Extremely minimally invasive mock-up-guided veneer preparations in the aesthetic area

To simulate the final result as already seen with the analogue wax-up as accurately as possible, the waxed-up model was scanned.² For moulding the mock-up from the wax-up (Figs. 4a & b), a silicone index was created on the wax-up (Fig. 4c). Composite (Structur 3, VOCO) was injected into this silicone key to create the mock-up. The diagnostic mock-up was temporarily cemented (Provicol QM Aesthetic, VOCO) in the patient’s mouth for a few days until the operative session.

At the next appointment, the mock-up took on the role of a working guide for controlled preparation. Controlled thickness reduction grooves were made in the mock-up for orientation, as they were used to determine the depth of the preparation and thus the desired material thickness of the veneers (Fig. 5). For providing clear orientation, the guiding grooves were marked with a pencil (Fig. 6). Where the residual mock-up remained, the tooth was intact (extremely minimally invasive preparation). Only in the areas where the mock-up had been completely ground down was there an effective preparation of the tooth structure (Fig. 7). Compared with conventional veneer preparation, for which the dentist grinds the tooth structure directly from the beginning, this procedure allowed for much more conservative tooth reduction. It was decided not to intervene in the lateral and protrusive movement.

The first step was to perform window or Walls, Steele and Wassell Type A preparations,³ meaning that the preparations were only carried out on the vestibular aspect, without finishing margins and without any reduction of the incisal edge. However, an incisal butt joint margin was carried out to cover the incisal edge without any vertical reduction in the palatal area. It has been shown that such a covering of the incisal edge achieves a higher survival rate than preparations with a palatal chamfer.^4,5

Once the final preparations had been obtained (Fig. 8a), they were scanned, initiating the digital phase of the workflow that ended with the fabrication of the veneers using a CAD/CAM milling unit (M2 Teleskoper, Zirkonzahn). The veneers were made of a highly filled nano-ceramichybrid material (Grandio blocs, Shade A2, low translucency; VOCO; Fig. 8b).

Once they had been cleaned, the prepared teeth were rinsed thoroughly and dried with a gentle jet of compressed air. The veneers were inserted carefully by exerting slight pressure. The chromatic effect met the expectations of both the patient and the clinician (Figs. 9 & 10). Before being finished and polished, the veneers created using CAD/CAM technology underwent chromatic characterisation so that the pigmentation (FinalTouch, VOCO) was fixed under this thin layer of composite.

The dental dam used to obtain isolation was secured using special cervical clamps for incisors (clamp #212, Hu-Friedy; Figs. 11 & 12). This was followed by proper adhesive priming of the surfaces to be luted to one another (inner surfaces of the restorations and surfaces of the prepared teeth). As a protective measure in view of the subsequent clinical steps, the adjacent surfaces that were not to be covered were isolated using PTFE tape.

The dental dam used to obtain isolation was secured using special cervical clamps for incisors (clamp #212, Hu-Friedy; Figs. 11 & 12). This was followed by proper adhesive priming of the surfaces to be luted to one another (inner surfaces of the restorations and surfaces of the prepared teeth). As a protective measure in view of the subsequent clinical steps, the adjacent surfaces that were not to be covered were isolated using PTFE tape.

The tooth surfaces were then conditioned, first by pretreatment with glycine powder, which through micro-abrasion increases the retentive potential of the bonding (Fig. 13). Etching was then performed using 35% orthophosphoric acid (Vococid, VOCO) for 20 seconds (Fig. 14). The acid was then removed by suction and rinsing for 20 seconds, and the surface was dried with compressed air to obtain a matt chalky white appearance. The universal adhesive (Futurabond U, VOCO) was applied and gently rubbed for 20 seconds using a brush (Single Tim, VOCO; Fig. 15). The solvent was then evaporated thoroughly with compressed air for at least 5 seconds to obtain a thin, immobile and shiny layer of adhesive, which was polymerised from various directions using a high-power LED curing light (Celalux 3, VOCO) for 10 seconds each time, in accordance with the manufacturer’s instructions. This created a matt–shiny preparation surface that was evenly coated with adhesive.

For the pretreatment of the inner surfaces of the veneers, abrasive sandblasting with 25–50μm particles of aluminium oxide was performed at 1.5–2 bar pressure, and a silane adhesive coupling agent (Ceramic Bond, VOCO) was applied and left to act for 60 seconds and then dried for 5 seconds. The veneers were finally cemented using a dual polymerising universal luting composite (Bifix QM, VOCO; Fig. 16). The veneers were inserted (Fig. 17) and fixed by means of polymerisation at marginal level using a Celalux 3 mesially and distally from the vestibular side, followed by mesial and distal polymerising from the palatal side. In order to avoid an oxygen inhibition layer and thus avoid poor polymerisation, a glycerine gel was applied to all margins prior to polymerisation (Liquid Strip, Ivoclar). By means of this oxygen inhibition gel, a significant improvement of the adhesive margins could be achieved. The glycerine was rinsed off, and at the end of the setting time of approximately 3 minutes, it was then possible to proceed with elimination of the excess material using a metal instrument and dental floss, interproximally. The interproximal contact zones were finished using abrasive strips.

After checking the occlusion and making corrections in accordance with conventional functional concepts, normal finishing and polishing was performed using diamond polishers (Dimanto, VOCO). The patient was completely satisfied with the significant improvement in his smile (Figs. 18–22).

Discussion

Based on an analysis of the scientific literature concerning the closure of anterior diastemas, a semi-indirect approach using nano-hybrid composite veneers was chosen.⁶ The clinical indication of diastema closure classifies the veneers used for this case as Type IIB according to the Magne–Belser classification.¹ Since feldspathic ceramic veneers were outside the patient’s budget, such an indirect technique was ruled out. The direct layering technique was ruled out because the patient had high aesthetic expectations. It was decided to use veneers on both the central and the lateral incisors, as this would make it possible to obtain more harmonious relative dimensional proportions.

The wax-up must first be transferred to the mouth in the form of a provisional prototype with a dual clinical function as a diagnostic mock up for aesthetic and functional aspects and as a working mock-up for calibrated preparation, that is, a guide for controlled, extremely minimally invasive tooth reduction.⁷ The diagnostic mock-up is the composite provisional restoration for the usual in-mouth fit test, and it allows immediate and effective communication with the patient and makes it possible to test in-mouth tolerability for a few days prior to the operative session. These prototypes fitted on the individual teeth have a wow effect on patients, as they provide an in-mouth preview of the aesthetic results to be achieved. In the initial stages of tooth preparation, the working mock-up for controlled preparation is calibrated based on the physical dimensions of the mock-up. With controlled preparation, the provisional restoration is gradually destroyed, resulting in a far more minimally invasive preparation than that performed directly on the tooth. Using special calibrated burs, this preparation ensures the most enamel sparing thicknesses possible and the highest aesthetic and functional characteristics. The working mock-up ensures greater thickness control of the veneers before proceeding with the precision impression for the digital design of the final veneers. The adhesive protocols described were compared with authoritative sources (Magne)⁸ and with recent literature (Blatz et al.).⁹

Conclusion

Full patient satisfaction was achieved. The success of the treatment was due to the combination of two factors: minimal tooth preparation and complete closure of the diastemas without adverse repercussions on shape, proportions or chromatic integration.

This case has demonstrated that less is better. Indeed, mock-up-guided veneer preparations reduce the biological sacrifice of the tooth to a minimum while guaranteeing function and maximising the long-term aesthetics. This approach also demonstrates how conventional and digital workflows can be combined effectively.