The anatomy and physiology of the periodontium in humans will be described in details as regards to the relationship which exist between the natural dentition, jaws and the oral environment. Science has helped to explore different aspects of the tissues that make up the periodontium which are the gingiva, cementum, periodontal ligament and alveolar bone. These structures all work together to make a strong supporting apparatus for the teeth that is either in function or in occlusion.
The main other function of the periodontium apart from supporting the teeth is to protect and provide nourishment to the teeth. The tissues of the periodontium also involve in the provision of Interdental linkage of the teeth, facilitating epithelial lining of the oral cavity especially in the areas of erupted tooth and the development of those tissues are also related or dependent on the tooth development. The periodontium is usually divided into two different parts which are the; gingiva and the attachment apparatus (periodontal ligament, cementum and alveolar bone).
Several factors have been noted to influence the anatomy and physiology of the periodontium. Some of those factors are the; orthodontic treatment, aging, disease states. For instance, orthodontic tooth movement usually transduces the applied forces to make a form of remodelling to the periodontal fibers and alveolar bone. An important aspect of this paper is that of the embryonic origin, composition, histological and clinical appearance of the periodontium. This paper will explore the listed areas for better understanding on how they relate to one another and the clinical importance. Understanding of the cells that make up the tissue and cellular product create a great view of the importance of the periodotium to the oral cavity.
The embryonic development of the tooth and periodontal
This usually starts at the 5th week embryonically when cells of the neural tube regarded as the neural crest cell start migrating. The migration of the neural crest cells to the branchial arch. The cell migrating are known as pluripotent neuroepithelial cells. They are the cells that give rise to the osteoblasts, chondrocytes, fibroblasts, cementoblasts, odontoblasts and ganglia. A layer tagged ectomesenchyme layer are formed beneath the oral epithelium. An in-growth of the oral ectoderm is what formed the dental lamina.
This is usually surrounded by the ectomesenchyme. Later, an immature bone known as woven bone is then formed. This is the tooth bud which is also sorrounded by the ectomysenchyme. The tooth bud later differentiate into dental organ and proceed into what is being considered as bud, cap and bell stages. This differentiation occurs chronologically. On the cap stage, the ectomysenchyme that surrounds the developing tooth condenses and then forms the dental papilla.
The outer enamel epithelium is made up of the cells that have a form of cuboidal shape and some which are star shaped cells that are tagged with the stellate reticulum. The structure that lies in between the two groups of cells (stellate reticulum and inner enamel epithelium) is the stratum intermedium. It is after the process that the inner enamel epithelium will then lead to the formation of the ameloblasts which is the part of the cells that forms the enamel of the tooth. The dental papilla is the part that will lead to the formation of the crown, root dentin and cells of the pulp.
Gingiva
This is the part of the oral mucosa that covers the alveolar processes of jaws and surrounds the necks of the teeth. It is anatomically divided into two major parts which are the attached and unattached gingivae. The unattached gingivae can further be classified as the marginal gingivae, and Interdental papilla. Other extensions that are related majorly to the unattached gingivae tissue are the epithelial attachment and gingival sulcus. Histologically, it is divided into three areas which are the part continuous with oral epithelium, the part in the sulcular epithelium (non-keratinized), and junctional epithelium (non-keratinized). The normal healthy gingivae is that soft tissue with pale pink coloration, a stippled appearance with well defined 'knife edge' margin.
This pink coloration may also vary due to physiological changes such as increase pigmentation. This increase pigmentation is a common feature in some races. It is highly vascular and receive the blood supply from the lingual, mental, buccal and palatine arteries.
Fig 1. This diagram illustrate the gingival tissue of the periodontium
The gingiva between two teeth is known as the interdental papilla. This periodontal tissue usually has a shape of triangular and knife-edge especially in the anterior region while that in the posterior aspect is more of square shaped tissue and broader. Gingiva texture has also been known to be influenced by aging which makes it to be stippled in adult. It is smooth in the youth. Marginal gingiva is located at the terminal edge and usually separated from the attached gingival by a shallow linear depression. The Gingival sulcus is the shallow crevice around the tooth. The attached gingival is continuous with the marginal gingiva. The tissue is firm and resilient with a tight bound to the alveolar bone. Attached gingival width is used as a clinical criteria for diagnosis (Caranza).
The part of the gingiva that is attached to the crest, covers the outer surface of the marginal gingiva and the attached gingiva surface is a keratinized epithelium or parakeratinized in nature. The epithelium in relations to the sulcular gingival is that which is of thin, nonkeratinized stratified squamous epithelium. The junctional epithelium is that which has stratified squamous nonkeratinized epithelium as the histological nature of the tissue. The internal structural component is made up of the internal basal laminal which is further made up of the lamina densa and a lamina lucida. Hemidesmosomes is attached to this lamina lucida (Caranza).
The physiology aspect of periodontium are related to the pain perception, sensation of pressure and touch. It also provides some form of defense mechanism against infection. It enables the change in tooth position and repair of the effects of traumatic insults. The periodontium also allows adaptation of function alteration in the oral cavity. There is an experience of turnover which occur at the junctional epithelium of the gingiva. This shows a characteristics turnover rate with the ratio of basal cells area in relations to the area of exfoliation. This part of the gingiva shows a turnover rate of 50-100 times in the oral gingival epithelium. Comparing this turnover of the gingival connective tissue with that of the dermis, it is noted that gingival turnover rate is higher. There is also evidence that the gingival fibroblast synthesize larger amounts of new collagen (Muller).
Periodontal ligament
Periodontal ligament is the connective tissue that joins the tooth structure with the alveolar bone. The tissue allows transmission of forces especially to the alveolar bone. This force transmission occurs during the mastication and occlusal function. Most of the periodontal ligament is made up of the dense connective tissue while the rest is usually by a form of loose connective tissue which contain the neurovascular structures. The cellular component of the periodontal ligament include osteoblasts, cementoblasts, osteoclasts, multipotent stem cells, epithelial remnants and fibroblasts (IntechOpen). These cells are components that help contribute to the healing and repair that happens in the periodontium.
In terms of size, the width of the periodontal ligament is about 0.15-0.25mm. This has the ability to get decrease or increase depending on the load. Periodontal ligament is affected by age. With an increasing age, there is decreasing vascularity, cell mitotic activity reduction, decrease fiber number and fibroblasts. These fibers are usually arranged in different position and orientation. This is usually used in the classification which are the transeptal, horizontal, alveolar, oblique, apical and radicular groups of periodontal fibres.
The tensile strength displayed by the ligaments is confered on it by the molecular configuration of the collagen fibres. Transeptal fibres; extend from cementum of a tooth, pass over the interseptal bone towards the cementum of the other tooth. Horizontal fibres; It is from the cementum to alveolar crest of the main tooth towared the root and alveolar surfaces. Alveolar group; This fibre is from the cementum to alveolar bone and originates apical of the cementoenamel junction (IntechOpen). Oblique group; most abundant which run root cementum to alveolar bone in an oblique direction. Apical fibres; originates from the cementum near the root apex and then attached to the alveolar bone. Radicular groups; only found in the multirooted tooth close to the furcation.
Fig 2. The structure showing the periodontal ligaments and their location
The physiological consideration in terms of the turnover rate of the periodontal ligament shows that this turnover rate is about twice that of the gingiva hence showing it be at a very high rate of tissue remodelling. The influence of this is that the structural organization of the periodontal ligaments fibres will be constant. During the process, there is associated synthesis and decomposition of the collagen fibres with subsequent balancing of the process (renewal and removal of collagen). Removal of the collage is by the phagocytosing fibroblasts. Aging is a component found to also decrease turnover rate. Physiological forces are contributed by the chewing forces hence led to stimulation of these processes.
Alveolar bone
Alveolar bone is the part of the periodontium that provides the housing for the tooth. It is usually thicker in the palatal and lingual regions. It gives the required support and attachment for the tooth and the periodontal ligaments respectively. The alveolar bone is made up of the alveolar bone proper, trabecular bone and compact bone. The alveolar bone is covered with the layer of bone known as the cribiform plate which usually appear as the white line on radiographs as lamina dura. Supporting alveolar bone is the cancellous and cortical bone which help support the alveolar proper. The other types of alveolar bone structures are the interproximal bone or interdental septum, and interadicular bone. The interdental septum is located between the roots of adjacent teeth while the interradicular bone is that which is located between the roots of multirooted teeth.
The radicular bone is the part which is located on the facial and lingual surfaces of the roots of the teeth. The cellular components of the alveolar bone are the osteocytes found within the lacunae, the osteoblasts and osteoclasts. It is usually characterised by dehiscences and fenestrations. Dehiscences is where there is loss of bone and coverage is missing in the region of the coronal portion of the root. Fenestrations is related some forms of bone loss leading to windows but covered by periosteum and gingiva.
Cementum
Cementum is the part of the tooth that is calcified mesenchymal tissue which forms the outer covering of the anatomic root. It also provide the means of attachment for the periodontal ligaments fibers. It is also made up of calcified collagen and ground substance. The width of the cementum usually increase with the age. There are basically two types of cementum which are the acellular and cellular types. The acellular part is usually located at the coronal regions while the cellular cementum is found in the apical regions of the root or the furcation areas. Acellular has no cells, covers the approximately the cervical third of the root, and usually formed before the tooth hard structure gets to the occlusal plane. cellular part relates to the acellular in terms of complete formation before reaching the occlusal plane. It contains cells in the lacunae, less calcified and common in the apical region. The cementum components is usually deposited throughout life and the thickest deposit is at the apical region.
References
Carranza F.A. & Bernard, G.W. 1996. The Tooth-Supporting Structures. Chapter 2. Pg 42-49. Ninth Edition.
Fatin, Awartani. Anatomy of the periodontium. Part II cementum and Alveolar bone.
Muller, Hans-Peter. 2006. Periodontology. The essentials. Page 2-9.
Palumbo, Anthony. 2011. Gingival Diseases-Their Aetiology, Prevention and Treatment. The Anatomy and Physiology of the Health Periodontium. Pg 2-21, 2011.
