Ruud R.M. Bos

Foreign body reactions to resorbable poly(L-lactide) bone plates and screws used for the fixation of unstable zygomatic fractures.

In a previous article in the Journal of Oral and Maxillofacial Surgery, the initial results of treating 10 patients with solitary, unstable, displaced zygomatic fractures using resorbable poly(L-lactide) (PLLA) plates and screws was reported (Bos et al, 1987). This article describes the long-term results in these patients. Three years postoperatively, four patients returned because they were concerned about an intermittent swelling at the site of implantation. The remaining patients were recalled after the same postoperative period. All patients were examined clinically, and six patients were operated on again for evaluation of the swelling and to investigate the nature of the tissue reaction. The explanted material showed remnants of degraded PLLA surrounded by a dense fibrous capsule. The swelling was classified as a nonspecific foreign body reaction to the degraded PLLA material. Ultrastructural investigation of the degraded material showed an internalization of crystal-like PLLA material in the cytoplasm of various cells.

In vivo degradation and biocompatibility study of in vitro pre-degraded as-polymerized polylactide particles

The degradation of high molecular weight as-polymerized poly(L-lactide) (PLLA) is very slow; it takes more than 5.6 yr for total resorption. Moreover, the degradation products of as-polymerized PLLA bone plates, consisting of numerous stable particles of high crystallinity, are related with a subcutaneous swelling in patients 3 yr postoperatively. In order to avoid these complications, polymers were developed that are anticipated to have comparable mechanical properties but a higher degradation rate and do not degrade into highly stable particles that can induce a subcutaneous swelling. On chemical grounds it can be expected that copolymerization of PLLA with 4% D-lactide (PLA96) or by modifying PLLA through cross-linking (CL-PLLA) will lead to less stable particles and a higher degradation rate. To evaluate the long-term suitability of these as-polymerized polymers, the biocompatibility of the degradation products should be studied. Considering the very slow degradation rate of as-polymerized PLLA, in vitro pre-degradation at elevated temperatures was used to shorten the in vivo follow-up periods. In this study, the biocompatibility and degradation of as-polymerized PLLA, PLA96 and CL-PLLA were investigated by implanting pre-degraded particulate materials subcutaneously in rats. Animals were killed after a postoperative period varying from 3 to 80 wk. Light and electron microscopical analysis and quantitative measurements were performed. The histological response of all three pre-degraded materials showed a good similarity with in vivo implanted material. Pre-degraded PLLA induced a mild foreign body reaction and showed a slow degradation rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Poly(L-lactide) implants for repair of human orbital floor defects: Clinical and magnetic resonance imaging evaluation of long-term results

PURPOSEnThe purpose of this study was to evaluate the long-term outcome of repair of orbital floor defects in patients with resorbable as-polymerized poly(L-lactide) (PLLA) implants and to determine whether these patients showed symptoms that could be indicative of the presence of a late tissue response.nnnPATIENTS AND METHODSnSix patients (four women, two men; mean age, 39 years; range, 18 to 67 years) treated with PLLA implants for orbital floor fractures were recalled for follow-up examination after a period ranging from 3 1/2 to 6 1/2 years. The examination consisted of an interview and a physical examination, including an ophthalmologic and orthoptic consultation. For evaluation of the orbital tissues, coronal spin echo T1- and T2-weighted magnetic resonance images (MRIs) were made through both orbits.nnnRESULTSnNone of the patients reported any problems in the years preceding the follow-up examination that might have indicated complications. Clinical examination of the operative sites revealed no abnormalities. At ophthalmologic and orthoptic consultation, normal eye function, without diplopia or restriction of motility, was found in all patients. The MRIs showed no indication of an abnormal or increased soft tissue reaction in the orbital region.nnnCONCLUSIONSnBased on the results of this study, it can be concluded that PLLA orbital floor implants have the potential for successful use in repair of human orbital floor defects.

HIGH-IMPACT POLY(L/D-LACTIDE) FOR FRACTURE FIXATION - IN-VITRO DEGRADATION AND ANIMAL PILOT-STUDY

The impact strength of amorphous lactide copolymers can be significantly improved by blending with biodegradable rubbers. Rubber toughening of amorphous poly(85L/15D -lactide) with the copolymer poly (50/50-trimethylenecarbonate-co-epsilon-caprolactone) results in a high-impact polymer (PDLLA/P(TMC-CL)). In vitro, the PDLLA/P(TMC-CL) blend retained its tensile and impact strength for a long period of time. Up to 45 weeks, the amount of water absorbed by the blend remained very low and no significant mass loss was observed. To test the suitability for fracture fixation, in a dog study mandibular fractures were fixated with PDLLA/P(TMC-CL) bone plates and screws. Bone healing was uneventful without premature failure of the implants. Although long-term degradation studies have to be carried out, PDLLA/P(TMC-CL) seems to be promising for application in fracture fixation.

Cytotoxicity of poly(96L/4D-lactide): the influence of degradation and sterilization.

The cytotoxicity of poly(96L/4D-lactide) (PLA96), and of its accumulated degradation products, was investigated following different sterilization methods and pre-determined heat-accelerated degradation intervals. PLA96 samples sterilized by either steam, ethylene oxide, or gamma irradiation were left untreated (S0 samples), or were degraded for 30 h or 60 h (S30 and S60 samples) at 90 degrees C in water. Extracts of the samples and of the remaining degradation fluids (F30 and F60) were prepared. The toxicity of both unfiltered and filtered extracts was analyzed in a cell growth inhibition (CGI) assay and a lactate dehydrogenase (LDH) leakage assay. Physical analysis of the extracted samples and of the degradation fluids also was performed. The S0 extracts demonstrated no significant CGI. The CGI of the S30 extracts ranged from 37 to 78%, whereas the CGI of the S60 extracts ranged from 6 to 33%. The CGI of the F30 extracts ranged from 19 to 38% and the CGI of the F60 extracts was 98 to 123%. The LDH leakage assay only showed a high response to the unfiltered F60 extracts. Neither sterilization nor filtration appeared to influence the cytotoxicity of the extracts. Particle accumulation, however, might affect cell membrane permeability resulting in LDH leakage. The results of this study suggest that the cytotoxicity of PLA96 is related to the pH and possibly the osmolarity of the tested extracts. The pH and osmolarity, in turn, may depend on variations in the amounts of solubilized lactic acid and oligomers. These variations appear to result from degradation stage-dependent differences in crystallinity, molecular weight and molecular weight distribution of the PLA96 samples.

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

OBJECTIVESnThe 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.nnnMATERIAL AND METHODSnIn 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.nnnRESULTSnNew 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.nnnCONCLUSIONSnIn 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.

Retrospective Study on the Treatment Outcome of Surgical Closure of Oroantral Communications

PURPOSEnA 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.nnnPATIENTS AND METHODSnA 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.nnnRESULTSnIn 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.nnnCONCLUSIONSnOverall 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.

Tissue Response to Pre-Degraded Poly(L-Lactide)

Poly(L-lactide) is a member of a group biodegradable aliphatic poly(lactone)esters which have found important use as biomaterials e. g. in prosthetics, sutures, and drug delivery systems. As-polymerized, high molecular weight poly(L-laetide) (PLLA) as synthesized according to Leenslag et al.1has been successfully used for fracture fixation and orbital floor reconstruction in animals and humans2-5. PLLA is considered to be a fully resorbable, biocompatible material6.

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.

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

OBJECTIVESnOur 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.nnnMATERIAL AND METHODSnTwo hundred and forty rats were included in this study. Block autologous bone grafts of 5xa0mm 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 12xa0weeks, the rat mandibles were retrieved and analysed by histological evaluation and μCT quantification.nnnRESULTSnThe 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.nnnCONCLUSIONSnOur 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.