Tooth coloured materials 1 Flashcards
Bonding to enamel is ……………….
what is the composition of enamel:
……….predictable and relatively easy:
95% hydroxyapatite 4 % water 1% non-collagenous protein
Etch and rinse
An acid of……….
PH is… how long does it take for decalcification to occur
what does etching do?
(mostly 30-40% phosphoric acid) is applied slighty agitated and risned off
PH is 0.2 (very strong acid) and decalcification occurs in 5-8 seconds
Etching decalcifies portions of enamel rods
How does etching work?
How is it not true adhesion?
Calcium salts are dissolved which exposes interprismatic and prism areas for interlocking tag formation with the bonding resin
This is purely mechanical bonding, not true adhesion
The effect of etching?
Remove debris and surface enamel
Produce 10-20 fold increase in surface area
Increase free surface energy of enamel so that it exceeds surface tension of resin
Increases wetting
Bonding to dentine is
Dentine contains?
It’s difficult because…
......... the problem area Dentine contains 33% volume of an organic component 45% by volume of inorganic component 23% by volume of water It is moist living tissue
Dentine bonding agent, Ultimate aim is…..
we therefore need to change….
…. to bond a hydrophobic, highly viscous composite to a hydrophilic adherent
We, therefore, need something to change the properties of the dentine surface or smear layer from hydrophilic to hydrophobic
Mechanism
The basic mechanism of bonding to enamel and dentine is essentially an exchange process involving replacement of minerals (removed from either of the hard dental tissue) by resin monomers, which upon setting, become micro-mechanically interlocked in the created porosities
the smear layer is created by….
this results in…………
The smear layer created by the mechanical cutting of dentine. Dentine debris of variable thickness and smear plugs are formed which block dentinal tubules.
What are the benefits and drawbacks of the smear layer?
Can protect dentine and ultimately the pulp from penetration of bacteria
Eliminates diffusion of dentinal fluid
Impairs bond on composite to dentine
Its self is only relatively loosely bound
Can harbour bacteria
Steps in bonding to dentine- Acid etching
Acid etching
Improves retention of the restoration
Increases the surface area of the dentine
Removes the smear layer from prep
Allows for penetration of bonding agent into dentine
Protect pulp exposure before using
Steps in bonding to dentine- Primer
Primer Resin-monomer Improves wettability of prep Penetrates etch dentin tubules Applied in a thin layer, thinned air;blot May require light curing
Steps in bonding to dentine- Bonding adhesive
Bonding adhesive Unfilled or lightly filled resin Adhesive bonds to collagen fibre in dentin- mechanically 'locks-in'- 'hybrid layer' Applied in a thin uniform layer Light cured 10-20 seconds New 'generations being developed Dental composite is then applied
Fillers
Fillers are placed in dental composite to reduce shrikage upon curing
Materials such as strontium glass,barium glass, quartz, borosilicate glass,cermaic,silica, prepolymerized resin
Fillers Classification
Fillers are classified by material, shape and size
Fillers are irregular or spherical in shape depending on the mode of manufacture
why spherical particle used as filler
Spherical partials are easier to incorporate into a resin mix and to fill more space leaving less resin
One size spherical particle occupies a certain space
Adding small particles fills the space between the larger particles to take up more space there is less resin remain so less shrinkage on curing
