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Comparative Morphology of Incisor Enamel and Dentin in Humans and Fat Dormice (Glis Glis)

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Comparative Morphology of Incisor Enamel and Dentin in Humans and Fat Dormice (Glis Glis) Coll. Antropol. 27 (2003) 1: 373–380 UDC 572.72:616.314.11 Original scientific paper Comparative Morphology of Incisor Enamel and Dentin in Humans and Fat Dormice (Glis glis) Dean Konjevi}1, Tomislav Keros2, Hrvoje Brki}3, Alen Slavica1, Zdravko Janicki1 and Josip Margaleti}4 1 Chair for Game Biology, Pathology and Breeding, Veterinary Faculty, University of Zagreb, Zagreb, Croatia 2 Croatian Veterinary Institute, Zagreb, Croatia 3 Department for Dental Anthropology, School of Dental Medicine, University of Zagreb, Zagreb, Croatia 4 Department of Forest Protection and Wildlife Management, Faculty of Forestry, University of Zagreb, Zagreb, Croatia ABSTRACT The structure of teeth in all living beings is genetically predetermined, although it can change under external physiological and pathological factors. The author’s hypoth- esis was to indicate evolutional shifts resulting from genetic, functional and other dif- ferences. A comparative study about certain characteristics of incisors in humans and myomorpha, the fat dormouse (Glis glis) being their representative as well, comprised measurements of enamel and dentin thickness in individual incisor segments, evalua- tion of external enamel index, and also assessment of histological structure of enamel and dentin. The study results involving dormice showed the enamel to be thicker in lower than in the upper teeth, quite contrary to enamel thickness in humans. In the up- per incisors in dormice the enamel is the thickest in the medial layer of the crown, and in the cervical portion of the crown in the lower incisors. The thickness of dentin in dor- mice is greater in the oral than in the vestibular side. These findings significantly differ from those reported in reference literature, but they are based on the function of teeth in dormice. Histological characteristics of hard dental tissues in dormice are similar to those in humans, with exception of uniserial structure of enamel and appearance of dentinoenamel junction. Key words: enamel, dentin, fat dormouse, humans Received for publication February 3, 2003 373 D. Konjevi} et al.: Incisors in Humans and Fat Dormice, Coll. Antropol. 27 (2003) 1: 373–380 Introduction non, caused by different directions of winding and interlacing of enamel rods. The fat dormouse is referred to as our Close to dentinoenamel junctions are ena- autochthonous game classified in the or- mel tufts and enamel spindles. The enamel der of Rodentia, the family of Muscaridi- tufts are filled with organic substance nidae, and the genus of Gliridae. Based enamelin and they are formed within dif- on the shape of the cranium, morphology ferently directed groups of enamel prisms of masticatory muscles and structure of in dentinoenamel junction. enamel and dentin, the rodents are clas- The natural structure of dentin is sified into three sub-groups and the Myo- made of odontoblastic processes located morpha sub-group includes the dormice. and protected within dentinal canaliculi With regard to diversity of functions, the that extend from periphery of the pulp to upper and the lower incisors leave differ- dentinoenamel junction and sometimes ent prints, so that the teeth of rodents further into the enamel and enamel spin- have prints characterized by grooves1. dles. Within the tubules there is peri- The function of gnawing is enabled by tubular dentin and the tubules are con- extremely hard enamel on incisors of dor- nected by intertubular dentin. The Von mice. The enamel is highly mineralized Ebner's incremental lines show the den- and hence the hardest tissue in living or- tin depositing rate, while the prenatal ganisms. Its physical characteristics com- dentin is separated from the postnatal prise thickness, hardness, density, per- one by the so-called neonatal line3–7. meability, color and elasticity. The thick- The purpose of the comparative study ness of enamel is not the same in each is to define the evolutional shifts in hu- part of the dental crown and dental types, mans and in animals indicating their but there are individual differences as similarities and differences that have re- well. In humans, for example, the enamel sulted from genetic, functional and other layer is gradually thinned toward the cer- distinguishing factors. Even though com- vical part of a tooth, while its density di- parative studies are of great importance minishes from the surface toward the for establishing the evolutional shifts, we dentinoenamel junction. Therefore in hu- have found only few articles about com- mans the surface of the enamel is more parative studies between human and ro- abundantly mineralized than its deeper dent teeth in the recent literature8–10. layers, enabling better protection of teeth from undesirable external influences. The color of enamel is determined by its thick- Materials and Methods ness, density and degree of mineralisa- The study sample comprised 30 fat tion1–5. dormice (20 females and 10 males) cap- The fundamental units of enamel tured in the region of Gorski Kotar. Body structure are referred to as enamel rods length and body masses were taken for enclosed in a prism sheath and separated all animals, the parameters were then by interprismatic spaces. In the enamel marked and specimens frozen. The prep- of humans the lines of Retzius, or incre- aration of study samples comprised sepa- mental lines, are visible and they reflect ration of the lower jaw from the rest of the rate of depositing. In the cervical part the cranial skeleton by special scissors of the tooth along the dentinoenamel across the temporomandibular joint, sep- junction the dia or para-zones, the so- aration of the left from the right half, and called Hunter-Schreger bands, are found removal of the remaining soft tissue. The and they are considered optical phenome- Sunshine diamond F6 199,014 turbo 374 D. Konjevi} et al.: Incisors in Humans and Fat Dormice, Coll. Antropol. 27 (2003) 1: 373–380 Kavo Estetic 1,024 drill (Kaltenbach & Results Voigt D – 7950), at 1,500 turns per second was used to cut the upper jaw immedi- The measurement results of fat dor- ately before the premolars. All the speci- mice physical features show that their mens were stored into properly signed body lengths ranged from 29.7 to 15.4 cm, compartments and preserved in 5% for- the mean value being 18.5cm and stan- malin. dard deviation 2.61 cm. The maximal body mass (weight) was 154 g and the When making thin cuts one side of the minimal was 84 g, while the mean value lower jaw and parts of the upper jaw were being 114.83 g and standard deviation dispensed in methacrylate in special 16.36 g. molds using the Varidur 10 powder (di- The thickness of enamel in the cervi- benzyl peroxide) and Varidur fluid (tetra- cal portion of the upper teeth ranged from hydrofurfuryl 2 methacrilate). All the 40.7 to 36.5 mm, the mean value being sections were made by Isomet 1000 cutter 38.18 mm and standard deviation 1.19 (Buehler), at 175–200 turns per second mm. The same measurement values for and 0.7 mm cut thickness. The obtained lower teeth ranged from 55.41 to 41.4 mm, sections were photographed by Olympus the mean value being 43.95 mm and stan- BH-2 microscope at the magnification of dard deviation 2.85 mm. The enamel 40, 100 and 200. The specimens were thickness in the medial part of the tooth measured by special micrometer scale, crown in the upper teeth ranged from using the 10 times magnifying eyepiece 40.8 to 37.0 mm, the mean value being and 40 times magnifying lens. 38.59 mm and standard deviation 1.25 The enamel thickness was measured mm. The same measurement values for in the cervical, medial and incisal parts of lower teeth ranged from 51.8 to 41.0 mm, the tooth crown. From the thickness of the mean value being 44.48 mm and stan- exterior and interior enamel layers, ex- dard deviation 2.51 mm. ternal index was calculated11. The ob- The thickness of enamel in the incisal tained measurements served to the calcu- edge of the upper teeth ranged from 40.7 lation of enamel external index based on to 35.0 mm, the mean value being 38.63 the following equation: and standard deviation 2.86, while in the lower teeth the range was from 52.5 to External index = (outer layer 41.0 mm, the mean value being 45.0 mm thickness/total enamel thickness) ´ 100 and standard deviation 2.86 mm. Figure 1 shows the correlation between The thickness of dentin was measured the thickness of external enamel layer in the incisal and medial thirds of the and the external index. The thickness of tooth crown, while in the medial third of external enamel layer ranged from 15.2 the crown the measurements were made to 11.3 mm, the mean value being 13.25 on the vestibular and oral sides of teeth. mm. This Figure shows that external in- dex of 30.68% is conditioned by the small- Many authors studied enamel and den- est thickness of outer enamel layer (11.3 tin characteristics of human incisors2,3,12–14. mm). The mean number of samples shows The results of these were compared with external index from 33 to 37%. dormice incisors in our investigation. Figure 2 shows the correlation be- The results were statistically analy- tween the thickness if internal enamel zed by SPSS program for Windows Re- layer and the external index. The thick- lease 6.1. ness of internal enamel layer ranged 375 D. Konjevi} et al.: Incisors in Humans and Fat Dormice, Coll. Antropol. 27 (2003) 1: 373–380 16 Series1 15 14 13 12 11 The thickness of superficial enamel layer 10 30 31 32 33 34 35 36 37 38 39 External index (%) Fig.
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