Journal of Conservative Dentistry

: 2022  |  Volume : 25  |  Issue : 2  |  Page : 166--172

Evaluation of the efficacy of diode laser in bleaching of the tooth at different time intervals using spectrophotometer: An in vitro study

Ishani Saluja1, Neeta Shetty1, Ramya Shenoy2, Sandeep Nayak Pangal3,  
1 Department of Conservative Dentistry and Endodontics, Manipal College of Dental Sciences, Mangalore, Affiliated to Manipal Academy of Higher Education, Karnataka, India
2 Department of Public Health Dentistry, Manipal College of Dental Sciences, Mangalore, Affiliated to Manipal Academy of Higher Education, Karnataka, India
3 Department of Media Technology, Manipal Institute of Technology, Manipal Academy of Higher Education, Manipal, Karnataka, India

Correspondence Address:
Dr. Neeta Shetty
Department of Conservative Dentistry and Endodontics, Manipal College of Dental Sciences, Mangalore, Affiliated to Manipal Academy of Higher Education, Lighthouse Hill Road, Mangalore - 575 001, Karnataka


Aim: This study aimed at comparative evaluation of the efficacy of tooth bleaching using different concentrations of carbamide peroxide (CP) with and without diode laser at 980 nm for 2.5 and 5 min time duration. Materials and Methods: Hundred intact human incisors were selected. Teeth were artificially stained using black tea solution. Samples were randomly allocated into four groups: Group I: distilled water, Group II: 15%, 20%, and 35% CP without laser, Group III: 15%, 20%, and 35% CP using diode laser for 2.5 min, and Group IV: 15%, 20%, and 35% CP using diode laser for 5 min. Color measurements were made using spectrophotometer. Data were statistically analyzed by ANOVA, repeated measures of ANOVA, and Tukey post hoc test. Results: 35% concentration of CP gave similar mean shade (ΔE) value at T2, as 15% CP at T3. At T3, 15% concentration of CP using diode laser for 2.5 min gave similar mean shade (ΔE) value, as 35% concentration of CP using diode laser for 2.5 min. Conclusion: 35% CP causes change in chroma and whitens the tooth at a faster rate with a significantly more lightening effect. Bleaching twice weekly produces a similar effect when using high or low concentrations of CP. Laser-assisted bleaching decreases the time of whitening process.

How to cite this article:
Saluja I, Shetty N, Shenoy R, Pangal SN. Evaluation of the efficacy of diode laser in bleaching of the tooth at different time intervals using spectrophotometer: An in vitro study.J Conserv Dent 2022;25:166-172

How to cite this URL:
Saluja I, Shetty N, Shenoy R, Pangal SN. Evaluation of the efficacy of diode laser in bleaching of the tooth at different time intervals using spectrophotometer: An in vitro study. J Conserv Dent [serial online] 2022 [cited 2022 Jul 2 ];25:166-172
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Discolored teeth are associated with a wide range of cosmetic problems and aesthetic issues, causing reluctance in interpersonal relationships, lack of confidence, and a pleasant smile.[1] Bleaching is accomplished using a chemical agent that alters the light-absorbing or light-reflecting nature of tooth material by increasing the perception of whiteness and thereby restoring the tooth color by oxidizing the discolored sections in the tooth structure.[2]

The bleaching techniques primarily use bleaching agents such as hydrogen peroxide (HP) or carbamide peroxide (CP) of different concentrations.[3] Vital bleaching of teeth involves the external application, whereas nonvital bleaching involves either internal (within the pulp chamber) and internal/external application of the bleaching agent.[4]

CP is a combination of HP and urea. 10% CP decomposes to produce 3.6% HP. A varying concentration of CP between 10% and 38% is used for vital bleaching.[5] Overall, tooth whitening efficacy is determined by the peroxide concentration in bleaching materials and exposure time.[6] It is prudent to use an efficacious product with minimal side effects; however, when time is an essential factor and the need for a quicker shade change overrides concerns about possible side effects, a clinician uses a higher concentration of bleaching agent.[7]

The latest development in power bleaching is laser-activated bleaching, which offers speed and convenience. Earlier used lasers were argon laser and CO2, but now, diode laser and potassium titanyl phosphate (KTP) are also used.

Diode laser (810–980 nm) has proved to be less harmful and more effective with short application in the office.[8] A limited number of investigations have been published analyzing diode-laser efficacy using different CP concentrations during the tooth-bleaching process. The study's null hypothesis is that there would be no difference in the tooth shade among the experimental groups when different concentrations of CP are used at two different time intervals and no rebound effect would be observed post bleaching.

 Materials and Methods

The study was conducted at the Department of Conservative Dentistry and Endodontics after obtaining ethical clearance from the Institutional Ethics committee (Reference no. 18,100). We selected one hundred healthy and intact human maxillary and mandible central/lateral incisors teeth extracted from adult males and females. Fractured/grossly decayed teeth with cracks or surface defects and multi-root teeth were excluded. The extracted teeth were autoclaved at 121°C, 15l bs psi for 20 min, polished using polishing paste (Prisma Gloss™, Dentsply Sirona, North Carolina) and rubber cups (Enhance Finishing System, Dentsply Sirona, North Carolina), and then thoroughly rinsed and dried in the laboratory. The teeth were then stored in distilled water under refrigeration (8°C) to keep them hydrated. Using spectrophotometer (X-rite i1 pro, Germany), the baseline shade of the specimen teeth was assessed.[9]

Staining procedure

Artificial staining of the specimens was carried out to standardize the tooth shade. Enamel surfaces were etched with 35% phosphoric acid gel (3M™ ESPE™ Scotchbond™ Multi-Purpose Etchant Gel, Australia) for 60 s and rinsed with distilled water for 30 s. Black tea solution was produced by boiling four instant tea bags (Taj Mahal Tea, India) in 200 mL of distilled water for 5 min. Each specimen was immersed over 1 week in standardized black tea solution at room temperature (25°C ± 2°C) in separate containers. Receptacles containing staining liquid were stirred once every day to avoid decantation of the staining products. After the immersion period, the teeth were rinsed for the second time and the CIEL * a*b* values were measured with a spectrophotometer (X-rite i1 pro, Germany). Specimens were then kept hydrated in distilled water at room temperature.[9]

Tooth shade measurement

After 7 days of immersion in black tea solution, shades of the stained specimens were again assessed using a spectrophotometer (X-rite i1 pro, Germany). The samples were minimum 8 mm in width, and the sample measurements were made at the same spot at all-time intervals. X-rite i1 pro comes with a spot measurement accessory which ensures where the device sensor is placed and measurement is taken. Since the study involved measurements at different time intervals, it was very essential that we measure the same spot on the sample. Hence during the first reading, the spot measurement accessory was marked on the base (flat thermocol sheet) with a marker ensuring it was placed in the same spot for multiple readings at different time intervals. A grove was made (on the flat thermocol sheet) to ensure the sample was placed in the same position and the same side was measured at each of the time intervals. This technique made sure that the sample was measured on the same spot for each of the readings. During the evaluation procedure, each sample was placed on white background with the spectrophotometer's active point set at the tooth's center to avoid potential absorption. During the evaluation procedure, each sample was placed on white background with the spectrophotometer's active point set at the tooth's center to avoid potential absorption. The system adopted is defined by the International Commission on Illumination: L* represents the value (lightness or darkness), a* is a measure of redness or greenness; and b* is a measure of yellowness or blueness. CIE L*a*b* values based on the rectilinear Cartesian co-ordinate system were recorded before and after each bleaching procedure.[10] Readings were calculated using the ΔE* values for each sample: ΔE* = ([ΔL*]2 + [Δa*]2 + [Δb*]2)1/2.

Bleaching procedure

The black tea-stained samples were randomly allocated (using permuted block randomization) to four groups (n = 100) [Figure 1].{Figure 1}

Control group: Group I (n = 10): ten teeth were stored in distilled water at room temperature and water changed daily for 2 weeks.

Groups (II, III, and IV) were further divided into three subgroups to be treated with different concentrations of carbamide peroxide.

15% CP (n = 10)20% CP (n = 10)35% CP (n = 10).

Group II (n = 30): 0.2 ml of bleaching gel (15%CP) was applied on the teeth' labial surface and kept for 10 min.

Group III (n = 30): The teeth' labial surfaces were covered with 0.2 ml of bleaching gel (CP 20%) and irradiated with 5W of output power from the diode laser (Doctor Smile Wiser LA8DO 001.3) for 2.5 min.

Group IV (n = 30): The teeth' labial surfaces were covered with 0.2 ml of bleaching gel (CP 35%) and irradiated with 5W of output power from the diode laser (Doctor Smile Wiser LA8DO 001.3) for 5 min.[7]

During each session, the gel was applied three times, and after each application, gel was removed with sterile gauze and washed with distilled water. This cycle was repeated at two sessions with 7 days of interval between them.[11] At the end of the bleaching treatment, the gel was carefully removed and stored in distilled water at 37°C until the next application.[12]

Apart from baseline (T0) and after staining (T1) evaluation, the color measurements were also made at the following time points: 7 days after the first bleaching session (T2); 7 days after the second bleaching session (T3); and 14 days after the bleaching treatment (T4).[11] Posttreatment teeth shades were assessed 14 days following the bleaching treatment to evaluate for the rebound effect.[13]

Statistical analysis

The data were analyzed using statistical software (SPSS Version 17.0 software, SPSS Inc.). Descriptive statistics were calculated. ANOVA, repeated measures of ANOVA, and Tukey post hoc test were applied to test the statistical significance, and the P value was kept <0.05.


After staining, the mean shade value (ΔE) in Group I (distilled water) was similar at different time intervals.

In Group II, the mean shade value (ΔE) for 15% CP (Group IIa) at baseline (T0) was 30.08 and after staining (T1), it increased to 40.08. After T2 and T3, ΔE value was reduced. Moreover, after 14 days of post bleaching, negligible rebound was observed [Table 1]. A similar pattern of results was observed in all other experimental groups with a gradual reduction in ΔE value [Table 1]. At T3, a significant color change was observed in Group IIc (35% CP). Since there was a significant difference between Group IIa (15% CP) and Group IIc (35% CP), 35% concentration was found to be more effective to use.{Table 1}

In Group III, for 15% CP + 2.5 min (Group IIIa), ΔE value at baseline (T0) was 29.14 and increased to 40.89 after staining (T1). At T2 and T3, reduction in ΔE value was observed and the greatest reduction was seen at T3, therefore achieving a lighter tooth shade than the baseline. On 14th day after the final bleaching treatment (T4), negligible rebound was noted (0.75) [Table 1]. In Group IV, 15% CP + 5 min (Group IVa), ΔE value at baseline (T0) was 29.06, which increased to 38.94 after staining (T1). A similar pattern of results was observed in Group IIIb, c, and Group IVb, c [Table 1].

At T1–T2 (Time interval), Group IIIc (35% CP + 2.5 min) had shown significant color change when compared to Group IIIb (20% CP + 2.5 min). Thus, 35% concentration of CP is more effective than 20% CP. In addition, from T1 to T3 (time interval), there was a significant color change in Group IIIb (20% CP + 2.5 min with a laser) and IVb (20% CP + 5 min with a laser) [Figure 2]. Group IVb (20% CP + 5 min with a laser) had presented more color differences than Group IIIb [Table 2].{Figure 2}{Table 2}

At T4, Group IVc (35% CP + 5 min) gave the lowest Δ E value and at T0–T4, it had shown more color difference with a reduction of discoloration when compared to Group IVa (15% CP + 5 min) and Group IVb (20% CP + 5 min) [Figure 2].

After the first bleaching session, 35% CP had a similar Δ E value as 15% CP had after the second bleaching session. At T3–T4, Group IVb (20% CP + 5 min) had shown significant color change compared to Group IVc (35% CP + 5 min), which means higher concentration had shown lesser rebound than a lower concentration of CP [Table 2].

At T1–T3, there was a change in color value (Δ E >3.3) in all the groups except the control group (Group I) and considered clinically perceptible. At T3–T4, there was a negligible change in color value (Δ E <3.3) in all the groups; hence, the rebound was not clinically detectable [Table 2]. Overall, we observed lighter tooth shades when we had bleached the teeth with 35% CP with laser for 2.5 min and 5 min compared to 15% concentration of CP alone.


The reactive oxygen species from carbamide-containing bleaching gels permeates the tooth structure, causing the oxidative breakdown of chromophore/pigment molecules present in dentin, and lightens the tooth.[14],[15] Bleaching products can produce desirable and effective tooth whitening when used in conjunction with lasers.[8]

Interestingly, 35% concentration of CP had a similar mean shade (ΔE) value after the first bleaching session, as 15% CP showed after the second bleaching session [Table 2]. This result is supported by an in vitro study conducted to compare shade changes in extracted teeth employing 5%, 10%, or 16% CP for 2 weeks, revealing that CP in lower concentrations, despite taking a longer time to whiten teeth, ultimately produces results similar to those achieved with higher concentrations.[7] Treatment with bleaching agents in higher concentration favors quicker, earlier, and more intense changes in chroma, although the different protocols' results tend to equalize over more extended analysis periods.[16],[17]

This study further found that the duration of laser application results in achieving a lighter shade. 20% and 35% concentration of CP with diode laser for 5 min presented significantly more lightness in color than 20% and 35% concentration of CP with diode laser for 2.5 min. However, a high HP (35%) concentration achieves a lighter shade compared to lower concentration HP at the laser application time (2.5 min) at the end of 2 weeks thus, corroborating that 35% concentration of CP is more effective than 20% CP. Nevertheless, de Almeida concluded that all treatments using bleaching gels with high HP concentrations (20%–35%) result in the same amount of color change. The reason is that higher concentration favors faster, more intense chromatic changes after the bleaching treatment.[18]

Several studies suggest that an improved color outcome is associated with longer bleaching time regardless of the bleaching agent's concentration.[19],[20],[21],[22] Clinical evidence indicates that 10% CP is as effective as higher concentrations but results in a lower incidence of sensitivity than higher concentrations.[23] However, Onwudiwe et al. evaluated the clinical efficacy and safety of 16% and 35% CP as in-office bleaching agents and concluded that 35% concentration achieved a lightening effect without additional side effects.[24] The more time the bleaching gel is in contact with the tooth, the more it diffuses into the dental tissue, increasing the enamel microporosities, allowing the acid to penetrate deeper into its structure, oxidizing more stain-containing molecules, and resulting in an enhanced whitening effect.[25] A study concluded that diode laser activation of bleaching agent presented significantly better results than the agent is used alone or when combined with the LED source. An added advantage is the bleaching agent's reduced contact time with the teeth, which minimizes the chances of sensitivity or irritation.[26] When the light of a specific wavelength is used that approximates the bleaching agent's absorption spectrum, the chemical reaction proceeds faster, thereby decreasing the exposure time of the bleaching agent to the tooth.[27] According to Klunboot et al., diode laser at low-power densities was highly efficient in tooth bleaching.[28]

In the present study, the staining period (7 days) represented a 168-h storage time, which simulated more than 12 months of coffee/tea staining in the oral cavity, as the regular time consumption of a tea/coffee cup is around 15 min, and the average daily intake of a person is 3.2 cups.[29]

We observed that at T1–T3 (after staining till second bleaching session), the bleaching efficacy (change in color value [ΔE]) was considered clinically perceptible since it equaled or exceeded 3.3.[30] Furthermore, at T3–T4 (after 14 days of bleaching treatment), the Δ E value readings were <3.3; hence, the color change was not clinically appreciable. The lack of rebound could be because regression of color is affected mainly by food, beverages, and habits. The bleaching agent induces morphological alteration within the dental surface. These alterations create channels for stains to penetrate deeper within the tooth surface, resulting in a relapse of the bleaching treatment.[31]

Dostalova et al. recommended a bleaching time of 5 and 2.5 min per session to achieve 2–3 lighter tooth shade. Moreover, in their study, they observed that laser bleaching decreases the time of bleaching without surface modification and avoids adverse effects.[30]

This study used the spectrophotometric shade analysis, an electronic method, as it is more accurate and reproducible than human color/shade assessment. Horn et al., in their research, concluded that spectrophotometers achieved 80% reproducibility of the tooth shade than the human eye, which showed only 65% reproducibility.[32] Standardization of tooth shade was done before the staining procedure by measuring the shade of the tooth using a spectrophotometer, hence reducing bias in sample selection.

One of the limitations of this study is not using saliva during the bleaching procedure. Studies have reported that the presence of saliva during the bleaching process would reduce the enamel susceptibility to demineralization and minimize the discoloration.[19],[33],[34],[35] In vitro studies are hard to mimic the biological complexity of the oral cavity; clinical extrapolation of the results should therefore be done carefully.

Further research is required to address the limitations of the present study. Tea was used for staining teeth in this study though other substances such as coffee, pomegranate juice, and beetroot juice also can be used. Further studies can also be done employing different types of light and lasers such as KTP for activation of bleaching agent[36] and different types of instrumental methods such as colorimeters, digital cameras, and imaging systems to evaluate the change in shade and tooth color measurement, analysis, and reproduction, verification, and communication of shades.[37] Within the study's limitation, it can be concluded that higher concentration laser-activated CP (35%) at both time intervals showed better tooth color change compared to lower concentration CP. Furthermoe, teeth irradiated with higher concentration laser-activated CP (35%) showed a lower rebound effect compared to lower concentration agents. However, achievement of similar changes in chroma by bleaching twice weekly using an agent in high or low concentration was observed. Diode laser activation of the bleaching agent produced better results compared to the agent being used alone.


Lasers are presently being used as a useful adjuvant in dental practice. Based on the outcome of the current study, it can be concluded that diode laser can be considered as an effective and reliable treatment option for bleaching of teeth. Laser-assisted bleaching reduces the time of whitening process. Nonlaser-assisted bleaching also gives similar outcomes with an increased time duration. For speedy whitening of teeth, using a higher concentration of bleaching agent with laser irradiation is a viable option.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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