Scientifica implantology

Medicina Oral, Patología Oral y Cirugía Bucal 2015; 20(1):e94-102

The strength and deformation of posts of different types screwed onto Kohno implants and subjected to static loads was evaluated. Rotational or repositionable posts made entirely in titanium showed greater resistance to deformation than posts with a titanium base and a resin sleeve, normally used for overcasting, and in this study considered as temporary fittings.

International Journal of Clinical and Experimental Medicine 2014; 7(4):817-825

This study on finished elements compared the results of the application of stress cycles on Global implants rehabilitated with single screw-retained crowns versus cement-retained crowns. The results showed that screw-retained prostheses exert greater stress on the tightening screw than cement-retained prostheses.

Implant Dentistry, Volume 22, Number 3 2013

In the last years many studies have highlighted the brilliant results of both immediate implants and immediate loading of implants. A natural evolution of these studies is the possibility to insert implants immediately after the extraction and to perform after this the prosthetic restoration. This concerns not only the replacement of a single tooth, but also a full arch restoration. The matter of indications to extraction should be analyzed in-depth on the evidence of the modern knowledge, evaluating very carefully the role of implants in treatment plans.
This kind of approach involves an accurate analysis of connection systems between implants and prosthetic superstructures with the aim to simplify the procedures and to optimize the passivity in the adaptation of the prosthesis. Premium/Kohno implants present a connection characterized by an internal hexagon and an external collar: this connection allows a minimal solicitation of the fixation screw, but it doesn’t help in creating a structure passively adaptable directly onto the implant platform in presence of minimal disparallelisms. To ease the procedure a simplified post was created, named “Simple”, where the hexagon was substituted by a small cylindrical portion which helps in centering and stabilizing the post inside the collar of the implant. The resistance of the Simple post towards functional solicitations was tested: the resistance of the implant-post joint was analyzed in presence of this kind of connection compared with three different variations. They were: the standard Premium/Kohno configuration, the connection with internal hexagon (without external collar) and another connection with traditional external hexagon. Finite
element method test was used to perform this analysis. The following connection hypothesis were compared:
• Case 1: COLLEX connection, internal hexagon + external collar, the one of Premium/Kohno implants;
• Case 2: Hypothetical connection with the traditional internal hexagon (without external collar);
• Case 3: Premium/Kohno implant connected with a Simple post (the post presents a cylindrical portion which helps centering and stabilizing the post itself inside the implant connection);
• Case 4: Standard external hexagon connection.
It is evidenced by the results that the use of a flat post connection, associated to a cylindrical portion which helps stabilizing itself inside the implant connection, doesn’t influence particularly the characteristics of the joint; this kind of connection presents values very near to the ones of the standard Premium/Kohno connection, thus supporting the use of this type of prosthesis, when it is necessary to connect a screwed prosthesis on many elements often disparallel between them.

This study documents the properties of strength of the COLLEX connection, present on Premium, Kohno and Shelta implants. COLLEX showed values 25% higher in terms of prosthetic robustness and stability compared to a connection with an internal hexagon but without a collar.

The increasing widespread use of intraosseous implants in oral treatments has led to placing more and more attention on experimental protocols capable of identifying
the mechanical risks connected to the different prosthetic choices.
The biomechanical interaction between the implant and biological tissues and between the implant and prosthesis has two important functions, on one hand, it stimulates the osseointegration and the remodelling of the bone and on the other hand, it determines the resistance of the components that enter into play.
For this reason, experimental research besides focusing on the biological approach has analysed mechanical aspects to learn more about resistance and distribuition
of forces, fundamental factors for evaluating the duration of an implant-supported prosthetic rehabilitation. Applying experimental mechanical protocols on the
interaction between the implant and prosthesis is a complicated procedure because it involves numerous variables, whose infl uence are still not well known today. At Sweden & Martina we have now standardised the phase of mechanical tests, implementing high corporate rigour in terms of efforts and costs. These sacrifi ces and our day-to-day commitment allow us to offer products with high safety standards. Generally, safety in mechanics is obtained by doubling a thickness and/or modifying
the materials with the same geometry. This is not possible in oral mechanics since the only material “allowed” is titanium and the anatomical limits are often insurmountable. The stress applied to the implants by the chewing action is completely unpredictable and complex because it has no preferential directions and is without repetitive cycles. This fact, also connected to the geometry of the prosthesis (asymmetrical and complex surfaces), involves a continuous variation
of the application point of the forces, which is therefore our No. 1 unknown factor. Compared to clinical research, experimental mechanical tests allow the tests to be repeated with a standardised protocol. In-vivo and clinical tests are subjected to major intrinsic and ethical restrictions and constitute a model that cannot be reproduced, while Finite Element Methods (FEM), fatigue tests and practical tests can be reproduced with the same patterns and, therefore, can be repeated
numerous times. Consequently, experimental research connected to mechanics, also as required by the regulations, becomes a crucial preventive instrument that guides the Research and Development Department, so that the defects can be predicted and eliminated beforehand and increasingly more innovative improvements can be tested and developed. This section brings together various studies relating to the mechanical, structural and functional behaviour of different implants and various prosthetic solutions, via FEM simulations, which are now a recognised surgical instrument for understanding the prosthetic kinematics. They are also important
because they provide the guidelines for product improvement or prosthetic design, and for conducting dynamic and cyclic fatigue tests.
In particular, tests were conducted on the resistances of different implants with different connections, in different types of bone, loaded with different prosthetic axes, using both FEM (Biancolini and Brutti) and dynamic tests with a thermographic system that considerably reduces the times compared to fatigue tests (Cilenti, Grasso, Pinco and Pulvirenti). The Finite Element Method verifi ed the effi ciency of the Toronto prosthetic systems (Risitano, Franceschini, Cicciù and Maiorana) even in the presence of different angles and implant placement (Cicciù, Risitano, Maiorana and Franceschini) or different prosthetic conformations (Cicciù, Risitano, Maiorana, Herford, Oteri and Cicciù). This Method also verifi ed the different behaviour of implants loaded with straight abutments, angled at 15° and at 25° (Cardelli, Montani, Gallio, Biancolini, Brutti and Barlattani). Since tests with mathematical models simulated with fi nite elements are not always adequate or capable of virtually simulating the complexity of the loading combinations of the real bone-implantprosthetic assembly, the FEM tests were validated by Sweden & Martina with dynamic and cyclic
fatigue tests, whose results were compared with the virtual results in order to evaluate the differences (Raddi).
Fatigue tests were conducted to verify the “infi nite life” of the male/female components of overdentures on ball attachments and the results showed how different material matrices (titanium, gold, resin) infl uence the holding power of the implant-prosthesis assembly (Branchi, Vangi, Virga, Guertin, Fazi). Finally, it should not be forgotten that theory and technology at times do not go hand-in-hand with the required handcrafted component of the prosthetic products. In order to make a correct connection, many factors come into play and invalidate what on paper looks like a “good project.” One of these factors is residual stress, which is one of the main causes of the unscrewing of fastening screws and of early breakage. For this reason, different authors have tested different passivation systems (Conforti and Madini). Suitable fl at-to-fl at components make it easier to obtain a good passivation of multiple structures even in the presence of major prosthetic differences, and the mechanical solidness and correct distribution of the loads (Covani) of these components was verifi ed. Recent market studies have shown that in Italy dentists still prefer to use prosthetic solutions cemented on abutments instead of screwed solutions, unlike the rest of Europe. The advantages and disadvantages of each solution were analysed, even from a clinical perspective (Cicciù, Beretta, Risitano and Maiorana). Numerous studies are still being conducted to evaluate new materials such as zirconium oxide, which is now used for producing individual prosthesis, or to test the effi ciency of screwed prosthetic solutions on a limited number of implants and highly-angled prosthesis. The test methods evolve with the changing of our technological knowledge and the introduction of more and more sophisticated
simulation software. All our efforts were and still are concentrated on providing “evidence of the facts”. Although conducted at different times and starting from different perspectives, all the tests on products (clinical, simulated, fatigue, in vitro, etc.) have the same goal and are devoted to developing a safe and functional product.

Relazione interna, Università di Catania, 2001

The Premium implants and respective prosthetic components tested with loads corresponding to the physiological loads and with higher loads, showed excellent dynamic resistance.

Relazione interna, Sweden & Martina, 15 gennaio 2003

This finite element analysis compared the mechanical behaviour and the distribution of stress on 4 different implant morphologies: Pilot, Stark-D, Outlink and a commercially available implant. In all cases, the part with the most stress was the fastening screw, however, no component was subjected to stress that exceeded the resistance limit. The stress distribution is better in the cortical bone than in the spongy bone.

Oral Implantology, 1:7-14, 2009

This finite element analysis shows that mechanical stress is always maintained within tollerable limits by the bone structures, but in relation to different prosthetic angles, it is concentrated in specifi c areas with different consequences on the remodelling methods of the bone around the implant. Abutments should not exceed angles of 25°.

The Journal of Implants and Advanced Dentistry, 2(9): 41-58, 2010

This finite element analysis suggests that a Toronto prosthesis is capable of better distributing the stress on six fi xtures, rather than on fi ve, and that it is always advisable to position two implants intraforaminally and instead of only one implant.

Relazione interna, Sweden & Martina, 2010

This study verifi ed the suitability of the test models adopted for checking the mechanical resistance of the Premium and Outlink implants, even with smaller diameters and in load conditions with wide angles (30°), and demonstrated how these implants are capable of adequately supporting dynamic fatigue stress.