Bond strength nd micro morphology of self-etching primer versus stndrd dhesive system with vrying etching times in primry teeth J.R. BOJ, A.M. MARTÍN, E. ESPASA, O. CORTÉS Astrct. Aims These were to firstly evlute the sher ond strength of composite resin to primry dentl enmel treted with stndrd dhesive system ut with vrying phosphoric cid etching times long with self-etching prime, secondly to nlyse the etching ptterns using SEM. Methods Forty primry molrs were used. In the first three groups, following cid etching, lyer of Prime & Bond NT dhesive ws employed, nd in group 4 the self-etching dhesive system (Prompt-L-Pop) ws used. A composite cylinder (Spectrum, Denstply, Germny) ws then pplied. After processing of the smples, the teeth were sujected to sher stress using n Instrom universl mchine. The study of primry enmel morphology fter etching for different time periods nd using different etching systems ws crried out with scnning electron microscope. Sttistics Dt were nlysed using one wy ANOVA, followed y Scheffé test to determine differences etween groups. Results In the groups sujected to cid etching for 5 nd 15 seconds significnt differences were recorded versus the self-etching group (p<0.0001). Regrding the SEM study of primry enmel morphology, there ws predomintely cler nd mrked type 2 etching pttern. Conclusions Longer cid etching times for primry enmel do not pper necessry, s 15 seconds suffice to otin retentive etching ptterns, nd the onding strengths otined with the trditionl etching technique followed y two-step dhesive ppliction re sufficient to ensure good composite resin onding to the enmel surfce. However, the self-etching dhesive system employed yields less thn optimum onding strength to primry enmel surfces. KEYWORDS: Bond strength, Enmel ptterns, Self-etching system. Introduction The use of resin sed restortive mterils hs incresed in recent yers thnks to improvements in the dhesive systems used. However, their ppliction to primry teeth my represent prolem, s primry nd permnent teeth show differences in enmel nd dentine morphology nd composition. One of the prolems with the use of these mterils in peditric dentistry is the working time needed. Erly studies indicted tht 2 minutes of etching time were needed in primry enmel to ensure good enmel ptterns. This time hs een chnged in susequent studies over the yers y different uthors. Nowdys mny reports stte tht etween 15 nd 30 Deprtment of Peditric Dentistry, Dentl School, University of Brcelon, Spin E-mil: ocortesl@infomed.es seconds of etching time would e enough for oth permnent nd primry enmel [Mzzeo et l., 1995; Megid nd Slm, 1997; Jumlongrs nd White, 1997]. An lterntive to reduce the totl working time nd the chnce of introducing errors during the dentl tretment is the use of self-etching primers, which void the rinsing nd the drying steps in the dhesion process [Fritz et l., 2001; Oerländer et l., 2001; Inoue et l., 2003]. In 1955 Buonocore introduced the cid etching technique, involving the ppliction of 30% phosphoric cid for 30 seconds, therey generting rough enmel surfce with microporosities tht cn e penetrted y the pplied dhesive resins [Perdigo et l., 1997; Kugel nd Ferrri, 2000; Ros nd Perdigo, 2000]. However, this technique, pplied to primry teeth, my not produce the sme effects, due to the greter thickness of the prismtic lyer in which the crystlline components of the enmel re distriuted in prllel nd perpendiculr to the surfce. EUROPEAN JOURNAL OF PAEDIATRIC DENTISTRY 4/2004 233
J.R. BOJ ET AL. Buonocore [1955] lso noted tht primry enmel is more resistnt to cid etching, nd in view of its chrcteristics could contriute to limited resin penetrtion, therey reducing the strength of restortive dhesive mteril onding to the primry tooth. At tht time, two minutes of cid etching of the enmel were recommended in such cses. However, recent studies show few significnt differences in the strength of dhesion etween primry nd permnent teeth. Thus, 15 seconds of cid etching seem to suffice for oth primry nd permnent enmel [Swift et l., 1995; Cehreli et l., 2000; Hosoy et l., 2000]. Acid etching induces importnt morphologicl chnges in the outer enmel lyers. The selective loss of tissue produces vriety of prismtic ptterns including the preferentil elimintion of orgnic nd inorgnic mteril from the center of the prisms nd their periphery. Glil nd Wright [1979] descried 5 cid etching ptterns following the exposure of humn dentl enmel to cid solutions: - Type 1 - etching pttern involving preferentil dissolution t the center of the prisms; - Type 2 - etching pttern involving preferentil dissolution t the periphery of the prisms; - Type 3 - etching pttern representing comintion of the previous two ptterns; - Type 4 - etching pttern in which the enmel shows jigsw, mp-like or network irregulrities; - Type 5 - etching pttern in which the enmel surfce ppers smooth nd level. The conventionl dhesive systems use three different gents: n enmel nd dentine conditioning cid, primer, nd n dhesive resin. An lterntive is offered y recently introduced self-etching dhesive systems. These simplify the dhesion process, eliminting the clensing nd drying step (criticl for the deminerlized mtrix), nd moreover shortening operting time nd reducing the possiility of operting field contmintion [Ferrri et l., 1997; Knc, 1997; Perdigo et l., 1999]. In ddition to the conventionl monomers such s 2- hydroxyethyl methcrylte (HEMA), these systems contin cidic monomers cple of etching nd penetrting the enmel simultneously. They fford n queous solution of phosphoric cid esters tht dissolve the superficil enmel nd dentinl zone, forming continuum etween the treted dentl surfce nd the dhesive mteril [ Bishr et l., 2001; Ty nd Pshley, 2001; Vn Meereek et l., 2001]. The im of the present study ws, therefore, to evlute the strength of dhesion of composite restortive mteril to primry enmel sujected to etching for different times (5, 15 nd 30 seconds) nd involving different etching nd dhesive systems: etching with 36% phosphoric cid followed y the ppliction of Prime & Bond NT dhesive (Dentsply, Germny) nd the new self-etching systems, Prompt L- Pop (ESPE, Germny) with n nlysis of the etching ptterns thus otined. Mterils nd methods Adhesion study. Forty primry molrs without cliniclly detectle structurl ltertions were used. The lingul nd vestiulr surfces of ech tooth were polished with discs (verge grin 5/8 nd fine grin 3/4) to reduce their convexity nd leve flt enmel re to e etched. The series ws divided into four groups of 20 working surfces ech: - Group 1 - etching with 36% orthophosphoric cid for 30 seconds; - Group 2 - etching with 36% orthophosphoric cid for 15 seconds; - Group 3 - etching with 36% orthophosphoric cid for 5 seconds; - Group 4 - single-step self-etching dhesive system for 15 seconds, following the instructions of the mnufcturer. Following cid etching, the smples in the first three groups were wshed for 10 seconds nd pressure ir dried for nother 10 seconds. A lyer of Prime & Bond NT dhesive ws pplied, followed y 30 seconds puse, then ir ws gently lown to dry nd the mteril polymerized for 10 seconds. A composite (Spectrum, Denstply, Germny) cylinder mesuring 4 mm in dimeter nd 3 mm in height ws then pplied. In the smples elonging to Group 4 the self-etching dhesive system (Prompt-L-Pop) ws pplied for 15 seconds, followed y drying until fine film ws otined, nd photopolymerized for 10 seconds. A composite (Spectrum) cylinder mesuring 4 mm in dimeter nd 3 mm in height ws then pplied. In order to simulte orl conditions, the prepred specimens were stored in distilled wter when not eing prepred or tested nd thermocycled for 500 cycles t 5ºC nd 55ºC with 30 seconds puse time. After processing of the smples, rtificil roots were prepred to llow inclusion in plster locks, leving only the crown with the treted surfces exposed. Sher ond loding test of ech composite resin cylinder until filure ws ccomplished using chisel shped lde, lined perpendiculrly with the cylinder of resin in n Instrom model 1011HIGH mchine t cross speed of 5 mm/minute. Sher ond strength ws clculted s the rtio of frcture lod nd onding re expressed in Megpscls (Mp). 234 EUROPEAN JOURNAL OF PAEDIATRIC DENTISTRY 4/2004
BOND STRENGTHS IN PRIMARY TEETH SEM study. This ws crried out with scnning electron microscope, employing 8 cries-free primry cnines lcking cliniclly detectle structurl ltertions. Ech cnine ws sectioned mesiodistlly nd longitudinlly, leving lingul nd vestiulr surfce. These surfces were in turn polished with discs (verge grin 5/8 nd fine grin 3/4). In order to evlute the etching ptterns, the smples were divided into four groups of four working surfces ech, followed y distriution of the groups s descried previously. After cid etching, the smples of the first three groups were wshed with wter for 10 seconds, nd pressure ir dried for nother 10 seconds. In Group 4 the self-etching dhesive system ws pplied for 15 seconds, followed y lcohol irrigtion to clen the surfce. An cetone lyer ws then pplied for 30 seconds to eliminte the dhesive, followed y pressure ir drying to llow visuliztion of the etching pttern creted y the cid monomers. The smples were coted with n electronconducting colloidl silver solution, dried nd vcuum spryed with gold. The specimens were then exmined under Hitchi 2300 scnning electron microscope, evluting the resulting etching ptterns ccording to the clssifiction of Glil nd Wright [1979]. Sttistics. Dt were nlyzed using ANOVA one wy, followed y Scheffé test to determine differences etween groups (p<0.05). Results Tle 1 summrizes the sher ond strengths (MP) otined for primry enmel tretment with 36% orthophosphoric cid t ech of the specified time periods nd using the self-etching dhesive system. The gretest strength corresponded to the group sujected to cid etching for 5 seconds with 36% orthophosphoric cid (26.4 MP), while the lowest vlue corresponded to the self-etching system (11.6 MP). The results considering the different 36% phosphoric cid enmel etching times were nlyzed y ANOVA one wy test nd no sttisticlly significnt differences etween groups were noted. Thus, the men dhesion strength otined in the group sujected to cid etching for 30 seconds ws 19.25 MP, versus 24.85 MP for the 15 second groups, nd 26.47 MP for the group sujected to etching for 5 seconds. Tking into ccount the cid etching system employed, it ws found tht the difference in dhesion strength etween the group sujected to etching for 30 seconds nd the self-etching ws not significnt. However, in the groups sujected to cid etching for 15 nd 5 seconds significnt differences were recorded versus the selfetching group. Regrding the SEM of primry enmel morphology, the smples sujected to 36% orthophosphoric cid etching showed Glil nd Wright [1979] type 1, 2 nd 3 etching ptterns, in the sme wy s the smples treted with the self-etching dhesive system (Fig. 1). However, in this ltter cse the resulting ptterns were more irregulr nd of lesser depth in some cses. The most frequently identified pttern corresponded to type 1. On the other hnd, on considering the influence of etching time, Figure 2 (corresponding to surfces etched for 30 seconds) shows cler nd mrked type 2 etching pttern t different mgnifictions, with cler dissolution of the periphery of the enmel prisms. The Glil nd Wright type 2 pttern likewise predominted in the specimens sujected to 36% orthophosphoric cid etching for 15 seconds, though in some cses type 1 imges were seen either lone or in comintion with type 5 imges (Fig. 3). Lstly, Figure 4 shows the pttern generted y 36% phosphoric cid pplied for 5 seconds. The most frequently oserved pttern gin corresponded to type 2, though we lso oserved types 1 nd 3, nd even some prismtic pttern imges. N Minimum Mximum Men ±SD Group 1 20 5.37 33.10 19.25 6.37 Group 2 20 8.12 40.72 24.85 8.53 Group 3 20 17.27 38.04 26.47 5.79 Group 4 20 2.34 37.37 11.63 7.73 Group 1 = 36% orthophosphoric cid - 30 seconds Group 3 = 36% orthophosphoric cid - 5 seconds Group 2 = 36% orthophosphoric cid -15 seconds Group 4 = single step self-etcing - 15 seconds TABLE 1 - Results of the dhesion strengths for different groups of primry teeth using self-etching or stndrd dhesive systems. EUROPEAN JOURNAL OF PAEDIATRIC DENTISTRY 4/2004 235
J.R. BOJ ET AL. FIG. 1 - Primry teeth smples processed with the self-etching dhesive system. Dissolution of the prism centres (type 1 pttern), in comintion with smoother zones (type 5), with scntly defined relief. ) Mgnifiction 1,500X; ) mgnifiction 1,000X. FIG. 2 - Primry teeth smples treted with 36% orthophosphoric cid for 30 seconds. ) Mgnifiction 1,500X; ) mgnifiction 3,000X. Discussion To study the sher ond strength of resin to enmel, the uccl surfce of premolr is usully used [Nör et l., 1997; El-Kll nd Grcí-Godoy, 1998]. As the present investigtion imed to study the sher ond strength to primry enmel, primry molrs were used. Due to the difficulty in otining sufficient molrs, it ws decided to use oth uccl nd lingul surfces of first nd second, mxillry nd mndiulr, primry molrs. The enmel surfces were polished to leve them flt nd for morphologicl conditions to e s similr s possile mong different surfces. It is generlly ccepted tht onding strengths of etween 17 nd 24 MP re required for permnent teeth to resist the forces generted y polymeriztion contrction or shrinkge. In our study the smples treted with 36% orthophosphoric cid for 5, 15, nd 30 seconds yielded dhesion strengths within the rnge considered dequte for permnent teeth. In the sme wy, Grcí- Godoy nd Gwinnett [1991; 1992] conducted dhesion tests with primry teeth, etching the enmel surfce for periods of etween 15 nd 120 seconds. No differences were oserved in the results otined not even on compring them with the results fforded y permnent teeth [Cost et l., 1998]. In turn, some uthors pulished similr results, no differences eing oserved etween phosphoric cid ppliction for 5 nd 30 seconds. Others likewise reported no differences etween 60 nd 240 seconds of etching [Grcí-Godoy nd Gwinnett, 1991; Gwinnett nd Grcí-Godoy, 1992]. Hosoy nd Goto, [1992] oserved tht smples etched for 10 seconds fforded greter dhesion strengths thn those etched for 20 seconds, though in contrst the specimens sujected to cid etching for 30 seconds exhiited the gretest onding strengths. In this study the smples processed with the self-etching dhesion system filed to yield the minimum onding strength required in the cse of permnent teeth, the men strength eing 11.63 MP (±7.73). Indeed, some of these teeth were rejected on the grounds tht the 236 EUROPEAN JOURNAL OF PAEDIATRIC DENTISTRY 4/2004
BOND STRENGTHS IN PRIMARY TEETH FIG. 3 - Primry teeth smples treted with 36% orthophosphoric cid for 15 seconds. ) Type 2 pttern, mgnifiction 1,500X; ) comintion of type 1 pttern, with cler dissolution of the prism centres, exhiiting smooth zones tht my correspond of type 5 etching pttern, mgnifiction 1,500X. FIG. 4 - Primry teeth smples treted with 36% orthophosphoric cid for 5 seconds. ) Cler type 2 pttern, with peripherl dissolution of the enmel prisms, mgnifiction 1,500X; ) scntly defined type 1 etching pttern, with peripherl dissolution of the enmel prism centres, mgnifiction 1,500X. composite cylinders detched spontneously without the ppliction of forces of ny kind. Our results coincide with those of other uthors who found the self-etching systems to fford poor performnce compred with the conventionl dhesion systems used for onding resintype composites nd compomer in oth primry nd permnent teeth [d Silv Telles et l., 2001; Agostini et l., 2001; Pshley nd Ty, 2001]. However, ccording to other studies these self-etching dhesive systems represent good lterntive, s they reduce the numer of required tretment steps versus the trditionl systems tht involve seprte cid etching nd dhesive ppliction procedures [Hnnig et l., 1999; Perdigo et l., 1999; Kden et l., 2002]. On the other hnd, the required durtion of cid etching of primry teeth is suject to controversy. A numer of studies hve used different etching times in n ttempt to produce dequte etching ptterns in primry enmel, vrying from 240 to 15 seconds [Grcí-Godoy nd Gwinnett, 1991]. In this study the 5 cid etching ptterns descried y Glil nd Wright [1979] were identified nd recorded more or less defined porosity ccording to the type of tretment used. The type 2 pttern predominted in the smples treted with 35% orthophosphoric cid for 5, 15 nd 30 seconds, with prior polishing of the enmel surfce, in coincidence with the oservtions of Cost et l. [1998], in which peripherl enmel prism dissolution ws the most frequent pttern ssocited with cid etching for 10, 20 nd 60 seconds. Likewise, Hosoy nd Goto [1992] found the type 2 pttern to e the most prevlent in primry teeth, regrdless of the durtion of cid etching or the tooth re treted. Other uthors, however, hve reported predominnce of the type 1 pttern fter 30, 60, nd 120 seconds of cid etching, while the type 2 pttern hs een fundmentlly ssocited with 15 seconds of cid tretment [Tndon et l., 1989]. In the cse of the smples treted with the self-etching dhesive system, type 1 nd type 2 etching ptterns were recorded, though the results were less uniform thn in EUROPEAN JOURNAL OF PAEDIATRIC DENTISTRY 4/2004 237
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