Pattern of Wear in Posterior Composite Restorations R. P. Kusy and K. F. LEINFELDER
Dental Rcsearch Centcr, Univcrsity of North Cruolina School of Dentisli-v, C hapc 1Hill, At oaith Carolina, 27514, USA Clinical evaluation of posterior restoratixe materials has showIn that wear proceeds at a mulch faster rate in coniposite resins than in amal"ams (PHILLIPS et al, J Prosth Dent 26:68. 197 1 28:164, 1972; LEINFELLDER et al, J Prosth Dent 33:407. 1975). With thc recent dexelopment of in vixo replication techniquies (e.g., TAx et a, Brit Dent J 137:463, 1974). wear patterns may be StUdied with the aid of the SEM. The purpose of the present iiote is to describe the Pattern of wear of posterior coinposite r estoratioris throrl'h tIre LISC of c nox0cl tWO-Stagel' Fr'e)p lication technique. C(ormcposite restoratiorns hic h hicac beuI llace'd uinder clinic ally controlledcl ocnlitiolus tiP to four vears ago were relilicated in xixvo corin" Xantopren BlcreU for both the negatix e imupressions arid the ptositixe replicas (R. P. Kusy and \fter preK. F L iNFiiDFoRn.tonprnlblishedc coatin" the seclond-stao'e replica witli carbon. Au-PcI was deposited prior to observation witth the SEM.t Lsing an acceleratin- xoltce,'e of 2. 5 KV, condens-i ctirrert of 0.7-0.9 anipj). anJ a work-iug distainc of cLa 20 nmn, the c ciriccsl-t 's wea.r Wcrs stulic;'c. Results (Flig' 1a) after thri vears of serice show that the wvear pattern foiris a hr oacl plane across iIIost of the restoration bccaurse of a This investigation was sLippcrted by NIHI Grant DE02668 from the Nartional lIistiticte of Denta/l Research and by NIH Grant RRt-05333 from the Divisioni of Research Facilities aind ResouLrces. Received for pLIIcrCierion Jtine 2.5/1976. Accepted focr ptiL/cicatlon Aoigirst 6, 1 976. Unitek Corporation, Monrovia, Ca. ETEC U-1 Atciroscan, Hayward, Ca
generalized loss of suibstance. The stirface of the restoration, howexTer, cutrves up slightly as it cointaets the exposed walls of the original cavitv preparatiori. This con avxe nienisicoid jinc tiorn l)robably resuilts from the inalbilitx of occlusal forues (via the food bolois) to contact the caxity wall and fiorn the struntt-ral rcinfofreicrent iffordeci bv the wall itself. At hi-her nra- nification (Fig 11) mia-ny of partioles of the dispensed p)hase may lie Setl protiud1ilg frorll the stUr&face. As thL matrixi contirtucs to wear awayv the abrasion resistarit partic les becorme soAffic centl exIpos d so tisto ( auLse their exfoliation. That these bar l)artirlcs do not xxwear away" can hbe s"ern b)v the shiarp) airUlatioris p)scscit on the expsciscd otrflacrs. a cof a Froii-n th}e,si, ob sxvationli. We'lliprfile ?osterior
xhh b a rIdIlu bOXVss i*re--olitr oef rhol rc'toitlorll ( t) is followed by thle sxstseu tic ftrrrmation of a cep cllerrscsionr t,). rlhe cii .s lnt xicxspoint Lx oci irs is that th.i x'ai tWhirri me'haniisilv filtie -Lt fi ulri tI-lc gnceriition of fine cracks at loi alzecl stiess corc < n/trationC c t ecl lix thn 111 tiecl of teith duiillileras;c.ltconl and frorli ten sil? stress>.s lietw'ecci the nicatrix arind filler lx lir,ce differeinc- iM thie thoecinaI exintaiatecl parsion co ec fiiint s. De,sl)ite gond adhesion between the txxcc phases. enitire particles of filler )1eak loosi as cither the pairticle-niatrix int r Dfacc or thc Thna1triX in close proximity to the anatlrationus of tlhte clispersed plhase fails (cf,Irrer xx s Fracture o Poly ci7ers. Elsex er. 'ex \ )ork, PI -13 -151.. 19611). CtLrrret laboratorv tests dlo not adlc'qiratelx riprescnt tlrt .c ttral c linical service reqtiirements xshich corinpolite rcsiris irctist niret.
FIG Wear pattern in a posterior composite restoration: (a), electron ruci.ro-raph of exposed tooth wall (arrows) between worn composite (C) and original enamel surface (E); (b), protrusion of particles through eroded matrix; (c), schematic illuistration of wear as a function of time (ca 4 years, t, [--I to t, [...]). Curtature of plane is dependent upon opposing occlusal contacts.
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