impacted against alveolar bone, surrounding mucosal soft tissue or a combination of these factors
When is a tooth considered partially erupted
when some of the tooth has erupted into the oral cavity
What is the incidence of impacted mandibular third molars
36-59%
What are the common possible consequences of impacted mandibular third molars
o Caries
o Pericoronitis
o Cyst formation
What are the nerves in close proximity to the M3M
IAN
lingual
nerve to mylohyoid
long buccal nerve
What nerves are we most concerned about damaging with third molar surgery/extraction
IAN
lingual
What is the IAN
Peripheral sensory nerve branching from the mandibular division of the trigeminal nerve
What does the IAN supply
All mandibular teeth
lower lip and chin up until the midline
Where does the lingual nerve branch from
mandibular division of the trigeminal nerve
What does the lingual nerve supply
Supplies the sensory anterior 2/3 of the dorsal and ventral mucosa of the tongue as well as a giving off a branch which supplies the lingual gingivae and floor of mouth
Carries fibers from the chorda tympani responsible for taste perception
Carries fibres responsible for secretory/motor innervation of sublingual and submandibular glands
Where does the lingual nerve lie
On the superior attachment of the mylohyoid muscle
Why is recovery of the lingual nerve slower than the IAN post-damage
As the IAN lies in a bony canal which can aid the healing and recovery whereas the lingual nerve is unsupported by bone and so recovery is slower
Is it common for the lingual nerve to be close to the lingual plate
Yes, the lingual nerve has a close relationship to the lingual plate in the mandibular and retromolar area and in 15-18% of cases, the lingual is at or above the level of the lingual plate
Are there any pre-operative factors that can help predict risk of damage
There aren’t any mentioned pre-operative factors related to lingual nerve injury, it is large due to surgical technique
What do the 3 guidelines come from for M3M removal
NICE
SIGN
FDS, RCS
What are the NICE guidelines called
[o https://www.nice.org.uk/guidance/ta1/chapter/1-Guidance]
guidance on extraction of wisdom teeth 2000 (guidance being updated)
What was the general consensus from the NICE guidelines
This guidance discouraged the removal of third molars unless pathology was present such as caries, periodontal disease, infection or cyst
What is the name of the SIGN guidelines for M3M removal
SIGN publication number 43 – management of unerupted and impacted third molar teeth 2000
What was the general consensus from the SIGN publication number 43
Provided similar guidance to NICE, removal of third molar should be justified and that is only the case when there is visible pathology
What is the name of the FDS, RCS guidelines regarding the M3M removal
[o https://www.rcseng.ac.uk/-/media/files/rcs/fds/guidelines/3rd-molar-guidelines–april-2021.pdf
FDS, RCS 2020 – Parameters of care for patients undergoing mandibular third molar surgery
What was the general consensus of the FDS, RCS guideliens
Guidance differs from that of NICE and SIGN
It encourages third molar removal more than the other 2 guidelines based on the premise that by not removing impacted third molars, inevitable surgery is being postponed and postponing this surgery makes the patient more prone to a more difficult surgical procedure
It therefore recommends changing from a simple therapeutic approach to a mixed range of interventions using a more holistic & informed approach
Based on the FDS, RCS guidelines, what are the indications for extraction of M3M split into
- therapeutic
- surgical
- medical
- accessibility
- age
- autotransplantation
- general anaesthetic
What are the therapeutic indications split into
infection
periodontal disease
cyst
tumour
external resorption of third molar/second molar
What is teh most common indiciation for extraction of M3M
infection
What types of infection may the M3M experience
- pericoronitis
- osteomyelitis
- osteonecrosis
- osteoradionecrosis
- caries (M3M or adjacent teeth)
- PA disease
Why is periodontal disease an indication
Untreated horizontal mesioangular impaction (30 to 90 degrees) is prone to causing bone loss distal to the 7
Early extraction can prevent further periodontal damage of the 7
What are symptoms of an M3M cyst
Generally no symptoms associated until they become large and infected
What is the most common cyst experienced with M3M
The most common cyst to be found associated with impacted third molars are **dentigerous cysts **which are odontogenic cysts that surround the crown of an impacted tooth, caused by fluid accumulation between the reduced enamel epithelium and the enamel surface, resulting in a cyst which the crown is located within the lumen and root or roots outside
When would a tumour be an indication for removal of M3M
If the tumour is in close proximity to the lower 8 and they are to be undergoing radiotherapy, then can remove the 8 prior to treatment to prevent ORN post-treatment
May plan this for this who are to be administered bisphosphonates, risk vs benefit can be planned when considering prognosis of M3M & future risk of MRONJ
What would be a surgical indication for removal of M3M
If present within the perimeter of a surgical field (orthognathic surgery, mandibular fracture management or resection of diseased tissue) then consider removal
What are medical indications of removal of M3M
o Have to make dentally fit for cardiac surgery etc
o Prevention of MRONJ, ORN may mean threshold for removal of third molars may be lowered
o Same principle for those on immunosuppressant therapy
What are accessibility indications for removal of M3M
o Restricted access to dental service
o E.g army/long overseas trip
Why is patient age an indication
o Complications + recovery time increase with age
What is autotransplanation
o Low success rate
o Uncommon
o Used to replace 6
When is GA an indication for removal of M3M
o If patient going for GA of one third molar, consider removing opposing/contralateral
What is pericoronitis
o Inflammation around the crown of a partially erupted tooth
o Tooth is normally partially erupted and visible but occasionally there may be very little evidence of communication and probing of the distal of the 7 will show a communication
o Food and debris can get stuck under the operculum resulting in inflammation or infection
What types of microbes are involved in pericoronitis
anaerobes (streptococci, actinomyces etc)
What are signs of pericoronitis
o Pain (throbbing)
o Swelling (can be intra or extra oral)
o Bad taste
o Pus discharge
o Occlusal trauma to operculum
o Ulceration of operculum
o Evidence of cheek biting
o Foeter oris (halitosis)
o Limited mouth opening
o Dysphagia
How can pericoronitis result in dysphagia
Very rarely can get extra oral swelling to submandibular/sublingually which can impact swallowing
What are the signs of systemic involvement in pericoronitis
o Pyrexia
o Malaise
o Regional lymphadenopathy
What is treatent for pericoronitis
o Incision and drainage of localised pericoronal abscess if required with or without LA
o Irrigation with warm saline/CHX mouthwash (10-20ml syringe with blunt needle under operculum)
o Extraction if upper third molar traumatising operculum
o Patient instructed on frequent warm saline or CHX mouthwashes
o Advise use of analgesia
o Instruct to keep hydrated and keep eating
When should a pericoronitis be referred to A/E
If large extra oral swelling, systemically unwell, trismus, dysphagia
When should antibiotics be prescribed for pericoronitis
Do not prescribe AB unless severe pericoronitis, systemically unwell, extra-oral swelling, immunocompromised
Why are operculectomy not done very often anymore
operculum grows back
Why are operculectomy not done very often anymore
operculum grows back
What are the predisposing factors to pericoronitis
o Partial eruption and vertical or distoangular impaction
o Opposing maxillary 8 or 7 causing mechanical trauma contributing to recurrent infection
o Upper respiratory tract infections as well as stress and fatigue
o Poor oral hygiene
o Insufficient space between ascending ramus of lower jaw and distal aspect of the 7
o White race
o Full dentition
What should we look at in an extra-oral examination
o TMJ
o Limited mouth opening
o Lymphadenopathy
o Facial symmetry
o Muscles of mastication
Why is the TMJ important for M3M pain
TMJ pain can be mistaken for pain of pericoronitis as TMJ pain can be periauricular
What do we look at for intra oral examination
o Soft tissue examination
o Dentition
o Health of the 7
o Eruption status of the mandibular third molar
o Occlusion
o Oral hygiene
o Caries status
o Periodontal status
When should we take a radiograph of the M3M
Only taken if surgical consideration considered, don’t take one if patient sure they don’t want the tooth out
What do we determine from the OPT
Presence/absence of disease in the third molar or elsewhere
Anatomy of the third molar (crown size, shape, condition, root formation)
Depth of impaction
Orientation of impaction
Working distance (distal of the lower 7 to the ramus of the mandible)
Follicular width
Periodontal status
The relationship of the proximity of upper third molars to the maxillary antrum and of lower third molars to the inferior dental canal
Any other associated pathology
Why do we look at the follicular width on an OPT
Studies suggest that if the width of the follicle is greater than 3mm then this is suspicious of pathology
What is the Rood & Shehab paper about
produced a paper that give indications of radiological prediction of inferior alveolar nerve injury during third molar surgery
What increases the likelihood of third molar/IAN relationship
if the molar is impacted
What are the Rood and Shehab signs
- darkening of the root
- deflected roots
- narrowing of the root
- dark and bifid root
- interruption of the white lines
- diversion of the inferior alveolar canal
- narrowing of the inferior alveolar canal
What is a normal root density
Usually the density of the root is the same throughout its length and this is not disturbed when the images of the tooth and inferior alveolar canal overlap
Why does the root appear darker when the IAN is related to the M3M
When there is impingement of the canal on the tooth root, there is loss of density of the root and the root appears darker
Darkening of the root is attributed to the decreased amount of tooth substance or loss of the cortical lining of the canal between the source of X-rays and the film
What are deflected roots
Deflected roots or roots hooked around the canal are seen as an abrupt deviation of the root when it reaches the inferior alveolar canal
The root may be deflected to the buccal or lingual side or to both sides so that it completely surrounds the canal or it may be deflected to the mesial or distal aspect
What does narrowing of the roots imply
If there is narrowing of the root where the canal crosses it, it implies that the greatest diameter of the root has been involved by the cnala or there is deep grooving or perforation of the root
What does dark and bifid root indicate
Appears when the inferior alveolar canal crosses the apex
Is identified by the double periodontal membrane shadow of the bifid apex
What are the white lines referred to by Rood and Shebab
White lines are the 2 radiopaque lines that constitute the roof & floor of the canal
These lines appear on a radiograph due to the dense structure of the canal walls
When are the lines considered interrupted
The white line is considered to be interrupted if it disappears immediately before it reaches the tooth structure
One or both white lines may be involved
What does interruption of the white lines indicate
The interruption of the white line is considered to indicate deep grooving fo the root if it appears alone or perforation of the root if it appears with the narrowing of the canal
When is a canal considered to be diverted
Canal is considered to be diverted if when it crosses the mandibular third molar, it changes direction
Why is the inferior alveolar canal diverted
An upward displacement of the canal to the contents of the canal passing through the root and hence during eruption of the third molar, the contents are dragged upwards with it
When is the inferior alveolar canal considered narrow
Considered narrow if, when it crosses the root of the mandibular third molar, there is a reduction of its diameter
Why does the inferior alveolar canal narrow
narrowing could be due to the downward displacement of the upper border of the canal or the displacement of the upper and lower borders towards each other with the hour glass appearance
What does an hourgalss form of the IAC indicate
encirclement of the canal or a complete encirclement
Which Rood and Shehab signs are associated with significantly increased risk of nerve injury during M3M surgery
o Diversion of the inferior dental canal
o Darkening of the root where it crosses the canal
o Interruption of the white lines of the canal
What is another sign of close relationship of the IAC & M3M that isn’t mentioned by rood and shehab
Juxta apical area
This will appear as a well circled radiolucent region lateral to the root of the third molar but not at the apex
Not pathological
What
How do we measure angulation if impaction
measured against curve of spee
What are the types of angulation
o Vertical
o Mesial
o Distal
o Horizontal
o Transverse or aberrant
What are the most common types of impaction
Vertical & mesial are most common
What does the depth of impaction give an indication of
amount of bone removal required
How would superficial impaction be
crown of the 8 related to the crown of the 7
How would moderate impaction be
crown of the 8 related to the crown + root of the 7
What would deep impaction be
crown of 8 related to the root of the 7
What are common treatment options for M3M
o Referral
o Clinical review
o Removal of M3M
o Extraction of third molar
o Coronectomy
What are common options for M3M
o Operculectomy
o Surgical exposure
o Pre-surgical orthodontics
o Surgical reimplantation/autotransplantation
When we consider GA for M3M surgery
Extreme anxiety
Extensive surgery
Sedation contraindicated
Genuine LA allergy
What type of consent is required for GA / IV sedation
written
although written always best practice
What are the risks of surgery/extraction of M3M
usual big 5
restoration fracture of adjacent tooth
mandibular fracture
anaesthesia
parasthesia
dysaesthesia
hypoaesthesia
heightened sensation
What are the big 5
pain, swelling, bruising, bleeding, infection
What predisposes a patient to mandibular fracture
Edentulous/atrophic mandible
Aberrant lower 8 close to lower border of mandible
Large cystic lesion associated with wisdom tooth
Would be fixed at later date in oral max fax
If there are concerns on the proximity of the IDC and the roots from the x-ray, what should the px be offered
CBCT
How is access gained
buccal mucoperiosteal flap
can be 3 sided flap or envelope
What is a mucoperiosteal flap
A mucoperiosteal flap includes the surface mucosa, submucosa and the periosteum, this shows clean bone and avoids unnecessary trauma to the underlying tissues which would delay healing
Importance placed on minimising trauma to interdental papillae
Why should the reflection be firmly on bone
Avoid dissection occurring superficial to periosteum
Reduce soft tissue bruising/trauma
What tissues are difficult tissues to reflect with minimal trauma
papilla
mucogingival junction
What instruments are used for reflection
Mitchell’s trimmer
Howarth’s periosteal elevator
Ash periosteal elevator
Curved Warwick James (used to reflect the papillae)
What is the aim of retraction
o Allows access to operative field
o Protects the soft tissue from falling back and getting caught in the bur
What instruments are used for retraction
Periosteal elevator
Rake retractor
Minnesota retractor
What is used to remove bone
Electrical straight handpiece with saline cooled bur is used
Round or fissure stainless steel burs & tungsten carbide burs used
Why must the handpiece be electric
as introduction of air into these tissues can result in surgical emphysema
Where is bone removal carried out
On buccal aspect of the tooth and onto the distal aspect of impaction
Buccal gutter should be started at the distal round to the mesial as allows more control of the bur and decreases risk of soft tissue damage/lingual nerve damage
What is the aim of bone removal
to create a deep, narrow gutter around the crown of the wisdom tooth to allow correct application of elevators on the mesial and buccal aspects of the tooth
There should be plenty of irrigation to maintain visibility and avoid bony necrosis
How is the tooth removed
either as whole or sectioned
whole if possible is best, with elevators and forceps
How can the tooth be divided
crown sectioned from roots
seperate crown, then seperate roots
vertically sectioned, both crown and roots
If the crown is divided from the roots, how should this be done
want to section the crown above the ACJ as this leaves some crown behind which allows for orientation and elevation
different from coronectomy where crown would be removed below the ACJ
What is the function of debridement post removal
any debris must be cleaned out and any follicular tissue or granulation tissue from chronic infection should be curetted, especially hidden behind the second molar
What are the types of debridement
physical
irrigation
suction
What is used to phsyically debride
Use a bone file/handpiece to remove sharp bony edges
Use a mitchell’s trimmer/Victoria curette to remove soft tissue debrirs
What is the function of suction in debridement
Aspirate under flap to remove debris, this must be done before the flap is repositioned
Check socket for retained apices
What is the function of suturing
o Approximates tissues + compresses blood vessels
What are the aims of suturing
Reposition
Cover bone
Prevent wound breakdown
Achieve haemostasis
What is coronectomy
o Alternative to surgical removal of entire tooth when there appears to be an increased risk of IAN damage with surgical removal
o The crown is removed with the deliberate retention of the roots adjacent to the IAN
What is the technique for coronectomy
o Similar access is required
o Transection of the tooth 3-4mm below ACJ
o Elevate/lever crown off without mobilising the roots
o Pulp left in place untreated
o If necessary, reduction of roots with a rose head bur to 3-4mm below alveolar crest
o Socket irrigated
o Flap replaced
Then follow up
When should the patient be followed up
Review 1-2 weeks
Further review 3-6 months then 1 year
Some review at 2 years but most discharge back to GDP after 6 months/1 year review
Radiographic review 6 months or 1 year or both
After this, only radiograph if symptomatic
Some take an immediate or 1 week post-op x ray
What are the warnings for coronectomy
If root is mobilised during crown removal then entire tooth must be removed, its more likely with conical fused roots
Leaving roots behind could result in infection although rare which would require further procedure
Can get a slow healing/painful socket, similar to dry socket
Roots may migrate later and begin to erupt through the mucosa and may require extraction
