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Uptake of elements contained within the glass of a novel polyalkenoate cement by adjacent tooth tissues
Ciinkai Materiais
1988: 3: 273-283
inal papers
e of elements contained within the glass polyalkenoate cement by adjacent toot argaret A Wilson and EC Combe Department of Restorative Dentistry, University Dental Hospital of Manchester
This paper presents a review of the effects of the elements strontium, alumrnium and boron on dental hard trssues. The effect of these elements contained in a novel strontrum aluminoborate polyalkenoate dental cement is described and their uptake by enamel and dentine was determined using electron probe microanalysis. It was found that strontium and aluminium were leached from the glass particles and penetrated into enamel and dentine to a depth of several microns.
Polyalkenoate cements have developed from the original work of Wilson and Kent’ and are now routinely used as adhesive cements in restorative dentistry. The glass powders of most commercially available aluminosilicate glass ionomer cements are two-phase systems, containing sheathed droplets of fluorides which are released by the action of the acidic liquid during the cement formation. Address for correspondence: Dr MA Wilson, Department of Restorative Dentistry, University Dental Hospital of Manchester, Higher Cambridge Street, Manchester Ml5 6FH, UK.
It has become apparent from studying the effect of fluoride release from glass ionomer cements, that beneficial effects can be achieved from the persistent release of biologically active trace elements. Although fluoride release has obvious beneficial effects on dental caries incidence, it is possible that the poor aesthetic appearance of some of these cements, for example, in terms of translucency, could be due to the presence of a two-phase glass. Thus it is of value to explore the possibility of obtaining an anticariogenic effect by the use of alternative elements. Simple single-phase threecomponent glasses may be an answer to the problem of combining aesthetics with anticariogenicity.
274
MA Wilson and EC Combe
The purpose of this study was to investigate a novel strontium aluminoborate polyalkenoate cement system,24 with a single-phase glass containing elements which are biologically active and believed to be available to tooth tissues. The presence of strontium could also confer radiopacity on the cement. Unlike other mineralized tissues, enamel and dentine once formed, do not metabolize or have a turnover rate. Changes do occur however, at the surface and subsurface layers due to posteruptive uptake of trace elements. Elements which are incorporated into the enamel while it is developing are restricted to those with an atomic number below 60. The presence of restorations which contain trace elements which could be available to the enamel and dentine is of particular interest, especially if that trace element has a cariostatic effect.5 It has been reported that certain trace elements are capable of producing an effect on dental caries similar to fluorides.6 The elements contained in the novel glass formulations were: aluminium, boron and strontium.
Biological activity of elements contained in strontium aluminoborate cement Effect of aluminium on dental caries Aluminium has been reported to be associated with a low caries experience.’ Aluminium is a polyvalent metal ion; in experiments using hydroxyapatite, it was found that three calcium atoms were replaced by two aluminium atoms with no loss of phosphate. In a review of epidemiological surveys of the effect of trace elements on caries,8 it was suggested that a relationship might exist between aluminium and strontium and caries prevalence in man and animals. More recent research has shown that aluminium ions reduce the dissolution of enamel.9 Effect of boron on dental caries Boron in the form of boric acid is now widely used as an additive in the food industry. It is not considered toxic when taken orally, as most of it is excreted in the urine.“’ Very few studies have been carried out to determine the effect of boron on caries prevalence. It is known that in areas where the drinking water contains high levels of
boron, the tooth enamel also contains high levels of boron.11,12 Although no mechanism for its effect has been suggested, a number of investigators have reported that the trace elements boron and strontium, when they occur together, may contribute to lowering caries prevalence. r3-16 showed a significant An in vitro investigation reduction in synthetic hydroxyapatite and enamel dissolution from acidogenic streptococci in a medium made with highly mineralized water from a low caries area. This water contained significantly higher amounts of boron and strontium.17 Although the individual effects of boron and strontium could not be identified, it was possible that the anticariogenic effect could have been produced by direct action on the plaque flora. Effect of strontium on dental hard tissues Strontium is a trace element which is deposited in calcified tissues, mainly in the apatite crystals. It is found in greater quantities than most other trace elements. lx When strontium is included into the mineral phase of bone and dentine, more stable compounds are formed than the analogous calcium compounds. I9 The presence of strontium in dental tissues was first demonstrated by Dreazo in 1936. The skeletal metabolic pathway of strontium in animals and man closely parallels that of calcium.21 A comprehensive review of studies carried out which demonstrate the distribution of strontium in dental tissues can be found in a paper by Nixon and Helsby.22 In animal experiments it has been found that in high local concentrations, strontium, like calcium, stimulates alveolar bone formation. The boney response to strontium is faster than that with calcium, but of shorter duration.23 To date there is no published work investigating the effect of strontium on dentinogenesis. Effect of strontium on dental caries The majority of investigations have shown that strontium is associated with a lower caries prevalence in man24 and in animals.2s In experiments on rats, when strontium was added to their drinking water, there was a reduction in smooth surface carious lesions.2h In addition if enamel was exposed to solutions containing strontium and fluoride, there was a lowering of the rate of dissolution in acidic media. A synergistic effect seemed to exist when these two trace elements occurred together.” The only survey which did
I/ptake of elements contained within the glass of a novel polyalkenoate not find an association between strontium and caries was that reported by Anderson.28 Subsequent investigations into this work revealed that the patients he examined were drinking water from a source far away from the high strontium area where they lived. The mechanism for the anticariogenic action of strontium has been shown to be the inhibition of the dissolution rate of hydroxyapatite in an acidic medium. This may be the result of the formation apatite complex: of a calcium-strontium Ca,Sr,(PO,),(OH), at the hydroxyapatite crystal surfaces.2y When strontium is incorporated into the hydroxyapatite crystal, the crystal size is increased, thus reducing the total surface area. There is evidence to suggest that the build up of strontium in enamel is mainly topical, rather than a systemic effect. 3o In teeth which had been extracted for orthodontic purposes, it was found that the enamel from low caries patients had twice as much strontium and fluoride in the surface and subsurface enamel when compared with patients with a high caries rate. There was also a marked gradation in both strontium and fluoride from the surface enamel inwards, with higher amounts on the surface layers, This observed phenomenon in humans has been confirmed experimentally in animals. Greatest reductions in smooth surface carious lesions occurred when strontium was administered in the drinking water posteruptively. More recent work suggests that strontium has an important role in the remineralization of carious !esions.31 Strontium has also been shown to be present in dental plaque. The concentration of strontium in plaque was found to be inversely associated with the cumulative individual caries experience, DMFT.‘2 In conclusion a glass of the strontium aluminoborate group would be expected to be not only radiopaque, but also have an anticariogenic effect on adjacent dental hard tissues.
Materials The cements were made by mixing a polymeric acid with a glass powder. The acid consisted of a solution of a 2: 1 copolymer of acrylic and itaconic
cement
275
acids, with a mean weight molecular -weight of 10,400, acid concentration of 49.05%: pH of 0.9, containing 5% tartaric acid. The glass was made by placing a mixture of oxides (SrO, 33.3mol%; Al,O,, 16.6mol% and B,03, .50mol%) into a platinum crucible and heating in a furnace to between 1200°C and 1450°C. The melt was shock cooled by passing it on to a clean stainless steel plate at room temperature. The rest&ant glass was reduced to a powder by comminution in a high speed mixing mill. The grinding was carried out in a closed cylinder or vial made of agate which contained two ball-shaped pestles also made of agate. After grinding the powder was passed through a 53pm sieve. Cement specimens in extracted teeth Caries free premolars which had been extracted less than 48 hours previously and stored in normal saline were selected for this test. Black’s Class V cavities were cut on the buccal and lingual surfaces of each tooth. The cavities were cut into dentine at high speed, with tungsten carbide burs, using water cooling. The experimental cements were mixed at a powder-to-liquid ratio of 2:l. The cavity on the buccal surface of each tooth was washed and dried carefully using a three-in-one syringe and the cements were packed into the cavity in small increments using a flat plastic hand instrument. A celluloid matrix strip was placed around the tooth and restoration until the cement had set, The teeth were then stored for 24 hours at 37°C and at 100% RH. The teeth were then embedded in epoxy resin and a horizontal section made through the restored tooth and cement. The cavity on the lingual surface was unfilled and kept as a control to establish the state of unrestored tooth tissues. The specimens were embedded in epoxy resin and sectioned. They were then ground fiat using a silicon carbide slurry on ground glass plates. The following sequence of abrasives were used: first, a medium grain of 12pm followed by a finer particle size of 7p.m. The specimens were then prepolished using 3pm silicon carbide. Specimens were polished on ‘Engis Kent’ polishing machines with Hyprocel Pellon paper laps using a diamond compound as a polishing medium. Polishing commenced with a 6,u.m compound for one hour followed by a 1p.m compound for one hour. Samples
276
MA Wilson and EC Combe
were then degreased carbon film.
and coated with 20nm of
Electron probe microanalysis
This technique was used to determine the effect of a restoration of the strontium alumino borate polyalkenoate cement on dentine and enamel adjacent to the material. The CAMECA Camebax used in this study was fitted with two wavelength dispersive spectrometers (WDS) and a Link systems 86&500 Energy Dispersive Spectrometer (EDS) system. Link systems ZAF--4/FLS software was used for manually operated EDS analysis and software called ‘SPECTA’ for automated EDS or EDS plus WDS analysis. The operating conditions were as follows: 15 kV accelerating potential 40 degree take off angle 3nA beam current for EDS + WDS analysis The ZAF-4/FLS software deconvoluted overlapping X-ray peaks and subtracts a background radiation by reference to a previously obtained library of standard peak profiles. The following element standards were used: for for for for
Al - corundum (a form of Al,O,) Ca - wollastonite (a form of Casio,) P - apatite (a form of Ca,(CaF)(PO&) Sr - celestine (SrSOJ
Results of microprobe
analysis
The basic shape of the glass particles was retained in the set cement, but the particles appeared to be embedded in a matrix. As polyacrylic acid does not contain any of the elements under investigation, (Al, Sr, B), their presence in the matrix would seem to indicate that they had been leached from the glass particles. The line scan across the set cement shows the distribution of the elements strontium and aluminium. The peaks on the graph are found where the electron beam passed directly over a glass particle and the troughs can be shown to represent areas of matrix between the glass particles. When Figures la and lb are compared, the strontium appears to be present in the matrix in greater amounts than the aluminium, possibly indicating a slightly greater or more rapid leaching
of strontium from the glass. In the line scan taken through the cement/enamel interface (Figure 2), the distribution of the elements strontium, aluminium, calcium and phosphorus is shown. The only source of Ca and P was abrasion debris from the tooth. It can be seen that the strontium appears to be taken up and incorporated into the enamel for several microns. This effect is not seen with aluminium . In dentine the distribution of the elements Sr, Al, Ca, and P is shown in Figure 3. The strontium appears to penetrate the dentine for several microns, there is also an extremely small amount of aluminium present in the dentine immediately adjacent to the restoration. The source of the Ca and P was the enamel and/or dentine of the tooth. The fate of the elements during the acid base reaction has been described for all elements except boron. This element is particularly difficult to identify using an electron probe as it has a very low atomic number. Even using a windowless probe, the boron could not be detected in the tooth tissues (Figure 4). Conclusions
1) Sr and Al are leached out of the glass particles to form a matrix. 2) Sr is acquired by the enamel and dentine adjacent to a restoration containing a strontium aluminoborate glass. This strontium is not removed by polishing techniques and appears to penetrate the tooth tissues for several microns. 3) Aluminium was found to be present in dentine, but did not penetrate the enamel. 4) The experimental cement system has potential for development as an anticaries adhesive dental cement.
Uptake of elements contained within the glass of a novel polyalkenoate
Distance
in
Microns
24
z
19.2
ti
14.4
x
9.59
s
4-79
I
42 Distance
in
Microns
Figure 1 Electron probe line scan across a specimen of strontium aluminoborate polyalkenoate cement: (a) distribution of strontium in the cement; (b) distribution of aluminium in the cement.
cement
277
278
MA Wilson and EC Combe
16.8
5.6
199 Distance
in
Microns
b 24
1
Distance
in
Microns
Figure2 Electron probe line scan across a section of a premolar containing a restoration of strontium alumlnoborate polalkenoate cement. The cement/enamel interface is marked with an arrow. (a) distribution of strontium; (b) distribution of aluminium; (c) distnbution of calcium; (d) distribution of phosphorus
Uptake of elements contained within the glass of a novel polyalkenoate
56
44.8
33.6
Distance
%Q .
in
Microns
17.199
5 6.599
0
Distance
in
Microns
cement
279
280
MA Wilson and EC Cornbe
a 28
*
11-2
c
. ’
L,n
5.6
Distance
in
163
Microns
b 26 -
z
20.8.
C
Distance
in
Microns
Electron probe line scan acrossa section of a premolar containing a restoration Figure3 of strontium aluminoborate polalkenoate cement. The cement/dentine interface is marked with an arrow. (a) distribution of strontium; (b) distribution of aluminlum; (c)distribution of calcium; (d) distribution of phosphorus
Uptake of elements contained within the glass of a novel polyalkenoate
Distance
in
Microns
163
0
Distance
in
Microns
cement
281
“282
MA Wilson and EC Combe c
s A
r
2‘lW
ke'v' CH
Figure 4
117=
Y.700 > 71L) CTS
Analysis for boron
References Wilson AD, Kent BE. A new translucent cement for dentistry. British Dental Journal 1972; 132: 133-35. Bertenshaw B W. Investigations on glass ionomer cements. PhD Thesis, University of Manchester, 1978. Watts TLP, Combe EC. Initial physical tests of aluminoborate cements in the context of periodontal dressing development. Journal of Oral Rehabilitation 1983; 10: 393-98.
4 Wilson MA. An investigation
into some novel adhesive dental materials. PhD Thesis, University of Manchester, 1987. 5 Curzon MEJ, Cutress TW. Trace elements and dental disease. Postgraduate Dental Handbook Series, Volume 9. John Wright PSG Inc. 1983. 6 Adkins, BL, Losee FL. A study of the covariation of dental caries prevalence and the multiple trace element content of water supplies. New York State Dental Journal 1970; 36: 618-22.
Uptake of elements contained within the glass of a novel polyalkenoate 7 Curzon MEJ, Cracker
DC. Relationships of trace elements in human tooth enamel to dental caries. Archives of Oral Biology 1978;
23 : 647-53. 8 Losee FL, Ludwig TG. Trace elements and caries. Journal of Dental Research 1970; 49: 1229-35.
9 Putt MS, Klebes CJ. Dissolution studies of human enamel treated with aluminium solutions. Journal of Dental Research 1985; 4: 438-40. 10 Schroeder HA, Mitchener M. Effect of boron on the life span of mice. Journal of Nutrition 1975; 105: 421-24.
11 Curzon MEJ, Adkins EL, Bibby BC, Losee FL. Combined effects of trace elements and fluorine on caries. Journal of Dental Research 1970; 49: 526-29. 12 Curzon MEJ, Spector PC, Iker HP. An
association between strontium in the drinking water supplies and low caries prevalence. Archives of Oral Biology 1978; 23: 317-21. 13 Shaw HJ, Griffiths D. Development and
postdevelopmental influences of experimental dental caries resulting from dietary supplementation by various elements. Archives of Oral Biology 1961; 5: 301-22. 14 Biittner W, Trace elements and dental caries in experiments on animals. Caries Research 1969; 3: 1-13. 1.5 Barmes DE. Caries etiology in Sepik villages.
Trace element, micronutrient and macronutrient content of soil and food. Caries Research 1969; 3: 44-59. 16 Curzon MEJ, Adkins BL, Bibby BC, Losee
FL. Combined effect of trace elements and fluorine on caries. Journal of Dental Research 1970; 49: 526-29. 17 Handleman SL, Losee FL. Inhibition
of enamel solubility in mineralised water. Journal
of Dental Research 1971; 50: 1605-09. 18 Turkian KM, Kulp JL. Strontium content of human bones. Science 1956; 124: 405-407.
19 Johnson AR, Armstrong WD, Singer L. The study of the mineral phase in the rat of powdered bone and dentine laden with strontium. Archives of Oral Biology 1970; 15: 401-409. 20 Drea WF. Spectrum analysis of dental tissues for ‘trace’ elements. Journal of Dental Research 2.936; 15: 403-406. 22 Bauer GCH, Ray RD. Kinetics of strontium
cement
283
metabolism in man. Journal of Bone and Joint Surgery 1958; 1: 171-85. 23 Nixon GS, Helsby CA. The relationship between strontium in water supplies and human tooth enamel. Archives of Oral Biology 1976; 21: 691-95. 23 Ferraro EF, Carr R, Zimmerman
K. A comparison of the effects of strontium chloride and calcium chloride on alveolar bone.
Calcified Tissue International 1983; 35: 258-60. 24 Vrbic V: Stupor J. Dental caries and the
concentration of aluminium and strontium in enamel. Caries Research 1980; 14: 141-47. 25 Ashrafi MH, Spector PC, Curzon MEJ. Pre and posteruptive effects of low doses of stronium on dental caries in the rat. Caries Research 1980; 14: 341-46. 26 Meyerowitz C, Spector PC, Curzon MEJ. Pre
and posteruptive effects of strontium alone or in combination with fluoride on dental caries in the rat. Caries Research 1979; 13: 203-10. 27 Dedhiya MG, Young F, Hefferen J, Higuchi WI. Mechanism for the retardation of the acid dissolution by Sr2+ and Mg2+, under partial saturation conditions containing F. Journal of Dental Research 1974; 52: 204. 28 Anderson CA. Dental caries prevaience in relation to trace elements. British Dental Journal 1966; 120: 271-75. 29 Dedhiya MG, Young F, Higuchi WI.
Mechanism for the retardation of the acid dissolution rate of hydroxyapatite by strontium. Journal of Dental Research 1973; 52: 1097-109. 30 Little MF, Barrett K. Strontium and fluoride
content of surface and inner enamel versus caries prevalence in the Atlantic Coast of the United States of America. Caries 1976; 10: 297-307. 31 Featherstone JDB, Nelson DG, McLean JD. An electron microscope study of the modifications to defect regions in dental enamel and synthetic apatites. Caries Research 1981; 15: 278-88. 32 Schamschula RG, Bunzel M. Angus H al. Plaque minerals and caries experience: associations and interrelationships. JournaE of Dental Research 1978; 57: 427-33. Received28 July 1988, sentfor revision I6 August 1988, accepted 4 October 1988).
1988: 3: 273-283
inal papers
e of elements contained within the glass polyalkenoate cement by adjacent toot argaret A Wilson and EC Combe Department of Restorative Dentistry, University Dental Hospital of Manchester
This paper presents a review of the effects of the elements strontium, alumrnium and boron on dental hard trssues. The effect of these elements contained in a novel strontrum aluminoborate polyalkenoate dental cement is described and their uptake by enamel and dentine was determined using electron probe microanalysis. It was found that strontium and aluminium were leached from the glass particles and penetrated into enamel and dentine to a depth of several microns.
Polyalkenoate cements have developed from the original work of Wilson and Kent’ and are now routinely used as adhesive cements in restorative dentistry. The glass powders of most commercially available aluminosilicate glass ionomer cements are two-phase systems, containing sheathed droplets of fluorides which are released by the action of the acidic liquid during the cement formation. Address for correspondence: Dr MA Wilson, Department of Restorative Dentistry, University Dental Hospital of Manchester, Higher Cambridge Street, Manchester Ml5 6FH, UK.
It has become apparent from studying the effect of fluoride release from glass ionomer cements, that beneficial effects can be achieved from the persistent release of biologically active trace elements. Although fluoride release has obvious beneficial effects on dental caries incidence, it is possible that the poor aesthetic appearance of some of these cements, for example, in terms of translucency, could be due to the presence of a two-phase glass. Thus it is of value to explore the possibility of obtaining an anticariogenic effect by the use of alternative elements. Simple single-phase threecomponent glasses may be an answer to the problem of combining aesthetics with anticariogenicity.
274
MA Wilson and EC Combe
The purpose of this study was to investigate a novel strontium aluminoborate polyalkenoate cement system,24 with a single-phase glass containing elements which are biologically active and believed to be available to tooth tissues. The presence of strontium could also confer radiopacity on the cement. Unlike other mineralized tissues, enamel and dentine once formed, do not metabolize or have a turnover rate. Changes do occur however, at the surface and subsurface layers due to posteruptive uptake of trace elements. Elements which are incorporated into the enamel while it is developing are restricted to those with an atomic number below 60. The presence of restorations which contain trace elements which could be available to the enamel and dentine is of particular interest, especially if that trace element has a cariostatic effect.5 It has been reported that certain trace elements are capable of producing an effect on dental caries similar to fluorides.6 The elements contained in the novel glass formulations were: aluminium, boron and strontium.
Biological activity of elements contained in strontium aluminoborate cement Effect of aluminium on dental caries Aluminium has been reported to be associated with a low caries experience.’ Aluminium is a polyvalent metal ion; in experiments using hydroxyapatite, it was found that three calcium atoms were replaced by two aluminium atoms with no loss of phosphate. In a review of epidemiological surveys of the effect of trace elements on caries,8 it was suggested that a relationship might exist between aluminium and strontium and caries prevalence in man and animals. More recent research has shown that aluminium ions reduce the dissolution of enamel.9 Effect of boron on dental caries Boron in the form of boric acid is now widely used as an additive in the food industry. It is not considered toxic when taken orally, as most of it is excreted in the urine.“’ Very few studies have been carried out to determine the effect of boron on caries prevalence. It is known that in areas where the drinking water contains high levels of
boron, the tooth enamel also contains high levels of boron.11,12 Although no mechanism for its effect has been suggested, a number of investigators have reported that the trace elements boron and strontium, when they occur together, may contribute to lowering caries prevalence. r3-16 showed a significant An in vitro investigation reduction in synthetic hydroxyapatite and enamel dissolution from acidogenic streptococci in a medium made with highly mineralized water from a low caries area. This water contained significantly higher amounts of boron and strontium.17 Although the individual effects of boron and strontium could not be identified, it was possible that the anticariogenic effect could have been produced by direct action on the plaque flora. Effect of strontium on dental hard tissues Strontium is a trace element which is deposited in calcified tissues, mainly in the apatite crystals. It is found in greater quantities than most other trace elements. lx When strontium is included into the mineral phase of bone and dentine, more stable compounds are formed than the analogous calcium compounds. I9 The presence of strontium in dental tissues was first demonstrated by Dreazo in 1936. The skeletal metabolic pathway of strontium in animals and man closely parallels that of calcium.21 A comprehensive review of studies carried out which demonstrate the distribution of strontium in dental tissues can be found in a paper by Nixon and Helsby.22 In animal experiments it has been found that in high local concentrations, strontium, like calcium, stimulates alveolar bone formation. The boney response to strontium is faster than that with calcium, but of shorter duration.23 To date there is no published work investigating the effect of strontium on dentinogenesis. Effect of strontium on dental caries The majority of investigations have shown that strontium is associated with a lower caries prevalence in man24 and in animals.2s In experiments on rats, when strontium was added to their drinking water, there was a reduction in smooth surface carious lesions.2h In addition if enamel was exposed to solutions containing strontium and fluoride, there was a lowering of the rate of dissolution in acidic media. A synergistic effect seemed to exist when these two trace elements occurred together.” The only survey which did
I/ptake of elements contained within the glass of a novel polyalkenoate not find an association between strontium and caries was that reported by Anderson.28 Subsequent investigations into this work revealed that the patients he examined were drinking water from a source far away from the high strontium area where they lived. The mechanism for the anticariogenic action of strontium has been shown to be the inhibition of the dissolution rate of hydroxyapatite in an acidic medium. This may be the result of the formation apatite complex: of a calcium-strontium Ca,Sr,(PO,),(OH), at the hydroxyapatite crystal surfaces.2y When strontium is incorporated into the hydroxyapatite crystal, the crystal size is increased, thus reducing the total surface area. There is evidence to suggest that the build up of strontium in enamel is mainly topical, rather than a systemic effect. 3o In teeth which had been extracted for orthodontic purposes, it was found that the enamel from low caries patients had twice as much strontium and fluoride in the surface and subsurface enamel when compared with patients with a high caries rate. There was also a marked gradation in both strontium and fluoride from the surface enamel inwards, with higher amounts on the surface layers, This observed phenomenon in humans has been confirmed experimentally in animals. Greatest reductions in smooth surface carious lesions occurred when strontium was administered in the drinking water posteruptively. More recent work suggests that strontium has an important role in the remineralization of carious !esions.31 Strontium has also been shown to be present in dental plaque. The concentration of strontium in plaque was found to be inversely associated with the cumulative individual caries experience, DMFT.‘2 In conclusion a glass of the strontium aluminoborate group would be expected to be not only radiopaque, but also have an anticariogenic effect on adjacent dental hard tissues.
Materials The cements were made by mixing a polymeric acid with a glass powder. The acid consisted of a solution of a 2: 1 copolymer of acrylic and itaconic
cement
275
acids, with a mean weight molecular -weight of 10,400, acid concentration of 49.05%: pH of 0.9, containing 5% tartaric acid. The glass was made by placing a mixture of oxides (SrO, 33.3mol%; Al,O,, 16.6mol% and B,03, .50mol%) into a platinum crucible and heating in a furnace to between 1200°C and 1450°C. The melt was shock cooled by passing it on to a clean stainless steel plate at room temperature. The rest&ant glass was reduced to a powder by comminution in a high speed mixing mill. The grinding was carried out in a closed cylinder or vial made of agate which contained two ball-shaped pestles also made of agate. After grinding the powder was passed through a 53pm sieve. Cement specimens in extracted teeth Caries free premolars which had been extracted less than 48 hours previously and stored in normal saline were selected for this test. Black’s Class V cavities were cut on the buccal and lingual surfaces of each tooth. The cavities were cut into dentine at high speed, with tungsten carbide burs, using water cooling. The experimental cements were mixed at a powder-to-liquid ratio of 2:l. The cavity on the buccal surface of each tooth was washed and dried carefully using a three-in-one syringe and the cements were packed into the cavity in small increments using a flat plastic hand instrument. A celluloid matrix strip was placed around the tooth and restoration until the cement had set, The teeth were then stored for 24 hours at 37°C and at 100% RH. The teeth were then embedded in epoxy resin and a horizontal section made through the restored tooth and cement. The cavity on the lingual surface was unfilled and kept as a control to establish the state of unrestored tooth tissues. The specimens were embedded in epoxy resin and sectioned. They were then ground fiat using a silicon carbide slurry on ground glass plates. The following sequence of abrasives were used: first, a medium grain of 12pm followed by a finer particle size of 7p.m. The specimens were then prepolished using 3pm silicon carbide. Specimens were polished on ‘Engis Kent’ polishing machines with Hyprocel Pellon paper laps using a diamond compound as a polishing medium. Polishing commenced with a 6,u.m compound for one hour followed by a 1p.m compound for one hour. Samples
276
MA Wilson and EC Combe
were then degreased carbon film.
and coated with 20nm of
Electron probe microanalysis
This technique was used to determine the effect of a restoration of the strontium alumino borate polyalkenoate cement on dentine and enamel adjacent to the material. The CAMECA Camebax used in this study was fitted with two wavelength dispersive spectrometers (WDS) and a Link systems 86&500 Energy Dispersive Spectrometer (EDS) system. Link systems ZAF--4/FLS software was used for manually operated EDS analysis and software called ‘SPECTA’ for automated EDS or EDS plus WDS analysis. The operating conditions were as follows: 15 kV accelerating potential 40 degree take off angle 3nA beam current for EDS + WDS analysis The ZAF-4/FLS software deconvoluted overlapping X-ray peaks and subtracts a background radiation by reference to a previously obtained library of standard peak profiles. The following element standards were used: for for for for
Al - corundum (a form of Al,O,) Ca - wollastonite (a form of Casio,) P - apatite (a form of Ca,(CaF)(PO&) Sr - celestine (SrSOJ
Results of microprobe
analysis
The basic shape of the glass particles was retained in the set cement, but the particles appeared to be embedded in a matrix. As polyacrylic acid does not contain any of the elements under investigation, (Al, Sr, B), their presence in the matrix would seem to indicate that they had been leached from the glass particles. The line scan across the set cement shows the distribution of the elements strontium and aluminium. The peaks on the graph are found where the electron beam passed directly over a glass particle and the troughs can be shown to represent areas of matrix between the glass particles. When Figures la and lb are compared, the strontium appears to be present in the matrix in greater amounts than the aluminium, possibly indicating a slightly greater or more rapid leaching
of strontium from the glass. In the line scan taken through the cement/enamel interface (Figure 2), the distribution of the elements strontium, aluminium, calcium and phosphorus is shown. The only source of Ca and P was abrasion debris from the tooth. It can be seen that the strontium appears to be taken up and incorporated into the enamel for several microns. This effect is not seen with aluminium . In dentine the distribution of the elements Sr, Al, Ca, and P is shown in Figure 3. The strontium appears to penetrate the dentine for several microns, there is also an extremely small amount of aluminium present in the dentine immediately adjacent to the restoration. The source of the Ca and P was the enamel and/or dentine of the tooth. The fate of the elements during the acid base reaction has been described for all elements except boron. This element is particularly difficult to identify using an electron probe as it has a very low atomic number. Even using a windowless probe, the boron could not be detected in the tooth tissues (Figure 4). Conclusions
1) Sr and Al are leached out of the glass particles to form a matrix. 2) Sr is acquired by the enamel and dentine adjacent to a restoration containing a strontium aluminoborate glass. This strontium is not removed by polishing techniques and appears to penetrate the tooth tissues for several microns. 3) Aluminium was found to be present in dentine, but did not penetrate the enamel. 4) The experimental cement system has potential for development as an anticaries adhesive dental cement.
Uptake of elements contained within the glass of a novel polyalkenoate
Distance
in
Microns
24
z
19.2
ti
14.4
x
9.59
s
4-79
I
42 Distance
in
Microns
Figure 1 Electron probe line scan across a specimen of strontium aluminoborate polyalkenoate cement: (a) distribution of strontium in the cement; (b) distribution of aluminium in the cement.
cement
277
278
MA Wilson and EC Combe
16.8
5.6
199 Distance
in
Microns
b 24
1
Distance
in
Microns
Figure2 Electron probe line scan across a section of a premolar containing a restoration of strontium alumlnoborate polalkenoate cement. The cement/enamel interface is marked with an arrow. (a) distribution of strontium; (b) distribution of aluminium; (c) distnbution of calcium; (d) distribution of phosphorus
Uptake of elements contained within the glass of a novel polyalkenoate
56
44.8
33.6
Distance
%Q .
in
Microns
17.199
5 6.599
0
Distance
in
Microns
cement
279
280
MA Wilson and EC Cornbe
a 28
*
11-2
c
. ’
L,n
5.6
Distance
in
163
Microns
b 26 -
z
20.8.
C
Distance
in
Microns
Electron probe line scan acrossa section of a premolar containing a restoration Figure3 of strontium aluminoborate polalkenoate cement. The cement/dentine interface is marked with an arrow. (a) distribution of strontium; (b) distribution of aluminlum; (c)distribution of calcium; (d) distribution of phosphorus
Uptake of elements contained within the glass of a novel polyalkenoate
Distance
in
Microns
163
0
Distance
in
Microns
cement
281
“282
MA Wilson and EC Combe c
s A
r
2‘lW
ke'v' CH
Figure 4
117=
Y.700 > 71L) CTS
Analysis for boron
References Wilson AD, Kent BE. A new translucent cement for dentistry. British Dental Journal 1972; 132: 133-35. Bertenshaw B W. Investigations on glass ionomer cements. PhD Thesis, University of Manchester, 1978. Watts TLP, Combe EC. Initial physical tests of aluminoborate cements in the context of periodontal dressing development. Journal of Oral Rehabilitation 1983; 10: 393-98.
4 Wilson MA. An investigation
into some novel adhesive dental materials. PhD Thesis, University of Manchester, 1987. 5 Curzon MEJ, Cutress TW. Trace elements and dental disease. Postgraduate Dental Handbook Series, Volume 9. John Wright PSG Inc. 1983. 6 Adkins, BL, Losee FL. A study of the covariation of dental caries prevalence and the multiple trace element content of water supplies. New York State Dental Journal 1970; 36: 618-22.
Uptake of elements contained within the glass of a novel polyalkenoate 7 Curzon MEJ, Cracker
DC. Relationships of trace elements in human tooth enamel to dental caries. Archives of Oral Biology 1978;
23 : 647-53. 8 Losee FL, Ludwig TG. Trace elements and caries. Journal of Dental Research 1970; 49: 1229-35.
9 Putt MS, Klebes CJ. Dissolution studies of human enamel treated with aluminium solutions. Journal of Dental Research 1985; 4: 438-40. 10 Schroeder HA, Mitchener M. Effect of boron on the life span of mice. Journal of Nutrition 1975; 105: 421-24.
11 Curzon MEJ, Adkins EL, Bibby BC, Losee FL. Combined effects of trace elements and fluorine on caries. Journal of Dental Research 1970; 49: 526-29. 12 Curzon MEJ, Spector PC, Iker HP. An
association between strontium in the drinking water supplies and low caries prevalence. Archives of Oral Biology 1978; 23: 317-21. 13 Shaw HJ, Griffiths D. Development and
postdevelopmental influences of experimental dental caries resulting from dietary supplementation by various elements. Archives of Oral Biology 1961; 5: 301-22. 14 Biittner W, Trace elements and dental caries in experiments on animals. Caries Research 1969; 3: 1-13. 1.5 Barmes DE. Caries etiology in Sepik villages.
Trace element, micronutrient and macronutrient content of soil and food. Caries Research 1969; 3: 44-59. 16 Curzon MEJ, Adkins BL, Bibby BC, Losee
FL. Combined effect of trace elements and fluorine on caries. Journal of Dental Research 1970; 49: 526-29. 17 Handleman SL, Losee FL. Inhibition
of enamel solubility in mineralised water. Journal
of Dental Research 1971; 50: 1605-09. 18 Turkian KM, Kulp JL. Strontium content of human bones. Science 1956; 124: 405-407.
19 Johnson AR, Armstrong WD, Singer L. The study of the mineral phase in the rat of powdered bone and dentine laden with strontium. Archives of Oral Biology 1970; 15: 401-409. 20 Drea WF. Spectrum analysis of dental tissues for ‘trace’ elements. Journal of Dental Research 2.936; 15: 403-406. 22 Bauer GCH, Ray RD. Kinetics of strontium
cement
283
metabolism in man. Journal of Bone and Joint Surgery 1958; 1: 171-85. 23 Nixon GS, Helsby CA. The relationship between strontium in water supplies and human tooth enamel. Archives of Oral Biology 1976; 21: 691-95. 23 Ferraro EF, Carr R, Zimmerman
K. A comparison of the effects of strontium chloride and calcium chloride on alveolar bone.
Calcified Tissue International 1983; 35: 258-60. 24 Vrbic V: Stupor J. Dental caries and the
concentration of aluminium and strontium in enamel. Caries Research 1980; 14: 141-47. 25 Ashrafi MH, Spector PC, Curzon MEJ. Pre and posteruptive effects of low doses of stronium on dental caries in the rat. Caries Research 1980; 14: 341-46. 26 Meyerowitz C, Spector PC, Curzon MEJ. Pre
and posteruptive effects of strontium alone or in combination with fluoride on dental caries in the rat. Caries Research 1979; 13: 203-10. 27 Dedhiya MG, Young F, Hefferen J, Higuchi WI. Mechanism for the retardation of the acid dissolution by Sr2+ and Mg2+, under partial saturation conditions containing F. Journal of Dental Research 1974; 52: 204. 28 Anderson CA. Dental caries prevaience in relation to trace elements. British Dental Journal 1966; 120: 271-75. 29 Dedhiya MG, Young F, Higuchi WI.
Mechanism for the retardation of the acid dissolution rate of hydroxyapatite by strontium. Journal of Dental Research 1973; 52: 1097-109. 30 Little MF, Barrett K. Strontium and fluoride
content of surface and inner enamel versus caries prevalence in the Atlantic Coast of the United States of America. Caries 1976; 10: 297-307. 31 Featherstone JDB, Nelson DG, McLean JD. An electron microscope study of the modifications to defect regions in dental enamel and synthetic apatites. Caries Research 1981; 15: 278-88. 32 Schamschula RG, Bunzel M. Angus H al. Plaque minerals and caries experience: associations and interrelationships. JournaE of Dental Research 1978; 57: 427-33. Received28 July 1988, sentfor revision I6 August 1988, accepted 4 October 1988).