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At least 883 records · Page 49Linked to original sources
PubMed2006

Evaluation of the biomechanical behavior of maxillary central incisors restored by means of endocrowns compared to a natural tooth: a 3D static linear finite elements analysis.

OBJECTIVE: The present study aimed at evaluating different restoring configurations of a crownless maxillary central incisor, in order to compare the biomechanical behavior of the restored tooth with that of a sound tooth. MATERIALS AND METHODS: A 3D FE model of a maxillary central incisor is presented. An arbitrary static force of 10 N was applied with an angulation of 125 degrees to the tooth longitudinal axis at level of the palatal surface of the crown. Different material configurations were tested: composite, syntered alumina, feldspathic ceramic endocrowns and glass post resorations with syntered alumina and feldspathic ceramic crown. RESULTS: High modulus materials used for the restoration strongly alter the natural biomechanical behavior of the tooth. Critical areas of high stress concentration are the restoration-cement-dentin interface both in the root canal and on the buccal and lingual aspects of the tooth-restoration interface. Materials with mechanical properties underposable to that of dentin or enamel improve the biomechanical behavior of the restored tooth reducing the areas of high stress concentration. SIGNIFICANCE: The use of endocrown restorations present the advantage of reducing the interfaces of the restorative system. The choice of the restorative materials should be carefully evaluated. Materials with mechanical properties similar to those of sound teeth improve the reliability of the restoartive system.

Aluminum Oxide↗
PubMed2004

Follistatin regulates enamel patterning in mouse incisors by asymmetrically inhibiting BMP signaling and ameloblast differentiation.

Rodent incisors are covered by enamel only on their labial side. This asymmetric distribution of enamel is instrumental to making the cutting edge sharp. Enamel matrix is secreted by ameloblasts derived from dental epithelium. Here we show that overexpression of follistatin in the dental epithelium inhibits ameloblast differentiation in transgenic mouse incisors, whereas in follistatin knockout mice, ameloblasts differentiate ectopically on the lingual enamel-free surface. Consistent with this, in wild-type mice, follistatin was continuously expressed in the lingual dental epithelium but downregulated in the labial epithelium. Experiments on cultured tooth explants indicated that follistatin inhibits the ameloblast-inducing activity of BMP4 from the underlying mesenchymal odontoblasts and that follistatin expression is induced by activin from the surrounding dental follicle. Hence, ameloblast differentiation is regulated by antagonistic actions of BMP4 and activin A from two mesenchymal cell layers flanking the dental epithelium, and asymmetrically expressed follistatin regulates the labial-lingual patterning of enamel formation.

Ameloblasts↗
PubMed2004

Age-related and regional differences in the stress-strain and stress-relaxation behaviours of the rat incisor periodontal ligament.

Groups of rats were killed at 2, 6, 12, and 24 months of age. From dissected left and right mandibles in each rat, three pairs of transverse sections were cut at the incisal, middle, and basal regions of the incisor. One section in each pair was loaded until failure and a stress-strain curve for the periodontal ligament (PDL) was obtained. The other section was loaded to up to 50% of the maximum shear stress as determined from the contralateral section and then kept at a constant strain for 10 min, to obtain the stress-relaxation curve at the same region of the PDL. The maximum shear stress and toughness increased with age at the incisal region and the maximum shear strain increased with age at the incisal and middle regions. The tangent modulus decreased with advancing age at the middle region. The stress-relaxation during 10 min decreased with advancing age at the incisal and basal regions, but not at the middle region. The relaxation process was well described by a sum of three exponential decay functions, reflecting the short-, medium-, and long-term relaxation components. The age-related decrease in the relaxation was mainly attributable to increases in the ratio and relaxation time of the long-term relaxation component. These results suggest that with advancing age the mechanical strength and toughness of the PDL are enhanced mostly at the incisal region and that the viscous fraction is relatively decreased at the incisal and basal regions along the long axis of the rat incisor.

Aging↗
PubMed2006

Flare up rate related to root canal treatment of asymptomatic pulpally necrotic central incisor teeth in patients attending a military hospital.

OBJECTIVES: This prospective study was conducted to determine the flare up rate related to root canal treatment of asymptomatic non vital maxillary central incisor teeth performed in one and two appointments and the relationship, if any between pain and number of treatment visits. METHODS: The frequency of postobturation pain and swelling was recorded and evaluated over an observation period of 1 week in a 120 consecutive patients undergoing root canal treatment. The patients were assigned randomly into one of two groups of 60 patients each. The canals of all teeth were prepared and filled using the step-back preparation and lateral condensation filling techniques. The data were analyzed statistically using Mann-Whitney test. RESULTS: Eight of the 120 patients were excluded from the analysis as they failed to attend for postoperative reviews. Out of the 112 patients involved in the study 90 patients had no pain, 9 patients had slight pain, 8 patients had moderate pain, and 5 patients had severe pain after 2 days. After 7 days 104 patients had no pain, 4 patients had slight pain, 3 patients had moderate pain and 1 patient had severe pain. CONCLUSIONS: No statistically significant difference in the incidence and degree of postoperative pain was found between one and two visit Endodontic procedures. The rate of post obturation flare up in asymptomatic Endodontically treated non vital maxillary centarl incisors was 11.6 and 3.6% after 2 and 7 days, respectively.

Acute Disease↗
PubMed2006

Nonsurgical endodontic treatment of a two-rooted maxillary central incisor.

This case report presents an uncommon case of a two-rooted maxillary central incisor with a periapical radiolucent lesion. A 17-yr-old female patient was referred for dental consultation after a motorcycle accident. The maxillary left central incisor had a bifurcated root that was confirmed by radiographs taken at different angles. Nonsurgical endodontic therapy was performed. At the 1 yr recall examination, the tooth was asymptomatic and the radiograph showed that the periapical radiolucent lesion had healed.

Adolescent↗
PubMed2006

Endodontic management of a fused maxillary lateral incisor with a supernumerary tooth: a case report.

Fusion is a rare occurrence and its definitive diagnosis is of prime importance for successful root canal treatment. This case report discusses the endodontic and esthetic management of fused maxillary lateral incisor with a supernumerary tooth that presented with spacing between the fused tooth and the adjacent central incisor. Nonsurgical endodontic treatment was performed on the fused teeth followed by postendodontic esthetic restoration. The patient remained symptom-free and there was a reduction in the size of periapical radiolucency after 1 year.

Adult↗
PubMed2006

Maxillary central incisor with two root canals: a case report.

The success of endodontic therapy requires a knowledge of the internal and external dental anatomy and its variations in presentation. The internal anatomy of the maxillary central incisor is well known and usually presents with one root and one radicular canal system. This case report describes an endodontic treatment of a maxillary central incisor with two roots and two canal systems, demonstrated by radiography and computerized tomography examinations.

Adult↗
PubMed2004

Maxillary lateral incisor implants: planning with the aid of orthodontics.

Implants are commonly used to replace congenitally missing lateral incisors in adolescent orthodontic patients. However, these restorations are often challenging for the orthodontist, surgeon, and restorative dentist. In some patients the space across the alveolar crest is too narrow to permit the surgeon to place the implant. Occasionally the root apices of the adjacent central incisor and canine are in close proximity. In other cases the ridge thickness could be inadequate and require augmentation. When the orthodontist opens the space, the papilla heights are adversely affected. Some adolescent patients have altered passive eruption after orthodontic treatment, which affects the level of the gingival margins. Finally, questions commonly arise regarding the appropriate age for implant placement in these young patients. If not addressed, these issues could compromise the aesthetics of the implant restoration. This article will use several clinical examples to discuss each of these 6 potential problems and provide guidelines for their solutions.

Adolescent↗
PubMed2006

Biomechanical study of a prosthetic solution based on an angled abutment: case of upper lateral incisor.

OBJECTIVES: To study the complex behaviour of an upper lateral incisor restoration using an angled abutment, a mechanical analysis of the abutment bearing capacity was firstly carried out. The evolution of bone properties around implant was then simulated as a function of time to estimate the maximal load that could be supported by the prosthetic solution without bone damage. MATERIALS AND METHODS: According to the Food and Drug Administration procedure, experimental tests were firstly carried out on five samples. A 25 degrees -angled abutment screwed to an implant embedded into a massive steel bloc was submitted to a static loading. Two finite element models were also built: the first one (I) to interpret and complete the results obtained in the experimental part and the second one (II) to simulate bone remodelling around implant considering a strain energy stimulus. RESULTS: According to experiments, the abutment straightening was observed for an average force of 869N. Numerical model (I) confirmed this result and indicated that the initial irreversible deformation (yielding) of abutment was obtained for a 283N compressive force. It could thus be deduced that this abutment can safely be used for an incisor restoration. Model (II) showed that, after 26 months, some of the cancellous bone initially present in an approximately one millimetre thick shell surrounding the implant had reached the density of cortical bone. A safe load notion corresponding to the force leading to the maximal admissible strain value for trabecular bone was introduced. It evolved from 44N after surgery to approximately 160N after 26 months.

Biomechanical Phenomena↗
PubMed2006

Intentional replantation for a periodontally involved hopeless incisor by using autologous platelet-rich plasma.

The aim of the present case is to describe the use of autologous platelet-rich plasma (PRP) in an intentional replantation procedure for a periodontally involved lower right central incisor with 18 months follow-up. Brief information is also given on the preoperative preparation of PRP in the dental office. PRP preparation is a new biotechnology, and the prepared material contains thrombocyte concentrates and high levels of growth factors. This material promotes healing time in a range of various sites. In this case, a tooth with severe periodontal breakdown was treated with PRP with intentional replantation procedure. This tooth was previously treated with root canal treatment and root planing. The tooth was extracted, and was replanted with autologous PRP. Clinical and radiographic follow-up for 18 months demonstrated new bone formation around the apical portion of the root and all clinical parameters indicated a trend of healing. The mobility of this previously grade III mobile incisor returned to normal limits. We speculate that intentional replantation with PRP application may induce wound healing and may induce bone formation.

Adult↗
PubMed2006

Spontaneous re-eruption of intruded permanent incisors: five case reports.

This report presents 5 cases of intrusive luxation in immature permanent central incisors. The intruded incisors, with careful monitoring, were allowed to spontaneously re-erupt, which avoided the need to reposition the tooth either orthodontically or surgically. All of the teeth re-erupted spontaneously in a few months. The root development continued in all of the cases and all pulps remained vital. There were no other signs of pulpal and/or periapical pathology. It can be concluded that intruded immature permanent teeth can spontaneously re-erupt, conserve their vitality, and continue their root development without any surgical or orthodontic management.

Child↗
PubMed2000

The permeability of the dentine and other tissues that are exposed at the tip of a rat incisor.

The tissues that form the incisal surface of a rat incisor include dentine, an atubular calcified tissue which lines the last-formed dentine, and calcified pulp remnants. The permeability of these tissues was investigated in vitro and in vivo using Evans blue dye. The incisal surface was prepared by etching it with acid or removing 1 mm by fracturing or with a diamond disc followed by etching. In some cases, 1.5-3.0 mm was removed to expose the soft tissue of the pulp. The dye was applied for 30 min, then longitudinal sections of the crown were cut and examined microscopically to determine the extent to which the dye had diffused into the underlying tissues. In only those teeth in which the dye had been applied direct to the pulpal soft tissue could any be detected below the exposed tooth surface. In previous experiments, it was found that both cat and human dentines were freely permeable to Evans blue when they were tested in vitro. It is concluded that the dentine and other tissues that form the incisal surface of a rat incisor are less permeable than cat or human dentine.

Acid Etching, Dental↗
PubMed2002

Tissue oxygen tension and blood-flow changes in rat incisor pulp with graded systemic hyperoxia.

The role of oxygen in the regulation of the pulpal microcirculation is unknown. This investigation is aimed to measure tissue oxygen tension and blood-flow changes in the pulp of rat lower incisors during graded systemic hyperoxia, and to determine the response of the pulpal vasculature to various oxygen tensions. Twenty-four Sprague-Dawley rats were anaesthetized and artificially ventilated with the appropriate gas mixture. Recessed oxygen-sensitive microelectrodes were used to measure pulpal tissue oxygen tension via a small access cavity filled with saline on the labial surface of the incisor. A laser Doppler flowmeter was used to record pulpal blood-flow. Inspired oxygen was increased stepwise from 20 to 100% in 20% steps. Systemic blood-gas concentrations were measured at each step. Systemic arterial oxygen tension at 100% oxygen ventilation reached 481.2 +/- 30.7% of the baseline at 20% oxygen breathing (n=21). Pulpal tissue oxygen tension did not change significantly whereas pulpal blood-flow fell dose-dependently to 74.6 +/- 5.0% at 100% oxygen ventilation (n=21). Systemic hyperoxia, therefore, induces a significant reduction in pulpal blood-flow whereas pulpal tissue oxygen tension remains relatively stable, indicating an oxygen-dependent local regulatory mechanism.

Analysis of Variance↗
PubMed2002

Oxygen distribution and consumption in rat lower incisor pulp.

The aim was to determine the oxygen tension (P(O(2))) and rate of oxygen consumption in the pulp. Twelve rats were anaesthetised and artificially ventilated. Under an operating microscope, a recessed oxygen-sensitive microelectrode was inserted into the pulp through a small saline-covered cavity on the labial surface of the lower incisor. P(O(2)) was measured as a function of the transverse distance from the saline medium through to the middle of the pulp. Oxygen profiles were characterised by a decline of oxygen tension outside the pulp in the saline medium and a steeper gradient across the interface, before a localised oxygen consuming region corresponding to the odontoblasts. A plateau with some localised fluctuations was then followed by an increase in oxygen tension in the middle of the pulp. The average oxygen tension in the plateau region was 23.2 mmHg+/-2.1 mmHg (n=12). A mathematical model was used to extract oxygen consumption data from P(O(2)) profiles recorded from non-perfused pulp (created by reducing systemic blood pressure). The analysis revealed that there was a distinct oxygen consumption zone in the outer pulp, which anatomically corresponded to the odontoblast layer. The average oxygen consumption rate of the odontoblasts was 3.2+/-0.2 ml O(2)/min per 100g pulp tissue. The zone of high oxygen consumption was 68.7 micro m+/-6.9 micro m (n=24) thick. It is concluded that pulpal oxygen distribution is heterogeneous and that the odontoblast could be a major oxygen consumer within the rat incisor pulp.

Animals↗
PubMed1987

Changes in glucose metabolism in submandibular salivary glands of rats after isoproterenol or incisor-tooth amputation.

Rats were injected daily with isoproterenol (2 mg/kg of body wt) for up to five days, or their incisor teeth were amputated on every other day for up to five amputations. The animals were subdivided in two subgroups killed 12 or 24 h after the first or last intervention. At 12 h all enzymes except hexokinase (HK) and pyruvate kinase (PFK) showed decreased activities after isoproterenol. After incisor amputation, only increased HK and PFK activities were observed. With both procedures, there is activation of beta-adrenergic receptors but results show that different biochemical events take place, suggesting different mechanisms.

Amputation, Surgical↗
PubMed1998

Scanning electron microscopy and energy-dispersive X-ray analysis of defects in mature rat incisor enamel after thyroparathyroidectomy.

The surface and the structure of the erupted enamel of the continuously growing rat incisor were studied by scanning electron microscopy (SEM) to analyse the effect of thyroparathyroidectomy on enamel formation. Ten male 21-day-old Wistar rats were thyroparathyroidectomized and five sham-operated rats were used as controls. Two months after surgery the rats were perfused with 1% glutaraldehyde and their mandibles dissected. The erupted ends of the incisors were cut off and routinely processed for SEM. An energy-dispersive analysis of X-rays (EDX analysis) was performed for the calcium:iron ratio of the enamel surface defects. Thyroparathyroidectomy induced surface defects and structural abnormalities in the outer layer of the mature erupted enamel. It was established that the surface and structural defects were related. The EDX analysis of the outer enamel showed that the enamel defects were associated with an abnormal elevation of the iron content. The SEM appearance and the EDX analyses indicated that these defects were hypomineralized and rich in iron. The reddish colour of the enamel is due to the high concentrations of iron.

Animals↗
PubMed1998

Expression and localization of ferritin mRNA in ameloblasts of rat incisor.

At the maturation stage, the ameloblasts of the rat incisor incorporate iron, supplied through the bloodstream, and deposit it into the surface layer of the enamel. In this unique iron transport system, ferritin functions as a transient iron reservoir in the cells. Here the expression of ferritin mRNA and its localization in the rat enamel organ was examined. Among various tissues, the enamel organ showed the highest expression for both ferritin H- and L-chain mRNA, as quantified by reverse transcription-polymerase chain reaction. In situ hybridization using digoxigenin-labelled cRNA probes for each chain demonstrated that both ferritin H- and L-chain mRNA were abundantly expressed in presecretory and secretory ameloblasts. The intensity of the positive hybridization signal gradually decreased toward the incisal direction. Differing from the mRNA localization, ferritin protein was immunologically undetectable in presecretory or secretory ameloblasts but was found in ameloblasts at the maturation stage, into which iron is known to be incorporated from the bloodstream. Thus, the expression of ferritin mRNA precedes the protein expression in the developmental stages of rat incisor ameloblasts, and the translation of ferritin and its half-life are probably controlled by the iron entry, as has been reported for other cell types.

Ameloblasts↗