physical properties of dental materials

lecture given 3/12/2026

ionic bond

very strong electrostatic force

covalent bond and metallic bond

strong electrostatic force

hydrogen bond

weak electrostatic force

van der waals forces

very weak electrostatic force

what are bulk material properties?

basic physics- mass, volume, state, density, porosity, phases

liquid- solution

solid- bulk, foam, grains, powder, particulate

multiple phases- paste, slurry, suspension, hydrogel, composite, IPN

optical- translucency, gloss, refractive index

solid mechanics- strength, toughness, resilience, hardness, ductility, brittleness

fluid mechanics- viscosity, viscoelasticity (creep, relaxation)

electric: resistance, electrochemical potential

thermal: melting point, boiling point, thermal conductivity, thermal expansion, glass transition point, thermal diffusivity

solubility: solvent resistance, water sorption

durability: color stability, resistance to thermal cycling, chemical cycling, permeability

color is NOT a real physical property

what are thermal properties?

thermal expasion: CTE (coefficient of thermal expansion)

thermal diffusivity, thermal conductivity: rates of conducting heat

thermal capacity: heat the material needs for elevated temperature

thermal expansion of different layer of materials can cause interfacial stress, leading to bonding failure

thermal expansion and shrinkage leads to…

internal stress, and decreased mechanical properties

list dental materials in order of thermal expansion, from highest to lowest

wax (250-400 or higher), acrylics, dental composite, amalgam, alumina, gold, dental cement / enamel, emax CAD, zirconia, feldspar, dentin (8.3)

list dental materials in order of thermal conductivity, from highest to lowest

gold (710), amalgam, alumina, feldspar, enamel, zirconia, dental cement / dental composite, dentin, wax, acrylics (0.5)

Tm

melting point, temperature of a crystalline material changes from solid to liquid

Tg

glass transition point- temperature of amorphous material becomes rubbery

t/f semi-crystalline material shows both Tm and Tg

true

viscosity

measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress

what is the viscosity coefficient?

η

dynamic (absolute) viscosity

μ or η, the SI physical unit of dyamic viscosity is the pascal second (Pa*s)

1cP = 1mPa*s = 0.001 Pa*s

kinematic viscosity (v)

μ/ρ

SI unit: m²/s, stoke (St)

the ratio of the intertial force of the viscous force

what is viscosity of a fluid highly dependent on?

temperature

shear stress (K)

(shear rate)^n

pseudoplastic (shear thinning)

n>1

newtonian (ideal liquids)

n=1

dilatant (shear thickening)

n<1

what are examples of bingham (plastic fluids)?

toothpaste, mayonnaise, tomato ketchup

what is an example of a newtonian (ideal) liquid in dentistry?

newly prepared zinc phosphate cement

what is an example of a bingham plastic (viscoplastic) in dentistry?

tooth paste

what are examples of psuedoplastic (shear thinning) liquids in dentistry?

polycarboxylate cements, non-water mixed glass ionomer cements, dental porcelain slurry, vinyl polysiloxane (PVS) impression paste, flowable composite, pit and fissure filling composite

what are examples of dilatant (shear thickening) liquids in dentistry?

traditional resin composites, liquid denture base resin, 3DP resin

what are examples of thixotropic liquids in dentistry?

they become less viscous when subjected to repeated pressure

prophy paste, some light-cure nano-particle filled composite resins, APF and topical fluoride gels, impression material

thixotropic is also pseudoplastic, but…

pseudoplastic is not also thixotropic

what are some surface properties?

adhesion, bonding, wettability, surface roughness, most cell interaction to biomaterials

related with bulk materials- hardness, color, gloss, roughness, wear

surface energy

the unique character of interfaces occurs because atoms at interfaces possess energies and reactivities significantly different from those of the same species in the bulk

liquid surface tension

a property of the surface of a liquid that allows it to resist and external force

occurs at the interface between liquid-gas, liquid-solid, immiscible liquids

what equation is used with capillary pressure?

young-laplace

contact angle (θ)

a quantitative measure of the wetting of a solid by a liquid

hydrophilicity is indicated by smaller contact angles and higher surface energy

static contact angle

static sessile drop method

dynamic contact angle

dynamic sessile drop method, so there is advancing and receding angle

surface free energy (SFE)

the work required to increase the area of a substance by 1m²

is the result of cohesive forces of a material

strong, hard solids usually have ____ surface free energy and are ____ easily wetted (metals, teeth, ceramics)

high, more

materials that are more hydrophobic with have better…

color stability and stain resistance

restorative materials with low surface energy will be better able to resist …

plaque formation

adhesive material requires good wetting of tooth surfaces to achieve ____

adhesion

surface treatment

improves surface wettability of resin and promotes bonding strength

silane

contains silicon-alkoxyl and methacrylic group

good for silicate and metal based

10-MDP

contains phosphate and methacrylic group

good for alumina and zirconia based, also for HAP (containing Ca)

surface roughness (Ra)

arithmetic surface roughness

tested by profilometer (contact or optical)

*solubility of polymer based restorative material

dry material weight loss of a dental material after soaking for 7 days at 37 C, unit μg/mm³ . <7.5 (ISO 4049)

the testing baseline must be dried dental material, for both ceramic and polymer based dental material

water sorption of polymer based restorative material

water intake of a dental material after soaking for 7 days at 37 C, unit μg/cm³ . <40 (ISO 4049)

the testing baseline must be dried dental material, for both ceramic and polymer based dental material

chemical solubility of ceramics based restorative material

immerse in 4% acetic acid for 16 hr at 80C, unit μg/cm² . <100 (ISO 6872 and 3696)

the testing baseline must be dried dental material, for both ceramic and polymer based dental material

which fundamental force is responsible for a material’s mechanical and physical properties?

electromagnetic force