Purpose: The aim of this study was to investigate the effects of tightening torque, screw head angle, and thread number on the preload force of abutment screws. Materials and Methods: The test specimens consisted of three self-manufactured components (ie, a thread sleeve serving as an implant analog, an abutment analog, and an abutment screw). The abutment screws were fabricated with metric M1.6 external threads. The thread number varied between one and seven threads. The screw head angles were produced in eight varying angles (30 to 180 degrees). A sensor unit simultaneously measured the preload force of the screw and the torsion moment inside the screw shank. The tightening of the screw with the torque wrench was performed in five steps (15 to 35 Ncm). The torque wrench was calibrated before each step. Results: Only the tightening torque and screw head angle affected the resulting preload force of the implant-abutment connection. The thread number had no effect. There was an approximately linear correlation between tightening torque and preload force. Conclusion: The tightening torque and screw head angle were the only study parameters that affected the resulting preload force of the abutment screw. The results obtained from this experiment are valid only for a single torque condition. Further investigations are needed that analyze other parameters that affect preload force. Once these parameters are known, it will add value for a strong, but detachable connection between the implant and abutment. Short implants and flat-to-flat connections especially will benefit significantly from this knowledge. Keywords: abutment, abutment screw, abutment screw configuration, dental implant, preload force, thread pitch

Purpose: This study aimed to test bacterial microleakage at the implant-abutment interface (IAI) before and after dynamic loading using a new chewing simulation. Materials and Methods: Fourteen implant systems (n = 5 samples of each) were divided into two groups: (1) systems with conical implant-abutment connections (IACs), and (2) systems with flat IACs. For collecting samples without abutment disconnection, channels (Ø = 0.3 mm) were drilled into implants perpendicularly to their axes, and stainless-steel cannulas were adhesively glued inside these channels to allow a sterilized rinsing solution to enter the implant interior and to exit with potential contaminants for testing. Implants were embedded in epoxy resin matrices, which were supported by titanium cylinders with lateral openings for inward and outward cannulas. Abutments were tightened and then provided with vertically adjustable, threaded titanium balls, which were cemented using composite cement. Specimens were immersed in a bacterial liquid and after a contact time of 15 minutes, the implant interior was rinsed prior to chewing simulation (0 N ⩠ static seal testing). Specimens were exposed to a Frankfurt chewing simulator. Two hundred twenty force cycles per power level (110 in ± X-axis) were applied to simulate a daily masticatory load of 660 chewing cycles (equivalent to 1,200,000 cycles/5 years). The applied load was gradually increased from 0 N to a maximum load of 200 N in 25-N increments. The implant interior was rinsed to obtain samples before each new power level. All samples were tested using fluorescence microscopy; invading microorganisms could be counted and evaluated. Results: No bacterial contamination was detected under static loading conditions in both groups. After loading, bacterial contamination was detected in one sample from one specimen in group 1 and in two samples from two specimens in group 2. Conclusion: Controlled dynamic loading applied in this study simulated a clinical situation and enabled time-dependent analysis regarding the bacterial seal of different implant systems. Conical IACs offer a better bacterial seal compared with flat IACs, which showed increased microleakage after dynamic loading. IAC design plays a crucial role in terms of bacterial colonization. Taking samples of the implant interior without abutment disconnection eliminates an error source. Keywords: abutment disconnection, bacterial microleakage, chewing simulator, implant-abutment connection

Purpose: The aim of this study was to demonstrate the potential of microcomputed tomography (micro- CT) technology in the assessment of retrieved dental implants. Cases are presented to illustrate the value of micro-CT imaging techniques in determining possible mechanical causes for dental implant failures. Materials and Methods: Eight retrieved dental implants were randomly selected from a pool and imaged using a micro-CT device. Source voltages (80 to 100 kV) and source-to-detector distances (65 to 70 mm) were based on signal quality requirements with an additional criterion of achieving the highest resolution with the sample entirely in the field of view in the projection plane. One additional sample was chosen for histology and tomographic imaging so that the information contained therein could be compared. Results: The micro-CT images displayed high contrast between the implant, bone, and background, with negligible metal artifacts. The micro-CT technology used in this study delivered excellent images of the retrieved implants. As a result of the quality and resolution (pixel size: 5.52 to 6.15 μm) of the images, surface morphology as well as internal structures of the retrieved implants could be observed in great detail. The majority of the retrieved implants had increased wear, dents, pits, regular shallow scratches, and deep scratches in the implant-toabutment engagement area. Furthermore, plastic deformations, microcracks, and brittle implant fractures were observed in two implants. Conclusion: The mechanical competence of dental implant components plays a major role in the success of implant treatment. When failures do occur, a nondestructive three-dimensional assessment of such failed implants and their components is helpful in understanding the underlying factors. Micro-CT was found to be a useful tool for the morphologic assessment of retrieved dental implants. Keywords: dental implants, mechanical damage, microcomputed tomography, nondestructive imaging, retrieved implants

Aufgrund der engen anatomischen Raumbeziehungen und dem damit verbundenen Risiko einer Wurzelverletzung besteht beim interradikulären Einsatz von Minischrauben bis heute eine Zurückhaltung bei vielen Kollegen. Dieser Beitrag beschreibt die Auswahl geeigneter Alveolarabschnitte bezüglich des verfügbaren Knochenangebots und des geringstmöglichen Verletzungsrisikos sowie das mechanisch-physikalische Verhalten der Schraube bei einem Wurzelkontakt. Es erfolgt eine Bewertung der Wurzelverletzungen anhand einer aktuellen Literaturrecherche. Auf der Grundlage aktueller Forschungsarbeiten in der internationalen Literatur bezüglich des interradikulär verfügbaren sowie nötigen Knochens wurde das tatsächlich innerhalb der befestigten Gingiva erreichbare Knochenangebot durch Auswertung von CT-Datensätzen ermittelt. Da die Ergebnisse in Abhängigkeit des jeweiligen Interradikulärraumes eine versehentliche Wurzelverletzung als Komplikation möglich erscheinen lassen, wurde das Schraubenverhalten bei frontalem Eindrehen in die Wurzel sowie bei lateralem Kontakt untersucht. Basierend auf den technischen Anforderungen an die Schraubendimension und den anatomischen Sicherheitszonen zum Wurzelbereich, wurde eine interradikuläre Knochenbreite von mindestens 3,1 mm vorausgesetzt. In den Bereichen 4/5 und 5/6 beider Kiefer und zusätzlich 6/7 im Unterkiefer konnte vor dem Erreichen der Mukogingivallinie eine ausreichende Knochenmenge nachgewiesen werden. Alle anderen Areale zeigten das geforderte Knochenlager erst nach dem Überschreiten der Mukogingivallinie. Zudem scheint eine taktile Wahrnehmung von Wurzelberührungen bei manueller Insertion aufgrund des nur gering veränderten Insertionsmoments nicht gegeben. Die Durchsicht der aktuellen Literatur zeigt, dass Wurzelverletzungen innerhalb des Zements und Dentinmantels ohne Konsequenzen ausheilen und selbst tiefere Schädigungen bis in die Pulpa nicht zwangsläufig zu endodontischen Maßnahmen oder gar zum Zahnverlust führen. Keywords: Minischrauben/Miniimplantate, interradikuläre Insertion, Wurzelverletzungen, Sicherheitszonen, anatomische Richtlinien

In einer In-vitro-Studie wurde das dynamische Verhalten unterschiedlich konstruierter Implantat-Abutment-Verbindungen untersucht. Hierbei wurden die Abutments unter 30° mit einer Kraft von bis zu 200 N belastet. Der Kraftangriffspunkt war 8 mm von der Implantatplattform entfernt, die Anstiegsgeschwindigkeit der Kraft betrug 0,3 N/ms. Das Interface der Implantat-Abument-Verbindung wurde röntgenologisch mit einer Videokamera (1.000 Bilder/s) erfasst und vermessen. Die Ergebnisse zeigen, dass unter simulierten klinischen Bedingungen komplexe Mechanismen für die Entstehung oder das Ausbleiben von Mikrobewegungen verantwortlich sind. Sämtliche Implantat-Abutment-Verbindungen ohne Selbsthemmung weisen Mikrobewegungen auf (Implantatsysteme: SIC®, Replace Select®, Camlog®, XIVE®, Straumann-synOkta und -Fräszylinder®, Bego-Semados®, Straumann-Massivsekundärteil®). Bei präzise gefertigten Konusverbindungen mit Selbsthemmung (Implantatsysteme: Ankylos®, Astra Tech®) konnten keine Mikrobewegungen beobachtet werden. Die klinische Relevanz der Ergebnisse kann derzeit jedoch nur theoretisch abgeleitet werden. Vermutlich spielt der durch die Mikrobewegung verursachte Pumpeffekt eine entscheidende Rolle bei der krestalen Knochenresorption. Angenommen wird eine Kontamination des Knochens mit der im Implantat enthaltenen Flüssigkeit. Keywords: Implantat-Abutment-Verbindungen, Stoßverbindungen, Konusverbindungen, Kaubelastung, Kausimulator, Mikrobewegungen

Introduction and Objectives: Implant-abutment connections (IAV) show in vivo loosenings (L) and fractures (F) probably as a result of preceding micro movements (MM). The failure modes and their causes shall be evaluated. Material and method: 9 IAV types ∅ = (4-5 mm, n=8) were exposed to 106 cyclic loadings each, (100 N, 90° to the implant axis, at a distance of 8 mm from the IAV). In addition to this, the actual force on the IAV per cycle was measured. A computer-assisted sound analysis was used for the online detection of MM, L and F. For the analysis of L and F X-ray, REM and light microscopic photos were used. At the IAVs which remained intact, the was measured as well. (the moment of solve of the abutment was intended.) Results: Two IAV types didn't show any failure modes, but wear traces at the connection areas as can be proved. By one IAV type, a MM was detected preceding a L. Fractures at the connection screws and the abutments appeared at six IAV types. Only at one IAV type implant fractures occured. At none conical IAV types the failure frequency correlates with decreasing implant-diameter. However, at conical IAVs there is no correlation between failure frequency and implant-diameter. Summary: The occurrence of wear traces or failure modes (MM, L, F) shows, that all of the IAVs, with regard to horizontal encumbrances, feature constructions-conditioned weaknesses, which, in case of a long -term osseointegration of implants, could lead to a clinical component-failure (constructional element-failure), particularly in case of single tooth implant restorations placed in the lateral region. Keywords: implant, abutment, failure mode, screw, fracture, loosening, Implantat, Aufbau, Pfosten, Versagensmodi, Schraube, Fraktur, Lockerung