the advent of titanium implants resulted in a treatment modality with a high level of 
 applicability in several clinical situations .
although the original protocol was initially designed for the 
 treatment of completely edentulous patients , the need arose to extrapolate treatment 
 alternatives with osseointegrated implants to partially dentate patients .
implant 
 dentistry added a new alternative in oral rehabilitation , but at no time , have 
 osseointegrated implants been capable of resembling natural teeth with regard to their 
 characteristics .
this combination was applied to 
 partially edentulous patients , contradicting branemark 's protocol , which was based on 
 isolating implants from natural teeth .
however , the distribution of the teeth in the 
 arch may induce the adoption of combined prostheses . for decades ,
tooth - implant - supported dentures have been questioned because of the 
 differences of mobility between the abutments , the risk of intrusion of the natural 
 abutment , as well as the atrophy of the periodontal ligament , and the high 
 general risk of technical complications .
the great difference between an osseointegrated implant 
 and a natural tooth is the form of the structural union with the bone and the different 
 mechanism of absorption and dissipation of force , which makes the tooth - implant bond a 
 biomechanical dilemma .
the possibility of connecting implants to teeth in fixed denture , with a favorable 
 prognosis has been studied by several authors who concluded that the tooth - implant bond does not have a 
 negative influence on the marginal bone and soft tissues .
therefore , it was not possible 
 to show any greater risk of deficiency for fixed tooth - implant - supported dentures 
 ( ftisd ) when compared with implant - supported dentures , which were well accepted , 
 particularly by patients in unfavorable financial situations , who were unable to have 
 the ideal number of implants placed . nevertheless , the connection of natural teeth and osseointegrated implants in a rigid 
 denture caused concern and publications , with studies and guidelines for both extremes . 

there is a significant difference in the absorption and distribution of force between 
 natural teeth and implants .
this occurs because in tooth - supported dentures there is a 
 system of cushioning causing a micro - movement of 100 to 300 m due to the 
 presence of the periodontal ligament , as load will be transmitted to the bone with 
 beneficial stimulation by transforming the stresses of pressure into uniform traction on 
 the alveolar cortical . in implants
, the resultant stress is concentrated on the bone 
 crest , and this different dissipation of force may cause a lever arm , which depends on 
 the length of the pontic producing torque on the implant , causing loosening or fracture 
 of the retention screw . in view of such a situation ,
the use of semi - rigid connections has been recommended , 
 taking into consideration that this type of connection could be more efficient in terms 
 of compensating for the difference in mobility between the abutments .
nevertheless , other authors have reported that the semi - rigid 
 connections are rarely indicated in unilateral fixed dentures .
this type of 
 connection does not improve the stress distribution between the abutments , and are the 
 cause of migration of the natural teeth .
ideal tooth - implant supported fixed dentures ( tisfds ) are those in which the space is 
 small , including one tooth and one implant with the possibility of a maximum of two 
 pontics .
nevertheless , other 
 authors have reported that the ideal tisfds are those with a larger number of natural 
 abutments to promote greater rigidity of this denture .
the aim of this study was to use finite element method ( fem ) to evaluate the generation 
 of stresses in a fixed tooth - implant - supported denture with a rigid connection , when 
 varying the number of teeth used as abutments .
over the last few years , fem applied to biomechanics has become an extremely useful tool 
 for numerically assessing stresses and deformations associated with the mechanical 
 behavior of biomaterials and human tissues . in this study , the 3-d model of the fem
is an approximate 
 representation of an in vivo geometry , with the physical 
 characteristics of a real model . in this study ,
the ansys revision 5.7 program was used 
 to develop a model of a partially edentulous maxilla , conceived by means of 3-d fem , in 
 which an implant - tooth supported fixed denture was constructed .
representative volumes 
 of the implants , abutments , prosthetic crowns and cortical and spongy bone were created . 

connection of this denture was simulated by means of a metal surface of a non - noble nicr 
 alloy , varying the number of teeth connected to an osseointegrated iti 
 strauman implant , 10.00 mm long , 4.1 mm in diameter , with a 4.8 mm 
 platform . to compose this denture ,
metal - ceramic crowns were constructed in the shape of 
 premolars , which were connected by means of a pontic , using rigid connection , in order 
 to be analyzed in two configurations : the first configuration contemplated one tooth and 
 one implant ( model 1 ) , and the second configuration contemplated two teeth and one 
 implant ( model 2 ) . from the basic geometry created , the elastic properties of the various materials were 
 attributed , using approximate values found in the literature ( table 1 ) .
the elastic properties of the materials were adopted in a 
 linear system , whose hypothesis is that the deformation of elastic bodies is 
 proportional to the force applied .
furthermore , these properties were considered 
 constant and isotropic ( equal in all directions ) .
elastic properties of several materials that compose the model from the creation of the basic geometry , the finite element mesh composed of 297.096 
 knots and 213.129 elements for the model with one tooth and one implant ( model 1 ) and 
 529.930 knots and 383.670 elements for the model with two teeth and one implant ( model 
 2 ) were generated , according to figures 1 and 
 2 .
finite element mesh model 1 finite element mesh model 2 the study of biomechanics is , however , an analysis of the distribution of forces to the 
 bone when teeth are occluding .
it has been observed in tests that the intensity of the 
 bilateral and unilateral physiological force is 569 n and 430 n respectively and clinical observations have shown 
 that lateral forces are not well tolerated by the dental and bone structures , as occurs 
 with axial forces . in this model , a 
 vertical load of 100 n was applied on the occlusal face of the entire prosthetic set , 
 distributed uniformly according to the number of elements of the respective surfaces 
 ( figures 3 and 4 ) .
nodal load of 100 n on the denture containing 3 elements nodal load of 100 n on the denture containing 4 elements
this model was designed and submitted to a vertical load , in which its effect was 
 assessed quantitatively in n / mm ( mpa ) and qualitatively .
the images 
 generated by the program used in the present study made it possible to gain a broad and 
 significant understanding of the distribution of these stresses in the bone tissue , as 
 well as in the prosthetic components and associated structures .
the quantitative results are summarized in table 
 2 with plotting of the von mises stress ( seqv ) for the tooth - implant - supported 
 dentures with one and two teeth .
the table also shows the results of maximum 
 displacement ( dmx ) of the set .
quantitative analysis seqv = von mises stress ; dmx = maximum displacement in a qualitative analysis , it may be observed that the vertical displacement of 
 tooth - implant - supported dentures with one tooth and one implant , the tooth showed 
 greater movement in the apical direction ( figure 
 5 ) .
however , when a tooth was added in the mesial region of this denture , a 
 reduction in its vertical movement was observed ( figure 
 6 ) . movement of the set in the occlusal - gingival direction ( model 1 ) movement of the set in the occlusal - gingival direction ( model 2 ) in the analysis of the seqv stresses , it was observed that the maximum stress in the 
 tisfds containing one tooth ( model 1 ) was 47.84 mpa , whereas for the denture containing 
 two teeth ( model 2 ) the maximum stress was 35.82 mpa , both located in the region between 
 the tooth and the pontic , as shown in figures 7 
 and 8 . in selecting the images ,
when the 
 structures that compose the prosthetic crowns are removed , we can verify that the 
 maximum seqv stress occurred on the mesial side of the implant neck region , at the 
 junction with the cortical bone , with values of 12.15 and 8.85 mpa for models 1 and 2 
 respectively , as illustrated in figures 9 and 
 10 .
it can be verified that in the denture 
 containing two teeth , the load is practically absorbed by the implant with a slight 
 increase in tension on the tooth closest to the pontic , however , these loads can be 
 considered insignificant .
von mises stress ( seqv ) in model 1 von mises stress ( seqv ) in model 2 von mises stress ( seqv ) in the implant region in model 1 von mises stress ( seqv ) in the implant and teeth in model 2 in the analysis of equivalent stresses of von mises ( seqv ) generated in metal , we note 
 that the maximum stress is found in the same region between the natural abutment and 
 pontic for both the models , with values of 50.0 mpa for model 1 and 34.14 mpa for model 
 2 ( figures 11 and 12 ) .
this location of the maximum value in metal indicates that there is 
 greater flexion of the metal bar in the region between the tooth and pontic .
von mises stress ( seqv ) in the metallic infrastructure ( model 1 ) von mises stress ( seqv ) in the metallic infrastructure ( model 1 ) in the electromyography study to assess the intensity of the bilateral and unilateral 
 physiological force , the result found for bilateral force was 569 n and 430 n when 
 measured unilaterally .
thus , according to table 3 , one may make a comparison for functional loads from the flow limit 
 of the materials .
this table allows one to observe that the porcelain with specific 
 properties used in this study , when submitted to load in model 1 , showed admissible 
 values for occlusal loads ( kx100n ) lower than the one found for maximum physiological 
 load .
maximum von mises stress ( seqv ) values compared with the se flow stresses and 
 admissible occlusal loads for the materials
starting from a real principle proposed in the literature , the connection between teeth 
 and implants must not be considered as the first alternative for rehabilitation and it 
 is preferable to adopt planning of isolated implant - supported dentures .
nevertheless , in case 
 of anatomic limitations that may require advanced surgical techniques at high costs or 
 if teeth already require restorative interventions and are favorably distributed in the 
 arch , a combination between teeth and implants may be adopted with success rates similar 
 to those of fixed implant - supported dentures .
there is a vast amount of literature with regard to the biomechanical challenge of the 
 connection between teeth and implants .
authors have reported that this complication is 
 due to the difference in mobility between them , different mechanisms of absorption and 
 dissipation of forces and mechanical - receptor properties . however ,
biomechanical 
 responses in the face of a force are completely different , and in 
 tooth - implant - supported dentures , special care must be taken in planning to compensate 
 this difference .
nevertheless , according to the literature it is conclusive that 
 in fixed tooth - implant - supported dentures , connections of the semi - rigid type generate 
 more stress in the denture components so that the rigid 
 connection has been preferred instead of the semi - rigid type . from analysis of the results ,
the present study allows one to observe that there was a 
 reduction in the displacement of the prosthetic set , as well as a lower stress , when a 
 natural abutment was added , confirming previous findings that if the placement of only 
 one implant were possible , then two natural abutments must be used as retainers to 
 support a pontic thereby improving the rigidity of the set .
this 
 difference in stresses can also be explained by the fact that although the loading value 
 had been equal , the loads were better distributed in model 2 .
according to the literature , the resulting stress in implants is concentrated on the 
 bone crest , which is in agreement 
 with the results obtained in this study , in which the maximum seqv stresses occurred on 
 the mesial side in the neck region of the implant , as reported elsewhere .
it has been stated that the ideal tooth - implant supported fixed dentures are those in 
 which the space between the abutments is small , including only one tooth and one 
 implant , with the possibility of a maximum of two pontics .
this configuration is necessary because the flexion of 
 the bar is proportional to the cube of the length of the edentulous space , in agreement 
 with the findings of this study , in which it was observed a greater displacement in the 
 pontic region , and higher tension located between the pontic and the abutments .
according to the quantitative and qualitative analysis of the present study , it may be 
 concluded that : tooth - implant - supported prostheses must be limited with regard to the edentulous 
 space and it is a feasible and biomechanically predictable treatment option ; the placement of additional teeth decrease the resultant stress values ; the type of alloy used in the metallic infrastructure plays a key role in denture 
 displacement , and preference should be given to those with the highest modulus of 
 elasticity .
the internal connection type of implant provides greater rigidity to the set 
 ( abutment / implant ) mechanically presenting lower stress levels .
 objectivesin some clinical situations , dentists come across partially edentulous patients , 
 and it might be necessary to connect teeth to implants . 
 the aim of this study was 
 to evaluate a metal - ceramic fixed tooth / implant - supported denture with a straight 
 segment , located in the posterior region of the maxilla , when varying the number 
 of teeth used as abutments . 
 materials and methodsa three - element fixed denture composed of one tooth and one implant ( model 1 ) , and 
 a four - element fixed denture composed of two teeth and one implant ( model 2 ) were 
 modeled . 
 a 100 n load was applied , distributed uniformly on the entire set , 
 simulating functional mastication , for further analysis of the seqv ( von mises ) 
 principal stresses , which were compared with the flow limit of the materials . 
 resultsin a quantitative analysis , it may be observed that in the denture with one tooth , 
 the maximum seqv stress was 47.84 mpa , whereas for the denture with two teeth the 
 maximum seqv stress was 35.82 mpa , both located in the region between the pontic 
 and the tooth . 
 conclusionlower stresses were observed in the denture with an additional tooth . based on the 
 flow limit of the materials , 
 porcelain showed values below the limit of functional 
 mastication . 