Extensive amalgam Flashcards
Why do we restore cavities?
- to restore the integrity of the tooth surface
- to restore the function of the tooth
- to restore the aesthetics of the tooth
What is an extensive amalgam restoration?
= involves rebuilding of cusps and the provision of auxiliary retention (use extra aids for retention)
When are extensive amalgam restorations indicated?
= to postpone the placement of cast restorations (less invasive, expensive and time)
What is the average survival time for routine amalgam fillings?
10 - 20 years (this is the same for well made extensive amalgam restorations)
How is amalgam retained in a cavity?
Undercuts (macro-mechanical retention)
When a cusp has been lost how do we retain an amalgam restoration?
There are different routes for amalgam to come out = need extra retention measures
What is retention form?
The features of the cavity preventing withdrawal of the restoration in the long axis of the preparation
What is resistance form?
The features preventing dislodgement of the restoration under all other forms of loading
What is Auxiliary retention?
Supplementary retention required for extensive restorations
What are the different types of Auxiliary retention?
Cavity design features
(Dentine) Pins
Adhesives
Which cavity design features can be used so that each part of the cavity is independently retentive?
Boxes
Axial grooves
Slots
Pits
What is a slot?
A long ditch just inside ADJ = approx 1 mm wide
(pic = occlusal view)
What is an axial groove?
Groove just along base of cavity along axial walls = retention from coming out of the side
What is the depth and width of slots and pits?
Depth = no greater than 1 mm
Width = little more than the diameter of the instruments used to prepare them
What type of internal form do they have?
Sharp internal form = increases stresses within the tooth and material = necessary to provide resistance form
What is the evidence of pins?
Lab tests = consistently perform well
Unfortunately the studies do not replicate the clinical situation (quite a lot of damage to a tooth and dangerous in the wrong instance)
What are the 3 different types of pin?
Cemeneted pins
Friction grip pins
Self-threading pins (most retentive)
How do you know how many pins to use?
- 1 pin per missing cusp
- 1 pin per missing line angle (i.e. mesiobuccal line = those that make up the 3D structure of the tooth)
- 1 pin per missing proximal surface
What is needed for a pin to be placed?
Sufficient bulk of HEALTHY dentine (remove caries first)… for self threaded pins:
- between 1-2 mm inside DEJ/CEJ
- 2 mm depth into dentine
- 2 mm depth into amalgam
- 2 mm from opposing tooth
Which diameter pins are more retentive?
Larger diameter
Why should pins be used with caution?
- They weaken both tooth structure and the restoration
- Failures in studies = due to fracture
- 1971 study concluded all pins other than cemented pins caused stresses within the surrounding tooth structure = cracks in dentine and enamel
- Incorrectly placed pins can perforate into the pulp and periodontal tissues (infection) -> generally placed in the direction of the long axis of the tooth
- pins placed too close to the pulp will cause post-operative sensitivity
- pins placed buccally or lingually will be superimposed on the pulp chamber and their angulation in the pulp/periodontal direction cannot be seen radiographically
Adhesives containng which materials are used in extensive amalgam restorations?
- 4META (AmalgamBond)
- MDP = Methyacryloyloxydecyl dihydrogen phosphate (Panavia)
What are the advantages of using adhesives in extensive amalgam restorations?
- Increase retention
- Conserve sound tooth structure (no pins or slots needed)
What evidence is there for use of adhesives?
No evidence reporting a difference in survival between bonded and non bonded amalgam restorations (therefore important to be mindful of the additional costs that may be incurred)
In which two ways can restorations fail?
- New disease (i.e. secondary/recurrent caries)
- Technical failure (e.g. fracture, loss of filling etc.)
List 4 thing that can cause technical failure:
- Defective contact point = traps food
- Overhanging restorations = plaque build up = periodontal disease
- Non retentive cavity
- Fractured restoration
When are teeth susceptible to new pulp problems?
- Heavily restored teeth = liable to pulpal inflammation
- > pulpal necrosis (sinus develops)
N.b. pulpal necrosis of heavily restored teeth can result from the original disease or the operative procedure used to restore it
Where can you get caries on an extensive amalgam restored tooth?
- New disease around existing restoration (secondary/ recurrent caries)
- At another site on the same tooth
What is replacement of a restoration?
The complete removal of restoration together with base or lining materials
What can replacement of a defective extensive amalgam restoration lead to?
- Inadvertantly removal of sound tooth tissues
- increase cavity size
- risk of damage to the dental pulp
- development of clinical symptoms
What is repair of a restoration?
Only the defective area of the restoration is removed and replaced
What are the advantages of repair over replacement?
Repair is…
- conservative
- quicker
- cheaper
- less traumatic to the patient and the tooth
- local anaesthesia may not be required
There is an absence of any high level reliable evidence on whether repair or replacement is better so the clinician should base their decisions on…
- clinical experience
- individual circumstances
- in conjunction with the patients’ preferences where appropriate
What is the difference between post and pins?
Posts are used more in the interior of teeth (where the tooth is root canal treated = extends into the root)
What distance should there be between the base of the pin and the cusps of the opposing tooth?
6mm
