Journal of Dentistry, 6, No. 1,1978,

pp. l-22.

Printed in Great Britain

Dental materials: 1976 literature review Part

I

M. Braden, BBC, PhD, FlnstP, FPRI (Editor) Dental School, London Hospital Medical Collqge D. Brown, BSc, PhD, MIM

T. C. Tranter, BSc, PhD

Dental Department, Guy’s Hospital, London

Dental School, Welsh National School of Medicine, Ordiff

E. C. Combe, MSc, PhD, CChem, FRIC Department of Prosthetics, Turner Dental School,

N. E. Waters, MSc, PhD, FlnstP

Manchester

School of Dental Surgery, Royal Dental Hospital

J. A. von Fraunhofer,

of London MSc,PhD,CChem,FRIC,MIM

Eastman Dental Hospital, London

C. H. Lloyd, Department

BSc,PhD of Dental Prosthetics, Dental School

and Hospital, Dundee

D. F. Williams, BSc, PhD, MIM School of Dental Surgery, University of Liverpool

A. D. Wilson, DSc, FRIC Laboratory of the Government Chemist, London

C. Main, Bsc. PhD Dental School, Glasgow

H. J. Wilson, PhD, DSc, FRIC Department

M. Miller, BSc, FRIC

of Prosthe tics, Birmingham

Dental

School

School of Dental Surgery, University of Edinburgh

ABSTRACT This paper, which is to be presented in two parts, reviews the work on dental materials published in 1976. Included in Part I are sections on amalgam, casting alloys, denture base polymers, composite fang materials, tissue conditioners and soft lining materials and fissure sealants. A review of the literature

relating to impression materials, dental ceramics, model and die materials, cements, dental implants and dental biomechanics will be presented in Part II.

INTRODUCTION

This review is the fourth in an annual series compiled by the Panel for Dental Materials Studies in the United Kingdom, and is intended as a source of reference for work on dental materials published in 1976. It covers the introduction of new materials, the evaluation of existing materials or their modification and developments in certain relevant techniques. A basic list of 37 journals was surveyed by all the contributors, but each contributor was free to include material from any other source. METALS Dental amalgam

the literature on dental amalgam is steadily growing, the rate of increase has tended to diminish. Thus the number of communications on amalgam was somewhat lower in 1976

Whilst

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and there were only two major reviews on the material (Brown, 1976; JQrgensen, 1976). In the review by Brown the clinical status of dental amalgam was reviewed with particular reference to the recently introduced dispersion-phase amalgam alloys. Clearly, these new alloys represent an advance in terms of the mechanical properties and corrosion resistance of the set amalgam restoration, but a full scale clinical appraisal is necessary before the full significance of their properties is established. Jbrgensen (1976) reviewed many of the physical properties of the new generation nonr2 alloys, including tensile and compressive strength, static creep and setting expansion. He also drew attention to the improved corrosion resistance of these new amalgams and to the fact that there is no release of mercury through corrosion of the r2 phase and this reduces mercuroscopic expansion. Thus the tendency to marginal failure will be diminished. Jdrgensen also mentioned the superior corrosion resistance of the new amalgams, although he commented on the greater solubility of the corrosion products compared with those of tin in the organic acids of plaque. The microstructure of six preamalgamated alloys has been studied by Jensen and Vrijhoef (1976). In all cases the presence of the rl (Ag-Hg) phase was established, whilst the or phase, also a silver-mercury phase, was detected in five of the alloys. The relative content of the y1 and pi phases appears to be dependent upon mercury diffusion during the preamalgamation process. Whilst these findings are interesting in themselves, the authors noted that further work is necessary on the relationship between the microstructure of the alloys and the creep behaviour and corrosion resistance of the set amalgams. The changes in the microstructure of set amalgams effected by copper additions to the alloys were studied by Marshall et al. (1976). Copper-rich amalgam microstructures have markedly reduced or eliminated r2-phase contents and this increases the corrosion resistance in chloride media. Various methods of introducing copper were investigated and in all cases the attendant reduced r2-phase content resulted in improved corrosion resistance to saline media. Wang Chen and Greener (1976) studied the effect of anodic polarization on the tensile strength of dental amalgam. They found that anodic polarization produced a significant strength reduction in -y2-containing conventional amalgams but had no effect on that of high copper amalgams. It was concluded that anodic corrosion of the susceptible 72 phase led to the reduced strength which could result in marginal breakdown in clinical practice. The tensile strength of setting amalgams, at 15 minutes after trituration, was studied by Spanauf et al. (1976). The study investigated amalgams prepared from conventional, spherical and dispersed phase alloys using two different trituration techniques and two condensation methods. It was found that although both the trituration and condensation technique significantly affected the tensile strength, that due to the ahoy used was far greater. Amalgams prepared from certain alloys did not satisfy the tensile strength requirements of the new ADA specification for dental amalgams, whilst the values for Dispersalloy amalgams were significantly greater than the minimum value. Various other studies on dental amalgam were also reported in 1976. Lavelle (1976) carried out a cross-sectional longitudinal survey into the durability of dental amalgams based on 6000 restorations spanning a 20-year period. His findings indicated that amalgam restorations were less durable than hitherto thought and that the primary factor affecting the length of life of a restoration was the dental surgeon placing the amalgam. The adaptation of amalgams to cavity walls was studied by @lo (1976). In this Investigation the margimd gap between tooth and restoration was determined for amalgam

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that expanded on setting, one that showed no change (i.e. a balanced amalgam) and two that exhibited a contraction. Good contact between restoration and cavity was found for the expanding and balanced amalgams, with small and scattered marginal defects being observed. In contrast, slit formation was found with the contracting amalgams and fairly large defects were frequently observed. In addition, polishing could fracture both the unsupported amalgam and enamel margins, leading to increased marginal defects. Marginal adaptation was found to be most satisfactory with the expanding amalgam, with a decrease in quality being observed with the contracting materials. The marginal breakdown of 3-year-old amalgam restorations was determined by Osborne et al. (1976) using five different evaluation techniques. The most useful evaluation method was considered to be one based on ranking of photographs of the restorations. It was found that the alloy having the lowest creep susceptibility exhibited the least marginal breakdown, whilst the alloy with the greatest creep showed the highest incidence of breakdown. An in vitro study of microleakage was performed using an artificial caries technique by Kidd (1976). The lesions produced in enamel adjacent to amalgam and composite restorations by a diffusion-controlled acidified gel were used as a method of assessing microleakage. Surprisingly, 77 per cent of amalgam restorations developed wall lesions whilst only 13 per cent of composites showed this effect. Furthermore, the depth of penetration of wall lesions was greater with the amalgam restorations. These findings suggest that freshly packed composites afford a better cavity seal than freshly packed dental amalgam. However, no conclusions can be drawn from this work on the long term comparative sealing efficiency of the two classes of materials. The effects of implanted amalgam on connective tissues using adult rats were reported by Martin et al. (1976). In this study the inflammatory response to implanted zinc-free and zinc-containing amalgams, zinc carbonate and stainless steel was evaluated at 2, 14 and 30 days. The results indicated that there were no significant differences in the connective tissue inflammatory response for any of the implanted materials. Finally, Goldschmidt et al. (1976) studied the effect of the corrosion products from dental amalgam on human gingival fibroblasts and HeLa cells when the cells were grown in culture. Both mercury and silver ions effected release of chromium and uptake of trypan blue dye. Furthermore, eluates of amalgam inhibited amino acid incorporation into protein-like material. In contrast, the stannous ion showed little if any cytotoxic potential. These results suggest that the corrosion products of dental amalgam are capable of causing cellular injury or destruction. Cellular reaction to amalgam implanted in guinea-pigs was reported by Eley et al. (1976). Disintegration of amalgam particles occurred in giant cells and macrophages. Amalgam fragments within the tissues lost copper and zinc rapidly but tin and mercury more slowly. Residual silver associated with sulphur, possibly forming a sulphide, this product becoming attached to components of the tissues and probably being phagocytosed by macrophages and fibroblasts. In view of the conflicting reports in the literature on the possible antibacterial action of dental amalgam, Nunez et al. (1976) have developed a biological test system for studying the influence of amalgam, alloy and mercury on the in vitro growth of Streptococcus mufans. A culture medium that provided a suitable growth environment together with a spectrophotometric measuring system was reported. Initial findings indicated that amalgam and amalgam alloy do influence the growth of the bacteria, the effect being influenced by the amount of material added.

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In conclusion, dental amalgam still appears to provide a fertile field for investigation, and the newer, high copper and dispersed phase alloys should stimulate continued research on this material. Casting alloys 1976 saw the publication of a series of papers by Strandman (Strandman, 1976a,b,c; Strandman and Glantz, 1976) quantitatively showing the effect of oxyacetylene torch variables on the melting of a cobalt-chromium-molybdenum alloy and its subsequent mechanical properties. Oxidizing flames were found to inhibit the melting process whereas considerable carbon pick-up occurred with some acetylene-rich flames. It is argued that the section of the flame used rather than the actual gas ratio is the determining factor for carbon pick-up, and provided that the acetylene feathers do not directly impinge on the alloy, acetylene-rich flames may be used. When carbon was picked up, hardness and strength were increased but elongation substantially reduced. Such alloys were also amenable to precipitation hardening without an intermediate solution treatment, the hardness increasing from 340 to 410 HV, again at the expense of ductility. In a detailed study of the fatigue strength of cast cobalt-chromium-molybdenum, Miller et al. (1976) found it advisable to reduce previously quoted safe stress levels by approximately one-third. The surface finish of cast alloys was considered in two publications. Lewis (1976) found that considerable surface roughness and sulphur pick-up occurred when casting a low fusing nickel alloy (Ticonium Premium 100) in gypsum-bonded investments. Arfaei and Asgar (1976) looked at roughness as a function of the bonding media and mould temperature. Gypsum investments gave the smoothest finish and in all cases roughness increased with increasing temperature. Farne and Nealey (1976) showed that both chemical and electrolytic etching were equally effective in providing space for a cement lute on the fitting surface of cast gold restorations, and that margins must be protected during this process to maintain their accurate fit. The effectiveness of several finishing techniques to burnish a type II gold alloy over a cement lute and produce a smooth surface finish was considered by Metzler and Chandler (1976), and on both counts, smooth sandpaper discs produced the best results. A clinical evaluation of inlays produced in type III gold alloy and its various substitutes (Loftstrom et al., 1976) resulted in acceptable fits for all but the base alloy and increased difficulty in burnishing with increasing baseness. The poor tit of such base alloy castings was confirmed by Lorey et al. (1976). Moon and Modjeski (1976) gave an empirical index of burnishability as the quotient of hardness and elongation. When they used values from ADA specification No. 5 for type III gold to obtain a standard value and compared those obtained from baser substitutes, half the alloys exceeded this in the soft condition and all did in the hard state. The tarnish resistance of these alloys has been shown to be less than that of noble metal alloy controls (Wirthner et al., 1976). Base alloys were tarnished more than the economy gold alloys in which an increased concentration of palladium reduces the nobility. The nature of tarnish has been investigated by, Ingersoll (1976) using a powerful tool, auger spectroscopy. In gold alloys, copper is the main tarnish-forming element, producing organic compounds in an oral environment whereas chemically induced tarnish consists mainly of inorganic oxides, sulphides and chlorides. An interesting incidence of corrosion was reported by Parvinen et al. (1976). Extensive electrolytic corrosion of a gold alloy bridge was reportedly brought

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about by an amalgam alloy containing noble metal screws which were left in place under the bridge. Schulman et al. (1976) published data on a gold-nickel alloy, containing 23 per cent nickel by weight, which has mechanical properties similar to those of a type IV gold alloy. Unless it is subsequently shown to offer particular advantages, it may prove to be only another interesting experimental alloy. The heat-hardening responses of two alloys (50Au 31Pd 15Ag and 50Pd 42Ag) were reported by Huget et al. (1976). The results are similar to those of the more traditional ‘white golds’, that is, mechanical properties broadly similar to those of type III golds but with a lower ductility. A cautionary tale was related by Stevens (1976) who surveyed the heat-treatment practice for gold alloys in dental laboratories in Brisbane, Australia. Of the replies received, 70 per cent stated that dentists using the laboratories never prescribed heat-hardening treatments; that it was the practice in 80 per cent of the laboratories to heat-harden if the technician thought it necessary although not prescribed and that one-third had seen clinical failures as the result of no heat-hardening treatment. It is interesting to speculate on the possibility of such an unsatisfactory state of affairs existing here and in other countries. Alloys for orthodontic

use

The effect of heat treatment on the mechanical properties of orthodontic wires has been reported (Fillmore and Tomlinson, 1976; Waters et al., 1976). Strength increases are produced through the precipitation of carbides in both stainless steel (up to 450°C) and cobalt-chromium alloy (up to 500 “C). Heating to higher temperatures coarsens these carbides and the strength falls. The explanation that some of the strength increase is due to stress relief should be treated with some caution. Waters (1976) found a large recovery in shape of bent, then annealed, stainless steel. This is consistent with the formation of stressinduced martensite, a shear process capable of producing a memory effect. Williams (1976) tried to correlate the increase in volume of this phase with the incidence of fracture in drawn stainless steel wire. Unfortunately, confusion over the formation and structure of martensite detracts from an otherwise plausible explanation. When a crystallographic restriction exists, on dislocation slip shape changes can be produced using shear processes. Such shears are metastable and can often be reversed by annealing through a transition temperature, and the metal appears to possess a memory as it regains its original shape. Use of this effect to produce adjustments in orthopaedic implants which would otherwise require a second operation has been demonstrated (Schmerling et al., 1976). The biocompatibility of the nitinol alloy implants used is better than conventional cobaltchromium alloy (Castleman et al., 1976). The force developed when recovery takes place has been shown to be comparable with that used in orthodontic appliances (Andreasen et al., 1976). However, the ability to use such an athermal transformation in a practical orthodontic appliance has yet to be demonstrated. POLYlMERlC

MATERIALS

Composite filling materials

Composites and other materials have been compared by Sockwell (1976) with regard to clinical performance. Eames et al. (1976) have traced the history of composites briefly, and then reviewed the present situation from the viewpoint of strength, abrasion resistance,

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Journal of Dentistry, Vol. ~/NO. 1

leakage, etching technique, finishing, polishing and glazing, shelf life and pulp damage including pain. This is an excellent paper. In experiments on dogs Hembree and Andrews (1976) utilized 45Ca as the method of determining leakage for Nuva-fil with and without acid-etching, and with various resin pretreatments. The authors concluded that both acid-etching and placing a layer of sealant first gave the best results. The Council on Dental Materials and Devices (1976) listed some clinical ‘do’s’ and ‘don’ts’for composites. A clinical technique paper by Faunce and Myers (1976) described the treatment of fractured, malformed or badly discoloured teeth. Cold-curing and ultraviolet-light-curing systems were studied in vitro by Eriksen and Buonocore (1976a) using a visual tracer system. Severe leakage occurred in conventional butt joint restorations, but was prevented in most cases when the restorations were extended on to peripheral etched enamel, either with or without sealant priming. Pahlaran et al. (1976) studied resin protection of enamel using three resins, and both scanning electron and polarized light microscopy. The depth of penetration appeared to be independent of the viscosity of the resin. An in vitro study by Heath and Wilson (1976) of a number of restorative materials showed the composites (along with silicates!) to wear away two to four times as fast as enamel (TD 71 and unfilled resins exhibited very high rates of abrasion). An in vitro method involving dye penetration was used by Eriksen and Buonocore (1976b) to assess leakage of restorations with both ultraviolet-light-cured and self-curing composites and sealants. Butt joint restorations placed in etched and sealant-primed cavities failed to prevent leakage. Both saucer-shaped and funnel-shaped cavities and cavities with rounded margins were able to prevent leakage when the restorations were bonded to etched and sealant-primed peripheral enamel. Less than 1 mm of available gingival enamel for bonding proved adequate to prevent leakage. A 20-pm mineral layer was formed on cut dentine in vitro by treatment with a calcifying fluid. This resulted in a threefold improvement in the shear strength of bonds formed between the dentine and polycarboxylate cement. These bonds proved stable in water for at least 6 months, but deteriorated by about 50 per cent in 12 months. The use of an intermediate epoxy resin bonding system was also discussed (Causton et al., 1976). Low and von Fraunhofer (1976) described the ,use of composite materials for the restoration of fractured incisors and the direct attachment of stainless-steel-gauze-backed metal brackets to teeth. As far as incisal edge restorations were concerned, there was no difference between the retention of composites and unfilled materials. Similarly, composites were adequate for the direct attachment of brackets, although low viscosity composites retained the gauze better. An in vitro study by Kidd (1976) used an artificial caries technique based on a diffusioncontrolled acidified gel. The lesions produced consisted of an outer lesion in relation to the enamel surface and a ‘cavity wall’lesion at the enamel-restoration junction. The latter were said to be a measurement of microleakage, and were present in only 13 per cent of the composite restorations compared with 77 per cent of amalgam restorations. These fmdings were discussed in relation to other major investigations in this area. Composites based on aromatic dimethacrylate resins were found to have superior mechanical properties to earlier materials based on methyl methacrylate, and to compare favourably with those of enamel and dentine (Hannah and Combe, 1976).

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In an investigation of two resins, Concise and Nuva-fi, Galon et al. (1976) used an in vitro method with 13’I in sodium iodide as the indicator. The results indicated that if sealant is used inside the cavity before placement of butt joint restorations, microleakage is virtually eliminated. Braden et al. (1976) showed that the uptake of water by composites is a diffusion process, and that the uptake is probably by and through the resin phase. Considerable concentration dependence of diffusion coefficients was observed. The in vitro wear resistance, tensile strength and hardness of seven widely used composite restorative resins were measured. There was no apparent correlation between abrasion resistance with either tensile strength or hardness (Harrison and Draughn, 1976). The bond strengths of seven anterior resins (one unfilled acrylic) were compared by Short et al. (1976) using the acid-etch technique. Adaptic had the best bond strengths, and Sevitron and Enamelite the worst. Using a spectrophotometer method, differences in colour were found by Grajower et al. (1976) to correspond to differences in spectra. Differences between teeth classified by the same shade number were found, and between natural and acrylic teeth. Two patents appeared during 1976, although they were in fact filed in Germany in 1975, (Kuhlzer and Ivoclar patents). Although the materials described are on the market in the United Kingdom, the claims in these patents are so substantial that it was thought advisable to draw attention to them at this stage. The two patents are for composites containing microfine fillers which are chemically silica or alumina, and which have particle sizes of the order of 0.07 /_t.Such composites are claimed to exhibit compressive strengths of the order of amalgam, to be polishable to a high surface gloss and to have high abrasion resistance and high transparency. Such materials are envisaged not only as composite filling materials, but, dispensed in different forms, to be used for crown and bridge work, veneers and the production of superior artificial teeth. If the materials measure up to these claims, their impact on dentistry will be profound. Clearly, however, such claims need to be substantiated or otherwise by dental research workers. Research at the ADA research unit at the National Bureau of Standards continues with work on both new monomers and fillers. New crystalline dimethacrylates, with better prospects for colour stability, have been produced (Antonucci and Bowen, 1976), as well as new semiporous fillers with the objective of improving the resin filer bond (Bowen and Reed, 1976a, b). Gjerdet (1976) has studied the viscoelastic behaviour of composites, and quite different results were obtained with a number of common materials. VerraIl (1976) has developed a new test, involving the compression of a sphere of material, for measuring relative stiffness and tensile strength. Denture base and other polymers

McCabe and Basker (1976) described a chromatographic method for determining the residual monomer in acrylic resin. Two case reports were discussed in terms of the residual monomer content of the patient’s dentures. Braden et al. (1976) reported the development of a new temporary crown and bridge resin, together with the results of physical and biological tests of the material. Hargreaves and Foster (1976) described some of the properties of Hydrocryl, a co-polymer of methyl methacrylate and hydroxyethyl methacrylate. The material has, predictably,

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higher water sorption, but also reduced strength and increased flexibility compared with conventional heat-cured acrylics; microporosity was also reported. There was some evidence of short term increased retention. Soft lining materials Suchatlampong et al. (1976) measured water absorption, solubility, compressibility and infrared absorption spectra for four soft lining materials. Two acrylic and two silicone rubber materials were investigated. The materials were tested at regular intervals after up to 3 months of conditioning in water. Specimens varying in thickness from 1 to 5 mm were used. Water absorption and specimen thickness were found to have a pronounced effect upon the properties of all four materials. A thickness of at least 2 mm was recommended to produce a stress-relieving action in the clinical situation. McCabe (1976) showed that a wide variation in composition exists amongst the acrylicbased soft lining materials. Some materials rely upon the combined effect of a higher methacrylate and plasticizer to produce the softening effect, whilst others appear to employ mainly methyl methacrylate with large quantities of plasticizer. Two materials had liquid components which contained no monomers but were mixtures of plasticizers with solvents such as ethanol and ethyl acetate. Wright (1976) investigated fifteen materials, with particular respect to chemical analysis, water absorption, solubility, bonding to acrylic resin and viscoelastic properties. He concluded that no ideal material existed. For best clinical use a 3-mm thickness of material was recommended. The silicone rubber materials possess the advantage of being permanently soft, but their susceptibility to high rates of water diffusion renders the bond formed with the acrylic base very weak. The acrylic materials tend to become hard over a short period of time owing to loss of plasticizer. Fissure sealants Interest in the fissure sealant technique continued at a high level during 1976, as is clearly demonstrated by the large number of papers published covering both the scientific aspects of the technique and the clinical evaluation of the effectiveness of these materials in reducing fissure caries. Gwinnett (1976), reviewing the factors influencing the effectiveness of adhesive resin sealants, stated that it is ‘important that a prophylaxis precede the acid conditioning to remove plaque and other accretions, since conditioning alone will not remove them totally’. It is perhaps appropriate to point out that this is not a view subscribed to by all workers in the field. The variations in etching behaviour of individual teeth are still incompletely understood. Silverstone and Dogon (1976) investigated in more detail the action of phosphoric acid on deciduous molars, since difficulties in obtaining suitable etch patterns have previously been attributed to the presence of a prismless layer. Silverstone and Dogon found it necessary to etch deciduous enamel for 120 seconds in order to obtain patterns comparable with those found in permanent enamel. These differences could not be explained entirely on the basis of areas of prismless enamel and are thought to be due to the presence of larger amounts of exogenous organic material in deciduous enamel resulting from its lower mineral content. The increase in bond strength of Nuva-Seal and Epoxy&e 9075 to enamel resulting from acid-etching has been examined by Williams et al. (1976), who found that varying the

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phosphoric acid concentration from 30 to 70 per cent had little effect on the bond strength, although in the case of Nuva-Seal, unbuffered acid tended to yield higher mean values than buffered acid. The need to apply sealants as soon as possible after tooth eruption has been underlined by Crabb (1976a). A premolar with only one cusp clinically visible, known to have been unerupted 4 months previously, was removed for orthodontic reasons and found to have fissure caries involving the dentine. The high initial susceptibility to caries may be due to an outer porous zone, which for premolars has been found to be 100-l 80 pm wide at the time of eruption (Crabb, 1976b). The effectiveness of this three-dimensional honeycombed structure for locking on sealants without acid-etching remains to be established. Ruyter and Gyorosi (1976), in an infrared spectroscopic study, used the C=C-stretching absorption band at l,639/cm to determine the quantity of remaining unreacted methacrylate groups in eight commercially available sealants after polymerization at 37 “C for 24 hours. Residual double bonds in polymeric materials are known to make them less resistant to degradation reactions. Nuva-Seal contained only 15 per cent of unreacted methacrylate groups (i.e. 85 per cent conversion), which could be reduced to 5 per cent by the use of short-wave ultraviolet radiation, probably as a result of the high yield of radicals obtained in this way. The high degree of conversion is attributed to the large number of small methyl methacrylate molecules, which are probably able to diffuse and react with active ends even after the viscosity has increased markedly. Epoxylite 9075 also showed approximately 85 per cent conversion. The other six sealants contained the bis-GMA monomer with diluting monomer triethyleneglycol dimethacrylate (Compact Enamel Bond, Concise Enamel Bond, Kerr Pit and Fissure Sealant), whilst Delton, Adaptic Bonding Agent and Adaptic Glaze also contained the difunctional monomer bisphenol-Adimethacrylate. Within this group of sealants the degree of conversion was lower and decreased with increasing bis-GMA content. In investigations into the retentive behaviour of sealants, Low and von Fraunhofer (1976) measured the transverse strengths and dimensional changes in water of Epoxylite 9075, ESPE 71730 and Nuva-Seal. Nuva-Seal had the highest transverse strength and Epoxylite 9075 the lowest. The transverse strength of both ultraviolet-light-cured materials continued to increase after the initial set, which would seem to imply that the 60 seconds’ irradiation time recommended by the manufacturers is too short to ensure complete polymerization. All three sealants expanded during the first 6 weeks in water, with Nuva-Seal and Epoxylite 9075 achieving stable dimensions after about 8 weeks, whilst ESPE 71730 began to shrink after about 6 weeks, possibly because of continuing polymerization. It was felt that the transverse strength gives an indication of how much deflection the sealant tags are likely to withstand before fracturing. The l-hour Nuva-Seal specimens were very flexible, and using five specimens (25 X 44 X 1 mm), none fractured at a deflection of 5.5 mm. Nuva-Seal exhibited the highest and Epoxylite 9075 the lowest flexural strength after 1 hour, 1 month and 3 months. Epoxylite 9075 showed its maximum strength after 1 hour, with the subsequent decrease ascribed to water absorption. The transverse strength of Nuva-Seal at 1 hour was 76 per cent of its maximum value, which was reached at 1 month, whilst the transverse strength of ESPE 71730 was only 40 per cent of its maximum value, which occurred after 3 months. It is suggested that the interaction of these materials with water, and with saliva in the clinical situation, may cast some doubt on their long term serviceability, but this does not appear to be so in practice. Overall, the authors concluded that the expansion following water absorption and the changes in strength of the fissure

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sealants appear to correlate reasonably well with their reported in vitro and clinical retentive behaviour. Particular importance is attached to the extent to which expansion due to water absorption compensates for polymerization shrinkage. No correlation could be found between any of the findings in this study and the rather limited published l-week tensile bond strengths, but it is pointed out that the wide range of values reported would suggest that variability of enamel and its response to acidetching may be a major factor in determining the success of sealants. The ability of cyanoacrylates to polymerize rapidly and to adhere firmly to moist tissues at room temperature is attractive. However, high polymerization shrinkage and poor resistance to the oral environment are major disadvantages which can be overcome to some extent by the addition of a suitable inorganic filler. Otsuki and Takeuchi (1976) reported bond strengths of 90-l 50 kg/cm’ for a thixotropic ethyL2cyanoacrylate containing lo-20 parts of colloidal silica to etched bovine enamel after immersion in water at 37 ‘C for 24 hours. Before application it was mixed with a small amount of dimethyl formamide as a mild initiator and then brushed on to the occlusal surface after treatment with 3M phosphoric acid for 30 seconds. Very rapid hardening was effected with alcohol containing 1 per cent (v/v) of dimethyl-p-toluidine. In water at 37 “C the tensile bond strength decreased by 50 per cent after 6 months, with failure usually occurring cohesively. It was thought that the increased viscosity resulting from addition of the initiator might prevent penetration into the enamel, but the presence of tags was confirmed microscopically. Breakspere and Wilton (1976) working with Nuva-Seal, concluded that brushing the sealant into the enamel surface was necessary to produce a good tag structure, the use of a cottonwool swab being much less effective. As might be expected, dampening the enamel surface with water also resulted in a much poorer tag development. Low et al. (1976) have looked at the tensile bond strength of Nuva-Seal to enamel surfaces treated with 8 per cent stannous fluoride. Specimens stored in distilled water at 37 “C showed no significant decrease in bond strength after 9 months, and the stannous fluoride did not produce any appreciable enamel staining. It is concluded, therefore, that the combined use of stannous fluoride and Nuva-Seal could form the basis of a clinical caries preventive procedure which might overcome the problem of uncontrollable loss of fissure sealant. In an examination of Delton Pit and Fissure Sealant, Retief and Austin (1976) reported high tensile bond strengths to human enamel, with cohesive failure generally occurring. The low viscosity sealant showed marked penetration into etched enamel surfaces immediately adjacent to grooves on buccal and lingual surfaces and into the full depth of narrow fissures on occlusal surfaces. Dye penetration techniques showed the absence of microleakage even after 8500 cyclical temperature changes over a range of 43 ‘C, which augurs well for the future clinical success of this material. Electrical conductivity measurements were used by Martinez and Greener (1976) for assessing marginal leakage in sealed teeth stored for 2 weeks in distilled water at 37’C, and they found a positive correlation with dye penetration results. Different threshold values of electrical conductivity existed for each sealant, and readings above these values indicated sealant failure or leakage. Tests were carried out with Nuva-Seal and Epoxylite 9075 to determine whether any leakage changes were likely to occur as a result of dally prophylaxis. After 7200 strokes on a toothbrushing machine, the specimens were immersed in 1 per cent methylene blue for 24 hours and then cut in half and assessed for dye penetration. None of

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the 8 Nuva-Seal controls exhibited dye penetration, the electrical conductivities ranging from 0.1-0.3 /.~a, whilst 6 of the Epoxylite 9075 controls (0.2-0.3 ~02) showed no dye penetration and 2 with conductivity readings of 0.5 @Z or greater did. After toothbrushing, 8 of 24 Nuva-Seal specimens with electrical conductivities of 0.3 PL? or greater showed dye penetration, whilst 12 out of 24 Epoxylite 9075 specimens with readings of O-4 CCQor greater showed dye penetration. The authors considered that the potential of the technique as an in uivo method of assessing leakage merits further investigation. A further thirteen papers giving the results of clinical trials with fissure sealants bear adequate testimony to the high continuing interest in the technique. Indeed, it might be pertinent to enquire why so many trials are apparently considered necessary to establish the effectiveness or otherwise of this procedure. A major point of interest is, however, the fact that two papers are now available covering 4-year trial periods. Thylstrup and Poulsen (1976) gave the results after 12 months for first permament molars sealed with Concise Enamel Bond system by a dental hygienist working without additional chairside assistance. Of the 451 sealed sites, sealant was present in 73 per cent, partly missing in 8 per cent and completely missing in 18 per cent. The caries reduction was about 70 per cent, and there was a strong correlation between the status of the sealant and occlusal decay. The distal fossae on maxillary first molars showed the greatest number of lost sealants (36 per cent), probably due to inadequate moisture control, whereas only 8 per cent of mandibular molars exhibited complete loss. In contrast with some other workers, no evidence was found of any extended protection after the sealant had been lost, but it was also evident that the etching process did not increase the caries susceptibility of the fissures. On the other hand, Stephen et al. (1976) obtained less satisfactory results in a trial in which TP2206 was applied by two dental practitioners after 1 day’s tuition. The study areas were Wigtownshire and Kirkcudbrightshire in Scotland, the former having most of its water fluoridated in two phases since 1967. At the 1Zmonth stage in the longest fluoridated area only 1 out of 193 sealed teeth (0.5 per cent) had completely retained the sealant and 18 per cent showed partial retention. In the other fluoridated area 6 per cent were completely sealed and 18 per cent partly sealed out of 190 originally sealed. In the non-fluoridated area where 190 teeth were also sealed, only 1 (0.5 per cent) had retained the sealant. The better retention in the fluoridated areas is somewhat surprising in view of the well-established effect of fluoride of reducing the solubility of enamel, which in turn would be expected to necessitate longer etching times. However, in spite of the heavy loss of sealant, reductions in caries incidence of 38-47 per cent were recorded for the three areas. This is attributed to retention of sealant tags, which seems a little unlikely, however, in view of the scale of sealant loss - general clinical experience suggests that if the tags are properly formed in the first place, then the sealant will usually still be detectable after several years. Contralateral sealing was not employed, but the authors concluded that sealing first permanent molars in children 6-7 years of age is a difficult procedure under field conditions, and the development of new materials is required in which satisfactory bonding to enamel is not so moisture-sensitive. This conclusion, however, is hardly in accord with other clinical experience. No fissure in which the sealant had been retained was found to be carious and no retention differences were found for upper and lower teeth. Attention is again drawn to the special difficulties experienced in sealing the distal aspect of upper molars. Unsatisfactory results for Nuva-Seal have also been reported by Higson (1976). Fifty children aged 6-8 years with four first permanent molars free from occlusal caries were

12

Journal of Dentistry,

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1

selected. One upper and one lower tooth were chosen at random for sealing and the contralateral teeth served as controls. The sealant status was assessed at 6-monthly intervals. Initially, retention for the lower teeth was far better than for the upper teeth, but after 2 years only 3 out of 90 sealed teeth (3 per cent) retained the sealant completely and 33 partly. Progressive loss of sealant during the trial was in contrast to the experience of other workers, indicating rapid loss after application if the technique had been faulty. There was no reduction in occlusal caries. The authors do admit that the poor retention figures may have been due to failure to keep the etchant agitated whilst it was on the occlusal surface. Going, Haugh et al. (1976), using 84 children aged lo-14 years, applied Nuva-Seal containing a red dye to 479 sound paired permanent teeth and 20 paired deciduous teeth, sealed teeth and contralateral controls being considered as study pairs. The sealant was fully retained on 69 per cent of all paired permanent teeth at 24 months. Difficulties were again encountered with the distal pit of the maxillary second molar, 83 per cent showing no retention of sealant. There was a relatively sharp decrease in retention during the first 6 months and, thereafter approximately 1 per cent of the teeth were losing part or all of their sealant per month. Retention of sealant on second premolars was superior to that on first premolars and also slightly better in the mandibular arch (74 per cent) compared with the maxillary arch (65 per cent). As expected, molars showed greater rates of decline in retention than premolars. It is suggested that lower retention figures in this study may be due to all eligible teeth being sealed regardless of occlusal anatomical features. It is concluded that the sealant should be inspected at 6-monthly intervals and defects or deficiencies remedied. If rubber dam isolation is not used, sealant may be partly missing at least 50 per cent of the time in areas such as the distal pit of the maxillary second molar in children in this age group. Going, Conti et al. (1976) found that after 24 months 38 per cent of all paired permanent control teeth were carious, whilst only 17 per cent of the treated teeth were affected (reduction of 5.5 per cent). It was estimated that 21 teeth in every 100 treated were saved from caries by sealant application, a net gain of 1 tooth in 70 per cent of the 84 children treated. When the sealant remained completely intact the effectiveness was 91 per cent. However, no appreciable gain or loss in caries protection was evident when the sealant was partially or completely missing. Caries protection was greater for premolars than molars and least for maxillary second molars. Although the relative reduction in caries rate was somewhat less for molars, so many more control molars were carious than premolars that the reduction obtained translated into a larger number of teeth being saved (361100 versus 13/100). Even when the sealant was partially lost, there was a 22 per cent relative reduction in caries rate compared with the control teeth. Ordinary clear Nuva-Seal and the same material containing a red dyestuff for better visibility were also used by Eden (1976) to seal teeth in 119 subjects aged 17-23 years. Retention of the tinted variety was much lower, presumably because the dyestuff inhibited penetration of ultraviolet radiation. It is claimed that a net gain of ody 7 OCChlSd surfaces after 16 months’ mean exposure for 712 pairs of teeth logically excludes sealant therapy as a cost-effective measure. The authors do, however, admit that this conclusion is suspect since the adult population in the study had passed the period of high caries susceptibility and the treatment was consequently of questionable value. Williams and Winter (1976) claimed to be the first to treat teeth on opposite sides of the mouth with two different sealants, thereby removing an element of bias which may have existed in previous studies. Nuva-Seal was used on one side and ASPA II, Epoxylite 9075 or

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Review of dental materials

13

EPSE 71729 on the other. A total of 726 teeth in 265 children in two age groups (6-8 years and 1 l-1 3 years) were sealed. Nuva-Seal was lost more gradually and its percentage retention (62 per cent) after 2 years was higher than that of the other materials, but this did not appear to influence the incidence of caries over a 2-year period. For Epoxylite 9075, ASPA II and ESPE 71729, the corresponding retentions were 44 per cent, 21 per cent and 20 per cent respectively. It is pointed out, however, that an improved version of ASPA II has recently been introduced commercially and the recommended application procedure has been modified. In the case of ESPE 71729 the lower viscosity and reduction in the polymerization time did not apparently enhance its retention or improve its cariostatic properties. A diluted composite (Concise Enamel Bond System) has been evaluated by Ulvestad (1976a). The fissure sealant was made by (1) diluting Universal Paste with an equal volume of Universal Resin and (2) diluting the same amount of Catalyst Paste with an equal volume of Catalyst Resin, and these two components were mixed immediately before application. This method of preparation resulted in a large number of ceramic filler particles being included in the sealant. The enamel was etched for 1 minute with 37 per cent phosphoric acid before application of the sealant. On the basis of a clinical evaluation involving 69 children for 24 months, it was concluded that the diluted composite was an acceptable alternative to other fissure sealing materials. The children were divided into two age groups, 6-9 years and 9-12 years, and permanent premolars and first molars were sealed. Fissures extending to the lingual surfaces in permanent maxillary first molars and to the buccal surfaces including a foramen caecum in permanent mandibular molars were also sealed. Retentions were in excess of 90 per cent and caries developed in only one distolingual fissure where the sealant had been lost more than 1 year previously. Clinically, the diluted composite had the advantage that slight discoloration after some time made detection easier. Generally, it appeared to be rather more resistant to attrition, presumably because of the high content of inorganic filler particles. A possible disadvantage suggested is that excess material often floats on to the occlusal surface so that the bite may be raised temporarily. This can be particularly so if the first permanent molar interrelationship tends to be a mesial or distal position, when it is felt that superfluous sealant should be removed with rotary instruments. Generally with sealants, the initial rate of wear is so great that this is not a serious problem in practice. Excellent retention figures were also obtained for the diluted composite after 3 years (Ulvestad, 1976b), which are quite comparable with those for NuvaSeal. Sealant wear was noticeable in both groups but particularly with Nuva-Seal, where recognition of the sealant was often difficult. In the Nuva-Seal group 32 molars were filled with amalgam, the presence of this large number being attributed to the difficulties in sealant recognition. Because of this, some 14 per cent of all occlusal surfaces sealed with Nuva-Seal were adjudged carious, whereas for the diluted composite where no amalgams had been inserted, the corresponding figure was only 2.5 per cent. The claim that the diluted composite is fully acceptable as an alternative to an ultraviolet-light-polymerized sealant thus seems to be fully justified. Ohmori (1976) has reported laboratory and clinical tests on a new fissure sealant Enamite, the major ingredients in which are a solution of 3 per cent 2-hydroxy-3-beta-naphthoxypropyl methacrylate in methyl methacrylate and polymethyl methacrylate powder using tributylborane as initiator. Enamite not only showed greater adhesion to enamel than Nuva-Seal but the bond strength was also affected to a much smaller extent by immersion in

14

Journal of Dentistry, Vol. ~/NO. 1

water for 1 month at 37°C or by thermal cycling. The sealant was applied to 161 first molars in 99 children aged 6-8 years, 98 of the teeth being intact and the remainder having incipient caries. Topping-up of sealant was resorted to when considered necessary, and after 2 years occlusal caries had been reduced by 57 per cent compared with the control teeth. When allowance was made for the caries retardation effect by including teeth initially carious but remaining sealed after 2 years, and classifying teeth with a resistance of more than 600 kG?at the final examination as ‘reversals’, then the caries reduction was actually 96 per cent. Results for Nuva-Seal after 3 years were also reported by Meurman and Helminen (1976). There were 60 boys and 58 girls involved in the trial and their mean age at the 3-year recall examination was 10 years. All were simultaneously receiving some form of fluoride treatment. Of 166 molars and 41 premolars sealed originally, 80 per cent were in good condition and 12 per cent in fair condition, while in 7 per cent the sealant was missing or partly missing. Some 8 per cent of the sealed molars were diagnosed carious whilst 71 per cent of the controls had decayed. For the premolars the corresponding figures were 5 and 7 per cent respectively. No carious fissures were found in sealed first permanent molars which had retained the sealant in good condition, but 92 per cent of those which had lost the sealant were filled and so presumably had decayed. There was thus no evidence of extended cariostasis after loss of sealant. The net gain in the study was 104 teeth and the effectiveness of the method 88 per cent. It is pointed out that there had been a gradual reduction in sealant during the trial, and so the authors saw no reason for changing their view that sealants should be checked at frequent intervals and any losses rectified by reapplication. Sealing only one or two molar teeth per subject had a demonstrable preventive effect on the fissure caries status of 60 per cent of the subjects. It is tentatively suggested that the spread of cariogenic micro-organisms within the oral cavity may be reduced because of the smaller number of cavities, thereby producing an improved caries status. Horowitz et al. (1976), using Nuva-Seal, claimed the first 4-year study report. After 4 years 50 per cent of ah initially sealed sites (927) retained the sealant fully, 16 per cent had sealant partly missing and in 34 per cent no sealant could be detected visually. The 465 sites where the occlusal sealant was fully retained did not decay, with one exception, whilst 87 per cent of the control sites did decay. Only 6 per cent of the 149 sites from which sealant was partly missing had become D, M or F, whilst 60 per cent of the paired control sites had become carious. This would seem to afford strong evidence that loss of sealant does not render the tooth more susceptible to carious attack than if it had not been sealed, but rather the opposite. Some 57 per cent of the sites from which the sealant had been completely lost became D, M or F, whilst 60 per cent of the paired unsealed sites were similarly affected. There is, therefore, nothing to suggest that etching or interference with normal maturation of the enamel by sealant placement has resulted in any increase in caries susceptibility. These findings after 4 years are certainly highly positive and very encouraging. Considering that virtually all the sites from which sealant was only partly lost were free from decay, it is suggested that any status other than totally missing could be considered ‘successful’retention. This would make the retention after 4 years 66 per cent of the treated sites. It is emphasized that this figure is a conservative one since an indeterminable number

Braden: Review of dental materials

15

of failures resulted solely from occlusal intervention in the restorative treatment of approximal decay, so that many of the restored occlusal surfaces may not themselves have been carious. I_eake and Martinello (1976), also using Nuva-Seal which was applied by two separate teams led by a dentist and a dental hygienist, were apparently less successful. The clinicians attended a 2-day orientation and technique course given by one of the developers of the material. They experienced some difficulty in adapting to the portable field equipment used in the study. The trial involved 518 children aged 5-7 years who were selected on the basis of having four caries-free first permanent molars. After 48 months the sealant was partially or totally lost from 80 per cent of the treated teeth and the occlusal caries reduction was 22 per cent. Where the sealant remained intact, the corresponding figure was 98 per cent. The application cost was naturally higher for the dentist but he achieved better retention (29 per cent compared with 9 per cent by the hygienist). The hygienist and dentist were equally effective in diagnosing and evaluating the teeth and in assessing the subsequent sealant status. There was a net gain in 142 of the 840 treated control pairs. Once again, teeth that had lost the sealant were no more susceptible to decay than untreated controls. It is concluded that this single preventive approach is not worth while on the basis of cost-benefit considerations, a conclusion which is difficult to reconcile with the results of other workers. Concern is frequently expressed regarding the dangers of sealing in early caries. Handelman et al. (1976) took samples of carious dentine from unsealed teeth and teeth that had been sealed for 2 years. The major decrease in viable organisms occurred during the first 2 weeks and then there was a gradual reduction in the total count. At the end of 2 years there had been a decrease of two thousand times in the number of cultivable micro-organisms, and the number surviving appeared to be too small to continue destruction of the tooth structure. It would be logical to assume that this was the result of an inadequate supply of nutrients to the entrapped bacteria. From a survey of the existing experimental data Handelman (1976) considered that this major clinical concern is unwarranted. As long as the sealant is intact and bonding effectively so that little or no leakage occurs, then entrapped bacteria will have great difficulty in surviving. Stiles et al. (1976) have carried out a clinical trial with Nuva-Seal to determine the durability of the sealant when applied by a dentist or a trained dental auxiliary. The study involved 166 children aged 5-21 years with 76 per cent aged between 7 and 15 years. Although at the end of 12 months the retention figures were slightly lower than those reported by other workers (51 per cent for complete retention), unlike I_eake and Martinello (1976), no difference could be detected in the durability of sealant applied by a dentist or a trained dental auxiliary, with the exception of one dental assistant with less training. Leske et al. (1976) on the basis of a more extended trial, reached a similar conclusion. Four teams consisting of a dental hygienist and a dental assistant, after a 2day training session, applied Nuva-Seal to caries-free first permanent molars in 1966 children from the fluoridated city of Rochester. The highest retention rates were recorded for mandibular molars, 85 per cent of which showed complete retention at 1 year and 41 per cent after 3 years. However, only 2.5 per cent of the buccal pits remained completely covered at the end of 3 years, and so it was concluded that long term caries protection cannot be expected from sealing this site. Difficulties in sealing effectively the distolingual groove are again clearly recognized. Although there were marked differences between the various teams, these could be related

16

Journal of Dentistry,

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1

to differences in previous experience, and the conclusion is that trained dental auxiliaries are capable of applying pit and fissure sealants satisfactorily. The effect of a sealant on fluoride retention after topical fluoride application has been examined by Friedman et al. (1976). The enamel was etched with O.OSiVphosphoric acid for 30 seconds and then treated with acidulated phosphate-fluoride solution for 2 minutes. After drying, the labial and lingual surfaces of the upper left and lower right anterior teeth were painted with 2(2,2,2,-trifluoroethoxy)-ethyl 2cyanoacrylate varnish. The corresponding teeth in the upper right and lower left quadrants were not coated and served as controls. The etching treatment only altered the enamel surface minimally and the characteristic prismend structure produced by stronger acids was absent. The study showed that the uptake of fluoride was greatly enhanced by the etching but that the subsequent use of temporary sealants had no additional beneficial effect on fluoride retention. This is at variance with the earlier results of Dogon et al. (1973). Swartz et al. (1976) have undertaken a laboratory study with three bis-GMA type resins (Nuva-Seal, Epoxylite 9075 and an experimental formulation of an isobutyl cyanoacrylate resin) aimed at exploring the possibility of imparting an anticariogenic property to fissure sealants by addition of sodium fluoride. During a 4-day period the bis-GMA resins released fluoride rapidly during the first 24 hours and then more slowly. The cyanoacrylate released more fluoride in the same period, and the release pattern approximated more closely to the straight line relationship given by silicates. Sealants containing sodium fluoride did increase the fluoride content of the enamel with which they were in apposition, and the solubility of the enamel was correspondingly reduced. For Nuva-Seal containing 35 per cent sodium fluoride the average decrease was 10 per cent, and increasing the sodium fluoride content to above 15 per cent produced no further reduction. Tensile bond strength, hardness, abrasion resistance, water sorption, bond strength and microleakage were not adversely affected by the addition of up to 10 per cent sodium fluoride. It is, however, recognized that difficulty was experienced in achieving and maintaining a uniform dispersion of the fluoride salt in the sealant, although this was less of a problem with the somewhat viscous Nuva-Seal. It is considered that further work is required to confirm the anticariogenic effect and to establish the best way of incorporating the fluoride. Long term clinical trials are clearly expensive in terms of both resources and time. O’Mullane (1976) drew a clear distinction between ‘an experimental clinical trial, carried out under ideal conditions, and a community clinical trial carried out under real life conditions’, although one wonders whether perhaps the time is ripe for trying to reduce the gap between these two situations. O’Mullane has examined two possibilities: first, a reduction in length either by planning the trial to run for a shorter period in the first place or by stopping the trial when the criteria for success have been satisfied, and secondly, reducing the number of subjects by excluding those whose contribution to the aims of the trial is likely to be low. These possibilities are illustrated by reference to the results of a 3-year topical fluoride trial. There would appear to be more basis in statistical theory for running a trial for say 18 months in the first place rather than analysing the data each year and then stopping the trial when the stated objectives have been achieved. Several review articles also appeared during 1976. Ripa (1976) summarized the evidence against the three main fears of dentists: that the technique is unsubstantiated by research, that it is possible to seal in decay and that sealants do not last very long in the mouth. The bulk of reported evidence contradicts these negative views and it would seem that increased

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Review of dental materials

17

use of sealants is really a function of improved education and communication regarding their function and value. Boudreau and Jerge (1976), reviewing the efficacy of fissure sealants as a preventive measure since their introduction in 1965, concluded that the reaction product of bis-GMA, which is the most effective material reported on so far, reduces pit and fissure caries by 65-99 per cent. At the time of this conclusion the longest clinical study reported was of 2 years’ duration. Silverstone (1976a) likewise concluded from the many trials carried out in various parts of the world that fissure sealants can have a highly significant effect in the prevention of occlusal caries and agrees that ultraviolet-light-activated materials have produced the most satisfactory and reproducible results. However, he did stress that more attention must be paid to the application technique if full effectiveness of the materials

is to be achieved. The wide divergence in the results of different clinical trials certainly justifies this view. After reviewing the results of clinical trials with his-GMA type fissure sealants Silverstone (1976b) examined the problems which arise in connection with the use of amalgam as a restorative material. The relationship between the preventive and restorative approaches in the control of caries was discussed. The Council on Dental Materials and Devices (1976) recognized that fissure sealants ‘properly applied, form an acceptable part of proven effective preventive measures’, but cautioned against the deliberate sealing of carious lesions. It is also perhaps a measure of the progress being made that the Expenditure Committee of the House of Commons in their recent report, Preventive Medicine, Vol. 1, Session 1976-77, suggested, amongst other recommendations, that more dental hygienists should be trained and employed, and that fissure sealants and topical fluoride application should be available on the National Health Service. Acceptance of these proposals by the government would represent a major step forward in the field of preventive dentistry. The present position is perhaps accurately summed up by Buonocore (1976) who stated that it would appear that ‘adhesive dentistry’ will assume an increasingly important role in modern dental technology for the benefit of all concerned.

REFERENCES Den tat amalgam

Brown D. (1976) The clinical status of dental amalgam. Br. Dent. J. 141, 80-84. Eley B. M., Garrett J. R. and Harrison J. D. (1976) Analytical ultrastructural studies on implanted dental amalgam in guinea-pigs. Histochem. J. 81,647-650. Goldschmidt P. R., Cogen R. B. and Taubman S. B. (1976) Effect of amalgam corrosion products on human cells. J. Periodon 1. Res. 11, 108-l 15. Jensen S. J. and Vriihoef M. M. A. (1976) Phases in pre-amalgamated silver amalgam alloy. Stand. J. Dent. Res. 84, 183-186. Jdrgensen J. D. (1976) Recent developments in alloys for dental amalgams: their properties and proper use. Int. Dent. J. 26,369-377. Kidd E. A. (1976) Microleakage in relation to amalgam and composite restorations-a laboratory study. Br. Dent. J. 141, 305-310. Lavelle C. L. (1976) A cross-sectional longitudinal survey into the durability of amalgam restorations. J. Dent. 4, 139-143. Marshall G. W., Finkelstein G. F., Marshall S. J. et al. (1976) Microstructural changes of dental amalgams by copper amalgams. J. Oral Rehabil. 3,359-370.

18

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1

Martin L. R., Tidwell E., Tenca J. I. et al. (1976) Histologic response of rat connective tissue to zinc-containing amalgam. J. Endodont. 2,25-27. Nunez L. J., Schmalz G. and Hembree J. (1976) Influence of amalgam, alloy and mercury on the in vitro growth of Streptococcus mutans: I. Biological test system. 1. Dent. Res. 55,257-261. @lo G. (1976) Adaptation

of amalgams to cavity walls. J. Oral Rehabil. 3,227-236. Osborne J. W., Phillips R. W., Gale E. N. et al. (1976) Three year clinical comparison of three amalgam alloy types emphasizing an appraisal of the evaluation methods used. J. Am. Dent. Assoc. 93, 784-789.

Spanauf A. tractions Wang Chen strength

J., Vermeersch A. G. and Vriihoef M. M. A. (1976) La Resistance aux forces de de l’amalgame acquise apres 25 minutes. Rev. Belge M&d. Dent. 31, 225-232. C. P. and Greener E. H. (1976) The effect of anodic polarization on the tensile of dental amalgam. J. Oral Rehabil. 3, 323-332.

Gasting alto ys

Arfaei A. H. and Asgar K. (1976) The influence of roughness to fit of dental castings. J. Dent. Res. Special issue B, abstr. 151. Fame J. F. and Nealey E. T. (1976) The effect of etching on the margins of cast gold restorations. J. Prosthet. Dent. 35, 273-278. Huget E. P., Dvivedi N. and Cosner H. E. (1976) The characterisation of AuPdAg and PdAg for ceramic-metal restorations. J. Prosthet. Dent. 36, 58-65. Ingersoll C. E. (1976) The characterisation of gold tarnish. J. Dent. Res. Special issue B, abstr. 144. Lewis A. J. (1976) Mould reactions with gypsum bonded investments. Aust. Dent. J. 21, 172- 176. Loftstrom L. H., Myers G. E. and Asgar K. (1976) The castability and burnishability of alternative alloys to type III dental gold. J. Dent. Res. Special issue B, abstr. 137. Lorey R. E., Morris II, F., Oberleas D. et al. (1976) A clinical evaluation of base metals used in porcelain metal systems. J. Dent. Res. Special issue B, abstr. 686. Metzler J. C. and Chandler H. H. (1976) An evaluation of techniques for finishing margins of gold inlays. J. Prosthet. Dent. 36, 523-53 1. Miller H. L., Rostoker W. and Galante J. 0. (1976) A statistical treatment of fatigue of the cast Co-Cr-Mo prosthesis alloy. J. Biomed. Mater. Res. 10, 399-412. Moon P. C. and Modjeski P. J. (1976) The burnishability of dental casting alloys. J. Prosthet. Dent. 36,404-407.

Parvinen T., Yu-Urpo A. and Aitasalo K. (1976) Corrosion

of a dental alloy in the mouth.

Proc. Finn. Dent. Sot. 72,210-212.

Schulman

A., Mukherjee

K., Milillo F. et al. (1976) Gold-nickel

alloys in dental prosthesis.

J. Dent. Res. 55,285-288.

Stevens L. (1976) The heat treatment of cast restorations. Aust. Dent. J. 21, 170- 17 1. Strandman E. (1976a) The influence of different oxy-acetylene flames on the carbon content of a dental cobalt-chromium alloy. Odontol. Revy. 27,223-238. Strandman E. (1976b) The influence of the carbon content on the mechanical properties of cast dental cobalt-chromium alloy. Odontol. Revy. 27,273-286. Strandman E. (1976c) The influence of different heat treatments on a dental cobaltchromium alloy. Odontol. Revy. 27,287-302. Strandman E. and Glantz P. 0. (1976) On the characterisation of oxyacetylene flames used in dental casting. Odontol. Revy, 27, 197-222. Wnthner J. M., Meyer J. M. and Nally J. N. (1976) The tarnish resistance of some dental casting alloys. J. Dent. Res. Special issue D, p. D159, abstr. 36.

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Alloys for orthodontic use

Andreasen G., Bigelow H. and Andrews J. (1976) Nitinol wire: the force developed as a function of elastic memory. J. Dent. Res. Special issue B, abstr. 359. Castleman L. S., Motzkin S. M., Alicandri F. P. et al. (1976) Biocompatibility of nitinol alloy as an implant material. J. Biomed. Muter Res. 10, 695-731. Fillmore G. M., and Tomlinson J. L. (1976) The heat treatment of cobalt-chromium alloy wire. Angle Orthod. 46, 187- 195. Schmerling M. A., Wilkov M. A., Sanders A. E. et al. (1976) Using the shape recovery of nitinol in the Harrington rod treatment of scoliosis. J. Biomed. Muter. Rex 10, 879-892. Waters N. E., Houston W. B. and Stevens C. D. (1976) The heat treatment of wires: a preliminary report. Br. J. Orthod. 3,217-222. Williams D. W. (1976) The magnetic susceptibility of some high resilience orthodontic wires. Br. J. Orthod. 3, 147-153.

Composite filling materials

Antonucci J. M. and Bowen R. L. (1976) Dimethacrylates derived from hydroxybenzoic acids. J. Dent. Res. 55, 8-15. Bowen R. L. and Reed L. E. (1976a) Semi-porous reinforcing fillers for composite resins: I. Preparation of provisional glass formulations. J. Dent. Res. 55, 738-747. Bowen R. L. and Reed L. E. (1976b) Semi-porous reinforcing fillers for composite resins: II. Heat-treatment and etching characteristics. J. Dent. Res. 55, 748-756. Braden M., Causton B. E. and Clarke R. L. (1976) Diffusion of water into composite filling materials. J. Dent. Res. 55, 730-733. Causton B. E., Samar-Wickrama D. Y. D. and Johnson N. W. (1976) Effect of calcifying fluid on bonding of cements and composites to dentine in vitro. Br. Dent. J. 140, 339-343. Council on Dental Materials and Devices (1976) Composite restorative materials: clinical suggestions for their use. J. Am. Dent. Assoc. 92,606-607. Eames W. B., O’Neal S. J. and Rogers L. B. (1976) Composite plain talk. J. Am. Dent. Assoc. 92, 550-554.

Eriksen H. M. and Buonocore M. G. (1976a) Marginal restorative materials; effect of restorative techniques. J. Eriksen H. M. and Buonocore M. G. (1976b) Marginal restorative materials in vitro. Effect of cavity design. J. Faunce F. R. and Myers D. R. (1976) Laminate veneer

leakage with different

composite 148. composite

Am. Dent. Assoc. 93, 1143-l

leakage with different

Oral Rehobil. 3,3 15-323.

restoration

of permanent

incisors.

J. Am. Dent. Assoc. 93, 790-792.

Galon J., Mondelli J. and Coradozzi J. L. (1976) restorative systems. J. Dent. Res. 55, 74-77. Gjerdet N. R. (1976) Elastic properties of resin-based

Marginal leakage filling materials.

of two composite Scund. J. Dent. Res.

84,426-429.

Grajower R., Revah A. and Sorin S. (1976) Reflectance spectra of natural and acrylic resin teeth.J, Prosthet. Dent. 36, 570-579. Hannah C. McD and Combe E. C. (1976) Mechanical properties of composite restorative materials. Br. Dent. J. 140, 167-l 70. Harrison A. and Draughn R. A. (1976) Abrasive wear, tensile strength and hardness of dental composite resins - is there a relationship? J. Prosthet. Dent. 36, 395-398. Heath J. R. and Wilson H. J. (1976) Abrasion of restorative materials by toothbrush. J. Oral Rehubil. 3, 121-138.

Hembree J. H. and Andrews J. T. (1976) In situ evaluation of marginal leakage using an ultra-violet activated resin system. J. Am. Dent. Assoc. 92, 414-418.

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Journal of Dentistry, Vol. ~/NO. 1

Kidd E. A. M. (1976)

Microleakage

in relation

to amalgam

and composite

restorations.

Br. Dent. J. 141,305-310.

Kuhlzer and Ivoclar Patents (1975) Deutsches Offenlegungschrift 2,403,211 and 2,405,518. Low T. and von Fraunhofer J. A. (1976) The direct use of composite materials in adhesive dentistry. Br. Dent. J. 141,207-213. Pahlaran A., Dennison J. B. and Caubeneau G. T. (1976) Penetration of restorative resins into acid etched human enamel. J. Am. Dent. Assoc. 93, 1170-l 176. Short G. M., Hembree J. H. and Knight J. P. (1976) The bond strengths of resin systems to etched enamel. J Prosthet. Dent. 36, 538-543. Sockwell C. L. (1976) Clinical evaluation of anterior restorative materials. Dent. Clin. North Am. 20,403-422.

Verrall R. J. A. (1976) A sphere compression test for measuring of dental composite materials. J. Dent. 4, 11-14.

the mechanical

properties

Denture base and other polymers

Braden M., Pearson G. J. and Campbell Keys, W. (1976) A new temporary crown and bridge resin. Br. Dent. J. 141,269-272. HargTeaves A. S. and Foster M. A. (1976) Hydrocryl: an aid to retention. J. Dent. 4, 33-41. McCabe J. F. and Basker R. M. (1976) Tissue sensitivity to acrylic resin. Br. Dent. J. 140. 347-350. Soft lining materials

McCabe J. F. (1976)

Soft lining materials:

composition

and structure.

J. Oral Rehabil.

3,

273-278.

Suchatlampong C., Davies E. H. and von Fraunhofer J. A. (1976) Some physical properties of four resilient lining materials. J. Dent. 4, 19-27. Wright P. S. (1976) Soft lining materials: their status and prospects. J. Dent. 4, 247-256. Fissure sealants

Boudreau G. E. and Jerge C. R. (1976) The efficacy of sealant treatment in the prevention of pit and fissure dental caries: a review and interpretation of the literature, J. Am. Dent. Assoc. 92, 383-387.

Breakspere

R. J. and Wilton A. (1976)

Poor fissure sealant adhesion.

Some causes? Dent.

Practice 14, 10.

Buonocore M. G. (1976) Foreward. J. Prev. Dent. 3,4-5. Council on Dental Materials and Devices (1976) Pit and fissure sealants. J. Am. Dent. Assoc. 93, 134.

Crabb H. S. M. (1976a) Fissures at risk. Br. Dent. J. 140, 303-307. Crabb H. S. M. (1976b) The porous outer enamel of unerupted human premolars. Caries Res. 10, l-7. Dogon I. L., van Leeuwen M. and Kirklin M. (1973) In viva studies on the ‘sealing’ of fluoride in teeth: two-year clinical results. Int. Assoc. Dent. Res. 51st General Meeting, Progm. abstr. No. 240. Eden G. T. (1976) Clinical evaluation of a pit and fissure sealant for young adults. J. Prosthet. Dent. 36, 51-57.

Friedman M., van der Merwe E. H. M., Bischoff J. I. et al. (1976) Effect of a sealant, used in conjunction with topical fluoride application, on fluoride concentrations in human tooth enamel. Arch. Oral Bio2. 21,237. Going R. E., Conti A. J., Haugh L. D. et al. (1976) Two-year clinical evaluation of a pit and fissure sealant. Part II: Caries initiation and progression. J. Am. Dent. Assoc. 92, 578-585.

Braden:

21

Review of dental materials

Going R. E., Haugh L. D., Grainger D. A. et al. (1976). Two-year CliniCal eVahatiOn of a Pit and fissure sealant. Part I: Retention and loss of substance. J. Am. Dent. Assoc. 9% 388-397, Gwinnett A. J. (1976) The scientific basis of the sealant procedure. J. Prevenf. Dent. 3, 15-28. Handelman S. L. (1976) Microbiologic aspects of sealing carious lesions. J. Pm. Dent. 3, 29-32. Handleman S. L., Washburn F. and Wopperer P. (1976) Two-year report of sealant effect on bacteria in dental caries. J. Am. Dent. Assoc. 93, 967-970. Higson J. F. (1976) Caries prevention in first permanent molars by fissure sealing. A 2-year study in 6-8-year-old children. J. Dent. 4, 218-222. Horowitz H. A., Heifetz S. B. and Poulsen S. (1976) Adhesive sealant clinical trial: an overview of results after four years in Kalispell, Montana. J. Rev. Dent. 3,38-49. Leake J. L. and Martinello B. P. (1976) A four year evaluation of a fissure sealant in a public health setting. J. Can. Dent. Assoc. 42, 409-415. Leske G. S., Pollard S. and Cons N. (1976) The effectiveness of dental hygienist teams in applying a pit and fissure sealant. J. Prev. Dent. 3, 33-36. Low T. and von Fraunhofer J. A. (1976) An in vitro assessment of the retentive behaviour of fissure sealants. J. Dent. 4, 131-138. Low T., von Fraunhofer J. A. and Winter G. B. (1976b) Short Communication. The long term bonding of a polymeric fissure sealant to stannous fluoride treated enamel. J. Oral Rehabil. 3, 311-313.

Martinez C. R. and Greener E. H. (1976) Utilization of electrical conductivity as an alternative method of assessing marginal leakage of pit and fissure sealants. J. Oral Rehabil. 3, 67--74.

Meurman J. H. and Helminen S. K. J. (1976) Effectiveness of fissure sealant three years after application. Stand. J. Dent. Res. 84,218-223. Ohmori I., Kikuchi K., Masuhara E. et al. (1976) Effect of the methyl methacrylate. tributylborane sealant in preventing occlusal caries. Bull. Tokyo Med. Dent. Univ. 23, 149-15s. O’Mullane D. M. (1976) Efficiency in clinical trials of caries preventive agents and methods. Comm. Dent. Oral Epidemiol. 4, 190-194. Otsuki A. and Takeuchi M. (1976) A simple fissure sealant and its tensile bond strength to etched bovine enamel. Caries Res. 10, 463-472. Retief D. H. and Austin J. C. (1976) A laboratory evaluation of a new pit and fissure sealant. J. Dent. Assoc. S. Afr. 31, 639-647. Ripa L. W. (1976) The current status of occlusal sealants. J. Prev. Dent. 3,6- 14. Ruyter I. E. and Gydiosi P.-P. (1976) An infrared spectroscopic study of sealants. Stand. J. Dent. Res. 84, 396-400.

Silverstone L. M. (1976a) Fissure sealants. Part 1. Dent. Update 3, 163-l 70. Silverstone L. M. (1976b) Should I be using pit and fissure sealants or amalgam? Znt. Dent. J. 26, 29-40.

Silverstone L. M. and Dogon I. L. (1976) The effect of phosphoric acid on human deciduous enamel surfaces in vitro. J. Znt. Assoc. Dent. Child. 7, 1 l-15. Stephen K. W., Sutherland D. A. and Trainer J. (1976) Fissure sealing by practitioners. First year retention data in Scottish 6-year-old children. Br. Dent. J. 140,45-51. Stiles H. M., Ward G. T., Woolridge E. D. et al. (1976) Adhesive sealant clinical trial: comparative results of application by a dentist or dental auxiliaries. J. Prev. Dent. 3, 8-11.

Swartz M. L., Phillips R. W., Norman R. D. et al. (1976) Addition fissure sealants-a feasibility study. J. Dent. Res. 55, 757-77 1.

of fluoride

to pit and

22

Journal of Dentistry, Vol. ~/NO. 1

Thylstrup A. and Poulsen S. (1976) Retention and effectiveness of a chemically polymerized pit and fissure sealant after 12 months. Comm. Dent. Oral Epidemiol. 4,200-204. Ulvestad H. (1976a) A 24-month evaluation of fissure sealing with a diluted composite material. Stand. J. Dent. Res. 84, 51-55. Ulvestad H. (1976b) Evaluation of fissure sealing with a diluted composite sealant and an W-light polymerized sealant after 36 months’ observation. Stand. J. Dent. Res. 84, 401-403. Williams B., von Fraunhofer 5. A. and Winter G. B. (1976) Etching of enamel prior to application of fissure sealants. J. Oral Rehabil. 3, 185-l 88. Williams B. and Winter G. B. (1976) Fissure sealants. A 2-year clinical trial. Br. Dent. J. 141.15-18,