ENAMEL BONDING

what is the most mineralised substance in your body

enamel

outline what enamel is

• teeth enamel is the hardest substance in your body 

• it covers the outer layer of each tooth and it is the most visible part of the tooth

is enamel vital or non-vital and why

• enamel is non-vital

• because once fully formed enamel does not contain blood vessels or nerves

• remineralisation can repair damage to a certain degree but damage beyond that cannot be repaired by the body

where is enamel the thickest on a tooth

• in humans, enamel varies in thickness 

• often it is the thickest at the cusp - up to 2.5mm

diagram of enamel on the Mohs hardness scale

outline the composition of enamel

• 96% hydroxyapatite

• 3% water

• 1% organic proteins

—

• hexagonal rods of mineral (5 micrometre diameter)

• prismatic arrangement perpendicular to tooth surface

• naturally covered in pellicle and usually plaque

why is enamel bonding done

so tooth coloured composite can be added to existing teeth and therefore:

• improve the appearance of teeth

• mask out discolouration

• prevent further wear and tear

how much tooth preparation does enamel bonding require

• no extensive tooth prep. is needed

• this means the tooth stays intact underneaath

• so should you need to remove the bonding materials your teeth underneath remains healthy

when did adhesive dentistry with acid etching begin

• in 1955

• with Buonocore

how is the enamel modified by acid-etch

• surface roughness is increased

• surface energy is raised

» better adhesion

how does the surface of enamel become rougher after acid-etch

• acid/ base reaction prompts partial dissolution of hydroxyapatite

• loss of enamel prism periphery and prism core constituents

• increase of surface bonding area

how does acid-etching raise the surface energy of enamel

• acid removes the pellicle which has low surface energy and exposes the underlying surface of enamel

  • pellicle - 28 mJ/m²

  • enamel - 42 mJ/m²

• acid raises surface tension and therefore encourages wetting

• typical surface tension of adhesive resin = 34-38 mJ/m²

what type of bonding does etching enamel allow for

micromechanical bonding

what % phosphoric acid is used to etch enamel 

35%

why is the concentration of phosphoric acid used 35%

higher concentrations would not offer better results 

what should be considered clinically when etching enamel to prevent problems

1. patient selection

2. enamel prophylaxis

3. application of etchant

outline patient selection and its importance

• the bonding area of enamel must be kept free of contaminants such as saliva or water because they are highly polar and resins are non-polar

• patients who will re-wet the dried surface should not be selected for the acid-etch technique » isolate with rubber dam

  • elderly/ frail

  • children

  • mentally ill

outline enamel prophylaxis in terms of restorative dentistry

• the resin needs to bond to the enamel, not the pellicle or any plaque on the tooth surface

• acid etchant will not completely remove plaque and the thick pellicle layer

• so the tooth must first be cleaned with a slurry of pumice and water for 30s using a bristle brush then dried

what is the best reason for not using prophylaxis pastes to clean the enamel prior to acid etching

oil residue reduces the wettability of enamel

what does this image show

outline the application of etchant

• apply the gel/ liquid by lightly dabbing the surface

• do NOT rub the etchant onto the surface

  • rubbing breaks the tags that the resin flows into and weakens the bond

• aspirate and wash the etched surface thoroughly to remove salts and excess acid

how quickly does the acquired pellicle form on a professionally cleaned tooth surface

≈ 1 minute

what is a dental material with a high contact angle

mercury