lecture 14

what are these physical properties:

viscosity

imbibition

solubility

adhesion

viscosity: the resistance of a substance to flow or deform under applied stress.

it affects: impression materials, dental cements, resin composites, adhesive materials

imbibition: process by which a material absorbs water or fluids from its surroundings. it affects dental impressions and gypsum products

solubility: extent to which a material can dissolve or leach its components when exposed to oral fluids or other media. it effects biocompatability, hydration and degradation, leaching of components and longevity of restorations

adhesion: bonding or joining of different components or surfaces within dental restorations or procedures. it effects: composite resins, bonding agents, sealants, cementations of restorations

what are these physical properties:

sorption

surface tension

wetting

electroconductivity

thermal conductivity

sorption: process of absorption or adsorption of substances into or onto the surface of the material. two types; absorption and adsorption

surface tension: the cohesive forces acting at the interface between the material and the surrounding medium. affects impression materials, dental waxes, bonding agents, restorative materials.

wetting: ability of a liquid or material to spread and form a thin, uniform layer over a solid surface. affects impression materials, biocompatability, surface treatment

electroconductivity: specifically in restorative dentistry, can influence their performance and behaviour in the oral cavity. metals exhibit high. ceramics exhibit low, resin based composite do not exhibit any.

thermal conductivity: material's ability to conduct heat

metals have high

amalgam has moderate

ceramics have lower than metal

composite resin have it close to natural tooth structure

what are these thermal properties:

expansion

shrinkage

expansion: change in volume or size of a material due to various factors such as temperature changes, moisture absorption, setting reactions, or polymerization. we have thermal, hygroscopic, setting/polymerisation, water absorption.

shrinkage: reduction in volume or dimensions that occurs during the setting or curing process of various dental materials. affects resin based composites, acrylic based materials, dental cements and impression materials

technological properties:

plasticity

forging/ hammering

punching

rolling (flatting)

traction/ pulling

plasticity - typical for waxes, impression and investing materials

forging/hammering - typical for waxes, impression and investing materials

punching: typical for steel, aluminium, and those that exhibit plasticity

rolling - typical for waxes, impression and investing materials

traction - typical for steel aluminium, copper and other alloys

technological properties:

drilling

cutting

milling

welding

thinness

grinding

polishing

drilling - typically used for metals, plastics, wood and composites

cutting - typically used for metals, plastics, ceramics, and wood

milling - zirconia

welding - spot welding, pressure welding, laser welding

thinness - metals, plastics, glass, and films

grinding - use of rotary instruments, such as dental drills or rotary burs, to remove excess material, adjust the shape, or create specific contours in dental restorations or prostheses

polishing - smoothing and refining the surface of dental restorations or appliances to achieve a smooth, glossy finish. performed after grinding

abrasion and air particle abrasion defn

abrasion - product that has a hard phase that provides many individual particles with sharp cutting edges.

air particle abrasion - material removal by way of air pressure propelled abrasive particles. used in surface cleaning, cavity prep and surface prep for bonding.

bonded abrasive defn

abrasive instrument containing a phase that holds abrasive particles in a tight grip with spaces btwn.

breaking away of grains from bond is desirable as they become dull.

bond materials include organic (resin or rubber), vitrified (glass or glass ceramic) and metal

buffing, bulk reduction and cutting defn

buffing - polishing with soft absorbent material like a cloth or leather.

bulk reduction - precedes finishing and polishing. excess restorative material is removed

cutting - reduction of a material by using an edged instrument like bladed dental burs. removes by slicing action

dressing, erosion and finishing defn

dressing - using a variety of tools to remove any debris that is clogging space on a bonded abrasive instrument. common instruments are diamond coated tools or bonded abrasive stones of aluminium oxide or silicon carbide

erosion - material removal by air particle abrasion, slurry erosion, chemical erosion/acid etching

finishing - removing surface defects/ scratches made during contouring process by cutting/grinding instruments

true/truing defn

process of correcting concentricity and shape of a grinding wheel.

classification of abrasion

natural - found in nature, such as natural diamond, emery, garnet, and pumice.

synthetic - synthetic diamond, silicon carbide, aluminium oxide, and boron nitride.

bonded - abrasive grains held together by a bonding material. aluminum oxide, silicon carbide, or diamond bonded by agents

non-bonded - loose abrasive grains not held together by any bonding agent. loose particles, powders, or compounds. aluminium oxide, silicon carbide, polishing and lapping compounds

what are the particles classified as

fine - 0-10µm

medium - 10-100µm

coarse - 100-500µm

what are the ISO standards for abrasive instruments

806 - materials

314 - type of attachment

1572 - shape and size of abrasive

012 - largest diameter of working head in 1/10mm

factors affecting abrasion rates

large difference between abrasive and substrate

particle size of abrasive

particle shape

speed

pressure

lubricants

factors affecting abrasion

large particle produces similar scratches with F1 than a smaller particle with F2

sharp particles produce deeper abrasion than rounder under the same applied force

deeper and wider scratched are produced by inc applied force from F1 to F2

pastes and powders

natural origin

- amorphous SiO2

- pumice

- chalk (CaCO3)

metal oxides

- Fe2O3

- Cr2O3

accessory materials

- sandpaper

- felt

- blackbrush (hard)

- white brush (soft)

- brushes from textile or leather

types of polishing pastes

according to aggregate state:

- hard

- semi hard

- mess like pastes

according to solvent:

- water

- petroleum products

according to particle size:

- harsh

- medium

- fine

according to abraded material:

- for base alloys

- for noble alloys

- for acrylics

- for composites

- for ceramics

- for amalgam

why do resin composite restorations present a unique polishing problem

they are composed of soft polymeric resin and a hard filling.

relief polishing may result from unequal resin and filler wear rates

this leaves "valleys" netween filler particles

possible wear mechanisms for dental composites

wear of polymer matrix

filler matric adhesive failure

shear of filler particle

cohesive failure thru matrix

exposure of air bubble

cutting effect eq

V= (3.14 x d x n) / 1000

methods for establishing roughness:

comparative method

imprecise

methods include visual comparison, tactile comparison and reference standards

methods for establishing roughness:

contact method

involves the use of instruments known as profilometers or surface roughness testers

stylus - use a stylus or probe that physically traces the surface profile. As the stylus moves across the surface, it detects minute vertical movements caused by surface irregularities, recording these variations to measure roughness parameters.

atomic force microscope - extremely high-resolution 3D imaging and measurement of surface topography at the nanoscale. It's highly precise and capable of analyzing surfaces with exceptional detail but might be limited in terms of the size of the measured area.

methods for establishing roughness:

non contact methods

white light interferometer -

Utilizes interferometric principles to measure surface roughness by analyzing the interference patterns generated by white light reflected from the surface. It offers high accuracy and is non-contact, suitable for both flat and curved surfaces.

laser microscope - non-contact imaging technique that utilizes laser light for high-resolution surface imaging and analysis.

measurement units

Ra - avg surface roughness

Rmax - vertical distance from peak to lowest valley

Rz - max avg height of profile

Sa - mean height/ extension of Ra to surface

importance of surface roughness

bacterial adhesion

oral cell interaction

surface finish