Caries Res. 12 (Suppl. 1): 103-112 (1978)
Operative Measures for Caries Prevention Leon M. Silverstone
In a community dependent upon an av erage civilized diet, the high prevalence of dental caries cannot be controlled by repar ative techniques alone. Caries prevention programmes must be run in addition to res torative procedures if the disease is to be controlled. However, many measures can be taken in connection with operative and res torative procedures in order to minimize the incidence of recurrent and new caries. This chapter is intended to summarize briefly the advances in this field during the last 25 years which in the author’s opinion have had the greatest effects or potentials.
Recurrent Caries
Recurrent caries has been shown to be a common cause of failure of restorations. Faults in cavity preparation, such as failure to apply the principle of extension for pre vention, predispose to secondary caries. Material problems will be dealt with in sub sequent sections. Many workers have sug gested that a relatively unaffected surface layer is closely associated with the special caries resistance of surface enamel. Chemical
studies have shown that if the original enamel surface is removed, the remaining enamel is more susceptible to acid demineralization. This greater resistance has been explained as being due to its higher degree of mineraliza tion compared with subsurface enamel [Thewlis, 1940; Brudevold, 1948; Hals et al., 1955], a higher fluoride and lead con tent [Isaac et al., 1958] and perhaps a greater amount of insoluble protein in the surface enamel [Darling, 1958]. However, von der Fehr’s [1967] and Silverstone's [1968] studies suggest that the ‘special’ physical and chemical properties of surface enamel, relative to subsurface en amel, are not entirely responsible for the presence of a well-mineralized surface zone above the small carious lesion. The sugges tion is that the surface zone remains intact and well mineralized because it is a site where calcium and phosphate ions, released by subsurface dissolution, or from the satu rated solution in plaque, become reprecipi tated into the surface enamel. The high fluoride concentration of surface enamel, presumably released at the initiation of sol ution of outer enamel, would also favor pre cipitation.
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Division of Cariology, Dows Institute for Dental Research, College of Dentistry, University of Iowa, Iowa City, Iowa
This surface phenomenon is extremely relevant with respect to preventive and op erative measures involving the enamel. This has been demonstrated in connection with recurrent caries in relation to restorations. In this process, the artificial caries tech nique has been used to study the nature of breakdown and the efficacy of the ‘seal’ be tween the filling material and enamel. The acidified-gcl technique has been employed to create caries-like lesions in relation to amalgam restorations in vitro [Hals and Nernaes, 1971; Kidd, 1975], The lesion consists essentially of two distinct parts. The ‘outer’ lesion is produced in relation to the enamel surface whereas the ‘cavity wall’ le sion is formed by diffusion of hydrogen ions along the enamel restoration interface. Kidd [1977] confirmed that cavity wall lesions were formed as a result of leakage of the restoration.
Amalgam As a material, amalgam appears to be susceptible to marginal deterioration which may predispose to secondary caries. Several factors are probably important in the mech anism of marginal breakdown. These in clude the fracture of excess amalgam re maining as a ‘flash’ over the cavity margin, the mercury content of the filling material, the type of alloy used, condensation pres sure and contamination during the packing of the restoration. It is a well-established clinical observa tion that amalgam restorations leak when first placed. This leakage is transitory and studies in vitro and in vivo have shown that marginal adaptation improves after 24 h. Although no conclusive evidence is availa
ble to explain this phenomenon, it has been suggested by many workers that corrosive products reduce or eliminate the marginal defects. However, other workers have showed that the use of cavity liners such as copal- or polystyrene-based varnishes also decrease marginal defects. The physical properties of dental amal gam are still of specific interest and a com prehensive review of both the physical properties and clinical aspects of dental amalgam has been published recently [Wing, 1975]. The clinical factors influenc ing the residual mercury content and the marginal adaptation of amalgam restora tions have been studied by Mathewson and Lu [1975]. It was found that the level of training of the dental assistant, the type of amalgamator and the accuracy of its timing device as well as the method of condensa tion of the amalgam were critical factors. The presence of tin oxide and tin oxychlo ride in the in vivo and in vitro corrosion products of dental amalgam have been re ported recently [Sarkar et al., 1975]. This analysis of the corrosion products of dental amalgam was supported by a scanning elec tron-microscopic and an energy-dispersive X-ray spectrometric study [Marshall et al., 1975]. The electrochemistry of the saline corrosion of conventional dental amalgam has been described by Sarkar and Greener [1975a]. In a further report [Sarkar and Greener, 1975b] they discussed the electro chemical properties of copper- and goldcontaining nonconventional dental amal gams. These studies were used to provide a mechanism for the observed corrosion be havior of dental amalgam and to account for the role of intermetallic compounds in modifying the electrochemistry of amalgam in corrosive media.
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Operative Measures for Caries Prevention
The incorporation of fluoride into dental cements and bases generally reduces the strength and increases the solubility of the material. With carboxylates, if fluoride is in corporated as part of the glass system, as in silicate or silicophosphate cements, fluoride release occurs without serious degradation of the cement. Cements with added fluoride show a significant impairment of physical properties after fluoride release. Greenland et al. [1974] have shown that the addition of stannous fluoride to a carboxylate cement produced a significant release of fluoride and good uptake of the fluoride by adjacent enamel. The most favorable results were obtained with the addition of 10% stannous fluoride. The cement maintained high com pressive tensile strength although the addi tion of fluoride produced an increase in sol ubility of the cement by approximately 1%. In composite systems, the rate of release of fluoride is very much slower. Generally, with amalgam it has been found that large amounts of fluoride must be added to pro duce a significant release. Even under these conditions, there is initial release of fluoride followed by a very slow release of these ions. This results in a degradation of the physical properties of the amalgam. The incorporation of fluoride into resins has not proved as successful as was hoped initially. Several of the earlier fissure seal ants had fluoride incorporated in the belief that fluoride ions would pass into the enam el surface and, in the event of loss of resin, a more caries-resistant surface would be formed. However, producing a resin that would allow fluoride ions to diffuse through freely resulted in a coating which was not
effective as a barrier. The porous coating also allowed other ions to pass from the oral milieu into the enamel and, on dissolution, calcium and phosphate would pass in the opposite direction. These coatings, most of which were polyurethanes, were also poorly retained by the enamel surface [5/7verstone, 1974]. Fluoride-containing varnishes containing either amine fluoride or monofluorophosphate are available, but at the present time, the consensus of opinion is that fluo ride varnishes should be regarded as experi mental agents. There is as yet insufficient evidence to justify their routine use in den tal practice.
Composite Resins
For many years, anterior teeth were res tored with silicate cements which were de veloped in Europe around the turn of the century. Whilst their esthetics were highly acceptable, they were criticized for the irri tative effects caused by the release of phos phoric acid. The advantages of the high fluoride content in silicates [Norman et al., 1960] is to reduce secondary caries, fluoride being released slowly by the soluble filling material. The self-curing acrylic resins were intro duced in the 1950s. These materials gave good aesthetics for a short time after place ment. However, the porous nature of the material together with a high coefficient of thermal expansion, causing the resin to shrink, led to marginal leakage and recur rent caries. As a result of his work at the National Bureau of Standards in Washington, DC, Bowen introduced the first composite mate
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Incorporation of Fluoride into Restorative Materials
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rial for dental use in 1964. In the following 1966; Guzman et al., 1969] have compared years, other composite materials appeared leakage around amalgam and composite res and have gained in popularity. The compo torations using radioisotope methods. Re sites are made of a resin matrix which is a sults showed a better initial seal with the cross-linked organic mixture of polymer and composite material than with amalgam. Al monomer, and inorganic filler particles. The though there is no corrosion phenomenon filler has been added up to 75% by weight associated with composites, they do absorb and varies depending upon the restorative water causing expansion of the material and material. Filler particles include glass beads, consequent reduction in the width of the glass rods, quartz, lithium aluminum sili initial microspace [Asmussen and Jorgensen, cate, and borosilicate. In order to promote 1972], This is one possible explanation of the bond of the resin to the filler, the parti the apparent good seal obtained with com cles are coated with a coupling agent, for posite materials. Dogon [1975] has demon which usually silane is utilized. These mate strated that isotope penetration around rials are, with reference to mechanical prop composite resin restorations, after thermal erties, superior to the conventional acrylic cycling, was prevented by the use of an in resins. Factors which are improved include termediary resin of low viscosity coating the (1) greater compressive and tensile strength; etched enamel. (2) higher modulus of elasticity; (3) superior In studies of artificial lesions produced hardness and resistance to abrasion; (4) in relation to restorations, the cavity wall le lower polymerization shrinkage, and (5) a sion is a measure of the extent of microleak reduced coefficient of thermal expansion. age. In a recent study, Kidd [1975] has A clinical evaluation of six commercial compared artificial lesions created in rela composite materials involving 668 restora tion to composite and amalgam restorations tions over a 2-year period has been reported in vitro. A total of 154 artificial lesions by Leinfelder et al. [1974], They found that were examined in relation to these restora the composites had good marginal adapta tions. Wall lesions were present adjacent to tion and resistance to interfacial staining. 77% of amalgam restorations, whereas only None of the 668 restorations exhibited evi 13% of the composite restorations showed dence of secondary caries. evidence of a wall lesion. In addition, the Several clinical trials have been carried depth of penetration of wall lesions was sig out on composites ranging from 2 to 4 years nificantly greater in relation to amalgam in duration [Phillips et al., 1973; Liatukas, restorations compared with composites. 1972; Leinfelder et al., 1974]. All of the This must reflect differences in microleak studies showed minimal incidence of recur age between the two restorative materials rent caries and good marginal adaptation of since all other parameters were identical. the material. In the study by Phillips et al. [1973], the composite material was com pared with amalgam in 124 paired posterior Fissure Sealants restorations, and superior marginal adapta tion was found with the composite. Two mi From all available evidence, fissure seal croleakage studies [Going and Sawinski, ants are likely to play an important role in
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caries prevention. Because the occlusal sur face accounts for nearly half the caries in children during their time at school [0swald, 1973], and because it is the surface least protected by fluoride [Backer-Dirks et al., 1961], the use of fissure sealants on oc clusal surfaces can have a highly significant caries-preventive effect. A number of techniques have been pro posed in an attempt to prevent occlusal car ies. Hyatt [1923] suggested the technique of prophylactic odontotomy whereby occlusal fissures were filled, but this was not widely accepted because it was necessary to pre pare cavities in sound teeth. The use of chemical agents to seal pits and fissures, such as ammoniacal silver nitrate [Klein and Knutson, 1942], zinc chloride and po tassium ferrocyanide [Ast et al., 1950] met with little success, as did the use of copper cement [Miller, 1950]. The eventual devel opment of new synthetic resins led to the possibility of sealing occlusal fissures with adhesive materials requiring no cavity prep aration. Early work with the epoxy resins was unsuccessful because the bond strength of these adhesives to the enamel surface was poor, due to the presence of water in the tis sue. The introduction of the cyanoacrylate group of adhesives seemed likely to over come this difficulty by using a small amount of water for polymerisation. The technique of fissure sealing is one in which the vulnerable occlusal fissures of teeth are coated with a thin layer of a plas tic-type material to prevent the initiation and progress of caries. The technique con sists essentially of two stages: etching of the tooth surface using an acid solution, and ap plication of the sealant resin material. The use of an acid solution to etch the
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enamel surface is an essential prerequisite for the successful bonding of resins to the hard tissue. In a recent report [Silverstone, 1974], a series of different acid solutions, together with phosphoric acid in the con centration range 20-70% (w/w), were inves tigated for their effect on human enamel in vitro. The results showed that an unbuffered solution of 30% (w/w) phosphoric acid pro duced the most favorable conditions for bonding. When the 30% solution of phos phoric acid was compared with the more commonly used buffered 50% solution, an increase in tensile bond strength of more than 50% was found [Rock, 1974], It has been shown that the acid solution produces changes to the enamel surface in two distinct ways [Silverstone, 1974]. In the first, a shallow layer of enamel is removed by etching. In this manner, plaque, surface and subsurface pellicles are effectively re moved from the site to be bonded. In addi tion, chemically inert crystallites in surface enamel are also removed, so favoring at tempts at chemical union between hard tis sue and resin. In the second, after removal of the surface layer by etching, the remain ing enamel surface is rendered porous by the acid solution. It is into this porous re gion that the resin is able to penetrate and so bond with the enamel. The depth of en amel rendered porous can be measured ac curately in polarized light [Silverstone, 1974], After application of sealant and sub sequent demineralization of the hard tissue, tags of resin which previously penetrated the enamel surface can be examined directly with the light or electron microscope. No evidence of caries of test teeth has been reported which could be related to the original etching of the enamel. Acid etching is an essential stage in the bonding mecha
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Operative Measures for Caries Prevention
nism and it appears to be confined to the cuspal slopes, rather than to the base of the fissure, and this is the region where the bond occurs [Gwinnett and Bitonocore, 1972: Silverstone, 1974], In addition, a number of studies have shown that etched enamel, not covered by resin, will be remineralized on contact with the oral fluid [Al bert and Grenoble, 1971; Silverstone, 1973b]. Quantitative studies on enamel dis solution rates have shown recently that the dissolution rate of acid etched enamel re turns to that of adjacent sound enamel after 24 h of exposure to oral fluid [Silverstone, 1977], In addition, fissure-scaled enamel surfaces artificially abraded in vitro show a lower dissolution rate than adjacent sound enamel [Silverstone, 1977], These results were interpreted as being due to the reten tion of tags of sealant, which penetrated up to 50 ,«m into the enamel surface. Thus, fissure-sealed enamel surfaces which have been worn down might well be less suscepti ble to caries than adjacent sound enamel. A number of sealant trials have been carried out to date and others arc in prog ress. Although initial trials with methyI-2cyanoacrylate produced significant results fCueto and Bitonocore, 1967], reapplication every 6 months was found to be necessary. A trial using this material in Britain [Parkhouse and Winter, 1971] showed an almost total failure by the 6-month recall period. Although these workers used slightly differ ent parameters in their use of the material, it displayed failure in the hands of others. C'rabb and Wilson [1971] showed that the bond strength of methyl-2-cyanoacrylate was reduced to one sixth of its dry value by immersion in water for 24 h. Thus, this fac tor may have been of significance regarding retention of the material. Today, as far as
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the author is aware, there is no fissure seal ant available commercially which is based entirely on the methyl-2-cyanoacrylate for mulation. The next stage in the development of the technique was the use of a new material as a fissure sealant, based on bispheno! A-glycidyl methacrylate (Bis-GMA). Bitonocore and his colleagues modified the Bis-GMA sealant system by using an ultraviolet lightsensitive catalyst, benzoin methyl ether. The material (Nuva-Scal, Caulk Co., Milford, Del.) was polymerized by long-wave ultra violet light using the Spectroline lamp. 2-year results of a clinical trial using this system, carried out in Rochester, N. Y., were reported by Bitonocore [1971]. He found that a single application of the sealant was almost completely effective in protect ing occlusal surfaces from caries. Occlusal caries was reported in only 1 out of 113 treated surfaces. However, in his trial, teeth were selected on the basis of having well-de fined pits and fissures. In later trials carried out by other workers, criteria for selection of teeth, such as specific morphological fea tures, were not used. This may be one rea son why the results of other trials arc less striking. More recently, Horowitz, et al. [1974] re ported on the effectiveness of Nuva-Seal in a 2-year trial. The children who took part in the trial were of two age-groups - 5-8 yearolds and 10-14 year-olds. After 1 year of the trial (table I) results on 900 pairs of homologous teeth showed an 81% reduction in caries and an 88% total retention of seal ant [McCune et al., 1973]. After the second year of the trial, the sealant was reported as showing a 67% reduction in caries relative to controls. 73% of test teeth showed full re tention of the sealant. The results, however.
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Operative Measures for Caries Prevention
are good regarding caries reduction espe cially when it is remembered that the seal ant was placed in less than optimal sur roundings, using portable equipment. Horowitz el al. [1976] reported their 4-year results recently. After 4 years, 50% of all sites showed complete retention. For all sites remaining fully sealed, there was a 99% reduction in caries. For sites showing partial retention of material a 90% reduc tion in caries was recorded. Table I. Nuva Seal [Horowitz et a!., 1974] Time since application years
Complete retention %
Caries reduction %
i 2
88 73
81 67
Table II. Nuva Seal retention [Rock, 1974] Time since application months
Full retention %
Partial retention %
Sealant lost %
6 12 24
91.1 86.2 80.0
7.2 10.3 15.3
1.7 3.5 4.7
Table III. Nuva Seal: incidence of occlusal caries [Rock, 1974] Time since application years
2
Teeth in study
170 n = Number.
Caries test teeth
control teeth
n
%
n
%
5
2.9
49
28.8
In the United Kingdom, several clinical trials using a number of fissure sealants have been carried out by Rock [1974], In his latest report, the results after 2 years in volving four commercial sealants were pre sented. Each sealant was applied to two teeth in the mouths of 100 children between 11 and 13 years of age. The teeth sealed were in diagonally opposite quadrants, and teeth on the opposite side of each arch served as matched contralateral controls. The results after 2 years with Nuva Seal are shown in tables II and III. One feature of re levance is that the numbers of teeth remain ing fully sealed after 2 years were very simi lar to the numbers retaining sealant 6 months after application. This indicates that if the sealant is to be lost, it is lost early on, probably as a result of an incorrect applica tion technique or polymerisation failure, rather than failure of the sealant/enamel bond. In a Nuva Seal study by Burt et al. [1975], 205 children between 5 and 17 years of age participated initially. Between them, 427 pairs of teeth were included in the study, one of each pair being sealed. At 6 months, the total retention figure was 83.2%. Douglas and Tranter [1975] reported on a 2-year study using Nuva Seal in the Aberdare region of South Wales. The age range of the 106 patients was 6-13 years, present ing a complete spectrum of the mixed denti tion. Of the 275 teeth sealed in the study, 86.2% were found to be fully sealed after 2 years. Regarding caries incidence, 9.1% of test teeth were classed as being carious, whereas 36% of controls became carious over the 2-year period. Thus, the results of many trials in var ious parts of the world have shown that fis
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and carious dentine was removed for bac teriological examination. There was approx imately a 50% decrease in the numbers of cultivatable microorganisms in the infected dentine from sealed teeth compared with the numbers grown from dentine from unsealed control teeth. A more recent report [Handelman et al., 1973] presented additional bacteriological results for patients examined up to 6 months after a single application of the seal ant. The reduction in the total viable count of infected dentine at 1, 2, 4 and 6 months was approximately 20-, 40-, 100- and 300fold, respectively. The 12-month recall X-rays of patients sampled in the bacterio logical study were compared to the X-rays taken when the teeth were sealed. In each instance, there was no evidence of progress of caries. After 2 years [Handelman et al., 1976], these workers reported a 3,000-fold de crease in the number of cultivable microor ganisms. Clinical and radiographic findings suggested that there was no progression of the carious lesions but further studies are required before this technique can be con sidered as an alterantive to conventional procedures.
References Albert, M. and Grenoble, O. E.: An in vivo study of enamel remineralization after acid etching. J. Sth. Calif, dent. Ass. 39: 747-751 (1971). Asmussen, E. and Jorgensen, K. D.: A microscop ic investigation of the adaptation of some plas tic filling materials to dental cavity walls. Acta odont. scand. 30: 3 (1972). Ast, D. B.; Bushel, A., and Chase, H. C.: A clinical study of caries prophylaxis with zinc chloride and potassium ferrocyanide. J. Amer. dent. Ass. 41: 437-442 (1950).
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sure sealants can have a highly significant effect in the prevention of occlusal caries. Most studies have shown that the ultraviolet activated materials produce the most satis factory, and reproducible, results. However, it is also evident that more attention must be paid to the application technique if the materials are to be highly effective in every one’s hands. Lewis and Hargreaves [1975] followed the surface status of first permanent molars in 142 children at ages 5, 6, 7 and 8 years. The findings showed that if the sealant was completely effective at the time of applica tion, the caries reduction for 6-7 year-olds would be 36-42°/o if the sealant was placed in occlusal surfaces only. However, if the lingual fissure of maxillary molars and the buccal pit of mandibular molars were also sealed, the caries reduction would be 91-95%. For 7- to 8-year-old children, the corresponding reduction figures were 23-25% and 83-91%. The data demon strate the greater benefit derived by the sealing of lingual and buccal pits also. Fissure sealant reviews have been pub lished by Barolet [1975], Buonocore [1975] and Ferrara [1975] and the proceedings of a first international symposium on the acid etch technique is also available [Silverstone and Dogon, 1975], Gift et al. [1975] exam ined the attitude of approximately 4,000 dentists in the USA towards fissure sealing. The technique was not used by 62% and the reasons given were inconsistent with the present state of knowledge of the materials. Occlusal fissures of permanent posterior teeth having caries detected clinically and by radiographic means were sealed with an ultraviolet-light-polymerized adhesive resin [Handelman et al., 1972]. One week later, traditional class I cavities were prepared
Backer Dirks, O.; Houwink, B., and Kwant, G. W.: The results of 6'/2 years of artificial fluo ridation of drinking water in The Netherlands. Archs oral Biol. 5: 284-300 (1961). Barolet, R. Y.: Pit and fissure sealant. J. Can. dent. Ass. 41: 157 (1975). Brudevold, F.: A study of the phosphate solubility of the human enamel surface. J. dent. Res. 27: 320-329 (1948). Buonocore, M. G.: Caries prevention in pits and fissures sealed with an adhesive resin polymer ized by ultraviolet light. J. Am. dent. Ass. 82: 1090-1093 (1971). Buonocore, M. G.: Pit and fissure sealing. Dent. Clin. N. Am. 19: 367-383 (1975). Burt, B.; Berman, D. S.; Gelbier, S., and Silverstone, L. M.: Retention of a fissure sealant six months after application. Br. dent. J. 138: 98-100 (1975). Crabb, J. J. and Wilson, H. J.: Use of some adhesives in orthodontics. Dent. Practnr. 22: 111 (1971). Cueto, E. and Buonocore, M. G.: Sealing of pits and fissures with an adhesive resin and caries prevention. J. Am. dent. Ass. 75: 121-128 (1967). Darling, A. I.: Studies of the early lesion of enam el caries with transmitted light, polarized light, and microradiography. Its nature, mode of spread, points of entry and its relation to en amel structure. Br. dent. J. 105: 119-135 (1958). Dogon, I. L.: Studies demonstrating the need for an intermediary resin of low viscosity for the acid etch technique; in Silverstone and Dogon, Proc. Int. Symp. on the Acid Etch Tech., pp. 100-118 (North Central Publishing Co., Minneapolis 1975). Douglas, W. H. and Tranter, T. C.: A clinical trial of a fissure sealant - results after two years. Proc. Br. paediat. Soc. 5: 17-28 (1975). Fehr, F. R. von der: A study of carious lesions produced in vitro in unabraded, exposed and F-treated human enamel surfaces with empha sis on the X-ray dense outer layer. Archs oral Biol. 12: 797-814 (1967). Ferrara, C. M.: Pit and fissure sealant: a review. N.Y. St. dent. J. 41: 536-543 (1975). Gift, H. C.: Frew, R., and Hefferren, J. J.: Atti tudes toward and use of pit and fissure seal ants. .1. Dent. Child. 42: 44-50 (1975).
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Going, R. E. and Sawinski, V. J.: Microleakage of a new restorative material. J. Am. dent. Ass. 73: 107 (1966). Greenland, L.; Flargreaves, J. A.; Smith, D. C., and Beagrie, G. S.: Fluoride uptake by enamel from polycarboxylate cement. 52nd Gen. Sess. IADR., Abstract No. 918. J. dent. Res. 53: (1974). Guzman, H. J.; Swartz, M. L., and Phillips, R. W.: Marginal leakage of dental restorations subjected to thermal stress. J. prosth. Dent. 21: 166 (1969). Gwinnett, A. J. and Buonocore, M. G.: A scan ning electron microscope study of pit and fis sure surfaces conditioned for adhesive sealing. Archs oral Biol. 17: 415 (1972). Hals, E.; Morch, T., and Sand, H. F.: Effect of lactate buffers on dental enamel in vitro ob served in polarizing microscope. Acta odont. scand. 13: 85-122 (1955). Hals, E. and Nernaes, A.: Histopathology of in vi tro caries developing around amalgam fillings. Caries Res. 5: 58 (1971). Handclman, S. L.; Buonocore, M. G., and Hesek, D. J.: A preliminary report on the effect of fis sure sealant on bacteria in dental caries. J. prosth. Dent. 27: 390 (1972). Handelman, S. L.; Buonocore, M. G., and Schoute, P. C.: Progress report on the effect of a fissure sealant on bacteria in dental caries. J. Am. dent. Ass. 98: 1189 (1973). Handelman, S. L.; Washburn, F., and Woppcrer, P.: Two-year report of sealant effect on bac teria in dental caries. J. Am. dent. Ass. 93: 967-970 (1976). Horowitz. H. S.; Heifetz, S. B., and McCune, R. J.: The effectiveness of an adhesive sealant in preventing occlusal caries: findings after two years in Kalispell, Montana. J. Am. dent. Ass. 89: 885 (1974). Horowitz, H. S.; Heifetz, S. B., and Poulson, S.: Adhesive sealant clinical trial: an overview of results after four years in Kalispell, Montana. J. prev. Dent. 3: 38-48 (1976). Hyatt, T. P.: Statistical studies of the location of dental caries. Oral Top. 7: 717-728 (1923). Isaac, S.; Brudevold, F.; Smith, F. A., and Gar dener, D. E.: Solubility rate and natural fluo ride content of surface and subsurface enamel. J. dent. Res. 37: 354-363 (1958).
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Kidd, E. A. M.: The enamel-restoration interface: the histological features of caries-like lesions produced in vitro in relation to amalgam and composite restorations; PhD thesis London (1975). Kidd, E. A. M.: The histopathology of artificial lesions created in vitro in relation to unfilled and filled cavities. Caries Res. 11: 173-177 (1977). Klein, H. and Knutson, J. W.: Effect of ammonia cal silver nitrate on caries in the first perma nent molar. J. Am. dent. Ass. 29: 1420-1426 (1942). Leinfelder, K. F.; Sluder, T. B.; Sockwell, C. L.; Strickland, W. D., and Wall, J. T.: Clinical evaluation of composites as anterior and pos terior restorative material. J. dent. Res. 53: 152 (1974). Lewis, D. W. and Hargreaves, J. A.: Epidemiology of dental caries in relation to pits and fissures. Br. dent. J. 138: 345-348 (1975). Liatukas, E. L.: A clinical investigation of compo site resin restorations in anterior teeth. J. prosth. Dent. 27: 616 (1972). Marshall, G. W.; Sarkar, N. K., and Greener, E. H.: Detection of oxygen in corrosion products of dental amalgam. Abstract. J. dent. Res. 54: 904 (1975). Mathewson, R. J. and Lu, K. H.: Influences of clinical factors on marginal adaptation and re sidual mercury content of amalgam. J. dent. Res. 54: 104-109 (1975). McCune, R. J.; Horowitz, H. S.; Heifetz, S. B., and Cvar, J.: Pit and fissure sealants: one year results from a study in Kalispell, Montana. J. Am. dent. Ass. 87: 1177 (1973). Miller, J.: A clinical investigation in preventive dentistry. Dent. Practnr dent. Rec. 1: 66-75 (1950). Norman, R. D.; Phillips, R. W., and Swartz, M. L.: Fluoride uptake by enamel from certain dental materials. J. dent. Res. 39: 11-16 (1960). Oswald, J.: The pattern of dental care. Proc. 80th Health Congr. R. Soc. Hlth, vol.3, pp. 71-73 (1973). Parkhouse, R. C. and Winter, G. B.: A fissure sealant containing methyl-2-cyanocrylate as a caries preventive agent: a clinical evaluation. Br. dent. J. 130: 16 (1971).
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Phillips, R. W.; Avery, D. R.; Mehra, R.; Swartz, M. L., and McCune, F. J.: Observations on a composite resin for Class II restorations: three year report. J. prosth. Dent. 30: 891 (1973). Rock, W. P.: Fissure sealants. Further results of clinical trials. Br. dent. J. 136: 317 (1974). Sarkar, N. K. and Greener, E. H.: Electrochem istry of the saline corrosion of conventional dental amalgam. J. oral Rehab. 2: 49-62 (1975a). Sarkar, N. K. and Greener, E. H.: Electrochemi cal properties of copper and gold containing dental amalgam. J. oral Rehab. 2: 157-164 (1975b). Sarkar, N. K.; Marshall, G. W.; Moser, J. B., et al.: In vivo and in vitro corrosion products of dental amalgam. J. dent. Res. 54: 1031-1038 (1975). Silverstone, L. M.: The surface zone in caries and in caries-like lesions produced in vitro. Br. dent. J. 125: 145-157 (1968). Silverstone, L. M.: The susceptibility to dissolu tion of fissure-sealed enamel surfaces artificial ly abraded in vitro. Abstract. Helv. odont. Acta 17: 64 (1973b). Silverstone, L. M.: Fissure sealants: laboratory studies. Caries Res. 8: 2-26 (1974). Silverstone, L. M.: Fissure sealants: the suscepti bility to dissolution of acid-etched and subse quently abraded enamel in vitro. Caries Res. 11: 46-51 (1977). Silverstone, L. M. and Dogon, 1. L. (eds): Pro ceedings of an international symposium on the acid etch technique, pp. 1-293 (North Central Publishing Co., Minneapolis 1975). Thewlis, J.: The structure of teeth as shown by X-ray examination. Spec. Rep. Ser. 38: (His Majesty’s Stationary Office, London 1940). Wing, G.: Dental amalgam; in von Fraunhofer, Scientific aspects of dental materials, pp. 245-276 (Butterworths, London 1975).
Prof. L. M. Silverstone, Division of Cariology, College of Dentistry, University of Iowa, Iowa City, IA 52242 (USA)
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Operative Measures for Caries Prevention Leon M. Silverstone
In a community dependent upon an av erage civilized diet, the high prevalence of dental caries cannot be controlled by repar ative techniques alone. Caries prevention programmes must be run in addition to res torative procedures if the disease is to be controlled. However, many measures can be taken in connection with operative and res torative procedures in order to minimize the incidence of recurrent and new caries. This chapter is intended to summarize briefly the advances in this field during the last 25 years which in the author’s opinion have had the greatest effects or potentials.
Recurrent Caries
Recurrent caries has been shown to be a common cause of failure of restorations. Faults in cavity preparation, such as failure to apply the principle of extension for pre vention, predispose to secondary caries. Material problems will be dealt with in sub sequent sections. Many workers have sug gested that a relatively unaffected surface layer is closely associated with the special caries resistance of surface enamel. Chemical
studies have shown that if the original enamel surface is removed, the remaining enamel is more susceptible to acid demineralization. This greater resistance has been explained as being due to its higher degree of mineraliza tion compared with subsurface enamel [Thewlis, 1940; Brudevold, 1948; Hals et al., 1955], a higher fluoride and lead con tent [Isaac et al., 1958] and perhaps a greater amount of insoluble protein in the surface enamel [Darling, 1958]. However, von der Fehr’s [1967] and Silverstone's [1968] studies suggest that the ‘special’ physical and chemical properties of surface enamel, relative to subsurface en amel, are not entirely responsible for the presence of a well-mineralized surface zone above the small carious lesion. The sugges tion is that the surface zone remains intact and well mineralized because it is a site where calcium and phosphate ions, released by subsurface dissolution, or from the satu rated solution in plaque, become reprecipi tated into the surface enamel. The high fluoride concentration of surface enamel, presumably released at the initiation of sol ution of outer enamel, would also favor pre cipitation.
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Division of Cariology, Dows Institute for Dental Research, College of Dentistry, University of Iowa, Iowa City, Iowa
This surface phenomenon is extremely relevant with respect to preventive and op erative measures involving the enamel. This has been demonstrated in connection with recurrent caries in relation to restorations. In this process, the artificial caries tech nique has been used to study the nature of breakdown and the efficacy of the ‘seal’ be tween the filling material and enamel. The acidified-gcl technique has been employed to create caries-like lesions in relation to amalgam restorations in vitro [Hals and Nernaes, 1971; Kidd, 1975], The lesion consists essentially of two distinct parts. The ‘outer’ lesion is produced in relation to the enamel surface whereas the ‘cavity wall’ le sion is formed by diffusion of hydrogen ions along the enamel restoration interface. Kidd [1977] confirmed that cavity wall lesions were formed as a result of leakage of the restoration.
Amalgam As a material, amalgam appears to be susceptible to marginal deterioration which may predispose to secondary caries. Several factors are probably important in the mech anism of marginal breakdown. These in clude the fracture of excess amalgam re maining as a ‘flash’ over the cavity margin, the mercury content of the filling material, the type of alloy used, condensation pres sure and contamination during the packing of the restoration. It is a well-established clinical observa tion that amalgam restorations leak when first placed. This leakage is transitory and studies in vitro and in vivo have shown that marginal adaptation improves after 24 h. Although no conclusive evidence is availa
ble to explain this phenomenon, it has been suggested by many workers that corrosive products reduce or eliminate the marginal defects. However, other workers have showed that the use of cavity liners such as copal- or polystyrene-based varnishes also decrease marginal defects. The physical properties of dental amal gam are still of specific interest and a com prehensive review of both the physical properties and clinical aspects of dental amalgam has been published recently [Wing, 1975]. The clinical factors influenc ing the residual mercury content and the marginal adaptation of amalgam restora tions have been studied by Mathewson and Lu [1975]. It was found that the level of training of the dental assistant, the type of amalgamator and the accuracy of its timing device as well as the method of condensa tion of the amalgam were critical factors. The presence of tin oxide and tin oxychlo ride in the in vivo and in vitro corrosion products of dental amalgam have been re ported recently [Sarkar et al., 1975]. This analysis of the corrosion products of dental amalgam was supported by a scanning elec tron-microscopic and an energy-dispersive X-ray spectrometric study [Marshall et al., 1975]. The electrochemistry of the saline corrosion of conventional dental amalgam has been described by Sarkar and Greener [1975a]. In a further report [Sarkar and Greener, 1975b] they discussed the electro chemical properties of copper- and goldcontaining nonconventional dental amal gams. These studies were used to provide a mechanism for the observed corrosion be havior of dental amalgam and to account for the role of intermetallic compounds in modifying the electrochemistry of amalgam in corrosive media.
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Operative Measures for Caries Prevention
The incorporation of fluoride into dental cements and bases generally reduces the strength and increases the solubility of the material. With carboxylates, if fluoride is in corporated as part of the glass system, as in silicate or silicophosphate cements, fluoride release occurs without serious degradation of the cement. Cements with added fluoride show a significant impairment of physical properties after fluoride release. Greenland et al. [1974] have shown that the addition of stannous fluoride to a carboxylate cement produced a significant release of fluoride and good uptake of the fluoride by adjacent enamel. The most favorable results were obtained with the addition of 10% stannous fluoride. The cement maintained high com pressive tensile strength although the addi tion of fluoride produced an increase in sol ubility of the cement by approximately 1%. In composite systems, the rate of release of fluoride is very much slower. Generally, with amalgam it has been found that large amounts of fluoride must be added to pro duce a significant release. Even under these conditions, there is initial release of fluoride followed by a very slow release of these ions. This results in a degradation of the physical properties of the amalgam. The incorporation of fluoride into resins has not proved as successful as was hoped initially. Several of the earlier fissure seal ants had fluoride incorporated in the belief that fluoride ions would pass into the enam el surface and, in the event of loss of resin, a more caries-resistant surface would be formed. However, producing a resin that would allow fluoride ions to diffuse through freely resulted in a coating which was not
effective as a barrier. The porous coating also allowed other ions to pass from the oral milieu into the enamel and, on dissolution, calcium and phosphate would pass in the opposite direction. These coatings, most of which were polyurethanes, were also poorly retained by the enamel surface [5/7verstone, 1974]. Fluoride-containing varnishes containing either amine fluoride or monofluorophosphate are available, but at the present time, the consensus of opinion is that fluo ride varnishes should be regarded as experi mental agents. There is as yet insufficient evidence to justify their routine use in den tal practice.
Composite Resins
For many years, anterior teeth were res tored with silicate cements which were de veloped in Europe around the turn of the century. Whilst their esthetics were highly acceptable, they were criticized for the irri tative effects caused by the release of phos phoric acid. The advantages of the high fluoride content in silicates [Norman et al., 1960] is to reduce secondary caries, fluoride being released slowly by the soluble filling material. The self-curing acrylic resins were intro duced in the 1950s. These materials gave good aesthetics for a short time after place ment. However, the porous nature of the material together with a high coefficient of thermal expansion, causing the resin to shrink, led to marginal leakage and recur rent caries. As a result of his work at the National Bureau of Standards in Washington, DC, Bowen introduced the first composite mate
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Incorporation of Fluoride into Restorative Materials
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rial for dental use in 1964. In the following 1966; Guzman et al., 1969] have compared years, other composite materials appeared leakage around amalgam and composite res and have gained in popularity. The compo torations using radioisotope methods. Re sites are made of a resin matrix which is a sults showed a better initial seal with the cross-linked organic mixture of polymer and composite material than with amalgam. Al monomer, and inorganic filler particles. The though there is no corrosion phenomenon filler has been added up to 75% by weight associated with composites, they do absorb and varies depending upon the restorative water causing expansion of the material and material. Filler particles include glass beads, consequent reduction in the width of the glass rods, quartz, lithium aluminum sili initial microspace [Asmussen and Jorgensen, cate, and borosilicate. In order to promote 1972], This is one possible explanation of the bond of the resin to the filler, the parti the apparent good seal obtained with com cles are coated with a coupling agent, for posite materials. Dogon [1975] has demon which usually silane is utilized. These mate strated that isotope penetration around rials are, with reference to mechanical prop composite resin restorations, after thermal erties, superior to the conventional acrylic cycling, was prevented by the use of an in resins. Factors which are improved include termediary resin of low viscosity coating the (1) greater compressive and tensile strength; etched enamel. (2) higher modulus of elasticity; (3) superior In studies of artificial lesions produced hardness and resistance to abrasion; (4) in relation to restorations, the cavity wall le lower polymerization shrinkage, and (5) a sion is a measure of the extent of microleak reduced coefficient of thermal expansion. age. In a recent study, Kidd [1975] has A clinical evaluation of six commercial compared artificial lesions created in rela composite materials involving 668 restora tion to composite and amalgam restorations tions over a 2-year period has been reported in vitro. A total of 154 artificial lesions by Leinfelder et al. [1974], They found that were examined in relation to these restora the composites had good marginal adapta tions. Wall lesions were present adjacent to tion and resistance to interfacial staining. 77% of amalgam restorations, whereas only None of the 668 restorations exhibited evi 13% of the composite restorations showed dence of secondary caries. evidence of a wall lesion. In addition, the Several clinical trials have been carried depth of penetration of wall lesions was sig out on composites ranging from 2 to 4 years nificantly greater in relation to amalgam in duration [Phillips et al., 1973; Liatukas, restorations compared with composites. 1972; Leinfelder et al., 1974]. All of the This must reflect differences in microleak studies showed minimal incidence of recur age between the two restorative materials rent caries and good marginal adaptation of since all other parameters were identical. the material. In the study by Phillips et al. [1973], the composite material was com pared with amalgam in 124 paired posterior Fissure Sealants restorations, and superior marginal adapta tion was found with the composite. Two mi From all available evidence, fissure seal croleakage studies [Going and Sawinski, ants are likely to play an important role in
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caries prevention. Because the occlusal sur face accounts for nearly half the caries in children during their time at school [0swald, 1973], and because it is the surface least protected by fluoride [Backer-Dirks et al., 1961], the use of fissure sealants on oc clusal surfaces can have a highly significant caries-preventive effect. A number of techniques have been pro posed in an attempt to prevent occlusal car ies. Hyatt [1923] suggested the technique of prophylactic odontotomy whereby occlusal fissures were filled, but this was not widely accepted because it was necessary to pre pare cavities in sound teeth. The use of chemical agents to seal pits and fissures, such as ammoniacal silver nitrate [Klein and Knutson, 1942], zinc chloride and po tassium ferrocyanide [Ast et al., 1950] met with little success, as did the use of copper cement [Miller, 1950]. The eventual devel opment of new synthetic resins led to the possibility of sealing occlusal fissures with adhesive materials requiring no cavity prep aration. Early work with the epoxy resins was unsuccessful because the bond strength of these adhesives to the enamel surface was poor, due to the presence of water in the tis sue. The introduction of the cyanoacrylate group of adhesives seemed likely to over come this difficulty by using a small amount of water for polymerisation. The technique of fissure sealing is one in which the vulnerable occlusal fissures of teeth are coated with a thin layer of a plas tic-type material to prevent the initiation and progress of caries. The technique con sists essentially of two stages: etching of the tooth surface using an acid solution, and ap plication of the sealant resin material. The use of an acid solution to etch the
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enamel surface is an essential prerequisite for the successful bonding of resins to the hard tissue. In a recent report [Silverstone, 1974], a series of different acid solutions, together with phosphoric acid in the con centration range 20-70% (w/w), were inves tigated for their effect on human enamel in vitro. The results showed that an unbuffered solution of 30% (w/w) phosphoric acid pro duced the most favorable conditions for bonding. When the 30% solution of phos phoric acid was compared with the more commonly used buffered 50% solution, an increase in tensile bond strength of more than 50% was found [Rock, 1974], It has been shown that the acid solution produces changes to the enamel surface in two distinct ways [Silverstone, 1974]. In the first, a shallow layer of enamel is removed by etching. In this manner, plaque, surface and subsurface pellicles are effectively re moved from the site to be bonded. In addi tion, chemically inert crystallites in surface enamel are also removed, so favoring at tempts at chemical union between hard tis sue and resin. In the second, after removal of the surface layer by etching, the remain ing enamel surface is rendered porous by the acid solution. It is into this porous re gion that the resin is able to penetrate and so bond with the enamel. The depth of en amel rendered porous can be measured ac curately in polarized light [Silverstone, 1974], After application of sealant and sub sequent demineralization of the hard tissue, tags of resin which previously penetrated the enamel surface can be examined directly with the light or electron microscope. No evidence of caries of test teeth has been reported which could be related to the original etching of the enamel. Acid etching is an essential stage in the bonding mecha
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Operative Measures for Caries Prevention
nism and it appears to be confined to the cuspal slopes, rather than to the base of the fissure, and this is the region where the bond occurs [Gwinnett and Bitonocore, 1972: Silverstone, 1974], In addition, a number of studies have shown that etched enamel, not covered by resin, will be remineralized on contact with the oral fluid [Al bert and Grenoble, 1971; Silverstone, 1973b]. Quantitative studies on enamel dis solution rates have shown recently that the dissolution rate of acid etched enamel re turns to that of adjacent sound enamel after 24 h of exposure to oral fluid [Silverstone, 1977], In addition, fissure-scaled enamel surfaces artificially abraded in vitro show a lower dissolution rate than adjacent sound enamel [Silverstone, 1977], These results were interpreted as being due to the reten tion of tags of sealant, which penetrated up to 50 ,«m into the enamel surface. Thus, fissure-sealed enamel surfaces which have been worn down might well be less suscepti ble to caries than adjacent sound enamel. A number of sealant trials have been carried out to date and others arc in prog ress. Although initial trials with methyI-2cyanoacrylate produced significant results fCueto and Bitonocore, 1967], reapplication every 6 months was found to be necessary. A trial using this material in Britain [Parkhouse and Winter, 1971] showed an almost total failure by the 6-month recall period. Although these workers used slightly differ ent parameters in their use of the material, it displayed failure in the hands of others. C'rabb and Wilson [1971] showed that the bond strength of methyl-2-cyanoacrylate was reduced to one sixth of its dry value by immersion in water for 24 h. Thus, this fac tor may have been of significance regarding retention of the material. Today, as far as
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the author is aware, there is no fissure seal ant available commercially which is based entirely on the methyl-2-cyanoacrylate for mulation. The next stage in the development of the technique was the use of a new material as a fissure sealant, based on bispheno! A-glycidyl methacrylate (Bis-GMA). Bitonocore and his colleagues modified the Bis-GMA sealant system by using an ultraviolet lightsensitive catalyst, benzoin methyl ether. The material (Nuva-Scal, Caulk Co., Milford, Del.) was polymerized by long-wave ultra violet light using the Spectroline lamp. 2-year results of a clinical trial using this system, carried out in Rochester, N. Y., were reported by Bitonocore [1971]. He found that a single application of the sealant was almost completely effective in protect ing occlusal surfaces from caries. Occlusal caries was reported in only 1 out of 113 treated surfaces. However, in his trial, teeth were selected on the basis of having well-de fined pits and fissures. In later trials carried out by other workers, criteria for selection of teeth, such as specific morphological fea tures, were not used. This may be one rea son why the results of other trials arc less striking. More recently, Horowitz, et al. [1974] re ported on the effectiveness of Nuva-Seal in a 2-year trial. The children who took part in the trial were of two age-groups - 5-8 yearolds and 10-14 year-olds. After 1 year of the trial (table I) results on 900 pairs of homologous teeth showed an 81% reduction in caries and an 88% total retention of seal ant [McCune et al., 1973]. After the second year of the trial, the sealant was reported as showing a 67% reduction in caries relative to controls. 73% of test teeth showed full re tention of the sealant. The results, however.
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are good regarding caries reduction espe cially when it is remembered that the seal ant was placed in less than optimal sur roundings, using portable equipment. Horowitz el al. [1976] reported their 4-year results recently. After 4 years, 50% of all sites showed complete retention. For all sites remaining fully sealed, there was a 99% reduction in caries. For sites showing partial retention of material a 90% reduc tion in caries was recorded. Table I. Nuva Seal [Horowitz et a!., 1974] Time since application years
Complete retention %
Caries reduction %
i 2
88 73
81 67
Table II. Nuva Seal retention [Rock, 1974] Time since application months
Full retention %
Partial retention %
Sealant lost %
6 12 24
91.1 86.2 80.0
7.2 10.3 15.3
1.7 3.5 4.7
Table III. Nuva Seal: incidence of occlusal caries [Rock, 1974] Time since application years
2
Teeth in study
170 n = Number.
Caries test teeth
control teeth
n
%
n
%
5
2.9
49
28.8
In the United Kingdom, several clinical trials using a number of fissure sealants have been carried out by Rock [1974], In his latest report, the results after 2 years in volving four commercial sealants were pre sented. Each sealant was applied to two teeth in the mouths of 100 children between 11 and 13 years of age. The teeth sealed were in diagonally opposite quadrants, and teeth on the opposite side of each arch served as matched contralateral controls. The results after 2 years with Nuva Seal are shown in tables II and III. One feature of re levance is that the numbers of teeth remain ing fully sealed after 2 years were very simi lar to the numbers retaining sealant 6 months after application. This indicates that if the sealant is to be lost, it is lost early on, probably as a result of an incorrect applica tion technique or polymerisation failure, rather than failure of the sealant/enamel bond. In a Nuva Seal study by Burt et al. [1975], 205 children between 5 and 17 years of age participated initially. Between them, 427 pairs of teeth were included in the study, one of each pair being sealed. At 6 months, the total retention figure was 83.2%. Douglas and Tranter [1975] reported on a 2-year study using Nuva Seal in the Aberdare region of South Wales. The age range of the 106 patients was 6-13 years, present ing a complete spectrum of the mixed denti tion. Of the 275 teeth sealed in the study, 86.2% were found to be fully sealed after 2 years. Regarding caries incidence, 9.1% of test teeth were classed as being carious, whereas 36% of controls became carious over the 2-year period. Thus, the results of many trials in var ious parts of the world have shown that fis
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and carious dentine was removed for bac teriological examination. There was approx imately a 50% decrease in the numbers of cultivatable microorganisms in the infected dentine from sealed teeth compared with the numbers grown from dentine from unsealed control teeth. A more recent report [Handelman et al., 1973] presented additional bacteriological results for patients examined up to 6 months after a single application of the seal ant. The reduction in the total viable count of infected dentine at 1, 2, 4 and 6 months was approximately 20-, 40-, 100- and 300fold, respectively. The 12-month recall X-rays of patients sampled in the bacterio logical study were compared to the X-rays taken when the teeth were sealed. In each instance, there was no evidence of progress of caries. After 2 years [Handelman et al., 1976], these workers reported a 3,000-fold de crease in the number of cultivable microor ganisms. Clinical and radiographic findings suggested that there was no progression of the carious lesions but further studies are required before this technique can be con sidered as an alterantive to conventional procedures.
References Albert, M. and Grenoble, O. E.: An in vivo study of enamel remineralization after acid etching. J. Sth. Calif, dent. Ass. 39: 747-751 (1971). Asmussen, E. and Jorgensen, K. D.: A microscop ic investigation of the adaptation of some plas tic filling materials to dental cavity walls. Acta odont. scand. 30: 3 (1972). Ast, D. B.; Bushel, A., and Chase, H. C.: A clinical study of caries prophylaxis with zinc chloride and potassium ferrocyanide. J. Amer. dent. Ass. 41: 437-442 (1950).
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sure sealants can have a highly significant effect in the prevention of occlusal caries. Most studies have shown that the ultraviolet activated materials produce the most satis factory, and reproducible, results. However, it is also evident that more attention must be paid to the application technique if the materials are to be highly effective in every one’s hands. Lewis and Hargreaves [1975] followed the surface status of first permanent molars in 142 children at ages 5, 6, 7 and 8 years. The findings showed that if the sealant was completely effective at the time of applica tion, the caries reduction for 6-7 year-olds would be 36-42°/o if the sealant was placed in occlusal surfaces only. However, if the lingual fissure of maxillary molars and the buccal pit of mandibular molars were also sealed, the caries reduction would be 91-95%. For 7- to 8-year-old children, the corresponding reduction figures were 23-25% and 83-91%. The data demon strate the greater benefit derived by the sealing of lingual and buccal pits also. Fissure sealant reviews have been pub lished by Barolet [1975], Buonocore [1975] and Ferrara [1975] and the proceedings of a first international symposium on the acid etch technique is also available [Silverstone and Dogon, 1975], Gift et al. [1975] exam ined the attitude of approximately 4,000 dentists in the USA towards fissure sealing. The technique was not used by 62% and the reasons given were inconsistent with the present state of knowledge of the materials. Occlusal fissures of permanent posterior teeth having caries detected clinically and by radiographic means were sealed with an ultraviolet-light-polymerized adhesive resin [Handelman et al., 1972]. One week later, traditional class I cavities were prepared
Backer Dirks, O.; Houwink, B., and Kwant, G. W.: The results of 6'/2 years of artificial fluo ridation of drinking water in The Netherlands. Archs oral Biol. 5: 284-300 (1961). Barolet, R. Y.: Pit and fissure sealant. J. Can. dent. Ass. 41: 157 (1975). Brudevold, F.: A study of the phosphate solubility of the human enamel surface. J. dent. Res. 27: 320-329 (1948). Buonocore, M. G.: Caries prevention in pits and fissures sealed with an adhesive resin polymer ized by ultraviolet light. J. Am. dent. Ass. 82: 1090-1093 (1971). Buonocore, M. G.: Pit and fissure sealing. Dent. Clin. N. Am. 19: 367-383 (1975). Burt, B.; Berman, D. S.; Gelbier, S., and Silverstone, L. M.: Retention of a fissure sealant six months after application. Br. dent. J. 138: 98-100 (1975). Crabb, J. J. and Wilson, H. J.: Use of some adhesives in orthodontics. Dent. Practnr. 22: 111 (1971). Cueto, E. and Buonocore, M. G.: Sealing of pits and fissures with an adhesive resin and caries prevention. J. Am. dent. Ass. 75: 121-128 (1967). Darling, A. I.: Studies of the early lesion of enam el caries with transmitted light, polarized light, and microradiography. Its nature, mode of spread, points of entry and its relation to en amel structure. Br. dent. J. 105: 119-135 (1958). Dogon, I. L.: Studies demonstrating the need for an intermediary resin of low viscosity for the acid etch technique; in Silverstone and Dogon, Proc. Int. Symp. on the Acid Etch Tech., pp. 100-118 (North Central Publishing Co., Minneapolis 1975). Douglas, W. H. and Tranter, T. C.: A clinical trial of a fissure sealant - results after two years. Proc. Br. paediat. Soc. 5: 17-28 (1975). Fehr, F. R. von der: A study of carious lesions produced in vitro in unabraded, exposed and F-treated human enamel surfaces with empha sis on the X-ray dense outer layer. Archs oral Biol. 12: 797-814 (1967). Ferrara, C. M.: Pit and fissure sealant: a review. N.Y. St. dent. J. 41: 536-543 (1975). Gift, H. C.: Frew, R., and Hefferren, J. J.: Atti tudes toward and use of pit and fissure seal ants. .1. Dent. Child. 42: 44-50 (1975).
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Going, R. E. and Sawinski, V. J.: Microleakage of a new restorative material. J. Am. dent. Ass. 73: 107 (1966). Greenland, L.; Flargreaves, J. A.; Smith, D. C., and Beagrie, G. S.: Fluoride uptake by enamel from polycarboxylate cement. 52nd Gen. Sess. IADR., Abstract No. 918. J. dent. Res. 53: (1974). Guzman, H. J.; Swartz, M. L., and Phillips, R. W.: Marginal leakage of dental restorations subjected to thermal stress. J. prosth. Dent. 21: 166 (1969). Gwinnett, A. J. and Buonocore, M. G.: A scan ning electron microscope study of pit and fis sure surfaces conditioned for adhesive sealing. Archs oral Biol. 17: 415 (1972). Hals, E.; Morch, T., and Sand, H. F.: Effect of lactate buffers on dental enamel in vitro ob served in polarizing microscope. Acta odont. scand. 13: 85-122 (1955). Hals, E. and Nernaes, A.: Histopathology of in vi tro caries developing around amalgam fillings. Caries Res. 5: 58 (1971). Handclman, S. L.; Buonocore, M. G., and Hesek, D. J.: A preliminary report on the effect of fis sure sealant on bacteria in dental caries. J. prosth. Dent. 27: 390 (1972). Handelman, S. L.; Buonocore, M. G., and Schoute, P. C.: Progress report on the effect of a fissure sealant on bacteria in dental caries. J. Am. dent. Ass. 98: 1189 (1973). Handelman, S. L.; Washburn, F., and Woppcrer, P.: Two-year report of sealant effect on bac teria in dental caries. J. Am. dent. Ass. 93: 967-970 (1976). Horowitz. H. S.; Heifetz, S. B., and McCune, R. J.: The effectiveness of an adhesive sealant in preventing occlusal caries: findings after two years in Kalispell, Montana. J. Am. dent. Ass. 89: 885 (1974). Horowitz, H. S.; Heifetz, S. B., and Poulson, S.: Adhesive sealant clinical trial: an overview of results after four years in Kalispell, Montana. J. prev. Dent. 3: 38-48 (1976). Hyatt, T. P.: Statistical studies of the location of dental caries. Oral Top. 7: 717-728 (1923). Isaac, S.; Brudevold, F.; Smith, F. A., and Gar dener, D. E.: Solubility rate and natural fluo ride content of surface and subsurface enamel. J. dent. Res. 37: 354-363 (1958).
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Operative Measures for Caries Prevention
Kidd, E. A. M.: The enamel-restoration interface: the histological features of caries-like lesions produced in vitro in relation to amalgam and composite restorations; PhD thesis London (1975). Kidd, E. A. M.: The histopathology of artificial lesions created in vitro in relation to unfilled and filled cavities. Caries Res. 11: 173-177 (1977). Klein, H. and Knutson, J. W.: Effect of ammonia cal silver nitrate on caries in the first perma nent molar. J. Am. dent. Ass. 29: 1420-1426 (1942). Leinfelder, K. F.; Sluder, T. B.; Sockwell, C. L.; Strickland, W. D., and Wall, J. T.: Clinical evaluation of composites as anterior and pos terior restorative material. J. dent. Res. 53: 152 (1974). Lewis, D. W. and Hargreaves, J. A.: Epidemiology of dental caries in relation to pits and fissures. Br. dent. J. 138: 345-348 (1975). Liatukas, E. L.: A clinical investigation of compo site resin restorations in anterior teeth. J. prosth. Dent. 27: 616 (1972). Marshall, G. W.; Sarkar, N. K., and Greener, E. H.: Detection of oxygen in corrosion products of dental amalgam. Abstract. J. dent. Res. 54: 904 (1975). Mathewson, R. J. and Lu, K. H.: Influences of clinical factors on marginal adaptation and re sidual mercury content of amalgam. J. dent. Res. 54: 104-109 (1975). McCune, R. J.; Horowitz, H. S.; Heifetz, S. B., and Cvar, J.: Pit and fissure sealants: one year results from a study in Kalispell, Montana. J. Am. dent. Ass. 87: 1177 (1973). Miller, J.: A clinical investigation in preventive dentistry. Dent. Practnr dent. Rec. 1: 66-75 (1950). Norman, R. D.; Phillips, R. W., and Swartz, M. L.: Fluoride uptake by enamel from certain dental materials. J. dent. Res. 39: 11-16 (1960). Oswald, J.: The pattern of dental care. Proc. 80th Health Congr. R. Soc. Hlth, vol.3, pp. 71-73 (1973). Parkhouse, R. C. and Winter, G. B.: A fissure sealant containing methyl-2-cyanocrylate as a caries preventive agent: a clinical evaluation. Br. dent. J. 130: 16 (1971).
Silverstone
Phillips, R. W.; Avery, D. R.; Mehra, R.; Swartz, M. L., and McCune, F. J.: Observations on a composite resin for Class II restorations: three year report. J. prosth. Dent. 30: 891 (1973). Rock, W. P.: Fissure sealants. Further results of clinical trials. Br. dent. J. 136: 317 (1974). Sarkar, N. K. and Greener, E. H.: Electrochem istry of the saline corrosion of conventional dental amalgam. J. oral Rehab. 2: 49-62 (1975a). Sarkar, N. K. and Greener, E. H.: Electrochemi cal properties of copper and gold containing dental amalgam. J. oral Rehab. 2: 157-164 (1975b). Sarkar, N. K.; Marshall, G. W.; Moser, J. B., et al.: In vivo and in vitro corrosion products of dental amalgam. J. dent. Res. 54: 1031-1038 (1975). Silverstone, L. M.: The surface zone in caries and in caries-like lesions produced in vitro. Br. dent. J. 125: 145-157 (1968). Silverstone, L. M.: The susceptibility to dissolu tion of fissure-sealed enamel surfaces artificial ly abraded in vitro. Abstract. Helv. odont. Acta 17: 64 (1973b). Silverstone, L. M.: Fissure sealants: laboratory studies. Caries Res. 8: 2-26 (1974). Silverstone, L. M.: Fissure sealants: the suscepti bility to dissolution of acid-etched and subse quently abraded enamel in vitro. Caries Res. 11: 46-51 (1977). Silverstone, L. M. and Dogon, 1. L. (eds): Pro ceedings of an international symposium on the acid etch technique, pp. 1-293 (North Central Publishing Co., Minneapolis 1975). Thewlis, J.: The structure of teeth as shown by X-ray examination. Spec. Rep. Ser. 38: (His Majesty’s Stationary Office, London 1940). Wing, G.: Dental amalgam; in von Fraunhofer, Scientific aspects of dental materials, pp. 245-276 (Butterworths, London 1975).
Prof. L. M. Silverstone, Division of Cariology, College of Dentistry, University of Iowa, Iowa City, IA 52242 (USA)
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