Traditional and minimally invasive access cavities in endodontics: a literature review

Article information

Restor Dent Endod. 2021;46.e46

Publication date (electronic) : 2021 August 13

doi : https://doi.org/10.5395/rde.2021.46.e46

Ioanna Kapetanaki, Fotis Dimopoulos, Christos Gogos

Department of Endodontology, School of Dentistry, Aristotle University of Thessaloniki, Thessaloniki, Greece.

Correspondence to Ioanna Kapetanaki, DDS. Dentist, Department of Endodontology, School of Dentistry, Aristotle University of Thessaloniki, Aristotelous 48, Euosmos, 56224 Thessaloniki, Greece. iwannakapetanaki@gmail.com

Received 2020 August 06; Revised 2021 March 25; Accepted 2021 March 25.

Abstract

INTRODUCTION

One of the most important steps of successful endodontic treatment is to prepare access to the pulp chamber and the root canal system [1]. Furthermore, an appropriate access cavity enables procedures such as localization, measurement, chemo-mechanical preparation, and obturation [2]. Insufficient cavity preparation might hinder the handling of the root canals. It could also lead to instrument fracture, aberration of the original root canal anatomy [3], and other iatrogenic problems. In such cases, the infection perseveres and the treatment fails [2].

The traditional endodontic cavity (TEC) approach has long remained the same, with only a few adjustments [1]. More often than not, the pulp chamber anatomy of the tooth to be treated marks the shape of the access cavity [2]. To be able to locate all orifices of the root canals and ensure direct access to the apical foramen, removal of the roof of the pulp chamber and cervical dentin protrusions and widening of the canal orifice are imperative [3]. In addition, modification of the shape of the access cavity may be required to enable direct access for endodontic files into the coronal third of the root canal. Iatrogenic problems can be prevented by straight-line access, which also allows the unimpeded insertion of rotary nickel–titanium instruments. However, despite the flexibility of these instruments, there is still a chance that they may be distorted and finally separated because of cyclic fatigue if the straight-line access is inadequate [3]. This access cavity type focuses on a conservative shape of the access cavity, conserving more tooth tissue and avoiding iatrogenic errors [45].

However, certain authors have argued that this type of cavity damages a large amount of dentin, which weakens the structure of the tooth and reduces fracture resistance [2]. Silva et al. [2], in their systematic review, mentioned studies according to which insufficient restoration of the dental structure of the endodontically treated teeth leads to extraction. Therefore, to improve the prognosis of endodontically treated teeth, it is essential that healthy dental substance be preserved [6].

An alternative approach to TEC, minimally invasive access (MIA) cavities have recently been proposed. These cavity types focus on retaining dental substance [7]. In conservative endodontic cavities (CECs), a type of MIA cavities, there is an emphasis on preserving an adequate part of the pulp chamber roof and pericervical dentin [8]. Furthermore, the truss cavity obtains direct access from the occlusal surface to reveal the mesial and distal canal orifices, and the intervening dentin remains intact [9]. From an ultra-conservative point of view, point endodontic cavities and ninja endodontic cavities (NECs) have been suggested. These access cavities are opened by removing the minimum amount of substance necessary to approach root canals [6]. Some authors have reported that this radical approach led to considerable improvements in tooth resistance to fracture and decreased the need for complex, more expensive prosthodontic restorations [19].

In recent years, guided endodontics emerged as a novel method for the treatment of calcified teeth and periapical pathosis. Seeking obliterated root canals is quite interesting and challenging [10]. Accessing and treating root canals in which the pulp chamber has been eliminated can often be difficult and time-consuming [11]. These challenges explain the frequent failure to provide success and an adequate prognosis [10]. In the above-described process of preparing root canals, there may be complications like the formation of an overextended access cavity and incorrect alignment of the access cavity, potentially leading to root perforation and fracture of files [12]. Non-invasive access cavity preparation have been developed to analyze the anatomy of the root canal in 3 dimensions. These imaging modalities can be a useful tool for clinicians to evaluate and treat teeth with calcification [13].

The use of special software, combined with cone-beam computed tomography (CBCT) and a surface scan, permits the virtual planning of an ideal access cavity. A 3-dimensional printer is used to produce a template that guides a minimally invasive drill to the calcified root canal. According to the guidelines of the European Society of Endodontology, a CBCT scan with a limited field of view and high resolution can be performed to clarify teeth apical pathosis or pulp canal calcification and provide a detailed view of the complex teeth anatomy [14]. The purpose of this review was to evaluate the effects of different access cavity preparations on endodontic treatment and tooth prognosis.

MATERIALS AND METHODS

Two independent reviewers performed searches without restrictions in the electronic databases PubMed, Science Direct, Scopus, Web of Science, and OpenGrey in the year 2020. Detailed individual search strategies for each database were carried out using the following Medical Subject Heading terms (MeSH) or text words (tw) and their combinations: ‘endodontic cavity’ (tw), ‘traditional endodontic cavity’ (tw), ‘conservative endodontic cavity’ (tw), ‘minimally invasive endodontics’ (tw), ‘stress fracture’ (MeSH), ‘fatigue’ (MeSH), ‘strength to fracture’ (tw), ‘resistance to fracture’ (tw), ‘fracture strength’ (tw) ‘fracture resistance’ (tw), ‘guided endodontics’(tw) and ‘ninja access cavity’(tw). After the electronic search, a supplementary manual search was conducted of the issues from the same time period of the following journals: Journal of Endodontics, International Endodontic Journal, and Australian Endodontic Journal. The reference lists of articles that advanced to the second-round screening were hand-searched to identify additional potential articles.

RESULTS

The majority of the included studies evaluated the influence of more contracted access cavity preparation according to a recent data survey. The studies analyzed different teeth categories, and the sample sizes presented discrepancies. Moreover, it was observed that there were differences in the methodological protocols of the in vitro studies. The total number of studies was 22. There were 3 researches [3815], 4 case reports [4101322], 1 systematic review [2], 2 observational study [1112] and 12 in vitro studies [1567916171819202123]. The parameter of fracture resistance in teeth with different access cavity designs was evaluated in 9 of the studies [15791617181920]. Other parameters that were analyzed included the instrumentation efficacy and the chemo-mechanical preparation [5192021], as well as the effectiveness of root canal detection [567]. Five of the included studies dealt with guided endodontic access cavities [1011132223], 11 compared minimal and traditional endodontic cavities [1245691718192021], 2 analyzed the new theories of contracted access cavities [815] and 1 dealt with the traditional approach [3].

DISCUSSION

The exploration and identification of pulp chamber and root canal anatomy have attracted keen interest among researchers and are of considerable importance for the outcomes of endodontic treatment [15]. Furthermore, according to the European Society of Endodontology, treatment and prevention of apical periodontitis remain the most important goals of root canal treatment and can be accomplished by cleaning and shaping root canals to eliminate microbes. The first invasive step includes preparing a cavity to gain access to the root canals [11]. Chemo-mechanical preparation and finally root obturation should then be done. Concurrently, adequate dental structure should be left for tooth functionality and fracture resistance [15], which are crucial for the outcomes, stability, and longevity of the tooth [11]. Straight-line access to the orifices of the root canals is recommended to facilitate disinfection and complete debridement [11]. However, it has been suggested that the long-term subsistence of endodontically treated teeth depends on retaining as much of the dental structure as possible (Table 1) [9].

Table 1

Summary of the descriptive characteristics of the included studies

For a traditional cavity, straight-line access to the root canal is recommended, with the goal of effective instrument operation and the prevention of iatrogenic complications. Notwithstanding, further removal of the coronal dental substance of the pulp chamber, along the chamber walls and around the canal orifices, weakens the architecture of the teeth. The removal of a large amount of dental tissue from the strategically important internal structure of the tooth poses a risk to its integrity and increases the probability of fracture [8]. Tan et al. [16] found that the ferrule dimensions affected the fracture resistance of endodontically treated teeth. To avoid these complications, contracted access cavity designs have recently been suggested [16].

The purpose of MIA cavities is to reflect researchers’ interest in retaining a greater amount of the dental substance [17]. According to some authors, the modification of traditional endodontic therapy with accurate access cavities, which protect the structure of the crucial dentin, may benefit the functional integrity, fracture resistance, and overall prognosis of teeth [18]. It has been argued that this approach may prevent the contingency of crown construction for endodontically treated teeth, as the restoration type depends on the remaining dental tissue [4]. As a result, the importance of conserving pericervical dentin, which is located about 4 mm above and below the alveolar crest, has recently been articulated. To achieve longevity and functionality of teeth, this section of dentin needs to be protected and maintained [15]. Conservative endodontic cavities have been suggested as a way to achieve the above-mentioned goals. Moreover, it has been suggested that MIA cavities limit the need for complicated and expensive prosthodontic restorations, while improving fracture resistance [18]. However, this clinical scenario is limited to a small proportion of teeth intended for endodontic therapy on the condition that they must be intact [1].

The included studies showed variability in the fracture resistance values of endodontically treated teeth with different access cavities. The speculative advantage that CECs may have better fracture resistance than TECs was presented in 4 of the included studies [1171819]. Jiang et al. [18] compared the biomechanical properties of first maxillary molars with different endodontic cavities through finite element analysis. They concluded that CECs, which maintained a larger amount of coronal hard tissue, could reduce stress distribution on cervical structures and provide better fracture resistance. They also showed a dramatic stress increase on the pericervical dentin when the access cavity became larger [18]. Krishan et al. [19] also found that CECs for mandibular molars and premolars may improve fracture resistance. However, the fracture resistance of the teeth was tested without filling and restoration. In another study, Plotino et al. [1] reached a similar conclusion that TECs showed lower fracture strength than CECs and NECs in maxillary and mandibular premolars and molars. They also added that NECs do not differ from CECs in terms of fracture resistance. Furthermore, some authors have claimed that TECs are responsible for endodontic treatment failure [17]. However, those were in vitro studies that could not simulate all intraoral conditions. From a methodological aspect, the effect of occlusal forces which cause strain on the root walls have not been fully identified [1].

On the contrary, CECs in comparison with TECs did not improve fracture resistance according to other studies [220]. Rover et al. [5] and Moore et al. [20] evaluated the influence of CECs in maxillary molars and they showed no statistically significant differences between TECs and CECs in terms of fracture resistance. In accordance with those studies, Silva et al. [2] conducted a systematic review of in vitro studies evaluating the impact of CECs on fracture resistance and found no proof that supports the use of CECs over TECs. They concluded that the influence of access cavity design on fracture resistance remains a controversial issue. The variability of the research methodology and the limited number of studies could account for the conflicting data in the literature.

An ideal endodontic access cavity should enable efficient chemo-mechanical preparation, instrumentation efficacy, and localization of the entirety of root canals, while minimizing procedural errors [3]. Biofilms can migrate into non-instrumented canals, with undesirable results [5]. Some authors have suggested that CECs endanger the treatment outcomes and long-term prognosis of endodontically treated teeth because some root canal orifices are missed and CECs have a negative effect on instrumentation efficacy; both of these factors may result in areas of greater microbial retention [2519].

In a study published in 2016, Eaton et al. [21] concluded that CECs led to the maintenance of the original canal curvature, which represented a high level of difficulty, as assessed using the American Association of Endodontists case difficulty assessment form. In addition, they found that mesial lingual (ML) canals required greater excision of dental tissue than mesial buccal canals to ensure similar reductions in canal curvature when establishing a TEC access design [21]. Furthermore, Krishian et al. [19] found that CECs compromised the efficacy of canal instrumentation in the distal canals of mandibular first molars. On the contrary, according to Rover et al. [5] and Moore et al. [19], the endodontic access cavity design had no impact on the instrumentation efficacy.

In other studies, the risks of bacterial infection and omission of the root canal were found to be higher when the access cavity was reduced [12]. Rover et al. [5] found that CECs in maxillary molars resulted in less root canal detection with no use of ultrasonic or optical microscopes. In contrast, Saygili et al. [6] evaluated the correlation between endodontic access cavity types and the detection of secondary mesiobuccal (MB2) canals in 60 extracted human maxillary first molars and reached the conclusion that it is not necessary to prepare a TEC in order to detect MB2 canals. However, they also pointed out that the preparation of upper first molars should be completed according to the tooth anatomy to identify MB2 root canals.

In many cases, endodontic treatment is challenging because of pulp space obliteration. In these cases, tertiary dentin formation may occur as a pulpal response to carious lesions and coronal restorations, as well as after vital pulp therapy procedures or tooth restoration [10]. Additionally, pulp space calcification occurs in teeth with open apices that undergo luxation injuries, such as lateral luxation, intrusion, and avulsion. The deposition of secondary dentin over time may also lead to a severe obliteration of the root canal system in older patients. Further, pulp canal calcification presumably arises from unfavorable orthodontic forces, which have been demonstrated to interfere with pulpal blood supply [13]. This inflammatory process often results in pulp chamber shape changes and the distortion of useful anatomical signs [11].

Some authors have argued that guided endodontics can be applied in such difficult cases, with advantages such as greater preservation of dental tissue, a reduced danger of perforation, and a shorter operating time. It is said that this technique constitutes a miniaturized and minimally invasive treatment approach for locating root canals in teeth with pulp calcification that cannot be predictably accessed via traditional endodontic therapy [11]. Burchgreitz et al. [11] suggested that aside from teeth with pulp canal calcification, guided procedures in endodontics may help easily and precisely access and treat specific areas of the root that are hampered due to resorptions, perforations, or fractured endodontic instruments. However, guided procedures should be used in straight root canals or the direct part of distorted canals [10]. Furthermore, natural morphological changes of the root canal are unavoidable while using the leading drill [21]. Another disadvantage of this technique is the possible formation of cracks on the root while opening the closed root canal. Further drawbacks are the likely increase of the root surface temperature, resulting in damage of the periodontal ligament, and the amount of radiation involved in the CBCT examination [10]. Nevertheless, there are only a few studies about this new method and the majority are case reports.

Considering all the above, this study concludes that TEC is the first choice for preparing access to the pulp chamber, as it constitutes a safe method that enables efficient chemo-mechanical preparation of the root canal system. The TEC method has been more widely applied in daily clinical practice, as it is a more suitable access cavity preparation type than MIA cavities, which are not as viable an option. This review analyzed the advantages and disadvantages of all access cavity types, giving clinicians the opportunity to choose an appropriate method for completing the first step of endodontic treatment. Therefore, the knowledge of different access cavity designs is of the utmost importance, as the access cavity constitutes an integral and crucial part of endodontic treatment.

CONCLUSIONS

It is concluded that the effectiveness of MIA cavities has not yet been well established by research data and that MIA cavities cannot replace the traditional straight-line access design. There is no scientific evidence that supports the use of MIA cavities over TECs. Although in vitro studies offer initial significant information about new types of access cavities, they have limitations in clinical practice.

More in vitro studies must be carried out before planning clinical studies. Furthermore, randomized controlled trials and retrospective and prospective studies need to be conducted before these new methods are widely accepted.

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