Prevention of Root Surface Caries Using a Dental Adhesive

PREVENTION OF ROOT SURFACE CARIES USING A DENTAL ADHESIVE E D W A R D J. S W IF T , D .M .D ., M .S .; S A R A A . H A M M E L , B .A .; J O R G E PER DIG AO , M E D . D E N T ., M .S .; J A M E S S. W E F E L, PH.D.

0 everal new dental adhesive systems use acids such as 10 percent phosphoric acid or 10 percent maleic acid to simul­ taneously etch enamel and dentin. The etchant removes the smear layer, opens and widens the orifices of the dentinal tubules and demineralizes the dentin to depths of up to 7.5 microns.1Hydrophilic primers (including resin monomers such as hydroxyethylmethacrylate, or HEMA) and unfilled resins are applied to the etched dentin. The resins penetrate not only the dentinal tubules, but also the demineralized intertubular dentin, polymerizing to form a mixed zone of resin and dentin to which the restorative m aterial is bonded. This socalled “hybrid layer” or “resininfiltrated layer” is considered the primary retentive mechanism of most new dentin adhesive systems.16 Some clinicians now use dentin bonding systems to treat or prevent dentin hypersensi­ tivity,7'8 although evidence about their efficacy remains largely anecdotal. A clinical study in which Gluma (Bayer/Miles Inc. Dental Products) was used to treat hypersensitivity was reported

A

B

S

R

A

C

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Dental adhesives might be applied as sealants to exposed root surfaces to prevent root caries. One resin adhesive system significantly reduced the incidence and severity of lesions in an artificial caries system.

recently. Gluma significantly reduced the sensitivity of teeth prepared for full crowns. This effect may be the result of altered dentin permeability caused by denaturation of proteins within the dentinal tubules.9Another study showed th a t Gluma and two other resin primers reduced dentinal sensitivity in rabbits, but the mechanism of desensitization is unclear.10 In contrast, the effectiveness of some adhesive systems in reducing hypersensitivity may be directly related to their bonding mechanism, th a t is, the formation of resin tags and resin-infiltrated zones or hybrid layers. Occlusion of the dentinal tubules is im portant in prevent­ ing dentinal hypersensitivity. Studies have shown th a t most tubules are open in hypersensi­ tive dentin, but most are

occluded in naturally desensi­ tized dentin.1112 Resin adhesive systems m ight provide a similar effect. According to Nakabayashi and others, “the hybrid layer forms an acidresistant envelope th a t seals the dentin, preventing hypersensitivity and secondary caries.”2 In addition to reducing hypersensitivity, some adhesives could theoretically seal dentin to prevent root surface caries, because “the hybrid layer is highly acid resistant. It rem ains intact even after both enamel and dentin have been dissolved in HC1. This suggests the intriguing possibility of simultaneously bonding to the tooth and rendering it caries-resistant without the use of fluoride.”2 The resin-infiltrated layer might provide caries protection for root surfaces analogous to th a t of pit and fissure sealants on occlusal surfaces.13 Although there have been no published reports about the efficacy of dental adhesives for root caries prevention, a prelim­ inary study was presented at the 1993 IADR meeting.14This study showed th a t Scotchbond Multi-Purpose (3M Dental Products) prevented the JADA, Vol. 125, May 1994

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formation of in vitro carieslike lesions on root surfaces. In this study, we evaluated the effectiveness of one popular adhesive system, All-Bond 2 (Bisco, Inc.), in preventing root surface caries in vitro. The complete bonding protocol and a simpler desensitization protocol were both tested using an artificial caries model. M A T E R IA L S A N D M ETHODS

Extracted hum an molars were thoroughly cleaned and examined for caries, restor­ ations and fracture lines. Thirty sound unrestored teeth were selected. The teeth were stored in a refrigerated thymol disinfectant solution, and were removed from the thymol solution and transferred to room tem perature distilled w ater 24 hours before the experiment. The apexes of each tooth were sealed with self-cured acrylic resin, and the buccal root surface was abraded with a coarse Sof-Lex disk (3M) to thin or remove cementum, sim ulating clinical wear of the cementum layer. Each tooth was completely coated with acid-resistant varnish except for a 3 X 2 millimeters rectangular “window” of exposed dentin on the buccal root surface. The teeth were randomly assigned to one of three groups (n=10). In the first group, the dentin was cleaned with flour of pumice slurry on a rotating rubber prophy cup in a slow-speed handpiece. These specimens were left untreated as the control group. The second group of teeth was treated using the All-Bond 2 desensitization protocol. Dentin was cleaned with a flour 572

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of pumice slurry. After the buccal root surface was rinsed with w ater and dried with compressed air, it was lightly moistened with w ater on a cotton pellet. One drop each of All-Bond 2 Primers A and B were mixed and applied to the surface. Five consecutive coats were applied, with no air drying between coats. After the final application, any remaining solvent was blown off with

Although the dentin adhesive tested in this stu d y d id not completely prevent root caries, the results suggest that treating exposed root surfaces with such an adhesive system might significantly reduce caries incidence and severity. compressed air. This process was repeated, and the primer mixture was visible light-cured for 10 seconds. The final group of specimens was treated with the entire AllBond bonding protocol. After it was cleaned with pumice, the dentin was etched for 15 sec with All-Etch, a 10 percent phosphoric acid polymerthickened gel. The etching gel was rinsed off thoroughly with water, and the surface was dried with compressed air. The surface was remoistened by applying water with a cotton pellet. Primers A and B were mixed and applied in five consecutive coats as described previously. After drying, additional coats of the primer mixture were applied as needed until the dentin appeared

glossy. An unfilled resin (Fortify, Bisco, Inc.) was applied to the surface, thinned with a brush and visible light-cured for 20 sec. A partially saturated buffer solution containing 2.2 mM calcium (from calcium chloride dihydrate), 2.2 mM phosphate (from potassium phosphate) and 50.0 mM acetic acid/potassium acetate buffer served as the artificial caries system.15The pH was adjusted to 3.5, and each specimen was immersed in 50 milliliters of the demineralizing solution at room tem perature for about 80 hours. The demineralization solution was stirred continuously. Several longitudinal sections were taken from each specimen with a Silverstone-Taylor hard tissue microtome (Sci-Fab) and ground to a thickness of about 100 microns using aluminum oxide abrasive slurry. Each section was imbibed in w ater and examined for carieslike lesions with a polarized light microscope. Lesion depths were m easured using the microscope’s eyepiece reticle, which was calibrated by placing a 10 micron/unit graticule on the microscope stage. In lesions with irregular advancing fronts, only the deepest measurement was recorded. D ata were analyzed using a PC-based statistical software program (Instat 2, GraphPad Software, Inc.). Representative specimens were also photographed under polarized light on color transparency film. RESULTS

Carieslike lesions formed in all of the control specimens. These lesions had the typical saucer­ shaped appearance of root caries lesions (Figure 1).

RESEARCH Lesions also formed in all of the specimens th a t were treated only with the All-Bond primers, but these were shallower and sometimes had a less regular shape (Figure 2). Except for isolated areas of décalcification in three specimens, no carieslike lesions formed in specimens th a t received the complete bonding protocol (Figure 3). The unfilled resin layer appeared to remain intact on the surface of these specimens, although the demineralizing solution may have dissolved it in some areas. Lesion depth data are summarized in the Table. Lesions in the control group had a mean depth of 181 ± 16 microns, and lesions in the primer-only group had a mean depth of 150 ± 15 microns. The mean lesion depth of the bonded group was 27 microns, but this figure overstates the lesion size somewhat. When lesions occurred, they were localized to small discrete areas. Because data in one group were not

normally distributed, nonparam etric (distribution-free) statistical methods were used to analyze the data. The KruskalWallis test revealed a statisti­ cally significant difference (P < .0001) between mean lesion depths of the three groups. A post hoc Dunn’s test showed th a t the mean lesion depth of the bonded group was significantly less than the control group at P < .001 and significantly less than the other treatm ent group at P < .05. However, the mean lesion depth of the primer group was not significantly different from th at of the control group. D IS C U S S IO N

The increased availability of fluorides and improvements in preventive dental care have led to a decline in the caries rate of children and adolescents during the last two decades.16Increased public awareness of oral health and advances in restorative dentistry have also allowed older adults to retain more

TABLE

DEPTH (MICRON) OF C A IS U K E LESION FORMED IN D00I SURFACES IMMERSED IN ARTIE C AE CAR ES SYSTEM. SURFACE TR E A TM E N T S P E C IM E N

C O M PLETE SYSTEM

NONE

P R IM E R S

1

170

167

O

2

188

144

75

3

150

158

O

4

192

150

75

5

200

163

O

6

182

167

O

7

180

133

o

8

175

125

o

9

169

158

125

IO

2 00

133

O

M ean

181

150

28

16

15

46

S .D .

teeth.17 Surveys suggest th a t the percentage of edentulous American adults declined from 55 percent in 1957 to 41 percent by 1986.18 These factors, combined with the increasing age of the U.S. population, mean th a t the number of teeth a t risk for caries is greater than ever and will continue to increase.19 Exposed root surfaces in the elderly are at particular risk for caries. Diagnosis and treatm ent of root surface caries are technically difficult and unpredictable.20Therefore, preventing root caries should be a concern not only for public health academicians, but also for the practicing dentist. The dental literature has much information on prevention of enamel caries, but little on prevention of root surface caries. Few clinical studies exist on the use of fluoride or other therapeutic agents to prevent root caries. One in vitro study,21 however, showed th a t the presence of 0.25 and 0.50 ppm fluoride in the demineralizing buffer can reduce carieslike lesion depth by 17 percent and 28 percent, respectively. A clinical trial22 conducted on 810 healthy adults, aged 54 and older, showed th a t a 1,100 ppm sodium fluoride dentifrice produced significant cariostatic activity. In comparison with the control group, root surface caries incidence was reduced by 67 percent in the test group during the one-year study. Also, a 0.05 percent neutral sodium fluoride mouthrinse signifi­ cantly reduced caries incidence on approximal root surfaces.23 Finally, epidemiologic evidence indicates th a t root caries incidence decreases as the concentration of fluoride in the JADA, Vol. 125, May 1994

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RESEARCH

Figure 1. Carieslike lesion in an untreated root surface.

Figure 2. Carieslike lesion in dentin that was treated with All-Bond 2 primers.

drinking w ater increases.24 A recent in situ study25using an antimicrobial varnish also gave promising results by inhibiting lesion depth and mineral loss by about 80 per­ cent. The control varnish had no effect and did not act as a barrier coating in these experiments. A clinical study26 of exposed root surfaces treated with an antimicrobial varnish showed suppression of S trepto­ coccus m utans populations, less need for restorative treatm ent and hardening of 574

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some initial lesions. Other methods for preventing root surface caries could be considered in addition to fluorides and antimicrobial varnishes. Physical barriers— resin pit and fissure sealants— prevent caries in susceptible areas of posterior teeth.27 Applying resins to exposed root surfaces might provide a similar protective effect against acid challenges. Resin root sealants have not been practical because, until recently, bond strengths of resins to dentin

were fairly weak.23 But advances in dentin bonding technology have improved shear bond strengths considerably,29 so sealing root surfaces with some resin adhesives may now be possible. Although the dentin adhesive tested in this study did not completely prevent root caries, the results suggest th at treating exposed root surfaces with such an adhesive system might significantly reduce caries incidence and severity. Clearly, more research will be needed to determine whether root sealing can become a routine and effective clinical procedure. Additional studies should be undertaken to answer specific questions about this procedure, including: ■* Do stresses such as tem pera­ ture changes, toothbrush abrasion, prolonged exposure to the complex chemistry of the oral environment and tooth flexure caused by occlusal forces adversely affect the durability and efficacy of root sealants? In one recent clinical study,30 an experimental light-cured unfilled resin was applied to hypersensitive root dentin of six teeth. The resin, which was not bonded with a dental adhesive, was completely lost a t six months. ■" Are certain adhesive systems more effective than others for sealing roots against caries attack? *"* Are root sealants more or less effective than fluoride varnishes or other fluoride treatm ents? Is a combination therapy more effective than either treatm ent alone? ■■ Does a fluoride-releasing adhesive (for example, OptiBond, Kerr Manufacturing) have any advantages over a

RESEARCH conventional adhesive? ■■ Can dentin adhesives be applied to incipient root caries lesions to slow their progression? ■■ Can practical clinical techniques be developed to adequately isolate and deliver adhesives to inaccessible areas of teeth, for example, approximal root surfaces? "■ Do root surface sealants have any adverse effects, such as gingival irritation by the bonding resin? Although some of this information could be obtained in laboratory studies, controlled clinical testing will ultimately be needed to determine the practicality and efficacy of resin adhesive sealants for root surface caries prevention. Clinical studies would also be required to determine cost/benefit ratios of, and specific indications for, placing resin root sealants. For example, should exposed root surfaces be sealed in virtually all patients, or should the procedure be reserved for highrisk populations only? Our study results indicate th at the unfilled resin m ust be applied to maximize the cariesprotective effect of the All-Bond 2 adhesive system. However, primer application alone provided some slight protection against caries. Lesions were shallower and less regular than in the control group, although the difference in lesion depth was not statistically significant. Instructions supplied with the All-Bond 2 system state th a t the primers can reduce dentinal hypersensitivity, and clinical experience supports this concept. Also, a recent study suggested th a t primers can reduce dentin permeability

Figure 3. Dentin that was bonded with the All-Bond 2 adhesive system and Fortify unfilled resin. Note the absence of a carieslike lesion.

Figure 4. Dentin that was etched with 10 percent phosphoric acid and treated with All-Bond 2 primers. Original magnification X5,000.

slightly.31However, our scanning electron microscopy evaluations show th a t the primers do not occlude open dentinal tubules or form a hybrid layer in etched intertubular dentin (Figure 4). If dentin is not etched, the primers appear to infiltrate and fix the smear layer, but do not plug the tubules. The reduced caries severity in the specimens

treated only with the primers might be attributed to increased acid resistance caused by primer infiltration of the intertubular dentin.32 In all specimens, we abraded the root surface with a finishing disk, which forms a sm ear layer of debris on the surface. The smear layer probably does not exist “naturally” on exposed root surfaces, so this is an area JADA, Vol. 125, May 1994

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RESEARCH to protect it from caries attack. However, more laboratory and clinical research on this technique is necessary before it can be recommended for clinical use. ■ D r. W e fe l is d ir e c t o r , D o w s In s t it u t e fo r

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reality. The primers might behave differently if applied to “natural” dentin. The effectiveness of the AllBond 2 system in reducing the frequency and severity of carieslike lesions in this study is directly related to its bonding mechanism. The primers and unfilled resin infiltrate the etched dentin surface, filling the spaces between collagen fibers and encapsulating the remaining hydroxyapatite crystals with resin.1’5,6This resin-protected dentin resists décalcification by acids, and thus is resistant to caries attack. C O N C L U S IO N

The results of this laboratory study suggest th at a dentin adhesive can be applied to exposed root surface dentin

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M aterials for th is project were supplied by Bisco, Inc., Itasca, 111. Inform ation about th e products m entioned in th is article is available from the author. N either the authors nor the Am erican Dental Association has any commercial in te re st in products m entioned. T he opinions expressed are those of the authors and do not necessarily reflect those of th e authors or th e American D ental Association. 1. Van M eerbeek B, Inokoshi S, B raem M, L am brechts P, V anherle G. Morphological aspects of th e resin-dentin interdiffusion zone w ith different dentin adhesive system s. J D ent Res 1992;71:1530-40. 2. N akabayashi N, N akam ura M, Y asuda N. Hybrid layer as a dentin bonding mechanism . J E sth et D ent 1991;3:133-8. 3. Suh BI. All-Bond—fourth generation dentin bonding system . J E sth et D ent 1991;3:139-47. 4. H eym ann HO, Bayne SC. C u rren t concepts in dentin bonding: Focusing on dentinal adhesion factors. JADA 1993;124(5):27-36. 5. V an Meerbeek B, Dhem A, Goret-Nicaise M, B raem M, L am brechts P, V anherle G. Com parative SEM and TEM exam ination of th e u ltra stru ctu re of th e resin-dentin interdiffusion zone. J D ent Res 1993;72:495501. 6. V an M eerbeek B, M ohrbacher H, Celis JP , e t al. Chemical characterization of the resin-dentin interface by m icro-Ram an laser spectroscopy. J D ent Res 1993;72:1423-8. 7. Clinical Research Associates. D entin bonding: sta te of th e art. CRA N ew sletter 1991;15(12):l-3. 8. Clinical R esearch Associates. Tooth desensitization before crown cem entation— ’93. CRA N ew sletter 1993;17(8):2-3. 9. Felton DA, Bergenholtz G, K anoy BE. E valuation of the desensitizing effect of G lum a dentin bond on teeth prepared for complete-coverage restorations. In t J Prosthodont 1991;4:292-8. 10. W atanabe T, Sano M, Itoh K, W akum oto S. The effect of prim ers on th e sensitivity of dentin. D ent M ater 1991;7:148-50. 11. Yoshiyama M, M asada J , U chida A, Ishida H. Scanning electron microscope characterization of sensitive vs. insensitive h um an radicular dentin. J D ent Res 1989;68:1498-502. 12. Duke ES, L indem uth J. V ariability of clinical dentin substrates. Am J D ent 1991;4:241-6. 13. Johnston AD, Bowen RL. Protective coatings for tooth crowns. JADA 1991;122(4):49-51.

14. Grogono A, Mayo J. Root caries: P relim inary investigation using dentin adhesives to prevent dem ineralization (A bstract No. 1716). J D ent Res 1993;72:318. 15. Ten Cate JM , D uijsters PPE. A lternating dem ineralization and rem ineralization of artificial enam el lesions. C aries Res 1982;16:201-10. 16. Graves RC, Stam m JW . O ral h ealth sta tu s in th e U nited States: prevalence of dental caries. J D ent Educ 1985;49:341-51. 17. W eintraub JA, B u rt BA. O ral h ealth sta tu s in th e U nited States: tooth loss and edentulism . J D ent Educ 1985;49:368-76. 18. H and JS , Kohout F J, C unningham MA. Incidence of edentulism in a non­ institutionalized elderly population. Gerodontics 1988;4:13-7. 19. R einhardt JW , Douglass CW. The need for operative dentistry services: projecting th e effects of changing disease p attern s. O per D ent 1989;14:114-20. 20. T itus HW. Root caries: Some facts and tre a tm e n t methods. Am J D ent 1991;4:61-8. 21. Wefel JS , Clarkson BH, H eilm an J. Histology of root surface caries. In: T hylstrup A, Leach SA, Qvist V, eds. D entine and dentine reactions in the oral cavity. London: IRL P ress Lim ited;1987:139-46. 22. Jen sen ME, Kohout F. The effect of a fluoridated dentifrice on root and coronal caries in an older ad u lt population. JADA 1988;117:829-32. 23. Ripa LW, Leske GS, Porte F, V arm a A. Effect of a 0.05% neu tral N aF m outhrinse on coronal and root caries of adults. Gerodontology 1987;6:131-6. 24. B urt BA, Ism ail AI, E klund SA. Root caries in an optim ally fluoridated and a highfluoride community. J D ent Res 1986; 65:1154-8. 25. Huizinga ED, Ruben J, A rends J . Effect of a n antim icrobial-containing varn ish on root surface dem ineralisation in situ. C aries Res 1990;24:130-2. 26. Schaeken MJM, Keltjens HMAM, van der Hoeven JS. Effects of fluoride and chlorhexidine on the microflora of d en tal root surfaces and progression of root-surface caries. J D ent Res 1991;70:150-3. 27. Sim onsen R J. Retention and effectiveness of dental sealant after 15 years. JADA 1991;122(7):34-42. 28. Eliades GC, Caputo AA, Vougiouklakis GJ. Composition, w etting properties and bond strength w ith dentin of 6 new dentin adhesives. D ent M ater 1985;1:170-6. 29. Triolo PT, Swift E J. S hear bond strengths of ten dentin adhesive system s. D ent M ater 1992;8:370-4. 30. Yoshiyama M, Ozaki K, E bisu S. Morphological characterization of hypersensitive hum an radicular den tin and the effect of a light-curing resin lin er on tu b u lar occlusion. Proc Finn D ent Soc 1992;88 (Supplem ent l):337-44. 31. Simpson MD, Ciarlone AE, Pashley DH. Effects of dentin prim ers on dentin perm eability (A bstract No. 185). J D ent Res 1993;72:127. 32. H arashim a I, H irasaw a T. A dsorption of 2-hydroxyethyl m ethacrylate on dentin from aqueous solutions. D ent M ater J 1990;9:3646.