Principles of Cavity Preparation Flashcards
1
Q
definition of a plastic
A
something that is mouldable, flexible till turns hard due to change in chemical compostition
2
Q
what 3 things determine cavity design?
A
- structure and properties of the dental tissues
- the diseases
- properties of restorative materials
3
Q
what diseases can cause a cavity?
A
- dental caries
- periodontal disease
- tooth surface loss (largely due to lack of hygiene, care and poor diet)
4
Q
in cavity design there is a strong relationship between….
A
- the position of the caries
- the extent of the caries
- the shape of the prepared cavity
- the final restorative material
each of these properties must be reviewed and reassessed continually when preparing a tooth to receive a restoration
5
Q
4 different caries positions
A
- pit & fissure
- approximal (posterior and anterior)
- smooth surface (typically around gingival margin)
- root
6
Q
when should you operatively intervene?
A
- lesion has cavitated
- patient can’t access the lesion for prevention
- the lesion is into dentine
- lesion is causing pulpitits
- lesion is unaesthetic
decisions can be difficult
7
Q
qualities of enamel
A
- brittle
- along prisms
- unsupported enamel and/or under occlusal load should be removed before restoration
- N.B. Dry tissue - need to etch
8
Q
importance of operative procedures around dentin-pulpal complex
A
operative procedures involving dentine affect pulp
9
Q
dentine qualities
A
- porous
- more elastic
- N.B wet tissue
10
Q
what happens to gingival tissues when plaque is present?
A
become inflammed
11
Q
structure of enamel effect on cavity design
A
prismatic structure
side cut or end cut effects etching
12
Q
what is the weakest point?
A
where 2 material join
- breaking point
consider where edges of cavity relate to where teeth are
13
Q
primary dentine structure
A
- open tubules
- wet as not as many materials can bond unlike enamel
14
Q
tertiary dentine structure
A
reaction of trauma to tooth
has a different structure - more unorganised
15
Q
principles of preparation are driven by:
A
- caries removal
- necessary finishing required for maximum adhesion, occlusal relationships, ease of patient cleaning, properties of the materials used
- no attempt should be made to remove any healthy tissue for any reason unless required
16
Q
only cases when remove healthy tooth tissue
A
- material used for the restoration requires it
- margins of the cavity are in contact with another tooth surface
- margins of the cavity cross an occlusal contact
17
Q
6 principles of cavity design & preparation
A
• Identify and remove carious enamel
• Remove enamel to identify the maximal extent of the lesion at the amelodentinal junction & smooth the enamel margins
• Progressively remove peripheral caries in dentine – from the ADJ first, then circumferentially deeper.
• Only then remove deep caries over pulp
• Outline form modification
o Enamel finishing
o Occlusion
o Requirements of the restorative material
• Internal design modification
o Internal line and point angles
o Requirements of the restorative material
18
Q
modification for amalgam
A
undercuts for retention
19
Q
modification for composite
A
none
20
Q
cavosurface margin
A
margin between internal enamel/dentine and external enamel
21
Q
what should the final cavosurface margin be like?
A
- remove any unsupported enamel by etch technique
- smooth cavosurafce margins and line angles
- ensure there are no excessively acute line angle transitions and that the outline form is smooth and rounded (sharp line angles can cause cracks potentially)
- check for stress concentrators
22
Q
when removing an existing restoration
A
ensure no traces of restorative material remaining
23
Q
what should line and point angles be like?
A
smooth
24
Q
line angle
A
junction between wall and floor
25
point angle
where 3 planes meet
26
5 points to remember for the final seal of the restoration
- smooth margins
- appropriate CSMA
- no unsupported tooth tissue
- no stress concentrators
- internal anatomy that allows adaptation of material
27
after preparation what do you need to do?
clean the cavity to ensure free from debris
28
how to remove an existing restoration?
start from the centre of the restoration and cut towards the edge of the cavity
NEVER remove a restoration by cutting around the edges as will increase the size of the cavity
- use high speed to cut into pieces
- chip out chunks where possible
- remove all and any underlying base material
29
how to detect dentinal caries?
brown stain or softened tissue when using a sharp probe
| sound dentine doesn't yield under probing
30
what does sticking of probe to dentine indicate?
residual carious dentine which should be removed
31
what should you never probe?
uncavitated carious enamel as can fracture
32
what do you remove first residual dentinal caries from ADJ or pulpal floor?
remove residual dentinal caries from ADJ first and then residual dentinal caries last from pulpal floor
33
how to remove caries from ADJ a?
• Hand-held excavator
• Round bur
• Chemo-mechanical caries removal
Caries detector dyes may be helpful
34
what do you need to be cautious about when removing caries from pulpal floor?
pulp exposure
| - birr more likely to expose pulp so better to use hand tools
35
what instrument should be used to remove caries from pulpal floor?
largest instrument which will conveniently work in the cavity
- large round burr
- large hand held excavator
- chemo-mechanical caries removal
too small = too deep too fast = pulp exposure
36
when is carious pulp exposure a necessity?
```
pulp therapy
• Direct and Indirect Pulp Cap (CaOH)
• Exposing a healthy pulp
• Importance of symptoms
traumatic exposure should be avoided
```
37
importance of the ADJ
always check for Caries at ADJ!
• If access can remove with slow or high speed
• Enamel brittle - can it be reinforced by restorative material to be stable
• Or remove (sometime if amalgam)
38
modification for enamel margins
etch
39
modification for cavosurface margin angle
ensure smoothed off
| check for stress concentrators
40
modification for occlsuion
junction with material and enamel going to be strong enough to withhold the occlusal force
41
modification for internal anatomy
check for stress concentrators
42
stress concentraotrs
ability of base of material to resist cracking
43
3 most commonly used materials for direct plastic restoration are:
- composite
- amalgam
- resin modified glass ionomer
44
what is the material of choice for restorations?
composite - no features needed for retention
45
8 advantages of composite
```
Aesthetics
Conservation of tooth tissue
Support for remaining tooth tissue
Adhesion/bonding
Command cure
Low thermal conductivity
Elimination of galvanism
Amalgam alternative?
```
46
disadvantage of composite
operator sensitive - can go greatly wrong
47
3 disadvantages of amalgam
- does not bond to enamel or dentine
- does not support the tooth
- not tooth coloured
48
how is amalgam held in?
by retention and resistance form
cut dentine may require sealed dentine layer
49
3 reasons why amalgam prevented from fracture
- adequate bulk (at least 2mm deep)
- retention and resistance - need to remove healthy tissue
- strong under occlusal load
less moisture and technique sensitive
50
positives of amalgam
less moisture and technique sensitive
| - simple, quick and relatively easy
51
what is amalgam retention?
features of cavity which prevent the restoration being dislodged in any occlusal direction
- anatomical cavity design features e.g. undercuts, dovetail, key, isthmus
52
when is retention not essential?
for adhesive restorations
53
what do non-adhesive restorations require?
retention factors
internal dimensions of the cavity greater than access into it
cavosurface angles adjusted to increase bonding area and ensure no unsupported enamel
54
what happens to cavosurface angles in amalgam restorations?
cavosurface angles adjusted to increase bonding area and ensure no unsupported enamel
- required for adhesive restoration
undercuts unnecessary
55
bevel
corner rounded out
56
line angle
2 planes intersect
57
point angle
3 planes intersect
58
how should the cavity margin/restoration interface be designed for maximum strength and minimum leakage? (3)
- all cavity margins should be caries free
- all cavity margins should be free of contact with the adjacent tooth
- all cavity margins should be accessible for cleaning
59
what is the general cavoisurface angle for amalgam?
90-120 degrees
| Butt joint
60
what is the most important factor to consider for cavity margins for amalgam?
avoid inappropriate CSMA or unsupported enamel
61
what will caries at cavosurface angle result in?
caries at the dentine-enamel junction will result in unsupported enamel and early breakdown of the restoration margin if micro-leakage occurs
62
configuraion factor
ratio of bonded:unbonded surfaces in the restoration
63
high configuration factor means
increased polymerisation contraction stress
| e.g. occlusal only one exposed surface, all the others in the tooth
64
low configuration factor means
reduced polymerisation contraction stress
65
what is the result of configuration stress?
- composite dimensional change
| - etch/bond is stronger than interstitial enamel strength
66
what bond strength is stronger - to enamel or dentine?
bond strength to enamel is stronger than to dentine
| more likely to have serious bond failure to dentine
67
what does polymerisation stess lead to?
enamel failure
| - etch/bond is stronger than interstitial enamel strength
68
how to clean up the cavity?
- wash the cavity with a mixture of air and water to remove loose debris
- rinse with chlohexidine and remove
- rinse with water and leave surface moist
69
what will be in the cavity after preparation?
- loose enamel and dentine chippings
| - organic and inorganic dentine debris smeared into the walls of the cavity
70
what should you do if caries close to the pulp?
manipulate over soft remaining caries to see if remineralised or tertiary dentine forms
• Means wait for patient
• And some risks
But can be better than breaching pulp - sometimes done in paeds
71
important points for cavity preparation
* Not always necessary to remove all the caries
* Protect the airway and the pulp
* Decide on your choice of material AFTER caries removal
* Design the cavity considering the remaining tooth tissue, its quality and the choice of material
* Think conservation of tooth tissue
* Think about sealing vital dentine
* Attention to detail avoids problems
72
principles of cavity design and preparation
* Identify and remove carious enamel
* Remove enamel to identify the maximal extent of the lesion at the amelodentinal junction & smooth the enamel margins
* Progressively remove peripheral caries in dentine – from the ADJ first, then circumferentially deeper.
* Only then remove deep caries over pulp
* Outline form modification
* Enamel finishing
* Occlusion
* Requirements of the restorative material
* Internal design modification
* Internal line and point angles
* Requirements of the restorative material
73
retention
the ability of a cavities anatomy to prevent loss of a non-adhesive restorative material
- undercuts (Shaping the cavity to have a wider base closer to the pulp and a narrower opening)
- occlusal extension of the cavity is wider on the occlusal surface when compared with access through the marginal ridge, this allows amalgam to interlock with the tooth without bonding
74
resistance
the ability of a cavities anatomy to prevent displacement of a non-adhesive restorative material
75
undercuts
internal dimensions of the cavity are greater than the access into it
- Shaping the cavity to have a wider base closer to the pulp and a narrower opening
76
why is it essential for the matrix band to adapt and enclose the gingival floor?
to avoid overhangs
