Flashcards in Dental materials - Luting cements Deck (32)
Properties of luting agents
Viscocity and film thickness
ease of use
Low to allow seating of restoration - dependant on filler particle size (<25micrometers)
ease of use
good setting and working time. Also easy to mix.
Able to see marginal breakdown and easily identified on Rg
Ideally bond to tooth - permenant and impeneatrable bond
Not shine through tooth, non staining and variable translucency
Fluoride releasing and bacteriostatic
No damaging pH, acceptable thermal reaction or conductivity.
High compressive, tensile strength
YM similar to tooth - 15GPa
Cement - ZInc Phosphate
Zinc Oxide - reactive agent
Magnesium dioxide - white colour/> compressive strength
Other oxides - alumina, silica - greater physical properties and varied translucency
aqueous solution of phosphoric acid
Oxides - buffer solution eg aluminium - consistency
Zinc oxide - slower setting reaction
Reaction of zinc phosphate
1. Acid base 2. Hydration
Aluminium oxide - prevents crystallisation leading to amorphous glassy matrix of acid salt surrounding unreacted ZnO powder. Insoluble but porous.This contains free water from setting reaction. Material matures and binds to water giving less porous material.
Issues with Zn Phosphate cement
Low initial pH 2 - Damage pulp, Exothermic setting reaction, Not adhesive to tooth or restoration, brittle, opaque, Npt cariostatic and final set takes 24hr
Zinc Polycarboxylate - Adv
BONDS TO TOOTH SURFACE, reduced heat of reaction, low pH quickly increases to neutral. Cheap.
Zinc Polycarboxylate - dis
Difficult to mix and manipulate.soluble in low pH environment, lower modulus and compressive strength that Zn Phos
Glass ionomer cements - Constituents
Acid - Liquid: Polyacrylic acid or tartaric acid
Base - Powder: Silica, alumina, aluminium fluoride, aluminium phosphate, calcium fluoride, sodium fluoride.
>silica means more translucent
GI - Setting reaction stages
Dissolution - acid in solution, H ions attack the glass particles causing the release of ions (Ca, Al, Na, F), leaves silica gel around glass particles.
Gelation - initial setting stage. Due to bivalent Ca ions crosslinking with polyacid by chelation with carboxyl groups. Formation of Calcium Polyacrylate.
Hardening - Trivalent Aluminium ions crosslinking causing an increasing in strength. Aluminium polyacrylate formation - takes 30mins to a week.
Difference between GI cement and luting cement
Smaller filler particle size - <20micrometers
How does GI bond to tooth
Ion exchange with calcium in enamel and dentine
Hydrogen bonding with collagen in dentine
NO bond to restoration - needs to be sandblasted for mechanical retention.
GI cement properties
low shrinkage, long term stability, insoluble once set, aesthetics good, self adhesive to tooth substance, fluoride release, cheap.
RMGI - contains HEMA, considerations of this.
HEMA is highly hydrophillic and can be cytotoxic if left uncured
Same acid base reaction but light curing causes polymerisation of HEMA and copolymers, some can have secondary REDOX reaction.
Improved properties of RMGI over GI
Command set, shorter setting time, longer working time, greater compressive and tensile strength, greater bond to tooth. reduced solubility.
Composite luting cement properties - use with DBA
Dual or light cured, better aesthetics, better mech properties
How to bond to direct composite
Composite can bond to composite.
Micromechanical - inlay rough internal surface
C=C chemical bond
Dual bond - can't light cure thoroughly
Tooth->DBA->Composite Luting Cement->Resin Inlay
Bonding to Porcelain
Porcelain = Brittle so needs to be bonded to tooth, prevent #
Treated porcelain with Hydrofluoric acid - etch surface
Gives rough retentive surface.
SUrface wetting agent required - Silane Coupling agent (SCA)
What is a silane coupling agent
Works like a DBA - Porcelain surface and oxide groups bond and C=C reacts with composite resin luting agent.
Bonding to Metal?
Metal needs to be treated - sandblasted to roughen surface. Etching or more likely sandblasting
Bonding to NPM
Materials with carboxylic/phosphoric acid derivatived resin monomers. Eg. MDP
Acidic and and C=C end
Acidic - metal oxide, renders surface hydrophobic.
(Metal Bonding Agent)
Bonding to Precious metal
Change composition to allow oxide formation eg. increaswe copper content and heat to 400 degrees