Dental materials - Luting cements Flashcards Preview

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Flashcards in Dental materials - Luting cements Deck (32)
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1

Properties of luting agents

Viscocity and film thickness
radiopaque
ease of use
marginal seal
aesthetics
solubility
cariostatic
biocompatible
Mechanical properties

2

Viscocity

Low to allow seating of restoration - dependant on filler particle size (<25micrometers)

3

ease of use

good setting and working time. Also easy to mix.

4

Radiolucent

Able to see marginal breakdown and easily identified on Rg

5

Marginal seal

Ideally bond to tooth - permenant and impeneatrable bond

6

Aesthetic

Not shine through tooth, non staining and variable translucency

7

Solubility

LOW

8

Cariostatic

Fluoride releasing and bacteriostatic

9

Biocompatible

No damaging pH, acceptable thermal reaction or conductivity.

10

Mechanical props

High compressive, tensile strength
High hardness
YM similar to tooth - 15GPa

11

Cement - ZInc Phosphate

Powder:
Zinc Oxide - reactive agent
Magnesium dioxide - white colour/> compressive strength
Other oxides - alumina, silica - greater physical properties and varied translucency

Liquid:
aqueous solution of phosphoric acid
Oxides - buffer solution eg aluminium - consistency
Zinc oxide - slower setting reaction

12

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.

13

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

14

Zinc Polycarboxylate - Adv

Polyacrylic acid
BONDS TO TOOTH SURFACE, reduced heat of reaction, low pH quickly increases to neutral. Cheap.

15

Zinc Polycarboxylate - dis

Difficult to mix and manipulate.soluble in low pH environment, lower modulus and compressive strength that Zn Phos

16

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

17

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.

18

Difference between GI cement and luting cement

Smaller filler particle size - <20micrometers

19

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.

20

GI cement properties

low shrinkage, long term stability, insoluble once set, aesthetics good, self adhesive to tooth substance, fluoride release, cheap.

21

RMGI - contains HEMA, considerations of this.
Setting reaction?

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.

22

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.

23

Composite luting cement properties - use with DBA

Dual or light cured, better aesthetics, better mech properties
Eg. NX3

24

How to bond to direct composite
eg. Inlay

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

25

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)
Tooth->DBA->Composite LC->SCA->Porcelain

26

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.

27

Bonding to Metal?

Metal needs to be treated - sandblasted to roughen surface. Etching or more likely sandblasting

28

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)

29

Bonding to Precious metal

Change composition to allow oxide formation eg. increaswe copper content and heat to 400 degrees

30

Explain self Adhesive composite resins

metal coupling agent incorporated into resin. Eg. MDP used in Panavia
Tooth->DBA->SEcomp(Panavia)->NPM