composites, polymerization, bonding

layer D

dentin

layer A

bonding agent

layer C

enamel

what is a composite

a material made up from two or more constituent materials w different physical or chemical properties than the ingredients

what is a dental composite generally made up of

essentially a complex combination of glass or ceramic filler in a resin polymer matrix

dental composite are increasingly popular materials for what type of restorations

direct restoration

what materials can you find in fillers

• glass

• non-glass base- like zirconia

what is the matrix primarily composed of

resin

is the filler or resin matrix more important

resin matrix

what is the family of the main dental monomers that are used in dental composites

di-methacrylate

what is the coupling agent that couples the glass to the resin (filler to the matrix)

silane coupling agent

what are the major components of composite

• matrix- polymer

• fillers- glass, ceramics

• coupling agent- organo-metallic compound

what are the minor components of composite

• initiator

• accelerator

• diluent

• surfactants

• pigments

• radio opaquer

how did older composites look radiographically

radiolucent → why there are radiopaquers that are put into composites

what is responsible for the radiopacity of the composite

fillers

what properties make a composite desirable

• good esthetics

• handling properties

• physical properties

what esthetic properties make a composite desirable

• shade matching

• durable gloss

• resistant to discoloration

what handling properties make a composite desirable

• adequate working time

• easy to manipulate

• good polymerization performance

• quick and easy polishing

what physical properties make a composite desirable

• matching mechanical properties of dental tissue

• durable under occlusal loads

• wear resistant, minimal abrasive wear effect on opposing teeth

• minimal shrinkage during and after light curing

dental composites are designed to have what relationship w water

designed to dislike water → hydroPHOBIC

cons to hydrophobicity of composite

• less bonding to water-based tissues

• cellular toxicity

pros to hydrophobicity of composite

• lower water sorption

• less water-driven expansion

• less staining

• less biofilm adhesion

is dentin or enamel more hydrophilic

dentin

what is the process of polymerization

the process of chemically linking many small monomers together to form a large polymer

degree of conversion

percentage of monomers that are incorporated into the polymer → WANT TO BE HIGH

residual monomer

unconverted monomers → we DO NOT LIKE

a ____ (low/high) degree of conversion and _____ (high/low) residual monomer is undesirable

a low degree of conversion and high residual monomer is undesirable

what type of polymerization rxn happens

free radical polymerization

what is the C-C double bond that will undergo polymerization from monomer to polymer

vinyl bond → will be broken and turn into polymer w some sort of radical, usually oxygen based

what does methyl methacrylate become after free radical vinyl polymerization

poly methyl methacrylate- PMMA

what is the bulky monomer that is the basis of most dental composites

BIS-GMA

size of these from smallest to largest:

BIS-GMA

HEMA

TEGMA

HEMA < TEGDMA < BISGMA

what is the single methacrylate called

HEMA

what are the di-methacrylates called

• BIS-GMA

• UDMA

• TEGMA

bulky monomers increase the viscosity or flowability

inc viscosity

less bulky monomers increase the viscosity of flowability

flowability

what is the linking in dental composites between di-methacrylate monomers

cross-linked

what is addition polymerization→ curing

when di-methacrylate monomers’ double bonds open up to allow the monomer to bond to neighboring monomers which results in the formation of cross-linked polymer network

what effect does the cross-linking network have on the composite

improves wear, lowers solubility, increases modulus, and increases strength

what is happening during polymerization shrinkage

C=C (vinyl) conversion results in smaller intermolecular distances, which in turn results in smaller composite volume

on average, composites shrink ___% linearly or __% by volume

0.5-1.5% linearly or 3% by volume

what can polymerization shrinkage lead to

debonding, leakage, caries, stress, hypersensitivity, fx, staining

what is the phase that does NOT react as part of the polymerization rxn

fillers → it is usually glass of ceramic in dental composites

how do fillers improve the physical properties of polymerized composites

• improve translucency, radiopacity, strength, wear resistance

• reduce volumetric shrinkage

what is the range of filler sizes used today

40 nm to 50 microns

how are composites names after

filler size:

• macrofill

• microfill

• nano-fill

• microhybrid fill

what are the two ways the degree of fill is measured

• volume %

• weight %

does volume % or weight % matter more to us, why

volume % → volume of the filler, the lower amount of shrinkage

what kind of strategies are used by manufactures to create a higher volume %

• pre-polymerized particles

• surfactants

• surface treatments

what happens if you have too much filler in a composite

results in unworkable viscous composite (high filler → high viscosity)

why are coupling agents important

critical to wear resistance, stain resistance, reduce crack propagation, surface integrity, and prevent particle dislodgment

what is dental curing

addition polymerization by free-radical initiation, an accelerator that facilitates free-radical formation

what are the three types of curing, put an asterisk by the one that is most common today

• heat cure

• chemical cure

• light cure*

when is heat cure typically used

• denture

• indirect restorations

• NOT IN PTS MOUTH

what are the main 2 types of LCU

• QTH light

• LED light

range of power density for QTH light

• older: 400-600

• newer: 800-1000

pros to QTH light

• broad spectrum

• high intensity- newer one

cons to QTH light

• lots of heat- even w filtering

• noisy

• fan

• cord

• longer curing time required

power density for LED light

1200

pros for LED light

• high output

• little heat

• battery driven

• no cord

cons for LED light

• the head or guide design may affect performance

• LED spectra may be too narrow for certain composites

what should you take into consideration for a light curing unit

• power density

• spectral output

• heat generation

• homogeneity of output

• intensity w distance

• tip design

• eye protection

why is power density a consideration factor for a light curing unit

must be sufficient to penetrate into the composite and cure the composite in a clinically reasonable time

why is spectral output a consideration factor for a light curing unit

must match the absorption of the photo-activator

why is heat generation a consideration factor for a light curing unit

show be low, or risk pulpal damage; should be <1 C rise for <1 min

why is homogeneity of output a consideration factor for a light curing unit

should be even across a cross-section of the output

why is intensity w distance a consideration factor for a light curing unit

degree of decay w distance

why is tip design a consideration factor for a light curing unit

should be convenient use

why is eye protection a consideration factor for a light curing unit

it is not UV but do NOT stare

what is etch made up of

phosphoric acid, 35% gel

etch is thixotropic, what does this mean

stays where you put it

why is it important to get a rough surface prior to bonding and placing composite

good micro-mechanical possibilities for bonding

anything you want to bond to, do you want to have a high or low surface energy

high

what is the purpose of etching

to increase surface energy → will rough surface, don’t want to do too much tho!

what is the main challenge to bond to dentin

dentin is wet, collagen mineral while composites are hydrophobic, the bonding agent will need to link the two

why is dentin etching not the same as enamel

it may be etched too deep, be too wet, or be too dry