Aspecte tehnologice în confecționarea punților dentare totale cu sprijin implantar (Partea a II-a)

Introduction

Total edentulism is a common health problem that significantly affects the patients’ quality of life (food intake, masticatory function, phonation, esthetic appearance and psychological impairment). Specifically, conventional complete dentures can ensure the restoration of the functions of the dental arches, but they can also present a series of shortcomings, such as insufficient retention, a feeling of nonfunctionality etc.^(1-4)

The introduction of dental implants in dental practice has offered the possibility of rehabilitating dental arches with much more resistant prosthetic restorations, fixed at the implant level. Implant-supported prosthetic restorations have brought about a series of expected improvements, mainly due to the materials from which they are made: they are much more resistant and have a longer lifespan, the level of esthetic reproduction is much higher, the stability is much better, and the patient has increased psychological comfort^(1-4).

General data

This paper will focus on the manufacturing of implant-supported complete dental bridges. Regarding the use of these implant-supported complete bridges, a number of their advantages should be mentioned, as follows: masticatory, phonetic and physiognomic functions are restored; occlusal relationships are restored; relationships between the levels of the face are restored; the patient can choose the shape and color of the new teeth, etc. However, in the case of making such prosthetic restorations, there are also a number of disadvantages, such as: very high costs; long healing time after dental implant insertion; increased risk of failure; particularly troublesome post-surgical inflammation and pain, etc. As in the first part of this material, practical aspects regarding the technology of making implant-supported complete bridges will be presented.

Cases presentation

Clinical case 1

A 56-year-old patient presented to the dental office for restoration of the mandibular arch. At the time of presentation, there was only one molar in mandibular left quadrant (tooth 3.8) that was of no prosthetic importance. Following a rigorous clinical examination, the dentist recommended the manufacturing of an implant-supported metal-ceramic prosthetic restoration. With the patient’s written consent, six dental implants were inserted into the mandibular arch. After the period of bone integration of the implants, the prosthetic stage of restoring the mandibular arch began. The mandibular arch was imprinted using an alginic material.

On the preliminary model obtained, an individual impression open tray was made of light-curing resin for precise impression of the arch (Figure 1). After the impression, the analog abutments were attached to the transfer abutments, and a material simulating the gum around the dental implants was inserted inside the impression (Figure 2). The functional model was made of type IV dental stone and, together with the mandibular model, they were mounted in an articulator using the occlusal record (Figures 3 and 4).

The prosthetic restoration was created using the digital workflows available in the dental laboratory. The functional model was scanned using a laboratory scanner, thus obtaining a virtual model on which the dental technician designed the virtual pattern of the metal component of the prosthetic restoration. The virtual pattern was sent to a specialized milling center to obtain the metal component from a Co-Cr dental alloy. The milled piece was checked at the level of the functional model, but also in occlusion in relation to the antagonist teeth (Figures 5 and 6). Subsequently, the metal component was sent to the dental office for try in.

After checking the metallic framework, the ceramic mass application stage was started. A first firing of the metallic framework was performed to obtain the oxide layer necessary for the chemical adhesion of the ceramic (Figure 7). The first layer applied was the opaque, to mask the metal component, followed by brushing of the ceramic masses corresponding to the dentin and enamel (Figure 8). The application of the ceramic masses also aimed to restore the gingival area in order to create a more natural appearance of the restoration.

The overall appearance of the restoration was checked both on the model and in the oral cavity in order to make any necessary corrections before applying the glaze layer. Once the glaze applied and thermally conditioned, the restoration was sent to the office for screw retain to the mandibular dental implants (Figure 9).

Clinical case 2

The last case presented describes the technical protocol for manufacturing an implant supported complete maxillary metal-ceramic bridge. A 49-year-old patient presented to the dental office for implant-prosthetic rehabilitation of a complete maxillary edentulous area. The dentist, in agreement with the patient, decided to insert six dental implants in the maxillary arch and to manufacture a screw-retained complete implant-supported bridge.

The functional impression of the maxillary arch was made using a standard closed impression tray equipped with retentions, using dual consistency silicone addition material (putty and light body). The impression of the antagonist arch was also made in a standard impression tray, using putty-consistency silicone condensation material (Figure 10). The impressions were washed for approximately 15 seconds under running tap water, after which they were decontaminated by immersion in potentially disinfectant substances based on quaternary ammonium salts, fully following the manufacturer’s instructions.

After decontamination of the impressions, they were cast following a protocol similar to that described in the previous case. The functional model contains the implant analogs fixed in type IV dental stone and in Gingifast, a material that reproduces the gums of the maxillary alveolar process (Figure 11). Since the patient was a totally edentulous maxillary patient, an occlusal rim was created to determine the intermaxillary relationships as accurately as possible (Figure 12). In addition to the occlusal relationship between the maxilla and mandible, the following data were also transmitted from the office to the laboratory at the level of the occlusion template: the position and shape of the vestibular curvature of the upper arch, the midline of the arch, the canine lines and the smile line. In the dental office, the dentist determined the occlusal relationship. Using the occlusal record, the dental technician mounted maxillary and mandibular models in an articulator.

The two models and the occlusal registration were scanned with a dental scanner to continue the process in a virtual environment (Figure 13). For high accuracy, scan abutments specific to the implant system used were scanned (Figure 14).

Using this information, the dental technician proceeded to the virtual modeling stage for the prosthetic restoration. Using the digital modeling program (Exocad), the dental technician set the type of work, framed the shape and size of the teeth in relation to the maxillary arch, and established the insertion axis of the retention screws for the prosthetic work (Figures 15 and 16).

Based on his experience, the dental technician adjusted the shape of the dental crowns in relation to the patient’s age and gender. He also modeled the connectors that join the teeth using a balance between the vestibular esthetic appearance and the strength of the prosthetic restoration (Figure 18).

At the end of the design process, the program generates a reduction based on type of prosthetic restoration set first. The reduction gives enough space for the esthetic material and preserves the resistance generated by the metallic framework (Figure 19).

The virtual pattern of the metallic framework was sent in digital format to a specialized milling center. After milling, the framework was sent back to the dental laboratory for fitting check on the functional model (Figure 20). Small adjustments were made before sending the framework to dental office for try in.

The dentist made a new occlusal recording with the framework attached to the dental implants. The dental technician remounted the models based on the new occlusal record for a proper result.

Subsequently, the dental technician performed the veneering with ceramic masses for physiognomic purposes of the metal infrastructure of the future implant-supported total bridge (Figure 21).

Discussion

The prosthetic restoration of completely edentulous dental arches has been and remains a real challenge for the medical team formed by the dentist and the dental technician^(5,6). The treatment possibilities have increased in diversity with the introduction of dental implants but also of digital technologies in technological flows⁽⁷⁾. Classic solutions based on removable dentures are becoming a secondary option among patients, especially because of the shortcomings they present⁽⁸⁾. Fixed solutions offered by the use of dental implants offer superior comfort and easier social reintegration⁽⁹⁾.

The cases presented in this article have shown, from a prosthetic point of view, how an edentulous arch can be transformed into a dentate arch using different types of prosthetic restorations. If we add to the advantage offered by dental implants and the new technologies in dental technique, the success and predictability of dental treatment become natural elements^(10,11).

Whether a provisional PMMA restoration was chosen as an intermediate step until the definitive treatment was carried out, or a definitive metal-ceramic restoration was chosen, the patient’s reintegration into social life was achieved much faster thanks to the digital technologies used^(12,13). Working times are considerably reduced for the dental technician without jeopardizing the quality of the prosthetic work. The image library contained in the digital editing program allows the generation of a design that is as appropriate as possible for each clinical case, improved by the experience of the dental technician. The only stage in which the technician plays the main role and has not yet been replaced remains the application of ceramic masses on the computer-made metal componen^t(14,15).

Conclusions

To restore the masticatory, phonetic and physiognomic functions, fixed prosthetics on dental implants is the best solution in the case of total edentulous teeth. Although it is not the cheapest therapeutic alternative, more affordable prosthetic options can be found. Due to the fixed nature, the patient can smile much more calmly, can resume his eating habits under normal conditions, but without exaggerating, because no material used in the manufacture of classic and implant-supported prosthetic restorations, whether they are fixed or removable, has the same resistance as that of natural teeth.

In terms of the means of manufacturing implant-supported prosthetic restorations, digital technology is preferable, although it is much more expensive than the classic one, because it shortens the working time and leaves less room for error. However, technical stages such as adaptation, finishing and application of ceramic masses cannot be done digitally in any way, as the direct involvement of the dental technician is required to carry out these operations. Therefore, we cannot yet speak of a fully automated process, but rather, overall, we are talking about a mixed automated-manual process.

Acknowledgement. Viorel Ștefan Perieanu and Mădă­lina Adriana Malița are corresponding authors (Viorel Ștefan Perianu: viorel.perieanu@umfcd.ro; Mădălina Adriana Malița: madalina.malita@umfcd.ro).

Autor corespondent: Viorel Ștefan Perieanu E-mail: viorel.perieanu@umfcd.ro; Mădălina Adriana Malița E-mail: madalina.malita@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.