A difficult clinical situation encountered all too often by restorative dentists is the restoration of one single upper or lower anterior tooth with a crown or resin-based composite.
If all of the anterior teeth in one arch need to be restored, the development of an acceptable aesthetic result is relatively easy, because all of the restored teeth match one another. However, restoration of a single anterior tooth is a genuine aesthetic challenge. Most mature dentists would agree that they have restored only a few single teeth to a near-perfect level in their entire careers.
There are many reasons for the difficulties encountered in restoring one tooth. Teeth exhibit different colours in the several types of lighting encountered in any one day, such as sunlight, incandescent light, cool white fluorescent light, warm fluorescent light and evening natural light. An artificial crown may match perfectly in one lighting condition but be significantly off-colour in another.
Natural teeth darken during life, whereas restorations do not. A crown placed in a 25-year-old patient will probably be lighter than the adjacent teeth a few years later. The superficial ceramic stains placed on almost all porcelain-fused-to-metal, or PFM, crowns dissolve in the presence of the acids in sodas, coffee, fruit juices and other foods and drinks. Removal of the stains usually makes crowns appear lighter in colour.
Gingival tissues recede as part of the normal, expected aging process. A patient who receives a new crown at 25 years of age should expect the gingival tissues to shrink away from the crown after a few years, potentially exposing the unsightly juncture between the crown and the remaining tooth root structure.
A significant percentage of people in the US bleach their teeth without a dentist’s supervision (1). As a result, the teeth become lighter, but the restorations do not become lighter. The appearance of bleached natural teeth adjacent to a previously placed crown is not pleasing.
Tooth bleaching has caused growing numbers of patients to seek additional aesthetic dentistry procedures, but when it is carried to an extreme or accomplished without a dentist’s supervision, tooth restorations adjacent to lighter bleached teeth may be aesthetically unacceptable. The acceptability of the most perfectly matched restorative dentistry can be destroyed by a patient who bleaches the natural teeth, not knowing that the restorations no longer will match the natural teeth.
The single-tooth restoration problem is clear to all restorative dentists. What are solutions to the challenge? In this article, I will provide a critical evaluation of the various methods of restoring a single anterior tooth with natural teeth adjacent to the tooth to be restored.
In making an assessment of the restorative possibilities, let us take the following clinical situation as an example: the tooth to be restored is one vital maxillary central incisor, the most difficult tooth colour–matching challenge in any mouth. The prepared tooth is not discoloured, and the tooth preparation is a normal dentin colour.
I will present several restorative options for this tooth. The conclusions about each option are my own observations and opinions after restoring thousands of teeth, as well as my observations of the experiences of the many dentists with whom I work in clinical dentistry, study clubs and clinical research.
Some practitioners forget that today’s directly placed resin-based composites make excellent large restorations or veneers for certain anterior tooth restoration needs (2-3). If a single tooth or a few anterior teeth need a colour change or correction of minor malpositioning, these procedures can be difficult with the popular indirectly made ceramic veneers.
The colour of an indirect veneer is a combination of the colours of the veneer, the cement and the underlying tooth structure. Conversely, correction of these aesthetic challenges using the myriad of colours and translucencies available with the current generation of resin-based composites is relatively easy. It can be accomplished in the office without laboratory involvement and is under the total control of the clinician.
Colour match can be achieved and the contour of natural teeth can be reproduced nearly exactly. Fees for directly placed veneers are less than those for indirect veneers, and therefore are more affordable for patients. In my opinion, resin-based composite should be used more often than crowns for correction of selected single anterior tooth restoration cases requiring colour and positioning changes.
Restoration of one anterior tooth with an indirect ceramic veneer is difficult at best. The blending of the ceramic veneer colour with the colour of the cement and the underlying tooth structure colour requires significant artistic ability and patience on the part of both the dentist and the technician.
Regardless of the restoration being placed, exposure of the mouth and teeth to the drying influence of the ambient room air causes the colour of the tooth being restored to lighten in colour. This lightening effect makes colour matching extremely difficult.
Although ceramic veneers are excellent restorations for multiple anterior teeth, the difficulty of matching the colour of one veneered tooth to the adjacent teeth makes this restoration a secondary choice. However, unlike indirect polymer veneers, ceramic veneers can be modified if colour change is needed before cementation. (4)
When veneering many anterior teeth, this technique is acceptable. However, when restoring one anterior tooth, an indirect polymer veneer is the last choice. If the colour of an indirect polymer veneer is wrong, it cannot be changed unless the entire restoration is remade.
Unfortunately, achieving an exact colour match between PFM restorations and adjacent natural teeth can be extremely difficult (4). Most practitioners will admit that the single PFM anterior crowns they have placed seldom match adjacent teeth in all types of lighting.
However, the higher the nobility of the coping metal, the greater the potential for matching the natural teeth. High-noble metal, with its goldlike colour, covered with fired ceramic and including a ceramic facial margin, provides one of the best possibilities to match adjacent natural teeth. Materials such as Captek (Scottlander, 01462 480848), with yellow-coloured metal directly underneath the ceramic, are very capable of matching adjacent teeth.
However, use of base metal or some compositions of noble-metal copings, accompanied by minimal laboratory technician expertise, usually produces a PFM crown easily recognizable as a crown when viewed at a conversational distance.
All-ceramic crowns with milled aluminous or zirconia copings. Several relatively new commercially available crown types fit into this category. Among them are Cercon-Zirconia (Dentsply, 01932 853422), Cerec inLab (Sirona Dental Systems 0845 0715040), Lava (3M ESPE, 01509 613361), Procera (Nobel Biocare 01895 452900) and several others (5).
These crowns, properly fabricated, offer a good possibility of matching adjacent teeth and provide strength when restoring a single tooth. However, to do so requires a deep tooth preparation of at least 1 to 1.5 millimetres on the tooth’s facial surface, matching the colour of the core material to the remaining tooth structure, and the services of a competent laboratory technician.
The presence of the relatively opaque internal ceramic core still may provide an impediment to matching some tooth colours, but the aesthetic potential of these new crown types is impressive.
Relatively unknown to many dentists, slip castings are becoming more popular. Vita Inceram (Ivoclar Vivadent, 0116 265 4055) and Wol-Ceram (Wolz Dental Technik, Germany) have the advantage of having a relatively thin fired internal coping fitted tightly to the die and, therefore, to the remaining tooth structure. The initial coping is infiltrated with glass and covered with fired ceramic.
Many practitioners have found that these crowns are reliable replacements for PFM crowns. The relatively opaque internal core blocks the colour of discoloured tooth preparations, such as tetracycline-stained teeth. However, our challenge in this article is to provide a restoration for a non-stained tooth, in which case this type of crown, properly made, still has a good chance of providing aesthetic acceptability.
Most restorative dentists have placed pressed ceramic crowns, and the aesthetic success has been excellent (6). These crowns, typified by the popular IPS Empress (Ivoclar Vivadent, 0116 265 4055), Cerinate (Den-Mat, [email protected]), Finesse (Dentsply, 01932 853422), 3G (Pentron, Wallingford, Conn, USA) and others, provide better aesthetic acceptability for single anterior crowns than do almost all other restorative options.
If a crown is selected for a single anterior tooth instead of a more conservative direct resin restoration, pressed ceramic crowns are the choice of most restorative dentists. However, they are not as strong as the other crowns mentioned in this article, and patients should be cautioned to use care in chewing hard substances to prevent premature failure.
Many tooth-coloured crown types are available today, and all of them can provide an acceptable result when restoring all of the anterior teeth on either arch. When only one anterior tooth is involved, the decision regarding which type of restoration to use becomes more perplexing. If enough tooth structure is remaining, restoration of the single tooth with one of the multicoloured directly placed resin-based composites is a wise choice.
Assuming that the tooth to be restored requires a crown, has natural colour and does not need superior strength, pressed ceramic crowns—fabricated by competent technicians—appear to be the type of crown having the greatest possibility of providing near-perfect colour match for the single-tooth restoration. However, there are some technicians who can produce near- perfect colour match with almost any of the crown types discussed in this article.
1. Christensen, GJ (2002). The tooth-whitening revolution. JADA 133:1277-9
2. Christensen, GJ (2003). Direct restorative materials: what goes where? JADA 134:1395-7
3. Christensen, GJ (2002). Has tooth structure been replaced? JADA 133:103
4. Christensen, GJ (1999). Porcelain-fused-to-metal vs. non-metal crowns. JADA 130:409-11p
5. Christensen, GJ (2001). Computerized restorative dentistry: state of the art. JADA 132:1301-3
6. Christensen, GJ (1997). Why all-ceramic crowns? JADA 128:1453-5