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Biomedical subjects

R R Bos

Publications and source records attributed to R R Bos.

At least 19 recordsLinked to original sources
PubMed2001

A computer study of biodegradable plates for internal fixation of mandibular angle fractures.

PURPOSE: This computer-based study was performed to determine the suitability of small biodegradable plate systems for mandibular angle fractures. MATERIALS AND METHODS: In a 3-dimensional computer model of the mandible, fracture mobility and plate strain were calculated for bite forces applied on 13 bite points on the dental arch. The angle fracture was fixed with 2 polylactide (PLA) midiplates or with 2 PLA maxiplates. The first plate was positioned buccally on the external oblique ridge. Two positions of the second plate were studied: halfway up the height of the mandible or on the lower border. Maximum fracture mobility was set at a limit of 150 microm to enable undisturbed fracture healing. Maximum plate strain was set at the yield strain of PLA. RESULTS: Fixation with the PLA maxiplates, with the second plate positioned halfway up the height of the mandible, resulted in fracture mobility below the set limit for all bite points. For the other PLA fixation strategies, fracture mobility exceeded the set limit. Fixation with the second plate positioned halfway up the height of the mandible generally resulted in less fracture mobility than with the plate positioned on the lower border. The yield strain of PLA was not exceeded in any of the fixation strategies. CONCLUSIONS: Based on the computer model, 2 PLA maxiplates are suitable for fixation of mandibular angle fractures. One plate should be positioned buccally on the external oblique ridge, and the other should be positioned halfway up the height of the mandible.

Absorbable Implants↗
PubMed2000

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.

Animals↗
PubMed1999

A computer study of fracture mobility and strain on biodegradable plates used for fixation of mandibular fractures.

PURPOSE: This computer-based study was done to determine whether a small biodegradable plate system was suitable for internal fixation of mandibular fractures. MATERIALS AND METHODS: In a three-dimensional computer model of the mandible, fracture mobility and plate strain were calculated for bite forces applied on 13 bite points on the dental arch. Simulated solitary angle, body, and symphysis fractures were fixed with one titanium miniplate, one polylactide (PLA) midiplate, one PLA maxiplate, or two PLA midiplates. Fractures with and without interfragmentary bone contact were studied. In the case of fractures with bone contact, the loads were transmitted through the fracture surfaces and the plate; when there was no contact, the loads were transmitted only through the plate. Maximum fracture mobility was set at 150 microm. Maximum plate strain was set at the yield strain of PLA and titanium. RESULTS: For fractures without interfragmentary bone contact, all plate fixations resulted in a fracture mobility and plate strain higher than the limits set, except for the symphysis fracture fixed with two PLA midiplates. Interfragmentary bone contact significantly reduced fracture mobility and plate strain. For the angle fracture with bone contact, all PLA plate fixations resulted in a fracture mobility above the limit, whereas the titanium miniplate fixation had a fracture mobility below the limit. For the body and symphysis fracture with bone contact, only double PLA midiplate fixation resulted in a fracture mobility below the limit. CONCLUSIONS: From a mechanical point of view, based on the computer model, small PLA plates are only suitable for symphysis fractures with and without interfragmentary bone contact and for body fractures with interfragmentary contact. However, fixation with two PLA plates is always necessary to provide sufficient reduction of fracture mobility and plate strain.

Absorbable Implants↗
PubMed1999

Complications of internal fixation of maxillofacial fractures with microplates.

PURPOSE: The aim of this retrospective study was to evaluate the complications of open reduction and internal fixation of maxillofacial fractures with microplates. PATIENTS AND METHODS: In 44 patients with maxillofacial trauma, fractures of the maxillofacial skeleton were treated by open reduction and internal fixation using a 1.0-mm and 1.5-mm microsystem. Simultaneously occurring fractures of the mandible or frontozygomatic suture were treated with a 2.0-mm miniplate system. Perioperative and postoperative complications were traced using patient charts, operation reports, and radiographs. The average follow-up was 46.8 months (range, 31 to 54 months). RESULTS: A total of 124 1.0-mm microplates and 546 1.0-mm microscrews, and 17 1.5-mm microplates and 75 1.5-mm microscrews, was used. The perioperative complication rate was 1.2% for the 1.0-mm screws (use of four emergency screws, breakage of one screw in the dense frontozygomatic suture area, and an insertion of a screw in a premolar root). The postoperative complication rate was 0.8% for the 1.0-mm screws (screw dislocation without clinical implication). No complications were observed with the 1.5-mm system. Plate-related infection did not occur. All fractures healed well. Three patients asked for plate removal because of a vague, persisting pain in the treated area. After removal, only one patient was free of pain. A loose 1.5-mm screw was found in this patient. CONCLUSION: The overall complication rate for microsystems was 2.0%. Both microsystems proved to be a reliable modality to fix fractures of the maxillofacial skeleton. Complications can be considered incidental and of neglectable clinical significance.

Adolescent↗
PubMed1999

Mandibular condyle fractures: a consensus.

A consensus was obtained following a two-day international conference to review the management of mandibular condyle fractures. Whilst areas of disagreement still exist, there are many areas of agreement. It is hoped this editorial will stimulate debate leading to internationally accepted guidelines.

Humans↗
PubMed1997

A three-dimensional study of bending and torsion moments for different fracture sites in the mandible: an in vitro study.

The aim of the study was to determine and compare bending and torsion moments across mandibular fractures, for different positions of the bite point and different sites of the fracture. Three identical resin mandibles, each with a single fracture, were used. The fracture sites were in the angle, body and symphyseal regions. A polyethylene bone plate was used for fixation. Simulated bite forces were applied at 13 bite points. For each bite point, the displacements of the fragments were registered and converted into bending and torsion moments across the fracture. Positive bending moments were defined as those moments that caused compression at the lower border and tension at the alveolar side of the mandible; negative bending moments did the opposite. Angle fractures had relatively high positive bending moments. Body fractures had positive as well as negative bending moments and the highest torsion moments. Symphyseal fractures had negative bending moments only and relatively high torsion moments. It was found that angle, body and symphyseal fractures each have a characteristic load pattern. These load patterns should play a decisive role in the treatment of mandibular fractures with regard to number and positioning of plates.

Adult↗
PubMed1997

[Maxillofacial trauma. How to treat?].

Fractures of the maxillofacial skeleton, often accompanied by dentoalveolar injuries, are no exception. Dentists may become primarily involved in the diagnosis of such a trauma and the treatment of dentoalveolar injuries. More often they will play an important role in the aftercare of such a patient (endodontics, prosthodontics). This paper describes the general principles of the treatment of such patients. The specific treatment of maxillofacial trauma will be described in the contributions of other authors in this special issue.

Humans↗
PubMed1997

[Fracture healing of the face. General principals].

To obtain good and uncomplicated primary fracture healing, anatomical repositioning, direct bone apposition and stable fixation are mandatory. The course of primary fracture healing starts with acute inflammation (cellular and vascular), stabilization (formation of new bone), and remodeling. Besides good fixation, local factors such as age and type of fracture will influence the healing. If good reposition, apposition or adequate stabilization of the bony fragments are not achieved, the bone healing will be secondary. In secondary healing fracture repair and stabilization occurs through the formation of callus.

Bone Remodeling↗
PubMed1997

[Fractures of the condylar process].

Fractures of the mandibular condyle are frequently seen. There is no consensus on the most appropriate treatment modality. Closed reduction with help of arch bars and guiding elastics is in most cases sufficient. Open reduction and fixation with a plate osteosynthesis or a specially designed lag screw is occasionally performed. Intracapsular fractures of the condylar head are only operated in case of severely reduced mobility, or ankylosis. Fractures of the mandibular condyle normally heal uneventfully. Complications mostly occur in bilateral condylar neck fractures, or intracapsular fractures.

Ankylosis↗
PubMed1997

[Zygomatic fractures].

The zygomatic bone is important for the midfacial contour and for protection of the orbital contents. Zygomatic fractures frequently occur. Because they are hidden behind a simple black eye in many instances, there is a potential risk of missing the diagnosis. Fresh zygomatic fractures are relatively easy to treat, but late secondary corrections are difficult and often have dissatisfying results. The most important clinical signs of a zygomatic fracture are: flattening of the zygomatic contour, edema, haematoma, unilateral nose-bleeding, disturbed sensibility, diplopia, restricted mandibular movements, contour defects. In this paper the clinical signs of a zygomatic fracture are emphasized to enable the general practitioner to examine the patient with a simple black eye appropriately and be able to recognize a zygomatic fracture.

Diagnosis, Differential↗
PubMed1997

[Fractures of the midface].

Midfacial fractures have a wide variety of appearance. The original classification by Le Fort is still in use. Nasal-orbital-ethmoidal (NOE) fractures deserve special attention. Next to clinical evaluation detailed computer tomography is necessary. Extended open reduction and internal fixation with various mini- and microplate osteosyntheses as well as immediate reconstruction with calvarian bone are essential components of surgical treatment aiming for adequate function and esthetics. Reduction of increased inner intercanthal distances is a substantial part of the treatment of NOE fractures. Surgical repair within 48-72 hours benefits the final result and limits the number and extent of secondary corrections.

Bone Transplantation↗
PubMed1996

A three-dimensional study of loads across the fracture for different fracture sites of the mandible.

The loads across the fracture depend on variables such as position of the fracture and the bite point. Up to now, no study has described systematically the influence of these two variables on these loads. The aim of this study was to describe and compare value and direction of the loads across the fracture for different positions of fractures in the mandible. In a three-dimensional model, bending and torsion moments and shear forces were compared for five mandibular fractures. The fractures were located in, respectively, the angle, posterior body, anterior body, canine and symphysis region. Positive bending moments were defined to give compression at the border, negative bending moments to give compression at the alveolar side of the mandible. The angle and posterior body fracture have high positive bending moments, small torsion moments and high shear forces. The anterior body, canine and symphysis fracture have high negative bending moments and high torsion moments with similar maximum values. The number of bite points with negative bending moments were different for all fractures. These bite points were always located on the fractured side. It is concluded that mandibular fractures can be divided roughly into two groups with similar load patterns across the fracture. One group consists of angle and posterior body fractures, the other group consists of anterior body, canine and symphysis fractures.

Adult↗
PubMed1996

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

PURPOSE: The 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. PATIENTS AND METHODS: Six 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. RESULTS: None 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. CONCLUSIONS: Based 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.

Adolescent↗
PubMed1996

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.

Biodegradation, Environmental↗