Evaluation of a novel transcortical pin-sleeve system in a calf model

Le desserrage des tiges est une complication fréquente des plâtres avec tiges transcorticales (TP) chez les grands animaux, nécessitant souvent leur retrait prématuré avant la guérison des fractures. Les charges excessives centrées sur le cortex à l’interface os-tige proximo-externe et disto-interne causent de l'ostéolyse. En utilisant un modèle de veau nouveau-né, ce projet a évalué un nouveau système de tige-manchon et anneau integré dans un plâtre (PS) optimisé pour réduire la contrainte péri-implant et le stress à l'interface os-implant. On a émis l'hypothèse que les PS se traduiraient par une ostéolyse péri-implant moindre par rapport aux TP. Dix veaux en bonne santé, de 3 semaines d'âge, ont été implantés avec les TP ou PS dans le métacarpe droit, à raison de 2 implants par veau. Les veaux ont été observés quotidiennement pour le confort et la boiterie et ont été euthanasiés à 28 jours. Les données recueillies comprenaient les radiographies à la chirurgie et à l'euthanasie et les mesures histomorphométriques de contact os-implant sur des échantillons non-décalcifiés avec les implants in situ. Les données ont été analysées en utilisant le test de Cochran-Mantel-Haenszel, une valeur de P <0,05 a été considérée comme significative. L'épaisseur corticale était plus importante pour les implants distaux que proximaux pour les deux groupes lors de la chirurgie (P = 0,03), mais était similaire entre les groupes (P > 0,3). Les veaux avec TP ont développé une boiterie plus tôt (au jour 21) que les veaux avec PS (P = 0,04). Histologiquement, il y avait plus de contact direct os-implant cortical pour les implants PS distaux que les implants TP (P = 0,04). La jonction métaphyso-diaphysaire osseuse où les implants proximaux étaient situés est impropre aux deux systèmes; chacun a un minimum de contact os-implant et de l'ostéolyse extensive. Le système PS n'ayant pas causé une ostéolyse importante lorsque implantés dans l'os diaphysaire et peut-être une alternative convenable aux TP pour des fractures comminutives des membres distaux.

Ice internal friction: Standard theoretical perspectives on friction codified, adapted for the unusual rheology of ice, and unified

Sea ice contains flaws including frictional contacts. We aim to describe quantitatively the mechanics of those contacts, providing local physics for geophysical models. With a focus on the internal friction of ice, we review standard micro-mechanical models of friction. The solid's deformation under normal load may be ductile or elastic. The shear failure of the contact may be by ductile flow, brittle fracture, or melting and hydrodynamic lubrication. Combinations of these give a total of six rheological models. When the material under study is ice, several of the rheological parameters in the standard models are not constant, but depend on the temperature of the bulk, on the normal stress under which samples are pressed together, or on the sliding velocity and acceleration. This has the effect of making the shear stress required for sliding dependent on sliding velocity, acceleration, and temperature. In some cases, it also perturbs the exponent in the normal-stress dependence of that shear stress away from the value that applies to most materials. We unify the models by a principle of maximum displacement for normal deformation, and of minimum stress for shear failure, reducing the controversy over the mechanism of internal friction in ice to the choice of values of four parameters in a single model. The four parameters represent, for a typical asperity contact, the sliding distance required to expel melt-water, the sliding distance required to break contact, the normal strain in the asperity, and the thickness of any ductile shear zone.

Effect of repeated torque/mechanical loading cycles on two different abutment types in implants with internal tapered connections: an in vitro study

Internal tapered connections were developed to improve biomechanical properties and to reduce mechanical problems found in other implant connection systems. The purpose of this study was to evaluate the effects of mechanical loading and repeated insertion/removal cycles on the torque loss of abutments with internal tapered connections. Sixty-eight conical implants and 68 abutments of two types were used. They were divided into four groups: groups 1 and 3 received solid abutments, and groups 2 and 4 received two-piece abutments. In groups 1 and 2, abutments were simply installed and uninstalled; torque-in and torque-out values were measured. In groups 3 and 4, abutments were installed, mechanically loaded and uninstalled; torque-in and torque-out values were measured. Under mechanical loading, two-piece abutments were frictionally locked into the implant; thus, data of group 4 were catalogued under two subgroups (4a: torque-out value necessary to loosen the fixation screw; 4b: torque-out value necessary to remove the abutment from the implant). Ten insertion/removal cycles were performed for every implant/abutment assembly. Data were analyzed with a mixed linear model (P <= 0.05). Torque loss was higher in groups 4a and 2 (over 30% loss), followed by group 1 (10.5% loss), group 3 (5.4% loss) and group 4b (39% torque gain). All the results were significantly different. As the number of insertion/removal cycles increased, removal torques tended to be lower. It was concluded that mechanical loading increased removal torque of loaded abutments in comparison with unloaded abutments, and removal torque values tended to decrease as the number of insertion/removal cycles increased. To cite this article:Ricciardi Coppede A, de Mattos MdaGC, Rodrigues RCS, Ribeiro RF. Effect of repeated torque/mechanical loading cycles on two different abutment types in implants with internal tapered connections: an in vitro study.Clin. Oral Impl. Res. 20, 2009; 624-632.doi: 10.1111/j.1600-0501.2008.01690.x.

Internal Residual Stress Measurements in a Bioactive Glass-Ceramic Using Vickers Indentation

The residual stress distribution that arises in the glass matrix during cooling of a partially crystallized 17.2Na(2)O-32.1CaO-48.1SiO(2)-2.5P(2)O(5) (mol%) bioactive glass-ceramic was measured using the Vickers indentation method proposed by Zeng and Rowcliffe (ZR). The magnitude of the determined residual stress at the crystal/glass boundary was 1/4-1/3 of the values measured using X-ray diffraction (within the crystals) and calculated using Selsing`s model. A correction for the crack geometry factor, assuming a semi-elliptical shape, is proposed and then good agreement between experimental and theoretical values is found. Thus, if the actual crack geometry is taken into account, the indentation technique of ZR can be successfully used. In addition, a numerical model for the calculation of residual stresses that takes into account the hemispherical shape of the crystalline precipitates at a free surface was developed. The result is that near the sample surface, the radial component of the residual stress is increased by 70% in comparison with the residual stress calculated by Selsing`s model.

In vitro evaluation of conventional and locking miniplate/screw systems for the treatment of mandibular angle fractures

This in vitro study evaluated the influence of the type of miniplate and the number of screws installed in the proximal and distal segments on the stability and resistance of Champy's osteosynthesis in mandibular angle fractures. Sixty polyurethane hemimandibles with bone-like consistency were randomly assigned to four groups (n = 15) and sectioned in the mandibular angle region to simulate fracture. The bone segments were fixed by different osteosynthesis methods using 2.0 mm miniplates and 2.0 mm x 6 mm rnonocortical screws. In groups 1 and 2, two conventional (G1) or locking (G2) screws were installed in each bone segment using a conventional (G1) or a locking (02) straight miniplate; in groups 3 and 4, three conventional (03) or locking (04) screws were installed in the proximal segment and four conventional (G3) or locking (04) screws were installed in the distal segment using a conventional (G3) or a locking (G4) seven-hole straight miniplate. The hemimandibles were loaded in compressive strength until a 4 mm displacement occurred between the segments, vertically or horizontally. Locking plate/screw systems provided significantly greater resistance to displacement than conventional ones (p < .01). Locking miniplates offered more resistance than conventional miniplates. Long locking miniplates provided greater stability than short ones.

Severe lateral luxation and root fracture: report of a case with 5-year follow-up

A case of severe lateral luxation and root fracture in upper incisors is reported. Treatment involved the repositioning and fixation of the injured teeth and endodontic treatment with calcium hydroxide. The importance of long-term follow-up is emphasized.

In vitro comparison of 1.5 mm vs. 2.0 mm screws for fixation in the sagittal split osteotomy

Purpose: Numerous "in vitro" investigations have been conducted to evaluate the role of screw size and pattern in determining optimal resistance to deformation, often these have been controversial. The aim of this study was to evaluate the effect of screw size and insertion technique on the stability of sagittal split osteotomies.Materials and methods: This study used twenty polyurethane replicas of human hemimandibles with a prefabricated sagittal split ramus osteotomy (SSRO). The hemimandibles were stabilized with 1.5 mm and 2.0 mm titanium screws inserted in an inverted L configuration. All specimens were tested to determine the strength and stability of the fixation.Results: In all cases there was failure of the synthetic bone before there was any evidence of screw failure. There were no significant differences in the load necessary to make the construct fail between the 1.5 or 2.0 mm screw sizes.Conclusion: There was no statistically significant difference between the strengths achieved with screws of 1.5 and 2.0 mm diameters for fixation of SSRO performed in synthetic mandibles. There was no fracture of the 1.5 mm or 2.0 mm diameter screws in any of the tests. 1.5 mm diameter screws in an inverted L pattern have as much stability and mechanical resistance as a 2.0 mm screw, may be safely used for this procedure. (C) 2010 European Association for Cranio-Maxillo-Facial Surgery.

Fracture resistance of bleached teeth restored with different procedures

This study evaluated the fracture resistance of teeth submitted to internal bleaching and restored with different non-metallic post. Eighty mandibular incisors were endodontically treated and randomly divided in 10 groups (n = 8): G1- restored with composite resin (CR), G2- CR + fiber-reinforced composite post (FRC, Everstick post, Sticktech) cemented with resin cement self-etch adhesive (RCS, Panavia F 2.0, Kuraray), G3- CR + FRC + self-adhesive resin cement (SRC, Breeze, Pentral Clinical), G4- CR+ glass fiber post (GF, Exacto Post, Angelus) + RCS, G5- CR + GF + SRC. The G6 to G10 were bleached with hydrogen peroxide (HP) and restored with the same restorative procedures used for G1 to G5, respectively. After 7 days storage in artificial saliva, the specimens were submitted to the compressive strength test (N) at 0.5 mm/min cross-head speed and the failure pattern was identified as either reparable (failure showed until 2 mm below the cement-enamel junction) or irreparable (the failure showed <2 mm or more below the cement-enamel). Data were analyzed by ANOVA and Tukey test (α = 0.05). No significant difference (p < 0.05) was found among G1 to G10. The results suggest that intracoronal bleaching did not significantly weaken the teeth and the failure patterns were predominately reparable for all groups. The non-metallic posts in these teeth did not improve fracture resistance.

Atypical dento-alveolar fracture fixed with screws: a technical note

Dento-alveolar process fracture is an important and common event in the dental office practice usually managed under the well-established protocols, but sometimes this kind of lesion is evaluated in the hospital emergency rooms without attention to the dental injuries. In this type of trauma, the time between the injury and the definitive resolution is essential for the treatment success, usually 1 h in cases of dento-alveolar fractures (tooth and alveolar bone). This paper describes the management of a patient with unusual dento-alveolar fracture caused by gunshot and treated using screw fixation.

Marginal and Internal Discrepancies Related to Margin Design of Ceramic Crowns Fabricated by a CAD/CAM System

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Fracture strength of bovine incisors after intra-radicular treatment with MTA in an experimental immature tooth model

Aim To evaluate, using an experimental immature tooth model, the fracture resistance of bovine incisors submitted to different reinforcement treatments with mineral trioxide aggregate (MTA).Methodology An immature tooth model was created by sectioning the coronal and apical portions of 40 bovine incisors 8 mm above and 12 mm below the cementoenamel junction. The root canals were irrigated with 1.0% sodium hypochlorite. They were enlarged both coronally and apically using number 703 carbide burs (ISO: 500-104-168-007-021) and their internal diameter was standardized to 2.1 mm. The specimens were assigned to four groups (n = 10): GI-control (without filling); GII-apical MTA plug + filling with gutta-percha and endodontic sealer; GIII-filling with MTA; GIV-apical MTA plug + filling with MTA + metallic post (Reforpost I). A polyether impression material was used to simulate the periodontal ligament. The specimens were submitted to a compressive load at a crosshead speed of 0.5 mm min(-1) in a servo-hydraulic universal testing machine (MTS 810) applied at 45 degrees to the long axis of the tooth until failure. Data were submitted to statistical analysis by the Kruskal-Wallis test at 5% significance level.Results GIV presented the highest fracture resistance (32.7N) and differed significantly from the other groups (P < 0.05). No statistically difference was found between GII (16.6N) and GIII (23.4N) (P > 0.05). GIII had a significantly higher fracture resistance than GI (P < 0.05).Conclusions the use of MTA + metallic post as an intra-radicular reinforcement treatment increased the resistance to fracture of weakened bovine teeth in an experimental immature tooth model.

Severe fracture of the maxillary alveolar process associated with extrusive luxation and tooth avulsion: A case report

Aim: The aim of this report is to present a case of severe fracture of the maxillary anterior alveolar process with substantial bone dislodgement associated with extrusive tooth luxation and avulsion. Background: Dentoalveolar trauma is a challenge to dentistry, especially in young patients, for it can lead to early tooth loss which compromises oral function, esthetics, self-esteem, and alter the long-term plan of care for the victim. Case Report: A 12-year-old girl with severe dentoalveolar trauma to the maxillary anterior region presented for emergency care for her injury. Treatment consisted of fracture reduction of the alveolar process, repositioning of the teeth that had suffered extrusive luxation, placement of a semi-rigid splint, and suturing of soft tissue lacerations. The traumatized teeth presented with pulpal necrosis and were treated endodontically. After 24 months of follow up, the fracture of the alveolar process was completely healed and the displaced teeth presented no signs of ankylosis or root resorption. Summary: First-aid care contributed remarkably to this case allowing the re-establishment of esthetics, function, and patient's self-esteem. In spite of trauma extension the treatment outcomes were favorable. Clinical Significance: Cases of dentoalveolar trauma should be evaluated on an individual basis. However, early emergency management and adequate follow-up can prevent further complications and contribute to treatment success.