An ex vivo assessment of resin-modified glass ionomer bonding systems in relation to ceramic bracket debond

Anex vivoassessment of a bonding technique using a self-etching primer

OBJECTIVE

This study assessed a new self-etch/priming system for use in orthodontic bonding.

SETTING

An ex vivo study.

METHOD

Three groups of 20 extracted premolar teeth were bonded with metal orthodontic brackets. Group 1 was bonded with Transbond using the conventional technique (control). Group 2 was bonded using the new Transbond-Plus combined etch/primer system to wet enamel and Group 3 to dry enamel. The teeth were debonded using an Instron Universal Testing Machine. The mean debond force was calculated for each group and compared statistically. The teeth were examined under the stereomicroscope to assess the site of debond and adhesive remnant index.

RESULTS

Group 2 (etch/primer on wet enamel) had the lowest mean debond value at 5.2 MPa. ANOVA and Tukey tests confirmed that the bond strength results of Group 2 were significantly lower than Groups 1 (P < 0.01) and 3 (P < 0.05). The enamel/resin interface was the commonest site of bond failure for both etch/primer groups (Groups 2 and 3). They had less retained resin and significantly (P < 0.001) lower ARI scores compared with Group 1 (control).

CONCLUSIONS

The results of this ex vivo study suggest that the self-etch primer should achieve adequate bond strengths when applied to dry enamel surfaces. In addition there should be less retained resin requiring removal at debond.

Smart materials in dentistry

Most dental materials are designed to have a relatively 'neutral' existence in the mouth. It is considered that if they are 'passive' and do not react with the oral environment they will be more stable and have a greater durability. At the same time, it is hoped that our materials will be well accepted and will cause neither harm nor injury. This is an entirely negative approach to material tolerance and biocompatibility and hides the possibility that some positive gains can be achieved by using materials which behave in a more dynamic fashion in the environment in which they are placed. An example of materials which have potential for 'dynamic' behaviour exists with structures which are partly water-based or have phases or zones with significant water content and for which the water within the material can react to changes in the ambient conditions. Such materials may even be said to have the potential for 'smart' behaviour, i.e. they can react to changes in the environment to bring about advantageous changes in properties, either within the material itself or in the material-tooth complex. The controlled movement of water or aqueous media through the material may cause changes in dimensions, may be the carrier for various dissolved species, and may influence the potential for the formation of biofilms at the surface. Some of these issues may be closely interrelated. Clearly, materials which do not have the capacity for water transport or storage do not have the potential for this sort of behaviour. Some materials which are normally resistant to the healthy oral environment can undergo controlled degradation at low pH in order to release ions which may prove beneficial or protective. It is doubtful whether such behaviour should be classified as 'smart' because the material cannot readily return to its original condition when the stimulus is removed. Other materials, such as certain alloys, having no means of transporting water through their structure, can display smart behaviour by undergoing predictable changes in structure in response to applied mechanical or thermal stimuli. It has been difficult to harness such behaviour to the benefit of patients but progress in this area is slowly being made.