Biomedical Engineering Reference
In-Depth Information
experimental sealer. The results showed that there was no statistically significant difference in api-
cal sealing ability when measuring penetration of the dye using stereo microscope. Taken together,
the above three reports may indicate promising initial reports that with further research may yield
superior materials.
21.2.3.3
Retro-filling and root-repair materials
Numerous studies have demonstrated the importance of root-end filling placement during periapical
surgery. According to Harty et al.
[51]
, the most important factor in determining the success of an
apicoectomy is the efficiency of the apical seal. Wu et al.
[52]
suggested that a tight and
long-lasting seal of root-end fillings are of primary clinical importance. Several studies have indi-
cated that the lack of a good root canal filling could compromise the surgical outcome
[53,54]
.
In addition, a number of clinical studies on healing after periradicular surgery have confirmed the
benefit of placing a high-quality root canal filling prior to surgery
[55,56]
.
The properties of an ideal root-end filling material have been well documented in the scientific
literature and are summarized as this material would adhere or bond to tooth tissue and ''seal'' the
root end three dimensionally; not promote, and preferably inhibit, the growth of pathogenic micro-
organisms; be dimensionally stable and unaffected by moisture in either the set or unset state; be
well tolerated by periradicular tissues with no inflammatory reactions; stimulate the regeneration of
normal periodontium; be nontoxic both locally and systemically; not corrode or be electrochemi-
cally active; not stain the tooth or the periradicular tissues; be easily distinguishable on radiographs;
have a long shelf life; and be easily handled. Although almost every available dental restorative
material or cement has at one time or another been suggested for root-end filling, these properties
have yet to be found in any one material. It may therefore be concluded that the ideal retrofill
material does not yet exist
[57]
.
Mineral Trioxide Aggregate (MTA) has become the material of choice of retrograde filling in
spite of its handling and long setting time. To overcome these disadvantages, a very recent study
by Saghiri et al.
[58]
evaluated a nanomodified MTA for enhanced physiochemical properties.
They concluded that the increased surface area of powder by nanodispersion can reduce setting
time and increase microhardness. This may help the MTA to set faster without losing its required
hardness once set. Other studies are investigating new materials rather than modifications to current
materials. A polymer nanocomposite (PNC) is a generalized term for polymeric materials that
is loaded with minimal amount of nanoparticles such as clays and CNTs
[59]
. As opposed to con-
ventional composites, the dispersed phase has a very high surface-to-volume ratio. PNCs have
therefore shown greatly improved mechanical and thermal properties of the material even at very
low filler content (typically between 0% and 5%). Previous studies have indicated substantial
improvements in heat resistance,
[59,60]
dimensional stability
[61]
, stiffness,
[62,63]
, reduced elec-
trical conductivity
[64,65]
, and most uniquely, drug elution capabilities
[66,67]
. Recently, two such
novel nanocomposites were investigated for initial apical seal along with a commonly used
polymer-based compomer in an in vitro model
[68]
. Although one of the PNCs did not significantly
reduce leakage, the results revealed that leakage of commercial compomer was more than 12 times
more likely than the second PNC. SEM of these PNCs placed as root-end filling materials revealed
a tight interface with the PNC entering into the dentinal tubules (
Figure 21.3
)
[69]
. This was cor-
roborated with equal or greater values (
Figure 21.4
) of push-out force required when compared to
MTA and Geristore
s
[70]
.
