Keywords
conservative access cavity - dental pulp - endodontics - endodontic access cavity
- traditional access cavity
Introduction
Endodontic treatment is the standard care for a nonvital or endodontically involved
tooth. However, endodontically treated teeth are weakened and generally are more prone
to fracture.[1]
[2] Loss of tooth structure, either due to caries or endodontic procedures, including
the loss due to endodontic access cavity preparation is considered a major risk factor
for fractures.[3] Minimally invasive treatments are trending in modern dentistry. Thus, in endodontics,
the concept of contracted access cavity was born because a tooth’s susceptibility
to fracture was found to be proportional to the amount of tooth structure removed.[4]
Traditional access cavity (TradAC) designs for all types of teeth have been the same
since decades with only slight alterations. TradAC involves removal of tooth structure
to allow access to the canals, facilitating complete cleaning, shaping, and obturation,
while preventing procedural complications. However, excessive tooth structure is removed
in a TradAC. Moreover, this affects the tooth’s strength to resist fracture when subjected
to loading in function. Thus, with a reduced and properly designed endodontic access
cavity, the prognosis of a tooth that undergoes endodontic treatment can be improved.[5]
[6]
Meanwhile, in a minimally invasive procedure called conservative access cavity (ConsAC),
tooth structure including the peri-cervical dentine can be preserved.[4] There are no particular rules to prepare a ConsAC. The main aim is to conserve maximum
tooth structure while locating all the canal orifices.
Truss access cavity (TrussAC) on the other hand has been recently introduced to further
preserve the tooth structure.[7] Cone beam computed tomography information of the tooth together with magnification
is used to prepare strategically located truss access.[8] These accesses are placed directly above the respective root canals, and through
these holes, cleaning, shaping, and obturation is performed. Hence, complete root
canal treatment (RCT) is performed either through existing restorative cavities or
by creating small entries leaving lateral pulp horns and the rest of the pulp chamber
unroofed.[7] Many studies have been performed to determine fracture resistance of teeth with
ConsAC[1]
[4]
[9]
[10]; however, there is limited and conflicting evidence available on the fracture resistance
of teeth with TrussAC.[11] Thus, this study aimed to determine the effect of three different access cavity
designs on fracture resistance of endodontically treated mandibular molars.
Materials and Methods
In this in vitro experimental study, 80 recently extracted first permanent mandibular
molars were obtained from dental clinics of School of Dental Sciences, Universiti
Sains Malaysia (USM), Kota Bharu, Kelantan, Malaysia. Teeth were extracted due to
periodontal conditions. The sample size calculation was done using input parameters,
effect size 0.04 with 80% power, and α of 0.05 as per a previous study[7] to obtain a sample size of 20 in each group. Ethics Committee for Human Research,
USM (Ref. USM/JEPeM/17040221) approved this study. All teeth were inspected for the
absence of previous restorations, fractures, or abrasion under a microscope (Leica
Microsystem Imaging Solutions, Cambridge, United Kingdom) at a 20× magnification.
Soft tissue remnants and calculus were cleaned off the surfaces of the selected teeth
with a hand curette. The teeth were then disinfected by soaking for 10 minutes in
sodium hypochlorite (NaOCl) (5.25%; Clorox Inc, Oakland, United States), followed
by rinsing with distilled water. Subsequently, the mesiodistal and buccolingual dimensions
of the teeth were measured using a digital caliper at the cervical margin. Teeth included
in the study had mesiodistal and buccolingual dimension of 10.61 mm (± 0.45 mm) and
10.25 mm (± 0.45 mm), respectively. The mean mesiodistal and buccolingual pulp chamber
distance were 3.76 and 4.39 mm, respectively, measured from preoperative computed
tomographic images. Teeth were stored in 10% formalin solution until use.
Eventually, 20 teeth were allocated to each group as follows:
Group 1: Teeth with TrussAC prepared.
Group 2: Teeth with ConsAC prepared.
Group 3: Teeth with TradAC prepared.
Group 4: Control group; intact teeth.
TrussAC, ConsAC, and TradAC were prepared on all teeth respectively using an endo
access bur size 2, 21 mm (Dentsply Maillefer, United States) mounted on a high speed
handpiece, water spray was used as coolant. In group 1, truss accesses were prepared
above the mesial and distal roots utilizing preoperative computed tomographic images
as a guide, ensuring the canal orifices could be located, leaving a truss in between
the mesial and distal cavities. Hence, a small access and tiny entries left the pulp
chamber roof and lateral pulp horns intact[7]
[12] ([Fig. 1A]). In group 2, the ConsAC preparation was initiated at the central fossa (mesial
quarter) and extended distally and apically until all canals were located. Peri-cervical
dentin removal mesiodistally, buccolingually, and circumferentially was minimized
ensuring pulp chamber roof was partly maintained and all root canal orifices could
be localized visually from the same angulation[4] ([Fig. 1B]). TradAC preparation was performed on teeth in group 3 following the TradAC principles
as reported in earlier studies[1]
[7] ([Fig. 1C]). RCT was then done in all access cavity groups. A K-file size 10 (FlexOFiles; Dentsply
Maillefer, Switzerland) was used to check canal patency. Working length was determined
by introducing a file till it was visible beyond the apical foramen, 1 mm was then
subtracted and determined as the working length. Instrumentation was then performed
using NiTi rotary files (S5 Sendoline, Sweden) until final apical size 30, 0.06 taper
following manufacturers’ instructions. Irrigation with 2.5% NaOCl solution (Lenntech,
Delfgauw, Netherlands) was performed during instrumentation. Finally, 5 mL of 17%
ethylenediaminetetraacetic acid solution (Promega Corporation, Wisconsin, United States)
followed by 10 mL of normal saline solution (RMBIO, Missoula, Montana, United States)
was used. Obturation was subsequently performed using gutta-percha (Dentsply Maillefer,
Switzerland) and AH Plus sealer (Dentsply Maillefer, Switzerland) using warm vertical
condensation technique. Throughout the endodontic procedure the teeth were handled
using a moistened gauze to avoid dehydration of the samples.
Fig. 1 Access cavity designs for each group: (A) Truss access cavity; (B) Conservative access cavity; (C) Traditional access cavity.
After completion of endodontic treatment, the access cavities were cleaned using a
spoon excavator followed by a moistened cotton pellet to remove all the debris. Phosphoric
acid 37% (Magic Acid Coltene, Brazil) was used for etching (enamel for 30 and dentine
for 15 seconds). Subsequently, the cavity was rinsed with water/air spray for 30 seconds,
and air-dried gently to avoid desiccation. An adhesive (OptiBond S; Kerr Corporation,
California, United States) was then applied, thinned by gentle air blowing, and polymerized
using a light-emitting diode for 10 seconds. Finally, composite resin (Zmack Comp,
Italy) was placed incrementally (2 mm increments) to restore the access cavities and
each increment polymerized for 40 seconds following the manufacturers’ instructions.
Subsequently, composite restoration was polished using a composite polishing kit (Shofu,
United States).
All teeth were then mounted with the roots 2 mm below the level of cementoenamel junction
embedded in self-cured resin. Silicon impression material was used to simulate the
periodontal ligament ((Panasil Light Body; Kettenbach GmbH & Co KG, Eschenburg, Germany).
Next, the specimens were mounted in a universal testing machine (AGS-X, Shimadzu,
Japan). The teeth were loaded using a spherical steel tip of 3 mm diameter at a speed
of 1 mm/min. Forces were then applied vertically on their central fossa, parallel
to the tooth’s long axis. The load at which the teeth fractured was recorded in Newton
(N) as indicated by the load testing machine software.[13] Fracture levels were then determined by examining the specimens using a stereomicroscope
(Stereo Discovery, Zeiss, Germany). The following was used to classify fracture patterns:
Restorable: Fracture above the bone simulation level (acrylic resin).
Unrestorable: Fracture extending below the bone simulation level.
Normality of distribution was determined using the Kolmogorov–Smirnov test. One-way
analysis of variance complemented with Bonferroni test was used for data analysis.
Chi-square test was used to analyze the types of fractures. Significance level was
set at p = 0.05.
A literature search was then performed on January 6, 2020 using PubMed and Google
Scholar to find relevant articles using keywords, “Truss access cavity preparation,”
“Fracture strength with truss access cavity,” “Truss access approach,” and “Influence
of truss access on fracture strength”; obtained literature was reviewed and summarized.
Results
The highest mean fracture resistance was found in group 4, followed by group 1, group
2, and group 3 demonstrating the lowest mean fracture resistance ([Table 1]). Besides, pairwise comparison of fracture resistance between groups showed significant
difference between all groups, TrussAC and TradAC (p < 0.001), TrussAC and control (p = 0.042), ConsAC and TradAC (p < 0.001), ConsAC and control (p = 0.007), and TradAC and control (p < 0.001) except between TrussAC and ConsAC (p = 0.524).
Table 1
Fracture strength (N) analysis with comparison among groups using one-way ANOVA complemented
with Bonferroni test
|
Groups
(n = 20)
|
Mean
|
SD
|
One-way ANOVA
test results
p-value
|
Bonferroni test
test results
p-value
|
|
ConsAC
|
TradAC
|
Control
|
|
Abbreviations: ANOVA, analysis of variance; ConsAC, conservative access cavity; SD,
standard deviation; TradAC, traditional access cavity; TrussAC, truss access cavity.
aStatistically significant (p < 0.05).
|
|
TrussAC
|
2068.07
|
357.39
|
< 0.001a
|
0.524
|
< 0.001 a
|
0.042 a
|
|
ConsAC
|
1954.41
|
224.30
|
|
< 0.001a
|
0.007 a
|
|
TradAC
|
1254.77
|
122.82
|
|
|
< 0.001 a
|
|
Control
|
2435.66
|
237.67
|
|
|
|
In intact teeth (control group), a significantly higher number of restorable fractures
were noted (p = 0.031). However, in all test groups, unrestorable fractures were significantly
higher than the restorable ones (p = 0.028). This data are illustrated in [Fig. 2]. No correlation between the type of cavity and the favorability of fracture was
found (p = 0.521).
Fig. 2 Bar chart showing the fracture pattern among the four groups.
Literature Review
[Table 2] summarizes the list of studies that assessed the influence of TrussAC. A study was
performed to determine whether the design of the endodontic access cavity (TradAC,
ConsAC, TrussAC) and the amount of remaining tooth structure had any influence on
the fracture strength of mandibular molars. It was found that loss of marginal ridges
significantly affected the fracture strength rather than the endodontic cavity design
itself. When the marginal ridges were intact, the teeth accessed with TrussAC, ConsAC,
or TradAC had no significant difference in their fracture strength.[7] Another similar study aimed to determine if different access cavity designs (TradAC
and TrussAC) and use of different restorative base materials influenced the fracture
strength of mandibular molars. It was found that the fracture strength did not increase
with TrussAC. Furthermore, the fracture strength of teeth with TradAC or TrussAC was
not significantly different when the same base material was used.[14] Another study was performed to assess the influence of using TradAC and TrussAC
access cavity design on the efficacy to debride the pulp chamber and mesial root canal
systems of mandibular molars. The authors concluded that pulp tissue remnants were
seen in both TradAC and TrussAC groups; however, the amount of pulp tissue remnants
were significantly lower in the pulp chamber of the TradAC group.[12] Furthermore, a recent study performed on endodontically treated mandibular first
molars compared the fracture resistance of teeth with TradAC, TrussAC, and artificial
truss restoration. The fracture resistance was not significantly different between
the groups.[15] Only one case report and one case series has been published on TrussAC design. However,
no posttreatment follow-up is presented.[16]
[17] Furthermore, posttreatment radiographic evaluation is not satisfactorily presented,
and the methodology was also not adequately explained.[16] Besides, both these reports did not use three-dimensional imaging to plan orifice-directed
access cavities (TrussAC) which might lead to failure of detecting additional/accessory
root canals.
Table 2
List of studies and cases that determined the effects TrussAC
|
Author (year)
|
Purpose of study
|
Methodology
|
Outcomes
|
|
Abbreviations: ATR, artificial truss restoration; ConsAC, conservative access cavity;
SDR, smart dentine replacement; TradAC, traditional access cavity; TrussAC, truss
access cavity.
|
|
Corsentino et al[7] (2018)
|
Assess influence of access cavity design (TradAC, ConsAC, TrussAC) and remaining tooth
substance on fracture strength
|
Sound mandibular molar teeth were selected. After access cavity preparation, and removal
of no, one, or two marginal walls, teeth were endodontically treated and restored.
The specimens were then loaded to fracture in a universal loading machine
|
TrussAC and ConsAC do not increase the fracture strength of endo treated teeth, rather
the loss of mesial and distal ridges reduced fracture strength of teeth significantly
|
|
Özyürek et al[14] (2018)
|
Assess the effects of endodontic access cavity preparation design (TradAC, TrussAC)
and different restorative base material on the fracture strength
|
Intact mandibular molar teeth were randomly assigned to TradAC or TrussAC group (with
one marginal wall missing), restored with either SDR or EverX posterior as base material.
Samples loaded after restoration until fracture
|
TrussAC did not increase the fracture strength of teeth. No difference in the fracture
strength between teeth with TradAC or TrussAC when the same base material was used
|
|
Neelakantan et al[12] (2018)
|
Assess the influence of using TradAC and TrussAC access cavity design on the efficacy
to debride the pulp space
|
Intact mandibular molar teeth randomly assigned to TradAC or TrussAC group, endodontically
treated and evaluated histologically after sectioning to determine remaining pulp
tissue
|
The amount of pulp tissue remnants was significantly lower in the pulp chamber of
TradAC group
|
|
Abou-Elnaga et al[15] (2019)
|
Assess the influence of TradAC, TrussAC, and ATR on fracture resistance
|
Intact mandibular 1st molars were randomly assigned to TradAC, TrussAC, and ATR. After
access cavity preparation, and removal of both marginal walls, teeth were endodontically
treated and restored. The specimens were then loaded to fracture
|
The fracture resistance was not significantly different between the groups
|
|
Auswin and Ramesh[16] (2017)
|
A case report on TrussAC new conservative approach
|
Right first molar root canal treatment using TrussAC preparation
|
This minimal invasive approach in access opening prevents unnecessary tooth structure
removal
|
|
Mooktiar et al[17] (2019)
|
A TrussAC preparation case series
|
Three permanent teeth with an indication for endodontic treatment were treated via
the TrussAC design
|
This minimal invasive approach in access opening avoids the need for conventionally
placed crowns
|
Discussion
In this study, the fracture resistance of sound teeth and teeth accessed with TrussAC,
ConsAC, and TradAC were compared. Endodontically treated teeth fracture most commonly
due to loss of tooth structure,[3] and following TradAC principles for endodontic access cavity preparation is one
of the most important causes of tooth structure loss.[18]
In an attempt to reduce the risk of fracture in endodontically treated teeth, ConsAC
and TrussAC were introduced.[10] However, to the best of our knowledge, only one previous study has compared the
fracture resistance of teeth accessed with TrussAC and ConsAC.[7] Thus, the present study tested the effect of TrussAC, ConsAC, and TradAC on the
fracture strength of teeth treated endodontically. In endodontically treated posterior
teeth, vertical fractures most commonly occur in mandibular molars,[7]
[19] thus they were selected in this study. Furthermore, to enable loading test and to
simulate procedures performed clinically, composite resin was used to restore the
endodontic access cavities. It has been observed that fracture strength is reinstated
by nearly 72% after endodontic access cavities are restored.[3]
All preparation of the specimen was performed by one expert operator to eliminate
differences in results caused by a difference in skills of the operator. In this study,
the fracture strength of the TradAC group was found to be the lowest in comparison
to the control, TrussAC, and ConsAC groups. Likewise, a previous study comparing the
fracture resistance of teeth with TradAC and ConsAC showed similar results.[1] When cavities are prepared with TradAC principles, the cavity floor is also the
pulp chamber floor.[7] Since, the centrally located tooth structure in mandibular molars is subjected to
heavy masticatory loads, in ConsAC, preserving a part of the pulp chamber roof helps
in distributing the occlusal forces, thereby reducing the amount of forces reaching
the pulpal chamber floor.[10] An additional aim in conservative access is to preserve the peri-cervical dentin,
which is very important for the lifetime and the optimal function of teeth. However,
studies that compared the fracture resistance of teeth accessed with ConsAC and TradAC
found no significant difference.[7]
[9]
[14] Furthermore, Abou-Elnaga et al[15] reported that in teeth prepared with TradAC and TrussAC, fracture resistance did
not differ significantly. Contrasting findings among studies comparing TradAC, ConsAC,
and/or TrussAC could be due to difference in the type of teeth used, methodology of
the study, and type of restorative material used.
Additionally, in this study, fracture resistance of teeth accessed with ConsAC and
TrussAC did not differ significantly. These results are in line with other studies
that tested the fracture resistance of teeth accessed with TrussAC.[7] However, fracture resistance of teeth with TradAC was significantly lower than those
with TrussAC in this study. This result is in line with a recent study that compared
the fracture resistance of teeth with TrussAC and TradAC with and without artificial
aging.[20] The authors concluded that TrussAC did not reduce the fracture strength as compared
with sound teeth, nevertheless, when subjected to thermal stress the fracture strength
of teeth accessed with both TrussAC and TradAC was significantly reduced.[20] Besides, the efficacy of the entire root canal therapy can be influenced by a reduced
access cavity.[10] TrussAC can particularly affect the ability of detecting root canals and influence
complete removal of debris and pulp tissue remnants.[12]
Moreover, looking at the pattern of fractures in intact teeth, unrestorable ones were
significantly lower than restorable ones. On the contrary, in TradAC, ConsAC, and
TrussAC groups, restorable ones were significantly lower than unrestorable ones. Similarly,
previous studies also reported a higher number of unrestorable fractures in accessed
teeth, irrespective of the access cavity design type used.[1] Extended preparation in TradAC design greatly reduces the amount of sound dentine,[21] thus increasing the tooth deformability resulting in fractures that are unfavorable
to restore. Although ConsAC and TrussAC preserve more peri-cervical dentin and pulpal
chamber roof, there is still a decrease in the fracture strength due to loss of tooth
structure, leading to more unfavorable fractures.[3]
The limitations of this study include the use of static instead of dynamic force to
determine the fracture strength. Additionally, the pH, temperature, and other intraoral
factors were not simulated; hence, results should be extrapolated to the clinical
situation cautiously.
Conclusion
Considering the limitations, it is concluded that, lower fracture strength was observed
in teeth with TradAC (group 3) as compared with TrussAC (group 1) or ConsAC (group
2). Furthermore, when accessed using TrussAC, the fracture strength was not greater
than in teeth with ConsAC. Moreover, unrestorable fractures were more than restorable
ones in all accessed teeth.
The literature review showed that accessing teeth with TrussAC had no significant
effect on the fracture strength, rather the fracture strength was significantly reduced
with the loss of one or more marginal ridges. Furthermore, TrussAC resulted in a higher
amount of pulp tissues remnants in the pulp chamber which may lead to failure of endodontic
treatment. These conclusions are based solely on in vitro studies and clinical translation
may not be completely pertinent.
