Incremental Lines in the Dentin of Alligator Teeth before and after Hatching

Transcription

1 Nihon Unill. ]. Oral Sei. 28 : , 2002 Incremental Lines in the Dentin of Alligator Teeth before and after Hatching Takashi Ozaki, Hiroyuki Mishima, Ruth M Elsey* Department of AnatomyIT Nihon University Schoolof Dentistry at Matsudo Matsudo, Chiba , Japan "Fur and RefugeWildlife Biologist,LouisianaDepartment of Wildlife and Fishers, RockefellerWildlife Refuge Grand Chenier, Louisiana, 70643, USA (Director: Prof. Yukishige Kozawa) mississippien- Key words: dentin, incremental line, hatching, Alligator sis Abstract: The present study was designed to examine the differences of the incremental lines deposited in the dentin of alligator (Alligator mississippiensis) teeth before and after hatching. Before hatching, the incremental lines were uniform, and their average width was 4,um. After hatching, incremental lines of three types of periodicity were observed in the dentin of the decalcified tooth specimens. The average width of short-period incrementallines was 4,um (Lrday interval). The average width of intermediate-period incremental lines was 53,um (approximately 14-day interval), but these lines were poorly defined. The average width of long-period. incremental lines was 107,um (approximately 2S-day interval). In ground sections of tooth specimens after hatching, incremental lines of three types periodicity were observed in the dentin. The average widths of short-period, intermediate-period and long-period incremental lines were 12,um (2-3 days interval), 56,um (approximately 14-day interval) and 112,um (approximately 28-day interval), respectively. Darker, wider and less calcified incremental lines were observed in a lunar cycle of approximately 28-day intervals. The lunar incremental lines (28 days) are due to the rhythmic deposition of minerals and organic matrix. Although the semi-lunar incrementallines (14 days) are caused by the rhythmic deposition of minerals and organic matrix, they strongly depend on the mineralization. The in- _fradian incremental lines (2-3 days) are due to the rhythmic deposition of minerals. The circadian incremental lines (daily) are based on the rhythmic deposition of organic matrix. The intervals of incremental lines may reflect the rhythm of the odontoblast function and the fundamental biorhythm of the animals. Matsudo, Chiba , Japan (Received 18 March, 2002/ Accepted 10 May, 2002) 143

2 Nihon Uniii.]. Oral Sci. 28 : , 2002 t; l!"1! tdj>t., If t.,* v;; $l! J% tlfflt ~ 1 b 5b Ruth M Elsey* B**~rtpm~lm m II MffiJ~~~ o~~7~3-.tt~.~w N1~7~m~ 'f- - '7 - t : ~;f~, P..lH~:~, Wf1t, Alligator mississippiensis JHi : llfii~f[jj{o)~;f~~;:.tn,'-c, fflim't1o)~t:t ~P..lG~~;b;~'S- ~ n,.:co)idp..lg;!~\ui*~;:""? ~,-clii'!l < ij>i? ~ffi1liij;iv ~ 0 L..iJ>L.., OOER!JatI:XrO)~;f~0)P..lG~~~;:OO9 ~ ~15fiY~~;: C c'~"?-c~'~o C < ~;:, Wf1tMO)~ER~0)~;f~0)P..lG~~~;:OO9~gC~lit:tPo.:c'::l' *1Vf~li, '7 =-~:a:"lh'-c, Wf1tM cwf1t1& c~' -) ~m~1tf;:~lt ~P..lG~*,Jj.!O)fflIM't1I;:~ "'ij;1:.t: ~ ij>c-)ij>~t-t L.., ~ i? 1;:P..lG~~0)fflIM't1O)~P..lG;!~\MI*~;:""? ", -C~~ :a:1ja;z tc; ffl~'t.:;f;t*,hi, 7.J.1)JJ71) 7-?'- (Alligator mississippiensis) O)Wf1tMO)llElm.&UWf 1t1&0)@]f;$:l' iv~ 0 ~f-+vi r:p't1* }v7 1)/' I;: -C1BJ5:E1~,ImERtJ*& U1VfIli~H~*c L. -C1'F~ L..t.:o ImERtJ*vi~7 r:f-v1) /,.:r..;:>fy/, (H-E) ~1S.&U~T17/'0)70j"-1 /'~U~ ~~.L..komER'&lf1Vf *~*~~ ~-C.~L.., P..lG~.O)fflIM~@.m~V~j" J.,.. f;: -C IT~U L..t:0 Wf1tMO)~;f~vU3~' -Cvi, f,!ijmrdj~ij'~i$j 4 f..lm O)*'Hi.pt:tP..lG~~iJ'.~~ nt.:owf1t1~ O)~;f~v;::lOp-C vi, ImERtJ*f;: J: ~.~-C-vi, 3 fi~o)f,!ijm't1o)~t:t ~P..lG~*,Jj.!iJ'.~~ n ts; *'Hip~'fflIMO)P..lG~~li, rl'l~j!;ij'~i$j4 u tt: l'iv"? te;.::o)*'hij't:tp..lg~~li, -13 fflimo) P..lG~~c~5:E~nkor:pmMO)P..lG~~~~i$J~f..lmO)OO~l'iV~, ~14l3mMO)to)l' iv"?t.:o ~mmo)p..lg~~vi~i$ji07f..lmo)rl'l~~l'iv~, ~28I3ffl1Ml'iV"?t.:o 1VfmtJ*~;: J: ~ll!~l'kt, *'HiJ't:tffllMO)P..lG~~O)rl'l'~vi~i$J 12 f..lm O)rl'l~~l'iV ~, ~ 2-3 I3ffl1M, r:p fflimo)p..lg~.vj:~i$j 56 f..lm O)rl'l~~l'~ D, ~ 14 BfflIM, ~fflimo)p..lg~.f;:l:1fli$j112 f..lm 0) OO~l'iV~,~~l3ffl1Ml'iV"?ko~mMO)P..lG~.~m~J:~ l'ivd,.~<, J:~ fj EER1t c ffe5:e~ nko '::ni?o)~~~i?,*ffi1li~-c-~*o)r~r~c~i?n~o L ftji!ilmo)nlg~. ( -J28 B Ji!ilM) fj:;lj!;~':&ln5erfto) jliij'11fo)~nlg:mtm1):;( J" '''C"jf~MG~ n s, 2. r:pmmo)p..lg~. (~14BfflIM) vi~~ceerftv;:j:~idp..lg1):;(j.,..o)-)is, EERfttt f:b's$ < ~W tt n~0 3. ~fflimo)p..lg~. ( -J2-3 BfflIM) fj:eer1to)i):;(j"l'~p..lgttn~0 ~ -BfflIMO)P..lG~.~~~O)tt f~.o)1):;(j.,..l'~p..lg~n~o 5. Wf1tMO)~;f~l'lj:-13 fflimo)p..lg~.t.: ft;b;t :te9 ~ 0 6..::n i? O)P..lG~~O)mMvi~;f3f*'HJlf~lO)$,t1O) 1):;(J.,..c ii.j!jo/jo)~*i Jt:t)\ -1 ;:>f1):;( J.,.. O)mli~fflR:~~O)~~~ttn~o Introduction The various types of incremental lines in mammalian dentin have been debated for many years 7-11,21-2S). The short-period incremental lines or von Ebner lines are considered to be daily markings indicative of circadian rhythmsl ). Klevezal'?' showed that the annual growth layers were the first rhythmic order in mammals, the monthly layers were the second order, and the daily or circadian layers were the third order. Ohtsuka and Shinoda"? found that the circadian increments and the ultradian increments coexisted in rat incisor dentin. However, there are few reports on the shortperiod incremental lines and long-period incremental lines in the dentin of the alligator teeth (Alligator mississippiensis) after hatching!". Also, there is little information on the incremental lines in the dentin of the alligator teeth before hatching>". Furthermore, there is no unified viewpoint about the incremental 144 I!., ~

3 Ozaki et al. : Incremental Lines in the Dentin of Alligator Teeth (N=2) and 1'0 years (N=2). Wild alligators reach sexual maturation at approximately 10 years old. The teeth of specimens were fixed in 10 % neutral formalin solution. After fixation, the teeth were ground parallel to the longitudinal axis. The ground sections (80 to 100,um thick) were observed by light microscopy and confocallaser scanning microscopy. Some of pre - and post-hatching specimens were decalcified with 10 % EDTA (ph 7.4). The decalcified sections (4,u m thick) were stained with hematoxylin and eosin (H-E) staining and Bodian protein silver impregnation. Chronological analysis was made by counting the number of incremental lines and measuring the widths of adjacent incremental lines using an image processing system (Win Roof, Mitani Co., Japan) equipped with a light microscope (Olympus AX80). lines before and after hatching. The present study was designed to examine the differences of the incremental lines before and after hatching and the periodicity of the short-period and long-period incremental lines. Materials and Methods Embryos of alligators (Alligator mississippiensis) before hatching (N=10) and alligators after hatching (N=4) were used in this study. The embryos ages were 42 (N=2), 48 (N=2), 54 (N=2), 60 (N=2) and 66 days (N= 2) of incubation (Ferguson's embryological stage 23-28)5). Ferguson's embryological stage bases on the morphology of embryo. These embryos were collected from eggs gathered from nests in the marshes of the Rockefeller Wildlife Refuge, Louisiana, USA. The alligators after hatching were collected from the Atagawa Tropical and Alligator Garden, and the ages of the specimens were approximately 4, -3 Fig.2 Micrograph of a d~calcified section of Al/igiltor rnississippiensis at 48 days of incubation. Stage 24. Narrow incremental lines (arrows) are observed in the dentin. Hematoxylin and eosin staining. 8ar=20,um. Fig.1 Micrograph of a decalcified section of Alligator mississippiensis at 42 days of incubation. Stage 21. Two incremental lines (arrows) are observed in the dentin. Hematoxylin and eosin staining. 8ar=20,um. 145

4 Nihon Univ. ]. Oral Sci. 28 : , 2002 Fig.4 Micrograph of decalcified section of Alligator mississippiensis at 60 days of incubation; Stage 27: Narrow incremental lines (arrows) are. observed uniformly in the dentin. Hematoxylin and eosin staining. Bar=20 }1m. Fig. 3 Micrograph of a decalcified section of Alligator mississippiensis at 54 days of incubation. Stage 25. Narrow incremental lines (arrows) are observed in the dentin. Hematoxylin and eosin staining. Bar=20 }1m. Results After 42 days of incubation, (embryological stage 23), two incremental lines (arrows) were observed in the dentin of decalcified sections (Fig. 1). The width of the incremental lines was 4.47±0.74,um. At 48 days of incubation (embryological stage 24), the incremental lines were observed in the dentin (Fig. 2)_The width of the incremental lines was 4.33±0.56,urn. At 54 days of incubation.(embryological stage 25), the incremental lines were also observed in the dentin (Fig. 3) at a width of 4.11 ± 0.22,u m. After 60 days of incubation (embryological stage 25), narrower incremental lines (arrows) were observed uniformly in the dentin (Fig. 4), and the width was 4.01 ±0.46,urn. After 66 days of incubation (embryological stage 28), narrower incremental lines (arrows) were observed in the dentin in crown formation stage of tooth development (Fig. 5). The width of the incremental lines was 3.51±0.78,um. In the Fig. 5 Micrograph of a decalcified section of Alligator mississippiensis at 66 days of incubation. Stage 28. Narrow incremental lines (arrows) are observed in the dentin. Crown formation stage of tooth development. Hematoxylin and eosin staining. Bar=20,um. specimen of same day, narrow incremental lines (arrows) were also observed at the root formation stage of tooth development (Fig. 6), and the width of the incremental lines was 3.72 ± 146

5 , :'.,"..,, Ozaki et at. : Incremental Lines in the Dentin of Alligator Teeth ;.'" e Fig. 6 Micrograph of a decalcified section of Alligator mississippiensis at 66 days of incubation. Stage 28. Narrow incremental lines (arrows) are observed in the dentin. Root formation stage of tooth development. Hematoxylin and eosin staining. 8ar=20 Ilm. Fig.8 Micrograph of a decalcified section of Alligator mississippiensis: After hatching. 4 years old: functional tooth. Incremental lines of three kinds of periodicity are observed in the dentin.'! : long-period incremental lines, 2: intermediate-period incremental lines, 3: short-period incremental lines. Hematoxylin and eosin staining. 8ar=100 Ilm. measured by Bodian protein silver impregnation was 3.50±0.39.um.,. After hatching, incremental lines of three kinds of periodicity were observed in the dentin in decalcified sections of the functional tooth from an approximately 4 year-old alligator (Fig. 8). The width of the long-period incremental lines was ±4.71.um. The intermediate-period incremental lines were weakly stained, with a width of 50.77±4.99.urn. The width of the short-period incremental lines was 4.24±0.47.um. At the same age, incremental lines of two kinds of periodicity were observed in the dentin of tooth germ (Fig. 9). The widths of the long-period and shortperiod incremental lines were ± zzm and 4.74±0.72 zzrn. At approximately 10 years old, incremental lines of three kinds of periodicites were observed in the dentin of decalcified sections of the functional tooth (Fig. 10). The width of the long Fig.7 Micrograph of a decalcified section of Alligator mississippiensis at 66 days of incubation. Stage 28. Narrower incremental lines (arrows) are observed in the dentin. Root formation stage of tooth development. Bocian protein silver impregnation. 8ar=20 Jim um. The narrow incremental lines were more clearly observed using Bodian protein silver impregnation compared with H-E staining (Fig. 7). The width of incremental lines 147

6 Nihon Univ. io-«sci. 28 : , 2002 "'" J' Fig. 11 Micrograph of a decalcified section of Alligator mississippiensis. After hatching. 10 years old: functional tooth. Incremental lines of three kinds of periodicity are observed in the dentin. 1 : long-period incremental lines, 2: intermediate-period incremental lines, 3: short-period incremental lines. Bodian protein silver impregnation. 8ar=100,um. b Fig.9 Micrograph of a decalcified section of Alligator mississippiensis. After hatching. 4 years old: root formation stage of tooth germ. Incremental lines of two kinds of periodicity are observed in the dentin. 1: long-period incremental lines, 2: short-period incremental lines. Hematoxylin and eosin staining. 8ar=100,um. Fig.12 Micrograph of ground section of Alligator mississippiensis. After hatching. 10 years old: functional tooth. Incremental lines of three kinds of periodicity are observed in the dentin. 1 : long-period incremental lines, 2: intermediate-period\ incremental lines, 3: short-period incremental lines. 8ar=100,um. were weakly stained. The width of the intermediate-period incremental lines was 53.70±3.88,um. The width of the short-period incremental lines was 5.54±O.64,um with H-E staining. Narrow incremental lines were more clearly observed using Bodian protein silver impregnation than with H-E staining (Fig. 11). By Bodian protein silver impregnation, the widths of the short-period incremental lines, intermediate-period, and long-period incremental lines were 3.43±O.53,um, 53.98±2.75,um and ±5.85 zzm, respectively. The width of the short-period incremental lines of ground section was wider than that of the decalcified section (Fig. 12). Using ground Fig.10 Micrograph of a decalcified section of Alligator mtsstssippiensis. After hatching. 10 years old: functional tooth. Incremental lines of three kinds of periodicity are observed in the dentin. 1: long-period incremental lines, 2: intermediate-period incremental lines, 3: short-period incremental lines.hematoxylin and eosin staining. 8ar=100,um. -period incremental lines was ±8.19,um. The intermediate-period incremental lines 148 J

7 Ozaki et at. : Incremental Lines in the Dentin of Alligator Teeth sections, the widths of the short-period, intermediate-period, and long-period incremental lines were 12.04±3.19,um, ± 1.82,um and ±8.17,urn, respectively. Discussion Before hatching, the incremental lines were uniform and the average width of these lines in the dentin was 4.02,um in the decalcified sections. In mammals, daily incremental lines or circadian incremental lines are formed in the dentins-io ).this periodicity reflects the daily rhythmic deposition of organic matrix in dentinl.s.13.16,23).dean et al." reported that the ameloblasts secreted an enamel matrix in a circadian manner. Ohtsuka et al. IS ) demonstrated that odontoblasts showed a circadian rhythm with regard to collagen synthesis and secretion. After hatching, incremental lines of three kinds of periodicity were observed in the dentin of decalcified tooth sections. The average width of short-period incremental lines was 4.34,urn. From the width, the short-period incremental lines are identified to have a circadian rhythm, similar to the incremental lines before hatching I6,20). The average width of intermediateperiod incremental lines was 52.81,um. Rosenberg and Simmons"? reported that an infradian rhythm might also exist in rabbit incisor dentin. In Eurasian lynx (Lynx lynx), the mean period of the layer formation was days (semilunar cycle)". From our previous study"? arid the average width of the circadian incremental lines, the period of formation of the intermediate-period incremental lines was judged to be approximately every 14 days. The average width of long-period incremental lines was ,um. From our previous study"? and the average width of circadian incremental lines, the period of formation of the long-period incrementallines was judged to be approximately every 28 days as in the lunar cycle. The incremental lines with a periodicity of approximately 28 days were intensely stained by hematoxylin.. Using ground sections, the incremental lines in the dentin of tooth after hatching were estimated to have periodicities of 2-3 days (average width; 12.04,um), approximately 14 days (average width; 56.11,um), and approximately 28 days (average width; ,urn). Klevezal and Kleinenberg'" reported that the incremental lines in the dentin in some animals were formed at monthly periodicity. Kasuya'" reported that the shorter cycle in the fetus of the Baird's beaked whale was a day cycle resembling the lunar cycle. The optical differences between the principal bands of a growth layer are determined by differences in the content and distribution of the mineral component of the dentin". The lunar cycle reflects a genetically controlled physiological rhythm". Darker, wider and less calcified incremental lines were observed following a lunar cycle at intervals of approximately 28 days!", The formation of incremental lines in dentin is determined not only by the change in the deposition of mineralization but also by the change in the deposition of organic matrix'", From the results of the ground and decalcified sections, the lunar incremental lines (approximately 28-day interval) are due to the rhythmic deposition of both minerals and organic matrix. The results of the decalcified sections show that the rhythmic deposition of the semi- Moon's age o o new moon mineralization + organic matrix 14 full moon mineralization> organic matrix 28 0 new moon (day) mineralization + organic matrix : rhythmic deposition of organic matrix (daily) ---: rhythmic deposition of mineralization (2-3 days apart) Fig.13 Periodicity of incremental lines. Before hatching, the incremental lines in the dentin are uniform and have a daily rhythm. The average width of these lines in the dentin is 4.02 J1 m. After hatching, incremental lines of four kinds of periodicity are observed in the dentin. 149

8 Nihon Univ. f. Oral Sci. 28 : , 2002 the animals. lunar incremental lines (approximately 14-day interval) strongly depends on mineralization. This opinion supports the hypothesis that the rates of collagen matrix production and collagen mineralization may be relatively independent!", The results of the ground sections show that the infradian incremental lines (2-3 days apart) are due to the rhythmic deposition of mineralization, while the results of the decalcified sections indicate that the circadian incremental lines are caused by the rhythmic deposition of organic matrix (Fig. 13). The rhythm of matrix formation may not correspond to the rhythm of the mineralization'y". The intervals of incremental lines may be related to the rhythm of the odontoblast function and the fundamental biorhythm of the animals. The authors speculate that the circadian and infradian incremental lines may be independent and driven by different oscillatory mechanisms. More data concerning the implication of these findings are needed to elucidate this phenomenon. Acknowledgements: The authors wish to thank Professor, Yukishige Kozawa, for many encouraging discussions on this subject, and the staff of the Department of Anatomy, Nihon University School of Dentistry at Matsudo, for assistance with this study. A part of this work was supported by the Nihon University General Joint Research Grant for 2001 (01-015), a grant from the Ministry of Education, Culture, Sports, Science and Technology of Japan to promote Multidisciplinary Research Projects (in and ), and a Grant-in-Aid for Scientific Research (C and C ) from Japan Society for the Promotion of Science. References 1) Avery JK: Dentin; in Orban's Oral Histology and Embryology (Bhaskar SN ed), 10th ed, , The C V Mosby Company, St Louis, ) Dean MC, Scandrett AE: The Relation between Longperiod Incremental Markings in Dentine and Daily Cross -striations in Enamel in Human Teeth, Archs Oral Bioi, 41 : , Conclusion 3) Dean MC: Incremental Markings in Enamel and Dentine: What They Can Tell Us about the Way Teeth Grow; in Development, Function and Evolution of Teeth (Teaford MF, SmithMM, Ferguson MWJ eds), 1st ed, , Cambridge University Press, Cambridge, Before hatching, the incremental lines in the dentin were uniform and had a circadian rhythm. 2. After hatching, incremental lines of four kinds of periodicity were observed in the dentin. 3. Darker, wider and less calcified incremental lines were observed followinga lunar cycle of approximately 28-day intervals. 4. The lunar incremental lines (approximately 2S-day interval) are due to the rhythmic deposition of both minerals and organic matrix. 5. The semi-lunar incremental lines (approximately 14-day interval) are due to the rhythmic deposition of minerals and organic matrix, but these incremental lines strongly depend on mineralization. 6. The infradian incremental lines (approximately 2 to 3-day interval) are due to the rhythmic deposition of mineralization. 7. The circadian incremental lines are due to the rhythmic deposition of organic matrix. 8. The intervals of incremental lines may be related to the rhythm of the odontoblast function and the fundamental biorhythm of 4) Dean C, Leakey MG, Reid D et al.: Growth Processes in Teeth Distinguish Modern Human from Homo erectus and Earlier Hominins, Nature, 414: , 200 I. 5) Ferguson MWJ: Post-laying Stages of Embryonic Development for Crocodilians; in Wildlife Management: Crocodiles and Alligators (Webb GJW, Manolis SC, Whitehead PJ eds), , Surrey Beatty and Sons, Sydney, ) Kasuya T: Age Determination and Growth of the Baird's Beaked Whale with a Comment on the Fetal Growth Rate, Sci Rep Whales Res Inst, 29: 1-20, ) Kawasaki K, Tanaka S, Ishikawa T: On the Incremental Lines in Human Dentine as Revealed by Tetracycline Labelling, J Anat, 123: , ) Kawasaki K, Tanaka S, Ishikawa T: On the Daily Incremental Lines in Human Dentine, Archs Oral Bioi, 24 : , ) Klevezal GA, Kleinenberg SE: Age Determination of Mammals from Annual Layers in Teeth and Bones (Salkind J Translated), 1st ed, 6-28, Israel Program for Scientific Translations Press, Jerusalem,

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