- Email: [email protected]
In Vitro Evaluation of Dentin Tubule Occlusion by Denshield and Neodymium-doped Yttrium-Aluminum-Garnet Laser Irradiation
Basic Research—Technology
In Vitro Evaluation of Dentin Tubule Occlusion by Denshield and Neodymium-doped Yttrium-Aluminum-Garnet Laser Irradiation Eleftherios-Terry R. Farmakis, DDS, MDSc, PhD,* Konstantinos Kozyrakis, DDS, PhD,* Marouan G. Khabbaz, DDS, PhD,* Ulrich Schoop, DMD, MD,† Franziska Beer, MD, DMD, DDS,† and Andreas Moritz, MD, MDM, PhD† Abstract Introduction: This in vitro study evaluated the efficacy of bioglass (Denshield; Novamin Technology, Alachua, FL) and Neodymium-doped yttriumaluminum-garnet (Nd:YAG) laser irradiation on dentinal tubuli orifice occlusion (DOO) by comparing samples examined under environmental scanning electron microscope (ESEM) after applying each desensitizing approach separately and in combination. Methods: Forty-eight human molars were collected, randomly organized in 4 equal groups, and had their cervical dentin exposed. Additionally, in half of the specimens of each experimental group, the smear layer was removed (subgroups A1, B1, C1, and D1). Group A received NovaMin paste treatment for 5 minutes (NM) to the experimental surface. Group B received Nd:YAG laser irradiation (0.5 w, 10 Hz, and 50 mJ) (L). Group C received NM followed by L. Group D was treated with L followed by NM. All specimens were stored for 24 hours and evaluated for DOO under ESEM by 4 blinded observers. Results: The presence of a smear layer significantly contributed to DOO regardless of the treatment modality (ordinal logistic regression, P < .001). Compared with group A, all other treatments delivered significantly more occluded dentin orifices (P < .001 for groups B and D and P < .05 for group C). A layer formation was observed in subgroups C2 and D2. Conclusions: Under these experimental conditions, a smear layer was essential for successful DOO. Laser irradiation alone and combined with NovaMin proved superior to NovaMin alone on DOO. This combined approach has the potential to improve the outcome of treatment for cervical dentin hypersensitivity. The biological significance of this newly formed layer needs to be elucidated. (J Endod 2012;38:662– 666)
Key Words Bioglass, cervical dentin hypersensitivity, dentin orifice occlusion, laser irradiation, Nd:YAG, NovaMin
C
ervical dentinal hypersensitivity (CDH) is a common problem that affects 8% to 30% of the adult population and 84% of patients who have undergone periodontal therapy (1). It is mainly localized on the buccal surfaces of canines and premolars. Among the factors that influence and increase CDH are gingival recession, brushing technique, and dental plaque. It is a frequent symptom of people working in industrial environments containing acidic gases. It also frequently affects bruxists because of the commonly found enamel cracks in cervical areas (2). Several theories have been proposed to explain this phenomenon such as the odontoblastic transduction theory (3, 4); the dentin innervation theory (5); and the Brannstrom hydrodynamic theory, which is most commonly accepted (6). It suggests that if thermal, chemical, or mechanical stimuli induce rapid displacement of the dentinal fluid, a shift of fluid in either direction could deform the odontoblast layer or stimulate A-delta nerve fibers, resulting in an immediate pain response. Some of the applied therapies to relieve CDH involve occlusion of the dentinal tubules, reduction of their diameter, stimulation of secondary dentin production, and/or desensitization of nerve fibers. In order to achieve the desired result, dentifrices or gels containing fluoride or other desensitizing agents (eg, KN03 [7], SnF2 [8], and oxalates [9]), formaldehyde (10), bonding agents (11), and laser irradiation (12) have all been applied (alone or combined) with variable results. Of those, sodium fluoride is widely used with predictable positive results in many cases (13). Additionally, iontophoresis has been shown to increase the uptake of fluoride (14). Recently, a new system has been introduced as a treatment for CDH (Denshield; Novamin Technology, Alachua, FL). NovaMin, the active ingredient in Denshield, is a bioactive glass that has been ground into a fine particulate with a median size of <20 mm and is composed of Ca, P, Na, Si, and O. When exposed to an aqueous environment, it releases Ca+2 and (PO4) 3 ions. A layer is formed through several reactions starting from nucleation sites and finally crystallizes into hydroxylcarbonate apatite, which is equivalent to hydroxyl-phosphate apatite in biological behavior (15, 16). The combination of the residual NovaMin particles and the hydroxyl-carbonate apatite layer results in the physical occlusion of dentinal tubules, which is claimed to relieve hypersensitivity. The aim of this study was to evaluate in vitro the efficacy of NovaMin and Nd:YAG laser irradiation in the presence and absence of a smear layer using environmental
From the *Department of Endodontics, Dental School, University of Athens, Athens, Greece; and †Department of Conservative Dentistry, Bernard Gottlieb Dental School, University of Vienna, Austria. Address requests for reprints to Dr Eleftherios-Terry R. Farmakis, 27 D. Gedeon Street, Peania 19002, Greece. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2012 American Association of Endodontists. doi:10.1016/j.joen.2012.01.019
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JOE — Volume 38, Number 5, May 2012
Basic Research—Technology scanning electron microscope (ESEM) to record the percentage of occluded dentinal tubuli orifices after applying each desensitizing approach (ie, NovaMin and Nd:YAG laser irradiation) separately and in combination as a potential treatment for CDH.
Materials and Methods Forty-eight sound, recently extracted human molars were collected. Any surrounding soft tissues were removed by immersion in 2.5% NaOCl solution for 10 minutes. The teeth were then stored in sterile saline (0.9% NaCl) until used. The buccal and lingual cervical enamel was removed with a diamond disc under tap water for cooling (Isomet 11-1180; Buehler Ltd, Evanston, IL), exposing the underlying dentin. On each tooth, the exposed buccal surface served as the experimental area, whereas the exposed lingual surface served as the control. Specimens were randomly organized into 4 equal groups (ie, groups A–D). All specimens had the smear layer removed by ultrasonication in deionized water for 30 seconds followed by an application of 0.5 mol/L EDTA (pH = 7.4) for 2 minutes. They were then rinsed with water spray for 30 seconds (17). This procedure was necessary to create patent tubules as observed in clinical cases of CDH. The surface of half of the specimens of each group (namely subgroups A2, B2, C2, and D2) were treated by 1 short passage of a medium blue polishing Sof-lex Disc (3M/ESPE Neodymium-doped Yttrium-Aluminum-Garnet, Seefeld, Germany) followed by a 1-minute water spray rinse to create an equal smear layer on all specimens. The null hypothesis would support that the smear layer has no influence on the outcome of any of the treatment modalities. The specimens were treated as follows. In group A, NovaMin paste was prepared according to manufacturer’s instructions and applied on the experimental surface for 5 minutes. In group B (as in all laserirradiated groups), the Nd:YAG laser was applied to the experimental surface under the following conditions: the laser handpiece was securely mounted on a stand so the optic fiber (0.3 mm in diameter) would vertically contact the experimental surface. The settings were
0.5 w, 10 Hz, and 50 mJ. Each section was mounted on a microscope observation glass slab and moved manually at a rate of approximately 5 mm/s in a sweeping motion, irradiating the total surface (18). The overall irradiation time was 30 seconds per sample. In group C, NovaMin paste was applied for 5 minutes followed by Nd:YAG laser irridiation as previously described. In group D, Nd:YAG laser was applied followed by NovaMin paste application for 5 minutes (as previously described). All specimens were stored in sterile saline (0.9 % NaCl) for 24 hours at room temperature and presented for examination under ESEM using 500 and 5000 magnification. Photographs were taken, and each specimen was evaluated for the percentage of occluded dentinal orifices. Scoring was categorized on a scale of 1 to 4 (1: 0%–24%, 2: 25%–49%, 3: 50%–74%, and 4: 75%–100%). There were 4 blinded evaluators. Three were required to be in agreement in order to record a score. Results were recorded and subjected to statistical analysis. Ordinal logistic regression was used because of the categoric and ordered nature of the outcome (orifice closure). The technique and the presence/absence of a smear layer were used as explanatory variables in a multivariable model. The odds ratios given in Figure 1 refer to the odds of higher orifice closure. When testing for techniques, comparisons were adjusted for the presence/absence of a smear layer. Conversely, when testing for the presence/absence of the smear layer, comparisons were adjusted for the technique used. The proportional odds assumption of the model was formally tested and was not rejected.
Results Results are shown in Figure 1, and representative photographs from each subgroup are shown in Figure 2. Statistical analysis revealed that the presence of a smear layer significantly contributed to dentinal orifice occlusion regardless of the treatment applied (P < .001). Compared with NovaMin application alone, all other treatments yielded significantly more occluded dentinal orifices (P < .001 for the lased-
Figure 1. The distribution of orifice closure by technique and the presence/absence of a smear layer. Odds ratios (P values) are derived from a multivariable ordinal logistic model and refer to the odds of higher orifice closure.
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Figure 2. Photographs of all experimental and control groups (500 magnification).
alone and lased-NovaMin groups and P < .05 for the NovaMin-lased group accordingly). Apart from the scoring, which reflected the occlusion of dentinal tubuli orifices, it should be noted that the surface of all specimens in subgroups C2 and D2 appeared to be covered by a granular layer, which is a finding unique to these 2 subgroups.
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Discussion CDH is a common problem among the adult population, especially after periodontal treatment. Normally, dentinal tubules occupy 20% to 30% of dentin volume, corresponding to 45.000/mm2 at the pulp, 29.500/mm2 in the middle, and 20.000/mm2 peripherically, with the JOE — Volume 38, Number 5, May 2012
Basic Research—Technology diameter of the tubules decreasing from 2.5 mm at the pulp to 0.9 mm peripherically, thus making dentin permeable (19). Permeability is reduced over time as the diameter of the tubules decreases because of mineralization (deposition of peritubular dentin). It is observed that in cases of dentin hypersensitivity, more dentinal tubules and tubules of greater diameter are observed compared with those of normal teeth (20). Treatment modalities aim at either partial or full occlusion of the exposed dentinal tubules or/and the desensitization of nerve fibers. Of all proposed treatments, none has been proven to be the ultimate or permanent cure. As early as 1985, laser irradiation had been applied for the treatment of dentin hypersensitivity (20–22). There are 2 categories of applications that have mainly been used: (1) low-power lasers (eg, diode [23] and Ga-Al-As [24]) and (2) medium-power devices (eg, CO2 [25] and Nd:YAG [22, 26]). For low-output power lasers (diode lasers [l = 80–900 nm] or He-Ne lasers [l = 632.8 nm]), the desensitizing effect seems to be related to laser activity at the nervous level (27). Only the Nd:YAG laser at 1,064 nm seems to have an additional analgesic effect, probably because the irradiation can temporally alter the ending of the sensory axons and block both C and Ab fibers (28, 29). Even more, Nd:YAG energy is not absorbed intensively by dentin and water because of its wavelength. Another possible mechanism of action is that Nd:YAG laser irradiation melts the superficial layer of dentin. When recrystallization occurs, it seals the dentin tubules in a depth of 3 to 4 mm without dentin surface cracking. This effect is pronounced when used along with a fluoridecontaining substance (30, 31). One in vitro study showed a durable 90% occlusion of the exposed dentinal tubules under scanning electron microscopic examination (30). During Nd:YAG laser irradiation of dentin, the thermal effects on the pulp are of concern. The thermal threshold for pulpal damage is generally not exceeded when the energy and power settings of the laser remain within the reported range (32). Apart from Nd:YAG, other types and wavelengths of laser irradiation have been used in vivo and in vitro with varying levels of success (30). Despite the aforementioned basic research evidence, a recent systematic review attempted to analyze all published randomized placebo-controlled clinical trials to assess evidence for the effectiveness and safety of laser dentinal hypersensitivity treatments. Sgolastra et al (27) investigated 18,661 potentially relevant titles and abstracts. Only 3 fulfilled the inclusive criteria, concluding that a placebo effect contributing to the therapeutic result has to be considered. A novel device for cervical dentin hypersensitivity is the application of bioactive glass (NovaMin). The suggested mechanism of action is the release of active Ca, P, and Na ions (along with small amounts of Si ions) when NovaMin is in an aqueous environment. The Ca and P ions are of the appropriate ionic form and relative ratios to immediately form hydroxy-carbon apatite on available nucleation surfaces. This apatite claims to be similar or identical to the endogenous tooth and bone substance (33). This formation is further aided by the release of Na ions, which created a more favorable pH environment, and by the presence of the Si ions, which have also been hypothesized to stimulate this formation. The manufacturer provides a 2-phase system (in office and at home). However, a recent study suggested that the at-home treatment is as drastic as the in-office and at-home treatment combined (34). The presence or absence of a smear layer seems to be a major influencing factor for effective tubular occlusion in this study. Although no literature was found to relate a smear layer to CDH, it should be expected that the smear layer may be acting as a multiple nucleation substrate, thus accelerating apatite formation. The combination of 2 desensitizing strategies was tempting, so we tried to document every potential therapeutic benefit in this study. JOE — Volume 38, Number 5, May 2012
Maybe the modified dentin surface as a result of the Nd:YAG laser application increases the adhesion of NovaMin (group D2). In the other treatment modality (C2), NovaMin may be incorporated within the dentin during the melting/recrystallization action of laser irradiation. A recent in vitro study showed that CO2 laser irradiation after bioglass application resulted in an increased dentin-bioglass interaction (35). Both treatment schemes (ie, NovaMin and then laser irradiation and laser irradiation and then NovaMin) produce a thick layer accompanied by a high percentage of closed tubules. It can be expected that if either (or both) of these layers is proved long lasting, it may work as a long-term device for the treatment of CDH. This layer may be seen as a lasting source of Ca, P, and Na ions, thus keeping the site stable. What needs to be further examined is whether this result is long lasting. A preliminary investigation proved these layers durable to storage for 6 months into sterile saline (0.9% NaCl) followed by 10 minutes of ultrasonic bathing. Another area for further investigation might involve assessing the penetration depth of the bioglass particles inside the dentin tubuli as well as determining the chemical composition of the created ‘‘plugs.’’
Conclusions Under these experimental conditions and within the limitations of this study, it was concluded that the presence of a smear layer is essential for successful dentinal tubule occlusion regardless of the applied modality. Additionally, the combination of the Nd:YAG laser and NovaMin applied either way in the presence of a smear layer, both occludes the tubules and is capable of forming a layer of uncertain biological significance.
Acknowledgments The authors thank Dr Nikos Pantazis, Athens University Medical School, Greece, for performing the statistical analysis and Dr H. Lee Adamo, New York, New York, for his valuable contributions in the editorial revision of this manuscript. The authors deny any conflicts of interest related to this study.
References 1. Rees JS, Addy M. A cross-sectional study of dentin hypersensitivity. J Clin Periodontol 2002;29:997–1003. 2. Bissada NF. Symptomatology and clinical features of hypersensitive teeth. Arch Oral Biol 1994;39(suppl):31S–2. 3. Bernick S. Innervation of the human tooth. Anat Res 1948;101:293–7. 4. Frank RM. Attachment sites between the odontoblast process of the intradental nerve fiber. Arch Oral Biol 1968;13:833–4. 5. Frank RM, Steuer P. Transmission electron microscopy of the human odontoblast process in peripheral root dentin. Arch Oral Biol 1988;33:91–8. 6. Br€annstr€om M, Astrom A. The hydrodynamics of the dentine; its possible relationship to dentinal pain. Int Dent J 1972;22:219–27. 7. Tarbet WJ, Silverman G, Stolman JM, Fratarcangelo PA. Clinical evaluation of a new treatment for dentinal hypersensitivity. J Periodontol 1980;51:535–40. 8. Miller JT, Shannon IL, Kilgore WG, Brookman JE. Use of a water-free stannous fluoride-containing gel in the control of dentinal hypersensitivity. J Periodontol 1969;40:490–1. 9. Greenhill JD, Pashley DH. Effects of desensitizing agents on the hydraulic conductance of human dentin in vitro. J Dent Res 1981;60:686–98. 10. Addy M, Mostafa P. Dentine hypersensitivity: I. Effects produced by the uptake in vitro of metal ions, fluoride and formaldehyde onto dentine. J Oral Rehab 1988;15:575–85. 11. Deiab H, EL-Soudany K. Comparative study of the clinical effectiveness between Nd:YAG laser and GLUMA desensitizer in the treatment of dentin hypersensitivity. Cairo Dent J 2007;23:193–200. 12. Kimura Y, Wilder-Smith P, Yonaga K, Matsumoto K. Treatment of dentine hypersensitivity by lasers: a review. J Clin Periodontol 2000;27:715–21.
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Basic Research—Technology 13. Pamir T. The efficacy of three desensitizing agents in treatment of dentin hypersensitivity. J Clin Pharm Ther 2005;30:73–6. 14. Wilson JM, Fry BW, Walton RE, Gangarosa LP. Fluoride levels in dentin after iontophoresis of 2% NAF. J Dent Res 1984;63:897–900. 15. Litkowski LJ, Hack GD, Greenspan DC. Compositions containing bioactive glass and their use in treating tooth hypersensitivity. US Patent 5,735,942. April 7, 1998. 16. Litkowski LJ, Hack GD, Greenspan DC. Methods of treatment using bioactive glass. US Patent 6,086,374. July 11, 2000. 17. Paes Leme AF, dos Santos JC, Giannini M, Wada RS. Occlusion of dentin tubules by desensitizing agents. Am J Dent 2004;17:368–72. 18. Farmakis ET, Kozyrakis K, Kontakiotis EG, Kouvelas N. Effect of Er:Cr:YSGG laser on human dentin collagen: a preliminary study. J Laser Dent 2008;16:17–22. 19. Br€annstr€om M. Sensitivity of dentine. Oral Surg Oral Med Oral Pathol 1966;21: 517–26. 20. Matsumoto K, Funai H, Shirasuka T, Wakabayashi H. Effects of Nd:YAG laser in treatment of cervical hypersensitive dentine. J Jpn Conserv Dent 1985;28:760–5. 21. Absy EG, Addy M, Adams D. Dentin hypersensitivity: A study of the patency of dentinal tubules in sensitive and non-sensitive cervical dentin. J Clin Periodontol 1987;14: 280–4. 22. Harper PR, Midda M. Nd:YAG laser treatment for dentinal hypersensitivity. Br Dent J 1992;172:13–6. 23. Theodoro LH, Hypek P, Bachman L, Garcia VG, Sampaio J. Effect of Er:YAG and diode laser irradiation on the root surface: morphologic and thermal analysis. J Periodontol 2003;74:838–43. 24. Vieira AHM, Passos VF, Silva de Assis J, Mendonc¸a JS, Santiago SL. Clinical evaluation of a 3% potassium oxalate gel and a GaAlAs laser for the treatment of dentinal hypersensitivity. Photomed Laser Surg 2009;27:807–12.
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25. Moritz A, Schoop U, Goharkhay K, et al. Long-term effects of CO2 laser irradiation on treatment of hypersensitive dental necks: results of an in vivo study. J Clin Laser Med Surg 1998;16:211–5. 26. Liu HC, Lin CR. Sealing depth of Nd:YAG Laser on human dentin tubules. J Endod 1997;23:691–3. 27. Sgolastra F, Petrucci A, Gatto R, Monaco A. Effectiveness of laser in dentinal hypersensitivity treatment: a systematic review. J Endod 2011;37:297–303. 28. Orchardson R, Peacock JM, Whitters CJ. Effects of pulsed Nd:YAG laser radiation on action potential conduction in nerve fibers inside teeth in vitro. J Dent 1998;26: 421–6. 29. Birang R, Poursamimi J, Gutknecht N, Lampert F, Mir M. Comparative evaluation of the effects of Nd:YAG and Er:YAG laser in dentin hypersensitivity treatment. Lasers Med Sci 2007;22:21–4. 30. Lan WH, Liu HC, Lin CP. The combined occluding effect of sodium fluoride varnish and Nd: YAG laser irradiation on human dentinal tubules. J Endod 1999;25:424–6. 31. Cakar G, Kuru B, Ipci SD, Aksoy ZM, Okar I, Yilmaz S. Effect of Er:YAG and CO2 lasers with and without sodium fluoride gel on dentinal tubules: a scanning electron microscope examination. Photomed Laser Surg 2008;26:565–71. 32. White JM, C, Goodis H E, Kudler J. Laser thresholds in pulp exposure: a rat animal model. Proc SPIE (2394) 1995:160–9. http://dx.doi.org/10.1117/12.207437. €. Bioactive glasses. In: Hench LL, Wilson J, eds. An Introduc33. Hench LL, Andersson O tion to Bioceramics. Singapore: World Scientific; 1993:45–7. 34. Patsouri A, Mavrogiannea A, Pepelassi E, Gaitantzopoulou M, Kakampoura A. Effectiveness of a desensitizing on cervical sensitivity after periodontal treatment. Am J Dent 2011;24:85–92. 35. Bakry AS, Takahashi H, Otsuki M, Sadr A, Yamashita K, Tagami J. CO2 laser improves 45S5 bioglass interaction with dentin. J Dent Res 2011;90:246–50.
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In Vitro Evaluation of Dentin Tubule Occlusion by Denshield and Neodymium-doped Yttrium-Aluminum-Garnet Laser Irradiation Eleftherios-Terry R. Farmakis, DDS, MDSc, PhD,* Konstantinos Kozyrakis, DDS, PhD,* Marouan G. Khabbaz, DDS, PhD,* Ulrich Schoop, DMD, MD,† Franziska Beer, MD, DMD, DDS,† and Andreas Moritz, MD, MDM, PhD† Abstract Introduction: This in vitro study evaluated the efficacy of bioglass (Denshield; Novamin Technology, Alachua, FL) and Neodymium-doped yttriumaluminum-garnet (Nd:YAG) laser irradiation on dentinal tubuli orifice occlusion (DOO) by comparing samples examined under environmental scanning electron microscope (ESEM) after applying each desensitizing approach separately and in combination. Methods: Forty-eight human molars were collected, randomly organized in 4 equal groups, and had their cervical dentin exposed. Additionally, in half of the specimens of each experimental group, the smear layer was removed (subgroups A1, B1, C1, and D1). Group A received NovaMin paste treatment for 5 minutes (NM) to the experimental surface. Group B received Nd:YAG laser irradiation (0.5 w, 10 Hz, and 50 mJ) (L). Group C received NM followed by L. Group D was treated with L followed by NM. All specimens were stored for 24 hours and evaluated for DOO under ESEM by 4 blinded observers. Results: The presence of a smear layer significantly contributed to DOO regardless of the treatment modality (ordinal logistic regression, P < .001). Compared with group A, all other treatments delivered significantly more occluded dentin orifices (P < .001 for groups B and D and P < .05 for group C). A layer formation was observed in subgroups C2 and D2. Conclusions: Under these experimental conditions, a smear layer was essential for successful DOO. Laser irradiation alone and combined with NovaMin proved superior to NovaMin alone on DOO. This combined approach has the potential to improve the outcome of treatment for cervical dentin hypersensitivity. The biological significance of this newly formed layer needs to be elucidated. (J Endod 2012;38:662– 666)
Key Words Bioglass, cervical dentin hypersensitivity, dentin orifice occlusion, laser irradiation, Nd:YAG, NovaMin
C
ervical dentinal hypersensitivity (CDH) is a common problem that affects 8% to 30% of the adult population and 84% of patients who have undergone periodontal therapy (1). It is mainly localized on the buccal surfaces of canines and premolars. Among the factors that influence and increase CDH are gingival recession, brushing technique, and dental plaque. It is a frequent symptom of people working in industrial environments containing acidic gases. It also frequently affects bruxists because of the commonly found enamel cracks in cervical areas (2). Several theories have been proposed to explain this phenomenon such as the odontoblastic transduction theory (3, 4); the dentin innervation theory (5); and the Brannstrom hydrodynamic theory, which is most commonly accepted (6). It suggests that if thermal, chemical, or mechanical stimuli induce rapid displacement of the dentinal fluid, a shift of fluid in either direction could deform the odontoblast layer or stimulate A-delta nerve fibers, resulting in an immediate pain response. Some of the applied therapies to relieve CDH involve occlusion of the dentinal tubules, reduction of their diameter, stimulation of secondary dentin production, and/or desensitization of nerve fibers. In order to achieve the desired result, dentifrices or gels containing fluoride or other desensitizing agents (eg, KN03 [7], SnF2 [8], and oxalates [9]), formaldehyde (10), bonding agents (11), and laser irradiation (12) have all been applied (alone or combined) with variable results. Of those, sodium fluoride is widely used with predictable positive results in many cases (13). Additionally, iontophoresis has been shown to increase the uptake of fluoride (14). Recently, a new system has been introduced as a treatment for CDH (Denshield; Novamin Technology, Alachua, FL). NovaMin, the active ingredient in Denshield, is a bioactive glass that has been ground into a fine particulate with a median size of <20 mm and is composed of Ca, P, Na, Si, and O. When exposed to an aqueous environment, it releases Ca+2 and (PO4) 3 ions. A layer is formed through several reactions starting from nucleation sites and finally crystallizes into hydroxylcarbonate apatite, which is equivalent to hydroxyl-phosphate apatite in biological behavior (15, 16). The combination of the residual NovaMin particles and the hydroxyl-carbonate apatite layer results in the physical occlusion of dentinal tubules, which is claimed to relieve hypersensitivity. The aim of this study was to evaluate in vitro the efficacy of NovaMin and Nd:YAG laser irradiation in the presence and absence of a smear layer using environmental
From the *Department of Endodontics, Dental School, University of Athens, Athens, Greece; and †Department of Conservative Dentistry, Bernard Gottlieb Dental School, University of Vienna, Austria. Address requests for reprints to Dr Eleftherios-Terry R. Farmakis, 27 D. Gedeon Street, Peania 19002, Greece. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2012 American Association of Endodontists. doi:10.1016/j.joen.2012.01.019
662
Farmakis et al.
JOE — Volume 38, Number 5, May 2012
Basic Research—Technology scanning electron microscope (ESEM) to record the percentage of occluded dentinal tubuli orifices after applying each desensitizing approach (ie, NovaMin and Nd:YAG laser irradiation) separately and in combination as a potential treatment for CDH.
Materials and Methods Forty-eight sound, recently extracted human molars were collected. Any surrounding soft tissues were removed by immersion in 2.5% NaOCl solution for 10 minutes. The teeth were then stored in sterile saline (0.9% NaCl) until used. The buccal and lingual cervical enamel was removed with a diamond disc under tap water for cooling (Isomet 11-1180; Buehler Ltd, Evanston, IL), exposing the underlying dentin. On each tooth, the exposed buccal surface served as the experimental area, whereas the exposed lingual surface served as the control. Specimens were randomly organized into 4 equal groups (ie, groups A–D). All specimens had the smear layer removed by ultrasonication in deionized water for 30 seconds followed by an application of 0.5 mol/L EDTA (pH = 7.4) for 2 minutes. They were then rinsed with water spray for 30 seconds (17). This procedure was necessary to create patent tubules as observed in clinical cases of CDH. The surface of half of the specimens of each group (namely subgroups A2, B2, C2, and D2) were treated by 1 short passage of a medium blue polishing Sof-lex Disc (3M/ESPE Neodymium-doped Yttrium-Aluminum-Garnet, Seefeld, Germany) followed by a 1-minute water spray rinse to create an equal smear layer on all specimens. The null hypothesis would support that the smear layer has no influence on the outcome of any of the treatment modalities. The specimens were treated as follows. In group A, NovaMin paste was prepared according to manufacturer’s instructions and applied on the experimental surface for 5 minutes. In group B (as in all laserirradiated groups), the Nd:YAG laser was applied to the experimental surface under the following conditions: the laser handpiece was securely mounted on a stand so the optic fiber (0.3 mm in diameter) would vertically contact the experimental surface. The settings were
0.5 w, 10 Hz, and 50 mJ. Each section was mounted on a microscope observation glass slab and moved manually at a rate of approximately 5 mm/s in a sweeping motion, irradiating the total surface (18). The overall irradiation time was 30 seconds per sample. In group C, NovaMin paste was applied for 5 minutes followed by Nd:YAG laser irridiation as previously described. In group D, Nd:YAG laser was applied followed by NovaMin paste application for 5 minutes (as previously described). All specimens were stored in sterile saline (0.9 % NaCl) for 24 hours at room temperature and presented for examination under ESEM using 500 and 5000 magnification. Photographs were taken, and each specimen was evaluated for the percentage of occluded dentinal orifices. Scoring was categorized on a scale of 1 to 4 (1: 0%–24%, 2: 25%–49%, 3: 50%–74%, and 4: 75%–100%). There were 4 blinded evaluators. Three were required to be in agreement in order to record a score. Results were recorded and subjected to statistical analysis. Ordinal logistic regression was used because of the categoric and ordered nature of the outcome (orifice closure). The technique and the presence/absence of a smear layer were used as explanatory variables in a multivariable model. The odds ratios given in Figure 1 refer to the odds of higher orifice closure. When testing for techniques, comparisons were adjusted for the presence/absence of a smear layer. Conversely, when testing for the presence/absence of the smear layer, comparisons were adjusted for the technique used. The proportional odds assumption of the model was formally tested and was not rejected.
Results Results are shown in Figure 1, and representative photographs from each subgroup are shown in Figure 2. Statistical analysis revealed that the presence of a smear layer significantly contributed to dentinal orifice occlusion regardless of the treatment applied (P < .001). Compared with NovaMin application alone, all other treatments yielded significantly more occluded dentinal orifices (P < .001 for the lased-
Figure 1. The distribution of orifice closure by technique and the presence/absence of a smear layer. Odds ratios (P values) are derived from a multivariable ordinal logistic model and refer to the odds of higher orifice closure.
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Figure 2. Photographs of all experimental and control groups (500 magnification).
alone and lased-NovaMin groups and P < .05 for the NovaMin-lased group accordingly). Apart from the scoring, which reflected the occlusion of dentinal tubuli orifices, it should be noted that the surface of all specimens in subgroups C2 and D2 appeared to be covered by a granular layer, which is a finding unique to these 2 subgroups.
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Discussion CDH is a common problem among the adult population, especially after periodontal treatment. Normally, dentinal tubules occupy 20% to 30% of dentin volume, corresponding to 45.000/mm2 at the pulp, 29.500/mm2 in the middle, and 20.000/mm2 peripherically, with the JOE — Volume 38, Number 5, May 2012
Basic Research—Technology diameter of the tubules decreasing from 2.5 mm at the pulp to 0.9 mm peripherically, thus making dentin permeable (19). Permeability is reduced over time as the diameter of the tubules decreases because of mineralization (deposition of peritubular dentin). It is observed that in cases of dentin hypersensitivity, more dentinal tubules and tubules of greater diameter are observed compared with those of normal teeth (20). Treatment modalities aim at either partial or full occlusion of the exposed dentinal tubules or/and the desensitization of nerve fibers. Of all proposed treatments, none has been proven to be the ultimate or permanent cure. As early as 1985, laser irradiation had been applied for the treatment of dentin hypersensitivity (20–22). There are 2 categories of applications that have mainly been used: (1) low-power lasers (eg, diode [23] and Ga-Al-As [24]) and (2) medium-power devices (eg, CO2 [25] and Nd:YAG [22, 26]). For low-output power lasers (diode lasers [l = 80–900 nm] or He-Ne lasers [l = 632.8 nm]), the desensitizing effect seems to be related to laser activity at the nervous level (27). Only the Nd:YAG laser at 1,064 nm seems to have an additional analgesic effect, probably because the irradiation can temporally alter the ending of the sensory axons and block both C and Ab fibers (28, 29). Even more, Nd:YAG energy is not absorbed intensively by dentin and water because of its wavelength. Another possible mechanism of action is that Nd:YAG laser irradiation melts the superficial layer of dentin. When recrystallization occurs, it seals the dentin tubules in a depth of 3 to 4 mm without dentin surface cracking. This effect is pronounced when used along with a fluoridecontaining substance (30, 31). One in vitro study showed a durable 90% occlusion of the exposed dentinal tubules under scanning electron microscopic examination (30). During Nd:YAG laser irradiation of dentin, the thermal effects on the pulp are of concern. The thermal threshold for pulpal damage is generally not exceeded when the energy and power settings of the laser remain within the reported range (32). Apart from Nd:YAG, other types and wavelengths of laser irradiation have been used in vivo and in vitro with varying levels of success (30). Despite the aforementioned basic research evidence, a recent systematic review attempted to analyze all published randomized placebo-controlled clinical trials to assess evidence for the effectiveness and safety of laser dentinal hypersensitivity treatments. Sgolastra et al (27) investigated 18,661 potentially relevant titles and abstracts. Only 3 fulfilled the inclusive criteria, concluding that a placebo effect contributing to the therapeutic result has to be considered. A novel device for cervical dentin hypersensitivity is the application of bioactive glass (NovaMin). The suggested mechanism of action is the release of active Ca, P, and Na ions (along with small amounts of Si ions) when NovaMin is in an aqueous environment. The Ca and P ions are of the appropriate ionic form and relative ratios to immediately form hydroxy-carbon apatite on available nucleation surfaces. This apatite claims to be similar or identical to the endogenous tooth and bone substance (33). This formation is further aided by the release of Na ions, which created a more favorable pH environment, and by the presence of the Si ions, which have also been hypothesized to stimulate this formation. The manufacturer provides a 2-phase system (in office and at home). However, a recent study suggested that the at-home treatment is as drastic as the in-office and at-home treatment combined (34). The presence or absence of a smear layer seems to be a major influencing factor for effective tubular occlusion in this study. Although no literature was found to relate a smear layer to CDH, it should be expected that the smear layer may be acting as a multiple nucleation substrate, thus accelerating apatite formation. The combination of 2 desensitizing strategies was tempting, so we tried to document every potential therapeutic benefit in this study. JOE — Volume 38, Number 5, May 2012
Maybe the modified dentin surface as a result of the Nd:YAG laser application increases the adhesion of NovaMin (group D2). In the other treatment modality (C2), NovaMin may be incorporated within the dentin during the melting/recrystallization action of laser irradiation. A recent in vitro study showed that CO2 laser irradiation after bioglass application resulted in an increased dentin-bioglass interaction (35). Both treatment schemes (ie, NovaMin and then laser irradiation and laser irradiation and then NovaMin) produce a thick layer accompanied by a high percentage of closed tubules. It can be expected that if either (or both) of these layers is proved long lasting, it may work as a long-term device for the treatment of CDH. This layer may be seen as a lasting source of Ca, P, and Na ions, thus keeping the site stable. What needs to be further examined is whether this result is long lasting. A preliminary investigation proved these layers durable to storage for 6 months into sterile saline (0.9% NaCl) followed by 10 minutes of ultrasonic bathing. Another area for further investigation might involve assessing the penetration depth of the bioglass particles inside the dentin tubuli as well as determining the chemical composition of the created ‘‘plugs.’’
Conclusions Under these experimental conditions and within the limitations of this study, it was concluded that the presence of a smear layer is essential for successful dentinal tubule occlusion regardless of the applied modality. Additionally, the combination of the Nd:YAG laser and NovaMin applied either way in the presence of a smear layer, both occludes the tubules and is capable of forming a layer of uncertain biological significance.
Acknowledgments The authors thank Dr Nikos Pantazis, Athens University Medical School, Greece, for performing the statistical analysis and Dr H. Lee Adamo, New York, New York, for his valuable contributions in the editorial revision of this manuscript. The authors deny any conflicts of interest related to this study.
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