Surface waves and crustal structure on Mars.

We detected surface waves from two meteorite impacts on Mars. By measuring group velocity dispersion along the impact-lander path, we obtained a direct constraint on crustal structure away from the InSight lander. The crust north of the equatorial dichotomy had a shear wave velocity of approximately 3.2 kilometers per second in the 5- to 30-kilometer depth range, with little depth variation. This implies a higher crustal density than inferred beneath the lander, suggesting either compositional differences or reduced porosity in the volcanic areas traversed by the surface waves. The lower velocities and the crustal layering observed beneath the landing site down to a 10-kilometer depth are not a global feature. Structural variations revealed by surface waves hold implications for models of the formation and thickness of the martian crust.

Determining anatomical localisations of cervical oesophagus, hiatal clamp and oesophagogastric junction with oesophagogastroduodenoscopy.

BACKGROUND: In this study, the purpose was to determine the anatomical localisations of the cervical oesophagus length, hiatal clamp, and oesophagogastric junction depending on age and gender in patients who undergo oesophagogastroduodenoscopy (EGD). MATERIALS AND METHODS: The images of the patients who underwent EGD between 2018 and 2020 were analysed retrospectively in this study. The distance of the anatomical localisations of the cervical oesophagus length, hiatal clamp, and oesophagogastric junction to the anterior incisors, and the relations of this distance with the demographic characteristics and clinical manifestations of the patients were investigated on the EGD data. RESULTS: A total of 298 patients (174 women, 124 men) were included in the study. The cervical oesophagus length and the distance of the oesophagogastric junction and hiatal clamp localisation of the patients were found to be 15.06 ± 0.57 cm, 37.51 ± 2.23 cm and 38.62 ± 2.23 cm, respectively. It was also found that the mean values of all lengths in males were higher at a statistically significant level than in females (p < 0.001; p < 0.01). CONCLUSIONS: Knowing these anatomical localisations may be important in predicting complications that may occur in this region in EGD and planning the precautions to be taken. We also believe that it will guide clinicians in determining hiatal hernia and related deficiencies.

Effect of a bovine collagen matrix on tendon adhesions during the repair of rat Achilles tendon.

Adhesion after a tendon injury is one of the major problems following upper extremity surgery. In the present study, we evaluated a new material that is clinically usable as an adhesion barrier. Twenty-four male Wistar albino rats were used in the study. These rats (48 legs) were divided into three groups: sham, control, and experimental. No surgical intervention was performed in the sham group. After making a full-thickness cut through the right Achilles tendon, the tendon was repaired using the modified Kessler technique in the control group, while bovine collagen matrix was wrapped around the surgically repaired tendon using the modified Kessler technique in the experimental group. Two months after surgery, the operated and non-operated tendons were resected and analyzed through biomechanical, macroscopic, and histopathological examinations. The results of the biomechanical testing did not differ significantly between the control and experimental groups. Macroscopic examination of the adhesions revealed less adhesions in the experimental group but this difference was not statistically significant. Moreover, the results of the histopathological examination, which was performed based on five criteria, did not differ significantly between the two groups. Our study's results indicate that a bovine collagen matrix can be used to prevent tendon adhesion; however, larger studies are needed to verify these findings.

Comparison of four different techniques for performing an osteotomy: a biomechanical, radiological and histological study on rabbits tibias.

This animal study compares different methods of performing an osteotomy, including using an Erbium-doped Yttrium Aluminum Garnet laser, histologically, radiologically and biomechanically. A total of 24 New Zealand rabbits were divided into four groups (Group I: multihole-drilling; Group II: Gigli saw; Group III: electrical saw blade and Group IV: laser). A proximal transverse diaphyseal osteotomy was performed on the right tibias of the rabbits after the application of a circular external fixator. The rabbits were killed six weeks after the procedure, the operated tibias were resected and radiographs taken. The specimens were tested biomechanically using three-point bending forces, and four tibias from each group were examined histologically. Outcome parameters were the biomechanical stability of the tibias as assessed by the failure to load and radiographic and histological examination of the osteotomy site. The osteotomies healed in all specimens both radiographically and histologically. The differences in the mean radiographic (p = 0.568) and histological (p = 0.71) scores, and in the mean failure loads (p = 0.180) were not statistically significant between the groups. Different methods of performing an osteotomy give similar quality of union. The laser osteotomy, which is not widely used in orthopaedics is an alternative to the current methods.

Influence of surgical technique, implant shape and diameter on the primary stability in cancellous bone.

Achievement of primary stability during surgical placement of dental implants is one of the most important factors for successful osseointegration depending on various anatomical, surgical and implant-related factors. Resonance frequency analysis (RFA) has been shown as a non-invasive and objective technique for measuring the stability of implants. The aim of this study was to evaluate the effect of some surgical and implant-related factors in enhancing primary stability and to estimate a correlation between RFA and insertion torque (IT) in proximal regions of cow ribs representing cancellous bone. Fifteen implant beds were prepared in the most proximal region of six fresh cow ribs. Ninety implants with three different shapes and two different diameters were placed with two different surgical techniques, and the primary stability was compared using RFA and IT. Significantly higher RFA and IT values were achieved when under-dimensioned drilling was used as the surgical method (P<0·01); significantly higher IT values were obtained with the use of wider implants (P<0·01) and partially conical Astra Tech implants showed the highest IT values (P<0·01). When all the implants were considered, significant correlations between the IT and RFA values were noted (%40·6, P<0·05). Partially conical implants with a wide diameter to be placed with the modified surgical technique proposed appear to be useful in enhancing the primary stability in cancellous bone.

A comparison of single-versus double-row suture anchor techniques in a simulated repair of the rotator cuff: an experimental study in rabbits.

We compared time-dependent changes in the biomechanical properties of single-and double-row repair of a simulated acute tear of the rotator cuff in rabbits to determine the effect of the fixation techniques on the healing process. A tear of the supraspinatus tendon was created in 80 rabbits which were separated into two equal groups. A single-row repair with two suture anchors was conducted in group 1 and a double-row repair with four suture anchors in group 2. A total of ten intact contralateral shoulder joints was used as a control group. Biomechanical testing was performed immediately post-operatively and at four and eight weeks, and histological analysis at four and eight weeks. The mean load to failure in group 2 animals was greater than in group 1, but both groups remained lower than the control group at all intervals. Histological analysis showed similar healing properties at four and eight weeks in both groups, but a significantly larger number of healed tendon-bone interfaces were identified in group 2 than in group 1 at eight weeks (p < 0.012). The ultimate load to failure increased with the number of suture anchors used immediately post-operatively, and at four and eight weeks. The increased load to failure at eight weeks seemed to be related to the increase in the surface area of healed tendon-to-bone in the double-row repair group.

The effect of occlusal contact localization on the stress distribution in complete maxillary denture.

The fracture of acrylic resin dentures is an unresolved problem in removable prosthodontics despite many efforts to determine its cause. Unfavourable occlusion could be playing an important role in the fracture of the denture. The aim of this study was to investigate the effect of occlusal contact localization on the stress distribution in complete maxillary denture bases utilizing two-dimensional finite element analysis. The results of this study have shown that maximum compressive stresses in a complete maxillary denture under functional masticatory forces concentrates always on the artificial tooth/denture base junction irrespective to the occlusal contact localization. Tensile stresses were observed in areas toward the midline, although the midline itself usually had lower stresses. Shifting the occlusal contacts to a more buccal localization resulted in an increase of the calculated stresses. As a conclusion, it can be speculated that the buccal placement of the occlusal contacts may play a role in the fatigue fracture of the complete maxillary denture.

Biomechanical analysis of cervical multilevel oblique corpectomy: an in vitro study in sheep.

BACKGROUND: Anterolateral oblique corpectomy is an alternative approach to treatment of multilevel cervical spinal disease. It is stated that the approach does not cause instability in the patients with hard discs, so fusion or instrumentation is not required. The authors undertook a study on stability of the cervical spine by an animal model to establish if this approach causes instability. MATERIAL AND METHODS: Thirty-seven C3 to C6 spinal segments obtained from 3 to 4-year-old male sheep were used. In vitro maximal loading values were obtained from seven sheep cervical specimens for flexion, extension, lateral flexion in both directions, axial rotation in both directions and axial loading, and load deformation curves were drawn by an electrohydrolic testing machine. Other specimens were divided into three groups: Control (n=10), C4 (n=10) and C4-5 (n=10) groups. In two study groups, one or two level oblique corpectomies were performed. In the control and study groups, biomechanical tests were obtained according to the maximal loading values. Load-deformation curves were drawn and displacement amounts were determined for all seven movements. RESULTS: No statistically significant differences were observed in load deformation curves and displacement amounts between all three groups for seven movements. CONCLUSION: These results support the opinion that anterolateral oblique corpectomy does not cause cervical instability.

Finite element model of the Jefferson fracture: comparison with a cadaver model.

This study tries to explain the reason why the Jefferson fracture is a burst fracture, using two different biomechanical models: a finite element model (FEM) and a cadaver model used to determine strain distribution in C1 during axial static compressive loading. For the FEM model, a three-dimensional model of C1 was obtained from a 29-year-old healthy human, using axial CT scans with intervals of 1.0 mm. The mesh model was composed of 8200 four-noded isoparametric tetrahedrons and 37,400 solid elements. The material properties of the cortical bone of the vertebra were assessed according to the previous literature and were assumed to be linear isotropic and homogeneous for all elements. Axial static compressive loads were applied at between 200 and 1200 N. The strain and stress (maximum shear and von Mises) analyses were determined on the clinically relevant fracture lines of anterior and posterior arches. The results of the FEM were compared with a cadaver model. The latter comprised the C1 bone of a cadaver placed in a methylmethacrylate foam. Axial static compressive loads between 200 and 1200 N were applied by an electrohydraulic testing machine. Strain values were measured using strain gauges, which were cemented to the bone where the clinically relevant fracture lines of the anterior and posterior arches were located. As a result, compressive strain was observed on the outer surface of the anterior arch and inferior surface of the posterior arch. In addition, there was tensile strain on the inner surface of the anterior arch and superior surface of the posterior arch. The strain values obtained from the two experimental models showed similar trends. The FEM analysis revealed that maximum strain changes occurred where the maximum shear and von Mises stresses were concentrated. The changes in the C1 strain and stress values during static axial loading biomechanically prove that the Jefferson fracture is a burst fracture.