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Biomedical subjects

Georg Watzek

Publications and source records attributed to Georg Watzek.

47 records · Page 3Linked to original sources
PubMed2002

Three-dimensional finite element analysis of implant stability in the atrophic posterior maxilla: a mathematical study of the sinus floor augmentation.

Sinus lifting is performed with a variety of materials and techniques without a precise knowledge of the quantity of augmentation. This study based on three-dimensional finite element analysis was designed to show which surgical procedure and which amount of peri-implant packing yields the best bony support for dental implants. Eight 3D-FE models were used. Four modeled standard situations simulated quantitatively different packing situations produced by differences in surgical approach: i. no packing; ii. thin 1 mm bony sheath; iii. oblique subcomplete packing; iv. complete bony peri-implant packing up to the implant end. A fifth model compared a standard implant with a length of 13.5 mm and a diameter of 3.75 mm with a 7-mm-long and 5-mm-thick implant. In three additional models the stress response of the bone-implant system was evaluated in the absence of a cortical layer, thus simulating an extreme degree of maxillary atrophy. In all models the modeled implants were loaded at their points of emergence with an assumed force of 100 N. The vector of the loading force was inclined 30 degrees posteriorly relative to the implant axis and 30 degrees away from the sagittal plane. The bone-implant interface was assumed to be perfect simulating full osseointegration. The final evaluation of the FE models showed complete peri-implant packing to reduce displacements of the implant tip by 32% vs. no sheathing/packing. Van Mises' equivalent stresses were used to assess the stresses in both human bone and titanium alloy implants. The highest stress levels in bone were predicted for the case without sufficient implant sheathing. In the models with adequate bony implant support, intrabony stresses were generally reduced by up to - 40%. The structural stiffness of the bone-implant system increased with the extent of sinus floor elevation. The results indicate that more extensive peri-implant packing reduces implant displacement, intrabony stresses and stresses at the bone-implant interface.

Alveolar Ridge Augmentation↗
PubMed2002

[A clinical and histological study of Bio-Oss in combination with guided bone regeneration membrane technique].

OBJECTIVE: To evaluate the reliability of Bio-Oss particles as bone grafts in combination with membrane-technique. METHODS: 6 small biopsy specimens were retrieved without causing iatrogenic damage in 6 patients (implant sites). The Donath's hard tissue section and micro grinding technique was adopted, and Leval Laczko staining method was used. RESULTS: The histological results showed Bio-Oss particles were easily distinguished from the newly formed bone, but new bone was formed among different particles of Bio-Oss, no connective tissue was found. Intimate contact between newly formed bone and particles of the graft was present. CONCLUSIONS: Bio-Oss appears to be highly biocompatible and osteoconductive. It can be used success fully as a bone substitute in combination with guided bone regeneration membrane technique.

Adult↗
PubMedDate not supplied

BMP-6-induced osteogenic differentiation of mesenchymal cell lines is not modulated by sex steroids and resveratrol.

Bone morphogenetic protein-6 (BMP-6) is a potent inducer of osteogenic differentiation and its expression is stimulated by 17beta-estradiol. The existence of a regulatory loop between sex steroids and BMP-6 is therefore reasonable to hypothesize. Here we determined whether the sex steroids 17beta-estradiol and dihydrotestosterone, and the phytoestrogen resveratrol can modulate BMP-6-induced alkaline phosphatase activity and osteocalcin expression. Mesenchymal cells of murine (osteoblastic MC3T3-E1 cells, preadipogenic ST2 cells, prechondrogenic ATDC5 cell) and human origin (osteosarcoma SaOS and HOS cells, primary bone marrow stromal cells) were cultured in the presence of recombinant BMP-6 under serum-free conditions. BMP-6 dose-, and time-dependently increased alkaline phosphatase activity in murine cell lines, but not in human cells. Osteocalcin expression was also increased upon stimulation with BMP-6. The presence of 17beta-estradiol, dihydrotestosterone, and resveratrol had no effect on BMP-6-induced alkaline phosphatase activity and osteocalcin expression. These data suggest that osteogenic differentiation in response to BMP-6 occurs independent of steroid hormones and resveratrol in mesenchymal cells that express basal receptor levels.

Alkaline Phosphatase↗
PubMedDate not supplied

Bone marrow stromal cells can provide a local environment that favors migration and formation of tubular structures of endothelial cells.

Findings suggest that mesenchymal progenitor cells can support the process of blood vessel formation, which may be relevant during granulation tissue formation at defect sites. The aim of this study was to investigate possible mechanisms of the angiogenic process that can be stimulated by mesenchymal progenitor cells. In the in vivo-like model of the chick embryo chorioallantoic membrane assay, we observed blood vessel ingrowth into collagen sponges containing conditioned medium from undifferentiated bone marrow stromal cells. In the Boyden chamber assay, the conditioned medium was chemotactic for human umbilical vascular endothelial cells and human uterus microvascular endothelial cells, and when cells were placed on Matrigel-coated culture dishes, formation of tubular structures was enhanced. The presence of vascular endothelial growth factor-neutralizing antibodies did not affect the outcome of the two in vitro assays. Bone marrow stromal cell-conditioned medium had no effect on proliferation of endothelial cells, as determined by measuring [3H]thymidine incorporation, and on matrix metalloproteinase 2 expression, as evaluated by reverse transcription-polymerase chain reaction and gelatin zymography. These data indicate that mesenchymal progenitor cells can provide a local environment that supports the ingrowth of blood vessels into a defect site.

Adult↗
PubMedDate not supplied

Porous hydroxyapatite for grafting the maxillary sinus: a comparative histomorphometric study in sheep.

PURPOSE: This experimental study in adult female sheep examined the value of nonresorbable porous hydroxyapatite (HA) as a grafting material in a single-stage sinus-lift procedure. MATERIALS AND METHODS: Two titanium plasma-flame-sprayed cylindric implants were placed bilaterally in each of 54 sinuses in 27 adult female sheep. In 2 groups of 18 sinuses each, the subantral hollow space was filled with porous HA or autogenous cancellous bone harvested from the iliac crest, respectively. Eighteen sinuses were not augmented and served as controls. The time course of new bone formation and bone remodeling was evaluated by sequential polyfluorochrome labeling. Observation periods were 12, 16, and 26 weeks after the surgical procedure. Six sinuses per observation period and test group were available for histologic evaluation. RESULTS: All implants were osseointegrated in the local host bone. New bone formation was observed in a triangular area bounded by the implant surface, local buccal antral wall, and submucous connective tissue around all implants. The mean length of bone-implant contact was 3.9 +/- 0.3 mm in the control group, 5.7 +/- 0.3 mm in the autogenous bone group, and 5.9 +/- 0.3 mm in the group augmented with porous HA. During the observation period, the relative length of direct bone-implant contact increased from 20% to 25.1% in the control group, from 30.4% to 35.5% in the autogenous bone group, and from 29.8% to 41.7% in the HA group. At a distance of 1 mm from the implant, the mean bone volume was 29.7 +/- 15.7% in the autogenous bone group. In the group augmented with HA the mean bone volume was 11.2 +/- 13.0%. DISCUSSION: There was no significant difference between HA and autogenous bone regarding bone-implant contact (P = .89). CONCLUSIONS: Both groups showed a significantly greater bone-implant contact (HA: P = .002; autogenous bone: P = .0005) than the empty control group. However, since the results varied widely, the use of HA alone for sinus grafting should be used with discretion in sinus-lift procedures.

Alveolar Ridge Augmentation↗
PubMedDate not supplied

Influence of platelet-rich plasma on osseous healing of dental implants: a histologic and histomorphometric study in minipigs.

PURPOSE: In the present study the time course of local bone formation following the application of PRP during implant placement was evaluated histomorphometrically and histologically. MATERIALS AND METHODS: The mandibular premolars of 12 adult minipigs were removed surgically and 72 sites were prepared for implant placement. Before the implants (MK III, Replace, and MK III TiUnite) were placed, autogenous PRP (8 x 10(5) to 10 x 10(5) platelets/microL) was instilled into the host sites on the left side. The animals were sacrificed at 3, 6, and 12 weeks, and undecalcified ground sections were prepared. RESULTS: The histomorphometric evaluation showed significantly more bone-to-implant contact after topical PRP application in the early healing phase (6 weeks), which varied as a function of the distance from the implant surface (controls = 24.2% versus PRP = 44.21%; P = .013). At 12 weeks, the extent of osteoneogenesis was comparable in the 2 groups (controls = 51.3% versus PRP = 44.2%; P = .251). Statistical analysis revealed no significant interaction between implant surface type and PRP. DISCUSSION: Topical PRP application significantly increased the activity of bone regeneration at implant host sites during early healing. CONCLUSION: In the present study PRP was found to have a time- and site-dependent effect on peri-implant bone healing.

Analysis of Variance↗
PubMedDate not supplied

Enhanced bone-to-implant contact by platelet-released growth factors in mandibular cortical bone: a histomorphometric study in minipigs.

PURPOSE: To determine the effects of platelet-released growth factors (PRGF) on bone-to-implant contact (BIC) in minipig cortical bone. MATERIALS AND METHODS: In each of 8 adult minipigs, 2 implants were placed in the facial wall of the mandible, one implant with and one without PRGF. PRGF was defined as the supernatant from washed, thrombin-activated, allogenic, platelet-rich plasma cells obtained after centrifugation. Four animals were sacrificed at 4 weeks, and the remaining 4 were sacrificed at 8 weeks. For histomorphometric analyses, undecalcified ground specimens were prepared and stained with the Levai-Laczko stain. RESULTS: For the entire follow-up time, 55.30% BIC was found with PRGF versus 38.91% without PRGF (P = .0198). At 4 weeks, BIC was 44.20% with PRGF versus 29.62% without PRGF (P = .0632), and at 8 weeks there was 70.36% BIC with PRGF versus 48.20% without PRGF (P = .1221). DISCUSSION: Growth factors and other molecules released upon activation of platelet-rich plasma cells can enhance implant anchorage in cortical bone. PRGF obtained from allogenic sources does not impair healing. CONCLUSION: The results indicated that a single application of PRGF before implant placement can be sufficient to increase the percent BIC in minipig cortical bone.

Animals↗
PubMedDate not supplied

Rotational panoramic versus intraoral rectangular radiographs for evaluation of peri-implant bone loss in the anterior atrophic mandible.

PURPOSE: In patients with atrophic mandibles, elevation of the floor of the mouth often prevents intraoral rectangular radiography for longitudinal follow-up studies, while extraoral techniques such as panoramic radiographs tend to produce distorted views of the interforaminal region. In this study, intraoral rectangular radiographs and panoramic radiographs were compared for their accuracy in evaluating peri-implant bone loss. MATERIALS AND METHODS: In a recall program, 22 patients with 88 screw-type implants (44 MKII and 44 Frios) were followed. Interforaminal marginal bone loss was evaluated by extraoral orthopantomograms and by intraoral rectangular radiographs. In addition, pocket depth, Periotest readings, and bleeding on probing were recorded. For statistical analysis, the Spearman coefficient of correlation was used. The effects on bone loss and clinical variables were computed with a mixed model and the Bland and Altman method. RESULTS: Computed as least square means, the mean difference between panoramic radiographs (2.4 +/- 0.2 mm for MKII implants and 1.6 +/- 0.2 mm for Frios implants) and intraoral radiographs (2.6 +/- 0.2 mm and 1.4 +/- 0.2 mm, respectively) was 0.2 mm (range, 0.1 to 0.8 mm). DISCUSSION: In this study, the 2 imaging techniques were comparable clinically in terms of the precision with which they could be used to measure marginal bone loss. CONCLUSION: For highly atrophic mandibles with unfavorable imaging conditions, rotational panoramic radiographs can be a useful alternative to intraoral small-format radiographs for evaluating peri-implant bone loss.

Adult↗
PubMedDate not supplied

Radiologic follow-up of peri-implant bone loss around machine-surfaced and rough-surfaced interforaminal implants in the mandible functionally loaded for 3 to 7 years.

PURPOSE: In this retrospective study, marginal peri-implant bone height around machined and sandblasted/acid-etched interforaminal implants in the mandible was evaluated radiologically at least 3 years after functional loading. MATERIALS AND METHODS: Fifty-one patients, each with 4 interforaminal screw-type implants placed between 1994 and 1998, were included in this study. Of these, 36 patients (70.6%) with a total of 144 implants (76 machined Mk II implants and 68 sandblasted/acidetched Frios implants) were available for follow-up studies. Interforaminal marginal bone loss was evaluated by extraoral rotational panoramic radiographs. In addition, predictive factors such as patient age and sex, nicotine use, implant position, implant life, and site of measurement were recorded, as well as bone loss at surgery (ie, baseline bone loss). Analysis of covariance for repeated measurements was used for statistical analysis. Between-group differences were expressed as least square means +/- standard error. RESULTS: Sandblasted/acid-etched implants showed significantly less marginal bone loss than machine-surfaced implants (2.4 +/- 0.23 mm vs 1.64 +/- 0.27 mm). Implants placed in the anterior of the arch showed significantly more peri-implant bone loss than implants placed in the posterior (P = .0001). DISCUSSION AND CONCLUSIONS: Significantly less long-term peri-implant bone loss was observed for rough implant surfaces compared to machine-surfaced implants. However, it was also demonstrated that both types of implants, in combination with bar-supported overdentures, can produce excellent long-term results in the atrophic edentulous mandible. Mesially placed implants showed more bone resorption than distally positioned implants, independent of surface roughness.

Acid Etching, Dental↗
PubMedDate not supplied

Nasal cavity perforation by palatal implants: false-positive records on the lateral cephalogram.

PURPOSE: Lateral cephalometric films were examined for their validity as a tool for the postoperative evaluation of palatal implant placement. MATERIALS AND METHODS: Cephalometric and histometric data of 20 partially edentulous human cadaveric maxillae were compared. Lateral cephalograms of the specimens were made, and the palatal complex was pencil traced. In addition, low-dose dental computerized tomography (CT) scans were obtained from every specimen. Based on the CT data, palatal implants (Orthosystem; Institut Straumann, Waldenburg, Switzerland) were placed. Postimplantation, another lateral cephalometric film was recorded. The specimens were prepared for histologic examination. The preoperative tracings were superimposed on the postoperative cephalometric films. RESULTS: Of 20 implants placed, 12 were 4 mm long and 8 were 6 mm long. The distance between the cranial end of the implants and the nasal floor on microscopy ranged from 0.3 to 9.3 mm. Perforation of the nasal floor was absent throughout on intraoperative probing, while 2 implants projected beyond the nasal floor on histologic analysis of the specimens. An analysis of the superimposed pre- and postoperative cephalograms showed 5 implants projecting beyond the nasal floor. Histologically, only 1 of these projecting implants had actually caused perforation of the palatal complex. A comparison between the histometric and the cephalometric data showed that cephalometry, on average, imaged the palatal complex 0.8 mm below the actual anatomic site. DISCUSSION AND CONCLUSIONS: Twenty percent of palatal implants projecting beyond the nasal floor were false-positive records on the postoperative lateral cephalograms. Despite CT scans, 10% of the implants placed caused fenestration of the nasal cavity by histologic evidence. If the palatal complex was perforated, intraoperative probing with a periodontal probe did not confirm the perforation. Bone perforations up to 1.3 mm did not necessarily result in frank perforation of the nasal mucosa. Two-dimensional images could not be related to actual penetrations into the nasal cavity.

Adult↗