Proper Preparation and Tissue Management for Anterior All-Ceramic Crowns
A Case Study
Bernard Touati, DDS, MS
Crown integration requires an ideal positioning of the cervical margin in the gingival sulcus and tooth reduction sufficient to allow the creation of harmonious crown morphology. For proper integration, the crown also needs appropriate resistance to fracture and a perfect emergence profile.
In this case, a 22-year-old male patient presented for metal-free restoration of the maxillary central incisors. After previous trauma, the maxillary left central incisor had fractured. Its incisal edge had been temporarily restored with composite resin. The right incisor became darker following the trauma but remained vital (Figure 1). Preparation included the following:
- A 1 mm to 1.2 mm chamfer, located subgingivally approximately 0.5 mm below the free gingival margin
- An 8- to 10-degree convergence of the axial walls, respecting the homothetic reduction of the tooth
- A 2 mm occlusal clearance in the incisal aspect (minimum 1.5 mm in the cingulum)
- Rounded angles and edges (Figure 2)
A double-cord technique was utilized to laterally displace the free gingival margin and allow access to the gingival sulcus during the impression step (Figure 3). Impressions were made using polyvinylsiloxane materials in the "wash" technique (Figure 4). The preparation of the palatal wall was determined by the requisites for final retention/stabilization of the crown. Care was taken not to exaggerate the convergence between the buccal and lingual walls. The latter, located between the cingulum and the cervical margin, is often not higher than 1 mm or 2 mm. Therefore, it is crucial to respect its axis during the lingual preparation, for this is what will determine the future retention of the crown in protrusive movements (Figure 5).
Several kits have been conceived for optimally preparing all-ceramic crowns, and one should never underestimate the importance of the design of rotary instruments. One should precisely know the diameter of each rotary instrument, from tip to junction with the shaft, to be able to control the invasiveness of the preparation. Massironi's chisels are perfect for smoothing the chamfer and controlling the subgingival penetration (Figures 6 and 7). Postoperative radiograph confirms the accuracy of the cervical margins. Radiolucency is a requisite of contemporary crowns, and aluminum oxide displays a radiolucency very close to human dentin, which is good for the control of cement washout or recurrent decay (Figure 8).
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Facial view of the outcome after cementation with a resin-modified glass ionomer cement. The crowns are aesthetically and biologically well integrated (Figure 9).