At the present stage of development of orthopedic dentistry, the action of such a factor as the material and advanced methods of manufacturing temporary protective fixed orthopedic structures comes to the fore, many authors believe [7,8,9].
Traditional methods for obtaining various types of temporary structures include direct and indirect methods [5,10,11].
Depending on the time of manufacture temporary prostheses are divided into the following types:
- direct prosthetics - "immediate prostheses" made before teeth preparation by clinical and laboratory methods;
- early prosthetics - prostheses made in one visit immediately after the preparation of teeth in the clinic [12].
Direct methods of fabrication of provisional prostheses.
A single-session, direct method of manufacturing dental prostheses with preserved anatomical shape of the teeth is known using matrix technologies, where silicone or alginate impression materials, celluloid caps, mouth guards ("strips") and thermoplastic materials ("LuxaForm", DMG, Germany; basic wax) are used as the matrix. However, it should be remembered that they are not able to accurately display prosthetic tissues and do not have elastic properties [13].
The authors [14] consider the lack of a direct method of manufacturing a temporary crown in a pre-received impression with a base layer of silicone mass to be the presence of a preserved anatomical shape of the tooth before its preparation, which does not always happen in practice.
The literature describes a method for manufacturing temporary dentures by matrix method when the crown part of the tooth is destroyed using a photopolymer material Block-out Resin, which is included in the set of the system for teeth whitening "Opalescence" ("Ultradent", USA). Block-out Resin is applied layer by layer to hard tooth tissues to restore the anatomical crown, without using adhesive systems. Block-out Resin is well layered, easily packed with filling tools, provides satisfactory adhesion to the tooth tissues and is well treated with abrasive tools. After temporary restoration, the production of a dental crown is carried out using an impression [15].
It is proposed to manufacture dental crowns in the partial absence of teeth using matrix technology in a direct way (manufacturing the matrix directly in the oral cavity) using a silicone matrix in the absence of one tooth. To temporarily eliminate a dental defect, standard plastic teeth are used from removable denture headsets, which are sanded taking into account the dental defect and occlusal relationships. Fixation of the plastic tooth is carried out using Block-out Resin. Before preparing the supporting teeth, an impression is made using silicone or alginate impression materials. After receiving the impression, the artificial tooth is removed and the supporting teeth are prepared. A prostheses is made based on a previously obtained impression (matrix) [12].
There are known clinical (single-session) methods of manufacturing temporary prostheses using standard factory sets of polymer temporary crowns of different sizes, styles, colors, and different firms. After selecting the crown of the required shape and size, it is stored in the neck edge in accordance with the contour of the neck of the tooth in the oral cavity. Then spend the specification of the topography of the stump of the tooth using self-curing plastic material, after polymerization of the plastic correction is made, the edges of the crown and fix it with temporary cements [12].
There is a direct method of manufacturing prosthetics using the free-form method, when the temporary restoration is made from polymer plastics of cold polymerization directly in the patient's mouth. After preparing the tooth for the future permanent structure, a plastic test is prepared. Next, the plastic is adapted to the stump of the tooth with closed dental rows. After hardening, excess plastic is removed by a milling cutter while simulating the anatomical shape of the future temporary crown [16].
There is a direct method of manufacturing temporary bridges from propylene, and their intermediate parts from self-hardening plastic [17].
As a result of a comparative clinical trial of temporary artificial crowns made directly from acrylic plastic-acryl oxide and composite plastic-Protemp-4, it was concluded that it is necessary to use Protemp-4 composite plastic, since It does not have a negative effect on the prepared teeth and surrounding tissues, as acryl oxide [18].
The effectiveness of the direct method of manufacturing temporary pin structures and crowns from fast-hardening TEMPRON plastic is proved [19].
There are known direct methods of manufacturing provisional stump structures made of self-curing composite material "Structur 2 SC" and a silicone template that must be fixed to a temporary non-ethylene cement "Temp-BondNE" [20].
In order to improve the effectiveness of the preparatory stage of prosthetics, it was proposed to reuse the patient's permanent dentures that are subject to replacement [21].
A comparison of the technological properties of materials for the manufacture of temporary structures during prosthetic treatment with a direct method of composite materials Protemp 4 Garant firm 3M and Strucrur 2 SC firm Voco for strength, fracture, fluidity and the degree of exothermic showed that each material has its own indications for the manufacture of prosthetics:
- Structur is best used for temporary inlays, single crowns and bridges with an intermediate part of no more than one tooth, Protemp-when increasing the intermediate part;
- Structur may make it difficult to remove a newly made temporary structure, as there is a high risk of breaking off in the neck area;
- with Structur it is preferable to work in the cold season, with Protemp-in the warm [22].
It is suggested that the manufacture of dental prostheses using the Wax-up method is the restoration of the shape of the future restoration with wax on a diagnostic plaster model, followed by the removal of the silicone wax-up template. The doctor-the stomatologist-orthopedist removes some silicone impressions with a wax reproduction on the model. One of the impressions is used as a matrix for making temporary structures, the rest are cut in different planes and used as templates for preparing the patient's teeth. After completion of the preparation, the initial matrix is filled with a polymer material and fixed in the patient's mouth [16].
Direct single-session methods of manufacturing temporary prostheses have their advantages: the production of dental prostheses is carried out in one visit; they accurately repeat the anatomical shape of the tooth, ensuring individual shape and maintaining the position of the teeth; they do not need to be modified; speed and relative ease of manufacture, strength and good stabilization of the prosthesis; patients easily adapt to these structures; they do not require expensive equipment and special training of staff, which makes it possible to use it in an outpatient appointment without additional financial expenses of the doctor and the patient for its implementation.
Despite the relative perfection and technical "working out" of the direct method of manufacturing temporary permanent dental prosthetics by fixing crowns, immediately after preparing the teeth, its potential or actual effectiveness still depends on a number of factors: compliance with the necessary treatment conditions; on the qualification of the specialist; on the patient's conscientiousness in relation to the treatment and diagnostic process [24].
Indirect method of manufacturing temporary prostheses.
In the dental laboratory, you can make more aesthetic temporary restorations. With the help of various masses, the dental technician can adapt the color and structure of the restoration to the characteristics of the patient's natural teeth as much as possible.
The first stage of manufacturing temporary structures by indirect method is the removal of impressions for the manufacture of diagnostic models. In the laboratory, a technician on a model dissects teeth for a future temporary construction. Next, a simulation of a temporary structure made of wax is performed, followed by its replacement with plastic. The finished design is sent to the clinic. In the clinic, an orthopedic doctor dissects teeth using a model and a ready-made design as a template. After being stored and relocated, the finished structure is fixed on temporary cement [16].
The indirect method involves the production of temporary protective prostheses in a dental laboratory, which takes a certain time (from several hours to one day). Taking into account the need to cover the teeth immediately after preparation, it is more rational to use the direct method [5, 25].
An improved standard method for manufacturing a temporary crown using the indirect method according To N. G. Abolmasov is performed as follows: the gingival edge is cut to the deepest imprint in the gingival groove, thereby ensuring minimal immersion of the plastic crown edge in the gingival groove (no more than 0.5 mm), then the anatomical shape is modelled using colorless wax [26].
There is a known method for manufacturing temporary prostheses in the partial absence of teeth by an indirect method using matrix technology in the case of a dental row defect. This method is shown in the absence of up to 4 incisors for the group of front teeth and 2-3 teeth in the lateral Department. Manufacturing of the matrix by an indirect method can be carried out in a dental laboratory in parallel with carrying out operative manipulations on preparation of supporting teeth in the clinic by a dentist-orthopedist. This method allows you to make dental prostheses in one visit, saving the time of the doctor and the patient [13].
A method for manufacturing bridge-like temporary prostheses with an impression engraving is described. Before preparing the supporting teeth, a working impression is obtained. In the resulting print and remove the display of the vestibule of the oral cavity margins 2-3 mm from the level of the necks of the teeth preserved, which simplifies the re-introduction of the print, and using cutting tools to create indentations in otlicnom the material in place of missing teeth. Next, the supporting teeth are prepared, the impression is filled with material for dental prostheses and the impression is inserted on the tissue of the prosthetic bed. At the end of the time of polymerization of the structural material, the impression is removed from the oral cavity, the prosthesis is separated from the impression material and processed. This method requires much more time, because it is almost impossible to engrave the impression in accordance with the anatomical shape of the missing teeth and with the preservation of occlusal relationships between the dentition [14].
An indirect method of manufacturing dental crowns on a plaster model of the dentition using a cellulose plastic mouth guard by thermoforming is proposed. From the obtained plate cut out the mouth guard, and then make cutting mouth guard on gingival line of restored teeth. After preparation of the supporting teeth, the mouth guard with artificial teeth is packed to the patient's dentition with a preliminary introduction of self-hardening plastic [26].
Each method of manufacturing temporary prostheses has disadvantages that can not be ignored:
1. on a plaster model made of self – curing plastic-disadvantages: time and material costs; inability to reuse a wax reproduction of a temporary structure in order to accurately copy it in compliance with individual typological characteristics of the terrain.
2. by hot polymerization or injection method under pressure in the patient's oral cavity using a silicone template made from an unassembled plaster model after preliminary wax modeling-disadvantages: frequent need to re-Refine the internal surface of the temporary crown, its correction when storing in the oral cavity; difficulty in reproducing all occlusal-articulation parameters and individual typological characteristics of the relief.
3. using a cap that is made from a set of "Adapta" - disadvantages: the use of an individually selected tooth from a set of artificial teeth does not provide the transfer of all individually typological characteristics of the relief of occlusal surfaces of teeth in the form of localization, areas of occlusal contacts and near-contact zones, occlusal surfaces of antagonizing teeth [27].
The literature also describes direct and indirect methods of manufacturing temporary crowns using a template tire, where a self - curing "paste-paste" system based on multifunctional ethers of methacrylic acid Structur 3 was used as a material for the temporary structure [28, 29].
Automatic CAD/CAM milling of temporary prostheses.
Currently, the most modern and most expensive method of manufacturing temporary structures using digital technologies is automatic CAD/CAM milling. The first stage of this method is to scan the model of the initial situation or take a digital impression of the patient's oral cavity. After scanning, the received data is processed, and special software allows you to simulate the type of future restoration on a computer screen and discuss it with the patient. The obtained data can be used for final prosthetics. As the source material, fully polymerized standard blanks are used, which consist of several layers and have an optimal shape. Blanks are available in 4 sizes (S, M, L, XL). The choice of a specific workpiece depends on the size of the temporary restoration. After milling, the finished restoration is separated from the standard workpiece by a cutting disc. In the clinic, the restoration is tried on in the oral cavity and fixed. Temporary structures do not require time-consuming polishing, as they have a high surface quality and glossy gloss immediately after milling.
Using the method of manufacturing temporary structures using FDM (fused deposition modeling) 3D-printing on a 3D-printer, the authors achieved high anatomical and functional accuracy of the provision structures, reduced the time spent by the dentist and the amount of waste of expensive dental materials, without the participation of a dental technician [30].
An integral factor in the clinical success of implant-based prosthetics is the restoration of the removed tooth with a temporary prosthesis made using modern CAD/CAM systems, which allows you to simulate the optimal contour of the intermediate part of the temporary bridge in the soft tissue surrounding the implant. This, in turn, allows you to close the existing defects and create optimal conditions for the formation of an aesthetic gingival profile for final restoration, reliably protecting the augmentation from contact with saliva and food. Patients leave the clinic with a temporary structure that does not load the implant, thus supporting the two-stage treatment process, and also protects it from adverse effects of the oral environment [31].
