Among the most common problems in modern dentistry is that of restoring the patient’s dental aesthetics. New technologies are available to practitioners to support this. For anterior teeth, for which aesthetics is paramount, dentists prefer the least mutilating treatments possible, such as layered veneers (cutback). In cosmetic dentistry, practitioners are often faced with cases requiring a multidisciplinary treatment plan or the use of different types of restorative materials. For cases of prosthetic restoration combining veneers, crowns and bridges, a difference in shade may be noticeable in the nal result, owing to the difference in restorative material, product, adhesion technique, thickness of the restoration and colour of the abutment, whether it is a vital or devitalised natural tooth or even an implant abutment. If the treatment plan requires veneers, crowns and bridges, it is prudent to choose zirconia as the only restorative material in light of the limited mechanical properties of lithium disilicate and feldspathic porcelain, contra-indicating their use for bridges.
There may be some reluctance among practitioners to use the zirconia veneer technique.3 This is attributable to various factors, one being the absence of a vitreous phase, making impossible to create an optimal adhesion surface with hydrofluoric acid at the level of the intaglio surface of the zirconia veneers. Another factor is the lack of translucency of the first-generation zirconia materials.
Modern zirconia materials, however, are particularly well suited for cases requiring a combination of veneers, crowns and bridges of the same optical appearance. This is due to their greater translucency and excellent mechanical properties. The following article describes and discusses a clinical case treated with veneers and a crown made from KATANA Zirconia UTML (Kuraray Noritake Dental). The veneers were cemented with PANAVIA Veneer LC (Kuraray Noritake Dental). The patient presented with an aesthetic problem at the level of an anterior implant-supported crown.
A 29-year-old female patient with no signicant pathological history presented to my dental ofce in January 2023 owing to an aesthetic problem negatively affecting her smile. The extra-oral examination was without abnormalities, and the intra-oral examination showed good oral hygiene, healthy soft tissue, thin free gingiva and a protruding zirconia crown on an implant in the region of the maxillary right central incisor (Figs. 1 & 2).
During the first consultation, it was established that the implant had been placed in 2020. The patient wished to have the crown aligned and the aesthetics of her smile improved before her wedding, taking place ten days after the first consultation. The patient’s former dentist had left Tunisia, and the patient had no documentation or information on the dental implant.
After obtaining the informed consent of the patient for replacement of the crown and for the placement of veneers for aesthetic reasons, the treatment was initiated. According to the treatment plan, seven maxillary anterior teeth (from rst premolar to rst premolar) would receive an incisal overlap preparation (depth of 0.1–0.3mm) for the placement of veneers made of KATANA Zirconia UTML. For the implant, it was planned to replace the existing crown with a crown made of KATANA Zirconia UTML without replacing the abutment. This was due to the lack of information about the implant type and the lack of time.
After taking the preoperative photographs (Fig. 3), choosing the colour of the veneers and anaesthetising the maxillary anterior region, the incisal overlap preparation was carried out on the seven maxillary teeth and the zirconia crown was removed from the implant. A cylindrical diamond bur was used to separate the crown from the abutment. Subsequently, a bite registration and impressions were taken using the wash technique. In addition, a temporary crown was produced and placed on the abutment.
In the dental laboratory, virtual models were created based on the conventional impressions (Fig. 4). The zirconia restorations were then designed in full contour, cut back for the veneering porcelain and nished by layering with CERABIEN ZR porcelain (Kuraray Noritake Dental).
At try-in during the second session, we checked the insertion, the gingival margins and the contact points between the veneers and the crown on the implant. Given the superior mechanical properties of the zirconia used, the shape and thickness of the veneers were modied chairside to obtain a harmonious anterior curve and a better aesthetic rendering. After determining the colour of the resin cement, the temporary crown was put back in place.
After glazing and preparation of the bonding surfaces in the laboratory, the veneers were cemented according to the PANAVIA Veneer LC protocol. We ended the session by removing excess cement. An occlusion check and postoperative photographs were taken after three days.
The zirconia used for the veneers and the crown has an yttrium oxide proportion of 5 mol%, leading to about 70% cubic zirconia phase, and therefore a higher translucency—51% (according to Kuraray Noritake Dental)— than earlier generations of zirconia. With this translucency, this zirconia allows us to achieve restorations with remarkable optical properties (Fig. 5).
The patient chose Shade B1 and requested a transparent incisal edge (Fig. 6). For this reason, a cutback design of the zirconia veneer (Fig. 7) with porcelain layering was the technique of choice. The zirconia veneer technique was chosen to avoid a colour difference between the crown on the implant and the veneers. The pleasant aesthetic appearance and harmonious smile were conrmed by the postoperative photograph (Fig. 8).
According to the manufacturer, the exural strength of KATANA Zirconia UTML is 557MPa, which is higher than that of lithium disilicate and feldspathic porcelains. As zirconia veneers will be more resistant to shear forces, it is possible to eliminate contact points that interfere during try-in or even safely modify the shape of the restorations in situ. This is done with specic burs adapted to zirconia during different stages of the fitting, according to the wishes of the patient. In the present case, we were able to adjust the crown until we had a perfect anterior line. It was thus possible to optimise the inclination of the crown without replacing the dental implant and in just one week.
Given the signicant shear resistance, the laboratory technician made the veneers with an average thickness of 0.3mm. Such a thin veneer requires less preparation of the dental tissue, limiting preparation to the enamel instead of extending into the dentine, where the adhesion value is lower owing to dentine’s lower mineral composition.
The expected difculty in bonding zirconia veneers is explained by the absence of a vitreous phase, given the poor adhesion of the crystalline phase to the bonding cement. However, the desired surface modication can be achieved with a different procedure: a tribo-chemical silica coating. This was used in the present case to improve the adhesion of the zirconia veneers to the resin cement system. Indeed, it was found in an in vitro evaluation that the tribo-chemical preparation technique and the application of the MDP monomer provide an optimised adhesive interface. In that study, dual-beam focused ion beam technology and scanning electron microscopy were used to compare the resin– zirconia bonding interface with tribo-chemical preparation and MDP and the bonding interface between resin and zirconia without this preparation.
The tribo-chemical process involves aero-abrasion of the zirconia surface with particles coated with silica combined with a silane primer containing MDP. The phosphate ester groups of this silane bind to the surface oxides of the zirconia, and the methacrylate group makes covalent bonds with the resin matrix of the PANAVIA Veneer LC cement. In the present clinical case, the KATANA Zirconia UTML veneers were abraded with silicon dioxide. As a primer, we chose CLEARFIL CERAMIC PRIMER PLUS (Kuraray Noritake Dental), because it contains the original MDP monomer developed by Kuraray Co.
To clean the veneers before applying CLEARFIL CERAMIC PRIMER PLUS, KATANA Cleaner (Kuraray Noritake Dental) was used. The presence of saliva and residue from ttings can alter the interface with the resin cement, posing a risk of bonding failure of zirconia veneers.
One of the most important challenges in this case was hiding the greyish colour of the implant abutment, which was visible through the zirconia crown. To hide the grey of the abutment, a resin opaquer was applied. This, combined with PANAVIA Veneer LC in white, gave us an optimal result (Fig. 9).
KATANA Zirconia UTML veneers have better mechanical properties compared with some other conventional veneer materials, allowing users to combine bridges, crowns and veneers without a noticeable difference in shade. It offers acceptable translucency and aesthetics according to our observation. The technique of bonding the zirconia veneers with PANAVIA Veneer LC combined with a tribo-chemical treatment and the application of MDP to the adhesion surfaces allowed for secure bonding and effective concealment of the discoloration caused by the implant abutment.
Dr Bassem Jaidane, Tunisia