H. Pistner

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.

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.

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.

Resorbable versus titanium osteosynthesis devices in bilateral sagittal split ramus osteotomy of the mandible — the results of a two centre randomised clinical study with an eight-year follow-up

BACKGROUND This study was conducted to compare the long-term clinical outcome of patients with jaw disproportion who had had fixation with resorbable polylactic acid containing positioning screws with those who had had titanium positioning screws in bilateral sagittal split ramus osteotomy of the mandible (BSSO). PATIENTS AND METHODS Sixty-six patients with isolated mandibular jaw disproportion were included and divided randomly into two treatment groups (resorbable and titanium). Patients were followed for 8 years postoperatively using a standardised protocol. Material-specific complications, functional problems and clinical findings within the former operation field were documented. Treatment stability was determined by occlusion criteria. RESULTS Thirty-four patients (54%) were followed until the end of the study. No significant differences were observed in the outcomes of patients in the two groups related to the materials used for osteosynthesis or the long-term treatment stability. During the study, no foreign body reactions were observed. CONCLUSION This study showed that resorbable and titanium positioning screws were equally effective as fixation devices in sagittal split osteotomy. Complete resorption of the resorbable screws could not be verified because of the absence of histological examination, however, the use of resorbable positioning screws can be considered as an alternative osteosynthesis material to conventional titanium osteosynthesis devices in sagittal split osteotomy.

Feasibility of alloplastic mandibular reconstruction in patients following removal of oral squamous cell carcinoma.

INTRODUCTION Microvascular bone grafts have evolved as the preferred technique for mandibular reconstruction in irradiated tumour patients. However immediate reconstruction by bridging plates remains an option for patients whose clinical condition is not favourable for microsurgical reconstruction. This retrospective study evaluates the performance of alloplastic mandibular reconstruction in patients following removal of oral squamous cell carcinoma. PATIENTS AND METHODS Three hundred and thirty-four patients with primary (biopsy proven) oral squamous cell carcinoma without distant metastasis (stages II-IV), who were all treated by segmental mandibular resection and reconstruction by means of a titanium bridging plate were included. Two hundred and seventy-two patients received preoperative treatment, consisting of concomitant radiochemotherapy (RCT) (n=228), chemotherapy (n=34) and radiotherapy (n=10). Median follow-up was 5.1 years (min 0.3, max 18.0). RESULTS The median 2-year-disease-specific survival rate (DSS) was 81.6%. Five-year-DSS and 10-year-DSS was 71.8% and 62.0%, respectively. One hundred and thirty-six plates were removed due to infection with intra- and/or extraoral exposure, seven plates because of fracture. Preoperative RCT (p=0.027), mandibular defects including the symphysis (p=0.016) and heavy smoking at the time of diagnosis (p=0.042) were associated with infection-related failure of the reconstruction plates. CONCLUSION Reconstruction of mandibular defects with titanium bridging plates seems crucial in heavy smoking tumour patients with preoperative RCT as well as in mandibular defects including the symphysis.

Craniofacial growth characteristics after bilateral fronto-orbital advancement in children with premature craniosynostosis

The standardized bilateral fronto-orbital advancement method of osteotomy established at the University of Wuerzburg is applied in all forms of craniosynostosis except scaphocephalus. The intention behind early operation is to halt progression of the disorder and to institute the physiological direction that growth should take. The preoperative severity of the disorder, the particular symptoms of the various malformations concerned, and the postoperative course of growth were analyzed and assessed both clinically and cephalometrically using the retrospective evaluations of the file data of 131 children with various forms of craniosynostosis. In contrast to linear craniectomy and so-called lateral canthal advancement, which have sometimes been thought to lead to undesirable postoperative growth development, only 11 relapses requiring renewed operation were found postoperatively in our own study of 131 children. It became evident that the greater the severity of the malformation, the more probable it was that a relapse would occur. Fronto-orbital advancement can only affect the pathologic growth pattern to a limited degree, especially when craniosynostosis is related to a syndrome. Cephalometric evaluation confirmed the limited potential for growth in the area of the anterior skull base and in the mid-face in the presence of syndrome-related brachycephaly and severe facio-craniosynostoses. In such clinical cases, compensatory growth of maxillary hypoplasia cannot be expected after fronto-orbital advancement.

Orale Rehabilitation von Tumorpatienten mit enossalen Implantaten

Zusammenfassung Im Rahmen einer prospektiven Studie sollte der Einfluß des Zustands der periimplantaren Hart- und Weichgewebe auf den Implantationserfolg bei Tumorpatienten untersucht werden. Aus 59 Tumorpatienten, die zwischen Juli 1988 und August 1996 mit 261 Implantaten versorgt worden waren, wurde ein Zielkollektiv von 23 Patienten mit 99 Implantaten ermittelt, die mindestens 1 Jahr prothetisch versorgt waren. 18 dieser Patienten litten an einem Plattenepithelkarzinom der Mundhöhle. 17 Patienten wurden präoperativ mit einer Dosis von 40 Gy radiiert. 68 von 99 Implantaten standen in zur Unterkieferrekonstruktion transplantiertem autologem Knochen. Zur Beurteilung der periimplantären Hart- und Weichgewebssituation wurden der Hygieneindex, der Sulcusblutungsindex, der Gingivaindex, die parodontale Sondierungstiefe, der periimplantäre Knochenabbau und das Dämpfungsverhalten der Implantate herangezogen. Das Kollektiv der Tumorpatienten wurde mit einem Kollektiv gesunder Implantatpatienten verglichen. Tumorpatienten zeigten eine signifikant schlechtere Situation bezüglich der erhobenen periimplantären Parameter als gesunde Implantatpatienten. Ein signifikanter Einfluß auf den Implantationserfolg konnte nur für die periimplantäre Taschentiefe nachgewiesen werden. Im Zielkollektiv lag die Erfolgsquote bei 77,8%. Summary In a prospective study, the influence of the status of the peri-implant hard and soft tissues on the success of enosseous dental implants in tumor patients was assessed. Out of 59 tumor patients with 261 implants, treated between July 1988 and August 1996, a pool of 23 patients with 99 implants provided with dentures for at least 1 year was obtained. Eighteen of these patients suffered from a squamous cell carcinoma of the oral cavity. Seventeen patients underwent preoperative radiation (40 Gy). A total of 68 out of 99 implants were inserted into autologous bone transplanted to reconstruct the mandible. In order to assess the peri-implant hard and soft tissues, the Hygiene Index, the Sulcus Bleeding Index, the Gingiva Index, the pocket-probing depth, the peri-implant bone resorption, and the periotest were used. The results in the tumor patients were compared with the results in a pool of nontumor patients. Tumor patients had significantly worse peri-implant parameters than nontumor patients. The peri-implant pocket-probing depth proved to have significant influence on the success rate. The overall success rate was 77.8%.In a prospective study, the influence of the status of the peri-implant hard and soft tissues on the success of enosseous dental implants in tumor patients was assessed. Out of 59 tumor patients with 261 implants, treated between July 1988 and August 1996, a pool of 23 patients with 99 implants provided with dentures for at least 1 year was obtained. Eighteen of these patients suffered from a squamous cell carcinoma of the oral cavity. Seventeen patients underwent preoperative radiation (40 Gy). A total of 68 out of 99 implants were inserted into autologous bone transplanted to reconstruct the mandible. In order to assess the peri-implant hard and soft tissues, the Hygiene Index, the Sulcus Bleeding Index, the Gingiva Index, the pocket-probing depth. the peri-implant bone resorption, and the periotest were used. The results in the tumor patients were compared with the results in a pool of nontumor patients. Tumor patients had significantly worse periimplant parameters than nontumor patients. The peri-implant pocket-probing depth proved to have significant influence on the success rate. The overall success rate was 77.8%.