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. 2025 Oct 9;25:1578. doi: 10.1186/s12903-025-06976-2

Impact of composite consistency and pre-heating on cervical adaptation in class II restorations: a micro-CT evaluation

Gülbike Demirel 1,✉, Özgür Irmak 2, Arda Buyuksungur 3, Kaan Orhan 4, Ivo Krejci 5, Tissiana Bortolotto 5
PMCID: PMC12512468  PMID: 41068769

Abstract

Background

To compare the cervical adaptation of paste-like bulk-fill resin composites placed with either conventional or pre-heating insertion techniques to that of flowable bulk-fill resin composites.

Methods

Six paste-like resin composites (one conventional, five bulk-fill) and five flowable resin composites (one conventional, four bulk-fill) were placed into Class II box-only cavities. Paste-like composites were placed with either conventional insertion or after pre-heating (68 °C). Flowable composites were placed only with the conventional insertion technique; no pre-heating was performed. After cavities were restored, specimens were subjected to thermal aging. Then, ammoniacal silver nitrate (AgNO3) tracer was used followed by micro-computerized tomography scanning. AgNO3 penetration volume was calculated. Data was analyzed with 2-way ANOVA followed by Tukey’s multiple comparison test (α = 0.05).

Results

Pre-heating improved the cervical adaptation of all composites compared to conventional placement (p < 0.05) except for the fiber-reinforced composite. All flowable resin composites showed higher AgNO3 penetration than their paste-like pre-heated counterparts (p < 0.05). AgNO3 penetration volume at the cervical margin was significantly lower when paste-like bulk-fill resin composites were pre-heated to 68 °C before they were placed into Class II box-only cavities.

Conclusions

Pre-heating significantly enhanced the cervical adaptation of paste-like bulk-fill resin composites, offering superior marginal integrity compared to both their non-heated counterparts and flowable composites.

Keywords: Bulk-fill composites, Cervical adaptation, Micro-CT, Pre-heating

Background

The marginal integrity of resin composite restorations is critical as marginal gap formation is associated with degradation of adhesive interfaces and secondary caries [1]. In this sense, it is essential to minimize marginal gaps when restoring a tooth to achieve durable restorations and preserve its vitality [2]. Several factors impact the quality of the tooth-composite interface, including polymerization shrinkage behavior, composite’s flow during curing, and adhesive strength between the composite and the tooth [3]. Achieving a complete marginal seal between the tooth and resin composite in Class II cavities is particularly challenging when the cervical margin extends onto dentin [4, 5]. One approach for improving sealing involves the application of a low-modulus flowable composite as a liner [6]. However, since these flowable resin composites are a heterogeneous group of materials with diverse rheological behaviors [7, 8], polymerization shrinkage characteristics [9, 10], and matrix compositions, their effectiveness in improving marginal integrity or reducing microleakage remains controversial.

The adoption of bulk-fill composites for posterior direct restorations is considered a major advancement in conservative dentistry. Due to their optimized polymerization characteristics [11], these materials can be applied in increments of 4–6 mm; significantly thicker than the 2 mm limit recommended for conventional composites [12]. Previously, conventional resin composites required an incremental placement technique, which was time consuming. However, restorations with bulk-fill resin composites can be completed with fewer increments [13]. The first generation of bulk-fill resin composites comprised low-modulus, flowable-type materials. These were intended for use as a base layer and required a paste-like conventional resin composite as a top capping layer [14]. More recently, high-viscosity, paste-like bulk-fill resin composites have been introduced to restore the entire cavity without a capping layer [13].

Bulk-fill resin composites are typically inserted into the cavity using a syringe tip or composite hand instrument. It is known that marginal and internal voids may form in the bulk of the polymerized material [15, 16]. As an alternative to low-modulus composite materials, pre-heated high-viscosity resin composites may be used to reduce film thickness and increase flow characteristics [17] without altering their mechanical properties [18]. Cavities restored with pre-heated resin composites have shown enhanced marginal adaptation [19] and reduced microleakage [20]. Furthermore, pre-heating significantly lowers shrinkage stresses compared to room-temperature composite [21] and promotes increased monomer-polymer conversion rate [22].

Polymerization contraction stresses associated with light-curing resin composites can lead to microleakage [23, 24]. Although bulk-fill resin composites have controlled polymerization contraction stresses [25, 26], restorations may still exhibit varying degrees of microleakage, particularly in the cervical region of the tooth-restoration interface where adhesion could be weaker [27]. Given the variability in filler type, filler content, and matrix composition across bulk-fill resin composites [13, 14] teeth restored with different materials may behave differently regarding microleakage.

Microleakage evaluation by micro-computed tomography (micro-CT) combined with Ammoniacal silver nitrate (AgNO3) tracer is a highly sensitive technique and can be used to evaluate the resin composite-tooth interface [28]. Silver ions in AgNO3 infiltrate tiny gaps along the interface and precipitate as metallic silver [29, 30] offering a non-destructive method that allows quantitative and qualitative examination of specimens. Additionally, this method enables the operator to distinguish materials, tooth structures and voids with great accuracy and resolution [15, 31].

While the microleakage behavior of various bulk-fill composites has been previously investigated [29, 30, 32], no study to date has assessed how pre-heating affects the marginal adaptation of different paste-like bulk-fill composites using micro-CT. Therefore, this study aimed to evaluate and compare the cervical adaptation of paste-like bulk-fill resin composites applied using either conventional hand-placement or pre-heating techniques, and to contrast these findings with those of flowable bulk-fill resin composites in box-only Class II cavities. The null hypotheses tested were: (1) that the pre-heating insertion technique would not affect the cervical adaptation of paste-like bulk-fill composites, and (2) that no differences in cervical adaptation would be observed between the flowable and pre-heated bulk-fill resin composites.

Materials and methods

This study protocol received ethical approval from the Ethics Committee for Human and Animal Research of Ankara University Faculty of Dentistry (07012019).

Group assignment

The study design incorporated the factors of material consistency (paste-like or flowable) and placement method (conventional or pre-heated). Six paste-like resin composites (one conventional paste-like resin composite as control and five bulk-fill paste-like resin composites) and five flowable resin composites (one conventional flowable as control and four bulk-fill flowable resin composites) were evaluated (Table 1). Paste-like materials were placed using either conventional or pre-heated placement techniques, while flowable materials were placed conventionally. This resulted in a total of 17 experimental groups. Each group consisted of five teeth, and each tooth had two cavities for composite restorations, resulting in 10 samples per group (n = 10). In total, 85 freshly extracted, sound human third molars were used. The allocation of teeth to groups was randomized using a computer-generated list by an investigator not involved in specimen preparation or evaluation. Study design is given in Fig. 1.

Table 1.

Composite materials and compositions used in the study

Brand name Consistency/Type Experimental placement Group codes Shade Matrix composition Filler % by weight Recommended
curing time and
irradiance		 Lot Number Manufacturer
Admira (ADM) Fusion X-tra Paste-like Bulk-fill (Ormocer) Conventional ADM-conv Universal Organically modified silicic acid, silicon dioxide nanofillers (20–50 nm), silicon oxide–based hybrid fillers 84 20 s ≥800 mW/cm2 2,031,434 VOCO GmbH, Cuxhaven, Germany
Preheated ADM-heat
Fusion X-base Flowable Bulk-fill (Ormocer) Conventional ADM-flow Universal Organically modified silicic acid, silicon dioxide nanofillers (20–50 nm), silicon oxide–based hybrid fillers 72 20 s ≥800 mW/cm2 2,030,279 VOCO GmbH, Cuxhaven, Germany
EverX (EVX) Posterior Paste-like Bulk-fill (Fiber-reinforced) Conventional EVX-conv Bulk shade Bis-GMA, TEGDMA, PMMA, E-glass fibres, Barium glass, Silicon dioxide 75 10 s ≥1200 mW/cm2 2,003,263 GC Corporation, Tokyo, Japan
Preheated EVX-heat
Flow Flowable Bulk-fill (Fiber-reinforced) Conventional EVX-flow Bulk shade Bis-MEPP, TEGDMA, UDMA, E-glass fibres, Barium glass, Silicon dioxide 52 10 s ≥1200 mW/cm2 1,908,021 GC Corporation, Tokyo, Japan
Filtek (FTK) One Bulk-Fill Restorative Paste-like Bulk-fill Conventional FTK-conv A2 AUDMA, AFM, diurethane-DMA, and 1, 12-dodecane- DMA, ytterbium trifluoride, zirconia/slica 76,5 10 s occlusal, 10 s buccal, 10 s lingual ≥1000–2000 mW/cm2 N907263 3 M Dental Products.St.Paul, USA.
Preheated FTK-heat
BulkFill Flowable Flowable Bulk-fill Conventional FTK-flow Universal BisGMA, UDMA, bisEMA, procrylat resins, ytterbium trifloride, zirconia/slica 64,5 20 s ≥1000–2000 mW/cm2 NA53935 3 M Dental Products.St.Paul, USA.
G-aenial (GNL) Posterior Paste-like Incremental Conventional GNL-conv A2 Pre-polymerized fillers, fluoroaluminosilicate glass, fumed silica, UDMA and dimethacrylate co-monomers 77 10 s ≥1000 mW/cm2 1905271X GC Corporation, Tokyo, Japan
Preheated GNL-heat
Universal Flow Flowable Incremental Conventional GNL-flow A2 UDMA, Bis-EMA, dimethacrylate component, UV-light absorber, stabilizer, photoinitiator 69 10 s ≥1000 mW/cm2 190902B GC Corporation, Tokyo, Japan
X-tra (XTR) Fill Paste-like Bulk-fill Conventional XTR-conv Universal BIS-GMA, UDMA, BHT, TEDMA 86 10 s ≥800 mW/cm2 1,946,276 VOCO GmbH, Cuxhaven, Germany
Preheated XTR-heat
Base Flowable Bulk-fill Conventional XTR-flow Universal Bis-EMA, MMA, silica 75 10 s ≥800 mW/cm2 1,823,197 VOCO GmbH, Cuxhaven, Germany
VisCalor (VSC) Bulk Paste-like Bulk-fill (Thermo-viscous) Conventional VSC-conv Universal Bis-GMA, aliphatic dimethacrylate, inorganic fillers 83 10 s ≥1000 mW/cm2 1,946,611 VOCO GmbH, Cuxhaven, Germany
Preheated VSC-heat
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Fig. 1.

Fig. 1

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Flowchart of the group assignments according to composite consistency and placement technique

Cavity preparation and restoration

Cavity preparations were performed by a single experienced operator (GD), who had been previously trained and calibrated to ensure methodological consistency. Two standardized proximal box-only cavities were prepared in each tooth. The buccolingual width of each cavity was approximately one-third of the intercuspal distance, and the mesiodistal width was one-third of the total mesiodistal width of the crown. Cervical margins were placed 1 mm apical to the cemento-enamel junction (CEJ). The cavity floor was finished as a butt joint without a bevel. A new cylindrical diamond bur (KG Sorensen, São Paulo, Brazil) was used for each preparation, mounted on a high-speed handpiece with water spray for cooling. After completing the proximal box preparations, occlusal surfaces of the teeth were flattened using a series of abrasive carbide papers (P1000 to P4000, Metkon Gripo 2v, Turkey) under continuous water cooling, resulting in cavity depths standardized at 4 mm. The final depth of each cavity was verified using a digital caliper (Mitutoyo 500, Mitutoyo Corporation, Kanagawa, Japan) with a resolution of 0.01 mm.

To facilitate restoration, a single-use circumferential metal matrix band (Adapt SuperCap Matrix no: 2182, Kerr-Hawe, Bioggio, Switzerland) was applied around each cavity. The bonding procedure was performed using a one-step self-etch adhesive (Clearfil S3 Bond Plus, Kuraray, Japan) according to the manufacturer’s instructions. A new matrix band was used for each cavity.

Paste-like resin composites were placed using either the conventional insertion technique or pre-heating technique. For the conventional insertion technique, a unidose composite dispenser (Prisma Compules Gun Dispenser, Dentsply Sirona, Pennsylvania, USA) was used and composites were injected directly into the cavity from the cavity floor to the occlusal surface. In the pre-heating technique, the same dispenser was used after warming the compules in a composite warmer (Caps Warmer, Voco GmbH, Cuxhaven, Germany) at 68 °C for 3 min. Pre-heated composites were injected into the cavity from bottom to the top immediately after removal from the heater. The mean time elapsed between removing the compule from the heating device and light curing was 27.4 ± 1.5 s. In both placement methods, injected paste-like resin composites were adapted to the cavity walls manually using a hand instrument (Polyfill, 1051/95, Carl Martin GmbH, Solingen, Germany) by applying vertical digital pressure. Flowable resin composites were injected directly from the base to the occlusal surface using their own syringe tips, without pre-heating. All bulk-fill composites were placed in a single increment, while conventional resin composites (Geanial Posterior and Gaenial Universal Flow) were applied in two separate 2 mm-increments. All resin composite increments were light-cured separately with the same LED light-curing unit (Elipar DeepCure-S LED Curing Unit, 3 M Dental Products, St. Paul, USA) according to the manufacturer’s instructions. The light output was regularly verified with the device’s built-in radiometer to ensure irradiance of at least 1000 mW/cm2. After restoration, the occlusal surfaces were finished and polished using aluminum oxide embedded discs (Sof-Lex; 3 M ESPE, St. Paul, USA) under water cooling. All restorative procedures were consistently performed by the same operator to minimize variability.

Specimens were then subjected to 10,000 thermal cycles between 5 °C and 55 °C in distilled water with a 30-s dwell time. To prepare for microleakage evaluation, the apices of all teeth were sealed using a flowable resin composite. All external surfaces were coated with two layers of nail varnish, leaving a 1-mm-wide margin around the tooth-restoration interface uncoated.

Micro-CT analysis

Silver nitrate tracer solution was used following the aging protocol [33]. All samples were soaked in 50% AgNO3 solution in the dark for 12 h. They were then rinsed thoroughly under running water for five minutes, immersed in a photographic developer, and exposed to light for 8 h to reduce silver ions to metallic silver. Prior to micro-CT scanning, teeth were cleaned with a toothbrush under running water and polished with aluminum oxide discs under water cooling to eliminate surface silver deposits.

High-resolution micro-CT imaging was performed using a desktop scanner (Bruker Skyscan 1275, Kontich, Belgium) with the following parameters: 80 kVp voltage, 125 mA beam current, 1 mm aluminum filter, pixel size of 24.0 μm, and rotation step of 0.2°. The system was calibrated before each scan using the manufacturer’s flat field correction. Each sample was scanned over a 360° rotation, with a total scan time of approximately 38 min per specimen.

Image reconstruction was conducted using NRecon software (ver. 1.7.10.4), and data analysis was performed with CTAn (ver. 1.18.1.2), both from Bruker. Approximately 900 cross-sectional images were reconstructed per tooth. For 3D visualization, CTVox software (ver. 3.3.0) was used. The region of interest (ROI) extended from the cervical margin to the occlusal surface in horizontal slices. Grayscale thresholding was applied to differentiate tooth structure, composite material, and AgNO3 infiltration (Figs. 2 and 3). Micro-CT data analysis was conducted by an examiner blinded to the group allocations to minimize bias.

Fig. 2.

Fig. 2

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Sagittal view of a representative reconstructed micro-CT image (arrow indicates AgNO3 penetration)

Fig. 3.

Fig. 3

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a, Horizontal cross-section of the restoration. b, Region-of-interest selection. c, Binary selection of composite and silver nitrate. White - composite and silver nitrate. Black - tooth hard tissue and air. d, Binary selection of silver nitrate. White - silver nitrate. Black - tooth hard tissue and air

Statistical analysis

AgNO₃ penetration rate (%) was calculated as the ratio of AgNO₃ penetration volume to total cavity volume, normalizing values by cavity size. Data distribution was assessed using the D’Agostino and Pearson omnibus normality test. The effects of composite consistency (paste-like or flowable) and application technique (conventional or pre-heated) on cervical adaptation were evaluated using two-way ANOVA followed by Tukey’s post-hoc test. Statistical analysis was conducted using a computer software (Prism 6.0, GraphPad Software, La Jolla, CA, USA) with significance set at 0.05.

Results

Mean AgNO3 penetration rates (%) of the tested composites are presented in Table 2, with visual summary in Fig. 4. Pre-heating significantly improved the cervical adaptation of all paste-like composites compared to conventional placement (p < 0.05) except for EVX. The percentage reduction in AgNO₃ penetration for each paste-like composite after pre-heating to 68 °C, relative to conventional placement, is shown in Table 3.

Table 2.

Mean AgNO3 penetration rates (%) at the cervical margin of cavities restored with bulk-fill composites of varying consistencies Means sharing a superscript letter are not significantly different (p>0.05). Uppercase letters compare means in each row. Lowercase letters compare means in each column. (Abbreviations: GNL, Gaenial; ADM, Admira; EVX, EverX; FTK, Filtek; VSC, VisCalor; XTR, X-tra conv, paste-like bulk-fill conventional placement; heat, paste-like bulk-fill pre-heated, flow, flowable bulk-fill)

GNL (control) ADM EVX FTK VSC XTR
conv 4.04± 0.59 Aa 5.13± 0.68 Ba 2.93± 0.16 Ca 5.02± 0.57 Ba 3.84± 0.42 Aa 4.35± 0.50 ABa
heat 2.67± 0.82 ABb 3.24± 0.36 Ab 2.67± 0.09 ABa 2.56± 0.70 ABb 1.92± 0.18 Bb 2.98± 0.69 Ab
flow 3.83± 0.20 Aa 4.19± 0.32 Ac 3.85± 0.17 Ab 3.83± 0.35 Ac n/a 3.81± 0.16 Aa
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Means sharing a superscript letter are not significantly different (p > 0.05)

Uppercase letters compare means in each row

Lowercase letters compare means in each column

Abbreviations: GNL Gaenial, ADM Admira, EVX EverX, FTK Filtek, VSC VisCalor, XTR X-traconv, paste-like bulk-fill conventional placement; heat, paste-like bulk-fill preheated, flow, flowable bulk-fill

Fig. 4.

Fig. 4

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Visual summary of mean AgNO₃ penetration rates (%) for the tested composites. (Abbreviations: GNL: G-aenial, ADM: Admira, EVX: EverX, FTK: Filtek, XTR: X-tra, VSC: VisCalor)

Table 3.

Percentage reduction in AgNO₃ penetration for paste-like bulk-fill composites when pre-heated (68 °C) versus conventional temperature. (Abbreviations: GNL: G-aenial, ADM: Admira, EVX: EverX, FTK: Filtek, XTR: X-tra, VSC: VisCalor)

AgNO₃ penetration rate Percent reduction
Composite Conventional placement (%) Pre-heated (%)
GNL 4.04 2.67 33.9%
ADM 5.13 3.24 36.8%
EVX 2.93 2.67 8.9%*
FTK 5.02 2.56 49.0%
VSC 3.84 1.92 50.0%
XTR 4.35 2.98 31.5%
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*Not statistically significant

All flowable resin composites showed higher AgNO3 penetration than their paste-like pre-heated counterparts (p < 0.05). This outcome was not observed when comparing paste-like conventionally placed and flowable composites; GNL-conv (4.04 ± 0.59) and GNL-flow (3.83 ± 0.20); XTR-conv (4.35 ± 0.50) and XTR-flow (3.81 ± 0.16) showed similar AgNO3 penetration rates (p > 0.05). ADM-flow (4.19 ± 0.32) and FTK-flow (3.83 ± 0.35) exhibited lower AgNO3 penetration rates than their conventionally placed paste-like counterparts ADM-conv (5.13 ± 0.68) and FTK-conv (5.02 ± 0.57) (p < 0.05).

Among the conventionally placed paste-like composites, EVX-conv (2.93 ± 0.16) showed the lowest AgNO3 penetration rates. For the pre-heated paste-like composites, VSC-conv (3.84 ± 0.42) showed the least penetration (p < 0.05). All flowable resin composites exhibited similar penetration rates (p > 0.05).

Discussion

This study evaluated the influence of pre-heating on the cervical adaptation of various paste-like bulk-fill resin composites, comparing their performance to flowable bulk-fill resin composites using micro-CT imaging. Based on the findings, both null hypotheses were rejected: pre-heating significantly affected cervical adaptation, and flowable and pre-heated paste-like composites showed different levels of marginal adaptation.

Previous studies [27, 34, 35] have reported that the cervical margin is the most common site for microleakage, primarily due to the difficulty in adapting restorative materials in this area, the absence of enamel, and the challenges of bonding to deep dentin. Therefore, a standardized Class II box cavity configuration was selected to assess adaptation at the cervical margin. Standardizing cavity dimensions also helped control the C-factor and minimize variability in polymerization shrinkage stress among groups.

The improved depth of cure offered by bulk-fill resin composites one of their primary advantages [13]. While conventional composites have a limited polymerization depth of 2 mm, bulk-fill resin composites offer polymerization depths of 4–5 mm depending on formulation [14]. In this study, cavity depth was standardized to 4 mm to permit single-layer placement of bulk-fill resin materials.

The resin composite pre-heating device used in this study had temperature settings of 37, 54 and 68 °C; with the latter two recommended by the manufacturer. Previous studies [19, 20] have shown that pre-heating conventional resin composites at 54–68 °C improves adaptation to cavity walls compared to room temperature placement. Although data on paste-like bulk-fill composites are limited, one micro-CT study reported significantly improved internal adaptation at 68 °C [36]. Common materials in that study and ours included VisCalor Bulk and Filtek One Bulk-Fill. In our findings, all tested paste-like composites except EverX Posterior demonstrated significantly enhanced cervical adaptation when pre-heated to 68 °C.

As previous reported [18, 37, 38], the optimal working time of pre-heated composites is relatively short. Accordingly, in this study, pre-heated composites were inserted into the cavity immediately after removal from the heating device to minimize heat loss. The average time between heating and light curing was 27.4 ± 1.5 s, which is consistent with prior literature [36, 39].

In this study, composite materials were selected from various manufacturers. Despite being classified as bulk-fill composites, differences in filler ratios, types, and monomer structures may contribute to variation in performance with or without pre-heating. Thermal energy absorption depends largely on the amount of inorganic filler content [40]. Highly filled composites may absorb heat more effectively, gaining improved flow characteristics.

All paste-like pre-heated resin composites showed better adaptation than flowable resin composites. This improvement may be attributed to temporary viscosity reduction induced by pre-heating, which improves flow and wall contact in deep or irregular areas [41, 42]. Although flowable composites are designed to be less viscous, pre-heating paste-like composites can offer great adaptability. Thermal imaging has shown that heat remains largely confined within the composite, with minimal transmission to dentin, indicating safety [43]. Thus, pre-heating high-viscosity bulk-fill composites may enhance marginal integrity without compromising biological safety, particularly in restorations with deep cervical margins [42, 43].

In addition to adaptation, pre-heating at 68 °C has been shown to improve fracture resistance [41], microhardness and depth of cure in various bulk-fill composites [42]. It does not compromise biocompatibility or increase monomer release [44]. These findings support the clinical use of pre-heated high-viscosity bulk-fill composites, particularly where optimal marginal adaptation is required.

Only EverX Posterior did not benefit from pre-heating. This composite contains randomly oriented short E-glass fibers that transfer stress from the resin matrix to the fibers [45]. It is possible that fiber content restricts molecular mobility during heating, limiting viscosity reduction. However, no direct evidence was obtained in this study to confirm this mechanism.

All flowable composites evaluated showed significantly lower AgNO3 penetration than their non-heated paste-like counterparts, except EverX. This outcome aligns with previous findings that flowable composites’ leveling properties enhance adaptation to cavity [46].

Marginal adaptation is influenced not only by viscosity and pre-heating, but also by adhesive system’s sealing ability [47]. To minimize variability, the same adhesive system was used in all groups. Therefore, observed differences can be attributed to the composite material and placement technique.

This study has limitations. Its in vitro design does not fully replicate the oral environment, including occlusal loading, pH fluctuations, and biofilm. Additionally, while thermal cycling was used to simulate aging, the lack of mechanical loading may underestimate the long-term effects of functional stresses. Evaluation was limited to post-aging adaptation, so long-term durability remains uncertain. Finally, only one adhesive system and cavity design were tested limiting generalization. Future studies should include mechanical fatigue testing, alternatives adhesives, and long-term simulations under clinical conditions.

Conclusions

For most paste-like bulk-fill resin composites tested, AgNO₃ penetration volume at the cervical margin was significantly lower when the materials were pre-heated to 68 °C before placement in Class II box-only cavities. Pre-heating resulted in a 31–50% reduction in AgNO₃ penetration for most paste-like composites, indicating a substantial improvement in cervical adaptation. These results suggest that pre-heating may enhance cervical adaptation in certain paste-like bulk-fill composites. Moreover, all pre-heated paste-like bulk-fill composites, except EverX Posterior, showed better cervical adaptation than the evaluated flowable bulk-fill composites. While not all materials respond equally, incorporating pre-heating into restorative protocols may be considered for specific composites. Further research is needed to confirm whether these laboratory findings translate into better clinical performance and restoration longevity.

Acknowledgements

The authors would like to thank the manufacturers for kindly providing the restorative materials used in this study.

Abbreviations

micro-CT

Micro-computed tomography

CEJ

Cemento-enamel junction

mm

Millimeter

min

Minute

s

Second

LED

Light emitting diode

3D

3 dimension

ROI

Region of interest

Authors’ contributions

GD contributed to the conception and design of the study, sample preparation, data acquisition, and data interpretation, and drafted and critically revised the manuscript. OI contributed to the study design, data acquisition, data interpretation, and manuscript drafting. AB and KO were responsible for the micro-CT analysis and contributed to data interpretation. IK and TB contributed to drafting and critically revising the manuscript. All authors read and approved the final version of the manuscript and agree to be accountable for all aspects of the work.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Data availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was conducted under all the provisions of the World Medical Association Declaration of Helsinki and the Ankara University Faculty of Dentistry’s local human subjects oversight committee guidelines and policies of the ethics committee for the study of humans and animals (Approval No: 07012019). Informed consent was obtained from all participants prior to their inclusion in the study.

Consent for publication

Written informed consent was obtained from the patients for publication.

Competing interests

The authors declare no competing interests.

Footnotes

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

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