IB: Dental Waxes

waxes

• moderately large hydrocarbons w/ weak IMFs

• very large thermal expansion and low yield points

simplest waxes are

alkanes, whether straight chain or branched

types of waxes

• natural

• synthetic

• pattern

• processing

• impression

mineral waxes

• composed primarily of linear and branched hydrocarbon chains (except Montan, which is mainly esters)

• paraffin

• microcrystalline

• barnsdahl

• ceresin

• montan

• ozokerite

plant waxes

• composed primarily of esters, hydrocarbons, alcohols, and/or acids

• carnauba

• ouricary

• candelilla

insect waxes

• composed primarily of myricyl palmitate, hydrocarbons, and/or organic acids

• beeswax

animal waxes

• composed mainly of esters

• not used in dentistry

• spermaceti

pattern waxes

• form temporary “model” of dental restoration then replaced by stronger material

• examples: inlay, casting, baseplate

problems with pattern waxes

• thermal change in dimension

• tendency to warp on standing

inlay wax

• make wax pattern of final restoration using lost wax technique

• for casting of metal or hot pressing of ceramic inlays, crowns, and bridge units

casting wax

• fabricate patterns for the metallic framework of removal partial dentures and other similar structures

• available in thin sheets

baseplate wax

• establish initial arch form in construction of complete dentures

• also for bite rim for occlusion of jaws

• available in sheets

processing wax

• mainly used as auxiliary aids in constructing restorations and appliances

• not part of final restoration

• examples: boxing, utility, sticky, blockout

boxing wax

• form dam around impression to confine the stone poured to form a model of arch and other impressions

utility wax

• typically used to modify/protect impression tray

• bring hydrocolloid impression materials to a more desirable contour to prevent sag and distortion

• makes tray longer/taller

• helps with high palates

• prevents excessive alginate from flowing down throat

sticky wax

• used where rigidity and adhesion are important

• temporarily hold broken dentures together

• obtain adhesion between casting waxes and stone models

• material is sticky when melted and adheres closely to applied surfaces

• at room temp, wax is firm, not sticky, and brittle

blockout wax

• fill undercut area on cast during processing of framework

impression wax

• correct small imperfections in other impressions

• rarely used to record complete impressions

• unique: need to flow readily at mouth temp and be soft at room temp

• examples: corrective, bite registration

corrective wax

• used in partial and complete denture prosthesis

• restore regions in edentulous impressions to correct undercut areas

• reproduce details of mucous membrane

bite registration wax

• record relationship between U and L teeth in dentulous patients

dental waxes mostly contain

paraffin with additives

ingredients in dental waxes to modify physical properties

• gums

• fats

• resins

gums

• natural products from plants that resemble waxes

• viscous, amorphous, harden when exposed to air

• change consistency of wax

• mixture of hydrocarbons

fats

• triesters of various fatty acids with glycerol

• modify melting range and hardness of waxes

• affect properties of paraffin by softening the wax and allowing for ease of polish

resins

• synthetic: polyethylene and vinyl

• plant: copa, dammar, sandarac, mastic, kauri, wood rosin, shellac (from insects)

• modify melting range, hardness, adhesiveness, flake-resistance, gloss, toughness of dental waxes

• also make films

properties of waxes

• thermal expansion and contraction

• melting range

• solidification shrinkage

• thermal conductivity and diffusivity

• solid-solid transformation

• ductility

• flow or creep

• stress relaxation

because natural waxes consist of a mixture of many compounds

• no single melting point, rather a melting range

• because wax is mixture, there are different melting temps of the components

• entire wax will not appear melted

melting point of straight chain alkanes is dependent

on chain length

the longer the chain length

the stronger the attraction between molecules → more heat to melt → higher melting point

waxes have unusually large change in

volume when changing from liquid to solid

waxes have the largest coefficients of

thermal expansion

mineral waxes have higher coefficients of expansion than

plant waxes

• mineral waxes have weak secondary valance forces → wax components can move

• plant waxes have high secondary valance forces → wax components have restricted movement

heating above the temperature required to reach a moldable condition results in

excessive shrinkage on cooling

waxes have the lowest

thermal conductivity and diffusivity

most dental waxes are orthorhombic at low temperatures but

transform to a hexagonal crystal lattice at high temps but below the melting range

flow/creep

• slow permanent deformation over time with low stresses

• exists due to slippage of molecules due to low intermolecular valance forces

wax ductility and flow increase with

temperature

waxes with wider melting ranges generally have

greater ductility

to avoid internal stresses

• assure completely uniform heating and plasticity when using the bulk-carve technique

• using wax additive technique in which each increment anneals previous increment

requirements for inlay waxes

• low thermal contraction

• flow

• easy to carve w/o chipping or flaking

• burn out cleanly w/o residue

• colored to contrast with tooth or die

type I inlay technique

• direct

• in patient’s mouth

• must be stable at 37° to minimize distortion on removal

type II inlay technique

• indirect

• on stone die

• soften at lower temps

• wax patterns invested w/in 30 minutes of completion

casting waxes

• need to be manipulated mostly at room temp

• must be ductile enough to double bend on itself without fracture at room temp

• do not need to exhibit low flow at body temps

• for metal frameworks

baseplate waxes

• may contain up to 80% of paraffin-based waxes or ceresin

• because used to set denture teeth, dimensional changes are very important

• thermal expansion should be <0.8% between 26-40°