DISCUSSION
Endodontic
treatment failures can be caused by microorganisms able to survive in
the apical root canal system or outside the apical foramen. Bacteria can
form an organized structure in a biofilm around the root. Conventional
treatment cannot remove this persistent infection due to its external
localization (PURICELLI et al., 2014).
Thus, if the endodontic retreatment by the conventional
endodontic treatment is unsuccessful, endodontic periapical surgery is
considered the last option before tooth extraction (SERRANO GIMENEZ M;
TORRES; ESCODA 2015). This procedure has a success rate between 69% and
93% (PINTO et al., 2020). The European Society of Endodontology
defines periapical surgery success as the absence of pain,
swelling, or other symptoms, satisfactory healing of soft tissues, and
radiological evidence of repair of apical periodontitis, including
restoration of the periodontal ligament. Occasionally, a radiolucent
area such as a “scar” should be followed up to 4 years. (ESE, 2006).
Endodontic periapical surgery consists of two stages. The first is root
preparation, which can be performed with drills or ultrasonic
instruments, and root-end filling. Root preparation aims to remove the
apical portion of the root contaminated with resistant microorganisms,
and the second step aims to seal the apex of the remaining canal (LI H
et al., 2021) to promote the elimination of apical periodontitis and
prevent new contamination (HARGREAVES K; BERMAN L, 2015)
Among the factors that influence the prognosis of endodontic
surgery are smoking, location, shape of the tooth, absence or presence
of dentinal defects, interproximal bone level, and filling material used
(PINTO D et al., 2020). Knowing that the quality of the root
canal filling material influences the success of surgical endodontic
treatment, it is expected that an ideal root filling material is
biocompatible, has dimensional stability, resistance to resorption is
bactericidal and bacteriostatic, easy to handle, and an excellent
sealing capacity (CHONG; FORD, 2005; PINTO et al., 2020; DEL FABBRO et
al., 2016).
This study analyzed the presence of empty spaces (quantifying
the volume and percentages of cavities filled with the root-end filling
material) both inside the root-end filling material and at the interface
between dentin and cement through computerized microtomography,
providing a three-dimensional volumetric analysis. It also allows
viewing the relationship between the root-end filling material interface
with the dentin and filling material interface without sample
destruction (GANDOLFI et al., 2013; ZASLANSKY et al., 2011; CAMILLERI et
al., 2012)
The results showed that all materials tested (MTA Angelus,
NeoMTA Plus, BioRoot RCS) failed after the set period. Empty spaces were
present at the cement-dentin interface and in the center of the root-end
filling material, as in figure 1. There was a statistical difference
between NeoMTA Plus and MTA and BioRoot RCS (p<0.05)
concerning the number of empty spaces, rejecting the null hypothesis.
(Table 1). The flaws in the root-end filling material may allow the
reinfection of the apex with residual bacteria from inside the canal,
which may migrate to the periodontal ligament due to its flaws.
(CAMILLERI et al., 2013). Although MTA and BioRoot RCS have different
chemical compositions, setting time and particle size (CAMILLERI, 2015b)
(DIMITROVA et al., 2015) and MTA has poor handling properties (SHETTY;
HIREMATH; YELI, 2017), while the manipulation and insertion of BioRoot
RCS in the root-end cavities was much easier than that of MTA, no
statistical differences were found in the percentage of empty spaces of
these materials after filling the root-end cavities. The distribution of
samples through stratified randomization and the performance of micro-CT
to measure the volume of root-end cavities made in bovine teeth ensured
the comparability of the groups, which could also be one of the reasons
for the absence of statistically significant differences between the
materials. In addition, MTA is composed of hydrophilic powder particles
that absorb water during powder hydration, causing the expansion of the
material during the setting process, providing better interfacial
adaptation than MTA Plus (SHETTY; HIREMATH; YELI, 2017) demonstrating
good marginal adaptation in the dentin walls (KÜÇÜKKAYA; PARASHOS,
2018). NeoMTA Plus is a calcium silicate-based cement with adequate
radiopacity according to ISO Standard 6876:2012 (root canal sealing
materials), finer powder particles than MTA, prolonged setting time, and
high-water release capacity. Calcium and hydroxyl ions (SIBONI et al.,
2017) resulted in greater solubility and mass loss during time than MTA
Angelus (QUINTANA et al., 2019; GANDOLFI et al., 2014), and this is
directly associated with the voids found in the NeoMTA Plus group.
During the setting process, the material was in a humid environment, in
contact with cotton rolls moistened with water. Materials containing
calcium silicate immersed in deionized water present more voids than
materials in contact with biological-type saline solutions (GANDOLFI et
al., 2011). Thus, when in contact with body fluids, calcium and hydroxyl
ions from the materials combine with phosphate from the periapical
fluids, precipitating a superficial layer of calcium phosphate to fill
the empty spaces opened at the adaptation interface between the root-end
filling material and dentin. (SIBONI et al. 2017)
It is also necessary to describe that other factor, such as
viscosity, could influence the presence of empty spaces within the
root-end filling materials analyzed. The lower the viscosity, the
greater the penetration of the materials into the dentinal tubules and
the prepared surface, and the better interfacial adaptation of the
root-end filling material (KÜÇÜKKAYA; PARASHOS, 2018). The conditions of
the cavity surfaces also influence interfacial adaptation. Although
ultrasound works under irrigation, debris remains after preparation
requiring additional irrigation, and when not performed, may leave
debris inside the cavity (KÜÇÜKKAYA; PARASHOS, 2018).