Spatial Segmentation and Temporal Gap Closure Delay Strategies of Semi-Split Bulk Filling Technique in Deep Occlusal Bulk-Fill Resin Composite Restorations - Part 1: Bonding Disparities between Cavity Walls and Pulpal Floors

Hassan KA and Khier SE

Published on: 2025-08-09

Abstract

Background
Successful adhesive performance in resin composite restorations depends on the integrity of bonding to both cavity walls and pulpal floors. These two substrates present distinct differences.

This paper is the first in a two-part series. It highlights disparities between these two substrates with regard to mechanical, adhesive, biological, and geometric parameters in deep occlusal bulk-fill resin composite restorations. Understanding these disparities is crucial for optimizing adhesion, mitigating stress, and minimizing restoration failure.

Objective
To compare the substrate characteristics, bonding behavior, and polymerization stress response of cavity walls versus pulpal floors, and to outline clinical implications for improved adhesion and composite placement strategies.

Methods
A narrative synthesis of literature on dentin substrate biology, adhesive infiltration, hybrid layer quality, and polymerization shrinkage stress distribution was performed. Key studies analyzing enamel-dentin bonding, dentin permeability, and stress development in occlusal bulk-fill resin composite restorations were reviewed.

Results
Cavity walls generally exhibit lower dentin tubular density, reduced permeability, and greater availability of intertubular dentin, resulting in higher bond strength and a more uniform hybrid layer. Enamel margins further enhance marginal sealing. In contrast, pulpal floors consist of deeper dentin with higher tubular density, greater fluid movement, and reduced intertubular dentin, leading to lower bond strength, increased nanoleakage, and higher risk of adhesive failure. Furthermore, stress concentration is greater at the pulpal floor due to its flat geometry and lower structural compliance, predisposing it to internal gap formation.

Conclusion
Bonding to cavity walls is generally more predictable than to pulpal floors due to distinct variations between these two substrates. Clinical protocols for both substrates should incorporate stress-mitigating strategies, such as spatial segmentation and temporal gap closure delay strategies within the semi-split bulk filling technique.