Mechanical and biomechanical measurements of five currently available osteosynthesis systems of self-tapping screws

Which type of method shows the best mechanical behavior for internal fixation of bilateral sagittal split osteotomy in major advancements with clockwise rotation? Comparison of four methods

PURPOSE

The aim of the present study was to evaluate the four methods for bilateral sagittal osteotomy fixation.

METHODS

In this study, 56 replicas of whole mandibles made of rigid polyurethane were used. After simulation of major advancement (11 mm) with clockwise rotation of the mandible (6^o) in relation to the occlusal plane, the bone segments were fixed with plates and screws of the 2.0-mm system on both the right and left sides: group I, double "H" plate; group II, two mini-plates; group III, "hybrid technique"; and group IV, three bicortical screws in the "inverted L" pattern. The mandibles were submitted to load on the central incisors and right first molar.

RESULTS

The mean value of group I was higher than those of groups IV and II in the displacement of 1 mm (F = 4.705; p = 0.010) with load on the incisor. The mean value of group III was higher than those of groups I and II in the displacement of 1 mm (F = 5.166; p = 0.007) and 3 mm (F = 5.166; p = 0.007). The mean value of group IV was higher than that of group II (F = 3.142; p = 0.044) with load on the molar.

CONCLUSION

Therefore, after the analyses, the hybrid technique was the one that showed the best results.

Do dual-thread orthodontic mini-implants improve bone/tissue mechanical retention?

PURPOSE

The aim of this study was to understand whether the pitch relationship between micro and macro thread designs with a parametrical relationship in a dual-thread mini-implant can improve primary stability.

MATERIALS AND METHODS

Three types of mini-implants consisting of single-thread (ST) (0.75 mm pitch in whole length), dual-thread A (DTA) with double-start 0.375 mm pitch, and dual-thread B (DTB) with single-start 0.2 mm pitch in upper 2-mm micro thread region for performing insertion and pull-out testing. Histomorphometric analysis was performed in these specimens in evaluating peri-implant bone defects using a non-contact vision measuring system.

RESULTS

The maximum inserted torque (Tmax) in type DTA was found to be the smallest significantly, but corresponding values found no significant difference between ST and DTB. The largest pull-out strength (Fmax) in the DTA mini-implant was found significantly greater than that for the ST mini-implant regardless of implant insertion orientation. Mini-implant engaged the cortical bone well as observed in ST and DTA types.

CONCLUSION

Dual-thread mini-implant with correct micro thread pitch (parametrical relationship with macro thread pitch) in the cortical bone region can improve primary stability and enhanced mechanical retention.

Biomechanical evaluation of magnesium-based resorbable metallic screw system in a bilateral sagittal split ramus osteotomy model using three-dimensional finite element analysis

PURPOSE

The aim of this study was to evaluate the stress distribution of a magnesium (Mg)-based resorbable screw system in a bilateral sagittal split ramus osteotomy (BSSO) and to compare its biomechanical stability with those of titanium (Ti)-based and polymer (IN)-based systems.

MATERIALS AND METHODS

A 3-dimensional BSSO model (10-mm advancement and setback) was constructed with Mimics. Bicortical screw fixation using Ti, IN, and Mg screws was performed with 4 different geometries of fixation. With an occlusal load of 132 N on the lower first molar, the von Mises stress (VMS) distribution was calculated using ANSYS.

RESULTS

The VMS distribution of Mg was more similar to that of Ti than to that of IN. In all cases, the highest VMS was concentrated on the screw at the most posterior and superior area. Stress was distributed mainly around the screw holes (cancellous bone) and the retromolar area (cortical bone). In the advancement surgery, fixation with 5 Mg screws (5A-Mg, 99.810 MPa at cortical bone) showed biomechanical stability, whereas fixation with the same number of IN screws did not (5A-IN, 109.021 MPa at cortical bone). In the setback surgery, although the maximum VMSs at cortical bone for Mg, IN, and Ti were lower than 108 MPa (yield strength of cortical bone), Mg screws showed more favorable results than IN screws because the maximum VMSs of Mg at cancellous bone were lower than those of IN.

CONCLUSION

The Mg-based resorbable screw system is a promising alternative to the IN-based system.

Direct and tomographic dimensional analysis of the inter-radicular distance and thickness of the vestibular cortical bone in the parasymphyseal region of adult human mandibles

We calculated the inter-radicular distances between the canine, and first and second premolars, of human mandibles and the thickness of the cortical bone at adjacent sites using computed tomographic (CT) imaging, and assessed the precision of the dimensional assessment made by CT compared with the same measurement made directly with calipers. We examined 100 adult cadaveric dentate human hemimandibles. At the level at which monocortical screws are inserted to place miniplates according to the current technique used to treat mandibular fractures, points A, B, and C referred to the canine, and first and second premolars, and were marked to calculate the level of the CT slice and as the reference for sectioning of the hemimandible. Our findings showed that there was no significant difference in the inter-radicular distance or in the thickness of cortical bone between the sides of the mandible. The vestibular cortical bone was less than 3.0mm thick in 91 of the samples. In 98 of the samples the inter-radicular distance between the canine and the first and second premolars was more than 2mm. There was no significant difference in micrometric precision between the dimensional assessment on CT and direct measurement using a caliper. In the region of the mental foramen the screws have cortical bone less than 3mm thick in which to be anchored. The inter-radicular distance suggests that there is a minimal risk of radicular injury when miniscrews are inserted between the alveolar structures. CT is a reliable tool for measuring the inter-radicular distance and the thickness of mandibular cortical bone.

Tomographic analysis of the interalveolar space and thickness of the vestibular cortical bone in the parasymphyseal region of adult human mandibles

PURPOSE

The aim of this study was to determine by computed tomography (CT) the interalveolar distance on mandible relative to the canine, first and second pre-molar, and the thickness of the cortical bone in the same region.

METHODS

A hundred adult cadaveric dentate human hemi-mandibles were examined. A point (P) above the upper margin of the mental foramen was determined, the height at which monocortical screws are inserted to place miniplate according to the technique to treat mandibular fracture. Then, points A, B and C at the same height as point P, referring to the dental units namely canine, first and second pre-molars were marked to determine the CT cut level to measure cortical bone thickness and the interalveolar distance.

RESULTS

The figures showed no statistically significant difference between the sides. The thickness of the vestibular cortical bone was less than 3.0 mm in 96% of the samples. In 91% of the samples the interalveolar distance between canine, first and second pre-molars was greater than 2 mm, a potentially safe condition to insert 2.0-mm diameter monocortical screws at the study points.

CONCLUSIONS

The individual actual anatomy of the region where screws are to be inserted above the mental foramen is important to perform the technique safely. We believe that the minimal cortical thickness to obtain sufficient screw anchorage should be studied in order to determine the actually safe shortest screw length. It is important to minimize the risk of tooth root damage or nerve injury and the amount of titanium in the human tissues.

Management of the fractured edentulous atrophic mandible

BACKGROUND

Fractures of the atrophic and edentulous (toothless) mandible (lower jaw) are fairly common in elderly people. Atrophy and weakening tend to occur as a result of reduced vascularity and decreased blood flow. Treatment options for reduction and fixation include closed and open techniques, with the degree of atrophy having a significant influence on the type of treatment. Many methods have been proposed for treating fractures of the atrophic mandible but there is still some uncertainty as to which method has the most successful outcomes.

OBJECTIVES

The objective of this review was to provide reliable evidence regarding the effectiveness of any interventions either open or closed that can be used in the management of fractured edentulous atrophic mandibles.

SEARCH STRATEGY

We searched the Cochrane Oral Health Group Trials Register; the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2005, Issue 4); MEDLINE from 1966 and EMBASE from 1980, both to 30th January 2006. Last search was done in January 2006.

SELECTION CRITERIA

Randomised controlled trials involving people over 55 years of age with fractures in the symphysis, parasymphysis, body, angle, ramus, condyle, and coronoid process of atrophic edentulous mandibles in which the fracture was a result of trauma, implant insertion or due to pathological fracture. Any studies that compared methods of management (open or closed reduction or fixation) were to be included.

DATA COLLECTION AND ANALYSIS

Screening of eligible studies was conducted in duplicate and independently by two review authors. Results were to be expressed as random-effects models using mean differences for continuous outcomes and risk ratios for dichotomous outcomes with 95% confidence intervals. Heterogeneity was to be investigated including both clinical and methodological factors.

MAIN RESULTS

No eligible randomised controlled trials were identified.

AUTHORS' CONCLUSIONS

This review illustrates that there is currently inadequate evidence for the effectiveness of a single approach, either open or closed, in the management of fractured atrophic edentulous mandibles and that until high level evidence is available treatment decisions should continue to be based on clinician's prior experience. This absence of evidence may in part reflect a certain lack of clarity and the apparent diversity and lack of reliability in some of the traditional and normative predictors of successful outcomes.

Three-dimensional finite element analysis used to compare methods of fixation after sagittal split ramus osteotomy: setback surgery-posterior loading

We used three-dimensional finite element analysis to compare the biomechanical stability of bilateral sagittal split ramus osteotomies fixed by lag screws with linear and triangular configuration, and double or single six-hole miniplates with monocortical screws after set-back operation. The three-dimensional finite element model contained 122,717 elements and 25,048 nodes. Posterior occlusal loads were simulated on the distal segments. MSC Marc software was used to calculate the stress fields on both the segments and the fixing appliances. We conclude that either triangular lag screw configuration or double miniplates led to better stability and lower mechanical stresses near the osteotomy than the linear lag screws or single oblique miniplates.

New implant designs for fracture fixation in osteoporotic bone

Screws are one of the limiting factors for fixation of implants, particularly in poor bone quality. A class of new implants with an implant-bone-interface optimized regarding load transition by increasing the peripheral area might improve the anchorage of implants in osteoporotic bone. However, the shape of these implants requires new technologies for insertion. The goal of the work presented here was to analyze the relevant parameters regarding implant geometry and to demonstrate the effect of new procedures for their insertion. The investigation was divided into three parts: 1) implant design optimisation, 2) efficiency of cortical bone ablation, and 3) implant insertion technology. Finite element analysis (FEA) was performed to investigate the influence of the number of lobes, the radius of the outer curvature and additional milling to remove any sharp changes of section around the lobe. Opening of the cortical bone with an Er:YAG laser was studied using calf cortex from 2 to 7 mm thickness. The effect of a) pulse energy and pulse duration, b) cortical thickness, c) wet or dry boundary conditions on volume and geometry of ablated bone, time required to penetrate the cortical bone and local bone tissue damage was quantified. Pneumatic and ultrasound based insertion were compared in the third experiment. The cortical bone was prepared in the following ways: a) no opening, b) predrilling of three holes (1 mm diameter each) and c) exact pre-cutting of the whole contour. Increasing the radius of the outer curvature from 2 to 5 mm reduces the peak stresses during loading in all planes in the implant as well as in the adjacent cortical bone by about 30-40%. An increase in the number of lobes from two to three decreases the mean peak stress by about 46% (alpha < 0.001) and the range between the minimal and maximal peak stresses for different loading directions by about 83%. Penetration of cortical bone with an Er:YAG laser was possible up to a cortical thickness of 6 mm with fewer than 100 pulses. The ablation rate per pulse increased more with increasing duration than with increasing energy. Signs of bone damage such as melting were only visible when high pulse energies and durations were used. Insertion of the prototype was possible with all devices, but only when the whole contour was cut out of the cortical bone. However, the use of the ultrasound vibrator led to heating up of the tissue fluid and subsequently to water evaporation and tissue damage. Insertion of the prototype was possible with both pneumatic vibrators, but only when the whole contour was cut out of the cortical bone. New implant designs may lead to reduced stress peaks in the surrounding bone and might be inserted with the help of new insertion technologies, namely laser cutting of cortical bone and pneumatic vibration. Further studies are required to optimize these technologies prior to clinical use.

Kleinfragmentschrauben vs. Plattenosteosynthese bei Gelenkwalzenfrakturen

AIMS

This prospective study evaluates the outcome after osteosynthesis of condylar head fractures using 1.7 mm small fragment screws (2/2000 ff), which were selected according to a previous biomechanical trial to optimize condylar head traumatology. Clinical and functional results were compared to a group of fractures fixed mainly by mini- and microplates (1993-2000) and to a control group after conservative therapy with early functional training.

PATIENTS AND METHODS

Functional values (axiography and MRI) regarding loss of vertical height, disk mobility, protrusive and translatory movements were assessed (a) in 34 of 83 condylar head fractures (groups V and VI according to Spiessl and Schroll, 22/69 subjects) managed by osteosynthesis with 1.7-mm small fragment screws (KFS), (b) a reference group (43/84 subjects) fixed mainly by mini- or microplates (PLO), comprising 56 of 101 fractures (1993-2000), and (c) 16 condylar head fractures after conservative therapy with early functional training (KT) as a control.

RESULTS

In cases of small fragment screws, loss of vertical height (0.3 mm) was significantly reduced (p<0.01) in comparison to PLO (1.6 mm) and KT (6.9 mm). Disk mobility in KFS reached 90% of the non-fractured sides (NFS), thus clearly superior (p<0.01) to PLO (63% of NFS) and KT (40% of NFS). Translatory movements after KFS showed better results, too (p<0.05), with mediotrusion 84% and protrusion 80% of NFS. After PLO, mediotrusion was 62%, protrusion 71% of NFS, whereas KT showed only 53% (mediotrusion) and 56% (protrusion) of NFS. High-grade limitations of translatory movements presented in about 30% after PLO and <10% in KFS (p<0.01). Fragment displacements were found in <5% after small fragment screws, and in the plate osteosynthesis group in 15% (p<0.01).

CONCLUSIONS

Due to better stability and reduced articular scarification osteosynthesis with 1.7-mm small fragment screws in condylar head fractures showed clearly superior functional results compared to mini- and microplates, and to conservative therapy.

Experimental and comparative study of the blood supply to the mandibular cortex in Göttingen minipigs and in man

INTRODUCTION

Since the blood supply to the mandibular cortex is an important factor for bone growth and bone repair, experimental studies on the blood supply in animal models (such as Göttingen minipigs) applicable to man are necessary. Their value depends on the requirement that the patterns of blood supply in the two species are similar.

MATERIAL AND METHODS

Twelve Göttingen minipig mandibles (24 halves) and four human mandibles (eight halves) were investigated for the blood supply to the mandibular cortex.

RESULTS

Only minor differences were found in blood supply to the mandibular cortex between the two species. Common to both was: in the cranial part of the mandible (including the condyle), the endosteal blood supply prevailed, whereas the periosteal blood supply predominated in the caudal part of the mandible (the body). Both patterns of blood supply were in balance in the centre section, i.e. angle and ascending ramus of the mandible.

CONCLUSION

The present study confirms that results obtained from Göttingen minipigs, used as an experimental animal model, are applicable to man: three different types of blood supply are evident in the mandibular cortex in both species.

A novel osteosynthesis plate design for routine corrective facial surgery

Plating systems for the osteosynthesis of facial osteotomies have different requirements to those used to treat facial fractures. The aim of fracture treatment is anatomical fragment reduction, functional/rigid immobilization, restoration of occlusion and aesthetics, and occasionally defect bridging. In corrective facial surgery however there is a need for intra-operative adjustments related to changes in occlusion and aesthetics, and defect bridging occurs frequently. Postoperatively, training elastics are used to control temporary neuromuscular imbalance. To accommodate these demands a new plating system is presented, based on five requisites: allowance of occlusal and aesthetic adjustment without hardware removal, plate dimensions that accommodate routine skeletal repositionings, reduced hardware volume compared with trauma plating systems, screws that fit the inter-dental spaces when tension banding, and capability for micro-screw fixation of bone grafts in the osteotomy site. The files of 1000 non-congenital facial deformity patients were analyzed. The sagittal, vertical and transverse movements were drawn and the bridging distances calculated. Slotted plates with double-armed interconnections were designed for maxillary, zygomatic-sandwich, chin and segmental osteotomies. A separate design was made for the sagittal split plate. A pilot study was performed using 20 patients. The system showed great versatility and adaptability, but a multicenter morbidity study is necessary, mainly to study postoperative stability.

Blood supply of the mandibular cortex: an experimental study in Göttingen minipigs with special reference to the condyle

INTRODUCTION

Blood supply of the mandible is an important factor that influences bone growth and bone repair.

MATERIAL AND METHODS

An experimental study was carried out in 24 mandibles of 12 Göttingen minipigs to study the blood supply of the mandibular cortex.

RESULTS

Endosteal blood supply prevails in the cranial part of the mandible including the condyle, whilst periosteal blood supply predominates in the caudal part of the mandible, the body. The two forms of blood supply are in balance in the ascending ramus and the angle of the mandible.

CONCLUSION

The mandibular cortex can be divided into three parts, each having different sources of blood supply. The results of this study may be of significance for man and could help to understand some pathological disorders of the mandible.