The evaluation of four conditioners for glass ionomer cements using field-emission scanning electron microscopy

Abstract

Objectives: The purpose of this study was to evaluate the GIC-dentine interface morphology using FE-SEM after four different conditioners (Ketac Conditioner, Dentin Conditioner, Cavity Conditioner, and an experimental conditioner K-930), used with two RM-GICs and one self-cured GIC, and to observe the effect with an AFM of the four different conditioners on the surface of polished human dentine.

Materials and methods: sample preparation for FE-SEM: Twenty-four 1-mm thick dentine discs were obtained from superficial occlusal dentine of extracted human third molars, and finished with wet 600-grit SiC paper. The discs were treated for each of the GICs using the conditioners according to the manufacturers’ instructions. The specimens were kept in tap water for 24 h at 37°C, and then assigned for one of two observational techniques; a fractured technique and an acid-base technique. Specimens were mounted on aluminium stubs, gold sputter-coated and observed using a FE-SEM.

Sample preparation for AFM: Four rectangular dentine blocks approximately 2 mm³ were prepared from two extracted human third molars, polished and finished with diamond paste down to 0.25 μm particle size. One half of each sample was treated with one of the conditioners according to the manufacturers’ instructions, and the other half was not conditioned. The samples were stored in distilled water prior to AFM contact mode observation.

Results: FE-SEM: All specimens of all materials demonstrated good adaptation to the underlying dentine. However, the specimens conditioned with K-930 showed increased demineralization and a thicker acid-base resistant layer (2.8–3.4 μm) compared with the others (1–2 μm).

AFM: The images of conditioned specimens showed demineralization of peritubular dentine. Funneling of dentinal tubule orifices of specimens conditioned with K-930 was observed, and was also seen for the FE-SEM specimens.

Significance: The use of surface conditioners resulted in similar adaptation to the non-conditioned specimens at the GIC-dentine interface. All of the GICs demonstrated intimate adaptation to the dentine surface whether it was conditioned or not.

Introduction

One of the features of glass ionomer cements (GICs) is that they are able to bond physico-chemically to tooth structure without any pretreatment of the surface [1], [2], [3]. However, conditioning of the tooth surface prior to the application of GICs has been reported to improve the bond strength [1], [4], [5], [6], [7], [8]. The objective of conditioning is to remove surface contaminants and the smear layer, which may limit the bond of the GIC to tooth structure, particularly the dentine [9], [10], [11]. It has been shown that laboratory bond strength results may be affected by the method of applying the conditioners, concentration of conditioners, duration of conditioning, material used and the nature of the pre-prepared surface [6], [12], [13], [14], [15], [16].

When a conditioning agent has been used in conjunction with a GIC, bond strength studies have been used as a preliminary evaluation of the adhesive strength. The microtensile bond strengths of GICs to human dentine using the conditioners in this study have been reported in a previous article [16], and the results seemed material dependent. On the other hand, studies on the ultramorphological structure of the adhesive interface are able to provide information regarding the interaction of a GIC with the tooth substrate [17]. Two preparation techniques have generally been used for scanning electron microscopy (SEM); the fractured specimen technique and the acid-base treatment technique [18]. With the use of a Field-Emission Scanning Electron Microscope (FE-SEM), better characterization of the ultramorphological interface is possible due to the enhanced resolution and reduced voltage which lessens damage to specimen surfaces [19], [20], [21]. However, few studies with GIC using the FE-SEM have been reported using these two techniques.

The Atomic Force Microscope (AFM) is a high resolution instrument which has been widely used to observe dentine in a wet environment [22], [23], [24], [25], [26], [27]. This tool allows the examination of specimens without the need for irreversible specimen processing which has the potential to cause distortion and subsequent artefacts [28]. However, limited AFM data are available which describe the morphology of dentine surfaces treated with commercial dentine conditioners used for GICs.

The aim of this study was to evaluate the GIC-dentine interface morphology after the use of four conditioners (Ketac Conditioner, ESPE Germany; Dentin Conditioner, GC International, Japan; Cavity Conditioner, GC International, Japan; and an experimental conditioner K-930, GC International, Japan) in conjunction with two resin-modified GICs (RM-GICs) (Photac-Fil Quick, ESPE, Germany; and capsulated Fuji II LC, GC International, Japan) and one self-cured GIC (capsulated Fuji IX GP, GC International, Japan) using a FE-SEM and AFM.