Biomedical Engineering Reference
In-Depth Information
The bacteriostatic and antibacterial properties are primarily related to the development of
the nanostructure and the nano-size porosity during hydration of the Ca-aluminate system.
The initial low pH ( < 8) of the system in the case of the presence of a polycarboxylic acid
for cross-linking, is such not a hindrance for the antibacterial properties. The requirements
of the microstructure of Ca-aluminate and/or Ca-silicate based biomaterials to achieve
antibacterial properties are related to the general nanostructure obtained; A
nanoparticle/crystal size of hydrates in the interval 15-40 nm, a nanoporosity size of 1-4 nm
and the number of pores per square micrometer of at least 500, preferably > 1000.
The above mentioned requirements will guarantee that the nanostructure will be free of
large pores meaning no escape of bacteria within the original liquid, paste or dental void,
during the hydration. The nanocrystals will participate on all walls, within the liquid, and
on all inert particles and on bacteria within the original volume. The formation of
nanocrystals will continue to all the void is filled. The bacteria will be totally encapsulated
and will be chemically dissolved. Also the number of nanopores will be extremely which
will have the possibility of catching and fasten bacteria to the hydrate surface - an analogue
to how certain peptides may function as antibacterial material due to a structure with
nanosize hole within the structure.
4. Materials and biomaterials application
Alternative dental materials and implant materials based on bioceramics are found within
all the classical ceramic families: traditional ceramics, special ceramics, glasses, glass-
ceramics, coatings and chemically bonded ceramics (CBC) (Ravaglioli and Krajewski, 1992).
The CBC-group, also known as inorganic cements, is based on materials in the system CaO-
Al
2
O
3
-P
2
O
5
-SiO
2
, where phosphates, aluminates, and silicates are found. Depending on in
vivo chemical and biological stability, the CBC biomaterials can be divided into three
groups: stable, slowly resorbable and resorbable. The choice for dental and stable materials
is the Ca-aluminate based materials (Hermansson et al 2008). Slowly resorbable materials
are found within Ca-silicates and Ca-phosphates, and fast resorbing materials among Ca-
sulphates and some Ca-phosphates. The stable biomaterials are suitable for dental
applications, long-term load-bearing implants, and osteoporosis-related applications. For
trauma and treatment of younger patients, the preferred biomaterial is the slowly resorbable
materials, which can be replaced by new bone tissue (Nilsson, 2002). In this section are
summarised some of the possible new applications using the strong chemically bonded
ceramics based on Ca-aluminate. The presentation is devided in three application areas;
dental, orthopaedics and drug delivery.
The following product areas have been identified based on experimental material data, pre-
clinical studies, pilot studies and on-going clinical studies (Jefferies et al, 2009). The
application areas are; Dental cement, endodontic products (orthograde and retrograde),
sealants, restoratives, and pastes for augmentation and dental implant coatings. For low-
viscosity and early hardening of the CA, a complementary glass ionomer can preferrably be
used. Clinical use of the materials is foreseen within the next coming years. The use of CA
within odontology is based on the following features; early/rapid anchoring, high strength,
long-term stability, no shrinkage, combined bonding and bulk material, biocompatibility
and in situ apatite formation ability (nanocrystals formed in the contact zone between
material and tissue).
