DM L1 Composites pt 3 Flashcards
(28 cards)
why are adhesives used in dentistry
tooth tissue is hydrophilic + restorative materials are hydrophobic -> no chemical bonding between them
- adhesives used to retain restoration in cavity, + bond the 2 for longevity
what can types of adhesive bonding are there
micromechanical
molecular entanglement
chemical
what are the 6 advantages of adhesives
- better aesthetics
- conservation of tooth tissue
- reinforcement of weak tooth structure
- range of techniques
- ↓ marginal leakage
- ↓potential for pulp sensitivity
what are the ideal requirements of adhesives
- provide high bond strength to enamel + dentine
- immediate + durable bond
- prevent ingress of bacteria
- safe + simple to use
what is the acid-etch technique which is the gold standard adhesive
bonding resin to enamel + used in placing anterior + posterior composites
describe enamel structure
- most dense calcified tissue
- heterogenous structure
- crystals of hydroxyapatite (Ca10(PO4)6(OH)2)
forming prisms - organic matrix/water holds prisms together
when would you need to bond composite restoratives to enamel
orthodontic appliances
bridges
what are the problems of bonding composite restoratives to enamel
- composites have no intrinsic adhesive qualities to tooth tissues
- composite resins = non-polar (hydrophobic)
+ enamel = hydrophilic - Surface tension of enamel < adhesive resin (~34-38mJ/m2)-> ↓ wetting (resin won’t cover enamel surface properly)
- Enamel has pellicle layer = ↓ surface energy ~ 28mJ/m2 prevents wetting
how is the pellicle layer removed + enamel is etched for restorative bonding?
acid-etch - 30-50% phosphoric acid added to enamel -> rough enamel results in micro-mechanical retention - good bonding between enamel + resin
what are the main reasons of using acid-etch technique for restorative bonding
removal of pellicle layer + contaminants allows:
- ↑ surface roughness of enamel -> ↑ bonding area
- ↑ surface energy
- ↑ wettability (resin runs into enamel rods)
- opens inner prism areas for interlocking tag formation
- ↑ contact area + micro-mechanical bonding for adhesion
what acid is used for acid etching and how does it work
- usual 37% phosphoric acid
- acid-base reaction starts
- acid dissolves enamel surface hydroxyapatite -> loss of enamel prism structure
- enamel = frosty look, etching is achieved
how do you apply the unfilled resin to the tooth + what to remember when applying
- apply low viscous resin ( unfilled Bis GMA)
- unfilled resin applied to dry/well etched enamel surface
- resin flows into etched enamel prisms + forms resin tags which penetrate to 30μm depth
- the filled resin applied on top of unfilled resin
how does microfilled resin bond to the unfilled resin in etched enamel + how does resin bond to etched enamel prisms
mech for adhesion for microfilled restorative resin bonding to unfilled resin = chemical bonding (methacrylate groups)
mech for adhesion into enamel prsims = molecular entanglement
what are the properties of enamel/resin
- Bond strength ~20MPa
-↑surface area
-Long-term efficacy - Failure of adhesive bond due to: poor clinical technique, failure of
bond along adhesive interface (due to contamination)
what 6 things is acid etch enamel technique can be used for
- fissure sealing
- direct composite/compomer restorations
- ceramic veneers
- resin bonded bridges
- orthodontic brackets
- periodontal splinting
why does a restorative resin have to be adhesively bonded to dentine
retain the restoration in cavity + eliminate marginal/internal gaps to prevent bacterial micro-leakage
why is it more difficult to bond restorative resin to dentine than enamel
- most resins = hydrophobic, but dentine = hydrophilic
- bonding agent needed to enhance bonding + retain restoration
- bonding agent = added strength to restored tooth
- prevent dentine hypersensitivity (dentinal tubules are sealed)
properties of dentine
Heterogeneous structure (70% mineral, 20% organic material, 10% water)
o Hydrophilic
o Vital (living tissue)
o Dentinal tubules communicate w/ pulp
what are the difficulties in bonding to dentine
when dentine cut:
- fluid is pumped through dentine tubules -> wet surface
- inorganic hydroxyapatite crystals broken + collage stretched, torn + smeared over cut surface
Cut dentine is covered by a smear layer. what is a smear layer
▸ composed of layer of denatured collagen + debris covering surface - weakly bound to dentine (0.5-5um thick)
▸ contaminated with bacteria (caries) + cutting debris
what are smear plugs
smear layer covers dentine tubules + can form smear plugs
how does the smear layer affect bonding to dentine
cut dentine results in wet surface - covered by smear layer –> acts as contaminant
so more difficult to bond to dentine
how do you achieve strong bonding to dentine + what happens to the dentine tubules
- strengthen in situ
- or remove smear layer completely
- when smear layer removed, dentine tubules are open + exposed to bacteria + irritants
why must the adhesive resin be effective seal that will seal dentine tubules ( why dentine bonding agents needed)
- when smear layer removed, tubules are open + exposed to bacteria + irritants
- adhesive resin must seal them so no contamination in the tubules
