**2.6 Clinical performance**

One of the principal benefits of GICs is their adhesion to the dental hard tissues, and this has been confirmed in non-undercut non-carious cervical lesions (NCCLs) where dentine is the main substrate. However, because of the low fracture toughness of GICs (including RM-GICs), they are recommended principally for non-stress-bearing areas, e.g., carious and noncarious cervical lesions and approximal anterior lesions. Nevertheless, the high powder:liquid ratio materials may be useful in the restoration of small cavities in deciduous

Measurement of the bond strength of GIC to enamel and dentine is complicated by the brittle nature of the GIC. Laboratory bond strength tests invariably result in cohesive failure of the GIC, rather than failure within the ion exchange layer. Consequently, the true strength of the ion-exchange layer is not known; values in the range 3-10 MPa are commonly

The release of fluoride ions is one of the notable characteristics of GICs. It is present originally as a flux in the manufacture of the glass, and is released from the glass particles on mixing with the polyalkenoic acid. The presence of fluoride also has benefits in increasing translucency and strength and improving handling properties [29]. The mechanism of release is complex and not fully understood. However, it is maximum in the first few days and decreases rapidly to a lower level over weeks, and maintains a low level over months. It has also been shown that GIC can be 'recharged' with fluoride, resulting in a subsequent short-term boost in release. Most of the fluoride is released as sodium fluoride, which is not critical to the cement matrix, and thus does not result in weakening or disintegration of the set cement. Resin-modified GICs show similar dynamics of fluoride release, although for both types of material the dynamics of release and the amounts

Several metallic ions are released from GIC, as well as fluoride. The highest release occurs from the unset material, and as described above, most research has been done on fluoride. Hydroxethylmethacrylate (HEMA) is released from RM-GICs and can diffuse through dentine in laboratory studies. Since HEMA can induce allergic and toxic responses, the clinical relevance of its release requires more investigation [70]. Nevertheless, to date there is no evidence that HEMA in dental materials is responsible for any local or systematic

Glass-ionomer cement has been shown to have an antimicrobial effect in several studies, and greater than that shown by other materials such as amalgam and resin composite. However, again it is difficult to do more than generalize, as the results depend on the experimental method, the bacteria used and the product tested [70]. There are several theories regarding the antibacterial activity. Most workers propose that fluoride is responsible, possibly acting synergistically with pH. However, other released agents have been cited as possible antibacterials, including zinc [77] and polyalkenoic acid [68], acting alone or synergistically

One of the principal benefits of GICs is their adhesion to the dental hard tissues, and this has been confirmed in non-undercut non-carious cervical lesions (NCCLs) where dentine is the main substrate. However, because of the low fracture toughness of GICs (including RM-GICs), they are recommended principally for non-stress-bearing areas, e.g., carious and noncarious cervical lesions and approximal anterior lesions. Nevertheless, the high powder:liquid ratio materials may be useful in the restoration of small cavities in deciduous

released depend on the particular material and the experimental design [79, 89].

reported, i.e., approximately the cohesive strength of GIC [76, 79].

**2.4 Fluoride release** 

**2.5 Biological properties** 

with pH and fluoride [79].

**2.6 Clinical performance** 

adverse effects.

teeth. Clinical studies on RM-GICs are less extensive because of their more recent introduction [6, 13]. However, the results are mixed with respect to both brand comparisons and comparisons with polyacid-modified resin composites. One presentation of an RM-GIC is in a low powder:liquid ratio form (Fuji Bond LC; GC International), and is used in a similar way to a dentine bonding agent. Excellent five-year results have been obtained for the retention by this material of resin composite in non-carious cervical lesions [78].

Evidence is accumulating that GIC may have an important role in minimum intervention dentistry. Modern concepts of operative dentistry propose that only the 'infected' dentine should be removed, leaving the 'affected' dentine which has the potential to remineralize. Recent evidence suggests that such remineralization may be potentiated by GIC [3], and this has special relevance in the ART technique [79].
