DM- Ch 5 Direct Polymeric Restorative Materials PT 1

Direct Polymeric Restorations

Polymeric restorations fabricated and placed directly into a prepared tooth cavity and hardened/polymerized chairside

-Tooth colored filling materials

Monomers

Small molecules

• Can form a repeating pattern when covalently bonded to one another

• Covalent bonding is the sharing of electrons between atoms

Covalent bonding

2 atoms share a pair of electrons

- Non-metals only

Polymers

chemical compound that is formed by chemically reacting molecular monomers that connect by covalent bonds

Polymers arrangement

simple repeating structure to form a larger molecule,

a macromolecule

- Multiple monomers connected by covalent bonds

Polymers shaped

like long chains; they can be linear in structure,

branched or cross-linked

Polymerization

chemical reaction that joins two or more monomer molecules together to produce a larger polymer molecule (macromolecule)

Two Types of Polymerization Reactions

1. Condensation Polymerization

2. Addition Polymerization

Condensation Polymerization (step-growth polymerization)

Reaction between two monomers, repeats itself as monomers are condensed to create a polymer

-Impression materials

Addition Polymerization (chain-growth polymerization)

• Acrylic resins

• Composite materials

• Cements

• Sealants

• Adhesives

Condensation Polymerization involves

a condensation reaction meaning byproducts such as water are released

• This is the type of reaction was discussed with impression materials

Addition Polymerization

Reaction between monomers, repeats itself as monomers are added to polymer, occurs in stages

• A chain reaction that adds new monomer units to the growing polymer molecule one at a time, the reaction creates NO BYPRODUCTS

Addition polymerization is

EXOTHERMIC

- reaction generates heat because the process breaks the weaker bonds in monomers and replaces them with stronger, more stable bonds in the resulting polymer chain

Addition polymerization involves

Carbon-to-Carbon double bond with side groups bonded to them that determine the chemical and physical properties

• Acrylic resins and composite materials (restorative materials, cements, sealants, and adhesives) are all set by Addition Polymerization

Types of Polymers

-Thermoplastic

-Thermoset

Thermoplastic Polymers involve

a physical change when converting soft to hard material

• Materials that can be heated (thermos) and molded or shaped (plastic) after the polymerization reaction

Example of thermoplastic polymers

You heat a mouthguard to soften it and bite into it to take on the shape of your teeth, as it cools, you have a harder material with the replica of your teeth

This reaction involved polymers

with linear chains, these melt easily

• Cross-linked polymers tend not to melt

These materials can be easily recycled

because they can be re-melted and reprocessed

Thermoset Polymers materials

with cross-linked structure, they don't melt, they decompose

• Cross-linking increases toughness and strength

Thermoset polymers cannot be heated and molded

they must be in their final shape when polymerized

Thermoset Polymers tend to

be STRONGER and tougher than thermoplastic materials

Most dental resins are cross-linked

and are THERMOSET

Steps of Addition Polymerization

• Initiation

• Propagation

• Termination

Initiation

Before anything can connect, the chemicals inside the resin need to be activated/energized to produce FREE RADICALS

Free radicals

atoms containing an unpaired electron

• This makes an unstable number of electrons in the outer shell making the atom in constant search to bind w/ another atom or molecule to stabilize themselves

Initiation Pt 1

A catalyst activates the reaction

• Occurs when the initiator molecule is activated to trigger the polymerization reaction

Initiation Pt 2

Free radicals, highly reactive particles with an unpaired electron that attack monomer molecules to start polymer chain reaction

Initiation Pt 3

Involves several activation methods

• Reaction can be initiated by heat, light, or a chemical reaction

A chemical reaction can

begin with two chemicals being mixed or started by light

Materials are classified by their activation methods

Heat, chemically, light, or dual cure activated

Heat activated

Heat cure

Chemically activated

Cold cure or chemical cure

Light activated

Photo or light cure

Dual Cure Activated

Cured by light and chemical activation

Activation of Addition Polymerization

• Heat Activated Acrylic Resins

• Chemically Activated Acrylic Resins

• Light Activated Dental Materials

• Dual-Cure Materials

Heat-Activated Acrylic Resins

Powder and liquid are mixed to create a dough material, molded, polymerized when heated, typically in a hot water bath

• Denture bases

Chemically Activated Acrylic Resins

Variety of chemicals used as the activator

• Typically a powder and a liquid mixed together causing a polymerization via chemical reaction

• Used to make temporary crowns, custom trays, orthodontic retainers, etc.

Light-Activated Dental Materials

Activator absorbs light, reacts with initiator, polymerization occurs due to light

• Single paste, no mixing required

• Commonly composite restorative materials, a few acrylic products

Dual-Cure Materials

Polymerization started with light, deeper material by chemical activation

Propagation

second reaction occurs no matter the activation method used in the first reaction

• Occurs when the free radical, which has an unpaired electron (unhappy) wants to form an atomic bond with one of the electron pairs of the carbon-carbon (C=C) pairs of the monomer

Instead of a group of three electrons during propagation

single C-C bond and another free radical on the end of the growing chain are formed

Propagation is the

initiation of chain-growth, explosive chain reaction and occurs repeatedly adding to the chain until there is no longer a free radical

As monomers join

they shift the free electron to the very end of the growing chain

Termination

The chain reaction does not go on forever, the chain growth ultimately stops

Chain growth ultimately stops when

• Two growing chains collide and their active free electrons cancel each other out

• All available monomers have been used up in the mixture

• The activation method halts, no more free radicals are produced

Working Time

The time to place, mold and shape the restoration

• It is longer with chemical activated and shorter with light activated

To be able to use dental materials properly,

an INHIBITOR is added to slow the rapid polymerization reaction to allow time to complete the task

• Usually involves destroying free radicals

Shelf Life

How long you can keep the resin before it expires

• There are added inhibitors in the liquid component to preserve and lengthen the shelf life

Acrylic Resins were

once used for anterior restorations

Acrylic resins

• They were very susceptible to recurrent decay

• Became obsolete when composites became available

• Currently, acrylic resins continue to be used primarily for denture bases

Dental composites come

in a variety of shades and colors

Handling Characteristics of Composites

• Can be flowable, more of a viscous liquid state

• Can be condensable, packed into a preparation

Components of Dental Composites

1. Matrix

2. Fillers

3. Silane Coupling Agents

4. Polymerization Systems

Factors of fillers

• Size

• Evolution

• Content

Polymerization Systems of Composites

• Chemically Activated Materials

• Light Activated Materials