Methods of determining pulp vitality

Question 1

Vital definition

Answer 1

“of, or pertaining to, accompanying, or characteristic of life; inherent in or exhibited by living things or organic bodies”

i.e. having an intact blood supply

Question 2

What is vitality?

Answer 2

Has an intact blood supply
Usually this means that the innervation (nerve supply) is also intact, but this is not necessarily the case all of the time (trauma, nerve injury, orthognathic surgery)

Question 3

Characteristic of an ‘ideal’ pulp tester

Answer 3

Effective on both anterior and posterior teeth (single/ multi-rooted)
Effective if tooth is carioius or if it has been restored
Effective when secondary dentine has been deposited
Must be effective in unusual circumstances (re-impanted, transplanted teeth)

Question 4

Current methods of vitality testing

Answer 4

Tests of integrity of innervation
-electrical stimuli
-thermal stimuli (cold: ethyl chloride, hot: gutta percha)
Tests of integrity of blood flow
-u.v. light photography
-oximetery/ photplethysmography 
-laser-Doppler flowmetry

Question 5

Principles of conventional pulp testing

Answer 5

Px indicates a response
Tests whole of pain pathway, not just pulp
Sensation uncomfortable at detection threshold, but not painful (pre-pain?)
Confirm by questioning that it is the pulp that is being stimulated, not gingiva or PDL

Question 6

General difficulties in pulp testing

Answer 6

Pulp is in an enclosed chamber making access difficult
Pulp chamber is practically opaque (n.b. dentinal tubules)
Electrical resistance (impedance) varies widely
Pulp size diminishes due to secondary dentine

Question 7

False positives

Answer 7

Pulp testers, like any other diagnostic test, can give ‘wrong’ result, even when they are correctly used
False + is when pulp testing indicates that tooth is vital, when actually it is not
Ideally, incidence should be low

Question 8

False negatives

Answer 8

Pulp testers, like any other diagnostic test, can give ‘wrong’ result, even when they are correctly used
False - is when pulp testing indicates that tooth is non-vital, when in reality it is vital
Ideally, incidence should be low

Question 9

Electrical pulp testers

Answer 9

Sensation uncomfortable but not painful at threshold
Avoid gingival margin and restorations (current spread)
Need good electrical contact
-toothpaste, not prophylactic paste (glycerine)
-electroconductive rubber
-indifferent electrode (monopolar stimulation) in hand or via handle and operator (no rubber gloves!)
Teeth isolated
-no saliva between teeth

Question 10

How electrical pulp testers work

Answer 10

Electrical pulp testers directly activate pulpal nerve fibres (bypass receptors)
Pulp testers achieve this by depolarising pulpal nerve fibres, so that they generate a.ps
For a nerve fibre to be depolarised, electrical current has to flow into it
BUT, most pulp testers generate voltage pulses, not current pulses
Therefore, the electrical resistance of the tooth (impedance) is important

Question 11

Physics

Answer 11

Typical electrical pulp tester can generate voltage pulses of about 100V
Most teeth have electrical thresholds<150µA, 0.1ms
So for tooth with resistance of 10 kΩ
I=V/R (Ohm’s Law)
=100/10,000
=10mV

Question 12

Electrical pulp testing options: monopolar vs. bipolar stimulation

Answer 12

Nerve fibres excited where current density is highest
Is this in dentinal tubules, at pulp-dentine junction or at apex?
Use cathodal stimulation (tip negative) for monopolar testing (risk of anodal block)

Question 13

Electrical pulp testing options: contant current vs. constant voltage

Answer 13

Most commercial pulp testers are of contant voltage type
-often cause false +ves because of stimulus spread to gingival margin & PDL
With constant current devices there are few false positives, but more false negatives
-not easily available

Question 14

Pain threshold

Answer 14

Stimulus intensity where it just becomes painful

Question 15

Threshold

Answer 15

Stimulus at which the px cannot tolerate pain anymore

Question 16

How well do pulp testers work clinically?

Answer 16

Moody et al 1989
Tested electrical thresholds of 50 teeth using constant current, cathodal stimuli
-compared both monopolar and bipolar stimuli, and also varied stimulus duration (0.1, 1 & 10ms)
Teeth then extracted and processed histologically so that state of pulp could be verified
64% correct monopolar to 150µA
72% correct bipolar to 200µA
No relationship between electrical threshold and pulp status

Question 17

Thermal testing: heat

Answer 17

Hot gutta percha
Sticks to teeth when surface dry- use vaseline
Difficult to control T

Question 18

Thermal testing: cold

Answer 18

Ethyl chloride spray (evaporative cooling)
Apply with cotton wool pledget to single tooth
Avoid soft tissues
Moody et al (1989): 80% correct, 2 false positives
-better than electrical

Question 19

Recording pulpal blood flow

Answer 19

Theoretically, should be ideal way of determining pulpal vitality
Main difficulty is gaining access to pulpal vessels
Several methods been used in experimental animals (radioactive microspheres, xenon washout, H2 polarography), these are too invasive for use on humans
Laser-Doppler techniques may be one soln

Question 20

Lase-Doppler flow meters

Answer 20

Optical fibre directs infra-red light to tissue to be studied
Light scattered by moving cells undergoes 4kHz change in freq. (Doppler shift)
Light scattered by moving objects (blood cells) mixes with light scattered by stationary objects, resulting in beating
> moving cells, > intensity of beating
Second fibre collects light analysed by photodetector to produce estimate of blood flow

Question 21

Problems with laser-Doppler methods

Answer 21

Signal produced (‘flux’) not in absolute units (ml blood/100 g/min), rather it is product of no. cells scattering light and velocity
Flux signal is only linear if volume fraction of red cells in tissue is < 1%
In humans, there is considerable gingival and periodontal contamination of blood flow signal recorded from tooth
Cost £10K and upwards