CON-B tutorial 6 + 7 Flashcards
How should we operatively manage caries that have extended into dentine?
When we have taken the decision to operatively manage caries that has extended into the dentine we should:
- adopt A biological approach
- preserve as much tooth structure as possible
- do our very best to maintain pulp vitality
- understand the likely Histology of the carious lesion as this will guide us in what carious dentine we should remove and what we should leave behind
- If the caries is deep, consider that the pulp may be stressed and therefore placed provisional restorative materials such as a glass ionomer/calcium silicate that can remineralise the dentine and encourage pulpal healing.
- Seal the cavity by dentine hybridization and enamel-resin tag formation
- Consider placing a directly bonded resin composite restoration in the first instance.
What do we need for our direct composite restoration to succeed?
A strong, durable adhesive interface between tooth structure and restoration
What adhesive do we use at Guys hospital?
Scotchbond universal adhesive - is acidic
What is scotchbond universal adhesive?
Scotchbond universal adhesive is a single-step light-cured adhesive, which contains MDP and Silane that enables it to bond to enamel, dentine, metal and ceramics.
It can be used in total-etch and self-etching mode
What is etching in dentistry?
Use of an acidic substance to prepare the tooth’s natural enamel for the application of an adhesive.
The acid roughens the surface, increasing the retention of resin sealent.
Etching enamel with acid removes smear layer and opens up enamel tubules
What are the two etching techniques?
Total-etch and self-etch
What do we need for good enamel bonding?
- First etch enamel surface with phosphoric acid for 20 seconds to roughen the enamel surface.
- Dry the surface
- Carefully apply adhesive and lightcure.
image - look on doc
What do we need to do for dentine bonding?
- The adhesive to dissolve any smear layer, infiltrate the dentine surface
- And create a high quality hybrid layer (VERY IMPORTANT)
The objective of adhering to dentine is to create at uniform, good quality hybrid layer with no porosities.
What is the smear layer? What does it do?
- Drilling and cutting tooth tissues creates a smear layer on the cavity walls and floor.
- Like crushed tooth debris.
-Has to be removed or treated in some way otherwise it stops the adhesive infiltrating the dentine below.
What is meant by a hybrid layer?
Neither resin nor tooth, hybrid of both.
The interface of the hybrid layer seals the surface of the restoration against leakage and provides acid resistance = caries resistance
Hybrid layer is less that 10 micrometres thick
Strength comes from resin intertwining with the collagen layer.
image - look on doc
What is an advantage of the hybrid layer?
-It is very strong and tough when properly formed - strength comes from resin intertwining with collagen fibres
-It seals and affords signifciant micromechanical retention for resin composites
What does the MDP monomer contain?
-Used in many dental adhesives today, very reliable
- A hydrophillic group which allows it to interact with dentine
-A hydrophobic group which allows it to interact with resin
How can we get the best out of scotchbond universal?
using a scrubing technique when applying mild self-etching adhesives could imporve resin monomer infiltration into dentine, chase water on adhesive surfaces and facilitate smear layer removal
(For dentine bonding, smear layer removal is needed in order to infiltrate the dentine surface)
What should be the first incremental layer of restoring a cavity?
A thin layer flowable composite, on the cavity floor over the scotch bond.
image - look on doc
What is the advantage of injecting a thin (less than 1 mm) of composite on the cavity floor?
Allows curing light to cure the last few molecules on the surface between the composite and adhesive.
This allows maximum strength
What is important when placing composite resin in proximal cavities?
Important to have good moisture control
What can a CR with higher diffuse transmission result in?
Superior shade blending in the margin without bevels.
image - look on doc
What concentration of phosphoric acid is used when etching?
37%
What is a fissure sealant?
Resin based liquid which is then harden to form a thin protective coating on the tooth’s surface
What is the procedure for applying a fissure?
- Etching of tooth for 20 seconds
- Rinse and dry tooth
- Add the liquid
- Light cure
What are the key factors for creating natural looking restorations?
Shade (hue, value, chroma)
Light reflection
Shape
image - look on doc
What are the 2 types of light reflection?
- Light reflection on the surface (high glossiness, more obvious margin)
- Diffuse transmission inside of materials (lower glossiness, less obvious margin)
image - look on doc
What is the air-inhibited layer?
After the adhesive is light-cured there will be a layer of uncured monomers on the surface of the adhesive. This is the air inhibited layer.
When a thin layer of composite resin around 1 millimetre is placed next this layer of monomers will be polymerised as long as sufficient light can pass through the composite.
This will ensure the composite is bonded to the adhesive. This will also ensure the adhesive layer has maximum mechanical strength to resist the shrinkage stress of the overlying composite resin.
This is repeated when another layer of composite resin is placed.
what happens when the adhesive can resist the stress?
If the adhesive cannot resist the stresses from the composite as it polymerises, it may crack particularly if the hybrid layer in the dentine was of ‘poor quality’
