Clinical Evaluation of Er:YAG,Nd:YAG,and Diode Laser Therapy for Desensitization of Teeth with Gingival Recession

Abstract

Objectives: The aim of this study was to evaluate the effectiveness of three types of lasers, Er:YAG, Nd:YAG, and GaAlAs (Diode), as dentin desensitizers, as well as to determine both the immediate and late therapeutic effects on teeth with gingival recessions. Materials and Methods: The study was conducted on 24 patients with 96 teeth with Miller's class I or class II gingival recessions with clinically elicitable dentin hypersensitivity (DH) divided into three test groups: (A) Er:YAG, 2,940 nm, 60 mJ/pulse, 2 Hz, 20 s; (B) Nd:YAG, 1,064 nm, 100 mJ/pulse, 15 Hz, 100 s, (C) diode; 808 nm, 100 mW, 20s; and one control group (d) control not irradiated. DH was assessed by means of air stimulus. A visual analogue scale (VAS) was used to measure DH. The selected teeth in three groups received laser therapy for three sessions. The measurements were performed before each treatment session and at 30 min after the laser application (immediate effect), and additional measurements were also performed at 15, 30, and 60 days after the conclusion of treatment (late effect) to assess the extent of desensitization obtained with the different laser devices. Results: Significant reduction of DH occurred at all times measured during the three treatment sessions in groups treated with Er:YAG, Nd:YAG, and diode lasers. Comparing the means of the responses in the three treatment sessions of the four groups, Group b showed a higher degree of desensitization in teeth with gingival recession compared with the other groups (p < 0.001). The immediate and late therapeutic effects of group b were more evident compared with the other groups. Conclusions: The Er:YAG, Nd:YAG, and diode lasers can be used to reduce DH. Nd:YAG laser irradiation is more effective in the treatment of DH than are Er:YAG and diode laser. Within the limitations of the present study, the Nd:YAG laser seems to be a suitable tool for successful reduction of DH, especially because the 3-month results of this treatment modality are promising.

Introduction

D entin hypersensitivity (DH) is an oral complaint frequently reported in clinical dental practice. This problem is characterized by short, sharp, severe pain arising from exposed dentin in response to stimuli, typically thermal, evaporative, tactile, osmotic, or chemical, and ceasing after their removal.^1ȓ4 The prevalence of this disorder has been reported in different studies to vary from 4% to 73%.^1,4 DH may affect patients of any age, and it affects women more often than men.¹ The condition may affect any tooth, but it most often affects canines and premolars.⁵ DH occurs when dentin is exposed in the oral cavity and dentinal tubules are opened. The exposure of dentin and its sensitivity may occur by one or both of two processes: either removal of enamel or denudation of the root surface by loss of the overlying cement and periodontal tissues. The most widely accepted mechanism of DH, the hydrodynamic theory, is based on the premise that sensitive dentin is permeable throughout the length of the tubules, and fluid flow within dentinal tubules is altered by thermal, tactile, or chemical stimuli near the exposed surfaces of the tubules.³ Relatively little is known of the etiology of DH and the nature of the lesion. DH can become a concern because of the increased number of teeth with gingival recession, incorrect tooth-brushing habits, parafunctional habits, abrasion due to overbrushing, dietary erosion, tooth abnormally positioned in the arch, chronic periodontal disease, periodontal surgery, root planing, occlusal wear, or aging, or a combination of these.^1,2 This condition may disturb the patient's daily habits of eating, drinking, brushing, and sometimes even breathing.

Various agents have been recommended to reduce DH by using different mechanisms such as formulations containing sodium fluoride and potassium ions, oxalates, resin-bonding agents, and abrasive dentifrices.^1,2 However, most treatments are either ineffective or last for a short period.

After initial experiments with the ruby laser,^6,7 other lasers such as He-Ne, GaAlAs (diode), CO₂, Nd:YAG, and Er:YAG have been used by clinicians for treatment of DH.² The first laser use for treatment of DH was reported by Matsumoto et al.^8,9 by using Nd:YAG and the 780-nm diode lasers. Nd:YAG laser,^{10

–17} semiconductor diode laser,^17

–20 and Er:YAG laser^10,21,22 have been used for the treatment of DH by many investigators. In most of them, despite varieties in methods and kinds of lasers, a relative success was described.

The mechanism by which the Nd:YAG laser affects DH is thought to be laser-induced occlusion or narrowing of dentinal tubules as direct nerve analgesia. Dentin may be fused by short exposures to the Nd:YAG laser, and then the fused dentin solidifies into a glazed, nonporous surface.¹⁰ After the application of the Nd:YAG laser, morphologic dentin changes are characterized by a melted and resolidified surface and by the presence of craters, cracks, and irradiation globules.^23

–26

The previous results of treatment of DH by the GaAlAs (diode) laser revealed that the laser interaction with the dental pulp causes a photobiomodulating effect, increasing the cellular metabolic activity of the odontoblast and obliterating the dentinal tubules with the intensification of tertiary dentin production.^18
–20

Treatment of DH with the Er:YAG laser revealed high efficacy in reducing the diameter of dentinal tubules under some specific conditions with a particular device (handpiece with optical fiber and without water), with partial obliteration of dentinal tubules and below the ablation threshold.²² This device is expected to show efficiency in medical and dental applications because of its thermomechanical ablation mechanism and the high absorption of its wavelength by water molecules in hydroxyapatites.²² The use of this device on DH decreases the dentinal fluid by evaporating the superficial layers.^25,27

Another hypothesis is the effect of Er:YAG laser on pulp nerves; however, this hypothesis is not proven.²⁸ Few published studies are available concerning this desensitizing treatment with Er:YAG laser.

Because of the great varieties in methods and types of lasers, it is impossible to propose a definitive method to treat DH. Although the use of lasers has often been promoted for this indication, before this study, no published data are available concerning the comparison of clinical effectiveness of Er:YAG, Nd:YAG, and GaAlAs (diode) laser in the treatment of DH. The aim of this study was to evaluate and compare the three types of lasers, Er:YAG, Nd:YAG, and GaAlAs (diode) as dentin desensitizers, as well as both the immediate and late therapeutic effects on teeth with gingival recessions.

Materials and Methods

The research protocol and consent form were initially submitted for approval of the Ethics Committee, and The Institutional Internal Review and Ethics Board at the Atatürk University, Faculty of Dentistry, approved the study (AU-IIREB reference code: 017). All participants provided written informed consent.

The study population consisted of 24 patients with 96 hypersensitive teeth with Miller's class I or class II gingival recession (13 women and 11 men; age, 18–52 years; mean age, 34.0 ± 9.8 years) who visited the periodontology clinic of Atatürk University, Erzurum, Turkey (Table 1).

Table 1.

Distribution of Age, Gender, Gingival Recession Type, Tooth Type and Laser Type in Patient Populations

Variable		n
Age, years	18–25	5
	26–35	8
	36–52	11
Gender	Female	13
	Male	11
Gingival recession type	Miller Class I	50
	Miller Class II	46
Tooth type	Anterior	38
	Premolar	34
	Molar	24
Laser type	Er:YAG-treated group	24
	Nd:YAG-treated group	24
	Diode-treated group	24
Not irradiated	Control group	24

Selection of subjects and test teeth

Inclusion criteria

The criteria used in selecting patients included generally in good systemic health with clinically elicitable DH and the ability to understand verbal or written instructions. All experimental teeth had Miller's class I or class II recessions.²⁹

Exclusion criteria

Patients with chronic or debilitating disease with daily pain episodes; those who were taking any analgesic, anticonvulsive, antihistaminic, sedative, tranquilizing, or antiinflammatory medications in the 72 h before treatment; those who had used any desensitizing paste or mouthwash in the last 3 months; and those who had had periodontal surgery in the last 6 months were excluded from the study. Teeth with cracked structure, carious lesions, restorations, nonvital, and with active periodontal disease were excluded.

Pain and DH assessment

A visual analogue scale (VAS) was used to measure DH. The VAS was administered in a standard manner, with the initial explanation given by the same clinician. All patients were asked to define their level of DH by using a VAS consisting of equal units from 0 to 10 (a line of 10 cm). On this scale, 0 and 10 represented “no pain/discomfort” and “worst pain/discomfort imaginable,” respectively. All pain assessments were performed in the morning in the same clinic, free of extraneous noise, music, or conversation. Patients were asked to mark the degree of pain they experienced by directing an air blast to the root surface before and after treatment of the DH. Before and after each session, we gave the patient a separate sheet of paper containing the printed interval scale (a line of 10 cm) so that he or she would not be influenced by the previous results. Data from the VAS were recorded by measuring in millimeters the distance between zero point and the sign marked by the patient on the 10-cm line. Reproducibility for the VAS was completed on two separate occasions by five patients. A strong correlation was found between the two responses in both procedures (Spearman's rho > 0.93; p < 0.001).

DH was assessed by means of air stimulus. The clinician directed an air blast (60 pounds per square inch, 22°C) derived from a dental syringe to the root surface for 1 s. The syringe was held perpendicularly, 2–3 mm from the root surface. After this stimulation, the patient again scored the pain by using the VAS. The air pressure, temperature, and distance between the root surface and the tip of the air syringe were kept constant for all cases in both pretreatment and posttreatment diagnosis of DH. All stimuli were given by one investigator in the same dental chair with the same equipment yielding similar air pressure and temperature each time.

Treatment

After the baseline pain assessment, the teeth were randomly assigned to Group A, Er:YAG-treated group; Group B, Nd:YAG-treated group; Group C, GaAlAs (diode)-treated group; and Group D, control (not irradiated).

Before laser therapy, all of the teeth received scaling, root-planing, and polishing. Afterward, the relative isolation of the region was carried out with the aid of a cotton roll and the drying of the buccal surface with gauze before each treatment session. The vitality of teeth was tested by a pulp tester after each treatment session. The patients did not know what kind of laser therapy each tooth was receiving.

The Er:YAG and GaAlAs (diode) lasers used in this study were Doctor Smile erbium&diode laser machine (Doctor Smile erbium&diode, Lambda Scientifica S.r.l., Vicenza, Italy), and the Nd:YAG laser used in this study was the Smarty A10 laser machine (Smarty A10, Deka, Italy).

The teeth in the Er:YAG group were given a 60 mJ/pulse, 2-Hz, 20-s, 2,940-nm, noncontact mode (4 mm from the surface) with air spray, perpendicular to the surface for scanning movements (0.8 mm/s), twice, and with a handpiece (LAEH4012.5, sapphire tip-diameter, 400 μm).

Teeth subjected to Nd:YAG laser treatment were radiated by a laser beam of 1W, 100 mJ/pulse, 15 Hz, 100 s, 1,064 nm, with a sweeping motion and without any coolants. In addition, the distance between the end of the fiberoptic (diameter, 300 μm) handpiece and the tooth surface was adjusted at ∼2 mm. Teeth subjected to GaAlAs (diode) laser treatment were also irradiated by a laser beam of 100 mW, 20 s, 808 nm (optical fiber, diameter: 300 μm), with continuous emission form, noncontact mode (2 mm from the surface), perpendicular to the surface for scanning movements, twice, in the region of the exposed dentinal neck. All laser applications were performed according to the instructions given by the manufacturer. When the lasers were in use, protective eyewear of appropriate optical density was worn by investigator and patients.

All the patients used a standardized toothbrush and toothpaste without any antihypersensitivity agent (including fluoride) during the 3 months of the trial. All participants completed the study and reported 100% compliance.

The laser therapy was performed by one investigator, and the pain was assessed by another investigator.

Study design

The treatments were carried out in three sessions, with intervals of 14 days between sessions, during a period of 30 consecutive days. The measurements were performed before each treatment session and at 30 min after the laser application to verify the capacity, the extent, and the duration of desensitization after irradiation. This result was called the immediate effect. Additional measurements were also performed at 15, 30, and 60 days after the conclusion of treatment to assess the extent of desensitization obtained with the different laser devices. This result was called the late effect.

Statistical analysis

Descriptive statistics, including means and standard deviations, were calculated for each group. The data thus collected were assessed by using SPSS 16.0 statistical software (SPSS, Inc., Chicago, IL). The Kruskal-Wallis test was used for multiple comparisons of the groups. The differences in mean VAS scores between pretreatment and 30 min after treatment were evaluated by using Wilcoxon's signed ranks test. The Friedman test was used to assess the differences in mean VAS values for the late effects of treatment (at 15, 30, and 60 d). In addition, the Mann-Whitney U test was used to compare the groups.

Results

The mean VAS scores before and after treatment of DH with the Nd:YAG, Er:YAG, and Diode laser at different times are shown in Table 2 (Fig. 1).

FIG. 1.

VAS index changes in the four groups at different times (n=24).

Table 2.

Comparison of the Mean VAS Scores in All Groups at Different Times

		Er:YAG	Nd:YAG	Diode	Control	p Value (Kruskal–Wallis test)
Immediate effect
Session 1	Pretreatment	8.33 ± 0.85	8.38 ± 1.07	8.29 ± 0.89	8.25 ± 0.97	>0.05
	30 min	7.54 ± 1.15^b	5.04 ± 0.84^c	7.75 ± 0.83^b	8.17 ± 0.94	<0.001
Session 2	Pretreatment	7.42 ± 1.26	4.96 ± 0.79	7.46 ± 1.22	8.33 ± 0.99	<0.001
	30 min	7.00 ± 1.08^a	3.50 ± 1.53^c	6.92 ± 1.04^b	8.25 ± 1.05	<0.001
Session 3	Pretreatment	6.79 ± 1.55	3.42 ± 1.44	5.75 ± 1.09	7.83 ± 0.80	<0.001
	30 min	4.71 ± 1.74^c	1.17 ± 1.07^c	5.50 ± 0.76	8.08 ± 0.76	<0.001
Late effect
15 days		3.04 ± 2.32	1.13 ± 0.97	4.46 ± 0.76	8.17 ± 1.21	<0.001
30 days		3.04 ± 2.03	1.08 ± 0.91	4.21 ± 1.00	8.25 ± 0.92	<0.001
60 days		2.96 ± 1.74	1.13 ± 0.83	4.25 ± 0.92	8.00 ± 1.22	<0.001

N = 24.

p < 0.05; ^b p < 0.01; ^c p < 0.001. Significant differences between pretreatment and 30 min (Wilcoxon's signed ranks test). No significant differences were found between 15, 30, and 60 days (Friedman test).

At pretreatment before session 1, no statistically significant differences between groups were found for the VAS scores (p > 0.05). For other periods, a statistically significant difference between the groups was found with Kruskal–Wallis testing (p < 0.001).

The mean VAS score at pretreatment of session 1 for the Er:YAG-treated group was 8.33 ± 0.85 (mean ± SD, n = 24). A significant decrease in mean VAS score in 30 min of session 1 occurred for Er:YAG-treated group (p < 0.01) (7.54 ± 1.15). The mean VAS score in pretreatment for session 2 for the Er:YAG-treated group was 7.42 ± 1.26, and in 30 min of session 2, the mean VAS score was 7.00 ± 1.08 (p < 0.05). Corresponding values for session 3 were 6.79 ± 1.55 and 4.71 ± 1.74 (p < 0.001). In the Nd:YAG-treated group, the corresponding values were 8.38 ± 1.07 and 5.04 ± 0.84 for session 1 (p < 0.001), 4.96 ± 0.79 and 3.50 ± 1.53 for session 2 (p < 0.001), 3.42 ± 1.44 and 1.17 ± 1.07 for session 3, respectively (p < 0.001). In the diode-treated group, the corresponding values were 8.29 ± 0.89 and 7.75 ± 0.83 for session 1 (p < 0.01), 7.46 ± 1.22 and 6.92 ± 1.04 for session 2 (p < 0.01), 5.75 ± 1.09 and 5.50 ± 0.76 for session 3, respectively.

The control group (not irradiated) showed no significant changes of VAS scores throughout the study period (p > 0.05). Compared the control group, other treatment forms showed significant decreases in mean VAS scores.

Table 2 also shows the mean VAS scores for late effects in the follow-up period of 15, 30, and 60 days after the conclusion of treatment of DH with the Er:YAG, Nd:YAG, and Diode lasers. No significant differences were found in the mean VAS scores (p > 0.05).

Table 3 shows a comparison of the all groups at different times.

Table 3.

Comparison of the all groups at different times

		Er:YAG-Nd:YAG	Er:YAG-Diode	Er:YAG-Control	Nd:YAG-Diode	Nd:YAG-Control	Diode-Control
Immediate effect
Session 1	Pretreatment	n.s.	n.s.	n.s.	n.s.	n.s.	n.s.
	30 min	^***	n.s.	^*	^***	^***	^*
Session 2	Pretreatment	^***	n.s.	^*	^***	^***	^**
	30 min	^***	n.s.	^***	^***	^***	^***
Session 3	Pretreatment	^***	^*	^*	^***	^***	^***
	30 min	^***	^*	^***	^***	^***	^***
Late effect
15 days		n.s.	n.s.	^***	^***	^***	^***
30 days		^**	n.s.	^***	^***	^***	^***
60 days		^***	^**	^***	^***	^***	^***

The asterisks indicate significant differences between groups (Mann–Whitney U test). N.s., not significant. p > 0.05; *p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001.

According to Table 3, similar statistically significant differences were observed between the comparison of Er:YAG–Control, Nd:YAG–Diode, Nd:YAG–Control, Diode–Control, and Er:YAG–Nd:YAG, except on day 15 of the late effect of Er:YAG–Nd:YAG. For Er:YAG-Diode, statistically significant differences were observed at pretreatment and 30 min of session 3 and on the day 60 of the late effect.

The vitality tests of the teeth were the same before and after laser treatment.

Discussion

DH can be a major problem for periodontal patients who frequently have gingival recession and exposed root surfaces. This study provides information about the clinical effectiveness of Er:YAG, Nd:YAG, and Diode lasers in the treatment of DH.

DH is a painful condition that is difficult to quantify. In the present study, a VAS was used to assess DH. In previous clinical studies, several investigators used a VAS, because it is simple to understand by patients, more sensitive in discriminating between various treatments and changes in pain intensity, and suitable for use in the evaluation of irritant responses in hypersensitivity studies.^17,18,21

The results of the present clinical trial demonstrated that all laser therapies resulted in overall relief of DH. However, when a comparison was performed between the Nd:YAG group and the other groups, VAS scores were significantly lower in the Nd:YAG group than in the other groups at each follow-up examination (p < 0.001).

The lasers parameters contributing to the effect on the amount of energy emitted to a surface are power (W), exposure time (seconds), pulsed versus continuous wave, energy density (J/cm²), distance, and the angle between the target tissue and the fiber tip. As a laser beam strikes a target tissue surface, the light energy can be affected in four ways: reflected, transmitted, absorbed, or scattered. Of the four, the changes in tissue are largely due to the absorbed energy, which is a thermal process.² Therefore, the most important issue in laser therapy is to determine the correct parameter for achieving satisfactory results without thermal detrimental pulpal effects, fractures and carbonization.

The results of the present study showed that the effect of Er:YAG laser is to decrease the pain of DH. A significant reduction of the VAS scores from 8.33 ± 0.85 to 2.96 ± 1.74 was shown in this study (p < 0.001). These results compare well with those reported by Birang et al.,¹⁰ Ipci et al.,²¹ and Schwarz et al.²² The first clinical use of the Er:YAG laser was reported by Schwartz et al.,²² who used this laser to achieved a reduction in DH from 3.6 ± 0.2 to 1.7 ± 0.5. Similar observations were made by several other investigators.^10,21

Reductions in DH have been reported with the use of the Er:YAG laser, due to its action of evaporating the water in the dentine, which leads to degranulation or coagulation of the organic elements, causing their accumulation and blockage of dentinal tubules.³⁰ However, potential problems exist with the mechanism of action of Er:YAG laser irradiation, as this laser can cause ablation of dentinal tubules rather than occluding them. Thus, the influence of different irradiation parameters on the dentine's morphology appears to be of extreme clinical importance.

It has been stated that applying 70 mJ/pulse and 20 Hz in noncontact mode perpendicular to the surface resulted in no ablation of the dentin.³¹ With such low energy densities, the temperature of evaporation is not reached, and ablation does not occur.³² Furthermore, the use of 60 mJ/pulse and 20 Hz has been reported to produce a thermally unaffected root surface.³³ Conversely, the laser used in this study, as other investigators' studies,^10,21,22 is low in power, and perhaps this situation can lead to this result. In addition, oral hygiene and bacteria penetration into dentinal tubules is one of the most important factors to make secondary dentin and decrease the amount of DH.³⁴ Perhaps the antimicrobial effect of the Er:YAG laser can cause this result.²²

In previous clinical studies, it was demonstrated that the Nd:YAG laser and the GaAlAs (diode) laser are effective devices in reducing DH to air spray.^{10

–14,18
–20} For the Nd:YAG laser, a significant reduction of the VAS scores from 8.38 ± 1.07 to 1.13 ± 0.83 was shown in the present study (p < 0.001). These findings are similar to results obtained by Birang et al.,¹⁰ who used the Nd:YAG laser and achieved a reduction in DH to air by 3.69 ± 0.56 to 0.3 ± 0.28.

Similar observations were made by other investigators. Kumar et al.¹¹ observed a decrease of 44–62% in mean VAS score in the Nd:YAG laser–treated group. Ciaramicoli et al.¹² showed a reduction of hypersensitivity in groups that received treatment with the Nd:YAG laser. However, great differences are found between the results of the present study and those of other studies, which showed no important effect of using Nd:YAG laser in DH treatment.^15,16 Perhaps it is because the use of water as a coolant on teeth during the use of Nd:YAG laser can limit the photothermal effect of the Nd:YAG laser on dentin and melting.

Several studies were performed to show the mechanism of the Nd:YAG laser irradiation in decreasing the DH. According to these studies, when the power of the Nd:YAG laser is < 1.5 W, lasing can cause alterations such as melting of dentin and closure of exposed dentinal tubules, cracking and fissuring on the root surface, and, when the power is > 1.5W, changes like cracks and fissures in dentin and changes in dentin protein can be seen, and the pulp may be injured.^26,35,36

It can be assumed that the dentin may be fused during Nd:YAG laser irradiation. Its effectiveness is probably due to an occlusion or narrowing of dentinal tubules, thereby blocking fluid flow across dentin. Recently, the GaAlAs (diode) laser was introduced in treating DH by means of inducing changes in neural transmission networks within the dental pulp, which may stimulate the normal physiologic cellular functions.^19,37 In addition, these lasers stimulated the production of sclerotic dentin, thus promoting the internal obliteration of dentin tubules.³⁸ A previous study reported that GaAlAs (diode) laser blocks the depolarization of C-fiber afferents.³⁹

A well-known difficulty and common feature of many clinical studies on DH is an improvement in all treatment groups, including the control.^10,15,40 This phenomenon may be a placebo effect, but just as likely is spontaneous improvement, or regression to the mode. These findings could not be supported by the present study. The untreated control teeth showed consistently high degrees of discomfort at each control session. This result is in accordance with the results of the previous study.²²

The vitality test before and after laser treatment was the same; therefore, we can say that lasers do not affect the pulp. The laser treatment seems to be beneficial and can be an alternative treatment for DH. However, the laser is found only in some clinics because of its high cost. Therefore, laser devices in dental clinics may become more widely used to relieve orofacial pain, treat periodontal disease, and repair bone.

Conclusions

The Er:YAG, Nd:YAG, and Diode lasers can be used to reduce DH. Nd:YAG laser irradiation is more effective in treatment of DH than are the Er:YAG and diode lasers. Within the limitations of the present study, the Nd:YAG laser seems to be a suitable tool for successful reduction of DH, especially because the 3-months results of this treatment modality are promising. Further studies are needed to evaluate the long-term stability of the obtained positive results.

Footnotes

Acknowledgments

The investigation was supported by grants (PN-2005/96 and PN-2005/243) from Atatürk University, Turkey. We thank Dr. Erkan Oktay for statistical assistance.

Author Disclosure Statement

No competing financial interests exist.

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