| Abstract | Mikrofrakture korijenskog dentina koje mogu dovesti do vertikalne frakture korijena, nastale
kao posljedica kemomehaničke obrade korijenskih kanala, često se povezuju s različitim
postupcima tijekom endodontskoga liječenja. Prednost mikro CT metode u odnosu na
sekcijske metode je njena neinvazivnost i mogućnost usporedbe uzorka prije i nakon
eksperimenta. Svrha ovog rada je bila procijeniti utjecaj obrade korijenskih kanala
instrumentima nove generacije, Self Adjusting File, Reciproc Blue i ProTaper Next s tri
različite vrste pokreta u korijenskom kanalu na pojavnost mikrofraktura pomoću mikro CT-a
i otpornost tako obrađenih korijenova na djelovanje pritisnih sila.
U istraživanju je korišteno 57 gornjih premolara s dva korijenska kanala ekstrahirana zbog
ortodontskih razloga od pacijenata u dobi od 16 do 20 godina. Uzorci su dekororirani i
uronjeni u akrilatne blokove, a parodontni ligament je imitiran polisiksanskim materijalom za
otiske. Zubi su skenirani pri strukturnoj rezoluciji od 20,2 μm industrijskim mikro CT-om
(Nikon XT H 225, Tring, UK) i randomizirano su podijeljeni u tri grupe koje su obrađene
trima sustavima instrumentacije kanala: Self Adjusting File (vibracijske kretnje), Reciproc
Blue (recipročne kretnje) i ProTaper Next (rotacijske kretnje). Kanali su obrađeni prema
uputama proizvođača uz predpripremu „glide path“ instrumentima. Tijekom instrumentacije
kanali su irigirani 12 ml 2,5% NaOCl i 4 ml 17% EDTA, svaki. Uzorci su ponovo skenirani
pod istim uvjetima i 24 sata nakon njihovog sušenja. Za analizu pojavnosti mikrofraktura u
stijenkama dentina korišten je program Volume Graphics VGStudio Max 3. Poslije toga
uzorci su prerezani na tri dijela i podvrgnuti ispitivanju otpornosti na pritisnu silu
univerzalnom kidalicom. Ni jedan dentinski defekt nije pronađen prije i nakon obrade kanala,
kao ni nakon 24 sata sušenja na suhom zraku. Rezultati testiranja otpornosti na lom nisu
pokazali statistički značajnu razliku između skupina. Pod uvjetima ovog istraživanja može se zaključiti da obrada kanala mladih pretkutnjaka vibracijskim Self Adjusting File, recipročnim Reciproc Blue i rotacijskim ProTaper Next instrumentima ne dovodi do pojave mikrofraktura u stijenci korijenskih kanala, a korijeni instrumentirani ovim tehnikama ne pokazuju statistički
značajne razlike u otpornosti na lom djelovanjem pritisne sile. |
| Abstract (english) | Introduction: Controversies about effects of the forces formed during root canal treatment
on dentinal microcracks formation still exist due to different results reported. The issue of
methodology, sample selection and storage of the specimens still require further analysis,
particularly because new instruments are constantly being developed. The aim of the study
was to explore microcrack formation after root canal preparation with Self-adjusting File
(SAF), Reciproc Blue (RB), and ProTaper Next (PTN) instruments on young premolars by
means of micro computed tomography.
Methods: Fifty-seven premolars, two-rooted with one canal (Vertucci type I) or single-rooted
teeth of Vertucci type II had been used for the study All the teeth were visually inspected
under the stereomicroscope with magnification of 12 x to exclude those with open apices,
those that were root fractured during the extractions and pre-existing dentinal defects. The
specimens were decoronated using a diamond disc to standardize the working length about 12
mm. The periodontal ligament was simulated by a thin layer of polysiloxane impression
material on the root surface and the samples were embedded in blocks made of acrylic resin.
Specimens were scanned at geometrical magnification of 6.3, which yielded a structural
resolution of 20.2 μm. All teeth were scanned at X-ray energy of 110 kV and X-ray tube
current of 140 μA with a 0.1 mm Cu filter, using 1440 projections at an exposure time of 333
ms. Beam hardening was reduced using a Hanning filter. Noise was reduced using a median
filter, and surface detection was performed using an adaptive search algorithm (Volume
Graphics VGStudio Max 3). Samples were randomly assigned into three groups of 19 teeth
each according the instrumentation technique: Self-Adjusting File (SAF), Reciproc Blue
(RB), and ProTaper Next (PTN) For the SAF group (vibration kinematics), the glide path was created using the Pre-SAF set
of instruments (ReDent Nova). An RDT3 handpiece was used for canal preparation with SAF
instrument 1.5 mm in diameter at frequency of 5000 vibrations per minute and amplitude of
0.4 mm for a total of four minutes. The canals were simultaneously irrigated with 2.5% NaOCl
at a flow rate of 4 ml/min for three minutes and one minute with 4 ml of 17%
ethylenediaminetetraacetic acid (EDTA) by use of a syringe and needle. In the RB group
(reciprocation kinemamatics), glide path was created with R-Pilot (WDV, Munich, Germany)
followed with Reciproc Blue until the working length was reached
The glide path in the PTN group (full rotary kinematics) was created with Proglider
(Dentsplay Maillefer) ProTaper Next X1 and subsequently ProTaper Next X2 were each used
in a brushing motion at a speed of 300 rpm with torque set to 4 Ncm to progress apically until
reaching the working length. During instrumentation in RB and PTN group, each canal was
irrigated with 12 ml of 2.5% NaOCl, and final irrigation was performed with 4 ml of 17%
EDTA to match the irrigation protocol used in SAF grous.
After the root canal preparation, post-operative scans were performed in the same specimen
positions and with the same micro-CT parameters as the first scan.
In order to check the influence of the moisture on visibility of microcracks, specimens were
kept in dry conditions for 24 hours and then scanned for the third time.
Two calibrated, blinded examiners evaluated the cross-sectional images using the imageprocessing
software Volume Graphics VGStudio Max 3. The roots were divided into cervical,
middle, and apical parts. Radiolucent lines present in the micro-CT sections would be
categorized as microcracks. If the microcracks had been observed on post-operative scans, the
corresponding pre-operative scan would have been analyzed to exclude pre-existing defects.
Ten specimens of each group were cut in horizontal slices and tested on fracture resistance in
a universal testing machine AGS-X, Shimadzu (Japan) at speed 0,5 mm/min.
Results: No dentinal defect was found in any evaluated specimen, neither in pre- and nor postoperative
scans in wet and dry condition. PTN group showed the lowest value for fracture
resistance (419,15 N) compering to RB (485,57 N) and (473,12 N). The differences were not
statistically significant (p=0.151).
Conclusion: Under the circumstances of this study instruments with three different
kinematics (SAF, Reciproc Blue and Protaper Next) do not cause dentinal microcracks in
young premolar teeth and does not cause differences in resistance to load to fracture. |
