Evaluation of the Efficacy of LASER, Desensitizing Agents, and their Combined Effect on Dentinal Hypersensitivity in Bicuspids: In Vitro Study

ABSTRACT

Aim:

This study aimed to know the potential of diode light amplification by stimulated emission of radiation (LASER) and desensitizing agents on blocking the dentinal tubules, which may further help in reducing the most common dental problem named dentinal hypersensitivity (DH).

Materials and Methods:

Sixty human permanent bicuspids were selected, and preparation was performed in the cervical region measuring 2.5 mm × 2.5 mm × 2.5 mm, followed by acid etching for 15 seconds. These are then divided according to the groups mentioned: group 1—nano-hydroxyapatite (HA) was applied for 15 minutes; group 2—biosilicate was applied for 15 minutes; group 3—diode LASER application was performed twice for 60 seconds in noncontact mode; group 4—nano-HA plus diode LASER application; and group 5—biosilicate plus diode LASER application. The same procedure was followed on the 1^st, 7^th, and 14^th days and then rinsed and stored in artificial saliva, and the saliva was changed every 24 hours. The dentinal tubular occlusion was observed under a scanning electron microscope (SEM) after the 14^th day.

Result:

The maximum dentinal tubular occlusion was observed in group 4, where nano-HA and diode LASER application was performed.

Conclusion:

All the investigated treatment groups have promising occluding potential, but the maximum was found in group 4 >group 5 >group 3 >group 1 >group 2. LASER plus desensitizing together prove to be potent and effective in reducing dentinal tubular diameter.

INTRODUCTION

Dentinal hypersensitivity (DH) is a response that arises from a non-noxious stimulus and is also a chronic condition with acute episodes; however, dentinal pain arises from a noxious stimulus and is generally an acute condition. The main feature of DH is pain of a short nature, sharp but of rapid onset, which arises from exposed dentin in response to which are thermal, osmotic, mechanical, or chemical, which cannot be simulated with any other dental disease or defect.[1] DH prevalence varies between 45 and 57 percent,[2] and females have been reported to have a higher incidence of hypersensitivity than males. Although this condition can affect any tooth, the most commonly affected teeth are canines and premolars.[3]

The hydrodynamic theory given by Brännström in 1964 is the most accepted theory.[4] It says that whenever any stimuli induce rapid displacement of the dentinal fluid inside the tubules the fluid flow excites the intradental nerves, which results in an immediate pain response. This theory states that for successful treatment of DH one needs to prevent or reduce fluid flow within the tubules. Thus, the use of physical or chemical methods to seal the exposed patent orifices of the dentinal tubules is the chief requirement.

The materials used for desensitization are applied to the exposed tubules to occlude them or to depress the dentinal sensory nerve activity, thus preventing the pain signal transmission to the central nervous system. Occlusion of dentinal tubules can be performed by in-office topical application of desensitizing agents or by self-application of prescribed agents by patients at their home.

Any treatment, which aims at reducing dentinal permeability, by occluding dentinal tubules causes a reduction in dentinal permeability, thereby diminishing the intensity of DH. Histologically, when observed under a transmission electron microscope, a sensitive tooth presents two times larger tubules and an increased number per area when compared to a normal tooth having no DH. However, macroscopically, the normal tooth and a hypersensitive tooth have the same dentin, but the difference lies in the symptoms, which suggest minor inflammation of pulp.[5]

The first experiment of light amplification by stimulated emission of radiation (LASER) for dental application was in the 1960s.[6] “LASER” is an acronym derived from light amplification by the stimulated emission of radiation. Laser–tissue interaction is the use of light energy that is absorbed by the tissue to produce a photobiological effect, which can be manifested as photodisruption, plasma-induced ablation, photoablation, thermal, and photochemical. The mechanisms of diode laser that lead to ablation or decomposition of biological materials are photochemical, thermal, or plasma mediated. The diode laser exhibits thermal effects using the “hot-tip” effect caused by heat accumulation at the end of the fiber and produces a relatively thick coagulation layer on the treated surface. Tissue penetration of a diode laser is less, while the rate of heat generation is higher than that of the neodymium-doped yttrium aluminum garnet (Nd: YAG) laser. The advantages of diode lasers over the other lasers are the smaller size of the units and the lower financial costs.[7]

Biosilicate consists of amorphous sodium–calcium–phosphosilicate and is a ceramic material, which is highly reactive in water. It comprises a fine-particle size powder, which has the potential to occlude dentinal tubules.[8] Hydroxyapatite (HA) is the chief component of teeth and human bones. It has a crystal structure similar to human teeth; thus, research studies exploring its effect in easing DH have been reported in recent years.[9]

Several agents and therapies have been tried for the treatment of hypersensitivity, but none of them have proven completely effective. Therefore, the aim of this study was to compare the efficacy of diode LASER, desensitizing agents, and their combined effect on dentinal tubular occlusion.

MATERIALS AND METHODS

Ethical approval was obtained before commencing the study. The ethical committee clearance reference number is CPGIDSH/587/17.

Inclusion criteria—bicuspids.

Exclusion criteria—carious teeth and restored teeth.

A total of 60 caries-free human extracted permanent bicuspids were collected and cleaned, and then cervical defect was prepared on all the teeth with International Organization for Standardization (ISO) no. 245 bur (Mani) to standardize the defects prepared in the extracted premolars. The bur was replaced after the preparation of every four cervical defects to maintain its efficiency of cutting. The depth of the cavity was kept as 2.5 mm, the length of the cavity was kept as 2.5 mm, and the width was kept as 2.5 mm. All the cavities were standardized by preparing them using a template prepared on graph paper. All the cervical defects were prepared with a high-speed air rotor under water spray. After the preparation, toileting of the cavity was performed, the cavity was performed, and the cavity was dried. Etching of the defect was performed with 37% phosphoric acid for 15 seconds, and then, it was washed.

Group 1 (nano-HA)—desensitizing agent, Aclaim containing nano-HA, was applied with the help of an applicator tip on the prepared cavity, and it was left for 15 minutes.

Group 2 (biosilicate)—desensitizing agent, Vantej containing biosilicate, was applied with the help of an applicator tip on the prepared cavity, and it was left for 15 minutes.

Group 3 (LASER)—LASER was used with 0.5 W, continuous noncontact mode, applied 2–3 mm away from the tooth surface for 60 seconds, and each site received two applications of 1 minute.

Group 4 (nano-HA plus LASER)—desensitizing agent, Aclaim containing nano-HA, was applied with the help of an applicator tip, and it was left for 15 minutes. Then, LASER was used with 0.5 W, continuous noncontact mode, applied 2–3 mm away from the tooth surface for 60 seconds, and each site received two applications of 1 minute.

Group 5 (biosilicate plus LASER)—desensitizing agent, Vantej containing biosilicate, was applied with the help of an applicator tip, and it was left for 15 minutes. Then, LASER was used with 0.5 W, continuous noncontact mode, applied 2–3 mm away from the tooth surface for 60 seconds, and each site received two applications of 1 minute.

The samples were then placed in prepared artificial saliva. This procedure was repeated on the 1st day, 7th day, and 14th day. The samples were prepared and viewed under a scanning electron microscope (SEM) (Zeiss Evo 18). Photomicrographs at 2000x were taken. The percentage of occluded tubules was calculated on the photomicrographs obtained for each sample. The observation was then sent for statistical analysis, which was performed using Statistical Package for Social Sciences (SPSS) version 15.0 Statistical Analysis Software. The results were then analyzed using descriptive statistics and making comparisons between treatment groups with respect to adaptation parameters. Discrete (categorical) data were summarized as proportions and percentages (%). Proportions were compared using the Chi-square (χ²) test. The presentation of values was performed in number (%) and mean ± standard deviation (SD). An analysis of variance (ANOVA) test was used for comparison of the within-group and between-group variances among the study groups. ANOVA provided “F” ratio, and a higher “F” value represented a higher intergroup difference.

RESULT

The samples were prepared and viewed under SEM (Zeiss Evo 18). Photomicrographs at 2000x were taken. The percentage of occluded tubules was calculated [Table 1]. The observation was then sent for statistical analysis (ANOVA) for obtaining the result.

Table 1.

Percentage of dentinal tubular occlusion in different groups

Sample no.	Group 1 efficacy in percentage	Group 2 efficacy in percentage	Group 3 efficacy in percentage	Group 4 efficacy in percentage	Group 5 efficacy in percentage
1	80	80	80	91	54
2	88	71	71	87	69
3	88	69	69	78	84
4	76	44	44	89	85
5	71	38	38	92	81
6	74	71	71	75	95
7	80	82	82	94	88
8	70	73	73	97	93
9	76	78	78	90	95
10	78	82	82	87	91
11	80	76	76	96	89
12	86	86	86	97	90

On comparing the efficacies of various groups [Table 2], it was found that the efficacy was seen maximum in group IV with a mean of 89.42 ± 6.99, which was followed by group V with a mean of 84.50 ± 11.99. The minimum efficacy was seen for group II. The ANOVA test showed highly significant differences in the efficacies of various groups (P = 0.001).

Table 2.

Comparative efficacy of various groups

Group	Efficacy (%)
	Mean	SD
Group I	78.92	6.05
Group II	70.83	14.92
Group III	83.50	7.39
Group IV	89.42	6.99
Group V	84.50	11.99
ANOVA F	5.808
P	0.001

On comparing the efficacies of various group pairs, it was found that the significant difference in efficacies was found between the group pairs II–IV (P < .001), II–III (P = .026), II–V (P = .013), and II–V (P = .013) [Table 3].

Table 3.

Comparative efficacy between various group pairs

A	B	Mean difference (A-B)	P
Group I	Group II	8.083	0.295
Group I	Group III	-4.583	0.798
Group I	Group IV	-10.500	0.093
Group I	Group V	-5.583	0.656
Group II	Group III	-12.667	0.026
Group II	Group IV	-18.583	<.001
Group II	Group V	-13.667	0.013
Group III	Group IV	-5.917	0.605
Group III	Group V	-1.000	0.999
Group IV	Group V	4.917	0.753
Group V	Group I	5.583	0.656
Group V	Group II	13.667	0.013

DISCUSSION

The nature of the exposed dentin is of importance, as all patients exhibiting dentin exposure will not develop sensitivity. Lasers can play a prominent role in treating hypersensitive dentin and providing reliable results. The groups treated with LASER present with reduced tubular diameter. This can be due to the melting effect caused by diode lasers as a result of thermal effects on surface dentin. When part of laser energy is absorbed by mineral structures of dentin, it causes a sufficient increase in temperature, which results in thermochemical ablation and thus melting of the dentin.[10]

HA is a natural substance and a compound of calcium and phosphate, which make up about 75 percent of the weight of dentin. It possesses excellent biological properties that are nontoxic and non-inflammatory and has bioresorption properties under physiological conditions. Nano-HA crystals mimic the size of natural dentinal HA (20 nm).

According to A R Pradeep et al., the biosilicate group presented effectiveness at reducing DH because of calcium sodium phosphosilicate (NovaMin), which is a bioactive glass in the class of highly biocompatible materials, which was originally developed as a bone-regenerative material. In the saliva, sodium ions (Na+) from calcium sodium phosphosilicate particles provide an immediate exchange with hydrogen cations (H+ or H3O+). This rapid exchange allows calcium (Ca2+) and phosphate (PO4 3−) to be released from the particle structure. There is a localized, transient increase in pH, which facilitates the precipitation of calcium and phosphate from both particles and saliva to form a calcium phosphate (Ca-P) layer on tooth surfaces. As this reaction and deposition of Ca-P complexes continue to occur, this layer crystallizes into hydroxycarbonate apatite, which is chemically and structurally similar to biological apatite.[11]

Interruption of stimuli transmission to the nerve endings of odontoblast processes can cause a reduction in fluid movement inside the dentinal canaliculi, by narrowing or occlusion of tubule openings,[12] whereas other treatment modalities such as laser therapy have also come into the light.

A diode laser (Doctor Smile) is a modern low-power laser that can provide good results in the treatment of DH. The mechanism behind the higher efficacy may be attributed, and it can cause changes in neural transmission within the pulp, rather than changes in the exposed dentine surface, as seen with other treatment modalities.[13] Normal physiological cellular functions can be stimulated by LASER therapy. Thus, they can also stimulate the production of sclerotic dentine, hence promoting the internal obliteration of dentinal tubules.

Our results are also consistent with those of Cox et al.[14] who observed melting and crazing of the dentin surface, slight debris formation, and also modification of dentin tubular structure where the tubular periphery had melted. In the present study, LASER achieved superior results in comparison with desensitizing agents. These results are in agreement with the data reported by Ipci et al.,[15] whereas the results of the present study are not in accordance with Rajeshwari et al.[16]

A few other mechanisms of LASER effect on dentin are thermal energy absorption, causing occlusion or narrowing of dentinal tubules. Whitters et al. suggested direct nerve analgesia, which might be the mechanism behind it,[17] whereas Funato et al. suggested thermally mediated effects on microcirculation. Some vascular changes were observed by them shortly after the LASER application was performed. The changes included were vascular shrinkage, degeneration, coagulation, and stasis associated with irradiation. Another mechanism is a low-level laser, which is a source of biostimulation using its thermal energy and light sources. It works on the regulation of cell physiological functions, analgesia effect, and bioregulation of the cell responses and provides anti-inflammatory effects. The analgesic effect of therapeutic LASER can be attributed to it as it affects the release of alpha- and ß-endorphins, which bind to the receptors from the nociceptive system, thus causing analgesia by blocking the transmission of the input substances.[18]

It is observed that laser energy had affected and modified the whole dentinal surface and not only the dentinal tubules, where melting and resolidification of the area surrounding the tubules were seen, particularly in groups 3, 4, and 5, where the samples had been lased for 2 minutes. The lased dentinal surface appears smooth and presents with round–elliptical bubble-like changes at and around the area of the dentinal tubular orifices. It can be attributed to the photothermal effect of the laser energy, where the high temperatures caused the tubular orifices to melt and swell, thus leading to this appearance.

According to Moritz et al., better results were obtained by the combined intervention of laser and desensitizing agent in the management of DH. Better results might be due to the higher adhesion of desensitizing agents to the dentinal tubules when combined with laser energy, and it can be possible that the laser-induced superficial melting permits longer tubular occlusion by desensitizing agent, thus resulting in a reduction in DH-related pain. A synergistic action of lasers with desensitizing agents can be seen.[19]

According to Arulmozhi et al.,[20] desensitizing agents along with LASER were said to penetrate the tubules for up to 10 mm, which is a reason for reduced hypersensitivity, and the same study presents that activating the desensitizing agents with LASER and observation through SEM revealed reduced tubular diameter than when desensitizing agents are used alone; hence, the results of this study favor the result of this study, which shows that the use of nano-HA plus LASER causes more dentinal tubular occlusion than when desensitizing agents or LASER was used alone.

The calcium phosphate-like layer, which binds to the dentin, results in occlusion of the tubules, and irradiation with diode LASER causes an additional thermal changes, providing lesser diameter values when compared to the teeth treated only with diode LASER.

This study presented maximum tubular occlusion in nano-HA plus LASER group, followed by biosilicates plus LASER, when compared to the other groups of LASER, nano-HA, and biosilicates when observed under a SEM.

CONCLUSION

Within the limitations of the present study, this conclusion was made that maximum percentage of dentinal tubular occlusion was observed when the samples were treated with nano-HA plus LASER and observed under a SEM as compared to other groups. Limitations of this study are, for more appropriate results, more study samples need to be included and in vivo study too should be included for comparing the efficacy of the groups. The quality of dentinal tubular occlusion was found to be as follows:

Group IV >group V >group III >group I >group II.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.