Use of infrared photobiomodulation with low-level laser therapy for reduction of bleaching-induced tooth sensitivity after in-office bleaching: a double-blind, randomized controlled trial

Abstract

The purpose of this study is to evaluate the use of infrared photobiomodulation with low-level laser therapy (PBM) to reduce bleaching-induced tooth sensitivity (TS) after in-office bleaching. Eighty-three participants were randomized in blocks into two groups. In the experimental group, the patients received an application after each session of in-office bleaching (35% hydrogen peroxide, 1 × 50 min; 2 sessions with 1-week interval), while the laser application was simulated in the control group. The PBM system was operated in continuous mode, using 3 J of energy. A dose of 100 J/cm² was applied for 30 s with 808 nm (100 mW of power) in the middle third of the crown. The risk and intensity of TS were recorded immediately after bleaching, 1 h, 24 h, and 48 h after each bleaching session, with a visual scale analog (0–10) and a five-point numerical scale (0–4). The color was recorded at the beginning, weekly, and 1 month after the end of the bleaching (VITA Classical, VITA Bleachedguide, and digital spectrophotometer). The risk of TS was 98% (95% CI 88 to 99%) for the laser group and 95% (95% CI 83 to 99%) for the control (RR = 1.03; 95% CI 0.94 to 1.12; p = 1.0). Similarly, no difference in the intensity of TS was detected for both pain scales (p > 0.65). Improvement in color change, regardless of the group, was observed (p > 0.15). The application of an PBM did not reduce the risk and intensity of TS when applied after the procedure using the parameters recommended by the manufacturer.

Trial registration number and date of registration: RBR-4HCVSG—04/06/2019.

Introduction

Dental bleaching is an effective cosmetic treatment that can increase patients’ satisfaction with their smiles [1]. However, TS is the most commonly reported adverse effect, affecting 49 to 100% of the patients submitted to the in-office protocol [2]. The TS starts during bleaching and usually takes up to 24 h after the procedure [2].

Hydrogen peroxide (HP) and its free radicals can oxidize the organic component of the dental structure, producing a whitening effect [3]. However, these agents are not limited to hard dental tissues. Due to its low molecular weight (34.01 g/mol⁻¹), HP can diffuse through enamel and dentin and penetrate the pulp tissue [3]. An inflammatory reaction, thus, takes place in the pulp tissue [4], resulting in an unpleasant but transient bleaching-induced TS [5]. To minimize this side effect, authors have investigated the preventive administration of oral analgesics and anti-inflammatories [6]. Still, they failed to minimize either the risk or the intensity of TS, as shown in a systematic review on this topic [6].

Photobiomodulation with low-level laser therapy (PBM) describes red and infrared laser (coherent, monochromatic, polarized light) at an intensity that stimulates biological processes [7]. PBM was already used in several fields of dentistry to regenerate damaged tissues [7], promote analgesia, and reduce tissue inflammation [8, 9]. Some studies showed PBM was effective for neural regeneration for paresthesia [10], control of postherpetic neuralgia [11], postoperative pain after retained third molar extraction [12], and symptom relief from temporomandibular disorders [13]. It is reported that cell respiratory chain components can absorb the visible red and near-infrared laser wavelengths, increasing cellular metabolism [14]. Consequently, analgesic, anti-inflammatory, and biomodulatory effects are expected to occur, thus helping tissue repair processes [7].

PBM can be presented as an alternative to reduce bleaching-induced TS [4, 15]. However, there is still a reduced number of randomized controlled trials (RCTs) evaluating this protocol [16–22]. Due to many variations in the laser parameters, commercial brands, techniques, and application areas, the effect of PBM on bleaching-induced TS deserve a more comprehensive investigation. Additionally, as pointed out in a recent systematic review of the literature [23], some studies did not evaluate the sole efficacy of infrared PBM because the procedure was associated with other desensitizing protocols such as potassium nitrate [19], fluoride dentifrice [21], and strontium chloride [16]. However, another recent systematic review [24] showed that the evidence is limited and more RCTs with low risk of bias are needed to reach a definitive conclusion on PBM in the control of TS.

Therefore, this parallel, double-blind RCT aimed to investigate whether the use of infrared PBM, following the manufacturer’s recommendations, could reduce the risk and intensity of TS in patients submitted to in-office bleaching. The impact of this protocol on the color change was also evaluated.

Methods

Ethics approval and protocol registration

This clinical investigation received approval (protocol 3.056.864) from the Ethics Committee of the State University of Ponta Grossa, PR, Brazil). This study was registered in the Brazilian Clinical Trials Registry under RBR-4HCVSG. The preparation of this article followed the protocol described in the Consolidated Standards of Reporting Trials statement for parallel designs [25].

Trial design, settings, and locations of data collection

This study was a parallel, double-blind RCT. This study was performed from November 2019 to January 2020 in the clinics of the School of Dentistry at the State University of Ponta Grossa, PR, Brazil.

Recruitment

Recruitment was performed by placing written advertisements on the university walls and using social media to obtain a convenient sample. The volunteers were informed about the study’s objectives, and they all signed an informed consent form before being enrolled in the study.

Eligibility criteria

The participants included in this RCT were at least 18 years old, had good general and oral health, and did not report any type of TS. The participants were required to have all six maxillary anterior teeth free of caries, restorations, and periodontal disease. The canines had to be shade A₂ or darker, as judged by comparison with a value-oriented shade guide (VITA Classical, VITA Zahnfabrik). Participants with anterior restorations, dental prostheses, orthodontic apparatuses, and severe internal tooth discoloration (tetracycline stains, fluorosis, and pulpless teeth) were not included. In addition, pregnant or lactating women, smokers, participants who had bruxism and had undergone tooth-bleaching procedures, and any other condition that could cause sensitivity (such as recession, dentin exposure, or visible enamel cracks) were also excluded.

Sample size estimation

This study’s primary outcome was the absolute risk of TS. The absolute risk of TS was reported to be approximately 90% for the bleaching product Whiteness AutoMixx 35% (FGM Dental Group, Joinville, SC, Brazil) [26]. For detecting an absolute risk difference of 25% between the control and experimental groups, a minimum sample size of 80 patients (power of 80%, alpha of 5%) was required.

Randomization

We performed blocked randomization (block sizes of 2, 4, and 6) using the website www.sealedenvelope.com. A third researcher not involved in the study implementation prepared consecutively numbered, opaque, and sealed envelopes containing information identifying the groups. Allocation concealment was guaranteed by only opening the envelope when the eligible patient was ready in the dental office for the treatment implementation.

Blinding

To guarantee participants’ blinding, we should prevent them from seeing the light and hearing the laser device’s sound. We made an impression with condensation silicone (Cub Kit Perfil, Vigodent Coltene, Alstatten, Switzerland) that involved the upper and lower incisors, canines, and premolars from both arches’ sides. Thus, we drilled a circular hole of 6 mm in diameter (Biopsy Punch, Miltex Instruments, USA) in the middle third of each involved tooth. The construction of this guide was able to reduce the amount of light that the participant could see during the procedure. In addition, all participants wore headphones with a playlist to prevent them from hearing the sound emitted by the laser device. These procedures were previously tested on a group of 8 participants, and it was shown to be effective in reducing the participant's awareness of the group assignment they underwent. All participants in this clinical study wore protective goggles provided by the manufacturer during laser therapy sessions. Operators were not blinded because they needed to activate the laser when necessary. However, the evaluators were blinded to the group allocation.

Study intervention

All participants underwent a prophylaxis and oral hygiene guidance procedure before the bleaching procedure. Three operators with more than 3 years of clinical experience performing the bleaching procedures. After placement of a lip retractor (ArcFlex, FGM Dental Group, Joinville, SC, Brazil) and protection of the gingival tissue with a light-cured resin dam (Top Dam, FGM Dental Group, Joinville, SC, Brazil), the 35% HP gel (Whiteness Automixx, FGM Dental Group, Joinville, SC, Brazil) was applied in a single 50-min application for both groups. At the end of the recommended time, the bleaching gel was removed with a disposable surgical saliva ejector, cleaned with gauze, and washed with an air–water spray. The light-cured resin dam was removed after the lip retractor. Two bleaching sessions were performed at a 1-week interval. All participants were instructed to brush their teeth regularly with fluoridated toothpaste.

After each bleaching in-office session (sufficient time to remove the gel, light-cured resin dam, and the lip retractor), the region for laser irradiation was standardized with the aid of the silicone guide. The silicone guide was punched with a 6 mm window in the middle third of the crown to create a window. This silicone was able to standardize and stabilize the area to be irradiated, as well as maintain intimate contact with the tissue to be irradiated. The laser group (n = 43) underwent PBM (Laser Duo, MMOptics, São Carlos, SP, Brazil). It is tip has a diameter of 6 mm², and it is light beam is 3 mm²., with a numerical beam aperture of 0.5 (45°). The device is a laser with an active semiconductor medium of gallium-aluminum arsenate (AsGaAl), emitting a wavelength of 808 nm. The laser was operated at a power of 100 mW. The energy supplied for each tooth was 3 J, and we applied it in the middle third of the crown (pulp tissue as the target of irradiation) for 30 s with an energy density of 100 J/cm². The laser emission mode is a continuous wave mode throughout the application time. For the application of the laser, we followed the recommendations of the dose protocols recommended by the manufacturer. It is important to consider that there is a distance from where the laser was applied to the target tissue and that fluence may have been reduced with doses close to 10–30 J/cm² [27]. Between each patient, the device was kept under constant load, and its power was checked before being used using an optical power meter with a calibration certificate (Power Meter Coherent). All procedures were repeated for the control group (n = 40), but the laser device was positioned but kept turned off.

Outcomes

Evaluation of tooth sensitivity

Participants had to record their pain intensity in the following time intervals: (1) during the treatment; (2) up to 1 h after each bleaching session; (3) between 1 and 24 h after each bleaching session; (4) between 24 and 48 h. After both bleaching sessions, the measurements were performed using the 5-point numerical rating scale (NRS; 0 = none, 1 = mild, 2 = moderate, 3 = considerable, and 4 = severe) [26, 28, 29] and a 0–10 visual analog scale (VAS) [26, 28, 29]. The VAS scale is a 10-cm horizontal line with scores of zero and 10 at their ends, in which zero means no sensitivity and 10 means severe TS. The patient had to mark the TS intensity with a vertical line across the scale’s horizontal line. Then, the distance in millimeters from the zero ends was measured with the aid of a millimeter ruler.

The worst score (NRS) or numerical value (VAS) obtained from all-time recalls was used in the statistical analysis. A patient who was insensitive to bleaching needed to score zero (no TS) during all assessments from both bleaching sessions. In all other circumstances, participants were considered to have TS. This dichotomization made it possible to calculate the absolute risk of TS, which represented the percentage of participants who reported TS at least once during treatment.

Color change

Two calibrated operators performed color evaluation before the bleaching session, one week after the first bleaching session, 1 week after the second, and 1 month after the bleaching treatment. The color evaluation was never performed immediately after each bleaching session so that the effect of dehydration and demineralization on color measures. The color evaluation was performed with the value-oriented shade guide Vita Classical (VITA Zahnfabrik, Bad Säckingen, Germany) and the VITA Bleachedguide 3D-MASTER (VITA Zahnfabrik, Bad Säckingen, Germany). In addition, an objective color evaluation was performed with the spectrophotometer VITA Easyshade (VITA Zahnfabrik, Bad Säckingen, Germany).

The 16 shade guide tabs from the VITA Classical shade guide were arranged from the highest (B₁) to the lowest (C₄) value for the subjective examination. The changes were treated as representing continuous and approximately linear color change ranking as performed in previous published studies [26, 28, 29]. The VITA Bleachedguide 3D-MASTER contains lighter shade tabs, organized from the highest (0M1) to the lowest (5M3) value.

The middle third of the right upper canine was used as the tooth-matching area. Color changes were calculated from the beginning of the active phase up to the individual recall times by calculating the difference in shade guide units (∆SGUs), which occurred toward the lighter end of the value-oriented list of shade tabs. In case of disagreements between the operators, the operators had to reach a consensus before the patient was dismissed.

For the objective evaluation, a preliminary impression of the maxillary arch was made with high-putty silicon paste (Cub Kit Perfil, Vigodent Coltene, Alstatten, Switzerland) to serve as a standard guide for the tip of the spectrophotometer. The silicone guide was punched with a 6 mm window in the medium region of the right upper canine to create a window. A calibrated evaluator measured the color in all participants using a spectrophotometer (VITA Easyshade Advance, VITA Zahnfabrik, Bad Säckingen, Germany) at the beginning of the first session and 30 days after the end of the bleaching treatment.

The objective color change was calculated with the CIELab parameters of L* (luminosity), a* (green to the red axis), and b* (blue to the yellow axis) obtained from the spectrophotometer. The difference between the baseline and 30 days after the end of the bleaching treatment was computed using the following CIELab formula: ∆E_ab = [(∆L*)² + (∆a*)² + (∆b*)²]^1/2. In addition, the color change was also calculated based on the CIEDE 2000 formula: ∆E₀₀ = [(ΔL/kLSL)² + (ΔC/kCSC)² + (ΔH/kHSH)² + RT (ΔC*ΔH/SC*SH)]^1/2 and whiteness index (WI_D) was calculated according to the following formula: WI_D = 0.551 × L − 2.324 × a − 1.1 × b. Moreover, changes in WI_D caused by each step were calculated by subtracting the values observed at each assessment time from those calculated in the prior step (ΔWI_D).

Statistical analysis

The statistician was blinded to the study groups. We performed the intention-to-treat analysis, including all randomized in the data analysis. Data analyses were conducted with the SigmaPlot version 11.0 software (Systat Software) with a significance level of 5%.

The risk of TS (reported at least once by participants) of both groups was compared using Fisher’s exact test. The relative risk and 95% confidence interval (CI) were also calculated. The intensity of TS of both groups was compared with the Mann–Whitney test (NRS scale) and t-test for independent samples (VAS scale). The mean difference of TS intensity in the VAS scale (95% CI) was also reported. Subjective color assessment (ΔSGUs) and objective color assessment (ΔE_ab, ΔE₀₀, and ΔWI_D) were compared with t-tests for independent samples. The mean difference and 95% CI were also calculated as the effective measures for the continuous outcomes.

Results

Characteristics of the eligible participants

One hundred and twelve participants were examined, and 83 were included in the clinical study (Fig. 1). Forty-three participants were randomized to the laser group and forty to the control group. The baseline features of the participants for both groups were very similar, showing they were balanced for these baseline variables (Table 1).

Fig. 1.

The CONSORT flow diagram of study design phases including enrollment and allocation criteria

Table 1.

Baseline characteristics of the participants

Groups (number of patients)	Laser group (n = 43)	Control group (n = 40)
Baseline color (SGU; mean ± SD)*	10.1 ± 3.1	10.1 ± 2.9
Age (years; mean ± SD)	25.7 ± 3.9	24.3 ± 3.6
Gender (female; %)	75	60

^*Abbreviations: SGU, shade guide unit measured by VITA Classical; SD, standard deviation

Tooth sensitivity

The absolute risk of TS was 98% (95% CI 88 to 99) for the laser group and 95% (95% CI 83 to 99) for the control group. In comparative terms, the relative risk for TS was 1.03 (95% CI 0.94 to 1.12; Table 2) with no statistical difference (p = 1.0). Similarly, no significant difference in the intensity of TS was observed for both pain scales (p > 0.05). The mean difference in the TS intensity in VAS units was − 0.3 (95% CI, − 1.6 to 1.0; Table 3).

Table 2.

Number of patients with TS during dental bleaching, and the absolute and relative risk of TS

Group	TS (number of patients)		Absolut risk (95% CI)	Relative risk (95% CI)*
	YES	NO
Laser group	42	1	98% (88 to 99)	1.03 (0.94 to 1.12)
Control group	38	2	95% (83 to 99)

Abbreviation: CI, confidence interval

^*Fisher’s exact test p = 1.0

Table 3.

Intensity of TS in VAS scale (means and standard deviations) and NRS scale (medians and interquartile ranges)

Scales		Laser group (n = 43)	Control group (n = 40)	Mean difference (95% CI)	p-value
VAS (0–10)	First week	2.8 ± 2.8	3.2 ± 3.0	− 0.4 (− 1.7 to 0.8)	0.52*
	Second week	2.7 ± 2.6	2.7 ± 3.1	0.0 (− 1.2 to 1.2)	0.99*
	Worst scenario	3.7 ± 2.8	4.0 ± 3.1	− 0.3 (− 1.6 to 1.0)	0.65*
NRS (0–4)	First week	1.0 (1.0–3.0)	1.0 (1.0–3.0)	–	0.83**
	Second week	2.0 (1.0–2.0)	1.0 (0.0–2.0)	–	0.52**
	Worst scenario	2.0 (1.0–3.0)	2.0 (1.0–3.0)	–	0.96**

* Student’s t-test for independent samples

** Mann–Whitney test

Color evaluation

The final color measurement was intended to be done 30 days after the bleaching protocol. However, as the end of the study coincided with the rise of the COVID-19 pandemic, 32 patients had their final color change evaluated in a time frame between 3 and 6 months after bleaching.

A significant whitening was observed after bleaching for both groups. The color change was approximately 5 units in the VITA Classical scale, 5 units in the VITA Bleachedguide, 11 units in the ∆E_ab, 6 units in the ∆E₀₀, and 13 units in the ∆WI_D (Table 4). No significant difference in color change was observed between the laser and control groups (Table 4; p > 0.15).

Table 4.

Color change (mean and standard deviation) obtained from different instruments and different times, mean difference and 95% confidence interval comparing the different groups

Color change instrument	Time assesments	Groups		Mean difference (95% CI)	p-value
		Laser (n = 43)	Control (n = 40)
ΔSGU VITA Classical	Baseline vs. 1-week	3.4 ± 2.3	3.5 ± 3.2	− 0.1 (− 1.3 to 1.1)	0.83
	Baseline vs. 2-week	5.9 ± 2.9	5.9 ± 2.8	− 0.0 (− 1.3 to 1.2)	0.94
	Baseline vs. 1-month	5.1 ± 2.9	5.6 ± 2.8	− 0.5 (− 1.8 to 0.7)	0.42
ΔSGU VITA Bleachedguide	Baseline vs. 1-week	3.5 ± 1.8	3.6 ± 2.2	− 0.1 (− 1.0 to 0.8)	0.80
	Baseline vs. 2-week	5.7 ± 2.2	6.1 ± 2.3	− 0.4 (− 1.3 to 0.6)	0.44
	Baseline vs. 1-month	4.9 ± 3.1	5.9 ± 2.9	− 0.9 (− 2.3 to 0.3)	0.15
ΔEab	Baseline vs. 1-week	8.7 ± 4.1	7.9 ± 4.1	0.8 (− 0.9 to 2.6)	0.37
	Baseline vs. 2-week	10.9 ± 4.1	11.1 ± 3.9	− 0.2 (− 1.9 to 1.6)	0.85
	Baseline vs. 1-month	11.4 ± 4.3	10.7 ± 3.7	0.7 (− 1.1 to 2.5)	0.43
ΔE00	Baseline vs. 1-week	5.5 ± 2.5	4.9 ± 2.7	0.5 (− 0.6 to 1.7)	0.34
	Baseline vs. 2-week	10.9 ± 4.1	11.1 ± 3.9	− 0.2 (− 1.9 to 1.5)	0.85
	Baseline vs. 1-month	6.7 ± 2.6	6.2 ± 2.2	0.4 (− 0.6 to 1.5)	0.41
ΔWID	Baseline vs. 1-week	12.0 ± 8.7	11.5 ± 7.9	0.4 (− 3.2 to 4.1)	0.79
	Baseline vs. 2-week	14.7 ± 9.8	15.8 ± 9.6	− 1.1 (− 5.3 to 3.1)	0.82
	Baseline vs. 1-month	12.6 ± 10.4	13.1 ± 7.3	− 0.5 (− 4.4 to 3.5)	0.80

^* Student’s t-test for independent samples

Discussion

Hydrogen peroxide has a low molecular weight and reaches the pulp chamber a few minutes after its application [3]. In pulp tissue, HP reduces cell viability, causes damage to the cell membrane, activates proteolytic enzymes, and degrades the extracellular matrix [30, 31]. In addition, inflammatory mediators such as neuropeptides, prostaglandins, adenosine triphosphate, and substance-P are released, whose functions are recognized in triggering the inflammatory response, exciting the nerve endings responsible for pain perception [32, 33].

Due to this common side effect, several approaches have been investigated to eliminate or at least reduce the risk of bleaching-induced TS. The present study investigated the PBM with an infrared laser (808 nm) and a power of 100 mW, following the manufacturer’s recommendations. The energy supplied to each tooth was 3 J for 30 s, with an energy density of 100 J/cm². Unfortunately, the PBM therapy tested did not reduce the risk or the TS intensity. In both groups, a high risk of TS was observed, affecting up to 95% of the participants, which agrees with previous studies in the literature that performed in-office dental bleaching [26, 29, 34].

Previous studies evaluated PBM for bleaching-induced TS, but they do not provide strong evidence of efficacy [16–22]. For instance, Calheiros et al. [20] assessed the application of an infrared laser (780 nm) at different periods and showed no reduction in TS. Moosavi et al., [17] comparing two different wavelengths (660 and 810 nm), reported that the infrared laser (810 nm) effectively reduced TS, but only after 24 h. However, the TS risk and intensity are usually not an important clinical issue during this period as TS reduces significantly 24 h postbleaching [2].

Another study showed positive findings for the PBM, but the laser was associated with other desensitizing agents, such as topical sodium fluoride [21], and the authors did not include control groups. The lack of a comparator prevents us from differentiating real treatment efficacy from the placebo effect, the natural evolution of the disease, the Hawthorne effect [35], and regression to the mean [36]. Thus, the findings of these two studies have a high risk of bias and should not be used to support a clinical recommendation.

The cellular response to the PBM depends on the wavelength [37], radiant power, irradiated area, and exposure time. These parameters allow the calculation of the radiant exposure or energy dose (energy per irradiated area), irradiance, and total radiant energy, which are also essential parameters [38]. The published studies on PBM for bleaching-induced TS show a considerable variation in irradiation, treatment parameters, and protocols (Table 5). In the studies listed in Table 5, one can see that the laser wavelengths varied between 660 to 810 nm, and power ranged from 40 to 200 mW. Differences in power density were even more pronounced than energy density and application time (Table 5).

Table 5.

Laser parameters of PBM used in clinical trials for desensitization of bleaching-induced TS

Study	Number of participants per group	Comercial name	Wavelengh (nm)	Power (mW)	Power density (W/cm2)	Energy (J)	Energy density (J/cm2)	Spot size area (cm2)	Application time per point(s)	Application location
Moosavi et al. 2016	22	Thor DD2 Control Unit*, Thor	660 810	200	8	3	12	0.25	15	Cervical crown
Calheiros et al. 2017	10	MMOptics	780	40	1	0.4	10	0.04	10	Middle crown Apical root
de Paula et al. 2019	25	Photon Laser III, DMC	808	100	35.7	1.7	60	0.028	16	Cervical crown Apical root
Alencar et al. 2018	25	Photon Laser III, DMC	808	100	35.7	1.7	60	0.028	16	Cervical crown Apical root
De Silva et al. 2020	21	Photon Laser III, DMC	808	100	35.7	1.7	60	0.028	16	Cervical crown Apical root
Pompeu et al. 2021	25	Photon laser III, DMC	808	100	35.7	1.7	60	0.028	16	Cervical crown Apical root
Present study	40	Laser Duo, MMOptics	808	100	33.3	3	100	0.04	30	Middle third crown

^*These laser devices have two laser wavelengths available for bleaching-induced TS

For the PBM to be effective, the irradiation parameters must be within certain ranges for the specific target living tissue [39]. As there are many parameters, finding the correct association to be effective is challenging. For instance, Lanzafame et al. [40] showed that LED radiation at 660 nm on their murine pressure ulcer model produced very different effects when applied with an increasing power density (irradiance) and decreasing irradiation time, despite keeping energy density (J/cm²) constant.

Earlier studies have shown the 810-nm infrared laser [16], and the higher dosimetry of energy density appears to be the most effective for analgesia [27]. Although we have followed the manufacturer’s recommendation in this study, there is at present no standard methodology or process for adopting treatment protocols. The current scenario shows the lack of complete parameters and significantly impacts the ability to integrate published data with current and future research in PBM (Table 6).

Table 6.

Description of protocols for desensitization after tooth bleaching with low power laser devices

Commercial name	Manufacturer	Composition	Wavelength (nm)	Power (mW)	Power density (W/cm2)	Energy (J)	Energy density (J/cm2)	Application time (s)	Application location
Photon Laser III infrared	DMC	Laser diode (AsGaAl)	808	100	35.7	1.7	60	16	Cervical crown and apical root
Whitening Lase II	DMC	Laser diode (AsGaAl)	808	100	35.7	2.5	90	25	Cervical crown and apical root
Thor DD2 Control	THOR	Laser diode (AsGaAl)	810	200	8	3	12	15	Cervical crown
Laser Duo	MMOptics	Laser diode (AsGaAl)	808	100	33.3	3–4	100	30–40	Middle or cervical crown

Applying a protocol without evidence support is not in line with practice-based evidence (PBE) principles [41]. Conceptually, PBE involves three fundamental principles: awareness of the best available evidence, guidance on the trustworthiness of the evidence, and trade-offs between the benefits and risks. At least the first principle has been ignored when PBM is indicated for bleaching-induced TS. The best evidence should come from systematic summaries of the evidence or from larger, high-power RCTs, which were not found in the available literature, or when found (Table 5), it was possible to observe a high variability among parameters. However, some considerations are necessary before instituting treatment. The target depth is something that needs to be observed; on average the anterior maxillary teeth (central incisors, lateral incisors, and canines) are around 3.3 mm thick (data not shown), away from the pulp tissue that is the target of work being considered subsurface. Energy loss at this distance is unavoidable as large optical scattering occurs, resulting in energy loss. By dividing the energy density of the device, we use which is 100 J/cm², by the depth of the target tissue, we will provide doses of 26–34 J/cm² in the target tissue, which is in accordance with the analgesia protocols indicated in the systematic review published by Paker et al. [27].

It is not by chance that the manufacturer’s recommendation is to combine the topical application of potassium nitrate before bleaching. However, a recent systematic review and meta-analysis [34] that evaluated the risk and intensity of tooth sensitivity after topical application of desensitizers containing potassium nitrate before dental bleaching showed a beneficial effect in reducing the intensity of TS, but with a low magnitude of effect, which means minimal clinical importance [34]. Also, most studies included were graded as low certainty assessment of evidence [34]. Also, when the association between PBM and desensitizer gel containing potassium nitrate in the prevention of TS was evaluated, no synergistic effect between both therapies in the reduction of TS after in-office bleaching was found [19]. In fact, the use associated between PBM and desensitizer gel containing potassium nitrate would create a messy factor, since it was not possible to know the individual contribution of each one in the decrease of TS.

The in-office gel used in the present study was previously evaluated in other clinical studies, and usually, a high risk of TS was observed, in agreement with the results in the present study [26, 28, 29]. This seems directly associated with its pH instability during the application time in contact with the dental structure [42, 43]. The bleaching gels on the market have always presented pH instability since most gels need to be renewed over time. The great problem of single-application gels associated with pH instability makes us think that these patients may present a greater intensity of TS. This can be explained by the fact that gels with more acidic characteristics increase the penetration of hydrogen peroxide into the pulp [44, 45] and generate a greater intensity of TS [46].

Regarding the color change, there was an effective whitening in both groups detected by the three color evaluation methods, which shows that the application of PBM did not jeopardize whitening. At the end of the bleaching protocol, the color change was approximately 6 and 5.5 units whiter in the VITA Classical and VITA Bleachedguide scales, respectively. These results agree with previous clinical studies that also used high-concentrate HP for in-office bleaching [26, 28, 29].

The objective color change evaluation demonstrated that both groups experienced effective and clinically perceptible tooth whitening with a color change of approximately 11, 6, and 13 units for ∆E_ab, ∆E₀₀, and ∆WI_D, respectively. Although the figures provided by objective evaluation are not easily understandable, we can compare them with the 50:50 perceptibility (PT) and acceptability (AT) thresholds [47, 48]. Paravina et al. [48] found that PT and AT values were 1.2 and 2.7, respectively, for the CIELab system and 0.8 and 1.8 for the CIEDE2000 system. Pérez et al. [47]found that PT and AT values were 0.7 and 2.6, respectively, for the Whiteness Index. In our study, the ∆E_ab, ∆E₀₀, and ∆WI_D figures after bleaching treatments were well above the 50:50 PT and 50:50 AT limits, indicating the color change was noticeable and clinically significant to most participants.

Conclusion

After in-office bleaching, the infrared PBM (808 nm, continuous mode, 100 mW of power, 3 J of energy, 100 J/cm², 30 s) did not reduce the risk and intensity of tooth sensitivity and did not jeopardize color change.

Author contribution

Laína Vochikovski: conceptualization, methodology, investigation, data curation, and writing—original draft. Michael Willian Favoreto: methodology, investigation, data curation, formal analysis, and writing—original draft. Marcia Rezende: conceptualization, methodology, investigation, data curation, and writing—original draft. Renata Maria Olenki Terra: methodology, investigation, data curation, and writing—review and editing. Fernanda Novak Gumy: methodology, investigation, data curation, and writing—review and editing. Alessandro Dourado Loguercio: conceptualization, formal analysis, writing—review and editing, and supervision. Alessandra Reis: conceptualization, methodology, resources, formal analysis, investigation, data curation, writing—review and editing, project administration, and supervision.

Declarations

Ethics approval

This clinical investigation received approval (protocol 3.056.864) from the Ethics Committee of the State University of Ponta Grossa, PR, Brazil). This study was registered in the Brazilian Clinical Trials Registry under RBR-4HCVSG. The preparation of this article followed the protocol described in the Consolidated Standards of Reporting Trials statement for parallel designs (CONSORT).

Consent to participate

Informed consent was obtained from all individual participants included in the study.

Consent for publication

Patients signed informed consent regarding publishing their data.

Conflict of interest

The authors declare no competing interests.