Variation in phosphoric acid concentration and treatment time and HEMA diffusion through dentin

Area of Science:

• Dental Materials Science
• Biomaterials Research
• Nanotechnology in Dentistry

Background:

• Understanding the diffusion of monomers like 2-hydroxyethylmethacrylate (HEMA) through dentin is crucial for dental adhesive efficacy and biocompatibility.
• Phosphoric acid etching is a standard dental procedure, but its impact on monomer penetration requires detailed investigation.
• The interaction between bonding resins, dentin, and phosphoric acid etching parameters influences the integrity of dental restorations.

Purpose of the Study:

• To investigate the in vitro effects of phosphoric acid concentration and etching duration on 2-hydroxyethylmethacrylate (HEMA) movement through dentin.
• To quantify HEMA diffusion from a bonding resin-composite system into the dentinal tubules.
• To evaluate how varying phosphoric acid etching protocols influence the rate and extent of HEMA penetration.

Main Methods:

• Human third molar teeth were prepared with occlusal cavities and subjected to different phosphoric acid etching conditions (10% or 37% for 15, 30, or 60 seconds).
• A closed chamber system was used to collect water samples from the pulp chamber over a 10-day period.
• High-performance liquid chromatography (HPLC) was employed to analyze HEMA concentrations in the collected water samples.

Main Results:

• HEMA was detected in pulp chambers within 4.32 minutes across all experimental groups.
• The highest HEMA diffusion rates were observed shortly after resin placement, significantly exceeding control levels in most acid-etched groups.
• The 37% phosphoric acid group etched for 60 seconds showed a significantly lower early HEMA diffusion rate compared to other etched groups and the control.

Conclusions:

• Phosphoric acid concentration and treatment duration significantly modulate HEMA diffusion through dentin.
• While most etching protocols enhance early HEMA movement, prolonged exposure to higher acid concentrations may alter dentin permeability differently.
• These findings have implications for optimizing dental adhesive protocols to control monomer diffusion and improve restoration longevity.