Giomer resin composite is a bioactive material known to offer high protection against the development of new carious lesions, which incorporates the strength and aesthetics of conventional resin composites and the fluoride release of glass ionomers. The basis of Giomer is that S-PRG filler, has started to be used and tested as a bioactive agent in different dental products apart from resin composites such as resin cements, fissure sealants, coating resin materials, temporary fillings, and polishing pastes; and many studies have demonstrated that Giomers exhibit antibacterial effects against oral bacteria [18–22]. Therefore, the success of bioactive Giomer resin composites with anticariogenic properties should be clinically discussed. There are lots of studies in the literature on the clinical success of resin composites; however, there are not many studies evaluating the clinical prognosis of bioactive Giomer resin composites or comparing them with alternative restorative materials in vivo [2]. Therefore, in this clinical observation, it was aimed to compare two resin composites with different properties, one of which is Giomer resin composite and the other is nanohybrid resin composite. The null hypothesis of this study was accepted that there was no difference in the clinical performance of Giomer resin composite and the nanohybrid resin composite.
When the Giomer was first introduced to dental clinicians, two PRG filler types involved in this technology were mentioned, namely a fully PRG (F-PRG) filler and a surface PRG (S‐PRG) filler. Beautifil (Shofu, Kyoto, Japan) was developed using S‐PRG technology was indicated for Class I through Class V cavities. Contributions to PRG technology have led to the emergence of the modified S-PRG filler, which includes a three-layer texture with a glass core of multifunctional fluoro-boro alumino-silicate glass and bifacial layers forming the PRG phase around the glass core, and a reinforced modified layer covering the surface of this PRG phase. Beautifil II, developed with this novel technology was considered as a second generation Giomer [23]. The Flowable Giomer resin composite, which offers applications in a different viscosity, and low-shrinkage Giomer resin composites are accepted as other current Giomer technologies [2].
The clinical success of bioactive Giomer resin composites has been tested in clinical studies comparing these materials with glass ionomers, resin composites and among themselves. In a clinical observational study comparing Giomer resin composites with glass ionomers, concluded that Giomer resin composites exhibited superior surface finishing and marginal adaptation, however they showed similar retention with resin modified glass ionomers [9]. Similar to this study, in a different clinical evaluation in which the success of Bioactive material Giomer resin composites in class V cavities was compared with two different resin-modified glass ionomers, one of which was nano, for one year, Giomer was observed to be superior in terms of surface finish and color match. The smooth surface characteristic was observed for Giomer restorations through the clinical observation periods, since the typical nature of this material is resin composite. It was stated in the same study that bioactive material Giomer resin composites presented worse results in terms of retention in the evaluation period however they showed similar clinical success with the resin modified glass ionomers [10].
When the observational studies in the clinical literature on bioactive material Giomer resin composites are examined, a three-year observational study comparing the traditional and flowable forms of Giomer resin composites in the restorations of class V cavities emphasized that, these materials provide similar clinical success [12]. In a different study comparing the clinical prognoses of these two materials in conservative Class I cavities, restorations made using conventional form Giomer resin composites achieved clinically better results compared to flowable ones after 3 years in service [11]. Considering the classification of Giomers as F-PRG and S-PRG, in an in vivo study comparing these different types, the success rate for cervical (Class V) S-PRG Giomer restorations after two years was 80%, while the success rate for cervical F‐PRG Giomer restorations was 71%; and the two-year clinical success of S-PRG Giomer restorations on occlusal surfaces has been observed to be excellent [8]. The longest follow-up study in the literature in which Giomer resin composites were clinically evaluated was an observation period of 13 years, after which most of the restorations maintained acceptable clinical qualities [13]. The literature in which researchers report long-term clinical data for adhesive restorative materials are scarce. Thus, the findings obtained after long-term clinical service are very valuable data on the clinical success of Bioactive material Giomer resin composites. In this evaluation process, which will be considered as long-term, there was no evidence that any of the restorations had been repaired. Although thirteen of the observed restorations did have some changes regarding the color match, marginal adaptation and staining and proximal contact criteria, after 13 years, restorations maintained satisfactory properties [13]. In the present study, a loss of retention was observed in the group of Giomer resin composite after two-year clinical service. Technical sensitivities encountered during the application of adhesive systems, as well as different factors related to the application technique of operators and adhesive systems, can be attributed to this failure. In addition to these reasons, providing isolation with cotton rolls rather than rubberdam can also be accepted as a limitation in this clinical observation. Like the present 3-year clinical observation study, examining the research comparing resin composites and Giomer resin composites in the literature, restorations were not different in any of the criteria evaluated [24, 25]. Considering the clinical studies in the literature involving bioactive material Giomer resin composites, it is observed that this material has similar postoperative sensitivity and secondary caries findings to the restorative materials it is compared to [10, 19]. In the present study, no postoperative sensitivity was observed at any follow-up period, however a small secondary caries lesion was detected in one restoration from the nanohybrid resin composite group that did not require intervention. For retention [10] and marginal staining [14] criterias, Giomer resin composites scored worse than other restorative materials with which they were compared. However, Giomer resin composites exhibited superior surface roughness when compared with resin modified glass ionomer restoratives [9]. For the surface luster parameter evaluated at the present clinical observation, slightly dull surfaces were generally observed for both materials tested. However, Giomer resin composites exhibited superior surface roughness when compared with resin modified glass ionomer restoratives [9] in a previous clinical study.
Giomer resin composites scored worse than other restorative materials for retention [10] and marginal staining [14] criteria in some literature. In this study, retention loss was determined after two years in a restoration belonging to the Giomer resin composite group. Durable adhesion to tooth tissues can be considered as one of the most important prerequisites to prevent early marginal deterioration, which could adversely affect the clinical success of adhesive restorative treatments [26]. A clinical observation study of direct adhesive posterior restorations mentioned that the marginal deterioration incidence was mostly due to the adhesive system used in restorative procedures [27]. Self-etch adhesive systems were introduced to dental clinicians to overcome disadvantages related to the etch-and-rinse technique, namely the sensitivity to differences in dentin tissue moisture and the possibility of the differences between demineralization depth and resin monomer diffusion. Despite all updates in adhesive dentistry, none of the novel adhesive strategies is exempt from technique sensitivity of adhesion procedures, and significant concerns have been detailed in the literature about interfacial aging due to degradation of the adhesive interface [26]. In short-term clinical evaluation studies in which self-etch adhesives are used in the application of direct adhesive posterior restorations, it has been stated that marginal integrity is generally the most adversely affected parameter [28, 29]. In this study, two-stage self-etch adhesive systems were preferred in restorative procedures. The adhesive system applied with the nanohybrid resin composite group contains 10-MDP as a monomer content. Two-step self-etch adhesive systems containing 10-methacryloxydecyl dihydrogen phosphate (10-MDP) monomer have similar adhesive efficiency to those of three-step etch-and-rinse adhesive systems [30].
The failure types observed in these two different adhesive restorative material groups, which were applied with both types of two-stage self-etch adhesive systems, were secondary caries development in the nanohybrid resin composite group and retention loss observed in the Giomer resin composite group. Apart from these, it can be counted as marginal deteriorations, which are observed at a similar rate in the restorations of both material groups, scored with 3 and accepted as clinically sufficient/satisfactory with minor shortcomings. While the long-term data of this study may reveal the superiority of Giomer in fluoride release from resin composites as a restorative material, 10-MDP containing adhesives were considered superior [26, 30] which was not compared in this study.
It has been reported in the dental literature that, matrix metalloproteinases (MMP), as a family of enzymes with the function of degrading the extracellular matrix, adversely affect dental adhesion over time [18, 31, 32]. Therefore, studies in adhesive dentistry have been focused on enzyme inhibition [33] or biomimetic remineralization strategies [34] to slow down the degradation, in order to reveal more successful adhesion in the long term. In addition to the bioactive remineralization effect of PRG technology [35, 36], due to its S-PRG content, this resin composite inhibits dentin matrix degradation by acting similarly to 2% chlorhexidine digluconate, known as an MMP inhibitor. [31, 32]. However, mild acidic self-etch adhesive system used with nanohybrid resin composite group preferred in this study was mentioned to cause a lower rate of bond degradation than other adhesive techniques in the literature [37, 38]. When the bioactive effect of S-PRG and the clinical long-term evaluation of its effects on MMPs are aimed, choosing an adhesive that has a negative effect on the effect of MMPs on bond degradation as a comparison group can be considered as one of the weaknesses of this study. However, long-term clinical follow-up is required to clearly reveal the possible effects of Giomer resin composites on MMPs’ activity and, consequently, on adhesion success.
Although there are limited studies with the current Giomer material, the associated failure was attributed to the resin content of the adhesive system. They emphasized that HEMA increased the water uptake of the resin composite and caused the gradual hydrolytic degradation, swelling and staining of these materials [14, 39]. In this study, both adhesive system groups tested contained HEMA, and the two materials exhibited similar clinical findings after 3 years of evaluation. The results of this study demonstrate that the clinical success of this restorative material with ion release features promising that can prevent the formation of secondary caries, being one of the most common failures of resin composites restorations. The patients are being followed up for long-term service.