Objective: To determine the degree of cure of a light-cured resin-modified glass ionomer (RMGI) under molar bands compared with a light-cured resin and a dual-cured resin.
Materials and Methods: The 3 cements used were Fuji Ortho LC, Eagle Spectrum resin, and Variolink II dual-cure. Each sample was indirectly light cured for 20 seconds (10 seconds occlusally, 10 seconds cervically) under sections of molar bands, and the degree of cure was evaluated with micro-MIR FTIR spectroscopy.
Results: The RMGI exhibited a significantly higher mean degree of cure (55.31%) than both of the resins (Eagle 19.23%; Variolink II, 25.42%), which did not differ significantly at α = .05 level of significance.
Conclusion: Higher degree of conversion can be obtained from RMGIs under molar bands compared with composite resin adhesives provided the proper curing technique is used

Bradley, T. Gerard

Eliades, George

Eliades, Theodore

Rejman, Daniel John

English

epublications@Marquette

Marquette Universitye-Publications@MarquetteSchool of Dentistry Faculty Research andPublications Dentistry, School of5-1-2008Polymerization Efficiency of Glass-Ionomer andResin Adhesives under Molar BandsDaniel John RejmanMarquette UniversityTheodore EliadesAristotle University of ThessalonikiT. Gerard BradleyMarquette University, thomas.bradley@marquette.eduGeorge EliadesUniversity of AthensPublished version. The Angle Orthodontist, Vol. 78, No. 3 (May 2008): 549-552. DOI. © 2008 The E.H. Angle Education and Research Foundation, Inc. Used with permission.Angle Orthodontist, Vol 78, No 3, 2008549DOI: 10.2319/022207-88.1Original ArticlePolymerization Efficiency of Glass-Ionomer and Resin Adhesivesunder Molar BandsDaniel John Rejmana; Theodore Eliadesb; Thomas G. Bradleyd; George EliadescABSTRACTObjective: To determine the degree of cure of a light-cured resin-modified glass ionomer (RMGI)under molar bands compared with a light-cured resin and a dual-cured resin.Materials and Methods: The 3 cements used were Fuji Ortho LC, Eagle Spectrum resin, andVariolink II dual-cure. Each sample was indirectly light cured for 20 seconds (10 seconds occlu-sally, 10 seconds cervically) under sections of molar bands, and the degree of cure was evaluatedwith micro-MIR FTIR spectroscopy.Results: The RMGI exhibited a significantly higher mean degree of cure (55.31%) than both ofthe resins (Eagle 19.23%; Variolink II, 25.42%), which did not differ significantly at   .05 levelof significance.Conclusion: Higher degree of conversion can be obtained from RMGIs under molar bands com-pared with composite resin adhesives provided the proper curing technique is used.KEY WORDS: Bands; Cement; RMGI; CureINTRODUCTIONDespite the continued advances in bonding molartubes, the use of molar bands continues to be popu-lar.1 Banded molars not only remain the standard foranchoring many appliances to the dentition, such asheadgear and expansion devices, but they are alsoused in preference to bonded tubes based on thepractitioner’s discretion and patient variation. Becausethe retention of bands is achieved mechanically to thetooth by close adaptation and by the cement itself,2various properties of cements have been tested anddeveloped to improve retention. Orthodontic applica-tions usually involve thin layers of adhesives and lackareas of bulk material that would seem to favor chem-a Resident, Department of Developmental Sciences, Ortho-dontics, Marquette University, Milwaukee, Wis.b Associate Professor, Department of Orthodontics, School ofDentistry, Aristotle University of Thessaloniki, Athens, Greece.c Professor, Department of Biomaterials, School of Dentistry,University of Athens, Athens, Greece.d Associate Professor, Department of Developmental Scienc-es, Orthodontics, Marquette University, Milwaukee, Wis.Corresponding author: Dr Daniel John Rejman, Departmentof Developmental Sciences, Orthodontics, Marquette University,1801 West Wisconsin Ave, Department of Orthodontics, Mil-waukee, WI 53233(e-mail: thomas.bradley@marquette.edu)Accepted: June 2007. Submitted: February 2007. 2008 by The EH Angle Education and Research Foundation,Inc.ical cure systems. Orthodontic bands, however, aresusceptible to areas of variable cement thickness3 andpresent a physically larger barrier to irradiation thanbrackets. Orthodontic cements lend themselves differ-ently to specific applications, and it is important to notethe differences in polymerization kinetics and how thismay relate to their utilization.Light-cured resins consist of 2 main components: anorganic matrix monomer and a powdered ceramic. Ac-tivation of free radicals is used to polymerize the un-saturated methacrytlate monomer. Increased irradia-tion time and light intensity lead to higher strength be-cause of the formation of a structure with a higher den-sity of cross-links (increased degree of cure).4 Inpractice, the dominance of surface properties overbulk properties favors the use of light-cured adhesiveresins.4 In dual-cured resin systems, polymerization isinitiated by surface exposure to a curing light while thebulk of the material continues to cure by a chemicalprocess. Benzoyl peroxide is used as an initiator,which is activated by a tertiary aromatic amine, andfree radicals are formed by a multi-step process. Glassionomers set as an acid–base reaction that leads tothe formation of polycarboxylate salts that make up thecement matrix. Resin-modified glass ionomer (RMGI)cements are dual setting; upon mixing the liquid andpowder the acid-base reaction occurs and the light-initiated free-radical polymerization of resin also oc-curs.550 REJMAN, ELIADES, BRADLEY, ELIADESAngle Orthodontist, Vol 78, No 3, 2008Figure 1. Schematic representation of the specimen preparation.Particular advancements have been made in theproperties of glass-ionomer cements, resin-modifiedglass ionomers, and compomers. The modified ce-ments combine the favorable properties of glass io-nomers: adhesion to enamel and metal, the ability toabsorb and release fluoride, and the ability to chemi-cally bond in the presence of moisture. The modifiedcements also include the favorable properties of res-ins: light curing for quick set and increased strength.5Because of their favorable properties, especially forbanding molars, these new cements have replaced thezinc phosphate and polycarboxylate cements thatwere used in the past.2Time to first failure, retentive strength, and shear-peel band strength of glass ionomers have been stud-ied6,7 but there is little information on the degree ofcure of cements under molar bands, which obviouslypose a larger physical barrier to light penetration thansmaller brackets. A recent study showed that theamount of occlusal metal coverage significantly affectsthe depth of cure of two resin band adhesives, as de-termined by Fourier transform infrared (FTIR) spec-troscopy.8Previous studies on dental composites have shownthat many characteristics of the material, includinghardness, tensile and compressive strength, and flex-ural modulus depend on the degree of resin polymer-ization.9 In particular, degree of cure modulates solu-bility and degradation, which affects the biological per-formance of the material.10 Adverse effects could in-clude bacteria reaching the enamel with resultingdecalcification, monomer leaching, and the release ofplasticizers, polymerization inhibitors, and inhibitors.These have been shown to have detrimental biologicaleffects in cell cultures.10The purpose of this study was to investigate the de-gree of cure of a light-cured RMGI under molar bands,compared with a light-cured resin and a dual-curedresin. This in vitro study sought to add further insightinto the complex subject of polymerization and how itmay relate to RMGI’s use as proper band cement.MATERIALS AND METHODSFifteen orthodontic band strip samples measuring 4mm  8 mm were sectioned from intact first molarbands (Orthos 0.022, Ormco Corp, Orange, Calif) anddivided into 3 groups of 5 bands each. A light-curedRMGI (Fuji Ortho LC, GC International, Tokyo, Japan),a light-cured resin (Eagle Spectrum, American Ortho-dontics, Sheboygan, Wis) and a dual-cure resin com-posite luting cement (Variolink II Dual Cure, IvoclarVivadent, Schaan, Liechtenstein) were selected forthis investigation. The adhesives were mixed accord-ing to manufacturer’s instructions, and approximately15 mg of each was applied to the base of each band.The amount of material was weighed. This is importantin establishing a reference or starting point in thesense that if a reduced amount is present, applicationof a standard pressure would result in different adhe-sive thickness compared with a bulk specimen. Anyexcess resin was removed from the specimen afterapplication of a uniform pressure by the operator. Theband samples were firmly pressed against a glassslide covered by a polystyrene strip (Figure 1). Excessresin was removed before polymerization. An EliparTrilight curing light (ESPE, GmbH, Seefeld, Germany)was standardized at 950 mw/cm2. Each sample wasindirectly irradiated for 10 seconds at the occlusaledge and 10 seconds from the cervical edge, with thetip of the curing light held at the edge of the band ata 30 angle. The time frame was chosen to allow forextended irradiation relative to the 10-second periodused for irradiation of adhesives under brackets.The plastic strips were removed, and the flat surfacewas placed in contact with a KRS-5 minicrystal (ThI-ThBr, n  2.4, 45 edge angle, 7 internal reflections,10  5  1 um). This was secured in a micro-multipleinternal FTIR spectroscopy accessory (Perkin-ElmerCorp, Norwalk, Conn). The accessory was placed ona FTIR spectrometer (Perkin-Elmer 6x, Perkin-ElmerCorp). From each sample micro-multiple internal re-flectance (MIR) FTIR spectra were obtained under theconditions: 4000 to 400 cm1 wave number range, 4cm1 resolution, 30 scan transients. Additional spectrawere collected from a sample of unpolymerized resinfor each of the 3 adhesives to serve as a reference.The spectra of each sample was analyzed, and thedegree of cure (DC) was estimated for each using arelative percentage basis with the two frequency meth-od and the tangent baseline technique.11 For the res-ins, the aliphatic (CC) bond stretching vibrations at1638 cm1 were chosen as the analytical frequency,while the aromatic (C · · · C) bond stretching vibrationsat 1605 cm1, which are unaffected by the polymeri-zation reaction were chosen as the reference frequen-cy. For the Fuji RMGI, the ester (CO) bond stretch-ing vibrations at 1712 cm1, which do not interfere withpolymerization, were chosen as the reference frequen-cy. The formula used to determine the % DC is:% DC  100  [1  (A/B  C/D)]551POLYMERIZATION OF BANDING CEMENTS AND ADHESIVESAngle Orthodontist, Vol 78, No 3, 2008Table 1. Mean Percentage Degree of Cure for a Resin Adhesive,a Dual-Cure Resin, and a Resin-Modified Glass IonomeraN Mean % DC SDTukeyGrouping*Eagle Resin 5 19.23 8.33 AVariolink II 5 25.42 12.99 AFuji Ortho LC 5 55.31 5.71 Ba N indicates number of samples; DC, degree of cure; SD, stan-dard deviation.* Means with same letter do not differ significantly at the   0.05level.For Eagle and VariolinkA: net peak absorbance area of the polymerized ma-terial at 1638 cm1B: net peak absorbance area of the unpolymerizedmaterial at 1638 cm1C: net peak absorbance area of the unpolymerizedmaterial at 1605 cm1D: net peak absorbance area of the polymerized ma-terial at 1605 cm1For Fuji Ortho LCC: net peak absorbance area of the unpolymerizedmaterial at 1712 cm1D: net peak absorbance area of the polymerized ma-terial at 1712 cm1Analysis of variance (ANOVA) was used to comparethe mean % DC of the different adhesives. Pairwisecomparisons were made using Tukey’s Studentizedrange test at   .05 level of significance.RESULTSThe mean degree of cure was 19.23% for the Eagleresin, 25.42% for Variolink II, and 55.31% for Fuji Or-tho LC (Table 1). Pairwise comparisons indicated (1)no significant difference between the mean % DC be-tween the Eagle and Variolink resins; (2) a significantdifference between the % DC of Fuji RMGI and Eagleresin; and (3) a significant difference between the %DC of Fuji RMGI and Variolink resin.DISCUSSIONIn deciding what material to use for banding molars,the clinician should ask which properties prevail: thinlayers of cement or areas with bulk volume. Bandedteeth possess both; thin layers dominate when fit well,but areas of relative bulk remain, lending themselveswell to dual-cured systems. The thin layers respondwell to light curing, where the degree of carbon-carbondouble-bond conversion is associated with curing time,light intensity, color shade, and filler loading.12A study on curing patterns demonstrated that belowsurfaces exposed to curing lights, there is adequatecuring until a certain depth, where both remaining dou-ble bonds and Knoops hardness pattern changed rap-idly. This was attributed to the attenuation of the initi-ating light as a function of distance.12 Thus, the vari-ability of adhesive thickness, and the influence of thesize of a barrier to the light (the molar band) shouldbe expected to influence the degree of cure of a ma-terial. The technique used to measure the degree ofcure analyzed the adhesives in the portion of the bandwhere presumably the least amount of irradiation pen-etration occurred, and thus the least amount of poly-merization. The spectrometer analyzed the surface ofthe materials at a mean depth of approximately 3 m,9and it is this surface that would be in contact with theenamel of the tooth.The main hypothesis tested in that study related tothe extent of carbon double-bond conversion under asignificantly larger obstacle (molar bands) than brack-ets. A previous study, using similar methods and cur-ing parameters for upper incisor steel brackets,showed a 68% DC for a dual-cured resin and a 48%DC for a light-cured resin.13 Although the resin man-ufacturers differed, the results of this study showed a25% DC (dual-cured resin) and 19% DC (light-curedresin), suggesting that the effect of a larger barrier isconsiderable and leads to a reduced conversion rela-tive to that obtained from brackets. The 55.3% DC ob-tained for the RMGI sample is significant comparedwith the resins, and this percentage also compareswell to previous findings that 33%–55% of doublebonds remain (45%–67% DC) after setting RMGI ce-ments.14 It could be implied that a favorable degree ofcure of RMGIs can be obtained under molar bands.The clinician must keep in mind that the method ofcuring cements under bands can affect the DC con-siderably,8 although the degree of cure affects the me-chanical properties of resins; no information is cur-rently available on degree of conversion’s effect onRMGI’s clinical performance.14The RMGI setting consists of an acid-base reactionaccompanied by a free radical polymerization reaction,and exposure of the cement to the curing light mayinhibit the acid-base reaction rate (which leads to theformation of the polycarboxylate salt cement matrix).14A study examining the efficiency of RMGI’s acid-basereaction has shown that the reaction was slowed bylight exposure, but Fuji II LC does exhibit an acid-basereaction and resultant salt formation. The study alsostated that there was little differences in top-surfaceand bottom-surface curing efficiency. This was attrib-uted to small specimen thickness and the relativelytransparent glasses used in modern RMGIs, which al-low higher levels of light transmittance.15 This may par-552 REJMAN, ELIADES, BRADLEY, ELIADESAngle Orthodontist, Vol 78, No 3, 2008tially explain the favorable DC of the RMGI in thisstudy.The Variolink II is also a dual-cure material, and finaldouble-bond conversion may differ from those mea-sured initially. A standardized backing was used for allthe samples, but it can be presumed that under clinicalconditions the enamel backing would differ in theamount of secondary illumination allowed.CONCLUSION• The degree of cure of the resin modified glass io-nomer under molar bands was significantly higherthan that of the two resins that were tested.REFERENCES1. Millett DT, Hallgren A, Fornell AC, Robertson M. Bondedmolar tubes, a retrospective evaluation of clinical perfor-mance. Am J Orthod Dentofacial Orthop. 1999;115:667–674.2. Millett DT, Hallgren A, McClusky LA, et al. A clinical retro-spective evaluation of 2 orthodontic band cements. AngleOrthod. 2001;71:470–476.3. Mizrahi E. Glass ionomer cements in orthodontics—an up-date. Am J Orthod Dentofacial Orthop. 1988;93:505–507.4. Eliades T. Orthodontic adhesive resins. In: Brantley WA,Eliades T, eds. Orthodontic Materials: Scientific and ClinicalAspects. Stuttgart, Germany: Thieme; 2001:201–219.5. Ewoldsen N, Demke RS. A review of orthodontic cementsand adhesives. Am J Orthod Dentofacial Orthop. 2001;120:45–48.6. Aggarwal M, Foley TF, Rix D. A comparison of shear-peelband strengths of 5 orthodontic cements. Angle Orthod.2000;70:308–316.7. Fricker JP. A 12-month clinical comparison of resin-modifiedlight-activated adhesives for the cementation of orthodonticmolar bands. Am J Orthod Dentofacial Orthop. 1997;112:239–243.8. Namura Y, Tsuruoka T, Shimizu N. Effects of different sizesof occlusal metal on curing depth of light cured orthodonticband cement. Am J Orthod Dentofacial Orthop. 2006;129:175.el–175.e5.9. Eliades T, Eliades G, Brantley WA, Johnston WM. Poly-merization efficiency of chemically cured and visible lightcured orthodontic adhesives: degree of cure. Am J OrthodDentofacial Orthop. 1995;108:294–301.10. Gioka C, Bourauel C, Hiskia A, Keletsas D, Eliades T, Eli-ades G. Light-cured or chemically cured orthodontic adhe-sives resins? A selection based on the degree of cure,monomer leaching, and cytotoxicity. Am J Orthod Dentofa-cial Orthop. 2005;127:413–419.11. Rueggeberg FA, Hashinger DT, Fairhurst CW. Calibrationof FTIR conversion analysis of contemporary dental resincomposites. Dent Mater. 1990;6:241–249.12. Eliades GC, Vougiouklakis GJ, Caputo AA. Degree of dou-ble bond conversion in light cured composites. Dent Mater.1987;3:19–25.13. Eliades T, Eliades G, Bradley TG, Watts DC. Degree of cureof orthodontic adhesives with various polymerization initia-tion modes. Eur J Ortho. 2000;22:395–399.14. Kakaboura A, Vougiouklakis G. Cements in orthodontics. In:Brantley WA, Eliades T, eds. Orthodontic Materials: Scien-tific and Clinical Aspects. Stuttgart, Germany: Thieme;2001:221–240.15. Kakaboura A, Eliades G, Palaghios G. An FTIR study onthe setting mechanism of resin-modified glass ionomer re-storatives. Dent Mat. 1996;12:173–178.

Polymerization Efficiency of Glass-Ionomer and Resin Adhesives under Molar Bands

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Polymerization Efficiency of Glass-Ionomer and Resin Adhesives under Molar Bands

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