Review objective

The objective of this review is to identify and synthesize the best available evidence on the effectiveness of nickel-titanium instrumentation compared to stainless steel instrumentation for non-surgical root canal therapy among adults

Background

The human adult dentition normally consists of 32 teeth. An adult human tooth structure is composed of a crown (coronal) and root(s). The coronal part is exposed in the oral cavity and the root is embedded in the alveolar bone for anchorage. There are four important tissues of a human tooth, namely, enamel, dentine, cementum and dental pulp. The outer most layer of the crown is covered by enamel which is a crystalline structure. The primary mineral is hydroxyapatite, which is a crystalline calcium phosphate.24 The middle layer is called dentine which extends from the coronal part to the root. By weight, 70% of dentin consists of the mineral hydroxyapatite, 20% is organic material, and 10% is water. It appears in yellow and it affects the color of a tooth due to the translucency of enamel. Dentin, which is less mineralized and less brittle than enamel, is necessary for the support of enamel.25 The cementum is a specialized calcified substance that covers the whole root surface. The cementum is the part of the periodontium that attaches the teeth to the alveolar bone by the anchoring periodontal ligament. The dental pulp is the central part of a tooth and it is a connective tissue. Like other connective tissues in the body, it consists of nerves, blood vessels, ground substances, interstitial fluid, odontoblasts, fibroblasts and other cellular components.24 Unlike other tissue, the dental pulp is encased within a rigid capsule consisting of enamel and dentine. Also it consists primarily of sensory nerve fibers. A small increase in tissue volume within the rigid pulpal chamber due to inflammation causes serious consequences, particularly pain. The various states of pulpal inflammation caused by insults will determine the need for a root canal treatment. Bacterial invasion into the dental pulp has serious consequences. Uncontrolled bacterial infection may eventually cause the death of pulpal tissue. If the condition is left unattended, the infection may spread through the periapical region to the surrounding tissue causing cellulitis. Cellulitis in the head and neck region may turn into a life threatening condition as the swelling induced by the inflammatory response may lead to blockage of airway. The spread of infection through the blood circulation will eventually cause systemic problems.27

Root canal treatment or endodontic therapy is a daily routine dental procedure to treat irreversible pulpitis (pulpal inflammation) and the necrotic pulp (death of dental pulp) as a result of dental trauma, tooth fracture, or dental caries (tooth decay).27 Root canal treatment can be provided by a general dentist or dental specialist (endodontist). Root canal treatment involves use of mechanical instrumentation to remove the organic pulpal tissue, any associated infected debris, and pathogenic bacteria with abundant irrigation using disinfection agents.1 This preparatory stage is one of the most important stages in root canal treatment and it aims to prepare the canal space to help disinfection by irrigants and medicaments more effectively.2,3 During instrumentation (filing) of root canal, a continuous taper enlarged (conical) form of canal is created. The original shape of canal and the apical foramen position should be maintained.3 After elimination of infection, the three dimensional root canal is filled with root canal filling material. This is called obturation. The aim is to achieve a hermetic seal and prevent reinfection. The latter is further enhanced by a sound coronal restoration.

Curved, calcified or narrow canals can cause difficulties and challenges in mechanical instrumentation.4 Conventional instrumentation is performed by hand filing with a stainless steel file. The aim of instrumentation is to centrally enlarge the root canal without over-removal of dentinal tissue and the weakening of root structure.3 However, the stiffness of these files (which increases with increasing sizes) causes straightening of curved canals and results in apical enlargement. Instrumentation/procedural errors such as canal transportation, zipping, elbowing, ledging, strip and root perforations5,6,7,8,9 and file breakage may occur during instrumentation. These procedural errors may increase the risk of endodontic treatment failure.10 The complicated root canal anatomy further aggravates the situation.

From the late 1980s, Nickel-titanium alloy (NiTi) was introduced for the manufacture of endodontic files. Ni-Ti has two main characteristics: memory shape and superior elasticity. Since then rotary nickel-titanium instrumentation has been developed and numerous types are commercially available.

Nickel-titanium files are much more elastic, flexible, fracture resistant in torsional ductility and durable than stainless steel files.11,12 The elastic limit in bending and torsion is two to three times higher than that of steel instrument. Due to these super properties, Ni-Ti instrumentation has greatly reduced procedural errors and can produce a more predictable result in canal shape, even in the presence of complicated canal anatomy.13 These instruments have been shown to prepare even severely curved root canal with fewer procedural errors than traditional stainless steel hand instruments.14,15,16 Consequently, it has gained wide acceptance in the endodontic and general dental profession in recent years. The teaching of Nickel-titanium rotary instrumentation is also becoming popular in undergraduate dental education.

However, the dental profession needs to look into the current available evidence before we support the promotion of Ni-Ti instrument. This review therefore asks the question: is the nickel-titanium instrumentation more effective than stainless steel instrument in non-surgical endodontic therapy?

A preliminary search of the Joanna Briggs Database of Systematic Reviews and Implementation Reports, Cochrane Library, PubMed, CINAHL, DARE and Prospero revealed there are currently no systematic reviews on this topic underway or published.

Inclusion criteria

Types of participants

This review will consider studies that include adult patients who had received non-surgical endodontic therapy and were followed up for one year and up to four years.21-23

Types of intervention(s)

This review will consider studies that evaluate non-surgical endodontic therapy using Ni-Ti instruments as compared to the same treatment using stainless steel instrument.

Types of outcomes

The treatment outcomes of interest will be measured by both clinical and radiographic presentation, i.e. patient's clinical signs and symptoms of the disease and the evaluation of periapical radiographs.

To be included, the outcomes of endodontic therapy should be defined in reference to healing and disease as follows: (i) healed: both the clinical and radiographic presentations are normal; (ii) healing: as healing is a dynamic process, reduced radiolucency combined with normal clinical presentation can be interpreted as healing in progress; (iii) disease: radiolucency has emerged or persisted without change, even when the clinical presentation is normal or clinical signs or symptoms are present, even if the radiographic presentation is normal;17 and (iv) "failure to heal": when the tooth is associated with a newly developed or an enlarging periapical lesion or with a radiolucent area of any size together with the presence of clinical signs and symptoms.17,18,19,20 Conditions (i) and (ii) are considered to be a "'success", (iii) is uncertain and (iv) is a failure.

The treatment outcomes of interest will be recorded for the following time periods:

- One year after treatment

- Between one and four years after treatment

- More than four years after treatment.

Radiographic studies have demonstrated that bone healing may take from two to five years.21-23

Any other unexpected outcome will be recorded if identified.

This review will consider secondary outcomes that arise as a benefit acquired by the use of the particular type of instrumentation in the endodontic therapy. These include: occurrence of post-operative pain, time of preparation of root canal, and incidence of fracture of the endodontic file in root canal.

Types of studies

This review will consider both experimental and epidemiological study designs including randomized controlled trials, non-randomized controlled trials, quasi-experimental, before and after studies, prospective and retrospective cohort studies, case control studies and analytical cross sectional studies for inclusion.

Search strategy

The search strategy aims to find both published and unpublished studies. A three-step search strategy will be utilized in this review. An initial limited search of MEDLINE and CINAHL will be undertaken followed by an analysis of the text words contained in the title and abstract, and of the index terms used to describe article. A second search using all identified keywords and index terms will then be undertaken across all included databases. Thirdly, the reference list of all identified reports and articles will be searched for additional studies. Studies published in the English language will be considered for inclusion in this review. Studies published from 1966 to present will be considered for inclusion in this review.

The databases to be searched include:

- Pubmed

- Scopus

- EMBASE

- CINAHL

- Cochrane register of controlled trials

- Clinical Evidence

- Expanded Academic Index

- Controlled Trials (CCT)

- UK Clinical Trials Gateway

- WorldWideScience.org

The search for unpublished studies will include:

- ProQuest Dissertations & Theses Database (PQDT)

- DIALOG

Initial keywords to be used will be:

(endodontic*[tw] OR root canal*[tw] OR pulpectom*[tw] OR pulp cavit*[tw] OR dental pulp devitali*[tw] OR dental pulp*[tw] OR root canal therap*[tw] OR pulpotom*[tw] OR pulp canal*[tw] OR dental canal*[tw] OR pulp chamb*[tw] OR pulp devitali*[tw]) AND (Nickel[tw] OR nickel*[tw] OR ni[tw] OR nicke*[tw] OR titanium[tw] OR titaniu*[tw] OR ti[tw] OR niti[tw] OR ni-ti[tw] OR nickel-titanium[tw] OR nitinol[tw]) AND (hand file*[tw] OR rotar*[tw] OR stainless steel[tw] OR stainless-steel[tw])

Assessment of methodological quality

Papers selected for retrieval will be assessed by two independent reviewers for methodological validity prior to inclusion in the review using standardized critical appraisal instruments from the Joanna Briggs Institute Meta-Analysis of Statistics Assessment and Review Instrument (JBI-MAStARI) (Appendix I). Any disagreements that arise between the reviewers will be resolved through discussion, or with a third reviewer.

Data extraction

Data will be extracted from papers included in the review using the standardized data extraction tool from JBI-MAStARI (Appendix II). The data extracted will include specific details about the interventions, populations, study methods and outcomes of significance to the review question and specific objectives.

Data synthesis

Quantitative data will, where possible, be pooled in statistical meta-analysis using JBI-MAStARI. All results will be subject to double data entry. Effect sizes will be expressed as odds ratios or risk ratios (for dichotomous data) and weighted mean differences (for continuous data) and their 95% confidence intervals will be calculated for analysis. Heterogeneity will be assessed statistically using the standard Chi-square and also explored using subgroup analyses based on the different study designs included in this review. Where statistical pooling is not possible the findings will be presented in a narrative form including tables and figures to aid in data presentation where appropriate.

Conflicts of interest

The author and primary reviewer is a dentist and declares that there is no conflict of interest.

Acknowledgements

This systematic review forms partial submission of the award of Masters of Clinical Science. A secondary reviewer, Mr Mark McMillan, will be used for critical appraisal only. The author would like to acknowledge Mr Mark McMillan for his support and guidance.

References