dental mater ials 2 4 ( 2 0 0 8 ) 13811390

avai lab le at www.sc iencedi rec t .com

journa l homepage: www. int l .e lsev ierhea l th .com/ journa ls /dema

ModiN-vinand

AlirezaJawwada DepartmeUniversity ob DepartmeMile End Roc Departmen20 Gordon S

a r t i c

Article histor

Received 27

Received in

22 February

Accepted 4

Keywords:

Glass-ionom

N-Vinylpyrr

Nano-hydro

Nanouoro

Free radical

Solgel tech

Synthesis

Mechanical

Reinforcem

CorrespoE-mail a

0109-5641/$doi:10.1016/cation of conventional glass-ionomer cements withylpyrrolidone containing polyacids, nano-hydroxyuoroapatite to improve mechanical properties

Moshaveriniaa, Sahar Ansaria, Zanyar Movasaghia, Richard W. Billingtonb,A. Darrc, Ihtesham U. Rehmana,

nt of Materials, Interdisciplinary Research Centre in Biomedical Materials, Queen Maryf London, Mile End Road, London E1 4NS, UKnt of Biomaterial in Relation to Dentistry, Queen Mary University of London,ad, London E1 4NS, UKt of Chemistry, University College London, Christopher Ingold Laboratories,treet, London WC1H 0AJ, UK

l e i n f o

y:

March 2007

revised form

2008

March 2008

er cements

olidone

xyapatite

apatite

polymerization

nique

properties

ent

a b s t r a c t

Objective. The objective of this study was to enhance the mechanical strength of glass-

ionomer cements, while preserving their unique clinical properties.

Methods. Copolymers incorporating several different segments includingN-vinylpyrrolidone

(NVP) in different molar ratios were synthesized. The synthesized polymers were copoly-

mers of acrylic acid and NVP with side chains containing itaconic acid. In addition,

nano-hydroxyapatite and uoroapatite were synthesized using an ethanol-based solgel

technique. The synthesized polymers were used in glass-ionomer cement formulations

(Fuji II commercial GIC) and the synthesized nanoceramic particles (nano-hydroxy or uo-

roapatite) were also incorporated into commercial glass-ionomer powder, respectively. The

synthesized materials were characterized using FTIR and Raman spectroscopy and scan-

ning electron microscopy. Compressive, diametral tensile and biaxial exural strengths of

the modied glass-ionomer cements were evaluated.

Results. After 24h setting, the NVP modied glass-ionomer cements exhibited higher

compressive strength (163167MPa), higher diametral tensile strength (DTS) (1317MPa)

and much higher biaxial exural strength (2326MPa) in comparison to Fuji II GIC

(160MPa in CS, 12MPa in DTS and 15MPa in biaxial exural strength). The nano-

hydroxyapatite/uoroapatite added cements also exhibited higher CS (177179MPa), higher

DTS (1920MPa) and much higher biaxial exural strength (2830MPa) as compared to the

control group. The highest values for CS, DTS and BFS were found for NVP-nanoceramic

powder modied cements (184MPa for CS, 22MPa for DTS and 33MPa for BFS) which were

statistically higher than control group.

Conclusion. It was concluded that, both NVP modied and nano-HA/FA added glass-ionomer

cements are promising restorative dental materials with improved mechanical properties.

2008 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

nding author: Tel.: +44 20 7882 5502; fax: +44 20 8983 1799.ddress: i.u.rehman@qmul.ac.uk (I.U. Rehman). see front matter 2008 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.j.dental.2008.03.008

1382 dental mater ials 2 4 ( 2 0 0 8 ) 13811390

1. Introduction

Glass-ionomat the Labo[1,2]. Thesepolyalkenothe reactiothe formatcomponensive to toounique proaction (duestructure. Ifor glass iostructure [disadvantastrength. Sthe inventiin order tstronger andling charatoughnessNVP modiof glass-ion[19,20]. Culacid-N-vinyratio haveties of theYamazakiin modiedin compari[24].

In this staining polreported bmodied mmolar ratio(AA-NVP-IAionomer lithat neithemechanicatensile strein this studwere syntheach othermoleculeswould actdrance of caof ionic bonthe nal se

Lucas eof the hydder has ththe cemen[21]. Furthcements coenhanced mcial glass-inano-hydro

the effect of incorporation of these bioceramic nanopowdersinto GIC formulations upon the mechanical properties was

gatensileteders alted

Ma

Ma

assmenInteth

eivedtaconfate,OC2yapadrat

(NH4H) w

Me

Polmenthe4,25nium0-mllic a(dened inwaandilledmagatedcondsk afhichto throppmplnaln atlymend Yithsize:1:1maki e

poly0 SPed ier cement (GIC) was invented by Wilson et al.ratory of the Government Chemist in early 1970materials are water-based cements, known as

ate cements [3]. Their generic name is based onn between silicate glass and polyacrylic acid, andion arises from an acid/base reaction between thets [4,5]. These cements are translucent and adhe-th structure [611]. Glass-ionomer cements haveperties such as, biocompatibility, anticariogenicto uoride release) and adhesion to moist toothn addition, the coefcient of thermal expansionnomers is low and close to the values of tooth

1215]. Besides their advantages they have someges such as brittleness and inferior mechanicalignicant improvements have been made sinceon of GIC and further improvements are requiredo enhance their physical properties. Althoughd more aesthetic materials with improved han-cteristics are now available, lack of strength andare still major problems [1618]. The concept thated polyacids would result in improved strengthomer cements has been found valid in dentistrybertson et al. reported that acrylic aciditaconiclpyrrolidone polymers with the different molarthe ability to increase the mechanical proper-glass-ionomer cements [19]. In another study

et al. showed that AA-MA-NVP polymer resultedglass-ionomer cements with higher CS and DTS

son to Fuji IX commercial glass-ionomer cement

tudy, a method employed to synthesis NVP con-ymers, which is a modication of the procedurey Culbertson et al. and Yamazaki et al. In thisethod, novel NVP modied polyacids with a new(8:1:1 and 8:2:2) and altered monomeric sequences) were synthesized, and incorporated into glass-

quid formulations. Previous studies have shownr 7:3:1 nor 7:1:3 molar ratios, exhibited optimuml strength values (highest compressive, diametralngth and biaxial exural strength) [19]. Therefore,y, polymers with 7:2:2, 8:2:2 and 8:1:1 molar ratiosesized and the resulting data were compared toand previous data. It was envisaged that NVP

interspersed between the itaconic and acrylic acid,as a spacer to decrease the degree of steric hin-rboxylic acid groups. Subsequently, the probabilityd formation and poly-salt bridge formation withint cement would be increased signicantly.t al. in their work showed that the additionroxyapatite particles to the glass-ionomer pow-e ability to increase the fracture toughness oft which maintained long-term bond to dentinermore, Gu et al. reported that glass-ionomerntaining 4%w hydroxyapatite particles exhibitedechanical properties in comparison to commer-

onomer cements [22,23]. Therefore, in this studyxyapatite and uoroapatite were synthesized and

investitral teevaluapolymof resu

2.

2.1.

The glexperiII (GCcals inas rec(AA), ipersul(CH3COhydroxtetrahyoride(NH4O

2.2.

2.2.1.Experition ofet al. [2ammoin a 25of acryof NVPdissolvsolutiosulfateof distwith aand heThe sethe ation waddedglass dwas coadditionitrogethe poet al. aNVP wsynthewith 8Yamaz[24].

Theard 2.dissolvd. The mechanical strength (compressive, diame-and biaxial exural strength) of the GICs were

and the effect of incorporation of NVP modiednd HA/FA nanopowders on the mechanical valuescements were investigated.

terials and methods

terials

powders and all liquids which were used in thets were of commercial grade obtained from Fujirnational, Tokyo, Japan). All the other chemi-is study were in analytical grade and applied

from SigmaAldrich Chemical Co. Acrylic acidic acid (IA), N-vinylpyrrolidone (NVP), ammoniummethanol (CH3OH) and anhydrous ethyl acetateH5) were used for polymer syntheses. For nano-tite and uoroapatite syntheses, calcium nitratee [Ca (NO3)24H2O], (NH4)2HPO4, ammonium u-F), ethanol (C2H5OH), and ammonium hydroxideere used as obtained.

thods

ymer synthesistal procedure employed in this study is a modica-method rst reported by Crisp et al. and Yamazaki]. Details are as follows: initially 0.075 g (0.1% wt) ofpersulfatewasdissolved in 75ml of distilledwater

three-neck ask. In the next step, 0.4mol (27.43ml)cid (density of 1.05 g cm3), and 0.05mol (5.31ml)sity of 1.045 g cm3) were measured and partiallyn 37.5ml of distilled water in a beaker. A thirdsmade up, consisting of 0.022 g of ammoniumper-0.05mol (6.5 g) of itaconic acid dissolved in 22.5mlwater in a beaker. The rst solution was stirrednetic stirrer (IKA Werke magnetic stirrer/heater)continuously up to 98 C under owing nitrogen.solution containing acrylic acid and NVP added toter the temperature reached 98 C. The third solu-contained the initiator and itaconic acid was thene three-neck ask in a dropwise manner using aing funnel at ca. 3ml/min rate. After the additionete, polymerization was allowed to proceed for an12h by maintaining stirring under the blanket of98 C. Different molar ratios were synthesized forrs. Using the previously mentioned process (Crispamazaki et al.) the copolymer of acrylic acid andside chains containing itaconic acid groups wasd. In order to synthesize an AA-IA-NVP polymerolar ratio, the same basic procedure as used byt al. was applied, albeit with different molar ratios

mers were freeze-dried for 24h at 266mbar (Wiz-Industries Co. The Virtis Company, NY, USA),

n anhydrous methanol (SigmaAldrich) and then

dental mater ials 2 4 ( 2 0 0 8 ) 13811390 1383

Table 1 Yields and molar ratios of the synthesizedpolymers

Polymer Molar ratio Yield (%)

AA-IA-NVP 8:1:1 63AA-NVP-IA 8:1:1 72AA-NVP-IA 8:2:2 62AA-NVP-IA 7:2:2 64

precipitated from anhydrous ethyl acetate in order to removeresidual mreaction arvalues.

2.2.2. NaNano-hydrsolgel metet al. and Fedissolved inCa (NO3)24make a 0.5using a droca. 5ml/miperature ofby dropwisof 5ml) dur

For FA sy[28]. The p(NH4)2HPO19.702 g (84ethanol in o(16.7mmolto the abovtion was addropwise mcarried out

The yie(Table 2). Tdrying (Wizthen heat tsamples weat that temto 800 C, acooling, thusing a mo

2.2.3. ChPolymers wonance (1Hpolymers hspectra are

Table 2 uoroapa

Material

HydroxyapFluoroapat

Raman spectra of the synthesized polymers were obtainedusing aNicolet AmelgaXRdispersive Raman spectrophotome-ter. Sampleobtained inat 2.0 s exp

FTIR spFA were o(Thermo EMTEC Photples were p

rgedd regmbestalo-Hesoleratlayer

Molar wer, n

stersd accorde/wt)ed. Tof aerine rot

Foronom

Speyme) propoly

ternandeded usm anut toor ths (1mto pral anntlyncuhe mC for

nanonomers. The yields of the each polymerizatione given in Table 1, and are at or near expected

no-HA/FA synthesisoxyapatite was produced by an ethanol-basedhod according to the methods similar to Kuriakoseng et al. Initially 6.6 g (50mmol) of (NH4)2HPO4 was50ml of ethanol. Separately, 19.702 g (84mmol) of

H2O was dissolved in 50ml of ethanol in order toM solution. This solution was added to the rst onepping funnel in a dropwise manner at the rate ofn. The reaction was carried out at constant tem-85 C for 4h. The pH of the solution was kept at 10e addition of NH4OH solution (up to total amounting the reaction [26,27].nthesis, the procedure of Cavalli et al. was adoptedrocess was as follow; initially 6.6 g (50mmol) of

4 was dissolved in 50ml of ethanol. Separately,mmol) of Ca (NO3)24H2O was dissolved in 50ml ofrder to make a 0.5M solution. Subsequently 0.62 g

) NH4F with an appropriate molar ratio was addede solution as the source of uoride ion. This solu-ded to the rst one using a dropping funnel in aanner at the rate of ca. 5ml/min. The reaction wasat constant temperature of 85 C for 4h.lds of all reactions are shown the table belowhe nanoceramic products were dried using freezeard 2.0 SP Industries Co. The Virtis Company) andreated in a Carbolite (Shefeld, UK) furnace. There heated up to 400 C at a rate of 10 C/min, heldperature for 2h, then heated with the same rate upnd held for another 2h at this temperature. Upone powders were gently ground by hand for 5minrtar and pestle.

aracterizationere characterized by using nuclear magnetic res-NMR) and the results conrmed that the nal

ad a spectra related to the desired structures (NMRnot included).

was puinfrare128 nuKBr cry

NanHigh Rwas opa thin

2.2.4.MolecuZetasizWorcemetho

In1:1 (wtpreparcationEnginespindl

2.3.glass-i

2.3.1.All pol(wt/wtto the(GC Inommepreparof 4mwere ctest. Fmouldordermateriand gefrom ufrom tat 37

test.ForYields of synthesized hydroxy andtite nanoparticles

Yield (%)

atite 78ite 69

ders, the g(w/w) waspowder, anaccuratelytar and pesdistributionprocess mwas placed in a quartz tube and spectra werethe range of 4000400 cm1 averaging 256 scans

osure time, and 4 cm1 resolution.ectra of the synthesized polymers, nano-HA andbtained using a Nicolet 8700 FTIR spectrometerlectron Corporation, UK) in conjunction with anoacoustic Sampling cell (PAS). The powder sam-ut in the sample holder and the sampling chamberwith dry helium. Spectra were obtained in themidion (4000400 cm1) at 4 cm1 resolution averagingrs of scans. The polymeric sampleswere cast on thedisks prior to obtaining FTIR spectra.A and FA powders were studied in a JEOL JSM 6300Fution Scanning Electron Microscope (SEM) whiched at 15keV. Samples were prepared by dispersingof the powders on carbon coated copper grids.

lecular weight and viscosity measurementeights of the polymers were estimated by usinganoseries analyzer (ZS, Malvern Instruments Ltd.,hire, UK) at 25 C using static light scatteringording to refractive index of PAA.r to measure the viscosity of the polymers,mixture of polymer and distilled water were rsthe viscosities of polymersweremeasured by appli-programmable reheometer (DV III V3.0, Brookeldg Laboratories, Inc., Stoughton, MA) at 25 C andational speed of 50 rpm.

mulation and evaluation of the modieder cements

cimen preparationrs were dissolved in distilled water in a ratio of 1:1portion. d (+)-Tartaric acid 5% by mass was addedmer solution. The glass powder was Fuji II GICtional) and the P/L ratio of 2.7/1 was used as rec-by the manufacturer. Cylindrical specimens wereing PTFE cylindrical shapedmoulds with diameterd 6mm height for compressive strength test and2mm thick cylinders for dimetral tensile strengthe biaxial exural strength test, PTFE disk shapedm thickness and 10mm diameter) were used in

epare samples. The moulds were lled with thed coveredwith PTFE tape and glass slides, attenedpressed by hand in order to remove air bubblesred cement paste. The specimen were removedoulds after 1h and conditioned in distilled water24h. Six specimens were made for each kind of

o-HA and FA (uoroapatite) containing glass pow-lass powder/HA and glass powder/FA ratio of 20:1applied. An appropriate amount of glass-ionomerd either nano-hydroxyapatite or uoroapatite wereweighed and gently mixed by hand with a mor-tle for 2min. After gaining uniform particle sizethe specimens were prepared by using the same

entioned for the polyacid modied samples. In

1384 dental mater ials 2 4 ( 2 0 0 8 ) 13811390

Table 3 Compositions and the abbreviations used for various experimental glass-ionomer samples in this study

Group

Fuji IIPM1PM2PM3PM4HMFMPH1PH2

the followiglass-ionomtioned.

2.3.2. MeMechanicaical testingwith the crstrength wwhere p is teter of thetensile stretion DTS=and t are dmen (mm)was placeddiameter (Ito fractureball endedrecorded. Fexural strtion:

S = P/h2(

0

where P isand diameof 1.13 is deies of Akntaken to betral tensilewere subjemeans werlevel.

3. Re

3.1. Ch

The FTIR sders showe471 cm1 whydroxyapaphosphatepeaks at 87It has beenture of theh

2. Tht 15isap090and

owdeere whmaR aners srisonenceks arespas suingondt172

c aci1

) C7 cmthe ostrucendiers.500oxylownano-icroge apres

scos290 crisonLiquid composition

Fuji II liquidAAVP IA 8:1:1AAA NVP 8:1:1AANVPIA 8:2:2AANVPIA 7:2:2Fuji II liquidFuji II liquidAANVPIA 8:1:1AAIANVP 8:1:1

ng table (Table 3) different experimental groups ofer cements and their abbreviation codes aremen-

chanical properties measurementsl tests were performed on a screw driven mechan-machine (Model 4206, Instron Corp., Canton, MA)oss-head speed of 0.5mm/min. The compressiveas calculated from the relationship CS=4p/d2,he load (N) at the fracture point and d is the diam-cylindrical specimen (mm) [n=7]. The diametralngth (DTS) was determined according to the equa-2P/dt, where the P is load (N) at fracture point, diameter and thickness, respectively, of the speci-. For biaxial exural strength test, each specimenon annular knife edge support ring with 8mm

nstron Universal Testing machine), and the loadat the rate of 0.5mm/min using a 3mm diameterindenter in a universal load testing machine, wasor each test 7 specimens were observed. Biaxialengths were calculated from the following equa-

.606 ln ah + 1.13

)

the load, h and a are thickness of the sampleter of the support ring, respectively. The constantrived from Poissons ratio. From the previous stud-imade et al. the value of the Poissons ratio was0.27 [29]. Data obtained from compressive, diame-and biaxial exural strength tests of specimenscted to statistical analysis using ANOVA and thee compared by Tukeys test at the 5% signicance

sults

air COsites) apeak dthe 110Ramanatite pthey wand Re

FTIpolymcompaoccurrof peaCH2,

tion wstretchC H bpeak aboxyli1176 cm( CH2at 107whilecyclicC H bpolymfrom 3of carbare shwere ntron mFA wer

Ourand vi12202compaaracterization of synthesized materials

pectra of synthesized nano-hydroxyapatite pow-d peaks at 3571, 1087, 1036, 936, 631, 601, 569 andhich were ascribed to the hydroxyl group of thetite, phosphate 3, phosphate 1, phosphate 4 and2 vibrations, respectively. There were only two5 and 1418 cm1 which belong to CO32 groups.reported that carbonate ions can enter the struc-ydroxyapatitewhich thought to beoriginated from

240kDa forresults shoacid, the viof the NVPBy changinchanging thcosity andof NVP enhand polyacmolecular wand compaPowder composition

Fuji II glass powderFuji II glass powderFuji II glass powderFuji II glass powderFuji II glass powder95% wt glass, 5% wt Hap nanopowder95% wt glass, 5% wt FA nanopowder95% wt glass, 5% wt Hap nanopowder95% wt glass, 5% wt Hap nanopowder

ey can easily replace OH (A sites) and PO43 (B001545 and 14201470 cm1, respectively. The OHpeared in uoroapatite spectra and a broad peak in0 cm1 region (Fig. 1). The peak assignments of theFTIR spectra of synthesized hydroxy and uoroap-rs conrmed that the nal products were pure andell correlated with former studies by Cavalli et al.n et al.d Raman spectra (Fig. 2) of the synthesizedhowed the disappearance of the C C bonds into spectra of the reactants which indicated the

of the polymerization reaction. The disappearancet 1620 and 1410 cm1 which ascribe to C C andectively, conrmed that the polymerization reac-ccessful. The peak at 2936 cm1 belongs to C H

( CH2 ) methylene. And these peaks belong to aof an aliphatic hydrocarbon with a long chain. The6 cm1 belongs to Carbonyl (C O) group of car-d structures. The peaks at 1650, 1530, 1311 andbelong to carbonyl group of NVP, C H stretch (orH twist) and CH2 rocking, respectively. The peaks

1 related to C C backbone (skeletal vibration)ne at 978 cm1 is related to C C bonds on the NVPture. Finally, the peak at 497 cm1 is correlated tong which conrm the chemical structure of nalThe products also showed a broad peak rangingto 2400 cm1 which are related to hydroxyl groupsic acid group. SEM images of the sample powdersin Fig. 3 (below) and revealed that all the powderssized range and granular in shape. Scanning elec-raphs showed that the particle sizes of the HA andproximately 100200nm or so [37].ults suggested that the molecular weight (Fig. 4)ity of the synthesized polymers, ca., 500kDa andP (1.2202.290Pa s), respectively, were higher into commercial Fuji II polymer (approximately

molecular weight and 680 cP for viscosity). The

wed that by decreasing themolar ratio of the acrylicscosity decreased and by increasing themolar ratio, a slight decrease in the viscosity was observed.g the order of monomers in the polymer and thee distance between AA and IA monomers, the vis-molecular weight both decreased. Incorporationanced the mixing properties of the glass powderid. In the following gure (Fig. 4) the viscosity andeight of the synthesized polymers are mentioned

red to Fuji II poly acid.

dental mater ials 2 4 ( 2 0 0 8 ) 13811390 1385

3.2. Me

The resultthe NVP coand HA/NVFig. 5 andFuji II glascant differthe PM1 saFig. 1 FTIR spectra of the hydroxyapatite (a) a

chanical properties

s of 1 and 24h of CS, DTS and BFS testing ofntaining glass ionomers, HA-ionomer, FA-ionomerP modied glass ionomer, are shown in theTable 4. Results were compared to values fors-ionomer cement as a control group. Signi-ence between the CS, DTS and BFS values ofmples [mixture of Fuji II and synthesized AA-

NVP-IA (8:1BFS=28.6samples [mpolyacid; Calso exhibinicant, st[CS=161.1tion, the PAA-NVP-IAnd uoroapatite (b).

:1) polyacid; CS=167.110.4, DTS=16.92.9 and3.0] and the control group were observed. PM2ixture of Fuji II, synthesized AA-IA-NVP (8:1:1)

S = 165.29.5, DTS=16.53.0 and BFS=27.94.0]ted comparably higher, but not statistically sig-rength values in comparison to the control group11.8, DTS=11.82.4 and BFS=14.82.3]. In addi-M4 glass [mixture of Fuji II and synthesized(7:2:2) copolymer; CS=163.413.0, DTS=12.81.8

1386 dental mater ials 2 4 ( 2 0 0 8 ) 13811390

and BFS=2test resultstionwith pet al. [19,24

Nano-Hmixed withstrength [Cthan the cfor the naples (FM) [CFig. 2 FTIR (a) and Raman (b) spectra of synthesiz

6.12.4] had the lowest values of all. Mechanicalof NVP containing samples were in good correla-

reviously reported data by Culbetson andYamazaki].A containing glass ionomer (HM), which wasthe liquid of Fuji II, exhibited higher mechanical

S = 178.112.8, DTS=19.83.1 and BFS=30.84.5]ontrol group and the same trend was observedno-uoropatite containing glass-ionomer sam-S=179.45.5, DTS=20.62.5 and BFS=32.34.1]

which werdata by Luhighest valtion of HAwith NVPing statistiwas considPH1/PH2 sanano-HA-iotion of naed AA-NVP-IA polymer.

e in good correlation to previously mentionedcas et al. and Moshaverinia et al. [21,37]. Theues for CS, DTS and BFS were observed by addi-nanoparticles to the glass powders and mixingcontaining copolymer (PH1 and PH2). Regard-cal analysis of mechanical strength data, thereerable difference between PM1/PM2 samples andmples [nano-HA-ionomer+AA-IA-NVP (8:1:1) andnomer+AA-IA-NVP (8:1:1)]; which showed, addi-noparticles were more promising in increasing

dental mater ials 2 4 ( 2 0 0 8 ) 13811390 1387

Fig. 3 SEM

the mechaication ofadded glascan be moexperimen

Fig. 4 Molecular weight (MW) and viscosity ofsynthesized polymers in comparison to Fuji II.

4. Discussion

Syn

sultite nas by]. The

Table 4 24h of sto

GIC group

Fuji IIPM1PM2PM3PM4HMFMPH1PH2

Each entrysignicantl4.1.

The reyapatistudie[3032of HAp (a) and FA (b) nanopowders (40,000).

nical properties in comparison to polymer mod-GIC (Fig. 5 and Table 4). The results for FA

s-ionomer samples were very promising whichre investigated in the next steps of our series ofts.

a broad peacorrelates wand AA-IAand molecumer studie

4.2. Eva

Mechanicacements bstorage in died with Nhigher DTSstrength (raFuji II cemeBFS). More t140% incresamples wcontaining

Mechanical test (compressive, diametral tensile and biaxial exurage in distilled water at 37 C

Compressive strength (MPa) Diametral tensile stre

161.0 (11.8)a 11.8 (2.4)b

167.1 (10.4) 16.9 (2.6)l

165.2 (9.5)a 16.5 (3.0)l

163.6 (8.6)a 14.6 (2.1)l

163.4 (13.0)a 12.8 (1.8)b

178.5 (12.8)c 19.8 (3.1)i

179.4 (15.5)c 20.6 (2.5)i

183.8 (16.0)g 23.5 (3.9)d

180.9 (14.1)g 22.9 (4.1)d

is the mean value and standard deviations are mentioned in parenthesy different (p>0.05).thesis and characterization

ng peaks of FTIR and Raman spectra of hydrox-noparticles were in agreement with the previousRehman et al., Nikcevic et al. and Redey et al.OH peak disappeared in uoroapatite spectra andk in the 1100900 cm1 region was observed whichith former studies by Wei et al. [33]. AA-NVP-IA

-NVP polymers exhibited Raman, FTIR, viscositylar weight results, which were correlated with for-

s by Yamazaki et al. and Culbertson [19,24].

luation of cements

l tests results showed that all the glass-ionomerecame stronger as they matured after 24h ofistilledwater. All the glass-ionomer cementsmod-VP also exhibited higher CS (range 163167MPa),(range 1317MPa) andmuch higher biaxial exuralnge 2326MPa) in comparison to the commercialnt (161MPa for CS, 12MPa for DTS and 14MPa forhan 45% increase in diametral tensile strength andase in a BFS of the NVP modied glass-ionomerere observed. This study showed that copolymerssegments of NVP have the ability to signicantly

ral strength) results of the GIC samples afterngth (MPa) Biaxial exural strength (MPa)

14.8 (2.3)28.6 (3.0)e

27.9 (4.0)e

26.9 (3.1)e

26.1 (2.9)e

30.8 (4.5)f

32.3 (4.1)f

36.0 (6.0)34.1 (6.5)

es. Results with the same superscript letters are not

1388 dental mater ials 2 4 ( 2 0 0 8 ) 13811390

Fig. 5 Meand 24h ofbiaxial ex

increase thcements. Trate the AAof poly-saltturn, led toBy changinpolymericthat theretion and thwhichwoutral strenghypothesizwith itaconpolymeric ostrength anto the contions of NVformationmodied Ghydrophilicplanes of aduring DTSvalues wer

The result of this study correlated well with what Culbertsonet al. They synthesized AA-IA-NVP polymer with 7:3:1molar

nd ureaseonomup (ghesorpots, tsed sl groa (CSl glainerlymeydropin thchanmere tos ionessiv3.94l Funanoratio aan incglass itrol grothe hiby inccemenincreacontro277MPimentamaintathe poized hforcesthe me

ForadditivIX glascomprDTS=1merciastudy,chanical strength values for GIC samples after 1maturation (compressive, diametral tensile andural strength).

e nal mechanical strength of the glass-ionomerhe NVP segments were used as spacers to sepa-and IA segments, in order to allow a high degreebridging and cross-linkage to be created, which inenhancedmechanical properties of the set cement.g the order of the IA and NVP monomers in thechain of the AA-IA-NVP polymer, it is presumedwill be more space available for ionic bond forma-e nal polymer will have more exible side chainsld cause an increase in the compressive and diame-th of resulted glass-ionomer cement [19]. It wased that the copolymer of AA-NVP has side chainsic acid groups. Results showed that altering therder, increased the compressive, diametral tensiled BFS of resulting glass ionomer in comparison

trol group. It is assumed that higher concentra-P, results in less opportunities for poly-salt bridgeand as a result, the mechanical strength of theICs was reduced. Moreover, as NVP exhibits strongdomains which can inhibit the separation of thetoms which affects the response of the materialand BFS test [19]. Therefore, higher DTS and BFS

e obtained from NVP containing glass ionomers.

uoroapatithemechanders had hglass-ionomfor CS, DTSpared to HAcan be relaof FA in dinano-HA. Breaction ofcomponenions.

The statnicant difand BFS tesison to condata whichNVP segmemechanicathe amounthe valueswand the da

For theof nanoparmeric chainpropertiesmodied ait comparepowder (by(by incorpo

By incorliquid andincrease inCS was obsdoubled whsed Fuji II glass-ionomer powder. Results showedin the mechanical strength of the experimentaler (CS=276MPa) in comparison to the Fuji II con-

CS=205MPa). However, the 7:1:3 polymer exhibitedt FS value [34,35]. Yamazaki et al. reported thatration of AA-MA-NVP into Fuji XI glass-ionomerhe mechanical properties of the glass ionomerlightly from 273MPa (CS), 20.5MPa (DTS) for theup (commercial Fuji IX glass-ionomer cement) to), 21.6MPa (DTS) for 8:1:1 polyacid modied exper-ss [24]. In addition to the role of NVP as a space, the nitrogen atom acts as a hydrophilic center inr. NVP, therefore, has the ability to support local-hilic domains which increase the bipolarbipolare matrix of the glass-ionomer cement. As a result,ical strength of the cement increases.

studies have shown that nano-HA is a promisingglass-ionomer powder, Yap et al. reported that Fujiomer with 4% wt HA in its composition had highere and diametral tensile strength (CS=177.27MPa,MPa) values in comparison to non reinforced com-ji IX (CS=135MPa, DTS=12.07MPa) [36]. In thisparticles (50100nm) of both hydroxyapatite andtewere added to glass-ionomer powder (5%wt) andical test results showed that both of the glass pow-

igher strength compared to the Fuji II commercialer cements. Nano-FA/ionomers had higher valuesand BFS (179, 23 and 35MPa, respectively) com-/ionomer (178, 19 and 32MPa, respectively), which

ted to the stability of FA and lower dissolution ratestilled water compared to the dissolution rate ofoth nano-HA and FA take part in the acid/basethe glass-ionomer cement and reactwith inorganict of GIC network via their phosphate and calcium

istical analysis results showed that there were sig-ferences between the mechanical results (CS, DTSts) of modied glass-ionomer samples in compar-trol group. The deference was more obvious for theobtained from BFS and DTS tests. Changing the

nt order in the polymeric chain (PM1) increased thel properties of the glass-ionomer cement; howevert of increasewas not considerable in comparison tohich obtained fromPM2 modied cement samples

ta which was reported by Yamazaki et al.entire test samples it was observed that additionticles were more effective than changing the poly-. Furthermore, the highest values for mechanical

were obtained when both powder and liquid werelthough the difference was not remarkable whend to the glass-ionomer samples which only theirincorporation of nanoceramic particles) or liquidration of NVP segments) were modied.poration of both NVP and nanoparticles into thepowder of glass-ionomer cements, the biggeststrength was observed. More than 14% increase inerved and the values for diametral tensile strengthile the biaxial exural strength tripled. This sug-

dental mater ials 2 4 ( 2 0 0 8 ) 13811390 1389

gested that these additives have an effect on the settingreaction, mechanism and degree of poly-salt bridge formationof the glassties of nal

Therebetween thand phospkind of phlarge numbresponsibleresulting eformation oof hydroxymatrix. Wiand inorgamechanicaadhesion toof more orpolymers)future.

Anotherability to reration of nled to widsize of glasresulted inoccupy thecles and acthe glass-iooride in thincrease thionomer ce

5. Co

In this studsynthesizedlation of Fuof the resuthat thesemrestorativeof NVP, nanability to encomparednanoparticwas moreacrylic acidevaluate uon the bondto optimizeand also todling propeFA reinforcendeavours

Acknowle

We wouldfor helpful

and to Professor William M. Johnston for his expert advice onstatistical analysis of data.

en

ilsonnslu71;21ilsonA: Qisp Sprov75;3:tsuy: DiehateriroAmilsonomedmbrvidsA: Qountide.cLeanmenateri79.ilsone gla35.wersateriilsonosthtsuymenhiyakusavundeithament BErmuloroa79;58cholsview.isp Sueous 197cLeanass iontinelbertlyme D, Crengtpolym98;35cas MnvenomatYWHA/Z05;26ionomer, which cause higher mechanical proper-set cement.should be some physiochemical interactionse carbonyl group of NVP in the polymer structurehate, hydroxyl and uoride ions of apatite. Thisysical bonding is weak, but since there are aer of these types of bonds, they might be partlyfor increase in the mechanical properties of the

xperimental glasses. Moreover, the possibility off H-bonds is much more because of the presence

l, phosphate, uoride and carbonyl groups in thethout doubt, stronger bonds between the organicnic network of the set cement, lead to higherl strength of nal set cement. Finally, the degree oftooth structure especially dentin (due to presenceganic matter in the composition of synthesizedshould increase, and will be investigated in

role for incorporated apatite nanoparticles is theiract with PAA. Due to their small size, the incorpo-anoparticles into glass powder of glass ionomers,er particle size distribution (the average particles-ionomer particles were around 1020m) whichhigher mechanical values. Consequently, they canempty spaces between the glass-ionomer parti-t as a reinforcing material in the composition ofnomer cements. In addition, the presence of u-

e uoride-substituted apatite has the potential toe amount of uoride release from the set glass-ments.

nclusions

y NVP containing polymer, nano-HA and FA were, characterized and incorporated into a formu-ji II commercial GIC. The mechanical propertieslting cements were evaluated and it was shownaterials are promising additives for glass-ionomer

dental materials. This study showed that additiono-HA and FA into glass-ionomer cements had thehance the mechanical strength (CS, DTS and BFS)

to the unmodied cement. However, the effect ofles addition on the mechanical properties of GICimpressive than addition of NVP modied poly-to GIC. In future work, we hope to be able to

oride release from the FA component and its effectstrength to the tooth structure. We also will seekthe molecular weight of the polyacid and P/L ratioinvestigate other physical properties (such as han-rties) of the NVP polyacid modied nano-HA anded glass-ionomer cements. The results of thesewill be reported in due course.

dgments

like to give sincere thanks to Professor M. Bradendiscussions and critical reading of the manuscript

r e f e r

[1] Wtra19

[2] WUS

[3] Crim19

[4] KaInmEu

[5] WbiCa

[6] DaUS

[7] Mgu

[8] Mnom58

[9] Wth13

[10] Pom

[11] WPr

[12] KaceIs

[13] AnSa

[14] Smen

[15] Kefou19

[16] Nire

[17] CraqRe

[18] Mglde

[19] CuPo

[20] Xistco19

[21] LucoBi

[22] Guof20c e s

AD, Kent BE. The glass-ionomer cement, a newcent cement for dentistry. J Appl Chem Biotechnol:313.AD, McLean JW. Glass-ionomer cement. Chicago,uintessence Books; 1988., Ferner AJ, Lewis BG, Wilson AD. Properties ofed glass-ionomer cement formulations. J Dent12530.ama S, Ishikawa T, Fujii B. Translated [into English].nelt DE, editor. Glass ionomer dental cement: the

als and their clinical use. St. Louis, Tokyo: Ishiyakuerican; 1993.AD, Nicholson JW. Acidbase cements: theirical and industrial applications. Cambridge:idge University Press; 1993.on CL. Advances in glass-ionomer cements. Chicago,uintessence Pub. Co.; 1999.GF. An atlas of glass-ionomer cements: a clinicians2nd ed. London: Martin Dunitz; 1994.JW, Nicholson JW, Wilson AD. Proposed

clature for glass-ionomer dental cements and relatedals London. Quintessence Int 1994;25:

AD, Kent BE. A new translucent cement for dentistry,ss ionomer cement. Brit Dent J 1972;132:

JM, Sakaguchi RL. Craigs restorative dentalals. 12th ed. London: Elsevier Mosby; 2006.AD. Developments in glass-ionomer cements. Int J1989;2:43846.ama S, Ishikawa T, Fuji B. Glass ionomer dentalt: the materials and their clinical use. Saint Louis:u EuroAmerica; 1993.ice KJ. Philips science of dental materials. 11th ed.rs: Philadelphia; 2003.DC. Polyacrylic acid-based cement: adhesion tol and dentin. Oper Dent 1999;5:17783., Lewis BG, Wilson AD. Glass ionomer cement

ations: I The preparation of novelluminosilicate glasses high in uorine. J Dent Res:160719.on JW. Chemistry of glass-ionomer cements: aBiomaterials 1998;6:48594., Lewis BG, Wilson AD. Gelation of polyacrylic acids solutions and the measurement of viscosity. J Dent5;54:11735.JW, Powis DR, Prosser HJ, Wilson AD. The use of

nomer cements in bonding composite resins to. Brit Dent J 1985;158:4104.son BM. Glass-ionomer dental restoratives. ProgSci 2001;26:577604.ulbertson BM, Johntson WM. Improved exuralh of N-vinylpyrrolidone modied acrylic aciders for glassionomers. JMS Pure Appl Chem

:161529.E, Arita K, Nishino M. Strengthening using a

tional glass ionomer cement hydroxyapatite.erials 2003;24:378791., Yap AUJ, Cheang P, Khor KA. Effects of incorporationrO2 into glass ionomer cement (GIC). Biomaterials:71320.

1390 dental mater ials 2 4 ( 2 0 0 8 ) 13811390

[23] Gu YW, Yap AUJ, Cheang P, Khor KA. Development ofzirconia-glass ionomer cement composites. JNon-Crystalline Solids 2005;351:50814.

[24] Yamazaki T, Brantley BW, Culbertson BM, Seghi R, SchrickerS. The measure of wear in N-vinyl pyrrolidinone (NVP)glass-ionomer cements. Polym Adv Technol 2005;16:1136.

[25] Crisp S, Kent BE, Lewis BG, Ferner AJ, Wilson AD.Glass-ionomer cement formulations II. The synthesis ofnovel polycarobxylic acids. J Dent Res 1980;59:105563.

[26] Kuriakose T, Kalkura N, Palanichamy M, Arivuoli D, Bocelli G,Betzel C. Synthesis of stoichiometric nano crystallinehydroxyapatite by ethanol-based solgel technique at lowtemperature. J Crys Growth 2004;263:51723.

[27] Feng W, Mu-sen L, Yu-peng L, Yong Q. A simple solgeltechnique for preparing hydroxyapatite nanopowders.Mater Lett 2005;59:916.

[28] Cavalli M, Gnappi G, Montenero A, Fini M. Hydroxy- anduorapatite lms on Ti alloy substrates: solgel preparationand characterization. J Mater Sci 2001;36:325360.

[29] Aknimade AO, Nicholson JW. Poissons ratio of glasspolyalkenoate cements determined by an ultrasonicmethods. J Mater Sci Mater Med 1995;6:15734838.

[30] Rehman I, Boneld W. Characterization of hydroxyapatiteand carbonated apatite by photo acoustic FTIR spectroscopy.J Mater Sci: Mater Med 1997;8:14.

[31] Nikcevic I, Jokanovic V, Mitric M, Nedic Z, Makovec D,Uskokovic D. Mechanochemical synthesis of nanostructureduorapatite/uorhydroxyapatite and carbonateduorapatite/uorhydroxyapatite. J Sol Stat Chem2004;17:256574.

[32] Redey S, Nardin M, Bernache-Assolant D, Rey C, Delannoy P,Sedel L, et al. Behavior of human osteoblastic cells onstoichiometric hydroxyapatite and type A carbonate apatite:role of surface energy. J Biomed Mater Res 2000;50:353.

[33] Wei W, Evans JH, Bostrom T, Grondahl L. Synthesis andcharacterization of hydroxyapatite, uoride-substitutedhydroxyapatite and uorapatite. J Mater Sci 2003;14:31120.

[34] Culbertson BM. New polymeric materials for use inglass-ionomer cements. J Dent 2006;34:55665.

[35] Xie D, Culbertson BM, Wang G. Microhardness ofN-vinylpyrrolidone modied glassionomers cements. JMacromol Sci Pure Appl Chem 1998;35:54761.

[36] Yap AUJ, Pek YS, Kumar RA, Cheang P, Khor KA.Experimental studies on a new bioactive material: HAIonomer cements. Biomaterials 2002;23:95562.

[37] Moshaverinia A, Ansari S, Moshaverinia M, Roohpour N, DarrJA, Rehman IU. Effects of incorporation of hydroxyapatiteand uoroapatite nano-bioceramics into conventionalglass-ionomer cements (GIC). Acta Biomater 2008;4:43240.

Modification of conventional glass-ionomer cements with N-vinylpyrrolidone containing polyacids, nano-hydroxy and fluoroapatite to improve mechanical propertiesIntroductionMaterials and methodsMaterialsMethodsPolymer synthesisNano-HA/FA synthesisCharacterizationMolecular weight and viscosity measurement

Formulation and evaluation of the modified glass-ionomer cementsSpecimen preparationMechanical properties measurements

ResultsCharacterization of synthesized materialsMechanical properties

DiscussionSynthesis and characterizationEvaluation of cements

ConclusionsAcknowledgmentsReferences