Low-level laser therapy of dentin hypersensitivity: a short-term clinical trial
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- Orhan, K., Aksoy, U., Can-Karabulut, D.C. et al. Lasers Med Sci (2011) 26: 591. doi:10.1007/s10103-010-0794-9
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The aim of this study was to evaluate low-level laser therapy in cervical dentin hypersensitivity. A randomized controlled clinical trial was conducted with a total of 64 teeth. Dentin desensitizer and diode laser were applied on the cervical dentin surfaces. Distilled water and placebo laser was used as the placebo groups. The irradiance used was 4 J/cm2 per treatment site. The baseline measurement of hypersensitivity was made by using visual analog scale (VAS). Twenty-four hours and 7 days after the application of desensitizer, diode laser and placebo groups, a new VAS analysis was conducted for the patients’ sensitivity level. The mean pain scores of placebo groups were significantly higher than the desensitizer’s and diode laser’s mean scores (ANOVA, p < 0.05). The VAS analysis revealed a significant decrease in dentin hypersensitivity in 7 days with the use of the desensitizer and low-level laser therapy and no statistically significant difference was observed between these two treatments (p > 0.05). Although low-level laser and glutaraldehyde containing desensitizer present distinct modes of action, experimental agents caused a significant reduction of dentin hypersensitivity without showing secondary effects, not irritating the pulp or causing pain, not discoloring or staining the teeth, and not irritating the soft tissues at least for a period of 1 week with no drawbacks regarding handling and/or ease of application. Low-level laser therapy and desensitizer application had displayed similar effectiveness in reducing moderate dentin hypersensitivity.
KeywordsDentin hypersensitivityLow-level laser therapyDesensitizerClinical trial
Current in-office dentin hypersensitivity treatments involve adhesives, varnishes, bonding agents, restorative materials, iontophoresis, and lasers. Treatment options are designed to reduce flow into the dentin tubules by occluding or sclerosing the tubules . However, the reported clinical efficacy of the desensitizers is quite variable . Controlled clinical trials are scarce in the literature . Because cervical dentin hypersensitivity is impractical to test in vitro, clinical trials of safety and both short- and long-term efficacy of desensitizing treatments are required .
It has been reported that because many topical desensitizing agents do not adhere to the dentin surface, their effects are temporary . Although application of desensitizer solutions and dentifrices containing ferric aluminum and potassium oxalates are the first treatment of choice, nevertheless their effect is not permanent . The durability of these topical treatments is influenced by several factors such as saliva and oral fluids, which result in dissolution of the desensitizer material . Although some of the traditional methods of treating dentin hypersensitivity have been clinically evaluated and found to provide some relief to patients, dental professionals continue to look for more-effective, faster-acting, and longer-lasting treatments, because in-office treatments and home-use products do not always provide the desired results . None of the desensitizing agents utilized, including potassium oxalate, potassium nitrate, and stannous fluoride, provide total dentinal tubule occlusion .
Alternative treatment options have been tested and reported; an in-office desensitizing paste containing arginine and calcium carbonate has been evaluated recently . Different kinds of high-intensity lasers have also been used [3, 9–11]. There are several different theories for explaining the effect of this kind of laser irradiation on dentin, but the most approved one indicates sealing of dentinal tubules by melting and re-crystallization of dentin .
Apart from high-intensity lasers, low-level laser therapy (LLLT) has also been considered as an alternative treatment option. Kimura et al.  summarized the current knowledge regarding laser applications for the treatment of dentin hypersensitivity. Several other studies evaluated the effectiveness of the clinical use of diode lasers for the treatment of dentin hypersensitivity and reported their use as effective in reducing initial hypersensitivity [13–19].
Three wavelengths (780, 830, and 900 nm), all within the infrared spectrum of (galium-aluminium-arsenide) GaAlAs diode laser, have been used for the treatment of dentin hypersensitivity . The use of red wavelength diode lasers has also been reported . These are physical methods which, even operating at different bands of wavelength, cause the dentin-pulp complex to respond to the irradiation with the obliteration of the dentinal tubules by means of a specific biological mechanism . Aranha et al.  also studied dentin treated with desensitizer products including low-intensity laser therapy in vitro and explained that; although the irradiation with low-intensity laser does not alter the morphology of the surface in contrast to high-intensity lasers, which ablate and modify the dentinal structure; the exact action mechanism of low-intensity lasers in dentin hypersensitivity is not thoroughly understood. The use of LLLT in dentin hypersensitivity is not well investigated as a treatment choice. There are only a few studies in the literature about this treatment modality . There is a need to review the various aspects of this subject and update the treatment technique.
Olusile et al.  reported that a glutaraldehyde containing desensitizer (Gluma Desensitizer, Heraeus Kulzer, Armonk, NY) performed best at 24 h having the highest difference between the baseline and 24-h mean pain scores and this agent may act both by the coagulation of dentin tubular protein by the glutaraldehyde component and secondly by the polymerization of the adhesive resin component. Ozen et al.  also reported that the short-term treatment of dentin hypersensitivity with the same desensitizer showed a statistically significant reduction in the sensation of pain when compared to the placebo. The current study was conducted to compare the influence of a red wavelength low-intensity diode laser with a desensitizer whose efficiency has been shown in providing short-term relief from dentin hypersensitivity. LLLT’s efficacy has been compared with a dentin bonding agent, a fluoride varnish, potassium nitrate and potassium oxalate gel in vivo [13, 15, 18, 19]. However there is no in vivo comparison of LLLT’s efficacy with a glutaraldehyde containing desensitizer in the literature. It was mentioned that glutaraldehyde reacts with proteins producing precipitation on the dentin surface .
Due to this, it was considered worthwhile to assess the efficacy of LLLT and compare it to a desensitizer containing glutaraldehyde in providing short-term relief from dentin hypersensitivity, and to help the clinician in choosing the most effective short-term treatment option for dentin hypersensitivity.
Materials and methods
A randomized controlled clinical trial was conducted with 16 patients (eight female, eight male). The age range was 21–51 years, with a mean age of 34.31 ± 3.17 years. A total of 64 teeth with sound-exposed cervical dentin on the facial surface were included in the trial. Informed consent was prepared and obtained according to the Helsinki Declaration II. The purpose and design of the investigation were explained and a consent form was signed by all of the participating patients.
Prior to desensitizing treatment, dentin hypersensitivity was assessed by a thermal/evaporative stimuli and patients’ response to the examination was considered to be a control. Each patient had four incisors, canines, or premolars with exposed cervical dentin on the facial surface that could be affected when air was applied. Sensitivity was assessed by means of evaporative stimuli, a 5-s cold air blast (temperature range of 19–20°C) at a distance of 0.5 cm from the site to be tested. All stimuli were given by one operator at the same dental chair with the same equipment yielding similar air pressure and temperature each time.
All the stimuli were applied on the cervical region of the experimental teeth after removing supra-gingival plaque with a low-speed handpiece with pumice powder and without fluoride. The adjacent teeth were isolated with cotton rolls and a suction device. The air stream was not extended longer than necessary to generate a response. The patients were given a visual analogue scale (VAS) upon which they were asked to place a pencil mark at a point on a linear scale marked from 0 to 100 to describe the pain experienced. After each stimulus to the suspected site, the degree of hypersensitivity was determined from 0 to 100 as the baseline VAS score for each individual painful tooth. In order to standardize the sample, the criterion for inclusion in the study was a sensitive dentinal response of a minimum of 40 in the 0 to 100 numeric scale for pain evaluation, characterizing moderate cervical dentin hypersensitivity.
After recording the first scores, the subjects were randomly assigned to one of the treatment or the placebo groups. The subjects were blind to the agent being used. The randomization process was conducted before the clinical steps and carried out by using sequentially numbered opaque sealed envelopes prepared with unrestricted (simple) randomization . Each treatment agent and placebo was written and sealed in envelopes before beginning the study. The dental operator who carried out all the treatments opened an envelope for each case at the beginning of the treatment.
Application of the treatments
Treatments were performed by the same experienced operator and the pain was assessed by another person to minimize errors and to avoid bias. Sixteen patients were distributed into four groups as desensitizer, LLLT, distilled water, and placebo laser group, by using the simple random sampling method. A single treatment was assigned to each subject to avoid intra-subject cross-contamination of different desensitizing agents applied to the same mouth . The manufacturer’s instructions were followed during the application of the desensitizer. All patients were treated without local anesthesia. Subjects with more than four teeth affected by sensitivity received treatment on all sensitive teeth, but only the four most sensitive teeth were included in this study and baseline evaluations were recorded .
In the first group, two layers of desensitizer (Gluma Desensitizer, Heraeus Kulzer, Armonk, NY) containing 2-hydroxyethylmethacrylate, glutardialdehyde, and purified water were applied to ensure adequate desensitization. Care was taken to ensure that the desensitizer only came into contact with the area to be treated and the smallest possible amount required for the treatment was applied using disposable brushes for avoiding cross-contamination and left for 60 s. Then the surface was carefully dried applying a stream of compressed air until the fluid film disappeared and the surface was no longer shiny. The surface was then rinsed thoroughly with water.
In the second group, a galium-aluminium-arsenide (GaAlAs) red wavelength low-intensity diode laser (RJ lasers, Vienna, Austria) was chosen for LLLT. The system delivers a 25-mW output that emits a wavelength of 655 nm. The operator and the patient wore laser-protective eyewear specific to the diode laser’s wavelength during the treatments. The laser was applied to the dentin surfaces in continuous mode with contact on the region of exposed dentinal area for 160 s in each session per tooth, in a uniform, sweeping, and scanning motion. The calculated deposited energy density was 4 J/cm2 per dental element. Laser treatments were carried out in six sessions, with no intervals between sessions, during a period of six consecutive days. In the third group, distilled water was used as the placebo group for the desensitizer. In the fourth group, the laser device was positioned but yet not activated . Placebo procedures were performed according to the same protocol used on their respective treatment groups. All patients were instructed to omit tooth brushing during the following 12 h or to chew food for 3 h following treatment. After 1 month, teeth in the placebo groups received desensitizer application for pain elimination.
The patients were instructed to maintain the same dietary regimens and good oral hygiene during the course of the investigation. All the patients used a standardized toothbrush and toothpaste without any anti-hypersensitivity agent (including fluoride) during the trial. Also, neither mouthrinses nor fluoride tablets were allowed during the experiment. The force, speed, and frequency of tooth brushing were also instructed and the use of abrasive agents were discouraged. All the patients were recalled at 24 h and 7 days after completion of each treatment to assess sensitivity over time. Pain was assessed 24 h and 7 days after the final session of LLLT.
The distribution of age, gender, and baseline VAS scores according to treatment groups
Baseline VAS scores
Mean ± SD
Mean ± SD
32 ± 5.35
65 ± 9.62
31.25 ± 8.80
67.75 ± 12.44
37.75 ± 11.64
60.25 ± 11.95
36.25 ± 9.10
68.75 ± 4.57
Mean VAS scores at baseline, 24 h and 7 days for each four teeth in female and male patients of different treatment groups
Desensitizer (4 patients, 16 teeth)
LLLT (4 patients, 16 teeth)
Distilled water (4 patients, 16 teeth)
Placebo laser (4 patients, 16 teeth)
Patient 1 Female
Patient 2 Female
Patient 3 Male
Patient 4 Male
Patient 5 Female
Patient 6 Female
Patient 7 Male
Patient 8 Male
Patient 9 Female
Patient 10 Female
Patient 11 Male
Patient 12 Male
Patient 13 Female
Patient 14 Female
Patient 15 Male
Patient 16 Male
Mean pain (VAS) scores and standard deviations at baseline, 24 h, and 7 days for the treatment groups
52–75/ 65 ± 9.62a
55–82 67.75 ± 12,44a
46–75/ 60.25 ± 11.95a
63–74/ 68.75 ± 4.57a
24–47/ 38.75 ± 10.24b
31–52/ 38.25 ± 9.673b
45–72/ 58 ± 11.22a
63–72/ 68 ± 3.91a
8–12/ 9.75 ± 1.70c
7–11/ 8.75 ± 1.70c
43–70/ 58 ± 12.02a
65–72/ 68.75 ± 2.98a
The mean baseline scores for each of the four treatments (first horizontal row in Table 3, 65 ± 9.62a, 67.75 ± 12,44a, 60.25 ± 11.95a, 68.75 ± 4.57a) are not statistically different from each other. The minimum pain level was 46, while the maximum pain level was 82, and the mean level of the pain was 65.43 ± 9.68 before treatment (baseline measurements in Table 2). Within 24 h of treatment, the mean VAS score decreased from 65a to 38.75b for the desensitizer. Within 24 h of treatment (after six applications), the mean VAS score decreased from 67.75a to 38.25b for LLLT. No change was detected in sensitivity for the distilled water group (the mean VAS score decreased from 60.25a to 58a) and for the placebo laser group (the mean VAS score decreased from 68.75a to 68a). Desensitizer and laser application resulted in a significant reduction in dentin hypersensitivity within 24 h.
While there was a significant decrease between the 24-h and the 7-day evaluation period of desensitizer (65 ± 9.62a, 38.75 ± 10.24b, 9.75 ± 1.70c) and LLLT (67.75 ± 12,44a, 38.25 ± 9.673b, 8.75 ± 1.70c) (p < 0.05), there was no statistical significance among these two treatments in terms of the degree of pain reduction both at 24 h (desensitizer:38.75 ± 10.24b, LLLT:38.25 ± 9.673b) and 7 days (desensitizer: 9.75 ± 1.70c, LLLT: 8.75 ± 1.70c) (p > 0.05). For clarifying the sources of differences, the Bonferroni post-hoc test was used, and it was reported that the distilled water and placebo laser group was extremely different from the other two groups (p < 0.05). For the placebo groups, the statistical analysis of data revealed no significant difference at three examination periods (p > 0.05), and there was no decrease in dentin sensitivity for these groups (distilled water: 60.25 ± 11.95a, 58 ± 11.22a, 58 ± 12.02a; placebo laser: 68.75 ± 4.57a, 68 ± 3.91a, 68.75 ± 2.98a). Comparing the differences, there is no statistical significance among the LLLT and the desensitizing agent in degree of pain reduction both at 24 h and 7 days (p > 0.05). LLLT showed significant reduction like the desensitizer both in 24 h and 7 days (p < 0.05). The VAS index in the four groups before treatment was similar (p > 0.05). However, the postoperative VAS index in the experimental and control groups after treatment was statistically significant (p < 0.05); indicating a decreased postoperative VAS in the diode laser and desensitizer groups. The relationship between gender and dentin sensitivity was also investigated by using the Pearson Chi-square test. In female patients, the baseline VAS score average was 65.25 ± 13.11, the 24-h VAS score average was 50.25 ± 17.39, and the 7-day VAS score average was 36.25 ± 29.41, while in male patients, it was measured as 65.62 ± 5.39, 51.25 ± 14.63, and 36.37 ± 30.17, respectively. The VAS score difference between male and female groups was not statistically significant (p > 0.05). Gender was found to have no significant effect on VAS scores. All teeth remained vital after laser treatment without adverse reactions or complications and no pathologic evidence was detected by radiography in the follow-up examination done after 7 days.
Because the laser therapy was generally reported to be performed with sequential appointments with a time interval between each one in dentin hypersensitivity studies using diode laser [13–19], the authors decided to perform consecutive applications without a time interval, in order to perform a different clinical treatment protocol. Mentioned studies evaluated the effectiveness of the clinical use of diode lasers for the treatment of dentin hypersensitivity and reported their use as effective in reducing initial hypersensitivity. This current study also found the treatment with the diode laser effective in a short-term time period. According to this result, further studies may be conducted to see whether the diode laser applications should be performed with or without a time interval for the treatment of dentin hypersensitivity. A 7-day short-term evaluation was made in this study. Aranha et al.  mentioned that a period of 1 week was chosen, because this is the period in which patients usually return to the office, complaining of pain. The mean age was 34.31 years for this study. Dentin hypersensitivity is prevalent among a large portion of individuals 30–40 years of age .
The results indicated significantly decreased pain scores at 24 h and 1 week post-treatment evaluations for desensitizer and red wavelength low-intensity diode laser. No relapse of sensitivity during the post-treatment evaluation period was detected for these treatments. The untreated control subjects showed high degrees of discomfort in both follow-up sessions. Sixteen patients participated in this study. However, in order to not affect the objective of the study, four groups having an equal number of hypersensitive teeth were obtained by a systematic random sampling and each group treated by any of the two agents or placebo groups. A placebo laser application was applied [3, 10, 18, 19]. Sicilia et al.  concluded that the application of diode laser has shown efficacy in rapid dentin hypersensitivity reduction compared to placebo laser in periodontal patients. It was stated by Kimura et al.  that in the use of laser in vivo, thermal effects on pulpal tissues are of concern. Healthy pulp tissue is not injured thermally if the laser equipment is used at a correct parameter so that any temperature rise within the pulp remains below 5°C. Sicilia et al.  mentioned that the application of a diode laser at a wavelength of <780 nm and at an output power below 30 mW, with an application time of <3 min, is a safe treatment with regard to pulp.
According to Walters , the creation of a smear layer or obliteration of the tubule can greatly increase the effectiveness of the treatment. The action mechanisms of diode lasers in dentin hypersensitivity treatments have been suggested by several authors. This type of low output power lasers mediate an analgesic effect related to depressed nerve transmission . According to experiments using the diode laser at 830 nm, this effect is caused by blocking the depolarization of C-fiber afferents. Diode laser irradiation at a maximum power of 60 mW does not affect the enamel or dentin surface morphologically, but a small fraction of the laser energy is transmitted through enamel or dentin to reach the pulp tissue . Both red and infrared wavelength lasers are effective in treatment; they cause the dentin-pulp complex to respond to the irradiation with the obliteration of the dentinal tubules by means of a specific biological mechanism. The laser interaction with the dental pulp causes a photobiomodulating effect, increasing the cellular metabolic activity of the odontoblasts and obliterating the dentinal tubules with the intensification of tertiary dentin production . It would be interesting to study the long-term effects of reducing dentin hypersensitivity from laser treatment since the mechanism induces the sclerotic dentin layer, thus promoting the internal obliteration of dentinal tubules .
The red wavelength diode laser group demonstrated similar results when compared to the desensitizer group in this in vivo study. This fast desensitizing effect of laser therapy observed in this conducted research may be attributed to the mentioned fiber afferents’ depolarization mechanism, relevant to the study of Corona et al. . However, a strong placebo effect is also commonly described in clinical dentin hypersensitivity trials . The usage of the diode laser in this study for the desensitization of hypersensitive teeth might have also caused an undefined placebo effect for an extent. However, the results clearly demonstrated that these types of lasers may have an acceptable therapeutic effect compared to the distilled water and the laser device positioned but yet not activated, besides this undefined placebo effect. In long-term clinical applications, diode laser treatments may also demonstrate an obliteration mechanism of the dentinal tubules. Dahnhardt et al.  mentioned that the two main treatment options for dentin hypersensitivity are desensitization of the nerve and the mechanical occlusion or covering of the dentin tubules. However, the study period was not long enough to examine such an effect in this study.
According to Corona et al. , the low-level GaAlAs laser showed improved results for treating teeth with a higher degree of sensitivity. However, Kimura et al.  concluded that in general, the efficiency for the treatment of dentin hypersensitivity using lasers is higher than in other methods, but in severe cases, it is less effective. It is necessary to consider the severity of dentin hypersensitivity before laser use [2, 12]. The patient groups used in this study had moderate dentin sensitivity.
Therapeutic and patient-related factors should be discussed using data from longitudinal clinical studies . Long-term evaluation of effectiveness of these treatments needs to be carried out to know the longevity of their performances and at what time interval hypersensitivity would reoccur . Recurrence of dentin hypersensitivity treatment is possible and is another clinical problem that should be evaluated in clinical cases. Kimura et al.  reported that the recurrence of hypersensitivity varied with each laser and treatment protocol and depended on the irradiation methods and time after treatment. The mechanism of recurrence has been reported as unknown. As laser effects were considered to be due to the effects of sealing of dentinal tubules, nerve analgesia, or placebo effect , the sealing and nerve analgesia effects can be considered durable, whereas the placebo effect can not.
Tengrungsun and Sangkla  compared the laser and dentin-bonding treatment procedures and reported that between the two tested methods, although the treatment time was approximately the same (about 1 min), the laser treatment seemed to be less complicated since the need to isolate the operation field was eliminated. The combination of laser irradiation with the desensitizer and whether the loss of occluded resin from physical force such as brushing will result in less effectiveness should be further evaluated for the desensitizer. The time span between desensitizer and laser applications should also be considered as a factor possibly influencing relief of pain in vivo. Researchers [10, 11] suggested that bacterial potentials of the tested desensitizer might have a role in insensitivity of teeth because the pain threshold of the nerve fibers seems to be lowered in the presence of inflammation mediators. Due to this effect, the antibacterial efficacy of the mentioned treatments used in this study can be further evaluated. Finally, age variations can be further assessed as Ladalardo et al.  mentioned that differences can be observed as a result of morphologic alterations of the dental structure.
Taking into account the parameters employed in this study, although confirmatory long-term controlled clinical studies further investigating these findings are required, the data in this in vivo explorative study suggest that the use of red wavelength diode laser and dentin desensitizer containing glutaraldehyde may be effective in the short-term treatment of cervical dentinal hypersensitivity. Studies reporting the effectiveness of alternative treatments like diode lasers for dentin hypersensitivity have been appearing with increasing frequency. However, the advantages and limitations of these treatments for clinical use have not yet been fully clarified. Within the limitations of this in vivo study, further studies fulfilling this study’s limitations are needed. Further studies are also needed in order to evaluate the long-term stability of the obtained positive results. Especially the mechanism of the laser-induced desensitization should be investigated in following studies . However, the reduction of cervical dentinal hypersensitivity can be greater when there is the association of the removal of etiologic factors .
Reduction of hypersensitivity at 7 days achieved by LLLT suggests the need for long-term and large sample-sized clinical studies in order to better understand the performance of this treatment when compared to desensitizer applications.