Photobiomodulation after Surgical Extraction of the Lower Third Molars: A Narrative Review

The surgical extraction of the lower third molar is widely practiced in oral surgery. Inflammatory complications such as pain, swelling, and trismus can cause discomfort to the patients after third molar extraction. Several methods have been used to reduce these postoperative sequelae, including the use of corticosteroids, nonsteroidal anti-inflammatory drugs, analgesics, antibiotics, less traumatic surgical methods, and the use of photobiomodulation. This narrative review summarizes the current evidence on the effect of photobiomodulation on pain, facial swelling and trismus after third molar surgery. A literature search using MEDLINE (NCBI PubMed and PMC), EMBASE, Scopus, Cochrane library, Web of Science, and Google Scholar was undertaken up to October 2021. Forty-one articles met the inclusion criteria. Photobiomodulation can be considered an alternative and useful method for controlling pain following impacted wisdom tooth surgery. The effectiveness of PBM in reducing swelling and trismus is still controversial. This review highlights the lack of consensus in the literature on protocols used in PBM therapy.


Introduction
The surgical extraction of the third mandibular molar is the most frequent procedure in oral and maxillo-facial surgery [1].
An impacted third molar can cause different consequences such as pericoronitis, distal caries and periodontal pocket of the second molar, odontogenic abscesses, and the development of follicular cysts [2].
The healing period following the surgical extraction of an impacted third mandibular molar is associated with an intense inflammatory response. This process is responsible for postoperative pain, facial swelling, and trismus, which negatively affect the quality of life of the patients during 7-10 days after the surgery [3]. These signs and symptoms are a consequence of the surgical wound and the duration of the surgery itself [4], as the result of a direct trauma on the blood and lymphatic vessels [5]. After local anesthesia wears off, the pain usually reaches maximum intensity 3 to 5 h after surgery, continuing for 2 to 3 days, and gradually diminishing until the seventh day [6,7]. Swelling reaches peak intensity in 12 to 48 h, influencing facial esthetics and social interactions. It usually resolves between the fifth and seventh days. Trismus may be considered initially as having a protective function by encouraging the patient to rest the surgical site and permit healing. However, it may lead to difficulty in eating and functioning if it persists for more than a few days.
Piezoelectric devices, which can be used instead of conventional burs, may be beneficial for surgeries at complex anatomical sites because they can preferentially cut mineralized structure [8,9]; furthermore, some authors reported a reduction in postoperative sequelae using the piezoelectric surgical technique in third molar extraction [10,11]. stated. Exclusion criteria were (1) conference proceedings, letters to the editor, short communications; (2) in vitro or in vivo animal studies; and (3) studies with less than ten subjects. Two investigators (D.P. and F.R.) independently assessed each eligible article, extracted data using a pre-established form, and collated all data into a Microsoft Excel spreadsheet (Microsoft Corp. Redmond, WA, USA).

Description of the studies
One hundred and thirty-six studies were obtained from the databases searched. After duplicates were removed, 91 articles were evaluated, of which 50 were excluded after title, abstract and full-text revision. Forty-one studies met the inclusion criteria. A detailed flow chart of the selection process is shown in Figure 1. Thirty-nine studies were RCTs; one was a case-series study. A total of 1833 subjects participated across the 41 studies. Nine studies did not record participants' gender; in the other studies, there were 727 female participants and 1106 male participants.
The characteristics of the included studies are presented in Tables 1 and 2.  Nine studies did not record participants' gender; in the other studies, there were 727 female participants and 1106 male participants.

Trismus
Twenty-eight studies assessed the impact of PBM on postoperative trismus. Eleven studies reported reducing of trismus with PBM [26,27,29,30,32,40,49,50,53,54,56]. In the included studies, wavelengths ranged between 660 and 980 nm, power ranged between 4 and 500 mW, and energy densities were between 4 and 212 J/cm 2 . As for swelling, the wavelength of 810 nm was the one that induced the worst outcome. Instead, the wavelength of 980 nm determined the better reduction of trismus ( Figure 4).

Trismus
Twenty-eight studies assessed the impact of PBM on postoperative trismus. Eleven studies reported reducing of trismus with PBM [26,27,29,30,32,40,49,50,53,54,56]. In the included studies, wavelengths ranged between 660 and 980 nm, power ranged between 4 and 500 mW, and energy densities were between 4 and 212 J/cm 2 . As for swelling, the wavelength of 810 nm was the one that induced the worst outcome. Instead, the wavelength of 980 nm determined the better reduction of trismus ( Figure 4).

Trismus
Twenty-eight studies assessed the impact of PBM on postoperative trismus. Eleven studies reported reducing of trismus with PBM [26,27,29,30,32,40,49,50,53,54,56]. In the included studies, wavelengths ranged between 660 and 980 nm, power ranged between 4 and 500 mW, and energy densities were between 4 and 212 J/cm 2 . As for swelling, the wavelength of 810 nm was the one that induced the worst outcome. Instead, the wavelength of 980 nm determined the better reduction of trismus ( Figure 4).

Discussion
The present narrative review evaluates the role of PBM in the management of pain, facial swelling, and trismus that accompany the postoperative period after the extraction of the third molars. Since the duration of surgeries correlates significantly with trismus and swelling, most surgery protocol was performed by a single oral surgeon, and the duration of the extractions was also recorded. All investigations reported that the duration of surgery was similar between groups, without statistically significant differences. On the other hand, individual pain intensity can vary between operations. In the split-mouth design, both lower third molars of one patient were extracted in two separate operations. Between the two operations, the individual's pain threshold may change due to the pain-related suffering experienced in the last extraction surgery.
The controversial results from the studies included in our review on the analgesic and anti-inflammatory effects of PBM after the surgical removal of third molars calls into question its efficacy. So far, the parameters of ideal PBM have not been determined due to the great diversity of variables such as the type of laser wavelength, power, time, and mode of application.
With reference to the effect of the PBM on postoperative inflammation, Marković and Todorović [48] wanted to compare the effect of the PBM used alone or in combination with topical and systemic corticosteroids after the extraction of third molars. In their study, 120 patients were divided into four groups. Group 1 received PBM immediately after the surgery (energy output 4 J/cm 2 with constant power density of 50 mW, wavelength 637 nm); group 2 also received i.m. injection of 4 mg dexamethasone into the internal pterygoid muscle; group 3 received PBM supplemented by systemic dexamethasone (4 mg i.m. in the deltoid region) followed by 4 mg of dexamethasone intraorally 6 h postoperatively; and group 4 (control) received only the usual postoperative recommendations such as cold packs, soft diet, etc. The best anti-inflammatory effect was obtained with the combination of PBM and local intramuscular (medial pterygoid) dexamethasone (group 2); the authors suggested that this effect was obtained through a summation effect of both procedures. However, with the use of PBM and systemic administration of dexamethasone (group 3), there was a higher anti-edematous effect than with the use of the PBM alone (group 1), although without statistically significant differences between the groups. For this reason, the authors did not justify the use of corticosteroids in case of using PBM.
The choice for intraoral or extraoral application varied between studies, pointing out more beneficial outcomes for intraoral use or associating the two methods of application.
Kahraman et al. [36] in their study on 60 patients used different groups (intraoral LLLT, extraoral LLLT, and control) to compare the two approaches in reducing postoperative pain. They observed statistically significant results for the intraoral group, while the extraoral did not differ from the control. On the contrary, Aras et al. [50] demonstrated that extraoral LLLT is more effective than intraoral LLLT for the reduction of postoperative trismus and swelling after extraction of the lower third molar.
The number and timing of PBM treatments varied greatly among the included studies. Some studies administered the treatment once, whereas others administered it several times. Some treatments were delivered before the surgery, whereas others were delivered at the suture or at different days after surgery. Petrini et al. [35] in their retrospective study on 45 patients demonstrated that a double dose of LLLT, one immediately before and another after the surgery, was effective in reducing pain and edema at 24 h. Although the authors have found no statistically significant differences between the group irradiated also in the pre-surgery phase (group 2) with respect to that irradiated only after the extraction (group 1), for pain and edema, the results gained clinical importance if we considered that the need of Ketoprofen assumption in the first 24 h was statistically significantly lower in group 2 with respect to the controls and group 1.
Abdel-Alim et al. [29] in their study on 80 patients treated one group with PBM therapy immediately after surgery and on the 3rd day postoperatively, and one group on the 2nd and 4th days postoperatively. Statistical results showed a significant reduction in pain, swelling, and trismus in the immediate PBM therapy group compared with the delayed PBM therapy group. In the split-mouth study conducted by Kumar Gulia et al. [58], PBM was applied immediately after the sutures on the test side. The results revealed that pain, swelling, and trismus following surgery were lower on the test side compared to the control side, but only the pain reduction was statistically significant.
The effect of PBM on pain was evaluated in most of the studies included. Most of them showed a positive effect especially in the first days, whereas only some investigations reported no statistically significant results.
Lòpez-Ramirez et al. in their study on 20 patients demonstrated that the intraoral application of an 810 nm diode laser did not significantly reduce pain after a surgical extraction of impacted lower third molars. On the contrary, Asutay et al. [23] reported that the pain level in the PBM group was significantly lower than that in the control and placebo groups.
While statistical significance indicates the reliability of the study results, clinical significance reflects its impact on clinical practice. For example, in the study by Amarillas-Escobar on 30 patients, the intensity of pain was lower in the laser group than in the control group, but without statistically significant differences [45].
The role of PBM on swelling was evaluated in 35 of the studies included. Nineteen studies demonstrated swelling reduction with PBM. The measurement of swelling differed across the studies. Most swelling measurements were taken as the distance between two facial points. In the study of Asutay et al., a three-dimensional photogrammetric system was used to measure volumetric postoperative swelling. The results of their study revealed that PBM reduced facial swelling but without significant differences among the three groups (control group, PBM group, and placebo group) [23].
From the twenty-eight studies on trismus, eleven demonstrated a statistically significant reduction in trismus with PBM. For example, in the study conducted by Ferrante et al. [32] on 30 patients, trismus in the LLLT group was significantly less than in the control group at the second and seventh postoperative days (p < 0.05). By contrast, the results of the study by Koparal et al. [33] on 45 patients demonstrated no statistically significant difference in the trismus occurring subsequent to surgery in Groups 1 (control group), 2 (single dose of PBM immediately after surgery), or 3 (two doses of PBM, immediately following surgery and on postoperative day 2) when compared with the interincisal opening prior to surgery.
There are some limitations that should be considered regarding the present review. Firstly, the patients in the included studies often used medications, such as analgesics and anti-inflammatories. Therefore, PBM was evaluated as an adjuvant modality, making it impossible to analyze its efficacy in reducing postoperative complications as the only therapy of choice. Secondly, as previously mentioned, pain experience is partly influenced by previous experiences; this is difficult to account for in an investigation and reduces the reliability of the results.

Conclusions
Despite the limitations, this narrative review provides a comprehensive synthesis of the topic. PBM is a safe procedure that may not cause adverse effects and shows reduction in pain in patients undergoing the surgical removal of the lower third molar. However, the administration of PBM presents a negligible benefit in reducing swelling and trismus after surgery compared with placebo or no treatment. There is still a need for future studies with a better methodological description to provide a greater quality of evidence.