A randomized, prospective clinical study evaluating effectiveness of a bulk-fill composite resin, a conventional composite resin and a reinforced glass ionomer in Class II cavities: one-year results

Abstract Bulk-fill restorative materials such as bulk-fill composite resins and high viscous glass ionomer cements have become very popular materials in operative dentistry because their application is easy and time-saving. Objectives: The aim of this clinical study was to evaluate the clinical performance of a highly viscous reinforced glass ionomer material, a bulk-fill composite resin and a micro hybrid composite resin in Class II restorations. Methodology: In total, 109 Class II restorations were performed in 54 patients using three different restorative materials: Charisma Smart Composite (CSC); Filtek Bulk Fill Posterior Restorative (FBF); Equia Forte Fil (EF). Single Bond Universal adhesive (3M ESPE, Germany) was used with composite resin restorations. The restorations were evaluated using modified USPHS criteria in terms of retention, color match, marginal discoloration, anatomic form, contact point, marginal adaptation, secondary caries, postoperative sensitivity and surface texture. The data were analyzed using Chi-Square, Fischer's and McNemar's tests. Results: At the end of one year, 103 restorations were followed up. No changes were observed during the first 6 months. At the end of one year, there were small changes in composite restorations (FBF and CSC) but no statistically significant difference was observed between the clinical performances of these materials for all criteria (p>0.05). However, there was a statistically significant difference between EF, FBF and CSC groups in all parameters except marginal discoloration, secondary caries and postoperative sensitivity in one-year evaluation (p<0.05). Conclusion: Bulk-fill composite resins and conventional composite resins showed more successful clinical performance than highly viscous reinforced glass ionomers in Class II cavities.


Introduction
In modern dental practice, the advances in adhesive techniques, allied to increased focus on the aesthetic qualities of dental restorations and adoption of a minimally invasive dentistry approach, have great influence on the treatment plan in the posterior and anterior regions. 1,2 In recent years, posterior composites have been generally preferred for back tooth restorations by direct methods because of their advantages such as single visit and short application time, aesthetics, ability to protect dental tissues during preparation, and being cheaper when compared to indirect methods. 3 Negative results such as poor marginal adaptation, at the interface between tooth and restorative material. 8,9 However, it has been reported that bulk-fill composites do not adversely affect the polymerization shrinkage, the adaptation of the cavities and the degree of conversion during application, and exhibit less polymerization shrinkage than conventional composite resins. 9 In addition, glass ionomer cements (GIC) are materials that can be used as an alternative to composite resins in conservative restoration of caries lesions in the posterior region. GIC have advantages such as having a similar thermal expansion coefficient to natural tooth tissue, physicochemical adhesion to tooth tissues, fluoride release, biocompatibility, low shrinkage, low marginal leakage, anti-caries properties on the restoration edges, and increased remineralization in adjacent proximal caries. 10,11 However, conventional GIC have disadvantages such as low fracture and abrasion resistance, inadequate color stability, moisture sensitivity and poor aesthetic properties. These disadvantages weaken the physical properties of the material and restrict its use in areas exposed to intensive chewing forces. 12 In recent years, to reduce moisture sensitivity of GIC in early stages of hardening, to increase their hardness and abrasion resistance, and to enable them to be used in areas exposed to chewing forces, the materials were strengthened by changing the powder/liquid ratio, particle size and distribution, and highly viscous glass ionomer cements (HVGIC) were presented to the market. 12 The hardening mechanisms of these newly developed HVGIC are the same as conventional GIC.
Besides, abrasion resistance, fracture toughness, flexural strength, and sensitivity to moisture are improved when compared to conventional GIC. 13 Moreover, early water exposure does not adversely affect the physical properties of these materials since the setting reaction is faster in HVGIC, unlike in conventional GIC. 14 Nonetheless, the manufacturer suggests that these materials should be applied with surface coating resins. 15 In 2007, a new HVGIC restorative system (EQUIA; GC Europe, Tokyo, Japan) was introduced, which could be an alternative to composite resins in the posterior region, and was designed for the use in the permanent restoration of Class I, II and V cavities by combining the advantages of HVGIC and a surface coating resin. 13,16 The application of surface coating resins to GIC surface enhances the surface brightness of the material, prevents the translucency reduction of the material over time, fills the gaps caused by the material and finishing processes and surface irregularities to provide a smooth surface, reduces moisture sensitivity in the early stages of hardening, increases the resistance to fracture and abrasion, and improves mechanical properties. 15   -The patient should be over 18 years of age -Absence of adjacent and antagonist teeth; -The patient should have good periodontal status -Extremely poor oral hygiene, severe or chronic periodontitis; -Teeth to be restored should be symptomless and vital -Pregnant or lactating women -Teeth to be restored should have proximal contacts on both mesial and distal surfaces and be in occlusion with the antagonist teeth -Teeth that have any restoration, endodontic treatment, periodontal and periapical pathology.
-Teeth that have class II caries lesions in external and middle 1/3 of dentine thickness radiographically -The patients who are undergoing orthodontic treatment

Clinical Evaluations of the Restorations
In this study, all the participating dentists were trained for calibration before the study conduction.
After restoration placement, patients were followedup after one week (baseline), six months and one year. The restorations were clinically examined using A randomized, prospective clinical study evaluating effectiveness of a bulk-fill composite resin, a conventional composite resin and a reinforced glass ionomer in Class II cavities: one-year results

Criteria Alpha Bravo Charlie
Anatomic form The restoration is continuous with existing anatomic form The continuity of restoration with teeth partially degraded, but clinically acceptable.
The continuity of restoration with teeth completely deteriorated, need to be replaced.

Contact point
Normal contact point / no contact point but no periodontal irritation.

_
No contact point, but there is a periodontal irritation finding / the patient wants to change the filling.

Marginal adaptation
There is no visible evidence of a crevice along the margin into which the explorer will penetrate.
There is visible evidence of a crevice along margin into which the explorer will penetrate or catch.
The explorer penetrates the crevice, and dentin or base is exposed.

Marginal discoloration
There is no discoloration anywhere on the margin between the restoration and the tooth structure.
Discoloration is present but has not penetrated along the margin in a pulpal direction.
Discoloration has penetrated along the margin in a pulpal direction.

Secondary caries
No evidence secondary caries. _ Evidence secondary caries.

Color match
The restoration matches the adjacent tooth structure in colour and translucency.
The mismatch in colour and translucency is within the acceptable range.
The mismatch in colour and translucency is outside the acceptable range.

Postoperative sensitivity
No postoperative sensitivity, after the restorative procedure and during the study.
Slight sensitivity at any stage of the study.
Severe sensitivity at any stage of the study.

Retention
No loss of restorative material. _ Fracture and/ or loss of restorative material.

Surface texture
The surface of the restoration does not have any defects.
The surface of the restoration has minimal defects.
The surface of the restoration has severe defects.

Results
In total, 109 restorations were placed in 54 patients and, with a 95% recall rate, 103 restorations were evaluated at 6-month and one-year recall. Regarding the teeth, 46 restorations (44.7%) were placed in premolars, whereas 57 (55.3%) were placed in molars.
Clinical evaluation scores of restorations at baseline, 6-months and one year are given in Table 1. There was no significant difference between premolar and molar teeth for all parameters and all evaluation periods (p>0.05).
At baseline evaluation, all CSC, FBF and EF restorations were scored as "Alpha" for all criteria except color match. In the EF group, although the most appropriate material color was selected, six restorations were scored as "Bravo" and 26 restorations scored as "Charlie" for color match due to lack of translucency. At the 6-month evaluation, when compared to the baseline evaluation, no significant change was observed in all groups for all criteria (p>0.05).
After one year, survival rates of the CSC and FBF groups were 100%, whereas the survival rate in the EF group was approximately 69%. Ten EF restorations had to be replaced or modified as base because of marginal fracture and material loss in the proximal area at one year.
At one-year evaluation, regarding anatomic form, all restorations in the CSC and FBF groups were scored as "Alpha". In the EF group, 26 restorations were scored as "Alpha"; four restorations were scored as "Bravo" and two restorations as "Charlie". For anatomic form criteria, statistically significant difference was found between the EF group and CSC group and between the EF and FBF groups (p<0.05), whereas there was no statistically significant difference between the CSC and FBF groups (p>0.05). At one-year evaluation, in marginal adaptation criteria, 34 FBF restorations were scored as "Alpha", two FBF restorations were scored as "Bravo"; 30 CSC restorations were scored as "Alpha" and five CSC restorations were scored as "Bravo"; in the EF group, 20 restorations were evaluated as "Alpha", 10 restorations as "Bravo" and two as "Charlie. For marginal adaptation criteria, there was statistically significant difference between the EF group and CSC group, and between the EF and FBF groups (p<0.05), whereas there was no statistically significant difference between the CSC and FBF groups (p>0.05).
At one-year evaluation, in retention criteria, all CSC and FBF restorations were scored as "Alpha". In the EF group, eight restorations were scored as "Charlie" due group was evaluated as "Bravo" in terms of color match. In the EF group, no color change was observed between evaluation periods. In term of surface texture, there was no change in the FBF and CSC groups, whereas nine restorations in the EF group were scored as "Bravo" and one restoration was scored as "Charlie" for surface texture. For color match and surface texture criteria, there was statistically significant difference between the EF and CSC groups, and between the EF group and FBF group (p<0.05), whereas there was no statistically significant difference between the CSC and FBF groups (Figures 6, 7) (p>0.05).
Regarding the marginal discoloration criterion, only two FBF restorations and one EF restoration were scored as "Bravo", whereas other restorations were scored as "Alpha". For marginal discoloration criteria, A randomized, prospective clinical study evaluating effectiveness of a bulk-fill composite resin, a conventional composite resin and a reinforced glass ionomer in Class II cavities: one-year results  there was no statistically significant difference between the groups (p>0.05). During the one-year evaluation, no postoperative sensitivity and secondary caries were observed in any of the restored teeth and all 103 restorations were scored as Alpha (p>0.05).

CRITERIA
In this study, ten EF restorations needed replacement at the end of one year. Distribution of failed restorations according to gender, age and type of teeth are shown Table 2.   In this study, cotton pellets and suctions were used to isolate the operative field. The safest way to maintain optimal moisture control is using a rubber dam; however, this is usually impractical in routine activity since it may disturb the patient, and sometimes the placement of the clamp can be traumatic for gingival tissues. Moreover, there are studies in the literature that showed that the use of rubber dam did not affect the clinical behavior of the materials, and that careful isolation with cotton rolls gives similar retention results. 19,20 Objective and reliable criteria for clinical trials should be used to determine the clinical performance of restorative materials. The USPHS criteria are often preferred in clinical follow-up studies and provide ease of direct application to study. 21,22 For this reason, this clinical study evaluated the clinical performance of tested restorative materials using a modified USPHS criteria under the supervision of two different experienced dentists.
A randomized, prospective clinical study evaluating effectiveness of a bulk-fill composite resin, a conventional composite resin and a reinforced glass ionomer in Class II cavities: one-year results  Universal adhesives are the latest generation adhesive systems that can be used in both etch & rinse and self-etch modes. In literature, studies report that there is no difference between the application strategies on clinical behavior of universal adhesives. 23,24 However, Marchesi, et al. 25 (2014) investigated adhesive stability over time of a universal adhesive applied using different bonding techniques on human coronal dentine. They concluded that improved bonding effectiveness of the tested universal adhesive system on dentine was obtained when the adhesive was applied with the self-etch approach. Furthermore, Single Bond Universal adhesive (SBU) contains Vitrebond (3M ESPE), a polyalkenoic acid copolymer that provides chemical bonding with hydroxyapatite crystals, and the high bond strength of SBU is considered to be associated with the polyalkenoic acid copolymer present in its content. [26][27][28] In this study, SBU was actively applied in self-etch mode (rubbing with a microbrush) to eliminate problems arising from the etching since such procedure is a step that requires a sensitive technique. The first explanation of this glass ionomer material loss in the proximal area may be related to protective resin. It is very difficult to apply the resin coating to the proximal wall of glass ionomer restoration effectively because the proximal area is not easily accessible.
If the surface-coating agent cannot be applied effectively, the proximal area is unprotected from moisture contamination during the initial hardening phase and the glass ionomer cement may dissolve. [33][34][35] Another explanation of this glass ionomer material loss in the proximal area is the use of metal matrices during restorative procedure. Glass ionomers can chemically adhere to metals, and micro cracks may occur in the glass ionomer cement with the force applied during removal of the matrix. These micro cracks may make the material more susceptible to chemical attacks. 34 In this study, there was a higher relative risk of failures in molar teeth compared to premolar teeth in EF group when ten failed restorations were analyzed according to tooth location. Moreover, five of these ten restorations were in lower molar teeth. These findings can be explained by the knowledge that restorations of molar teeth are subjected to higher masticatory stresses than restorations of premolar teeth. In addition, chewing forces are strong in lower molar teeth and the increased stress could cause fatigue and fracture of the material, as a result of the position of the lower molar teeth in the dental arch depending on von Spee's curve. 18,36 Furthermore, it has also been reported that surface-coating agents wear over time. 37 In our study, a slight increase in surface roughness was observed due to the wear of the surface-coating agent at the 12-month evaluation, whereas no surface changes were observed at the 6-month evaluation of EF restorations.
In this study, another problem with EF restorations was color match with the surrounding dental tissue.
HVGICs have more translucency than conventional GICs and HVGIC also has more color options. Even so, color and translucency properties of HVGIC restorations were still not enough and its color match was not as good as composite resin restorations during follow-up period in this study. In our study, since the restorations were in the posterior region and the patients were not disturbed by their appearance, the replacement due to color mismatch was not For deep caries lesions, stepwise caries removal could also be an option to avoid pulpal complications during disease control. In this treatment protocol, after 6-8 months, temporarily treated teeth are re-entered, all remaining demineralized dentin is removed, and a final treatment is provided as appropriate. 40 In this study, it was found that high viscosity glass ionomer material was unsuitable as permanent restorative material within the tested situations. However, the use of this glass ionomer material as semi-permanent material can be considered.
Short evaluation time is one of the limitations of this study. Although long-term follow-up is important to compare and evaluate the clinical performances of restorative materials, short-term clinical data can also give some useful information about the clinical performances of the materials. Although our study is a short-term clinical study, the patients will continue to be followed-up for additional evaluations.
The fact that it is not designed as split-mouth is another limitation of this study. Split-mouth study designs can reduce most inter-patient variability such as oral hygiene, diet and brushing habits etc. on the longevity of restorations. The possible patient loss is a disadvantage of split-mouth designs since more restorations than one would be lost when a patient did not come for follow-up appointment. Although this study was not designed as split-mouth and the variables between patients were ignored, the patients not fulfilling the inclusion criteria were excluded in the study.

Conclusion
At the end of one year, both highly viscous bulkfill composite resin and conventional micro hybrid composite resin showed similar and successful clinical performance whereas HVGIC showed worse. However, the use of high viscosity glass ionomer material as a semi-permanent restorative material in stress bearing Class II cavities rather than permanent material might be more appropriate since high failure rates were observed after one year.