Resistance to horizontal forces of dowel and amalgam-core restorations: a comparative study

Four designs of amalgam-core anchorage were compared in a laboratory study for the inability to withstand the horizontal component of occlusal force. Amalgam cores were constructed for extracted teeth with either composite resin-cemented Dentatus dowels, or with Para-post or Flexi-post dowels cemented with phosphate cement. All the posts were of comparable length and diameter. These anchorage designs were compared with each other and to a self-threading (TMS) pin-retained amalgam core, by application of horizontal force and recording forces causing failure. Flexi-post-retained amalgam cores failed at a mean force of 36.5 (+/- 8.5) kg while Dentatus-retained and Para-post-retained cores failed at 41.7 (+/- 8.0) kg and 46.6 (+/- 11.4) kg, respectively. TMS-retained cores resisted forces up to a mean force of 53.5 (+/- 4.5) kg. Patterns of failure varied widely among these groups. Composite resin-cemented Dentatus dowels were retained in the tooth in nine out of ten samples, while none of the ten Flexi-post dowels and only one of the ten Para-post dowels did so. Tooth fracture on failure occurred in seven out of ten Flexi-post-retained cores, while only three out of ten of the Para-post-retained cores and none of the Dentatus dowel-retained cores presented this unrepairable type of failure. Possible reasons for these differences are discussed.