Histomorphometric evaluation of stress shielding in mandibular continuity defects treated with rigid fixation plates and bone grafts

Duplex Fluorinated and Atomic Layer Deposition-Derived ZrO2 Coatings Improve the Corrosion Resistance and Mechanical Properties of Mg-2Zn-0.46Y-0.5Nd (wt.%) Alloy Plates and Screws

This study investigated the corrosion resistance and mechanical properties of Mg-2Zn-0.46Y-0.5Nd (wt.%) alloy plates and screws with fluorinated coatings and atomic layer deposition (ALD)-derived zirconia (ZrO2) coatings in vitro under physiological stress conditions. Synthetic polyurethane hemimandible replicas were split and fixed as the following three groups of magnesium alloy plates and screws: no additional surface coating treatment (Group A), with fluorinated coatings (Group B), and with duplex fluorinated and ALD-derived 100 nm ZrO2 coatings (Group C). A circulating stress of 1-10 N was applied to the distal bone segment, and a 4-week simulated body fluid immersion test was employed to study the remaining material volume and the mechanical properties of the different groups. Compared with Group A and Group B, the degradation rate of magnesium alloy plates and screws' head regions was significantly slowed down under the protection of duplex MgF2/ZrO2 coatings (p < 0.01). There was no significant difference in the degradation rate of the screw shaft region between groups (p = 0.077). In contrast to fluoride coatings, duplex MgF2/ZrO2 coatings maintained the mechanical strength of magnesium alloy plates and screws after a 14 day in vitro SBF immersion test. We conclude that duplex MgF2/ZrO2 coatings exhibited a certain protective effect on the Mg alloy plates and screws under physiological stress conditions.

Titanium Alloy Implants with Lattice Structures for Mandibular Reconstruction

In recent years, the field of mandibular reconstruction has made great strides in terms of hardware innovations and their clinical applications. There has been considerable interest in using computer-aided design, finite element modelling, and additive manufacturing techniques to build patient-specific surgical implants. Moreover, lattice implants can mimic mandibular bone's mechanical and structural properties. This article reviews current approaches for mandibular reconstruction, their applications, and their drawbacks. Then, we discuss the potential of mandibular devices with lattice structures, their development and applications, and the challenges for their use in clinical settings.

Finite element analysis of 3D-printed personalized titanium plates for mandibular angle fracture

This paper discussed the size of 3 D-printed personalized titanium plates that can gain maximum stability of mandibular fracture and minimize stress shielding through finite element analysis. A 3 D virtual model of mandible with mandibular angle fracture was created from the CT data of patient. 3 D-printed personalized titanium plates varying in length and thickness were designed, and finite element analysis was performed under different loading conditions and fracture healing periods. After that, the stress distribution and deformation of the mandible with gonial fracture could be observed, and the stress shielding rate could be obtained. Finally, SPSS21.0 was used for statistical analysis. The results of finite element analysis indicated that as the thickness of titanium plates and the healing time decreased, the maximum displacement increased, under a certain condition in which the pore size, the width, the hole distance and the bridge spacing were 2.0 mm, 4.0 mm, 6.0 mm, 12.0 mm, respectively. What's more, in this condition, the thicker the titanium plate and the shorter the healing time were, the higher the stress shielding was at central occlusion. When the thickness of the personalized 3 D-printed titanium plate was 1.0 mm, the maximum displacement tended to be stable and the stress shielding was minimized. It can not only improve the bone stability after tension band fixation, but also minimize the stress shielding, which is expected to expand the indications of tension band fixation.

Anatomical Location of Initial and Repeat Mandible Fractures: A 5-Year, Multi-Institution Retrospective Study

PURPOSE

The purpose of the present study was to investigate new fracture patterns resulting from low velocity mechanisms in subjects who had previously fractured their mandible and had been treated with open reduction and internal fixation (ORIF) or closed reduction.

METHODS AND MATERIALS

A multi-institutional retrospective cohort study was designed to analyze subjects presenting at 2 tertiary care centers with mandibular fractures with specific interest in subjects who had repeat mandible fractures. Variables recorded included demographic (age, sex, etc) data, fracture location of all fractures treated, and the location of previous fracture. Descriptive and bivariate analyses were completed of the data.

RESULTS

The sample included a total of 492 subjects and 875 total fractures from both institutions. Four hundred fourty-four (91.1%) were male. The average age of all subjects was 36.4 ± 14.9 years. Twenty-six (5.28%) subjects were previously treated for a mandible fracture. All subjects' subsequent fractures occurred outside of previous ORIF except for 1 subject. Original fracture location (P = .596) and previous ORIF type (P = .689) did not influence if the subsequent fracture was within a site of previous ORIF.

CONCLUSIONS

The present study demonstrates that repeat mandible fractures are relatively rare, likely to occur only 5% of the time at large tertiary care centers. The repeat fracture is not likely to occur in a site of previous ORIF, regardless of the ORIF modality. Furthermore, the fracture is likely to occur on the contralateral side. This is 1 of the largest data sets on repeat mandible fractures, which, given their rarity, are difficult to study.

The Concept of Stress Shielding in Nonvascularized Bone Grafts of the Mandible-A Review of 2 Cases

Two cases are shown to demonstrate stress shielding in nonvascularized bone grafts to the mandible to reconstruct segmental defects, where rigid fixation is used. The effects are reversed on removal of the rigid fixation.

Bioabsorbable Osteofixation Materials for Maxillofacial Bone Surgery: A Review on Polymers and Magnesium-Based Materials

Clinical application of osteofixation materials is essential in performing maxillofacial surgeries requiring rigid fixation of bone such as trauma surgery, orthognathic surgery, and skeletal reconstruction. In addition to the use of titanium plates and screws, clinical applications and attempts using bioabsorbable materials for osteofixation surgery are increasing with demands to avoid secondary surgery for the removal of plates and screws. Synthetic polymeric plates and screws were developed, reaching satisfactory physical properties comparable to those made with titanium. Although these polymeric materials are actively used in clinical practice, there remain some limitations to be improved. Due to questionable physical strength and cumbersome molding procedures, interests in resorbable metal materials for osteofixation emerged. Magnesium (Mg) gained attention again in the last decade as a new metallic alternative, and numerous animal studies to evaluate the possibility of clinical application of Mg-based materials are being conducted. Thanks to these researches and studies, vascular application of Mg-based biomaterials was successful; however, further studies are required for the clinical application of Mg-based biomaterials for osteofixation, especially in the facial skeleton. The review provides an overview of bioabsorbable osteofixation materials in maxillofacial bone surgery from polymer to Mg.

Do mandibular miniplates increase the risk of complex fracture in facial trauma recurrence? Case series

Whether to conserve or remove miniplates, widely used in oral and maxillofacial surgery, has not been agreed on in the literature. Complications such as pain, infection, and screw exposure or loosening have already been largely described. We present the consequences of a trauma recurrence on a mandible with miniplates. The data of 13 patients who had a mandibular fracture previously surgically treated with miniplates (ten mandibular fractures and three mandibular osteotomies) were analysed. All the patients were male; the average age was 32 years (range, 20-64 years). The mechanism of the second trauma was assault in most of the cases. The average time between the first osteosynthesis and the new fracture was 35 months (range, 6-128 months). The fractures occurred at a distance from the miniplates in all the cases except two. No plate fracture was reported. We hypothesised that miniplates reinforced the underlying bone, protecting it from fractures, and transmitted the forces to areas anterior or posterior to the miniplates or to the condyle. Thus, the risk of mandible trauma recurrence should be taken into account in the indication of plate removal, and the biomechanical consequences of the conservation of the miniplates should be studied.

Efficacy and Safety of Biodegradable Osteofixation Devices in Oral and Maxillofacial Surgery: a Systematic Review

The use of osteofixation devices should be evidence-based if uncomplicated bone healing is to be achieved. Numerous studies describe and claim the advantages of biodegradable over titanium devices as a bone fixation method. Here, we systematically review the available literature to determine the clinical efficacy and safety of biodegradable devices compared with titanium devices in oral and maxillofacial surgery. In addition, related general aspects of bone surgery are discussed. We conducted a highly sensitive search in the databases of MEDLINE (1966–2005), EMBASE (1989–2005), and CENTRAL (1800–2005) to identify eligible studies. Eligible studies were independently evaluated by two assessors using a quality assessment scale. The study selection procedure revealed four methodologically ‘acceptable’ articles. Owing to the different outcome measures used in the studies, it was impossible to perform a meta-analysis. Therefore, the major effects regarding the stability and morbidity of fracture fixation using titanium and biodegradable fixation systems were qualitatively described. Any firm conclusions regarding the fixation of traumatically fractured bone segments cannot be drawn, due to the lack of controlled clinical trials. Regarding the fixation of bone segments in orthognathic surgery, only a few controlled clinical studies are available. There does not appear to be a significant short-term difference between titanium and biodegradable fixation systems regarding stability and morbidity. However, definite conclusions, especially with respect to the long-term performance of biodegradable fixation devices used in maxillofacial surgery, cannot be drawn. Abbreviations: CENTRAL, Cochrane Central Register of Controlled Trials; MeSH, Medical Subject Heading; VAS, Visual Analogue Scale; and W, weight.

OPTIMIZATION OF FEMORAL PROSTHESIS BASED ON COMPREHENSIVE EVALUATION OF STRUCTURE AND MATERIAL PROPERTIES

In this study, the optimized structure of a femoral prosthesis for a patient was determined by biomechanical analysis, and the materials that match the model of the prosthesis were determined by multi-objective comprehensive evaluation using a fuzzy matter-element method. The suitable material for the ellipsoidal femoral head of the prosthesis was determined to be a carbon-fiber-enhanced polyether-ketone (CF/PEK) composite, and that for the stem was determined to be a zirconium–niobium alloy (Zr–Nb alloy). The study successfully demonstrated the potential of the developed method for use in selecting the best structure and materials for fabricating a customized prosthesis.

A double-barrelled fibula graft restoring pelvic stability after late posterior ring instability related to a surgical treated osteitis pubis: a case report

BACKGROUND

Osteitis pubis or symphysitis pubis is a rare occurring non-infectious inflammation of the symphysis, the adjacent pubic bones and surrounding tissue. The therapy might be conservative or surgical by a resection of the symphysis and involved parts of the pubic bone. Nevertheless, this resection might lead to an anterior instability impairing the posterior arch and the sacroiliac joints in the aftermath.

CASE PRESENTATION

Here, we report about a 50-year-old women suffering from osteitis pubis treated by wedge resection of the symphysis and parts of the pubic bone. To maintain stability and for local antibiotic treatment a cement spacer was implemented. By clinical inconspicuous findings and the patient's desire, no further surgery was performed. However, 2 years after surgery the spacer dislocated and the patient complained about pain in the posterior arch due to an impaired mobility. Reconstruction surgery was planned including the bridging of the accrued space with a vascularized double-barrelled fibula graft, plate osteosynthesis and rectus abdominis flap coverage. The performed surgery led to pain relief and increased mobility.

CONCLUSION

The present case highlights the possible complication of surgical treated osteitis pubis leading to anterior arch instability affecting the posterior arch and thus impairing pelvic ring stability and patient mobility. Furthermore, we describe an opportunity to treat this complication or other etiologies contributing to anterior pelvic ring stability with large bone defects using a vascularized double-barrelled fibula graft to restore pelvic stability.

Dental materials for cleft palate repair

Numerous bone and soft tissue grafting techniques are followed to repair cleft of lip and palate (CLP) defects. In addition to the gold standard surgical interventions involving the use of autogenous grafts, various allogenic and xenogenic graft materials are available for bone regeneration. In an attempt to discover minimally invasive and cost effective treatments for cleft repair, an exceptional growth in synthetic biomedical graft materials have occurred. This study gives an overview of the use of dental materials to repair cleft of lip and palate (CLP). The eligibility criteria for this review were case studies, clinical trials and retrospective studies on the use of various types of dental materials in surgical repair of cleft palate defects. Any data available on the surgical interventions to repair alveolar or palatal cleft, with natural or synthetic graft materials was included in this review. Those datasets with long term clinical follow-up results were referred to as particularly relevant. The results provide encouraging evidence in favor of dental and other related biomedical materials to fill the gaps in clefts of lip and palate. The review presents the various bones and soft tissue replacement strategies currently used, tested or explored for the repair of cleft defects. There was little available data on the use of synthetic materials in cleft repair which was a limitation of this study. In conclusion although clinical trials on the use of synthetic materials are currently underway the uses of autologous implants are the preferred treatment methods to date.

Pyrene-end-functionalized poly(L-lactide) as an efficient carbon nanotube dispersing agent in poly(L-lactide): mechanical performance and biocompatibility study

In order to improve the mechanical properties of poly(L-lactide) (PLLA) based implants, a study was made of how far well dispersed multi-walled carbon nanotubes (MWCNTs) within a PLLA matrix were able to positively affect these properties. To this end, pyrene-end-functionalized poly(L-lactide) (py-end-PLLA) was evaluated as a dispersing agent. Transmission electron microscopy (TEM) analyses and mechanical tests of MWCNTs-based materials demonstrated an enhancement of MWCNT dispersion in the PLLA matrix and improved Young's modulus (E) when 4 wt% of py-end-PLLA was used as the dispersing agent. Subsequently, the bioacceptance of PLLA/py-end-PLLA/MWCNTs nanocomposites was evaluated using human bone marrow stromal cells (HBMC) in vitro. The inclusion of py-end-PLLA and MWCNTs supported HBMC adhesion and proliferation. The expression levels of the bone-specific markers indicated that the cells kept their potential to undergo osteogenic differentiation. The results of this study indicate that the addition of MWCNT combined with py-end-PLLA in PLLA/py-end-PLLA/MWCNTs nanocomposites may widen the range of applications of PLLA within the field of bone tissue engineering thanks to their mechanical strength and cytocompatibility.

Prototyped grafting plate for reconstruction of mandibular defects

To esthetically and functionally restore a 40-mm canine mandibular discontinuity defect using a custom-made titanium bone-grafting plate in combination with autologous iliac bone grafts. Individualized titanium bone-grafting plates were manufactured using a series of techniques, including reverse engineering, computer aided design, rapid prototyping and titanium casting. A 40-mm discontinuous defect in the right mandibular body was created in 9 hybrid dogs. The defect was restored immediately using the customized plate in combination with autologous cancellous iliac blocks. Sequential radionuclide bone imaging was performed to evaluate the bone metabolism and reconstitution of the grafts. The specimens were evaluated by biomechanical testing, 3-dimensional microcomputed tomographic scanning, and histological examination. The results revealed that the symmetry of the mandibles was reconstructed using the customized grafting plate, and the bony continuity of the mandibles was restored. By 12 weeks after the operation, the cancellous iliac grafts became a hard bone block, which was of comparable strength to native mandibles. A fibrous tissue intermediate was found between the remodelled bone graft and the titanium plate. The results indicate that the prototyped grafting plate can be used to restore mandibular discontinuous defects, and satisfactory aesthetical and functional reconstruction can be achieved.

Effect of xenogenic cortical bone on fracture healing in a canine fracture model

The purpose of this study was to investigate the effect of xenogenic cortical bone (XCB) on fracture repair in the canine ulna. The entire group of animals (n = 12) had a transverse resection of 5 mm length at the middle part of the right ulnar diaphysis. In Group A (eight beagles), the fracture was treated with XCB and metal bone screw. In Group B (four beagles), the fracture was treated with metal bone plate and screw. Radiological, micro-computed tomography (micro-CT), histological examination and mechanical testing were employed to evaluate bone healing and reaction of XCB in the host bone. In Group A, bone union was noticed in 6 out of 8 dogs (75%), starting from the 4th week onwards. Micro-CT and histological examinations showed that the XCB was absorbed and incorporated into the host bone. Incorporation of XCB was observed in 7 cases (88%); it started from the 10th week onwards and continued to week 32 after surgery. Biomechanical strength of the bone fracture site was higher in Group A than in Group B, and was similar to that of normal bone. XCB enhances the bone healing process and can be used as absorbable internal fixation for the management of long bone fractures in dogs.

Enhancement of biomechanical behavior on osseointegration of implant with SLAffinity

The purpose of this study was to investigate stresses resulting from different thicknesses of hydroxyapatite- and titanium dioxide (TiO(2))-treated layers at the interface between temporomandibular joint (TMJ) implants and bones using three-dimensional finite element models. For ensuring osseointegration of implant treatment, one must examine the stresses of interface between implant and bone tissue. Treated layers on TMJ implants are a very important factor in clinical application. Several studies have investigated finite element models for TMJs, but few have examined a model for TMJ implants with treated layers. In this study, TMJ models were reconstructed using computer tomography data, and the effects of treated layer thickness on the stress field during jaw movement were investigated; this index has not yet been reported with respect to TMJ implant. The maximum stresses in the bone occurred at the position of the first screw. Data analysis indicated a greater decrease in this stress in the case of using TMJ implants with TiO(2)-treated layers, and the stresses decreased with increasing layer thicknesses. Results confirmed that the treated layers improve biomechanical properties of the TMJ implants and release abnormal stress concentration in them. The results of our study offer the potential clinical benefit of inducing superior biomechanical behavior in TMJ implants.

Evaluation of post-surgical relapse in maxillary surgery using resorbable plate

BACKGROUND

This study was carried out to evaluate the vertical and horizontal changes after maxillary surgery using resorbable plates made of an l-lactic acid and d-lactic acid copolymer of PLA (P(L/DL)LA), and to analyze factors of skeletal pattern and surgical movement affecting the post-surgical change.

MATERIALS AND METHODS

The subjects consisted of 20 patients who underwent bimaxillary surgery using P(L/DL)LA resorbable plate (Inion CPS, Inion Ltd., Tampere, Finland). Lateral cephalograms were taken at 1 month before (T0), 1 month after (T1) and 6 months after surgery (T2). They were divided into two groups, one showing less relapse (LR) and one more relapse (MR) using K-means clustering analysis of post-surgical relapse (T2-T1). In terms of linear and angular variables of maxillary relapse, the two groups were compared with measurements at the pre-surgical stage (T0), the surgical change obtained (T1-T0) and post-surgical relapse (T2-T1) using Mann-Whitney test.

RESULTS

Because Frankfort horizontal (FH) to anterior nasal spine (ANS) showed the largest variance in post-surgical relapse of the maxilla, it was used for clustering analysis to define the MR and LR groups. Comparison between the MR and LR groups showed that a short preoperative anterior facial height (AFH) was a significant factor in maxillary relapse. The AFH of the MR group was significantly shorter pre-surgically (p<0.01) and was significantly increased postoperatively (p<0.05) when compared to the LR group. In post-surgical relapse, AFH, FH to A, FH to ANS and the palatal plane angle of the MR group were significantly decreased.

CONCLUSIONS

In the case of a short AFH, P(L/DL)LA resorbable plates may not provide enough vertical stability in the maxillary position due to the muscle force. Facial height might be an important factor when deciding to use P(L/DL)LA resorbable plates for maxillary surgery.

Biomechanical characteristics of regenerated cortical bone in the canine mandible

To test the mechanical properties of regenerate cortical bone created using mandibular bone transport (MBT) distraction, five adult male American foxhound dogs underwent unilateral distraction of the mandible with a novel MBT device placed to linearly repair a 30-35 mm bone defect. The animals were sacrificed 12 weeks after the beginning of the consolidation period. Fourteen cylindrical specimens were taken from the inner (lingual) and outer (buccal) plates of the reconstructed mandible and 21 control specimens were removed from the contralateral aspect of the mandible. The mechanical properties of the 35 cylindrical cortical bone specimens were assessed by using a non-destructive pulse ultrasound technique. Results showed that all of the cortical mechanical properties exhibit higher numerical values on the control side than the MBT regenerate side. In addition, both densities and the elastic moduli in the direction of maximum stiffness of the regenerate cortical bone specimens are higher on the lingual side than the buccal side. Interestingly, there is no statistical difference between elastic modulus (E(1) and E(2) ) in orthogonal directions throughout the 35 cortical specimens. The data suggest that not only is the regenerate canine cortical bone heterogeneous, but the elastic mechanical properties tend to approximate transverse isotropy at a tissue level, as opposed to control cortical bone, which is orthotropic. In addition, the elastic mechanical properties are higher not only on the control side but also in the lingual anatomical position, suggesting a stress shielding effect from the presence of the reconstruction plate.

Accurate reconstruction of discontinuous mandible using a reverse engineering/computer-aided design/rapid prototyping technique: a preliminary clinical study

PURPOSE

To improve the reconstructive surgical outcome of a discontinuous mandibular defect, we used reverse engineering (RE), computer-aided design (CAD), and rapid prototyping (RP) technique to fabricate customized mandibular trays to precisely restore the mandibular defects. Autogenous bone grafting was also used to restore the bony continuity for occlusion rehabilitation.

PATIENTS AND METHODS

Six patients who had undergone block resection of the mandible underwent reconstruction using a custom titanium tray combining autogenous iliac grafts. The custom titanium tray was made using a RE/CAD/RP technique. A virtual 3-dimensional model was obtained by spiral computed tomography scanning. The opposite side of the mandible was mirrored to cover the defect area to restore excellent facial symmetry. A bone grafting tray was designed from the mirrored image and manufactured using RP processing and casting. The mandibular defects were restored using the trays in combination of autologous iliac grafting. An implant denture was made for 1 of the 6 patients at 24 weeks postoperatively for occlusion rehabilitation.

RESULTS

The trays fabricated using this technique fit well in all 6 patients. The reconstructive procedures were easy and time saving. Satisfactory facial symmetry was restored. No severe complications occurred in the 5 patients without occlusion rehabilitation during a mean 50-month follow-up period. The reconstruction in the patient with occlusion lasted for only 1 year and failed eventually because of bone resorption and infection.

CONCLUSIONS

Mandibular reconstruction was facilitated using the RE/CAD/RP technique. Satisfactory esthetic results were achieved. However, the rigidity of the cast tray could cause severe stress shielding to the grafts, which could lead to disuse atrophy. Therefore, some modification is needed for functional reconstruction.

A biomechanical analysis of titanium miniplates used for treatment of mandibular symphyseal fractures with the finite element method

OBJECTIVE

This study aimed to evaluate the stress distribution and stress shielding effect of titanium miniplates used for the treatment of symphyseal fractures using finite element (FE) analysis.

STUDY DESIGN

Two 3-D FE models of symphyseal fractured mandibles reduced by technique 1, reduction with a single miniplate, and technique 2, reduction with 2 miniplates, respectively, were developed. Three basic loading conditions were simulated.

RESULTS

The ratios of stress shielding of miniplates were different. Ratios of the lower miniplates in technique 2 were much higher than the upper miniplates and the miniplates in technique 1 during all conditions, and that value of the lower miniplate gained a maximum value of 83.34% during left unilateral molar clenching. The stress areas were concentrated on the central section of the miniplates. However, the stress distribution varied with masticatory conditions.

CONCLUSION

The study demonstrated that miniplate stress distribution and stress shielding effect ratio were affected not only by the way in which the mandible was loaded but also by the number of the miniplates fixing the fracture.

Comparison of titanium and resorbable copolymer fixation after Le Fort I maxillary impaction

INTRODUCTION

Advances in skeletal stabilization techniques have led to the use of titanium devices for rigid fixation. Their advantages include strength and skeletal stability, but they also have disadvantages. The purpose of this study was to investigate the stability of a resorbable copolymer as a potential alternative to titanium for fixation of Le Fort I maxillary impaction.

METHODS

Fifty consecutive patients underwent maxillary impaction with nonsegmental monopiece Le Fort I osteotomy. Twenty-five patients were treated with titanium fixation; 25 patients were treated with resorbable copolymer fixation (82% poly-L-lactic acid: 18% polyglycolic acid). Lateral cephalograms were obtained 1 week preoperatively, 1 week postoperatively, and a minimum of 8 months postoperatively. Linear and angular measurements were recorded digitally to evaluate 2-dimensional skeletal changes.

RESULTS

Statistical analysis showed no significant radiographic differences (P <0.05) in long-term stability in or between the 2 groups. No clinical or radiographic evidence of wound healing problems was noted.

CONCLUSIONS

These results support the use of resorbable copolymer fixation for Le Fort I impaction as a viable alternative to titanium fixation.

Comparison of pullout strength of resorbable screws and titanium screws in human cadaveric laryngeal cartilage

OBJECTIVES

To compare the pullout strength of titanium screws and resorbable screws from human fresh-frozen cadaveric laryngeal cartilage. The importance of drill hole diameter, screw diameter, and whether the drill hole was tapped (resorbable screws only) was also determined.

STUDY DESIGN

Prospective.

METHODS

Sixteen cartilage specimens were tested after debridement of connective tissue and perichondrium. Linear pullout strength of screws was measured using a load cell. Titanium and resorbable screw sizes of 1.5 and 2.0 mm were tested using drill hole diameters of 1.1 and 1.5 mm. For the resorbable-tapped group, screw diameters of 1.5 and 2.0 mm were tapped with 1.5 and 2.0 mm taps, respectively. All tested screws were 6 mm in length.

RESULTS

We found a uniformly constant difference between the three screw types (P < .001). Post hoc analysis indicated a significant difference between the resorbable-untapped screw and both the resorbable-tapped screw and the titanium screw. We failed to find a significant difference, however, between the resorbable-tapped screw and the titanium screw. We also found a significant effect in regard to screw size (P = .0133), with post hoc analysis demonstrating the 1.1/1.5 mm combination to be inferior to the 1.1/2.0 and 1.5/2.0 mm combinations. There was no significant difference between the 1.1/2.0- and 1.5/2.0-mm combinations.

CONCLUSIONS

Resorbable screws with untapped drill holes result in higher resistance to linear loads than both titanium screws and resorbable screws with tapped drill holes. The 1.1/2.0- and 1.5/2.0-mm drill/screw combinations are superior to the 1.1/1.5-mm combination when considering untapped resorbable screws.

Mechanical evaluation of mandibular defects reconstructed using osteogenic protein-1 (rhOP-1) in a sheep model: a critical analysis

Osteoinductive bone morphogenetic proteins (BMPs) have been used extensively in experimental and clinical orthopaedic research. It is a natural progression for these growth regulators to be tested in the craniofacial region. The aim of this investigation was to analyse the mechanical properties of the sheep mandibles reconstructed using recombinant human osteogenic protein type 1 (rhOP-1). A unilateral 35 mm osteoperiosteal continuity defect was created at the parasymphyseal region of the mandible in six adult sheep. The animals were sacrificed 3 months after surgery and mechanical properties of the regenerated bone at the operated sides (OS) were compared to the corresponding bone at the non-operated side (NOS). The regenerated tissue at the OS were then submitted for histological and histomorphometric analysis. Although all the animals achieved complete bony union, a wide range of mechanical properties was found. The rhOP-1-induced bone achieved a mean of 36% of the strength of the bone at the NOS (P < 0.05). The mean value of the stiffness of the OS was 24% of the NOS (P < 0.05). While half of the samples of the OS had 'weak' mechanical properties (9-25% strength compared to NOS) and a low stiffness (6-18%), the rest showed relatively higher strength (47-63%) and were stiffer (35-47%). Unlike the NOS, the operated sides failed under tensile stresses and cracks initiated at the superior border of the mandible. The wide mechanical variations suggest that further basic bone biology research is needed to provide better understanding of the cellular and molecular events which take place during the process of osteoinduction.

A retrospective evaluation of rigid fixation in orthognathic surgery using a biodegradable self-reinforced (70L:30DL) polyactide

OBJECTIVE

This study was designed to evaluate clinical and radiological evidence of osteotomy site healing in orthognathic surgery after rigid fixation using a biodegradable plating system.

STUDY DESIGN

A follow up of 30 patients who underwent orthognathic surgery using a biodegradable self-reinforced (70L:30DL) polylactide plating system was presented. The follow-up schedule for all patients consisted of regular appointments at 1-180 days after surgery. Clinical evaluation involved notation of any abnormal swelling, infection, discoloration, or discharge at the osteotomy sites. Stability was evaluated by manual palpation. For radiographic evaluation, panoramic radiographs were taken immediately after surgery, and again at 7-180 days. The radiographs were analyzed for any visual changes in osteotomy fragments, resorptive changes in osteotomy fragments, callus formation, and union of the osteotomy segments.

RESULTS

No clinical complications and no radiological changes in the osteotomy sites were observed. Regarding the clinical usefulness of the biodegradable fixation system, fixation at the time of operation was considered as excellent in all 30 cases.

CONCLUSIONS

The conclusions of this study were that self-reinforced (70L:30DL) polylactide was considered to be comparable to other forms of rigid internal fixation for orthognathic surgery.

Successful Use of Biosorb Osteofixation Devices in 165 Cranial and Maxillofacial Cases: A Multicenter Report

Bioabsorbable osteofixation devices were developed to avoid problems associated with metals. Bioabsorbable devices are mostly made of the polymers polylactide, polyglycolide, and their copolymers [polyglycolide-co-polylactide and P(L/DL)LA]. Using the technique of self-reinforcement of bioabsorbable materials, it is possible to manufacture osteofixation devices with ultra high strength. Self-reinforced polyglycolide-co-polylactide 80/20 was selected to make devices (Biosorb PDX) for this study because of its favorable degradation characteristics. The aim of this study was to evaluate the efficacy of using self-reinforced polyglycolide-co-polylactide 80/20 (Biosorb) plates and screws in the fixation of osteotomies in craniomaxillofacial surgery. In a prospective study, 165 patients (161 children and 4 adults) were operated on in four European Union centers (Paris, Innsbruck, London, and Oulu) from May 1, 1998 to January 31, 2002. Indications included correction of dyssynostotic deformities (n = 159), reconstruction of bone defects after trauma (n = 2), tumor removal (n= 2), and treatment of encephalocele (n = 2). Plates used were 0.8, 1, or 1.2 mm thick, and screws had an outer (thread) diameter of 1.5 or 2 mm and a length of 4, 6, or 8 mm. Tacks had an outer diameter of 1.5 or 2 mm and a length of 4 or 6 mm. During surgery, the devices were easy to handle and apply and provided stable fixation apart from 2 cases. Postoperative complications occurred in 12 cases (7.3%), comprising infection (n = 6), bone resorption (n = 4), diabetes insipidus (n = 1), delayed skin wound healing/skin slough (n = 2), and liquorrhea (n = 1). Accordingly, self-reinforced polyglycolide-co-polylactide 80/20 (Biosorb) plates and screws can be used safely and with a favorable outcome in corrective cranioplasties, especially in infants and young children.

Self-reinforced bioresorbable poly-L/DL-Lactide [SR-P(L/DL)LA] 70/30 miniplates and miniscrews are reliable for fixation of anterior mandibular fractures: A pilot study

OBJECTIVE

Bioresorbable osteofixation devices are being increasingly used in orthognathic surgery and in cases of trauma to avoid problems associated with conventional metal osteofixation devices. The aim of this clinical study was to assess the reliability and efficacy of bioresorbable self-reinforced poly-L/DL-lactide (SR-P(L/DL)LA 70/30) plates and screws in the fixation of mandibular fractures in adults.

STUDY DESIGN

Ten patients (20 to 49 years old) with isolated anterior mandibular parasymphyseal fractures were treated by means of open reduction and internal fixation using SR-P(L/DL)LA 70/30 bioresorbable plates and screws.

RESULTS

During the minimum of 6 months of follow-up, no problems were encountered except for 1 case where a plate became exposed intraorally and infected. This required debridement and later excision of the exposed part of the plate. Despite this setback the fractured bone healed well.

CONCLUSIONS

SR-P(L/DL)LA 70/30 plates and screws are reliable for internal fixation of anterior mandibular fractures in adults. Proper soft tissue coverage should be ensured to avoid plate exposure. Should implant exposure occur, it might be necessary to excise the exposed part after fracture healing (6-8 weeks postoperatively).

Spotlight on naturally absorbable osteofixation devices

The practice of using implants is growing day by day, and more foreign materials are being inserted for various indications. The field of implantology thus deserves intensive research and careful evaluation of results. Solutions to overcome current problems and risks are necessary. It has taken a long time to arrive at where we are now. Bioabsorbable devices were explored in the 1960s for surgical bone fixation. Failures were followed by changes in ways of thinking and innovations. Improvements in the strength properties and biocompatibility were achieved. Bioabsorbable polymeric materials such as high-molecular-weight polymers were used and also reinforced with other material or, more recently, by self-reinforcement to produce small yet strong devices. New generations of implants include those that contain bioactive substances such as antibiotics and growth factors. Developments in bioabsorbable materials continue to accommodate the new way of thinking brought about by the emergence of the field of tissue engineering. Surgeons, conversely, are also inventing new surgical techniques and methods to exploit the plastic and bioabsorbability properties of these materials for the better future of our patients. Such a multidisciplinary approach that involves surgeons and materials scientists should help to find solutions to the current limitations of these devices.

Removal of titanium plates coated with anodic titanium oxide ceramic: retrospective study

Transformation of the surface of metallic titanium with titanium oxides prepared in various ways is a modern procedure. For more than 15 years, the authors have been utilizing fixing elements coated with titanium oxide ceramics, prepared by anodic oxidation and thermal treatment, for purposes of jawbone osteosynthesis. The aim of the authors' work was to assess the extent to which the titanium oxide ceramic coating influences the fate of the plates used for osteosynthesis within the human organism, in regard to the possible need for their removal. During a 5-year period, 108 of 1,396 plates coated with anodic titanium oxide had to be removed for various reasons: plate exposure (47), osteomyelitis (25), palpable swelling and tenderness (21), patient request for psychological reasons (13), or fracture of the plate (2). In none of these 108 cases was metallosis observed, which otherwise is reported relatively frequently in the vicinity of traditional titanium fixing elements, nor was any tissue damage connected with the surface of the plates. The results indicate the favorable properties of the titanium oxide ceramic surface.

The use of bioabsorbable osteofixation devices in craniomaxillofacial surgery

Because of problems associated with the conventional osteofixation devices used in craniomaxillofacial surgery, bioabsorbable devices have presented an appealing alternative. Devices made of the polymers polyglycolide (PGA) and polylactide (PLA) and their copolymers (PLGA and PLDLA) are currently the most commonly used. Strong implants can be manufactured from these polymers with a self-reinforcing technique and used in the treatment of fractures and osteotomies. Self-reinforced devices have been studied for nearly 2 decades by our multidisciplinary research group for internal fixation of the bone in both experimental and clinical settings. In craniomaxillofacial fractures and osteotomies they have been used for as long as 10 years with no significant clinical problems. Because of more favored degradation characteristics, currently the copolymer devices (PLDLA and PLGA) represent the advancing front in the application of absorbable devices in craniomaxillofacial surgery. By using bioabsorbable devices, several problems associated with conventional biostable devices can be avoided, especially in children. New techniques that are not possible with biostable devices can be developed by using bioabsorbable devices, too. Our experience with and research on self-reinforced devices are shared here.

The efficacy of resorbable plates in head and neck reconstruction

OBJECTIVE/HYPOTHESIS

The advent of malleable macroporous resorbable plates has allowed the surgeon a greater range of reconstructive options and has decreased the morbidity of conventional plating procedures. Completely malleable after warming to 55 degrees C, resorbable plates can readily conform to most morphologic appearances of fractures or defects and provide rigid fixation when cooled. The plating systems used in head and neck reconstruction are described.

STUDY DESIGN

Nine patients were selected for reconstruction using a resorbable plating system. The resorbable system was tested under a variety of clinical situations including frontal sinus fractures (three patients), midface fractures (two patients), mandibular defects (two patients), and laryngeal fractures (two patients).

METHODS

Each case was evaluated for rigidity of fixation, and ease of plate contouring and application. Furthermore, the postoperative functional and cosmetic results and complications were contrasted between the resorbable plating systems and each surgeon's vast experience with traditional plating systems.

RESULTS

The resorbable plating system was found to be as effective as traditional plating systems with respect to rigidity of fixation, functional results, and complications. In addition, the resorbable system was far easier to contour and, consequently, to apply, while producing higher cosmetic satisfaction after plate resorption than traditional plating.

CONCLUSIONS

Based on our experience, resorbable plates appear to be safe, easy to contour and apply, as well as effective for a wide range of head and neck reconstructive applications. In addition, the shortcomings of permanently retained plates such as plate migration, bone growth restriction, and imaging artifact are avoided.

Developments in craniomaxillofacial surgery: use of self-reinforced bioabsorbable osteofixation devices

Because of the problems associated with the conventional osteofixation devices used in craniomaxillofacial surgery, absorbable devices present an appealing alternative. Devices made of the polymers polylactide, polyglycolide, and their copolymers (PLGA and P[L/DL]LA) are currently the most commonly used. Ultrahigh-strength implants can be manufactured from these polymers with the self-reinforcing technique. Over the authors' almost two decades of study, both in experimental and clinical settings, self-reinforced devices have proved to be biocompatible, easy to handle, and mechanically strong, even for the fixation of femoral neck fractures. In craniomaxillofacial surgery, the authors have used self-reinforced devices for over 8 years without complications. Because of the more favored degradation characteristics, currently the copolymeric self-reinforced devices (P[L/DL]LA, Biosorb FX and PLGA, Biosorb PDX; Elite Performance Technologies, Solana Beach, Calif.) represent the advancing front in the application of absorbable devices in craniomaxillofacial surgery. The authors' share their experience and their studies of self-reinforced devices, which possess the highest strength and ductility of all bioabsorbable products.

The self adapting washer for lag screw fixation of mandibular fractures: finite element analysis and preclinical evaluation

Besides rigid fixation, lag screws have distinct advantages compared with plates in appropriate indications in mandibular fractures. However, in current lag screw systems, the relatively small area of the screw head has to transfer the tensile force which can exceed 1000 N in the symphysis, to the thin cortical bone plate. Countersinking, which is obligatory in most systems, will weaken the cortical plate. Finite element analysis (FEA) revealed that load in this situation can exceed the normal tensile strength of metal and bone. Consequently, a new washer was constructed which both increased the supporting surface and did not require countersinking. The washer is self adapting (SAW) to the cortical plate in a defined position, forming a ball and socket joint with the screw head. Using the FEA model, a ten-fold reduction in load on bone and metal was observed with the new washer. In a miniature pig mandibular symphysis fracture model, the clinical applicability and a favourable histological reaction were demonstrated, compared with conventional lag screw designs.

Functional reconstruction of the mandible: a modified titanium mesh system

This paper describes a method for mandibular reconstruction utilizing autogenous cancellous bone in a titanium mesh. The mesh is designed preoperatively based on a duplicate of the patient's mandible which is modified to simulate an anatomically correct edentulous segment in the region to be reconstructed. The duplicate mandible is articulated with a maxillary dental cast, and a locating splint is fabricated for intraoperative use to aid the positioning of the mesh in relation to the upper teeth. The method facilitates future rehabilitation with dental implants and results in a symmetric and highly functional reconstruction of the mandible.

Poly(L-lactide) bone plates and screws for internal fixation of mandibular swing osteotomies

This study evaluated bone healing after mandibular swing osteotomies fixed with biodegradable poly(L-lactide) (PLLA) bone plates in four patients. A step osteotomy treated with two PLLA bone plates (n=3), and a straight osteotomy treated with one PLLA bone plate (n=1) were performed. Bone healing was uneventful in all patients; only in the patient with the straight osteotomy was callus observed. After 5.5 years, radiologic changes at the site of implantation were observed in the remaining patient. Histologic examination revealed a nonspecific foreign-body reaction on highly crystalline PLLA remnants which were still present. It is concluded that the PLLA bone plates provided enough strength to enable undisturbed bone healing. The long-term degradation results are comparable with those of other studies on as-polymerized PLLA implants.

Structural properties of mandibular bone following application of a bone plate

PURPOSE

Similarities in strain patterns between long bones and the mandible suggest that plates may induce stress shielding, resulting in deleterious long-term changes. This study is an investigation of the use of bone plates on the mandible in four adult rhesus monkeys.

MATERIAL AND METHODS

A stainless steel plate was attached facially along the inferior border of each mandibular corpus. On the left, a thick (2.5-mm) plate was engaged with four screws. On the right, a thin (0.5-mm) plate was attached with one screw. Monkeys were killed a year after plate placement. At the beginning and end of the experiments, bone strain was recorded inferior to each bone plate during evoked maximal incisal clenching. After death, bone was removed from the mandibles around and under the plates and examined. Gross dimensions and density were measured. An ultrasonic technique was used to measure the material properties, including the elastic and shear moduli.

RESULTS

Bone strain inferior to the plates was reduced by 34% to 53% after attachment of the thick plates. Little change in strain was found after attachment of the thin plates. However, no significant differences in structural or mechanical measurements, such as density, cortical thickness, elastic and shear moduli, and Poisson's ratios, were detected between the two sides in each monkey.

CONCLUSION

Long-term placement of bone plates, and the resulting stress shielding, were found to result in structural changes in the mandibular corpus.

Histomorphometric examinations of free revascularised iliac crest bone after transplantation for mandibular reconstruction

At the present time the vascularised bone graft is the best procedure for reconstruction of mandibular defects in poor recipient tissues. We obtained 23 drill biopsies from different regions of vascularised bone transplants during the removal of the osteosynthesis plates from 14 patients who had poor recipient tissues. For comparison, we took five biopsies from the native iliac crest and eight biopsies from six patients with avascular bone transfer into unimpaired surrounding tissues. Microradiographs of the bone preparations were used for a computerised semi-automatic morphometric analysis. We evaluated the volumetric density (VV, %) and the mean trabecular diameter (D-TRAB, micron). In the central regions, the revascularised transplants decreased in volumetric density and in mean trabecular diameter. Compared with the average values of iliac crest bone, the avascular grafts increased in both parameters. The revascularised grafts showed significantly lower volumetric density and significantly lower mean trabecular diameters in the central regions than in the regions near to the mandibular stump. The avascular grafts actually showed the reverse effect. The results are discussed with particular reference to the quality of the recipient tissues, to the maintenance of graft viability, to functional stress, and to the design of the transplant.

Mandibular reconstruction with the Dacron urethane tray: a radiologic assessment of bone remodeling

A retrospective study was made of 22 consecutive patients who underwent mandibular reconstruction with a Dacron (Osteo-mesh, Xomed Inc, Jacksonville, FL) tray technique from September 1988 to April 1992. Free autogenous iliac bone, in the form of particulate cancellous chips and marrow, was densely packed into the Dacron tray, that was adapted to bridge the mandibular segmental defect. Sixteen cases underwent uneventful healing with the formation of a continuous bony bridge and union with the remaining mandible. The pattern of bone remodeling and rate of resorption in these cases were assessed by sequential panoramic radiographs taken up to 3 years postoperatively. The mean horizontal dimension of the mandibular defects was 75 mm and the mean vertical reconstructed height was 25 mm. When the grafted bone was radiographically of uniform density, it progressed into a mature trabecular pattern matching that of the normal mandible. However, when there were areas of radiolucency, most likely from inadequate condensation of the graft, such areas were not replaced by bone in the long term. The bony height at both ends and the middle of the reconstructed segment underwent reasonably even resorption and retained about 80% of the bony height over a 3-year period. The rate of resorption was highest in the first 6 months and stabilized at about 2 years. There were six failures, all showing significant irregular bony resorption prior to tray removal.

Bone strain following application of a rigid bone plate: an in vitro study in human mandibles

This study evaluated the effect of a bone plate on mandibular bone strain patterns during static loading. A stainless steel bone plate was unilaterally attached to five human mandibles, which were then subjected to static loads of 60 kiloponds. Four strain gauges attached to the cortical bone were used to measure the strain patterns within the mandible both before and after the bone plate was attached. The results showed that statistically significant alterations in the strain patterns occurred following plating of the mandible. The mandible with the plate attached became more stiff, presumably due to the difference in modulus of elasticity between the plate and the bone. However, this increase in stiffness was relatively small when compared with both total strain under load and strain produced by tightening of the bone screws.

Radiologic follow-up of bone transplants to bridge mandibular continuity defects

Special radiologic imaging techniques were used to evaluate the results of nonvascularized bone grafts combined with rigid mandibular reconstruction plates. The radiologic findings divided 21 cases into three clearly distinct groups on the basis of resorption: slight (less than 15%), moderate (15% to 30%), and massive (more than 30%) (mean follow-up, 26 months). This division predicted the clinical results well. In contrast to earlier reports, it was shown that rigid plate bridging did not adversely influence the prognosis of the graft. Nor was early plate removal necessary to reach good ossification. Narrow-beam radiography and spiral tomography proved to be excellent tools for adequate evaluation of bone resorption and bony healing of mandibular grafts.

Titanium mesh (TiMesh) osteosynthesis: a fast and adaptable method of semi-rigid fixation

Titanium mesh has been used in the USA for the fixation of fractures of the facial skeleton since the Vietnam war. Despite the increasing use of titanium mesh osteosynthesis for trauma, orthognathic and reconstructive surgery in the USA, it is only in recent years that it has gained acceptance in Europe. This paper appraises the original titanium mesh osteosynthesis system (TiMesh) in a wide range of surgical contexts in the maxillofacial region. It has been found to be quick and reliable in placement, highly adaptable and to have considerably reduced the operating time. Its further potential advantages in reducing stress-shielding and improving functional bone healing due to its semi-rigid nature are discussed.

Studies on heat treatment for immediate reimplantation of resected bone

Extracorporeal heat treatment for devitalizing the tumour-infiltrated bone segment without destroying its regenerative potential was investigated for the purpose of immediate reimplantation of the resected bone. Effects of heat treatment on cell viability and bone inductive properties were studied in cultured tumour cells and animal models. Heat treatment at 65 degrees C for 30 to 120 minutes resulted in complete devitalization of cells, preserving osteogenetic properties of the allogenic bone implant in the rabbit. The results of the experiments indicate that this procedure has advantages in devitalizing the resected bone for its immediate reimplantation and justify clinical application. The clinical application of this heat treatment in 3 cases is presented.