Keywords
access cavity preparation - angular deviations - canal detection - cone-beam computed
tomography - guided endodontics - linear deviation
Introduction
Conventionally, endodontic intervention aims to prevent the incidence of apical periodontitis.[1] This could further become difficult with the presence of an obliterated pulp canal,
characterized by hard tissue deposited in root canal space.[2] This can be brought on by carious lesions, coronal restorations, pulp capping, and
luxation injuries following dental trauma.[3]
Root canal therapy done to prevent apical periodontitis follows cleaning and shaping
procedures to remove microbes. The first yet crucial step in achieving this aim is
to prepare the cavity in a manner to obtain access to the root canal that determines
the outcome, stability, and longevity. A straight line access is recommended for total
debridement and disinfection, but with least invasiveness to decrease risk of fracture
to the restored teeth.[4] Also, gaining endodontic access to calcified root canals is a difficult task. It
is susceptible to technical failures such as altercations in the root canal morphology
and significant loss of hard tissue, which may subsequently weaken a tooth or cause
root perforation.[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
During access cavity preparation, marginal ridges are reduced resulting in loss of
cuspal stiffness. Hence the concept of minimally invasive endodontics arose to preserve
the tooth structure. However, certain clinical scenarios challenge this concept. Calcification
in the coronal area or sclerosed canals demand excessive removal of tooth tissue compromising
tooth structure and increase chances of perforation. This has paved the path for Guided
Endodontics (GE)—a concept utilizing a three-dimensional (3D) imaging system, i.e.,
cone-beam computed tomography (CBCT)—for access cavity guidance. Since its advent,
CBCT has opened up numerous prospects for treatment planning. CBCT is frequently employed
in the field of dental implantology for 3D design, bone-level measurement, or to view
anatomical structures like the mandibular nerve canal.[13] Another use of CBCT in guided implant surgery is the use of templates for implant-site
preparation and insertion. With the help of matched 3D surface scans and CBCT data,
these templates can now be produced utilizing 3D printing technology. CBCT images
represent a considerable advancement in recent years. More recent devices and creative
software with more resources have made it possible to create a more accurate reproduction
of the internal anatomy of teeth while avoiding distortions that cause inaccuracy
and access mistakes.[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[31] In the vast majority of indicated circumstances, guided access may therefore be
efficiently planned with the removal of image artefacts caused by high-density materials.
The procedure for GE includes obtaining volumetric data from CBCT and surface scan
from an intraoral scanner. Both sets of data are then superimposed for planning a
virtual access cavity and creating a template in the computer-aided design (CAD) software.
The template is then created using 3D printing, and cavity prepared through drills.
The present study was undertaken to answer the research questions “What is the accuracy
of GE in navigation and location of root canals as compared to conventional technique,”
“What is the difference in deviation between planned and performed procedure in virtual
endodontics,” and “What is the difference in procedural time taken between the conventional
and guided techniques.”
Materials and Methods
Study Models
Six similar sets of mandibular and maxillary jaw with 10 extracted teeth in each were
used for the present study. The sample size was calculated at 80% power and 0.05 level
of significance to detect medium effect size in outcomes, such as procedural time
and deviation. This size ensured sufficient precision and robustness for binary and
continuous outcomes. Teeth extracted for orthodontics or periodontal reasons and with
a single root were chosen. Teeth restored endodontically or with severe dental caries
were excluded. Models were divided into GE group and conventional canal preparation
group. The teeth were randomly assigned to either group using a computer-generated
randomization sequence. Additionally, the allocation of teeth to the two endodontists
was randomized to reduce operator-related bias. Blinding was only partially used in
the study. Because of the nature of the procedures, the operators were aware of the
technique they were doing; nevertheless, the evaluation of accuracy (linear and angular
deviations) and procedural outcomes was performed by an impartial assessor who was
blinded to the group assignments.
Intraoral periapical radiographs were used for the conventional technique. Teeth in
each model were adjoined using cold cure polymer at the cervical region alone barring
root surface. A removable base made of putty silicone was then made to facilitate
stability during clinical procedure.
Preoperative CBCT on all models was obtained using Carestream equipment, with voxel
sizes of 150 m (110 kV; 30 mA; field of view: 128 cm), and data were stored in Digital
Imaging and Communication in Medicine (DICOM) format. Furthermore, surface data were
saved in the stereolithography (STL) file format after the models were scanned with
an intraoral scanner. For virtual access cavity design, both types of data were superimposed
using dental CAD software. A planning tool for guided implant surgery was used to
import CBCT data. A virtual bur measuring a total length of 37 mm, having a working
length of 18.5 mm, and a diameter of 1.5 mm was created. For planning purposes, a
virtual sleeve for guidance with dimensions of 1.5 mm on the inside, 2.8 mm on the
outside, and 6 mm on the length was also developed. To enable direct access to the
apical part of the root canal, the virtual bur was placed on each tooth. The surface
scans were submitted to the implant planning program in order to make a template for
“GE.” By lining up the teeth's crowns, scans and CBCT data were compared. Finally,
using a coDiagnostiX software tool, a virtual template was created.
Access Cavity Preparation
Two trained endodontists with normal visual acuity performed the access cavity preparation
in both upper and lower arch models. Each operator performed five sets using GE and
five sets with conventional technique. Dental loupes were used by both operators.
Conventional Cavity Preparation
A high-speed contra-angle handpiece and a cylindrical diamond bur with rounded edges
were used to prepare the initial access cavity. Root canal was located using long
pulp burs or an ultrasonic instrument with 25 size K file. The operators were permitted
to halt the procedure if they were unable to reach a root canal or determined that
the tooth was too compromised to be retained due to perforations.
CBCT or Virtual Imaging
Each model had templates attached to it. The bur was pecked through the template's
sleeve with a low-speed handpiece until it came to rest against the resin sleeve's
mechanical stop. Gauze was used to clean the bur, sodium hypochlorite irrigation was
done at every 2 mm while drilling, and the bur was changed after working on 10 canals.
Each canal was examined with a size 10 K-file (Dentsply Sirona, Charlotte, United
States) to determine the accessibility of the canals after guided access cavity preparation
was finished. The operation was classified as a canal accessibility if the K-file
could enter the root canal by guided access cavity preparation without encountering
any resistance; otherwise, it was classified as a canal inaccessibility. [Figs. 1]
[2]
[3]
[4]
[5] to [6] show the workflow for GE, including preoperative mandibular models, stabilization
techniques, 3D-printed templates, virtual template designs using CBCT and STL data,
and visualizations of planned and guided access cavities with precise angular deviations.
Fig. 1 Preoperative model of mandibular arch for guided and conventional endodontics.
Fig. 2 Mandibular model with cold cure polymer stabilization for endodontic access preparation.
Fig. 3 3D-printed template for guided endodontic access cavity preparation. 3D, three-dimensional.
Fig. 4 Superimposed CBCT and STL data for virtual template design in guided endodontics.
CBCT, cone-beam computed tomography; STL, stereolithography.
Fig. 5 Visualization of planned guided endodontic access cavities in the maxillary arch.
Fig. 6 Virtual path of burs for guided endodontic access with angular deviations marked.
Quantifying Accuracy
Postoperative CBCT scans of the models were performed following access cavity preparation.
By comparing the pre- and postoperative CBCT scans, data were uploaded into the coDiagnostiX
program to assess the variation between the intended and performed access cavities.
The virtual burs used for planning were placed on the access cavities of the postoperative
scan after both scans had been aligned. The software automatically determines the
divergence between the created cavity and the virtual planning at the base point (coronal
end point of the working length of the bur) and tip of the bur. Variations in mesial/distal
and buccal/palatal aspect, depth, and angle were identified.
Statistical Analysis
Data were analyzed using Statistical Package for Social Sciences (SPSS) version 25.0.
Descriptive statistics were calculated for linear and angular deviations in coronal
and apical areas. A paired “t”-test was used to assess the difference between planned and performed access cavities
and procedural time for both groups. For all analyses, the level of significance was
set below 5 percent.
Results
Sixty teeth were evaluated and categorized into two groups: guided and conventional.
Outcomes assessed were key differences in terms of canal detection rates, procedural
time, and accuracy between the planned and performed access cavities.
Canal Detection Rates
When assessed for the canal detection rates, the GE technique showed a superior canal
detection rate by locating all 10 canals in each model, with a 100% success rate.
Conversely, the conventional technique identified 7 out of 10 canals in the models,
accounting for a success rate of 70%. Although the difference was not statistically
significant, the difference in detection rates highlights the efficacy of guided techniques
in navigating and locating root canals, particularly in challenging clinical scenarios
like calcified canals.
Procedural Time
When evaluating procedural time, the guided technique was significantly faster than
the conventional method for both operators. The mean procedural time for Operator
1 using the conventional technique was 22.58 ± 2.73 minutes, whereas the guided method
reduced this time to 17.41 ± 1.51 minutes, with a statistically significant difference
(p = 0.000). Similarly, Operator 2 required 21.76 ± 2.19 minutes for the conventional
technique, which decreased to 17.65 ± 1.54 minutes using the guided method, also showing
a significant difference (p = 0.000) as observed in [Table 1]. The reduction in procedural time with GE can be attributed to the preoperative
planning and the precision provided by the templates.
Table 1
Operative time
|
Parameter
|
Conventional
|
Guided endodontics
|
Chi-square statistic
|
p-Value
|
|
Canals detected
|
|
|
|
Operator 1
|
8/10
|
10/10
|
2.222
|
0.136 (NS)
|
|
Operator 2
|
7 / 10
|
10 /10
|
3.529
|
0.060 (NS)
|
|
Procedural time required (in minutes)
|
ANOVA statistic
|
p-Value
|
|
Operator 1
|
22.58 ± 2.73
|
17.41 ± 1.51
|
|
|
|
Operator 2
|
21.76 ± 2.19
|
17.65 ± 1.54
|
|
|
Accuracy of Access Cavity
The accuracy of access cavity preparation was quantified by comparing the deviations
between the planned and performed cavities in both techniques. Linear deviations were
measured at the coronal and apical ends of the cavity, while angular deviations were
also recorded. For Operator 1, the linear deviation in the coronal region was 0.164 ± 0.190 mm,
and in the apical region, it was 0.254 ± 0.223 mm. Operator 2 showed similar results,
with coronal deviation being 0.197 ± 0.237 mm and apical deviation measuring 0.216 ± 0.155 mm.
These deviations were minimal and indicated that GE closely adhered to the virtual
plan. The angular deviations were almost identical between the two operators, averaging
1.818 ± 1.228 degrees across all samples as seen in [Table 2]. In comparison, the conventional technique showed greater variability in linear
and angular deviations due to the lack of guidance and reliance on manual control.
This shows the enhanced precision of GE, which is particularly valuable in clinical
cases with complex canal anatomies or calcifications.
Table 2
Accuracy between cavity created and virtually planned
|
Variables
|
Mean + SD
|
Minimum
|
Maximum
|
|
Linear deviation (coronal), in mm
|
|
Operator 1
|
0.164 ± 0.190
|
0.00
|
0.52
|
|
Operator 2
|
0.197 ± 0.237
|
0.00
|
0.64
|
|
Linear deviation (apical), in mm
|
|
Operator 1
|
0.254 ± 0.223
|
0.00
|
0.74
|
|
Operator 2
|
0.216 ± 0.155
|
0.01
|
0.48
|
|
Angular deviation, in degrees
|
|
Operator 1
|
1.804 ± 1.238
|
0.02
|
3.86
|
|
Operator 2
|
1.832 ± 1.218
|
0.02
|
3.93
|
|
Average
|
1.818 + 1.228
|
|
|
Discussion
This study showed that GE fared well compared to the conventional form in terms of
locating canals and time taken for the procedure. When evaluating for GE, it was observed
there was minimal difference between the planned and performed procedures in terms
of linear and angular deviations.
The first laboratory research on the predictability of guided endodontic cavity preparation
was reported by Buchgreitz et al[32] and Zehnder et al.[33] Both studies found minor variations between virtually planned and practically carried
out preparations in extracted human teeth. Subsequent clinical case reports also reported
on the successful treatment of calcified anterior teeth in the maxilla by Krastl et
al[34] and van der Meer et al.[35]
Our study showed a linear deviation of 0.213 ± 0.33 mm in the apical region and 0.180 ± 0.233 mm
in the coronal region. This was similar to the other studies in the existing literature.
Buchgreitz et al assessed the accuracy between drilled and guided paths on 48 teeth
mounted with calcified canals and found it to be 0.42 mm. Another study conducted
by Su et al[3] noted a linear deviation of 0.13 mm in the coronal part and 0.46 mm in the apical
part. Angular deviation reported in our study was 1.818 ± 1.228 degree, which was
slightly lesser than that reported by Su et al[3] but was almost similar to that of Zehnder et al.
Decurcio et al[36] have recommended GE in cases of endodontic surgery for better positioning of the
lesion site and dental apex. Coronary access to calcified tooth is a demanding surgical
task, making it difficult to keep the correct trepanation direction when it mostly
involves the middle and apical thirds. It can lead to deviations or perforations even
for skilled endodontists, increasing the likelihood of failure. Employing the guided
approach offers the patient improved safety, enhanced predictability, lesser amount
of tooth tissue removal, and a shorter duration of clinical visit. Additionally, these
guided techniques lessen the possibility of trans- and postoperative problems such
bleeding or injury to nearby anatomical tissues and in turn a better prognosis.
The benefit of GE is that it takes less investment in the office because digital planning
centers are equipped with tools for image acquisition, virtual planning, and guides
printing. Additionally, it requires fewer clinical appointments, which improves patient
comfort and lowers professional stress. The use of GE is recommended in a variety
of clinical settings. Greater practical applicability was made possible by a deeper
comprehension of its features and by exploring digital resources in endodontics. Indications
must regard this as an adjunct to aid the endodontist's arsenal rather than as a particular
convenience resource and facilitator for practitioners with less clinical expertise
and/or who do not employ the right technology for difficult endodontic procedures.
However, with the advancement of technology, extensive research and applications for
digital endodontics are needed.
A variety of endodontic guiding systems are now introduced, such as the sleeveless
guide system and the dynamic navigation system (DNS).[37]
[38] The path is guided by guiding rails and cylinders attached to the handpiece in the
sleeveless guide system. This method could be utilized to address the issue of a shortage
of vertical space in the molar area because it takes up lesser space above the occlusal
surface and offers better visibility than a sleeve template. On the other hand, DNS
offers precision comparable to static templates and has the capacity to modify the
direction of the access cavity in real time.[39] However, operating DNS requires stronger eye–hand coordination and technological
practice, which adds to the increased cost.
The complex architecture of root canals might limit the utilization of GE, even when
proposed as an indication. Only the straight section of the root canal may be reached
with guided access, and the accuracy decreases as the root canal curves. In this regard,
careful planning is required, with only the straight portion being subjected to wear
and drilling to prevent bending. The diameter of the root is another feature of dental
anatomy. The use of burs in this area is incompatible due to the diverse root configurations
in the various dental groups, which may result in roots with limited thickness in
the mesiodistal and/or buccolingual direction (e.g., lower incisors or mesiobuccal
roots of the upper molars). Patients with limited mouth opening may make guided access
more difficult or even dangerous, especially for posterior teeth. The virtual planning
and accuracy of the prototype guides for the procedure may also be restricted by CBCT
tests that exhibit image artefacts in the region.
Comparing our study's canal detection rates with those reported in the literature,
our success rate surpasses the conventional technique's findings of merely 70 to 80%
success by quite some margin. Kostunov et al[40] present results that stand in contrast to these: their employment of traditional
methods yielded an impeccable track record—achieving a perfect score—a feat not replicated
by any means using guided techniques, which earned only slightly lower at 93.3%. Both
methods, in alignment with Hildebrand et al,[41] successfully detected canals; however, the studies may exhibit variations due to
differences in tooth selection type, degree of present calcification, or specific
methodologies employed. The study of Kostunov et al observed that modalities indeed
preserve more tooth structure compared to the conventional technique, in terms of
the removal of dental substance; our study however—while not providing quantitative
data on tooth substance removed—suggests through minimal deviations between planned
and executed cavities: it is likely that guided techniques result in less loss of
tooth structure.
Our study further reveals that when we scrutinize procedural times, guided techniques
demonstrate a reduction in procedure duration compared to the conventional technique.
However, these findings somewhat contradict those of Hildebrand et al[41]; their research did not unveil any significant difference in the time taken for
procedures using either method. The complexity of the cases handled, the operators'
experience level, or the specific guided technology utilized may attribute to these
differences. Hildebrand et al[41] underscored the necessity for extra radiographs, requiring a total of 31 supplementary
ones in procedures employing GE; nonetheless, our study did not scrutinize the quantity
of radiographs taken. This aspect—potentially indicative of overall efficiency and
time-saving benefits—is worth considering when assessing its merits. Should the guided
approach indeed require additional radiographic imaging, it may undermine certain
benefits—specifically, those pertaining to time efficiency.
By incorporating guided techniques into their daily operations, dentists might potentially
reduce treatment durations. Consequently, they could accommodate a larger patient
load without sacrificing care quality. This enhanced efficiency may yield superior
throughput and satisfaction among patients: they would value not only speedier procedures
but also decreased discomfort levels. Moreover, the exceptional accuracy of this approach
proves especially advantageous in managing challenging cases with intricate anatomy
or when conventional landmarks become obscured. The transition, however, necessitates
a learning curve and an initial investment in requisite technology and training. Dentists
should balance these considerations with the potential benefits: they must not only
evaluate the short-term impact on their practice but also forecast long-term improvements
in treatment outcomes. When contemplating this shift, practices need to incorporate
ongoing expenses of materials—as well as maintenance costs linked directly to the
implemented technological advancements—into their deliberations.
The experimental setup utilized in our study may not entirely replicate the conditions
encountered during endodontic access in a live clinical environment. We selected single-rooted
teeth for this study—specifically extracted for distinct reasons: to limit case diversity
and potentially influence external validity and applicability of results towards complex
root system or differently indicated extraction cases. We also excluded teeth that
had received previous endodontic treatment or were significantly decayed. Yet, this
selection criterion might have omitted a large patient population who typically needs
endodontic intervention; therefore, it fails to depict the entire spectrum of clinical
scenarios. The models constructed fixed teeth in place with a polymer at the cervical
region only; this method could compromise procedural stability and inaccurately mimic
the natural support that surrounding tissues provide in a patient's mouth. All dental
practices, particularly those in resource-limited settings, may not have the accessibility
or practicality to rely on advanced imaging techniques such as preoperative CBCT and
sophisticated virtual planning software. The comparative assessment between the two
techniques could potentially incorporate an element of subjectivity and inconsistency
due to the operator's discretionary power in halting conventional procedures. Scans
obtained after the procedure and software analysis heavily influence the quantification
of accuracy; however, this approach–though thorough–falls short in capturing every
clinical variable impacting access cavity preparation's success. These unaccounted
factors include: the clinician's tactile feedback or their decision-making process
throughout the procedure.
Integrating GE into ordinary clinical practice necessitates a careful study of its
benefits, costs, and practical implications. Though GE provides higher benefits such
as improved accuracy, shorter procedure times, increased safety, and less tooth structure
loss, adoption of these techniques requires significant financial and technological
resources. The initial expenditure covers the CBCT system, intraoral scanners, CAD
software, and 3D printing capabilities, as well as continuous maintenance and material
costs. Although these costs may be prohibitively expensive for small or resource-constrained
clinics, the potential benefits, especially in complex instances such as calcified
or destroyed canals, justify their usage in enhancing treatment outcomes and reducing
procedural mistakes. GE's ability to reduce treatment time can improve practice throughput,
allowing physicians to accommodate more patients while providing high-quality care.
However, its use necessitates training to understand digital workflows such as CBCT
imaging, virtual planning, and template fabrication, which has a modest learning curve.
High-resolution CBCT systems and dependable 3D printers are critical for reaching
the precision that GE claims. Practices that cannot afford these investments could
work with centralized planning centers for imaging and guide production, lowering
their financial load while providing access to this advanced approach. As a result,
its routine application may be more appropriate for complex circumstances requiring
precision, whereas simpler scenarios may not merit the additional cost and labor.
Conclusion
GE was better than the conventional procedure when compared to location of canal and
time taken. The precisional accuracy of guided path and followed path was also acceptable
in the GE procedure. The procedure time was notably reduced with the guided method.
Deviations from the virtual plan to the actual cavity preparation were minimal. The
assessments support the integration of guided techniques into routine endodontic practice
to improve the precision and efficacy of treatments. In challenging situations, such
as those requiring obliterated or calcified canals, the guided technique results in
a more predictable outcome with fewer iatrogenic mistakes, such as perforations or
excessive tooth structure removal. The guided technique's modest deviations highlight
its ability to preserve tooth structure while maintaining the integrity of the remaining
tooth. This is consistent with the concepts of minimally invasive endodontics, which
aim to improve treatment outcomes while minimizing tooth harm.
