Evaluation of Low-shrinkage Giomer Versus Resin-Modified Glass Ionomer in Cervical Caries Lesions: A Clinical Trial

The development of cervical lesions in permanent dentition may be related to carious or non- carious origin. Class V caries lesions may occur due to different factors such as poor oral hygiene, dietary habits, or xerostomia.

Management of cervical lesions presents serious problems with any restorative material. The two most common reasons for restoration failure are secondary caries at the tooth-restoration interface and loss of retention. Class V lesions often exhibit a low retentive cavity configuration (C-factor); which is responsible for marginal gaps around the restorations. Cervical margins -lying in either dentin or cementum- show unfavorable bonding performance, besides being usually subgingival where moisture control is difficult. The subgingival margin is not clinically desirable due to difficulty in cleaning and increased biofilm accumulation. Therefore, the selection of the restorative material can be challenging.

In this context, fluoride containing adhesive materials are considered ideal in restoring class V carious lesions. Resin modified glass ionomers (RMGI) are highly recommended in the restoration of cervical lesions. The most important advantages of glass ionomer are its chemical adhesion to the tooth structure, and its fluoride release. However, RMGI has lower weakness and esthetic properties compared to resin composite.

In our study, the comparator material will be light cured resin reinforced glass ionomer restorative. RMGI is recommended to restore carious cervical lesions; especially with its ability to inhibit secondary caries due to its fluoride releasing ability. The main advantage of RMGI is its capability to chemically bond to tooth structure, even in the presence of moist dentin. RMGI reaction can be achieved by both acid-base reaction (induced by glass ionomer component) and polymerization reaction (induced by resin component). Thus, RMGI has better mechanical properties, wear resistance, and improved esthetics compared with conventional glass ionomer. In addition, the coefficient of thermal expansion of glass ionomer which is similar to that of tooth structure, allows for proper marginal adaptation without marginal leakage.

Resin composites have been widely used in dental practice; because of their high mechanical properties, excellent esthetic properties, and ease of clinical application.

However, when compared with glass ionomers, resin composite has no cariostatic effect on tooth structure. In addition, polymerization shrinkage of resin composite is of major concern; where mechanical stresses are developed due to contraction leading to break the marginal seal between resin composite and tooth structure. Polymerization shrinkage can cause clinical issues as restoration or tooth fracture, bond degradation and solubility, and microleakage. The microleakage caused by polymerization shrinkage of resin composite leads to plaque accumulation and secondary caries. Thus, choosing a fluoride-releasing and low-shrinkage resin composite may play a critical role in success of cervical restorations.

The continued development of resin composites has led to the introduction of Giomer technology. By combining the characteristics of resin composite and glass ionomer, hybrid products called giomers have been obtained. Giomer resin composite offers protection against caries, along with improved functional and esthetic properties; through incorporating particles of pre-reacted glass fillers (PRG) into the matrix of resin composite. The PRG-ionomer phase has the capability to release six key ions which are fluoride, aluminum, borate, silicate, strontium, and sodium ions. These ions exhibit acid neutralizing ability and help prevent demineralization of enamel and dentin, leading to decrease the possible incidence of secondary caries. This PRG technology provides giomer with both fluoride release and recharge, similar to glass ionomer while still maintaining the original physical properties of resin composite.

Beautifil™ II LS (Low shrinkage) giomer resin composite (Shofu Inc, Kyoto, Japan) shows both sustained fluoride release and recharge, and low volumetric shrinkage of less than 1% with low resultant polymerization shrinkage stress. Such remarkable feature is due to the novel SRS (Steric Repulsion Structured) molecule which is designed to decrease polymerization shrinkage through molecular steric repulsion resulting in a stable restoration microstructure. Thus, low shrinkage giomers are best indicated in class V cavities where the dentin bonding agent does not have high strength.

A recent clinical trial compared the clinical performance of giomers versus resin modified glass ionomer in proximal lesions. Marginal adaptation was higher in giomers than resin-modified glass ionomers after 12 months. Also, a systematic review investigated in vivo longevity of giomers compared to other adhesive restorative materials (hybrid resin composite, composmer, and RMGIC), and concluded that RMGIC was the most successful material in terms of biological properties while giomers had the longest survival rate. An in-vitro study evaluated the surface roughness and fluoride release of Beautifil II and Fuji II LC (resin-modified glass ionomer). Resin-modified glass ionomer showed the highest fluoride release, while the giomer showed an intact, smooth surface with no irregularities as those found in glass ionomer. Thus, the smooth surface of giomers inhibit biofilm formation, decreasing the risk of dental caries and periodontal diseases. Regarding the mechanical properties of giomers, it has exhibited a higher flexural strength value when compared to glass ionomer cements. The hardness values were twice as high for the giomer when compared to self-curing and light-curing glass ionomer cements.