Deformation suffered by the materials that make up the implant-supported overdentures with an increase in the number of implants: from 1 to 4. Bibliographic bibliography

A bibliographic review was made on the evidence published in the last 10 years, 2006 2016 about the four alternative therapeutic options for a complete prosthesis in a complete mandibular edentulous patient: overdenture on 1, 3 or 4 implants, and with the All on protocol four. For this, one of the main search engines in biomedical sciences was used, such as PubMed, through the library of the Faculty of Medicine and Health Sciences of the University of Oviedo. Throwing a total of 1539 results, that after the different fi lters of year of publication, percentile of the magazine and keywords were limited to 34 articles. Research Article


Introduction
The demand for greater prosthetic stability on the part of patients with conventional full dentures has been and is a constant in daily clinical practice. This, together with the presence of important bone atrophies or limiting economic factors that contraindicate the planning of an implantsupported 'all-fi xed' rehabilitation treatment, has made overdentures the preferred prosthesis in many cases. The overdentures are prosthesis of full arcade mucosoportadas and implantoretenidas that constitute a valid and reliable option of indication for a total toothless of one or another arch, more after negative experiences with a complete removable prosthesis [1]. Although a fi xed prosthesis is always preferable whether implanted or not, it is known that the aesthetics of edentulous patients with a moderate to advanced bone loss improves with an overdenture when compared to a fi xed restoration, and so much so that the labial support and Facial is often the deciding factor in deciding between a fi xed prosthesis or an overdenture, since the fi xed prosthesis has a limited capacity to compensate for vertical and horizontal bone loss, while the overdenture easily replaces both vertical alveolar defects as horizontal being able to restore tissue volumes lost over the years, restoring the correct relationships between lip, nasolabial line and base of the nose, basis of the aesthetics of rejuvenation that most patients seek (Misch 2007 ;Eckert and Carr 2004) [2] . Multiple evidences [1][2][3] have shown that overdentures are a predictable treatment modality especially in edentulous patients with adaptation problems for a conventional full denture. So much so that since the beginning of the implant era, overdentures were indicated and the fi rst articles about its success were published with mandibular subperiosteal implants or with stabilized root implants immediately loaded in the anterior part of the jaw [4]. Regarding the number and disposition of the implants, it has been the object of a wide analysis to fi nd the best relation between cost-effectiveness, having used two, three, four and even a single implant to retain a mandibular overdenture. Currently there is a certain consensus in admitting two implants placed in an appropriate position, they are enough to get an overdenture with good retention and stability for masticatory function. For the rest of the questions, the evidence is not so evident and there are hardly any articles in the dental literature.

General objective and specifi cations
The general objective of this work is to determine which restoration is the most suitable for edentulous mandibular patients using four implants: fi xed or removable option.

Objective specifi cations:
1 -To quantify the stress transmitted to support terrain and other constituent elements of a removable prosthetic restoration such as an overdenture or fi xed, such as hybrid prostheses.

Implant retained overdentures: Constitutive elements, number of implants parts and types
An overdenture consists basically of artifi cial teeth, an acrylic base with or without metallic reinforcement and a retention system that joins it to the implants [6], being able to establish two types of relationships with the supporting ground: overdentures implantoretenidas and mucosoportadas and implantoretenidas and implant-supported sobredentaduras.
It follows therefore that the correct design and construction of the prosthesis, among others, takes on special importance and in the second stage the selection of the type of attachment to be used. They can be classifi ed with a reductionist criterion in axillae, like those of our study, and bar type [7]. The main reason for opting for the axial type, and specifi cally for the subtype locator will be, in addition to the simplicity in their technique, the biomechanical advantages and stability that the restoration will grant. In implant-retained and mucosalsupported overdentures the prosthesis is retained mainly by the implants and basically supported by the edentulous basal area and to a lesser extent by the implants. With this design, the prosthesis has retention and some resilience allowing some movements such as intrusion of the prosthesis and some other depending on the anchoring system, which in theory should reduce the overload on the implants (Weimberg LA, 1993). In this line, with the aim of canceling or minimizing the overload on the support terrain (implants and osteofi bromucosa) caused by uncontrolled prosthetic movements, a multitude of attachments have been designed and projected, which with a reductionist criterion can be classifi ed into axial attachments and bar type ataches, remembering that according to Laney et al. [7], in the Glossary of Oral and Maxillofacial Implants, with the name of atache is designated a "particular type of retentive mechanism formed by two corresponding and compatible components called patrix and matrix . Matrix refers to the receptacle component of the atache and patrix to the portion that has friction and fi ts and fi ts into the matrix.

Possibilities of attaches
This type of attachment partially solves the disadvantages of the ball type; On the one hand, it solves discrepancies of up to 40º of disparallelism between implants by simply placing the green shirt on the female, although for greater discrepancy it is preferable to use bars; and on the other hand it is possible to choose more or less capacity of retention between a range of 1.5 pounds to 5 pounds (according to the commercial house), just by changing the color of the shirt transparent, pink, blue, green or red. It is currently the most frequently used system in professional practice and it is also the system chosen in this research project, so it is necessary to know more about its clinical performance. The Locator attachment offers resilient retention by means of elastic connection and rotational movement and has low vertical height of the order 3.7mm with external hexagonal connection and 2.5mm in implants with non-hexagonal connection. It is easy to use, so that the patient can place and remove the prosthesis easily, without the need for a correct and sometimes complex alignment of the prosthesis. It can also be placed on overdentures with 2, 3 or 4 implants.  Its name comes from the use of 4 implants By maxilla, although 5 or 6 may be necessary in certain cases of the maxilla.

No. of implants
One of the most attractive points of the technique is that they can be applied in a high percentage of cases with success rates higher than 95% (Lower implants will be interforaminal even in situations of extreme resorption; in the maxilla they will be placed between the maxillary sinuses Decreasing the need for regeneration that would contraindicate the technique) (2,3). In addition, it is an intervention in which we place a smaller number of implants than usual, which facilitates hygiene and, in addition, we cheapen the costs. 5. The patient must collaborate in his task of daily oral cleansing, for which he has a great variety of auxiliary means and methods.

Overheads Vs Hybrids
Regarding the distributon and location of the implants for a mandibular overdenture, globally to meet the conditions of

Conclusion
It has been demonstrated that implant-supported prostheses are an excellent option for the rehabilitation of total edentulous patients, since they restore function and aesthetics, which allows them to improve their social and psychological condition. It has also been observed that this type of prosthesis provides many advantages, among these advantages can be mentioned: lower bone loss, improved access for oral hygiene and more space to correct discrepancies in the ratio of the dental arch and also improves retention and stability of the 4. There is an absence of contrasted evidence, and more long-term on the reduction or not of the overload when modifying the angulation of the implants, following the protocol All on four.