30 May 2021

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How much can the preparation design interfere with the marginal adaptation of CAD-CAM onlays in reinforced composite

Lara Figini

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Compared to full crowns, onlays can restore the damaged occlusal surface with minimal tooth reduction. However, the long-term results must be considered when evaluating the success of a prosthetic rehabilitation. Poor marginal fit, for example, can cause microleakage, secondary caries and periodontitis and can lead to clinical treatment failure. But what is the preparation drawing for composite onlays with CAD-CAM technique that leads to a better marginal fit?

MATERIALS AND METHODS
In an in vitro study, published in the October 2020 Journal of Prosthodontic, the authors investigated the effect of tooth preparation design on marginal and internal fit for CAD-CAM ceramic-reinforced composite resin onlays. The authors prepared ten standardized right mandibular first molars (A5SAN-500; Nissin Dental Products, Inc) which were divided into a traditional preparation group and a shoulder preparation group, with 5 teeth for each group. The onlay preparations were performed by the same clinician. Primarily all teeth were prepared for a standard mesio-occluded-distal (MOD) box with a depth of 3.0mm with mesial / distal finishing lines positioned 1.0mm above the amelo-cementitious (CEJ) line. Then the teeth in the traditional preparation group received an occlusal reduction of 1.5 mm with a 1.0 mm chamfer borne by the mold head and a 0.5 mm bevel borne by the cutting head. For the shoulder preparation group all teeth were prepared with a uniform cusp reduction of 2.0 mm. The digital silicone replication technique was used to determine marginal discrepancies between dental preparations and onlay restorations. A total of 100 measurements of marginal adaptation were carried out in 3 distinct regions: the buccal margin, the lingual margin and the internal area. Independent Student t tests were used to determine significant differences (a = .05).

Results
The specimens of the traditional preparation group showed significantly smaller overall discrepancies (50.9 ± 0.5 mm and 139.1 ± 5.4 mm, P <.001) and minor marginal discrepancies in the buccal part (49.7 ± 1.4 mm and 135.8 ± 2.2 mm, P <.001) and in the lingual areas (47.1 ± 1.0 mm and 133.4 ± 1.1 mm, P <.001).

Conclusions
Based on the results of this in vitro study, which must be confirmed in other similar studies, the following conclusions can be drawn:

- In CAD-CAM-made ceramic-reinforced composite resin onlays, traditional preparations led to fewer marginal and internal discrepancies between restorations and dental preparations than shoulder preparations.

- The silicone digital replication method can be used to assess both marginal and internal discrepancies

Clinical implications
With the rapid development of CAD-CAM technology, onlays prepared with the traditional method show better marginal adaptation than those prepared with the shoulder preparation, so they can guarantee better long-term success.

For additional information:  Effect of tooth preparation design on marginal adaptation of composite resin CAD-CAM onlays.