Three-year Clinical Performance of Two Giomer Restorative Materials in Restorations

INTRODUCTION

Resin composites have been used in dentistry for more than five decades. In recent years, their formulations were significantly improved to expand the range of clinical indications.¹ Different manufacturing techniques, compositions, filler types, and filler sizes affected the overall properties of these materials. Improvements in filler technology and formulations made composite resin materials suitable even for the stress-bearing areas of posterior teeth.² Nanocomposites are among the most recent developments, offering reduced polymerization shrinkage, increased mechanical properties such as tensile and compressive strength to fracture, improved optical characteristics, and better retention.^2,3

Flowable resin composites are lower viscosity resins that typically have a lower filler content than universal composites. Their flow characteristics make them useful for restoring small cavities or as a cavity liner for improved adaptation to the cavity walls of larger cavities.⁴ They effectively seal the microstructural irregularities of cavity preparations prior to conventional resin composite placement. Therefore, it has been confirmed that using flowable resin composites as a liner improves marginal integrity and reduces the microleakage of resin composite restoration.⁵ Filler content and monomer composition vary among different brands of flowable resin composites, offering various properties.

Giomer (glass ionomer + polymer) restorative materials were introduced more than 15 years ago, and they contain prereacted glass ionomer (PRG) filler particles embedded in a resin matrix.⁶ Giomers are manufactured by reacting acid-reactive fluoride-containing glass with polyacids in the presence of water.⁷ PRG fillers are divided into two categories: full reaction type PRG (F-PRG) fillers and surface reaction type PRG (S-PRG) fillers. In F-PRG fillers, the entire filler particle reacts with polyacrylic acid and releases a large amount of fluoride as the core of the particle is completely reacted. Therefore, unlike S-PRG fillers, F-PRG fillers degrade faster. In S-PRG fillers, only the surface of the filler reacts with polyacrylic acid, and the glass core remains intact.⁸ Giomers offer improved clinical handling and physical characteristics compared with conventional and resin-modified glass ionomers while providing the esthetic properties of resin composites.⁸ S-PRG fillers in giomer materials also allow for the release and recharge of fluoride that is comparable to glass ionomer materials but is more than that of fluoride-containing resin composites.⁹

Giomers have a successful short- to long-term clinical history in Class I, II, and V lesions.^7,8,10–12 Beautifil II (Shofu Inc) is one of the universal second-generation giomer restorative resin materials, which combines the characteristics of both composite resins and glass ionomers. This giomer-based resin actually represents a special class of composites that offers both protection against caries and provides functional and esthetic results. Based on S-PRG technology, it is comprised of aluminofluoro-borosilicate glass and multifunctional glass fillers, with particle sizes ranging from 0.01–4.0 μm. Additionally, it contains discrete nanofillers (10–20 nm) and has a total filler content of 83.3 wt% (68.6 vol%),¹³ which means that a glass-ionomer-like structure surrounds multifunctional glass fillers, with an external hard glass layer. Therefore, the fillers gain great physical strength and release fluoride (F) and 5 other ions (Na, sodium; B, borate; Al, aluminum; Si, silicate; and Sr, strontium) without causing deterioration of the properties of the material.¹⁴ More recently, a flowable giomer restorative material, Beautifil Flow Plus F00 (Shofu Inc), was introduced. It is indicated as a flowable base, liner, and final restorative material. Similar to Beautifil II, Beautifil Flow Plus F00 is also based on S-PRG technology. It has a filler content of 67.3 wt% (47.0 vol%).^15,16 Both materials are indicated for Class I–V lesions.

The longevity of resin composite restorations has been previously reviewed;¹⁷ they exhibit lower clinical success than other materials.^18,19 The main reasons for the failure of composite resin restorations are secondary caries and fracture.¹⁷ The properties of resin restorative materials utilizing PRG technology include increased wear resistance and a high level of radiopacity, due to the presence of multifunctional glass fillers and shade conformity, owing to the improved light diffusion and fluorescence of the material.⁸ One of the very specific advantages of giomer restoratives is their release of fluoride²⁰ and, therefore, their possible ability to prevent secondary caries.²¹ Giomers with S-PRG fillers could release a greater amount of fluoride than that of other fluoride releasing resin composites.^22,23 Additionally, it was speculated that the amount of released fluoride was possibly related to the flow level of the restorative material: the higher the flow, the greater the amount of fluoride release.²²

This prospective study investigated and compared the three-year clinical performance of a flowable and a conventional fluoride-releasing giomer restorative material containing S-PRG fillers, bonded with a two-step, self-etch adhesive to restore posterior Class I lesions. The null hypothesis tested was that there would be no difference in the clinical performance of the two giomer materials.

METHODS AND MATERIALS

In this prospective, open clinical study, 44 pairs of Class I cavities were restored with either a flowable giomer restorative material (Beautifil Flow Plus F00; Shofu Inc) or a conventional giomer restorative material (Beautifil II; Shofu Inc) after the application of a two-step, self-etch adhesive system (FL-Bond II; Shofu Inc) and a flowable giomer liner (Beautifil Flow Plus F03; Shofu Inc) (Table 1).

Table 1. Restorative Materials and Adhesive System Used in the Study

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Clinical Evaluation of the Restorations

The restorations were evaluated according to the modified United States Public Health Service criteria²⁴at baseline, 6-month, 18-month, and 36-month follow-up visits (Table 2). Two calibrated examiners who were not involved in the operative process evaluated the restorations with a mirror, explorer, and air stream. In case of a disagreement, examiners re-evaluated the restorations until a consensus was reached. Digital color photographs of the lesions and the restorations were taken at baseline and at each follow-up visit for documentation purposes.

Table 2. Evaluation Criteria of the Restorations According to Modified United States Public Health Service Criteria

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Both tested materials were compared with Fisher’s exact test. Each tested criterion for each material was analyzed separately (with respect to different follow-up periods) using Friedman’s test.

RESULTS

Of the 44 original pairs of restorations placed, 39 were available for evaluation at the 3-year follow-up visit. The number of patients, score percentages, and statistical significance values for the criterions, which revealed different outcomes at different follow-up periods, are presented in Tables 3, 4, 5, and 6. None of the restorations showed retention loss, postoperative sensitivity, secondary caries, or color change. For the marginal integrity, marginal discoloration, and surface anatomic form, Friedman’s test revealed that the quality of Beautifil II restorations was significantly lower at 36 months than at baseline (p=0.007) (Tables 3, 4, 5). However, there was no significant difference between the baseline and 36-month follow-up scores for the surface texture criteria with Beautifil II (p>0.05) (Table 6). For Beautifil Flow Plus F00, no differences were found between the baseline and the 36-month follow-up scores for any of the criteria (p>0.05).

Table 3. Results of Clinical Evaluation of Marginal Integrity Criterion

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Table 4. Results of Clinical Evaluation of Surface Anatomic Form Criterion

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Table 5. Results of Clinical Evaluation of Marginal Discoloration Criterion

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Table 6. Results of Clinical Evaluation of Surface Texture Criterion

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Fisher’s exact test revealed no difference between the performance of Beautifil Flow Plus F00 and Beautifil II at 36 months for all the criteria evaluated (p>0.05).

DISCUSSION

Clinical studies can provide important information in respect to material performance and changes over time.²⁵ This study employed a 36-month observation period with 6- and 18-month intervals. The recall rate of this study was 100% at 6 months and 88.64% at 18 months and 36 months. A similar study reported a recall rate of 80% at 36 months,¹⁶ while another study revealed a recall rate of only 59%,²⁶ which is far lower than that of this study.

In this study, all restorations of the presented patients (39 patients) remained intact, with no postoperative sensitivity or secondary caries at the 36-month follow-up. The absence of postoperative sensitivity may be attributed to the use of a two-step, self-etch adhesive, which does do not entirely remove the smear layer.²⁶ Therefore, the outcomes in respect to this parameter may not be solely related to the type of the giomer resin material used. The only deterioration observed was minimal loss of marginal integration and slight marginal discoloration in the teeth restored with Beautifil II after 36 months. Regarding marginal integrity and marginal discoloration, 10.3% of the restorations received Bravo ratings for both of these criteria. Another study found higher Bravo ratings—41.9% for marginal integrity and 16.1% for marginal discoloration—for Beautifil II.²⁴ The difference between the results could be due to lower recall rates in the previous study. Additionally, in this study, a flowable material, Beautifil Flow Plus F03, was used as a liner underneath both restorative materials. Such a low-modulus material could act as an elastic layer and dissipate the stresses generated by occlusal loads,²⁷ which may explain the different findings. Additionally, the use of a flowable material as a liner could improve the adaptation of the initial increment of the covering restorative material and may, therefore, influence the outcomes.

Teeth restored with the flowable giomer restorative material, Beautifil Flow Plus F00, did not exhibit any significant changes at the 36-month recall compared with baseline. Its flowable behavior has the ability to provide better adaptation to the cavity walls,^28,29 which may be a contributing factor for the sustained marginal integrity over time.

Previous clinical studies reported an acceptable clinical performance of first-generation giomer restorative materials.^7,8 In this study, a second-generation giomer restorative material, Beautifil II, also showed clinically acceptable results, confirming the results of previous studies with Beautifil II.^16,26,30 A recent observation showed that surface roughness, marginal adaptation, and marginal discoloration were the most frequent changes observed for Beautifil II after 36 months.²⁶ Forty percent of the restorations showed signs of slight crevices along the margin at occlusal surfaces.²⁶ This study revealed similar results for Beautifil II.

In a clinical trial,¹⁶ which compared Beautifil II and Beautifil Flow Plus F00 for 3 years, Beautifil Flow Plus F00 showed better performance regarding marginal integrity, marginal discoloration, surface roughness, and surface morphology (anatomic form) at the 36-month recall. Those materials performed similarly in this study.

Among the most prevalent factors for gap formation during long-term clinical service are polymerization shrinkage and differences between the thermal expansion coefficients of the restorative material and the tooth structure.³¹ This gap along the restoration–tooth interface potentially leads to leakage, marginal discoloration, secondary caries, and postoperative sensitivity. Cavities with high configuration factors may produce contraction stresses along the cavity walls,³² affecting the long-term marginal integrity of the restoration. In this study, Class I cavities, which have the highest configuration factor, were restored with giomer restoratives with different viscosities. The high cavity configuration factor must be viewed as a reason for the Bravo ratings observed for marginal integrity and marginal discoloration with Beautifil II at 36 months. Lower viscosity and higher elasticity may be contributing factors for the finding that Beautifil Flow Plus F00 performed better at the 36-month follow-up in respect to marginal integrity and discoloration. Besides material-dependent properties, finishing/polishing procedures, and chipping of restorative material at the cavosurface margins also influence marginal deterioration.⁸

Flowable restorative materials typically have a lower filler load than conventional composite resins.³³ The flowable giomer restorative material Beautifil Flow Plus F00 has a filler load of 67.3 wt % (47.0 vol %), which is higher than that of conventional flowable composites.³³ The high filler content with S-PRG fillers has shown to provide the flowable giomer material with superior physical properties and increased fluoride release over time.¹⁵ Therefore, it can be assumed that these superior properties can expand the range of indications for this material to the posterior regions. However, further clinical studies would be necessary to test this hypothesis. Although the hardness value of Beautifil Flow Plus F00 was reported to be lower than that of Beautifil II,¹⁵ 36-months follow-up evaluation did not yield any difference between them in respect to anatomic form. It was reported that fluorosilicate glass fillers in giomers are susceptible to degradation by weak acids³⁴ and that both Beautifil II and Beautifil Flow Plus F00 can be degraded by citric acid,¹⁵ which might influence their anatomic form during clinical service. However, longer-term follow-up trials would be needed to verify this. In addition, the size and the location of the restorations influence occlusal wear of the restorative materials.³⁵ Wear increases with a larger surface area and length of cavosurface margins. Since it was not possible to standardize cavities in this study, the location and the size of the restorations have possibly impacted the outcomes.

In general, it has been confirmed that giomer restorative materials present promising clinical outcomes.^{7,8,10–12,16,26} In this study, second-generation giomer restorative materials, both Beautifil II conventional giomer restorative and Beautifil Flow Plus F00 flowable giomer materials, clinically showed very good results without any significant difference from each other for all parameters evaluated in the study.