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Dental Material Science > Adhesion to Enamel and Dentine > Flashcards

Adhesion to Enamel and Dentine Flashcards

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1
Q

Definition of adhesion

A
  • Complex physiochemical process occuring at the interface of 2 (solid) materials brought into intimate contact
  • Results in the formation of an attractive force between two materials
  • Covalent or ionic bonds are not necessary
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2
Q

Definition of adhesive

A

-Holds two substances together (adherend) without failure of the bond

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3
Q

Requirements of an adhesive to make a good bond

A
  • Intimate contact with the surface

- Adhesive layer thickness

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4
Q

Different forms of adhesion

A
  • Mechanical
  • Chemical
  • Intermolecular bonding
  • Diffusion
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5
Q

Mechanical adhesion definition and examples

A

-Rough or porous surface provides stronger adhesion due to:
Large interfacial area
Micromechanical retention of the adhesive into the surface microvoids

Eg. acid etching of enamel
orthodontic brackets

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6
Q

Chemical adhesion definition and examples

Distinguishing between types of chemical bonds

A
  • Molecules of the adhesive may form chemical bonds with the molecules of the adherend
  • Chemical bonds can be ionic or covalent
  • Amount of electronegativity determines the amount of covalent/ionic that occurs
  • Ionic is when there is dissimiliar electronegativity
  • Covalent is when there is similiar electronegativity
  • Examples:
  • Free radical reaction of vinyl groups (impression materials)
  • Reaction of isocyanates to hydroxyl groups
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7
Q

Diffusion adhesion definition and examples

A

-If the molecules of the adhesive and adherend are similiar, it may allow for the molecules to move across the interface

-For example,
Composite repairs (placing a composite on a previously broken composite)
Dentine bonding agent

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8
Q

Ideal properties of an adhesive

A
  • Should wet the surface of the adherend
  • Low contact angle and surface energy appropriate to allow wetting
  • Surface energy of the adhesive must be lower than the surface energy of the substrate
  • A lower surface energy material will wet a higher surface energy surface

-Flow over the substrate
Initially you want a low viscosity adhesive

-Thickness of adhesive layer very important
Should be as thin as possible to effectively cover all the surface
Allows intimate contact between the two materials

-Displacement of air from interface
Almost all adhesives undergo polymerisation so all have an oxygen inhibition layer
Helps minimize stress concentration
Avoid inhibition of polymerisation

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9
Q

Adhesion test methods

A
  • Depends upon adhesive application
  • Utilize shear and tensile tests
  • Basically work out the force to break the two adherends

Peel tests
Wedge tests
MMDB and End Notch Flexure (ENF) tests

Microtensile Testing

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10
Q

Best way to calculate composite bond strength to enamel/dentine in a tooth

A

Microtensile bonding

  • Bond composite occlusally
  • Cur up the tooth into slices
  • Cut each slice into matchsticks
  • Calculate tensile force required to pull composite from each matchstick
  • Can do the same thing but bond the resin to the enamel outside and make the slices that way
  • Basically it can be sectioned whichever way you want
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11
Q

Best way to calculate composite bond strength to coronal dentine/cervical dentine/middle root dentine

A

Microtensile bonding

  • Cut cavity in the long axis of the tube
  • Build up composite along the long axis of the tooth
  • Section the tooth into slices perpendicular to the long axis (enamel, coronal dentine, cervical dentine etc)
  • Trim the bonding surfaces further to give a bonded surface area of 1mm^2
  • Measure tensile bond strengths at a cross head spead of 1mm/min
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12
Q

Structure of an adhesive joint

A
  • Substrate 1
  • Interface between Structure 1 and Adhesive
  • Adhesive
  • Interface between Adhesive and Substrate 2
  • Substrate 2
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13
Q

Features of the adhesive joint and what they control

A
  • Physical and chemical properties of the adhesive may differ at the non contact points (Especially the core as it will be homogenous)
  • Generally believed that the boundary layer composition controls the durability and strength of an adhesive joint
  • Also mainly responsible for the transfer of stress from one adherend to another
  • Frequently the sit of environmental attack leading to joint failure
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14
Q

Modes of failure of adhesion

A

Structural failure: within the material
Cohesive failure: within the adhesive itself
Adhesive failure: at the interface

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15
Q

What type of failure is likely to result from a thick adhesive layer

A

Cohesive failure

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16
Q

Enamel etching process and resultant surface

A
  • Leads to an irregular surface due to selective dissolution of hydroxyapatite
  • Allows fluid adhesive to penetrate, which leads to the micromechanical retention
  • Acid etching of the enamel selectively erodes certain hydroxyapatite formations that facilitates penetration of the adhesive forming resin tags
  • Standard etchant is 37% orthophosphoric acid for 20 seconds
  • Very large increase in surface area

-High energy micro-rough surface is created after rinsing and drying

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17
Q

Difference in etching procedures with uncut and cut enamel

A
  • 37% OP acid for 20s on cut enamel

- 37% OP acid for 30-60s on uncut enamel (ortho treatment)

18
Q

What does acid etching achieve

A

-Removes about 5 microns from the surface including the adsorbed pellicle, amorphous CaP layer, smear layer if present (cut surfaces)

  • Exposes enamel prism/rod structure
  • When dry a high energy surface results
  • Incrreases surface area for bonding
  • Produced micro-irregularities/micro-porosities in the prismatic enamel surface. Surface roughness will provide the micro-mechanical retention for the resin
19
Q

Liquid v gel prosphoric acid

A
  • Studies show you get more uniform spreading if it is a gel
  • More homogenous
  • Compared to liquid phosphoric acid
20
Q

When etching enamel, where are you most likely to get a failure and why

A
  • Interrod region
  • Different orientation to enamel rods
  • Path of local fracture in most instances is through the interrod and parallel to the rod head
21
Q

How does enamel etching change with rod orientation and clinical relevance
How was this measured
What if you used self-etching systems instead of etch and bond

A

If you etch parallel to the rods, there is a 40% reduction in bond strength compared to if you etch perpendicular to the rod direction
-How you cut your enamel affects bond strength

-But, sometimes you cant avoid cutting parallel to the rods

Microtensile bonding when you cut the enamel in different planes

-Self etching systems provide more unifrom bonds when cavity walls are considered no matter of the plane in which you are measuring

22
Q

Sealant definition and types

A
  • Cost effective caries preventive measurement
  • Care in placement is critical to success
  • Filled, unfilled
  • Self cured
  • Light cured
  • No difference in efficacy
  • Phosphoric acid etching required
23
Q

Difficulty in bonding to dentine and contents of a DBA

A
  • Dentine hydrophilic
  • Composites hydrophobic
  • Dentine is vital and has organic and inorganic components
  • Dentine is covered by a smear layer

-Dentine bonding agent may consist of an etchant, primer, sealant/bonding agent
or
Weak self etching primer/strong self etching primer
bond

24
Q

Adhesive monomers for dentine
Examples of hydrophilic end
Examples of adhesive monomers

A

-Di/bifunctional monomers with hydrophobic and hydrophilic end groups separated by a hydrocarbon chain
-Hydrophobic end undergoes polymerisation
-Chain length between groups is important
-Hydrophilic groups:
Hydroxyl
Carboxyl
Phosphate
Sulphate

  • For example HEMA and 4-META
  • In presence of moisture, the anhydride reacts to form two carboxyl groups
  • Responsible for adhesion
  • Monomer requires special catalyst for polymerization
  • Bonds to metal (base) and enamel/dentine
  • Component of dentine bonding agents
  • MDP (methacrylate demethylphosphate) is a component of dentine bonding agent
  • It is an etch and bond molecule
  • Phosphate group has a mild etching effect but can also bond to hydrophilic part of dentine
25
Q

How does 4-META monomer work

A
  • In presence of moisture, the anhydride reacts to form two carboxyl groups
  • Responsible for adhesion
  • Monomer requires special catalyst for polymerization
  • Bonds to metal (base) and enamel/dentine
26
Q

How does MDP monomer work

A
  • Methacrylate decamethylphosphate
  • Key component of DBAs and for cements adhesive to metals
  • Length of carbon chain is critical to the performance
27
Q

How many adhesive monomers should be present compared to total number of monomers to be effective

A
  • 2-10% by weight of total monomers to be effective

- Alternative is to apply from solvent to coat a surface

28
Q

Use of adhesive monomers in the bonding to ceramics

A
  • Adhesive monomers effective in the bonding to ceramics
  • Achieved by samdblasting to create a roughened surface
  • Then place adhesive monomer in order to bond to alumina and zirconia
29
Q

How do dentine tubules change as you go from pulp to EDJ and what is the significance of this

A
  • Tubules are bigger in diameter closer to the pulp

- Get smaller closer to the EDJ

30
Q

What you can do with the smear layer of dentine

How is a smear layer produced

A

-Can either remove the smear layer achieved by acid etching
-Smear plugs into dentine tubules
or you can incorporate the smear layer into the bond
-Any mechanical manipulation of dentine creates a smear layer
-Bur, hand instrument, wooden stick

31
Q

Difference in bond strengths between tubules at the pulp and EDJ and why

A
  • Tubule diameter increases as you get closer to the pulp
  • So you have higher bond strengths closer to the EDJ
  • Reduces the closer you get to the pulp
32
Q

Significance of composite shrinkage stress in Class I restorations

A
  • Deformation of tooth places additional stress on the bonding
  • Weakest bond fails (pulpal floor)
  • Often fluid flow path to pulp leading to postoperative hypersensitivity
33
Q

Role of etching on dentine

A
  • Removes the dentine smear layer
  • Helps to unblock and widen the dentine tubule orifices
  • Exposes the network of collagen n the dentine matrix
34
Q

Significance of aqueous environment when etching dentine

A
  • If air-dried, the collagen matrix collapses

- If moist bonding occurs, the collagen remains erect

35
Q

Why you shouldn’t overetch dentine

A

-Overetching coupled with incomplete rehydration of collagen might leave unfilled micro/nano-porosities within the depth of the hybrid zone and subsequent fluid movement may lead to post operative sensitivity and bond degradation over time

36
Q

Hybrid zone definition

A

-Degree of resin penetration into collagen

37
Q

Type 1 DBA

A
  • Each stage considered separately
  • Dentine should be etched for 10-15s, enamel for 20s with 37% OP acid
  • Washed away thoroughly and dried until enamel appears frosty white
  • Primer contains water so over-dried collaged on the dentine surface will rehydrate up to a point, permitting the primer and bond to penetrate the collagen network
  • Then you place bond (resin component of the composite without the filler particles)
  • Universally accepted that type 1, 3-bottle systems provide a good quality and reliable bond and are the gold standard for dentine bond measurement in lab studies
38
Q

Type 2 DBA

A

‘Total Etch or Etch and Rinse’

  • Initial etch which is then rinsed away thereby removing the smear layer
  • Imperitive not to overdry the exposed collagen network as not rehydrated by the secod bottle
  • Moist bonding must be employed using cotton wool pledgets or very gently air drying
  • Ensures collagen network remains erect and supported
  • Primer and bond are combined
  • Essential to evaporate the solvent carrier (acetone or alcohol based) as remnants will contaminate and weaken the final bond
  • Also thins adhesive on cavity walls and operator must ensure that there is enough adhesive present before the photo curing stage (cavity walls must appear shiny)
  • Multiple applications of adhesive may be required prior to resin composite restoration placement
39
Q

Type 3 DBA

A
  • Acid phosphate monomers in the primer act as a mild etchant
  • No separate etching/rinsing/drying phase is required
  • No moist bonding
  • Dentine is etched sufficiently to partially dissolve the smear layer and expose collagen network
  • However, enamel margins may be etches less effectively, possibility of stained margins of restorations therefore in the long term
  • Problem is prevented by pre-etching the enamel margins with 37% orthophosphoric acid for 20 seconds
  • solvent again must be evaporated after the acidic primer is rubbed on to the dentine surface as in type 2 systems
40
Q

Type 4 DBA

A
  • Cinically most simple
  • But each stage is compromised
  • Decent bond strngths
  • presence of water blisters in the adhesive layer as it acts as a semi permeable membrane, drawing water from the wet dentine tubules
  • As hydrolysis of polymeric dentine bonds occur, there is evidence that marginal discolouration is more of an issue with these adhesives
  • Vigorous evaporation of water based solvent in the adhesive may reduce this problem

Dental Material Science (13 decks)

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