Table 3.
The main factors affecting veneer color changes, with examples.
| Factor | Examples |
|---|---|
| Improper patient selection | The patient is a heavy smoker (marginal discoloration) [30] and has poor oral hygiene. |
| The tooth underwent a previous endodontic treatment [30]. | |
| Improper material selection | Selection of a material (feldspathic porcelain) for cases that need staining or are adjacent to crowns [16]. |
| Improper communication with dental laboratory | Failure to select the opacity (MO *, HO *, zirconia) of dark teeth occurring after tooth preparation due to poor communication with the dental laboratory [16,17,41,44]. |
| Making a thinner veneer for a dark substrate [16,17,41,44]. | |
| Producing a thick veneer without an appropriate reason (thicker veneers decrease the translucency) [16,17,41,44]. | |
| Large number of firing cycles are used, which will burn the coloring metallic oxides and the veneer will be darker [45]; the quantity and position of the veneers during firing [46]. | |
| Poor glazing and polishing [47]. | |
| Normal aging process of the tooth | The tooth has ability to change color over time [48]. |
| Improper cementation technique | No verification of the veneer color occurred before cementation by using try-paste [49]. |
| Use of dual-cure resin cement for thin veneers (≤1 mm), with HT *, LT *, and MT * glass-ceramics [41,50] | |
| Microleakage presented as a dark line at the gingival margin | Lack of bonding agent; use of a scaler to remove resin cement; subgingival margin at the dentin or root surface is more likely to be prone to leakage, poor isolation, and tissue management (proper subgingival margin isolation before and during bonding is vital to prevent interference from the sulcular fluids with the bonding surfaces, which causes yellowish discoloration.); use of thick adhesive layer; and lack of margin fit [51]. |
* TEGDMA = triethylene glycol dimethacrylate, CQ = camphorquinone, TPO = diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide, MO = medium opacity, HO = high opacity, HT = high translucency, LT = low translucency, and MT = medium translucency.