The interior of a tooth, the endodontium, is to a large extent hidden from direct inspection by the operator. Even passing roentogen rays through the tooth provides only limited clues to the structure. For this reason, much time and energy have been invested in research into the “normal” anatomy and the statistical incidence of different variations in form (review: Bauman 1995). It is hoped that this information will be helpful in the daily practice of endodontics. This research has already created awareness of the complexity of the root canal system, which is not simply conical tube but rather a branching system with a pulp chamber, primary canals, lateral canals (communicating with the periodontium), and accessory canals (multiple ramifications in the apical third of the root). This knowledge is a basic requirement for successful endodontic treatment. The theoretical pulpal anatomy that we expect to encounter, though, can only provide initial orientation because the actual situation encountered during treatment always reveals new variations.

The first detailed systematic description of root canal anatomy found in the literature is by Carabelli (1844). The same manner of representation with longitudinal and transverse sections in different planes is still used in modern textbooks (eg., Cohen and Burns 1994). Some of these illustrations go back to the original sections and serial sections (Black 1902; Miller 1904). In addition to direct observation with the unaided eye and the microscope, the chemical dissolution method has provided much valuable information. In this process the tooth is opened, the pulp digested, and the empty pulp space filled. The famous Swiss pulp researcher Hess (1917) perfected this technique in which he filled the pulp space with vulcanized India rubber and then dissolved the surrounding tooth substance with 50% hydrochloric acid. This acid dissolution preparation showed the complex branching of the pulp tissues and, with it, the root canal system. Whereas the previous sections, slides, and drawings were only two-dimensional, now for the first time it was possible to see a spatial representation of the entire root canal system. Hess studied 2800 teeth of the permanent human dentition and his student Zurcher (1922) studied deciduous teeth. Together they gathered statistical data on the number of canals and their ramifications.

METHODS OF REPRODUCING ROOT CANAL ANATOMY

Most techniques require the destruction of the tooth. However, at the beginning of the twentieth century the transparency method was developed (Adolf 1913) in which the integrity of the tooth and the spatial relationships of the root canal and its outer contours were preserved. Various substances (from colored gelatin and paraffin to silicone) were introduced into the pulp space through an access opening, and the tooth was then made transparent by means of oil of cedar, benzol, salicylic acid compounds.

While histologic sections have long provided information on the structure of the root canal and the pulp tissue, Meyer (1955-1970) set new standards. From special sections of all 16 types of permannet teeth he made 50x scale models of the apical canals (the last 6 mm of each) of 800 teeth by projecting the circumference of the canals and building wax models layer by layer. This study further clarified the complexity of the pulp space, from then on called the root canal system (Meyer 1955 b, 1960).

Awareness of the existence of large numbers of lateral canals and diverticula renders obvious the impossibility of full preparation of all the branches during root canal treatment. Asignificant outcome of this is the technique of combined chemical-mechanical preparation. After radiographs began to be used in laboratory studies, images in two planes became standard. Pineda and Kutler (1972) performed what is probably the largest in vitro study on over 40000 teeth. Their study covered the extent of branching and variations in canals, roots, and apical deltas, and the influence of age on their occurence.

Hession (1977a-d) showed the shape of the root canal system radiographically before and after in vitro treatment. The abundant range of research tools is complemented by in vivo radiographs, microradiographs, scanning electron microscopy (SEM), computer reconstructions, monographs of individual cases, and many other aids (Baumann 1995). Subsequently, an immense body of facts has been accumulated and these are presented in excellent didactic style in books,videos, slide series, reports, seminars, and demonstration. This new information should be offered in further education courses (Baumann 1994, 1955).

THREE – DIMENSIONAL COMPUTER RECONSTRUCTION

From a historical perspective we see a long tradition of striving to better describe the anatomy of the teeth. Preparations of 20 micrometer thick frozen sections were continuously recorded on videotape, producing data to serve as the basis for computerized three-dimensional reconstructions. In a contour-based reconstruction only the surface outlines of the tooth and the canals are used for input (Baumann et al. 1993d, 1994b). From this emerges a contour line, surface, or solid body model that can be viewed from any desired angle.

Faster computers permit the use of all shades of gray in a video image to create a volume-based reconstruction (volume rendering). Through ray-tracing, isotropic voxels (points in space) are created in which the raw unaltered data is drawn upon for three-dimensional reconstruction (Baumann 195, Baumann et al. 1993d).

Images are created that can be viewed, sectioned, colored, zoomed, or rotated in any desired plane. This makes possible views into the endodontic space that were prevoiusly unknown.

MAGNETIC RESONANCE IMAGING (MRI)

Normally, only vague images of bone and tooth can be obtained by magnetic resonance tomography (MRT). Baumann (1995; Baumann et al. 1993 a-d) was the first to succeed in producing a visual representation of the H+ protons of dental hard structures by using measurement sequences from solid body spectroscopy and especially strong magnetic fields. The soft pulpal tissue is elusive becuase of the small scale of the MRI. The first magnetic resonance images have now been realized with BRUKER SPECTOMETER AMX 300 WB (7 tesla, 300MHz).

Computer processing of data from the MRI permits creation of two and three-dimensional reconstructions that can be rotated and sectioned (Bauman 1995; Baumann and Doll, in press). Now for the first time we have a nondestructive method that does not use ionizing radiation. Two-dimensional sections of molars give rise to the hope that it will be possible to depict differences in tissue texture, which would be a great aid in the diagnosis of pulpitis. The spatial reconstruction of an individual canal configuration would be a great enlightment for endodontic treatment.

Reference – Color Atlas of Dental Medicine

ENDODONTOLOGY

Rudolf Beer, Michael A. Baumann, and Syngcuk Kim

Intensive microbiologic, immunologic, and morphologic research investigations, especially during the past decade, have shown that colonization of tooth surface by pathogenic bacteria is accompanied by humoral and cellular defense mechanisms of the organism not only during the more advanced stage of infection, but also throughout the initial stages. Penetration of these complex defenses, which is usually of limited duration, disturbs the equilibrium of the system and results in disease. Within the dental pulp, this biologic equilibrium has to do with the balanced calcium and phosphate ion exchange during the continuous demineralization and remineralization of the enamel and exposed dentin. As long as a disease process is reversible, as is incipient caries, the capacity for progression and regression is present. Carious breakdown means that enamel is being demineralized by acidogenic plaque more rapidly than it can be remineralized. In its early stages, the caries has become a chronic destructive process, in which irreversible structural changes will preclude any further remission.

Looking at the dynamics of demineralization and remineralization, and the etiology of caries against the epidemiologic background, and comparing them with the results of therapy, a pattern of active disease spurts alternating with resting phases emerges. During these periods of remission, the chronic destructive process is not reversed, but is only brought to a standstill. This concept of progression and stagnation ( Socransky et al. 1984) is strongly influenced by the defensive capability of the organism.

Progression is defined by invasion of caries into dentin with inflammation and loss of connective tissue. Stagnation means the defenses are increased, there are defensive inflammatory cells in the tissues, and connective tissue is being replaced by secondary dentin or granulation tissue. Histologically, this ever-changing dynamic process in carious teeth is recorded over the years through deposition and destruction of dentin.

For the practitioner, the obvious questions that arise are how to classify the histopathologic condition of the pulp and the apical periodontal tissues, and how to initiate treatment that is appropriate, considering the background of stagnation or progression. Based upon clinical findings, differentiations are made between a clinically sound pulp, reversible pulpitis, irreversible pulpitis, a necrotic pulp, and apical periodontitis. These distinctions are based solely upon clinical observations; generally, a correlation between certain symptoms and a specific pathologic entity cannot be expected. Making the distinction between reversible and irreversible inflammations of the pulpal tissues can be a diagnostic problem, because they can present similar clinical symptoms. Histologically, the diagnosis of acute inflammation is based upon the predominance of neutrophilic granulocytes. However, this diagnostic picture does not always coincide with the appearance of pain symptoms because neutrophilic granulocytes can also be found in cases where there is no pain ( Langeland 1981, Lin and Langeland 1981 b, Lin et al. 1984 ).

DIAGNOSIS OF PROXIMAL CARIES

Caries begins with microscopic demineralization of the affected enamel or cementum surface. As it progresses, the enamel first becomes chalky, then its surface is broken through. In this stage, the caries is easy to detect, but has frequently progressed so far that extensive restorative and endodontic treatment in necessary. More difficult to diagnose, on the other hand, are lesions that are in their early stages and dentinal lesions with macroscopically intact surfaces.

Epidemiologic studies have shown that – coincident with a general decrease in caries prevalence in industrialized countries – the occlusal surfaces of the permanent molars of children and young adults are the surfaces most frequently attacked by caries. In contrast to fissure caries, proximal and smooth surface caries is much less frequent. Radiographically evident incipient lesions in enamel of the proximal surfaces have likewise shown a decline. In adults, the probability that these lesions would penetrate further has increased, and this has caused the proportion of proximal caries to rise again.

During clinical examination using explorer many carious lesions with cavity go undiagnosed, so for their proper diagnosis bitewing radiographs, and fiberoptic transillumination (FOTI) are used. Bitewing radiographs are still the method of choice for the diagnosis of approximal caries, and account for the detection of approximately three-fourths of dentinal carious lesions ( Mileman and van der Weele 1990, Noar and Smith 1990). Studies found that where there is a dentinal lesion, there is a surface that has been broken through, which precludes any chance for remineralization (Marthaler and Germann 1970; Bille and Thylstrup 1982; Mejare and Malmgren 1986). Even though the actual extent of caries is underestimated with the radiograph, it may be concluded that the specificity, that is, the ability to recognize sound teeth as sound, is approximately 95% ( Mileman and van der Weele 1990). As far as caries diagnosis is concerned more sensitive X-ray films seem to be the equal of earlier films as far as caries diagnosis is concerned but as they produce same degree of contrast with significantly less radiation, their use is now highly recommended. Preventive measures can impede further penetration and even promote remineralization, provided that the enamel surface has not yet been disrupted.

The progression of caries can be monitored with periodic radiographs. Their interval depends, among other things, upon the individual’s susceptibility to caries. Patients at high risk of caries should be radiographed every year while those at very low risk need only be radiographed every 2-4 years. The time in which it takes caries to penetrate the enamel of a mature permanent molar in a patient with good oral hygiene can exceed 5 years. This offers the opportunity to post-pone invasive restorative treatment and to observe whether the caries progresses or regresses. The rate at which penetration progresses can be estimated by comparing radiographs produced at different times by a standardized technique. Recently erupted teeth, on the other hand, demonstrate a markedly reduced penetration time (Marthaler and Wiesner 1973, Shwarz et al. 1984).

In order to minimize overlapping of the images of approximating tooth surfaces, a film holder is recommended. A deviation of the horizontal angle of the X-ray tube by only a few degrees will result in a substantial decrease in correct diagnoses. Radiolucency in dentin should be treated as invasive only if there is also an unmistakable radiolucency in the enamel region. The radiograph should be inspected carefully under magnification and away from the influence of any light coming from the sides.

FOTI can be used in addition to bitewing radiographs if there is no interference from adjacent interproximal fillings that are other than tooth colored. More than 70% of dentinal lesions in anterior teeth can be detected by means of FOTI. Dentinal lesions in posterior teeth, however, can be differentiated only with great difficulty ( Pieper and Schurade 1987, Choski et al. 1994 ).

Reference – Color Atlas of Dental Medicine

ENDODONTOLGY

Rudolf Beer, Michael A. Baumann, and Syngcuk Kim