A Textbook
E-Book, Englisch, 271 Seiten, ePub
ISBN: 978-3-13-257950-7
Verlag: Thieme
Format: EPUB
Kopierschutz: 6 - ePub Watermark
Features:
- Easy-to-reference presentation of dental morphology and treatment guidelines - Chapter on how to avoid and manage potential complications - More than 550 high-quality illustrations demonstrating important concepts.
This book is a valuable resource for students that will enable them to fully grasp the fundamental concepts of clinical endodontics. It is also serve as a refresher for general practitioners, postdoctoral students, and endodontists.
Autoren/Hrsg.
Fachgebiete
Weitere Infos & Material
1 The Endodontium
2 The Apical Periodontium
3 Endodontic Symptomatology
4 Endodontic Examination and Diagnosis
5 Treatment of Teeth with Vital Pulp
6 Treatment of Nonvital Teeth
7 Endodontic Emergency Treatment
8 Endodontic Aspects of Root Resorption
9 Endodontic Instruments
10 Endodontic Materials
11 Endodontic Techniques
12 Dental Morphology and Treatment Guidelines
13 Endodontic Complications
14 Endodontic Retreatment
15 Bleaching of Discolored Teeth
16 Restoration of Endodontically Treated Teeth
17 Prognosis of Endodontic Treatment
1
The Endodontium
Structure
The endodontium comprises the dentin and pulp of the tooth. Both tissues develop from the dental papilla, and although the dentin mineralizes and the pulp remains a soft tissue, they maintain an intimate structural and functional relationship throughout the life of the tooth. All the cells of the endodontium are located in the pulp and only cellular extensions, odontoblast processes, and nerve endings are found in the dentin. Thus, tissue reactions in the dentin are dependent to a great extent on the activity of cells in the pulp. Conversely, pulpal reactions may be significantly modified by tissue changes in the dentin. The Dentin Composition and Morphology The dentin is composed of approximately 70% inorganic material in the form of hydroxyapatite crystals. The organic matrix, about 15–20%, consists of collagen. Noncollagenous proteins constitute 1–2% of the tissue, whereas the remaining 10–12% is water. The dentin of the fully formed tooth is called primary dentin. It constitutes the bulk of the tooth and is especially characterized by the presence of dentinal tubules (Fig. 1.1). The tubules generally extend from the area of the dentin–enamel and the dentin–cementum junctions to the pulp. The tubules are surrounded by peritubular dentin, which is a dense, highly mineralized tissue with a noncollagenous matrix. Between the tubules we find the intertubular dentin, which consists of mineralized collagen. Unmineralized predentin lines the pulpal aspect of the dentin. Fig. 1.1 Scanning electron micrographs of fractured coronal dentin from an impacted canine in a 13-year-old. a Dentin from the middle area of the crown with crosscut dentinal tubules (diameter: 2 µm). Fibers are seen leaving some of the tubules (× 1700). b Dentin near the enamel–dentin junction (mantle dentin) with crosscut dentinal tubules (arrows). Note small diameter (0.5 µm) of the tubules (× 1700). c Predentinal surface with intertubular fibrous matrix (× 2600). Unmineralized matrix may also be seen inside the mineralized primary dentin. Well known is interglobular dentin, which occurs when mineralizing globules fail to coalesce. From a clinical point of view, it is more important that the buccal and lingual portions of the incisal dentin not always unite, but leave an unmineralized central streak or a soft tissue-containing space, sometimes extending all the way to the incisal dentin–enamel junction (Fig. 1.2). Clearly, in such teeth, an apparent uncomplicated crown fracture will cause exposure of the pulp. Dentinogenesis continues, but at a slower rate, even after the teeth are fully formed. This dentin is called physiologic secondary dentin and it differs from the primary dentin in that its structure and composition may vary within the tooth and from one tooth to the next. As will be discussed later (see p. 26), increased secondary dentin formation in localized areas of the tooth may occur in response to external irritation. The structure of this tissue will depend on the severity of the irritation and the degree of tissue injury in the pulp and appears to be completely unpredictable (Fig. 1.3). As a rule, the secondary dentin formed in response to external irritants is more irregular than the physiologic secondary dentin. Fig. 1.2 Microradiograph of an incisor from an 11-year-old. Accentuated incremental lines of buccal and lingual dentin (arrows) meet at the radiopaque central streak, but do not join because of a slit in the dentin at this location. Dentinal Tubules It is well established that the dentinal tubules may serve as portals of entry for external irritants into the pulp. Thus, from a clinical point of view, the tubules are the most important and interesting component of the dentin. In the crown of the tooth, the dentinal tubules generally extend from the area of the dentin–enamel junction to the pulp. In the root, the most peripheral dentin is atubular and the tubules thus begin in an area slightly pulpal to the dentin–cementum junction and extend to the pulp. The diameter of the tubules varies from 0.5 µm in the peripheral dentin to 3–4 µm near the pulp. In the bulk of the dentin they have a diameter of about 2 µm. Due to the much larger peripheral than pulpal surface of the dentin, the number of tubules per square millimeter area increases dramatically in a pulpal direction. Thus, at the dentin–enamel junction, the number of tubules is about 8000 per mm2, halfway between the dentin–enamel junction and the pulp it is 20 000–30 000 per mm2, and near the pulp the number may be as high as 50 000–60 000 per mm2. Similarly, the total volume of the dentinal tubules increases in a pulpal direction and may constitute up to 80% of the total volume of the coronal dentin near the pulp. The dentinal tubules contain tissue fluids (dentin liquor) which is fluid from the pulp tissue filling out the hollows of the dentin. Odontoblastic processes are present in most tubules and they are especially well visualized close to the pulp. Unmyelinated nerve endings may be present as well, usually in intimate contact with the odontoblastic processes (Fig. 1.4). In addition, unmineralized and mineralized collagen fibers are seen in many tubules at all levels of the dentin (Fig. 1.5). Mineralized deposits of various structure and appearance occur in the dentinal tubules under various clinical conditions. Sometimes these deposits have the appearance of peritubular dentin, and have generally been regarded as resulting from a continuous formation of the peritubular dentin (Fig. 1.6). This is probably a misconception since peritubular dentin is a developmental and not an acquired structure and since it forms in full thickness concomitantly with the intertubular dentin. Toward the lumen of the tubule, the peritubular dentin appears to be lined by an organic sheath which has been termed the lamina limitans (Fig. 1.6). A proper term for tubular deposits inside the lamina limitans would therefore be intratubular dentin. Fig. 1.3 Localized secondary dentin formation as a result of external irritation (hematoxylin-eosin). a Secondary dentin (SD) with regular tubular structure indicating mild stimulation of odontoblasts. b Secondary dentin with an atubular, cell-containing zone at the dentin–secondary dentin interface due to severe disturbance of odontoblast function. The cells have recovered and have continued to lay down tubular dentin. c Secondary dentin with few tubules due to death of most odontoblastic cells. Fig. 1.4 Scanning electron micrograph of a tubule from circumpulpal dentin in a 21-year-old. In addition to the odontoblastic process, a slim fiber which divides into two branches and which is interpreted as a nerve fiber is present (× 9000). Fig. 1.5 Scanning electron micrograph of a tubule from the coronal dentin of a 42-year-old. A fiber consisting of fibrils with the cross-banding typical of collagen visible on their surface is present in the tubule (× 10 000). Age Changes Both macroscopic and microscopic changes occur in the dentin with increasing age, and both types of changes are of considerable clinical importance. The macroscopic age changes are characterized by the lifelong formation of physiologic secondary dentin which continually modifies the size and to some extent the shape of the pulp chamber and the root canal. At first these changes are beneficial in that they give the root canal a size and form that enhances the possibilities for successful endodontic treatment. However, in old age, the root canals may be obliterated to such an extent that necessary endodontic treatment becomes extremely difficult. Physiologic secondary dentin formation also occurs on the walls of lateral and accessory root canals, often causing a complete occlusion of these narrow spaces. This is the reason why accessory canals, for instance, in the furcation area of molar teeth which may be readily demonstrable in young teeth are evident only in rare instances during endodontic treatment of adult patients. Fig. 1.6 a Electron micrograph of a cross-cut tubule from partly demineralized root dentin. An electron-dense line (lamina limitans) is recognized between the peritubular dentin matrix and the material beginning to occlude the tubule (×20 000). b Crosscut tubule from undemineralized dentin occluded with material (intratubular dentin) with electron density different from that of peritubular dentin (PD) (×19 000). The microscopic age changes of the dentin are characterized by the fact that an increasing number of dentinal tubules become obliterated by mineralized tissue. The occluding material is homogenous and consists of a noncollagenous matrix and small hydroxyapatite crystals. Its appearance is similar to that of peritubular dentin, but as a rule it can be distinguished from this tissue by a difference in density or by the presence of the lamina limitans (Fig. 1.6). From a...
