Mohammad Sabeti, DDS, MS,* Majid Kazem, DDS, MS,†‡ Omid Dianat, DDS, MS,‡§ Nazanin Bahrololumi, DDS, Amirreza Beglou, DDS, Kasra Rahimipour, DDS, and Farshad Dehnavi, DDS

1. IMPACT OF ACCESS CAVITY DESIGN AND ROOT
CANAL TAPER ON FRACTURE RESISTANCE OF
ENDODONTICALLY TREATED TEETH: AN EX
VIVO INVESTIGATION
Mohammad Sabeti, DDS, MS,* Majid Kazem, DDS, MS,†‡ Omid
Dianat, DDS, MS,ठNazanin Bahrololumi, DDS, Amirreza Beglou,
DDS, Kasra Rahimipour, DDS, and Farshad Dehnavi, DDS
1

2. • Tooth fracture is one of the most undesirable phenomena in
endodontically treated teeth (ETT) and usually leads to tooth
extraction.
• It is mainly associated with the loss of tooth structure because of
dental carries or the therapeutic endodontic procedures such as access
cavity and root canal preparation.
• The endodontic access cavity is considered an important step in
endodontic treatments.
INTRODUCTION
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3. • New concept of a conservative access cavity (CAC), inspired by
concepts of minimally invasive dentistry, has been designed and
developed in order to minimize the removal of the chamber roof and
pericervical dentin .
• For instance, newly developed ultraflexible canal preparation
instruments make straight-line access to the canals less important;
also, the progress in visual magnification makes it easier to find canal
orifices without the need for excessive expansion of access cavity
walls.
• However, inadequate access cavity also increases the prevalence of
iatrogenic complications during endodontic procedures.
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4. • The higher instrument tapers lead to superior canal and canal wall
cleanliness, excessive removal of radicular dentin because of increased
instrumentation taper.
• Accordingly, the aim of the present study was to evaluate and compare
the effect of access cavity preparation and 3 different root taper
preparations on ETT fracture resistance of maxillary molars.
4

5. Sample Preparation
• 78 sound maxillary first and second molars were collected based on the
inclusion and exclusion criteria.
• 30 maxillary first molars were similarly decoronized. Three roots of each tooth
were divided by burs (ISO no. 806 104 199 544 016; NTI, Kahla, Germany) under
sufficient water cooling. The distobuccal roots were randomly assigned to 1 of
3 groups (n = 10) for tapering evaluation (ie, a .04 taper, a .06 taper, or a .08
taper).
• Roots with more than 20% deviation were replaced. 5
Materials and Methods

6. • All specimens of the tapering groups were prepared for endodontic
treatment.
• After establishing the working length, canals were instrumented up to an
apical size of 25; instrumentation was performed with the Twisted Files
rotary system (taper .04, .06, and .08; Kerr Co, Glendora, CA) according to
the manufacturer’s instructions.
• Intermittent irrigation with 5 mL 2.5% sodium hypochlorite was applied
with 30-G needles.
6

7. • The another 48 teeth, which were similar in buccolingual and mesiodistal
size, were randomly assigned to 1 of 3 groups (n = 16):
• Group 1: Intact teeth; no treatment (negative control)
• Group 2: Traditional access cavity (TAC, positive control)
• Group 3: Conservative access cavity (CAC, experimental)
• Access cavities were prepared using coarse, flat-end diamond burs (ISO
no. 806 104 199 544 016, NTI) in a high-speed handpiece with sufficient
water cooling.
• In the TAC group, traditional endodontic access cavities were prepared
following conventional guidelines.
7

8. • In the CAC group, in order to determine the outlines of the access
cavity and locate the pulp chamber and canals, they used 2 periapical
radiographs made from buccal and mesial aspects as a guide.
• Then starting from central fossa, cavities were extended only as
necessary to visualize and locate canal orifices while taking care to
preserve pericervical dentin.
8
Conventional
access cavity
Conservative
access cavity

9. • To simulate the periodontal ligament space, roots were covered before
acrylic embedment with a uniformly thin 0.2-mm layer of light body
silicone impression material.
• For both experimental groups (ie, the tapering and cavity preparation
groups), a fracture resistance test was conducted.
• To analyze the results, statistical software (SPSS 17; SPSS
Inc,Chicago, IL) was used
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10. 10
Results
Root Canal Tapers

11. 11
Different access cavity designs

12. • Endodontic procedures encompass various steps such as access cavity
preparation and root canal preparation, which may result in the loss of
excessive tooth structure, weakening of the tooth, and a subsequent reduction
in the tooth’s capability to resist forces
• conservative approaches have gained attention for the restoration of tooth
stability.
• As shown in a study by Krishan et al , minimal access cavities were
associated with compromised canal instrumentation in the distal canals of
mandibular molars. Moreover, the lack of straight-line access because of
inadequate tooth tissue removal may compromise the delivery of irrigants to
the apical portion of the roots because it avoids the needle reaching further
into the canal
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Discussion

13. • However, some researchers believe that conventional access preparation
removed unnecessary sound dentin and can decrease resistance to tooth
fracture.
• In agreement with the results, Moore et al reported that the fracture
strength in maxillary molars with CACs and TACs was remarkably lower
than that of intact molars.
• Although the CAC’s fracture strength was 23% greater than that of
TAC, this difference was not statistically significant; this finding
suggests that, in comparison with TAC preparation, CAC preparation
provides insignificant advantages with regard to fracture strength.
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14. • The removal of the pulp chamber roof and the disruption of tooth
integrity may have been responsible for the substantial reduction in
fracture resistance of the ETT of both groups in comparison with the
intact teeth, which is supported by the finding of many other studies.
• Rover et al, suggested a reduced possibility of canal orifice detection
in the CAC group in comparison with the TAC group. They also
observed an increased possibility of canal transportation associated
with CACs.
14

15. • The primary aim of endodontic treatment is to eliminate
microorganisms. Research has established that bacteria can penetrate
into and colonize almost half the length of dentinal tubules
• Accordingly, inadequate removal of infected dentin within the canals
can decrease the prognosis and lead to posttreatment failures.
• For root canal shaping, the current study showed no significant
reduction of the fracture resistance of the root by .06 taper
instrumentation compared with .04, whereas preparation with the .08
taper showed a significant decrease in fracture resistance.
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16. • In agreement with our results, a previous study has shown that during
instrumentation, maintaining the natural geometry of the root canals is a
paramount stabilizing factor for the tooth.
• Possibly, in their study, the decrease in fracture resistance that followed .08
taper instrumentation might have been the result of geometric alterations
of the root canals because .08 taper files are more rigid and less adaptable.
• Root fracture occurs as a result of propagation of microcracks created in the
root canal shaping process with occlusal forces . Thus, they suggest that the
increased risk of fracture with the .08 taper in this study might be
associated with the greater number of craze lines and the greater degree of
imposed stress in root dentin
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17. • 1 limitation of the present study is that the variability of the tested teeth
may have confounded the results. In addition, preparing the conventional
and conservative access cavities with the same degree of accuracy in all
teeth is difficult.
• They suggest that in order to achieve experimental conditions that are
more similar to clinical conditions, subsequent studies should use finite
element analysis.
• The data achieved in this ex vivo study provide insight into the fracture
resistance of different access designs and root canal tapers in the clinical
setting. However, for more certain results, clinical trials with long-term
follow-ups are required.
17
Limitation

18. 18
Conclusion
• The following can be concluded:
1. Increasing the tapering of root canal preparation can
detrimentally affect tooth fracture resistance
2. Conservative endodontic access in maxillary molars was not
shown to significantly increase fracture resistance over traditional
access

19. 19
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22. Thankyou!
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