Meyer, Ulrich

Purpose: The aim of this study was to determine the possibility and extent of artifact reduction by an optimized use of cone beam computed tomography (CBCT) parameter configuration (geometric resolution, implant geometric parameters, and image analyses). It furthermore sought to determine the distance from correctly reproduced bone tissue to an implant, where the grayscale values are equal to the pre-implantation values. Materials and Methods: Titanium implants were inserted into pig tibia under standardized conditions. CBCT investigations in the form of bone density mapping were performed under various CBCT settings and implantation situations. The circumference of the implants was measured in order to determine the extent of metal artifacts. This was done by determining grayscale and comparing it to the bone area prior to implantation. Results: Using CBCT to determine bone density postimplantation showed a correlation in dependence of CBCT parameter configuration. Higher resolution led to a better detection of correct bone density values in the peri-implant region. Normal bone density values can be recognized at a distance of 370 μm from the implant surface, when the spatial resolution is 125 μm. Therefore, higher resolution in CBCT is accompanied by an improved bone detection in peri-implant bone, despite the presence of metal artifacts. Peri-implant bone defects that extend 400 μm around implants were reliably detected by using a spatial resolution of 125 μm. In specimens, where multiple implants are present in one line, pronounced artifact formations were present. The artifacts were visible as a combination of streak-like hardening and extinction effects. Conclusion: Bone geometric data and density values may be determined correctly in close proximity to the implant surface, and can detect peri-implant bone defects. When multiple implants are placed, the implant radiation direction geometry must be considered. Keywords: CBCT, grayscale, implant, metal artifact, peri-implant defects, spatial resolution

Over the last few decades, reconstructive surgery has shifted from a resection-oriented approach toward strategies focusing on repair and regeneration of tissues. As the main aim of maxillofacial reconstruction has been the restoration of bone form and function, surgeons used artificial tissue substitutes in the early decades of bone reconstruction. These artificial materials significantly improved the ability of surgeons to restore the form and, to some extent, the function of defective bones. Despite the fact that every artificial material has specific disadvantages, the use of biomaterials is a common treatment option in clinical practice even today. Due to the more detailed understanding that exists concerning transplantation of cells and tissues, autogenous grafts are the second mainstay in clinical practice. However, the main disadvantage of using autogenous grafts is donor site morbidity and donor shortage. Research is currently in progress into the use of cell-based approaches in reconstructive surgery, since cells are the driving elements for all repair and regeneration processes. Various cell populations have been reported on in the relevant literature. These cells can be classified according to differentiation capacity and the tissue from which they originated. In this review, unrestricted cells, multipotential progenitor cells, determined cells, and genetically modified cells are described systematically, and their advantages as well as limitations are discussed. (More than 50 references.) Keywords: alveolar process, dental esthetics, dental implants, facial growth, jawbone, orthodontics, puberty

Cell-based bone tissue engineering is a rapidly evolving therapy option in bone reconstruction strategies. Some cell-driven approaches, especially the biophysical stimulation of the host cell population surrounded by the bone defect, are common treatment methods in maxillofacial surgery. Others, such as autologous cell implantation, have now gained acceptance for clinical trials. More advanced or complex therapeutical options (extracorporeal tissue engineering, stem cell use, genetic engineering) have been tested in preclinical investigations but have not reached the level of clinical use. Two different aspects are of special relevance in cell-based bone reconstruction therapies. The source of cells used to regenerate bone (discussed in detail in a complementary review in this issue of The International Journal of Oral and Maxillofacial Implants) as well as the principal approach of a cell-driven bone regeneration therapy influence the outcome of such engineering strategies. All of the cell-driven repair strategies are under intensive investigation in an effort to provide surgeons with a limitless supply of tissue for bone repair and reconstruction in future procedures. An overview of the basic biological aspects as well as the inherent constraints of different cell-based approaches are given in this paper. (More than 50 references.) Keywords: alveolar process, dental esthetics, dental implants, facial growth, jawbone, orthodontics, puberty

Purpose: Computer-aided technologies have been recently employed for use in extracorporeal bone tissue engineering strategies. In this pilot animal experimental study, the intention was to test whether autologous osteoblast-like cells cultured in vitro on individualized scaffolds can be used to support bone regeneration in a clinical environment. Materials and Methods: For this purpose, mandibular bone defects were surgically introduced into the mandibles of minipigs and the scaffold of the defect site was modeled by computer-aided design/computer-aided manufacturing technique. Autologous bone cells from porcine calvaria were harvested from minipigs and grown in culture. Cells were seeded on scaffolds generated by rapid prototyping of polylactic acid/polyglycolic acid copolymers. The defects were then reconstructed by implanting the tissue constructs. Results: The intraoperative sites as well as the postoperative computerized tomographic scans demonstrated an accurate fit in the defect sites. The implanted scaffold constructs enriched with osteoblast-like cells were well tolerated and appeared to support bone formation, as revealed by histologic and immunohistochemical analyses. Discussion: These results indicated that in vitro expanded osteoblast-like cells spread on a resorbable individualized scaffold can be capable of promoting the repair of bony defects in vivo. Conclusion: These results warrant further attempts to combine computer modeling and tissue engineering for use in bone reconstructive surgery. Keywords: animal model, bioengineering, bone, osteoblasts

Es wird eine innovative Leistungserweiterung im Bereich Einzelkronenfertigung vorgestellt. In Form und Farbschichtung präfabrizierte Kronenrohlinge werden mit einer speziell entwickelten Software in die Zahnreihe integriert und mit einem CAM-Schleifprogramm apikal an den Stumpf angepasst. Eine rationelle Art der digitalen Kronenherstellung mit guten Ergebnissen. Keywords: Präfabrizierte Kronenrohlinge, Halbzeug, CAD/CAM-Krone, Kunststoffmantelkrone, schichtungsbedingte, ästhetische Wirkung

An innovative extension of performance in the area of single crown production is presented. Prefabricated crown blanks with color layering are inserted in the row of teeth with specially developed software and adapted apically to the stump with a CAM milling program. Keywords: prefabricated crown blanks, semi-finished product, CAD/CAM crown, plastic jacket crown, layering-induced esthetic effect, Cerec, inLab

Die chirurgische Aufbereitungstechnik dient dazu, bei der Insertion von dentalen Implantaten eine möglichst stabile und somit feste Implantatverankerung zu erzielen. Verschiedene Techniken erlauben eine Vorbehandlung des Implantatlagers, um die primäre Implantatstabilität zu erhöhen. Ziel dieser Studie war es, die Implantatstabilität zu verschiedenen Zeitpunkten und nach unterschiedlicher Vorbehandlung des Knochenlagers im Tiermodell zu evaluieren. Dazu wurden bei insgesamt acht Göttinger Minischweinen 84 Schraubenimplantate (ITI, Durchmesser: 4,1 cm, SLA, Länge: 10 mm) in die rechten und linken Tibiakondylen inseriert. Die Vorbereitung des Implantatlagers erfolgte durch Bohren oder Knochenkondensation. Ausgewertet wurde die Implantatfestigkeit nach sieben und 28 Tagen durch Ausdrehversuche und Histologie (Trenndünnschliff). Die mechanische Festigkeit (Ausdrehversuch) war nach konventioneller Aufbereitungstechnik (Bohren) signifikant größer als nach Knochenkondensation (p > 0,001). Am siebenten Tag konnten im histologischen Bild Mikrofrakturen nachgewiesen werden. Durch die Aufbereitung des Implantatlagers mit Knochenkondensoren wurden Mikrofrakturen verursacht, die zu einer signifikanten Abnahme der biomechanischen Primärstabilität führten. Keywords: Implantatstabilität, Sofortbelastung, Biomechanik, Knochenkondensation

Purpose: The treatment of patients with early or immediately loaded dental implants has renewed interest in the behavior of osteoblasts at the implant surface under load. A newly designed dental implant indicated for immediate loading was tested in vivo for early stages of osteoblast behavior at the implant surface. Materials and Methods: Thirty-two implants were placed in the mandibles of 8 minipigs. Half of the implants (n = 16) were immediately loaded under occlusal contacts, and implants placed in non-occlusal relations served as a control. Results: All implants, except 1 that showed signs of tissue infection, healed uneventfully and were stable throughout the experimental period. Ultrastructural analysis of mandibular specimens revealed an intimate attachment of osteoblasts to the material surface beginning as early as day 1. Application of either occlusal or non-occlusal load did not alter the phenotypic morphology of the attached osteoblasts. Transmission electron microscopy and x-ray diffraction analysis demonstrated a direct contact of bone-like minerals over the whole implant surface with no signs of crestal hard tissue alteration. Electron diffraction analysis showed a slight release of titanium from the implant side. Discussion: These results indicate that immediate loading of specially designed dental implants can be performed without disruption of the titanium/bone interface or disturbance of osteoblast physiology in the early loading phase. Conclusion: Immediate loading protocols can be performed without disturbance of normal bone biology.