Seventh-Generation Bonding Materials as Cavity Liners: Scientific Rationale and Clinical Technique

The number of tooth-colored restorations dentists place is increasing as patients demand optimum aesthetics and function. The materials used for these restorations are constantly being modified by manufacturers, as are the techniques for their placement. Coincident with these changes in materials is a change in the approach to cavity preparation. Conventional cavity preparations followed Black's Rules of Cavity Preparation.1 Today, newer materials allow more conservative approaches, requiring less removal of sound tooth structure. Nevertheless, postoperative sensitivity remains a concern.

At one time it was thought that the toxic effects of dental materials could adversely affect the pulp, leading to pulpal inflammation and postoperative sensitivity.2 Later, a new theory developed, suggesting that the influx of bacteria and their toxins into dentinal tubules caused adverse pulpal reactions. The bacteria were believed to originate in the smear layer,  or were present deep in the dentinal tubules and were inaccessible to caries-excavating procedures.3 Nevertheless, the current belief is that postoperative sensitivity is not due to bacterial contamination but is primarily due to fluid movement within gaps at the tooth-restoration interface.4 The fluid may also contain bacteria. With respect to restorative dentistry, one of the goals of treatment is to reduce or eliminate these gaps, which would result in a reduction and possibly elimination of postoperative sensitivity.

With this outcome in mind, materials (liners, bases, and cements) are available for placement under a restoration. Cements are indicated for luting of crowns and bridges. The use of a base below a restoration appears to be less popular than in the past (unpublished online survey by Weiner, Dentaltown.com, October 2002). Liners are materials that provide a thin coating (usually 0.5 mm) on the cut surface of a cavity preparation. Although they provide a barrier to chemical irritants, they are not used for thermal insulation or to add bulk to a cavity preparation.5  Materials that can be used as a liner can be classified as a varnish, calcium hydroxide, zinc phosphate, glass ionomer, or resin.

The newest type of cavity liner is resin-based. These products generally have low solubility and are available in a number of shades and viscosities. This category can be divided into 2 classes: flowable composites and dentin bonding agents. Studies confirm that placing adhesives below amalgam restorations reduces microleakage, thus supporting their use as liners.6,7

An inherent problem when using traditional composite resins is the polymerization shrinkage that occurs. This shrinkage results in gap formation, and therefore an increase in microleakage. The flowable resin was developed in an attempt to overcome some of the problems associated with polymerization shrinkage. Although flowables have a higher polymerization shrinkage than do conventional resins, their better flow and reduced modulus of elasticity theoretically reduce microleakage by increasing adaptation of the material to the cavity preparation and by forming a stress-absorbing layer.8 The result is a decrease in gap formation at the flowable resin-tooth interface, which will ultimately lead to a decrease in secondary caries and pulpal inflammation and a longer-lasting restoration.9

Dentin bonding agents not only act as an adhesive for the resin restoration, they are also a cavity liner. This is because the material is placed in the cavity preparation prior to any restorative material. Thus, they fulfill the characteristics of a cavity liner, as mentioned previously. Dentin bonding agents can be used under composite resin, amalgam, and gold restorations. The major disadvantage of many dentin bonding agents is that these materials are technique sensitive. The use of these materials involves a number of steps, and the clinician must pay close attention to the details. Fortunately, the manufacturers of dental materials are making strides to improve the ease of use.

Twenty-five years ago the second generation of bonding products became available, but these materials did not bond to dentin (etching of the dentin was not included in the technique). In the early 1990s, the fourth generation of these materials was introduced. These materials were able to bond to dentin and involved the use of dentin primers. The use of these systems involved 3 steps: acid etching, followed by the application of a cavity primer, which was then followed by the placement of an unfilled resin-adhesive (as a cavity sealer).

Table. Classification of Self-Etching Products.
Material Classification Number of Bottles/Containers Number of Steps (includes application, drying, and curing) Examples
sixth generation: Type 1
2
5
Clearfil SE (Kuraray)
sixth generation: Type 2
2
4
Adper Prompt L-Pop (3M ESPE
seventh generation
1
3
i-Bond (Heraeus Kulzer)
G-Bond (GC America)
Clearfil S3 Bond (Kuraray)

The sixth generation of bonding agents was characterized by the elimination of a separate etching step. The etchant was combined with the primer, making it self-etching. The products were classified into either of 2 groups. The Type 1 products (eg, Clearfil SE, Kuraray) place the primer and adhesive in 2 different bottles, each to be applied separately. Type 2 products (eg, Adper Prompt L-Pop, 3M ESPE) have both the self-etching primer and the adhesive in the same bottle (Table).

Recently, the seventh generation of bonding agents was introduced. These include i-Bond (Heraeus Kulzer), G-Bond (GC America), and Clearfil S3 Bond (Kuraray). These are single-bottle materials that etch, prime, bond, and desensitize the cavity preparation; i-Bond also disinfects the cavity preparation. These materials involve only a single step (no mixing), so they are easier to use and save time (Table).

The reduction in postoperative sensitivity that is achieved when using self-etching agents is the result of dissolving the smear layer without exposing the dentinal tubules.10 An online survey (DentalTown.com, June 10, 2004) found that 34% of the respondents used a desensitizing agent when treating cervical sensitivity. Further, of those who currently use or have used a self-etching bonding agent, 64% responded that these products reduced postoperative sensitivity.

As previously mentioned, any existing gap at the tooth-restoration interface will result in microleakage. Seventh-generation bonding a-gents generally allow the clinician to place a resin restoration with no gap at this interface. The definition of a gap is any space larger than 0.1 um. Bacteria are larger than this, eliminating the chance that the gaps will be infected.

The i-Bond material is available in 2 dispensing systems, single-dose containers (0.2 mL) and 4-mL bottles. G-Bond and Clearfil S3 Bond are available in multidose containers. A study compared the total working time (setup, application, and cleanup) of self-etching primers, evaluating both sixth- and seventh- generation materials in unidose and multidose versions. Unidose systems had significantly shorter setup and cleanup times than did those materials provided in multidose bottles.11

An important aspect of a patient recall appointment is to determine if recurrent caries is present. Radiographically, if the bonding agent is too thick, a radiolucent zone will appear on the bitewing radiograph between the cavity floor and the bottom of the restoration. This radiolucency could be interpreted as recurrent caries. Use of a bonding agent that would not cause this radiolucent zone would theoretically improve the accuracy of diagnosis. The use of seventh-generation materials is not associated with this radiolucency, as the consistency of these newer materials is thinner than the bonding agents from previous generations. Ito, et al demonstrated that applying more coats of the adhesive (Xeno III [DENTSPLY Caulk] and i-Bond) resulted in improved strength and quality of dentin adhesion.12  However, applying multiple layers of adhesive may create the radiolucent zone that can interfere with diagnosis. Dentists must determine which is preferred: no visible radiolucent line or an increase in dentin adhesion.

It should be noted that the manufacturer specifically recommends that i-Bond be used only on freshly prepared enamel. If it is to be used on sclerotic dentin or unprepared dentin, the clinician must etch with phosphoric acid for 30 seconds prior to use.

Prior to the development of dentin primers, it was taught that the cavity preparation should be dry before any restorative materials, including cavity liners, were placed. This degree of "dryness" was an area of controversy in dentistry. According to the manufacturers, this is not a concern when using sixth- and seventh-generation materials because they can be used equally well on wet or dry dentin. Butt and colleagues compared the dentin shear bond strength of 3 self-etching primers in the presence of moisture. They found that the moisture tolerance of these materials eliminates this as an important concern in bonding.13 This study confirms that cavity liners are now available that can be placed in a moist (not wet) preparation and still seal the cavity preparation.

Clinical Example Illustrating the Use of a seventh-Generation Cavity Liner Materials

To illustrate, a clinical case report is described that demonstrates a tooth being restored with i-Bond and Venus Composite Resin system (Heraeus Kulzer), which includes a flowable resin and a final restorative resin. Other combinations may be used, following manufacturers' instructions.

The refractive indices of the fillers and matrix of the Venus Composite Resin system mimic the shades of the adjacent tooth, resulting in less visible margins. A shade guide is provided that is matched to the Vita shades and has 27 shades and 3 opacities. Further, since barium aluminum fluoride glass is a component of the filler, it is highly radiopaque. Due to the fact that the particle size is less than 1 um, the resin polishes to a high luster.

Treatment

Figure 1a. Tooth No. 5, preoperative view. Figure 1b. Preoperative bite-wing radiograph.

A 33-year-old female patient presented for a recall visit, and a carious lesion was detected on the mesial surface of the maxillary right first premolar (Figures 1a and 1b). The patient requested an aesthetic restoration.

Local anesthesia was administered, and a rubber dam was placed from teeth Nos. 4 to 7.

Figure 2. Completed cavity preparation. Figure 3. Cavity preparation with matrix and wedge in place after i-Bond was applied.

The cavity preparation was completed (Figure 2) using a No. 245 bur in a highspeed handpiece and a No. 6 round bur in a slow-speed handpiece, followed by a spoon excavator. To begin the restorative phase the tooth was fitted with a matrix (Tofflemire retainer and No. 1 Deadsoft band) and was wedged (Premier Dental Products, Figure 3). The i-Bond was then placed as per the manufacturer's directions. A total of 3 coats of i-Bond was placed, with the application starting on the enamel and moving to the dentin. After a 30-second period, a gentle stream of air was directed into the preparation until no movement of the liquid was seen and the cavity surface had a glossy appearance. The material was then light-cured (Cotolux, Coltene/Whaledent) for 20 seconds.

Figure 4. Venus Flow in the axial-pulpal area.
Figure 5a. Completed restoration. Figure 5b. Postoperative bite-wing radiograph.

The next step was placement of a flowable composite. The product used in this case was Venus Flow shade A2 (Heraeus Kulzer, Figure 4). To ensure proximal contact, a ContactPro (CEJ Dental) was used. The remainder of the cavity was filled with Venus Composite Resin shade A2 under shade T1. The restoration was completed by finishing with 30 fluted carbide burs (Midwest) and composite polishing tips (Politip, Ivoclar Vivadent),  followed by a slurry of pumice. The rubber dam was removed, and the occlusion was checked (Figure 5a). A postoperative bite-wing radiograph indicated that there was no discernible space between the floor of the cavity and the bottom of the restoration (Figure 5b).

A small amount of composite on the buccal surface of the teeth can be seen. This is because at the time the patient was undergoing orthodontic treatment with Invisalign, and the composite was required for that treatment.

CONCLUSION

A number of products are available for use as cavity liners. Some of these, such as glass ionomers and zinc phosphate, can also be used as bases and cements. Dentin bonding agents serve to increase the retention of a resin restoration to the cavity preparation. While doing so, they are acting as a cavity liner by sealing the dentin (as do conventional liners). Numerous dentin bonding agents are available. The recently introduced seventh-generation bonding products are much easier to use than previous materials. Their primary advantages are a reported decrease in postoperative sensitivity due to effective cavity-lining properties and a decrease in treatment time compared to earlier versions.

Dentin bonding agents are not meant to eliminate the need for other conventional liners. However, they are an addition to the cavity liners available for clinical use.


References

1. Baum L, Phillips R, Lund M. Textbook of Operative Dentistry. Philadelphia, Pa: WB Saunders; 1981:19, 2.

2. Weiner R. Liners, bases, and cements in clinical dentistry: a review and update. Dent Today. Aug 2003;22:88-93.

3. Brannstrom M. Reducing the risk of sensitivity and pulpal complications after the placement of crowns and fixed partial dentures. Quintessence Int. 1996;27:673-678.

4. Brannstrom M. Etiology of dentin hypersensitivity. Proc Finn Dent Soc. 1992;88(suppl 1):7-13.

5. Baum L, Phillips RW, Lund MR. Textbook of Operative Dentistry. 3rd ed. Philadelphia, Pa: WB Saunders; 1995.

6. Hagan K, Davis A, Belcher M, et al. Microleakage of class II restorations. J Dent Res. 2003;special issue:Abstract 933.

7. Vettraino JT, Neme A-ML, Pink FE, et al. Effect of cavity treatment on in vitro amalgam leakage. J Dent Res. 2003;special issue:Abstract 1322.

8. Bayne SC, Thompson JY, Swift EJ Jr, et al. A characterization of first-generation flowable composites. J Am Dent Assoc. 1998;129:567-577.

9. Bergenholtz G, Cox CF, Loesche WJ, et al. Bacterial leakage around dental restorations: its effect on the dental pulp. J Oral Pathol. 1982;11:439-450.

10. Farah J, Powers J. Self-etching bonding agents. The Dental Advisor. Oct 2003;20:1-2.

11. Peuker M, Janz K, Dubbe J. Comparison of total working times of self-etching adhesives. J Dent Res. 2003;special issue:Abstract 861.

12. Ito S, Tay FR, Hashimoto M, et al. Effects of multiple all-in-one adhesive coatings on dentin bonding. J Dent Res. 2004;special issue:Abstract 233.

13. Butt S, Burgess JO, Xin X. Dentin bond strength of bonding agents to moist and dry dentin. J Dent Res. 2003;special issue:Abstract 562.



Dr. Weiner
received his DMD degree from Tufts University in 1986. He is a fellow of the Academy of General Dentistry, the American College of Dentists, and the Pierre Fauchard Academy. He has written many articles and presented numerous lectures on the topic of liners, bases, and cements. He maintains a private practice in family and cosmetic dentistry in Millis, Mass, and can be reached at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .


 

Continuing Education Test No. 70.1



After reading this article, the individual will learn:

• why cavity liners are used, and
• why seventh-generation bonding agents can be used as cavity liners.

 

1. Current understanding is that postoperative sensitivity exists due to _____ :
a. the toxic effects of dental materials.
b. the influx of bacteria into the dentinal tubules.
c. fluid movement within the gaps at the tooth-restoration interface.
d. none of the above.

2. The following is (are) a characteristic(s) of a cavity liner:
a. It is a barrier to chemical irritants.
b. It is not used for thermal insulation.
c. Materials are usually 0.5 mm thick when placed.
d. all of the above

3. Which of the following materials is NOT used as a cavity liner?
a. varnish
b. calcium hydroxide
c. zinc polycarboxylate
d. glass ionomers

4. Traditional resins undergo polymerization shrinkage, which allows a gap to form at the tooth-resin interface. Flowable resins have a higher modulus of elasticity, which promotes a reduction in microleakage.
a. Both statements are true.
b. Both statements are false.
c. The first statement is true, and the second statement is false.
d. The first statement is false, and the second statement is true

5. Sixth-generation bonding agents are products that have the etchant, primer, and bonding agent in separate containers, while seventh-generation agents have the etchant, primer, and bonding agent in the same bottle.
a. Both statements are true.
b. Both statements are false.
c. The first statement is true, and the second statement is false.
d. The first statement is false, and the second statement is true.

6. What percentage of respondents who currently use or have used a self-etching bonding agent report a reduction in postoperative sensitivity?
a. 34%
b. 44%
c. 54%
d. 64%

7. Bonding agents with a high film thickness will tend to exhibit a radiolucent zone on a bite-wing radiograph, and seventh generation products are not associated with this phenomenon.
a. Both statements are true.
b. Both statements are false.
c. The first statement is true, and the second statement is false.
d. The first statement is false, and the second statement is true.

8. Self-etching dentin bonding agents CANNOT be used on ______:
a. sclerotic dentin without pre-etching.
b. sclerotic dentin with pre-etching.
c. dry dentin.
d. wet dentin.


To submit Continuing Education answers, download the answer sheet in PDF format (click Download Now button below). Print the answer sheet, identify the article (this one is Test 70.1), place an X in the box corresponding to the answer you believe is correct, and mail to Dentistry Today Department of Continuing Education (complete address is on the answer sheet).

 

 

 



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