Background: The aim of study was to investigate the effectiveness of low-level laser therapy (LLLT) use before in-office bleaching to prevent risk and intensity of tooth sensitivity.

Methods: thirty patients were selected for this clinical trial. Before bleaching procedures with 38 % hydrogen peroxide, the participants were randomly divided into two groups of 15 subjects. Test group: the patients teeth received a preliminary LLLT procedure by an 810 nm diode laser with 0.5 Watt for 30 s for an energy density of 15 J/cm2 and a group placebo: the patients received the same preliminary LLLT but with the device switch off. All patients were instructed to report their cold sensitivity experiences immediately, 1 h, 24 h, and 48 h after the end of bleaching by a visual analog scale score between 0-10.

Materials and methods The sample used for this study was of 30 subjects with explicit request for teeth whitening and was conducted in agreement with a randomized double-blind and placebo controlled clinical trial. This search was led in accordance with the ethical standards of the committee responsible for human experimentation (institutional and national), and with the Helsinki Declaration of 1975, as revised in 2013. Only patients at least 18 years old with teeth of a shade darker than C2, using the shade guide of Vita Classical A1-D4®- Germany, were recruited. All patients were in good general health with maxillary and mandibular anterior teeth without caries, visible defects, and any restoration. Subjects who exhibited a negative vitality test for any teeth, from 1.4 to 2.4, were excluded from the study. Patients who used analgesics, anti-inflammatory, or antioxidant medicine to therapeutic purposes and those with smoking habits, also were excluded from the study as well as patients with bruxism habits or with any pathologic defect such as gingival recession or dentin exposure. None of the patients recruited reported symptoms attributable to dental sensitivity. Two weeks before the bleaching treatment, the participants underwent professional oral hygiene and received oral hygiene instructions to brush their teeth twice per day with a similar toothbrush and toothpaste during the research time. Each patient was informed, verbally and in writing, about the treatment procedures and was asked to sign an informed consent document before the study commencement. All the teeth from 1.4 to 2.4 of each patient that had to be subjected to whitening treatment were evaluated for dental sensitivity by means of the cool sensitivity test (baseline).

Cold sensitivity Test (CST): The degree of tooth sensitivity was determined using an air stimulus defined as a 3 s cold air blast (temperature range of 19-20° C) at a distance of 2-3 mm from the test site. Each tooth under examination was isolated using cotton rolls and by shielding the neighboring teeth with the gloved fingers of the operator. All patients were asked to report their degree of sensitivity for each tooth after the CST employing a visual analog scale (VAS) to objectify the degree of intensity of pain/discomfort felt, consisting of a 100-mm horizontal line on a sheet of paper with 0-10 points where the ends were represented from 0 (the left side) indicating no pain/discomfort and 10 (the right side) representing the worst possible pain never warned [14].

Patients reporting VAS values greater than 4 for at least one tooth were excluded from the study.

The in-office bleaching procedure The thirty patients selected have randomly divided into two groups (n=15) using a Random Number Generator Software by a not-clinician investigator. The mean age of the patients was similar in the two study groups (test group 23.4 ± 5.8 and placebo group 5.5 ± 6.2), as well as there was no significant difference in the sex of the participants between the two groups (8 and 7 females respectively in test and placebo group).

• Test group: all teeth to be whitened of each patient, before bleaching, received an irradiation procedure by a LLLT using a diode laser (Soft Touch; 810 nm, 5 W, Creation). The laser probe (a fiber of 400 µm diameter) was positioned in contact mode with the enamel of the tooth to be irradiated for 30 s in continuous-wave using 0.5 W, with horizontal and vertical moving to cover the whole area. Each tooth received an energy density of 15 J/cm2. Subsequently each patient underwent the teeth whitening procedure using the protocol recommended by the product manufacturer. The gingival tissues of the teeth to be bleached were isolated from the bleaching gel using a light-cured resin dam (OpalDam Kit, Ultradent; Corsico- MILAN, Italy). A 38 % ready-to-use Hydrogen peroxide-containing gel (The Smile® Strong, Italy) was applied from the first premolar right to the first premolar left of both jaws for a total period of 20 minutes for a 1 single whitening session.
• Placebo group: all teeth to be whitened of each patient, before bleaching, to avoid interference psychological of patients on outcomes of study, received a preventive laser procedure applying the identical parameters used for group test except the device was kept in idle mode. Subsequently he teeth whitening procedure was identical to that of the test group.

Following the bleaching treatment, the gel was rinsed off. The laser procedure and the whitening procedure were performed by two different clinical operators who were not aware of the organization of the two study groups.

Subsequently, the first operator, already employed to collect VAS score in baseline, and who was unaware of the assigned clinical protocols, underwent again all participants of the study to CST asking them to record the degree of dental sensitivity, for each bleached tooth, perceived from immediately, to 1 h, to 24 h, and to 48 h after the end of bleaching treatment using the VAS score.

Statistical analysis To quantify the cold discomfort experience for each patient a single VAS value was considered, obtained from the sum of the individual VAS values from each tooth exposed to cold test. While, for the comparsion of discomfort between the two groups, the total VAS score of each group was used, resulting from the sum of the VAS values of each patient collected at the different study times. The VAS values of each group was confronted with each other and also compared with the baseline value of reference at different study times.The statistical analysis was performed with GraphPad Prism software version 9 (by Dotmatics, San Diego CALIFORNIA, USA.) The significance level for all tests was predetermined at p< 0.05.

Results All 30 participants completed the study. The table 1 shows the total value VAS (mean and standard deviation, SD) for each study group at different time points of the clinical trial. The comparison of the total VAS scores for each group study within the same study time revealed statistically significant values using the Wilcoxon signed-rank test in times of immediately, after 1h, and after 24 h while there was no significant difference for the VAS values 48 h after whitening treatment (Table 1 and figure 1). The comparison of VAS score of each group with the corresponding value at baseline time shows high significance for both groups in immediately and only with the equivalent VAS value of placebo group after 1 h and 24 h after whitening.

Inclusion Criteria:

• patients with teeth of a shade darker than C2, using the shade guide of Vita Classical A1-D4®- Germany
• patients in good general health with maxillary and mandibular anterior teeth without caries, visible defects, and any restoration.

Exclusion Criteria:

• Subjects who exhibited a negative vitality test for any teeth, from 1.4 to 2.4,
• Patients who used analgesics, anti-inflammatory, or antioxidant medicine for therapeutic purposes and those with smoking habits, also were excluded from the study as well as patients with bruxism habits or with any pathologic defect such as gingival recession or dentin exposure.
• Patients with symptoms attributable to dental sensitivity.

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• an investigator was employed for patient recruitment and to perform preliminary sensitivity tests at baseline for all selected patients (baseline)
• a non-clinical investigator was used to divide the patients into two study groups using random distribution software.

The laser procedure and the whitening procedure were performed by two different clinical operators who were not aware of the organization of the two study groups.

Subsequently, the first operator, already employed to collect scores in baseline, and who was unaware of the assigned clinical protocols, underwent again all participants of the study to sensitivity Test asking them to record the degree of dental sensitivity, for each bleached tooth, perceived from immediately, to 1 h, to 24 h, and 48 h after the end of bleaching treatment using the score.