Original study - ZZI 03/2017

A pilot study for evaluating interfaces by OCT: loading of a Resin Nano Ceramic on one-piece ZrO2 implants

The changes to the signal lines at the interfaces which were visible in the OCT-B-Scans were of note following the chewing simulation. These were evaluated according to an optical/visual scoring system as „more pronounced“, „indistinct“ or „equal“. In this context the brightness/intensity and width of the signal lines were decisive. According thereto the evaluation „more pronounced“ is associated with an increase in brightness/intensity and/or width of the signal line. Accordingly, „indistinct“/„equal“ stand for a decrease or no change of the signal (Fig. 7).

By an individualised retaining construction at the OCT device it was possible to ensure that the samples were maintained in the retainer of the chewing simulator, thus achieving a well reproducible retainer facility of the samples prior to and after the chewing simulation, and furthermore enabling the comparable frames to be optimally evaluated. The static evaluation of the OTC was performed with a descriptive approach.

The CS and thermocycling were both performed simultaneously by means of CS-4.8 professional line (5 chambers, SD-Mechatronik GmbH, Feldkirchen-Westerham, Germany) in over 1.2 million cycles at 50 N and 1.6 Hz frequency whereby a 3 mm steatite ball was used as antagonist and alternating baths of 5–55 °C for 60 sec each took place. That thus simulated a clinical load of approx. 5 years. In the next step a stereomicroscopy control took place to identify cracks and fractures of the restoration material and/or the implants (Auflicht-Hellfeld, Stemi 2000-C, Digital Microscope Camera AxioCam ICc 1 Rev.4, Control Software AxioVision Rel. 4.8, Carl Zeiss MicroImaging GmbH, Göttingen, Germany).

Results

After completing the examinations none of the samples had any signs of a fracture or destruction. One sample revealed a hairline crack within the RNC in the OCT-B-Scan (Sample 2_SB_o) after CS. This, however, was not identifiable from the exterior and did not impair the stability of the crown during the chewing simulation.

Changes to the interfaces

After CS none of the changes were evaluated with „indistinct“. At the interface RNC/SU+RU (= crown-bonding material-interface) a signal line was identified at a surface (sample No. 9, SB, distal) which, after CS, was evaluated as „equal“. No other samples revealed any signal line between the crown and bonding material (Fig. 8).

In all other samples not only prior to, but also after the CS in the OCT-B-Scan for all evaluated surfaces (mesial, distal, occlusal) a signal was visible along the interface SU+RU/ZrO2 (= bonding material-abutment-interface).

This was more pronounced in the case of samples without CoJet pre-treatment (non-SB) already before the CS than in the case of samples with (SB).

After the CS the changes to the signals in the case of the lateral scans (mesial, distal) of the non-SB samples were all evaluated with „equal“, in the case of SB, however, these were evaluated with „more pronounced“.

Analog to that the signals in the occlusal B-Scans at SB were „more pronounced“, but only at 4 of the non-SB samples „equal“. In the other 6 samples a second signal line was identified, as a result of which it was no longer possible to evaluate the surface according to a previously applied pattern (Fig. 9).

Discussion

In this pilot study the interfaces at 20 one-piece zirconium dioxide implants were examined with the help of OCT after prosthetic treatment of the crowns using a Resin Nano Ceramic with adhesive bonding.

In the following some aspects on material and method will be discussed. As this is a pilot study and above all the feasibility of the method described is at the focus, the examination was performed with a reduced case number of samples.

With regard to the OCT-B-Scans examined, these are selective sectional views of a sample which have been summarised in a cumulative evaluation. In order to obtain an initial impression of the presentability and visualisation in OCT for the areas examined (interfaces) and the changes thereto following chewing simulation, an initial visual scoring is deemed to be necessary. Despite simple decision parameters for the respective cumulative evaluation, this scoring does not represent any statically objective evaluation in the classic sense of the word and has to be seen as limitation of this examination. After a positive development of this pilot study a further development of the evaluation system to a binary evaluation, respectively a quantification of line signals with metric specifications makes sense. The impact on the individual evaluations is therefore to be initially seen in the light of the close limits of this examination.

Changes to interfaces

At one sample a signal line at one of the surfaces to be evaluated in the OCT-B-Scan was identified at the transition between the crown and the bonding material (sample No. 9_SB). This suggests a lacking compound at the evaluated surface, as apparently the transition of light from RNC in air led to a dispersion/reflection. A lacking CoJet pre-treatment or faulty netting of the surface with adhesive bonding material could be the cause. Neither debonding during the CS nor visible changes to the existing signal line after CS took place. In general the lacking signal lines at the other samples imply a more homogeneous compound between the crown and bonding material with regard to the location examined.

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