Comparative Evaluation of Different Endodontic Access Cavity Designs with Different Burs—An in vitro Experimental Insight into the Aspect of Fracture Resistance

ABSTRACT

Introduction:

In vitro fracture resistance of extracted mandibular molars treated with various access cavity designs, including traditional endodontic cavity (TradAC), conservative/contracted endodontic cavity (ConsAC), ninja endodontic cavity (UltraAC), truss endodontic cavity (TrussAC), caries-driven access cavity (CariesAC), and intact teeth, is the focus of this study

Materials and Methods:

Six groups of 20 mandibular molars, totaling 120, were used in the investigation. While the other five groups underwent various access cavity preparations, chemomechanical preparation, and obturation procedures before being repaired with composite resin, Group 1 was left unaltered (the control). A 6 mm round head tip was used to apply the fracture force, which was measured in newtons, at a crosshead speed of 1 mm/min until fracture developed.

Results:

According to the current study, the intact control group had the maximum fracture resistance. The access cavity groups’ mean values were maximum in CariesAC followed by ConsAC, TrussAC, UltraAC, and TraditonalAC respectively

Conclusion:

While among the four minimally invasive designs, CariesAC showed a higher fracture resistance despite the results being statistically insignificant, TradAC had a significantly lower resistance than other conservative access cavity designs.

INTRODUCTION

Endodontically treated teeth are more prone to fracture, which makes rehabilitation difficult. This vulnerability is mostly related to dentin dryness and the destruction of tooth structure during endodontic therapy. Finding root canal orifices requires careful cavity preparation, which can weaken the tooth’s structure and increase its susceptibility to fracture. Due to these drawbacks, ConsAC was developed, a design intended to protect tooth tissues, especially essential pericervical dentin, for better stress distribution. Despite its clinical success, minimally invasive endodontics (MIE) lacks solid scientific support.[1,2,3,4,5]

An even more conservative approach known as “ninja” access (UltraAC) and truss-access (TrussAC)[6] were developed based on the same idea.

To gain access, UltraAC creates a tiny occlusal hole, maintaining tooth integrity but making pulp tissue removal and canal shaping more difficult. By preserving a dentin bridge and providing two distinct access cavities on the mesial and distal aspects,[7] TrussAC is a minimally invasive procedure.

Additionally, CariesAC is an intentional effort to get access from the location of the carious lesion by gently excavating caries and simultaneously preparing the access while protecting all the important oral structures, including delicate architectural features. Some research studies comparing conventional and minimally invasive access designs have been conducted in the literature; nevertheless, this novel study emphasizes the significance of maintaining sound dentin when comparing fracture resistance with conventional all newer methods, including caries.

MATERIALS AND METHODS

Specimen selection and preparation

The Institutional Review Board of our institution gave its approval to this study. Human first and second molars with separate, completely developed root canals were utilized in the course of the study. Teeth with previous root canal therapy, root caries, or restorations were excluded. For testing purposes, the intraoral environment was mimicked by setting each tooth at a 30° angle within the resin and immersing it in salt water to simulate natural compressive loading.

Based on the averages of tooth measurements, the following homogeneous groups were developed to reduce the impact of shape and size variation [Table 1]:

Table 1.

Study Groups

Group A: The control group	Group B: TradAC
Group C: ConsAC	Group D: UltraAC
Group E: TrussAC	Group F: CariesAC

Access cavity preparation

The Cavity Access Kit (Dentsply Sirona) was used to prepare TradACs, and the EndoZ bur (Dentsply Sirona) was used to refine them. While enlarging the access cavity to smaller dimensions under direct observation and instrumentation with the specialized Endoguide Burs (SS White Dental),[8] ConsAC aims to protect tooth structure.

Canal orifices for UltraAC were accessed through the tiny occlusal hole created using size 856 diamond burs (Komet Italia srl, Milan, Italy) similar to the technique by Gianluca Plotino et al.[4] For TrussAC, an orifice directed dentin preservation method was employed[9] with the same size 856 bur was used to create two separate mesial and distal holes preserving the intermediate dental bridge harbouring the central fossa. For CariesAC, to simulate a Class II carious lesion, standard cavities were prepared on the samples with buccolingual width of 2 mm, occlusogingival height of 3.5 mm and axial depth of 1.5 mm on the mesial surfaces. Pulp chamber and orifices were then accessed with the help of a size 2 round bur (Mani Inc, Japan) and the same size 856 bur.

Endodontic treatment

After access cavity preparations, root canals were negotiated with size 10 K files (Mani INC), working length determined, and instrumented with Protaper Gold rotary instruments (Dentsply Sirona) up to size F2.

During file changes, root canals were irrigated with 2 mL of 5.25% sodium hypochlorite (Prime Dental), followed by 2 mL of 17% EDTA (CanalPro, Coltene). Warm vertical obturation was performed with Fastpack and Fastfill (Eighteenth Medical) with a small heat carrier using AH Plus as a sealer.

Access cavities were restored with direct composite restorations (IvoclarVivadent), conforming to tooth occlusal anatomy, and then polished using finishing and polishing discs (SofLex).

Fracture strength test

In the present study, 120 tooth samples were categorized, placed on metal jigs, and embedded in self-curing resin 2 mm below the cementoenamel junction for fracture evaluation. A 6 mm rod was used to apply controlled pressure to tooth specimens that were angled at 90 degrees to measure the Newton force and examine the fracture pattern under a stereo microscope.

Statistical analysis

Tests used in this study are the Kolmogorov–Smirnov test, one-way ANOVA, and post hoc Bonferroni tests in IBM SPSS version 23, with a significance level of 5%. Multiple comparisons by Post hoc Bonferroni test, **P < 0.001were highly significant.

RESULTS

In comparison to the other groups, the control group demonstrated the highest mean fracture resistance with statistically significant values. In comparison to the other test groups, the TradAC group showed the lowest fracture resistance with statistically significant values. The MIE groups went in the following order: even though the difference was statistically negligible, the order was CariesAC > ConsAC > TrussAC > UltraAC > TraditonalAC [Table 2].

Table 2.

Comparison of load at fracture (mean±standard deviation) among different groups

Groups	n	Mean±Standard deviation	95% CI	P
Control	14	1792.29±185.52	1685.17–1899.40	<0.001**
TradAC	14	867.43±158.49	775.92–958.94
ConsAC	14	1319.50±175.44	1218.20–1420.80
UltraAC	14	1291.57±233.14	1156.96–1426.18
TrussAC	14	1266.50±221.87	1138.40–1394.60
CariesAC	14	1366.50±218.50	1240.34–1492.66

** Highly significant

DISCUSSION

Significant tooth structure is removed during endodontic operations. For a better prognosis, a least intrusive approach is required because TEC principles in access may impair structure. 10. To reduce differences, teeth from patients between the ages of 20 and 45 were chosen for their uniform dentin makeup.[10]

Specimens were carefully chosen using CBCT to guarantee exact anatomical matching.[11] To standardize the investigation, a constant loading force was adopted; however, clinical situations entail varying occlusal forces.

TEC demonstrated low fracture resistance in the current study as a result of severe tooth structure loss. The study by Gianluca Plotino et al. (2017)[4] found that the conservative and ultraconservative designs outperformed the traditional ones and that among the minimally invasive designs, the caries-driven access cavity showed the highest resistance compared to conservative, truss, and ultraconservative designs. The latter analysis, however, did not take into account the truss and caries-driven access designs.

According to results from another study by Rajesh Krishan et al. (2014),[12] the conservative design raised the chances of procedural mistakes while reducing canal instrumentation and improving fracture resistance when compared to the standard one.

In a study by Brent Moore et al. (2016),[13] instrumentation efficacy was not jeopardized by a conservative design, nevertheless. However, the current study doesn’t focus on that issue.

Additionally, Taha Özyürek et al. (2018)[1] identified TradAC problems in mandibular molar treatment, combining the pulp chamber and cavity floor, potentially harming the core high-pressure area. By maintaining the pulp chamber roof and cervical dentin, conservative designs seek to spread occlusal forces.[11] For the endodontically treated teeth to remain in the oral cavity for the long term, the treatment must be successful in this regard.[14]

The design of conventional endodontic cavities considerably damages tooth structure. As a result, conservative access cavities have proven to be a reliable method for lowering the risk of fractures in teeth that have undergone endodontic treatment; however, more research is needed to establish its routine use in clinical practice.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.