The idea that immediate dentin sealing (IDS) can increase bond strength by more than 400% comes essentially from the classic study by Magne et al. published in 2005, in which the delayed dentin sealing (DDS) group showed extremely low bond-strength values compared with IDS. In the previous post on this blog, we reviewed the studies by Ribeiro da Silva et al. (2016) and van den Breemer et al. (2019), which used broadly similar experimental models but did not observe the same reduction in bond strength in their DDS groups.
So, if performing the bonding procedure on dentin that was prepared two or three weeks earlier does not, by itself, seem to explain the loss of bond strength, an interesting question arises: what actually happened in the DDS group of Magne et al. (2005)?
Explanations for the poor performance of the DDS group
To briefly recap, in Magne et al. (2005), the IDS group reached 58.25 MPa, a value almost identical to the 55.06 MPa obtained by the control group. This is perhaps not particularly surprising, since bonding was performed on freshly prepared dentin in both groups. What is truly striking is what happened in the DDS group, where bond strength dropped to only 11.58 MPa.
The authors proposed mainly three explanations for this large difference, which I will discuss below.
1. Contamination from provisional cements
During the provisional phase, exposure of dentin to provisional cements may significantly reduce bond strength. It certainly makes sense that a contaminated or unclean dentin substrate would be less favorable for bonding. However, no provisional cement was used in the methodology of this particular study. Therefore, this explanation alone cannot account for the extremely low bond-strength values observed in the DDS group.
The provisional restoration used was Tempfil Inlay (Kerr), a light-cured resin material placed directly on freshly prepared dentin. After two weeks of storage in saline solution, the dentin surface was cleaned by airborne-particle abrasion using RONDOflex and CoJet. Ribeiro da Silva et al. (2016) also used a light-cured resin-based provisional material, Clip F (Voco), and after cleaning the dentin with a curette and pumice, they did not observe lower bond-strength values. Likewise, van den Breemer et al. (2019) placed a zinc polycarboxylate cement, Durelon (3M), directly on dentin, and after three weeks of water storage and removal of cement remnants with pumice, their DDS group also did not show particularly low bond-strength values.
From a conceptual standpoint, freshly prepared dentin offers favorable conditions for bonding, partly because it has not yet undergone a provisional phase that may modify or contaminate its surface. Nevertheless, in Magne et al. (2005), it cannot be concluded that contamination was the reason for the poor performance of the DDS group. The cleaning methods used in these studies also deserve attention, as they may play an important role in achieving reliable bonding with DDS.
2. Immediate stress
When bonding is performed immediately before placement of a restoration, the newly formed adhesive interface is immediately subjected to stresses generated by composite polymerization shrinkage and, clinically, by occlusal loading.
However, this explanation seems insufficient on its own to account for the extremely low DDS values reported by Magne, because Ribeiro da Silva et al. (2016) and van den Breemer et al. (2019) also used flat dentin surfaces, with a low-retentive configuration and low C-factor, yet found no significant difference between DDS and IDS.
3. Collapse of the hybrid layer
In the DDS group, after airborne-particle abrasion of the dentin, the adhesive was applied but left uncured, following the clinical rationale that a polymerized adhesive layer might interfere with the seating of an indirect restoration. The first increment of resin composite was then placed directly over the uncured adhesive, and both were light-cured simultaneously. According to the authors, pressure exerted during restoration placement onto an unpolymerized adhesive interface could cause collapse of the demineralized dentin and compromise the cohesion of the bonded interface.
The mechanism is plausible, but the experimental design does not demonstrate that this pressure was responsible for the reduction observed. The DDS group did not receive an indirect restoration or a resin cement. Instead, increments of Z100 (3M) were placed directly onto a flat dentin surface. We therefore do not know whether the pressure generated during manual placement of the composite was sufficient to produce the proposed collapse, or how closely this procedure reproduces the seating of a rigid indirect restoration with resin cement.
Ribeiro da Silva et al. (2016) light-cured the adhesive and did not find reduced DDS values. In contrast, van den Breemer et al. (2019) also did not independently light-cure the adhesive applied in DDS before placing the composite, yet they still found no significant reduction compared with IDS when the surface was cleaned with pumice. Their protocol did, however, include other methodological differences, such as heating the OptiBond FL adhesive resin to 40 °C and using an LED curing unit delivering a radiant emittance of >1000 mW/cm². These are potentially relevant methodological variables.
The explanation proposed by Magne et al. is based on a mechanism clinically related to seating an indirect restoration, although in their experimental model the final restoration was built directly with resin composite. For this reason, it is difficult to determine to what extent the proposed collapse alone explains the 11.58 MPa observed in DDS. In addition to the lack of prepolymerization, other aspects of the protocol—including dentin surface treatment, adhesive characteristics, and light-curing conditions—should also be considered as possible contributing variables.
A final reflection on IDS
IDS is an interesting and clinically reasonable protocol, particularly because it allows dentin to be sealed immediately after tooth preparation, protects it during the provisional phase, and may help reduce sensitivity between appointments. It has also become a widely adopted strategy in adhesive dentistry.
However, this does not mean that it is accurate to state, as a general rule, that IDS increases bond strength by more than 400%.
We should also be more cautious with the idea that the main advantage of IDS comes from bonding to “freshly cut” dentin. So far, there does not appear to be sufficient evidence showing that simply waiting a few weeks turns dentin into a substantially poorer bonding substrate.
Perhaps the real issue is not simply that the dentin is no longer “freshly cut,” but rather what happens to that dentin during the provisional phase—and, especially, how the surface is cleaned and how the bonding procedure is performed. In other words, dentin that has remained unsealed for several weeks may still provide adequate bonding if it is clean and properly conditioned. What remains to be determined is which methods can reliably produce such a surface without negatively affecting the substrate.
This question still deserves to be investigated using experimental designs capable of properly isolating each of these variables. In the meantime, to avoid unnecessary problems, let us perform IDS.
And one more thing: did you know that IDS and a build-up are not the same procedure? If, in addition to applying an adhesive to dentin, you begin reconstructing the preparation with a restorative material, you are moving into a different concept. Where does one end and the other begin? Can both techniques be performed simultaneously? I will come back to that in a future post.