Failed Amalgam Restoration UL6

The UL6 has a ditched amalgam and recurrent caries. A piece of amalgam has fractured away from the disto-palatal cusp.

Notice the exposed dentine pin in "supporting" the disto-palatal amalgam.

The tooth is asymptomatic and responds normally to thermal stimuli. There is no sensitivity to occlusal loading of the cusps.

The tooth is isolated with rubber dam and sealed with a floss ligature.

Removal Of The Amalgam Restoration

The amalgam restoration is removed with a combination of high speed rotary and ultrasonic instruments. The use of ultrasonic instruments allows the break up of the amalgam without enlarging the cavity outline.

The dentine pin is left in situ. With the microscope: It is now possible to fully appreciate the extent of the caries.

The cavity is disinfected with 5% NaOCl prior to removing any of the caries.

Caries Removal

Caries is removed with a combination of rotary and hand instruments. The colour of the dentine is does indicate either the infectivity of the dentine or its state of demineralisation.

The cavity is periodically disinfected with 5% NaOCl to reduce the bacterial burden. Bur changes are also made to avoid contaminating deeper portions of the dentine with infected burs.

The dentine pin is still left in

Assessment of Cavity And Dentine Pin X10

Under the microscope it is plainly seen that a crack extends mesially from the dentine pin. This crack extends diagonally along the floor of the cavity towards the mesio-buccal cusp.

With the magnified well illuminated vision afforded by the microscope; cracks associated with the placement of screw-type pins are frequently observed.

The routine observation of fractures and secondary caries associated with dentine pins, has dissuaded the author from using pins for retention, even for large restorations and cores.

Removal Of Dentine Pin And Residual Caries

The pin and associated remaining caries are removed. Initial attempts at dislodging the pin is with ultrasonic instruments at low or medium power. High power will cause the pin pin to break up rather than be ejected intact.

If ultrasonic energy fails to free the pin, then a "blunt" high speed diamond bur can be gently applied perpendicular to the pin along its entire length. The clockwise motion of the bur will often persuade the pin to disengage from the dentine by rotating counter-clockwise.

In very rare instances the pin may need to be removed in sections with small rotary instruments.

Disinfection of Cavity

Following removal of the pin and remaining caries the matrix band and wedges are applied. The matrix band should be burnished after tightening to support the desired contact shape.

Notice that the rubber dam clamp is applied on the outside of the matrix band. The most suitable clamp for molars is a W56. The W56 clamp is not sufficiently stable to retain the rubbed dam. To retain the rubber dam a W8A is of better design.

The cavity is then flooded with 5%NaOCl for 60 seconds. To assist in the disinfection of the crack; micro-brushes are rubbed along its length.

Etching Of Enamel With Phosphoric Acid

The enamel is etched for 15 seconds with phosphoric acid.

Self etching primers do not demineralise the enamel sufficiently to provide a reliable enamel bond. A poor enamel bond gives rise to marginal breakdown, microleakage and subsequent hydrolysis of the hybrid layer. All these factors contribute to reducing the prognosis of the final restoration.

The unparallel vision offered by the microscope, allows for the etching of enamel without any of the deleterious effects of etching dentine.

Priming And Bonding

The enamel and dentine can be etched and primed with a self etching primer. The enamel margins should also be covered with the etch/primer.

If using a dual cure bonding system; then in order to apply the bond, a filter must be placed over the light source. Failure to do so will result in the premature curing of the bonding agent and its failure to adhere to the amalgam.

The author has no experience of using a chemical-only cured bonding agent with amalgam.

Packing Of Amalgam

The cavity should be progressively and incrementally filled with thoroughly condensed amalgam.

Excess bonding material should be squeezed against the cavity walls in order to reduce film thickness and avoid leaving small gaps between the amalgam and tooth.

Surplus bond should be encouraged to the surface where it can be easily removed with a probe.

Carving Of Amalgam

The wedges and W56 rubber dam clamp are removed. In order to avoid damaging the marginal ridges when removing the matrix band the amalgam fillet in the marginal ridge area is removed with a probe and contoured.

The matrix band should be first displaced apically prior to its removal along the conventional occlusal path and away from the tooth. Sometimes it is necessary to section the matrix band and slide each section through the contact areas.

The rubber dam is now cut through the interproximal areas and removed. Any remaining amalgam fragments are dislodged with floss.

The occlusion is refined with a combination of excavators, and amalgam carvers. The fissure pattern is finalised with a conventional dental probe.