Ⅰ. INTRODUCTION
Dentin hypersensitivity (DH) is defined as short and sharp pain caused by external stimuli such as heat, vaporization, contact, osmotic pressure, and chemical stimulation in a normal tooth, rather than due to disease or tooth damage1). Gingival recession resulting from abrasion or periodontal disease is considered the primary etiological factor for exposed dentin2). The dentin hypersensitivity appears mainly in the exposed dentin. The exposure of the dentin is affected by chronic trauma due to tooth-brushing, acid-erosion due to various environments, acid reflux, dietary habit, anatomical factors of the white porcelain enamel boundary, loss and exposure of the root surface due to gingival recession by periodontal disease.
The mechanisms of dentin hypersensitivity are odontoblast transduction theory, direct nerve stimulus theory, and hydrodynamic theory. The most prevalent hypothesis at present is "hydrodynamic theory" in which the sensory nerves in the dentin are stimulated by the fluid movement of the dentin-dental complex when the dentin is exposed and the irritation occurs at this site3). Two methods are applied for this treatment. First, the method of inhibiting the excitation of the sensory nerve in the dimension by stimulating the depolarization of the nerve by increasing the K+ ion concentration. Second, physically blocking the dentinal tubule to block the fluid movement4). Currently widely used products for the treatment of dentin hypersensitivity are fluoride agent type hypersensitivity agent, oxalate type hypersensitivity agent and resin type hypersensitivity agent. Fluoride type hypersensitivity agent is used to deposit calcium fluoride on the tooth surface, thereby increasing the resistance to external stimuli5). The disadvantages are that it is dissolved in saliva and the effect is limited because of the rapid disappearance of fluoride6-8). Oxalate-type hypersensitivity treatment is deposited in the dentine tubules to reduce their diameter, thereby reducing dentin hypersensitivity9). The disadvantage is that the surface sediment can be dissolved in the saliva, so only the short-term effect is valid10,11). Resin type hypersensitivity agent is used as adhesive resin with excellent adhesion for dentin hypersensitivity treatment 12). However, in the case of resin filling, proper use of an appropriate bonding system affects the prognosis, and there is a disadvantage in that hypersensitivity may remain after the treatment13). As mentioned above, the fluoride agent can be disappeared quickly and only temporary effects can be expected. In the case of the oxalate type hypersensitivity agent, the precipitate is dissolved in the saliva, so that the short-term effect can be expected and it needs to apply it frequently. In addition, for the resin filling, an appropriate bonding system should be used and may also develop symptoms of hypersensitivity after treatment. It is necessary to overcome the disadvantages of the existing methods and to be able to effectively treat tooth hypersensitivity without any side effects. For this reason, among 200 plant extracts, Buddleja officinalis was selected as candidate for dentin hypersensitivity treatment. Buddleja officinalis is a deciduous shrub belonging to Loganiaceae. It is a dried flower buds and inflorescences which is collected when the flower is not yet bloomed in spring. It is known to have functions of the antibacterial effect14), antioxidant effects15), protection of nerve cell16), suppression of aldose reductase activity17) and antiinflammatory effects18). However, there are no reports related to dentin hypersensitivity.
This study is based by using ethanol extracts of Buddleja officinalis and is to investigate if it can protect the enamel and dentin and if it can resist on acid and/or alkali after its coating on tooth.
Ⅱ. MATERIALS AND METHODS
1. Manufacture of specimen
300 g of the dried Buddleja officinalis is pulverized with a blender and 2 L of 70 % EtOH is added and extracted at room temperature for 48 hr. The extract was filtered using a filter paper (No. 2, Whatman), and the filtrate was concentrated at 39 ℃ using a rotary vacuum evaporator (EYELA N-1000). After vacuum evaporation, the extract is incubated with 0.5 N HCl at room temperature for 24 hr and then waited until chemically stabilized. Thereafter, the mixture was concentrated under vacuum evaporator at 39℃ again. 20 ml of 100% EtOH was added, homogenized using a vortex and a sonicator, and then centrifuged at 3000 rpm for 15 minutes. After centrifugation, the supernatant was taken and concentrated again at 39℃ using a rotary vacuum evaporator. After vacuum evaporation, the extracts was diluted with PBS to 0.04 mg/㎖ and used as further experiment.
2. tooth coating and Scanning Electron Microscopy
Teeth were gently rinsed in running water with a soft toothbrush and then allowed to dry at room temperature. Next, the Buddleja officinalis extract was applied to the tooth surface (enamel) using a cotton swab and 635 nm light was irradiated to the tooth at an energy density of 10 mW at intervals of 90 seconds. And observation with an electron microscope was done.
3. Scanning Electron Microscopy Observation after Immersion Treatment of Exposed Enamel rod and dentinal tubules
Teeth were gently rinsed in running water with a soft toothbrush and then allowed to dry at room temperature. Denture bur and specimen manufacturing saw was used to expose enamel rods and dentinal tubules. the Buddleja officinalis extract was applied to the tooth surface (enamel) using a cotton swab and 635 nm light was irradiated to the tooth at an energy density of 10 mW at intervals of 90 seconds. And observation with an electron microscope was done.
4. Effect of tooth coating on pH
Teeth were gently rinsed in running water with a soft toothbrush and then allowed to dry at room temperature. And the next, the Buddleja officinalis extract was applied to the tooth surface (enamel) using a cotton swab and 635 nm light was irradiated to the tooth at an energy density of 10 mW at intervals of 90 seconds. The coated teeth were immersed in a beaker containing a pH 3, pH 5, pH 7, and pH 9 aqueous solution for 24 hours and observed using a scanning electron microscope.
Ⅲ. RESULTS
1. Confirmation of tooth coating
As a result of the experiment to confirm the optimum coatings, the coating effect was observed at a light irradiation time of 0.04 mg/ml with Buddleja officinalis extract for 30 seconds or more. However, uniform and stable results were obtained when light irradiation was performed for 90 seconds. Based on these results, the light irradiation was performed for 90 seconds, and the results of coating to the number of times is as shown in Fig. 1. The surface (Fig. 1-B) treated for 90 secons was shown to be more smooth and regular comparing to the surface untreated (Fig. 1-A). Then, as the coating process was repeated, the surface of the tooth, which can be seen in the photographs (Fig. 1-C ~ 1-F), showed a snowy cluster shape.
2. Effects of extracts of Buddleja officinalis on exposed enamel rods and dentinal tubules
The tooth was cut with a saw for making specimens, and the exposed enamel rods (Fig. 2) and dentinal tubules (Fig. 3) were observed with a scanning electron microscope. In Fig. 2-A and Fig. 3-A, the exposed enamel rods and dentinal tubules were visible. However, after treating with Buddleja officinalis, every grooves and fissures were sealed in Fig. 2-B & 3-B. This implies that the extracts of Buddleja officinalis can block or seal the dentinal tubules which may cause the dentin hypersensitivity.
3. Effects of coating states according to pH
The scanning electron microscope picture of Fig. 4-1A (before processing) and Fig. 4-1B (after processing) showed no change before and after the treatment. This means that it is resistant to a relatively strong acid at pH 3. Similarly, a scanning electron microscope photograph of Fig. 4-4A (before treatment) and Fig. 4-4B (after treatment) showed no difference before and after the treatment. This also means that the coated tooth has a resistance to pH 9. As a result of the experiment in an aqueous solution of pH 5 and pH 7, no odds in the tooth surface was observed before and after the treatment.
Ⅳ. DISCUSSION
Exposure of dentin cause dentin hypersensitivity according to hydrodynamic theory, and the its main treatment is to occlude the exposed dentinal tubules and reduce the dermal tubular permeability3). Presently, the most commonly used products for closing these dentinal tubuli are fluoride agent type hypersensitivity agent, oxalate type hypersensitivity agent, and resin type hypersensitivity agent 6). High concentration of fluoride to relieve dentin hypersensitivity is applied locally to the teeth. This method has a short contact time with the teeth, however, there is a risk of swallowing during the application process, and may cause the discoloration or erosion of existing esthetic restoration. On the other hand, dentin hypersensitivity treatment with extract of Buddleja officinalis is relatively safe because it is inactive when not irradiated, and is aesthetically helpful because the teeth tend to be transparent and bright due to the coating effect. In addition, dentin coated with a fluoride agent was observed with a scanning electron microscope and found to be that CaF2 crystal phase was not observed clearly19). In the case of the coating using extract of Buddleja officinalis, dentinal tubules were densely filled as seen in SEM (Fig. 3) so that more effective blockade of the dentinal tubules can be expected. The oxalate type of hypersensitivity agent that can form insoluble deposits in the dentinal tubules tends to be strong acids20-22). The properties of these products having hydrophilic potassium oxalate chemically interacts with dentin of exposed dentinal tubules and forms insoluble deposit, calcium oxalate, which may seal off the dentinal tubules20-22). Products with these strong acids, such as SuperSeal (pH 2.7) and BisBlock (pH 1.5-1.8), give the dentin an excessive acid-corrosion effects to promote the demineralization of dentin, which can strikingly reduce the adhesive strength of the dentin20-22). On the other hand, since the extract of Buddleja officinalis is a pH 6.3, it is unlikely that the adhesive strength of the dentin bonding agent is remarkabley lowered because the excessive acid-etching treatment is not performed. In recent years, the prevalence of dental erosion in children and early teenagers has been investigated, and tooth erosion as well as dental caries have been mentioned quite often as oral health problems in children 23). Several in vitro and in situ studies evaluating the potential for tooth erosion of acidic beverages have supported the possibility of tooth erosion in fruit juices, sports drinks and carbonated beverages24-26). The possibility of preventing tooth erosion by acidic drinks and food has been found in dentin hypersensitivity treatment using the extract of Buddleja officinalis. As can be seen in Fig. 4, when coated with the extract of Buddleja officinalis, the resistance to pH changes is strong. Additional clinical trials are needed to commercialize.
