Thread lift procedures are gaining popularity, as less invasive rejuvenation treatments for facial aging are being favoured. Facial thread lifts use absorbable materials, such as polydioxanone (PDO) threads, etc. In general, most thread materials are absorbed within six months after a procedure, and the therapeutic effect may last around one year [1]. The reason why the thread lift produces these effects is that the threads offer multiple key mechanisms of action, such as physical thread pulling effects, strong collagen synthesis around the thread, and the intra-tissue mechanism of mechanotransduction.

Additionally, the soft tissues surrounding the thread materials undergo wound healing processes, and they promote cell regeneration via numerous signalling dynamics within the extracellular matrix (ECM), as well as collagen synthesis. Laser or energy based devices may also be used alone or as a combined treatment and noninvasive method for skin rejuvenation.

Boosting treatments applied to the entire facial skin using laser or energy-based devices, especially during the first three months of greatest remodelling activity, are thought to maximize the rejuvenation effect around the thread, thereby improving the efficacy and patient satisfaction of the PDO thread lift procedure.

Seven healthy middle-aged female patients underwent symmetrical thread lift procedures for the improvement of their jawline and mouth corner sagging between March and July, 2019. The mean age of the patients was 56.0 years (47.0–61.1 years). None of the patients had underlying disorders or have undergone aesthetic procedures in the past year. Patients who had undergone surgical lifting were excluded. Patient consent for participation in the and photo usage was obtained. Prior to the procedure, we separated the face into two halves for the aim of assessing the degree of sagging. Grade was divided into five levels from 0 to 4, according to the Merz Scale [2] The half face with a higher sagging score in each patient was treated with split laser-boosting treatments for three months.

Procedures

Thread lifting protocol

Using a 2% lidocaine solution, regional nerve block was performed on infraorbital and mental nerves, and additional local anesthesia was performed at the thread insertion site. The PDO used in the thread lift procedure was an absorbable thread material (N-FIX 19-G, 100 mm; N-FINDERS, Seoul, Korea), which was operated symmetrically.

Two patients (patient 1 and 4) with high sagging scores (grades 3 and 4, respectively) were treated with symmetrical bidirectional absorbable thread (Dual Line USP 2-0 V8 and Dual Line USP 2-0 Mini; Medi Square, Daejeon, Korea), as shown in Fig. 1.

Figure 1. Design of the symmetrical thread lift procedure. Left: sites targeted by the Dual Line^® procedure. Right: sites targeted by the N-FIX^® procedure. Procedures were operated symmetrically on both sides.

Lastly, one patient (patient 7) aimed for an improvement of her wrinkles; the medial infraorbital groove and infraorbital hallows were treated with symmetrical use of filler (Teosyal Redensity; DN Company, Seoul, Korea).

Laser boosting treatment protocol

The half face with a higher sagging score was treated with the 1,450-nm laser for three months, starting on the day after the thread lift procedure. Laser boosting was performed on the facial skin below the eyes (i.e., midface, chin, mandibular area, and submandibular area 2–3 cm from the neck line), following the protocol outlined in Table 1. During the first week after the procedure, laser boosting was performed three times a week (two times during the first three days), using a very low thermal technique. In total, 3,000 shots (10 mm spot, 2.0 J/cm²) were irradiated using a moving technique, and the treatment was stopped at the time of mild warming (Table 1).

Table 1 . Laser boosting treatment protocol.

Variable	Very low thermal			Thermal
	POD 3	POD 7		POD 2 months	POD 3 months
Frequency	2 times/3 day	3 times/wk		2 times/wk	Weekly
Energy	2.0 J/cm2			5.6–6.0 J/cm2
Shots	3,000 shots			1,500–2,000 shots
End point	Mild warming			Moderate Hot

Specifics: 1,450 nm, 10-mm spot, Neobeam; Union Medical, Uijeongbu, Korea..

POD, postoperative day..

One week after the procedure, split laser boosting was performed twice a week for the first two months. For the third month, it was performed weekly (Table 1). Between 1,500–2,000 shots were irradiated at a moderately hot (pinching sensation, 10-mm spot, 5.6–6.0 J/cm²) energy level using a moving technique.

Assessments

A comparative assessment was made between the half face treated with thread lift only (TO) and half face treated with thread lift and laser (TL). On postoperative day (POD) 3 and 7, the patients were asked to report their pain and discomfort level on a visual analogue scale (VAS), ranging from 0 (no pain and discomfort) to 10 (most severe pain and discomfort). Another patient survey was conducted three months after the procedure. Improvement and satisfaction were assessed using a five-point scale (0, 25, 50, 75, 100; 0, not at all satisfied; 25, slightly satisfied; 50, moderately satisfied; 75, very satisfied; and 100, completely satisfied), specifically for elasticity, skin tone, sagging of mouth corners, jawline sagging, and overall patient satisfaction. According to the Merz Scale [2], the grade of sagging of mouth corner and jawline sagging were compared statistically before and after the treatment, and the difference in scores between the TO and TL sides were also compared (Table 2).

Table 2 . Comparison of pre- and post-treatment analysis according to the score system.

Variable	Mouth corner					Jaw sagging
	N	TO	TL	Δ		TO	TL	Δ
Pre-treatment	7	2.71±0.76	3.14±0.90	0.43±0.54		2.00±0.82	2.57±0.79	0.57±0.54
Post-treatment	7	2.29±0.95	1.43±0.54	-0.43±1.40		1.29±0.76	1.00±0.82	0.00±1.16
p-value		0.180	0.016*	0.119		0.025*	0.020*	0.157

Values are presented as mean±SD..

N, number of patients; TO, thread lift only; TL, thread lift and laser treatment..

All statistical analysis was performed using Wilcoxon signed-rank test (*p-value<0.05)..

Photos were taken preoperatively and at one week after the three-month laser boosting Treatment. The evaluations were conducted by filling out individual patient questionnaires and photographic evaluation for the Merz Scale. The scores of sagging of mouth corner and jawline sagging from the Merz Scale are given as mean±standard error of mean. The significance of difference was assessed by the Wilcoxon signed-rank test using IBM SPSS (version 21.0; IBM Corp., Armonk, NY, USA). Difference were considered to be significant at p<0.05.

Comparison of pain and discomfort after the procedure

During the first week after the procedure, the TO and TL sides showed reduction in pain and discomfort levels over time. However, a comparison of the average scores for all the patients showed a faster reduction of pain and discomfort on the TL side (Fig. 2A). For the comparative assessment of pain and discomfort reduction effects between the two sides, the changes in scores from POD 0 to POD 3 (score at POD 0 minus score at POD 3) and 7 (score at POD 0 minus score at POD 7) were calculated for each patient (Fig. 2B, C). Five of the seven patients showed difference on the TL side than on the TO side at POD 3 (Fig. 2B) and POD 7 (Fig. 2C). The sum of differences in scores between the two sides for the seven patients was 11 at POD 3 and 13 at POD 7.

Figure 2. Comparison of pain and discomfort during the first week after the procedure. (A) Comparison of average scores between the TO and TL sides. Visual analogue scale (0–10): 0, no pain and discomfort; 10, extreme pain and discomfort. POD 0, immediately after the procedure; POD 3, 3 days after the procedure; POD 7, seven days after the procedure. (B) Difference in scores between the TO and TL side at POD 3 for each patient (score at POD 0–score at POD 3). (C) Difference in scores between the TO and TL side at POD 7 for each patient (score at POD 0–score at POD 7). The sum of score differences between the TO and TL side was 11 on POD 3 and 13 on POD 7. POD, postoperative day; TO, thread only; TL, thread and laser.

Comparison of elasticity, skin tone, mouth corner and jawline sagging, and overall patient satisfaction after three months

Elasticity, skin tone, sagging of mouth corners, jawline sagging, and overall patient satisfaction improved on both the TO and TL sides (Fig. 3). For improvements in elasticity, a score ≥75 was reported by four patients on the TL side and one patient on the TO side (Fig. 3A). For improvements in skin tone, a score ≥75 was reported by five patients on the TL side. No patient reported a score exceeding 75 on the TO side (Fig. 3B). For improvements in sagging of mouth corners, a score ≥75 was reported by three patients on the TL side and one patient on the TO side (Fig. 3C). For improvement in jawline sagging, six of the seven patients reported an improvement of at least one stage (25 points) on the TL side compared to the TO side. Among these patients, one patient (Fig. 4, patient 7) reported an improvement in two stages (≥50 points) (Fig. 3D, 4). For overall satisfaction, all the seven patients reported a score ≥75 on the TL side, while only two patients reported a score ≥75 on the TO side (Fig. 3E). Average patient scores were compared between the TL and TO sides for each category (Fig. 5). For all the categories, including elasticity, skin tone, sagging of mouth corners, jawline sagging, and overall satisfaction, the improvement was greater on the TL side compared to the TO side. More specifically, the differences were greater for the scores on skin tone, jawline sagging, and overall patient satisfaction (Fig. 5).

Figure 3. Comparison of improvements in (A) elasticity, (B) skin tone, (C) sagging of mouth corners, (D) jawline sagging, and (E) overall satisfaction for each patient (scored on a visual analogue scale, 0–25–50–75–100: 0=no improvement/completely dissatisfied; 100=great improvement/completely satisfied). TO, thread lift only; TL, thread lift and laser treatment.

Figure 4. Pre- and postoperative pictures of case 7 with two-step improvement (≥50 points) of jawline sagging in TL side. POD, postoperative day; TO, thread lift only; TL, thread lift and laser treatment.

Figure 5. Comparison of average scores on elasticity, skin tone, sagging of mouth corners, jawline sagging, and overall satisfaction between the TO and the TL side (n=7, 90 days after the procedure). TO, thread lift only; TL, thread lift and laser treatment.

Comparison of Merz Scale in sagging of mouth corner and jawline sagging after three months

The average scores of the Merz Scale were significantly different in the TL side of sagging mouth corner and jawline sagging (Table 2). Additionally, the average scores before and after the thread lift were significantly different in the TO side of jawline sagging (Table 2). However, there was no significant difference in TL-TO (delta) values before and after the treatment.

Thread lift procedures using absorbable materials are widely used for facial rejuvenation because they are relatively simple and lead to faster recovery than surgical lifting. While tissue damage from threads inserted during the procedure promote wound healing processes to induce strong collagen synthesis, they also cause temporary early-stage side effects, including discomfort from pain, edema, or bruises. Meanwhile, thread lifts have diminishing therapeutic effects due to its absorbable nature, and recurrence of sagging at early stages can lead to patient dissatisfaction. We hypothesized that during the first three months of the active remodelling process caused by tissue damage from the thread lift procedure, boosting treatments with laser or energy-based devices performed on the entire facial skin and its extracellular matrix can enhance the rejuvenation effect of thread lift procedures.

Nonablative rejuvenation can increase collagen remodeling via dermal heating without interfering with daily activities. Infrared laser procedures, along with radiofrequency (RF) therapy, are commonly used in nonablative rejuvenation at frequently used wavelengths of 1,064, 1,320, 1,450, and 1,550 nm [3]. During the early stage after the thread lift procedure, therapies that involve physical contact with the skin (e.g., RF therapy) can exert mechanical force to the thread and could result in a deformation. Therefore, we applied laser boosting treatments. Moreover, the embedded thread was placed in the subcutaneous layer while the 1,450-nm laser only reaches the deep dermal layer; thus, the impact on the thread was expected to be minimal. One previous study reported on a 1,450-nm laser that uses water as chromophores to penetrate deep into the dermal layer, thereby inducing thermal damage to the dermal collagen and sebaceous glands to promote improvement of wrinkles, scars, and acne [4]. The 1,450-nm laser used in their study was a Smoothbeam (Candela Corp., Wayland, MA, USA) model with 6-nm spot size and a cooling system for the procedure. In the present study, a Neobeam (Unionmedical, Uijeongbu, Korea) laser with a 10-mm spot was used for the procedures.

Since larger laser diameters indicate deeper penetration, the procedure could be applied safely up to the moderate hot end point with lower energy in the absence of a cooling system. During the first week after the thread lift procedure, a low-energy procedure with an increased number of shots was used to minimize potential side effects due to additional thermal injuries to the already-existing tissue damage.

Afterwards, the laser energy was increased for more aggressive skin rejuvenation using a thermal technique. The mechanism of action of an infrared laser, which is identical to the 1,450-nm laser used in this study, can be described by two separate mechanisms: first, the laser energy activates thermosensitive transient receptor potential (TRP) ion channels; and second, the laser energy generates reactive oxygen species and adenosine triphosphate to exert various biological effects, thereby impacting cell proliferation and differentiation [5,6].

TRP ion channels are polymodally activated by nonselective cation channels on the cell surface [7] that are ubiquitously found across the human body, which are also involved in various physiological and pathological processes in the skin and other tissues. The channel is activated by various stimuli, including thermal and mechanical stimuli, osmosis, and chemical substances. More specifically, the transient receptor potential vanilloid (TRPV) group is known for each of the subtypes being activated at specific temperatures during thermoception. For example, the activation temperatures for TRPV1, TRPV2, TRPV3, and TRPV4 have been reported to be ≥42°C, ≥52°C, ≥31°C, and 27°C–35°C, respectively [8].

Keratinocyte differentiation and proliferation is associated with TRPV3 [9], which plays an important mediator role in the wound healing process and skin homeostasis mechanism [1,10]. Epidermal barrier homeostasis is associated with TRPV4 [1], and activated TRPV4 results in accelerated barrier recovery [11]. Further, there are studies assessing the association of TRPV3 or TRPV4 with the process of collagen synthesis or ECM remodeling. In an earlier study on TRPV3 in dermal fibrosis, activating TRPV3 in dermal fibroblasts using carvacrol promoted myofibroblast differentiation, collagen production, and TSLP expression via the TRPV3/Smad2/3 signaling pathway [12]. The collagen remodeling process is controlled by TRPV4, which has an impact on ECM mechanical property by controlling the Ca2⁺ signalling pathway and cellular function of ECM remodeling [13].

Additionally, TRPV4 is considered to hold the key to matrix remodeling mechanisms, including myofibroblast differentiation, matrix molecule synthesis, cellular contractility, matrix metalloproteinases activity, and cytokine production [13].

During the laser booting treatment, if sufficient thermal stimulation is applied with gradually increasing intensity (mild to moderately hot) so that the patient does not feel discomfort, a gradual increase in temperature is assumed to provide ample signalling to promote the gate opening of TRPV4 ion channels followed by TRPV3 channels. A better understanding and the clinical utilization of thermosensitive ion channels at the molecular level will contribute to improving patient satisfaction, increasing therapeutic effects, and minimizing side effects by boosting the biologic and thermal signalling processes during the wound healing and skin rejuvenation process. Further, our study demonstrates clear improvements in elasticity, skin tone, sagging of mouth corners, jawline sagging, and overall patient satisfaction three months after the procedure. We can find the changes and differences in Merz Scale by comparing the results before and after the treatment and laser treatment effect, except difference in sagging of mouth corner in TO before and after the treatment (Table 2). However, there was no significant difference in the TL-TO (delta) values before and after the treatment. Looking at the average, the degree of improvement in TL after treatment is greater. Therefore, there may be a difference if the number of patients increases. Compared to the TO side, improvements were greater on the TL side, and noticeable improvements due to the laser boosting treatment were specifically reported for skin tone, jawline sagging, and overall patient satisfaction. Additionally, the improvement effect of sagging of mouth corner and jawline sagging by thread lift within three months is evident, and early combined treatment of laser boosting therapy has a significant improvement effect on treatment and patient satisfaction.

This suggests that in patients consulting for thread lift procedures for the improvement of jawline sagging, laser boosting treatments should be actively considered.

There are limitations to this study. While improvements and satisfaction scores were higher on the TL side for the majority of categories measured, some differences were minimal, and patient 4 reported a diminished therapeutic effect on the sagging of her mouth corners after the laser boosting treatment. Additional studies are needed and concomitant therapies should be considered for patients who exhibit severely reduced skin elasticity. Furthermore, additional comparative studies assessing laser boosting treatment as a combination therapy after thread lift procedures should be performed over longer durations (mid- to long-term studies, 6–12 months in duration) and in larger participants capable of securing sufficient numbers for statistical verification. In addition to 1,450 nm, infrared lasers in other wavelength bands with water chromophores such as 1,320nm and 1550nm are expected to have similar effects, so it is necessary to compare the effectiveness and safety of boosting treatment using these lasers.

In conclusion, a thread lift procedure improved elasticity, skin tone, sagging of mouth corners, jawline sagging, and overall satisfaction during the first three months after treatment in this study. A 1,450-nm laser boosting treatment rapidly alleviated pain and discomfort, following the thread lift procedure. At three months after the procedure, the half face treated with threads and laser exhibited greater improvement in elasticity, skin tone, sagging of mouth corners, jawline sagging, and overall satisfaction than the half face treated with threads only. Understanding the molecular biological mechanisms underlying the effects of infrared laser on skin rejuvenation and the application of thermal stimulation to the skin rejuvenation process can enhance the improvement achieved with thread lift procedures, as well as patient satisfaction.

We would like to express our deep gratitude to Professor Nam Kyu Lim (Department of Plastic and Reconstructive Surgery, Dankook University College of Medicine) for thinking about this thesis together. In addition, we would like to thank Hana Kwon (Korean Society of Korean Cosmetic Surgery and medidine, Seoul, Rep. of Korea) who helped communicate and organize documents, and Editage (www.editage.co.kr) for English language editing.

The authors have nothing to disclose.