Biomedical Engineering Reference
In-Depth Information
2.6.2
Silver nanoparticles in restorative dental materials
Silver has a long and intriguing history as an antibiotic in human health care
[65]
. It has been used
in water purification, wound care, bone prostheses, reconstructive orthopedic surgery, cardiac
devices, catheters, and surgical appliances. Advancing biotechnology has enabled the incorporation
of ionizable silver into fabrics, for clinical use to reduce the risk of nosocomial infections and for
personal hygiene
[66]
. The antimicrobial, antifungal, and antiviral action of silver or silver com-
pounds is proportional to the amount of released bioactive silver ions (Ag
1
) and its availability to
interact with bacterial or fungal cell membranes
[67]
. Silver and inorganic silver compounds can
ionize in the presence of water, body fluids, or tissue exudates. The silver ion is biologically active
and can readily interact with proteins, especially those with thiol groups, amino acid residues, free
anions, and receptors on mammalian and eukaryotic cell membranes
[68]
. Bacterial sensitivity to
silver is genetically determined and relates to the levels of intracellular silver uptake and its ability
to interact and irreversibly denature key enzyme systems
[66]
. Bacterial biofilms are responsible
for dental diseases, such as caries and periodontitis. Due to the high frequency of recurrent caries
after restorative treatment, much attention has been paid to the therapeutic effects revealed by
direct-filling materials. Resin composites containing silver ion implanted fillers that release silver
ions have been found to have antibacterial effects on oral bacteria, e.g., Streptococcus mutans
[69]
.
Most studies available on the antimicrobial effect of silver containing composites describe the
effect of the silver particles on different species of cariogenic bacteria or deal with modified mate-
rial properties related to the addition of silver particles. Some of these studies tested the mechanical
properties of the silver containing composite
[70]
.
2.7
Nanocomposites in bone regeneration
Replacement of tooth and bone with metal implants and plates is one of the most frequently used
and successful surgical procedures. The introduction of modern implants started with the work of
Branemark, who in 1969 observed that a piece of titanium embedded in rabbit bone became firmly
attached and difficult to remove
[71]
. Due to their strength and toughness, metal implants have
been used in orthopedic and dental surgeries for many years. Titanium (Ti) and its alloys have had
considerable advantages over other metals because of their inertness, which yields excellent
biocompatibility and nonsensitization of tissues. However, issues concerning the release of Ti and
alloying elements from implants and the formation of Ti debris due to wear during implantation
still remain. Metal and metal alloys (i.e., Ti, Al, V, and Ni) in implants and dental bridges have the
potential for allergic reactions. Ceramic materials are known to have excellent esthetics, corrosion
resistance, and biocompatibility; several ceramic implants have been already commercialized. The
continuing interest in the use of modern ceramics for the fabrication of dental implants is under-
scored by several presentations during recent meetings of the International Association of Dental
Research and by recent research efforts by several European and Japanese companies (Kyocera,
Dentsply, Metoxit, etc). Unfortunately, in contrast to metallic materials, most ceramics suffer from
almost a complete lack of plastic deformation; this is due to the absence of mobile dislocation
activity, although other modes of inelastic deformation, such as microcracking and in situ phase
transformation, can provide limited alternative deformation mechanisms
[72]
. Alumina/zirconia
