The effect of casting and masticatory simulation on strain and misfit of implant-supported metal frameworks

Materials Science and Engineering C 62 (2016) 746–751

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The effect of casting and masticatory simulation on strain and misfit of implant-supported metal frameworks Cláudia Lopes Brilhante Bhering a, Isabella da Silva Vieira Marques a, Jessica Mie Ferreira Koyama Takahashi b, Valentim Adelino Ricardo Barão a,⁎, Rafael Leonardo Xediek Consani a, Marcelo Ferraz Mesquita a a b

Department of Prosthodontics and Periodontology, Piracicaba Dental School, University of Campinas, Piracicaba, Sao Paulo, Brazil Department of Prosthodontics, Health Sciences Graduate School, Amazonas State University, Manaus, Amazonas, Brazil

a r t i c l e

i n f o

Article history: Received 6 April 2015 Received in revised form 6 August 2015 Accepted 11 February 2016 Available online 13 February 2016 Keywords: Marginal misfit Stress analysis Cyclic loading Strain gauges Multiple prostheses Prosthetic cylinder

a b s t r a c t The influence of casting and masticatory simulation on marginal misfit and strain in multiple implant-supported prostheses was evaluated. Three-unit screw retained fixed dental prosthesis (FDP) and screw retained full-arch fixed dental prosthesis (FAFDP) frameworks were made using calcinable or overcasted cylinders on conical dental implant abutment. Four groups were obtained according to the cylinder and prosthesis type (n = 10). Frameworks were casted in CoCr alloy and subjected to strain gauge analyses and marginal misfit measurements before and after 106 mechanical cycles (2 Hz/280 N). Results were submitted to ANOVA, Tukey's HSD and Pearson correlation test (α = 0.05). No difference was found on misfit among all groups and times (p N 0.05). Overcasted frameworks showed higher strain than the calcinable ones (FDP — Initial p = 0.0047; Final p = 0.0004; FAFDP — Initial p = 0.0476; Final p = 0.0115). The masticatory simulation did not influence strain (p N 0.05). No correlation was observed between strain and misfit (r = 0.24; p N 0.05). In conclusion, the marginal misfit value in the overcasted full-arch frameworks was higher than clinical acceptable data. It proved that overcasted method is not an ideal method for full-arch prosthesis. Overcasted frameworks generate higher strain upon the system. The masticatory simulation had no influence on misfit and strain of multiple prostheses. © 2016 Elsevier B.V. All rights reserved.

1. Introduction The perfect fit between prosthetic framework and implant results in a lower amount of stress on the bone—implant interface [1,2]. Neglecting this factor can lead to biological or mechanical complications [3], even when external forces are not applied. Biological complications may include adverse tissue reactions, pain, tenderness, marginal bone loss, and loss of osseointegration [4]. Therefore, a passive relationship is a prerequisite for the long-term success of implant-supported rehabilitations [5]. The torque application in prosthetic screws of a non-passive framework generates bending moments and axial forces on the osseointegrated system [6,7]. This can lead to overload and/or fracture of components and retaining screws [4], micro fractures of cancellous bone, which can result in fibrointegration and loss of implant functionality [6]. Even though the dental implant rehabilitation can be considered a predictable treatment [8], complications can occur within the prosthesis, affecting the joint stability, which jeopardizes the predictability of treatment. Nonetheless, the achievement of a passive framework is often limited by conventional casting techniques for obtaining prosthetic ⁎ Corresponding author at: Av. Limeira, 901, Piracicaba, Sao Paulo 13414-903, Brazil. E-mail address: [email protected] (V.A.R. Barão).

http://dx.doi.org/10.1016/j.msec.2016.02.035 0928-4931/© 2016 Elsevier B.V. All rights reserved.

frameworks. The clinical and laboratory procedures involved in obtaining the prosthesis, even if properly executed, contribute to its final distortion [9]. The majority of the distortions occur due to volumetric change of materials and used techniques, such as impression material, plaster model, framework waxing, inclusion in investment, alloy casting, and veneering stage [9]. Therefore, the precision of casted frameworks is influenced by dimensional changes that occur during all stages of its fabrication [10]. The casting process is a potential agent for distortions that compromise the fit of the framework to the implant platform or abutments. In an attempt to minimize the changes resulting from the casting procedure, manufacturers developed dental implants abutments and cylinders with a metallic pre-machined strap, so that only the remainder of the cylinder body is plastic and therefore, it is subjected to casting [11, 12]. These components are known as pre-machined cast-on [13–15] or overcasted [11,12] abutments/cylinders. These cylinders were developed to minimize casting distortion at the strap of the components [11, 12], in an attempt to enhance the fit and passive of implant-supported frameworks. The better framework fit, the lower the load on the set, ensuring maximum effectiveness of the component [14]. Despite the cylinder's type to be an important factor for the stability of the system, according to authors' best knowledge there is no study that evaluated the influence of mechanical load conditions on the misfit and strain of full-arch implant-supported prosthesis fabricated with different

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prosthetic cylinders (entirely calcinable or used for overcasting). Most of the studies only assess single-unit restorations. The biomechanical behavior of single- and multi-unit implant-supported prosthesis differs [16,17]. In addition, the number of completely edentulous patients seeking full-arch restorations has increased worldwide [18–20]. In addition to the passive fit, the location and magnitude of occlusal forces affect the quality and amount of stress transmitted to the system [21]. During masticatory activity, forces act in different directions on the implants and are transmitted to the peri-implant bone. In vitro studies have performed mechanical cycling to simulate masticatory function and to evaluate the interaction between detorque, stress and misfit [11,12,15]. Mechanical loading is an important methodology for evaluating biomechanical behavior and longevity of the implant-supported system since it may change the properties and characteristics of the materials [22]. This procedure is fundamental to assist professionals in choosing the material to be used clinically, not only based on a costeffective approach, but mainly regarding the biomechanical performance of such restorations. In vivo studies are very time-consuming and sometimes impossible to be performed owing to ethical problems. Regarding the influence of manufacturing procedures in obtaining passive frameworks and stress transmission to the osseointegrated system, the aim of this study was to evaluate the influence of casting and masticatory simulation on the marginal misfit and strain in multiple implant-supported prostheses manufactured with two cylinder types (calcinable and overcasted). Additionally, we investigated the correlation between misfit and strain generated in multiple implant-support prostheses. The hypotheses tested were: (1) calcinable cylinders present higher misfit than overcasted ones, and (2) calcinable cylinders present higher strain than overcasted ones. 2. Materials and methods 2.1. Prosthetic framework and model fabrication A steel master model was manufactured according to each clinical situation evaluated in this study: a partially edentulous area to be rehabilitated with a three-unit screw retained fixed dental prosthesis (FDP) of lower first pre-molar to first molar retained by two implants; and a completely-edentulous area to be rehabilitated with a mandibular screw retained full-arch fixed dental prosthesis (FAFDP), retained by five implants. Dental implant abutment analogs with platform diameter of 4.1 mm (Mini-Abutment Analogs, SIN — Sistema de Implante, Sao Paulo, Sao Paulo, Brazil) were fixed to it using transversal screws and designated as Pillar A and Pillar B (FDP), and Pillars A, B, C, D, E (FAFDP), from right to left (Fig. 1). Calcinable or overcasted abutment cylinders (SIN — Sistema de Implante, Sao Paulo, Sao Paulo, Brazil) were screwed on steel master model and master frameworks were waxed with a low-shrinkage acrylic resin (Duralay II−Reliance Dental Mfg. Co., Chicago, USA). The FDPs were fabricated with 3.5 × 4.0-mm connector cross-section and the

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FAFDP with 5-mm bar cross-section and 15-mm bilateral cantilever extension. The master frameworks were impressed (Flexitime Easy Putty Correct Flow — Heraeus-Kulzer, Hanau, Germany) and duplicated to obtain forty frameworks that were divided in four groups (n = 10) according to the cylinder type (calcinable or overcasted) and prosthesis design (FDP or FAFDP). The fit of the waxed frameworks was evaluated on the master model by single-screw test [12,23–24]. All waxed frameworks were sectioned and reunited with a low-shrinkage acrylic resin to verify the full fit on the master model according to single-screw test [12]. The steel master model was impressed with silicone (Zeta Labor; Zhermack, São Paulo, SP, Brazil) to obtain a silicone matrix for stone cast models fabrication with the same dimensions of master model. One stone cast model with the same dimensions as the master model was obtained for each prosthesis type using modified conical dental implant analogs (Fig. 2) from master waxing framework. The master waxed frameworks were screwed to the modified dental implant analogs (Fig. 2), the set was positioned perpendicular to the ground, with a parallelometer, and 9 mm of the analog stem was included in a silicone matrix filled with type IV dental stone cast (Durone IV — Dentsply, New York, USA) (Fig. 3). Type IV dental stone cast was manipulated according to manufacturer recommendation (19 mL of water and 100 g of powder for 30 s in vaccum). The models were acquired before framework casting in order to verify the misfit related to the casting procedures. Afterwards, the models were fabricated, the frameworks were invested (Gilvest HS — BK Giulini, Ludwigshafen, Germany), and casted or overcasted in CoCr alloy (Starloy C — Degudent, Dentsply, HanauWolfgang, Germany) using the lost-wax casting technique. No section or welding procedure was applied to evaluate the effect of the prosthetic cylinder in obtaining of frameworks with one-piece casting technique. After casting, the frameworks were blasted with 100 μm aluminum oxide particles at 0.55 MPa pressure followed by finishing and polishing with tungsten carbide drills at low speed. These procedures are required to remove the remaining investing material adhered to the surface of the casted framework. The metallic strap region of the cylinder was protected from such procedure to not compromise the fit of the cylinder. Therefore, these procedures neither affect the masticatory simulation nor the misfit levels of the frameworks when subjected to mechanical cycles. 2.2. Marginal misfit evaluation The marginal misfit evaluations were performed according to the single-screw test [12,23,24], which proposes the marginal misfit reading of the loop presented while the screw of the opposite pillar is tightened. The pillar A prosthetic screws of the FDP and FAFDP samples were tightened with 10 N cm torque using a 0.1 N cm precision digital torque meter (Torque Meter TQ-8800 — Lutron, Taipei, Taiwan) and then the misfit measurements were taken on the buccal and lingual gap sides

Fig. 1. Steel master model — FDP (A), FAFDP (B).

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2.3. Strain gauge analysis

Fig. 2. Conventional mini abutment analog (A); Modified mini abutment analog: external (B) and internal (C) surface.

of pillar B (FDP) and pillars C and E (FAFDP) [12]. Subsequently, the pillar A prosthetic screw was released, and the opposite-end screw was tightened with a torque of 10 N cm (pillar B of FDP and pillar E of FAFDP). Then, marginal misfit readings were performed on buccal and lingual gap sides of pillar A (FDP) and pillars C and A (FAFDP) [12]. All misfit readings were performed on the same stone cast model. The measurements were performed following the right-to-left sequence and then the left-to-right sequence for both designs (FDP and FAFDP). The procedure was done on both framework extremities and an average value was obtained for each framework. All measurements were completed in diametrically opposite positions, using a 1.0 μm precision microscope and 120× magnification (VMM-100-BT — Walter UHL, Asslar, Germany) equipped with a digital camera (KC-512NT — Kodo BR Eletronics Ltd., Sao Paulo, Brazil) and analyzer unit (QC 220-HH Quadra-Check 200 — Metronics Inc., Bedford, USA). The observations were made twice: before (initial misfit) and after (final misfit) the masticatory simulation, by a calibrated examiner (intraclass correlation coefficient = 0.997).

The strain gauge analysis consists in used electrical resistors (strain gauges) bonded to the surface of objects, which under tensile or compression forces, change their resistive potential [25]. The resulting electrical current is measured by a Wheatstone bridge configuration associated with a measuring amplifier [25], which allows the quantitative analysis of the variables studied. In this study, the strain was evaluated using strain gauge analysis before (initial) and after (final) masticatory simulation. Modified conical dental implant abutment analogs were used for strain gauge positioning. The modified abutment analog is a replica of the conventional analog, machined in titanium with an extended stem (18 mm) and inner hollow surface (Fig. 2). The extended stem provided larger surface for strain gauge bonding, and the inner hollow granted a more accurate measurement of the elastic deformation. One strain gauge (PA-06-060-BG-350 L — Excel Sensores Ltd., Embu, Sao Paulo, Brazil) was bonded parallel to the long axis of the modified analog with cyanoacrylate-based glue (Loctite Super Bonder, Henkel, Düsseldorf, Germany) (Fig. 3A,B). The strain gauge was positioned 10 mm from the lower portion of the analog. The electric circuit was mounted in a 1/4 Wheatstone bridge (Fig. 3C,D) with temperature control. The average strain value was obtained for each sample with a 5-minute interval beginning 3 min after clamping torque was applied. The mean strain of each group was obtained by the average strain values presented for all frameworks that group. The strain gauge analysis was performed using ADS 2000 equipment (Lynx Tecnologia Eletronica Ltd., Sao Paulo, Brazil), with data processed by a specific software (AqAnalysis 2000, Lynx Tecnologia Eletrônica Ltd., Sao Paulo, Brazil). All strains measurements were performed on the same stone cast model. To standardize the readings, the strain gauges were set to zero before the fixation of each framework [26]. This procedure also allowed one to verify that there was no plastic deformation on modified analogs. Tightening and loosening protocol to fix the frameworks was performed following a predetermined sequence (A-B for the FDP and A-E-B-D-C for FAFDP) [12,27]. 2.4. Masticatory simulation After the initial analysis, the screws were tightened with 10 N cm torque using a digital torque meter, and the forty specimens were

Fig. 3. Positioning of strain gauges — FDP (A), FAFDP (B); Electric circuit in ¼ Wheatstone bridge — FDP (C), FAFDP (D).

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submitted to 106 mechanical cycles [28] (Mechanical Fatigue Simulator ERIOS, model ER11000 Plus, Sao Paulo, Brazil), with 2 Hz frequency [29] and a 280 N compressive load [30] with a 30° angle to the analog long axis [29]. The pistons were placed on the occlusal surface of Pillar B (FDP) and Pillar E (FAFDP). The specimens remained immersed in artificial saliva (1.5 mM Ca, 3.0 mM P, 20.0 mM NaHCO3, pH 7.0) [11,12,31], at 37 °C during the experimental test. 2.5. Statistical analysis

3. Results Table 1 shows the mean values of marginal misfit for the FDP and FAFDP groups. No statistically significant difference was observed in marginal misfit of calcinable and overcasted frameworks, regardless of the time and prosthesis design (p N 0.05). There was no statistically significant difference in marginal misfit before and after the masticatory simulation in all evaluated groups (p N 0.05). Table 2 shows the mean strain values of FDP and FAFDP groups, as well as the p-value. The overcasted frameworks showed higher strain than the calcinable ones, regardless of the evaluated time. No difference was observed in initial and final strains (p N 0.05). No correlation was observed between strain and misfit (r = 0.24; p N 0.05). 4. Discussion Despite recent advances in implant dentistry, most clinical methods for evaluating the misfit are empirical and based on subjective examiner analysis. Under laboratory conditions, clinically acceptable frameworks may present considerable misfit [32]. Therefore, in vitro studies are essential to establish prerogatives regarding framework fit and assess any technique or manufacturing material prior to clinical use [33], supporting best option determination based on cost-effective and biomechanical aspects. The evaluation of framework distortion caused by cylinders casting procedure shows no difference in the misfit, regardless of the prosthesis type (FDP or FAFDP). Therefore, the hypothesis that calcinable cylinders present higher misfit than overcasted ones was rejected. These findings confront previous results that demonstrated better fit of overcasted frameworks than calcinable ones [11,14]. Nonetheless, these studies evaluated single-unit prostheses, which suggest a different behavior when it comes to multiple-unit prostheses. Furthermore, the results of this study may have been affected by misfit measurement on modified analogs. Evaluation of misfit on a model with conical dental implant abutment could result in different findings since the platform settlement of these components differs (Fig. 4). The manufacturing of partial or full-arch fixed prostheses requires the union of multiple retainers forming a single body. During casting, Table 1 Mean marginal misfit values (μm) for FDP and FAFDP according to cylinder type and time interval. Prosthesis design

FDP FAFDP

Table 2 Mean strain values (μstrain) in FDP and FAFDP according to cylinder type and time interval. Prosthesis design

Cylinder

FDP

Calcinable Overcasted p-value Calcinable Overcasted p-value

FAFDP

All data were submitted to 2-way analysis of variance (ANOVA) and Tukey's HSD test (α = 0.05) using Statistica (Statsoft South America − StatSoft Inc. 2012, version 11, Tulsa, USA). Correlation between marginal misfit and strain was performed using Pearson correlation test (α = 0.05).

Cylinder

Calcinable Overcasted Calcinable Overcasted

Time Initial

Final

54.80 (21.63) 57.93 (22.79) 178.08 (94.08) 375.51 (164.54)

53.05 (19.02) 57.53 (21.98) 161.83 (80.99) 356.74 (162.65)

No statistical difference was observed between cylinder types and evaluation time within each prosthesis design according to ANOVA (α = 0.05).

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Time

p-value

Initial

Final

243.31 (95.69) Ba 424.64 (109.12) Aa 0.0047 255.42 (103.93) Ba 409.46 (169.62) Aa 0.0476

284.83 (119.42) Ba 513.66 (120.45) Aa 0.0004 245.14 (107.33) Ba 443.33 (146.14) Aa 0.0115

0.8391 0.2978 0.9983 0.9425

Means followed by same letters (capital — column, minor — line) indicate no statistical difference according ANOVA/Tukey tests (α = 0.05) for each prosthesis design.

each cylinder can be submitted to distortion in many directions. Since multiple retainers connected to each other affect the fit of the framework [34], each casted piece may present different levels of fit. In the case of single-unit prostheses each cylinder is casted separately, thus the distortion can have less influence on frameworks' final fit. In single-unit prostheses, accuracy of the anti-rotational system and metal strap are crucial factors to obtain fit. In these cases, the benefits provided by the overcasted components are more evident due to better reproduction of the edges and angles of the anti-rotational polygon as well as the overall surface of the metal strap, which ensures better settlement and stability of the framework [11]. However, in multiple-unit prostheses, the presence of the pre-fabricated metallic strap appears to be less relevant due to the absence of the anti-rotational polygon and the wider magnitude of the distortions that the piece may be submitted. Despite the pre-fabricated condition, there is still a chance that the overcasted component will distort due to the overcasting procedure [14], polishing [35], porcelain firing [14], or a combination of those [14]. Therefore, after the casting process, pre-fabricated and calcinable components can present similar behavior. Regardless of the type of cylinder, the misfit observed after casting (initial misfit) suggests that the greater the number of retainers, the greater the magnitude of the distortion. These findings emphasize the difficulty in connecting multiple elements with minimum misfit [36, 37]. According to previous studies [1,5,38], the framework presents passive fit when values between 10–150 μm are observed. Thus, the FDP group misfit can be considered clinically acceptable, with average value similar to the 72 μm previously reported [10] for one-piece frameworks casted in CoCr alloy. The FAFDP groups, however, show higher values than those reported as clinically acceptable. When microscopically inspected, full-arch prostheses considered clinically acceptable can exhibit gaps of 170 [39] to 275 μm [3]. This suggests that, for this type of prosthesis, methods such as electrical discharge machining [9,23], alternative imprinting techniques [36], welding [40], and the use of CAD-CAM systems [41] should be preferred. The values measured in this study were determined by the single screw test and can be considered, therefore, representative of the overall casting distortion of the piece. This method allows measurement of the maximum gap presented in the framework when each screw is tightened, causing an exacerbation of the measured misfit. The evaluation of the marginal misfit by single screw test appears to be more rigorous than the assessment made when all the framework screws are tightened. This method of analysis was chosen because the marginal misfit can be masked when all the framework screws are tightened, even in the presence of a misfit value previously known (simulated) [7]. No correlation was observed between marginal misfit and strain on the system. These results are consistent with the previous report that showed no correlation between these variables [42], suggesting that the distortion from the casting process is only one of the factors that can influence the strain on the set. However, this variable alone does not determine the characteristic of force distribution among framework, dental implants, and abutments. In addition, in the present study only

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Fig. 4. Platform settlement of the modified analogs and conical dental implant abutment.

vertical misfit was measured, while the strain and distortion are of three-dimensional nature. This factor may have contributed to nonobservance of linearity between misfit and strain. In future studies, the tridimensional misfit analysis may contribute to elucidate this relationship. The strain evaluation showed that overcasted frameworks present higher strain at all times despite the prosthesis design. Thus, the hypothesis that calcinable presents higher strain was rejected. These findings can be attributed to the metallic pre-fabricated strap for juxtaposition to the abutment, present in the overcasted cylinders. This strap implies greater contact between the seating surface of the screw head and the internal portion of the cylinder [14]. This suggests that after the torque was applied, these screws presented better seating, promoting a more rigid fixation of the system, thus, generating higher levels of strain on the analogs. In the case of calcinable frameworks, the strain is probably concentrated in the neck of retention screw, which may not be properly seated due to imperfections of the casting, preventing it from stretching enough to promote a satisfactory fixation system and thus generating a lower strain distribution for the modified analogs. Even under adequate fit situation, frameworks are subjected to some degree of strain [33]. The strain is inevitable due to the application of the clamping torque of the frameworks [33]. This report supports the hypothesis that the settling of the screws in the inner portion of the cylinder can influence the stress transmitted to the system, explaining the higher levels of strain presented by the cylinders with pre-fabricated metallic strap. Moreover, according to Frosts' classification [43], the measured strain values can be considered suited to the adaptive stage of bone physiology. Therefore, bone tissue would be susceptible to physiological remodeling without compromising the osseointegration. The use of modified analogs can be considered a favorable and reliable technique for application in strain gauge analysis, allowing the simulation of the strains transmitted to implant − abutment set. Most studies recommend bonding the strain gauges on a framework with epoxy resin. Since strain gauges have the limitation of only reading the strain in the area that is bonded, these procedures may have some disadvantages. When the strain gauges are bonded to the framework, the study is limited to the use of a single framework for all analyses (n = 1) or the limitation of bonding the strain gauges to each assessed framework, which may introduce bias in the results due to different positioning. Moreover, the metallic framework is massive and cannot present a strain similar to those of analogs/implants, leading to an inadequate measurement of strain. Epoxy resin is a resilient material and poor electrical conductor, which may compromise the transmission signs measured by strain gauges, since these are electrical resistors. Furthermore, its elasticity modulus is similar only to cancellous bone, so that outcome may be influenced by the lack of strength and stiffness of the cortical bone. The modified analog application has as advantage the use of a single model to perform the analysis, which avoids variation of the location where the strain gauges are bonded and allows the evaluation of many frameworks, thereby ensuring the accuracy of the analyses. Additionally, this technique avoids the use of resilient materials that may lead to underestimate the strain levels.

Framework dynamic loading is also important to evaluate the influence of masticatory process on the analyzed variables. Functional loading can lead to changes in the mating surfaces of the components [44, 45]. The changes may occur due to the wear at the component interface with the mating surface, which may modify the levels of misfit or strain initially observed. We expected that such wear could increase the fit of the implant-supported system with consequent reduction of the strain. However, the masticatory simulation had no influence on the misfit and strain of the groups evaluated. These results corroborate with previous studies [45–47], in which no changes were observed in the vertical misfit after mechanical cycling. This shows that dynamic loading does not necessarily cause changes on the mating surfaces of the components. Herein, loading conditions may have affected our results. As the load was applied asymmetrically (i.e. only on the occlusal surface of one of the pillars), the cycling force and period may not have been sufficient to promote changes in mating surfaces. There is no study that applied bilateral load under simulated masticatory condition. Clinically, the asymmetric load condition is appropriate as the foodstuff is located just at the working side in the beginning of masticatory cycle. In turn, there is no occlusal contact on the nonworking side [48]. The load application was performed at the molar region as it has the greatest loading force support into the oral cavity [49]. An oblique load was selected to mimic the masticatory cycles. Mechanical loading parameters (280 N and 2 Hz) were estimated from the assumption that an individual performs three episodes of masticatory movements per day. Each movement accounts 15 min in duration at a frequency of 60 cycles per minute, which is equivalent to 2700 cycles per day and approximately 1 million of cycles per year [11,28]. Although the parameters applied attempt to simulate clinical use [28], the in vitro masticatory simulation is still limited. In vivo condition subjects the prosthesis to eccentric forces of different magnitudes and directions. This could lead to accelerated change in matting surface of the components that could change the misfit and strain values. Additional studies simulating longer periods of clinical use may help to clarify the influence of dynamic loading on the analyzed variables. 5. Conclusions Based on the results obtained in the present study it can be concluded that: • The marginal misfit value in the overcasted full-arch frameworks was higher than clinical acceptable data. It proved that overcasted method is not an ideal method for full-arch prosthesis. • Overcasted frameworks present higher strain upon the implantsupported system. • No correlation between vertical marginal misfit and strain was noted on the implant-supported system. • The 1-year clinical masticatory simulation did not influence the marginal misfit and strain of the multiple-unit prostheses. Further studies simulating greater period of clinical use and different load forces are warranted.

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