Haci Saglam

Comparison of stability of absorbable and titanium plate and screw fixation for sagittal split ramus osteotomy

Six unembalmed adult sheep mandibles were stripped of all soft tissues and sectioned at the midline. Each side had a sagittal split ramus osteotomy (SSRO) and was advanced 5 mm. Six of the hemimandibles were fixed with four-hole extended titanium miniplates and titanium screws, and the other six were fixed with four-hole extended absorbable plates and absorbable screws. All specimens were mounted in a servohydraulic testing unit, and a range of forces (0-140 N) was applied. Displacement of each proximal segment was recorded at 10 N increments from 0 to 140 N. Values for the two groups were compared using the Mann-Whitney U-test, and significant differences in displacement were seen only at loads between 10 and 50 N. The results indicate that when absorbable miniplates are used intermaxillary fixation may be necessary to stabilise the bony fragments in the early postoperative period.

An experimental investigation as to the effect of cutting parameters on roundness error and surface roughness in cylindrical grinding

This paper presents the results of an experimental investigation as to the effects of grinding parameters on roundness error and surface roughness in cylindrical grinding. Many variables including the wheel materials, wheel loading and dressing, workpiece metallurgy, work drive mechanisms, work holding methods, coolant types, feeds and speeds, machine stiffness and age, surface conditions, centre conditions, floor vibrations all influence the quality of ground parts. However, the composite sum of these grinding parameters creates static and dynamic forces. It is obvious that the roundness error and surface roughness are created by many parameters, but in this study, only the effects of the depth of cut, work speed and feed rate which create the grinding forces in cylindrical grinding are investigated. The grinding experiments were planned according to the principles of orthogonal arrays (OAs), developed by Taguchi, and were performed so as to understand the effects of these parameters on roundness error and surface roughness. The experimental data was analysed by using statistical tools: the percent contribution from an analysis of variance (ANOVA) and the correlation between machining parameters with roundness error (R) and also surface roughness (Ra). Roundness was found to be the most related with the cutting speed, grinding force and depth of cut, while surface roughness is related to feed rate and work speed.

Comparison of stability of 2.0 mm standard and 2.0 mm locking miniplate/screws for the fixation of sagittal split ramus osteotomy on sheep mandibles

Ten unembalmed adult sheep mandibles were used. The mandibles were sectioned in the midline, followed by sagittal split ramus osteotomies to obtain 20 hemimandibles. Each distal segment was advanced 5mm on each hemimandible. Ten of the specimens were fixed with 4-hole extended 2.0 mm titanium miniplates and screws and the other 10 were fixed with 4-hole extended 2.0 mm locking miniplates/screws. Each fixed specimen was mounted on a servo-hydraulic testing unit with the fixation device, and was tested to a range of forces of 0-140 N. The displacement values (mm) under 20, 60, 120, and 140 N were compared with the help of the Mann-Whitney U-test, and there were no significant differences between them at any force tested. Locking miniplate/screws and standard miniplate/screws showed similar displacement values at the range of forces tested.

The Effects of Cutting Speed and Depth of Cut on Machinability Characteristics of Austempered Ductile Iron

Ductile iron can acquire enhanced thermal and mechanical properties from austempering heat treatment. The present study aims to identify the function of different cutting parameters affecting machinability and to quantify its effects. Turning was performed to test machinability according to the ISO3685-1993 (E) standard. After austenitizing at 900 C for 90 min, austempered ductile iron (ADI) specimens were quenched in a salt bath at 380 C for 90 min. The cutting force signals along three directions were measured in real time, whereas flank wear and surface roughness were measured offline. For the cutting parameters, the cutting speed and depth of cut were varied, but the feed rate was kept constant. In the flank wear tests, machining length was corresponded to tool life. In addition, in order to find out the effect of cutting parameters on surface roughness (Ra), tangential force (Ft), and flank wear (VB) during turning, response surface methodology (RSM) was utilized by using experimental data. The effect of the depth of cut on the surface roughness was negligible but considerable in the cutting forces. The increased cutting speed produced a positive effect on surface roughness. It is found that the cutting speed was the dominant factor on the surface roughness, tangential force, and flank wear. [DOI: 10.1115/1.4005805]

Evaluation of strain values of critical anatomic regions for two different pterygomaxillary approaches in Le Fort I osteotomy: an experimental study

Background The purpose of this experimental study was to measure stresses both on the pterygoid plates and the skull base following two different pterygomaxillary approaches in Le Fort I osteotomy. Material and Methods The prepared skull models were randomly divided into 2 groups of 7. In the first group (A), the pterygomaxillary area was left intact. In the second group (B), pterygomaxillary separation was performed with a fine bur. The stresses were measured by using strain gauges. These strain gauges were attached to 6 different anatomical sites. The skull models were mounted on a servo-hydraulic testing unit. Each model was then subjected to a continuous linear tension until a plastic deformation was seen. Results The statistical analyses showed that there were no significant differences (p >.05) between the 2 groups regarding the strain values. Moreover, no statistical differences (p >.05) were found between the two groups in terms of maximum applied forces. Conclusions Considering the clinical conditions, the present study shows that when Le Fort I osteotomy performed without pterygomaxillary separation, there is no significant stress on the skull base during the downfracture. Moreover, it is considered that there is no need for an excessive force applied to perform downfracture in Le Fort osteotomies without pterygomaxillary separation. Key words:Le Fort I, osteotomy, strain, base of skull, pterygoid process.

Biomechanical evaluation of different fixation systems after Le Fort I osteotomy in polyurethane models of unilateral clefts

We compared the stability of three different titanium plate-and-screw fixation systems after Le Fort I osteotomy in polyurethane models of unilateral clefts. Thirty-six models were divided into 3 groups. In the first group, we adapted standard Plates 1mm thick with 2.0mm screws and placed them bilaterally on the zygomatic buttress and the piriform rim. In the second group, we did the same and added Plates 0.6mm thick with 1.6mm screws between the standard 2mm miniplates on both sides. In the last group, we placed Plates 1.4mm thick with 2.0mm screws bilaterally on the maxillary zygomatic buttress and piriform rim. Each group was tested in the inferosuperior (IS) and anteroposterior (AP) directions with a servo-hydraulic testing unit. In the IS direction, displacement values were not significantly different up to 80N, but between 80 and 210N, those in the 2×1.4mm group were better. In the AP direction, displacement values were not significantly different up to 40N, but between 40 and 180N, they were better in the standard with 1.6×0.6mm group and the 2×1.4mm group. When normal biting forces (90 - 260N) in the postoperative period are considered, the greatest resistance to occlusal loads was seen in the 2×1.4mm group. In the others, the biomechanical properties were better in the AP direction.