1. The dental clinic, its equipment. Safety. Periodontium, definition. Anatomy, histology, physiology of periodontium, periodontal protective mechanisms. Periodontal disease.
Facility Physical Environment
The Dental facility should be clean and properly maintained and have adequate lighting and ventilation. The space allocated for a particular function or service should be adequate for the activities performed.
In general Dental clinic shall comprise at least the following:
§ Dental room with space are a not be less than 14 square meters with wash basin and taps water
§ Reception area/Nursing station viewing the waiting area
§ Separate waiting area for males and females
§ Toilet (minimum of two)
§ Dedicated area for storing patient’s records
The physical layout of dental clinic should be arranged to assure its easy cleaning. Floor, walls and ceiling of the dental room should be made from smooth nonporous material that doesn’t support the harbor of dirt, micro and macro organisms. Junction between floor and wall in the dental room shall be smooth curved lines without angles. Toilet doors for patient use shall open outward Prefabricated warehouse type building is not suitable as dental facility, this type of building dose not support a smooth curved lines and angles, and possible cracks and gapes that can be infested with different species of pests.
Dental Equipments
The facility should be equipped with the appropriate medical equipment, supplies, and pharmacological agents which are required in order to provide the dental services and resuscitation services if required.
All equipment used in patient care, testing, or emergency situations should be inspected, maintained, and tested on a regular basis and according to manufacturers’ specifications. The facility should have appropriate fire-fighting equipment, signage, emergency power capabilities, lighting, and an evacuation plan. Dental clinic equipment shall include, but not limited to the following:
1. Dental unit
2. Dentist stool
3. Assistant stool
4. Adequate Halogen light
5. Heavy Duty Suction apparatus
6. Three way syringes
7. Saliva Ejector
8. Scaler Unit either Ultrasonic or Air
9. Amalgamator (optional)
10. Standard dental x-ray unit (optional) if available there shall be
Simple dental X-Ray viewer
Lead Appron
11. Autoclave machine
12. Light Cure Machine
13. Stethoscope with sphygmomanometers
14. Doctor desk with two chairs for patient his/her companion.
15. Sufficient amount of linen or disposable medical towel paper.
16. Refrigerator to keep vaccine and drugs.
17. Medical prescription book, Patients records, referral book, etc
18. Instrument cabinets with drawers
19. Instrument Trolley (minimum of one)
20. Kidney Shape dishes or equivalents (minimum of three)
21. Plastic Aprons/Bibs (preferably disposable type) (minimum of three)
22. Hand Disinfectant e.g. Hibiscrub dispense or equivalent (minimum of two)
23. Sharp needles Dispenser (minimum of three)
Good Clinical Dental Practice
Here you will find practical instructions regarding good dental clinic practice:
· Dental stone cast and models must not be displayed in the dental room and should be stored in a cabinet in different place.
· All heat sensitive dental materials must be stored inside refrigerator, No food shall be kept in such refrigerator.
· Dental cabinet shall be made of smooth nonporous material that doesn’t support the harbour of dirt, micro and macro organisms. Wooden cabinets and shelves are not permitted inside the dental room.
· At least three scalar tips should be available for each dental unit
· Root canal instrument (files, remmers,) must individualise as a full seat inside sterile pouches for each patient. (Metal box style to keep the root canal instrument must not be permitted).
· Dental trays must be washed and sanitised after each patient.
· Good Dental Practice should adapt protective steps whether directly or indirectly relate to dental treatment…Exp:
· Dental needle preferably not be used in more than tow insertion on same patient.
· Use protective goggles.
· Ansthetic dental cartridge must be disposed even after minimal use.
§ Use a preloaded amalgam capsules only. (The possibility of mistakes in accurate measurement of un dosed powder and mercury may lead to heavy metal intoxication and room contamination from mercury)
· In each dental unit there must be built-in separator for environmental issue.
§ As a preventive measures dentist has the right to ask the patient for a specific medical test for safety.
· Plastic instruments, dental composite tubes, cement containers…must be wiped with medicated sanitising solution after each use.
· Arsenical products should not permit in dental practice.
· It is good practice to use to use eye loops.
· All sterlisation, santisation and cleaning procedure must be evaluated, monitored and verified by the dentist in charge.
· All dentists must have sound and solid knowledge and practice in life saving measures for immediate intervention during emergency in dental practice; therefore it is the responsibility of department of health to adopt short training courses for dental practitioners.
The periodontium (pert = around,odontos = tooth) comprises the following tissues
. The alveolar bone consists of two components, the alveolar bone proper (ABP) and the alveolar process.
The alveolar bone proper, also called “bundle bone” is continuous with the alveolar process and forms the thin bone plate that lines the alveolus of the tooth. The main function of the periodontium is to attach the tooth to the bone tissue of the jaws and to maintain the integrity of the surface of the masticatory mucosa of the oral cavity. The periodontium, also called “the attachment apparatus” or “the supporting tissues of the teeth”, constitutes a developmental, biologic, and functional unit which undergoes certain changes with age and is, in addition, subjected to morphologic changes related to functional alterations and alterations in the oral environment. The development of the periodontal tissues occurs during the development and formation of teeth. This process starts early in the embryonic phase when cells from the neural crest (from the neural tube of the embryo) migrate into the first branchial arch. In this position the neural crest cells form a band of ectomesenchyme beneath the epithelium of the stomatodeum (the primitive oral cavity). After the uncommitted neural crest cells have reached their location in the jaw space, the epithelium of the stomatodeum releases factors which initiate epithelial-ectomesenchymal interactions.
Once these interactions have occurred, the ectomesenchyme takes the dominating role in the further development. Following the formation of the dental lamina, a series of processes are initiated (bud stage, cap stage, bell stage with root development) which result in the formation of a tooth and its surrounding periodontal tissues, including the alveolar bone proper. During the cap stage, condensation of ectomesenchymal cells appears in relation to the dental epithelium (the dental organ (DO)), forming the dental papilla (DP) that gives rise to the dentin and the pulp, and the dental follicle (DF) that gives rise to the periodontal supporting tissues . The decisive role played by the ectomesenchyme in this process is further established by the fact that the tissue of the dental papilla apparently also determines the shape and form of the tooth.If a tooth germ in the bell stage of development is dissected and transplanted to an ectopic site (e.g. the connective tissue or the anterior chamber of the eye), the tooth formation process continues. The crown and the root are formed, and the supporting structures, i.e. cementum, periodontal ligament and a thin lamina of alveolar bone proper, also develop. Such experiments document that all informatioecessary for the formation of a tooth and its attachment apparatus is obviously residing within the tissues of the dental organ and the surrounding ectomesenchyme. The dental organ is the formative organ of enamel, the dental papilla is the formative organ of the dentinpulp complex, and the dental follicle is the formative organ of the attachment apparatus (the cementum, the periodontal ligament and the alveolar bone proper). The development of the root and the periodontal supporting tissues follows that of the crown. Epithelial cells of the external and internal dental epithelium (the dental organ) proliferate in apical direction forming a double layer of cells named Hertwig’s epithelial root sheath (RS). The odontoblasts (OB) forming the dentin of the root differentiate from ectomesenchymal cells in the dental papilla under inductive influence of the inner epithelial cells. The dentin (D) continues to form in apical direction producing the framework of the root. During formation of the root, the periodontal supporting tissues including acellular cementum develop. Some of the events in the cementogenesis are still unclear, but the following concept is gradually emerging. At the start of dentin formation, the inner cells of Hertwig’s epithelial root sheath synthesize and secrete enamel-related proteins, probably belonging to the amelogenin family. At the end of this period, the epithelial root sheath becomes fenestrated and through these fenestrations ectomesenchymal cells from the dental follicle penetrate and contact the root surface. The ectomesenchymal cells in contact with the enamel-related proteins differentiate into cementoblasts and start to form cementoid.
This cementoid represents the organic matrix of the cementum and consists of a ground substance and collagen fibers,which intermingle with collagen fibers in the not yet fully mineralized outer layer of the dentin. It is assumed that the cementum becomes firmly attached to the dentin through these fiber interactions. The formation of the cellular cementum, which covers the apical third of the dental roots, differs from that of acellular cementum in that some of the cementoblasts become embedded in the cementum.The remaining parts of the periodontium are formed by ectomesenchymal cells from the dental follicle lateral to the cementum. Some of them differentiate into periodontal fibroblasts and form the fibers of the periodontal ligament while others become osteoblasts producing the alveolar bone proper in which the periodontal fibers are anchored. In other words, the primary alveolar wall is also an ectomesenchymal product. It is likely, but still not conclusively documented, that ectomesenchymal cells remain in the mature periodontium and take part in the turnover of this tissue.
GINGIVA
The oral mucosa (mucous membrane) is continuous with the skin of the lips and the mucosa of the soft palate and pharynx. The oral mucosa consists of the masticatory mucosa, which includes the gingiva and the covering of the hard palate, the specialized mucosa, which covers the dorsum of the tongue, and the remaining part, called the lining mucosa.. The gingiva is that part of the masticatory mucosa which covers the alveolar process and surrounds the cervical portion of the teeth. It consists of an epithelial layer and an underlying connective tissue layer called the lamina propria. The gingiva obtains its final shape and texture in conjunction with eruption of the teeth. In the coronal direction the coral pink gingiva terminates in the free gingival margin, which has a scalloped outline. In the apical direction the gingiva is continuous with the loose, darker red alveolar mucosa (lining mucosa) from which the gingiva is separated by a, usually, easily recognizable borderline called either the mucogingival junction (arrows) or the mucogingival line. There is no mucogingival line present in the palate since the hard palate and the maxillary alveolar process are covered by the same type of masticatory mucosa. Two parts of the gingiva can be differentiated:
1. the free gingiva (FG)
2. the attached gingiva (AG)
The free gingiva is coral pink, has a dull surface and firm consistency. It comprises the gingival tissue at the vestibular and lingual/palatal aspects of the teeth, and the interdental gingiva or the interdental papillae. On the vestibular and lingual side of the teeth, the free gingiva extends from the gingival margin in apical direction to the free gingival groove which is positioned at a level corresponding to the level of the cementoenamel junction (CEJ). The attached gingiva is in apical direction demarcated by the mucogingival junction (MGJ).. The free gingival margin is often rounded in such a way that a small invagination or sulcus is formed between the tooth and the gingiva . When a periodontal probe is inserted into this invagination and, further apically, towards the cementoenamel junction, the gingival tissue is separated from the tooth, and a “gingival pocket” or “gingival crevice” is artificially opened. Thus, iormal or clinically healthy gingiva there is in fact no “gingival pocket” or “gingival crevice” present but the gingiva is in close contact with the enamel surface. In the illustration to the right, a periodontal probe has been inserted in the tooth/gingiva interface and a “gingival crevice” artificially opened approximately to the level of the cemento-enamel junction.
After completed tooth eruption, the free gingival margin is located on the enamel surface approximately 1.5 to 2 mm coronal to the cemento-enamel junction.. The shape of the interdental gingiva (the interdental papilla) is determined by the contact relationships between the teeth, the width of the approximal tooth surfaces, and the course of the cemento enamel junction. In anterior regions of the dentition, the interdental papilla is of pyramidal form while in the molar regions, the papillae are more flattened in bucco-lingual direction . Due to the presence of interdental papillae, the free gingival margin follows a more or less accentuated, scalloped course through the dentition.
In anterior regions of the dentition, the interdental papilla is of pyramidal form while in the molar regions, the papillae are more flattened in buccolingual direction . Due to the presence of interdental papillae, the free gingival margin follows a more or less accentuated, scalloped course through the dentition.. In the premolar/molar regions of the dentition, the teeth have approximal contact surfaces rather than contact points. Since the interdental papilla has a shape in conformity with the outline of the interdental contact surfaces, a concavity —a col — is established in the premolar and molar regions, as demonstrated in Fig. 1-9b, where the distal tooth has been removed. Thus, the interdental papillae in these areas often have one vestibular (VP) and one lingual/ palatal portion (LP) separated by the col region.
The col region, as demonstrated in the histological section, is covered by a thion-keratinized epithelium (arrows). This epithelium has many features in common with the junctional epithelium . The attached gingiva is, in coronal direction, demarcated by the free gingival groove (GG) or, whensuch a groove is not present, by a horizontal plane placed at the level of the cemento-enamel junction. In clinical examinations it was observed that a free gingival groove is only present in about 30-40% of adults. The free gingival groove is often most pronounced on the vestibular aspect of the teeth, occurring most frequently in the incisor and premolar regions of the mandible, and least frequently in the mandibular molar and maxillary premolar regions.
The attached gingiva extends in the apical direction to the mucogingival junction (arrows), where it becomes continuous with the alveolar (lining) mucosa ( AM). It is of firm texture, coral pink in color, and often shows small depressions on the surface. The depressions, named “stippling”, give the appearance of orange peel.
It is firmly attached to the underlying alveolar bone and cementum by connective tissue fibers, and is, therefore, comparatively immobile in relation to the underlying tissue. The darker red alveolar mucosa (AM) located apical to the mucogingival junction, on the other hand, is loosely bound to the underlying bone. Therefore, in contrast to the attached gingiva, the alveolar mucosa is mobile in relation to the underlying tissue. It describes how the width of the gingiva varies in different parts of the mouth. In the maxilla the vestibular gingiva is generally widest in the area of the incisors and most narrow adjacent to the premolars. In the mandible the gingiva on the lingual aspect is particularly narrow in the area of the incisors and wide in the molar region. The range of variation is 1-9 mm. It illustrates an area in the mandibular premolar region where the gingiva is extremely narrow. The arrows indicate the location of the mucogingival junction. The mucosa has been stained with an iodine solution in order to distinguish more accurately between the gingiva and the alveolar mucosa. It depicts the result of a study in which the width of the attached gingiva was assessed and related to the age of the patients examined. It was found that the gingiva in 40 to 50-year-olds was significantly wider than that in 20 to 30-year-olds. This observation indicates that the width of the gingiva tends to increase with age. Since the mucogingival junction remains stable throughout life in relation to the lower border of the mandible, the increasing width of the gingiva may suggest that the teeth, as a result of occlusal wear, slowly erupt throughout life.
Microscopic aa t o m y
Oral epithelium
The epithelium covering the free gingiva may be differentiated as follows:
• oral epithelium (OE), which faces the oral cavity
• oral sulcular epithelium (OSE), which faces the tooth without being in contact with the tooth surface
• junctional epithelium (JE), which provides the contact between the gingiva and the tooth.
The connective tissue portions which project into the epithelium are called connective tissue papillae (CTP) and are separated from each other by epithelial ridges — so-called rete pegs (ER). In normal, non-inflamed gingiva, rete pegs and connective tissue papillae are lacking at the boundary between the junctional epithelium and its underlying connective tissue . Thus, a characteristic morphologic feature of the oral epithelium and the oral sulcular epithelium is the presence of rete pegs, while these structures are lacking in the junctional epithelium.
The oral epithelium is a keratinized, stratified, squamous epithelium which, on the basis of the degree to which the keratin-producing cells are differentiated, can be divided into the following cell layers:
1. basal layer (stratum basale or stratum germinativum)
2. prickle cell layer (stratum spinosum)
3. granular cell layer (stratum granulosum)
4. keratinized cell layer (stratum corneum)
It should be observed that in this section, cell nuclei are lacking in the outer cell layers. Such an epithelium is denoted orthokeratinized. Often, however, the cells of the stratum corneum of the epithelium of human gingiva contain remnants of the nuclei (arrows). In such a case, the epithelium is denoted parakeratinized.. In addition to the keratin-producing cells which comprise about 90% of the total cell population, the oral epithelium contains the following types of cell:.
1. melanocytes
2. Langerhans cells
3. Merkel’s cells
4. inflammatory cells
These cell types are often stellate and have cytoplasmic extensions of various size and appearance. They are also called “clear cells” since in histologic sections, the zone around their nuclei appears lighter than that in the surrounding keratin-producing cells. The photomicrograph shows “clear cells” (arrows) located in or near the stratum basale of the oral epithelium. Except the Merkel’s cells, these “clear cells”, which are not producing keratin, lack desmosomal attachment to adjacent cells. The melanocytes are pigment- synthesizing cells and are responsible for the melanin pigmentation occasionally seen on the gingiva. However, both lightly and darkly pigmented individuals present melanocytes in the epithelium.
The Langerhans cells are believed to play a role in the defense mechanism of the oral mucosa. It has been suggested that the Langerhans cells react with antigens which are in the process of penetrating the epithelium.
An early immunologic response is thereby initiated, inhibiting or preventing further antigen penetration of the tissue. The Merkel’s cells have been suggested to have a sensory function. The cells in the basal layer are either cylindric or cuboid, and are in contact with the basement membrane that separates the epithelium and the connective tissue. The basal cells possess the ability to divide, i.e. undergo mitotic cell division. The cells marked with arrows in the photomicrograph are in the process of dividing. It is in the basal layer that the epithelium is renewed. Therefore, this layer is also termed stratum germinativum, and can be considered the progenitor cell compartment of the epithelium.. When two daughter cells (D) have been formed by cell division, an adjacent “older” basal cell (OB) is pushed into the spinous cell layer and starts, as a keratinocyte, to traverse the epithelium. It takes approximately 1 month for a keratinocyte to reach the outer epithelial surface, where it becomes shed from the stratum corneum. Within a given time, the number of cells which divide in the basal layer equals the number of cells which become shed from the surface. Thus, under normal conditions there is complete equilibrium between cell renewal and cell loss so that the epithelium maintains a constant thickness. As the basal cell migrates through the epithelium, it becomes flattened with its long axis parallel to the epithelial surface. The basal cells are found immediately adjacent to the connective tissue and are separated from this tissue by the basement membrane, probably produced by the basal cells. Under the light microscope this membrane appears as a structureless zone approximately 1 to 2 μm wide (arrows) which react positively to a PAS stain (periodic acid-Schiff stain). This positive reaction demonstrates that the basement membrane contains carbohydrate (glycoprotein’s). The epithelial cells are surrounded by an extra cellular substance which also contains protein-polysaccharide complexes. At the ultra structural level, the basement membrane has a complex composition. The basal cell (BC) occupies the upper portion of the picture. Immediately beneath the basal cell an approximately 400 A wide electron lucent zone can be seen which is called lamina lucida (LL). Beneath the lamina lucida an electron dense zone of approximately the same thickness can be observed. This zone is called lamina densa (LD). From the lamina densa socalled anchoring fibers (AF) project in a fan-shaped fashion into the connective tissue. The anchoring fibers are approximately 1μm in length and terminate freely in the connective tissue. The basement membrane, which appeared as an entity under the light microscope, thus, in the electronmicrograph, appears to comprise one lamina lucida and one lamina densa with adjacent connective tissue fibers (anchoring fibers).The cell membrane of the epithelial cells facing the lamina lucida harbors a number of electron-dense, thicker zones appearing at various intervals along the cell membrane. These structures are called hemidesmosomes (HD). The cytoplasmic tonofilaments (CT) in the cell converge towards such hemidesmosomes. The hemidesmosomes are involved in the attachment of the epithelium to the underlying basement membrane.. Stratum spinosum consists of 10-20 layers of relatively large, polyhedral cells, equipped with short cytoplasmic processes resembling spines. The cytoplasmic processes (arrows) occur at regular intervals and give the cells a prickly appearance. Together with intercellular protein-carbohydrate complexes, cohesion between the cells is provided by numerous “desmosomes” (pairs of hemidesmosomes) which are located between the cytoplasmic processes of adjacent cells. The dark-stained structures between the individual epithelial cells represent the desmosomes (arrows). A desmosome may be considered to be two hemidesmosomes facing one another. The presence of a large number of desmosomes indicates that the cohesion between the epithelial cells is solid. The light cell (LC) in the center of the illustration harbors no hemidesmosomes and is, therefore, not a keratinocyte but rather a “clear cell” . A desmosome can be considered to consist of two adjoining hemidesmosomes separated by a zone containing electron-dense granulated material (GM). Thus, a desmosome comprises the following structural components: (1) the outer leaflets (OL) of the cell membrane of two adjoining cells, (2) the thick inner leaflets (IL) of the cell membranes and (3) the attachment plaques (AP), which represent granular and fibrillar material in the cytoplasm
Melanocytes are present in individuals with marked pigmentation of the oral mucosa (Indians and Negroes) as well as in individuals where no clinical signs of pigmentation can be seen. In this electronmicrograph a melanocyte (MC) is present in the lower portion of the stratum spinosum. In contrast to the keratinocytes, this cell contains melanin granules (MG) and has no tonofilaments or hemidesmosomes. Note the large amount of tonofilaments in the cytoplasm of the adjacent keratinocytes.
When traversing the epithelium from the basal layer to the epithelial surface, the keratinocytes undergo continuous differentiation and specialization. The many changes which occur during this process are indicated in this diagram of a keratinized stratified squamous epithelium. From the basal layer (stratum basale) to the granular layer (stratum granulosum) both the number of tonofilaments (F) in the cytoplasm and the number of desmosomes (D) increase.In contrast, the number of organelles such as mitochondria (M), lamellae of rough endoplasmic reticulum (E) and Golgi complexes (G) decrease in the keratinocytes on their way from the basal layer towards the surface. In the stratum granulosum, electron dense keratohyalin bodies (K) and clusters of glycogen containing granules start to occur. Such granules are believed to be related to the synthesis of keratin.
Keratohyalin granules (arrows) are seen in the stratum granulosum. There is an abrupt transition of the cells from the stratum granulosum to the stratum corneum. This is indicative of a very sudden keratinization of the cytoplasm of the keratinocyte and its conversion into a horny squame.The cytoplasm of the cells in the stratum corneum (SC) is filled with keratin and the entire apparatus for protein synthesis and energy production, i.e. the nucleus, the mitochondria, the endoplasmic reticulum and the Golgi complex, is lost. In a parakeratinized epithelium, however, the cells of the stratum corneum contain remnants of nuclei. Keratinization is considered a process of differentiation rather than degeneration. It is a process of protein synthesis which requires energy and is dependent on functional cells,i.e. cells containing a nucleus and a normal set of organelles.
Summary
The keratinocyte undergoes continuous differentiation on its way from the basal layer to the surface of the epithelium. Thus, once the keratinocyte has left the basement membrane it cao longer divide but main tains a capacity for production of protein (tonofilaments and keratohyalin granules). In the granular layer, the keratinocyte is deprived of its energy- and protein-producing apparatus (probably by enzymatic breakdown) and is abruptly converted into a keratinfilled cell which via the stratum corneum is shed from the epithelial surface. Fig. 1-30 illustrates a portion of the epithelium of the alveolar (lining) mucosa. In contrast to the epithelium of the gingiva, the lining mucosa has no stratum corneum.Notice that cells containing nuclei can be identified in all layers, from the basal layer to the surface of the epithelium
Dento-gingival epithelium
The tissue components of the dento-gingival region achieve their final structural characteristics in conjunction with the eruption of the teeth.. When the enamel of the tooth is fully developed,the enamel-producing cells (ameloblasts) become reduced in height, produce a basal lamina and form, together with cells from the outer enamel epithelium, the so-called reduced dental epithelium (RE).The basal lamina (epithelial attachment lamina: EAL) lies in direct contact with the enamel. The contact between this lamina and the epithelial cells is maintained by hemidesmosomes. The reduced enamel epithelium surrounds the crown of the tooth from the moment the enamel is properly mineralized until the tooth starts to erupt.. As the erupting tooth approaches the oral epithelium, the cells of the outer layer of the reduced dental epithelium (RE), as well as the cells of the basal layer of the oral epithelium (OE), show increased mitotic activity (arrows) and start to migrate into the underlying connective tissue. The migrating epithelium produces an epithelial mass between the oral epithelium and the reduced dental epithelium so that the tooth can erupt without bleeding. The former ameloblasts do not divide.. When the tooth has penetrated into the oral cavity, large portions immediately apical to the incisal area of the enamel are covered by a junctional epithelium (JE) containing only a few layers of cells. The cervical region of the enamel, however, is still covered by ameloblasts (AB) and outer cells of the reduced dental epithelium.. During the later phases of tooth eruption, all cells of the reduced enamel epithelium are replaced by a junctional epithelium. This epithelium is continuous with the oral epithelium and provides the attachment between the tooth and the gingiva. If the free gingiva is excised after the tooth has fully erupted, a new junctional epithelium, indistinguishable from that found following tooth eruption, will develop during healing. The fact that this new junctional epithelium has developed from the oral epithelium indicates that the cells of the oral epithelium possess the ability to differentiate into cells of junctional epithelium.. The enamel (E) is to the left. Towards the right follow the junctional epithelium (JE), the oral sulcular epithelium (OSE) and the oral epithelium (OE). The oral sulcular epithelium covers the shallow groove, the gingival sulcus located between the enamel and the top of the free gingiva. The junctional epithelium differs morphologically from the oral sulcular epithelium and oral epithelium, while the two latter are structurally very similar. Although individual variation may occur, the junctional epithelium is usually widest in its coronal portion (about 15-20 cell layers), but becomes thinner (3-4 cells) towards the cemento-enamel junction (CEJ). The borderline between the junctional epithelium and the underlying connective tissue does not present epithelial rete pegs except when inflamed.
Like the oral sulcular epithelium and the oral epithelium, the junctional epithelium is continuously renewed through cell division in the basal layer. The cells migrate to the base of the gingival sulcus from where they are shed. The border between the junctional epithelium (JE) and the oral sulcular epithelium (OSE) is indicated by arrows. The cells of the oral sulcular epithelium are cuboidal and the surface of this epithelium is keratinized.
There are distinct differences between the oral sulcular epithelium, the oral epithelium and the junctional epithelium:
1. The size of the cells in the junctional epithelium is, relative to the tissue volume, larger than in the oral epithelium.
2. The intercellular space in the junctional epithelium is, relative to the tissue volume,comparatively wider than in the oral epithelium.
3. The number of desmosomes is smaller in the junctionalepithelium than in the oral epithelium.
Note the comparatively wide intercellular spaces between the oblong cells of the junctional epithelium, and the presence of two neutrophilic granulocytes (PMN) which are traversing the epithelium
Lamina propria
The predominant tissue component of the gingiva is the connective tissue (lamina propria). The major components of the connective tissue are collagen fibers (around 60% of connective tissue volume), fibroblasts (around 5%), vessels and nerves (around 35%) which are embedded in an amorphous ground substance (matrix).
The fibroblast is the most predominant connective tissue cell (65% of the total cell population).The fibroblast is engaged in the production of various types of fibers found in the connective tissue, but is also instrumental in the synthesis of the connective tissue matrix. The fibroblast is a spindle-shaped or stellate cell with an oval-shaped nucleus containing one or more nucleoli. A part of a fibroblast is shown in electron microscopic magnification. The cytoplasm contains a well-developed granular endoplasmic reticulum (E) with ribosomes. The Golgi complex (G) is usually of considerable size and the mitochondria (M) are large and numerous. Furthermore, the cytoplasm contains many fine tonofilaments (F). Adjacent to the cell membrane, all along the periphery of the cell, a large number of vesicles (V). The mast cell is responsible for the production of certain components of the matrix. This cell also produces vasoactive substances, which can affect the function of the microvascular system and control the flow of blood through the tissue. A mast cell is presented in electron microscopic magnification. The cytoplasm is characterized by the presence of a large number of vesicles (V) of varying size. These vesicles contain biologically active substances such as proteolytic enzymes, histamine and heparin. The Golgi complex (G) is well developed, while granular endoplasmic reticulum structures are scarce. A large number of small cytoplasmic projections, i.e. microvilli (MV), can be seen along the periphery of the cell. The macrophage has a number of different phagocytic and synthetic functions in the tissue. A macrophage is shown in electron microscopic magnification. The nucleus is characterized by numerous invaginations of varying size. A zone of electrondense chromatin condensations can be seen along the periphery of the nucleus. The Golgi complex (G) is well developed and numerous vesicles (V) of varying size are present in the cytoplasm. Granular endoplasmic reticulum (E) is scarce, but a certaiumber of free ribosomes (R) are evenly distributed in the cytoplasm. Remnants of phagocytosed material are often found in lysosomal vesicles: phagosomes (PH). In the periphery of the cell, a large number of microvilli of varying size can be seen. Macrophages are particularly numerous in inflamed tissue. They are derived from circulating blood monocytes which migrate into the tissue.
Besides fibroblasts, mast cells and macro phages, the connective tissue also harbors inflammatory cells of various types, for example neutrophilic granulocytes, lymphocytes and plasma cells. The neutrophilic granulocytes, also called polymorphonuclear leukocytes, have a characteristic appearance. The nucleus is lobulate and numerous lysosomes (L), containing lysosomal enzymes, are found in the cytoplasm. The lymphocytes are characterized by an oval to spherical nucleus containing localized areas of electron-dense chromatin. The narrow border of cytoplasm surrounding the nucleus contains numerous free ribosomes, a few mitochondria (M) and, in localized areas, endoplasmic reticulum with fixed ribosomes. Lysosomes are also present in the cytoplasm. The plasma cells (Fig. 1-40c) contain an eccentrically located spherical nucleus with radially deployed electron- dense chromatin. Endoplasmic reticulum (E) with numerous ribosomes is found randomly distributed in the cytoplasm. In addition, the cytoplasm contains numerous mitochondria (M) and a well-developed Golgi complex. Fibers The connective tissue fibers are produced by the fibroblasts and can be divided into:
(1) collagen
(2) reticulin fibers,
(3) oxytalan fibers and
(4) elastic fibers.
The collagen fibers predominate in the gingival connective tissue and constitute the most essential components of the periodontium. The electronmicrograph shows cross- and longitudinal sections of collagen fibers. The collagen fibers have a characteristic cross-banding with a periodicity of 700 A between the individual dark bands. The smallest unit, the collagen molecule, is often referred to as tropocollagen. A tropocollagen molecule (TC) which is seen in the upper portion of the drawing is approximately 3000 A long and has a diameter of 15 A. It consists of three polypeptide chains intertwined to form a helix. Each chain contains about 1000 amino acids. One third of these are glycine and about 20% proline and hydroxyproline, the latter being found practically only in collagen. Tropocollagen synthesis takes place inside the fibroblast from which the tropocollagen molecule is secreted into the extracellular space. Thus, the polymerization of tropocollagen molecules to collagen fibers takes place in the extracellular compartment.
First, tropocollagen molecules are aggregated longitudinally to protofibrils (PF), which are subsequently laterally aggregated parallel to collagen fibrils (CFR), with an overlapping of the tropocollagen molecules by about 25% of their length. Due to the fact that special refraction conditions develop after staining at the sites where the tropocollagen molecules adjoin, a cross-banding with a periodicity of approximately 700 A occurs under light microscopy. The collagen fibers ( CF) are bundles of collagen fibrils, aligned in such a way that the fibers also exhibit a cross-banding with a periodicity of 700 A. In the tissue, the fibers are usually arranged in bundles. As the collagen fibers mature, covalent crosslinks are formed between the tropocollagen molecules, resulting in an age-related reduction in collagen solubility. Cementoblasts and osteoblasts are cells which also possess the ability to produce collagen.
Reticulin fibers — as seen in this photomicrograph exhibit argyrophilic staining properties and are numerous in the tissue adjacent to the basement membrane (arrows). However, reticulin fibers also occur in large numbers in the loose connective tissue surrounding the blood vessels. Thus, reticulin fibers are present at the epithelium-connective tissue and the endothelium-connective tissue interfaces.
Oxytalan fibers are scarce in the gingiva but numerous in the periodontal ligament. They are composed of long thin fibrils with a diameter of approximately 150 A. These connective tissue fibers can be demonstrated light microscopically only after previous oxidation with peracetic acid. The photomicrograph illustrates oxytalan fibers (arrows) in the periodontal ligament, where they have a course mainly parallel to the long axis of the tooth. The function of these fibers is as yet unknown. The cementum is seen to the left and the alveolar bone to the right.
Elastic fibers in the connective tissue of the gingiva and periodontal ligament are only present in association with blood vessels. However, as seen in this photomicrograph, the lamina propria and submucosa of the alveolar (lining) mucosa contaiumerous elastic fibers (arrows). The gingiva (G) seen coronal to the mucogingival junction (MGJ) contains no elastic fibers except in association with the blood vessels. Although many of the collagen fibers in the gingiva and the periodontal ligament are irregularly or randomly distributed, most tend to be arranged in groups of bundles with a distinct orientation. According to their insertion and course in the tissue, the oriented bundles in the gingiva can be divided into the following groups:
1. Circular fibers (CF) are fiber bundles which run their course in the free gingiva and encircle the tooth in a cuff- or ring-like fashion.
2. Dentogingival fibers (DGF) are embedded in the cementum of the supra-alveolar portion of the root and project from the cementum in a fan-like configuration out into the free gingival tissue of the facial, lingual and interproximal surfaces.
3. Dentoperiosteal fibers (DPF) are embedded in the same portion of the cementum as the dentogingival fibers, but run their course apically over the vestibular and lingual bone crest and terminate in the tissue of the attached gingiva. In the border area between the free and attached gingiva, the epithelium often lacks support by underlying oriented collagen fiber bundles. In this area the free gingival groove (GG) is often present.
4. Transseptal fibers (TF), seen on the drawing to the right, extend between the supra-alveolar cementum of approximating teeth. The transseptal fibers run straight across the interdental septum and are embedded in the cementum of adjacent teeth. illustrates in a histologic section the orientation of the transseptal fiber bundles (arrows) in the supra-alveolar portion of the interdental area. It should be observed that, besides connecting the cementum (C) of adjacent teeth, the transseptal fibers also connect the supra-alveolar cementum (C) with the crest of the alveolar bone (AB). The four groups ofcollagen fiber bundles reinforce the gingiva and provide the resilience and tone which is necessary for maintaining its architectural form and the integrity of the dento-gingival attachment.
Matrix
The matrix of the connective tissue is produced mainly by the fibroblasts, although some constituents are produced by mast cells, and other components are derived from the blood. The matrix is the medium in which the connective tissue cells are embedded and it is essential for the maintenance of the normal function of the connective tissue. Thus, the transportation of water, electrolytes, nutrients, metabolites, etc., to and from the individual connective tissue cells occurs within the matrix. The main constituents of the connective tissue matrix are protein carbohydrate macromolecules. These complexes are normally divided into proteoglycans and glycoproteins. The proteoglycans contain glycosaminoglycans as the carbohydrate units (hyaluronan sulfate, heparan sulfate, etc.), which, via covalent bonds, are attached to one or more protein chains. The carbohydrate component is always predominant in the proteoglycans. The glycosaminoglycan called hyaluronan or “hyaluronic acid” is probably not bound to protein. The glycoproteins (fibronectin, osteonectin, etc.) also contain polysaccha- rides, but these macromolecules are different from glycosaminoglycans. The protein component is predominating in glycoproteins. In the macromolecules, mono- or oligosaccharides are, via covalent bonds, connected with one or more protein chains.
Normal function of the connective tissue depends on the presence of proteoglycans and gly cosaminoglycans. The carbohydrate moiety of the proteoglycans, the glycosaminoglycans, are large, flexible, chain formed, negatively charged molecules, each of which occupies a rather large space In such a space, smaller molecules, e.g. water and electrolytes, can be incorporated while larger molecules are prevented from entering.
The proteoglycans thereby regulate diffusion and fluid flow through the matrix and are important determinants for the fluid content of the tissue and the maintenance of the osmotic pressure. In other words, the proteoglycans act as a molecule filter and, in addition, play an important role in the regulation of cell migration (movements) in the tissue. Due to their structure and hydration, the macromolecules exert resistance towards deformation, thereby serving as regulators of the consistency of the connective tissue If the gingiva is suppressed, the macromolecules become deformed. When the pressure is eliminated, the macromolecules regain their original form. Thus, the macromolecules are important for the
resilience of the gingiva.
Epithelial mesenchymal interaction
There are many examples of the fact that during the embryonic development of various organs, a mutual inductive influence occurs between the epithelium and the connective tissue. The development of the teeth is a characteristic example of such phenomena.The connective tissue is, on the one hand, a determining factor for normal development of the tooth bud while, on the other, the enamel epithelia exert a definite influence on the development of the mesenchymal components of the teeth. It has been suggested that tissue differentiation in the adult organism can be influenced by environmental factors. The skin and mucous membranes, for instance, often display increased keratinization and hyperplasia of the epithelium in areas which are exposed to mechanical stimulation. Thus, the tissues seem to adapt to environmental stimuli. The presence of keratinized epithelium on the masticatory mucosa has been considered to represent an adaptation to mechanical irritation released by mastication. However, research has demonstrated that the characteristic features of the epithelium in such areas are genetically determined. Despite the fact that the transplanted gingiva (G) is mobile in relation to the underlying bone, like the alveolar mucosa, it has retained its characteristic, morphologic features of a masticatory mucosa. However, a narrow zone of new keratinized gingiva (NG) has regenerated between the transplanted alveolar mucosa (AM) and the teeth. Since elastic fibers are lacking in the gingival connective tissue (G), but are numerous (small arrows) in the connective tissue of the alveolar mucosa (AM), the transplanted gingival tissue can readily be identified. The epithelium covering the transplanted gingival tissue exhibits a distinct keratin layer (between large arrows) on the surface, and also the configuration of the epithelium- connective tissue interface (i.e. rete pegs and connective tissue papillae) is similar to that of normal non-transplanted gingiva. This observation demonstrates that the characteristics of the gingiva are genetically determined rather than being the result of functional adaptation to environmental stimuli.
Epithelial cells have migrated from the alveolar mucosal transplant (AM) onto the newly formed gingival connective tissue (NG). Thus, the newly formed gingiva has become covered with a keratinized epithelium (KE) which has originated from the non-keratinized epithelium of the alveolar mucosa (AM). This implies that the newly formed gingival connective tissue (NG) possesses the ability to induce changes in the differentiation of the epithelium originating from the alveolar mucosa. This epithelium, which is normally non-keratinized, apparently differentiates to keratinized epithelium because of stimuli arising from the newly formed gingival connective tissue (NG). (GT: gingival transplant.) This tissue portion has attained an appearance similar to that of the normal gingiva, indicating that this connective tissue is now covered by keratinized epithelium. The transplanted connective tissue from the alveolar mucosa (AM) is covered by non-keratinized epithelium, and has the same appearance as the surrounding alveolar mucosa.
The transplanted gingival connective tissue is covered by keratinized epithelium (between arrowheads)
The epithelium-connective tissue interface has the same wavy course (i.e. rete pegs and connective tissue papillae) as seen in normal gingiva. Note the distinct relationship between keratinized epithelium (arrow) and “inelastic” connective tissue (arrowheads), and between non-keratinized epithelium and “elastic connective tissue. The establishment of such a close relationship during healing implies that the transplanted gingival connective tissue possesses the ability to alter the differentiation of epithelial cells as previously suggested. From being nonkeratinizing cells, the cells of the epithelium of the alveolar mucosa have evidently become keratinizing cells. This means that the specificity of the gingival epithelium is determined by genetic factors inherent in the connective tissue.
PERIODONTAL LIGAMENT
The periodontal ligament is the soft, richly vascular and cellular connective tissue which surrounds the roots of the teeth and joins the root cementum with socket wall. In the coronal direction, the periodontal ligament is continuous with the lamina propria of the gingiva and is demarcated from the gingiva by the collagen fiber bundles which connect the alveolar bone crest with the root (the alveolar crest fibers). In radiographs, two types of alveolar bone can be distinguished:
1. The part of the alveolar bone which covers the alveolus, called “lamina dura” (arrows).
2. The portion of the alveolar process which, in the radiograph, has the appearance of a meshwork.
This is called the “spongy bone”. The periodontal ligament is situated in the space between the roots (R) of the teeth and the lamina dura or the alveolar bone proper (arrows). The alveolar bone (AB) surrounds the tooth to a level approximately 1mm apical to the cemento-enamel junction (CEJ). The coronal border of the bone is called the alveolar crest (arrows).
The periodontal ligament space has the shape of an hourglass and is narrowest at the mid-root level. The width of the periodontal ligament is approximately 0.25 mm (range 0.2-0.4 mm). The presence of a periodontal ligament permits forces, elicited during masticatory function and other tooth contacts, to be distributed to and resorbed by the alveolar process via the alveolar bone proper. The periodontal ligament is also essential for the mobility of the teeth. Tooth mobility is to a large extent determined by the width, height and quality of the periodontal ligament (seeChapters 18 and 30). The tooth is joined to the bone by bundles of collagen fibers which can be divided into the following main groups according to their arrangement:
1. alveolar crest fibers (ACF)
2. horizontal fibers (HF)
3. oblique fibers (OF)
4. apical fibers (APF)
The periodontal ligament and the root cementum develop from the loose connective tissue (the follicle) which surrounds the tooth bud. The sche matic drawing depicts the various stages in the organization of the periodontal ligament which forms concomitantly with the development of the root and the eruption of the tooth.
The tooth bud is formed in a crypt of the bone. The collagen fibers produced by the fibroblasts in the loose connective tissue around the tooth bud are, during the process of their maturation, embedded into the newly formed cementum immediately apical to the cemento-enamel junction (CEJ). These fiber bundles oriented towards the coronal portion of the bone crypt will later form the dentogingival fiber group, the dentoperiosteal fiber group and the transseptal fiber group which belong to the oriented fibers of the gingiva.
The true periodontal ligament fibers, the principal fibers, develop in conjunction with the eruption of the tooth. First, fibers can be identified entering the most marginal portion of the alveolar bone.
Later, more apically positioned bundles of oriented collagen fibers are seen.
The orientation of the collagen fiber bundles alters continuously during the phase of tooth eruption. First, when the tooth has reached contact in occlusion and is functioning properly, the fibers of theperiodontal ligament associate into groups of welloriented dentoalveolar collagen fibers. These collagen structures undergo constantremodeling (i.e. resorption of old fibers and formation of new ones).. The alveolar bone proper (ABP) is seen to the left, the periodontal ligament (PL) is depicted in the center and the root cementum (RC) is seen to the right.. First, small, fine, brush-like fibrils are detected arising from the root cementum and projecting into the PL space. The surface of the bone is, at thi stage, covered by osteoblasts. From the surface of the bone only a small number of radiating, thin collagen fibrils can be seen.
Later on, the number and thickness of fibers entering the bone increase. These fibers radiate towards the loose connective tissue in the mid-portion of the periodontal ligament area (PL), which contains more or less randomly oriented collagen fibrils. The fibers originating from the cementum are still short while those entering the bone gradually become longer. The terminal portions of these fibers carry finger-like projections.. The fibers originating from the cementum subsequently increase in length and thickness and fuse in the periodontal ligament space with the fibers originating from the alveolar bone. When the tooth, following eruption, reaches contact in occlusion and starts to function, the principal fibers become organized in bundles and run continuously from the bone ton the cementum.
(Sharpey’s fibers) have a smaller diameter but are more numerous than those embedded in the alveolar bone proper (Sharpey’s fibers). The periodontal ligament also contains a few elastic fibers associated with the blood vessels. Oxytalan fibers are also present in the periodontal ligament. They have a mainly apico-occlusal orientation and are located in the ligament closer to the tooth than to the alveolar bone. Very often they insert into the cementum. Their function has not been determined.The cells of the periodontal ligament are: fibroblasts, osteoblasts, cementoblasts, osteoclasts, as well as epithelial cells and nerve fibers. The fibroblasts are aligned along the principal fibers, while cementoblasts line the surface of the cementum, and the osteoblasts line the bone surface. The cells, called the epithelial cell rests of Mallassez, represent remnants of the Hertwig’s epithelial root sheath. The epithelial cell rests are situated in the periodontal ligament at a distance of 15-75 μm from the cementum (C) on the root surface.
The principal fibers embedded in the cementum epithelial cell rests of Mallassez, which in ordinary histologic sections appear as isolated groups of epithelial cells, in fact form a continuous network of epithelial cells surrounding the root. Their function is at present unknown.
