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Biomedical subjects

H Pistner

Publications and source records attributed to H Pistner.

At least 37 records · Page 2Linked to original sources
PubMed1997

[Osteosynthesis after sagittal division of the mandible. Biomechanical stability of various methods in a pig mandibular model].

Forty years after the introduction of sagittal split osteotomy for transposition of the mandible according to Obwegeser, very different procedures for osteosynthesis are still discussed and practised. In a simple biomechanical model in the porcine mandible, five different methods for osteosynthesis using metallic screws (titanium, cobalt-chromium-molybdenum alloy) and one using a polymer screw (polylactic acid-copolymer blend), as well as the use of miniplates, were studied with regard to the stability of the compound. The Kruskal-Wallis H-test (variance analysis by ranks) showed statistically highly significant differences (P = 0.00017) regarding maximum stability. Osteosynthesis by miniplates was very stable with regard to the maximum load (Fmax = 234 N +/- 47), but not so in terms of three-dimensional stability of the osteosynthesis itself. The highest stability of osteosynthesis with screws only (Fmax = 183 N +/- 65) was found for a 2.7-mm titanium screw in triangular geometry. The use of 2.7-mm cobalt-chromium-molybdenum screws (Fmax = 173 N +/- 42) and 3.5-mm titanium screws (Fmax = 160 N +/- 76) did not make an statistical difference (P = 0.37). The mechanical values of 2.0-mm titanium screws in linear (Fmax = 113 N +/- 37) or triangular (Fmax = 136 N +/- 62) geometry and of 3.5-mm polylactic acid-copolymer blend screws (Fmax = 121 N +/- 33) did not differ statistically from each other (P = 0.75) but they did from the previous group (P = 0.019). In consideration of the low biting forces following sagittal split osteotomy, all tested procedures of osteosynthesis meet the mechanical requirements for clinical practice.

Animals↗
PubMed1997

[Interventions for improving the facial profile with osteoinductive bone implants].

Osteoinductive bone allografts (autolyzed, antigen-extracted, allogeneic bone; AAA bone) were implanted in 207 cases. The patients had plastic surgery procedures to improve their profiles and were followed up for a maximum of 72 months. Twenty-two patients had an asymmetric mandible corrected with AAA bone chips. In 14 cases AAA bone implants were used for genioplasties. Forehead defects were reconstructed in 20 patients using AAA bone. Hypoplasia of the midface was corrected in 88 cases by augmentations with AAA bone chips or powder. A total of 63 patients underwent rhinoplasties in which AAA bone chips were used to shape or erect the dorsum nasi. Patient follow-up and reoperations to remove the osteosynthesis material revealed that the AAA bone implants were remodeled in the patients' own bone within several months. Less than 3% of the AAA bone implants were lost due to local infections. Except for rhinoplasties, secondary resorption of the bone allografts was extremely low. However, in cases in which strong tension resulted from scar formation or from lack of soft tissue, considerable resorption was observed, especially when AAA bone was implanted in the nose (25% of the rhinoplasties). On the other hand, this biodynamic behavior protected the implants from soft tissue perforation. In summary, AAA bone implants represent a convenient alternative to bone autografts in recipient beds with strong regenerative capacity. Since they are remodeled into the patient's bone none of the late complications found with alloplastic implants need to be expected.

Adolescent↗
PubMed1997

[Rhinoplasty using the coronal approach after extensive facial skull fractures].

Functional, aesthetically perfect restoration of the face of patients suffering from a severely smashed facial skeleton requires exact centrifugal repositioning and miniplate osteosynthesis of all bony fragments. Nevertheless, the original height and form of the nose will not be restored with these means in some cases. Therefore, in 23 cases with shattered noses out of 487 midface-trauma patients in the years 1990-1995 the noses were onlay-grafted as the primary procedure in 9 cases via the coronal approach and as the secondary one when the metal plates were removed in 10 cases. A combination of primary and secondary procedures was done in 4 cases. Five times autogenous bone from outer calvarium was used and 22 times allogenic, conserved bone from organ donors (AAA bone). According to extent of the damage, mini-screws and/or mini-plates served to fixate the graft. In addition to the group of 13 patients in the years 1990-1993 with nasal bone grafts via the coronary approach, another group the same size with the same amount of trauma but without rhinoplasty was defined and compared to the first group. An aesthetic analysis was done by grading the results according to simple criteria from 0 to 6 points by the patient and by the examiner. Noses grafted via the coronary approach were evaluated as being significantly (P = 0.004, t-test for independent samples, SPSS) better (2.1 points on average +/- 1.1 SD) than conventionally treated noses (3.5 points on average +/- 0.8 SD).

Bone Plates↗
PubMed1996

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

The standardized bilateral fronto-orbital advanced 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 pathological 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.

Cephalometry↗
PubMed1996

[Microcystic adnexal carcinoma of the skin. An underestimated tumor].

Microcystic adnexal carcinoma is a rare semimalignant cutaneous neoplasm characterised by slow but locally aggressive growth. Its histogenesis and nomenclature are still a subject of controversy. Under-recognition and the tumor's bland cytologic features lead to frequent misdiagnoses. In addition, subclinical tumour invasion explains the high incidence of local recurrence. Thus, the tumour makes great demands on the planning of its surgical removal. We report the case of an 81-year-old woman with a microcystic adnexal carcinoma of the lower lip, which was treated by micrographic surgery. On the basis of this case, differential diagnoses, histogenesis and micrographic surgery as the treatment of choice are discussed.

Aged↗
PubMed1996

[Treatment outcome and complications of surgical and conservative management of mandibular fractures].

Retrospective analysis of 712 patients with 1166 mandibular fractures and follow up-study of 374 patients with 593 fractures was performed for discrimination of differences in wound- and bone-healing as well as late results between operative and conservative fracture treatment. 46.1% (328) of all patients have been treated conservatively, 53.9% (384) have been treated by operation. The follow up was performed on 255 patients with operative fracture treatment and 119 patients with conservative treatment. In 3.0% of the operatively treated patients bacterial infections occurred, in comparison to 8.7% of conservatively treated patients. From the viewpoint of functional aspects, such as occlusion, articulation and mandibular movement as well as radiological signs in the fractured region patients after operative treatment have shown partly significantly better results during the follow up compared to the group of conservatively treated patients. Neurological testings of inferior alveolar nerve and mental nerve have shown significantly better results in the group of conservatively treated patients. Since the functional results are much better after operative treatment, osteosynthesis with miniplates should be performed if there are no contraindications. The more precise reconstruction and stabilization of the fragments shortens time of hospitalization and leads to sooner functionality of the mandible.

Bone Plates↗
PubMed1996

[Therapeutic concept in comminuted and defect fractures of the mandible].

Immediate live-saving emergency treatment of patients with heavily communited and partially defective mandibles by airway intubation, control of haemorhage and primary treatment of wounds necessarily must be followed by a staged concept of treatment for the functional and aesthetic rehabilitation of hard and soft tissue in order to enable the patient to survive not only biologically but also socially. Out of 384 patients with surgically treated mandibular fractures, 120 had multiple fractures, 24 heavily comminuted fractures and 6 sustained vast defects. All multiple and communited fractures could be treated successfully by an intraoral approach using function-orientated miniplate-osteosynthesis and in 30 cases functionally stable plates. In patients having sustained vast avulsions of soft and hard tissue, immediate emergency-revascularisation was well to the fore. In cases of tissue destruction, primarily the position of the jaw stumps was secured by plates and reconstruction was done in the early secondary stage using composed microvascularly transferred scapular flaps.

Adult↗
PubMed1995

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.

Aged↗
PubMed1995

[Comparative studies with apicoectomy using various surgical techniques and filling materials].

Follow-up examinations were made retrospectively on 799 apicoectomized teeth from a group of patients with a total of 3,524 apicectomies, the mean postoperative interval of observation being 4.2 years. An intraoperatively orthograde root-canal filling was performed in 51.3%, an intraoperatively retrograde in 23.7% and a preoperative filling in 25.0% of the patients. Apart from 126 teeth that had already been extracted, a further 160 teeth had been clinically and/or radiologically conspicuous, so that a total of 286 failures was to be recorded. The dentally related success graphs computed according to Kaplan and Meier (1958) showed a significantly worse success probability for the preoperative filling compared to the two other techniques. With regard to the different materials employed in orthograde application, the silver filling had a higher and the guttapercha filling a less favourable success quota compared to a titanium filling. Moreover, in the retrograde method, amalgam resulted in a significantly higher success probability than glass ionomer cement. With an attendant cyst there was a significantly improved success quota over apical parodontitis or a renewed operation. With regard to the localization of apicectomies, maxillary front teeth attained the highest success rate. The present results point unequivocally to an unfavourable outcome after preoperative endodontics and underscore the good prognosis of an intraoperatively orthograde filling. Due to the fact that biocompatibility is in the forefront today, time-tested materials, such as silver and amalgam, are clearly being used less.

Adult↗
PubMed1994

Poly(L-lactide): a long-term degradation study in vivo. Part II: Physico-mechanical behaviour of implants.

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 Young's 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.

Animals↗
PubMed1994

[Microsurgical scapula transplants for reconstruction of the facial skull--experiences with 44 patients].

Great versatility gives composed scapular flaps a particular significance for the reconstruction of defects in face and skull: According to individual requirements one up to five separate elements may be transferred with one vascular pedicle. Anatomical studies of 120 scapulas measured a mean length of 13.4 cm and a mean diameter of 1.2 cm of the lateral margin offering sufficient bone for most indications in the visceral skull. Up to three cutaneous flaps may cover nearly every defect in the head. 44 patients were treated in the years 1989 to 1993 using scapular flaps, most of them combinations consisting of bone and skin elements. In two patients a so called 4-in-1-flap was transferred including the latissimus-dorsi-flap. All donor sites could be closed primarily. Venous thrombosis caused one loss of a flap. Infections healed without sequelae. Medical gymnastics brought full rehabilitation of the donor site within 6 months.

Bone Transplantation↗
PubMed1994

[Temporomandibular joint reconstruction with free rib and iliac crest bone transplants].

From 1981-1992 we reconstructed the temporomandibular joint in 42 patients. In 33 cases reconstruction followed tumour resection of the mandible, almost advanced squamous cell carcinomas of the retromolar region. Primary reconstruction was made by an alloplastic condylar prosthesis combined with a plate for mandibular reconstruction. 2 years after first treatment secondary reconstruction followed by transplantation of a free iliac bone graft. In some cases a new condylus was formed using autogenous rib graft or allogenous cartilage. Result was adequate and painless oral aperture. For reconstruction after ankylosis, arthrosis or arthritis we use a autogenous costochondral graft. 9 patients received such treatment. In 5 or 9 cases with severe ankylosis we prefer a two-time-approach: after resection of the ankylosis we first fix an alloplastic implant (Palacos) at the skull base for distraction of the scar. Two or three years later we do secondary reconstruction with a costochondral graft. The final result strongly depends on functional postoperative treatment and the compliance of the patient.

Adolescent↗
PubMed1993

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.

Animals↗
PubMed1993

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.

Animals↗
PubMed1990

[Experience in mandibular fracture treatment with osteosynthesis during the growth period].

The experiences in the treatment of 19 fractures of the mandibular body in 14 children and 30 similar fractures in 23 adolescents are reported. The average hospitalization of the conventionally treated children lasted 19.5 days compared with 14.8 days in the osteosynthesized group, which originally suffered from heavier fracture dislocations. Intermaxillary fixation (IMf) was maintained for 23 days on an average in the conventionally treated and 14 days in the osteosynthesized children, where it was necessary only in 4 out of 7 cases. In 2 children an injury of dental roots of altogether three teeth had to be diagnosed by x-ray, probably caused by 7-mm-screws used earlier. In order to avoid injury of germs especially in the region of the canine, we are now using screws of a maximum length of 5 mm for miniplate osteosynthesis.

Adolescent↗