Principles of cavity preparation and pulp protection Flashcards
What is direct trauma?
To odontoblast cell processes during drilling
What is indirect trauma?
To odontoblasts due to desiccation (drying)
To pulpal tissues due to temperature increase (burning)
What are the ways in which we can prevent trauma?
Light pressure
Slow hand pieces cause less damage than high speed
Make sure to have a sharp bur during cavity prep
Maintained handpieces
Water coolant
Use of rubber dam/isolation to prevent bacterial
infection in large cavities
Great care, especially with deep lesions
Why do we restore teeth?
- To remove diseased tissue
- To restore integrity of tooth surface
- To restore function of tooth
- To restore appearance of tooth
What is GV Black classification for carious lesion?
the first textbook published in 1908 describing the ideal cavity form and prescribing a systematic method of cavity preparation
What has changed since the GV Black classification?
shift towards preventative dentistry and adopting more conservative methods to preserve the tooth which may have no ideal cavity form
What are some disadvantages of GV Black’s classification?
Black’s classification doesn’t acknowledge all causes of a cavity such as NCTTL/NCTSL, only caries whereas the current terminology does
Cavity design based purely on amalgam
Relied on mechanical retention (so undercuts, divergent walls, slots and grooves had to be
implemented)
Cavities had to be quite large as a result
Extension for prevention – this is a principle of removing the caries then running out all pits and fissures (to prevent spread)
Why are cavities prepared under Black’s classification identical?
They all follow this list…
- Outline form (including extension for prevention)
- Resistance form
- Retention form
- Convenience form
- Removal of remaining caries
- Finishing of cavity margins/enamel walls
- Cavity toilet (washing out the cavity at the end)
How can we compare the cavity preparations then and now?
Then all the pits and fissures have all been run out, now the preparations are more minimal
Then more amalgam was used, now this is phased out and composite is used
What are the general principles of tooth preparation determined by today?
- Nature and extent of lesion (via clinical and radiograph)
- Quantity and quality of tooth tissue remaining after preparation
- Functional load
- Nature and properties of restorative material used
What do the retentive features include?
undercuts, grooves, boxes, etc – beware this involves removing sound tooth tissue
What are the 3 different concepts in pulp protection?
- Protection from thermal stimulus with a base – for metal restorations
- Protection from chemical stimulus with a liner – etched/bonded restorations
- More recent protection from bacterial stimulus with a sealer – to give well sealed restorations
What was historically thought about the the thermal sensitivity theory?
there was direct thermal shock to the pulp
Temperature changes in oral cavity transmitted to pulp through restorative material, especially when remaining dentine is thin
Therefore, we need to place an insulting base
What is the issue of large bases?
weaken the overlying restoration
Why is the thermal sensitivity theory no longer believed?
as fluid movement causes pain – not conduction
What was historically thought about the the cytotoxic effect theory?
primary cause of pulpal inflammation was related to cytotoxic effect of restorative material
So, protective liner must be placed to prevent effect of material but now they are known to be mild and transitory
Why is the remaining dentine thickness one of the most important factors?
0.5-1mm remaining dentine reduces toxicity levels of materials by 75% and 90% respectively
Why can the theory of cytotoxicity theory be dismissed?
Although dental materials may cause varying degrees of pulp irritation, the pulp can usually recover provided bacteria and their toxins are excluded
What does Brannstrom theory say?
Inflammation is due to microleakage (bacteria) and not the restorative material itself
The presence of bacteria is the single most determinant factor of pulpal inflammation
What is micro leakage?
The passing of fluids, microorganisms or ions between the restorations and adjacent preparation walls
This can occur around all restorations including those that are adhesively bonded to enamel and dentine
What clinical conditions occur as a result of micro leakage?
Marginal discolouration
Pulpal irritation
Pulpal necrosis
Postoperative sensitivity
Recurrent caries
Eventual failure of restorations
Where does bacterial contamination come from?
Initial carious lesion
During cavity preparation
During restoration placement
Smear layer
Microleakage – after restoration is placed
How does dentinal tubular fluid flow cause pain?
Normally, there is a slow outflow of fluid from dentinal tubules
The change in temperature causes this fluid flow to change as well
Any cold/hot application leads to increase in flow and pain
As deeper dentine has more tubules, they are more permeable so more susceptible to changes causes change in fluid flow – hence, more pain
What are bases?
A material, usually a type of cement, used in a prepared cavity before the insertion of a permanent restoration to protect the pulp
