Hitoshi Yamamoto et al.: Distribution of Acellular and Cellular in Human Teeth Journal of Hard Tissue Biology 18[1] (2009) p40-44 © 2009 The Hard Tissue Biology Network Association Printed in Japan, All rights reserved. CODEN-JHTBFF, ISSN 1341-7649 Original

Diversity of Acellular and Cellular Cementum Distribution in Human Permanent Teeth

Hitoshi Yamamoto1,2), Toshihide Niimi1), Rumi Yokota-Ohta1,2), Kunihiro Suzuki1,2), Toshiro Sakae1,2) and Yukishige Kozawa1,2)

1) Department of Histology, Cytology and Developmental Anatomy, Nihon University School of Dentistry at Matsudo,Chiba, 271- 8587, Japan 2) Research Institute of Oral Science, Nihon University School of Dentistry at Matsudo,Chiba, 271-8587, Japan (Accepted for publication, December 27, 2008)

Abstract:Cementum is divided into acellular cementum and cellular cementum based on the absence and presence of cementocytes in the cementum matrix. Since the distribution of acellular and cellular cementum is affected by physical conditions such as aging and pathological conditions like inflammation and hyper occlusal pressure causing hypercementosis. Moreover, it has been reported in many text books that acellular and cellular cementum distribute irregularly. However, it is generally known that acellular cementum is located from the cervical margin to the cervical half or one-third and cellular cementum is observed from the apical half or two-thirds to the apical portion. In the present study, we have observed labio-lingual grinding sections of extracted human permanent teeth used for student practice (50 incisors and 78 molars) and classified the distribution pattern of acellular and cellular cementum into five types as following: 1) Typical distribution type of the acellular and cellular cementum as explained above, 2) Type with thick acellular cementum at the cervical portion. In this type, thick acellular cementum is observed at the cervical portion, although the acellular and cellular cementum is distributed as same as type 1 except in the cervical portion, 3) Type with thick cellular cementum at the cervical portion. This type showed that thick cellular cementum is distributed at the cervical portion instead of acellular cementum in type 2, 4) Type with acellular cementum from the cervical area to apical portion. This type showed acellular cementum covering from the cervical to apical portion of the tooth root surface, although the cellular cementum was located near the dentino-cement junction, 5) Type with cellular cementum from the cervical to apical portion. Cellular cementum distributed from the cervical to apical portion of the tooth root surface, although the acellular cementum is located inside the surface cellular cementum. In type 5, we found holes of various sizes and shapes in the hypertrophied cementum. Since these holes were large and cement canaliculus surrounding the holes extended toward the holes, it is suggested that the hypertrophied cementum enfolded a part of the periodontal ligament.

Key words: Acellular cementum, Cellular cementum, Human, Tooth

Introduction distributed irregularly1-3). In mammals, the tooth root is covered by cementum. Cementum differentiate from cells during is divided into two types, acellular cementum and cellular tooth root formation. In addition, it is generally thought that cementum, based on the absence or presence of cementocytes acellular and cellular cementum formation depends on the speed originating from cementoblasts in the cementum matrix. It is of cementum matrix formation. Briefly, since cellular cementum generally known that acellular cementum is located adjacent to is formed at a faster rate than acellular cementum formation and the dentin surface from the cervical margin to the cervical half to cementoblasts are embedded into the cementum matrix secreted one-third, while the cellular cementum is distributed from the by cementoblasts, cellular cementum is formed1-3). It was reported apical half to two-thirds to the apical portion of the tooth root and recently that growth factors such as TGF-beta, FGF and IGF, furcation area. Although cellular cementum usually covers adhesion molecules like sialoprotein and osteopontin, and acellular cementum, acellular and cellular cementum are BMPs regulate cementogenesis4-7). Especially, in regenerative Corresponddence to: Hitoshi Yamamoto, DDS., Ph.D.Department of research, Hammerström described that enamel matrix proteins are Histology, Cytology and Developmental Anatomy, Nihon University involved in the formation of acellular cementum8). However, School of Dentistry at Matsudo, 2-870-1, Sakaecho Nishi, Matsudo City, Chiba 271-8587 Japan. Fax: 81-47-360-9324 , Tel: 81-47-360-9323,.e- Sculean et al. reported that diseased human root surfaces treated mail:: [email protected] with enamel matrix proteins showed new tissue formation 40 J.Hard Tissue Biology Vol. 18(1):40-44, 2009

Figure 2. a: lower magnification of tooth root (bar: 1mm) b: higher magnification of the cervical portion of tooth root (bar: 500µm) Acellular cementum was located as a typical pattern like Fig. 1. However, Figure 1. a: lower magnification of tooth root (bar: 1mm) at the cervical portion, thick acellular cementum was observed and a part b: higher magnification of the cervical portion of tooth root (bar: 300µm) of the acellular cementum formed a small cementum spur (arrow in b). c: higher magnification of the middle area of tooth root (bar: 300µm) d: higher magnification of the apical portion of tooth root (bar: 300µm) Acellular and cellular cementum distribute as a typical pattern (a). At the In the present study, we attempted to classify the distribution cervical portion of the tooth root, only acellular cementum was observed pattern of acellular and cellular cementum using labio-lingual (b). Cellular cementum is located from the middle of the tooth root (arrow in c). At the apical portion, cellular cementum distributed from the inner grinding sections of extracted human permanent teeth prepared to outer layer of cementum (d). for student practice as the first step in tooth root morphogenesis research. resembling cellular cementum9,10). Moreover, it was indicated that the timing of mineralization of the mantle dentin matrix might be Materials and methods the key determination of the types of cementum deposited on the 128 labio-buccal grinding sections of extracted human growing surface11). However, Tenorio et al. described the existence permanent teeth (50 incisors and 78 molars) archived by our of two phenotypes of cementoblasts, one associated with cellular department for students practice of oral histology were observed cementum formation and the other associated with acellular by light microscopy. Age, sex, reason for extraction, history of cementum formation12). These findings suggest that the formation individual teeth and type of tooth were unknown. Incisors and of both acellular and cellular cementum may be controlled by molars were discriminated according to the form of the grinding numerous factors. section. Since cementoblasts remain in the periodontal ligament, cementum is formed continuously throughout life under Results physiological conditions. Pathologically, cementum is thickened The distribution pattern of acellular and cellular cementum by chronic inflammation and hyper occlusal pressure13,14). In can be roughly divided into five types as follows: addition, systemic and hereditary diseases might cause hypercementosis15,16). Although cementum is considered an active 1) Type of typical distribution of acellular and cellular cementum hard tissue, there is a little of information about the distribution (Fig. 1) of acellular and cellular cementum based on physiological Acellular cementum was observed from the cervical margin to cementum formation and/or pathological hypercementosis. the cervical half to one-third. Especially, only a thin acellular 41 Hitoshi Yamamoto et al.: Distribution of Acellular and Cellular Cementum in Human Teeth

Figure 3. a: lower magnification of tooth root (bar: 500µm) Figure 4. a: lower magnification of tooth root (bar: 500µm) b: higher magnification of the cervical portion of tooth root (bar: 250µm) b: higher magnification of the apical portion in a (bar: 100µm) In the majority of the cervical half, acellular cementum was observed, Acellular cementum was located on the root dentin surface from the although thick cellular cementum was located near the cemento-enamel cervical to apical portion (a). junction (arrowheads in a, b). Cellular cementum covered the acellular cementum from the middle portion of tooth root (arrow)(a). was distributed at the cervical portion on the acellular cementum. cementum was located at the cervical portion. Cellular cementum covered the acellular cementum from the apical half to two-thirds 4) Type with acellular cementum from the cervical to apical to the apical portion of the tooth root. At the apical portion, thick portion (Fig. 4) cellular cementum was observed. Moreover, acellular cementum Acellular cementum was distributed from the cervical to apical was sometimes absent at this portion. portion. Even at the apical portion, cellular cementum was not observed in this type. 2) Type with thick acellular cementum at the cervical portion (Fig. 2) 5) Type with cellular cementum from the cervical to apical In this pattern, the distribution of acellular and cellular portion (Fig. 5) cementum was the same as the typical pattern. Although cellular Thick cellular cementum was distributed from the cervical to cementum was observed at the apical portion, and acellular apical portion. Moreover, cellular cementum formed a cement cementum distributed at the cervical portion. However, this pattern spur at the cervical margin in some specimens. In addition, thick was characterized by the thick acellular cementum at the cervical cellular cementum projection was formed at the cemento-enamel portion. junction. At this projection, cement canaliculus extended toward the space between enamel and cementum. Moreover, holes of 3) Type with thick cellular cementum at the cervical portion various sizes and shapes were present in the hypertrophied (Fig. 3) cementum. Acellular cementum formed the walls of some holes. The basic distribution pattern of acellular and cellular Cement canaliculus around the holes extended toward these holes. cementum was similar to the typical pattern. Namely, acellular cementum was located from cervical portion to the apical half to Discussion one-third of the tooth root, although cellular cementum was Cementum is considered a dynamic and active hard tissue, since observed from the apical half to two-thirds of the tooth root. cementum is formed not only under physical condition like aging, However, as characteristics of this pattern, thick cellular cementum but also in pathological conditions like chronic inflammation, 42 J.Hard Tissue Biology Vol. 18(1):40-44, 2009 vessel19). However, the sizes of holes in hypertrophied cementum in the present study were larger than those of blood vessels in a previous description. Moreover, a previous work did not find numerous holes in hypertrophied cementum. Cement canaliculus surrounding the holes in hypertrophied cementum extended toward these holes. Since cementocytes are supplied with nutrition by fusion from the periodontal ligament by diffusion and there is no large blood vessel near the cementum, this is the first report suggesting that the hypertrophied cementum enfolds a part of the periodontal ligament. Since extracted permanent teeth were examined in this study, it is thought that variations in the distribution of acellular and cellular cementum were caused by diseases such as inflammation. However, it is considered that acellular and cellular cementum formation during inflammation is controlled by certain unidentified factors, although this distribution differs from cementogenesis during tooth development. Cementum is a very dynamic organ in the tooth comparable to enamel and dentin and similar to bone not only in morphology but also in reactivity to stimulation. We would like to observe the developmental process of human teeth as the next step in tooth root morphogenesis research. Figure 5. a: lower magnification of tooth root (bar: 450µm) b: higher magnification of the cervical portion (bar: 170µm) c: higher magnification of the hole area (bar: 170µm) Acknowledgements From the cervical to apical portion, cellular cementum was observed (a). Especially, a thick cement spur was formed by cellular cementum (b). In This study was supported by Nihon University Individual the cement spur, the cement canaliculus extended toward the space between Research Grant for 2007 (No. 07-096) and a Grant-in aid for enamel and cement spur (b). Interestingly, there were holes in the cellular Scientific Research from Japan Society for Promotion of Science cementum (c). Cement canaliculus around the holes extended toward the holes. The dentin-side wall of the hole consisted of acellular cementum, (No. 20592153, No. 20592154) and a Grant for Supporting Project although the periodontal ligament-side wall of the hole was formed by for Strategic Research of Nihon University School of Dentistry cellular cementum (c). at Matsudo by the Ministry of Education, Culture, Sports, Science and Technology, 2008-2012. hyper occlusal pressure, systemic and hereditary diseases13-16). Moreover, cementum is formed with the regeneration of References periodontal tissue, although cementum does not remodel in the 1. Furseth R and Mjör I A. Cementum. In: Histology of the same way as bone8-10,17,18). Therefore, it is written in textbooks , ed. by Mjör I.A. and Pindborg J.J., Munksgaads, that the distribution of acellular and cellular cementum is irregular1- Copenhagen, 1973, pp97-119. 3). However, “irregular distribution of acellular and cellular 2. Berkovitz B K B, Holland GR and Moxham BJ. Cementum. 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