Hubertus Spiekermann

Impact of rhBMP-2 on regeneration of buccal alveolar defects during the osseointegration of transgingival inserted implants

OBJECTIVE New approaches to enhance vertical bone regeneration in clinically relevant implant models are needed. Therefore, we analyzed the impact of recombinant human bone morphogenic protein 2 (rhBMP-2) on the healing of large buccal alveolar defects during osseointegration of transgingivally inserted implants. STUDY DESIGN Twenty-four dental implants were inserted transgingivally in the mandibles of 6 labrador/golden retriever cross-bred dogs. Before implantation, a standardized buccal bone defect was created and refilled with either calcium phosphate as a carrier containing rhBMP-2 or calcium phosphate alone. Either ceramic abutments that enabled immediate implant loading or healing distance collars to prevent loading were mounted. Sixteen weeks after intervention, bone implant units were analyzed by radiofrequency analysis and histomorphometry. RESULTS In total, 14 implants (58.3%) were available for further analysis. The mean depth of the bone defects, the gain of regenerated bone, the vertical osseointegration of the implants, and the bone-to-implant contact in the newly formed bone were slightly greater in the rhBMP-2-containing samples. In contrast, the osseointegration in the preexisting bone was even superior within the non-rhBMP-2-treated specimen. However no differences were statistically significant. CONCLUSIONS When rhBMP-2-conducted bone regeneration was compared with control samples, no significant differences of newly formed bone were found at the bone-implant interface. The amounts of rhBMP-2 applied do not seem suitable to enhance implant osseointegration in large buccal defects.

Computer aided prediction and control of shrinkage porosity in titanium dental castings

OBJECTIVES The main objectives were to investigate the possibility and reliability of quantitative prediction and control of the concentrated shrinkage porosity (macroporosity) in titanium dental castings by means of a numerical simulation technique; and finally to optimize the filling and feeding system design for dental castings. METHODS A commercial software, MAGMASOFT (Giessereitechnologie GmbH, Germany), was employed to simulate the mold filling and solidification process, and predict the shrinkage tendency in a sample dental casting, two simplified tooth crowns with a connector bar between them. The numerically predicted shrinkages were compared with the experimental results. The experiments were carried out on a centrifugal casting machine. The same geometric and processing parameters of the casting as in the simulations were strictly controlled. RESULTS The computer predicted shrinkage porosity coincided with the performed experiments, demonstrating the reliability of the numerical model and the thermal physical data chosen for the calculations. Based on the above numerical model, several filling and feeding systems for the same casting were numerically simulated and compared. Finally an optimized design for this sample casting was proposed, and porosity-free castings were obtained. SIGNIFICANCE It was expected that the numerical simulation technique could be further developed for dental laboratories to aid the real dental casting design.

Numerical study of porosity in titanium dental castings

A commercial software package, MAGMASOFT (MAGMA Giessereitechnologie GmbH, Aachen, Germany), was used to study shrinkage and gas porosity in titanium dental castings. A geometrical model for two simplified tooth crowns connected by a connector bar was created. Both mold filling and solidification of this casting model were numerically simulated. Shrinkage porosity was quantitatively predicted by means of a built-in feeding criterion. The risk of gas pore formation was investigated using the numerical filling and solidification results. The results of the numerical simulations were compared with experiments, which were carried out on a centrifugal casting machine with an investment block mold. The block mold was made of SiO2 based slurry with a 1 mm thick Zr2 face coat to reduce metal–mold reactions. Both melting and casting were carried out under protective argon (40 kPa). The finished castings were sectioned and the shrinkage porosity determined. The experimentally determined shrinkage porosity coincided with the predicted numerical simulation results. No apparent gas porosity was found in these model castings. Several running and gating systems for the above model casting were numerically simulated. An optimized running and gating system design was then experimentally cast, which resulted in porosity-free castings.

Anterior disk displacement of the temporomandibular joint

SummaryIn order to examine the diagnostic significance of typical clinical symptoms in temporomandibular joint (TMJ) disorders for diagnosis of anterior disk displacement, clinical findings were compared with the degree of disk displacement in 84 TMJs of 59 patients with TMJ disorders, who were examined clinically and by means of magnetic resonance imaging (MRI). The control group consisted of 31 subjects with no TMJ symptoms. No significant correlation between the degree of anterior disk displacement and palpation pain of the masticatory muscles or clicking/crepitus of the TMJ could be found. Joint clicking was observed in 65% of patients with TMJ symptoms in normal disk position (NDP). The percentage of joint clicking was almost the same in patients with anterior disk displacement with reposition (ADWR) (68%). There were significant correlations between active mouth opening and disk position as well as between a history of pain and disk position. Patients with NDP and ADWR had almost identical mouth opening values: 48 (±5) mm and 46 (±5) mm respectively. In contrast to these groups the mean values decreased significantly to 42 (±6) mm in patients with anterior disk displacement without reposition (ADWOR). There were no significant correlations between occlusal findings (centric relation and habitual relation, early occlusal contacts, abrasion facets) and disk position when viewed either collectively or individually.ZusammenfassungZur Überprüfung der Wertigkeit typisch klinischer Symptome für Funktionsstörungen zur Diagnose von Diskusverlagerungen wurden 84 Kiefergelenke von 59 Patienten mit Funktionsstörungen und 31 Kiefergelenke von klinisch asymptomatischen Probanden mittels Magnetresonanztomographie (MRT) untersucht und die einzelnen klinischen Befunde der Art der Diskusvergerung gegenübergestellt. Zwischen dem Grad der anterioren Diskusverlagerung und einem positiven Palpationsbefund der Kaumuskulatur, einem Palpationsschmerz der Kiefergelenke und dem Auftreten von Gelenkgeräuschen ergaben sich keine signifikanten Beziehungen. Bei funktionsgestörten Patienten zeigte sich mit 65% bei normaler Diskusposition (NDP) fast ebenso oft ein Gelenkknacken wie bei Patienten mit anteriorer Diskusverlagerung mit Reposition (VMR, 68%). Signifikante Beziehungen bestanden zwischen aktiver Mundöffnung und Diskusposition sowie anamnestisch angegebenen Schmerzen und Diskusposition. Während bei NDP- und VMR-Patienten mit 48 (±5) mm und 46 (±5) mm ähnlich hohe Mundöffnungswerte vorlagen, nahmen diese bei Patienten mit anteriorer Diskusverlagerung ohne Reposition (VOR) auf 42 (±6) mm signifikant ab. Okklusale Befunde (Differenz zwischen zentrischer und habitueller Okklusion >2 mm, vorzeitige okklusale Kontakte, Auftreten von Schliffacetten) zeigten in ihrer Gesamtheit wie auch in der Einzelbetrachtung keine signifikanten Beziehungen zur Diskusposition. Die Ergebnisse zeigen, daß für die Diagnostik von Funktionsstörungen allgemein als bedeutend anerkannte klinische Symptome in bezug auf die Art und das Vorliegen einer anterioren Diskusverlagerung allein keine sichere Aussage zulassen. Dies betrifft besonders die anteriore Diskusverlagerung ohne Reposition. Gleichzeitig wird die Zuverlässigkeit der MRT für die klinisch oft schwierige Diagnostik der Bestimmung der Diskusverlagerung bei Patienten mit Funktionsstörungen des Kausystems bestätigt.

Numerical simulation of the casting process of titanium tooth crowns and bridges

The objectives of this paper were to simulate the casting process of titanium tooth crowns and bridges; to predict and control porosity defect. A casting simulation software, MAGMASOFT, was used. The geometry of the crowns with fine details of the occlusal surface were digitized by means of laser measuring technique, then converted and read in the simulation software. Both mold filling and solidification were simulated, the shrinkage porosity was predicted by a “feeding criterion”, and the gas pore sensitivity was studied based on the mold filling and solidification simulations. Two types of dental prostheses (a single-crown casting and a three-unit-bridge) with various sprue designs were numerically “poured”, and only one optimal design for each prosthesis was recommended for real casting trial. With the numerically optimized design, real titanium dental prostheses (five replicas for each) were made on a centrifugal casting machine. All the castings endured radiographic examination, and no porosity was detected in the cast prostheses. It indicates that the numerical simulation is an efficient tool for dental casting design and porosity control.