Bonding to Tooth Flashcards Preview

BDS2 CLINICAL Dental Materials > Bonding to Tooth > Flashcards

Flashcards in Bonding to Tooth Deck (63)
Loading flashcards...

what are the properties of a dental adhesive

 Provide a high bond strength to tooth tissues
 Immediate high strength bond
 Durable bond
 Impermeable bond (doesn’t allow fluid to pass through)
 Easy to use
 Safe


what are the factors that govern the ability of the adhesive to make intimate contact with substrate

 The wettability of the substrate by the adhesive
 The viscosity of the adhesive
 The morphology or surface roughness of the substrate


describe the structure of enamel

heterogenous structure
densely packed prisms
95% mineralized
made up of tiny crystals of hydroxyapatite which are packed together to form prisms, held together by organic matrix


describe the structure of the prisms in enamel

long, rod like shapes having a key hole cross section - aligned perpendicular to the tooth surface


describe the structure of hydroxyapatite crystals

flattened hexagonals
spaces left between crystals is occupied by water and organic material


enamel does have water in it, so why does it remain dry?

much of the water is bound within enamel structure and not easily removed on drying


What is the acid etch technique

surface modification through the application of acid


what does the acid etch do to the enamel

roughens the surface of the enamel
this allows micro mechanical interlocking of resin filling material


what does the acid etch do to enamel in terms of surface energy

increases the surface energy of the enamel surface
increases wettability of the enamel


what does an increased wettability allow

wettability allows resin to adapt better to roughened enamel surface


why must enamel be dry after acid etch

Moisture contamination will prevent flow of the resin into the etched surface.


what is enamel bonding essentially



what is usually used for enamel etching

35% phosphoric acid


what happens after the enamel is etched

 Generally a low viscosity bis-GMA resin or any one of a number of dentine bonding agent resins (often phosphorylated Bis-GMA) is applied to the etched and dried enamel surface to penetrate into the rough surface and light cured
 The higher viscosity composite resin filling material is then applied on top


what happens to the resin after it flows into the 'roughness'

 It polymerises which creates a strong bond greater than 20MPa which is more than enough to keep it in the mouth when chewing


describe the structure of dentine

permeable tubules
70% inorganic - mostly HA
20% organic - mostly collagen


what is the issue with the dentinal tubules being permeable

Fluid pumps up from the pulp to the dentine floor of any cavity making the surface wet


describe how dentine is an inconsistent material

o Dentine near the pulp has more tubules and increased moisture content
o Aged dentine is more mineralized


why does dentine have a low surface energy

because it is wet
dentine is hydrophilic but most bonding agents are hydrophobic


what is the smear layer

cadherent layer of organic debris that remains on the dentine surface after the preparation of the dentine during the restoration of a tooth
generally contaminated with bacteria
variably attached to dentine surface
0.5-5 microns thick


what are the requirements of a dentine bonding agent

ability to flow
Potential for intimate contact with dentine surface
low viscosity
adhesion to substrate mechanically, chemically and through van der waals


describe mechanical bonding in dentine

achieved by dentine bonding agent and the dentine surface meshing and interlocking with minimum gaps


describe what the etch does to the dentine surface

demineralizes the dentine surface so exposing the network of collagen in the dentine matrix and resin infiltrates the tubules


describe chemical adhesion in dentine

bonding at a molecular level


what type of bond does mineralized dentine have

ionic bond type


what type of bond does organic dentine have

covalent bond type


describe van der waals adhesion

based on electrostatic or dipole interaction between bonding agent and substrate


what does the strength of van der waals adhesion depend on

contact angle which is a good indication of wettability of a solid by a specific liquid


what is the contact angle which means the solid surface is hydrophilic

90 degrees


what is the critical surface tension

The critical surface tension of a liquid is the surface energy that will just spread on the surface of a solid