d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 600–607 available at www.sciencedirect.com journal homepage: www.intl.elsevierhealth.com/journals/dema Effect of a new desensitizing material on human dentin permeability夽 Richard P. Rusin a,∗ , Kelli Agee b , Michael Suchko b , David H. Pashley b a b 3M ESPE Dental Products, Saint Paul, MN, USA Medical College of Georgia, Augusta, GA, USA a r t i c l e i n f o a b s t r a c t Article history: Objectives. Resin-modified glass ionomers (RMGI) have demonstrated clinical success pro- Received 12 July 2009 viding immediate and long-term relief from root sensitivity. RMGIs have been recently Received in revised form introduced as paste-liquid systems for convenience of clinical usage. The objective of this 5 November 2009 study was to measure the ability of a new paste-liquid RMGI to reduce fluid flow through Accepted 23 February 2010 human dentin, compared to an established single-bottle nanofilled total etch resin adhesive indicated for root desensitization. Methods. Dentin permeability was measured on human crown sections on etched dentin, Keywords: presenting a model for the exposed tubules typical of root sensitivity, and permitting mea- Dentin sensitivity surement of the maximum permeability. In the first two groups, the etched dentin was Dentin permeability coated with either the RMGI or adhesive, and permeability measured on the coated dentin. Glass ionomer In a third group, a smear layer was created on the dentin with sandpaper, then the speci- Hybrid layer mens were coated with the RMGI; permeability was measured on the smeared and coated Resin tag dentin. Specimens from each group were sectioned and examined via scanning electron microscopy (SEM). Results. Both the resin adhesive and the new paste-liquid RMGI protective material significantly reduced fluid flow through dentin, and exhibited excellent seal on dentin with either open tubules or smear-layer occluded tubules. The RMGI infiltrated the smear layer with resin during placement, penetrated dentin tubules, and formed resin tags. Significance. The RMGI was equivalent to the adhesive in its ability to reduce fluid flow and seal dentin. It is therefore concluded that the new RMGI and the adhesive show the potential to offer excellent sensitivity relief on exposed root dentin. © 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. 1. Introduction Dentin sensitivity from exposed roots afflicts many people [1–4]. As the gingiva recedes, the cementum initially covers and protects the tubules, but is gradually removed by toothbrushing, acid erosion, etc., leaving tubules open and exposed. Because these fluid-filled tubules are in direct contact with pulpal nerve endings, exogenous stimuli are quickly transmitted and nerve depolarization occurs, leading to the sensation of sharp, well-localized pain [5,6]. This phenomenon is referred to as hydrodynamic conductance or the hydrody- Portions of this study were presented at the AADR meeting, April 2–5, 2008, Dallas, and at the IADR meeting, July 2–5, 2008, Toronto. Corresponding author at: 3M ESPE Dental Products Laboratory, 3M Center 260-5S-12, Maplewood, MN 55144, USA. Tel.: +1 651 733 0127; fax: +1 651 575 0692. E-mail address: rprusin@mmm.com (R.P. Rusin). 0109-5641/$ – see front matter © 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2010.02.010 夽 ∗ d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 600–607 namic theory. The theory was first reported by Gysi in 1900 [7], studied heavily and corroborated in the 1950s and 1960s by Bränström [8,9] and remains the most widely accepted theory of tooth sensitivity to date [10,11]. Occluding or sealing the exposed dentin tubules provides relief from root sensitivity [11,12] by preventing intratubular fluid shifts. There are a variety of strategies for this, including via precipitation of poorly soluble salts, or plasma proteins within dentinal fluid, and coating and sealing with either rosins or polymerizable materials [13]. Glass ionomers have demonstrated clinical success providing immediate and longterm relief from root sensitivity [14–16]; in addition, they offer protection of the adjacent tooth structure [17–23] and fluoride release [24,25]. To date, however, the clinical use of glass ionomers for root desensitization has been limited, perhaps because the prevalent powder-liquid format is less convenient than alternative liquid materials. The recent availability of glass ionomer materials in paste-liquid or paste–paste formats might encourage the wider use of these materials; however, little information is available in the literature regarding their performance. The objective of this study was to measure the ability of a new paste-liquid resin-modified glass ionomer (3MTM ESPETM VanishTM XT Extended Contact Varnish, VXT) to reduce fluid flow through exposed human dentin, compared to an established resin adhesive (3MTM ESPETM AdperTM Single Bond Plus Dental Adhesive, SBP). VXT and SBP are both indicated for the treatment of root sensitivity. SBP is a single-bottle total etch resin adhesive with a silica nanofiller. VXT is based on the methacrylate-modified polyalkenoic acid technology first commercialized in 3MTM ESPETM VitrebondTM Glass Ionomer Liner/Base, as well as other 3M ESPE dental materials; it is applied directly to dentin without etching or surface conditioning in a thin layer (up to approximately 0.5 mm). The liquid component consists of methacrylatemodified polyalkenoic, 2-hydroxyethylmethacrylate (HEMA), water, initiators (including camphorquinone), and calcium glycerophosphate. The paste is a combination of HEMA, 2,2bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane, water, initiators and fluoroaluminosilicate glass. Calcium glycerophosphate, whose benefit in oral care has been demonstrated [26–30], was also added to provide bioavailable calcium and phosphate to the oral cavity [23]. The direct measurement of fluid flow through dentin, or dentin permeability, has been used to evaluate desensitization materials [31–33], and has been correlated with various stimuli that induce pain in root dentin [34]. While post-treatment reduction of dentin permeability compared to pre-treatment is accepted as a good measure of the ability of a material to occlude tubules [13,35,36], and the incidence of pain with respect to dentinal fluid flow has been investigated [37], the precise correlation between permeability reduction and desensitization is not established [11]. In these models, open tubules obtained by etching or polishing the dentin surface represent one extreme of the clinical condition where the cementum layer has been completely removed by, for example, acid erosion, abrasion from toothbrushing or food, while dentin with an abrasive-applied smear layer represents the condition where only partially exposed tubules exist, such as in the early stages of root exposure. In this study, the perme- 601 ability reduction was measured for VXT applied to phosphoric acid-etched dentin, and for dentin covered with an abrasivecreated smear layer, in order to characterize its behavior on each of these surfaces; for comparison, permeability reduction was also measured for SBP. 2. Materials and methods 2.1. Tooth preparation Unerupted, unidentifiable extracted human third molars were screened to determine if they were permeable enough to be used in this study. The teeth were mounted enamel side down on cylindrical aluminum stubs using extra fast set epoxy cement (Hardman, Belleville, NJ, USA). Two sections were made using a slow-speed diamond saw under water lubrication (Isomet: Buehler Ltd., Lake Bluff, IL, USA). The first section, made 90◦ to the long axis of the tooth, removed the roots approximately 3 mm below the cementum–enamel junction. The second section, made in the same plane, was made 2–3 mm below the deepest occlusal pit or central groove to expose middle to deep coronal dentin. This removed all occlusal enamel and superficial dentin, creating a crown segment with a remaining dentin thickness between the highest pulp horn and the exposed dentin surface of between 0.6 and 1.2 mm, as measured with a digital pincer micrometer (Renfert GmbH, Hilzingen, Germany). This dentin thickness is permeable enough for screening desensitizing agents via this in vitro model [31,38]. The pulpal soft tissue was removed taking care not to touch the soft surface lining of the pulp chamber. The crown segment was then mounted to 2 cm × 2 cm × 0.5 cm squares of acrylic with a viscous cyanoacrylate adhesive (ZapitTM Glue, Dental Ventures of American, Corona, CA, USA). The center of the acrylic square was penetrated by a 1.5 cm length of 18 gauge stainless tubing, permitting the pulp chamber to be filled with fluid. A 0.02% sodium azide aqueous solution was used as the liquid medium to prevent microbial growth. All air bubbles were removed from the pulp chamber using a 23 gauge needle and syringe filled with the azide solution. 2.2. Fluid flow (permeability) measurements The rate of fluid flow through a dentin specimen was measured using the Flodec device (DeMarco Engineering, Geneva, Switzerland) illustrated in Fig. 1, which follows the movement of a tiny air bubble as it passes down a 0.6 mm diameter glass capillary located between a water reservoir under 140 cm (2 psi) of water pressure and the dentin specimens [31]. An infrared light source passes through the capillary and is detected by a diode, allowing the unit to follow the progress of the air bubble along the length of the capillary. Linear displacement is automatically converted to volume displacement per unit time, from which the instantaneous volumetric flow rate is calculated and logged into a spreadsheet. Flow was measured until a steady-state was reached, typically 0–3 min; then the flow was measured for at least 2 min; since one datum was taken every second, this resulted in at least 100 readings for 602 d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 600–607 Fig. 1 – Schematic of permeability measurement system. each condition. Permeability was expressed as a fluid flow rate in ␮L min−1 . All teeth were acid-etched with 37% phosphoric acid for 30 s to ensure maximum permeability was achieved for each specimen. Following etching, dentin permeability was determined. After measuring the baseline permeability of all specimens, they were placed into three groups so that the mean permeability values were not statistically significantly different. During the investigation, some failures of the glue or of the dentin at thin pulp horns resulted in loss of specimens and thus in slightly different numbers of specimens among the groups; the final groups were still found to be balanced with respect to post-acid-etch (baseline) permeability. 2.3. Application of coating materials Two materials were used in this study: a one-bottle, total etch adhesive with stabilized silica nanofiller, and a resin-modified glass ionomer coating material; lot and expiration date information are shown in Table 1. In group SBP-OPN, SBP was applied per manufacturer’s instructions to 11 acid-etched crown segments with open (OPN) tubules that had been measured for acid-etched (baseline) permeability. Two layers of SBP were applied in rapid succession to visibly moist dentin; after each layer the solvent was evaporated with an air stream for 5–10 s. The adhesive was light-cured for 20 s with a dental curing light (VIPTM Variable Intensity Polymerizer, Bisco Dental Products Co., Schaumburg, IL, USA). The oxygen-inhibited layer was removed with a KimwipeTM tissue (Fisher Scientific) saturated with 100% ethanol. After 10 min in air, the treated crown segment was inverted into a small beaker half-filled with 0.02% sodium azide aqueous solution to prevent evaporative water loss [38] from the dentin and to hydrate the dentin and adhesive; permeability was then measured again. In group VXT-OPN, material VXT was mixed according to the manufacturer’s instructions, then applied to 11 blotdried, moist dentin specimens that had been acid-etched with open (OPN) tubules as in the SBP treatment. After spreading the material in a thin layer, it was light-cured for 20 s. The cured VXT was kept hydrated via immersion at all times. Ten minutes after light-curing, permeability was measured in the same manner as group SBP-OPN. In group VXT-SMR, a thin smear (SMR) layer was created after acid-etch (baseline) permeability measurements were made. The smear layer was created by lapping the etched dentin surface with three manual strokes on wet 400 grit silicon carbide abrasive paper. After measuring permeability through the smear-layer dentin, thereby confirming the presence of a smear layer (via decreased permeability), VXT was applied to the smear layer-covered dentin of 7 specimens as described above; the cured VXT was kept hydrated at all times. Again, 10 min after light-curing, permeability of the coated tooth specimens was measured. Permeability reduction and residual permeability were calculated as a percent of the maximum (i.e. acid-etched) of each crown segment; for group VXT-SMR, permeability reduction and residual permeability were also calculated as a percent of the smear layer-covered value. Thus, each tooth served as its own control. 2.4. Scanning electron microscopy (SEM) After completing the permeability measurements, a composite build-up (FiltekTM Z100 Restorative: 3M ESPE, Maplewood, Table 1 – Materials investigated. Manufacturer 3MTM ESPETM 3MTM ESPETM Product AdperTM Single Bond Plus Dental Adhesive VanishTM XT Extended Contact Varnish Code SBP VXT Lot 289118 (EXM-713) paste A: Lot 142/B2 liquid B: Lot 144/B1 Expiration 2009-04 May-09 603 d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 600–607 Table 2 – Average permeability, average percent reduction in permeability, and average percent residual permeability (standard deviation). Within each column, groups with the same letter superscript are not statistically different. Group n SBP-OPN VXT-OPN VXT-SMR 11 11 7 Permeability of etched dentin, ␮l/min (S.D.) 13.85 (5.64)a 12.08 (6.13)a 14.67 (13.13)a Permeability of smeared dentin, ␮l/min (S.D.) n/a n/a 3.67 (2.44) MN, USA) was placed and light-cured over the coating on three teeth from each group in order to minimize the effects of dehydration. The specimens were then divided longitudinally via cryofracturing into equal halves. The fractured surfaces were acid-etched with 37% phosphoric acid for 5 s to remove any smear layer created by cryofracturing, and then treated with 5% NaOCl for 2 min to remove any uninfiltrated dentin matrix. All specimens were rinsed extensively in water prior to processing through an ascending alcohol series and critical-point drying [39,40]. Each half was sputter coated with gold and examined by SEM. 3. Results The percent reduction in permeability afforded by the coating materials was calculated for each specimen by comparing the post-coating permeability to the acid-etch (baseline) permeability. For the specimens in group VXT-SMR, the percent reduction was also calculated by comparing the post-smearlayer permeability to the acid-etch (baseline permeability) and by comparing post-coating permeability to the post-smearlayer permeability. The average permeability reduction for each treatment group was calculated from the individual values. These results are shown in Table 2. Levene’s test of equal variances showed that the variances were not statistically significantly different in etched permeability (p = 0.155), coated permeability (p = 0.210), and percent reduction in permeability at the coated stage (p = 0.169). The data were analyzed via one-way ANOVA and compared with Tukey’s t-test (p < 0.05). The mean permeability values of the three groups were not statistically different at the acidetched (baseline) stage (p = 0.784), confirming that the etched specimens were sorted into balanced groups. In all of the treatment groups, the mean permeability values after the coatings were applied were statistically significantly lower than mean permeability values observed for the acid-etched (baseline) surface. The mean permeability values after the coatings were applied and the percent reduction in permeability from the etched to coated conditions were not statistically different among the three groups (p = 0.223 and p = 0.218, respectively); the percent reduction in permeability from the etched to coated stages was 93.3 ± 8.0%, 87.9 ± 13.9%, and 96.5 ± 6.0% for the SBP-OPN, VXT-OPN, and VXT-SMR groups, respectively. The percent reduction in permeability for VXT applied to smeared dentin (group VXT-SMR, calculated between the smear and coated conditions) was not statistically different from VXT applied directly to etched dentin (group VBPOPN) (p = 0.787); both were not statistically different from SBP applied to etched dentin (group SBP-OPN) (p = 0.567). Permeability of coated dentin, ␮l/min (S.D.) 0.93 (1.30)a 1.27 (1.38)a 0.25 (0.32)a Permeability reduction of coated vs. etched, % (S.D.) 93.3 (8.0)a 87.9 (13.9)a 96.5 (6.0)a Permeability reduction of coated vs. smear, % (S.D.) n/a n/a 87.9 (13.6) In the SEM image of an SBP-OPN specimen in Fig. 2, the bottom two-thirds of the hybrid layer are empty. The presence of resin tags penetrating from the overlying adhesive into the open tubules of the underlying dentin demonstrated that the resin had penetrated the 5 ␮m deep demineralized dentin; some tags fell out of several tubules when the specimens were cryofractured. The adhesive (A) above the hybrid layer, and the resin tags seemed to resist the action of NaOCl; the 5 ␮m wide gap between the bottom of the adhesive and the dentin (D) is due to the NaOCl treatment removing all collagen exposed by the original phosphoric acid-etching and any acid-etched dentin matrix that was not well-infiltrated by SBP. The open arrowhead in the adhesive layer identifies what appears to be a liquid droplet phase change. The top of the hybrid layer (H) seems to have resisted the action of NaOCl. The SEM image in Fig. 3a shows the bonded interface between VXT and acid-etched dentin (group VXT-OPN). Some large (approximately 20 ␮m diameter) filler particles are seen (E) in addition to the more numerous 1–10 ␮m particles. In this particular specimen there was no apparent hybrid layer remaining after challenging the interface with acid and base. The gap (20–30 ␮m wide) between the VXT and the underlying mineralized dentin (D) appears to be real because there is no evidence of material in the depth of the gap. In Fig. 3b, another group VXT-OPN specimen shown at a relatively high magnification exhibits an interfacial zone that was filler-poor and resin-rich (RZ) between the VXT and dentin. Below that resin layer was a resin-infiltrated hybrid layer (H) cut tangentially rather than in cross-section, allow- Fig. 2 – SEM of SBP-OPN specimen. (A) Bottom of the adhesive; (D) underlying mineralized dentin; (H) top of the hybrid layer; (T) resin tags of adhesive that passed through the hybrid layer; the arrowhead points to what appears to be a liquid droplet phase within the polymerized adhesives. 604 d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 600–607 Fig. 3 – SEMs of group VXT-OPN specimens. (a) (E) large (approximately 20 ␮m diameter) filler particles; (D) underlying mineralized dentin; the black zone represents a gap between the underlying dentin and the overlying material where the acid-etched, demineralized dentin matrix was solubilized by NaOCl treatment. (b) (RZ) filler-free, resin-rich zone between the VXT and acid-etched dentin; (H) hybrid layer that is apparently 10–15 ␮m thick penetrated by resin tags (open arrow heads); (E) VXT. ing visualization of resin tags (open arrow heads) that passed through the hybrid layer but were cut-off during preparation of the specimen; the resin tags appear to be passing through the hybrid layer at about a 45◦ angle. Although the hybrid layer appears to be 10–15 ␮m thick in some areas, it was probably thinner in perpendicular cross-section. H is a true hybrid layer because it resisted phosphoric acid/NaOCl challenge. The SEM image in Fig. 4a shows VXT applied to smear layer-covered dentin (group VXT-SMR). There is evidence of residual smear layer beneath the VXT (E) at the extreme left and right of the image (see open arrow heads). The thickness of the smear layer on the right appears to be thinner than that on the left (open arrowhead), indicating that the smear layer on the left curled upward during specimen preparation. Note the appearance of the smear layer, about 0.5 ␮m thick, on top of the mineralized dentin (D) on the right. The fact that the smear layer is present indicates that they were made chemically resistant by resin-infiltration. Fig. 4 – SEMs of a group VXT-SMR specimens. (a) (E) VXT, (D) dentin, open arrow heads point to resin-infiltrated smear layer. (b) (S) smear layer; (D) dentin; (*) the smear layer curled away from the underlying dentin; (pointers) indicate the presence of smear plugs that pulled out of tubules when the smear layer separated from the dentin. Fig. 4b shows another VXT-SMR specimen at higher magnification. The resin-infiltrated smear layer appears to be 6–8 ␮m thick but was probably only 0.5 ␮m thick as was shown in Fig. 4a. However, the entire smear layer appears to have curled away from the underlying mineralized dentin. Note the presence of a few smear plugs that pulled out of tubules (pointers) when the smear layer peeled away; this indicates that the smear layer and the smear plug is resin-infiltrated. This may have given them enough cohesion to remain attached to the overlying smear layer when it separated from the dentin in response to shrinkage forces that developed during specimen processing. The presence of a large clump of debris below the asterisk, between the smear layer and the dentin, is probably contaminating grinding debris. The VXT is not evident in this SEM; it had separated from the smear layer and was out of the field of this image. 4. Discussion These permeability results indicate that there were no statistically significant differences in the ability of SBP or VXT to d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 600–607 seal dentin; and, that VXT is capable of sealing dentin with open tubules or smear layer-covered dentin. Both conditions are common among patients with dentinal hypersensitivity. Permeability reduction results previously reported for dental adhesives (42 values) range from 16% to 98%, with about half the values in the range 60–90% [41–51]. The value of 93.3% obtained for the 5th generation adhesive SBP in the present study is consistent with published results; the values for both SBP and VXT in the present study reside within the top quartile of the range reported for dental adhesives of various types. Permeability reduction results previously reported for glass ionomer materials range from 73.8% to 93.1% [41,52,53]. The values obtained for the RMGI material VXT in the present study fall within this range. Many materials used for chairside treatment of root sensitivity are designed to occlude exposed dentin tubules via precipitation or complexation [54,55], for example, glutaraldehyde-based solutions, oxalate solutions, or calcium phosphate salt solutions; other materials penetrate the tubules, coating and sealing them, for example, dental adhesives or rosin varnishes [13,33]. Permeability reduction results previously reported for glutaraldehyde-based solutions are 28.0%, 39.8%, 62.0% [32,33,56]; for oxalate-based solutions, 46% and 97.5% [33,56]; for rosin-based varnishes, 2.2%, 60.0%, 67.0% [57,58]. The wide range of permeability reduction reported for various classes of materials reflects not only intrinsic material performance, but also differences in experimental design and execution. Nevertheless, this survey of published literature confirms that products indicated for root desensitization demonstrate permeability reduction in this model. While drawing correlations between permeability and clinical data is beyond the scope of this study, it is likely that higher degrees of permeability reduction are associated with greater levels of tubule sealing and sensitivity relief [31,32,34,59]. The permeability reduction and low residual permeability observed for VXT in the present study, therefore, demonstrates a strong potential for this coating material to reduce dentinal hypersensitivity. Previous research has indicated that RMGI materials can create hybrid layers and resin tags. One of the first such studies [60] clearly showed that light-cured RMGIs penetrated acidetched dentin. Titley et al. [61] showed resin tags in open tubules with the liquid component of an RMGI (3MTM ESPETM VitrebondTM Light Cure Glass Ionomer). A high resolution SEM study by Carvalho et al. [62] revealed a hybrid layer about 3.0 ␮m thick when an RMGI (CaulkTM VariGlass VLC Glass Ionomer) was applied to dentin etched with 10% maleic acid for 15 s prior to bonding. This hybrid layer resisted 6N HCl etching for 30 s. The microscopic Raman spectroscopy work of Spencer and Wang [63] and Wang et al. [64–66] indicates that polyalkenoic acid cannot penetrate into the hybrid layer, while bisGMA can only enter the top third of the hybrid layer. Their work suggests that HEMA easily penetrates the bottom two-thirds of the hybrid layer; however, the HEMA may react with water in the hybrid layer to form an elastomeric hydrogel around collagen fibrils that cannot resist the action of NaOCl. Since the VXT resin comprises HEMA and polyalkenoic acid, it is likely that HEMA-penetrated collagen was dissolved by the NaOCl, similar to that observed in the SBP specimen. In this study, etching with phosphoric acid partially dissolved the 605 dentin, enhancing its ability to be penetrated by resin. The VXT instructions do not include an etching step for dentin; while it is plausible that acidic beverages and foods might have a similar effect over time, the clinical presence of a hybrid layer cannot be assumed. The hybrid layers and resin tags observed with VXT in the present study are similar to those observed in prior studies, and contribute to micromechanical bonding at the interface between VXT and the tooth. Chemical bonding is also a significant factor in the sealing ability of the RMGI material VXT to dentin. The VXT composition is based on the same RMGI chemistry as the VitrebondTM and VitremerTM families of products, which include a methacrylate-modified copolyalkenoic acid molecule that participates in both the ionomeric reaction and the visible light-activated methacrylate curing. Fourier-transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) data show that the carboxyl groups in this molecule form ionic carboxylate bonds to the calcium in hydroxyapatite, the mineral component of dentin [67]. Indeed, it is this chemical bonding in part that allows VXT to be used as a self-adhesive material on dentin. The robustness of the VXT seal to both open tubule or smear layer-covered dentin means it should work well in a range of clinical situations. Resin-modified glass ionomers are well known for their ability to reduce or eliminate sensitivity in dental restorations [68], and have demonstrated clinical success for treating root hypersensitivity [14–16]. VXT is similar in composition to the EXM-609 material that demonstrated excellent clinical results in the study by Tantbirojn et al.; they observed approximately 90% coating retention (none or minor material loss) at 6 mo, and average VAS (visual analog scale) scores for tactile and cold painful stimulation at 6 mo that were not different from those collected immediately post-placement. Since VXT has demonstrated strength and fluoride release comparable to other low-viscosity RMGI materials [23,69], and excellent bonding and sealing ability in this study, the present results support the prediction that VXT and SBP show the potential to offer excellent sensitivity relief on exposed root dentin. 5. Conclusions The new paste-liquid RMGI protective material, VXT, significantly reduced fluid flow through dentin, and exhibited excellent seal on dentin with either open tubules from etching, or with smear layer partially occluded tubules. 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