In natural dentition, there is microscopic clearance or passive contact between teeth when they are in rest position, which is called Interproximal Relief (IR)*, and when a crown is fabricated, it is necessary to adjust the crown on the proximal contact surfaces to restore IR, and to achieve complete marginal seating for patient comfort and functionality.
The following references to scientific literature illustrate the need for proper interproximal adjustment:
Spaces of at least 0.0005-in. (0.0127mm) may exist naturally between teeth in 80%-90% of the proximal contacts.
The fixed partial denture be adjusted until 0.0005-in. shim stock will pass through proximating contacts with very slight resistance.
-W.V. Campagni 1984
Observed spaces ranging from 3 to 21 microns between adjacent teeth at rest.
-K. Kasahara 2000
Small spaces occur between natural teeth. Most of the authors recommend checking the proximal contact with dental floss, and floss does not properly detect these spaces.
-J.T. Lindquist 1951
The contact should not be so tight as to cause wedging of the teeth.
-W.W. Howard 1981
The properly restored proximal contact should be passive contact or microscopic clearance that relieves pressure between the proximal contact surfaces of indirect restorations and adjacent teeth. The relief of pressure is referred as interproximal relief (IR).
-D.S. Kim 2007
The following figures are an example of a step-by-step procedure using the ContacEZ Restorative Strip System to achieve complete marginal seating for a new crown.