How the introduction of the acid-etch technique revolutionized dental practice

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1 Spotlighting articles from past ADA Journals that have achieved landmark status thanks to their lasting impact on dental care and the dental profession Originally published May 1971, The Journal of the American Dental Association, Vol. 82, No. 5, To read full article, visit centennial How the introduction of the acid-etch technique revolutionized dental practice Domenick T. Zero, DDS, MS Over the last 100 hundred years, only a handful of discoveries have revolutionized the practice of dentistry. Without question, the introduction of acid etching to condition the enamel surface as a means of retaining pit-andfissure sealants and its much broader impact on the blossoming of restorative and esthetic adhesive dentistry must be considered to be at the very top 990 JADA 144(9) September 2013 of the list. While the potential for dental sealants to prevent pit-and-fissure caries and to inhibit the progression of early caries has yet to be fully realized due to underutilization, sealants have had a major effect in reducing caries prevalence in children, 1-3 especially through school-based programs. 4 Dr. Michael Buonocore was not the only one who envisioned the potential of adhesive dentist-

2 ry, but his discovery of the acid-etch technique was the major catalyst for driving the field forward. Much of what dentists do routinely today in their practices follows from this innovation, including anterior and posterior composite restoration, the splinting of teeth, ceramic veneers and bonding of orthodontic brackets. 5 Buonocore and colleagues 6,7 also introduced the concept of sealing proximal tooth surfaces, which foreshadowed the more recent interest in the infiltration/ sealing of proximal surfaces. 8,9 The uniqueness of the setting in which this important discovery occurred at the Eastman Dental Center in Rochester, N.Y., has been elegantly captured in an article by Handelman and Shey. 5 At the time, Dr. Stanley Handelman was a part-time instructor who went on to make important contributions to our understanding of sealing over active caries; Dr. Zia Shey was a pediatric dentistry graduate student who worked in Dr. Buonocore s laboratory. Their article provided a firsthand account of the special nature of the environment that could be largely attributed to thendirector of Eastman, Dr. Basil G. Bibby, who recruited Dr. Buonocore to Rochester. The photo of Dr. Buonocore and his longtime laboratory assistant, Richard Glena (Figure 1), portrays the working environment, which I had the good fortune to experience during my training at Eastman in the late 1970s. Dr. Buonocore clearly recognized the advantages of developing a dental adhesive system that would not require cutting into the tooth structure. 10 At the time of his pioneering research, the prophylactic odontotomy as recommended by Hyatt, 11 involving the preparation of the deep pits and fissures and restoration placement, and the widening of the fissures (fissurotomy) advocated by Bödecker 12 were still considered to be effective measures of preventing occlusal caries. 10 Figure 1. Michael Buonocore (left) working with his long-standing laboratory technician Richard Glena. Reproduced with permission of the Eastman Institute for Oral Health, Rochester, N.Y. This landmark article by Michael Buonocore 13 that is the basis of this commentary provided the two-year clinical data documenting the effectiveness of dental sealants following from an earlier publication in JADA that reported the results after one year. 6 These articles were the first to establish that the combination of acid etching (to condition the tooth surface) and resin polymer was effective in preventing pit-andfissure caries. The resin formulation involved three parts bisphenol A and glycidyl methacrylate and one part methyl methacrylate monomer. A light-activated catalyst, benzoin methyl ether, was mixed in just before curing with ultraviolet light. In an earlier study, Cueto and Buonocore 10 used a mixture of methyl 2-cyanoacylate and siliceous filler material similar to what was used in silicate cements commonly in use in dental practice at that time. Although this was the first pit-and-fissure sealant study using the acid-etch method, the results did not meet Dr. Buonocore s expectations owing to an unacceptable rate of sealant loss necessitating reapplication every six months. He recognized that for sealants to be broadly adopted, they must be able to provide a substantial reduc tion in dental caries from a single application and not require frequent repeat applications due to sealant loss. In this landmark article, he 13 reported almost complete protection against pit-and-fissure caries in permanent teeth (99 percent reduction) and primary teeth (87 percent reduction) over a two-year period after one application in a very high caries-risk population. What is most apparent in Dr. Buonocore s approach to the development of dental sealants was that he combined his knowledge in chemistry, dental materials and clinical dentistry to painstakingly develop an approach that would ultimately lead to the successful dental bonding system for preventing dental caries. His idea to JADA 144(9) September

3 acid-etch the enamel surface in advance of applying an adhesive material was based on his knowledge that phosphoric acid was used to pretreat metal surfaces to obtain better adhesion of paint and resin coatings. 14 Furthermore, phosphoric acid was commonly used in phosphate cements, which lessened any clinical safety concerns about using an acid on tooth structure. 14 He made incremental improvements in the method of enamel etching and placing sealants and the materials used that clearly reflected the translation of his laboratory findings into highly innovative clinical applications. A careful reading of Dr. Buonocore s 13 landmark article reveals his many findings and insights, most of which have held up more than 40 years later. These include several clinical observations: sealants are better retained and more effective in preventing caries in the permanent dentition than in the primary dentition; occlusal fissures with multiple crevices have the best retention; the presence of resin tags may explain the observed caries protection, even when sealant appear to be lost clinically; and the addition of fluoride to sealant material may provide additional protection. Dr. Buonocore also provided guidance on how to place sealants that have endured the test of time, which included the importance of a properly etched surface with a uniform dull appearance on drying, thoroughly washing the etched tooth surface, preventing saliva contamination after etching and, most importantly, drying the etched tooth surface with warm air that is free of water and oil immediately before sealant application. Michael Buonocore must be considered one of dentistry s greatest innovators and visionaries. The conceptual framework that he laid out in his article published in remains the basis for the use of pit-and-fissure sealants and modern adhesive dentistry, which has not changed much over nearly 60 years: We foresee that the formation of good bonds, of the sort we have demonstrated, to enamel surfaces open the possibility of successfully sealing pits and fissures for purposes of caries prevention. In addition, good bonding at the enamel cavity margins would protect against secondary or marginal decay. As noted in the introduction to this article, there was a general understanding at that time that existing restorative materials had limitations owing to their lack of adhesion to tooth structure and that development of materials or ways of conditioning the enamel surface that resulted in the adhesion to the tooth structure would be a major advance for dentistry. 14 This led to the pursuit of different strategies to ob- tain bonding between restorative materials and tooth structure. Dr. Buonocore outlined several approaches: developing new materials with adhesive properties; modifying existing materials to make them more adhesive; using coatings with adhesive properties between restorative material and tooth; and altering the tooth surface chemically to permit better adhesion. 14 It was this last approach that he pursued and which started the revolution. At the time of the first clinical trial, 10 there was not a full understanding of the mechanism behind the remarkable increased adhesion observed both in laboratory studies and clinically. Dr. Buonocore 14 had postulated that this mechanism could be due to several factors: increased surface area for bonding due to acid etching; exposure of the organic matrix for the resin to adhere; the formation of a new surface layer due to precipitation of reaction products to which the acrylic might adhere; etching away of the existing surface layer exposing a more reactive surface; and the creation of an adsorbed layer of highly polar phosphate groups as a result of the acid exposure. The actual mechanism by which the dramatic increase in bonding occurred was not scientifically resolved until later when Dr. Buonocore, in collaboration with Drs. Matsui and Gwinnett, 15 observed that enamel surfaces etched with phosphoric acid were penetrated by prism-like resin tags in comparison with nonconditioned enamel (Figure 2), which exhibited poor bonding and the absence of resin tags. They concluded that enamel bonding was primarily mechanical in nature, where the penetration of the resin in monomer form fills the micropores (interprismatic and intraprismatic spaces) enlarged by acid etching. The resin tags can be readily seen in a scanning electron micrograph of the undersurface of a sealant after the enamel has been partially dissolved by strong acid (Figure 3). 16 They went on to define the characteristics of an ideal material to facilitate bonding, which included wettability and surface tension and the ability to form into an impermeable and abrasion- and bacteria-resistant polymer. 15 Over the years following Dr. Buonocore s trailblazing research, there have been efforts by manufacturers, researchers and clinicians to improve on his basic concept. 17 The phosphoric acid concentrate has been reduced from the 50 percent 6,10,13 originally used by Dr. Buonocore in his early clinical studies to the 35 percent and 37 percent commonly used today. Acid-conditioning times have been reduced from 60 seconds 6, JADA 144(9) September 2013

4 dations to seal noncavitated carious lesions. Many of the issues surrounding the use of sealants to prevent progression of early carious lesions have been with us since the turn of the last century. Thaddeus Hyatt s 25 report, read at a meeting of the New York Academy of Dentistry on Oct. 22, 1925, and the discussion that followed provide some interesting insights into the controversy surrounding the prophylactic odontotomy at that time. Given the thoughtful rationale that he provided in the then prefluoride, presealant era, I believe it s safe to assume that Dr. Hyatt would have fully embraced the use of dental sealants for the prevention of caries in clinically sound teeth and the sealing of teeth with noncavitated carious lesions without operatively altering tooth structure in light of the curdown to 20 seconds. 17 Ultraviolet light-initiated resin sealants no longer are in use owing to poorer performance compared with visiblelight initiated sealants 18 and autopolymerizing resin sealants. 19 Both visible-light initiated and autopolymerizing resin-based sealants are now the standard evidencebased methods. 2 There are trade-offs between filled and unfilled sealants, with filled sealants providing better wear characteristics and unfilled sealants better retention, and both clear and opaque sealants are being marketed. 17 In concert with Dr. Buonocore s original thinking that the incorporation of fluoride in sealant material may provide additional caries protection, 6,13 there has been considerable interest in developing sealants with the ability to release fluoride fluoride-releasing resin, glassionomer and, more recently, resin-modified glass-ionomer sealants. 17 Clinical recommendations from a 2008 evidence-based report of the American Dental Association (ADA) Council on Scientific Affairs published in JADA on pit-and-fissure sealant use indicate that resin-based sealants remain the first choice, and glass-ionomer sealants should be used as interim preventive agents in situations where moisture control may compromise the use of resin-based sealants, such as in erupting teeth. 2 Interestingly, this landmark article by Dr. Buonocore 13 did not make the cut in any of the recent systematic reviews regarding the effectiveness of sealants in preventing dental caries, 1-3 nor is Dr. Buonocore s contribution to the field mentioned. Although his early studies 6,10,13,14 may not meet today s quality standards for clinical trials, time has proven that they were based on sound scientific thinking and integrity, and that their far-reaching impact on our profession is irrefutable and yet to be fully actualized. Figure 2. Diagram of resin tags. Reproduced with permission of Elsevier from Buonocore and colleagues. 15 E Figure 3. Scanning electron micrograph of the undersurface of an adhesive sealant (A) after the enamel (E) has been partially dissolved by strong acid. Source: Buonocore. 16 In closing, it s worthwhile to look at Dr. Buonocore s contribution to dentistry in light of where we are heading (or should be heading) as a profession. There has been an ongoing debate on how to manage dental caries properly as long as there has been a dental profession. The current controversy centers on the diagnostic threshold of when nonoperative versus operative approach is used to managing noncavitated carious lesions. 20 The weight of available evidence is clearly on the side of taking a conservative, nonoperative approach whenever possible in managing noncavitated carious lesions. Dr. Handelman A along with Dr. Buonocore and others at Eastman were the first to establish that sealants were effective in reducing bacteria s viability and preventing progression of early carious lesions. 19,21,22 These findings have been substantiated by several systemic reviews, 3,23 including the evidencebased report of the ADA Council on Scientific Affairs published in JADA. 2 On the basis of a 2011 survey, 24 U.S. dentists have not yet adopted recommen- JADA 144(9) September

5 rent scientific evidence. Maybe it s time for our component dental societies to rekindle this kind of debate among their members. n Dr. Zero is the director, Oral Health Research Institute, and a professor, Department of Preventive and Community Dentistry, School of Dentistry, Indiana University, 415 Lansing St., Indianapolis, Ind , dzero@iu.edu. Address reprint requests to Dr. Zero. 1. Ahovuo-Saloranta A, Forss H, Walsh T, et al. Sealants for preventing dental decay in the permanent teeth. Cochrane Database Syst Rev 2013;3:CD Beauchamp J, Caufield PW, Crall JJ, et al; American Dental Association Council on Scientific Affairs. Evidence-based clinical recommendations for the use of pit-and-fissure sealants: a report of the American Dental Association Council on Scientific Affairs. JADA 2008;139(3): Griffin SO, Oong E, Kohn W, Vidakovic B, Gooch BF; CDC Dental Sealant Systematic Review Work Group, et al. The effectiveness of sealants in managing caries lesions. J Dent Res 2008;87(2): Gooch BF, Griffin SO, Gray SK, et al; Centers for Disease Control and Prevention. Preventing dental caries through schoolbased sealant programs: updated recommendations and reviews of evidence. JADA 2009;140(11): Handelman SL, Shey Z. Michael Buonocore and the Eastman Dental Center: a historic perspective on sealants. J Dent Res 1996; 75(1): Buonocore M. Adhesive sealing of pits and fissures for caries prevention, with use of ultraviolet light. JADA 1970;80(2): Davila JM, Buonocore MG, Greeley CB, Provenza DV. Adhesive penetration in human artificial and natural white spots. J Dent Res 1975;54(5): Paris S, Meyer-Lueckel H, Kielbassa AM. Resin infiltration of natural caries lesions. J Dent Res 2007;86(7): Martignon S, Ekstrand KR, Gomez J, Lara JS, Cortes A. Infiltrating/sealing proximal caries lesions: a 3-year randomized clinical trial. J Dent Res 2012;91(3): Cueto EI, Buonocore MG. Sealing of pits and fissures with an adhesive resin: its use in caries prevention. JADA 1967;75(1): Hyatt TP. Prophylactic odontotomy: the cutting into the tooth for the prevention of disease. Dent Cosmos 1923;65: Bödecker CF. Eradication of enamel fissures. Dent Items Interest 1929;51: Buonocore MG. Caries prevention in pits and fissures sealed with an adhesive resin polymerized by ultraviolet light: a two-year study of a single adhesive application. JADA 1971;82(5): Buonocore MG. A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res 1955;34(6): Buonocore MG, Matsui A, Gwinnett AJ. Penetration of resin dental materials into enamel surfaces with reference to bonding. Arch Oral Biol 1968;13(1): Buonocore MG. Adhesives in the prevention of caries. JADA 1973;87(5 special issue): Simonsen RJ. Pit and fissure sealant: review of the literature. Pediatr Dent 2002;24(5): Mertz-Fairhurst EJ, Fairhurst CW, Williams JE, Della- Giustina VE, Brooks JD. A comparative clinical study of two pit and fissure sealants: 7-year results in Augusta, GA. JADA 1984;109(2): Handelman SL, Leverett DH, Espeland M, Curzon J. Retention of sealants over carious and sound tooth surfaces. Community Dent Oral Epidemiol 1987;15(1): Zero DT, Zandona AF, Vail MM, Spolnik KJ. Dental caries and pulpal disease. Dent Clin North Am 2011;55(1): Handelman SL, Buonocore MG, Heseck DJ. A preliminary report on the effect of fissure sealant on bacteria in dental caries. J Prosthet Dent 1972;27(4): Handelman SL, Washburn F, Wopperer P. Two-year report of sealant effect on bacteria in dental caries. JADA 1976;93(5): Oong EM, Griffin SO, Kohn WG, Gooch BF, Caufield PW. The effect of dental sealants on bacteria levels in caries lesions: a review of the evidence. JADA 2008;139(3): Tellez M, Gray SL, Gray S, Lim S, Ismail AI. Sealants and dental caries: dentists perspectives on evidence-based recommendations. JADA 2011;142(9): Hyatt TP. Prophylactic odontotomy: an operative procedure for the prevention of decay. J Dent Res 1924;6(4): Introducing Sensodyne Repair & Protect toothpaste Our new layer of protection for dentin hypersensitivity Sensodyne Repair & Protect toothpaste builds a robust reparative layer over and within dentin tubules. 1,2 The layer begins to form from the fi rst use, and provides proven, lasting protection from dentin hypersensitivity. 2,3 Layer over exposed dentin Layer penetrates within the tubules at the surface 1 µm In vitro SEM image of dentin cross section after a single brushing. Think beyond pain relief and recommend Sensodyne Repair & Protect toothpaste. References: 1. Earl J et al. Am J Dent 2013, Special Issue A. In press. 2. Burnett G et al. Am J Dent 2013, Special Issue A. In press. 3. Parkinson et al. Am J Dent 2013, Special Issue A. In press GlaxoSmithKline Consumer Healthcare with twice daily brushing. 994 JADA 144(9) September 2013