Old dental amalgam fillings replacement by indirect CAD-CAM composite restorations

Digital - Tips and tricks - Indirect posteriors
16 Feb 2017

Partial indirect CAD/CAM reconstructions, such as onlays and overlays made by ceramics or composite, are suitable to substitute worn dental amalgam fillings. These old restorations should be carefully examined as dentinal sensitivity to cold and hot might disclose dentinal cracks or cuspal fractures that could determine chronic pulpal disease or pulpal necrosis. The digital workflow in these clinical situation could be a great opportunity for the clinician to replace old fillings with new indirect restorations made by esthetics materials, such as composite or ceramics, thus improving the quality of the entire system, i.e. dental tissues and reconstruction material.

Dental amalgams fillings should be constantly monitored as, in aging process, might present marginal chipping, enamel microfractures or hidden dentinal cracks; sensitivity to cold drinks is one of the features related to the degradation of the restoration, due to a micro-infiltration of bacteria toward the inner part of the tooth, thus stimulating pulpal reactivity.

A proper diagnosis is mandatory and a careful examination of the borders might disclose these problems before an irreversible pulpitis takes place.

Dental amalgams replacement is not a “free of biological costs” process; part of the dentin and of the enamel should be removed, in addition, demineralized dentin should be carefully examined and drilled out. At the end of this process the cavity floor and the cavity walls are composed by a wide area of different type of dentin – reactive and sclerotic ones – in a frame of thin enamel.

Frequently dental cusps are too thin to be preserved and a cuspal coverage indirect reconstruction should be considered as the first choice.

In all these cases, particularly in those needing an indirect reconstruction made by CAD-CAM systems, a preventive sealing of the dentin (IDS) and a proximal box elevation (PBE) are both advisable.

PBE has been proposed in 1994  by Dietschi D & Spreafico R (1) and was confirmed by different studies (2,3,4), also IDS was introduced in late nineties but recently confirmed by Magne et al. (5,6,7) and has been widely accepted as a good clinical practice to prevent post operative sensitivity in the case of indirect restorations. Some studies reported (6,7) a better adhesion of the indirect manufactures to the dentin sealed before the impression procedure.

CAD/CAM chairside restorations have been report as a clinical highly reliable procedure to obtain inlays, onlays and overlays (8,9,10).

In the clinical case presented two dental amalgams should be replaced by indirect restorations; a composite – made for CAD/CAM restoration (Lava Ultimate, 3M, USA) – was chosen and both PBE and IDS was performed before the digital impression.

Proper conditioning of the cavity was accomplished and of the inner part of the CAD/CAM restoration conditioned by a gentle use of sandblasting (50 microns alumina-oxide powder).

A flowable composite was used as a luting agent. The time needed for the whole process was monitored and resulted in two hours and a half.

Fig. 1

Img. 1 – The initial situation: broken lingual cusp and secondary caries on the premolar. Dental amalgam fillings should be constantly monitored as, in aging process, they might present marginal chipping, enamel microfractures or hidden dentinal cracks

Fig. 2

Img. 2 – Removal of the previous restorations. There is still some carious dentin present on both molar and premolar. Due to a fracture, the remaining lingual cusp must be removed. The cervical margin relocation is necessary in order to stabilize the rubber dam, to facilitate impression and luting, finishing and polishing procedures.

Fig. 3

Img. 3 – After complete removal of the carious tissues, the margin relocation (Deep Margin Elevation, DME or Proximal Box Elevation, PBE) is performed at the same time of the immediate dentinal sealing and a small build-up. A composite – made for CAD/CAM restoration (Lava Ultimate, 3M, USA) – was chosen and both PBE and IDS was performed before the digital impression

Fig. 4

Img. 4 – After complete removal of the carious tissue, the margin relocation is performed at the same time of the immediate dentinal sealing and a small build-up also on the premolar.

Fig. 5

Img. 5 – Before the final cavity preparation, both the partial reconstructions are covered with glycerin and polymerized again

Fig. 6

Img. 6 – The two cavities after the final preparation. All the margins are located supragingivally and in a position where impression taking and cementation procedures are facilitated

Fig. 7

Img. 7 – The optical impression with the highlighted marginal line

Fig. 8

Img. 8 – The final proposal design of the restorations

Fig. 9

Img. 9 – Try-in of the inlay and the onlay before the characterization, in order to check the fit and the tightness of the contact point

Fig. 10

Img. 10 – Slight reshaping of the occlusal morphology and deepening of the sulci

Fig. 11

Img. 11 – Light characterization of the central sulcus using a light brown stain

Fig. 12

Img. 12 – Last try-in and general check before cementation

Fig. 13

Img. 13 – Insulation of the premolar with PTFE tape, gentle use of sandblasting (50 microns aluminum oxide powder), etching with phosphoric acid, application of a primer and a bonding agent and cementation of the onlay on the molar using a flowable composite.

Fig. 14

Img. 14 – After removal of the excess cement on the molar, the same adhesion procedures and cementation previously used on the molar, are performed for the inlay on the premolar

Fig. 15

Img. 15 – Result after excess removal and final polishing

Fig. 16

Img. 16 – The finished case at the end of the procedure

 

Conclusions

Main tip: Substitution of old dental amalgam fillings by indirect partial CAD/CAM reconstruction is better accomplished by a previous adhesive preparation of the dentinal substrate by Immediate Dentinal Sealing (IDS) and Proximal Box Elevation (PBE), also named as Deep Margin Relocation.
CAD/CAM indirect partial restorations are suitable to substitute old dental amalgam fillings; proper preparation procedures like PBE and IDS should be at first considered to create a precise cavity base; this feature will help both during the digital impression phase and during the luting process.

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