Marginal adaptation of thermoviscous bulk-fill composite in class II cavities

Nermeen A Ramadan; Mostafa M A. Hasan; Ali I Abdalla

doi:10.4103/tdj.tdj_50_22

ORIGINAL ARTICLE

Year : 2023 | Volume : 20 | Issue : 2 | Page : 77-83

Marginal adaptation of thermoviscous bulk-fill composite in class II cavities

Nermeen A Ramadan BDS , Mostafa M A. Hasan, Ali I Abdalla
Department of Restorative Dentistry, Faculty of Dentistry, Tanta University, Tanta, Egypt

Date of Submission	24-Oct-2022
Date of Decision	24-Jan-2023
Date of Acceptance	05-Feb-2023
Date of Web Publication	11-May-2023

Correspondence Address:
Nermeen A Ramadan
Master's Degree Student, Department of Restorative Dentistry, Faculty of Dentistry, Tanta University, Elgeish Street, Tanta
Egypt

Source of Support: None, Conflict of Interest: None

Check

DOI: 10.4103/tdj.tdj_50_22

Abstract

Objective
To evaluate the marginal adaptation of thermoviscous bulk-fill, preheated, and conventional nanohybrid composite resins in class II cavities.
Patients and methods
Thirty extracted human sound molars were selected in this in vitro study. Simple class II cavities were prepared using carbide bur. The overall dimensions and depth of cavities were standardized as follows: 4 mm length occlusocervically, 4 mm width buccolingually, and 2 mm depth axially. The teeth were randomly divided into three groups (n = 10 each). Futurabond DC (one-step self-etch adhesive) was applied in all groups. Group 1: cavities were restored with VisCalor bulk composite, group 2: cavities were restored with Grandio composite, group 3: cavities were restored with preheated Grandio composite. The specimens of each group were thermocycled in a thermocycling apparatus by alternating immersion in a water bath at 5 and 55°C with a dwell time of 2 min for 600 thermal cycles. Impressions of the teeth were made and then poured with epoxy resin and replicas were examined under scanning electron microscopy to examine marginal gaps. All data were collected, tabulated, and statistically analyzed.
Result
The highest percentage of marginal gap length was recorded for group 2, recording 22.93%, while there was no significant difference between group 1 and group 3, recording 13.44 and 13.83%, respectively. One-way analysis of variance test was used to compare the tested groups at a level of significance (P < 0.05).
Conclusion
The marginal gaps decreased when VisCalor bulk and Grandio composite resins were applied after preheating so preheating composite resins considerably improves marginal adaptation.

Keywords: marginal gap, preheating, resin composite, VisCalor bulk

How to cite this article:
Ramadan NA, A. Hasan MM, Abdalla AI. Marginal adaptation of thermoviscous bulk-fill composite in class II cavities. Tanta Dent J 2023;20:77-83

How to cite this URL:
Ramadan NA, A. Hasan MM, Abdalla AI. Marginal adaptation of thermoviscous bulk-fill composite in class II cavities. Tanta Dent J [serial online] 2023 [cited 2023 May 28];20:77-83. Available from: http://www.tmj.eg.net/text.asp?2023/20/2/77/376638

Introduction

In recent years, the indications for resin-based composite restorations were constantly increased due to advances in the technology of composite materials and related adhesive systems ^[1].

Several types of composite resins have been developed to improve the physical properties and performance of composite restorations, such as nanohybrid composites which entered the market with claims of less polymerization shrinkage, reduced shrinkage stress, and even higher wear resistance ^[2].

Marginal adaptation and absence of leakage are the most important factors determining the longevity of the restoration. Even if a perfect marginal seal isn't achievable clinically, good marginal quality should be the major target for clinicians ^[2],[3].

Traditional composites are applied in individual increments of a maximum 2 mm thickness because of their particular polymerization properties and limited depth of cure. Each increment is polymerized separately for 10–40 s, counting on the light intensity of the curing device used, the shade and translucency level of the composite paste, and the type and concentration of the photoinitiator system of the restoration material ^[4],[5].

The incremental technique is often very time-consuming and complicated ^[4]. That is why many dentists are trying to find an alternative to this complex multilayer placement technique ^[6].

The bulk-fill composites have been developed in recent years in response to this increased demand to shorten the application time and provide ease of use of resin composites. These materials can be placed into cavities in increments of 4–6 mm with short polymerization times of 10–20 s per increment when a high-intensity curing light is used ^[7].

These materials can be divided into flowable (low-viscosity) and packable (high-viscosity). High-viscosity bulk-fill composites are highly resistant to slumping and contain more inorganic fillers, whereas low-viscosity (or flowable) bulk-fill composites generally adapt better on the cavity walls, especially on irregular surfaces. So the flowable composites have better marginal adaptation because of their flow consistency during application. However, they exhibit lower mechanical properties than packable composites because of their lower filler load ^[8].

A high reduction of viscosity can be achieved by preheating the packable composite before application ^[9]. The temperature rise reduces the composite's viscosity by increasing the mobility of the matrix monomers, which facilitates the molecular slippage of the fillers ^[10]. This can approximate the material viscosity close to the flowable composite ^[11].

Preheating may have a beneficial impact on marginal adaptation by reducing the viscosity of composite resins. Increased flowability can facilitate the application of the filling material, consequently making the procedure less time-consuming ^[12].

Viscalor bulk (Viscalor bulk composite; VOCO, Cuxhaven, Germany) is a thermoviscous bulk-fill material that has been developed recently. It is the first nanohybrid composite specially developed for heating up ^[9]. As a result, VisCalor bulk affords the advantages of both a flowable composite and a packable composite during the application of the restoration. This allows restorations without several working steps for base filling or covering layers ^[13]. The viscosity of VisCalor bulk is decreased to a rate higher than 90% at 69°C ^[11].

However, the composite resin can be warmed, the rise of temperature must be limited. Beyond this limit (close to 90°C), reactive, low-molecular-weight components can be volatized, impairing the polymerization kinetic ^[14].

The aim of this study was to evaluate the marginal adaptation of thermoviscous bulk-fill, preheated, and conventional nanohybrid composite resins in class II cavities.

Patients and methods

Ethical consideration

Approval for this project was obtained from Faculty of Dentistry, Tanta University Research Ethics Committee. The purpose of this study was explained to the patients and informed consents were obtained to use their teeth in the study according to the research guidelines on human research published by the Research Ethics Committee at Faculty of Dentistry, Tanta University.

The study design

This study was conducted as a randomized controlled laboratory trial.

The sample size

Thirty extracted human sound molars were selected in this study. Teeth were extracted for periodontal, orthodontic, or impaction reasons. Teeth with caries, cracks, fractures, or defects in the enamel development were excluded ^[15]. The teeth were stored in distilled water containing 0.2% thymol antiseptic solution for 48 h at 37°C immediately after extraction. They were cleaned of debris using a rubber cup and were polished with pumice using a low-speed handpiece then stored in normal saline solution for less than 3 months in the refrigerator to prevent dehydration ^[16].

Materials

The materials that were used in this study were two types of composite materials:

Viscalor bulk (thermoviscous bulk-fill composite).
Grandio (nanohybrid composite).
Futurabond DC adhesive (one-step self-etch adhesive).

The chemical compositions, manufacturer, and website of tested materials are shown in [Table 1].

Table 1 Materials, composition, manufacturers, and website

Click here to view

Methods

Preparation of specimens

Each tooth was fixed with sticky wax to the base of plastic cylinder. The cylinder was filled with self-curing acrylic resin so that only roots were embedded. Simple class II cavities with parallel walls were prepared ^[17]. The cavities were prepared using carbide bur (#245, SS White, Meta Dental Com, Korea) using a high-speed handpiece with water-cooling. Each bur was replaced after five preparations ^[18]. The cervical margin was established 1.5 mm above the cemento–enamel junction. The overall dimensions and depth of cavities were standardized as follows: 4 mm length occlusocervically, 4 mm width buccolingually, and 2 mm depth axially. The cavity depth and length were judged with a permanent mark on the bur and then verified using a periodontal probe (Hu-Friedy Mfg. Co., Chicago, Illinois, USA.) ^[19].

Grouping of specimens

The teeth were randomly divided into three groups (n = 10 each) according to the procedure of restoration:

Futurabond DC adhesive was applied in all groups using a disposable microbrush, rubbed for 20 s, dried with gentle stream of air for 5 s, and cured using the LED light-curing device (Woodpecker, Guilin, China) with 1000 mW/cm² of power intensity for 10 s at a distance of 1 mm according to the manufacturer's instructions.

Group 1: VisCalor bulk was preheated before the application with the VisCalor Dispenser at 68°C, according to the operating instructions, due to its thermoviscous behavior, then applied in bulk to fill the entire cavity and cured for 20 s using the lightcuring device according to manufacturer's instructions.

Group 2: Grandio composite resin was applied incrementally and each increment was in 2 mm thickness then cured for 20 s using the light-curing device according to the manufacturer's instructions.

Group 3: Grandio composite was preheated to 55°C in the Ena Heat device and then inserted into the cavities. The composite syringe was then returned to the Ena Heat device after application of the first increment to avoid temperature loss during curing of the first increment ^[20]. The composite was cured for 20 s using the light-curing device.

After that, all restorations were finished under water-cooling by finishing diamond stones and polished with flexible disks (TOR VM, Moscow, Russia). Then, all teeth were kept in distilled water for 24 h ^[21].

Thermocyling

The specimens of each group were thermocycled in a thermocycling apparatus (custom made apparatus at Conservative Dentistry Department, Faculty of Dentistry, Alexandria University) by alternating immersion in a water bath at 5 and 55°C with a dwell time of 2 min for 600 thermal cycles which corresponds to 12 months of clinical service ^[22].

Evaluation of marginal adaptation

Impressions of the teeth were made using a polyvinyl Siloxane material (Zetaplus, zhermack, Germany) (light body). The impressions were then poured with epoxy resin (Kemapoxy 131, CMB, Egypt). These replicas were left 24 h for complete setting. Then, gold sputtered to render the surface electrically conductive.

These replicas were examined under scanning electron microscopy (SEM) (JSM-5300 scanning microscope; JEOL, Peabody, Massachusetts, USA) at 30 Kv power with different magnifications (×20 and ×1000) to examine marginal gaps. The low magnifications (×20) provided an overview of the proximal surface of each sample at the level of the interface, whereas with high magnification (×1000) viewed the selected area of the tooth–restoration interface.

The resultant SEM micrographs were scanned on a monitor screen, then they were transferred onto Orion 6.60.4 software program and these micrographs appeared on the computer to determine marginal fit.

The degree of marginal gaps was determined as the ratio of the length of gaps to the total length of the margins for cervical and proximal margins, and then converted to a percentage, and the width of gaps was measured.

Statistical analysis

The recorded data related to each group were collected, tabulated, and statistically analyzed using statistical package for the social sciences (SPSS, version 23) (SPSS Inc., Chicago, Illinois, USA) with one-way analysis of variance and Tukey's test ^[23].

Results

Gap length and width

Length of the marginal gap

SEM micrographs of the tested specimens were used for gap length measurement using AutoCAD software. The length of marginal gap was calculated as a percentage of the entire margin length.

The mean ± SD marginal gap length values (mm) of the data collected from all tested groups were tabulated in [Table 2].

Table 2 Mean (mm) and SD of marginal gap length values in the proximal cavity of the three tested groups

Click here to view

It was found that, the highest mean value of marginal gap length was recorded for group 2 followed by group 3, while the lowest mean marginal gap length value was recorded for group 1.

One-way analysis of variance test was used to compare the tested groups at a level of significance P value less than 0.05 and reported statistically significant difference.

Tukey's test was performed to find out which group is responsible for the recorded difference and found that the responsibility falls on group 2.

It was found that the highest percentage of marginal gap length was recorded for group 2, recording 22.93% followed by group 3, recording 13.83%, while the lowest percentage of marginal gap length value of 13.44% was recorded for group 1.

Gap width

The composite/tooth interface was divided into three regions and measurements of marginal gap widths in each region were made at (×1000) magnification. The largest marginal gap width in each region was recorded in micrometers, and the mean gap widths for tested groups were calculated.

(1) Width of the cervical gap:

The mean ± SD values of marginal gap width (μm) of the data collected from all tested groups were tabulated in [Table 3].

Table 3 Mean (μm) and SD of mean values of width of cervical gaps of the three tested groups

Click here to view

It was found that, the highest mean value of gap width cervically was recorded for group 2 followed by group 3, while the lowest mean marginal gap width value was recorded for group 1.

Tukey's test was performed to find out which group is responsible for the recorded difference and found that the responsibility falls on group 2.

Representative SEM micrographs are shown in [Figure 1], [Figure 2], [Figure 3].

Figure 1 SEM micrograph of a restoration in group 1 with no gap formation in the cervical wall (magnification ×1000). SEM, scanning electron microscopy.

Click here to view

Figure 2 SEM micrograph of a restoration in group 2 with gap formation in the cervical wall (magnification ×1000). SEM, scanning electron microscopy.

Click here to view

Figure 3 SEM micrograph of a restoration in group 3 with gap formation in the cervical wall (magnification ×1000). SEM, scanning electron microscopy.

Click here to view

(2) Width of the proximal gap:

The mean ± SD values of marginal gap width (μm) of the data collected from all tested groups were tabulated in [Table 4].

Table 4 Mean (μm) and SD of mean values of width of proximal gaps of the three tested groups

Click here to view

It was found that the highest mean value of gap width proximally was recorded for group 2 followed by group 3, while the lowest mean marginal gap width value was found at group 1.

Tukey's test was performed to find out which group is responsible for the recorded difference and found that the responsibility falls on group 2. Representative SEM micrographs are shown in [Figure 4] and [Figure 5].

Figure 4 SEM micrograph of a restoration in group 2 with gap formation in one proximal wall (magnification ×1000). SEM, scanning electron microscopy.

Click here to view

Figure 5 SEM micrograph of a restoration in group 3 with gap formation in the proximal wall (magnification ×1000). SEM, scanning electron microscopy.

Click here to view

Discussion

In the current study, it was found that the highest percentage of marginal gap length was recorded for group 2 followed by group 3, while the lowest percentage of marginal gap length was recorded for group 1. This may be attributed to the reduced viscosity of preheated resin composites. As the temperature rises, the flow capacity of the resin is improved due to enhanced radical mobility, resulting in better adaptability to the walls of a cavity ^[24],[25].

This result was agreed with Demirel et al. ^[26] who have evaluated the effects of preheating on the internal adaptation of bulk-fill composites and they concluded that the lowest gap percentages were observed for preheated VisCalor bulk. Preheating considerably improved the internal adaptation of all resin composites.

A similar result was obtained by Elkady et al. ^[16] who evaluated the marginal integrity of preheating composite of class II composite resin restorations and they reported that preheating the resin composite to elevated temperature, that is 60°C, is a useful technique since it increases the adaptation and lowers the total gap surface area.

Additionally, Moustafa et al. ^[25] found that preheating of the bulk-fill composite resin presented better marginal adaptation compared to the conventional composite that was placed by incremental technique.

Metalwala et al. ^[27] also found that preheating of the nanohybrid composites considerably improves their flowability and can improve clinical placement and adaptation regardless of the resin composite material.

In contrast to our results, Elsayad ^[28] found that preheating composite resins to very high temperatures, such as 68°C, would not improve the marginal adaptation, the author claimed that when the temperature was elevated, a more rapid photopolymerization occurred. These high reaction rates may cause higher stress formation and faster development of the gel point, providing unfavorable effects on the integrity of the restoration–tooth interface.

Additionally, Deb et al. ^[29] and Sabatini et al. ^[30] reported that even if marginal adaptation may be better due to the improved flowability of preheated composite resins, shrinkage may also be increased because of higher monomer conversion. They emphasized that increased shrinkage may offset the improved adaptation achieved by preheating composites, resulting in no significant difference in gap formation of composites cured under different temperature conditions.

In the current study, it was found that there was no significant difference between group 1 and group 3 in both marginal gap length and width.

This came in agreement with Karaarslan et al. ^[31] who found no significant differences among the preheated groups (composite preheated to 37, 54, and 68°C).

Also, this result agrees with Alharbi et al. ^[3], who analyzed the marginal integrity of bulk-fill composites compared to traditional composites and reported that bulk-fill composites provide similar marginal performance to incremental technique.

Moreover, Agarwal et al. ^[32] agree with our result who evaluated the marginal and internal adaptation of posterior bulk-fill composites of different viscosities and reported that there were not significant differences in marginal and internal adaptation at the cervical tooth–restoration interface in cavities restored by the bulk-fill or the incremental technique.

On the other hand, Alqudaihi et al. ^[18] the incrementally placed resin composite material showed less gap formation and better internal adaptation to the cavity floor than the bulk-fill restorative materials. This result might be due to the reduced material volume and C-factor of each layer which accordingly reduced the polymerization shrinkage and generated contraction stresses.

Additionally, Oskoee et al. ^[33] and Kreitzer et al. ^[34] reported that bulk-fill composite resins had fewer gaps compared to conventional composite resins due to differences in polymerization mechanisms of these composite resins. The difference between the results may be due to the difference in the materials used.

Conclusions

Under the limitations of the present study, the following conclusions can be made:

The marginal gaps decreased when VisCalor bulk and Grandio composite resins were applied after preheating so preheating composite resins considerably improves marginal adaptation.
There is no significant difference between bulk fill and incremental technique.
The marginal gaps increased in cervical margins.

Recommendations

Based on the findings of this in-vitro study, the following recommendations could be drawn:

In-vivo studies are required to evaluate the clinical performance of thermoviscous bulk-fill composite.
More in-vitro studies are required to test the mechanical and physical properties of thermoviscous bulk-fill composite.
Also, studies are required to evaluate the effect of preheating on the dentine-pulpal organ.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

1.	Cangül S, Adıgüzel Ö. The latest developments related to composite resins. Int Dent Res 2017; 7:32–41.
2.	Salem GA, Gamal WM, Elhiny OA. Evaluation of the adhesive efficiency of preheated composite for bonding orthodontic brackets. Eur J Mol Clin Med 2020; 7:8933–8942.
3.	Alharbi F, Kaisarly D, Bader D, El Gezawi M. Marginal integrity of bulk versus incremental fill class II composite restorations. Oper Dent 2016; 41:146–156.
4.	Marí LG, Gil AC, Puy CL. In vitro evaluation of microleakage in class II composite restorations: high viscosity bulk-fill vs conventional composites. Dent Mater J 2019; 38:721–727.
5.	Chesterman J, Jowett A, Gallacher A, Nixon P. Bulk-fill resin-based composite restorative materials: a review. Br Dent J 2017; 222:337–344.
6.	Margeas RC. Bulk-fill materials: simplify restorations, reduce chairtime. Compend Contin Educ Dent 2015; 36:1–4.
7.	Czasch P, Ilie N. In vitro comparison of mechanical properties and degree of cure of bulk fill composites. Clin Oral Investig 2013; 17:227–235.
8.	Gerula-Szymańska A, Kaczor K, Lewusz-Butkiewicz K, Nowicka A. Marginal integrity of flowable and packable bulk-fill materials used for class II restorations – a systematic review and meta-analysis of in vitro studies. Dent Mater J 2020; 39:335–344.
9.	Loumprinis N, Maier E, Belli R, Petschelt A, Eliades G, Lohbauer U. Viscosity and stickiness of dental resin composites at elevated temperatures. Dent Mater 2021; 37:413–422.
10.	Yang J, Silikas N, Watts DC. Preheating effects on extrusion force, stickiness and packability of resin-based composite. Dent Mater 2019; 35:1594–1602.
11.	Marcondes RL, Lima VP, Barbon FJ, Isolan CP, Carvalho MA, Salvador MV, et al. Viscosity and thermal kinetics of 10 preheated restorative resin composites and effect of ultrasound energy on film thickness. Dent Mater 2020; 36:1356–1364.
12.	Kincses D, Böddi K, Őri Z, Lovász BV, Jeges S, Szalma J, et al. Preheating effect on monomer elution and degree of conversion of contemporary and thermoviscous bulk-fill resin-based dental composites. Polymers 2021; 13:3599–3618.
13.	Manhart J. Direct cusp replacement in the molar region using a thermoviscous bulk-fill composite restorative material–a clinical case report. Int Dent Afr Ed 2020; 9:22–33.
14.	Daronch M, Rueggeberg F, De Goes M, Giudici R. Polymerization kinetics of pre-heated composite. J Dent Res 2006; 85:38–43.
15.	Forster A, Braunitzer G, Tóth M, Szabó BP, Fráter M. In vitro fracture resistance of adhesively restored molar teeth with different MOD cavity dimensions. J Prosthodont 2019; 28:325–331.
16.	Elkady YA, Abdalla AI, Hasan MM. The effect of preheating and flowable composite on the marginal integrity of class II composite resin restorations. J Med Dent Sci 2020; 19:6–15.
17.	Marzouk MA Simonthon AL Gross RD. Operative Dentistry: Modern Theory and Practice. 1^st Indian ed. Madras: All India Publishers & Distributors; 1997. p. 140–155.
18.	Alqudaihi FS, Cook NB, Diefenderfer KE, Bottino MC, Platt JA. Comparison of internal adaptation of bulk-fill and increment-fill resin composite materials. Oper Dent 2019; 44:32–44.
19.	Choudhary N, Kamat S, Mangala T, Thomas M. Effect of preheating composite resin on gap formation at three different temperatures. J Conserv Dent 2011; 14:191–195. [PUBMED] [Full text]
20.	Silva JC, Rogério VR, Rege IC, Cruz CS, Vaz LG, Estrela C, et al. Preheating mitigates composite degradation. J Appl Oral Sci 2015; 23:571–579.
21.	Duarte SJ, Lolato AL, De Freitas CR, Dinelli W. SEM analysis of internal adaptation of adhesive restorations after contamination with saliva. J Adhes Dent 2005;7:51–56.
22.	Gale M, Darvell B. Thermal cycling procedures for laboratory testing of dental restorations. J Dent 1999; 27:89–99.
23.	Ibrahim HA, Shalaby ME, Abdalla AI. Marginal fit of class II cavities restored with bulk-fill composites. Tanta Dent J 2018; 15:1–6. [Full text]
24.	Arora V, Arora P, Shamrani A, Fahmi M. A new, simple and innovative technique for preheating/prewarming of dental composite resins in thermal assisted light polymerization technique. J Dent Oral Biol 2017; 2:1–2.
25.	Moustafa MN, Abd Elfattah WM, Alabbassy FH. Effect of composite preheating and placement techniques on marginal integrity of class V restorations. Alex Dent J 2020; 45:93–99.
26.	Demirel G, Orhan A, Irmak O, Aydın F, Büyüksungur A, Bilecenoğlu B, et al. Effects of preheating and sonic delivery techniques on the internal adaptation of bulk-fill resin composites. Oper Dent 2021; 46:226–233.
27.	Metalwala Z, Khoshroo K, Rasoulianboroujeni M, Tahriri M, Johnson A, Baeten J, et al. Rheological properties of contemporary nanohybrid dental resin composites: the influence of preheating. Polym Test 2018; 72:157–63.
28.	Elsayad I. Cuspal movement and gap formation in premolars restored with preheated resin composite. Oper Dent 2009; 34:725–731.
29.	Deb S, Di Silvio L, Mackler HE, Millar BJ. Pre-warming of dental composites. Dent Mater 2011; 27:51–59.
30.	Sabatini C, Blunck U, Denehy G, Munoz C. Effect of preheated composites and flowable liners on class II gingival margin gap formation. Oper Dent 2010; 35:663–671.
31.	Karaarslan ES, Usumez A, Ozturk B, Cebe MA. Effect of cavity preparation techniques and different preheating procedures on microleakage of class V resin restorations. Eur J Dent 2012; 6:87–94.
32.	Agarwal RS, Hiremath H, Agarwal J, Garg A. Evaluation of cervical marginal and internal adaptation using newer bulk fill composites: an in vitro study. J Conserv Dent 2015; 18:56–61.
33.	Oskoee SS, Bahari M, Navimipour EJ, Ajami AA, Ghiasvand N, Oskoee AS. Factors affecting marginal integrity of class II bulk-fill composite resin restorations. J Dent Res Dent Clin Dent Prospects 2017; 11:101–109.
34.	Kreitzer M, Harsono M, Finkelman M, Kugel G. Microleakage evaluation of bulk-fill layering techniques in class II restorations. Int J Dent Res 2013; 12:1–4.