Interfacial gap formation of class II composite restorations with proximal box elevation using bulkfill materials - a micro-CT study

Sep 30, 2026

Uploaded by James

Evaluate the effect of proximal box elevation (PBE) using different bulk-fill resin composites on interfacial gap formation of Class II direct restorations at the cervical region via micro-computed tomography (micro-CT). Standardized mesial and distal box-shaped cavities were prepared on 25 extracted lower molars and allocated to five groups based on bulk-fill type or no PBE control. After self-etching with a dual-cure universal adhesive and thermocycling, gap areas at the gingival floor were quantified and compared using Welch ANOVA with Games-Howell post hoc tests. Low-viscosity and bioactive dual-cure PBE reduced interfacial gaps compared with higher-gap groups, supporting suitability for deep margins.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages10

Reading Time25 min

AccessFree to download

Introduction

Background on composite restoration failures and microleakage

Cervical margin relocation and proximal box elevation

Bulk-fill resin composites for proximal box elevation

[www. nature.com/scientificreports](www. nature.com/scientificreports) OPEN Interfacial gap formation of class II composite restorations with proximal box elevation using bulkfill materials: a micro-CT study Ceren Deger1􀀍, AyseAslı Senol2, PınarYılmazAtalı2 & Burcu Oglakci Ozkoc1 To evaluate the effect of proximal box elevation (PBE) using different bulk-fill resin composites on interfacial gap formation of Class II direct restorations at the cervical region using micro-computed tomography (micro-CT). Standardized two separate box-shaped Class II cavities were prepared on both mesial and distal surfaces of 25 sound human lower molars. Cavities were divided into five groups (n = 10) based on different bulk-fill composites used for PBE: (1) Group SB: sonic-activated bulk-fill,(2) Group EB: low-viscosity bulk-fill,(3) Group VB: thermo-viscous bulk-fill,(4) Group AB: bioactive dualcure bulk-fill, and (5) Group FZ: no PBE (control)-conventional resin composite. A dual-cure universal adhesive was applied in self-etch mode. In PBE groups, a 3 mm bulk-fill layer was applied before layering conventional composite, while no PBE group was restored using conventional composite. Specimens underwent thermocycling (10,000 cycles, 5–55 °C) . Micro-CT analysis measured interfacial gap formation based on radiolucent areas at the gingival floor of tooth-restoration interface. Data were analyzed using Welch ANOVA and Games-Howell post hoc tests (p < 0.05) . Groups SB and VB showed significantly higher gap formation than Groups EB and AB, as well as Group FZ(control/no box elevation) (p < 0.05). No significant differences in gap formation were found between Groups EB, AB, and FZ (p > 0.05). PBE with low-viscosity and bioactive dual-cure bulk-fill composites effectively minimized interfacial gaps at the cervical region, suggesting their suitability for deep Class II restorations. PBE using low-viscosity bulk-fill composite resin and bioactive dual-cure bulk-fill composite resin could be preferred due to superior cavity adaptation in the cervical region compared to no proximal elevation. Keywords Bulk-fill composite, Proximal box elevation, Deep margin elevation, Micro-computed tomography, Gap formation The success of dental restorationsis evaluated based on their achievement of clinical outcomes such as functionality and aesthetics. For restorative materials, the desired features include optimal mechanical and physical durability, as well as the ability to form ideal bonds with dental tissues and minimal technique sensitivity during application. However, resin composites, one of the most commonly used restorative materials, have varying clinical lifespans depending on the oral environment and the functional load. The formation of secondary caries, microleakage, and fractures are the most frequently observed failures that limit the clinical lifespan of composite restorations1. Microleakage in composite restorations may occur due to shrinkage stresses during polymerization, differences in the coefficient of thermal expansion between the restorative material and the tooth structure, and inadequate hybridization caused by fluid trapped in the gap between the adhesive system and collagen fibrils2. In cavities extending below the cementoenamel junction, the presence of subgingival margins lacking enamel tissue creates significant technical challenges that may lead to microleakage3. Moreover, bonding to deep dentin tissue is more challenging than enamel tissue due to dentin tissue’s high organic content, tubular structure, and increased permeability4. In such cases, the biological width required between the alveolar crest and the restoration margin, as well as the conditions required for restoration procedures, can be achieved through surgical crown lengthening or orthodontic tooth extrusion5. However, in cases where invasive procedures cannot be performed, the subgingival margin can be repositioned supragingivally using resin composite ma

FAQs

What is proximal box elevation (PBE) in this study?

PBE is achieved by applying a 3 mm bulk-fill layer in Class II cavities to relocate the margin toward a more favorable bonding location before restoring with a conventional composite.

How was interfacial gap formation measured?

Interfacial gaps were assessed using micro-computed tomography (micro-CT), quantified by radiolucent areas at the gingival floor of the tooth-restoration interface.

Which bulk-fill materials produced the best gap outcomes?

Groups using low-viscosity bulk-fill and bioactive dual-cure bulk-fill in PBE showed effectively minimized interfacial gaps at the cervical region, with no significant differences among EB, AB, and the control group.

Sep 30, 2026

Uploaded by James