Luting agents or cements are used for retaining indirect restorations on teeth or implant abutments. The functions of a luting agent are:
- Retention for preventing dislodgement of the restoration. However, retention alone is insufficient for success. A restoration may be in situ but, if microleakage is present, this may lead to pulpal and gingival irritation, requiring removal of the offending restoration;
- Hermetic seal between the tooth and restoration to minimise microleakage, prevent secondary caries and pulpal and gingival inflammation. In addition, an efficacious seal retards dentinal fluid movement, mitigating hypersensitivity;
- Resist oral functional and parafunctional forces, which are particularly significant for tooth preparations with inadequate resistance form.
The cementation mechanism of cements is classified as:
- Non-adhesive or mechanical interlocking retention by engaging tooth surface and restoration intaglio surface irregularities, measuring 20–100 µm. This mechanism is applicable for all dental cements;
- Micromechanical ‘adhesion’ is engaging finer surface irregularities of <2 µm created by etching, air abrasion, and usually in combination with a dentine bonding agent (DBA), to form a hybrid layer (0.5–10µm) – discussed in Chapter 45;
- Chemical (molecular) adhesion by bipolar, Van der Waals forces and chemical bonds, which is the ideal adhesion, and contemporary cements strive to achieve this ideal.
The mechanism of retention by cements can broadly be termed luting or bonding. Luting provides non-adhesive retention, while bonding implies a closer approximation of the cement with the tooth and restoration, which includes micromechanical and