[Impacted wisdom teeth: To extract or not to extract? Review of the literature].

Impacted wisdom teeth are the last teeth to erupt and many times the first to be extracted. Unlike the teeth erupting earlier in life, eruption of wisdom teeth is often accompanied by pain, difficulty in mastication, dysphagia and acute pericoronitis which require systemic medication and surgical removal. Wisdom teeth extraction is a relativelycommon procedure in oral surgery. However, the surgical procedure itself is not devoid of complications, particularly those of deep- impacted, full-bony teeth or severely-angulated teeth. There for, there are many cases in which the practitioner prefers to avoid the surgical procedure and instead recommends follow-up routine only. It is a well known fact that the longer impacted wisdom teeth remain in the jaws, the higher the risk for related pathologies such as dental caries, Periodontal disease, cysts and tumors. In addition, as the patient ages, the risk of local and systemic complications increases, during or after the extraction. Our aim was to review the literature regarding the effects of asymptomatic impacted wisdom teeth during the course of human life.

[Distraction osteogenesis of deficient alveolar bone prior to dental rehabilitation].

Implant supported rehabilitation has become very common in treatment plans nowadays, yet many patients lack the vertical and horizontal bone dimensions required for endosseous implant insertion. Distraction osteogenesis is a technique in which bone is generated by progressive elongation of two bone fragments following an osteotomy or corticotomy. Distraction osteogenesis of the alveolar ridge as a treatment modality in implant dentistry is a very useful technique that allows for adequate bone formation suitable for implant insertion. Alveolar distraction can be unidirectional, bidirectional, multidirectional or horizontal. Alveolar distraction osteogenesis can be performed by using intraosseous distraction devices, intraosseous distraction implants or by extraosseous devices which are the most prevalent today. Distraction osteogenesis has many advantages such as gradual lengthening of the bone with no need for an autogenous bone graft and lack of the associated donor site morbidity as well as distraction of the surrounding soft tissue together with the transported bone. One of the major challenges when using alveolar distraction osteogenesis is controlling the vector of distraction, this problem should be further addressed in future researches. We describe different methods for alveolar distraction osteogenesis, including the surgical procedure, latency period, lengthening and consolidation period. We also discuss the advantages, disadvantages and complications of the method. In this manuscript a case of mandibular alveolar deficiency following mandibular fracture and loss of teeth and the alveolar bone is presented. This patient was treated by alveolar distraction osteogenesis with excellent results. This patient was later rehabilitated . using endosseous implants as demonstrated by radiographs. Alveolar distraction osteogenesis provides a method to regain both hard tissue and soft tissue without additional grafting and is an efficient modality in cases of medium to severe bone loss.

Enthalpy of collagen interfibrillar bonds in fetal membranes.

During pregnancy, the fetal membrane (FM) is subjected to mechanical stretching that may result in preterm labor. The structural integrity of the FM is maintained by its collagenous layer. The disconnection and reconnection of molecular bonds between collagen fibrils are the fundamental processes that govern the irreversible mechanical and supermolecular changes in the FM. Here, we study the activation enthalpy of interfibrillar bonds in ex-vivo human FM. We analyze the strain-rate and temperature dependence of the irreversible deformations in FM subjected to inflation tests, which apply mechanical conditions similar to those experienced by the FM prior to and during the initiation of labor contractions. The obtained activation enthalpy of interfibrillar bonds matches the typical enthalpy values of polyvalent ionic bonds, implying on another important role that ions like Ca and Mg may play in the gestation and labor.

Collagen bundling and alignment in equibiaxially stretched human amnion.

We study irreversible collagen arrangement processes in ex-vivo human amnions subjected to inflation tests, which simulate the mechanical conditions prior to and during the initiation of labor uterine contractions. The investigation is focused on the center of the membrane where the stresses are maximal and equibiaxial. Second harmonic generation reveals an unexpected collagen rearrangement in the compact layer that is responsible for the structural integrity of the fetal membrane. The observed bundling and alignment of the collagen fibers indicate a deviation from the expected equibiaxial stress state. The statistical analysis of the fiber orientations provides information on two driving forces for collagen alignment: microscale flaws and macroscale deviation from the equibiaxial strain. As the pressure increases, the macroscale effect becomes dominant, and a high density of fibers that are aligned along a specific direction is observed. A model that explains these observations and relates them to the material properties is presented. The results of this study indicate that a temporal increase in intrauterine pressure or uterine cervix dilatation causes irreversible changes in collagen molecular connections that may lead to biological changes, such as the initiation of term and preterm labor.

Skeletal stability in patients with clefts after large maxillary advancements using intraoral distraction.

Maxillary hypoplasia is a common outcome in patients with cleft lip and palate after surgical and orthodontic interventions, and maxillary distraction osteogenesis has become a useful procedure for patients with extensive maxillary deformities. The aim of this study was to evaluate long term (two years) stability after maxillary advancement of more than 10mm by distraction osteogenesis in cleft patients using internal devices. We organised a retrospective study on 42 patients with cleft lip and palate using cephalometric analysis before and after maxillary distraction osteogenesis and evaluated them for 24 months. Postoperative measurements showed a marked advancement with an increase of 13.3mm and 10.8° in the length of the maxilla (Co-A) and SNA, respectively, including a shift from Angle class III to class I in dental relations. Follow-up observations showed preservation of maxillary length with a relapse of only 6.0 % (mean (SD) 0.8 (0.7) mm) and 10% relapse in SNA angle (mean (SD)1.1 (1.4) °) one year postoperatively and a negligible regression at the two years' follow up. This large-scale study shows stable results of skeletal advancement using distraction osteogenesis, indicating safe and reliable outcomes among patients with cleft lip and palate.

Sandwich osteotomy for the reconstruction of deficient alveolar bone.

Alveolar bone deficiency is a very common problem encountered by the practitioner when planning dental implants. The severity of the deficiency is variable. Many practitioners perform augmentation using the method they feel comfortable with and do not necessarily use the most appropriate method. This is a retrospective study on 21 patients between the ages of 25 and 63 years exhibiting moderate vertical alveolar bone deficiency and treated by the sandwich technique. Mean vertical bone gain was 7.5mm. Sixty-one dental implants were inserted showing a survival rate of 96.7% with a median of 3.1 years follow-up. Main advantages of the method include minimal relapse, single operation and preservation of the native cortical bone in the occlusal surface. We believe the surgeon should maintain the capability of using different augmentation techniques and utilize them appropriately for different severities of deficiency. We wish to establish a paradigm for using different augmentation methods We recommend using the sandwich technique in the moderate deficient cases as described in this work, using alveolar distraction osteogenesis for the severe cases as described in our previous work, where lack of soft tissue for proper closure is a major limitation, and using guided bone regeneration for minor deficiencies.

Two-stage reconstruction of the severely deficient alveolar ridge: bone graft followed by alveolar distraction osteogenesis.

Distraction osteogenesis for the augmentation of severe alveolar bone deficiency has gained popularity during the past two decades. In cases where the vertical bone height is not sufficient to create a stable transport segment, performing alveolar distraction osteogenesis (ADO) is not possible. In these severe cases, a two-stage treatment protocol is suggested: onlay bone grafting followed by ADO. An iliac crest onlay bone graft followed by ADO was performed in 13 patients: seven in the mandible and six in the maxilla. Following ADO, endosseous implants and prosthetic restorations were placed. In all cases, the onlay bone graft resulted in inadequate height for implant placement, but allowed ADO to be performed. ADO was performed to a mean total vertical augmentation of 13.7mm. Fifty-two endosseous implants were placed. During a mean follow-up of 4.85 years, two implants failed, both during the first 6 months; the survival rate was 96.15%. In severe cases lacking the required bone for ADO, using an onlay bone graft as a first stage treatment increases the bone height thus allowing ADO to be performed. This article describes a safe and stable two-stage treatment modality for severely atrophic cases, resulting in sufficient bone for implant placement and correction of the inter-maxillary vertical relationship.

Testing system for ferromagnetic shape memory microactuators.

Ferromagnetic shape memory alloys are a class of smart materials that exhibit a unique combination of large strains and fast response when exposed to magnetic field. Accordingly, these materials have significant potential in motion generation applications such as microactuators and sensors. This article presents a novel experimental system that measures the dynamic magnetomechanical behavior of microscale ferromagnetic shape memory specimens. The system is comprised of an alternating magnetic field generator (AMFG) and a mechanical loading and sensing system. The AMFG generates a dynamic magnetic field that periodically alternates between two orthogonal directions to facilitate martensitic variant switching and to remotely achieve a full magnetic actuation cycle, without the need of mechanical resetting mechanisms. Moreover, the AMFG is designed to produce a magnetic field that inhibits 180 degrees magnetization domain switching, which causes energy loss without strain generation. The mechanical loading and sensing system maintains a constant mechanical load on the measured specimen by means of a cantilever beam, while the displacement is optically monitored with a resolution of approximately 0.1 microm. Preliminary measurements using Ni(2)MnGa single crystal specimens, with a cross section of 100x100 microm(2), verified their large actuation strains and established their potential to become a material of great importance in microactuation technology.

Visualization of surface acoustic wave scattering by dislocations.

Stroboscopic X-ray topography at the synchrotron beam line was used to visualize the propagation of a 580 MHz surface acoustic waves (SAW) in LiNbO3 crystals. For this purpose, the X-ray bursts coming from the synchrotron storage ring with periodicity of 5.68 MHz were synchronized with the SAW frequency in a phase-locked mode. This method allowed us to "stop" the SAW in time and to observe the X-ray diffraction contrast caused by the dynamic deformation field of SAW. The X-ray topographic images showed well-resolved individual acoustic wave fronts of 6 microm SAW as well as their distortions due to SAW scattering by linear dislocations. Some of the images revealed an exceptional contrast of the concentric rings about the dislocation line, which is caused by coherent interaction of the secondary elastic waves. This contrast is similar to the Fresnel zones in optics, and this conclusion is confirmed by direct summation of secondary waves emitted by local elements of a vibrating dislocation string.

Stroboscopic X-ray imaging of vibrating dislocations excited by 0.58 GHz phonons.

We report on direct imaging, by means of stroboscopic x-ray topography, of phonon-induced dislocation vibrations. X-ray images taken from LiNbO3 crystals excited by 0.58 GHz surface acoustic waves, showed individual acoustic wave fronts as well as their distortions when crossing the dislocation line. The observed contrast is well explained by considering the dynamic deformation field of vibrating dislocation. Comparing simulated deformation maps and x-ray images permitted determination of the local velocities of vibrating dislocations and their viscosity coefficients. We found unexpectedly high velocity values (not far from the speed of sound) and extremely low viscosity coefficients, 2-3 orders of magnitude lower than previously measured in ductile materials.

Large local deflections of a dynamic crack front induced by intrinsic dislocations in brittle single crystals.

We show that intrinsic dislocations in brittle single crystals can be a source of strong local perturbations along the crack path. A theoretical model was developed which predicts substantial crack front deflections. Investigating the crack surfaces in Si crystals with induced dislocation density of 10(9)-10(10) cm(-2) revealed a significant amount of crack front perturbations in the form of V-shaped grooves, which were completely missing in dislocation-free Si specimens. The measured depths of the perturbations were in the range of 2-20 nm and in excellent agreement with the theoretical model.