Efficacy of Various Laser Wavelengths in the Surgical Treatment of Ankyloglossia: A Systematic Review

Ankyloglossia, commonly known as tongue-tie, is the most common disorder of tongue morphology characterized by aberrant attachment of the lingual frenum. This study aimed to provide a comprehensive literature review and evaluate the effectiveness of various laser wavelengths in the surgical treatment of patients with ankyloglossia. An electronic screening of PubMed and the Cochrane Central Register of Controlled Trials (CENTRAL) databases was conducted on 8 November 2021. The following search terms were used to review the available data on the subject of interest: (ankyloglossia OR tongue tie OR short lingual frenulum OR lingual frenectomy OR lingual frenulectomy OR lingual frenotomy OR lingual frenulotomy) AND laser. The use of lasers in ankyloglossia treatment resulted in shorter procedure time, reduced indications for general anesthesia, reduced administration of postoperative analgesics, fewer sutures or none needed, reduced postoperative bleeding, and improved healing. Despite many advantages, this method has its clinical limitations: it requires the use of expensive equipment; well-trained personnel familiar with lasers; and personal protective equipment for the patient, caregiver, operator, and assistant. The laser procedure does not eliminate the need for myofunctional exercises and work with a speech therapist.


Introduction
Ankyloglossia, commonly known as tongue-tie, is the most common disorder of tongue morphology characterized by improperly attached (too short or thickened) frenulum of the tongue. The lingual frenulum is formed by the dynamic elevation of a midline fold in the floor of the mouth fascia. This diaphragm-like structure suspends the tongue and the floor of mouth structures within the arc of the mandible, creating a balance between mobility and stability [1][2][3]. Type I and III collagen fibers and type III elastin fibers constitute a large share in the structure of the tongue frenulum [1]. Ankyloglossia can impair breastfeeding (nipple pain, poor infant weight gain, and early weaning), speech, swallowing, breathing, sleep, and oral hygiene. Furthermore, it can cause oral dysfunction, social problems related to impaired language function, and even postural problems [4][5][6][7][8][9][10][11]. The incidence of ankyloglossia reported in the literature ranges from 0.02% to 10.7% [4,[12][13][14][15][16]. This discrepancy, in part, may be related to different assessment methods and classifications used to diagnose this disease entity. Various studies reported the clinical significance of

Protocol
The review was prepared in accordance with the PRISMA statement [60], as well as the Cochrane Handbook of Systematic Reviews of Interventions [61]. Details of the selection criteria are presented in Figure 1.

Eligibility Criteria
Studies were considered acceptable for inclusion in the review if they fulfilled the following criteria:  Studies involving human subjects;  Surgical use of dental lasers in the treatment of ankyloglossia;  Studies in English language;  Clinical reports amounted to 10 or more cases;  Non-randomized controlled clinical trials (NRS);  Randomized controlled clinical trials (RCT).
The exclusion criteria the reviewers agreed upon were as follows:  Non-English papers;  Opinions;  Letters to the editor;  Editorial papers;  Review articles;  Clinical reports with fewer than 10 cases;

Eligibility Criteria
Studies were considered acceptable for inclusion in the review if they fulfilled the following criteria:

Information Sources, Search Strategy, and Study Selection
An electronic screening of PubMed and the Cochrane Central Register of Controlled Trials (CENTRAL) databases was conducted on 8 November 2021. To review the data available on the subject of interest, the following search terms were used: (ankyloglossia OR tongue-tie OR short lingual frenulum OR lingual frenectomy OR lingual frenulectomy OR lingual frenotomy OR lingual frenulotomy) AND laser. The search was limited to human subjects and studies with other eligibility criteria. The references of all selected fulltext papers and related reviews were screened. Only articles with available or accessible full-text versions were considered. An attempt was made to contact the corresponding authors of unpublished or missing data if needed.

Data Collection Process, Data Items
Study selection was conducted in two phases. Four reviewers independently extracted data from articles that met the inclusion criteria (IM, AM, JM, and KGL). Articles marked for inclusion by at least two reviewers were retained for the second phase of full-text review. Two reviewers examined all full-text articles independently (IM, AM), and two reviewers (KGL, JM) were consulted to resolve any disagreements. The data used were as follows: first author, year of publication, title, study design, study groups, study results (number of study groups, age of respondents, presence of myofunctional and speech therapy recommendations before after surgery, suturing after surgery, the type of anesthesia used, laser type, and laser parameters). Extracted data were entered into a standardized Excel file.

Risk of Bias in Individual Studies
In the initial study selection, to minimize the potential for reviewer bias, each author screened titles and abstracts independently. The Cohen k test determined the level of agreement between reviewers [62]. Discussion between the authors resolved any difference in opinion on the inclusion or exclusion of a study.

Quality Assessment
The methodological quality of each of the included studies was assessed by two reviewers working independently. The criteria on which the project, implementation, and analysis are based are as follows: • Randomization (1) or its absence (0); • Group size of at least 10 subjects (1) or its absence (0); • Given laser parameters, e.g., wavelength, power, energy density, frequency, and applicator (1), or its absence (0); • Assessment of the functions of the tongue before and after the procedure (1) or its absence (0); • Recommended myofunctional therapy (1) or its absence (0); • Presence of a control group without a laser (1) or its absence (0); • Minimum 3-month observation period (1) or its absence (0); • Description of the technique of the performed procedure, detailed information, e.g., additional instruments supporting the procedure, duration of the procedure (1), or its absence (0); • A study containing a simple size (1) or its absence (0).
The descriptive information about the studies was graded. Studies were scored on a scale from zero to nine points (score 0-3 low, 4-6 moderate, and 7-9 high quality of a study). Any disagreements were resolved through discussion until reaching a consensus.

Risk of Bias across Studies
After summing up the results of each study, an overall calculation of the risk of bias (low, moderate, or high) for each publication, as recommended by the Cochrane Handbook for Systematic Reviews of Interventions, was performed [61].

Study Selection
Initially, 58 studies were identified as subject to analysis. After screening the titles and abstracts, 34 studies were excluded. Fifteen studies were selected for further full-text analysis, from which three were excluded according to predefined inclusion [63][64][65]. The reasons for exclusion were described in Table 1.

General Characteristics of the Included Studies
Of the twelve studies included in the review, two were randomized controlled trials [9,66], one was a pilot study [36], and nine were prospective case series [4,10,28,34,[42][43][44][45]67]. Various types of lasers have been used in studies to treat ankyloglossia. Diode lasers were used in six studies [9,10,28,34,36,66], a CO 2 laser was used in five studies [42][43][44][45]67], and an Er:YAG laser was used in two studies [4,66]. Two different laser wavelengths were used in two studies: two diode lasers [34] and the diode and Er:YAG laser [66]. Detailed information on the parameters of the lasers used was provided in seven studies [4,9,10,34,43,45,67]. Various methods of anesthesia were used before the procedure. Local anesthesia was used in seven studies [4,9,28,[43][44][45]66,67], only topical anesthesia was used in one study [10], and no information about the anesthesia was reported in two manuscripts [34,36]. In one study, local anesthesia was used as optional and not for each patient [66], one study used general or local anesthesia optionally [42], and one study used both topical and local anesthesia [45].
The age of the subjects included early childhood, preschool, and school-aged children in seven studies [4,9,28,[42][43][44][45], two studies included only a group of newborns and infants [4,34], two studies included children and adults with an extensive age range of respondents [36,67], and one study included only adults [66]. As for the type of laser used, the one study with early childhood and school-aged children used Er:YAG laser [4], two scientific experiments with newborns and infants used diode lasers [10,34], and one study involving adults used two different lasers (diode and Er:YAG) [66]. The general characteristics of the included studies are presented in Table 2.

Subjects of the Study
Studies included in the review were evaluated for the type of laser and its correlation with the use of analgesics, antibiotics, and postoperative sutures, for treatment of ankyloglossia. After analyzing research, the following information was obtained: analgesics were administrated in three studies using CO 2 lasers [43,45,67] and in one using a diode laser [10]. Analgesics with antibiotics were used in one study by Komori et al. [42]. No data were available regarding the use of antibiotics and/or analgesics in the articles with diode [9,28,34,36,66] and Er:YAG [4,66] lasers. Sutures were only needed for eight patients who received treatment for ankyloglossia with a CO 2 [42] and Er:YAG laser [4] (for available articles see Table 3).  [4] Most of the included studies recommended myofunctional therapy after surgical ankyloglossia treatment [4,9,10,28,36,42,43,45]. In two studies including newborns and infants, standardized survey questionnaires were used to evaluate subjects at the same follow-up period (1 month) [10,34]. Both of these studies reported a significant improvement in language functions. In six studies where the age groups were not homogeneous, different methods and classifications were used to assess the improvement of tongue functions. The observation periods in these studies also varied significantly, ranging from 1 day to 12 months [4,9,28,36,43,67]. Eight studies reported significant improvement in language functions [4,9,10,28,34,36,43,67]. Post-operative tongue functions were not assessed in four studies [42,44,45,66]. A significant improvement in body posture following laser treatment of ankyloglossia was observed by Olivi et al. [4]. One study reported an improvement in obstructive sleep apnea symptoms [9] (for available articles see Table 4). Table 4. Characteristics of methods for assessing the improvement of tongue functions, observation period, applied myofunctional therapy, and age of the patients.

First Author
Myofunctional Therapy

Evaluation of Functions or/and Measurements of Frenulum, Pain, Wound
Healing, Body Posture

Age of the Respondents
Tripodi et al. [28] Speech therapy protocol rehabilitation 3 months 12 months Pre and post intervention Ruffoli's classification of the lingual frenulum length. Pre-surgery and post-surgery at 1 week, 1 month, 3 months, 6 months, and 12 months follow-up.  Pre-surgery questionnaire (respiration; difficulties in making speech sounds; damaging oromyofunctional habits (thumb sucking, pacifier sucking); and inadequate postural habits or discomfort during feeding (pacifier sucking).

Quality Assessment and Risk of Bias across Studies
The paper by Fioravanti et al. [9] included in the review was qualified as high-quality scoring. Nine articles were scored as moderate-quality [4,10,28,34,42,43,45,66,67]. Two articles were obtained as low-quality (high risk of bias) [36,44]. Quality assessment and risk of bias of the included studies were described in Table 5.
The authors of qualified studies recommend administering local infiltration anesthesia in the sublingual area before the procedure [4,9,28,[42][43][44][45]66,67]. Some authors point out that in the case of laser procedures, the amount of anesthetic administered can be significantly reduced [4,42,44]. The use of only topical anesthesia before the procedure was recommended by Ghaheri et al. [10] and Fiorotti et al. [45]. Apart from topical anesthesia, Aras et al. [66] suggested the use of infiltration anesthesia, depending on the type of laser used for the procedure (in the case of a diode laser, additional infiltration anesthesia was recommended, while for Er:YAG it was was optional). Baxter et al. [43] emphasized the possibility of using additional sedation with nitrous oxide, if necessary, while Komori et al. [42] recommended that children under three years of age should undergo the procedure under general anesthesia. The overwhelming majority of authors [9,10,28,34,36,[43][44][45]66,67] did not report the need for suturing after ankyloglossia treatment with lasers. In only one case, among patients in the Olivi et al. [4] study, suturing was needed to improve haemostasis.
Additionally, Komori et al. [42] trial required suturing in 7 of 15 patients. The use of lasers for ankyloglossia treatment indicates the simplification of surgical treatment, especially when this procedure is performed on children, where the shortening of the procedure time is beneficial for the patient.
Most of the authors of the qualified studies note the need for myofunctional therapy in patients undergoing laser ankyloglossia treatment [4,9,10,28,36,42,43,45]. In studies involving infants and very young children, the implementation of myofunctional therapy was entrusted to the caregivers of children and involved the immediate postoperative period [10,42,43,45]. Baxter et al. [43], for the children aged 13 months to 13 years, recommended to manually stretch the wound 2 to 3 times per day. Komori et al. [42] and Fiorotti et al. [45] recommended tongue extension exercises for the children aged below 15 years. For newborns and infants aged 0-12 weeks, Ghaheri et al. [10] recommended a very detailed set of myofunctional exercises that gently elevate the tongue and massage the wound four to six times per day for several weeks. Myofunctional therapy, as an adjunctive to surgical treatment of ancyloglosia, significantly improved the mobility and functions of the tongue [4,9]. However, it should be highlighted that due to the different research methodologies and ages of the children, as well as the differences in the recommended myofunctional exercises, including duration, frequency, and the period after which the comparative assessment was made, it is difficult to clearly state which model of recommended myofunctional therapy is the most beneficial for patients. It is certain, however, that the use of myofunctional therapy simultaneously with the surgical treatment of ankyloglossia can significantly improve the tongue function [4,9,10,28,36,42,43,45].
Another important issue in the qualified studies concerns the postoperative administration of analgesics and the healing process after laser treatment of ankyloglossia. The recommendations regarding the use of analgesics and antibiotics involve preferably limiting or excluding the use of the aforementioned drugs. Several of the qualified studies did not provide any information on the use of drugs following laser surgery [4,9,28,36,44,66]. The administration of analgesics has been reported in four studies [10,43,45,67]. Four authors [10,43,45,67] reported the administration of acetaminophen for the first one to two days as needed, but the majority of infants needed little, if any, analgesia post procedure. Neither author reported impaired healing of a surgical wound after ankyloglossia surgery. The only reported complication was the reattachment of the frenum, found only in one case of the 15 subjects in the study described by Komori et al. [42]. Additionally, in the study of Olive et al. [4] the authors reported a complication in the form of bleeding immediately after the laser surgery in the one of 29 patients.
Last but not least, in two studies, apart from the improvement of tongue function, an attempt was made to assess body posture after laser treatment on the lingual frenulum [4,36]. However, these studies differ in the period of postoperative follow-up. Saccomanno et al. [36] performed an immediate postoperative examination by spirometry and observed no significant postural improvement. Olivi et al. [4] performed a body posture assessment before and two months after the procedure using a proprietary device and observed significant postural improvement in 18 of 30 patients. Further studies should be conducted to examine whether laser-assisted ankyloglossia surgery combined with myofunctional therapy improves body posture and speech function in children.

Conclusions
The use of lasers for the surgical treatment of ankyloglossia seems to be an effective and promising method for children and adults. The employment of lasers offers several benefits, including shorter procedural time, reduced use of general and local anesthesia and suturing, a reduced need for the administration of analgesic and/or anti-inflammatory drugs, favorable postoperative healing, and a reduction in postoperative bleeding and complications (in the form of inflammation or hematomas).
Despite its many advantages, this method has its clinical limitations: it requires the use of expensive equipment; well-trained personnel familiar with laser handling and operation;