Influence of high-irradiance light curing on the marginal integrity of composite restorations in primary teeth

Frank et al. BMC Oral Health (2023) 23:569 https://doi.org/10.1186/s12903-023-03291-6 BMC Oral Health Open Access RESEARCH Influence of high-irradiance light curing on the marginal integrity of composite restorations in primary teeth Janina Frank1, Tobias T. Tauböck1, Marcus Zimmermann1, Thomas Attin1 and Blend Hamza2* Abstract Background Reducing the necessary time to restore primary teeth improves the cooperation of paediatric patients. This study aimed to investigate the marginal integrity of restorations prepared with a bulk-fill resin-based composite (RBC) containing additional fragmentation chain transfer (AFCT) compared to a conventional RBC when light cured with a rapid high-irradiance (3 s) and a regular (10 s) curing mode. Methods Forty class-II cavities were prepared in 40 primary molars. The molars were randomly divided into four groups based on the applied light-curing modes (regular: 10 s @ 1200 mW/cm2 or high-irradiance: 3 s @ 3000 mW/cm2) and the used restorative material (AFCT-containing bulk-fill RBC “Power Fill” or AFCT-free conventional RBC “Prime”). After thermo-mechanical loading, the marginal integrity was analysed using scanning electron microscopy. A beta regression model and pairwise comparisons were used to statistically analyse the data. Results The mean marginal integrity (% ± SD) of the restorations for each group was as follows: Power Fill (10 s: 79.7 ± 15.6) (3 s: 77.6 ± 11.3), Prime (10 s: 69.7 ± 11.1) (3 s: 75.0 ± 9.7). The difference between the RBCs for the same light-curing mode was statistically significant (p ≤ 0.05). The difference between the light-curing modes for the same RBC was not statistically significant (p ˃ 0.5). Conclusions AFCT-containing bulk-fill RBC “Power Fill” achieves similar marginal integrity when light-cured with either high-irradiance or regular light-curing modes. “Power Fill” achieves better marginal integrity than the conventional RBC “Prime” regardless of the applied light-curing mode. Keywords Rapid high-irradiance light-curing, Bulk-fill composite, Primary molars, Marginal integrity, Scanning electron microscopy *Correspondence: Blend Hamza 1 Clinic of Conservative and Preventive Dentistry, Center of Dental Medicine, University of Zurich, Plattenstrasse 11, Zurich 8032, Switzerland 2 Clinic of Orthodontics and Pediatric Dentistry, Center of Dental Medicine, University of Zurich, Plattenstrasse 11, Zürich 8032, Switzerland © The Author(s) 2023. 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The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Frank et al. BMC Oral Health (2023) 23:569 Background Resin-based composites have become a solid restorative material option in both permanent and primary teeth [1–3]. Some reports considered the classical incremental layering technique (i.e., the consecutive application of 2-mm-thick composite layers into the tooth cavity) as complicated and connected it with possible air entrapment between the layers and long treatment duration [3]. As an attempt to simplify and shorten the restoration procedure, bulk-fill composites, which can be applied in 4–5 mm layers, were introduced and proven to be a valid alternative to conventional composites, both in vitro and in vivo [4–6]. This comparable good performance of bulk-fill composites was attributed to improved depth of cure and shrinkage stress [7, 8]. Yet another attempt was made to shorten the treatment duration by introducing bulk-fill composites that require much less photo-polymerisation time, namely only 3 s instead of other polymerisation times that usually begin at 10 s [9]. Two major developments led to the possibility of such short polymerisation time: the introduction of high-power light emitting diode (LED) polymerisation units that can produce high radiant exitance (e.g., 3000 mW/cm2), and the incorporation of an β-allyl sulfone addition fragmentation chain transfer (AFCT) reagent in the matrix of the bulk-fill composite [9, 10]. AFCT reagent is supposed to regulate the radical polymerisation reaction of the composite matrix [11]. In other words, when an AFCT-free composite is photo-polymerised, composite monomers, usually methacrylate groups, will rapidly bond to free radicals. This reaction chain progresses rapidly with more monomers being incorporated into the growing polymer network until the concentration of available monomers decreases and the radical chain cannot continue to grow through the gel-becoming composite matrix [12]. This results in unreacted monomers being trapped within the polymer network and hence to irregular, long-chained and brittle network [11]. On the other hand, the presence of AFCT reagents prevents the formation of the mentioned long chains and promotes a step-like growth of the polymer chain enhancing the homogeneity of the polymer network and its thermal and mechanical properties [11, 13]. It has been reported that children show more behaviour difficulties with an increase of the treatment duration [14]. Therefore, the aforementioned shortening of treatment duration and simplifying the restoration procedure could bring important benefits in paediatric dentistry. However, the performance of composite restorations photoactivated with high-irradiance light-curing modes has not yet been investigated on primary molars. This invitro study was therefore carried out to investigate and compare the marginal integrity of an AFCT-containing bulk-fill RBC (Power Fill “high-viscous”, Ivoclar Vivadent, Page 2 of 10 Schaan, Liechtenstein) and a conventional RBC (Prime “high-viscous”, Ivoclar Vivadent) when light-cured using regular and high-irradiance light-curing modes in primary molars. The first null-hypothesis was that the lightcuring mode (high-irradiance for 3 s compared to regular for 10 s) would have no effect on the marginal integrity. The second null-hypothesis was that the tested RBCs (AFCT-containing bulk-fill RBC compared to conventional RBC) would have no effect on the marginal integrity regardless of the used light-curing mo (...truncated)