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PubMed2000

A histological study of root-resected and root-transected rat incisors when eruption ceases, shortly before they are exfoliated from the socket.

Resection of the odontogenic region or root transection of normal (impeded) rat lower incisors showed that eruption ceased from 1 to 13 weeks when the base of the resected teeth (87.5%) or of the distal segment of the transected ones (86%) reached the alveolar-crest region. When the operated teeth reached the crestal region, the enamel-related periodontal tissues were absent and the periodontal ligament (PDL) was the only periodontal tissue that remained. The PDL of the crestal region may be considered as mature PDL, showing a length of approx. 5-6 6 mm at the mesial face of the tooth, 4-5 mm at lingual face and 1 mm at distal face; from these limits towards the apical end of the socket the PDL becomes gradually immature. The mature PDL seems not to have a role in the process of tooth eruption. Several factors can be suggested to explain the more frequent retention, at the crestal region of the socket, of impeded rather than unimpeded incisors submitted to the same procedures. The connective tissue that develops between the base of the tooth and the bone that fills the alveolus may have more time to organize itself in impeded than in unimpeded teeth, which erupt at a faster rate; this tissue could support and retain the impeded operated teeth longer than the unimpeded ones. The decrease in the mechanical properties of the PDL in the unimpeded condition may ease the traumatic effects and lead to exfoliation. Eruption might be stopped by the increase in occlusal forces, per unit area of root surface, as the root becomes shorter; this effect is likely to be greater in impeded than unimpeded teeth.

Alveolar Process↗
PubMed1997

Calretinin-like immunoreactivity in the Ruffini endings, slowly adapting mechanoreceptors, of the periodontal ligament of the rat incisor.

The distribution and ultrastructural localization of calretinin (CR)-like immunoreactivity (-LI) were investigated in the lingual periodontal ligament of rat incisors. Some thick nerve fibers within the nerve bundle displayed CR-LI; these CR-like immunoreactive (-IR) nerve fibers entered the alveolar half of the lingual periodontal ligament of the incisor where dendritic terminal arborization was exhibited. Thin and beaded CR-IR nerve fibers were rarely observed in the periodontal ligament. Observations of adjacent sections immunostained with protein gene-product 9.5 (PGP 9.5) revealed that most, if not all, PGP 9.5-IR nerve terminals showing a dendritic arborization expressed CR-LI. Immunoelectron microscopic observations showed that electron-opaque immunoreaction products were localized in the axoplasm of the axon terminals, except for the mitochondria, which were surrounded by Schwann sheaths and multiple-layered basal lamina. Neither cell bodies, the cytoplasmic extension of terminal Schwann cells, nor other cellular elements such as periodontal fibroblasts exhibited CR-LI. The present findings suggest that Ruffini endings, an essential mechanoreceptor in the periodontal ligament and categorized as a slowly adapting mechanoreceptor, express CR-LI, and that CR may participate in the Ca2+ homeostasis against external stimuli in the periodontal Ruffini endings.

Animals↗
PubMed1998

Carbonic anhydrase isozyme II immunoreactivity in the mechanoreceptive Ruffini endings of the periodontal ligament in rat incisor.

The present study describes the distribution of carbonic anhydrase isozyme II (CA II) in the lingual periodontal ligament of the rat incisor. Some thick nerve fibers in the nerve bundle displayed CA II-like immunoreactivity (LI) as well as non-neuronal elements such as osteoclasts. At the alveolar half of the lingual periodontal ligament of the incisor, thick CA II-like immunoreactive (-IR) nerve fibers showed a tree-like raminification, but thin and beaded CA II-IR nerve fibers were rare. Under the electron microscope, CA II-LI were diffusely localized in the axoplasm of the axon terminals surrounded by Schwann sheaths which were immunonegative for CA II. The cell bodies of the terminal Schwann cells associated with the periodontal Ruffini endings did not exhibit CA II-LI. The present immunohistochemical evidence indicates that CA II may participate in the regulation of the intra-neuronal ion in the periodontal Ruffini endings which are thought to be in a state of high neuronal activity.

Animals↗
PubMed1998

Growth-associated protein-43 (GAP-43) in the regenerating periodontal Ruffini endings of the rat incisor following injury to the inferior alveolar nerve.

Alterations in the levels of growth-associated protein 43 (GAP-43)-like immunoreactivity (-LI) were examined in the lingual periodontal ligament of the rat incisor following two types of injury (resection and crush) to the inferior alveolar nerve (IAN). In normal animals, GAP-43-like immunoreactive (IR) structures were observed as tree-like ramifications in the alveolar half of the lingual periodontal ligament of incisors. Under immunoelectron microscopy, GAP-43-LI appeared in the Schwann sheaths associated with periodontal Ruffini endings; neither cell bodies of the terminal Schwann cells nor axonal profiles showed GAP-43-LI. During regeneration of the periodontal Ruffini endings following resection of the IAN, GAP-43-LI appeared in the cytoplasm of the terminal Schwann cell bodies and axoplasm of the terminals. The distribution of GAP-43-LI in the Ruffini endings returned to almost normal levels on days 28 and 56 following the injury. The changes in the distribution of GAP-43-LI following the crush injury were similar to those following resection; however, expression of GAP-43-LI was slightly higher for the entire experimental period compared with the resection. The transient expression of GAP-43 in the terminal Schwann cells and axonal profiles of the periodontal Ruffini endings following nerve injury suggests that GAP-43 is closely associated with axon-Schwann cells interactions during regeneration.

Animals↗
PubMed2000

Immunohistochemical detection of heme oxygenase-2 in the periodontal Ruffini ending of the rat incisor.

The present study was carried out to examine the occurrence of heme oxygenase-2 (HO-2) in the periodontal ligament of the rat incisor. HO-2-like immunoreactive (-IR) structures showed dendritic profiles, resembling the Ruffini endings, in the alveolar half of the ligament of rat incisor. Neither thin nerve fibers nor perivascular nerve fibers displayed HO-2-like immunoreactivity (-LI). No non-neural elements exhibited HO-2-LI. Electron microscopy revealed that immunoreactions were diffusely observed in the axon terminals of the Ruffini endings, but neither terminal Schwann cells nor Schwann sheaths contained immunoreactions for HO-2. Both most neurons in the trigeminal ganglion and trigeminal mesencephalic nucleus showed HO-2-LI. The presence of HO-2 in the periodontal Ruffini endings and its absence in the periodontal thin nerve fibers suggest the involvement of carbon monoxide produced by HO-2 in mechanoreception in the periodontal ligament.

Animals↗
PubMed1977

Solitary maxillary central incisor and short stature.

Seven patients, three males and four females, each with a single (unpaired) deciduous and permanent maxillary central incisor, were studied. All the males and two the female children were growth hormone deficient. One adult woman and a female infant with a single maxillary central incisor were short in stature but had normal growth hormone responses. No other dental anomalies or pituitary-hypothalamic dysfunctions were found. The dental anomaly was not familial. No eye abnormalitis were present in the patients or their families.

Adult↗
PubMed1999

Rationalization of incisor shape: experimental-numerical analysis.

STATEMENT OF PROBLEM: Moving from the posterior segment in the anterior direction within the dental arch, the process of "incisivization" takes place. The occlusal table is gradually replaced by an incisal edge that has the function of cutting. PURPOSE: This study considers these genetically controlled changes by using strain gauge measurements and finite element analyses to rationalize the clinical and biologic advantages of incisal form. A direct clinical link in the common esthetic procedure of anterior veneering is expected. MATERIAL AND METHODS: Six maxillary incisors were mounted in a positioning device and equipped with 2 strain gauges bonded to the palatal surface: gauge 1 (G1) in the concavity and gauge 2 (G2) on the cingulum. A 50 N load was applied on the palatal side of the incisal edge, perpendicular to the long axis of the tooth. Displacement of the load tip and the palatal strain were recorded after successively removing one third, two thirds, and the total thickness of the facial enamel. The same experiment was reproduced with the finite element method (FEM). Four additional experimental designs were tested with the FEM by simulating the progressive thinning and elimination of palatal enamel and a thickened palatal lobe. Surface tangential stresses and local strain in the area corresponding to gauges 1 and 2 were calculated from the postprocessing files. RESULTS: The FEM was validated by experimental results considering both displacement of the load tip ( approximately 120 +/- 30 microm) and tangential surface strain at G1/G2. Recorded strains were always higher in the concavity when compared with the cingulum; high tensile strains were recorded at G1 after the total removal of the facial enamel. The entire facial surface was submitted to compressive forces. Subsequent compressive stresses were higher ( approximately 150 MPa) when facial enamel was thin or when the palatal enamel was removed. However, their absolute value never reached the elevated and potentially harmful tensile stresses measured in the palatal concavity, especially in the absence of facial enamel (272 MPa). Multiple experimental cracks were generated in the remaining palatal enamel as a consequence of stress redistribution. However, smooth and convex surfaces with local enamel bulk such as the cingulum, the marginal ridges, and the facial cervical third of the anatomic crown showed the lowest stress level. The optimal configuration with regard to the stress pattern was given by the modified natural tooth that exhibited thick palatal enamel and a mostly convex palatal surface. CONCLUSIONS: Palatal concavity that provides the incisor with its sharp incisal edge and cutting ability proved to be an area of stress concentration. This shortcoming can be compensated by specific areas that feature thick enamel such as the cingulum and the marginal ridges. When enamel is worn or removed from the facial surface, its replacement should be carried out by using materials with properties similar to enamel to restore the original biomechanical behavior of the tooth.

Compliance↗
PubMed1995

Proteoglycans in cementum- and enamel-related predentin of young mouse incisors as visualized by cuprolinic blue.

In rodent incisors, dentin associated with cementum (root-analogue dentin) appears to differ considerably from that associated with enamel (crown-analogue dentin), both with respect to the composition of certain matrix components and the mineral. Since it is not known whether these dentin portions also differ with respect to their proteoglycans, the morphological appearance and spatial distribution of these components was studied in predentin by employing cuprolinic blue, a dye selective for proteoglycans. Lower incisors of five-day-old mice were stained with the dye and processed for electron microscopic examination. Cuprolinic blue-positive precipitates were found in both cementum- and enamel-related predentin. In cementum-related predentin these structures were thick and short. In the enamel-related portion, however, they were long, slender and frequently stellate-shaped. The number of precipitates was similar between the two predentin portions and also no differences were found between the basal and the apical (adjacent to the mineralization front) aspects of the predentin layers. It is suggested that the differences in proteoglycan architecture among the predentin layers is somehow related to differences in the three-dimensional collagenous meshwork or to different patterns of mineralization.

Animals↗
PubMed1996

Endodontic retreatment of unusually long maxillary central incisors.

Anatomical and morphological variations in teeth may affect the success and prognosis of endodontic therapy. The reported data regarding such variations in the maxillary central incisors are limited. This article presents a case of endodontic retreatment in unusually long maxillary central incisors.

Adolescent↗
PubMed1994

Root canal ramifications in mandibular incisors and efficacy of low-temperature injection thermoplasticized gutta-percha filling.

The frequency of root canal ramifications in mandibular central and lateral incisors and the efficacy of low-temperature injection thermoplasticized gutta-percha in filling these canals were determined, and any evidence of apical leakage was evaluated. Forty mandibular incisors were instrumented; the external root surfaces were coated with nail polish except for the apical foramen, and the teeth were obturated with injection of gutta-percha and sealer. The teeth were centrifuged in India ink for 20 min at 3000 rpm before being suspended in ink for 30 days and then cleared. Under a stereomicroscope at x30 magnification, 62.5% of the teeth showed a simple main canal, 15.0% a bifurcated canal, 7.5% a lateral canal, and 25% accessory canals. Except for the two lateral and three accessory canals, the thermoplasticized gutta-percha was found to be highly effective in filling the root canal ramifications as well as the main canals. The extent of ink penetration was limited to the main canal in seven teeth showing leakage. However, the reliability of conventional apical leakage assessment by only exposing major foramen to dye needs to be reexamined with regard to the potential presence of multiple foramina on the root surfaces.

Adult↗
PubMed1995

The mandibular incisor: rethinking guidelines for post and core design.

In post and core research, little attention has been given to the tooth with minimal bulk and mesialdistal width. The purpose of this in vitro study was to investigate retention and fracture characteristics of lower incisors restored with variable dowel designs. Fifty freshly extracted mandibular incisors were endodontically treated. Four groups of 10 teeth, decoronalized and dowel- and core-restored, were tested for retention characteristics and fracture resistance. One group of 10 teeth restored with composite resin in intact natural crown acted as controls. Dowel variables included a prefabricated round cross-sectional design and a morphologic dowel that reproduced the canal space. A universal testing machine created tensile and transverse loads, and failure was measured and recorded. Results showed no difference in resistance to transverse loading between morphological and standardized dowels (p > 0.05). However, when analyzing modes of failure, ferruled morphological post and core design was less likely to result in a catastrophic root or post fracture. In addition, morphological dowels were significantly more retentive than standardized round dowels in teeth with narrow cross-sections (p = 0.007). This study also reaffirmed the findings of previous investigations, that the intact natural crown of an endodontically treated tooth provides maximum resistance to root fracture.

Analysis of Variance↗
PubMed1995

A three-dimensional finite-element stress analysis of an endodontically prepared maxillary central incisor.

This study is an application of a three-dimensional Finite-Element Method to investigate the changes in stress characteristics of a prepared maxillary central incisor. The purpose of this study was to analyze stress distributions in this tooth after simulated canal preparation and static loading. A maxillary central incisor was embedded in acrylic, sectioned, photographed, and digitized. A three-dimensional finite-element model was generated by a computer and appropriately modified to simulate canal preparation. Data identified the highest stress magnitudes to be located between the middle and coronal thirds of the root; an area clinically observed to be prone to fracture during treatment. In addition, the magnitude of generated stresses was directly correlated with the simulated prepared canal diameter. The development of a validated three-dimensional finite-element method could identify areas that may predispose a tooth to structural failure during condensation loads.

Computer Simulation↗
PubMed1991

Treatment considerations in a geminated maxillary lateral incisor.

A patient with anomalous maxillary lateral incisor was referred for endodontic therapy. A diagnosis of irreversible pulpitis of a geminated maxillary lateral incisor was made. The preoperative radiograph revealed an image of a single root canal but in fact the tooth had two separate and distinct root canals. Treatment considerations of this anomaly are discussed.

Adult↗
PubMed1989

Twelve-year follow-up of a replanted incisor.

A case report with a 12-yr follow-up of a replanted maxillary incisor is presented. A maxillary incisor, #8, with incomplete root formation was replanted without splinting following a 2-h sojourn in salt water. The pulp responded positively to the electric pulp tester for 2 yr. There was no response to the electric pulp tester 5 yr postoperatively. Although there was some external root resorption, the root appeared to have reached normal length. Two parallel vertical radiolucent slits were present in a trabeculated substance in the site normally occupied by the pulp. This case illustrates an example of revascularization and pulp obliteration. Interestingly, at the 12-yr follow-up, the replanted tooth, as well as tooth 7, showed blunted apices that occurred following orthodontic tooth movement.

Child↗
PubMed1989

An in vitro study of the effect endodontic access preparation has upon the retention of porcelain fused to metal crowns of maxillary central incisors.

Endodontic therapy often requires cutting access preparations through existing restorations. The purpose of this study was to determine whether endodontic access preparation affected the retention of porcelain fused to metal crowns of maxillary central incisors. Retentive forces required to displace porcelain fused to metal crowns of maxillary central incisors were measured using an Instron constant displacement rate testing machine. Using a paired t test analysis, a significant difference was found between crown retention before and after endodontic access preparation.

Crowns↗
PubMed1998

Endodontic treatment of a fused maxillary lateral incisor.

A case report of endodontic treatment of a maxillary lateral incisor that fused with a supernumerary tooth is presented. The fused maxillary lateral incisor was in supraposition on the maxillary dental arch and required orthodontic treatment. The fused tooth was prepared for endodontic therapy. Cleaning and shaping of the root canals were performed. Then, the Ultrafil technique was used for obturation of the root canals. After orthodontic treatment, the teeth was mesiodistally reduced in size and restored with an anterior composite resin.

Adolescent↗
PubMed1990

The effect of adriamycin on dentinogenesis and 3H-thymidine incorporation into the enamel organ of the rat incisor.

The effect of adriamycin (5 mg/kg) on 3H-thymidine incorporation and on dentin formation was studied in rat incisors. Male Sprague Dawley rats received an intravenous injection of adriamycin. Some of these also received a subcutaneous injection of 3H-thymidine at a dose of 2 mCi/kg one day later. One group of control animals received an intravenous injection of a volume of physiological saline equal to that of the adriamycin dose. Another group received physiological saline, and one hour later was given an additional injection of 3H-thymidine at a similar dose as above. All the animals were killed by perfusion with 2.5% phosphate buffered glutaraldehyde 1 h, 1 d, 4 d, 8 d, 16 d, 28 d, and 32 d after 3H-thymidine treatment. Light microscopy revealed irregular dentin deposits between the mantle and circumpulpal layer of the labial dentin at 16 d. Within these deposits were trapped cells. The latter, through radioautographic labelling, appeared to be cells from the odontoblast layer. Also, the labelling pattern of the enamel organ in both the control and experimental groups indicated that the eruption rate of the tooth was not affected. Serial sectioning and examination of the lingual portion of the incisors at 28 d revealed a lack of dentin formation and a failure in the closure of the apical foramen. Electron microscopic observations showed an irregular and random arrangement of collagen fibers within the deposits of irregular dentin, and the presence of twisted odontoblastic processes. Examination of the lingual surface showed the presence of fibroblasts and collagen fibers bridging the gap that resulted from the failure in dentin formation. These cells, which were similar to periodontal ligament cells, appeared to have arisen from that area. These results indicate that adriamycin has no effect on tooth eruption, but has a reversible effect on the function of secretory odontoblasts, which manifested itself as a periodic deposition of irregular dentin on the labial surface, and on dentin formation on the lingual surface which manifested itself as a failure in dentin formation, and consequently, the closure of the apical foramen.

Animals↗