Clinical Performance of Glass Ionomer Cement in Load-Bearing Restorations: A Systematic Review

Background

STUDY DESIGN:

This systematic review complied with the standards outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) 2020 [31,32]. According to the hierarchy of evidence and OLE, the randomized controlled trial (RCTs) is the most widely used study format. Therefore, this review only included results from RCTs.

FORMULATING THE RESEARCH QUESTION:

A total of 5585 studies on the use of GIC in load-bearing restorations were obtained. The preliminary examination of the research topic specified whether the research question (is GIC clinically suitable for loading bearing restoration?) is appropriate for the topic of this review. This question was formulated using the PICO framework, which considers the population (patients requiring load-bearing restoration), intervention (GIC restorations), comparison (other dental restorations), and outcome (clinical direction for GIC use in load-bearing restorations) [33,34]. This framework was selected because it is often used for systematic reviews of clinical trials [35].

KEY TERMS:

For each aspect of PICO, we generated key terms to have a structured and consistent search methodology for all databases. The existing literature underwent screening employing keywords, nesting methods, and Boolean operators. The nesting search method uses synonyms to create themed phrases. The keywords include (Glass Ionomer Cement OR GIC), Restoration and Restorations as Class I and II ‘AND’ and ‘OR’ were used with the nesting method to broaden the search [36,37].

INCLUSION CRITERION:

Including studies published from 2018 and 2022 years ensures that the data collected is accurate and up to date. A Crowe Critical Appraisal Tool (CCAT) of >70% was applied. We included studies that examined dentition type (primary or permanent) and used either GIC or resin-modified GIC. Articles written in a language other than English, systematic reviews, cohort studies, case reports, case series, editorials, expert opinions, gray literature, and restoration of endodontically-involved dentition were excluded.

DATABASES SEARCH:

EBSCOhost (https://library.port.ac.uk), PubMed (https://pubmed.ncbi.nlm.nih.gov), and Embrace and Cochrane databases (https://www.cochranelibrary.com/central/doi/10.1002/central/CN-00978608/full) were searched with the corresponding search terms. The search was implemented in accordance with the PRISMA 2020 statement (Figure 1). An overwhelming result was achieved (52 864 studies), and another overwhelming result was found through the initial broad search. After applying the eligibility criteria and removing duplicates, we selected 37 studies for further screening. The studies were independently screened by reading their titles and abstracts. Finally, 13 studies were deemed suitable for critical appraisal, but only 12 studies met the inclusion criteria (Table 1).

CRITICAL APPRAISAL:

The CCAT is a valid and dependable tool for evaluating the integrity of diverse research designs. It has multiple categories that conclude with a score for interpretation. The literature within the final screening was assessed using the CCAT because it is a widely used tool for RCTs [38,39]. The CCAT score for each appraisal was correlated to a percentage using the CCAT instructions. Only studies with a CCAT score of >70% were included [38,39].

CRITICAL ANALYSIS:

Data collected were subjected to subgroup analysis according to the FDI World Dental Federations’ Clinical Criteria for the Evaluation of Direct and Indirect Restorations [40–42]. These criteria can be used in comprehensive procedures for evaluating dental materials and can be divided into 3 groups: esthetic, functional, and biological properties. Each main group contain 16 subgroups, and each subgroup has scores of 1–5 (1, clinically very good; 2, clinically good; 3, clinically sufficient/satisfactory; 4, clinically unsatisfactory; 5, clinically poor). The last 2 were classified as failures.

The included studies used an alternative criterion, such as USPSH, and we made appropriate amendments to coincide subgroups and achieve evidence-based comparison of homogeneous data. Each subgroup’s dichotomous results are presented in tables and narratively for a comprehensive summary. Subgroups based on participant age, type of dentition (primary or secondary), surface, and material that result in dichotomous outcomes were established (Table 2). Furthermore, as recommended by the PRISMA 2020 statement, we used the WHO’s Grading and Recommendations Assessment, Development, and Evaluation Framework to determine the subjective certainty of evidence, which was rated as very low, low, moderate, or high (Table 2) [43,44].

RISK OF BIAS ASSESSMENT:

As this systematic review’s contents are RCTs, we indicated the Cochrane risk of bias, which was subjectively rated as “low,” “some concerns,” and “high” and was assessed according to 4 domains (Figure 2): D1, D2, D3, and D4. If a study was marked as high in 1 of the domains, the study was deemed high overall.

Table 2 shows the 12 studies included in this review, showing the characteristics of each study, such as comparison, commercial name, participant age group, number of participants, number of restorations, dentition, class, study length, preferred material, COE, and authors. All the studies have a comparison: GIC versus RC, GIC versus stainless-steel crown, and GIC versus GIC. The outcomes were described as dichotomous outcomes because 2 groups were compared. The investigated GIC materials included in the 12 studies are shown in Table 3, with information on their composition and indications. Some studies were not included in each table because they did not explore all the 16 FDI criteria. Only the studies that produced results for the criterion were included in the table. The top row is the recall period that the results correlate to. It can be used to interpret the results in the tables. For example, a score of 2 for surface luster indicates that the material is slightly dull and contains isolated pores. Fotiadou et al found that 87.5% of EQUIA restorations had an FDI score of 2 for surface luster at 12-month recall. When the difference in results between the baseline and recall periods was insignificant, the column was filled with NA. A P>0.05 indicated that a study explored this criterion [45]. Table 4 shows the parameters evaluated during different recall periods in relation to the type of material used and authors.

STAINING SURFACE OR MARGIN:

Six studies investigated the staining surface [46–51], but only 2 of them found statically significant results regarding staining surface and margin when GIC was compared with RC (P<0.05) [47,48]. The effect was observed only in minor surface staining, which was easily removed and did not exert a detrimental effect. None of the studies found a clinically significant difference in recalls for the materials investigated, and no significant differences in dichotomous outcomes were observed (P>0.05) [49].

COLOR MATCH AND TRANSLUCENCY:

Three of the included studies found statically significant results regarding color match. The results ranged from good color match to distinct deviation, and the latter only affected GIC. One study observed that Filtek Z250 outperformed other GIC materials in terms of color match (P<0.001). EQUIA Forte restoration’s color match was superior to that of Ketac Universal or Riva HV restorations at 5-year recall [47]. Similarly, Gurgan et al [49] observed that Gradia DP outperformed EQUIA Fil. Menezes Silva et al [50] compared Z350-3M with EQUIA Fil (P<0.05). Three studies found no clinical significance in recalls for the materials investigated and no significant differences among dichotomous outcomes (P>0.05) [46,48,51].

ESTHETIC ANATOMICAL FORM:

Two of the included studies found statistical significance regarding the esthetic anatomical form of GIC [47,49], and most of the materials were esthetically acceptable. Menezes et al [50] found a statistically significant difference in esthetic anatomical form between EQUIA Fil and Z350-3M. After 5 years, Ketac Universal and Riva HV restorations displayed a substantial change in esthetic anatomic form relative to the baseline [47]. Two studies found no clinical significance in recalls for the materials investigated and no significant differences in dichotomous outcomes [48,49].

RETENTION AND FRACTURE OF MATERIAL:

The results regarding retention or fracture and retention showed that GIC is frequently minimally retentive with regard to dichotomous outcomes (Table 4) [46–50,52–55]. The 2 studies of dichotomous outcomes showed that EQUIA Fil was superior to Fuji IX GP Fast Set at each recall period [45,56]. Similarly, EQUIA Fil exhibited higher retention performance that Riva Self Cure HV and Ketac Universal Aplicap at 1, 3, and 5 years of recall [47]. Only 1 study yielded significant results regarding fracture alone for EQUIA Fil and Fuji IX Fast Set [45]. Another study found fracture to be the leading cause of failure for EQUIA Fil and Fuji IX Fast Set [56]. However, 5 studies found no clinical significance in recalls for the materials investigated and in dichotomous outcomes [47,49,51,52,54]. Focusing on the average retention of GIC, a study found that at a 3-month recall, the retention of GIC restorations was 97.06% [48]. At a 6-month recall, the retention of GIC averaged 95.6% [46,48,50]. At 12-month recall, the retention of GIC averaged 93.35% [45–50,53]. At 2-year recall, the retention of GIC averaged 91.1% [45–46,50,53,54]. At 3-year recall, the retention of GIC averaged 83.35% [44,47,49,52,54]. One study reported the retention of GIC at a 4-year recall [49].

MARGINAL ADAPTATION:

Four of the included studies found statistically significant marginal adaptation results. The results ranged from harmonious outlines to partial or complete looseness of the restoration and significant gaps and irregularities, and only the last result affected GIC. One study observed irregularities in the EQUIA Fil group. However, the RC groups remained similar at 6 and 12 months of recall (P=0.029 and P=0.034, respectively) [48]. Wafaie et al [47] found that Filtek Z250 underwent no significant change from the baseline to the recall periods, but all GIC groups did (P<0.05). One study found that EQUIA showed statistically significant changes from baseline to 3 years of recall (P=0.039), whereas the changes in Fuji IX GP Fast Set was less notable [45]. However, another study found significant changes from baseline to 6 years of recall for EQUIA Fil and Fuji IX GP Fast Set (P 0.017 and P 0.011, respectively) [56]. Two studies found no clinical significance in recalls for materials investigated and for dichotomous outcomes [49,51].

APPROXIMAL ANATOMICAL FORM, POSTOPERATIVE SENSITIVITY, AND TOOTH VITALITY:

The results ranged from clinically excellent to clinically poor. There was a significantly greater incidence of loss of contact point integrity in Vitremer compared with Filtek Z250 (P=0.03) [53]. Five studies found no clinical significance in recalls for the materials investigated, and no significant differences in dichotomous outcome were observed [45,47,50,54]. In relation to postoperative sensitivity and tooth vitality, no clinical significance was observed at recalls for each material, and no significant differences was found for dichotomous outcomes [45,49,51,56].

SURFACE LUSTER/TEXTURE:

Six of the included studies found deterioration of surface luster as an outcome of GIC at 6-year recall [45–47,50–51,56]. The deterioration varied from slight deviation from enamel to dull surfaces with pores. The most common outcome was a slightly dull appearance. Compared with RC, the results were statistically significant (P<0.05). One study found no significant differences for dichotomous outcomes in recalls for materials investigated with regard to surface luster [49].

RECURRENCE OF CARIES EROSION ABFRACTION AND TOOTH INTEGRITY:

No clinically significant differences were observed at recalls for each of the materials with regard to dichotomous outcomes (P>0.05) in relation to the recurrence of caries and erosion abfraction [45–49,51–54,56] or tooth integrity [45,47,56].

PERIODONTAL RESPONSE/GINGIVAL HEALTH:

Two of the included studies found statically significant results regarding patient satisfaction. The results varied from clinically excellent to clinically poor. One study found a significant decline in patient satisfaction with EQUIA Forte and Riva HV restorations from baseline to 5-year recall [47]. However, the dichotomous comparison of stainless-steel Hall Crown versus EQUIA Forte indicated a preference for EQUIA Forte [52]. Two included studies found no clinical significance observed at recalls for each of the materials investigated, and no significant differences were found for dichotomous outcomes [41,44]. One study found statistically significant results regarding periodontal response [47]. At 12-month recall, Filtek Z250 was associated with significantly more bleeding on probing BOP compared with Vitremer (P=0.005), and no clinical significance observed at recalls for each material investigated, and no significant differences were found for dichotomous outcomes [53].

Discussion

This study collated the results of 12 RCTs, focusing on the clinical suitability of GIC for load-bearing restorations according to the FDI criteria. After analyzing the results, we found significant differences in surface luster, staining surface/margin, color match and translucency, esthetic anatomical form, retention and fracture of material, marginal adaptation, occlusal contour, and approximal anatomical form. No statistically significant differences were found in postoperative sensitivity and recurrence of caries. The present results generally demonstrate that the clinical performance of the GIC materials were similar for most of the above-mentioned parameters. This finding may influence clinicians’ decision-making when considering restoration placement in class II restorations, suggesting that GIC is clinically suitable in appropriate systems. GIC exhibited acceptable performance for posterior teeth after 24 and 36 months [57].

Surface luster, which indicates the ability of a surface to reflect light, is fundamental to the esthetic appearance of restorations and is inversely proportional to surface roughness. The clinical success of a restoration is greatly influenced by the surface texture of a dental material [58]. All surfaces within the oral cavity are covered by the acquired pellicle and undergo biofilm adhesion. Bacteria are associated with dental diseases, such as periodontal disease and dental caries. Accordingly, surface roughness affects a surface’s ability to modulate and limit bacterial attachment and propagate microorganisms [59]. GIC is inferior to RC, but the surface luster of GIC is comparable to that of the enamel. GIC exhibits slight deviation to dull surfaces but can be enhanced by covering it with a film of saliva or multiple pores on more than one-third of its surface. Therefore, no GIC failed for this purpose according to the FDI criteria (4 and 5). Many of the studies used surface coatings and recorded improved surface luster [47,60–62], indicating that resin coatings are effective in transforming restoration surface texture without excessive polishing. However, extended recall periods revealed that the coatings degrade after enduring mastication and show a dull appearance [63]. Therefore, surface texture deterioration may be attributed to the positive correlation between surface roughness and wear [64].

Few GIC groups showed significant differences from RC in surface staining from baseline to recall periods. The lack of profound staining may be due to GIC’s self-adhesion properties to enamel and dentin, eliminating the need for bonding agents [65]. Surface staining may be influenced by the combination of extrinsic stimulus and surface roughness, which correlates with wear [66]. Additionally, fractures, defects, gaps at the margins, and marginal staining in the crevice between the restoration and the cavity wall can be related to pigment absorption [47]. Marginal staining was observed in few cases during 6-year recall period [60]. Despite the minor statistical significance of the results, no GIC was significantly affected by staining or margin criteria because stains can be easily removed by polishing [40].

In relation to color matching of GIC restorations at different recalls, GIC groups performed worse than the RC groups in 3 studies. This result may be related to GIC’s optical properties, which were outperformed by RC because of GIC’s lack of translucency [67,68]. This conclusion contrasts with the findings of other investigations, which found that neither GIC nor RC restorations have a significant color mismatch with the surrounding tooth structure. In 1 study, EQUIA Forte had a better color match with adjacent tooth structures than the other GIC groups because of the small highly reactive glass particles within EQUIA Forte and the coating [47,69]. Two studies revealed an improvement in color matching for the GIC group at 5- and 10-year recall, which may be connected to GIC’s maturation over time [47,49]. This result is congruent with the findings of a 3-year clinical study conducted by Diem et al [70], who found that the color match of GIC restorations improved during the study period.

Esthetic anatomic form is the acceptability of the esthetics of a restoration [40]. Significant results for GIC’s esthetic anatomical form were found in studies that compared GIC with RC, ranging from an ideal form to a form that deviates from the norm but is still acceptable. This deviation can be related to the high wear rate or material fracture for GIC [71]. By contrast, 2 studies found no appreciable deviation in the form of the anatomical esthetic [47,49], which is supported by a systematic review by Dias et al [28], who found no deficiency for this parameter.

In relation to fracture and retention of GIC materials, only 1 study found significant differences I fracture rates, and another found fracture as the leading cause of failure, despite yielding no significant results. The remaining studies investigating material fracture found no significant difference from baseline to recall periods and in comparisons with RC. These findings contradict the existing literature, which suggests that CGIC is highly prone to fracture, especially compared with RC [72]. The studies included in this review used reinforced restorative systems indicated for load-bearing restorations (Table 3). This may increase the fracture toughness and durability of the restorations we explored. These restorative systems frequently included a paired surface coating, such as EQUIA Fil and EQUIA COAT, improving mechanical properties, such as fracture resistance. Increased fracture resistance and high strength were observed after the application of coating agents, which prevented contamination caused by intra-oral fluids before hardening. This type of contamination can lead to loss of matrix-forming ions, weakens a material, and degrades reinforcing properties within a coating’s matrix [73–75]. A review of material longevity shows that GIC typically has a success rate of 93–98% within the primary dentition for the tooth’s lifespan and 5 years within the adult dentition [76]. Therefore, the result from this study exceeds this expectation because many restorations have been retained for up to 10 years. The existing literature regarding the lifespan of GIC within load-bearing restorations was created 13 years ago. Therefore, developments in the composition of different brands of GIC may account for the improvement in retention.

Concerning marginal adaptation, an acid- or base-resistant layer is created by the chemical adhesion of GIC to the tooth structure, creating a long-lasting marginal seal [77]. Furthermore, the dimensional stability of GIC is due to its hydrophilicity, which promotes the absorption of any fluid produced from the cavity prep, and adhesion to enamel ensures that the seal is fixed [13]. Additionally, GIC has the same coefficient of thermal expansion as the tooth structure, and the microgap between a restoration and a tooth is small [78]. Coatings reduce the formation of marginal gaps and were applied in the included studies [79]. Reducing the risk of marginal gaps is necessary, as the dentin pulp complex is exposed to the oral environment by restorations with poor marginal adaptation, and restorations are vulnerable to microleakage and plaque retention [80]. These results varied, and 2 studies showed failures for this subgroup; both compared Fuji IX and EQUIA, but reported contradictory results. Thus, both materials may be at risk of marginal gaps after 3-year recall [70].

Clinical evaluation of wear is performed to determine how materials behave when subjected to challenging masticatory changes in the mouth. All the restorations were clinically acceptable in terms of wear resistance according to the findings of this study. This might be explained by the modern GIC’s increased flexural strength and wear resistance. Additionally, the coating agent permeates the pores and stops cracks in restorations from spreading [81]. Only 1 study stated that the participant’s occlusion was normal, preventing excessive wear rates caused by clenching or bruxism habits [70]. Progressive occlusal wear was reported in all studies despite the absence of failure. The impact of coarse particles in dietary components and the strong occlusal forces in the posterior region may reflect pitting and wear [82].

The tightness and durability of the proximal contact points of restorations are crucial because poor contact results in food impaction and discomfort during mastication [83]. Small changes in approximal anatomical form occurred in Vitremer and Filtek after a 2-year recall [53]. Cyclic loads generated occlusal-proximal marginal fractures and damaged the proximal point [84]. Given that only 1 study produced significant results, GIC may fit the requirements for approximal anatomical shape. However, a recent RCT identified approximal anatomical shape as one of the primary causes of a class II GIC restoration failure [85].

In relation to periodontal response, a single study found a significant difference in gingival health between Vitremer and Z250. At 12- and 24-month recalls, Santos et al [86] found that RMGIC positively affected subgingival biofilm composition more than RC. According to Atieh, open-sandwich restorations exposing Vitremer in their proximal aspect resulted in considerable improvement in gingival health when compared to SSC [87].

Despite the success of outcomes regarding GIC within this review, most of the included studies covered less than 5 years of recall. Therefore, large studies with long follow-up times are required. Attention should be placed on approximal restorations. In addition, the guidelines in the WHO’s Prevention and Treatment of Dental Caries with Mercury-Free Products and Minimal Interventions have recommended GIC for single-surface occlusal restorations [88]. The heterogeneity of the studies can be considered another limitation of this review, and the GIC and RMGIC have distinct compositions and microstructures.

This review did not focus on surface coatings within GIC systems. However, the GIC and surface coating are promising materials at appropriate indications and cavity geometries when mechanical factors are considered. Further research may be required, especially long-term clinical studies that evaluate the efficacy of surface coatings in enhancing the mechanical properties of GIC in load-bearing restorations.

Conclusions

Our study found that GIC is suitable for load-bearing restorations. Notably, RC is superior to most subgroups with regard to dichotomous outcomes. However, the differences were considerable. Notable differences in surface luster, color match, translucency, and marginal adaptation were observed.