Everything said in Class II deep subgingival box  applies, except that now we need to adapt the band to the interproximal concave root perimeter – the furcation. The Bandbender is consummate in this regard. After creating the proximal convexity on the band as usual, turn the matrix over on the Bandbender and bend the gingival margin in reverse, creating a concavity to approximate the root fluting.

Attempt to adapt the band to the root surface with packed pledglets, wedges, large diameter retraction cord ,PVS or other approaches. Sometimes nothing works perfectly, and there are gaps between root and band. In this case, adapt the band tightly to the root surface with an instrument or perio probe and place Starfill 2B in a small increment  and spot cure . Once  satisfied with the initial increment, complete the box up to 6mm of depth as discussed in  Class II deep subgingival box

If the first increment inadvertently runs out of control, and an overhang develops in the furca, all is not lost. Finish the furca margin with a 7902, in exactly the same fashion as a margin of a Class V, and accept that the tissue will be traumatized through this. Most likely the field will be impossible to control henceforth at this appointment.Temporize with IRM. Alternatively, paint the preparation with temporary crown and bridge cement using a regular Centrix Bendabrush and restore temporarily with a LC dense white product such as Voco Calcimol LC, or perhaps a bulk fill material. This will create a temporary filling with high contrast, poor adhesion and yet will be comfortable because the dentin has been sealed with the standard bonding protocol.  Re-appoint in a few weeks ensuring that the patient follows proper tissue control. You can expect on their return that the tissue line will be perfect, and it will be a simple matter to finish the restoration, repeating the bonding sequence. Divide and conquer: manage the the gingival increment today, and the rest, later. Rebook, and  proceed from the certainty of a biologically correct interproximal margin.

Wedging a furcated tooth usually requires improvisation. Tongue depressors shaped with a denture bur, multiple wedges stacked upon each other, or topical applicators trimmed to fit may all execute the job at hand. The rules are: observe the presenting geometry and innovate as needed.