Aspecte practice în refacerea morfologiei și a funcționalității aparatului dento-maxilar prin restaurări protetice de acoperire (Partea a II-a)

Introduction

Prosthetics and, especially, dental esthetics have gained momentum in recent decades, alongside the growing interest in achieving a proper dental appearance and, consequently, a more pleasant facial esthetic. Advances in dental technology have inevitably led to greater attention being paid to the esthetic component, not just the functional one, popularizing the concept of the “Hollywood smile”, characterized by perfectly aligned teeth, whiter teeth, contoured lips, and sophisticated makeup^(1-4).

General data

The development of contemporary technologies directly leads to increased capabilities and efficiency for dental technicians and, indirectly, to the generation of well-being and societal progress. In most studies conducted so far, the application of esthetic principles in dental prosthetics is associated with creating a positive impact on individuals, allowing for the individual and contextual characterization of each smile^(1-5).

The technical objectives focus on designing a prosthetic restoration compatible with the patient’s existing anatomical structures, meeting a series of criteria such as stability, good adaptation to the prosthetic field, functional performance, and superior esthetics. The ultimate goal is to obtain a complete, high-quality product, finished and ready for use in a real environment.

Next, some highly interesting practical aspects will be presented regarding the manufacturing of fully esthetic prosthetic restorations, veneered with ceramic materials for aesthetic purposes.

Case presentations

Clinical case 1

A 43-year-old patient presented to the dental office for the prosthetic rehabilitation of an edentulous area caused by the absence of teeth 1.5 and 1.6. In this case, teeth 1.3, 1.4 and 1.7 were used as abutments, with 1.5 and 1.6 as pontic. The metal framework was obtained using the lost wax technique from a Co-Cr-based dental alloy, utilizing an automatic casting machine.

In the first stage, the dentist performed both the appropriate endodontic treatments and the necessary tooth preparations on the abutment teeth of the future dental bridge. This resulted in the required preparations for impression-taking. The functional impression was taken using a standard impression tray and condensation silicone materials in dual consistency (putty and light body), while the mandibular opposing impression was also taken with a standard impression tray using condensation silicone material with a putty consistency (Figure 1).

Using the two impressions, working models were created. The maxillary functional model was cast from type IV dental stone and subsequently sectioned to obtain removable dies, while the mandibular opposing arch model was cast from type III dental stone (Figure 2).

These models were then mounted in an articulator based on the occlusal relationship recorded by the dentist in the dental office. In the next stage, the manufacturing of the metal framework was initiated.

First, a wax pattern was created and prepared for the investment process.

The wax pattern of the future metal framework was then invested to obtain the mold (Figure 3). The mold was heated to a temperature above 960°C, followed by the casting of the Co-Cr-based dental alloy to produce the metal framework using an automatic casting machine.

After the casting was completed and the mold was slowly cooled, the next steps involved devesting, processing and adapting the metal framework to the functional model (Figure 4). Finally, the metal framework was sandblasted to prepare it for the subsequent veneering with ceramic materials for esthetic purposes.

The metal framework was then sent to the dental office, where the dentist performed a trial fitting in the patient’s oral cavity.

The next steps in creating this prosthetic restoration involved applying ceramic materials to the metal framework to achieve the esthetic appearance. First, a wash-opaque layer was applied, followed by successive layers of opaque, dentin, and enamel. These layers were applied by brushing and were fired sequentially in a specialized ceramic furnace. Each firing process was performed according to the manufacturer’s recommended programs for each ceramic layer (Figure 5).

The opaque layers serve to block the metal from showing through the ceramic material, while the dentin and enamel layers replicate the natural appearance of the tooth. The final appearance of the full-coverage prosthetic restoration was achieved by applying and subsequently firing the glaze layer. Additionally, in the mucosal area of the pontic, a pink ceramic layer was applied to mimic the color of the gingival tissues (Figure 6). The completed prosthetic restoration was then sent to the dental office for try-in.

Clinical case 2

A 48-year-old patient presented to the dental office for the esthetic restoration of one of the upper central incisors, specifically tooth 1.1, expressing dissatisfaction with its appearance. The treatment plan proposed by the dentist involved creating a full-coverage ceramic zirconia crown. For the manufacturing of this type of crown, the Exocad digital software was used. After pulp removal and tooth preparation of 1.1, an intraoral scan of the prosthetic field was performed. 

The obtained data were sent in digital format (.stl files) to the dental laboratory. These were used to obtain virtual models but also to position them in the virtual articulator based on the occlusal recording (Figure 7).

Using these models, the design of the zirconia coping was also created. The final shape of the prosthetic restoration was generated by the virtual modeling program and, subsequently, through reduction, taking into account aspects related to strength and esthetics, the shape of the zirconia coping was obtained.

The information regarding the virtual coping was transmitted to the milling machine, and the working models were printed in the same time (Figure 8). After the coping was sintered and the models were finished, the fitting of the coping to the model was checked and the procedures for applying the ceramic masses were started to obtain the esthetic appearance.

A primer was applied on the surface of the zirconia coping to improve the bond between the zirconia and the ceramic materials (Figure 9). After the primer was fired, the ceramic materials corresponding to the different hard dental structures – namely, dentin and enamel – were added. Their firing was followed by shape corrections to achieve symmetry with the homologous tooth (Figure 10).

The last step in this meticulous process was the application of the glaze layer to achieve a natural appearance of the prosthetic restoration (Figure 11).

Clinical case 3

The last case is of a 36-year-old patient who presented to the dental office for morphological and functional restoration of teeth 1.5, 2.1 and 4.6, using full-coverage metal ceramic prosthetic restorations. In all three cases, the metal copings were fabricated using the conventional lost wax technique with a Cr-Co dental alloy, utilizing an automatic casting machine. The ceramic material used for veneering the metal structures was IPS Style Ceram from Ivoclar Vivadent.

The impression of the prosthetic field was made using a silicone condensation material in a dual consistency: putty and light body (Figure 12). The sectional working models were made of type IV dental stone, their mounting in the articulator being easily achieved due to the large number of stable dental contacts (Figure 13).

A wax pattern of uniform thickness was made for each prepared tooth. These were invested with a specific investing material for Cr-Co alloys and followed the specific lost wax technique process to obtain the metal copings (Figure 14). Following the devesting process, the copings were processed and properly adapted to the working model. They were then sent to the dental office for adjustment verification (Figure 15).

The process of applying the ceramic masses began by sandblasting the copings and oxidizing them in the ceramic furnace. Two layers of opaque material were applied to the oxidized surface to favor the achievement of esthetic results but also to facilitate the bond between the alloy and the ceramic masses. The layers of ceramic corresponding to dentin and enamel were applied by brushing (Figure 16).

After making the necessary shape corrections, the glaze layer was applied for a more natural appearance of the metal-ceramic restorations (Figure 17).

Discussion

Restoring the morphology and functionality of the dental arches using ceramic materials presents both a challenge and a reward for the medical team, consisting of the dentist and the dental technician^(4,5). The combined use of available materials and dental laboratory technologies aims to achieve a natural appearance of the prosthetic restorations, while providing strength comparable to the hard tissues they replace^(6,7).

Metal-ceramic restorations – whether crowns or bridges – offer an accessible technology that combines the lost-wax technique with the layered application of ceramic materials⁽⁸⁾. The final appearance of these restorations allows for seamless integration into the esthetics of the dental arches without compromising the masticatory function. The strength provided by dental alloys enables the absorption and distribution of masticatory forces in a physiological manner^(9,10).

In the anterior region, where esthetics plays a crucial role, the use of zirconium dioxide eliminates the esthetic drawbacks associated with dental alloys^(11,12). Although zirconia formulations have been significantly improved in terms of esthetics, the manual application of ceramic layers by the dental technician adds a personalized touch to each clinical case^(13,14).

Conclusions

• Following the review of this material, several highly interesting aspects can be concluded, as follows:
• Fixed dental prosthetics have evolved significantly in recent years, to the point where patients now seek more esthetic prosthetic restorations, not just functional ones. 
• With the help of the CAD/CAM system, prosthetic restorations are produced more rapidly compared to traditional methods, while also improving quality and increasing the success rate of treatments.
• The use of single- and/or multi-unit fully esthetic prosthetic restorations, whether metal-ceramic or zirconia-based, is increasingly popular among both practitioners and patients. 
• The esthetic and biological properties of ceramic materials make them highly suitable for widespread use in dental practice.
• Ceramic materials are contraindicated for patients with bruxism. In such cases, semi-esthetic prosthetic restorations with occlusal surfaces made from metal alloys are recommended.

Acknowledgement. Viorel Ștefan Perieanu and Camelia Ionescu are corresponding authors (Viorel Ștefan Perieanu: viorel.perieanu@umfcd.ro; Camelia Ionescu: camelia.ionescu@umfcd.ro).

Autor corespondent: Viorel Ștefan Perieanu E-mail: viorel.perieanu@umfcd.ro; Camelia Ionescu E-mail: camelia.ionescu@umfcd.ro

CONFLICT OF INTEREST: none declared.

FINANCIAL SUPPORT: none declared.

This work is permanently accessible online free of charge and published under the CC-BY.