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Am J Dent. Author manuscript; available in PMC 2016 July 13. Published in final edited form as: Am J Dent. 2015 December ; 28(6): 321–332.

Adhesive sealing of dentin surfaces in vitro: A review Manar M Abu-Nawareg, BDS, MSc, PhD1,2, Ahmed Z Zidan, BDS, MSc, PhD3,4, Jianfeng Zhou, DDS, PHD5, Kelli Agee, BS7, Ayaka Chiba, BDS6, Jungi Tagami, DDS, PhD6, and David H Pashley, DMD, PhD7 1Department

of Restorative Dentistry, Biomaterials Division, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia

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2Biomaterials

Department, Faculty of Oral and Dental Medicine, Cairo University, Egypt

3Department

of Restorative Dentistry, Biomaterials Division, Faculty of Dentistry, Umm Al-Qura University, Mekkah, Saudi Arabia

4Biomaterials

Department, Faculty of Dentistry, University of Modern Sciences and Arts, Egypt

5Department

of Prosthodontics, Peking University School and Hospital of Stomatology, Beijing,

P.R. of China 6Department

of Cariology and Operative Dentistry, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan

7Department

of Oral Biology, Georgia Regents University, College of Dental Medicine, Augusta,

GA, USA

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Abstract Purpose—The purpose of this review is to describe the evolution of the use of dental adhesives to form a tight seal of freshly prepared dentin to protect the pulp from bacterial products, during the time between crown preparation and final cementum of full crowns. The evolution of these “immediate dentin sealants” follows the evolution of dental adhesives, in general. That is, they began with multiple-step, etch-and-rinse adhesives, and then switched to the use of simplified adhesives. Methods—Literature was reviewed for evidence that bacteria or bacterial products diffusing across dentin can irritate pulpal tissues before and after smear layer removal. Smear layers can be solubilized by plaque organisms within 7–10 days if they are directly exposed to oral fluids. It is

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a3M ESPE, St. Paul, MN, USA bKerr, Orange, CA, USA cKuraray America Inc., New York, NY, USA ddG-C Corp., Tokyo, Japan eIvoclar Vivadent, Schaan, Liechtenstein CORRESPONDING AUTHOR: David H. Pashley, DMD, PhD, Department of Oral Biology, College of Dental Medicine, Georgia Regents University, Augusta, GA, 30912, Tel: 706-721-2031; [email protected]. Disclosure Statement: Drs. Abu Nawareg, Zidan, Zhou, Chiba, Tagami and Pashley have no commercial interest in any of the products used in this study. None of the authors claim any conflict of interest.

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likely that smear layers covered by temporary restorations may last more than one month. As long as smear layers remain in place, they can partially seal dentin. Thus, many in vitro studies evaluating the sealing ability of adhesive resins use smear layer-covered dentin as a reference condition. Surprisingly, many adhesives do not seal dentin as well as do smear layers. Results—Both in vitro and in vivo studies show that resin-covered dentin allows dentinal fluid to cross polymerized resins. The use of simplified single bottle adhesives to seal dentin was a step backwards. Currently, most authorities use either 3-step adhesives such as Scotchbond MultiPurposea or OptiBond FLb or two-step self-etching primer adhesives, such as Clearfil SEc, Unifil Bondd or AdheSEe, respectfully.

Introduction Author Manuscript

When indirect restorations are used to restore function, dentists must seal the exposed dentin with temporary materials during the interval required to fabricate and cement the final restoration. Full crown preparations expose up to 1 cm2 of dentin that contains more than 3 million tubules/cm2.1 Such tubules represent millions of microscopic “pathways to the pulp” because they all terminate in the tooth pulp. Both enamel and cementum are impermeable and nerve-free. These peripheral seals have very low permeabilities. However, once these surface sealing hard tissues are removed from dentin surfaces, the exposed dentin becomes highly permeable and very sensitive to hydrodynamic stimuli2. Because dentinal tubules contain collagen fibrils/fibers, constrictions etc. their functional diameter (0.1 µm) is far smaller than their 1.0 µm anatomical diameter3. This allows dentin to function like a 0.1 µm Millipore filter to prevent bacteria from invading the pulp via dentinal tubules. However, soluble bacterial products can permeate through dentin to the pulp where they provoke immunological reactions and pulpal inflammation that threaten pulpal health4–6.

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Prevention of pulpal inflammation Current prosthodontists recommend conservative tooth preparations using copious air-water spray and intermittent cutting. This is followed by temporizing the preparations using a variety of temporary filling materials and crown formers as long as there are no pre-existing signs of pulp pathology. The rationale is that a healthy pulpodentin complex reacts to tooth preparation by the deposition of tertiary dentin under those tubules that were cut during cavity preparation that should wall off the prepared dentin and prevent bacterial invasion7.

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On the other hand, old teeth have smaller pulps with fewer mesenchymal cells, and a poorer blood supply8. Tertiary dentin requires more than 30 days to begin to form and that dentin will not form if the pulp under the cut tubules produces an inflammatory response7. Old pulps contain pulp stones that interfere with endodontic treatment. If a temporary crown is lost and the cut dentin is exposed, bacterial products will begin to diffuse down the tubules toward the pulp. Pulpal cells will react to these bacterial antigens as if actual bacteria were invading the pulp. This will trigger neurogenic inflammation in the pulp leading to pulpal symptoms9,10. Those that advocate immediate dentin sealing (IDS) of freshly prepared dentin seek to protect the pulp from bacteria and bacterial products, using adhesive resins11–24. These

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resins should prevent dentinal fluid from permeating from inside dentin, through polymerized resin to the surface. The resins should also prevent the inward diffusion of bacterial products through the polymerized resin. This involves acid-etching dentin with 37% phosphoric acid for 15 sec when using etch-and-rinse adhesives. When using selfetching adhesives, the two-bottle primer adhesives are preferred over single-bottle systems because the acidic primer is covered with a solvent-free adhesive, rich in dimethacrylates that create stronger resin films than monomethacrylates. Thicker resin seals are better than thinner coatings, because they are less likely to be lacerated by multiple setting of crowns during their final adjustments.

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Combinations of resin adhesives covered by flowable composites provide tougher IDS than resin films alone. Optibond FLb is an example of a 3-step, etch-and-rinse adhesive that uses an adhesive that contains 48% fumed SiO2 and barium aluminoborosilicate Na2SiF625. Scotchbond Multi-Purposea adhesive contains few fillers and is often covered with a flowable composite to make the IDS stronger. The final adhesive material is covered with glycerin gel before polymerization to prevent the formation of an oxygen-inhibited layer. Such a layer of unpolymerized comonomers interferes with polymerization of impression material26.

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Advantages of IDS include eliminating post-cementation sensitivity27, eliminating the potential risk of bacterial leakage and pulpal irritation. Local anesthesia is often not required for try-ins and occlusal adjustments. IDS should be considered for any patients at increased risk of pulpitis due to immunosuppression, aged pulps, previous history of tooth sensitivity, patients taking bisphosphonates, etc. who are at risk of developing bisphosphonate-induced osteonecrosis of the jaw28. If such patients require root canal therapy and the roots are perforated during RCT, such extraction sites fail to heal properly. Abutment teeth in such patients should receive IDS as a precautionary measure. The influence of the thickness of IDS materials has also been reported29. That group found that thicker adhesives increased fracture resistance of IDS Empress 2 ceramic crowns. The purpose of this review was to follow the evolution of the use of dental adhesives to create an immediate dentin seal to protect the pulpodentin complex from inflammatory insults, in vitro. This review will begin with etch-and-rinse adhesives, followed by selfetching primer/adhesives and finally single-bottle, simplified self-etching adhesives.

Historical review Author Manuscript

The work of Bergenholtz4,5 showed that bacterial products could diffuse across freshly prepared dentin to induce pulpal inflammation. This lead Pashley et al. in 1992 to propose sealing freshly prepared dentin with adhesive resins11. This was endorsed by Davidson’s group in 199612, Paul and Schaerer 199713, and Özturk et al.14. Prof. Tagami advocated “resin coating” of freshly cut dentin to prevent pulpal irritation15–17, and to increase adhesion to dentin. Others have also stressed the importance of resin sealing18–24. In their bKerr, Orange, CA, USA a3M ESPE, St. Paul, MN, USA

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1992 paper, Pashley et al.,11, the authors mounted the crowns of extracted human third molars on plexiglass blocks and prepared full crown preparations (Fig. 1). They measured dentin permeability as a hydraulic conductance before and after sealing the preparations with Prisma Univeral Bond 2f, Scotchbond 2a, Superbond C&Bg, Amalgambondh, Gluma Bondi or Clearfil Photobondc. All adhesives reduced dentin permeability in vitro by at least 50%, with Prisma Universal Bond 2f sealing the best followed by Superbond C&Bg, Amalgambondh and Scotchbond 2a. The worst seals were produced by Gluma Bondi. Bonds made with Scotchbond 2a and Clearfil Photobondc gave excellent initial seals, but began to leak after thermocycling the bonded dentin.

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Bouillaguet et al.20 used extracted human third molar crowns flattened on the occlusal surface and glued to a plexiglass base penetrated by 18 ga. stainless steel tubing to permit measurement of dentin permeability. They measured the hydraulic conductance of acidetched dentin before and after bonding with Scotchbond Multi-Purposea, Prime & Bond 2.0f or All-Bond 2j (Table 1). All of these etch-and-rinse adhesives reduced dentin permeability by 83%, 90% or 96.6%, respectively. Unfortunately, the authors only measured the initial reduction in permeability. When Gregorie et al.30 evaluated the sealing ability of Optibond Solo Plusb, Single Bonda, Excitee and Prime & Bond NTf, all these etch-and-rinse adhesives only reduced dentin permeability to a residual value of 40%, while the self-etching adhesives Clearfil SE Bondc, and Prompt-L Popa only reduced dentin permeability down to a residual value of 36 and 16%, respectively (Table 2). They also only measured initial permeability. Better initial permeability results were reported when Vaysman et al.31 using Clearfil SE Bondc and Optibond Solo Plusf to seal acid-etched dentin. Both adhesives sealed dentin 80–95%. All of the above authors remarked that no dental adhesive reduced dentin permeability 100%.

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Elgalaid et al.32 were the third group to attempt to seal full crown preparations with Prime & Bond NTf or leave them covered with a smear layer as controls. They were surprised to discover that smear layers sealed dentin as well as the adhesive, but that either approach only reduced dentin permeability by 55–64% for up to 3 weeks (the longest time studied). Unfortunately, smear layers are very acid-labile and can solubilize in as little as one week when exposed33. Carrilho et al.34 repeated Elgalaid’s32 work in 2007, and obtained similar in vitro results. That is, smear layer/smear plugs seal dentin better than adhesive resins/resin tags.

Water movement across resins, in vivo Author Manuscript

Unfortunately, few clinical studies of “immediate dentin sealing” have been reported. Hu and Zhu18 reported that the incidence of post-cementation hypersensitivity was significantly lower in teeth that received immediate dentin sealing with Prime & Bond NTf compared to

fDentsply, York, PA, USA gSun Medical Co. Ltd., Shiga, Japan hParkell, Edgewood, NY, USA iHeraeus Kulzer, Hanau, Germany cKuraray America Inc., New York, NY, USA jBisco, Inc., Schaumberg, IL, USA eIvoclar Vivadent, Schaan, Liechtenstein

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abutment teeth that were prepared and temporized without immediate dentin sealing. Tay35 and others have prepared human teeth for full crowns and then taken polyvinyl siloxane impressions of smear layer-covered dentin (controls) or adhesive-coated dentin. These impressions were poured up in epoxy resin for SEM examination of in vivo fluid transudation across dentin “sealed” with smear layers or adhesives, as evidenced by the presence of tiny bubbles of dentinal fluid on smear layer-covered or “adhesive-sealed” dentin (Fig. 2). All two-step, self-priming, total-etch adhesives tested (Single Bonda, Prime & Bond NTf, One-Stepj, Excite DSCe) were covered with fluid droplets indicating that dentinal fluid had transudated across the polymerized adhesives in the 3–4 min required for self-polymerization of the polyvinyl siloxane impression material. Less fluid droplets came across smear-layer covered dentin than across polymerized resins.

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Chersoni et al.36 extended the in vivo work of Tay et al.35 by making replicas of resincovered dentin in vivo and also conducting fluid filtration studies across crown segments in vitro (Fig. 3). When self-etch adhesives Adper Prompta, Xeno IIIf, iBondi and One-Up Bond Fk were used to seal dentin, Adper Prompta and Xeno IIIf could not seal dentin as well as did smear layer-covered dentin (Table 3). One-Up Bond Fk sealed dentin as well as did smear layers. When the two-step self-etching system Unifil Bondd was used to seal dentin, it reduced dentin permeability to 2.1% of smear layer covered dentin values (Table 3)! This was due to the fact that the acidic primer layer was covered by a solvent-free hydrophobic layer (Fig. 3). Unifil Bondd produced the best seal of dentin, in part, because it was a selfetching system, and because it was covered with a neat hydrophobic resin that absorbed little water30.

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Clearly, not all polymerized resins should be used for immediate dentin sealing, for if dentinal fluid can transudate across the “resin-sealed dentin,” those water droplets might interfere with polymerization of impression materials. Ghiggi et al.37 sealed dentin with Clearfil SE Bondc (CSE) alone or CSE covered with a glycerin jelly to exclude oxygen and polymerized through jelly. Other specimens were treated with CSE that was polymerized in air, but the oxygen-inhibited layer was removed with alcohol, or the CSE was covered with Protect Liner Fc (PLF), a flowable composite alone or the flowable was covered with a glycerin jelly or the polymerized PLF was scrubbed with alcohol before taking impressions with Express XTa or Impreguma. Their results showed that small amounts of impression material remained attached to dentin sealed with CSE alone or PLF, but were not found on CSE covered with jelly or scrubbed with alcohol. Magne and Nielsen24 reported that only CSE used with Extrudeb generated ideal impressions. They did not recommend Impreguma for taking impressions of immediate dentin seals.

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Immediate dentin seals, if treated properly, can serve as a foundation for indirect composite inlays. Duarte et al.38 found that immediate dentin sealing with Adper Single Bonda gave microtensile bond strengths of 51.1 MPa, while Adper Prompt L-Popa only gave 1.7 MPa bond strength. If dentin is temporized without immediate dentin sealing, the subsequent use

kTokuyama Corp., Tokyo, Japan ddG-C Corp., Tokyo, Japan

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of Optibond FLb or CSEc for indirect restorations falls 11.6 MPa or 1.81 MPa, respectively39. When those same adhesives were used for immediate dentin sealing and the final restoration delayed 1–12 weeks, the microtensile bond strengths exceeded 45 MPa for both adhesives39. Dillenburg et al.40 reported that immediate dentin seals should be cleaned of temporary cement with aluminum oxide powder and 37% phosphoric acid treatment, followed by a second layer of the same adhesive. These microtensile bond strengths were similar to the controls that were never temporized.

Water movement across polymerized resins, in vitro

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Özok et al.41 prepared class II cavities (Fig. 4) in crown segments in vitro, and measured the permeability of smear layer-covered dentin. Then the cavities were bonded with Scotchbond 1a or Prompt L-Popa following the manufacturer’s instructions, under 15 cm H2O of pulpal pressure or 0 cm H2O pulpal pressure. Scotchbond 1a reduced dentin permeability 48% when bonded under 15 cm H2O pressure, but 88% when no pressure was applied (Table 4). In contrast, Prompt L-Popa reduced dentin permeability 88% when 15 cm H2O was applied during bonding, but 95% when no pulpal pressure was applied. Itthagarun et al.42 created exposed, flat dentin surfaces in human dentin and then bonded them with Prompt-L-Popa, Etch & Prime 3.0m, One-Up Bond Fk, Reactmer Bondl or Unifil Bondd. Unifil Bondd lowered dentin permeability 98% to a residual post-bonded permeability of only 2% of smear layer values (similar to the results of Chersoni et al.36 above), while Prompt L-Popa and Etch & Prime 3.0m didn’t seal dentin any better than did the smear layer (Table 5). One-Up Bond Fk and Reactmer Bondl were better than Prompt LPopa and Etch & Primem but not as good as Unifil Bondd (Table 5).

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Magne23 recommended the etch-and-rinse adhesive, OptiBond FLb, to seal dentin. After acid-etching and priming of dentin, the final adhesive layer is solvent-free and relatively hydrophobic, like the adhesive of Unifil Bondd and creates an excellent seal. Indeed, Scotchbond Multi-Purpose’sa adhesive produces good dentin sealing because it is also solvent-free. Clearfil SE Bondc adhesive is another example of a solvent-free, relatively hydrophobic resin blend that seals dentin well.

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Grégorie et al.43 bonded smear layer-covered dentin in vitro with ten self-etching adhesives. Smear layers reduced dentin permeability 40–50% compared to acid-etched values. However, when they bonded the 4000 grit SiC smear layers with Xeno IIIf, AdhSEe, Adper Prompt L-Popa, Etch & Primem or One-Up Bond Fk, the post-adhesion permeability fell 50– 60% compared to the initial acid-etched value (Table 6). Optibond Solo Plusb, Prime & Bond NTf-treated dentin reduced dentin permeability 45.6 to 42.3%. Prime & Bondf nonrinse conditioner and 1 layer of Prompt L-Popa only reduced dentin permeability 16% (Table 6).

mDegussa AG, Hanau, Germany lShofu Inc., Kyoto, Japan

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Use of potassium oxalate to seal tubules with crystals

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Yiu et al.44 reported that the in vitro dentin permeability of smear layer-covered dentin varied from 9–11% of acid-etched values. When acid-etched dentin was treated with BisBlockj (2.8% oxalic acid), the permeability fell to between 9.4- 11.9% of acid-etched values, much like the smear layer covered dentin (Table 7). When acid-etched dentin was bonded with One-Stepj, Single Bonda, OptiBond Solo Plusb or Prime & Bond NTf, the permeability only fell to 31–34% of acid-etched values that were all significantly higher than the smear layer or BisBlockj values (Table 7). However, when BisBlockj was used to pretreat dentin prior to bonding with One-Stepj or Single Bonda, the dentin permeability fell to values that were only 2 or 6%, respectively, far lower permeability values than were produced by smear layers or by BisBlockj alone, indicating that a double seal by calcium oxalate crystals and resin tags lowers dentin permeability. One-Stepj and Single Bonda reduced dentin permeability almost to zero. In contrast, when BisBlockj-treated dentin was bonded with OptiBond Solo Plusb or Prime & Bond NTf, the permeability of dentin only fell to 27–28%, about like the use of these adhesives without BisBlockj (Table 7). Further studies were done to try to determine why OptiBond Solo Plusb and Prime & Bondf were not as effective as One Stepj and Single Bonda. Table 7 shows that the pH of OptiBond Solo Plusb and Prime & Bond NTf were 2.8 and 2.7, respectively. Clearly, OptiBond Solo Plusb and Prime and Bond NTf were more acidic than the other two adhesives. When the adhesives were analyzed for ionic fluoride, One-Stepj and Single Bonda contained 70 and 130 ppm F-, while OptiBond Solo Plusb contained 4527 ppm F- and Prime & Bond NTf contained 3641 ppm F- (Table 7). Further, TEM studies of ammoniacal silver nitrate immersed specimens revealed the presence of globular deposits into dentinal tubules that may be CaF2-phosphate complexes. These were not found in One-Stepj or Single Bonda bonded specimens. When low viscosity polyvinyl siloxane impressions were made of the BisBlockj pretreated, resin-bonded surfaces, epoxy resin replicas were made for SEM examination. Figure 5 shows only a few droplets of water on the surface of One-Stepj or Single Bonda bonded dentin, but extensive amounts of water had filtered across the polymerized resin of Prime & Bond NTf or Optibond Solo Plusb in the 3–4 min required for setting of the impression material. Clearly, low pH and high fluoride concentrations somehow interfere with the sealing properties of OptiBond Solo Plusb and Prime & Bond NTf, but not with One Stepj or Single Bonda. When less acidic, low fluoride adhesives are combined with pretreatment by oxalic acid, one obtains double sealing of dentinal tubules45.

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Fluid movement across polymerized resins Sauro et al.46 extended the work of Tay et al.35 and Chersoni et al.36 by quantitating the number of water droplets on various adhesive resins bonded to dentin (Fig. 6), and to then correlate it with actual fluid flow transudation across the bonded dentin using the hydraulic conductance technique (Fig. 7). They published a highly significant positive linear

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regression equation showing an R2 = 0.96 of the relationship between the number of fluid droplets on resin surfaces and the permeability of the adhesives (Fig. 7). Two years later, Sauro et al.47 measured droplet formation by tandem confocal scanning microscopy (TSM) dentin sealed with G-Bondd, DC-Bondc, Single Bonda, OptiBond FLb or Filtek Siloranea. The best sealing was obtained using G-Bondd. This was the exact opposite of their results obtained in 2007. The authors explain that the polymerized G-Bondd films looked frothy, but did not allow much fluid transudation. OptiBond FLb sealed dentin gave the next to the best seal. DC Bondc and Single Bonda gave the worst seals.

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Grégorie et al.48 tested the moisture-sensitivity of Prompt L-Popa versus Scotchbond 1XTa by measuring the ability of these resins to seal dentin compared to their acid-etched values. Scotchbond 1XTa was more sensitive to overly dry dentin than was Prompt L-Popa. Scotchbond 1XTa reduced dentin permeability by 55%, while Prompt L-Popa reduced it by 62%, although these values were not significantly different. These relatively poor seals suggest that the ability of adhesive resins to seal dentin had not improved much over the 2000–2009 period.

Use of resin-modified glass ionomers

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Rusin et al.49 evaluated the resin-modified glass ionomer (Vitrebond Plusa) for its ability to seal dentin, when applied to acid-etched or smear layer-covered dentin. When applied to smear layers, Vitrebond Plusa reduced dentin permeability 98.9 ± 1.1%, because it was a second layer on top of a smear layer that contained smear plugs in the tubules. This is the best seal that we have seen published in the literature. When Vitrebond Plusa was placed on acid-etched dentin it created a hybrid layer complete with resin tags (Fig. 8). The Vitremer Plusa matrix separated from the filler particles creating Vitremer Plus matrix resin tags about 2 µm long. Vitrebond Plusa reduced the permeability of acid-etched dentin by 87.7 ± 18.6%. This means that some specimens produced perfect seals, while others only sealed dentin 69%.

Use of 2-bottle self-etching primer adhesives

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Clearly, most resins do not seal dentin as well as do enamel or cementum. Two step, selfetching adhesives tend to seal better than do etch-and-rinse adhesives because the mildly (pH 2–2.4) acidic versions barely etch through smear layers (Fig. 9). As many smear plugs are more than 2 µm long and are covered by 1 µm thick smear layers, the mild etching of self-etching adhesives fails to remove the smear plugs, preventing dentinal fluid from contaminating dentin surfaces44. Self-etching adhesives only contain 25–35% water, while etching dentin with phosphoric acid and rinsing with water, leaves demineralized dentin floating in 70 vol% water41. Thus, it is easier to displace 25–35% water from thin hybrid layers than trying to displace 70 vol% water using etch-and-rinse adhesives. For some etch-and-rinse adhesives (One-Stepj and Single Bonda), surface water can be controlled by applying oxalic acid to acid-etched dentin prior to bonding. Oxalates do not work with more acidic, high fluoride-containing products like OptiBond Solob or Prime & Bond NTf44. Am J Dent. Author manuscript; available in PMC 2016 July 13.

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The two-step self-etching primer/adhesives like Unifil Bondd, Clearfil SE Bondc or Clearfil Protect SEc or AdheSEe, confine their water and acidic monomers to their primers and cover the primed dentin with solvent-free, relatively hydrophobic resins that seal dentin much better than do simplified, single bottle adhesives (e.g. G-Bondi, iBondj, Xeno IIIf, etc.). If we assume that higher resin-dentin bond strengths represent improved dentin sealing, then there are several papers that show that multiple resin coats improve dentin bonding.

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Attempts to seal dentin using multiple coatings of adhesives has resulted in mixed success. Pashley et al.50 compared applications of one versus two coats of Prompt L-Popa. Using one layer of adhesive, as recommended, produced microtensile bond strength of only 14.2 ± 7.2 MPa (n=24). Application of two layers produced a µTBS of 29.7 ± 5.7 (n=23, p

Adhesive sealing of dentin surfaces in vitro: A review.

This review describes the evolution of the use of dental adhesives to form a tight seal of freshly prepared dentin to protect the pulp from bacterial ...
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