Study of stress distribution with finite element method in a root with prefabricated threaded split shaft post - Part I

A finite element analysis was carried out to study the role of prefabricated threaded split shaft post (Flexi-Post) on dentinal stress in pulpless tooth. Three dimensional plane strain model of mesio-distal section of a human maxillary central incisor without restoration was analysed with the MSC/NASTRAN (MacNeal/ Schwendler) general purpose finite analysis program was executed on a microcomputer. The model as discretized into 48.954 axisymmetric finite elements defined by 10.355 nodes. Each element was assigned unique elastic properties to represent the materials modeled. Homogeneity, isotropy and linear elasticity were assume for all material. A simulation of static load of 100N was applied to the incisal edge of the post; vertical. Maximal principal stresses and von Mises equivalent stress were calculated. Using the element analysis model employed in this study, the following can be concluded concerning threaded split shaft post (Flexi-Post): Maximum principal stresses in dentin were located at cervical place and at the post apex. The apical threads of the post not redirecting stresses away from the root.

DESIGN AND TEST OF A 7-T SPLIT-PAIR MAGNET FOR MAGNETIC SEPARATION

A 160 mm bore, 7 T split-pair magnet was constructed and tested aiming to mineral processing through HGMS (high gradient magnetic separation) or HCMS (helical channel magnetic separation.) This work describes the design and test results of the pair of coils operating under current in parallel mode. In the case of antiparallel current mode large repulsive force between coils is generated and a strong magnetic field gradient outside the magnet is created. A continuous magnetic separation system made with a helical channel magnetic separator for application in TiO2 processing is analysed.

Evaluation of autogenous bone grafts, particulate or collected during osteotomy with implant burs: Histologic and histomorphometric analysis in rabbits

Purpose: the aim of this study was to evaluate bone regeneration in bone cavities filled with particulate autogenous bone either harvest in blocks and subjected to milling procedures or collected during osteotomy with implant burs. Materials and Methods: In 12 rabbits, 3 noncritical unicortical cavities 7 mm in diameter were prepared with a trephine drill on the right tibia. The cavities were filled respectively with particulate autogenous bone achieved with a manual bone crusher ( particulate group), with particulate autogenous bone obtained using bone collector during osteotomy ( collected group), and with blood clot ( control group). Animals were sacrificed at 7, 15, and 30 days after surgery ( 4 animals for each time period). The sections were examined by histologic and histomorphometric analysis. Results: At 7 days, the samples were filled by coagulum, and bone particles were observed only in the collected (24%) and particulate groups (44.75%). At 15 days, there was connective differentiation in all groups, with presence of grafted bone particles and onset of newly formed bone in the collected (38.88%) and particulate groups (46.0%). At 30 days, there was bone fill ( immature trabecular bone) of the cavities in the control (50%), collected (64.63%) and particulate groups (66%). Conclusion: No significant difference was demonstrated between noncritical unicortical bone defects in rabbit tibiae filled with particulate bone harvested as a block and subjected to milling and those filled with bone collected during osteotomy with implant drills when the defects were observed up to 30 days following their creation.

Induction of the split sting trait in Africanized Apis mellifera (Hymenoptera : Apidae) by cold treatment of pupae

Split sting is the name given to a nonfunctional honey bee sting characterized by lancets not attached to the stylet. It has appeared in a mutant line in Brazil, and has provoked interest as a possible means to reduce honey bee colony defensiveness. We induced this alteration in Africanized Apis mellifera L. workers and queens by maintaining pupae at 20 degrees C. In particular, we determined the pupal phase most susceptible to alterations in the sting caused by cold treatment, and we investigated whether this treatment also affected survival to the adult phase and wing morphology. The highest frequency of split sting was detected in workers treated at the pink-eyed pupal phase. The lowest frequency was observed in the bees treated at the oldest worker pupal phase studied (brown-eyed pupae with lightly pigmented cuticle). Both queen pupal phases tested (white and pink-eyed pupae) were equally sensitive and produced high percentages of adults with split sting. However, the 20 degrees C treatment of workers and queens, at the different pupal phases, resulted in high frequencies of adults with deformed wings. Also, fewer workers and queens treated at the earlier pupal stages reached adult emergence. There was also an arrest in developmental time, corresponding to the period of cold treatment.

A variation on split-cast mounting for complete denture construction

dThis article describes a variation of the split-cast mounting technique wherein the border of the definitive cast is wrapped with masking tape to form a container for the dental plaster normally used to affix the cast to the articulator. The entire inferior surface of the cast is coated with a thin film of petroleum jelly, and the cast is mounted in the articulator. After the dental plaster has set, the cast is retained by means of the masking tape. The cast is separated from the dental plaster simply by removing the masking tape.

Orthognathic Surgery in the Young Cleft Patient: Preliminary Study on Subsequent Facial Growth

Purpose: This study evaluated the long-term effects of orthognathic surgery on subsequent growth of the maxillomandibular complex in the young cleft patient. Patients and Methods: We evaluated 12 young cleft patients (9 male and 3 female patients), with a mean age of 12 years 6 months (range, 9 years 8 months to 15 years 4 months), who underwent Le Fort I osteotomies, with maxillary advancement, expansion, and/or downgrafting, by use of autogenous bone or hydroxyapatite grafts, when indicated, for maxillary stabilization. Five patients had concomitant osteotomies of the mandibular ramus. All patients had presurgical and postsurgical orthodontic treatment to control the occlusion. Radiographs taken at initial evaluation (T1) and presurgery (T2) were compared to establish the facial growth vector before surgery, whereas radiographs taken immediately postsurgery (T3) and at longest follow-up (T4) were used to determine postsurgical growth. Each patient's lateral cephalograms were traced, and 16 landmarks were identified and used to compute 11 measurements describing presurgical and postsurgical growth. Results: Before surgery, all patients had relatively normal growth. After surgery, cephalograms showed statistically significant growth changes from T3 to T4, with the maxillary depth decreasing by -3.3° ± 1.8°, Sella-nasion-point A by -3.3° ± 1.8°, and point A-nasion-point B by -3.6° ± 2.8°. The angulation of the maxillary incisors increased by 9.2° ± 11.7°. Of 12 patients, 11 showed disproportionate postsurgical jaw growth. Maxillary growth occurred predominantly in a vertical vector with no anteroposterior growth, even though most patients had shown anteroposterior growth before surgery. The distance increased in the linear measurement from nasion to gnathion by 10.3 ± 7.9 mm. Four of 5 patients operated on during the mixed dentition phase had teeth that erupted through the cleft area. A variable impairment of postoperative growth was seen with the 2 types of grafting material used. No significant difference was noted in the effect on growth in patients with unilateral clefts versus those with bilateral clefts. The presence of a pharyngeal flap was noted to adversely affect growth, whereas simultaneous mandibular surgery did not. After surgery, 11 of 12 patients tended toward a Class III end-on occlusal relation. Conclusions: Orthognathic surgery may be performed on growing cleft patients when mandated by psychological and/or functional concerns. The surgeon must be cognizant of the adverse postsurgical growth outcomes when performing orthognathic surgery on growing cleft patients with the possibility for further surgery requirements. Performing maxillary osteotomies on cleft patients would be more predictable after completion of facial growth. © 2008 American Association of Oral and Maxillofacial Surgeons.

Cephalometric evaluation of surgical mandibular advancement

The treatment of Class II adult individuals with mandibular deficiency has been the combination of orthodontic treatment and orthognathic surgery. Therefore, a study was conducted in which cephalometric analysis was used to evaluate the influence of dentoalveolar decompensation in Class II patients submitted to orthodontic and surgical treatment for mandibular advancement, by bilateral osteotomy of the mandibular ramus. A sample of 15 leukoderma adult female patients were selected and three cephalometric radiographs of each patient, taken before the orthodontic treatment, before surgery and after at least 6 months postoperatively, were analyzed in a total of 45 roentgenograms. The tracings were made by the manual method and the points were digitalized using software. The results showed that values of SNB increased from 75.6 to 78.6°. The measures BNP and PGNP were reduced from -12.7 to -7.7 mm and -12.7 to -6.6 mm, respectively. For ANB there was a reduction of 3.23° (from 8.1° to 4.9°). Likewise, the values of AOBO were diminished by 6.3 mm (from 7.6 to 1.3 mm), and in the values of OJ there was a reduction of 5.7 mm (from 9 to 3.3 mm). It was concluded that the pre-surgical orthodontic treatment promoted minimal and variable dental and skeletal changes in the final result. The surgical treatment caused significant skeletal changes, especially in the measurements related to the mandible (SNB, BNP, PGNP and SNPM) or indirectly to it (ANB, AOBO and OJ).

Modeling Habitat Split: Landscape and Life History Traits Determine Amphibian Extinction Thresholds

Habitat split is a major force behind the worldwide decline of amphibian populations, causing community change in richness and species composition. In fragmented landscapes, natural remnants, the terrestrial habitat of the adults, are frequently separated from streams, the aquatic habitat of the larvae. An important question is how this landscape configuration affects population levels and if it can drive species to extinction locally. Here, we put forward the first theoretical model on habitat split which is particularly concerned on how split distance - the distance between the two required habitats - affects population size and persistence in isolated fragments. Our diffusive model shows that habitat split alone is able to generate extinction thresholds. Fragments occurring between the aquatic habitat and a given critical split distance are expected to hold viable populations, while fragments located farther away are expected to be unoccupied. Species with higher reproductive success and higher diffusion rate of post-metamorphic youngs are expected to have farther critical split distances. Furthermore, the model indicates that negative effects of habitat split are poorly compensated by positive effects of fragment size. The habitat split model improves our understanding about spatially structured populations and has relevant implications for landscape design for conservation. It puts on a firm theoretical basis the relation between habitat split and the decline of amphibian populations. © 2013 Fonseca et al.

Dynamics of bone healing after osteotomy with piezosurgery or conventional drilling - histomorphometrical, immunohistochemical, and molecular analysis

Background: Piezosurgery is an osteotomy system used in medical and dental surgery. Many studies have proven clinical advantages of piezosurgery in terms of quality of cut, maneuverability, ease of use, and safety. However, few investigations have tested its superiority over the traditional osteotomy systems in terms of dynamics of bone healing. Therefore, the aim of this study was to evaluate the dynamics of bone healing after osteotomies with piezosurgery and to compare them with those associated to traditional bone drilling.Methods: One hundred and ten rats were divided into two groups with 55 animals each. The animals were anesthetized and the tibiae were surgically exposed to create defects 2 mm in diameter by using piezosurgery (Piezo group) and conventional drilling (Drill group). Animals were sacrificed at 3, 7, 14, 30 and 60 days post-surgery. Bone samples were collected and processed for histological, histomorphometrical, immunohistochemical, and molecular analysis. The histological analysis was performed at all time points (n = 8) whereas the histomorphometrical analysis was performed at 7, 14, 30 and 60 days post-surgery (n = 8). The immunolabeling was performed to detect Vascular Endothelial Growth Factor (VEGF), Caspase-3 (CAS-3), Osteoprotegerin (OPG), Receptor Activator of Nuclear Factor kappa-B Ligand (RANKL), and Osteocalcin (OC) at 3, 7, and 14 days (n = 3). For the molecular analysis, animals were sacrificed at 3, 7 and 14 days, total RNA was collected, and quantification of the expression of 21 genes related to BMP signaling, Wnt signaling, inflammation, osteogenenic and apoptotic pathways was performed by qRT-PCR (n = 5).Results: Histologically and histomorphometrically, bone healing was similar in both groups with the exception of a slightly higher amount of newly formed bone observed at 30 days after piezosurgery (p < 0.05). Immunohistochemical and qRT-PCR analyses didn't detect significant differences in expression of all the proteins and most of the genes tested.Conclusions: Based on the results of our study we conclude that in a rat tibial bone defect model the bone healing dynamics after piezosurgery are comparable to those observed with conventional drilling. © 2013 Esteves et al.; licensee BioMed Central Ltd.

Avaliação histológica e histomorfométrica do reparo ósseo em tíbias osteotomizadas de ratos (Rattus novergicus albinus) frente à ausência de carga e tratamento com ultrassom

Pós-graduação em Ciência Animal - FMVA

Assessment of first molars sagittal and rotational position in Class II, division 1 malocclusion

OBJECTIVE: This study assessed the anterior-posterior positioning of the upper and lower first molars, and the degree of rotation of the upper first molars in individuals with Class II, division 1, malocclusion. METHODS: Asymmetry I, an accurate device, was used to assess sixty sets of dental casts from 27 females and 33 males, aged between 12 and 21 years old, with bilateral Class II, division 1. The sagittal position of the molars was determined by positioning the casts onto the device, considering the midpalatal suture as a symmetry reference, and then measuring the distance between the mesial marginal ridge of the most distal molar and the mesial marginal ridge of its counterpart. With regard to the degree of rotation of the upper molar, the distance between landmarks on the mesial marginal ridge was measured. Chi-square test with a 5% significance level was used to verify the variation in molars position. Student's t test at 5% significance was used for statistical analysis. RESULTS: A great number of lower molars mesially positioned was registered, and the comparison between the right and left sides also demonstrated a higher number of mesially positioned molars on the right side of both arches. The average rotation of the molars was found to be 0.76 mm and 0.93 mm for the right and left sides, respectively. CONCLUSION: No statistically significant difference was detected between the mean values of molars mesialization regardless of the side and arch. Molars rotation, measured in millimeters, represented ¼ of Class II.

Long-term skeletal and dental effects and treatment timing for functional appliances in Class II malocclusion

Objective: To analyze the long-term skeletal and dentoalveolar effects and to evaluate treatment timing of Class II treatment with functional appliances followed by fixed appliances.Materials and Methods: A group of 40 patients (22 females and 18 males) with Class II malocclusion consecutively treated either with a Bionator or an Activator followed by fixed appliances was compared with a control group of 20 subjects (9 females and 11 males) with untreated Class II malocclusion. Lateral cephalograms were available at the start of treatment (mean age 10 years), end of treatment with functional appliances (mean age 12 years), and long-term observation (mean age 18.6 years). The treated sample also was divided into two groups according to skeletal maturity. The early-treatment group was composed of 20 subjects (12 females and 8 males) treated before puberty, while the late-treatment group included 20 subjects (10 females and 10 males) treated at puberty. Statistical comparisons were performed with analysis of variance followed by Tukey's post hoc tests.Results: Significant long-term mandibular changes (Co-Gn) in the treated group (3.6 mm over the controls) were associated with improvements in the skeletal sagittal intermaxillary relationship, overjet, and molar relationship (similar to 3.0-3.5 mm). Treatment during the pubertal peak was able to produce significantly greater increases in total mandibular length (4.3 mm) and mandibular ramus height (3.1 mm) associated with a significant advancement of the bony chin (3.9 mm) when compared with treatment before puberty.Conclusion: Treatment of Class II malocclusion with functional appliances appears to be more effective at puberty. (Angle Orthod. 2013;83:334-340.)

Tomographic follow-up of bone regeneration after bone block harvesting from the mandibular ramus

Autogenous bone is still considered the gold standard, and the applicability of autogenous bone grafts is well established. However, the possibility of second harvesting from the same donor region remains unclear. The aim of this study was to perform a prospective evaluation of hard tissue deposition in the mandibular ramus after bone block harvesting using cone beam computed tomography (CBCT). Twenty-two patients with indications for augmentation procedures using autogenous bone from the mandibular ramus were selected. Three CBCT scans were performed with a tomographic guide before bone harvesting (T1) and at 14 days (T2) and 6 months (T3) after the surgical procedures. Measurements were obtained in 2D (area, mm(2)) and 3D (volume, mm(3)), and were subsequently compared. In the 2D analysis, the mean bone formation rate was 56%, while for the 3D analysis the mean rate was 9.7%. Despite this difference, there was a significant correlation between area and volume measurements. Our findings demonstrated the presence of hard tissue in the mandibular ramus at 6 months after bone harvesting, which suggests that it would be possible to reuse the same region for a second block harvesting. However, the second bone harvesting would involve less bone for transplantation when compared to the first bone harvesting.

Evaluation of Bone Heating, Drill Deformation, and Drill Roughness After Implant Osteotomy: Guided Surgery and Classic Drilling Procedure

Purpose: This study evaluated and compared bone heating, drill deformation, and drill roughness after several implant osteotomies in the guided surgery technique and the classic drilling procedure. Materials and Methods: The tibias of 20 rabbits were used. The animals were divided into a guided surgery group (GG) and a control group (CG); subgroups were then designated (G0, G1, G2, G3, and G4, corresponding to drills used 0, 10, 20, 30 and 40 times, respectively). Each animal received 10 sequential osteotomies (5 in each tibia) with each technique. Thermal changes were quantified, drill roughness was measured, and the drills were subjected to scanning electron microscopy. Results: Bone temperature generated by drilling was significantly higher in the GG than in the CG. Drill deformation in the GG and CG increased with drill use, and in the CG a significant difference between GO and groups G3 and G4 was observed. In the GG, a significant difference between GO and all other groups was found. For GG versus CG, a significant difference was found in the 40th osteotomy. Drill roughness in both groups was progressive in accordance with increased use, but there was no statistically significant difference between subgroups or between GG and CG overall. Conclusion: During preparation of implant osteotomies, the guided surgery technique generated a higher bone temperature and deformed drills more than the classic drilling procedure. The increase in tissue temperature was directly proportional to the number of times drills were used, but neither technique generated critical necrosis-inducing temperatures. Drill deformation was directly proportional to the number of times the drills were used. The roughness of the drills was directly proportional to the number of reuses in both groups but tended to be higher in the GG group.