Ceramics and composites - Orthopaedic Biomaterials in Research and Practice - page 219

Table 8.7 advantages and disadvantages of casting materials

Matrix type Advantages Disadvantages

Plaster Low cost Slow setting

Familiarity 24 h to maximum strength

Easy revision Heavy/bulky

Weight restricts
patient activity

Significant heat generation during
setting

Good conformability Radiopaque

Not waterproof
Low fatigue resistance
Impervious

Plaster-resin Intermediate cost Slow setting

Handles like plaster Heavy/bulky

Weight restricts
patient activity

Radiopaque

Water resistant Impervious

Resin Lightweight Higher cost

Rapid setting Poor conformability

Waterproof Possible hazard to cast technician

Permeable Resin adheres to skin and clothes

Radiolucent Some flammable when impregnated

with flammable liquids
Tissue irritation (adjacent skin)

Note: These are generic advantages and disadvantages; they may not all be pos-
sessed by any particular product.

relative abilities of the layers to adhere, to be able to form a tuck,
to turn at an angle, and so on. The points are then combined into
an overall score or index number.

2. A single-cycle diametral “crush strength” test of a cylinder formed,
usually of 5 to 10 layers around a 2- to 3.5-inch-diameter mandrel
(removed after setting, before mechanical testing).

Neither of these two techniques has become recognized standard
practices; thus, reliable comparative data on casting materials are not
available. In addition, a reliable consensus test of fatigue properties is
needed for realistic functional comparison of these various materials.
Casting materials with plaster matrices typically display crush
strengths of 175-250 N (3.5 inch mandrel, 6 layers, 1 week after fabrica-
tion), whereas those with plaster-resin or resin fillers may be expected
to be two to three times stronger. Plaster and, presumably, plaster-resin
matrix casting materials have strengths that are strongly dependent on
their water content and time after setting. They are usually “optimized”
for equilibrium water contents of 20% of initial dry weight; higher or
lower water contents or excess water content during setting will produce
a weaker material.