Improved micro-tensile strength test developed by NIOM reveals key to successful repair of restorations

Jon E. DahlSigfus Thor Eliasson

Sigfus Thor Eliasson | Jon E. Dahl
Visiting Scientist | Managing Director


A new method for tensile bond testing.

A more reliable and less time-consuming test method to evaluate the micro-tensile strength of the repair bond between old and new composites has recently been published. The improved test method is based on studies carried out previously at NIOM.

These studies showed that, in general, a thinner bonding layer renders a repair bond stronger, and that silane surface treatment significantly improves repair strength. The results support the reliability and effectiveness of the clinical procedure that the new investigation proposes.


Repairing composites increases the longevity of restorations

There is growing evidence that repairing composites increases the longevity of restorations. Methods to achieve the best repair have been explored in a number of investigations. The majority of these studies compare both different adhesives and various surface treatments of the composite to be repaired. In addition to roughening with diamond burs, sandblasting, etching with hydrofluoric acid, lasers and silane application have been suggested. To date, there appears to be no consensus on the most appropriate way to prepare the substrate.

Avoid curing the adhesive before placement of repair composite

New test method adds further support to previous studies

The most recent NIOM investigation confirmed the results from the previous studies. Application of freshly prepared silane and the use of a thin bonding layer lead to higher micro-tensile bond strength. The recommended procedure to obtain intimate contact between the old restoration and repair composite is to avoid curing the adhesive before placement of the repair material. This makes composite repair simpler and less time consuming.

Clinical implication

A feasible clinical procedure for composite repair is:

  • roughen with a diamond bur
  • acid etch
  • apply bis-silane and adhesive
  • squeeze the repair composite on to the uncured adhesive before curing.