Biomedical Engineering Reference
In-Depth Information
prepared tooth and building up the tooth before the material sets. Indirect dental
restorative composites, which are laboratory-processed to be utilized for indirectly
fabricated inlay, onlay, and crown restorations [
11
], are becoming increasingly
important in dentistry, with expanding applications resulting from processing and
materials innovations [
12
,
13
]. Some of them have shown clinical advantages, par-
ticularly a substantially higher mechanical resistance than other currently available
composites [
14
,
15
]. Many of the improvements in the indirect dental composites—
particularly those stemming from the fi ller particle type, the increased degree of
cure (DC) of monomers, or an improved fi ller/matrix adhesion—are based on
materials property measurements [
13
,
16
,
17
]. Resin-based composite materials
have gained in popularity in restorative dentistry recently because the color resem-
bles natural tooth color. In addition, the acid-etch technique brings a number of
conveniences for the composite restoratives to reconstruct the shape of teeth.
However, remarkable improvements in the component elements and processing
techniques fail to avoid the excessive wear of composite resins during mastication,
and this wear rate is far more signifi cant than that of metals or ceramics, which is
supposed to limit the wide use of composite materials in indirect restoration.
Generally, the wear process of composite materials is related to the material's
characteristics and oral condition. Material factors usually include the characteris-
tics, content, and distribution of fi ller; the nature of the matrix; and the interfacial
bond strength between the fi ller and the matrix.
Filler characteristics, such as size, shape, hardness, and brittleness, play an
important part in the wear process of dental composites. Compared to composites
containing large fi ller particles (>1
m), microfi lled and small-particle hybrid com-
posites were frequently mentioned to have a tendency to display better abrasion
resistance because of their smoother surface, decreased interparticle spacing, and
decreased friction to food particles [
18
]. In contrast to sharp and pointed particles,
the presence of spherical and irregular particles could benefi t both the composite
wear and the opposing enamel wear [
19
]. Hard fi ller particles could protect the soft
matrix and enhance the material's overall resistance to abrasion [
20
]; however, the
hardness of fi ller particles must not be higher than that of human enamel hydroxy-
apatite crystals. Under high stress, brittle fi ller particles will easily fracture and
cause rapid abrasion of the material itself but have a less antagonistic engagement.
It is well accepted that a smooth surface provides reduced frictional wear at the
occlusal contact area, which will lessen the wear of both composite and antagonistic
enamels. Whenever fi ller particles protrude and are big and extremely hard, there
can be high antagonistic wear rates, which could cause catastrophic loss of the tooth
substance in time [
20
,
21
].
Obviously, the ability of a resin composite to resist abrasive action depends on
fi ller-matrix interactions. Therefore, the fi ller content and distribution and interpar-
ticle spacing signifi cantly infl uence the physical properties and thus the wear resis-
tance of dental composites [
20
]. The wear resistance of microfi lled composites was
remarkably enhanced by the fi ller volume, with an increase from 25 to 30 vol%.
Filler particles situated very close to each other can protect the softer resin matrix
from abrasives, thus reducing wear. The use of fi ner particles for a fi xed-volume
μ
