Directed polymerization shrinkage versus a horizontal incremental filling technique: interfacial adaptation in vivo...

(1) To evaluate the interfacial adaptation to dentin and enamel of Class II composite resin restorations placed in vivo with the directed shrinkage technique, a combination of a self-curing (Bisfil 2B) and a light-curing composite resin (AElitefil); (2) To compare this technique with a horizontal incremental filling technique, where the gingival layer of the light-curing composite resin was cured with a transparent light-tip; (3) To evaluate the effect of a hydrophilic bonding system (All-Bond 2) on the marginal adaptation of both application techniques.

In each of 34 premolars, scheduled to be extracted for orthodontic reasons, a mesial and a distal cavity was restored with composite resin filling material using the directed shrinkage technique (Bisfil 2B/AElitefil) and a horizontal incremental filling technique (AElitefil). In six groups, a hydrophilic dentin bonding system (All-Bond 2) was applied. As control, an enamel bonding agent (Gluma 4) was used in one of the directed shrinkage and in one of the horizontal incremental filling groups. For conditioning of the cavities a 10% phosphoric acid gel was used in six groups and a 32% acid gel in the other two groups. The teeth were extracted after 1 month, sectioned and replicas of the sections were made. Quality of the interfacial adaptation was studied with a scanning electron microscope.

On the pairwise comparisons between the two application groups, no significant differences were found between the directed shrinkage technique and the horizontal incremental filling technique. The groups using the hydrophilic bonding system showed a significant better adaptation, with gap-free attachment in 77%-87% of the length of the dentin margins investigated. No significant differences for adaptation to enamel were seen between the investigated groups. The adhesive failures were found mostly between the hybrid layer and the composite resin, while the dentin was still sealed. No significant difference in interfacial quality was seen between the cavities using the 10% or the 32% phosphoric acid conditioning. A relative high frequency of enamel fractures, parallel to the interfaces, was found in the 10% phosphoric acid-conditioned cavities, especially in the cervical enamel interfaces.