Healing of Periapical Lesions After Surgical Endodontic Retreatment: A Systematic Review

Background: Surgical root canal retreatment is required when peri-radicular pathosis associated with endodontically treated teeth cannot be treated by non-surgical root canal therapy (retreatment), or when retreatment was ineffective, not feasible or contraindicated. Endodontic failures maybe happen when irritants remain within the confines of the root canal, or when an extra-radicular infection cannot be eradicated by orthograde root canal treatment. Following enhanced microsurgical techniques in the last years, the success rates of surgical root canal retreatment have improved considerably. Objective: The aim of this systematic review is to gather updated data in regard to the surgical root canal (retrograde) retreatment to heal the periapical lesions. Materials and methods: The electronic databases PubMed and Google Scholar were searched in this review using specific inclusion and exclusion criteria. The search was performed in June 2019 and updated in November 2019. Among 3900 studies, 10 studies satisfied the eligibility criteria and were included in the review to be analyzed. Results: The 10 studies showed the importance of surgical root canal retreatment as a treatment option in removing infections within the root canal system and its efficiency in periapical tissue healing. These studies investigated different aspects of healing of periapical lesion after surgical (retrograde) retreatment including success rates, follow-up duration, and updated studies in surgical (retrograde) retreatment. Conclusions: Surgical root canal (retrograde) retreatment demonstrates its efficiency in reducing the period needed for healing of the periapical lesions in short-term follow-up compared to conventional orthograde retreatment.


Introduction And Background
Periapical lesions are one of the common pathological conditions affecting periradicular tissues [1]. The microbial invasion and subsequent infection of the canal systems of a root play a decisive role in the initiation and progression of periapical lesions [2]. Periapical lesions are mostly classified as radicular cysts, dental granulomas or abscesses [3,4]. Among all periapical lesions, the incidence of cysts varies from 6% to 55% [5]. Also, the occurrence of granulomas spans from 9.3% to 87.1%, and of abscesses from 28.7% to 70.07% [6]. According to clinical evidence, lesions that are larger in size, are most likely radicular cysts. Still, some of these large lesions may appear to be granulomas [7].
The preliminary purpose of all endodontic procedures, especially cleaning and shaping, is to eliminate necrotic tissue and infective bacteria [8]. Large periapical lesions are of inflammatory origin as well as apical true cysts and should be treated initially with a nonsurgical approach [9]. When intra-or extra-radicular infections are persistent, and periapical pathology fails to resolve after nonsurgical endodontic management protocols, only then a surgical option should be considered [10]. Broad cross-sectional studies from various countries have stated that the prevalence of apical periodontitis and other post-treatment periradicular diseases can transcend 30% of all root-filled teeth population [11][12][13][14]. These facts recommend a significant requirement for the treatment of this condition [11][12][13][14]. Microsurgical endodontic treatment is better than conventional endodontic treatment and has high success rates [15].
There are several studies that were conducted to discuss the healing of periapical lesion after nonsurgical (orthograde) retreatment or surgical root canal treatment. However, few studies have investigated the healing of periapical lesion after surgical (retrograde) retreatment. Consequently, the aim of this review was to collect all updated and available studies including imperative information concerning the surgical root canal (retrograde) retreatment to heal periapical lesions.

Material and methods
This review has been compiled according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines.

Research Question
The following was the research question for the systematic review: "The best endodontic treatment option for the healing of periapical lesions: is it surgical retrograde retreatment or conventional orthograde retreatment?".

Literature Search
With respect to the question of the study, we searched the literature and identified relevant studies. The literature search was formulated in June 2019 and then updated in November 2019. A web search was done through PubMed (2009-2019) and Google Scholar (2009-2019) with MesH terms and/or in various combinations ("healing", "periapical lesion", "surgical root canal retreatment OR surgical endodontic retreatment", "endodontic microsurgery retreatment").
Relevant articles had been read and assessed by the introduction of the close meaning ideas by the study reviewers. Full articles were obtained for most of the titles and abstracts that met the inclusion criteria, the full text was accessed. From each included article, study design, interventions, and findings were extracted. Articles used were categorized into two main groups (free and restricted). Free ones have been downloaded directly by the URLs generated from the database. The restricted group has been downloaded by the institutional access of the King Abdulaziz University (KAU) library. Even though some articles did not match the main idea, they have been reviewed again & decided to be either relevant or irrelevant.  3. Studies carried out on human subjects only.

Exclusion Criteria
1. Articles that described healing of periapical lesion with management techniques excluding the surgical root canal retreatment.
2. Articles that discussed healing of periapical lesion after surgical root canal retreatment by percentages and samples taken from animals.

Critical Appraisal
Eligible studies were independently analyzed by all reviewers according to the eligibility criteria as well as PRISMA guidelines. Any disagreement between the reviewers was resolved using discussion.

Data Extraction and Presentation
The search strategy using the keywords and MeSH of the databases like PUBMED and Google Scholar yielded a total of 3,900 studies, of which 3,580 were either unrelated or duplicate topics. Among the potential 140 studies, the eligibility criteria were applied and ten studies were included in this systematic review. The summary of the search flow chart for this systematic review has been depicted in (Figure 1).

Results
The search culminated in 10 studies that fulfilled both the inclusion and exclusion criteria and which were conducted in the last 10 years ago. These studies investigated the healing of periapical lesion after surgical root canal (retrograde) retreatment including success rates, follow-up duration, and updated studies in surgical root canal (retrograde) retreatment. The studies included in this systematic review were one randomized controlled trial study, two prospective studies, one retrospective study, and six case reports [16][17][18][19][20][21][22][23][24][25]. The systematic review included ten studies with a total sample of 376 subjects that were treated from primary care centers and also universities outpatient departments of dental schools and hospitals. In all of the studies, the procedures were performed on systemically healthy persons. In regard to the duration of follow-up performed, one study ranged from 1 to 3 year recalls, four studies were performed with 1-year recall and different studies up to "2 years recalls", "5 year recalls", "6 year recalls", and "10 year recalls" [16][17][18][19][20][21][22][23][24][25]. In regard to the surgical technique performed, the placement of root-end filling material was made in four studies, and in the other six studies, root-end filling material was not placed [16][17][18][19][20][21][22][23][24][25]. In regard to the effect on the healing of the periapical lesions, all the studies showed a high significant success rate of complete healed or remained healed of the periapical lesion after surgical retrograde retreatment [16][17][18][19][20][21][22][23][24][25]. In regard to the most success rate of endodontic surgery, two studies found that microsurgical techniques had a high success rate in healing the periapical lesions compared to conventional orthograde treatment [23,24]. All included studies were summarized in Table 1. A summary of all current systematic and meta-analysis reviews are summarized in Table 2.

Discussion
The systematic review presents a comprehensive compilation of evidence taken from ten articles which included original studies. The sample size was up to 376 subjects seeking endodontic retreatment by the use of surgical retrograde retreatment. All included studies confirmed faster treatment time by surgical root canal (retrograde) retreatment (  Table 2) [26]. When the data were reviewed and analyzed in the follow-up periods, they found the microsurgery group had a significantly superior success rate than the retreatment group in the short-term follow-up, while no significant difference was improved in the long-term follow-up [26].  [27,28]. They found the surgically treated cases seem to indicate a higher success rate after one year. However, after 2-4 years relative success rates show equivalent or reversed [27,28]. This clearly shows agreement in the conclusions reached by these systematic/meta-analysis reviews in regards to the healing of periapical lesions by surgical retrograde retreatment compared to the conventional orthograde retreatment especially after one year of procedure (short-term followup). When examining our included studies individually, 10 studies favored the use of surgical root canal (retrograde) retreatment, whereas most of the studies concluded that there was a high significant success rate of complete healed or remained healed of periapical lesions after the (retrograde) retreatment in short-term follow-up, but there are some studies showed significant healing of periapical lesions after different long-term follow-ups [16][17][18][19][20][21][22][23][24][25]. In addition, two studies found that microsurgical techniques have a high success rate in healing of the periapical lesions compared to conventional orthograde treatment [23,24]. Our results clearly reveal the controversy in the literature; however, there is, indeed, a strong trend toward supporting the microsurgical retreatment. Hence, more studies are needed to formulate the proper guidelines and parameters of how and when surgical retrograde retreatment can be used and considered as an accurate and reliable treatment option to heal the periapical lesions.

Conclusions
Surgical root canal (retrograde) retreatment is defined as an important invasive procedure that permits fast treatment options minus the necessity of the extensive traditional method. Surgical retrograde retreatment demonstrates its efficiency in reducing the period needed for healing of the periapical lesions and suggests benefits that will result in better recognition among patients seeking faster results in short-term follow-up, but on the long-term followup showed not significant difference for healing of periapical lesions compared to conventional orthograde retreatment. However, more clinical trials are encouraged to inspect the results of surgical retrograde retreatment on the healing of periapical lesions.