Quantitative Three-Dimensional Computed Tomography Measurements Provide a Precise Diagnosis of Fractures of the Mandibular Condylar Process.

As 2D quantitative measurements are often insufficient, a standardized 3D quantitative measurement method was developed to analyze mandibular condylar fractures, and correlate the results with the mandibular condylar fracture classifications of Loukota and Spiessl and Schroll and clinical parameters. Thirty-two patients with a unilateral mandibular condylar fracture were evaluated using OPT, 2D (CB)CT images, and 3D imaging to measure the extent of the fractures. The maximum mouth opening (MMO) was measured. Ramus height loss could be measured only in OPT, but not in 2D CT images. The Intraclass Correlation Coefficient was excellent in the 3D measurements. In the Loukota classification, condylar neck fractures had the largest median 3D displacement and the highest rotations of the fracture fragments. The largest fracture volume was observed in base fractures. According to the Spiessl and Schroll classification, type V fractures had the largest median 3D displacement and the highest rotation in the X-axis and Z-axis. Type I fractures had the largest fracture volume. We found a moderate negative correlation between MMO and 3D displacement and rotation on Z-axis. The 2D quantitative analysis of condylar fractures is limited, imprecise, and not reproducible, while quantitative 3D measurements provide extensive, precise, objective, and reproducible information.

Reliability and accuracy of the torque applied to osteosynthesis screws by maxillofacial surgeons and residents.

Applying the right torque to osteosynthesis screws is important for undisturbed bone healing. This study aimed to compare test-retest and intra-individual reliabilities of the torque applied to 1.5 mm and 2.0 mm osteosynthesis screws by residents and oral and maxillofacial surgeons (OMF-surgeons), to define the reference torque intervals, and to compare reference torque interval compliances. Five experienced OMF-surgeons and 20 residents, 5 of each 4 residency years, were included. Each participant inserted six 1.5 × 4 mm and six 2.0 × 6 mm screws into a preclinical model at two test moments 2 weeks apart (T1 and T2). Participants were blinded for the applied torque. Descriptive statistics, reference intervals, and intra-class correlation coefficients (ICC) were calculated. The OMF-surgeons complied more to the reference intervals (1.5 mm screws: 95% and 2.0 mm screws: 100%) than the residents (82% and 90%, respectively; P = 0.009 and P = 0.007) with the ICCs ranging between 0.85-0.95 and 0.45-0.97, respectively. The residents' accuracy and reliability were inadequate regarding the 1.5 mm screws but both measures improved at T2 for both screw types compared to T1, indicating a learning effect. Training residents and/or verifying the applied torque by experienced OMF-surgeons remains necessary to achieve high accuracy and reliability, particularly for 1.5 mm screws.

Titanium or Biodegradable Osteosynthesis in Maxillofacial Surgery? In Vitro and In Vivo Performances.

Osteosynthesis systems are used to fixate bone segments in maxillofacial surgery. Titanium osteosynthesis systems are currently the gold standard. However, the disadvantages result in symptomatic removal in up to 40% of cases. Biodegradable osteosynthesis systems, composed of degradable polymers, could reduce the need for removal of osteosynthesis systems while avoiding the aforementioned disadvantages of titanium osteosyntheses. However, disadvantages of biodegradable systems include decreased mechanical properties and possible foreign body reactions. In this review, the literature that focused on the in vitro and in vivo performances of biodegradable and titanium osteosyntheses is discussed. The focus was on factors underlying the favorable clinical outcome of osteosyntheses, including the degradation characteristics of biodegradable osteosyntheses and the host response they elicit. Furthermore, recommendations for clinical usage and future research are given. Based on the available (clinical) evidence, biodegradable copolymeric osteosyntheses are a viable alternative to titanium osteosyntheses when applied to treat maxillofacial trauma, with similar efficacy and significantly lower symptomatic osteosynthesis removal. For orthognathic surgery, biodegradable copolymeric osteosyntheses are a valid alternative to titanium osteosyntheses, but a longer operation time is needed. An osteosynthesis system composed of an amorphous copolymer, preferably using ultrasound welding with well-contoured shapes and sufficient mechanical properties, has the greatest potential as a biocompatible biodegradable copolymeric osteosynthesis system. Future research should focus on surface modifications (e.g., nanogel coatings) and novel biodegradable materials (e.g., magnesium alloys and silk) to address the disadvantages of current osteosynthesis systems.

Biocompatibility and degradation comparisons of four biodegradable copolymeric osteosynthesis systems used in maxillofacial surgery: A goat model with four years follow-up.

Applying biodegradable osteosyntheses avoids the disadvantages of titanium osteosyntheses. However, foreign-body reactions remain a major concern and evidence of complete resorption is lacking. This study compared the physico-chemical properties, histological response and radiographs of four copolymeric biodegradable osteosynthesis systems in a goat model with 48-months follow-up. The systems were implanted subperiosteally in both tibia and radius of 12 Dutch White goats. The BioSorb FX [poly(70LLA-co-30DLLA)], Inion CPS [poly([70-78.5]LLA-co-[16-24]DLLA-co-4TMC)], SonicWeld Rx [poly(DLLA)], LactoSorb [poly(82LLA-co-18GA)] systems and a negative control were randomly implanted in each extremity. Samples were assessed at 6-, 12-, 18-, 24-, 36-, and 48-month follow-up. Surface topography was performed using scanning electron microscopy (SEM). Differential scanning calorimetry and gel permeation chromatography were performed on initial and explanted samples. Histological sections were systematically assessed by two blinded researchers using (polarized) light microscopy, SEM and energy-dispersive X-ray analysis. The SonicWeld Rx system was amorphous while the others were semi-crystalline. Foreign-body reactions were not observed during the complete follow-up. The SonicWeld Rx and LactoSorb systems reached bone percentages of negative controls after 18 months while the BioSorb Fx and Inion CPS systems reached these levels after 36 months. The SonicWeld Rx system showed the most predictable degradation profile. All the biodegradable systems were safe to use and well-tolerated (i.e., complete implant replacement by bone, no clinical or histological foreign body reactions, no [sterile] abscess formation, no re-interventions needed), but nanoscale residual polymeric fragments were observed at every system's assessment.

Efficacy and morbidity of biodegradable versus titanium osteosyntheses in orthognathic surgery: A systematic review with meta-analysis and trial sequential analysis.

Titanium osteosynthesis is currently the gold standard in orthognathic surgery. Use of biodegradable osteosyntheses avoids removal of plates/screws in a second operation. This systematic review aimed to assess the efficacy and morbidity of biodegradable vs. titanium osteosyntheses in orthognathic surgery (PROSPERO CRD42018086477). Patients with syndromic disorder(s) and/or cleft lip/palate were excluded. Randomised, prospective and retrospective controlled studies were searched for in nine databases (February 2021). The time periods perioperative, short-term, intermediate, long-term, and overall follow-up were studied. Meta-analyses were performed using random-effects models. A total of 9073 records was assessed, of which 33 were included, comprising 2551 patients. Seven RCTs had 'some concerns' while another seven RCTs had 'high' risk of bias (Cochrane-RoB2). No differences in malunion (qualitative analyses), mobility of bone segments [RR 1.37 (0.47; 3.99)], and malocclusion [RR 0.93 (0.39; 2.26)] were found. The operative time was longer in the biodegradable group [SMD 0.50 (0.09; 0.91)]. Symptomatic plate/screw removal was comparable among both groups [RR 1.29 (0.68; 2.44)]. Skeletal stability was similar in most types of surgery. Biodegradable osteosyntheses is a valid alternative to titanium osteosyntheses for orthognathic surgery, but with longer operation times. Since the quality of evidence varied from very low to moderate, high-quality research is necessary to elucidate the potential of biodegradable osteosyntheses.

Comparison of the mechanical properties of biodegradable and titanium osteosynthesis systems used in oral and maxillofacial surgery.

To guide the selection of osteosynthesis systems, this study compared the mechanical properties of biodegradable and titanium osteosynthesis systems. SonicPins Rx and xG were subjected to pull-out tests. Additionally, 15 biodegradable (Inion CPS 2.0 and 2.5 mm; LactoSorb 2.0 mm; Macropore 2.0 mm; Polymax 2.0 mm; BioSorb FX 2.0 mm; ResorbX 2.1 mm; Osteotrans-MX 2.0 mm with plate thicknesses 1.0 and 1.4 mm; SonicWeld Rxplate/Rxpins, xGplate/Rxpins and xGplate/xGpins 2.1 mm without and with tapping the burr hole) and six titanium (CrossDrive (2006), CrossDrive (2018), MaxDrive; all 1.5 and 2.0 mm) straight, four-hole osteosynthesis systems were evaluated. All systems were subjected to tensile, bending and torsion tests. Pull-out loads of the SonicPins were comparable (P = 0.423). Titanium systems' tensile loads were higher than biodegradable systems (P < 0.001). CrossDrive (2018) and MaxDrive systems' tensile and torsional stiffness were lower, accompanied with higher ductility, than corresponding CrossDrive (2006) systems (P < 0.001). Bending stiffness of 1.5 mm titanium systems was comparable to, and of the 2.0 mm systems higher than, all biodegradable systems (P < 0.001). Regarding biodegradable systems, Inion CPS 2.5 mm had highest tensile load and torsional stiffness, SonicWeld 2.1 mm highest tensile stiffness, and BioSorbFX 2.0 mm highest bending stiffness (P < 0.001). On the basis of the results of this study, the CrossDrive (2018) and MaxDrive 1.5 mm titanium systems are recommended for midface fractures (e.g., zygomatic or maxillary fractures) and osteotomies (e.g., Le Fort I osteotomy), and the CrossDrive (2018) and MaxDrive 2.0 mm titanium systems for mandibular fractures and osteotomies when a titanium osteosynthesis system is used. When there is an indication for a biodegradable osteosynthesis system, the SonicWeld 2.1 mm or BioSorbFX 2.0 mm are recommended for midface fractures and osteotomies, and the Inion CPS 2.5 mm biodegradable system for mandibular osteotomies and non-load bearing mandibular fractures, especially when high torsional forces are expected (e.g., mandibular symphysis fractures).

Orbital floor repair using patient specific osteoinductive implant made by stereolithography.

The orbital floor (OF) is an anatomical location in the craniomaxillofacial (CMF) region known to be highly variable in shape and size. When fractured, implants commonly consisting of titanium meshes are customized by plying and crude hand-shaping. Nevertheless, more precise customized synthetic grafts are needed to meticulously reconstruct the patients' OF anatomy with better fidelity. As alternative to titanium mesh implants dedicated to OF repair, we propose a flexible patient-specific implant (PSI) made by stereolithography (SLA), offering a high degree of control over its geometry and architecture. The PSI is made of biodegradable poly(trimethylene carbonate) (PTMC) loaded with 40 wt % of hydroxyapatite (called Osteo-PTMC). In this work, we developed a complete work-flow for the additive manufacturing of PSIs to be used to repair the fractured OF, which is clinically relevant for individualized medicine. This work-flow consists of (i) the surgical planning, (ii) the design of virtual PSIs and (iii) their fabrication by SLA, (iv) the monitoring and (v) the biological evaluation in a preclinical large-animal model. We have found that once implanted, titanium meshes resulted in fibrous tissue encapsulation, whereas Osteo-PMTC resulted in rapid neovascularization and bone morphogenesis, both ectopically and in the OF region, and without the need of additional biotherapeutics such as bone morphogenic proteins. Our study supports the hypothesis that the composite osteoinductive Osteo-PTMC brings advantages compared to standard titanium mesh, by stimulating bone neoformation in the OF defects. PSIs made of Osteo-PTMC represent a significant advancement for patients whereby the anatomical characteristics of the OF defect restrict the utilization of traditional hand-shaped titanium mesh.

Accuracy and outcome of mandibular fracture reduction without and with an aid of a repositioning forceps.

PURPOSE: It is presumed that adequate reduction of a fracture of the mandible favors bone healing and diminishes the risk of complications. In this retrospective study, we compared the accuracy of fracture alignment and complication rate of mandibular fractures reduced without or with aid of a repositioning forceps. METHODS: Retrospective analysis of consecutive 252 patients with mandibular fractures treated between January 2010 and December 2016. Eligible for this study were patients with isolated mandibular fractures needing open reduction and internal fixation in whom pre- and postoperative radiographs and patient records were available. In total, 131 (252 fractures) patients fulfilled the inclusion criteria. RESULTS: Seventy-one (54%) patients were men. Mean age of the patients was 33 ± 16.5 years, and the median and interquartile range of age was 25 (20;41). In 54 patients, mandibular fractures were reduced without the aid of repositioning forceps, and in the remaining 77 patients, the fractures were reduced with the aid of the repositioning forceps. Anatomical alignment of the fractures was poor in the non-forceps-aided group (48%) compared to the forceps-aided group (58%) (P = .067). Overall complication rate was higher in the group of fractures reduced without the aid of forceps (17%) than in the forceps-aided group (7%) (P = .045; OR, 2.7; 95% CI, 1.0-7.4). CONCLUSIONS: Mandibular fractures reduced with the aid of repositioning forceps are accompanied by a lower complication rate and better alignment. This is an important observation as better alignment of the fracture fragments favors bone healing and reduces complications.

A Treatment Protocol for Fractures of the Edentulous Mandible.

PURPOSE: The incidence of fractures of edentulous mandibles is relatively low. Knowledge about the management of these fractured edentulous mandibles relies heavily on case reports and observational studies. On the basis of the current literature, we compiled a treatment protocol for fractures of the edentulous mandible and hypothesized that this protocol would result in fewer complications. PATIENTS AND METHODS: We conducted a retrospective cohort study of edentulous patients with mandibular fractures. The predictor variable was the fulfillment of the treatment protocol (yes or no). The outcome variables were postoperative complications and reoperations. Patient demographic characteristics were collected from patient records. The χ2 test was used for statistical analysis between predictor and outcome variables. RESULTS: Of 61 edentulous mandibular fractures (36 patients), 53 were treated according to the protocol and 8 were not. We observed 4 complications in the first group (complication rate, 7.5% [4 of 53]) and 4 in the second group (complication rate, 50% [4 of 8]). The fracture treatments that followed the protocol had a significantly lower postoperative complication rate (P = .001; odds ratio, 0.082) and needed fewer reoperations (P = .0001; odds ratio, 0.019) compared with the treatments that did not follow the protocol. CONCLUSIONS: The results of this study show that following the compiled treatment protocol for fractures of edentulous mandibles significantly reduces postoperative complications and reoperations.

Single-Step Resection of an Intraosseous Meningioma and Cranial Reconstruction: Technical Note.

OBJECTIVE: Simultaneous tumor resection and cranial reconstruction can be a challenging task. Surgical navigation is an indispensable tool in making this single-step procedure possible. In this technical note, we describe a new technique for this procedure to ensure a precise resection and optimal fit of the implant in a patient with an intraosseous meningioma. METHODS: We generated a 3-dimensional (3D) model of the patient's skull based on a computed tomography scan and created a digital "resection line" object using 3D Studio Max 2016 software. Based on this object, the patient-specific implant was generated and printed with a 3D printer. Before surgery, the digital object was transferred to the neuronavigation system to enable a navigated resection of the lesion to ensure maximum precision. During surgery, the craniotomy was performed, and the custom-made implant was fitted in a single step. RESULTS: The planned resection was achieved, and the implant could be fitted without need for further adjustments to the resection border. CONCLUSIONS: We provide a simple technique to digitally define a planned resection site and create a custom-made implant using specialized software and 3D printing to enable single-step resection of a skull lesion and cranial reconstruction, thereby reducing surgical time and costs and ensuring a good cosmetic result.

Non-IMF mandibular fracture reduction techniques: A review of the literature.

BACKGROUND: Intermaxillary fixation (IMF) techniques are commonly used in mandibular fracture treatment to reduce bone fragments and re-establish normal occlusion. However, non-IMF reduction techniques such as repositioning forceps may be preferable due to their quick yet adequate reduction. The purpose of this paper is to assess which non-IMF reduction techniques and reduction forceps are available for fracture reduction in the mandible. METHODS: A systematic search was performed in the databases of Pubmed and EMBASE. The search was updated until February 2016 and no initial date and language preference was set. RESULTS: 14 articles were selected for this review, among them ten articles related to reduction forceps and four articles describing other techniques. Thus, modification and design of reduction forceps and other reduction techniques are qualitatively described. CONCLUSION: Few designs of repositioning forceps have been proposed in the literature. Quick and adequate reduction of fractures seems possible with non-IMF techniques resulting in anatomic repositioning and shorter operation time, especially in cases with good interfragmentary stability. Further development and clinical testing of reduction forceps is necessary to establish their future role in maxillofacial fracture treatment.

Poly(trimethylene carbonate)-based composite materials for reconstruction of critical-sized cranial bone defects in sheep.

PURPOSE: The use of ceramic materials in repair of bone defects is limited to non-load-bearing sites. We tested poly(trimethylene carbonate) (PTMC) combined with ß-tricalcium phosphate or biphasic calcium phosphate particles for reconstruction of cranial defects. MATERIALS AND METHODS: PTMC-calcium phosphate composite matrices were implanted in cranial defects in sheep for 3 and 9 months. Micro-computed tomography quantification and histological observation were performed for analysis. RESULTS: No differences were found in new bone formation among the defects left unfilled, filled with PTMC scaffolds, or filled with either kind of PTMC-calcium phosphate composite scaffolds. Porous ß-TCP scaffolds as control led to a larger amount of newly formed bone in the defects than all other materials. Histology revealed abundant new bone formation in the defects filled with porous ß-TCP scaffolds. New bone formation was limited in defects filled with PTMC scaffolds or different PTMC-calcium phosphate matrices. PTMC matrices were degraded uneventfully. New bone formation within the defects followed an orderly pattern. CONCLUSIONS: PTMC did not interfere with bone regeneration in sheep cranial defects and is suitable as a polymer matrix for incorporating calcium phosphate particles. Increasing the content of calcium phosphate particles in the composite matrices may enhance the beneficial effects of the particles on new bone formation.

Evaluation of novel resorbable membranes for bone augmentation in a rat model.

OBJECTIVES: Our study compared two novel, biodegradable poly(trimethylene carbonate) (PTMC) barrier membranes to clinically applied barrier membranes in maintaining volume of block autologous bone grafts in a rat mandible model. MATERIAL AND METHODS: Two hundred and forty rats were included in this study. Block autologous bone grafts of 5 mm in diameter were harvested from the mandibular angles and transplanted onto the contralateral side. The bone grafts were either covered with a membrane or left uncovered. The applied membranes included pure PTMC membranes, biphasic calcium phosphate (BCP) incorporated PTMC composite membranes, expanded poly(tetrafluoroethylene) (e-PTFE) membranes (Tex) and collagen membranes (Geistlich Bio-Gide). After 2, 4 and 12 weeks, the rat mandibles were retrieved and analysed by histological evaluation and µCT quantification. RESULTS: The histological evaluation revealed that in time the block autologous bone graft was well integrated to the recipient bone via gradually maturing newly formed bone and did not show signs of resorption, independent of membrane coverage or types of membrane. µCT quantification showed the volume of the bone graft and recipient bone together was maintained by new bone formation and recipient bone resorption. CONCLUSIONS: Our study showed that the use of PTMC membranes and PTMC-BCP composite membranes resulted in similar bone remodelling to the collagen membranes and e-PTFE membranes and that the use of barrier membranes did not interfere with bone remodelling of the bone grafts and recipient bones. However, the used barrier membranes seemed not to contribute in maintaining the volume of block autologous bone grafts.

Digital planning of cranial implants.

Computer-aided techniques can be used in the reconstruction of defects in the skull, although there are limitations for large defects. We describe a technique for the digital design of an implant for cranioplasty using one, easy-to-use, piece of generic industrial software that shows a curvature-based, hole-filling algorithm. This approach is suitable for all kinds of defects, including those that extend across the midline of the skull. The workflow gives the user full control over the design, production, and material used for the implant.

Retrospective study on the treatment outcome of surgical closure of oroantral communications.

PURPOSE: A retrospective cohort study concerning the surgical closure of oroantral communications (OACs) was carried out to facilitate a comparison between treatment outcomes of conventional surgical treatment and new strategies for closure of OACs. Data were statistically analyzed to gather insight into possible predictor variables of recurrent OAC. PATIENTS AND METHODS: A cohort of patients treated for an OAC from 2004 through 2008 was reviewed. Recorded data included patient age and gender, location and duration of OAC, method of removal of the (pre)molar, presence of maxillary sinusitis, disturbed wound healing, and surgical treatment method. Data analysis included descriptive and multivariate logistic regression analyses with recurrence of OAC as the outcome variable. RESULTS: In total, 308 patients were included in the sample, of which 28 patients (9.1%) required a second intervention to repair an OAC. Of these 28 patients, 4 patients needed a third intervention, making the total number of recurrent OACs 32 (10.4%). In most cases (60.7%), a buccal advancement flap according to the method of Rehrmann was used to close the perforation. Multivariate regression analysis showed a 15 times higher risk of recurrence with maxillary sinusitis at follow-up. CONCLUSIONS: Overall results of the study showed that OACs recur in about 1 of 10 patients and requires a second intervention after surgical closure. New strategies should therefore result in an equal or better treatment outcome to be considered a suitable treatment option. Furthermore, it was demonstrated that the presence of maxillary sinusitis at follow-up is an important determinant of the treatment outcome of OAC repair.

Vivosorb, Bio-Gide, and Gore-Tex as barrier membranes in rat mandibular defects: an evaluation by microradiography and micro-CT.

OBJECTIVES: The objectives of this study were to determine whether a new degradable synthetic barrier membrane (Vivosorb) composed of poly(dl-lactide-epsilon-caprolactone) (PDLLCL) can be useful in implant dentistry and to compare it with collagen and expanded polytetrafluoroethylene (ePTFE) membranes. MATERIAL AND METHODS: In 192 male Sprague-Dawley rats, a standardized 5 mm circular defect was created through the right angle of the mandible. New bone formation was evaluated by post-mortem microradiography and micro-CT (muCT) imaging. Four groups (control, PDLLCL, collagen, ePTFE) were evaluated at three time intervals (2, 4, and 12 weeks). In the membrane groups the defects were covered; in the control group the defects were left uncovered. Data were analysed using a multiple regression model. RESULTS: New bone formation could be detected by post-mortem microradiography in 130 samples and by muCT imaging in 112 samples. Bone formation was progressive in 12 weeks, when the mandibular defect was covered with a membrane. Overall, more bone formation was observed underneath the collagen and ePTFE membranes than the PDLLCL membranes. CONCLUSIONS: In contrast to uncovered mandibular defects, substantial bone healing was observed in defects covered with a PDLLCL membrane. However, bone formation in PDLLCL-covered defects tended to be less than in the defects covered with collagen or ePTFE. The high variation in the PDLLCL samples at 12 weeks may be caused by the moderate adherence of this membrane to bone compared with collagen. These results indicate that further study is needed to optimize the properties of PDLLCL membranes.

A comparison of micro-CT, microradiography and histomorphometry in bone research.

OBJECTIVE: Intraobserver reliability and agreement were determined for microradiography (MR), micro-computed tomography (microCT) and histomorphometry (HM). These three modalities were compared for quantitative measurements of bone formation and graft modelling in rat mandibular defects and grafts. DESIGN: Twelve rats were randomly selected from a larger experiment, evaluating bone formation in rat mandibular defects and bone modelling in grafts. Twelve lateral microradiographs were taken of the grafts. microCT images were obtained from all defects and grafts (24 specimens). Defects and grafts were cut perpendicularly through their centre. Microradiographs, microCT images and histological sections were obtained from the resulting 48 specimens. New bone volume and graft volume were measured using image analysis software on MR and microCT images. Defect width and graft width were measured using images from HM, MR and microCT. The results were compared to each other. RESULTS: The intraobserver reliabilities for the measurements of new bone volume by microCT, and the measurement of graft modelling by MR and graft volume by microCT were high. The differences between MR, HM and microCT were larger in defect width measurements than in graft width measurement. MR measured smaller defects than HM and microCT. The 95% confidence interval was larger in defect width measurements compared to graft width measurements. CONCLUSIONS: The methods of MR and microCT image analysis are reliable but preferably should be used in combination as to obtain valid conclusions. HM, MR and microCT for graft widths measurements showed more agreement than for defect width measurements. MR appears to overestimate bone formation.

Is there evidence that barrier membranes prevent bone resorption in autologous bone grafts during the healing period? A systematic review.

INTRODUCTION: Autologous bone is considered the "reference standard" for bone-grafting procedures. A barrier membrane covering an autologous bone graft (guided bone regeneration [GBR]) is expected to prevent graft resorption. Good clinical results have been reported for GBR, although potential complications and relatively high costs have been implicated as disadvantages. However, most studies on the subject have been uncontrolled. PURPOSE: The aim of this systematic review was to evaluate the available evidence that barrier membranes prevent bone resorption in autologous onlay bone grafts. The primary outcome measure was bone resorption. RESULTS: The search yielded 182 articles. Two observers independently appraised 32 relevant studies methodologically, yielding 14 controlled studies. The articles included human and animal experiments with heterogenous objectives and outcome variables. Although most authors concluded that they had found evidence for the protective effect of barrier membrane on bone resorption in bone grafts, this systematic review reveals that the available evidence is too weak to support this. Most included studies were animal experiments; thus, extrapolation to the human situation is difficult. Most studies also had a small number of test sites, and sample size justification was generally not reported. Furthermore, ambiguity and lack of significance were found in many studies, along with additional limitations such as implantation site, nonsuitable designs, and varying outcome measures. CONCLUSION: Based on a systematic review of the literature, further evidence is needed to determine whether barrier membranes prevent bone resorption in autologous onlay bone grafts.

Tissue response to partially in vitro predegraded poly-L-lactide implants.

The in vivo local reaction of as-polymerized poly-L-lactide composed of 96% L-lactide and 4% D-lactide (PLA96) was investigated by histology at 2, 13 and 26 weeks after subcutaneous implantation in rats. In order to simulate possible end stage reactions the PLA96 was also predegraded in vitro until approximately 50% weight loss. The local reaction of predegraded PLA (PLA96(168)) was compared to the local reaction of polyethylene (PE) and non-predegraded PLA (PLA96). For PE and PLA96 a mild local reaction was observed at all time points consisting of a minimal layer of macrophage like cells with incidentally multinucleated giant cells at the implant interface, surrounded by a mild connective tissue capsule. For PLA96 at weeks 13 and 26 some minimal alterations in terms of degradation and ingrowth of cells was noted. The in vitro incubation (90 degrees C for 168 h) of PLA96(168) resulted for the thin 0.2 mm samples in complete degradation. Predegraded 0.5, 1.0 and 2.0 mm PLA96(168) samples were implanted and evaluated. The 1.0 and 2.0 mm samples could be evaluated for all time points investigated, but some 0.5 mm PLA96(168) samples were already completely resorbed at week 2 after implantation. In general, responses found for the predegraded PLA96(168) at weeks 2, 13 and 26 were similar with a pronounced macrophage infiltrate containing birefringent material, encapsulation of polymer fragments, and the presence of a debris area consisting of polymer and cellular remnants. In lymph nodes foamy macrophages with birefringent material were only observed in lymph nodes draining sites with predegraded PLA96(168). Immunohistochemistry was performed for further characterization of the cellular infiltrate. At the implant interface of the non-degrading PE and PLA96, ED1 and OX6 (MHC class II) positive cells were identified. In the capsule macrophage like cells expressed all three macrophage markers ED1, ED2, and ED3. CD4 and CD8 positive cells, indicating T helper and T supressor/cytotoxic cells, respectively, could be observed in low numbers, CD4 more than CD8. Both CD4 and CD8 were occasionally observed within the degrading PLA96(168) implant. Polymorphonuclear neutrophilic granulocytes were mainly observed at 2 weeks after implantation. We showed that predegradation could be used as a means to study late tissue reactions to polymers. Complete degradation may be studied with relatively thin implants, but this may lead to rather optimistic interpretation of resorption periods. When materials are intended to be used for screws and/or plates for bone fixation, implants of at least 1.0-2.0 mm thickness should be used as these may show a more realistic representation of the resorption characteristics of the material under investigation.