Vol. 10, No. 2 - July - Dec. 2007, 9-12 J. 8aqai Med. Univ.

Development of -IonomerCements as Dental Restorative Materials

Kefi IqbaP, Iqbal Ahmad2 and Mohammad Aminuddin2

ABSTRACT:

Physico-chemical adhesion with sabstance has necessitated the production of polyacrylic acid based cements such as glass-ionomer cements (GICs) as dental restorative material. These materials undergo specific adhesion with hydroxyapatite and have been proved to possess properties that are satisfactory for a variety of clinical applications. In order to improve toughness, speed of setting and ressitance to dehydration, hybird materials are incorporated in the formulations to achieve desired ambient polymerization.

FTIR, IR and Raman spectroscopic techniques have been used for observing the physico-chemical changes involved in the setting process. Different formulations used for this purpose have been presented.

INTRODUCTION (3) alumino-silicate polyacrylic acid (ASPA) 9 Glass ionomer cements 1 (GIC) belong to polyacrylic cement , IO. All these are available as : acid based cements and are extensively used as dental i) Powder /liquid in bottles restorative materials. These materials are shown to ii) Powder/distilled water (water settable cement) undergo specific adhesion with hydroxyapatite and iii) Pre-proportioned powder/liquid in capsules.II have proved to possess properties that are satisfactory for a variety of clinical applications. The development General composition of ionomer cements: of , and porcelain restorative materials in the first quarter of the nineteenth century stimulated Powder the development of dental cements as luting and lining It consists of an ion-leachable calcium aluminofluoro materials and as more aesthetic materials. oxide­ silicate glass. phosphoric acid cement2 superseded the oxychloride and oxysulphate cements because of its lower irritation Modern cement powders (by weight) are composed to the and greater durability. The modern day of silicon dioxide (41.9%), aluminum oxide (28 .6%), cemenet3 and the and calcium fluoride (15.7%). Also present may be cement became' very Popular, especially the later was aluminum phosphate (12%), aluminum fluoride (8%), found to have a remarkable obtundent effect. A more and sodium fluoride (9%).12 aesthetic filling material, the silicate cement, was developed in England in 1873. This material received Liquid popularity only after an improved version was The liquid is an aqueous solution of and developed in 19044. Later in 1908 a material was copolymers of acrylic acid. developed that contained fluoride. Thus by the end of first quarter of the last century5 three basic types of The setting of glass ionomer cement is complex and 6 8 cements: (1) zinc phosphate ,7 (2) Zinc oxide eugeno1 may vary with the composition. Gles can be described 6 and (3) silicate cement ,7 were established for the as moderately hard brittle materials, with a relatively bonding of the inlays, , posts, bridges and high compressive strength, but with low fracture orthodontic bands or on in the tooth and cavity linings. toughness, flexural strength and wear resistance. The cements' physical properties remain unaltered due to The ionomer cements may be classified as follows: the release of fluoride. Fluoride release is greatest (1) Polyalkenoate cement immediately after placement and diminishes over l3 (2) glass lonomer cement time . A large release occurs over the first 24 to 48

~1:~B~a~qa~i ~De~n~ta~IC~o~II~~~e~, ~2:~B~a~qa~ieln~st~i tu~te~o~f~Peha~rm~a~c~eu~ti~ca~l~sc~ie~n~ce~s~, B~a~qa~i~M~ed~ic~a~lu~neiv~e~rs~ity~, S~u~p~er~H~ig~h~wa~y~, K~a~ra~Cehi~.~~~~~~~~~~~ Vol. 10, NO. 2· July· Dec. 2007, 9· 12 J. Baqai Med. Univ. hours which is then followed by a rapid decline. 14 polyacid by the basic glass. Infra-red22 ,23 has been particularly useful in characterizing the acid-base Compressive strength of GIC that is restorative cement reaction. More recently the IR technique has been containing glass particles up to 50 microns in diameter applied to show replacement of water in GICs by less has been observed to increase over a one year periodls . polar molecules, inhibiting the acid base reaction. 18 Glass ionomers expand under moist and contract FTIR24 and Raman spectroscopy2S have been useful under dry conditions. for reaction quantification and characterization of GICS glass. Setting reactions in glass ionomer cements . LITERATURE REVIEW have also been monitored by techniques such as rheologyl8 and differential scanning calorimetry26 . Glass-Poly (alkenoate) dental cements commonly Physical properties of glass ionomer cements have 27 known as glass ionomer cements (GICs) are set by an considerable influence on clinical perforrnance • There acid-base reaction between polymeric acid typically is an evidence of chemical bonding at bio-material a polyacrylic acid (PAA) and an acid degradable glass. hard interfaces28. The investigation shows that an ultra Control over the reaction rate is often achieved by the thin layer of the polyalkenoic acid can be prepared addition of tartaric acidl6 . In more recent developed on a hydroxyapatite based substrate by careful removal resin-modified glass-ionomer cements there is also a of non-bonded molecules. The percentages of light-catalyzed free radical polymerization reaction of functional groups of the polyalkenoic acid that bonded a hydrophilic methacrylate-based monomer8,17. The to calcium of hydroxyapatite have also been quantified. extent of setting in GICs has largely been investigated The properties of glass polyalkenoate cements based by studies of cement properties such as surface on the generic glass composition (6+ X) Si02, (4-X) hardness, compression and flexural strength, sample Ah03, 1.5 P20 S, 4 CaOCaF2 with varying aluminum solubility and rheologyl8. The chemistry of simple to silicon ratio have been investigated29. Setting and glass ionomer cements without resin has recently been working time of the cement pastes, compressive reviewed by Nicholson (1998)23 . Various techniques strength, unnotched fracture strength, young's modulus, including pH studiesl9, 13CNMR20 and ICp21 fracture toughness and toughness have been evaluated spectroscopic studies have shown that setting of the for the cements. Some typical glass ionomer powder cement involves a first step, neutralization of the formulations and their composition is given in Table 1.

Table 1: Composition of glass powder formulations

Formulation Composition (%) Ref.

1 Si02 AI20 3 CaO F Na20 P20 S 30 20-60 10-50 1- 40 1- 40 0-10 0-10

2 Si02 AI20 3 CaF2 AIF3 Na2AIF6 P20 S La20 3 MgO 31 18.22 10.60 12.50 11 .00 5.88 2.60 38.20 1.00

3 SiOz AI20 3 CaF2 AIF3 NaF AIP04 12 41.9 28.6 15.7 8 9 12

4 Si02 AI20 3 CaF2 AIF3 Na2AIF6 AIP04 20 29.0 16.6 34.3 5.3 5 9.8

5 SiOz AI20 3 CaF2 AIF3 AIP04 44 29.0 16.5 34.3 7.3 9.9 Vol. 10, No. 2 - July - Dec. 2007, 1-2 J. Baqai Med. Univ.

The studies of long term flexural strength,32 CONCLUSION comparative strength of commercial GICs with and Glass ionomer cements belong to polyacrylic acid - without metal addition, mechanical properties and based cements and are extensively used as dental microstructure of GICS33 and structure property restorative materials. Various formulations of these relationships in G1Cs34 have led to the knowledge of cements are available in the literature which includes the fracture surfaces, strength of the cement and different ingredients and variable compositions. The fluorine bonding to the calcium ions. GICs containing physico-chemical characteristics of these formulations niobium might be used in the composition to achieve have been studied by FTIR, lR and Raman a best possible result in dental applications.35 spectroscopic techniques to ascertain the chemical setting properties and leaching process. The aesthetic Other investigations include reactivity of fluoride aspects are also an important consideration in the containing calcium aluminosilicate glass,36,37 in vitro choice of these materials. All these factors are fluoride release from a light-cured glass-ionomer important and dependent on the composition of glass liner/bases,38 effect of monovalent ions in GICs on ionomer cements, therefore, we need to evaluate the their interaction with sodium fluoride solution39 and different formulation of these cements to achieve the the stoichiometry of the leaching process of fluoride best possible results in their clinical application. containing alumino silicate glass ionomer4o to help establish the exact relationship between the REFERENCES composition of the glass and the properties.41 1. Wilson, A.D., Kent, B.E. A new translucent cement Expansion of the concept of incorporation of for dentistry. The glass ionomercement.Br.Dent.,J., polymerization and polyelectrolyte salt formation 1972; 132: 133-135. mechanism within one molecule or a combination of 2. Culbertson, B.M . Glass ionomer de; tal molecules has led to a spectrum of materials42 which restoratives, Prog. Polym. Sci. , 200 I; 26: 577-604. range from classical acid-base GIC to modified 3. Smith, D.e. Development of glass ionomer cement polymerceramic (glass) composites with little systems, Biomaterials, 1998, 191 : 467-478. polyelectrolyte character. The objectives sought in the 4. · Steenbock, P. Glass lonomer Cement, German later materials are to improve the strength, toughness Patent 1903; 174,557. and resistance to dissolution whilst retaining the 5. Shoenbeck, F. Process for the production of tooth fundamental attributes of adhesion, fluoride release material, United States Patent 1908; 897160. and biocompatibility associated with the GIC system. 6. Going, R.E., Mitchen, J.e. Cement for permanent These cements, a component of conventional ionomer luting., J. Am. Dent. Assoc. , 1975; 91 ; 1: t07 -117. like AL +3 has been linked with poor bone 7. Smith, D.e. Dental Cements. Dent. Clin. North mineralisation and neurotoxicity.43 Am., 1971 ; 15:3-31. 8. Milosevic, A . Calcium hydroxide in restorative DISCUSSION dentistry, J. Dent., 1991 ; 19: 313. 9. Millet, D.T. , Mc Cabe, J.F. Orthodontic bonding The present literature review on GIC as dental with glass ionomer cement. A review. Eur. J. Orth., restorative material indicates that the development of 1996; 18: 385-399. GIC powders·over the time has led to the availability to. White, S.N., Yu, Z., Kipnis, V. Film thickness of of such materials to meet the physico-chemical and new adhesive luting agents. J. Prosthet. Dent., biological requirements in clinical applications. The 1992;6:476-481. compositional variations in glass powder formulations 11 . Mc Cabe, J.F. , Resin modified glass ionomers. may influence the quality of GIC in terms of its Biomaterials, 1998; 19: 521-528. restorative properties. The development of these 12. Philips, A. K. J. Science of Dental Materials, 2003; formulations is based on the study of physical, chemical 11 th ed., Elsevier Science, London. and biological factors to achieve the desired standard. 13. Forsten, L. Short- and long-term fluoride release The chemical aspects of GIC formulations can be best from glass ionomer and other fluoride-containing studied by the application of various spectroscopic filling materials in vitro. Scand. J. Dent. Res. , techniques as conducted by various workers mentioned 1990; 98: 179-185. in the literature review. It is necessary to meet to 14. DeSchepper, EJ. , Berry, E.A., Cailleteau, J.G., desirable physical and mechanical properties of GIC Tate W.H. A comparative study of fluoride release to achieve the best possible clinical performance. from glass-ionomer cements. Quintessence Int., 1991; 22: 215-220. •• Vol. 10, No. 2 - July - Dec. 2007, 9-12 J. Baqai Med. Univ.

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