Genes and related proteins involved in amelogenesis imperfecta

Dental enamel formation is a remarkable example of a biomineralization process. The exact mechanisms involved in this process remain partly obscure. Some of the genes encoding specific enamel proteins have been indicated as candidate genes for amelogenesis imperfecta. Mutational analyses within studied families have supported this hypothesis. Mutations in the amelogenin gene (AMELX) cause X-linked amelogenesis imperfecta, while mutations in the enamelin gene (ENAM) cause autosomal-inherited forms of amelogenesis imperfecta. Recent reports involve kallikrein-4 (KLK4), MMP-20, and DLX3 genes in the etiologies of some cases. This paper focuses mainly on the candidate genes involved in amelogenesis imperfecta and the proteins derived from them, and reviews current knowledge on their structure, localization within the tissue, and correlation with the various types of this disorder.

Evaluation of periapical radiographs in the recognition of C-shaped mandibular second molars

AIM

The purpose of this study was to evaluate in a blind trial the efficacy of radiographs to recognize C-shaped mandibular second molars and to determine the incidence of this entity amongst second mandibular molars treated in the Department of Endodontology at the School of Dentistry of the University of Thessaloniki during a seven-year period (1989 - 95).

METHODOLOGY

A total of 480 clinical records of root treated mandibular second molars were reviewed. The preoperative, working length, and final radiograph of each tooth alone and in combination were examined in groups as follows: group 1 (preoperative radiographs only), group 2 (working length radiographs), group 3 (final radiographs), group 4 (preoperative and working length radiographs), group 5 (preoperative and final radiographs) and group 6 (all three radiographs). The efficacy of each combination to identify the C-shaped cases was evaluated based on the interpretation of three experienced dentists looking simultaneously at each case. Films were examined on a viewer using a magnifying glass and allowing a two-week interval between groups. Results were compared with the clinical diagnoses stated on the patients' records (group 7).

RESULTS

The review of clinical records revealed that 4.58% of second molars had C-shaped canals. Radiographic interpretation was overall more effective when based on film combinations (groups, 4, 5, and 6) than on single radiographs. Amongst the latter, working length radiographs were more helpful than the preoperative and final ones. Preoperative radiographs were the least effective in diagnosing C-shaped cases.

CONCLUSIONS

Simultaneous interpretation of preoperative, working length and post-treatment radiographs is important when attempting to diagnose a C-shaped configuration.

The use of 3D computerized reconstruction for the study of coronal microleakage

AIM

The purpose of this study was to evaluate a new method for studying coronal microleakage associated with root-filled teeth.

METHODOLOGY

Twenty human mandibular posterior teeth were prepared chemomechanically with the stepback technique and then divided into two groups of 10 teeth each. The canals were filled using lateral condensation of gutta-percha points; Roth's 801 was used as a sealer for the first group, and Ketac-Endo for the second. After 48 h, the temporary fillings in the access cavities were removed, the roots coated with three layers of nail polish and then the teeth were exposed to artificial saliva for 40 days. Subsequently, the crowns of the teeth were placed into Indian ink for 4 days before the coating was removed and the teeth embedded in a two-phase polyester resin. Serial cross sections were taken from each specimen using a microtome, and each cross section photographed under a stereoscopic microscope. The photographs of the cross sections were digitized using an image scanner and the contours of the external surface of the teeth, the obturated root canals and the boundaries of dye penetration were followed. Finally, a three-dimensional surface representation was achieved using the triangulation method.

RESULTS

Although the sample size and the experimental methods were not designed to form valid groups, the results showed that all roots obturated with Ketac-Endo sealer had dye microleakage, whilst only three teeth of the Roth's 801 group had dye microleakage.

CONCLUSIONS

The 3D reconstruction of dye microleakage proved to be an interesting method and a useful tool for the evaluation of coronal microleakage when using different types of root canal sealers.

Three-dimensional reconstruction: a new method for the evaluation of apical microleakage

The purpose of this study was the evaluation of a new method for studying apical microleakage by using a three-dimensional (3-D) reconstruction method. Fourteen human single-rooted mandibular teeth were used for this work. The canals were prepared with hand instruments by using the step-back technique. To supply a focus to the study of the method, the teeth were divided into two groups that were obturated using two different sealers. India ink was used for passive stain. Serial cross-sections 0.75 mm thick were taken from each specimen by using a special microtome. Each section was photographed under a stereoscopic microscope. Each photograph was digitized and processed to obtain a 3-D reconstruction of the external surface of the teeth, their corresponding prepared root canals, and their apical microleakage. Sample size and experimental methods were not designed to make valid groups; however, apical microleakage was observed in both groups ranging between 2.25 to 8.25 mm height. The 3-D reconstruction method has proved to be a useful tool in the study of apical microleakage.

Dense-cored vesicles in human dental macrophage-like pulpal cells

In the human dental pulp of five healthy premolars, we detected the presence of vesicles in the cytoplasm of macrophage-like cells. There were, in general, two types of vesicles, with regard to their size and content. The first was of smaller size (35 to 55 nm), and they were electron optically empty. The second type included larger vesicles (100 to 150 nm) presenting a heavily and homogeneously osmiophilic dense core. Their overall morphology was strikingly similar to the well-known, dense-cored vesicles of the sympathetic and neuroendocrine systems. This morphological evidence may be considered as an adjunctive support for the neural crest derivation of the dental pulp.

SEM examination of secondary dentine under and opposite cervical carious lesions

The deposition of calcified secondary dentine underlying carious lesions and on the wall opposite to the carious lesions was examined in this study. Twenty single rooted human teeth were used in this work. The teeth were cleaned and fractured into two longitudinal halves, which were examined under a scanning microscope. The results showed complete disappearance of the dentinal tubules, globular mineralized deposits, and mineralized deposits of fibrous morphology underlying carious lesions, while on the dentinal walls opposite to the carious lesions were calsospherites, mineralized secondary dentine, and typical deposition of secondary dentine.

Computerized 3-D reconstruction of two "double teeth"

"Double teeth" is a root malformation in the dentition and the purpose of this study was to reconstruct three-dimensionally the external and internal morphology of two "double teeth". The first set of "double teeth" was formed by the conjunction of a mandibular molar and a premolar, and the second by a conjunction of a maxillary molar and a supernumerary tooth. The process of 3-D reconstruction included serial cross-sectioning, photographs of the sections, digitization of the photographs, extraction of the boundaries of interest for each section, surface representation using triangulation and, finally, surface rendering using photorealistic effects. The resulting three-dimensional representations of the two teeth helped us visualize their external and internal anatomy. The results showed: a) in the first case, fusion of the radical and coronal dentin, as well as fusion of the pulp chambers; and b) in the second case, fusion only of the radical dentin and the pulp chambers.

3D reconstruction of two C-shape mandibular molars

Two mandibular second molars, with an indication of C-shape morphology were processed for 3-D reconstruction. After serial cross sectioning, photographs of the sections were digitized and by using surface representation, 3D reconstruction was achieved. The first molar as the 3D reconstruction showed was single rooted with one C-shaped root canal with two foramens, while the second one was double rooted with two root canals, one C-shaped and one thin, having a common foramen.

Role of cementoenamel junction on the radicular penetration of 30% hydrogen peroxide during intracoronal bleaching in vitro

Intracoronal bleaching of nonvital, teeth with 30% hydrogen peroxide is occasionally associated with external cervical root resorption. The exact mechanism by which bleaching induced root resorption occurs is not yet fully understood. The relationship of cementum to the enamel at the cementoenamel junction may have clinical significance. Seventeen single rooted human mandibular premolars extracted atraumatically for orthodontic reasons were used. The radicular hydrogen peroxide penetration in each tooth was measured in vitro by an indirect colorimetric method. Thereafter, the teeth were examined with a scanning electron microscope to determine the type of the cementoenamel junction. It was found that the radicular penetration of 30% hydrogen peroxide was related to the type of cementoenamel junction.

Three computer methods to reconstruct pulpal blood vessels and nerves

This study describes three methods of computerized three-dimensional reconstruction of the main neurovascular pulpal bundle of human teeth, using serial cross-paraffin sections, digital image processing, and three-dimensional computer graphics. These methods are surface representation, representation by means of a stack of slices, and volume representation.

Computerized reconstruction of TEM examined pulpal blood vessels and nerves

Five healthy premolars were used for transmission electron microscopy examination and three-dimensional (3D) reconstruction of pulpal blood vessels and their surrounding nerves. Serial Epon thin sections were taken from specimens. After a series of preprocessing steps that included digitization, contrast enhancement, slice alignment, segmentation and interpolation, three dimensional surface representation was performed using the triangulation method. The findings showed that vessels were usually accompanied by a number of myelinated and unmyelinated nerves. The nerves shared a more or less common course with the vessels. Small arteries presented greater number of nerves in their vicinity, compared to small veins. In the sections examined, no direct contact between the nerve trunks and the wall of the vessels was found; the closest distance measured was approximately 67 microns. The common course of vessels and nerves suggested autonomic innervation on part of the myelinated axons.

Computerized three-dimensional reconstruction: a method to study pulpal vessels and nerves

This study describes a method of computerized three-dimensional reconstruction of the main neurovascular pulpal bundle of human teeth, using serial cross paraffin sections, digital image processing, and three-dimensional computer graphics.

Pinocytotic vacuoles in human dental pulp capillaries

Dental pulp capillaries were studied in human. They were of the continuous type, with the exception of a small number which were of the fenestrated type, located in the vicinity of the odontoblasts. A characteristic morphological peculiarity was found in the endothelial cells. In places there was a large quantity of multi-sized vacuoles. The vacuoles were evidently of pinocytotic origin, and their content was emptied into the extracapillary space. The initiation of their formation was indicated by the creation of cytoplasmic flaps, which could not be characterised as typical pseudopodia, and which in cross sections resembled microvilli. The flaps engulfed a quantity of plasma and then, after bending over, their edge fused with the cell, creating a vacuole. The vacuole, after being moved abluminally, was emptied into the pericapillary area by exocytosis. There was indication that flaps created at the borders of the endothelial cells (flanges) acted likewise, transporting vacuoles through the intercellular spaces. Micropinocytosis, was a distinctly different phenomenon, contributing, to a very small degree, to the intracellular enlargement of the vacuoles. It seems that this vacuolar mechanism of transportation serves an augmented metabolic need of the surrounding tissue.

[Histological investigation of neural plexus on developing permanent teeth. Study on puppies]

On permanent premolars of 9 puppies (three groups of 45 days, 3 and 4 months old) the neural plexus was studied, using the Alcian blue/PAS and Bielschowsky staining techniques. Nerve fibres were observed on the 45 days group, directed to the odontoblastic layer, as well as fine nerve bundles, parallel to the vessels. On the 3-months group nerve fibres were seen in the dental papilla and the dental sac. Furthermore a significant increase in number size of the nerve fibres was noticed on the 4-months group, comparing with those of the 3-months group.

[Effect of antibiotic administration on the healing of replanted teeth. Experimental investigation in dogs]

Administration of antibiotics is usually recommended when an avulsed tooth is replanted although: a. no immediate acute infection as a consequence of tooth replantation has been known, b. their administration following tooth replantation has been questioned. The purpose of this experimental study was to investigate the effect of antibiotic administration on the healing of replanted teeth. 16 maxillary and mandibular permanent lateral incisors of four dogs aged from 5 to 7 months were immediately replanted without endodontic treatment. Oxytetracycline was administered intramuscularly the day of the experiment and twice daily through the experimental period in two of the dogs (8 teeth). The animals were sacrificed so as to provide observation periods of 15 and 22 days. Results were evaluated histopathologically in haematoxyline eosine stained sections. Results obtained showed shallower resorptine cavities without inflammatory cells in the experimental group (administration of antibiotics) than those found in the control group where inflammatory cells were also present.

[Histomorphological appearance of epithelial root diaphragm during the cervical root development in multirooted teeth]

The epithelial diaphragm during the I stage of root development was studied in premolar teeth of dogs by light microscopy. There were observed such with a rounded tip or with a sharp. In the rounded tip there were appeared three cell layers, and with a sharp tip there was no difference between cells of outer and inner layer.

[Development of dental tissues innervation in primary teeth. Experimental study on dogs]

In this work it was studied the innervation of pulp-dentin in primary premolars on experimental - dogs of 15, 35, 55 days old, with the aid of stainings Alcian blue/PAS and Bielschowsky. On 15 days old experimental dogs there were seen nerve fibres subodontoblastically. On 35 days old experimental dogs nerve fibres were directed towards the odontoblasts, there were also seen neural loops subodontoblastically and terminal nerve fibres on the exterior surface of the vessels. On 55 days old experimental dogs there was seen a great number of argyrophilic fibres in the district of the relapse of the dentine and pulp.