Test Methods with Special Reference to Nanostructural Chemically Bonded Bioceramics - Nanostructural Bioceramics: Advances in Chemically Bonded Ceramics - page 36

The materials are evaluated with regard to compressive strength
(ISO 9917), biaxial flexural strength (ASTM F-394, flexural strength
testing of ceramic materials), and Young´s modulus (slope of
compressive strength-strain curve) as a function of time when stored
in water or a phosphate buffer solution at body temperature. The
mechanical properties are determined after selected time periods.
The typical test time is after 1 hour, 24 hour, 7 days, 4 weeks, and a
selected long time period of half a year or longer.
A qualitative value of the mechanical properties is the fracture
toughness, . This value is an intensive property and relates to the

energy needed for a fracture to occur. It also relates to the possible
strength of the material related to the largest defect in the stressed
zone of the material. A practical consequence of the understanding of
fracture toughness is therefore to achieve a consistency of the CBBC
materials to avoid larger pores to be introduced during preparation
and handling of the paste.

K IC

5.2.3 Dimensional Stability: Shrinkage or Expansion?

Confusion has been related to how dimensional stability should be
tested for CBBCs [2, 9, 10]. This mainly relates to determination
of water uptake in biomaterials and how this in general is related
to expansion. For organic polymer- or glass ionomer-based
biomaterials dimensional changes, especially expansion, are related
to water uptake [9]. For chemically bonded bioceramics (CBBCs),
where hydration is the main binding reaction, the hydration often
contributes to shrinkage. However, for CBBCs, in many cases where
nanostructures dominate, dimensional stability or a small expansion
can occur.
Aspects related to how dimensional stability is judged are also
related to test methods. This has been treated in detail in several
papers [1, 9-13] and is summarised in Table 5.1.

5.3 Summary

Caution must be shown when testing CBBCs, since these low-
temperature-formed biomaterials can show different behaviours