Effect of angled installation of orthodontic mini-implants on primary stability

AIM: The aim of this work was evaluate the insertion and removal torque for orthodontic mini-implants inserted in different inclination. Materials and methods: Ten self[drilling mini-implants from the brand SIN (Sistema de Implantes Nacional, São Paulo/SP, Brazil), and the surgical kit for their insertion were used. Two plaques of synthetic bone of 120mm x 170mm x 41,5mm were used (Sawbones, Pacific Research Laboratories Inc, Vashon, Wash), with 1,5mm height, simulating the cortical bone (density 40 pcf) and 40 mm simulating the medullary bone (density 15 pcf). In each block, five areas were demarcated for each mark, totalizing ten areas. The ten mini-implants were inserted by the same operator, previously calibrated; five of them at 900 and five at 600, using the manual key kit. After the insertion of all the mini-implants, the final threading and the reading of insertion torque value were carried out with a manual torque wrench digital Lutron TQ[8800 (Lutron Electronic Enterprise Co., Ltd, Taipei, Taiwan) until the trans-mucosal profile achieve the cortical bone. The maximum insertion torque value was registered in N/cm. After all the implants inserted, the measurement of removal torque was started, performed in the same way of insertion, but in the opposite anticlockwise. The results were submitted to the T test (parametric) and to a Mann-Whitney test (non-parametric). Results: The results demonstrated that the insertion torque was lower than the removal one in both insertion degrees, with statistically significance. Despite insertion torque at 90 degrees had been lightly higher than that inserted at 60 degrees, they were not statistically significant. Conclusion: In view of the results, it was possible conclude that insertion at 60º angulation does not offer advantages to the primary stability for orthodontic mini-implants.

Ideal Insertion Point and Angle of Cervical Pedicular Screws in Korean

STUDY DESIGN: A retrospective study. OBJECTIVES: Using computed tomography, it is to measure pedicle size of lower cervical spine in Koreas to find ideal insertion point and angle in fixating pedicular screws. SUMMARY OF LITERATURE REVIEW: Although techniques in pedicular screw fixation and pedicle's anatomical shape in foreign populations have been well documented and studied, no anatomical study on lower cervical pedicle in Korean population has been reported. MATERIALS AND METHODS: A total of 180 patients with computed tomography taken at our institution were selected for the study. Width, total length, and length of pedicle, insertion point and angle, and safe insertion angles were measured on axial view. On sagittal view, height of pedicle, insertion point and angle, and safe insertion angles were determined. RESULTS: Mean height of study subject was 164.2cm. Mean width of pedicle was 5.5mm, mean height 7.2mm, mean total length 31.2mm, and mean length 14.8mm. Mean insertion point from 3rd to 7th cervical spines was medially 3.3mm from lateral mass and downward 4.7mm from margin of upper facet. Mean insertion angles from 3rd to 7th cervical spines were 41.6degrees axially and 6.4degrees sagittally. Calculated safe insertion angles were 8degrees on medial and lateral sides and 14degrees on superior and inferior sides. CONCLUSIONS: Using computed tomography images, ideal insertion point and angle were measured for pedicular screw insertion, but, due to individual variation, preoperative measurement of insertion point and angle on computed tomography is necessary.

Surface Anatomical Landmark and Optimal Insertion Angle in Cervical Epidural Block

OBJECTIVE: The aim of this study is to evaluate the surface anatomical landmark for the cervical epidural block by investigating the proportion of patient's prominence in the 7th cervical vertebra. And the most optimal insertion angle over the mid point between the 6th and the 7th cervical spinous process is also measured. METHOD: Patients who did a plane x-ray examination of cervical spine were selected. We performed plane x-ray after marking on cervical vertebra prominence that was assumed as the spinous process of the 7th cervical vertebra by inspection and palpation. We identified where the marker were located on the spinous process. Moreover, we measured optimal insertion angle in the plane x-ray of cervical spine lateral. RESULTS: A total 100 cases were identified. The vertebra prominence was on the 7th cervical vertebra in 62 cases and the 6th cervical vertebra in 29 cases. The 1st thoracic vertebra was in the 2 cases and the 6th and 7th cervical vertebra in the 7 cases. CONCLUSION: The vertebra prominence was identified as the spinous process of the 7th cervical vertebra in sixty two percent of the cases. And the most optimal insertion angle is a -25.28 degree angle from the perpendicular line of the skin.

Three-dimensional finite element analysis for stress distribution on the diameter of orthodontic mini-implants and insertion angle to the bone surface / 대한치과교정학회지

The present study was performed to evaluate the stress distribution on the diameter of the mini-implant and insertion angle to the bone surface. To perform three dimensional finite element analysis, a hexadron of 15 x 15 x 20 mm3 was used, with a 1.0 mm width of cortical bone. Mini-implants of 8 mm length and 1.2 mm, 1.6 mm, and 2.0 mm in diameter were inserted at 90 degrees, 75 degrees, 60 degrees, 45 degrees, and 30 degrees to the bone surface. Two hundred grams of horizontal force was applied to the center of the mini-implant head and stress distribution and its magnitude were analyzed by ANSYS, a three dimensional finite element analysis program. The findings of this study showed that maximum von Mises stresses in the mini-implant and cortical and cancellous bone were decreased as the diameter increased from 1.2 mm to 2.0 mm with no relation to the insertion angle. Analysis of the stress distribution in the cortical and cancellous bone showed that the stress was absorbed mostly in the cortical bone, and little was transmitted to the cancellous bone. The contact area increased according to the increased diameter and decreased insertion angle to the bone surface, but maximum von Mises stress in cortical bone was more significantly related with the contact point of the mini-implant into the cortical bone surface than the insertion angle to the bone surface. The above results suggest that the maintenance of the mini-implant is more closely related with the diameter and contact point of the mini-implant into the cortical bone surface rather than the insertion angle.

Measurement of the Axial Isthmus for Atlantoaxial Transarticular Screw Fixation / 대한해부학회지

Pre-operative evaluation of the anatomy of the axis, such as the size and angle of the axial isthmus, is very important to minimize complications in atlantoaxial transarticular screw fixation. To provide basic data useful for atlantoaxial transarticular screw fixation in Korean, the width and height of the axial isthmus as well as ideal insertion angle of the screw were measured in this study. Fifty seven (male, 36; female, 21) dried axes obtained from Korean adult cadavers, 60.5 years old in average, were used. The shortest distance in the width and height of the axial isthmus was measured at the level of transverse foramen by using Vernier calliper. The ideal screw insertion angle was set up as an angle between a parasagittal line and the line passing through the center of the isthmus and screw insertion point which is located 2 mm lateral to and 3 mm superior to the posteromedial end of the inferior articular surface of the axis. The mean width of the axial isthmus was 8.14 mm (8.42 mm in male; 7.86 mm in female) in the right and 8.46 mm (8.80 mm in male; 8.12 mm in female) in the left side, and 8.61 mm in male and 7.99 mm in female. Although the width of the axial isthmus was slightly greater in the left and in male, there was no significant difference between both sides or sexes. The mean height of the axial isthmus was 7.17 mm (7.49 mm in male; 6.84 mm in female) in the right and 7.43 mm (7.90 mm in male; 6.96 mm in female) in the left side, and 7.69 mm in male and 6.90 mm in female. However there was no significant difference between both sides or sexes, as like in the width. In the atlantoaxial transarticular screw fixation, the axis with isthmus lesser than 5 mm in its width or height is regarded as risk group in general. The frequency of the risk group in the width was 3.5% (2 cases) in the right and 1.8% (1 case) in the left, while that in the height was 8.8% (5 cases) in the right and 7.0% (4 cases) in the left. The mean ideal insertion angle of the screw was 5.6 degrees, 4.4 degrees in the right and left side of male, and 4.7 degrees, 5.5 degrees in the right and left side of female respectively. However the insertion angle dispersed over a wide range between 0 degree ~ 12 degrees. In conclusion, measurement of the isthmus height and insertion angle, besides the isthmus width, should be involved in the pre-operative examination, to minimize complications during the atlantoaxial transarticular screw fixation.

Correlation between Anterior and Posterior Obliquity of the Sliding Lag Screw and Stability in Unstable Intertrochanteric Fractures

PURPOSE: To investigate the characteristics of the sliding pattern of the proximal fragment (head and neck) in unstable intertrochanteric fractures, which were fixed with a dynamic hip screw (DHS) with anterior to posterior or posterior to anterior insertion angle in the axial view. MATERIALS AND METHODS: AO type A2.1 intertrochanteric fracture was reproduced in 10 proximal femur model (Synbone, Malans, Switzerland). Five fractured models were reduced and fixed using DHS with anterior to posterior insertion angle (group 1) and five models were fixed with posterior to anterior angle (group 2). Load of 500 N (30 cycles) was applied to the fracture fragment-plate complex using Instron 6022. Data on the distance of sliding and the angle of rotation of the proximal fragment were collected and analyzed. RESULTS: No significant difference was noted statistically in the distance of sliding between the two groups (p=0.92). However, the mean angle of rotation was 13.4degrees and 8.0degrees in group 1 and 2, respectively and the difference was statistically significant (p=0.012). Anterior cortical fracture of distal fragment was noted in 3 cases of group 1. There was no fracture of the anterior cortex in group 2. CONCLUSION: In unstable intertrochanteric fracture, the insertion angle of the lag screw in axial view does seem to play a role in the fate of bone-plate complex. Early eccentric contact of both fragments caused rotation of the proximal fragment in all cases and anterior cortical fracture of the distal fragment in 3 cases of group 1.