Aspecte practice în confecționarea protezelor totale (Partea I)

Introduction

Dental prosthetics represents one of the most important fields of modern dentistry, aiming at the functional and esthetic restoration of the dento-maxillary system. In this context, complete dentures constitute an essential therapeutic solution for patients suffering from total edentulism, a condition involving the complete loss of teeth from one or both dental arches^(1-4).

In recent years, the field of dental prosthetics has undergone a significant transformation through the integration of modern technologies into the design and manufacturing processes. Traditionally, complete dentures were fabricated through time-consuming procedures largely dependent on the manual skills of the dental technician. Today, due to the rapid evolution of digital technologies, methods such as computer-aided design and computer-aided manufacturing (CAD/CAM), both additive and subtractive techniques, are increasingly used. These methods contribute to the fabrication of more precise prostheses with superior esthetics; however, they are often less comfortable for patients compared to dentures manufactured using conventional techniques^(1-4).

One of the main reasons for addressing the topic of complete denture fabrication in this study is the continuous increase in the number of totally edentulous patients, particularly among the elderly population. In this respect, there is a genuine need for efficient, accessible and durable prosthetic solutions.

Understanding the stages involved in complete denture fabrication, from impression taking and modeling to final adaptation and finishing, is essential for anyone practicing or intending to practice in the field of dental technology^(1-4).

Given the ongoing increase in the number of totally edentulous patients, especially among elderly individuals, there is a pressing demand for effective, affordable and long-lasting prosthetic solutions. Therefore, in this two-part article, a comparative analysis between conventional and modern methods of complete denture fabrication, highlighting the advantages of each therapeutic approach, was conducted. Specifically, the objective of this study was to enhance the understanding of how technology contributes to improving patient quality of life, while also increasing the efficiency of both the dentist’s and dental technician’s work.

Technological aspects in the manufacturing of complete dentures

Case 1: Manufacturing of complete dentures by mould polymerization (injection and heat-curing polymerization)

A 60-year-old patient presented to the dental clinic complaining of functional and esthetic difficulties due to complete tooth loss in both dental arches. Following anamnesis and clinical examination, a diagnosis of complete bimaxillary edentulism (maxillary and mandibular) was established.

The patient had not previously worn complete dentures and expressed the desire to benefit from durable prosthetic restorations with improved esthetics and enhanced comfort. After discussion between the dentist and the patient, it was decided to fabricate two complete dentures using the injection technique with a biocompatible synthetic polymer (Polyan), free of methyl methacrylate monomer, combined with an acrylic artificial tooth set in shade A2. Given that both arches were completely edentulous, particular attention was paid to determining the vertical dimension of occlusion and intermaxillary occlusal relationships.

Polyan-injected dentures belong to the category of flexible dentures, and are fabricated from a modified polyamide thermoplastic material, injected under pressure at high temperatures. This material has become widely adopted in modern prosthetic practice due to its superior biomechanical and esthetic properties compared to traditional rigid materials. Moreover, it represents a highly suitable alternative for complete denture fabrication in patients with allergies or intolerance to conventional acrylic resins. Compared to PMMA, this material exhibits increased elasticity, superior adaptability to complex prosthetic fields and enhanced comfort during use, particularly in areas with pronounced mucosal mobility^(1-4).

From a technological standpoint, Polyan is supplied in granular form and heated in a specialized injection device to temperatures of approximately 270-290°C, depending on the material formulation. After melting, the material is injected under pressure into a metal flask, where it precisely adapts to the working model. After cooling, the prosthesis is deflasked and finished using specific procedures, without requiring further polymerization.

In the initial stage, preliminary impressions of the fully edentulous prosthetic fields were taken using standard impression trays and condensation silicone materials in double consistency (putty and light-body). The impressions were rinsed under running tap water for 20 seconds and subsequently decontaminated by immersion in disinfectant solutions for the duration recommended by the manufacturer.

The dental technician then poured the two preliminary models using type II dental stone. Based on these models, two custom impression trays were manufactured from light-curing composite resin (Figure 1).

The subsequent technical stages involved taking functional impressions by the dentist and manufacturing the occlusal rims in the dental laboratory.

Functional impressions were obtained using the previously fabricated custom trays and light-body condensation silicone materials. The impressions were rinsed under running tap water for 20 seconds and disinfected by immersion in chemical disinfectant solutions according to the manufacturer’s recommendations. Functional models were obtained using type III dental stone (Figure 2).

Occlusal registration rims were designed and made on the functional models using shellac plates and wax rims. They were used to record the intermaxillary occlusal relationship of the patient.

In the dental office, the dentist determined and recorded the intermaxillary relationship using occlusal registration rim, and then the dental technician mounted the functional models in an articulator. Based on the marks drawn on the wax rims and the data transmitted in the laboratory sheet, the dental technician made a wax pattern of the future dentures. In this case, teeth with shade A2 (according to the VITA shade guide) were used (Figure 3).

The preliminary wax dentures were sent to dental office for try-in and additional changes. When they were returned to the dental laboratory, the dental technician made the final touches, such as: engraved the maxillary model at the junction between the hard and soft palate (Ah line); he made the last esthetic changes on the wax and artificial teeth to obtain the definitive wax dentures (Figure 4).

Subsequently, the definitive wax dentures, maxillary and mandibular, were invested. The model and the wax denture were placed in the first half of the injection flasks, the excess dental stone used to invest the dentures was removed, and wax sprues were attached to form the future injection channels for the Polyan material (Figure 5).

The second half of the flask was mounted and the dental technician poured dental stone to fill the space that remained between the wax denture and the second flask. Using wet heat, the wax melted and residues were washed from the flask using hot water to obtain the mould (Figures 6 and 7).

The dental technician performed mechanical retentions on the acrylic teeth using a laboratory micromotor and special burs. The dental stone surfaces were coated with a specific alginate-based insulating agent (Figure 8). The two parts of the flask were remounted, a Polyan cartridge inserted in the injection device for injection process (Figure 9).

The final technical stages of manufacturing the complete dentures from Polyan type material were also dental laboratory stages (technical stage) and consisted of:

• deflasking the dentures;
• removing the plaster from the surface of the obtained complete dentures;
• cutting the injection rods of the Polyan type material and the actual processing of the complete dentures (Figure 10).

Finally, the dental technician polished and completed the two Polyan flexible complete dentures, which were then delivered to the dental clinic for intraoral insertion (Figure 11).

Discussion

Technological developments in dentistry have brought new treatment options for completely edentulous patients^(5,6). However, economic limitations and the large number of patients have necessitated a rethinking of the materials used for the base of dentures^(7,8). This is reflected in improved comfort for patients in daily activities⁽⁹⁾.

The new materials used, such as Polyan, bring a number of advantages over classic materials, with an increasing preference among doctors, but especially among patients⁽¹⁰⁾. The most important aspect is the significantly reduced amount of residual monomer, a substance with an irritating effect on the soft tissues, with which the dentures come into contact^(11,12).

Benefiting from an exact dosage provided by the manufacturer, the material has a homogeneous composition, and the large number of crossed fibers provides a smooth surface after processing, which is maintained for a long period of time⁽¹³⁾. At the same time, it offers superior color stability compared to classic acrylates^(13,14). The same fibers give the material increased resistance to breaking or bending, unlike classic materials that exhibit brittle behavior in the event of accidental falls during sanitation operations^(15,16).

The most important aspect is related to the elasticity of the material, transforming the prosthesis from a rigid body into an element that adapts faster and better to the tissues in the oral cavity, reducing the discomfort created by such prosthetic works^(14,17).

Conclusions

Polyan material exhibits several essential properties that make it suitable for the manufacturing of injected complete dentures. The main advantages include:

• controlled elasticity, allowing functional deformation without loss of original shape;
• natural translucency, providing an esthetic appearance similar to natural gingiva;
• high resistance to impact and fracture due to its homogeneous composition and uniform internal structure;
• low weight, significantly increasing wearing comfort;
• low water absorption and good resistance to discoloration, provided adequate oral hygiene is maintained.

However, Polyan also presents important limitations, including:

• difficulty of direct intraoral adjustments, complicating post-insertion modifications;
• impossibility of conventional repairs if damage occurs, the entire denture must be remade.  

CONFLICT DE INTERESE: niciunul declarat.

SUPORT FINANCIAR: niciunul declarat.

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