Third Molars Flashcards
What is the usual eruption age of third molars
18-24 years
When is the calcification of the crown begin and complete in third molars e
7-10. Years and complete by 18 years
At what age if the third molar is missing on a radiograph would you expect it to. Never develop
14
Where does the lingual. Nerve lie
On the superior attachment of the mylohyoid
What is the incidence of impacted M3M
36–30%
What are the 4 therapeutic indications for c extraction of M3M
Infection
Cysts
Tumours
External resorption of 7 and 8
What is the most common cyst arise from M3M
Dentigenergous cyst arising from the reduced enamel epithelium separating from the crown
What two ways of impaction are higher risk of disease
Mesial-angular
Horizontal
What is pericornitis
Inflammation around a partially erupted tooth
Food and debris gets trapped under the operculum and causes inflammation and infection
Name three anerobic Microbes involved in pericornitis
Actinomyces
Streptococci
Beta lactamase producing prevotella intermedia
What two kinds of impaction predispose a patient to pericornitis
Vertical and distoangular
Insufficient space between what two structures can result in pericornitis
Ascending ramus of lower jaw and distal aspect of M2M
What is the risk of temporary numbness following extraction of a lower third molar
10-20%
What is the risk of permanent numbness following XLA of lower 3rd molar
<1%
Name 4 reasons for Indication of extraction of a lower third molar
Infection - caries, periodontal dsieae or local bone infection
Cyst
Tumour
External respotion of 7 0r 8
Impaction leading to high risk of disease
Medical indications
What muscle does the lingual nerve lie on the superior attachment of
The mylohyoid muscle
What 4 nerves are at risk during extraction of a mandibular third molar
Inferior alveolar nerve
Lingual nerve
Nerve to mylohyoid
Long buccal nerve
What are 5 predisposing factors to periocoronitis
Partial eruption and vertical or distoangular impaction
Opposing M3M or M2M causing mechanical trauma contributing to recurrent infection
Upper respiratory tract infections
Poor oral hygiene
Insufficient space between the ascending ramus of the lower jaw and the distal aspect of the M2M
A full dention
White race
Why is it so important to check the TMJ on patients with third molar pain
Often patients that are referred in for third molar pain aren’t actually having third molar pain it is instead TMD pain
What is the working space distance when discussing M3M
Distance between distal of the M2M and the ascending ramus
It is essentially the space you have to get it out
When assessing follicular width above what measuremt would you be concerned that there is pathology
Anything more than 2-3mm
There are many radiographic signs that can indicate a close relation ship of the ID canal to the roots of the M3M
What three are we most worried about that have been identified to carry the most increased risk of nerve injury during molar surgery
Diversion of the inferior dental canal
Darkening of the root where crossed by the canal
Interruption of the white lines of the canal
What is the angulation/ortientaion of an impaction measured against
Measured against the curve of spee
The depth of an impaction gives us an indication of what
The amount of bone removal required
There are 3 categories for depth of an impacted M3M what are they and what do they mean
Superficial - crown of 8 related to the crown of the 7
Moderate - crown of 8 related to crown and root of 7
Deep - crown of 8 related to root of 8
What percentage of people require consious sedation for routine dental treamtent
7%
When discussing numbness with the patient what areas do u refer to
Lower lip, chin and side of tongue
After what period of time would there not be much hope for nerve recovery
18-24 months
What acronym can be used for refferals and explain it
SBAR
S - situation ; 23/m pain LL8
B - background ; HPC, episodes of periocornitis>?, any antibiocos
A - assessment ; LL8 PE, moderate mesial impaction, caries, food packing, MH SH DH
R - recommendation ; pt keen for surgical removal and i believe it is indicate here
Three basic principles of surgical removal
Risk assessment
Aseptic technique
Minimal trauma to hard and soft tissues
What are the 8 steps in surgical removal
Anaesthesia
Access
Bone removal as necessary
Tooth divsion as necessary
Debridement
Suture
Achieve haemostatis
Post operative instructions ; verbal and written
What is the aim of the surgical access in removal of M3M
Maximum access with minimal trauma
Name 3 instruments that can be used to reflect the mucosa during surgical extraction
Mitchell’s trimmer
Howarths periosteal elevator
Ash periosteal elevator
Name 2 instruments that can be used for retraction
Minnesota
Rake retractor
What kind of handpiece and bur do we use for bone removal and why
Electrical straight handpiece with saline cooled bur - to avoid necrosis of teh bone
Air driven hand pieces may lead to surgical emphysema
Tungsten carbide burns
What’s is the aim of bone removal
Create a deep narrow gutter around the crown of the wisdom tooth
What must we be wary of when removing bone
Tissues behind the 3rd molar contain the lingal nerve
What are the 3 kinds of surgical debridement
Physical ; bone file or handpiece to remove sharp bony edges ( mitchell’s trimmer)
Irrigation ; sterile saline into socket and under mucoperiosteal flap
Suction ; aspirate to remove debris and check socket for retained apices
What are 4 aims of suturing
Reposition tissues
Cover bone
Prevent wound breakdown
Achieve haemostatis
If a patients roots are in close proximity to the IAN canal what treamtent option can we offer
Coronectomy
What is the aim of a corenecotmy
The crown is removed with the deliberate retention of the root adjacent to the IAN
The aim is to reduce the risk of IAN damage
How far down should you take off in a corenectomy
Transection of tooth 3-4mm below the enamel of he crown into dentine
When should we review a corenectomy patient
Review 1-2 weeks
Further 3-6 months
1 year
Radiographic review at 6 months or a year or both
What are the 3outcomes for the roots left behind in a corenectomy
- Roots remain where they are and the gum heals - 70%
- Roots migrate to surface, will feel like they tooth is coming through and they then need to be extracted - 20-30%
- Roots become infected 5-10%
What 4 things must you warn a patient about if you are going to do a corenecotmy
If the roots are mobilised during the crown removal the entire tooth needs to be removed - risk of infection too high.
Leaving roots behind can result in infection - rare
Can get slow painful healing - dry socket
They roots may migrate and begin to erupt through mucosa so need to be extracted
