| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
RESEARCH REPORTS |
1 Department of Restorative Dentistry and Dental Materials, University of Siena, Italy;
2 Department of Dental Sciences, University of Bologna, Italy;
3 Department of Oral Biology and Maxillofacial Pathology, School of Dentistry, Medical College of Georgia, Augusta, USA; and
4 Pediatric Dentistry and Orthodontics, Faculty of Dentistry, Prince Philip Dental Hospital, University of Hong Kong, 34 Hospital Road, Pokfulam, Hong Kong, SAR, China;
* corresponding author, kfctay{at}netvigator.com
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
|---|
KEY WORDS: adhesive permeability • simplified adhesives • root canal • fluid transudation
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
|---|
An immediate consequence of adhesive simplification is a sacrifice of the universality of the multi-bottle adhesives, with most of the simplified versions capable of bonding only to light-cured composites (Sanares et al., 2001; Pfeifer et al., 2003). Although the adhesion of auto-/dual-cured composites may be improved with the adjunctive use of ternary catalysts that offset the acid-base incompatibility between acidic methacrylate monomers and tertiary amines (Suh et al., 2003), the bonding efficacy of both simplified total-etch (Tay et al., 2003b) and simplified self-etch adhesives (Tay et al., 2003a) to auto-/dual-cured composites/resin cements is hampered by the intrinsic permeability of these adhesives to the water that results from their increase in hydrophilicity (Carvalho et al., 2004; Chersoni et al., 2004a).
Transudation of dentin fluid through simplified dentin adhesives has been shown to occur in vivo in bonded vital crown dentin (Chersoni et al., 2004b; Tay et al., 2004), since these adhesives behave as permeable membranes after polymerization (Tay et al., 2002a). This may result in the entrapment of water blisters between the adhesive surface and slow-setting resin composites/cements. The water blisters may act as stress raisers and account for the apparent incompatibility of these adhesives with the bonding of indirect restorations, even in the absence of the true adhesive incompatibility derived from adverse acid-base reactions (Tay et al., 2003a).
Although a positive pulpal pressure is absent in endodontically treated teeth, an increase in radicular permeability may follow reduction in root dentin thickness and removal of sealers that penetrated the dentinal tubules during the preparation of spaces for the cementation of endodontic posts (Fogel et al., 1988; Guignes et al., 1996). This is particularly so when total-etch adhesives and the aggressive type of self-etch adhesive (Tay and Pashley, 2001), that completely remove or dissolve the smear layers, are used for bonding to root canals (Tao et al., 1991). Since vital teeth and endodontically treated teeth do not differ significantly in their moisture content (Papa et al., 1994), the effect of adhesive permeability on bonding to root canals with conventional or simplified total-etch and self-etch adhesives is unknown. Thus, the objective of this in vivo study was to examine, by a novel impression replica technique (Chersoni et al., 2004), the permeability of adhesive-bonded intra-radicular dentin to fluid movement. The null hypothesis tested was that there is no difference among the 4 different classes of dentin adhesives (i.e., three-step total-etch, two-step total-etch, two-step self-etch, and one-step self-etch) in preventing fluid movement across bonded intra-radicular dentin.
|
MATERIALS & METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
|---|
The coronal part of each root filling was removed, with a root canal filling of 5–6 mm remaining, and a post space was created for the insertion of a size 2 DT Light-Post (RTD, Grenoble, France), a radiopaque glass fiber post, by use of the corresponding drills. The residual thickness of remaining dentin around the dowel space of each tooth was evaluated radiographically to be at least 1.5 mm. Debridement was performed with distilled water under the microscope to ensure that the post space was free of cutting debris, and that the coronal portion of the remaining gutta-percha could be identified from the base of the post space. Prior to the bonding procedure, each post space was air-dried with a triple syringe equipped with a Stropko irrigator (SybronEndo, Orange, CA, USA) and further dried with 4 paper points to ensure that the post space was free from residual moisture (Hosoya et al., 2000).
Experimental Design
Six dentin adhesives were randomly selected for application to 4 teeth in each experimental or control group. They included: All-Bond 2 (Bisco Inc., Schaumburg, IL, USA), a conventional three-step total-etch adhesive that was used as the control; Single Bond (3M ESPE, St. Paul, MN, USA) and One-Step Plus (Bisco), as representatives of simplified two-step total-etch adhesives; Tyrian SPE/One-Step Plus (Bisco), a two-step self-etch adhesive; and Xeno III (Dentsply DeTrey, Konstanz, Germany) and One-Up Bond F (Tokuyama Corp., Tokyo, Japan), examples of simplified one-step self-etch adhesives.
Since the experimental protocol required a polymerized adhesive surface for impression-taking, the uncured Pre-Bond resin in All-Bond 2, that was to be placed over the primed dentin, was replaced with a mixture of Pre-Bond and D/E resin, so that a curable adhesive layer could be obtained (B.I. Suh, personal communication). For the 3 total-etch adhesives, the post spaces were blot-dried with paper points after the phosphoric acid was rinsed, to provide a moist substrate for the wet-bonding technique. Although the one-step self-etch adhesives were not recommended for the coupling of auto-cured composites, they were used with the understanding that the incompatibilities associated with these 2 adhesives were apparent in nature, and were attributed to the permeability of the adhesives instead of to adverse acid-base interactions (Tay et al., 2003a). To ensure that subsequent restorative treatments were performed in the best interest of the subjects, we placed an additional thin coat of Scotchbond Multi-Purpose bonding resin (3M ESPE) over these adhesives and light-cured them after the experimental impression-taking protocol. This additional step converts these adhesives from one-step to two-step self-etch adhesives, making certain that they are compatible with auto-/dual-cured resin cements.
To ensure optimal curing, we applied each adhesive to the post spaces with a microbrush, and light-cured it via a slightly undersized, non-bonding, light-transmitting plastic post (Luminex, Dentatus AB, Hägersten, Sweden), that was inserted into the post space and transilluminated from the top by means of a LED light-curing unit (L.E. Demetron 1, Sybron-Kerr, Orange, CA, USA) for 40 sec at an output of 800 mW/cm2. Since the uncured adhesive caused by oxygen inhibition must be removed prior to impression-taking, a second coat of the adhesive was applied. Removal of the adhesive oxygen inhibition layer was performed by means of acetone and a microbrush.
The bonded post space was air-dried for 10 sec by insertion of the Stropko irrigator into the root canal. An impression was immediately taken with a polyvinyl siloxane impression material (Affinis light-body, Colténe AG). The material was injected into the post space and distributed by means of a spiral, followed by the insertion of the previously used plastic post as an anchor. After 4 min, the polymerized impression material was removed and de-gassed for 24 hrs. Positive replicas were then fabricated with a polyether impression material (Permadyne Garant, 3M ESPE), with the polyvinyl siloxane negative replica used as a mold, according to the polyether replica technique reported by Chersoni et al.(2004a). Since there is no chemical reaction between polyether and polyvinyl siloxane, this replica technique has been shown to be effective in replicating water exudation from dentin hybrid layers. The polyether replicas were cut into hemisections by means of a sharp razor blade, coated with gold/palladium, and examined under a scanning electron microscope (SEM; Model 5400, JEOL, Tokyo, Japan) at 5–10 kV. Five SEM images of each of the 4 post spaces in each group were taken randomly from different areas of the replicas (N = 20). The number of fluid droplets/1000 µm2 of polymerized adhesive was recorded by two co-authors who did not participate in bonding and were unaware of the group designations. Data from the 6 groups were statistically analyzed by Kruskal-Wallis ANOVA and Dunn’s multiple-comparison tests at 
= 0.05.
Controls
The remaining 4 dowel spaces were not bonded with adhesives and were used as controls. For 2 of these dowel spaces, impressions were taken of the smear-layer-covered intra-radicular dentin after the cutting debris was rinsed off and the dentin dried with paper points. For the other 2 dowel spaces, impressions were taken of the intra-radicular dentin after being acid-etched with 32% phosphoric acid (Uni-etch, Bisco) for 15 sec, then rinsed and dried with paper points. Polyvinyl siloxane replicas were prepared and examined as previously described.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
|---|
) and after acid-etching (Fig. 1B). All-Bond 2, the control three-step total-etch adhesive, exhibited no fluid transudation across the polymerized adhesive in 3 of the specimens examined (Fig. 1C), and minimal fluid droplets were observed only in the fourth specimen (Fig. 1D).
|
) and One-Step Plus (Fig. 2B).
|
). Similarly, fluid droplets were seen in specimens bonded with the simplified one-step self-etch adhesives Xeno III (Fig. 3B) and One-Up Bond F (Fig. 3C). Based on morphologic examination, the sizes of the fluid droplets were smaller in the self-etch adhesives.
|
. All Bond 2 exhibited significantly fewer fluid droplets than the other 5 experimental groups (P < 0.05). There were no differences in the numbers of fluid droplets/1000 µm2 among the other 5 groups (Fig. 3D
).
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Since root canal sealers can penetrate only 35–80 µm into the dentinal tubules, even with complete smear layer removal (Kouvas et al., 1998), residual dentinal tubules are likely to be devoid of sealers when dentin thickness is reduced after post space preparation. Rinsing with water during the course of a total-etch technique probably results in the retention of substantial amounts of water within the widened tubular entrance created by acid-etching, that may not be completely removed via the use of paper points. This may account for the occurrence of larger fluid droplets in the simplified total-etch adhesives (Figs. 2A, 2B). With the use of self-etch adhesives, we speculated that water could have been partially derived from the residual water that is retained in these water-containing adhesives (Tay et al., 2002b), and partially from the unbound water that is present in pulpless teeth (Helfer et al., 1972; Papa et al., 1994). Since the smear plugs were not removed with the use of these self-etch adhesives (Tay and Pashley, 2001), this could have resulted in the appearance of smaller fluid droplets (Figs. 3C, 3D). In this study, we have refrained from recording the actual dimensions of these fluid droplets, due to the inaccuracy involved with interpretation of micrographs that were taken at different specimen tilts. The volume of fluid that permeates these adhesive in intra-radicular dentin should be quantified in the future by means of fluid filtration protocols (Fogel et al., 1988; Abramovitz et al., 2001) or electrical impedance methods (Momoi et al., 2003).
Previous fluid transport studies reported the presence of an inferior seal along the coronal two-thirds of the root-filled canals after post space preparation, when compared with intact root fillings (Abramovitz et al., 2001; Wu et al., 2003). Presumably, the use of dentin adhesives would improve the seal of this critical region, minimize coronal leakage, and improve the prognosis of endodontic therapy. However, the in vivo observation of fluid transudation through simplified adhesives in endodontically treated teeth suggests that a hermetic seal of the coronal third of root canals is unlikely to be achieved with the use of either simplified total-etch or self-etch adhesives. Theoretically, the use of a two-step self-etch adhesive should minimize water movement through the adhesive (Carvalho et al., 2004). However, the system we examined utilizes a fairly permeable adhesive (One-Step Plus; Fig. 2B) over the intra-radicular dentin that was treated with the self-priming etchant Tyrian SPE. Nguyen et al.(1996) investigated the permeation of water through multiple layers of organic resin coatings. They observed that increasing the number of coats of a hydrophilic resin affected only the time required for water to move from the outside to the inside of the coatings, but did not reduce the permeability of the coatings. It is only when a polymer exhibits a notable change in diffusion coefficient that the permeability of the coatings can be substantially reduced. This could have accounted for the permeability observed for Tyrian SPE/One-Step Plus. The permeability of other two-step self-etch adhesives in endodontically treated teeth should be further examined.
Although the use of bonded posts has been clinically successful, a recent SEM study of endodontically treated teeth extracted after clinical service reported that subclinical gap formation and adhesive failures occurred along the resin-dentin interfaces, in spite of the absence of clinical failure (Mannocci et al., 2003). Unfavorable cavity configuration factors in post spaces have been cited as the major reason for low bond strengths and marginal gap formation (Morris et al., 2001; Bouillaguet et al., 2003). Slow-setting resin cements have been recommended to offset the development of high polymerization shrinkage stresses along root canal walls (Goracci et al., 2004). The extended setting time for these resin cements, which is perceived to be beneficial in reducing shrinkage stresses, may be offset by the use of simplified total-etch or self-etch adhesives, since this prolongs the time for water diffusion through the adhesives, creating fluid blisters along the adhesive-cement interface that act as stress-raisers and precipitate bond failure (Carvalho et al., 2004). In the event that coronal leakage occurs during functional stresses, leaching of resin components from these highly hydrophilic adhesives may further contribute to the degradation of the bonds between the adhesive and intra-radicular dentin. Although simplified acidic adhesives may be rendered compatible with auto-/dual-cured resin cements via the use of ternary catalysts (Suh et al., 2003), they must be used with caution for bonding to root canals, in light of the fluid movement that occurs through these adhesives under in vivo conditions. The use of conventional, less permeable adhesives appears to be a more rational alternative.
|
ACKNOWLEDGMENTS |
|---|
Received March 8, 2004; Last revision July 23, 2004; Accepted January 2, 2005
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Bouillaguet S, Troesch S, Wataha JC, Krejci I, Meyer JM, Pashley DH (2003). Microtensile bond strength between adhesive cements and root canal dentin. Dent Mater 19:199–205.[ISI][Medline]
Carvalho RM, Pegoraro TA, Tay FR, Pegoraro LF, Silva NR, Pashley DH (2004). Adhesive permeability affects coupling of resin cements that utilise self-etching primers to dentine. J Dent 32:55–65.[ISI][Medline]
Chersoni S, Suppa P, Breschi L, Ferrari M, Tay FR, Pashley DH, et al. (2004a). Water movement in the hybrid layer after different dentin treatment. Dent Mater 20:794–803.
Chersoni S, Suppa P, Grandini S, Goracci C, Monticelli F, Yiu C, et al. (2004b). In vivo and in vitro permeability of one-step self-etch adhesives. J Dent Res 83:459–464.
Fogel HM, Marshall FJ, Pashley DH (1988). Effects of distance from the pulp and thickness on the hydraulic conductance of human radicular dentin. J Dent Res 67:1381–1385.
Goracci C, Tavares AU, Fabianelli A, Monticelli A, Raffaelli O, Cardoso PEC, et al. (2004). The adhesion between fiber posts and root canal walls: comparison between microtensile and push-out bond strength measurements. Eur J Oral Sci 112:353–361.[ISI][Medline]
Guignes P, Faure J, Maurette A (1996). Relationship between endodontic preparations and human dentin permeability measured in situ. J Endod 22:60–67.[ISI][Medline]
Helfer AR, Melnick S, Schilder H (1972). Determination of the moisture content of vital and pulpless teeth. Oral Surg Oral Med Oral Pathol 34:661–670.[ISI][Medline]
Hosoya N, Cox CF, Arai T, Nakamura J (2000). The walking bleach procedure: an in vitro study to measure microleakage of five temporary sealing agents. J Endod 26:716–718.[ISI][Medline]
Kouvas V, Liolios E, Vassiliadis L, Parissis-Messimeris S, Boutsioukis A (1998). Influence of smear layer on depth of penetration of three endodontic sealers: an SEM study. Endod Dent Traumatol 14:191–195.[ISI][Medline]
Mannocci F, Bertelli E, Watson TF, Ford TP (2003). Resin-dentin interfaces of endodontically-treated restored teeth. Am J Dent 16:28–32.[ISI][Medline]
Momoi Y, Akimoto N, Kida K, Yip KH, Kohno A (2003). Sealing ability of dentin coating using adhesive resin systems. Am J Dent 16:105–111.[ISI][Medline]
Morris MD, Lee K-W, Agee KA, Bouillaguet S, Pashley DH (2001). Effects of sodium hypochlorite and RC-prep on bond strengths of resin cement to endodontic surfaces. J Endod 27:753–757.[ISI][Medline]
Nguyen T, Byrd E, Bentz D, Lin C-J (1996). In situ measurement of water at the organic coating/substrate interface. Proc Org Coat 27:181–193.
Papa J, Cain C, Messer HH (1994). Moisture content of vital vs endodontically treated teeth. Endod Dent Traumatol 10:91–93.[ISI][Medline]
Perdigão J, Duarte S Jr, Lopes MM (2003). Advances in dentin adhesion. Compend Contin Educ Dent 24:10–16.
Pfeifer C, Shih D, Braga RR (2003). Compatibility of dental adhesives and dual-cure cements. Am J Dent 16:235–238.[ISI][Medline]
Sanares AM, Itthagarun A, King NM, Tay FR, Pashley DH (2001). Adverse surface interactions between one-bottle light-cured adhesives and chemical-cured composites. Dent Mater 17:542–556.[ISI][Medline]
Suh BI, Feng L, Pashley DH, Tay FR (2003). Factors contributing to the incompatibility between simplified-step adhesives and self-cured or dual-cured composites. Part III. Effect of acidic resin monomers. J Adhes Dent 5:267–282.[ISI][Medline]
Tao L, Anderson RW, Pashley DH (1991). Effect of endodontic procedures on root dentin permeability. J Endod 17:583–588.[ISI][Medline]
Tay FR, Pashley DH (2001). Aggressiveness of contemporary self-etching systems. I: Depth of penetration beyond dentin smear layers. Dent Mater 17:296–308.[ISI][Medline]
Tay FR, Pashley DH (2002). Dental adhesives of the future. J Adhes Dent 4:91–103.[Medline]
Tay FR, Pashley DH, Suh BI, Carvalho RM, Itthagarun A (2002a). Single-step adhesives are permeable membranes. J Dent 30:371–382.[ISI][Medline]
Tay FR, King NM, Chan KM, Pashley DH (2002b). How can nanoleakage occur in self-etching adhesive systems that demineralize and infiltrate simultaneously? J Adhes Dent 4:255–269.[Medline]
Tay FR, Pashley DH, Yiu CKY, Sanares AME, Wei SHY (2003a). Factors contributing to the incompatibility between simplified-step adhesives and self-cured or dual-cured composites. Part I. Single-step self-etch adhesive. J Adhes Dent 5:27–40.[ISI][Medline]
Tay FR, Suh BI, Pashley DH, Prati C, Chuang SF, Li F (2003b). Factors contributing to the incompatibility between simplified-step adhesives and self-cured or dual-cured composites. Part II. Single-bottle, total-etch adhesive. J Adhes Dent 5:91–105.[ISI][Medline]
Tay FR, Frankenberger R, Krejci I, Bouillaguet S, Pashley DH, Carvalho RM, et al. (2004). Single-bottle adhesives behave as permeable membranes after polymerization. I. In vivo evidence. J Dent 32:611–621.[ISI][Medline]
Van Meerbeek B, De Munck J, Yoshida Y, Inoue S, Vargas M, Vijay P, et al. (2003). Buonocore memorial lecture. Adhesion to enamel and dentin: current status and future challenges. Oper Dent 28:215–235.[ISI][Medline]
Wu MK, van der Sluis LW, Ardila CN, Wesselink PR (2003). Fluid movement along the coronal two-thirds of root fillings placed by three different gutta-percha techniques. Int Endod J 36:533–540.[ISI][Medline]
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| IADR Journals | Advances in Dental Research ® |
| Journal of Dental Research ® | Critical Reviews (1990-2004) |
