Fracture of Human Dentin: A High Resolution Scanning Electron Microscope Study MYRON SPECTOR and SANDRA E. TAYLOR Biological and Physical Sciences, College of 1ental Medicine, ledical University of South Carolina, Charleston, South Carolina 29401, USA Previous stuidies have used scanning electron micioscopy to examine featuires of the letitinal fiactute sulrfacc (BOYDE anI(I LrSTER, Cailcif Tis
suce les 1: 122-136, 1967; RENSON El Al, A-hli Orail Biol 19: 447-454, 1974) . Thtese studlies hiave slhown the isotropic char-acer of dentin suibjectcl to betndItig and totrsionial failure. '1'he purpose of the present study was to use highl resoltution scanning electron microscopy to reveal ultrastrtuctutral features of tire (etiti nal fiactui-e stit-face that might provi(de some insighit inlto the failure mechanism. Ilcitan noncarious teethi obtained( fh-om stirgery vere immediately placed into cacolylate
bl)ffer or 10% cacodlylate-buffered glritaral(-l hiyde. The teeth were par-tially embedded in hfygon tray acrylica andI sectioned on a pr-ecision sawv wvitih a cliamotrd( wafer blade. 1-he teethi were kept nioist thIroughiouit the procedure. Twv hundred-micrometer (,um) thick sectionis of dlentini wer-e then fracture(d by benching while in btIffer at room teinpej-attri-e or- delhlydr-atedI in etiranol and fractured in liquid niti-ogen. Tire ioom temperature-fractured sections xsere fixeri in glutar aldellyde and dlehydrated in ethianol. All sectionis were air dried from absolute etlhanol and examine(d in a scanning electi-on microscope,' The surface of specimens fractured at room MIs. Tavlsor's work iti this insestigation ssas supported, in part, by National Institutes of Healtlh Contract No.
72-4371. Received for pubtlication October 23, 1975. .Xccepted for putblication April 2, 1976. Hygienlic IDerntal Manufacturing Co., Akroni, Ohio. Coates and Welter scanning electron microscopc (50 A resolution) Sunnyvale, Calif.
temper attire consistedI of (liscrete fibers protrudinrg from tIre (lciitiir at all airigles (sirrgle ar-owss in Fig I anti inset) Tie fibers sv-ci abotrt 600 A in (liameter antI tircir appearance was coInsistent witlr the collagen fiber-s seen in transmissioni celctr-on microscopy (TEM) (JOtHANSEN and1C PARKS, Archl Oral Biol 7: 185-193, 1962). The surfaces of specimens fractured along planes parallel and perpendicuilar to the tribules were similar. Groovelike featutres andl hloles produce(d I)V tir ptrllouLt of fibeisI flom the (lenti- wer-e al.so ob))served in thie fractrir-e strrface (dotrble at roivs in Fig 1) TI-re perittLibtla- zone of tire ilerltiii appr-oximately 0.5 pum thiick was (listinguishecl by th:e marke(d (limiirrrtioni of protiriitug tibers or grooves. Conisi(ler-ing dentin as a collagen fiber-reinforced composite, tIre fi-actiro-e surface clrsplayed a I)r ittle failLir-e of the mineral matrix accotnpierictl lby fiber pullotit (BROUc I NIAN ar(i KROCK, Comtiposite Mater ials V'ol 5, 1974, p 109) This failture mode wsotlcl indicate that the fibernsatrix ptrllorrt strength is less than the tensile strength of the collagetr fibers. Assuming the pr-esenlce of fibrils in the peritublilar r-egion as inldicated by TEM (JOIrANSEN and PARKS, 1962), tire r-elatively smooth fracttrre of the peritubular lentini suggests a str-onger fiber-matrix couipling orsnveaker fibers in ttins hypermineralizecl zone. 'I'he puillorit type of fracture in Figure I 'was compated with a dentinial fracture produced uincler conditions designetI to generate a solely brittle failutre (Fig 2) In thiis instance, the fractulre sur-face mvas relatively smoothi witth tie peritubular zone indistinguishable fr om the
intertLubular dentin. UltrastluctlCral featLures of the clentinal fractti-e suIr-face sk-ere conisistent bvith a pullout-type
of failtire mechaniism.
FIG 1.-Scanning electron micrograph of dentin fractuired in buffer at room temperature. Collagen fibers (single arroNvs and inset) and lholes and grooves (double arrows) produced by fiber pullout can be seen in fracture surface.
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FlI 2.-Scanning clectr-oni mic-ograph of dentiir fixed in glutaraldehyde, dehydrated in ethairol, aniI fracturrel ins licjuid nitrogen. J Dent Res November-December 1976, Vol 55 No. 6 Downloaded from jdr.sagepub.com at UCSF LIBRARY & CKM on March 24, 2015 For personal use only. No other uses without permission.
suce les 1: 122-136, 1967; RENSON El Al, A-hli Orail Biol 19: 447-454, 1974) . Thtese studlies hiave slhown the isotropic char-acer of dentin suibjectcl to betndItig and totrsionial failure. '1'he purpose of the present study was to use highl resoltution scanning electron microscopy to reveal ultrastrtuctutral features of tire (etiti nal fiactui-e stit-face that might provi(de some insighit inlto the failure mechanism. Ilcitan noncarious teethi obtained( fh-om stirgery vere immediately placed into cacolylate
bl)ffer or 10% cacodlylate-buffered glritaral(-l hiyde. The teeth were par-tially embedded in hfygon tray acrylica andI sectioned on a pr-ecision sawv wvitih a cliamotrd( wafer blade. 1-he teethi were kept nioist thIroughiouit the procedure. Twv hundred-micrometer (,um) thick sectionis of dlentini wer-e then fracture(d by benching while in btIffer at room teinpej-attri-e or- delhlydr-atedI in etiranol and fractured in liquid niti-ogen. Tire ioom temperature-fractured sections xsere fixeri in glutar aldellyde and dlehydrated in ethianol. All sectionis were air dried from absolute etlhanol and examine(d in a scanning electi-on microscope,' The surface of specimens fractured at room MIs. Tavlsor's work iti this insestigation ssas supported, in part, by National Institutes of Healtlh Contract No.
72-4371. Received for pubtlication October 23, 1975. .Xccepted for putblication April 2, 1976. Hygienlic IDerntal Manufacturing Co., Akroni, Ohio. Coates and Welter scanning electron microscopc (50 A resolution) Sunnyvale, Calif.
temper attire consistedI of (liscrete fibers protrudinrg from tIre (lciitiir at all airigles (sirrgle ar-owss in Fig I anti inset) Tie fibers sv-ci abotrt 600 A in (liameter antI tircir appearance was coInsistent witlr the collagen fiber-s seen in transmissioni celctr-on microscopy (TEM) (JOtHANSEN and1C PARKS, Archl Oral Biol 7: 185-193, 1962). The surfaces of specimens fractured along planes parallel and perpendicuilar to the tribules were similar. Groovelike featutres andl hloles produce(d I)V tir ptrllouLt of fibeisI flom the (lenti- wer-e al.so ob))served in thie fractrir-e strrface (dotrble at roivs in Fig 1) TI-re perittLibtla- zone of tire ilerltiii appr-oximately 0.5 pum thiick was (listinguishecl by th:e marke(d (limiirrrtioni of protiriitug tibers or grooves. Conisi(ler-ing dentin as a collagen fiber-reinforced composite, tIre fi-actiro-e surface clrsplayed a I)r ittle failLir-e of the mineral matrix accotnpierictl lby fiber pullotit (BROUc I NIAN ar(i KROCK, Comtiposite Mater ials V'ol 5, 1974, p 109) This failture mode wsotlcl indicate that the fibernsatrix ptrllorrt strength is less than the tensile strength of the collagetr fibers. Assuming the pr-esenlce of fibrils in the peritublilar r-egion as inldicated by TEM (JOIrANSEN and PARKS, 1962), tire r-elatively smooth fracttrre of the peritubular lentini suggests a str-onger fiber-matrix couipling orsnveaker fibers in ttins hypermineralizecl zone. 'I'he puillorit type of fracture in Figure I 'was compated with a dentinial fracture produced uincler conditions designetI to generate a solely brittle failutre (Fig 2) In thiis instance, the fractulre sur-face mvas relatively smoothi witth tie peritubular zone indistinguishable fr om the
intertLubular dentin. UltrastluctlCral featLures of the clentinal fractti-e suIr-face sk-ere conisistent bvith a pullout-type
of failtire mechaniism.
FIG 1.-Scanning electron micrograph of dentin fractuired in buffer at room temperature. Collagen fibers (single arroNvs and inset) and lholes and grooves (double arrows) produced by fiber pullout can be seen in fracture surface.
1136
FlI 2.-Scanning clectr-oni mic-ograph of dentiir fixed in glutaraldehyde, dehydrated in ethairol, aniI fracturrel ins licjuid nitrogen. J Dent Res November-December 1976, Vol 55 No. 6 Downloaded from jdr.sagepub.com at UCSF LIBRARY & CKM on March 24, 2015 For personal use only. No other uses without permission.
