The influence of flap design on patients’ experiencing pain, swelling, and trismus after mandibular third molar surgery: a scoping systematic review

Abstract Third molar removal surgery usually comes accompanied by postoperative discomfort, which could be influenced by the surgical approach chosen. This scoping systematic review aimed at compiling the available evidence focused on the influence of flap design, including envelope flap (EF), triangular flap (TF), and modified triangular flap (MTF), on postoperative pain, swelling, and trismus, as primary outcome measures, and any result mentioning healing promotion or delay, as secondary outcome measure, after mandibular third molar extraction surgery. An electronic search, complemented by a manual search, of articles published from 1999 to 2020 was conducted in the Medline (PubMed), EMBASE and Web of Science databases including human randomized controlled trials, prospective, and retrospective studies with at least 15 patients. The risk of bias of the included studies was assessed either with the Cochrane’s Risk of Bias tool or with the Newcastle-Ottawa scale. Every step of the review was performed independently and in duplicate. The initial electronic search recovered 2102 articles. After applying the inclusion criteria, 12 articles were included. For patient’s perceived postoperative pain, TF and MTF frequently reported better results than EF. For swelling, the literature is divided, despite a trend favoring EF. For trismus, data showed that its occurrence is mostly associated with the duration of the surgery rather than with the chosen flap. For healing, the limited data is inconclusive. Finally, randomized studies showed a high risk of bias, whereas nonrandomized studies were mostly of good quality and low risk of bias. Although there was no clear consensus regarding the influence of different flap designs for third mandibular molar extraction on postoperative clinical morbidities; the surgeon’s experience, estimated surgical difficulty, molar position and orientation, and surg ery duration should be considered when choosing among the different flap designs.


Introduction
Impacted teeth refer to a particular anatomical condition in which a tooth fails to erupt within the expected time of physiological development. Third molars are the most common impacted teeth, present in almost 77% of people, and its extraction is the most common oral surgical procedure. 1 In fact, 33% of the population has at least one impacted third molar, which frequently leads to food retention, caries, pain, edema, and second molar root resorption and, consequently, its surgical extraction.

Methodology Protocol
The protocol for executing this scoping systematic review, including selection, extraction, and risk of bias assessment phases, was approved a priori by all the authors and was constructed following the The influence of flap design on patients' experiencing pain, swelling, and trismus after mandibular third molar surgery: a scoping systematic review J Appl Oral Sci. 2021;29:e20200932 3/9 recommendations of the PRISMA-P checklist, with no posterior amendments. 6 In addition, for the reporting of this systematic review, the PRISMA Statement was followed accordingly. The formulated focused PICO research question was the following: "In patients (P) that require mandibular third molar surgery (I) is there a difference among performing EP, TF, or MTF reporting, and other biases, was used by assessing the following parameters: random sequence generation, allocation concealment, blinding of the examiner and/ or patient, post-operative follow-up and incomplete outcome data. 8 Moreover, to analyze nonrandomized clinical studies, the Newcastle -Ottawa Scale (NOS) was used. 9 This scale uses a star system, in which a study is judged based on three broad perspectives: The selection of the study groups (up to 4 stars), the comparability of the groups (up to 2 stars), and exposure or outcome of interest for case-control or cohort studies, respectively (up to 3 stars). Studies that met five or more of the Newcastle -Ottawa Scale criteria were considered as low risk of bias and good quality. Finally, data from the included studies were assessed in a qualitative manner.

Results
The initial search identified 2,102 potential items.
After reading the titles and abstracts, 41 articles were selected for full-text revision. Then, the full-text analysis excluded 32 studies that did not evaluate at least two of the examined flaps or at least two of the postoperative clinical outcomes. Finally, nine articles were considered eligible. Subsequently, three articles were added after the manual search, leading to a total of 12 articles included in the review, 10-21 as shown in the data selection flow chart ( Figure 2). The data regarding the number of patients, the examined flaps, and clinical outcomes are shown in Table 1 and  (2013) described that MTF-intervened patients also reported less postoperative pain. Kirk, et al. 19 (2007), in turn, showed no statistically significant differences between the EF and MTF groups regarding pain.
Although EF is the most commonly used surgical approach for lower third molar removal, the extensive exposition of buccal bone from the adjacent second molar during this procedure has been frequently associated with patients perceiving more pain, when compared with the other less invasive approaches. 15 This could be also attributed to the incision, the damage to the second molar periodontal tissues,  of the surgeon, type of impact, administration of preoperative or postoperative corticosteroids, and compliance to postoperative instructions could also affect the pain experienced by the patient. 17,18 Finally, most articles agreed that pain was the most frequently reported comorbidity, mostly on the immediate days after surgery, and that it decreased continuously over the healing course, regardless of the surgical technique. Since it requires a soft diet and several rest days, it negatively affects patient's daily routine and, consequently, the patient's quality of life. 22 Flap selection effect over postoperative swelling Alqahtani,Khaleelahmed and Desai 10 (2017) compared EF and MTF during third molar surgery, showing significantly better outcomes for the EF group regarding postoperative swelling. Similarly, Baqain, et al. 16 (2012) reported that patients intervened with EF, when compared with TF, showed significantly less postoperative swelling. On the other hand, Dolanmaz, et al. 20 (2013) showed no significant differences regarding swelling when comparing patients treated with an EF approach and with an MTF approach.
Sandhu, Sandhu and Kaur 18 (2010) also claimed that there was no difference in postoperative swelling between the patients treated with EF and those treated with MTF. Koyuncu and Cetingül 15 (2013) and Kirk, et al. 19 (2007), in turn, reported less swelling among the patients treated with the MTF approach when compared with the EF group; however, these differences were not statistically significant. Despite the considerable trend favoring that the EF approach could lead to less postoperative swelling after third molar extraction, the literature available is divided.
TF and MTF association with increased facial swelling could be explained, at least partly, by the buccal releasing incision, which provokes increased local inflammation and subsequent edema in the buccal tissues. 10, 16 In fact, surgical incisions extension and quantity of bone removal have been associated with the severity of facial swelling. Furthermore, the incidence of facial swelling also depends on the type of third molar impact, the difficulty of extraction operation, and the oral hygiene of the patient.
Although many studies have attempted to determine predictive factors and preventive interventions for facial swelling, inconsistency between the results compromises patients' perception of the quality of the dentist's service, follow-up, and of their own quality of life. 23 Flap effect over postoperative trismus Erdogan, et al. 17 (2011) reported that there were no statistically significant differences between the EF and TF groups regarding trismus. Similarly, Sandhu, Sandhu and Kaur 18 (2010) and Kirk, et al. 19 (2007) showed no differences in the occurrence of postoperative trismus between patients approached with EF and those approached with MTF. Conversely, Baqain, et al. 16 (2012) showed a statically significant difference favoring TF over EF group regarding trismus. Nevertheless, Mobilio, et al. 12 (2017) showed that the duration of surgery, and not the flap design, was   associated with the acute postoperative symptoms, including trismus, after lower third molar extraction.
Thus, the analyzed data showed that the occurrence of trismus could be associated with the duration of the surgery, although patients treated with TF or MTF flaps presented fewer trismus events.
Traumatic manipulation of tissues during third molar extraction can lead to trismus. Mouth opening length reduction accompanied by a decrease of masticatory muscle activity has been frequently reported after third molar surgery. Indeed, the reduction of muscular activity on the intervened site has been considered as an innate protective and analgesic function to diminish pain. Moreover, direct muscle damage and acute inflammation may provoke adjacent muscle spasms and lead to limited mouth opening. 24 Finally, trismusprovoked dysphagia is also a frequent undesired effect of third molar surgery, which negatively affects patient' s quality of life by limiting conventional eating and requiring unpleasant soft or liquid diets. 25 Flap effect over tissue healing Healing is often not reported as a clinical parameter after third molar surgery; however, the few articles analyzing healing showed better healing in patients treated with the MTF approach. 11,14,18 Mohajerani, et al. 11 (2018) showed that the application of MTF might lead to a reduction in dry socket incidence and better healing 7 days after lower-impacted third molar surgeries. On the other hand, Desai, et al. 14 (2014) Table 4. The scores of the five nonrandomized studies eligible for the NOS ranged from 5 to 8 stars. 10,13,15,[17][18][19][20][21] According to the authors' definitions, the overall  ranking showed no studies with a low risk of bias and that all of them were of good quality. Each of the three analyzed flaps has particular advantages and disadvantages. 30 According to Mohajerani, et al. 11 (2018) According to two recent systematic reviews, Lopes da Silva, et al. 35 (2020) and et al. 36 (2020)

Conflict of interest
The authors declare no conflict of interest, any suggestion of plagiarism or copyright infringement regarding the publication of this paper.