Improper Light Curing of Bulkfill Composite Drives Surface Changes and Increases S. mutans Biofilm Growth as a Pathway for Higher Risk of Recurrent Caries around Restorations.

Haifa Maktabi,Isadora Martini Garcia,Mary Anne S Melo,Abdulrahman A Balhaddad,Howard Strassler,Qoot Alkhubaizi,Fabrício Mezzomo Collares,Carmem S Pfeifer,Ana Paula P Fugolin,Maria Salem Ibrahim

doi:10.3390/dj9080083

Abstract

How dentists cure a resin-based material has deleterious effects on the material’s properties and its interaction with surrounding dental tissues. Biofilm accumulation has been implicated in the pathogenesis of carious lesions around dental restorations, with its composition manifesting expressed dysbiosis in patients suffering from dental caries. To evaluate the influence of varying radiant exposure on the degree of conversion (DC%), Streptococcus mutans biofilm growth, and surface roughness of bulk-fill composites under different light-curing conditions. Two light-curing units (LCU) at 600 and 1000 mW/cm2 were used to simulate curing conditions with different angulations (∢20° and ∢35°) or 2 mm-distance displacements of the LCU tip. The radiant exposure (RE) was assessed, and the composites were analyzed for DC%. Biofilm formation was induced over the bulk-fill composites and analyzed via colony-forming units counting and scanning electron microscopy (SEM). The surface roughness was analyzed via a profilometer and SEM after biofilm formation. Curing conditions with different angulation or displacement decreased RE compared to the “optimal condition”. The moderately (∢35°) angulated LCU tip and low (600 mW/cm2) radiant emittance significantly reduced the DC% (p < 0.05). The difference in DC% between the top and bottom of the composites ranged from 8 to 11% for 600 mW/cm2 and 10 to 20% for 1000 mW/cm2. Greater S. mutans biofilm and surface changes were found in composites with non-optimal RE delivery (e.g., tip displacement and angulation) (p < 0.05). Inadequate polymerization of bulk-fill composites was associated with more biofilm accumulation and surface topography changes. Overall, non-optimally performed curing procedures reduced the amount of delivered RE, which led to low DC%, more biofilm formation, and higher surface roughness. The improper light-curing of bulk-fill composites compromises their physicochemical and biological properties, which could lead to inferior clinical performance and reduced restorative treatments’ longevity.

Highlights

Appropriated photoactivation that enables optimal curing and cross-linking of polymer chains is essential for a reliable dental resin behavior [1,2]
We present the effects of radiant exposure (RE) and radiant emittance performed in optimum and underperformed conditions on the degree of conversion (DC%), Streptococcus
In LCU1000, the RE value of the optimal condition was significantly higher than the other underperformed conditions (p < 0.05) (Figure 2A)

Summary

Introduction

Appropriated photoactivation that enables optimal curing and cross-linking of polymer chains is essential for a reliable dental resin behavior [1,2]. This class of composites was developed to overcome limitations associated with conventional resin-based composites (RBCs), such as limited depth of cure and polymerization shrinkage [4,5]. Conventional RBCs should be limited to 2 mm increments to allow adequate light transmittance [7]. Bulk-fill composite is more translucent and has a higher depth of cure than conventional RBCs [8,9]. The light transmittance up to 4 mm can be attributed to a different photoinitiator incorporated into the bulk-fill composite system [9]. More modern bulk-fill composites undergo RAFT (reversible addition–fragmentation chain transfer) polymerization resulting in more cross-linking and improved depth of cure [10]

Results

Discussion

Conclusion