Aspecte tehnologice în confecționarea punților dentare totale cu sprijin implantar (Partea I)

Introduction

Tooth loss and dental conditions have always posed a significant problem with a major impact on individuals, ranging from their appearance to temporomandibular joint (TMJ) disorders caused by edentulism. Therefore, over time, dental practitioners have sought therapeutic solutions to address all types of edentulous patients through the use of highly varied prosthetic methods.

Thus, restoring carious lesions as well as edentulous spans is by no means a simple task: it requires a steady hand, attention to every detail, and advanced knowledge in dentistry in order to achieve a prosthetic restoration, removable and/or fixed, that are as accurate and comfortable as possible for the patient^(1-4).

The introduction of dental implants into dental practice has offered the possibility of rehabilitating dental arches with much more durable prosthetic restorations, fixed at the implant level. Implant-supported prosthetic restorations have brought a series of improvements, primarily due to the materials from which they are made of: they are significantly more durable and long-lasting, offer a superior level of aesthetic reproduction, provide much better stability, and offer the patient increased psychological comfort.

General data

This material will present ways to manufacture complete temporary implant-supported dental bridges. As for complete edentulism, it is a common health issue that significantly affects patients’ quality of life (nutritional intake, masticatory function, speech, esthetic appearance, and psychological well-being). Specifically, conventional full dentures can restore the functions of the dental arches, but they may also present a number of drawbacks, such as insufficient retention and changes in taste sensitivity, among others.

Fixed full-arch implant-supported bridges are multiunit prosthetic restorations anchored on dental implants either by cementation or screw retention. They consist of a fixed component, usually metallic (the framework or support structure), which provides mechanical strength to the prosthetic work, and a cosmetic component (acrylic resins, ceramic materials, zirconia, or a combination of zirconia and ceramics for enhanced esthetics) that covers the prosthetic framework (the metallic support infrastructure). The esthetic appearance is determined by the degree to which the support structure is covered with material that mimics the natural dental structure. Additionally, there are also full-arch implant-supported bridges made entirely of PMMA (polymethyl methacrylate), many of which serve a provisional role.

Next, in this material structured into two parts, several technological aspects regarding the manufacturing of fixed total bridges with implant support will be presented.

Cases presentation

Clinical case 1

A 45-year-old patient presented at the dental office for the restoration of a completely edentulous mandible using a multiunit implant-supported prosthetic restoration made of PMMA (polymethyl methacrylate). Specifically, this refers to a full-arch PMMA bridge screw-retained onto dental implants. With the patient’s written consent, the dentist inserted five dental implants into the edentulous mandibular arch, on which multi-unit abutments were placed.

The functional impression with the transfer abutments was taken by the dentist using a standard impression tray and a polyether material. The impression of the opposing arch was also made using a standard tray and a putty-consistency condensation silicone material. During the same appointment, the dentist also recorded the occlusal relationship using a putty-consistency condensation silicone strip. Before being sent to the dental laboratory, the impression was decontaminated by immersion in antimicrobial chemical solutions for the time period recommended by the manufacturers.

The functional mandibular model was cast using type IV dental stone, while the opposing maxillary model was cast using type III dental stone. Based on the intermaxillary occlusal relationship previously determined and recorded by the dentist in the dental office, the dental technician mounted the functional mandibular model and the opposing maxillary model into an articulator.

The mandibular and maxillary models and the occlusal record were scanned using a dental laboratory scanner. Using the Exocad software, the dental technician created the digital pattern of the future multi-unit implant-supported prosthetic restoration. Once the digital design was completed, the files were exported into MillBox to generate the milling file. For this, a virtual PMMA disc with a thickness of 18 mm and shade A3 was selected. The virtual pattern was positioned at the level of the virtual image of PMMA disc. Subsequently, a sufficient number of support pins were applied to ensure that the prosthetic restoration would not break during computerized milling. Each pin was placed at the point of maximum convexity to avoid interfering with accurate milling. Additionally, the position of the future prosthetic restoration was horizontally adjusted to ensure there are no collisions or excessive material buildups.

After completing the computerized milling process, the PMMA disc is cleaned with an air spray to remove any remaining debris. Then, the implant-supported full-arch bridge is detached from the PMMA disc using a very fine bur and a dental laboratory micromotor.

The implant-supported full-arch bridge made of PMMA was processed, smoothed, and each individual tooth of the prosthetic restoration was customized. Afterwards, each abutment will be tested and adjusted to fit perfectly into the PMMA implant-supported full-arch bridge. Then, all the abutments will be placed on the functional model in their correct positions, and a trial fitting of the PMMA implant-supported full-arch bridge will be performed. The implant-supported prosthetic restoration must fit precisely on the abutments and should not rock when alternate pressure is applied. Additionally, it is important to check that the screw channels are clear, as there is a risk they could be obstructed.

The abutments will be sandblasted and cemented, and the occlusal contacts will be adjusted to eliminate any premature contacts. This step is carried out with the models mounted in the articulator and the full-arch bridge fixed onto the abutments. Once all these checks have been completed, the dental technician applies a la­yer of glaze using a brush, which will then be light-cured according to the manufacturer’s instructions, to provide the prosthetic restoration with increased resistance in the oral environment and an aesthetic appearance as close as possible to natural teeth. Finally, the PMMA implant-supported full-arch bridge will be sent to the dental office to be mounted on the dental implants from mandibular arch.

Clinical case 2

A 58-year-old patient presented at the dental office for the implant-prosthetic rehabilitation of a complet­ely edentulous mandible, using a multi-unit prosthetic restoration also made of PMMA. Specifically, this refers to a PMMA implant-supported full-arch bridge manufactured using digital technology, which, as in the previous case, will be fixed in the patient’s oral cavity by screw retention.

As this case involved a completely edentulous mandible, the dentist, with the patient’s written consent, decided to place four dental implants at this level which were loaded in a very short time after surgical stage. Consequently, the manufacturing of an implant-supported full-arch bridge made of PMMA was initiated.

The impression was taken using an open impression tray. Analogs were attached to transfer abutments and the artificial gum material has been placed.

The excess Gingifast material was removed to ensure easy dislodgement, followed by casting the functional model using type IV dental stone and the maxillary opposing model using type III dental stone. Based on the occlusal relationship determined and recorded by the dentist in the dental office using a strip of putty-consistency silicone material, the two models were then mounted in an articulator.

Next, the functional mandibular model, the opposing maxillary model and the occlusal record were scanned using a dental laboratory scanner. Using the Exocad software, the dental technician created the digital pattern of the future multiunit implant-supported prosthetic restoration. Once the digital design was completed, the files were exported into MillBox to generate the milling file. For this, a virtual PMMA disc with a thickness of 14 mm, and shade A3.5 was selected. The following step involved positioning the design of the future implant-supported full-arch bridge onto this virtual PMMA disc. Subsequently, a sufficient number of support pins were applied to ensure that the prosthetic restoration would not break during computerized milling. Each pin was placed at the point of maximum convexity to avoid interfering with proper milling. Additionally, the position of the future prosthetic restoration can be adjusted in any direction to ensure there are no collisions or excessive material buildups.

After completing the computerized milling process, the PMMA disc is cleaned with an air spray to remove any remaining debris. Then, the implant-supported full-arch bridge is detached from the PMMA disc using a very fine bur and a dental laboratory micromotor.

Discussion

Implant-supported prosthetic restorations are complex procedures involving multiple branches of dentistry. On one hand, the surgical branch is responsible for the selection and optimal placement of dental implants in relation to the patient’s available bone structure⁽⁵⁾. On the other hand, the prosthetic branch is responsible for the visible part of the restoration, both esthetically and functionally. As different as the activities of these two branches may seem, they influence each other and must be carried out in balance from the design phase onward⁽⁶⁾. The placement of a dental implant must take into account the size and positioning of the future prosthetic restoration in order to avoid situations where an implant is located in an interdental space^(7,8). At the same time, the use of inappropriate materials, an unsuitable shape, or even an uneven distribution of forces within the prosthetic restoration can have harmful effects on the peri-implant tissues^(9,10).

The final prosthetic restoration must take into account the specific characteristics of each clinical case, and transitioning from an edentulous arch to a fully and/or partially dentate arch is a true challenge⁽¹¹⁾. The shape, color, size and positioning of the new teeth lie at the intersection of the patient’s desires (as the final recipient), the knowledge of the medical team (including the dental technician), and the limitations imposed by the clinical situation. Thus, provisional restorations play an important role in implant-prosthetic treatment. They can be used to establish the correct shape both visually and in relation to the peri-implant soft tissues, thanks to the possibility of making adjustments either by adding or subtracting material^(12,13). These provisional restorations also allow for the evaluation of the shade initially selected by the dentist in collaboration with the patient⁽¹⁴⁾. Depending on the appearance of the soft tissues, daily dietary habits, or other routines, the shade can be adjusted to achieve the most natural and personalized result for the patient^(15,16). From the perspective of color as well, where the situation requires it, materials that mimic the color of artificial gingiva can be used – especially in cases where bone resorption is significant and the artificial teeth appear excessively elongated compared to the size of natural teeth. Thus, the artificial gingiva not only adds a touch of color but also contributes to a shape much closer to that of the natural dentition⁽¹⁷⁾.

Conclusions

To restore masticatory, phonetic and esthetic functions, fixed prosthetics on dental implants are the best solution in cases of complete edentulism. Although it is not the most affordable therapeutic option, more accessible prosthetic alternatives can be found.

Thanks to its fixed nature, the patient can smile more confidently and resume normal eating habits (though without excess) since no material used in the fabrication of conventional or implant-supported prosthetic restorations, whether fixed or removable, matches the resistance of natural teeth.   

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).

Corresponding authors: Viorel Ștefan Perieanu E-mail: viorel.perieanu@umfcd.ro; Mădălina Adriana Malița E-mail: mădălina.malița@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 licence.