Cone-beam computed tomography in assessment of periodontal ligament space: in vitro study on artificial tooth model

The aim of this in vitro study was to compare cone-beam computed tomography (CBCT) to conventional radiography (RG) in the assessment of the periodontal ligament space. A phantom with a variable "artificial" periodontal ligament space (0, 100, 200, 300, and 400 microm) was used as a model. The examinations were performed simultaneously with RG and NewTom 9000 digital volume tomograph. Assorted after increasing widths, 15 RGs and 15 CBCT images were presented for judgment to 20 dentists (DD), 20 dental assistants, and 20 dental students. Several weeks later, the same images were randomly mixed and presented to the same 20 DD again. The trial shows that RG gaps wider than 200 microm could be correctly identified by all participants with an accuracy of nearly 100%. A significant difference was observed between the modalities (p<0.05 and p<0.001) where conventional RGs performed better than CBCT for assessment of periodontal ligament space. Interobserver variation in relation to each technique was evaluated and no significant difference was found (p>0.05). In subjective evaluations of image quality with CBCT, the results were basically inferior for images of artificial periodontal ligament space, regardless of the experience of the observers.     

Technique sensitivity of dentin bonding: effect of application mistakes on bond strength and marginal adaptation

This in vitro study evaluated dentin bond strength and marginal adaptation of direct resin composites according to the manufacturers' instructions and with simulated application errors. One hundred and forty cavities were prepared into disks of freshly extracted human third molars and filled with one resin composite. Dentin adhesives of the third (with self-etching primer: Syntac Classic), fourth (with total etching: Scotchbond Multi-Purpose Plus) and fifth generation (one-bottle adhesive: Prime&Bond 2.1) were used for bonding. Simulated application mistakes were as follows: 1) prolonged etching; 2) excessive drying after conditioning; 3) drying primers immediately after application and 4) drying primers excessively. After 21 days of storage and 24 hours thermocycling (1150 cycles), replicas were made and push-out testing was performed. Replicas were examined for marginal adaptation using SEM (X200 magnification). Compared with values of the control groups, application errors resulted in dramatically decreased bond strengths and reduced percentages of gap-free margins for all products tested (p < 0.05). Excessive drying after conditioning exhibited significantly less effect for the third generation adhesive than for products requiring total etching/wet bonding.     

Zur Frage der Veränderung des Funktionszustandes des stomtognathen Systems durch die kieferorthopädische Multibanbdehandlung beim Erwachsenen

Zusammenfassung Bei zehn erwachsenen Patienten wurden vor Beginn einer kieferorthopädischen Multibandbehandlung (T=0) und im Durchschnitt 12,6 Monate danach (T=1) ein klinischer und ein axiographischer Funktionsstatus erhoben. Während der klinische Funktionsstatus von T=0 nach T=1 nur geringe Veränderungen zeigte, wurden Veränderungen von allen untersuchten axiographischen Parametern festgestellt. Dies macht deutlich, daß moderne axiographische Verfahren wichtige zusätzliche Informationen für die Gelenk diagnostik liefern können. Die beobachteten Veränderungen deuten auf eine Funktionsumstellung während der kieferorthopädischen Behandlung hin. In der Mehrzahl der Fälle blieben axiographische Parameter jedoch unverändert. Besonders auffällig war die Persistenz von diskoordinierten Bahnen in der Horizontalebene. Dies zeigt, daß Veränderungen der okklusalen dentalen Relation nicht unmittelbar Veränderungen von Muskel- und Gelenkfunktion nach sich ziehen müssen.

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Summary Ten patients who undergo an orthodontic therapy with a full-band modified straight-wire-appliance were examined clinically and by means of an electronic-axiographic device (SAS-system) at the beginning of treatment and after an average of 12.6 months, respectively. While the clinical functional status showed only minor changes, alterations of all examined axiographic parameters could be detected. This finding reemphasizes the necessity of modern axiographic means to get additional information about the functional status of the TMJ. The alterations point to a shift in the functional pattern of articular and muscular components during orthodontic treatment. In the majority of cases, axiographic parameters remained constant, however. In that respect, it might be of special interest that even discoordinated tracings, mainly in the horizontal plane, kept up its characteristic appearance. These findings show clearly, that alterations of occlusal relationships must not influence articular functional patterns immediately.

     

Dentin bond strength and marginal adaption after NaOCl pre-treatment

The aim of this in vitro study was to compare the dentin bond strength and marginal adaptation of direct composite resins with and without additional NaOCl treatment after the etching process. A total of 150 cavities were prepared into disks of freshly extracted human third molars and filled with direct composite resins. Dentin adhesives of the fourth (with total etching: Scotchbond Multi-Purpose Plus, EBS, and Solid Bond), and fifth generation (one-bottle adhesives: Prime&Bond 2.1, Syntac Sprint) were used in combination with corresponding composite resin materials. Dentin disks without cavity preparation treatment served as controls. After 24 hours of storage and 24 hours of thermocycling (1150 cycles), replicas were made and push-out testing was performed. Replicas were examined regarding marginal adaptation using SEM (X200 magnification). In general, fourth-generation dentin adhesives produced better results in bond strength and marginal adaptation than fifth-generation one-bottle systems (P < 0.05). Within the fourth generation, Scotchbond Multi-Purpose Plus and EBS achieved significantly higher push-out values and percentages of gap-free margins than Solid Bond (P < 0.05). After hypochlorite treatment, dentin bond strength (-25%) and marginal adaptation (-30%) decreased significantly (P < 0.05) in all groups.