Adhesion Flashcards
What is bonding?
force that binds two dissimilar materials together when they are
brought into intimate contact
What is adhesion?
surface attachment that involves some types of
intermolecular attraction between adhesive & substrate
What is an adhesive (adherent)?
material or film added to produce adhesion
(always liquid)
What is an adherend?
substrate to which the material adhered (tooth and restorations)
What is a adhesive joint?
the result of interactions of a layer of intermediate material (adhesive) with two surfaces (adherends) producing two adhesive
interfaces
What is the meaning of hydrophilic?
having a tendency to mix with, dissolve in, or be wetted by water (water lover)
What is the meaning of hydrophobic?
having a tendency to repel or fail to mix with water
What is smear layer?
a layer of microcrystalline & organic particle debris that is found spread on surface of tooth structures (enamel & dentin) after
instrumentation
What is etching?
selective demineralization of tooth structures by using strong acid (phosphoric acid) for certain period of time (15-30 seconds) to create micro pores (for resin composite)
What is conditioning?
cleaning of tooth structures by using weak acid (polycarboxylic acid) for certain period of time (10-20 seconds) for glass ionomer,
What is infiltration/impregnation?
flow of adhesive inside the previously created micro pores and in-between the exposed collagen fibrils
What is priming?
preparation of dentin surface after etching to facilitate adhesive
infiltration in between collagen fibrils to form a hybrid layer and It is done by a liquid called primer
What is done to prepare dentin surface?
- re-expansion of collapsed collagen fibrils (for infiltration)
- dry the wet dentin surface
- copolymerize with the adhesive
What is the hybrid layer?
a layer formed in dentin only due to infiltration of adhesive in between exposed collagen fibrils & inside the demineralized inorganic
part of dentin; formed on inter-tubular dentin & responsible of the bond
strength to dentin surface
What are micro-tags?
when adhesive is inside micro-pores (infiltrated) and setting is done
What is the different between micro-tags and tags?
micro-tags are done on enamel while tags are done on dentin
Micro-pores are also known as…
micro-irregularities
What is the clinical significance of adhesion?
- provide stable and long term retention of restoration
- provide better resistance against fracture of tooth or restoration so the tooth and restoration act as one unit and so reinforce the weakened tooth structure
- maximise tooth conservation (no removal of sound tooth structure to provide resistance and retention)
- reduce microleakage at tooth/restoration interface (no post-operative hypersensitivity, marginal staining or caries)
- expand use of aesthetic restorative dentistry (repair of restorations, aesthetic “invisible” direct restorations, veneers and orthodontics)
Wat are the mechanisms of adhesion?
- physical adhesion: involves electrostatic interactions that are weak
- chemical adhesion: where there is bonding at the atomic or molecular level across the interface
- mechanical adhesion: substrate has undercuts or irregularities that produce interlocking of materials
What type of retention do adhesive restorations have?
micro-mechanical retention
What is the mono-block concept?
restoration and tooth structure act as one unit to avoid wedging of amalgam
Bonding is not material, it is…
principle
What are the requirements for adhesion?
good wetting
What is wetting?
degree of spreading of one drop of liquid on a solid surface
How is wetting measured?
contact angle (angle formed by adhesive with adherend)
What are the types of contact angle and their relation to adhesion?
- 0 or 180 degrees = maximum adhesion
- less than 90 degrees = moderate adhesion
- more than 90 degrees = poor adhesion
What are the requirements for successful wetting of adhesive?
- intimate contact between adhesive and tooth tissues (adherend)
- cleanliness and dryness of tooth tissues
- high surface energy of tooth tissue
- low surface tension of adhesive material (adherent)
- low viscosity of adhesive to flow and displace air and moisture
What is required for sufficient wetting?
surface tension of adhesive must be less than surface energy of the adherend
What are the types of classifications of contemporary dental adhesion?
- according to smear layer handling mechanism
- according to adhesion strategy
- according to clinical application steps
- chronological classification (not required)
According to smear layer handling mechanism, there is…
- smear layer removing adhesives (total removal of smear layer and smear plug)
- smear layer dissolving adhesives (dissolution)
- smear layer modifying adhesives (rinsing and adhesive)
What are the disadvantages of smear layer removing adhesives?
- hypersensitivity
- death of pulp
What are the advantages of smear layer dissolving adhesives?
- no hypersensitivity
- no death of pulp
According to adhesion strategy (scientific classification), there is…
- etch and rinse adhesives
- self-etch adhesives
- glass ionomer adhesives
What is the strongest adhesive for bonding of enamel and dentin?
etch and rinse adhesives
According to clinical application steps, there is…
etch and rinse adhesives
- 3 steps (etching + priming + bonding)
- 2 steps (etching + primer and adhesion in one bottle)
self etch system
- 2 steps (self-etch primer + adhesive)
- one step (all in one adhesive)
glass ionomer system
- 2 steps (conditioning + bonding)
What are the disadvantages of etch and rinse adhesives?
- post-operative hypersensitivity
- risk of pulp necrosis
When is universal adhesive is used?
- self etching for dentin
- etch and rinse for dentin
What is the gold standard adhesive?
etch and rinse adhesives
What are the advantages of self-etch adhesives?
- no separate etching
- good bonding to dentin
Is bonding to enamel easier than bonding in dentin?
yes
Why is enamel easier to bond than dentin?
- enamel is almost homogenous in composition and structure, irrespective of its depth or location
- composed of 96 wt% in-organic content, mainly hydroxyapatite crystals arranged as enamel rods
- possesses a high surface-free energy
What are the problems in bonding to dentin?
- heterogeneous composition: it contains high percentage of water and organic content, mainly collagen, and only 70 %wt hydroxyapatite
- complex histological structure: It is composed of numerous dentinal
tubules surrounded by peri-tubular dentin in addition to inter-tubular
dentin which is less mineralized - inherent intrinsic wetness: the dentinal tubules are filled with dentinal fluid at constant wetness (deep dentin has more intrinsic wetness)
- dentin is a dynamic tissue with continuous physiologic and pathologic changes
- presence of smear layer on the cut surface
What causes the formation of smear layer?
cutting of dentin with hand and rotary instrumentation –> smear layer (2-5 microns) is formed on the surface of dentin
Is smear layer found in enamel?
yes
What are the properties of smear layer?
- this layer is burnished on the cut surface by the effect of heat and
pressure of cutting –> not removed by rinsing - tt is formed of chips, hydroxyapatite crystals, collagen, saliva and blood and microorganisms
- becomes packed inside the dentinal tubule –> smear plug
- in enamel, it is composed of larger apatite crystals tightly bound by
salivary glycoprotiens and microorganisms
What is selective etch and rinse adhesive (smear layer removing
adhesives)?
- incorporate etching step (total etching of enamel and dentin) using 30-40% phosphoric acid and etching time of 15-30 seconds
- acid etchant is supplied in the form of a liquid or colored gel (gel form is preferred because it is easier to control)
- etchant must be rinsed with water for 5-10 seconds to remove the
acid and the dissolved calcium phosphates
What are the steps of selective acid and etch adhesive?
- selective demineralization (etching)
- priming
- bonding (infiltration of adhesive resin)
What are the advantages of etch and rinse adhesives?
- effective bonding with enamel and dentin with long-term clinical results
- 3-steps adhesives are considered the gold standard of adhesives
What are the disadvantages of etch and rinse adhesives?
- time consuming due to multi-steps required
- risk of over-etching (pulp necrosis) due to aggressive phosphoric acid
- post-operative sensitivity due to dentinal fluid movement
What are self-etch adhesives (smear layer dissolving adhesives)?
- self-etch adhesives are without separate etching step
- they use acidic primers, called self-etching primers, which condition and prime the tooth substrate at the same time
- dissolved smear layer and the demineralization products are not rinsed away but incorporated in the adhesive resin and into the hybrid layer.
- the system is either 2-step or 1-step (all in one)
What is the procedure glass ionomer adhesives (smear layer modifying adhesives)?
- conditioning dentin with weak concentration (10-20%) polyalkenoic
(polyacrylic) acid for 10 seconds removes the smear layer but not the smear plugs –> clean dentin surface –> shallow demineralization for hybridization and sufficient residual hydroxyapatite for chemical bonding - the acid is then rinsed with water
- the resin-modified glass ionomer bond is placed
What are the advantages of glass ionomer adhesives?
- self-adhesive system
- cariostatic potential by release of fluorides
What is the disadvantage of glass ionomer adhesives?
no long term clinical data
What is the ideal bonding protocol with cases in which bonding to enamel and dentin will be needed
selective etch technique
What is the protocol of selective etch technique?
enamel etching using phosphoric acid for 30 seconds
- no etching of dentin is required
- application of universal adhesive on enamel & dentin –> with enamel it works as etch & rinse adhesive (it requires etching) –> with dentin it works as self-etch adhesive (no need for etching)
- light curing of the universal adhesive for 20 seconds
What are the advantages of selective etch technique?
- provides maximum bond with enamel & dentin
- etching of enamel guarantee perfect sealing of the restoration margin (no leakage)
- minimizes post-operative hypersensitivity & risk of pulp injury as dentin etching was excluded
What are the indications of selective etch technique?
- Anterior & posterior resin composite restorations
- cementation of indirect composite and ceramic restorations
- cementation of ceramic crowns & veneers
- used in all cases of bonded restorations
