The development of the mandible was traced on serial sections of 20 human
embryos aged 5-8 weeks (developmental stages 13-23). Special consideration
was given to the differentiation of skeletal units proposed by Sperber. The first
skeletal units, namely the mandibular body, the alveolar unit and the condylar
unit, may be distinguished in the 7th week. The primordia of all units are identified
by the end of the embryonic period (8 weeks)

Bruska, M.

Przystańska, A.

Woźniak, W.

English

Via Medica Journals

Folia Morphol. Vol. 66, No. 3, pp. 328–331Copyright © 2007 Via MedicaISSN 0015–5659www.fm.viamedica.plO R I G I N A L   A R T I C L E328Address for correspondence: Dr. A. Przystańska, Department of Anatomy, University of Medical Sciences, Święcicki 6, 60–781 Poznań,Poland, tel: +48 61 854 65 64, fax: +48 61 854 65 68, e-mail: aprzyst@amp.edu.plSkeletal units of the human embryonicmandibleA. Przystańska, M. Bruska, W. WoźniakDepartment of Anatomy, University of Medical Sciences, Poznań, Poland[Received 19 August 2007; Accepted 24 October 2007]The development of the mandible was traced on serial sections of 20 humanembryos aged 5–8 weeks (developmental stages 13–23). Special considerationwas given to the differentiation of skeletal units proposed by Sperber. The firstskeletal units, namely the mandibular body, the alveolar unit and the condylarunit, may be distinguished in the 7th week. The primordia of all units are identi-fied by the end of the embryonic period (8 weeks).Key words: human embryonic period, facial skeleton, mandible,skeletal unitsINTRODUCTIONThe mandible and the maxilla are the most im-portant bones in the development of the orofacialstructures. Although the mandible as the movablebone is antagonistic to the maxilla [3], these twobones show similarities during development [1]. Theyreflect developmental analogies based on:— origin from the ectomesenchyme migrating intofirst pharyngeal arch;— the requirement for epithelial-mesenchymal in-teraction prior to ossification;— the developing dental apparatus;— the close relation of ossification centres to bifurca-tion of the main branches of the trigeminal nerve;— the relationship to the primary cartilaginous se-lection, Meckel’s cartilage, and the nasal capsulefor the mandible and maxilla respectively;— the presence of secondary or accessory cartilages.It was found [7, 8] that the head and neck havea number of independent but integrated functions,which are carried out by functional components.Such components consist of soft tissues responsiblefor function, and a skeletal unit supporting and pro-tecting the soft tissues. Symons [11] and Moss [7]described five regions in the mandible viz. a basilarregion related to the inferior alveolar bundle, as wellas the alveolar, coronoid, condyloid, and angularregions. Sperber [10] included the chin as a mandi-bular skeletal unit.The aim of the paper is to trace the developmentof the mandible in human embryos aged between5 and 8 weeks with special attention to differentia-tion of the primordia of skeletal units.MATERIAL AND METHODSFor the study 20 embryos were used from thecollection of the Department of Anatomy, PoznańUniversity of Medical Sciences. The embryos werestaged according to 23 developmental stages. Seri-al sections of the embryos were made in the frontal,sagittal and horizontal planes. Sections of 10 µm inthickness were stained according to the Mallorymethod with haematoxylin and eosin and cresyl vio-let and impregnated with Bodian’s protargol.RESULTSIn this section the differentiation of particularunits will be described.The basilar unit develops laterally to Meckel’scartilage. The primary ossification centre in this unitappears at stage 18 (44 days). This centre is closelyassociated with the inferior alveolar nerve and is329A. Przystańska et al., The human embryonic mandiblebelow the formation of the future mental foramen(Fig. 1). During weeks 7 and 8 (stage 19–23) in em-bryos the bone spreads from this centre medially andposteriorly, lying below and lateral to the inferioralveolar nerve (Fig. 2, 3).The primordium of the alveolar unit appears asa dental lamina in embryos at stage 15 (36 days)(Fig. 4). With the growth of the mandible and thedevelopment of dental papillae and teeth buds, thealveolar unit fuses with the mandibular body (Fig. 2, 5).The upper part of the body divides into two lami-nae, which embrace the developing alveolae.The angular unit may be distinguished at stage19 (46 days). Its development is related to the growthof the masticatory muscles and proceeds throughapposition of the periosteum (Fig. 6).The coronoid unit can be observed in embryos atstage 20 (50 days) and is closely related to the temporalFigure 1. Frontal section of embryo at 18 stage. H+E.a — Meckel’s cartilage, b — nferior alveolar nerve, c — ossifi-cation center.Figure 2. Coronal section of embryo at stage 20. Mallory.a — palatine process of maxilla, b — tooth bud, c — Meckel’scartilage, d — ossification center.Figure 3. Frontal section of embryo at stage 21. H+E.a — mandibular nerve, b — masseter muscle with nerve,c — inferior alveolar nerve, d — Meckel’s cartilage, e — ossify-ing mandible, f — lingual nerve.Figure 4. Sagittal section of embryo at stage 15. H+E.a — maxillary prominence, b — dental lamina, c — mandibularprocess.330Folia Morphol., 2007, Vol. 66, No. 4Figure 5. Sagittal section of embryo at stage 21. H+E. a — den-tal lamina, b — ossifiacyion center, c — Meckel’s cartilage.Figure 6. Frontal section of embryo at 20 stage. H+E.a — tooth bud, b — ossifying body of mandible in regionof angle, c — Meckel’s cartilage, d- ossification center.Figure 8. Frontal section of embryo at stage 19. H+E.a — tongue, b — Meckel’s cartilage, c — primordium ofcondylar process.muscle (Fig. 7). In this early development it is a fibrocel-lular mesenchymal condensation. It differentiates asa separate bony structure related to the temporalmuscle.The primordium of the condylar unit is seen inembryos at stage 19 (46 days) (Fig. 8) and is respon-sible for the longitudinal growth of the mandible.Figure 7. Frontal section of embryo at stage 23. H+E.a — mandibular nerve, b — inferior alveolar nerve,c — Meckel’s cartilage, d — ossifying mandible.Figure 9. Horizontal section of embryo at stage 23. H+E.a — Meckel’s cartilage, b — symphysis, c — dental lamina.It growths superiorly and laterally and is in contactwith the lateral pterygoid muscle (Fig. 9).331A. Przystańska et al., The human embryonic mandibleThe mental unit in the embryonic period is repre-sented by a mandibular symphysis in the midline.It may be concluded that all the skeletal units ofthe mandible are evident by the end of 8th week.DISCUSSIONMany studies have been dedicated to the prena-tal development of the human mandible and Meck-el’s cartilage [3–5, 9]. Meckel’s cartilage influencesthe ossification of the mandible. Lee et al. [3] foundthat the ossification of the condylar blastema is close-ly associated with Meckel’s cartilage, which is alsoimportant in craniofacial morphogenesis [4]. Lee etal. [3] distinguished three stages which are crucialduring mandibular development: stage 16 (appear-ance of Meckel’s cartilage), stage 19 (beginning ofossification) and stage 23 (changes in muscular at-tachments). In the present study we observed theprimary ossification centre at stage 18.The development and growth of the mandibledepends upon several factors [2, 6]:— epitheliomesenchymal interactions between theoral epithelium and underlying mesenchyme;— prenatal activity of the masticatory muscles;— growth of the tongue;— the inferior alveolar nerve and its branches;— development and migration of the teeth.In the present study, which describes the primor-dia of the skeletal units in the embryonic period forthe first time, it was shown, that these units are char-acterised by the following features:— the appearance of the alveolar unit as a dentallamina and the relation of its development toodontogenesis;— the very early differentiation of the basilar unitand its ossification as the first unit;— growth of the angular and coronoid units closelyrelated to the muscles of mastication;— growth of the condylar unit dependent on sec-ondary cartilage formation.REFERENCES1. Dixon AD (1958) The development of the jaws. DentPractit, 9: 10–17.2. Dixon AD (1997) Prenatal development of the facialskeleton. In: Dixon AD, Hoyte DAN, Rönning O (ed)Fundamentals of craniofacial growth. CRC Press, BocaRaton, New York: 59–97.3. Lee SK, Kim YS, Oh HS, Yang KH, Kim ECh, Chi JG (2001)Prenatal development of the human mandible. AnatRec, 263: 314–325.4. Lorentowicz-Zagalak M, Przystańska A, Woźniak W(2005) The development of Meckel’s cartilage in stagedhuman embryos during the 5th week. Folia Morphol,64: 23–28.5. Merida-Velasco JR, Rodriguea-Vazquez JF, Merida-Velasco JA, Sanchez-Montesinos I, Espin-Ferra J, Jimenez-Collado J (1999) Development of the human temporo-mandibular joint. Anat Rec, 255: 20–33.6. Mills JRE (1983) A clinician looks at facial growth.Br J Orthod, 10: 58–65.7. Moss ML (1960) A functional analysis of humanmandibular growth. Am J Prosthet Dent, 10: 1149––1158.8. Moss ML, Simon M (1968) Growth of the human man-dibular angular process: a functional cranial analysis.Am J Phys Anthrop, 28: 127–138.9. Radlanski RJ, Renz H, Klarkowski MC (2003) Prenataldevelopment of the human mandible. 3D reconstruc-tions, morphometry and bone remodelling pattern,sizes 12–117 mm CR. Anat Embryol, 205: 1–24.10. Sperber GH (1989) Craniofacial Embryology. 4th ed.Wright, London.11. Symons NBB (1951) Studies on the growth and formof the mandible. Dent Rec, 41: 53–64.

Skeletal units of the human embryonic mandible

https://journals.viamedica.pl/folia_morphologica/article/download/16014/12652

Skeletal units of the human embryonic mandible

Abstract

Similar works

Full text

Available Versions

Via Medica Journals