Posterior_Direct_Restorations Salvatore_compressed
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FIG 5-15 (a and b) Sector isolation. (c and d) Inserting a wedge. In this example, the wedge is inserted palatally because those embrasures are wider (ie, there is more space). (e and f) Protecting the adjacent tooth. (g and h) Preparing the marginal ridge. (i) The preparation is carried out in a buccolingual direction (double arrow), preserving the marginal ridge. (j and k) Cavity design is defined based on the extent of the caries lesion and structural requirements. (l) Axial walls. (m) The small residual wall is often detached while defining the axial walls. (n) If the residual wall does not detach, it can be removed using manual tools or the same cylindric round bur used for preparation. (o) Preparation of the cervical step. (p) The bur is moved quickly in a buccolingual direction (double arrow) without exerting a great deal of pressure. (q) Defining the axial walls using a flame bur. (r) If buccal access is possible, reciprocating diamond files can be used. (s and t) This stage can also be performed using coarse-grained disks or manual tools (scalpels). (u and v) The axial walls and cervical step also can easily be defined using sonic inserts. (w and x) Marginal finishing. If the margin is accessible, it can be prepared using medium-grained disks. (y and z) Cervical step emergence can be modified in a mesiodistal direction. This modification must be performed only when indicated.
The wedge protects the deep interproximal area (see Figs 5-15c and 5-15d; see also Figs 5-13b and 5-13c) as well as the dam, which could become damaged during box preparation. The wedge can be inserted buccally or lingually. It is advisable to insert it where the embrasures are wider. Devices are available to protect the adjacent tooth (see Figs 5-15e and 5-15f; see also Fig 5-10). As discussed, Lussi et al showed that the adjacent tooth is always involved during a Class 2 preparation, even
when magnification is used.23,24
A small round cylindric bur is used to prepare the inside of the marginal ridge (see Figs 5-15g and 5-15h), preserving the interproximal wall. The preparation is generally deepened by 2 to 3 mm to gain a direct view of the extent of the caries lesion (see Fig 5-12).
It often feels as though the bur is drilling into nothing as it enters the demineralized area, which offers less resistance. The preparation is carried out in a buccolingual direction, preserving the marginal ridge (see Fig 5-15i). Maintaining as much of the interproximal wall as possible, the cavity design is finalized in buccolingual and mesiodistal directions (see Figs 5-15j and 5-15k). The final design will be further modified after cleaning the dentin, given that enamel walls often turn out to be unsupported. The same bur (or a flame bur) is used to define the axial walls (see Fig 5-15l). If not already removed, the interproximal wall is gradually weakened to make it easier to remove (see Figs 5-15m and 5- 15n).
A flat cervical step is prepared (see Fig 5-15o).The cervical step must be prepared accurately to achieve:
A good fit for the sectional matrix
Good bonding material wettability
Good restoration material fit
Correct emergence
VIDEO: CLASS 2 PREPARATION
The margin can be easily achieved by using end-cutting burs to avoid damaging the neighboring tooth (if protection has been removed) or the axial walls (Fig 5-16). The movement to be adopted when using this bur
is gentle pressure but relatively fast buccolingual movements (see Fig 5- 15p).