Aim. To investigate (a) variability in powder/liquid proportioning and (b) effect of variability on diametral tensile strength (DTS), in a zinc phosphate cement. Statistical analyses (α = 0.05) were by Student's t-test in the case of powder/liquid ratio and one-way ANOVA and Tukey HSD for pair-wise comparisons of mean DTS. The Null hypotheses were that (a) the powder-liquid mixing ratios would not differ from the manufacturer's recommended ratio (b) DTS of the set cement samples using the extreme powder/liquid ratios would not differ from those made using the recommended ratio. Methodology. 34 dental students dispensed the components according to the manufacturer's instructions. The maximum and minimum powder/liquid ratios, together with the manufacturer's recommended ratio, were used to prepare samples for DTS testing. Results. Powder/liquid ratios ranged from 2.386 to 1.018. The mean ratio (1.644) was not significantly different from the recommended value of 1.718 (P = 0.189). DTS values for the maximum and minimum ratios were both significantly different from each other (P < 0.001) and from the mean value obtained from the recommended ratio (P < 0.001). 
Conclusions. Variability exists in powder/liquid ratio for hand dispensed zinc phosphate cement.  This variability can affect the DTS of the set material

Burke, Francis M.

McKenna, Gerald

McKenna, Jill E.

Ray, Noel J.

English

PubMed

Aim. To investigate (a) variability in powder/liquid proportioning and (b) effect of variability on diametral tensile strength (DTS), in a zinc phosphate cement. Statistical analyses () were by Student’st-test in the case of powder/liquid ratio and one-way ANOVA and Tukey HSD for pair-wise comparisons of mean DTS. The Null hypotheses were that (a) the powder-liquid mixing ratios would not differ from the manufacturer’s recommended ratio (b) DTS of the set cement samples using the extreme powder/liquid ratios would not differ from those made using the recommended ratio.Methodology. 34 dental students dispensed the components according to the manufacturer’s instructions. The maximum and minimum powder/liquid ratios, together with the manufacturer’s recommended ratio, were used to prepare samples for DTS testing.Results. Powder/liquid ratios ranged from 2.386 to 1.018. The mean ratio (1.644) was not significantly different from the recommended value of 1.718 (). DTS values for the maximum and minimum ratios were both significantly different from each other () and from the mean value obtained from the recommended ratio ().Conclusions. Variability exists in powder/liquid ratio for hand dispensed zinc phosphate cement. This variability can affect the DTS of the set material.</jats:p

Jill E. McKenna

Noel J. Ray

Gerald McKenna

Francis M. Burke

Crossref

Hindawi Publishing CorporationInternational Journal of DentistryVolume 2011, Article ID 679315, 4 pagesdoi:10.1155/2011/679315Research ArticleThe Effect of Variability in the Powder/Liquid Ratio on theStrength of Zinc Phosphate CementJill E. McKenna, Noel J. Ray, Gerald McKenna, and Francis M. BurkeRestorative Dentistry, Cork University Dental School and Hospital, University College Cork, IrelandCorrespondence should be addressed to Gerald McKenna, g.mckenna@ucc.ieReceived 6 July 2011; Revised 27 October 2011; Accepted 27 October 2011Academic Editor: Ali I. AbdallaCopyright © 2011 Jill E. McKenna et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.Aim. To investigate (a) variability in powder/liquid proportioning and (b) eﬀect of variability on diametral tensile strength (DTS),in a zinc phosphate cement. Statistical analyses (α = 0.05) were by Student’s t-test in the case of powder/liquid ratio and one-way ANOVA and Tukey HSD for pair-wise comparisons of mean DTS. The Null hypotheses were that (a) the powder-liquidmixing ratios would not diﬀer from the manufacturer’s recommended ratio (b) DTS of the set cement samples using the extremepowder/liquid ratios would not diﬀer from those made using the recommended ratio. Methodology. 34 dental students dispensedthe components according to the manufacturer’s instructions. The maximum and minimum powder/liquid ratios, together withthe manufacturer’s recommended ratio, were used to prepare samples for DTS testing. Results. Powder/liquid ratios ranged from2.386 to 1.018. The mean ratio (1.644) was not significantly diﬀerent from the recommended value of 1.718 (P = 0.189). DTSvalues for the maximum and minimum ratios were both significantly diﬀerent from each other (P < 0.001) and from the meanvalue obtained from the recommended ratio (P < 0.001). Conclusions. Variability exists in powder/liquid ratio for hand dispensedzinc phosphate cement. This variability can aﬀect the DTS of the set material.1. IntroductionIndirect restorations play an important role in clinicaldentistry. Whilst clinicians often spend considerable timechoosing materials or type of restorations, the cementationprocess is often considered less important and manufac-turer’s instructions modified or ignored [1]. Luting materialsare necessary to retain such restorations on teeth and toprevent leakage at their margins [2]. One such material iszinc phosphate cement which is used routinely by almostone-third of UK practitioners [3].Clinically, the cement is presented as powder andliquid components which must be mixed together priorto application to the restoration or the tooth. Often theproportions of the two elements used are measured by eyeor with operator-dependent measuring systems. They arethen mixed together in varying environments (temperatureand humidity) under diﬀering mixing conditions—time andmanipulation technique [4]. While low-grade mixing errors(<10–20%) may not have serious implications regardingthe integrity of traditional luting agents, there is concernregarding high-grade errors [1]. Such errors are likely tooccur with less experienced operators, such as undergraduatedental students and inexperienced dental nurses.As a measure of mechanical integrity of the set cement,compressive strength has been found to increase with theamount of powder mixed with a constant amount of liquid[4–8]. In addition, diametral tensile strength (DTS) is awell-established and reproducible measure of mechanicalintegrity in very brittle materials such as zinc phosphatecement and has been extensively used in the testing ofappropriate dentally related materials [9–11].The aim of this study was to (a) investigate whetherhigh-grade powder-liquid proportioning errors might occurin a cohort of inexperienced dental undergraduate studentsmixing zinc phosphate cement and (b) determine the eﬀectof any such variability on the diametral tensile strengthof the set material. The Null hypotheses were that (a) the2 International Journal of Dentistrypowder-liquid mixing ratios observed would not diﬀer fromthe manufacturer’s recommended ratio and (b) DTS of theset cement samples using the extreme powder/liquid ratiosobserved would not diﬀer from those made using the manu-facturer’s recommended ratio.2. MethodologyThe entire third year undergraduate dentistry class from adental school in Ireland was invited to participate in thestudy. Thirty four students contributed to the experiment,none of whom had previous experience of working with zincphosphate cement but had experience of mixing other dentalmaterials including glass ionomer cement in the clinicalenvironment. Each student received verbal and written direc-tions in measuring powder and liquid components accordingto the manufacturer’s instructions (Fleck’s Cement, Mizzy,Cherry Hill, NJ, USA). The instructions stated that 0.8 g ofpowder should equate with “2 fillings to the shoulder of thepowder cap dome” and 0.3mL liquid should equate with “12drops of liquid” (luting ratio). The students measured thepowder and liquid using the powder cap and liquid dropperonto a preweighed plastic container and the mass of eachwas recorded (Mettler AE 100 balance, Mettler InstrumentsAG, Greifensee, Zurich). A calibrated pipette was used todetermine the density of the cement liquid yielding the massequivalent of the manufacturer’s recommended volume of0.3mLs and a powder/liquid ratio (m/m) of 1.718.The observed maximum (2.386) and minimum (1.018)powder/liquid ratios, together with the manufacturer’s rec-ommended ratio (m/m), were used subsequently by a singleexperienced dental clinician to prepare cylindrical samples(n = 3 × 34), of nominal dimensions 6mm × 3mm, usinga stainless steel split mould. The samples were hand mixedon a chilled glass slab and the mix transferred and packedinto the split mould. The samples were left to initially mature(60mins) before being removed from the mould. Excessmaterial was removed using a sharp scalpel. The specimenswere further matured in deionised water (37 ± 2)◦C for 48hours. Before testing, each specimen was dried gently on allsides using soft tissue paper and the diameter and heightmeasured using a micrometer gauge. Compression across adiameter was carried out using a universal testing machine,H10KS (Tinius Olsen), at a constant crosshead speed of0.75mm/min. Failure load data were converted to DTS usingthe expression σ = 2P/πdl (σ = diametral tensile strength, P= load at failure, d = diameter of cylinder, and l = height ofcylinder). All testing was at 23± 2◦C.The Null hypotheses were that (a) the powder-liquidmixing ratios observed would not diﬀer from the man-ufacturer’s recommended ratio and (b) DTS of the setcement samples would not diﬀer from those made using themanufacturer’s recommended ratio. Statistical analyses (α =0.05) were by Student’s t-test in the case of powder/liquidratio and one-way ANOVA and Tukey HSD for for pair-wisecomparisons of mean DTS (R version 2.8.0—R Foundationfor Statistical Computing). Appropriate tests were carriedout for normality and constant variability.Table 1: Extreme powder/liquid mixing ratios & correspondingmean diametral tensile strength.Maximum Minimum Mean Manufacturer’sPowder/liquidratio, m/m (SD)2.386 1.0181.644(341)1.718Diametral tensilestrength, MPa (SD)7.19(1.50)2.65(1.01)—6.01(1.30)3. ResultsThe extreme powder/liquid mixing ratios (m/m) observedfrom the student cohort, together with the manufacturer’srecommending ratio, and corresponding data regardingDTS are presented in Table 1. The mean powder/liquidratio obtained for the student cohort was not significantlydiﬀerent from the manufacturer’s recommended value (P =0.189). The mean DTS values recorded for the maximumandminimum ratios for the student cohort were significantlydiﬀerent from that obtained from the manufacturer’s recom-mended powder/liquid ratio (P < 0.001) and from each other(P < 0.001).4. DiscussionIt is clear that high-grade powder-liquid proportioning er-rors were observed in this cohort of dental undergraduatestudents in the sense that the extreme powder-liquid ratiosresulted in significant impacts on DTS. These proportioningerrors have occurred notwithstanding explicit verbal andwritten instructions given immediately before the mixingprocess. While it is attractive to attribute this eﬀect to“inexperience,” as might be relevant to undergraduate dentalstudents and inexperienced dental nursing staﬀ, more sub-stantial and quantifiable concerns must address the mixingmethodology. Ideally, themixing process should be “fail safe”in that it should only be possible to mix material correctly, ornot at all. In this regard, a number of opportunities for errorpresent.The volume of powder delivered using volume dispen-sation is very operator dependent and variations can becommon due to the diﬀerences in cement powder packingdensities when filling the scoop [12, 13]. For dispensingthe liquid the opportunity for inaccuracy is potentially evengreater. The amount of liquid expressed is dependent on themanner in which the bottle is held and the force exertedon it. Excessive force can cause a stream of liquid to beexpressed rather than a series of drops and air bubblescan further complicate measurement [13]. Operators oftentend to mix cements and other restorative materials by“experience”, adding extra powder or liquid to gain theconsistency or properties they desire [14]. A report quotedrelatively good intraoperator consistency in mixing zincphosphate cement (single commercial product) among acohort of 40 qualified dental nurses in the UK but littleintra-operator consistency [15]. Clearly, such a report isnot conducive to the expectation of acceptable performanceamong inexperienced operators and begs the overall questionInternational Journal of Dentistry 3of whether an alternative approach should be used in themanner of a standard operating protocol per product. Aplausible solution to addressing variability in powder/liquidratio (and presenting the possibility of consistent mixing)is the encapsulation of cement components (single-usecapsules) which certain manufacturers have done with zincphosphate and other luting cements such as glass ionomer[16]. Encapsulation would also remove the problem ofsolvent evaporation from the cement liquid with possiblephosphate deposition yielding the liquid unusable.It is, however, unclear what parameters the manufac-turer’s recommended powder/liquid address. Presumably,the resultant mixture is required to be suﬃciently thin to wetthe adherend but with the ability to yield acceptable strengthon setting. A report on the eﬀect of powder/liquid ratio onthe clinical performance of resin-modified glass ionomercement [17] indicates that higher powder/liquid ratios com-promise surface wetting with an increased incidence of sub-sequent retention failures when used as a tooth restorative.The reported mean value for DTS, mixed accordingto the manufacturer’s ratio, was generally consistent withpreviously reported values for other brands of zinc phos-phate cement relating to similar specimen dimensions andstorage [18, 19]. This would suggest that the observedlow value obtained from the minimum powder/liquid ratiomay be generalised as inappropriate proportioning. Thevalue was less than 38% of the strength associated withthe manufacturer’s mixing ratio and must raise concernsregarding mechanical adequacy of the set material. Apartfrom concerns regarding compromised mechanical prop-erties, there are likely clinical consequences to the useof an inappropriate powder to liquid ratio. For example,incorporation of too much powder into the luting cementmay result in a thick mix of cement which could makecomplete seating an indirect restoration diﬃcult [20]. Thiscould result in open margins and/or a high restoration whichcould cause patient discomfort in the short term and thefailure of the restoration in the long term.While the use of encapsulated products might appearattractive to obviate arbitrary mixing ratios with attendantproblems, a reported comparison of an encapsulated zincphosphate cement with a hand-mixed analogue highlightedcertain deficiencies in the encapsulated material [21, 22]No significant advantages in terms of reliability or strengthwere observed in the encapsulated product. In addition, thelatter was observed to be more porous than the hand-mixedmaterial, most likely due to the entrapment of air during therelatively vigorous mechanical trituration.5. ConclusionsNull hypotheses (a) and (b) are rejected. High-grade propor-tioning errors relating to Fleck’s Cement, for a luting consis-tency, were observed among a cohort of dental undergradu-ate students. These errors resulted in significant diﬀerencesbetween the DTS values of the set cement and those whichrelate to the manufacturer’s recommended ratio. Apart fromcompromised mechanical performance resulting from inap-propriate proportioning, incorporation of too much powderinto the luting cement may result in a thick mix of cementwhich could make complete seating an indirect restorationdiﬃcult. This could result in open margins and/or a highrestoration. Routine encapsulation of zinc phosphate cementcomponents, in the form of single-use disposable capsules, issuggested as a method of addressing variability in propor-tioning powder-liquid cements especially amongst inexperi-enced operators.References[1] M. Behr, M. Rosentritt, H. Loher et al., “Changes of cementproperties caused by mixing errors: the therapeutic range ofdiﬀerent cement types,” Dental Materials, vol. 24, no. 9, pp.1187–1193, 2008.[2] F. J. Burke, “Evaluating restorative materials and procedures indental practice,”Advances in Dental Research, vol. 18, no. 3, pp.46–49, 2005.[3] P. A. Brunton, G. J. Christensen, S. W. Cheung, F. J. T. Burke,and N. H. F. Wilson, “Contemporary dental practice in theUK: indirect restorations and fixed prosthodontics,” BritishDental Journal, vol. 198, no. 2, pp. 99–103, 2005.[4] G. J. P. Fleming, R. M. Shelton, G. Landini, and P. M.Marquis, “The influence of mixing ratio on the tougheningmechanisms of a hand-mixed zinc phosphate dental cement,”Dental Materials, vol. 17, no. 1, pp. 14–20, 2001.[5] J. R. Savignac, C.W. Fairhurst, and G. Ryge, “Strength, solubil-ity and disintegration of zinc phosphate cement with clinicallydetermined powder-liquid ratio,” The Angle Orthodontist, vol.35, pp. 126–130, 1965.[6] W. B. Eames, S. D. Monroe, J. D. Roan, and S. J. O’Neal, “Pro-portioning and mixing of cements: a comparison of workingtimes,” Operative Dentistry, vol. 2, no. 3, pp. 97–104, 1977.[7] T. R. Walton, “The flow properties of zinc phosphate cement:an argument for changing the standard,” Australian DentalJournal, vol. 25, no. 4, pp. 215–218, 1980.[8] G. C. Paﬀenbarger, W. T. Sweeney, and A. Isaacs, “A prelim-inary report on the zinc phosphate cement,” Journal of theAmerican Dental Association, vol. 20, pp. 1960–1922, 1933.[9] X. S. Timoshenko, Theory of Elasticity, McGraw-Hill, NewYork, NY, USA, 1st edition, 1934.[10] R. G. Fonseca, T. P. Artusi, J. G. dos Santos, and G. L. Adabo,“Diametral tensile strength of dual-curing resin cementssubmitted exclusively to autopolymerization,” QuintessenceInternational, vol. 38, no. 9, pp. e527–e531, 2007.[11] I. S. Medeiros, M. N. Gomes, A. D. Loguercio, and L. E.Filho, “Diametral tensile strength and Vickers hardness of acomposite after storage in diﬀerent solutions,” Journal of OralScience, vol. 49, no. 1, pp. 61–66, 2007.[12] G. J. Mount, “Instructions for dental assistants,” in An Atlasof Glass-Lonomer Cements: A Clinician’s Gui, pp. 123–131,Martin Duntz, London, UK, 2nd edition, 1994.[13] R. W. Billington, J. A. Williams, and G. J. Pearson, “Variationin powder/liquid ratio of a restorative glass-ionomer cementused in dental practice,” British Dental Journal, vol. 169, no. 6,pp. 164–167, 1990.[14] J. F. McCabe and A. W. Walls, Applied Dental Materials,chapter28, Blackwell, London, UK, 9th edition, 2008.[15] G. J. P. Fleming, P. M. Marquis, and A. C. C. Shortall, “Theinfluence of clinically induced variability on the distributionof compressive fracture strengths of a hand-mixed zinc phos-phate dental cement,” Dental Materials, vol. 15, no. 2, pp. 87–97, 1999.4 International Journal of Dentistry[16] A. H. Dowling and G. J. P. Fleming, “Is encapsulation ofposterior glass-ionomer restoratives the solution to clinicallyinduced variability introduced on mixing?” Dental Materials,vol. 24, no. 7, pp. 957–966, 2008.[17] A. D. Wilder, A. A. Boghosian, S. C. Bayne, H. O. Heymann, J.R. Sturdevant, and T. M. Roberson, “Eﬀect of powder/liquidratio on the clinical and laboratory performance of resin-modified glass-ionomers,” Journal of Dentistry, vol. 26, no. 4,pp. 369–377, 1998.[18] E. A. Galun, N. Saleh, and I. Lewinstein, “Diametral tensilestrength and bonding to dentin of type I glass ionomercements,” The Journal of Prosthetic Dentistry, vol. 72, no. 4, pp.424–429, 1994.[19] S. Ban and K. J. Anusavice, “Influence of test method on failurestress of brittle dental materials,” Journal of Dental Research,vol. 69, no. 12, pp. 1791–1799, 1990.[20] S. A. Osman, J. F. McCabe, and A. W. Walls, “Film thicknessand rheological properties of luting agents for crown cemen-tation,” The European Journal of Prosthodontics and RestorativeDentistry, vol. 14, no. 1, pp. 23–27, 2006.[21] G. J. P. Fleming, A. C. C. Shortall, R. M. Shelton, and P.M.Marquis, “Encapsulated verses hand-mixed zinc phosphatedental cement,” Biomaterials, vol. 20, no. 22, pp. 2147–2153,1999.[22] G. J. P. Fleming, G. Landini, and P. M. Marquis, “Properties ofencapsulated and hand-mixed zinc phosphate dental cement,”American Journal of Dentistry, vol. 15, no. 2, pp. 91–96, 2002.Submit your manuscripts athttp://www.hindawi.comHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Oral OncologyJournal ofDentistryInternational Journal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014International Journal ofBiomaterialsHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014BioMed Research InternationalHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Case Reports in DentistryHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Oral ImplantsJournal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014 Anesthesiology Research and PracticeHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Radiology Research and PracticeEnvironmental and Public HealthJournal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014The Scientific World JournalHindawi Publishing Corporation http://www.hindawi.com Volume 2014Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Dental SurgeryJournal ofDrug DeliveryJournal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Oral DiseasesJournal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014 Computational and  Mathematical Methods in MedicineScientificaHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014PainResearch and TreatmentHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Preventive MedicineAdvances inHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014EndocrinologyInternational Journal ofHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014OrthopedicsAdvances in

International Journal of Dentistry

The Effect of Variability in the Powder/Liquid Ratio on the Strength of Zinc Phosphate Cement

Aim. To investigate (a) variability in powder/liquid proportioning and (b) effect of variability on diametral tensile strength (DTS), in a zinc phosphate cement. Statistical analyses (α = 0.05) were by Student's t-test in the case of powder/liquid ratio and one-way ANOVA and Tukey HSD for pair-wise comparisons of mean DTS. The Null hypotheses were that (a) the powder-liquid mixing ratios would not differ from the manufacturer's recommended ratio (b) DTS of the set cement samples using the extreme powder/liquid ratios would not differ from those made using the recommended ratio. Methodology. 34 dental students dispensed the components according to the manufacturer's instructions. The maximum and minimum powder/liquid ratios, together with the manufacturer's recommended ratio, were used to prepare samples for DTS testing. Results. Powder/liquid ratios ranged from 2.386 to 1.018. The mean ratio (1.644) was not significantly different from the recommended value of 1.718 (P = 0.189). DTS values for the maximum and minimum ratios were both significantly different from each other (P &lt; 0.001) and from the mean value obtained from the recommended ratio (P &lt; 0.001). Conclusions. Variability exists in powder/liquid ratio for hand dispensed zinc phosphate cement. This variability can affect the DTS of the set material.</p

McKenna, Jill E

Ray, Noel J

Burke, Francis M

Queen's University Belfast Research Portal

The effect of variability in the powder/liquid ratio on the strength of zinc phosphate cement

Aim:  To investigate (a) variability in powder/liquid proportioning (b) effect of the extremes of any such variability on diametral tensile strength (DTS), in a commercial zinc phosphate cement. Statistical analyses (a = 0.05) were by Student's t-test in the case of powder/liquid ratio and one-way ANOVA and Tukey HSD for for pair-wise comparisons of mean DTS. The Null hypotheses were that (a) the powder-liquid mixing ratios observed would not differ from the manufacturer's recommended ratio (b) DTS of the set cement samples using the extreme powder/liquid ratios observed would not differ from those made using the manufacturer's recommended ratio. Methodology:  Thirty-four undergraduate dental students dispensed the components according to the manufacturer's instructions. The maximum and minimum powder/liquid ratios (m/m), together with the manufacturer's recommended ratio (m/m), were used to prepare cylindrical samples (n = 3 x 34) for DTS testing. Results:  Powder/liquid ratios ranged from 2.386 to 1.018.The mean ratio (1.644 (341) m/m) was not significantly different from the manufacturer's recommended value of 1.718 (p=0.189). DTS values for the maximum and minimum ratios (m/m), respectively, were both significantly different from each other (p<0.001) and from the mean value obtained from the manufacturer's recommended ratio (m/m) (p<0.001). Conclusions:  Variability exists in powder/liquid ratio (m/m) for hand dispensed zinc phosphate cement. This variability can affect the DTS of the set material

Cork Open Research Archive

Title The effect of variability in the powder/liquid ratio on the strength of zincphosphate cementAuthor(s) McKenna, Jill E.; Ray, Noel J.; McKenna, Gerald; Burke, Francis M.Editor(s) Abdalla, Ali I.Publication date 2011-11Original citation Jill E. McKenna, Noel J. Ray, Gerald McKenna, and Francis M. Burke,“The Effect of Variability in the Powder/Liquid Ratio on the Strength ofZinc Phosphate Cement,” International Journal of Dentistry, vol. 2011,Article ID 679315, 4 pages, 2011. doi:10.1155/2011/679315Type of publication Article (peer-reviewed)Link to publisher'sversionhttp://www.hindawi.com/journals/ijd/2011/679315/http://dx.doi.org/10.1155/2011/679315Access to the full text of the published version may require asubscription.Rights Copyright © 2011 Jill E. McKenna et al. This is an open accessarticle distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, andreproduction in any medium, provided the original work is properlycited.http://creativecommons.org/licenses/by/3.0/Item downloadedfromhttp://hdl.handle.net/10468/551Downloaded on 2017-02-12T07:14:38ZHindawi Publishing CorporationInternational Journal of DentistryVolume 2011, Article ID 679315, 4 pagesdoi:10.1155/2011/679315Research ArticleThe Effect of Variability in the Powder/Liquid Ratio on theStrength of Zinc Phosphate CementJill E. McKenna, Noel J. Ray, Gerald McKenna, and Francis M. BurkeRestorative Dentistry, Cork University Dental School and Hospital, University College Cork, IrelandCorrespondence should be addressed to Gerald McKenna, g.mckenna@ucc.ieReceived 6 July 2011; Revised 27 October 2011; Accepted 27 October 2011Academic Editor: Ali I. AbdallaCopyright © 2011 Jill E. McKenna et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.Aim. To investigate (a) variability in powder/liquid proportioning and (b) eﬀect of variability on diametral tensile strength (DTS),in a zinc phosphate cement. Statistical analyses (α = 0.05) were by Student’s t-test in the case of powder/liquid ratio and one-way ANOVA and Tukey HSD for pair-wise comparisons of mean DTS. The Null hypotheses were that (a) the powder-liquidmixing ratios would not diﬀer from the manufacturer’s recommended ratio (b) DTS of the set cement samples using the extremepowder/liquid ratios would not diﬀer from those made using the recommended ratio. Methodology. 34 dental students dispensedthe components according to the manufacturer’s instructions. The maximum and minimum powder/liquid ratios, together withthe manufacturer’s recommended ratio, were used to prepare samples for DTS testing. Results. Powder/liquid ratios ranged from2.386 to 1.018. The mean ratio (1.644) was not significantly diﬀerent from the recommended value of 1.718 (P = 0.189). DTSvalues for the maximum and minimum ratios were both significantly diﬀerent from each other (P < 0.001) and from the meanvalue obtained from the recommended ratio (P < 0.001). Conclusions. Variability exists in powder/liquid ratio for hand dispensedzinc phosphate cement. This variability can aﬀect the DTS of the set material.1. IntroductionIndirect restorations play an important role in clinicaldentistry. Whilst clinicians often spend considerable timechoosing materials or type of restorations, the cementationprocess is often considered less important and manufac-turer’s instructions modified or ignored [1]. Luting materialsare necessary to retain such restorations on teeth and toprevent leakage at their margins [2]. One such material iszinc phosphate cement which is used routinely by almostone-third of UK practitioners [3].Clinically, the cement is presented as powder andliquid components which must be mixed together priorto application to the restoration or the tooth. Often theproportions of the two elements used are measured by eyeor with operator-dependent measuring systems. They arethen mixed together in varying environments (temperatureand humidity) under diﬀering mixing conditions—time andmanipulation technique [4]. While low-grade mixing errors(<10–20%) may not have serious implications regardingthe integrity of traditional luting agents, there is concernregarding high-grade errors [1]. Such errors are likely tooccur with less experienced operators, such as undergraduatedental students and inexperienced dental nurses.As a measure of mechanical integrity of the set cement,compressive strength has been found to increase with theamount of powder mixed with a constant amount of liquid[4–8]. In addition, diametral tensile strength (DTS) is awell-established and reproducible measure of mechanicalintegrity in very brittle materials such as zinc phosphatecement and has been extensively used in the testing ofappropriate dentally related materials [9–11].The aim of this study was to (a) investigate whetherhigh-grade powder-liquid proportioning errors might occurin a cohort of inexperienced dental undergraduate studentsmixing zinc phosphate cement and (b) determine the eﬀectof any such variability on the diametral tensile strengthof the set material. The Null hypotheses were that (a) the2 International Journal of Dentistrypowder-liquid mixing ratios observed would not diﬀer fromthe manufacturer’s recommended ratio and (b) DTS of theset cement samples using the extreme powder/liquid ratiosobserved would not diﬀer from those made using the manu-facturer’s recommended ratio.2. MethodologyThe entire third year undergraduate dentistry class from adental school in Ireland was invited to participate in thestudy. Thirty four students contributed to the experiment,none of whom had previous experience of working with zincphosphate cement but had experience of mixing other dentalmaterials including glass ionomer cement in the clinicalenvironment. Each student received verbal and written direc-tions in measuring powder and liquid components accordingto the manufacturer’s instructions (Fleck’s Cement, Mizzy,Cherry Hill, NJ, USA). The instructions stated that 0.8 g ofpowder should equate with “2 fillings to the shoulder of thepowder cap dome” and 0.3mL liquid should equate with “12drops of liquid” (luting ratio). The students measured thepowder and liquid using the powder cap and liquid dropperonto a preweighed plastic container and the mass of eachwas recorded (Mettler AE 100 balance, Mettler InstrumentsAG, Greifensee, Zurich). A calibrated pipette was used todetermine the density of the cement liquid yielding the massequivalent of the manufacturer’s recommended volume of0.3mLs and a powder/liquid ratio (m/m) of 1.718.The observed maximum (2.386) and minimum (1.018)powder/liquid ratios, together with the manufacturer’s rec-ommended ratio (m/m), were used subsequently by a singleexperienced dental clinician to prepare cylindrical samples(n = 3 × 34), of nominal dimensions 6mm × 3mm, usinga stainless steel split mould. The samples were hand mixedon a chilled glass slab and the mix transferred and packedinto the split mould. The samples were left to initially mature(60mins) before being removed from the mould. Excessmaterial was removed using a sharp scalpel. The specimenswere further matured in deionised water (37 ± 2)◦C for 48hours. Before testing, each specimen was dried gently on allsides using soft tissue paper and the diameter and heightmeasured using a micrometer gauge. Compression across adiameter was carried out using a universal testing machine,H10KS (Tinius Olsen), at a constant crosshead speed of0.75mm/min. Failure load data were converted to DTS usingthe expression σ = 2P/πdl (σ = diametral tensile strength, P= load at failure, d = diameter of cylinder, and l = height ofcylinder). All testing was at 23± 2◦C.The Null hypotheses were that (a) the powder-liquidmixing ratios observed would not diﬀer from the man-ufacturer’s recommended ratio and (b) DTS of the setcement samples would not diﬀer from those made using themanufacturer’s recommended ratio. Statistical analyses (α =0.05) were by Student’s t-test in the case of powder/liquidratio and one-way ANOVA and Tukey HSD for for pair-wisecomparisons of mean DTS (R version 2.8.0—R Foundationfor Statistical Computing). Appropriate tests were carriedout for normality and constant variability.Table 1: Extreme powder/liquid mixing ratios & correspondingmean diametral tensile strength.Maximum Minimum Mean Manufacturer’sPowder/liquidratio, m/m (SD)2.386 1.0181.644(341)1.718Diametral tensilestrength, MPa (SD)7.19(1.50)2.65(1.01)—6.01(1.30)3. ResultsThe extreme powder/liquid mixing ratios (m/m) observedfrom the student cohort, together with the manufacturer’srecommending ratio, and corresponding data regardingDTS are presented in Table 1. The mean powder/liquidratio obtained for the student cohort was not significantlydiﬀerent from the manufacturer’s recommended value (P =0.189). The mean DTS values recorded for the maximumandminimum ratios for the student cohort were significantlydiﬀerent from that obtained from the manufacturer’s recom-mended powder/liquid ratio (P < 0.001) and from each other(P < 0.001).4. DiscussionIt is clear that high-grade powder-liquid proportioning er-rors were observed in this cohort of dental undergraduatestudents in the sense that the extreme powder-liquid ratiosresulted in significant impacts on DTS. These proportioningerrors have occurred notwithstanding explicit verbal andwritten instructions given immediately before the mixingprocess. While it is attractive to attribute this eﬀect to“inexperience,” as might be relevant to undergraduate dentalstudents and inexperienced dental nursing staﬀ, more sub-stantial and quantifiable concerns must address the mixingmethodology. Ideally, themixing process should be “fail safe”in that it should only be possible to mix material correctly, ornot at all. In this regard, a number of opportunities for errorpresent.The volume of powder delivered using volume dispen-sation is very operator dependent and variations can becommon due to the diﬀerences in cement powder packingdensities when filling the scoop [12, 13]. For dispensingthe liquid the opportunity for inaccuracy is potentially evengreater. The amount of liquid expressed is dependent on themanner in which the bottle is held and the force exertedon it. Excessive force can cause a stream of liquid to beexpressed rather than a series of drops and air bubblescan further complicate measurement [13]. Operators oftentend to mix cements and other restorative materials by“experience”, adding extra powder or liquid to gain theconsistency or properties they desire [14]. A report quotedrelatively good intraoperator consistency in mixing zincphosphate cement (single commercial product) among acohort of 40 qualified dental nurses in the UK but littleintra-operator consistency [15]. Clearly, such a report isnot conducive to the expectation of acceptable performanceamong inexperienced operators and begs the overall questionInternational Journal of Dentistry 3of whether an alternative approach should be used in themanner of a standard operating protocol per product. Aplausible solution to addressing variability in powder/liquidratio (and presenting the possibility of consistent mixing)is the encapsulation of cement components (single-usecapsules) which certain manufacturers have done with zincphosphate and other luting cements such as glass ionomer[16]. Encapsulation would also remove the problem ofsolvent evaporation from the cement liquid with possiblephosphate deposition yielding the liquid unusable.It is, however, unclear what parameters the manufac-turer’s recommended powder/liquid address. Presumably,the resultant mixture is required to be suﬃciently thin to wetthe adherend but with the ability to yield acceptable strengthon setting. A report on the eﬀect of powder/liquid ratio onthe clinical performance of resin-modified glass ionomercement [17] indicates that higher powder/liquid ratios com-promise surface wetting with an increased incidence of sub-sequent retention failures when used as a tooth restorative.The reported mean value for DTS, mixed accordingto the manufacturer’s ratio, was generally consistent withpreviously reported values for other brands of zinc phos-phate cement relating to similar specimen dimensions andstorage [18, 19]. This would suggest that the observedlow value obtained from the minimum powder/liquid ratiomay be generalised as inappropriate proportioning. Thevalue was less than 38% of the strength associated withthe manufacturer’s mixing ratio and must raise concernsregarding mechanical adequacy of the set material. Apartfrom concerns regarding compromised mechanical prop-erties, there are likely clinical consequences to the useof an inappropriate powder to liquid ratio. For example,incorporation of too much powder into the luting cementmay result in a thick mix of cement which could makecomplete seating an indirect restoration diﬃcult [20]. Thiscould result in open margins and/or a high restoration whichcould cause patient discomfort in the short term and thefailure of the restoration in the long term.While the use of encapsulated products might appearattractive to obviate arbitrary mixing ratios with attendantproblems, a reported comparison of an encapsulated zincphosphate cement with a hand-mixed analogue highlightedcertain deficiencies in the encapsulated material [21, 22]No significant advantages in terms of reliability or strengthwere observed in the encapsulated product. In addition, thelatter was observed to be more porous than the hand-mixedmaterial, most likely due to the entrapment of air during therelatively vigorous mechanical trituration.5. ConclusionsNull hypotheses (a) and (b) are rejected. High-grade propor-tioning errors relating to Fleck’s Cement, for a luting consis-tency, were observed among a cohort of dental undergradu-ate students. These errors resulted in significant diﬀerencesbetween the DTS values of the set cement and those whichrelate to the manufacturer’s recommended ratio. Apart fromcompromised mechanical performance resulting from inap-propriate proportioning, incorporation of too much powderinto the luting cement may result in a thick mix of cementwhich could make complete seating an indirect restorationdiﬃcult. This could result in open margins and/or a highrestoration. Routine encapsulation of zinc phosphate cementcomponents, in the form of single-use disposable capsules, issuggested as a method of addressing variability in propor-tioning powder-liquid cements especially amongst inexperi-enced operators.References[1] M. Behr, M. Rosentritt, H. Loher et al., “Changes of cementproperties caused by mixing errors: the therapeutic range ofdiﬀerent cement types,” Dental Materials, vol. 24, no. 9, pp.1187–1193, 2008.[2] F. J. Burke, “Evaluating restorative materials and procedures indental practice,”Advances in Dental Research, vol. 18, no. 3, pp.46–49, 2005.[3] P. A. Brunton, G. J. Christensen, S. W. Cheung, F. J. T. Burke,and N. H. F. Wilson, “Contemporary dental practice in theUK: indirect restorations and fixed prosthodontics,” BritishDental Journal, vol. 198, no. 2, pp. 99–103, 2005.[4] G. J. P. Fleming, R. M. Shelton, G. Landini, and P. M.Marquis, “The influence of mixing ratio on the tougheningmechanisms of a hand-mixed zinc phosphate dental cement,”Dental Materials, vol. 17, no. 1, pp. 14–20, 2001.[5] J. R. Savignac, C.W. Fairhurst, and G. Ryge, “Strength, solubil-ity and disintegration of zinc phosphate cement with clinicallydetermined powder-liquid ratio,” The Angle Orthodontist, vol.35, pp. 126–130, 1965.[6] W. B. Eames, S. D. Monroe, J. D. Roan, and S. J. O’Neal, “Pro-portioning and mixing of cements: a comparison of workingtimes,” Operative Dentistry, vol. 2, no. 3, pp. 97–104, 1977.[7] T. R. Walton, “The flow properties of zinc phosphate cement:an argument for changing the standard,” Australian DentalJournal, vol. 25, no. 4, pp. 215–218, 1980.[8] G. C. Paﬀenbarger, W. T. Sweeney, and A. Isaacs, “A prelim-inary report on the zinc phosphate cement,” Journal of theAmerican Dental Association, vol. 20, pp. 1960–1922, 1933.[9] X. S. Timoshenko, Theory of Elasticity, McGraw-Hill, NewYork, NY, USA, 1st edition, 1934.[10] R. G. Fonseca, T. P. Artusi, J. G. dos Santos, and G. L. Adabo,“Diametral tensile strength of dual-curing resin cementssubmitted exclusively to autopolymerization,” QuintessenceInternational, vol. 38, no. 9, pp. e527–e531, 2007.[11] I. S. Medeiros, M. N. Gomes, A. D. Loguercio, and L. E.Filho, “Diametral tensile strength and Vickers hardness of acomposite after storage in diﬀerent solutions,” Journal of OralScience, vol. 49, no. 1, pp. 61–66, 2007.[12] G. J. Mount, “Instructions for dental assistants,” in An Atlasof Glass-Lonomer Cements: A Clinician’s Gui, pp. 123–131,Martin Duntz, London, UK, 2nd edition, 1994.[13] R. W. Billington, J. A. Williams, and G. J. Pearson, “Variationin powder/liquid ratio of a restorative glass-ionomer cementused in dental practice,” British Dental Journal, vol. 169, no. 6,pp. 164–167, 1990.[14] J. F. McCabe and A. W. Walls, Applied Dental Materials,chapter28, Blackwell, London, UK, 9th edition, 2008.[15] G. J. P. Fleming, P. M. Marquis, and A. C. C. Shortall, “Theinfluence of clinically induced variability on the distributionof compressive fracture strengths of a hand-mixed zinc phos-phate dental cement,” Dental Materials, vol. 15, no. 2, pp. 87–97, 1999.4 International Journal of Dentistry[16] A. H. Dowling and G. J. P. Fleming, “Is encapsulation ofposterior glass-ionomer restoratives the solution to clinicallyinduced variability introduced on mixing?” Dental Materials,vol. 24, no. 7, pp. 957–966, 2008.[17] A. D. Wilder, A. A. Boghosian, S. C. Bayne, H. O. Heymann, J.R. Sturdevant, and T. M. Roberson, “Eﬀect of powder/liquidratio on the clinical and laboratory performance of resin-modified glass-ionomers,” Journal of Dentistry, vol. 26, no. 4,pp. 369–377, 1998.[18] E. A. Galun, N. Saleh, and I. Lewinstein, “Diametral tensilestrength and bonding to dentin of type I glass ionomercements,” The Journal of Prosthetic Dentistry, vol. 72, no. 4, pp.424–429, 1994.[19] S. Ban and K. J. Anusavice, “Influence of test method on failurestress of brittle dental materials,” Journal of Dental Research,vol. 69, no. 12, pp. 1791–1799, 1990.[20] S. A. Osman, J. F. McCabe, and A. W. Walls, “Film thicknessand rheological properties of luting agents for crown cemen-tation,” The European Journal of Prosthodontics and RestorativeDentistry, vol. 14, no. 1, pp. 23–27, 2006.[21] G. J. P. Fleming, A. C. C. Shortall, R. M. Shelton, and P.M.Marquis, “Encapsulated verses hand-mixed zinc phosphatedental cement,” Biomaterials, vol. 20, no. 22, pp. 2147–2153,1999.[22] G. J. P. Fleming, G. Landini, and P. M. Marquis, “Properties ofencapsulated and hand-mixed zinc phosphate dental cement,”American Journal of Dentistry, vol. 15, no. 2, pp. 91–96, 2002.

Aim. To investigate (a) variability in powder/liquid proportioning and (b) effect of variability on diametral tensile strength (DTS), in a zinc phosphate cement. Statistical analyses (=0.05) were by Student’s t-test in the case of powder/liquid ratio and one-way ANOVA and Tukey HSD for pair-wise comparisons of mean DTS. The Null hypotheses were that (a) the powder-liquid mixing ratios would not differ from the manufacturer’s recommended ratio (b) DTS of the set cement samples using the extreme powder/liquid ratios would not differ from those made using the recommended ratio. Methodology. 34 dental students dispensed the components according to the manufacturer’s instructions. The maximum and minimum powder/liquid ratios, together with the manufacturer’s recommended ratio, were used to prepare samples for DTS testing. Results. Powder/liquid ratios ranged from 2.386 to 1.018. The mean ratio (1.644) was not significantly different from the recommended value of 1.718 (=0.189). DTS values for the maximum and minimum ratios were both significantly different from each other (<0.001) and from the mean value obtained from the recommended ratio (<0.001). 
Conclusions. Variability exists in powder/liquid ratio for hand dispensed zinc phosphate cement.  This variability can affect the DTS of the set material

Directory of Open Access Journals

Aim:  To investigate (a) variability in powder/liquid proportioning (b) effect of the extremes of any such variability on diametral tensile strength (DTS), in a commercial zinc phosphate cement. Statistical analyses (a = 0.05) were by Student\u27s t-test in the case of powder/liquid ratio and one-way ANOVA and Tukey HSD for for pair-wise comparisons of mean DTS. The Null hypotheses were that (a) the powder-liquid mixing ratios observed would not differ from the manufacturer\u27s recommended ratio (b) DTS of the set cement samples using the extreme powder/liquid ratios observed would not differ from those made using the manufacturer\u27s recommended ratio. Methodology:  Thirty-four undergraduate dental students dispensed the components according to the manufacturer\u27s instructions. The maximum and minimum powder/liquid ratios (m/m), together with the manufacturer\u27s recommended ratio (m/m), were used to prepare cylindrical samples (n = 3 x 34) for DTS testing. Results:  Powder/liquid ratios ranged from 2.386 to 1.018.The mean ratio (1.644 (341) m/m) was not significantly different from the manufacturer\u27s recommended value of 1.718 (p=0.189). DTS values for the maximum and minimum ratios (m/m), respectively, were both significantly different from each other (p<0.001) and from the mean value obtained from the manufacturer\u27s recommended ratio (m/m) (p<0.001). Conclusions:  Variability exists in powder/liquid ratio (m/m) for hand dispensed zinc phosphate cement. This variability can affect the DTS of the set material

Irish Universities

A .D .W i l d e r ,A .A .B o g h o s i a n ,S .C .B a y n e ,H .O .H e y m a n n

a n dN .H .F .W i l s o n ,“ C o n t e m p o r a r yd e n t a lp r a c t i c ei nt h e UK: indirect restorations and ﬁxed prosthodontics,”

A preliminary report on the zinc phosphate cement,”

Applied Dental Materials,

Changes of cement properties caused by mixing errors: the therapeutic range of diﬀerent cement types,” Dental Materials,v o l .2 4 ,n o .9 ,p p .

Diametral tensile strength and bonding to dentin of type I glass ionomer cements,”

Diametral tensile strength and Vickers hardness of a composite after storage in diﬀerent solutions,” J o u r n a lo fO r a l Science,

Diametral tensile strength of dual-curing resin cements submitted exclusively to autopolymerization,”

disintegration of zinc phosphate cement with clinically determined powder-liquid ratio,”

F.J.Burke,“Evaluatingrestorativematerialsandproceduresin dentalpractice,”AdvancesinDentalResearch,v ol.18,no .3,pp .

Film thickness and rheological properties of luting agents for crown cementation,”

Instructions for dental assistants,” in An Atlas of Glass-Lonomer Cements:

Is encapsulation of posterior glass-ionomer restoratives the solution to clinically induced variability introduced on mixing?”

Properties of encapsulated and hand-mixed zinc phosphate dental cement,”

Proportioning and mixing of cements: a comparison of working times,”

S.BanandK.J.Anusavice,“Inﬂuenceoftestmethodonfailure stress of brittle dental materials,” J o u r n a lo fD e n t a lR e s e a r c h ,

The ﬂow properties of zinc phosphate cement: an argument for changing the standard,”

The inﬂuence of clinically induced variability on the distribution of compressive fracture strengths of a hand-mixed zinc phosphate dental cement,”

The inﬂuence of mixing ratio on the toughening mechanisms of a hand-mixed zinc phosphate dental cement,”

Theory of Elasticity,

Variation in powder/liquid ratio of a restorative glass-ionomer cement used in dental practice,”

http://downloads.hindawi.com/journals/ijd/2011/679315.pdf

The Effect of Variability in the Powder/Liquid Ratio on the Strength of Zinc Phosphate Cement

Abstract

Similar works

Full text

Available Versions

Crossref

Queen's University Belfast Research Portal

Cork Open Research Archive

Directory of Open Access Journals

Irish Universities