In vivo resin-dentin interdiffusion and tag formation lateral branches of two adhesive systems

with

Marco Ferrari, MD, DDS, PhD,a and Care1 Leon Davidson, PhDb University of Siena, Siena, Italy, and Academic Center for Dentistry Amsterdam, Amsterdam, The Netherlands

The close contact of the primer and the conditioned dentin is critical in the bonding of resin composites to dentin. In this study two different adhesive primers were tested in vivo with a separate conditioning procedure (Scotchbond Multipurpose) and a self-etching primer (Clearfil Liner Bond 2). The formation of lateral branches of tubule tags was investigated to substantiate the effectiveness of infiltration as a contribution to retention. Scanning electron microscopy revealed the formation of a resin-dentin interdiffusion zone and penetration into the lateral canals of the tubules for both primers. The resin tags with lateral branches were observed primarily at the floor of the class II cavities. In vivo effectiveness of self-etching priming was demonstrated. (J Prosthet Dent 1996;76:250-3.)

T he close contact of the primer and the conditioned dentin is of paramount importance in the bonding of resin composites to dentin, whether through micromechanical interlocking,1 chemical bonding,2 or a combination of these two mechanisms.3 Good wetting and infiltration of bis- glycerol methacrylate (his-GMA) resin into dentin tubules has been demonstrated to occur in viv~,~ but it has shown to provide an insufficient bond strength.5 Modern dentin bonding is based on the resin impregnation of intertubu- lar dentin after the collagen fiber network’s exposure at the surface to acid demineralization6 Proper infiltration and retention is required because a close adaptation is always challenged by polymerization shrinkage.7s 8

Recently it has been shown in an in vitro study that the primer does not only infiltrate the tubules but also the openings within the tubule shafts that lead to the lateral branches of the resin tags.g It has been concluded that a network of interconnecting resin tags might be a substan- tial contribution toward an effective bond.

The purposes of this study were (1) to investigate whether such an interconnecting resin network from the lateral branches of tubule tags is also formed when the primer is ap- plied on a conditioned dentin substrate in vivo and (2) to de- termine whether self-etching primerslo, l1 perform under these conditions in such an effective manner as primers that need a separate conditioning procedure.

MATERIAL AND METHODS

Eighteen periodontally involved posterior teeth were used. Fifteen volunteer patients participated in the study; the average age of the patients was 54 years. Each patient had one or two severely compromised, unrestored, caries- free posterior teeth scheduled for extraction, Before the study was commenced, the vitality of the experimental

“Clinical Professor of Restorative Dentistry, University of Siena. bProfessor and Chairman, Department of Dental Materials Sci-

ences, Academic Center for Dentistry Amsterdam.

250 THE JOURNAL OF PROSTHETIC DENTISTRY

Table I. Dentin bonding systems investigated

Conditioner Resin and primer Bonding composite

Scotchbond Maleic acid MDP, bis- Z 100a A3 Multipurpose 10% (7541), GMA (7543) (5904A2) (Batch No.) HEMA-poly-

alcanoic acid (7542)

Liner Bond 2 Phenyl-P, MDP, HEMA, Photo-Anterior (batch No.) HEMA, Bis-GMA A35 (1640)

5-NMSA (LB-D1103) (LPB-0001, LPA-D1103)

Z 100 resin composite, 3M; Photo Anterior resin composite, Kuraray. HEMA hydroxyethyl methacidate; MDP, methylene diphosphate; NMSA, N methoxyloyl B-amino salacylic acid.

teeth was confirmed by thermal and electrical vitality tests. The bonding agents selected for this study were Scotchbond Multipurpose (3M, Dental Division, St. Paul, Minn.) and Liner Bond 2 (Kuraray, Osaka, Japan), which were combined with a corresponding resin composite (Ta- ble I). The teeth were divided into two groups (Table II).

Group 1

Ten teeth were selected to study hybrid layer formation in vivo. A flat surface of approximately 8 to 9 mm2 was prepared in the dentin by the removal of approximately 1 mm of dental structure buccally with a diamond bur at an ultra-high-speed and by abundant water cooling. In this way the vestibular thickness of enamel was removed com- pletely and the dentin was exposed. A rubber dam was then applied.

Each bonding system was tested on five samples. After a 30-second application of the Scotchbond Multipurpose conditioner (10% maleic acid), the cavity was rinsed with water for 30 seconds and gently dried with air for 10 sec- onds. The Scotchbond Multipurpose primer was applied with a soaked pellet for 30 seconds to the whole cavity wall

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Fig. 1. Sample of group 1. Resin-dentin interdiffusion zone obtained with Scotchbond Multipurpose material. (Scanning electron microscope, original magnification x3000.) (d, Dentin; r, resin; h, hybrid layer.)

Table II. Schematic demonstration of procedures for samples of groups 1 and 2

Eighteen posterior teeth in viva

Group 1 (10 buccal flat surfaces)

Group 2 (8 class II cavities)

Five SBMP Five CLB2 Four SBMP Four CLB2 samples samples samples samples

Photo Protect liner ZlOO Anterior

Immediate extraction Immediate extraction Split fracture 37% Hydrochloric acid for 2

days Acid treatment of interface Resin replica Scanning electron microscope Scanning electron microscope

Fig. 2. Sample of group 1. Resin-dentin interdiffusion zone obtained with Clearfil Liner Bond 2 material. (Scan- ning electron microscope, original magnification x3500.) (d, Dentin; r, resin; h, hybrid layer.)

SBMP, Scotchbond multipurpose; CLB2, Clearfil Liner Bond 2.

and the substrate was gently air dried. Subsequently, the bonding resin was applied and light-cured for 20 seconds.

The other five cavities were treated with the self-etching primer (Liner Bond 2) for 30 seconds, after which the ma- terial was reapplied for another 30 seconds and then gen- tly air dried. A layer of the bonding resin was placed and light-cured for 20 seconds. Finally, a layer of Protect Liner resin (Kuraray) was placed on top of the bonding resin for all samples and then light-cured for 20 seconds.

The sample teeth were carefully extracted immediately after the resin composite had been cured, and the teeth were stored for 1 to 2 weeks in an aqueous solution that contained 0.5% chloramine. The roots of the teeth were cut from the crowns with a diamond blade under abundant water cooling. Perpendicular fractures were produced through the flat treated dentin surfaces with a wedge- shaped instrument, the cutting edge of which was acting on a lingually prepared notch on the crown surface. Both halves of each specimen were etched for 1 minute in a 10%

Fig. 3. Sample of group 2. Tubule tags of Scotchbond Multi- purpose with interconnecting network of lateral branches. (Scanning electron microscope, original magni&ation x3500.)

citric acid solution and rinsed in deionized water before deproteinization in sodium hypochlorite solution ( 10%) for 5 seconds and final washing in deionized water.

The interdiffusion zone was defined as a pronounced band representing a solvent-resistant zone between the covering resin and the dentin. Each sample in group 1 was measured at a point located approximately between the incisal and cervical margins. The data were statistically analyzed by analysis of variance.

Group 2

The remaining eight teeth were used to evaluate the presence of a dentinal tubule interconnection. Class II cavities 3 mm in length and 2 mm deep were made in the mesial-occlusal surfaces by use of a diamond bur in an ul- tra-high-speed hand piece with an air-water spray coolant. Each preparation was located with the cervical margin 1 mm

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THE JOURNAL OF PROSTHETIC DENTISTRY FERBARI AND DAVIDSON

Fig. 4. Sample of group 2. Resin replica of pulpal wall of class II cavity. Clear61 Liner Bond 2 adhesive tubule tags vary in length. (Scanning electron microscope, original magnification x1500.1

Fig. 6. Higher magnification of Fig. 5. Clear-Ill Liner Bond 2 tags with lateral branches and replica of collagen network layer of intertubular dentin can be discriminated. (Scanning electron microscope, original magnification x15,000.)

Fig. 5. Sample of group 2. Lateral branches of Clearfil Liner Bond 2, most of which appear to terminate within intertubular dentin. (Scanning electron microscope, origi- nal magnification x5000.)

below the cementoenamel junction. After the adhesives were applied, the corresponding resin composite (Table I) was placed in the cavity by an incremental procedure. After poly- merization of the composite, the specimens were immediately extracted and placed in 37% hydrochloric acid solution for 2 days and subsequently in a 5% sodium hypochlorite solution for 2 hours. Finally, all samples were mounted on aluminum stubs, sputter-coated with gold (Edwards Coater S150B, Ed- wards Co., London, UK), and observed under a scanning electron microscope (JSM, T300, Jeol Ltd., Tokyo, Japan).

RESULTS Group 1

The specimens were observed to detect the presence and thickness of the hybrid layer. All the tested specimens

treated with Scotchbond Multipurpose bonding agent ex- hibited a resin-dentin interdiffusion zone. The average width of this layer was 4.2 urn (SD 1.7) (Fig. 1). The sam- ples treated with Clearfil Liner Bond 2 bonding agent re- vealed a layer between the resin and the dentin with an average thickness of 1.65 pm (SD 0.9) (Fig. 2). The resin- dentin interdiffusion zone of Clearfil Liner Bond 2 bonding agent appeared smoother and thinner than that created by Scotchbond Multipurpose bonding agent (Fig. 1). Statisti- cal analysis of the data revealed significant differences on the hybrid layer thickness between the samples treated with Scotchbond Multipurpose and Clear61 Liner Bond 2 bonding agents.

Group 2

Under the experimental conditions of this study the two adhesive systems exhibited a dentin tag formation with lateral branches (Figs. 3 through 6). Some of the lateral canal branches in the interconnecting network seem to have terminated within the intertubular dentin. The pres- ence of extensive dentin tag formation and lateral branches was evident at the floor of the cavity close to the pulp. Also the collagen network of the conditioned intertubular den- tin was well reproduced by the bonding system (Figs. 5 and 6).

DISCUSSION

The microscopic evaluation undertaken in this study showed that Scotchbond Multipurpose bonding agent with a separate etching procedure and the Clearfil Liner Bond 2 system can form a resin-dentin interdiffusion zone in vivo. The hybrid layer formed with these adhesive systems had a different appearance. Scotchbond Multipurpose bonding agent formed a rougher and thicker layer than the Clearfn Liner Bond 2 bonding agent did. This may be due

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to the maleic acid of Scotchbond Multipurpose demineral- izing the dentin more than the self-etching primer of Clear51 Liner Bond 2 bonding agent did. The Phenyl-P resin system may demineralize partially or completely the smear layer. In the former situation it may keep the ma- terial incorporated in the resin while penetrating into the substrate and thereby create a hybrid layer that contains part of the original smear layer.lO, l1 In the latter situation the Phenyl-P resin system may dissolve the smear layer completely and demineralize the peritubular dentin open- ing the tubule apertures. r2 The etching time, application technique, and type of dental substrate directly influenced the etching pattern. The effectiveness of both systems was confirmed by in vitro tests of tensile bond strengthg> i1 and other parameters.13-l5

2. Both materials formed characteristic reverse cone- shaped resin tags with lateral branches in the dentinal wall closest to the pulp.

REFERENCES

1.

2.

3.

4.

5.

The contribution of resin tags to bond strength is still unclear. Gwinnett16 evaluated the quantitative contribu- tion of resin infiltration of intertubular dentin to be approximately two thirds and the contribution of tubule tags to be approximately one third of the total shear bond strength. Schnuepbach et a1.17 confirmed the findings about the role of resin tag formation in bond strength. Bouillaguet et alIs correlated the bond strengths with dif- ferent sites in dentin.

6.

7.

8.

9.

The role of the resin tags in relation to the hybrid layer in dentin bonding could vary tremendously. This would depend on the dentin bonding agent used, the orientation of the den- tinal tubules, the type of dentinal surface, the different invivo conditions, and the dentin depth.lg, 2o Under the conditions of this study, with the chosen bonding systems the presence of lateral branches was evident, in particular in those areas close to the pulp. In another in vivo study lateral branches attached to intratubular dentin within the deepest layer of the hybrid zone were identified.20

10.

11.

12.

Soderhiilm KJ. Correlation of in viva and in vitro performance of ad- hesive restorative materials: a report of the ASC MD 156 Task Group on Test Methods for the adhesion of restorative materials. Dent Mater 1991;7:74-83. Asmussen E, Munksgaard EC. Adhesion of restorative resins to den- tinal tissue. In: Vanherle G, Smith DC, editors. Posterior composite resin dental materials. Utrecht: Peter Zule, 1987:121-3. Bowen RL, Matjenhoff WA. Development of an adhesive bonding sys- tem. Oper Dent 1992;17:(suppl 5):X+30. Nordenvall KJ, Briinnstrtim M. In viva resin impregnation of dentinal tubules. J Prosthet Dent 1980;44:630-7. Prati C, Pashley DH, Montanari G. Hydrostatic intrapulpar pressure and bond strength of bonding systems. Dent Mater 1991;7:54-8. Van Meerbeek B, Inokoshi S, Braem M, Lambrechts P, Vanherle G. Morphological aspects of the resin-dentin interdiffusion zone with dif- ferent dentin adhesive systems. J Dent Res 1992;71:1530-40. Davidson CL, de Gee AJ, Feilzer AJ. The competition between the composite-dentin bond strength and the polymerization contraction stress. J Dent Res 1984;63:1396-9. Tay FR, Gwinnett AJ, Pang KM, Wei SH. Structural evidence of a sealed tissue interface with a total etch wet-bonding technique in viva. J Dent Res 1994;73:629-36. Chappell RP, Cobb CM, Spencer P, Eick JD. Dentinal tubule anasto- mosis: a potential factor in adhesive bonding? J Prosthet Dent 1994;72:183-8. Chigira H, Yukitami W, Hasegawa T, Manabe A, Itoh K, Hayakawa T, Debori K, Wakwmoto S, Hisamitsu H. Self-etching dentin primers containing phenyl-P. J Dent Res 1994;73:1088-95. Watanabe I, Nakabayashi N, Pashley DH. Bonding to ground dentin by a phenyl-P self-etching primer. J Dent Res 1994;73:1212-20. Cagdiaco MC, Ferrari M. Bonding to dentin. In: De Batte 0, editor. IF Livorno: 1995:113-20.

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Watanabe I. Photocure bonding agents to ground dentin. Jpn J.Dent Mater 1992;11:955-73. Barkmeier WW, Los SA, Trio10 PT. Laboratory evaluation of an ex- perimental dental adhesive system [abstract]. J Dent Res 1994;73: 199.

15.

The lateral branches appear only in the first part of the tubule, where the shape is conical as a result of dissolution of the peritubular dentin. Therefore the lateral branches may add to the bond strength because they are situated just beneath the hybrid layer.

Sano H, Takatsu T, Ciucchi B, Harrier JA, Pashley DH. Nanoleak- age: leakage within the hybrid layer [abstract]. J Dent Res 1994;73: 276.

16.

The formation of a hybrid layer and reverse cone-shaped resin tags with lateral branches that result from the self- etching primer is a strong argument that such a system is ready for routine clinical use.

Gwinnett AJ. Quantitative contribution of resin infiltratiotiybridiza- tion to dentin bonding. Am J Dent 1993;6:7-9. Schnuepbach P, Krejci I, Lutz F. The resin dentin hybrid layer: com- parative SEM, TEM and confocal microscopic examination [abstract]. J Dent Res 1994;73:107. Bouillaguet S, Ciucchi B, Sane H, Pashley DH. Influence of dentin thickness and region on tensile bond strength [abstract]. J Dent Res 1994;73:296. Garberoglio R, Brtinnstrtim M. Scanning electron microscopic in- vestigation of human dentinal tubules. Arch Oral Biol 1976;21:355- 62.

CLINICAL SIGNIFICANCE

17.

18.

19.

20.

The formation of a hybrid layer and reverse cone-shaped resin tags with lateral branches that resulted from both bonding agents may improve the bond strength of adhesive restorations. The routine clinical use of a self-etching primer system can simplify the procedures of esthetic re- storative dentistry.

Walshaw PR, MC Comb D. SEM evaluation ofthe resin-dentin interface with proprietary bonding agents in human subjects. J Dent Res 1994;73:1079-87,

Reprint requests to: DR. MARCO FERRARI P.ZA ATWAS 19 LIVORNO 57125 ITALY

CONCLUSIONS Copyright 0 1996 by The Editorial Council of The Journal of Prosthetic Dentistry.

The following conclusions were drawn from this study.

1. Both tested bonding agents created a hybrid layer in vivo.

0022-3913/96/$5.00 + 0. 10/l/74061

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