Bond strength and nanoroughness assessment on human pretreated cementum surfaces

Investigating the surface topography of human acellular and cellular tooth cementum by atomic force microscopy

INTRODUCTION

Dental cementum plays a key role in maintaining the health and functional integrity of teeth throughout an individual's life. While different cementum types are distinguished according to location and function, their specific properties are not yet fully understood.

OBJECTIVE

The study aimed to compare the structural properties of different types of tooth cementum by analysing their surface texture using tapping mode atomic force microscopy (TM-AFM).

METHODS

Transverse and longitudinal sections of five anterior teeth extracted from four male individuals were prepared and analysed by TM-AFM (Core AFM) both with and without hydrochloric acid etching. The TM-AFM measurements were further analysed using the Gwyddion software to determine the roughness parameters (root mean square of height irregularities and mean roughness).

RESULTS

The acid-etched sections exhibited distinctive features with regard to fibre structure and orientation compared to the unetched sections, with fundamental differences between acellular and cellular cementum. In contrast to acellular extrinsic fibre cementum (AEFC), cellular intrinsic fibre cementum (CIFC) showed increased roughness values after acid etching, with some variability, both between teeth and between subjects. The relative percentage difference (RPD) between the cementum types varied between 11.4 % in unetched transverse sections and up to 89.8 % in etched sections. The AEFC images revealed finely branched fibres between radial Sharpey's fibre bundles.

CONCLUSION

Our results show that TM-AFM imaging combined with acid etching is a suitable technique for characterising the surface texture of different types of tooth cementum.

Decision tree protocol for demineralized gingival margin extension in class II composite cavity preparations

This study proposed the development of a protocol for class-II preparations with demineralized gingival margins for the improvement of the longevity of restorations. Evidence sources such as location/color/surface hardness/width of demineralized gingival margin with enamel/demineralized enamel (DE)/dentin/cementum were reviewed based on methodological studies and systematic reviews. A decision tree protocol was developed with criteria (i) lesion location: demineralized gingival margins in enamel must be removed, but if close to cementoenamel-junction, color should be evaluated. (ii) Color: yellow/brown lesions must be removed, but if white/opaque, then the surface hardness should be evaluated. (iii) Surface hardness: soft/demineralized gingival margin must be removed, but if adequately hard, width should be evaluated. (iv) Width: lesions less than half-enamel thickness and impenetrable by an explorer, remineralization is possible and the lesion does not need to be removed. A decision tree protocol was set up with the current available literature. Further continued investigations will be needed for the appropriate protocol updates.

Determining efficacy of monitoring devices on ceramic bond to resin composite

Objectives: This paper aims to assess the effectiveness of 3D nanoroughness and 2D microroughness evaluations, by their correlation with contact angle measurements and shear bond strength test, in order to evaluate the effect of two different acids conditioning on the bonding efficacy of a leucite-based glass-ceramic to a composite resin. Study Design: Ceramic (IPS Empress) blocks were treated as follows: 1) no treatment, 2) 37% phosphoric acid (H3PO4), 15 s, 3) 9% hydrofluoric acid (HF), 5 min. Micro- and nano-roughness were assessed with a profilometer and by means of an atomic force microscopy (AFM). Water contact angle (CA) measurements were determined to assess wettability of the ceramic surfaces with the asixymetric drop shape analysis contact diameter technique. Shear bond strength (SBS) was tested to a resin composite (Z100) with three different adhesive systems (Scotchbond Multipurpose Plus, Clearfil New Bond, ProBOND). Scanning electron microscopy (SEM) images were performed. Results: Nanoroughness values assessed in 50x50 μm areas were higher for the HF group, these differences were not detected by profilometric analysis. HF treatment created the nano- roughest surfaces and the smallest CA (p<0.05), producing the highest SBS to the composite resin with all tested adhesive systems (p<0.05). No differences existed between the SBS produced by the adhesive systems evaluated with any of the surface treatments tested. Conclusions: Nano-roughness obtained in a 50x50 µm scan size areas was the most reliable data to evaluate the topographical changes produced by the different acid treatments on ceramic surfaces.

Key words:Dental ceramic, acid etching, bonding efficacy, resin composite, adhesive systems, contact angle, roughness.