J. Reuther

Stereolithography in oral and maxillofacial operation planning

Stereolithography (STL) is a method of organ-model-production based on computed tomography scans which enables the representation of complex 3-dimensional anatomical structures. Surfaces and internal structures of organs can be produced by polymerization of UV-sensitive liquid resin using a laserbeam. In oral and maxillofacial surgery this technique is advantageous for reconstruction of severe skull defects because a more accurate preoperative planning is possible. Using recently developed software we are able to reconstruct unilateral bony defects by virtual mirror imaging of the contralateral side and production of a STL mirror model as well as the reconstruction of non-mirrorable defects by superposition. Advantages of STL are the representation of complex anatomical structures, high precision and accuracy, and the option to sterilize the models for intraoperative use. More accurate planning using this method improves postoperative results, decreases risks and shortens treatment time.

Poly(L-lactide): a long-term degradation study in vivo. Part III. Analytical characterization.

Three poly(L-lactides) with different molecular weights were synthesized as solid blocks from the melt. Two batches were ground and small specimens were produced by injection moulding. The third block was processed by machining, yielding crystalline parts. All were implanted as small rods into the dorsal muscle of rats. The implants were recovered, weight loss was determined, and the samples analysed. The samples degraded very fast, reaching the same molecular weight level after 20 wk, then degraded simultaneously. Analysis showed differences depending on the solid state of the polymer. The differences in the degradation behaviour of the amorphous and crystalline samples can be explained by assuming a simple hydrolysis as the main degradation mechanism, affecting the whole polymer, if in an amorphous state, but only the amorphous domains in a crystalline polymer.

Poly(l-lactide): a long-term degradation study in vivo

Three different poly(L-lactide) rods (25 x 3 x 2 mm) were produced either by injection moulding or machined out of a solid as-polymerized polylactide block and were implanted for 1-116 months into the dorsal muscle of rats. After recovery, the polylactide specimens were carefully cleaned, dried, photographed and weighed. Bending strength and Youngs modulus of elasticity were determined. The surfaces of the broken rods were examined by scanning electron microscopy. Block polylactide samples initially looked milky. They became friable and broke into white or brownish fragments during the implantation period, whereas total disintegration could not be observed. Electron scanning microscopy revealed a porous surface with crystalline elements persisting for the whole time. Mechanical stability fell from 127 +/- 3 MPa at implantation time to about half after 3 wk (61 +/- 4 MPa) and about a quarter (32 +/- 4 MPa) after 6 wk. Both injection-moulded polyactides (A1 and A2) were clear and transparent initially. After implantation they gradually became whitish, fragmented after about 64 wk and disintegrated 90 wk later into small parts and powder. Electron scanning microscopy at first showed a homogeneous surface. A kind of cortex developed after about 4 wk and deep cracks ran through the rod after 32 wk. Round pores of 1.5-10 microns diameter developed after 1 yr of implantation. Bending strengths were 130 +/- 8 MPa (A1) and 115 +/- 14 MPa (A2); these remained nearly stable over about 12 wk, then declined linearly. Although a higher initial mechanical strength is desirable for use in osteosynthetic devices, mechanical stability of amorphous injection-moulded polylactides over the first 12 wk and total disintegration thereafter approaches the requirements for their use as a material for osteosynthesis.

Poly(l-lactide): a long-term degradation study in vivo: I. Biological results

Three poly(L-lactides) with different molecular weights were synthesized. Small blocks (3 x 3 x 2 mm) and rods (25 x 3 x 2 mm) were produced either by injection moulding (amorphous parts, Mvis 200,000 and 120,000, respectively) or machined out of a solid aspolymerized polylactide block (crystalline parts, Mvis 429,000) and implanted into the dorsal muscle of rats. After 1 to 116 wk the rats were killed and the implants were recovered. Histological preparation was carried out using the cutting-grinding technique. All three polylactides had incorporated well, forming a collagenous fibrous layer. Crystalline block polylactide remained stable in form and structure over the whole observation period. Amorphous injection-moulded specimens developed a rough surface within weeks, then deep resorptive lacunae after ca. 1 yr and became totally degraded (Mvis 120,000) or nearly totally degraded (Mvis 200,000) after 2 yr. This velocity of biodegradation seems to meet the requirements for an absorbable material for osteosynthesis. Long-term implantation into rodents brings the problem of foreign-body tumorigenesis independent of the chemical nature of implants (the Oppenheimer effect). Observations in this study and in the literature are discussed.

Inductive properties of recombinant human BMP-2 produced in a bacterial expression system

Recombinant human BMP-2, produced in E. coli, refolded and concentrated to a purity of more than 98%, has been demonstrated to be biologically active. In vitro, amounts of 0.4 microg BMP-2 or more induced new cartilage formation in 27 out of 47 samples of a neonatal muscle tissue assay, with chondroneogenesis occurring 14 days after a four-hour contact between BMP-2 and the muscle tissue. In vivo, BMP-2 was implanted in the thigh muscle of ICR mice for a period of three weeks. Amounts of 4 microg BMP-2 and more showed heterotopic bone formation in 15 out of 17 samples. When BMP-2 was combined with a collagen carrier, amounts of 0.4 microg protein or more induced heterotopic bone formation in 30 out of 33 samples four weeks after the implantation in the abdominal wall of Sprague-Dawley rats. The results show that the E. coli-derived BMP-2 was active in different assay systems in concentrations equal to those required with mammalian cell-expressed BMP-2. It could also be demonstrated that a single morphogen (BMP-2) is enough to initiate the differentiation process associated with bone induction. The presented bacterial expression system also offers the opportunity to produce large quantities of recombinant BMP-2 for clinical applications.

Poly(l-lactide): a long-term degradation study in vivo: Part II: physico-mechanical behaviour of implants

Abstract Three different poly( l -lactide) rods (25 × 3 × 2 mm) were produced either by injection moulding or machined out of a solid as-polymerized polylactide block and were implanted for 1–116 months into the dorsal muscle of rats. After recovery, the polylactide specimens were carefully cleaned, dried, photographed and weighed. Bending strength and Youngs modulus of elasticity were determined. The surfaces of the broken rods were examined by scanning electron microscopy. Block polylactide samples initially looked milky. They became friable and broke into white or brownish fragments during the implantation period, whereas total disintegration could not be observed. Electron scanning microscopy revealed a porous surface with crystalline elements persisting for the whole time. Mechanical stability fell from 127 ± 3 MPa at implantation time to about half after 3 wk (61 ± 4 MPa) and about a quarter (32 ±4 MPa) after 6 wk. Both injection-moulded polylactides (A1 and A2) were clear and transparent initially. After implantation they gradually became whitish, fragmented after about 64 wk and disintegrated 90 wk later into small parts and powder. Electron scanning microscopy at first showed a homogeneous surface. A kind of cortex developed after about 4 wk and deep cracks ran through the rod after 32 wk. Round pores of 1.5–10 μm diameter developed after 1 yr of implantation. Bending strengths were 130 ± 8 MPa (A1) and 115± 14 MPa (A2); these remained nearly stable over about 12 wk, then declined linearly. Although a higher initial mechanical strength is desirable for use in osteosynthetic devices, mechanical stability of amorphous injection-moulded polylactides over the first 12 wk and total disintegration thereafter approaches the requirements for their use as a material for osteosynthesis.

Osteoinductive, morphologic, and biomechanical properties of autolyzed, antigen-extracted, allogeneic human bone**

Autolyzed, antigen-extracted, allogeneic (AAA) bone was prepared from human cortical bone and its morphologic, biomechanical, and osteoinductive properties were compared with untreated (frozen) as well as lyophilized human bone. Scanning electron microscopy revealed removal of inorganic calcium phosphates and persistence of shrunken collagen fibrils on the surface of AAA bone matrix. Biomechanical testing of differently prepared bone samples showed that lyophilization increased both the modulus of elasticity (P < .00001) and the compressive strength (P < .00001). Depending on the depth of decalcification in the preparation of AAA bone, both measured values decreased in rehydrated AAA bone compared with untreated bone (P < .00001). Completely demineralized and rehydrated AAA bone was soft, flexible, and showed very little compressive strength. Differences in biomechanical behavior between samples drilled longitudinally or perpendicularly to the diaphyseal bone axis were observed. Xenogeneic human bone samples were implanted in muscle pouches of Sprague-Dawley rats for 6 weeks. AAA bone implants showed chondrogenesis and osteogenesis in 50% of the cases, while untreated or lyophilized bone implants induced no new cartilage or bone formation. As decalcification exposed xenogeneic organic matrix components, AAA bone implants provoked the highest inflammatory reaction. When AAA bone samples were implanted in immunosuppressed rats, the inflammatory reaction was suppressed and 94% of the implants showed endochondral bone formation. The chondroinductivity of the bone samples also was tested in vitro using neonatal rat muscle tissue to avoid interference with inflammatory cells and secreted cytokines. In this assay, 68% of AAA bone samples induced chondroneogenesis, while untreated as well as lyophilized bone samples failed to induce any cartilage formation. The results clearly demonstrate that AAA bone has osteoinductive properties. Biomechanical stability of AAA bone implants depends on the degree of demineralization. Thus, they can be prepared in an appropriate manner for different indications in oral and maxillofacial surgery.

Repair of human skull defects using osteoinductive bone alloimplants

To estimate the efficacy of cranioplasty in clinical practice, autolyzed, antigen-extracted, allogenic (AAA) bone was prepared from cortical bones of human organ donors. AAA bone implants consisted of completely demineralized bone powder, completely demineralized pliable bone chips, surface-demineralized bone chips with pliable crevices, surface-demineralized rigid bone chips, or combinations thereof. 21 patients received AAA bone cranioplasties and were followed-up for between 12 and 58 months (average: 29 months). No infection or rejection of any of the AAA bone implants occurred. X-ray assessments as well as bone scintigraphies revealed osseous integration and remodelling of the AAA bone implants with minimal resorption, with the exception of completely demineralized AAA bone chips which showed partial resorption (2 cases). However, the partial resorption of completely demineralized AAA bone chips ceased after the implants had been remodelled. In 4 cases, the osteosynthesis material was removed between 10 and 18 months after the cranioplasty. In another case, a re-entry was necessary because of recurrence of an intracranial tumor. All of these five AAA bone reconstructions showed bleeding surfaces and osseous consolidations at the time of re-entry. A bone biopsy taken from one of these cranioplasties showed osteoinduction on the surface of the AAA bone implants. This first clinical review of cranial reconstructions using osteoinductive AAA bone implants emphasizes the therapeutical application of AAA bone for cranioplasty. Large AAA bone chips from human skull bones facilitate the reproduction of the skulls convexity especially when combined with preoperative stereolithography-based planning.

p53 and Ki-67 as predictive markers for radiosensitivity in squamous cell carcinoma of the oral cavity? an immunohistochemical and clinicopathologic study.

PURPOSE Previously published data relating the expression of p53 and Ki-67 to radiation response in head and neck cancer are conflicting. This may be due to differences in patient selection and treatment modalities. In this study of a homogenous population of patients with oral cavity cancer, Ki-67 and p53 indices were correlated with histopathologically assessed tumor regression after preoperative radiochemotherapy and longterm outcome. METHODS AND MATERIALS Eighty-eight patients with squamous cell carcinoma of the oral cavity and treated between September 1985 and November 1995 by preoperative radiochemotherapy and definitive surgery were included in this analysis. By immunohistochemistry (IHC) the pre-irradiation expression of p53 and of Ki-67 were analyzed and correlated with the histopathologically proven tumor regression, overall survival and local control. RESULTS The overall 2- and 5-year survival rates were 76.5% and 63%, the locoregional control rates were 84% and 79%, respectively. After preoperative radiochemotherapy 29 patients (33%) showed complete tumor regression (ypT(0) classification). Survival and local control rates were significantly higher for patients showing ypT(0) classification than ypT(1-4) classification (p < 0.01). This effect was independent of pretreatment tumor classification in multivariate analysis. Pre-irradiation p53 status and Ki-67 index had no influence on tumor regression and clinical outcome in these patients. CONCLUSION Complete tumor regression after preoperative treatment is related to an improved outcome in combined modality treatment of oral cavity cancer. The presented study could not demonstrate an influence of p53 and Ki-67 status as detected by immunohistochemical staining on survival, local control, or tumor regression after radiochemotherapy.

Outcome and Histopathologic Regression in Oral Squamous Cell Carcinoma after Preoperative Radiochemotherapy

Background and Purpose:Preoperative radiochemotherapy has been reported to enhance tumor response and to improve long-term survival in advanced squamous cell carcinoma of the head and neck. This retrospective study evaluates regression rate and long-term survival in 228 patients with primary oral squamous cell carcinoma treated by neoadjuvant radiochemotherapy and radical surgery.Patients and Methods:All patients with biopsy-proven, resectable oral squamous cell carcinoma – TNM stages II–IV without distant metastasis – received preoperative treatment consisting of fractioned irradiation of the primary and the regional lymph nodes with a total dose of 40 Gy and additional cisplatin (n = 160) or carboplatin (n = 68) during the 1st week of treatment. Radical surgery and neck dissection followed after a delay of 10–14 days. The study only included cases with histologically negative resection margins.Results:After a median follow-up of 5.2 years, 53 patients (23.2%) had experienced local-regional recurrence. The median 2-year disease-specific survival (DSS) rate was 86.2%. 5-year DSS and 10-year DSS were 76.3% and 66.7%, respectively. Complete histological local tumor regression after surgery (ypT0) was observed in 50 patients (21.9%) and was independent of pretreatment tumor classification. Uni- and multivariate survival analysis revealed that ypT- and ypN-stage were the most decisive predictors for DSS.Conclusion:Preoperative radiochemotherapy with cisplatin/carboplatin followed by radical surgery attains favorable long-term survival rates. This applies especially to cases with complete histological tumor regression after radiochemotherapy, which can be assumed for one of five patients.Hintergrund und Ziel:Die präoperative simultane Radiochemotherapie soll die lokale Tumorkontrolle erhöhen und das Gesamtüberleben beim Plattenepithelkarzinom des Kopf-Hals-Bereichs verbessern. Hierzu wurden retrospektiv die Regressionrate und das Langzeitüberleben bei 228 Patienten mit primären oralen Plattenepithelkarzinomen, die durch neoadjuvante Radiochemotherapie und radikale Tumorresektion behandelt wurden, untersucht.Patienten und Methodik:Bei 228 Patienten mit bioptisch-histologisch gesicherten, operablen oralen Plattenepithelkarzinomen – TNM-Stadien II–IV ohne Fernmetastasen (Tabelle 1) – wurde eine präoperative Bestrahlung des Primärbefunds und der regionalen Lymphknoten mit einer Gesamtdosis von 40 Gy bei zusätzlicher Gabe von Cisplatin (n = 160) oder Carboplatin (n = 68) in der 1. Woche durchgeführt. Im Anschluss folgten die radikale Tumor- und Lymphknotenresektion. In die Analyse wurden lediglich Fälle mit histologisch negativen Resektionsrändern eingeschlossen.Ergebnisse:Nach einer medianen Beobachtungszeit von 5,2 Jahren war es bei 53 Patienten (23,2%) zu einem Lokalrezidiv gekommen. Die mittlere tumorspezifische 2-Jahres-Überlebensrate lag bei 86,2%, das 5- und 10-Jahres-Überleben bei 76,3% bzw. 66,7% (Abbildung 1). Eine histologisch komplette lokale Tumorregression im Resektionspräparat (ypT0) konnte bei 50 Patienten (21,9%) festgestellt werden, unabhängig von der präoperativen Tumorgröße (Tabellen 2 und 3). In der uni- und multivariaten Analyse erwiesen sich ypT und ypN als wichtigste prognostische Parameter (Abbildung 2, Tabelle 4).Schlussfolgerung:Die präoperative Radiochemotherapie mit Cisplatin/Carboplatin und nachfolgender Tumorresektion erzielt hohe Langzeitüberlebensraten (Tabelle 5). Dies gilt insbesondere in Fällen kompletter histologischer Tumorregression nach Radiochemotherapie, welche bei einem von fünf Patienten zu beobachten ist.