Do Conservative Access Cavity Designs Increase The Etiological Complications Incidence Rate? (in Vitro Study)

Keywords

Conservative; Ultra-Conservative; Traditional Endodontic Access Cavity; ‘‘Ninja’’; Etiological Complication; Minimally Invasive Dentistry.

Introduction

The aim of Endodontic treatments is to preserve the function of teeth and thepatient’s health and periodontal tissues. But to achieve these goals, organisms in root canal system should be eliminated by well cleaning and shaping and sufficient irrigation to get high quality of sealing and obturation.[1]

Access cavity preparation is the foremost procedural step and one of the most important steps for successful endodontic treatment. [2]

The Traditional Endodontic Access Cavity (TEC) has been utilized for many decades as a gold standard for preparing access cavity in order to optimize the biological goals of endodontic treatmentby achieving sufficient entrance to root canal. In addition, an uncomfortable access might lead to etiological complications [3-5].

However, the removal of tooth structure is required for access cavity preparation which may undermine the tooth strength to fracture under functional loads [6, 7].

Extraction is the most frequent consequence of fractured endodontically treated teeth (ETT) [8, 9]. Extended preparation of endodontic access cavities critically reduces the amount of sound dentin [10, 11] and increases the deformability of the tooth [12], compromising the fracture strength of ETT.[10]

There are many developments in the field of dentistry including new instruments design, irrigation systems and tips, utilizing advanced imaging modalities and computer software and improving the accuracy of techniques; employing increased magnification and lighting for visualizing the pulpal space.[13] Because of these developments, new designs for conservative endodontic accesscavity designs have been advocated in order to minimize tooth structure removal.[14]

The approach of conservative endodontic access cavity (CEC) preparation aims to minimize tooth structure removal and preserve some of the chamber roof and pericervical dentin was reported in literature [14, 15]. This sound dentin preservation could be achieved with the help of cone-beam computed tomographic (CBCT) imaging to identify all the canals [16, 17].

Following this concept, an extreme conservative approach has recently been proposed, which is conventionally known as “ninja” 42.

Many studies showed a noticed higher fracture strength of conservative patterns of access cavity preparation [18, 19].

To date, according to author knowledge there aren’t enough studies about the effect of these conservative approaches about increasing the risk of iatrogenic complication incidence. Therefore, this study investigates the potential riskof depending on these conservative paradigms in access cavity in severe curvature root molars.

Materials And Methods

Specimen selection and preparation: After ethics approval, thirtyfreshly extracted intact human maxillary and mandibular molars from Syrian population with completely formed apices and classified as severe curvature root canal according to Schneider’s classification [21].

Exclusion criteria are the presence of caries or restorations could effect on the access cavity designs, and any molar which has root canal deformation, j shape canals, coronal root curvature, S shape canals, or molars that have nosevere curvature.

The specimen was cleansing with rubber cup and restored with 0.1% thymol solution until used in this study and between experimental phases to prevent dehydration [22]. Every molar was merged in heated flowing wax and then was merged in an acrylic mold to facilitate dealing with molar for take photos, radial images, and do endo-treatment.

The molars were distributed into 3 groups by using the website https://www.random.org for randomization, the upper and mandible molars randomized separately. Every group had 3 upper molars and 7 mandibular molars (n=10).The radial scanning CBCT done by (PaX-i3D Green - @VatechGyeonggi-do, 445- 170, South Korea) for planning the designs of access cavities of groups.http://www.vatech.com.

Study Groups

Group A: Traditional Endodontic Access Cavity TEC (Control Group).

Group B: Conservative Endodontic Access Cavity CEC.

Group C: Ultraconservative Endodontic Access Cavity Ultra- CEC.

TEC: It’s a geometrically predesigned shapes10. This access cavity design performed the straight access line to primary curved of canal or apical foramen and full removal of pulp roof and the walls of access cavity is perpendicular to the pulp floor and occlusal surface. (shape1)

CEC group molars were prepared following the recommendation of Clark & Khademi [14, 15], the orifices in the same visual site could be approximately seen, and the outline enamel beveled at 45°, without paying attention to the principles of TEC; deroofing and getting straight access line to the primary apical curvature. (shape1)

Ultra-CEC group molars were prepared following the rule of getting an access from a central fossa to all orifices and the pulpal roof maintained as possible. The “Ninja” Ultra-CEC access derived from the oblique projection from every orifice to the central fossa, so only one orifice can be seen in the same time.42 (shape1) Endodontic Treatment: Accesses of molars for all groupsTEC, CEC, and Ultra-CEC have drilled with Mani TR25 199/016 (Mani, Japan) mounted on a hand piece with water cooling19. And probed the orifices with DG16 Endo-prob (Dentaluck- Pakistan). Root canals were negotiated with size #8-#10 K-type files (Mani,Inc. TOCHIGI, JAPAN) to the major apical foramen, and canals were instrumented to length with one glide path file (Proglider; DentsplyMaillefer, Ballaigues, Switzerland) and one shaping file (WOG; WaveOne Gold Primary;

DentsplyMaillefer, Ballaigues, Switzerland).

The Files are replaced every 9 canals or when separation occurred, for each group separately. Irrigation has done with NaOCl 5.25% between phases, 2ml for every new file and every three biking motion. endoEze ( Ultradent, USA) irrigation tips were used. All steps were done under microscope (Dental SEMORR Dom 3000-E microscope, China) and the treatment done by the same operator with five years of experience.

Recording the results: The canals which couldn’t be scouted or negotiated by manual files, were recorded, and it’s excluded from the later treatment steps.

By the complete treatment of canals with rotary files, it was recorded any iatrogenic complication happened like “Ledges, perforations, separated instruments”. Statistical Analysis: The software SPSS version 24 was used to perform the statistical analysis.Thus, the results were statistically evaluated using analysis of Chi Square test for multiple comparisons and Fisher’s Exact Test for dual comparisons studying iatrogenic complication.

Significance level established at 5% (P<0.05).

Results

Group C (Ultra-CEC) showed significant difference by having a higher iatrogenic complication incidence (P<0.05) more than other Groups TEC,CEC. There is no significant difference between TEC, CEC for increasing the risk of iatrogenic complications. There aren’t any significant differences among the groups by dual comparison or multiple comparison for each type of investigated iatrogenic complications (P>0.05).

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Figure 1:

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Shape 1. Photographs clarify the deference among the three study groups in endodontic access designs for both upper and mandible molars for each group.

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Figure 2:

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Figure 2.

Discussion

One of the most important causes of dental fractures is the loss of tooth structure. The preparation of endodontic access cavity following TEC principles was reported as the second largest cause of loss of tooth structure [23]. Thus, a proper and contracted endodontic access design could improve the prognosis for ETT [24].

Many studies of finite elements analysis showed that the loss of tooth structure has the most important reason of tooth fracture. And the cervical strains increased by increasing the taper of preparing coronal canal space [25-27].

Recently, CEC and Ultra-CEC were proposed to reduce the fracture risk in ETT [18].

It is deemed that all subsequent steps which follow endodontic cavity preparation may be compromised if adequate access is lacking. An endodontic cavity that has been inadequately prepared will make the locating, negotiating, debriding, disinfecting, and filling of the root canal system a challenging tasks. An adequate endodontic cavity also aids in preventing iatrogenic complications during endodontic treatment procedures. Any of the above complications may contribute to reduce prognosis of endodontic therapy. [2-4, 28].

Recently many studies have been done to investigate the benefit of CEC, Ultra-CEC and Truss access in many teeth types for increasing dental structure strength to occlusal forces. And others investigating the influence of contracted designs on root canal geometry, disinfection, shaping efficacy and influence on root canal detection. But the results still compromised [2, 18, 19, 22, 29, 40] and this is possibly because there were no determined developed protocols for minimally invasive endodontic, and many differences found in methodology of accessing the cavity between studies in each type of conservative designs and methodology of applying experimental tests.

In this study all cases chosen from the severely curved canals according to Schneider’s classification because the fact of; the more curved canal the more complications will happen. And some curves don’t appear on the periapical radiographs when it is in the buccal-lingual plane [41]. And the classification has been unified to eliminate the selective bias from this study. CBCT has beendone to plan for access design and avoiding errors when preparing the access cavity.[19]

The same operator has performed all specimen preparation procedures in order to avoid the effects of the operator skills effect. [19]

Some authors pointed that although the CEC designs increase the tooth strength but it may increase the risks of inefficient canal instrumentation and the incidence of procedural errors [18, 19]. Depending on thermo-files treated system design may decrease the potentiality of causing iatrogenic complications like ledges and instruments separation because of high flexibility and have a good insufficient shaping and it has more resistance for cyclic fatigue.

Many studies pointed that no complications happened during treatment, but others excluded some specimens because of the occurrence of some errors without pointing to their nature. And all previous studies were trying to avoid falling in complications by the single use of rotary files per molar or per 4-5 canals in maximum. And there is an obvious difference between the degree of curved root among studies and what were chosen“severe degree curved canals”.

Ultra-CEC showed significantlystatistical difference in increasing iatrogenic complications than TEC and CEC. This can be illustrated because of the coronal obstructions which put more stress on instruments and have a negative impact on handle sensation and operator control. Ultra-CEC design focused on preservation of occlusal access plane (the less important tissue) more than pericervical dentine (the more important tissue).

The term of conservative endodontic access is still a description terminology and it should be controlled by more precise criteria considering the effect on negotiation possibility, and quality of cleaning and shaping, irrigation and obturation. Depending on high quality modern systems in diagnosing, illumination, magnification, preparation, irrigation and obturation could improve our access cavity to be more conservative.

Conclusion

Within the limitations of this study, it can be concluded that depending on conservative designs should be judiciously assessed before being accepted into routine clinical practice, because of Ultra-CEC design increased the incidence of iatrogenic complications, and then would make treatment steps more complicated. The CEC access cavity design seems morelikely acceptable design to be less invasive without increasing iatrogenic complications incidence rate.