BONDED AMALGAM SEALANTS: TWO-YEAR CLINICAL RESULTS

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BONDED AMALGAM SEALANTS: TWO-YEAR CLINICAL RESULTS MICHAL STANINEC, D.D.S.; W. STEPHAN EAKLE, D.D.S.; STEVE SILVERSTEIN, D.D.S., M.P.H.; GRAYSON W. MARSHALL, D.D.S., PH.D., M.P.H.; NELSON ARTIGA, D.D.S., M.P.H.

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The authors used bonded amalgams as pit and fissure sealants without mechanical preparation. They compared the two-year retention of the bonded amalgams with that of resin-based pit and fissure sealants. Clinical examinations at six months, one year and two years revealed no difference between the retention of the two sealants. This technique opens up the possibility of using bonded amalgam in pits and fissures surrounding very conservative preparations in a preventive amalgam restoration.

Modern adhesive techniques have made possible very conservative

methods of restoring carious tooth structure in both anterior and posterior teeth. Adhesive dentistry commenced with Buonocore’s discovery of phosphoric acid etching of enamel to enhance the retention of acrylic resins.1 Soon afterward, composite resin techniques incorporated this procedure as a routine. Pit and fissure sealants were an early offshoot of this technique and, gradually, with new adhesive materials, other techniques were developed for bonding cements, bases, liners, porcelain and cast metals to tooth structure. This generally resulted in considerable saving of tooth structure by eliminating much use of the retention-and-resistance form associated with traditional restorative techniques. Until recently, no material was available to bond amalgam to tooth structure, so amalgam preparations and the placement technique have not changed drastically since the times of G.V. Black. However, the recent findings that some adhesive resins can bond freshly mixed amalgam to tooth structure2 have led to improvement of existing techniques and development of clinical techniques for amalgam that were not previously possible. Staninec3 demonstrated in laboratory studies that adhesives can retain amalgams under simulated occlusal loads in proximal cavities better than undercuts can. Torii and colleagues4 demonstrated that the adhesive amalgam technique can inhibit recurrent caries in vitro. The clinical technique for extensive bonded amalgam restoration was described by Lacy and Staninec,5 and several clinicians have used the technique and reported good results in casual testimonials. Some controlled clinical studies have now been reported.6,7 Staninec and colleagues8 recently reported results from a pilot retrospective clinical study that examined the condition of bonded amalgams after several years of clinical service in primary molars. In another study, the adhesive technique was found to improve the fracture resistance of teeth more than the traditional technique in vitro.9 Staninec and colleagues10 also recently reported data on bond strengths of proprietary amalgam adhesives. The placement of resin-based pit and fissure sealants is a welldocumented and effective technique for preventing pit and fissure decay.11-13 Resin-based sealants are unfilled or lightly filled and are limited in their clinical longevity by loss and wear. Within five to

JADA, Vol. 129, March 1998 Copyright ©1998-2001 American Dental Association. All rights reserved.

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RESEARCH TABLE 1

MATERIALS AND METHODS

MATERIALS USED. PURPOSE

PRODUCT

BATCH NO.

MANUFACTURER

Etching

Unietch (32 percent phosphoric acid semi-gel)

29254

Bisco Dental Products Inc.

Primer

All-Bond 2 Primer A (Na-NTG GMA* in acetone) All-Bond 2 Primer A (BPDM† in acetone)

29094

Bisco

19214

Bisco

Liner

Liner F base Liner F catalyst

29154 29264

Bisco Bisco

Sealant

Bisco Pit & Fissure Sealant

29034

Bisco

Amalgam

Tytin, spherical high copper alloy

Not available

Kerr Manufacturing Co.

* Na-NTG GMA: sodium salt of N-tolylglycine glycidyl methacrylate. † BPDM: biphenyl dimethacrylate.

seven years, much of the sealant material is lost and may need to be replaced. Amalgam, on the other hand, is a material with wear resistance similar to that of tooth structure, which can withstand the stresses to which the occlusal surfaces are subjected over a long period. If amalgam is adhesively bonded to occlusal pits and fissures, it is possible that it might provide a longer period of clinical service and thus longer protection against pit and fissure caries. Adhesively bonded amalgam in pits and fissures adjacent to a carious lesion might be used as a sealant, thus eliminating the need to extend the preparation into pits and fissures that are deep but not carious. This technique would be analogous to the preventive resin restoration described by Simonsen.14 Additionally, if amalgam can be retained in a thin layer on occlusal surfaces of teeth in vivo, it will be demonstrated that the bond of amalgam to tooth mediated by the adhesive resin is 324

stable in the clinical environment. This information will have implications for amalgam restorations that replace carious or broken tooth structure. PURPOSE

The hypothesis we tested was that adhesively bonded amalgam can be used instead of resin-based pit and fissure

Adhesively bonded amalgam in pits and fissures adjacent to a carious lesion might be used as a sealant. sealants and that such amalgam sealants will be retained as well as or better than resin-based sealants, and will be more wearresistant and provide longer clinical service than resin-based pit and fissure sealants. We also tested the hypothesis that the amalgam-resin-tooth bond is stable in vivo after two years of clinical service.

We screened and selected patients in good health who had no contraindications to routine dental treatment and needed at least two pit and fissure sealants. These patients were screened and treated at the Family Dental Center, a community outreach dental clinic of the University of California, San Francisco School of Dentistry. The protocol was approved by the Committee on Human Research of the UCSF dental school and informed consent was obtained before treatment. We attempted to find contralateral pairs of teeth in the same patient, one of which would be sealed with a traditional resin-based sealant and the other with the adhesive amalgam sealant. A total of 114 teeth in 26 patients were initially included in the study. The ages of the patients ranged from 6 to 25 years at placement. Table 1 shows the materials used for this investigation. Each tooth was photographed before treatment. The sealants were placed as follows: dThe teeth receiving the experimental amalgam sealants were cleaned with a prophylaxis brush with nonfluoridated pumice, isolated with a rubber dam, etched with phosphoric acid for 30 seconds and rinsed for 30 seconds, then gently dried to the point that the surface was slightly moist. A mixture of AllBond 2 Primer A & B (Bisco Dental Products Inc.) was placed in several coats until the surface was glossy. The surface was then dried thoroughly, and the primer was light-cured for 30 seconds. Liner F (Bisco Dental Products Inc.) was mixed and painted in a thin layer over the

JADA, Vol. 129, March 1998 Copyright ©1998-2001 American Dental Association. All rights reserved.

RESEARCH set primer; the amalgam was then immediately condensed over the surface and burnished into all grooves. Excess was carved away. The rubber dam was removed and occlusion was checked and adjusted. dThe control resin sealant teeth were treated in the same way up to and including the primer step. Then a conventional sealant was placed in all grooves and light-cured for 30 seconds. Each tooth in both groups was photographed before we dismissed the patient. Recall appointments were scheduled at six months, one year and two years after placement. At each recall visit, we performed a clinical examination in which we assigned a retention rating to each sealant. (Table 2 shows the rating scale, and Table 3 summarizes the numbers of teeth treated at placement and examined at recall visits.) Additionally, a polyvinyl siloxane impression and a photograph of the sealant were made at each recall visit. We made epoxy casts from the impressions so that we could examine interesting features with scanning electron microscopy, or SEM. All of the sealants were placed by two operators and each clinical evaluation was done by two trained examiners working together, from a total of five examiners. Any disagreements in ratings were resolved by discussion and consensus. Because of the obvious difference between amalgam and resin sealants, examiners could not be blinded in the examinations. STATISTICAL METHODS

Several approaches were used to test the null hypothesis that there was no difference in the two-year clinical scores of the

TABLE 2

U.S. PUBLIC HEALTH SERVICE CRITERIA FOR SUCCESS OF SEALANTS. CRITERIA

RATING Alfa

Complete retention; no exposed grooves judged to be at risk of developing caries

Bravo

Partial retention with some grooves exposed, but not judged to be at risk of developing caries

Charlie

Partial retention; exposed grooves judged to be at risk of developing caries—reapplication indicated

Delta

Total loss of material

TABLE 3

NUMBERS OF TEETH TREATED AND EXAMINED. VARIABLE

TIME OF EVALUATION At Placement

Total No. of Patients

Six Months One Year Two Years After After After Placement Placement Placement

26

26

24

22

Total No. of Teeth Treated

114

114

108

97

Total No. of Perfectly Matched Pairs

45

45

42

37

Molars With Amalgam Sealants Treated and Examined

37

37

34

31

Molars With Resin Sealants Treated and Examined

36

36

33

29

Premolars With Amalgam Sealants Treated and Examined

20

20

20

18

Premolars With Resin Sealants Treated and Examined

23

23

23

21

two types of dental sealants. The materials were tested primarily by using a matched-pair study design (contralateral teeth of the same tooth type randomly assigned to the type of sealant, n = 34 pairs) and the outcome measure was an ordinally scaled

numeric variable. For the paired analysis, the outcome measure was scored from 1 (high) to 4 (low) and the variable for analysis was the difference in the clinical outcome score for each pair of teeth. The difference in the two-year score was tested by

JADA, Vol. 129, March 1998 Copyright ©1998-2001 American Dental Association. All rights reserved.

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RESEARCH TABLE 4

CLINICAL RATINGS OF AMALGAM AND RESIN SEALANTS. RATING

PERCENTAGE OF AMALGAM SEALANTS MEETING CRITERIA

PERCENTAGE OF RESIN SEALANTS MEETING CRITERIA

Six Months After Placement

One Year After Placement

Two Years After Placement

Six Months After Placement

One Year After Placement

Two Years After Placement

Alfa (No Loss)

80.4

72.0

46.0

72.2

66.0

58.5

Bravo (Slight Loss)

11.8

16.0

40.0

20.4

20.8

17.1

7.8

10.0

12.0

7.4

11.3

22.0

0

2.0

2.0

0

1.9

2.4

Charlie (Repair Required) Delta (Total Loss)

using the nonparametric Wilcoxon’s signed ranks test. The other analytic approach we used treated the outcome measure as an ordinally scaled categorical variable. In this analysis, we used the MantelHaenszel χ2 test of trend to determine whether there was a linear relationship between the type of sealant and the two-year clinical score. This analysis ignored the paired nature of the data. We conducted it first for all teeth in participants who had matched pairs treated (n = 68 teeth), and then repeated it for all treated teeth in both the matched-pair participants and the participants with individual or multiple treated teeth that were not paired (n = 94 teeth). RESULTS

Table 4 shows the summary of results at each recall. In the matched-pair analyses, we found no difference between the two types of sealant in the two-year clinical scores (mean difference in score between resin sealants and amalgam sealant = -0.08, standard deviation = 0.83; Wilcoxon’s 326

signed ranks score = -12; P = .66). Similarly, the Mantel-Haenszel χ2 test of trend score was not significant for teeth in participants in the paired study design (P = .63) or for teeth in the all-

Bonded amalgam cannot yet be recommended for routine sealing of pits and fissures because it appears to be only equal and not superior to conventional resin sealants. participants analysis (P = .60). This pattern also held when we stratified the analysis by tooth type (premolars and molars). However, there was limited statistical power to detect a significant difference in this study. For the Wilcoxon’s signed ranks test, the power to detect the observed mean difference in clinical score at α = 0.05, under the null hypothesis of µ = 0, was 9 percent.

Qualitative observations showed that when the resin sealants failed, it was mostly because of debonding; some of the grooves and pits lost all of the sealant, leaving a deep fissure. In the amalgam group, the amalgam sometimes appeared to debond along with the underlying resin, leaving an exposed deep fissure; in other cases, the amalgam debonded from the resin, leaving a layer of resin in the fissure. Figure 1 shows an example of an amalgam sealant that received an Alfa rating at the twoyear recall, and Figure 2 shows a resin sealant that received a Charlie rating at the two-year recall. Figure 3 shows resin sealants with Alfa ratings and an amalgam sealant with a Bravo rating. Figure 4 shows an SEM photomicrograph of a replica of an amalgam sealant rated Charlie, in which one of the occlusal grooves appears to be completely exposed. DISCUSSION

Our first hypothesis was that bonded amalgam sealants would be superior to resin sealants. An improved, longerlasting method of sealing pits and fissures would result in a reduction of caries in cases in which patients do not return for recall visits. For those who do return, sealants could be reapplied less frequently, resulting in savings of time and money. However, bonded amalgam cannot yet be recommended for routine sealing of pits and fissures because, in this study, the bonded amalgam technique appears to be only equal and not superior to the conventional technique, and the duration of the study so far is relatively short. However, if future long-

JADA, Vol. 129, March 1998 Copyright ©1998-2001 American Dental Association. All rights reserved.

RESEARCH

Figure 1. Amalgam sealant rated Alfa at two years in a lower first molar. No significant loss of material was noted.

Figure 3. Amalgam sealant rated Bravo at two years is present in the upper second molar. Slight loss of material was noted. The resin sealants in the second premolar and first molar were rated Alfa. The stain in the lingual pit was present at placement.

term results show that bonded amalgam is more effective than resin, it may be recommended as a more durable alternative to patients for whom esthetics are not a primary concern. Although cost effectiveness was not examined in the present study, amalgam sealants would clearly be more expensive, as more materials and steps are involved in the amalgam procedure. If amalgam is to be recommended instead of resin as a sealant, it will have to prove to be significantly more effective than resin in the future. Most studies that have

Figure 2. Resin sealant rated Charlie at two years. Note the presence of sealant in the central pit and loss of sealant from the distolingual groove of the upper first molar.

Figure 4. Scanning electron microscopic replica of an amalgam sealant rated Charlie at two years. Note loss of material from distolingual groove of this upper first molar. Amalgam is still present in the central pit area.

demonstrated the effectiveness of sealants for caries prevention have used a split-mouth design with one side sealed and the other unsealed.11-13 This usually results in some caries formation on the unsealed surfaces, with little or no caries on the sealed surfaces. As the effectiveness of sealants is wellestablished, we feel that leaving susceptible occlusal surfaces deliberately unsealed would be unethical. This is one of the reasons that the amalgam sealants were compared with resin sealants. Both were 100 percent

effective in preventing caries for the duration of the study. This may be attributed partly to the fact that any Charlie- or Deltarated surfaces were resealed. Another use for bonded amalgam sealants is the sealing of pits and fissures around amalgam restorations. As amalgam sealants appear to be effective, the use of extension for prevention could be eliminated even for deep pits and fissures at the margins of preparations, and pits and fissures could be sealed in the same step and at the

JADA, Vol. 129, March 1998 Copyright ©1998-2001 American Dental Association. All rights reserved.

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RESEARCH

Figure 5. The preventive amalgam restoration. A. A minimally invasive preparation on the mesial surface of an upper first molar. Extensions allowed for caries removal, but no additional tooth structure was removed.

same time that a carious lesion is restored with the adhesive amalgam technique. This would save a considerable amount of tooth structure that now is often removed for preventive reasons when amalgam restorations are placed. Such a restoration can be termed a “preventive amalgam restoration,” analogous to the preventive resin restoration introduced by Simonsen.14 Based on the results of the present study, this technique can be recommended when amalgam is being used as a restorative material (Figure 5). A further ramification of the results of the present study is the implication for bonded amalgam restorations in conventional or modified preparations. Some authors have expressed doubts about whether bonded amalgam restorations are worth the extra trouble,15 and whether the bond between amalgam, resin and tooth is sufficient to replace mechanical retention in vivo.6 Several studies have now been published or presented on clinical results of bonded amalgams in conventional preparations. Generally, no significant differences are reported between 328

B. The preventive amalgam restoration. After etching the preparation and the surrounding pits and fissures, it was treated with a primer and painted with adhesive resin. Next, the amalgam was placed as restorative into the preparation and as a sealant in the pits and fissures.

nonbonded and bonded amalgams.6,7 However, placing bonded amalgams in conventional preparations is not a particularly demanding test of the bond. Conventional amalgam restorations, especially of high copper type, are known to perform well for 10 to 15 years, although some marginal dyscra-

The stability of the amalgam-resin-tooth structure bond appears to be as good as that of the resin sealants. sia is usually seen after five years.16 The addition of bonding might be expected to improve the margins somewhat, but this is not likely to be seen in the short term. On the other hand, the present study used bonded amalgam in a much more severe test, because there was no preparation at all. Without bonding, amalgam sealants would be expected to fail immediately. The amalgam was bonded to the

teeth in a thin layer, with no definite margin, whereas conventional preparations demand bulk for strength; a minimum thickness of approximately 1.5 millimeters; a 90-degree angle of departure at the margin; and undercuts in the form of dovetails, walls that converge occlusally or proximal grooves for retention. Because the bonded amalgam was mostly retained without any of these features, our results call into question the need for any of these features in the restoration of carious lesions with bonded amalgam. Further research should answer questions about the need for conventional features of amalgam preparations when bonding is used. However, it is likely that more conservative designs are possible, limiting or eliminating the need to remove noncarious tooth structure. On the other end of the scale, very large amalgams replacing one or more cusps may be retained with little or no mechanical retention, saving what little tooth structure is left. Evidence of such possibilities has already been presented.17

JADA, Vol. 129, March 1998 Copyright ©1998-2001 American Dental Association. All rights reserved.

RESEARCH

Dr. Staninec is a

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Dentistry.

Francisco School of Dentistry.

San Francisco, Calif. 94143-0758.

If bonding is used in convenStaninec. tional preparations, the bond and therefore the seal should be maintained at least as well as those of the sealants, with some possible reinforcement of the tooth structure, as has been demonstrated in vitro.9 The stability of the amalgam-resintooth structure bond appears to be as good as that of the resin sealants, enough to retain most of the amalgam in place over the two years. If the bond had seriously deteriorated, we would expect all of the amalgam sealants to be lost over this period. Amalgam is a brittle material that needs bulk for strength when placed without adhesives; therefore, a 90-degree cavosurface angle is recommended in traditional cavity preparations. However, as the results of this study demonstrate, amalgam bonded to the underlying tooth structure is not subject to brittle fracture to the same extent that nonbonded amalgam would be. Address reprint requests to Dr.

This is analogous to the use of thin layers of porcelain for veneering teeth for esthetic purposes. Without bonding, porcelain veneers are brittle, but once bonded, they are strong enough to withstand many years of functional clinical service. CONCLUSION

Amalgam was bonded in a thin layer into unprepared pits and fissures as a sealant and was retained as well as resin sealant at two years. Conventional retentive features and a 90-degree cavosurface angle might not be necessary for amalgam restorations when bonding is used. ■ The authors gratefully acknowledge support by a grant from Bisco Dental Products Inc., Itasca, Ill.; technical assistance by Drs. Carmen Basurto and Herman Chang; and statistical analysis by Dr. Scott Tomar. This article is based on a paper presented at the 75th General Session of the International Association for Dental Research in Orlando, Fla., March 1997. 1. Buonocore MG. A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res 1995;34:849-53.

2. Staninec M, Holt M. Bonding of amalgam to tooth structure: tensile adhesion and microleakage tests. J Prosthet Dent 1988;59(4):397-402. 3. Staninec M. Retention of amalgam restorations: unDr. Artiga is direcdercuts vs. bonding. tor, Family Dental Quintessence Int Center, University 1989;20:347-51. of California, San 4. Torii Y, Staninec Francisco School of M, Kawakami M, Dentistry. Imazato S, Torii M, Tsuchitani Y. Inhibition in vitro of caries around amalgam restorations by bonding amalgam to tooth structure. Oper Dent 1989;14:142-8. 5. Lacy AM, Staninec M. The bonded amalgam restoration. Quintessence Int 1989;20:521-4. 6. Belcher MA, Stewart GP. Two-year clinical evaluation of an amalgam adhesive. JADA 1997;128(3):309-14. 7. Ruzickova T, Staninec M, Setcos JC, Mach Z. Bonded amalgam restorations: twoyear clinical results (Abstract no. 426). J Dent Res 1997;76(Special Issue):67. 8. Staninec M, Marshall GW, Lowe A, Ruzickova T. Clinical research on bonded amalgam restorations. Gen Dent 1997;45(4):356-62. 9. Eakle WS, Staninec M, Lacy AM. Effect of bonded amalgam on the fracture resistance of teeth. J Prosthet Dent 1992;68:257-60. 10. Staninec M, Torii Y, Watanabe LG, Kawakami M, Tonn EM. Tensile adhesion evaluation in a new universal test. Am J Dent 1992;5:187-91. 11. Weintraub JA. The effectiveness of pit and fissure sealants. J Public Health Dent 1989;49:317-30. 12. Simonsen RJ. Retention and effectiveness of dental sealant after 15 years. JADA 1991;122(11):34-42. 13. Henderson HZ, Setcos JC. Pit and fissure sealants. In: McDonald RE, Avery DA, eds. Dentistry for the child and adolescent. St. Louis: Mosby; 1987. 14. Simonsen RJ. Preventive resin restoration: three-year results. JADA 1980;100:535-9. 15. Mahler DB, Engle JH, Simms LE, Terkla LG. One-year clinical evaluation of bonded amalgam restorations. JADA 1996;127(3):345-9. 16. Anusavice KJ. Phillips’ science of dental materials. 10th ed. Philadelphia: Saunders; 1996:405-7. 17. Burgess JO, Summitt JB, Osborne JW, Berry TG, Robbins JW. One-year evaluation of Amalgambond Plus and pin-retained amalgam restorations (Abstract no. 428). J Dent Res: 1997;76 (Special Issue):67.

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