Dental Materials: Dental Polymers

Comprehensive vocabulary flashcards covering the history, classifications, mechanical properties, polymerization reactions, and acrylic resins from Chapter 6: Dental Polymer.

Vulcanized rubber

A plant-derivative latex crosslinked with sulfur introduced in 1853 as an elastomeric denture base material that was flexible, allowed easy fabrication, and simulated the look of gingival tissues.

Celluloid

A nitrocellulose material adapted in 1853 as a denture base material; it absorbed stains, gradually became grossly discolored, developed odors, and was flammable.

Gutta percha

A plant exudate containing trans-polyisoprene introduced in the 1890s; a thermoplastic polymer used for temporary crowns, cavity fillings, permanent restorations, and root canal filling materials.

PMMA (Polymethylmethacrylate)

A polymer introduced in 1936 as a heat-processed, thermosetting material, and adapted in 1940 to fabricate inlays, crowns, and fixed dental prostheses.

Sevriton

The first tooth-colored resin for anterior teeth introduced in the 1950s (LD Caulk Inc., Milford, DE), composed of methylmethacrylate (MMA) monomer blended with powdered PMMA.

Resin-based composites (self-cured)

Materials introduced in the late 1950s by Dr. Ray Bowen based on a difunctional methacrylate monomer (bis-GMA or UDMA) reinforced by a dispersed phase ceramic particle filler, forming a highly crosslinked, durable polymer network.

Polymer

A macromolecule originating from the Greek 'polymeros' ('poly' meaning many, 'meros' meaning part), consisting of long chains of organic molecules with repeating units called monomers or 'mers'.

Polymerization

A repetitive intermolecular chain growth reaction that can reach molecular weights up to $50\text{ million}$.

Homopolymer

A polymer containing only one type of repeating mer unit, represented schematically as $\text{A-A-A-A-A-A-}$.

Copolymer

A polymer containing two or more chemically different mer units joined along the chain.

Random copolymer

A copolymer in which no sequential order exists among the two or more mer units along the polymer chain.

Block copolymer

A copolymer in which identical monomer units occur in relatively long sequences (blocks) along the main polymer chain.

Graft or Branched copolymer

A copolymer in which sequences of one type of mer unit are grafted onto a backbone chain of a second type of mer unit to form a branched configuration.

Thermoplastic Resins

Polymers that soften on heating and harden on cooling through a reversible reorganization of molecular chains, can melt, and are typically soluble in organic solvents (e.g., acrylic, polycarbonate, nylon).

Thermosetting Resins

Crosslinked polymers that undergo an irreversible chemical change during setting, char and decompose rather than melt, and are not softened by heat.

Plastic strain

Irreversible deformation that cannot be recovered and results in a permanent shape due to slippage (flow) among polymer chains.

Elastic strain

Reversible deformation that is quickly and completely recovered when stress is removed, caused by polymer chains uncoiling and recoiling.

Viscoelastic strain

A combined deformation consisting of both elastic and plastic components, where only the elastic portion is recovered once the applied stress is reduced.

Plastic Flow

An irreversible strain behavior where polymer chains slide past one another and relocate within the material, resulting in permanent deformation; it is impeded by branching and crosslinking.

Elastic Recovery

A reversible strain behavior in amorphous regions of polymers where randomly coiled chains straighten and recoil like springs to their original positions without sliding.

Plasticization

The lubricating effect produced when absorbed molecules (such as water) push polymer chains apart and facilitate slippage between them.

Addition Polymerization

A polymerization reaction in which monomers are activated one at a time and join sequentially without producing low-molecular-weight by-products.

Condensation Polymerization

Step-growth polymerization in which difunctional components are active simultaneously and link stepwise, typically releasing a low-molecular-weight by-product such as water or alcohol.

Induction stage

The initial stage of addition polymerization involving activation (generating free radicals via heat, chemicals, or light) and initiation (reaction of a free radical with a monomer double bond).

Propagation stage

The stage of addition polymerization where the active free radical center sequentially adds monomer units, rapidly extending the polymer chain with the release of exothermic heat.

Chain Transfer

A process during addition polymerization in which the active free radical of a growing chain is transferred to another molecule, creating a new radical center for further chain growth.

Termination stage

The final stage of addition polymerization where growth stops because reactive centers are destroyed through direct coupling or hydrogen atom transfer.

Methylmethacrylate (MMA)

A transparent liquid monomer with a high vapor pressure, molecular weight of $100\,\text{g/mol}$, boiling point of $100.8\,^\circ\text{C}$, and volumetric polymerization shrinkage of $\sim 21\%$.

Glycol dimethacrylate

A cross-linking agent added to MMA liquid that reduces crazing in the cured acrylic resin.

Hydroquinone

An inhibitor added to methylmethacrylate liquid to prevent premature polymerization during storage.

Sandy stage

The first stage of the polymer-monomer reaction characterized by no interaction at the molecular level and a coarse or grainy consistency.

Stringy stage

The second stage of the polymer-monomer reaction where polymer chains disperse into the monomer liquid, creating stringiness or stickiness when pulled apart.

Dough-like stage

The third stage of the polymer-monomer reaction in which an increased number of polymer chains enter solution, making the mixture smooth and ideal for compression molding.

Rubbery/Elastic stage

The fourth stage of the polymer-monomer reaction where the mixture rebounds when compressed or stretched and can no longer be molded.

Stiff stage

The final stage of the polymer-monomer mixture caused by evaporation of free monomer, leaving a dry mass that resists mechanical deformation.