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At least 379 records · Page 21Linked to original sources
PubMed2005

[Effect of cone angle on fracture resistance force of root and post-core system].

OBJECTIVE: To study the effect of cone angle on fracture resistance force of root and post-core system. METHODS: Forty-two simulated tooth roots made of polymethacrylate (PMMA) were divided into six groups according to the root canal cone angles of 0 degrees, 3.93 degrees, 5.71 degrees, 7.48 degrees, 11.31 degrees and 14.71 degrees. Cast post and cores were manufactured and cemented with zinc polycarboxylate cement (PC). Casting the post and core to restore every simulated tooth root. Each specimen was embedded in acrylic resin and then fixed in a special jig on the universal load-testing machine. A compressive load was applied at a 90-degree angle to the long axis of the core until fracture, at a crosshead speed of 1 mm/min. The maximum of load was recorded. RESULTS: The mean values of load in root and post-core system were 0.1225 kN, 0.1498 kN, 0.1600 kN, 0.1893 kN, 0.1078 kN and 0.0945 kN. There were significant differences in the fracture resistance among groups. CONCLUSION: The fracture resistance force of cast post and core increased with the enlargement of post cone angles under certain conditions.

Crowns↗
PubMed2002

Assessment of root curvature and distance using computed tomography.

The safety and efficacy of subgingival root surface instrumentation may be enhanced by optimized adaptation between instrument and treated surface. Thus, detailed knowledge of root geometry may allow advances in instrument design. The aim of this study was therefore to measure root radii of various tooth types as well as distances between tooth roots using computed tomography. Two hundred sixteen teeth in eight patients were studied, with cross sections of teeth at the level of the cemento-enamel junction (CEJ) being regarded as ellipses. The maximum radii of ellipses were calculated and averaged for each tooth surface within various tooth groups. In addition, the spacing between roots at CEJ level and 5 mm below the CEJ was measured. Mean radii varied from 1.09+/-0.50 mm (lower incisor, lingual) to 13.7+/-0.96 mm (upper molar, mesial). Radii of 1 mm to 6 mm were most frequently found at buccal, palatal, and lingual surfaces, whereas the majority of radii were between 2 mm and 11 mm at mesial and distal sites. Root distance varied between 1.04+/-0.49 mm (lower incisors, CEJ level) and 2.81+/-1.70 mm (lower molars, 5 mm below CEJ). The curvature of an instrument for root surface instrumentation should correspond to a radius of at least 11 mm to achieve maximum adaptation to the treated surface, and the width of the working end should be less than 1 mm to allow sufficient interdental instrumentation.

Adult↗
PubMed1997

Underlying mechanisms at the bone-surface interface during regeneration.

The goal of regenerative therapy around teeth and implants is to create a suitable environment in which the natural biological potential for functional regeneration of periodontal ligament and/or bone can be maximized. In order for the regenerative process to be successful, the following factors must be addressed: prevention of acute inflammation from bacteria, mechanical stability of the wound, creation and maintenance of blood clot-filled space, isolation of the regenerative space from undesirable competing tissue types, and the creation of a desirable surface chemistry, energy, roughness and microtopography that can directly influence cellular response, ultimately affecting the rate and quality of new tissue formation and, therefore, the regeneration process. This paper will review how surface characteristics (chemistry and roughness) can affect cell response and local factor production. To evaluate the effect of surface chemistry on cell proliferation and differentiation costochondral chondrocytes were grown on standard tissue culture plastic dishes sputter-coated with different materials. The results indicate that surface materials can elicit differential responses in cell metabolism and phenotypic expression in vitro. In a second study, the effect of varying titanium surface roughnesses on osteoblast-like cell behavior was examined. Surface roughness was found to alter osteoblast proliferation, differentiation and matrix production in vitro. In addition, production of PGE2 and TGF beta by these cells was also shown to increase with increasing surface roughness, indicating that substrate surface roughness also affects cytokine and growth factor production. The role of surface roughness in determining cellular response was further explored by comparing the response of osteoblasts grown on new and previously used surfaces. The results of these latter studies showed that cell proliferation, expression of differentiation markers and overall matrix production are not altered when cells are grown on used vs. virgin surfaces. This suggests the possibility that implants may be re-used, especially in the same patient, if they are appropriately treated. In this context, it should also be noted that rougher titanium surfaces may require more extensive cleaning procedures. From a global perspective, these studies provide some insight into how bone regeneration can be optimized in the presence of an implant or tooth root residing at the site of a bony defect. Since the new bone being produced, during regeneration, grows from a distal area toward the implant or tooth root surface, it is hypothesized that the osteoblasts growing on the surface of the implant may produce local factors that can affect the bone healing process distally. In short, it appears that the surface characteristics of an implant, particularly roughness, may direct tissue healing and, therefore, subsequent implant success in sites of regeneration by modulating osteoblast phenotypic expression.

Alkaline Phosphatase↗
PubMed2001

The formation of apical delta of the permanent teeth in dogs.

To determine the process of formation of apical delta, a histological study on the permanent teeth was carried out in dogs. A litter of 7 clinically healthy beagle dogs and 33 adult dogs (4- to 15- year-old) of 12 breeds with periodontal disease were used for the experiments. Teeth extracted from 6-,7-,8- and 9-month-old beagles were sectioned and stained with HE solution. Tooth roots obtained from adult dogs with periodontal disease were ground. Each tooth was classified into the following root types under a light microscope: Type I (no apical delta = no apical closure), II (few apical delta), IIIA (low apical delta) and IIIB (high apical delta). In the 6-month-old beagles, more than half the tooth roots were classified as type I. In the 7-month-old beagles, type IIIB apical delta was the most predominant and types I, II and IIIA apical delta were occassionally seen. Apical closure and delta were observed in all beagles at 8 months of age histologically. In the 8- and 9-month-old beagles, all root apexes observed were type IIIB. Most of the 314 tooth roots extracted from 33 adult dogs were type IIIB, but a few were type IIIA.

Animals↗
PubMed1997

Long-term assessment of early alveolar bone grafts using three-dimensional computer-assisted tomography: a pilot study.

Fifteen patients with complete unilateral cleft lip and palate who had primary alveolar bone grafting were studied with computer-assisted tomography at a mean age of 12 years. Keeping the maxillary alveolar crest parallel to the plane of the scan, 1.5-mm cuts of the maxilla were made from the infraorbital rim to the gingival third of the crowns of the teeth. A single operator reformatted the data into three-dimensional images using the Maxiview 3200 computer workstation. This allowed examination of the position, size, and spatial relationship of the grafted area and quantification of the amount of bone coverage of root surface and bone height of the alveolus in or adjacent to the graft site. Ten patients showed a lateral incisor in the line of the cleft. The average bony coverage of these tooth roots was 76.5 percent. In the five patients in whom there was lateral incisor agenesis, the canine root had average bony coverage of 82.6 percent. The average height of bone at the lateral incisor was 8.7 mm; at the canine, 14.1 mm. In two patients in whom there was only 42 percent tooth root coverage, the teeth were still viable, stable, and without mobility. Computed tomographic (CT) scans of the 15 patients demonstrated good graft survival with adequate volume. The functional and aesthetic status of the dentition in the area of the cleft also was demonstrated.

Adolescent↗
PubMed2001

Development of an orthodontic simulator for measurement of orthodontic forces.

In this research we developed an orthodontic simulator for analysis of orthodontic forces distribution in the case of the continuous arch technique. In order to take into account vertical force, besides horizontal force and occlusogingival moment on instrumented artificial tooth, tooth root was designed as a ring load cell. Fixing each artificial tooth onto combined mechanical stages enabled variation of tooth anteroposterior position and inclination related to occlusal plane. Calibration of forces and moment of each instrumented artificial tooth showed linearity of outputs and provided the generalized inverse matrix for evaluation of forces and moments from measured strain data. A simulation to retract the anterior teeth was accomplished, and distribution of forces and moment acting at the bracket of each tooth were determined. The average accuracy was 82% and 97% in the horizontal and vertical direction, respectively, by comparing the applied forces and the evaluated ones.

Algorithms↗
PubMed2000

Incisor root resorptions due to ectopic maxillary canines imaged by computerized tomography: a comparative study in extracted teeth.

The purpose of the study was to analyze the ability of computerized tomography (CT) scanning to discriminate maxillary incisor root resorptions caused by ectopically erupting canines. Seventeen maxillary incisors were radiographed in vivo by CT scanning. Contiguous transverse CT scans with a slice thickness of 2 mm were exposed perpendicular to the long axis of the lateral incisors and through the crown of the adjacent, ectopically positioned maxillary canine. Each scan was analyzed and the resorptions on the roots of the laterals were graded according to the maximum depth of the cavity. After the lateral incisors were extracted they were clinically inspected, photographed in different light settings and views, and probed at the contact area between the laterals and the canines. The assessment of the extent of resorption in 4 stages on the CT images compared with the in vitro observations of the extracted roots showed a high degree of agreement for the extent of loss of root substance for all teeth. We conclude that CT scanning performed with good technique accurately reveals tooth root resorption. The presence and influence of the inherent artifacts of tooth root resorption on CT scans are discussed.

Artifacts↗
PubMed1988

Radiography after orthognathic surgery. Part II. Surgical complications.

In a retrospective review of the radiographs from 100 patients who had undergone orthognathic surgery, the authors found that 10% of radiographs had evidence of surgical complications. These complications were fractures, temporomandibular joint dislocations, transected tooth roots, retained surgical devices, avascular necrosis, malunion or nonunion of osteotomy fragments, and osteomyelitis. Some of these complications are of little significance, while others require immediate intervention. Opacified maxillary sinuses and lucencies around tooth roots are frequent findings that may be confused with abnormalities; however, they represent postoperative blood in the sinuses and resorption of bone due to stress from orthodontic appliances, respectively.

Adult↗
PubMed2003

Tuned-aperture computed tomography versus parallax analog and digital radiographic images in detecting second mesiobuccal canals in maxillary first molars.

OBJECTIVE: We sought to evaluate the detectability of second mesiobuccal (MB2) canals in the MB root of maxillary first molar teeth by comparing (1) parallax with pairs of conventional direct-exposure film intraoral radiographs (both D-speed and F-speed), (2) parallax with pairs of charge-coupled device-based digital images acquired through the use of Trophy RVG-ui, and (3) charge-coupled device-based images acquired through the use of a Trophy RVG-ui sensor and tomosynthetically reconstructed by TACT (tuned-aperture computed tomography) Workbench Software. STUDY DESIGN: Maxillary first molars were mounted in simulated bone. Pairs of images were generated by conventional D-speed and F-speed radiography and digital radiography with a charge-coupled device-based sensor, the RVG-ui. Sequences of images were also acquired for TACT reconstruction by using the digital sensor. Observers viewed sets of images to determine the number of canals present within the MB root of each tooth. Roots were horizontally cross-sectioned and viewed under an operating microscope to determine the actual number of canals present. RESULTS: The frequency of detection of MB2 canals was remarkably similar across techniques: 39.2% to 39.6% with parallax for both types of film and for RVG-ui images, and 37.9% with TACT. No statistically significant difference was found in the detectability of MB2 canals between the modalities tested. TACT had higher correlation coefficients than the other 3 modalities with respect to intrarater and interrater reliabilities. CONCLUSIONS: (1) There was a less than 40% chance of locating MB2 canals in the MB root of maxillary first molar teeth by using parallax with pairs of digital or analog radiographs. (2) TACT did not significantly affect the rate of detection of MB2 canals.

Analysis of Variance↗
PubMedDate not supplied

Periodontal aspects of the juvenile form of paracoccidioidomycosis.

Three cases of the juvenile form of paracoccidioidomycosis are reported. Emphasis has been given to the oral manifestations, particularly the periodontal involvement. The main periodontal findings were: generalized and progressive alveolar bone destruction leading to gingival recession with exposure of the tooth roots, and spontaneous tooth losses. The gingival mucosa was predominantly smooth, erythematous and slightly swollen. These aspects, although rare, may be the earliest signs of the disease and sometimes its only manifestations.

Adolescent↗
PubMed1981

Innervation of the periodontium in the monkey.

The distribution and structure of the sensory nerves and various neural endings in the periodontium were examined in adult monkeys, Macaca irus, by means of the silver nitrate technique. 1. The nerve fibers enter the periodontium passing through the bottom and the lateral wall of the bony socket. They are accompanied by blood vessels after entering the periodontium. 2. In the whole height of the periodontium, the area of richest nerve supply is the apical one third of the tooth root, while fewer nerves occur in the upper and middle third. In the apical third periodontium, nerve bundles with blood vessels are located near the alveolar bone, whereas single nerve fibers tend to occur adjacent to the cementum and surround the root of the tooth. 3. The nerve endings in the periodontium can be classified into three types by their structure. (1) Free endings or knob-like endings which, though found in the whole area of the periodontium, are concentrated near the alveolar bone. (2) Tree- or bush-like terminations located in the central part of the periodontium and near the cementum. They occasionally send out numerous branches to the cementum. (3) Specialized endings closely resembling Meissner's corpuscles. They are fairly rare. (4) Tree- or bush-like terminations localized at regular intervals as if each takes its own share of innervation territory. This type of terminals is presumed to represent periodontal mechanoreceptors.

Animals↗