A Cerec inlay is an indirectly (outside the mouth) fabricated ceramic inlay filling; here the abbreviation Cerec stands for ceramic reconstruction. The great advantage of this type of filling restoration compared to other esthetic restorations is that the restoration is made of high-quality ceramic and can be fabricated without an impression within one treatment session in the dental office, eliminating the need to wait several days for completion in the dental laboratory. The Cerec system was developed in the 1980s at the University of Zurich and is now in its 4th generation. The technically complex overall concept consists of a camera system for optical impression taking, 3D software for designing the inlay (CAD process) and a milling system with electric motors that mills the inlay out of an industrially produced ceramic block within a few minutes (CAM process). Blocks of feldspar ceramic, leucite- or lithium silicate-reinforced glass ceramic, and zirconium oxide can be used as materials.
Indications (areas of application)
The indication for a Cerec inlay is determined on the one hand by the degree of destruction of a tooth, and on the other hand the patient’s desire for a durable, high-quality and aesthetic restoration contributes to this. Intolerance to other filling materials can also lead to the selection of a ceramic restoration. Thus, a Cerec inlay is used under the following aspects:
- Amalgam intolerance;
- Gold intolerance (rare! );
- Aesthetic requirement;
- Incompatibility of impression materials;
- Patient’s fear of impressions, possibly in conjunction with pronounced gag reflex;
- Care of molars (posterior molars);
- Restoration of premolars (anterior molars), for which aesthetic aspects are more decisive than for molars;
- Required cavity supply with permanently good oral hygiene;
- Medium-sized cavity, which includes the fissure area of the tooth and one or both approximal surfaces (interdental surfaces);
- Treatment time as a limiting factor.
The procedure
Unlike laboratory-made inlays (inlay fillings), the Cerec inlay is produced chairside, i.e. in the dental practice, the preparation (grinding) of the tooth is not followed by the impression of the jaws and the temporary (transitional) restoration, which is followed by a processing phase in the laboratory of several days, but the inlay is finished and inserted immediately afterwards. The working steps are divided as follows:
First treatment phase on the patient:
- Caries removal;
- Preparation (grinding):
- In principle, any preparation technique must be as gentle on tooth tissue as possible: sufficient water cooling, rounded preparation shapes, no excessive roughness depths, as little substance removal as possible and sparing the adjacent teeth.
- Slightly divergent preparation angle, because the inlay must be able to be removed from or placed on the tooth without jamming or creating undercuts (unprovided cavities);
- Removal occlusal (in the occlusal surface area) at least 2 mm;
- Preparation in the approximal area (interdental area) slightly divergent and box-shaped, in the marginal area undercut-free with defined step; here, the use of sonic preparation attachments instead of rotating instruments is advantageous.
- The proximal contact (contact with the adjacent tooth) must be released, i.e. the inlay to be fabricated must later have contact with the adjacent tooth.
- Loading of the tooth to be restored with contrast spray, with which reflective surfaces are matted;
- Optical impression: scanning the three-dimensional tooth structure and the opposing dentition with a camera that uses short-wave blue light to produce high-resolution images.
Manufacturing phase
The inlay is designed using the 3D software on the screen and requires a high degree of precision from the practitioner. The occlusal surface design is supported by an extensive database of predefined occlusal reliefs for both the tooth to be restored and the dentition of the opposing jaw. Second treatment phase on the patient:
- If possible, application of rubber dam (tension rubber) for absolute drainage;
- Disinfection of the tooth , eg.B. with chlorhexidine digluconate – not with hydrogen peroxide, as this inhibits (hinders) the curing of the luting material;
- Enamel conditioning for 30 – 60 sec with 35% phosphoric acid gel;
- Dentin conditioning for 15 sec, then application of a dentin bonding agent on the previously only carefully dried, not dried dentin;
- Etching the lower surface of the inlay with 5% hydrofluoric acid for 2 min ; spray off, dry, silanize (chemical bonding of a silane compound to a surface);
- Insertion of the inlay in adhesive technique with a luting composite, preferably with a dual-curing (both light and chemical curing) cement, which sets faster due to light polymerization; cement excess removal before light curing!
- Correction of occlusion and articulation (final bite and chewing movements) with fine-grained diamond burs;
- Finishing and smoothing the margins with fine-grained diamonds and ceramic polishers;
- Fluoridation of the restored tooth.
Possible complications
Possible complications can arise from the multitude of intermediate steps involved in the procedure. Last but not least, the computer-aided CAD-/CAM-manufacturing process poses a challenge for the practitioner:
- Errors during optical impression taking;
- Fracture of the inlay due to too sparing substance removal in the occlusal surface area of the tooth;
- Problems with the computer-based 3D design;
- Tooth sensitivity or pulpitis (pulp inflammation) in response to the adhesive cementation technique;
- Marginal caries due to insufficient luting cement in the marginal joint;
- Medium-term marginal caries due to inadequate toothbrushing technique.
