Abstract

A two-dimensional finite element analysis was used to evaluate the effects of implant length and diameter on the stress distribution of a single-implant supported crown and the strain distribution of its surrounding bone prior to and after the phase of osseointegration. The effect of length was investigated using implants with a diameter of 3.75 mm and lengths of 8 mm, 10 mm, 12 mm, and 14 mm. The effect of diameter was investigated using implants with a length of 10 mm and diameters of 3 mm, 3.75 mm, 4.5 mm, and 5mm. The phase prior to osseointegration was simulated by assuming a coefficient of friction for the interface between the implant and the surrounding bone, while the phase after osseointegration was simulated by assuming a fixed bond on the interface between the implant and the surrounding bone. The FEA results indicated a tendency towards stress reduction on the implant, both prior to and after osseointegration, when the length was increased. However, the calculated stresses on the implant were lower after the phase of osseointegration. Although no specific correlation could be seen regarding the influence of implant diameter, the calculated stresses on the implant were again lower after the phase of osseointegration. For all these cases, the maximum stress concentration occurred at the abutment-implant interface. As far as bone tissue was concerned, there was a tendency towards strain reduction, before and after osseointegration, when the length of the implant was increased from 10 mm up to 14 mm. This tendency was not manifested for the range of 8 to 10 mm. The effect of implant diameter on bone tissue was not clear. It appears that implants of a diameter more than 5 mm are not preferable for immediate loading. Finally, it seems that cortical bone is not influenced by the phase of osseointegration, while trabecular bone is highly affected.

Introduction

The concept of osseointegration is one of a dynamic biological healing tissue process, during which the initial acute trauma results in a direct functional and structural connection between ordered living bone and the surface of a load-bearing implant.1,3 

A variety of factors control osseointegration, inadequate control of which compromises the stable anchorage of the implant to the bone tissue.4,5 These factors can be categorized as surgical (primary stability and surgical technique), tissular (quality and quantity of bone, healing, remodeling), implantological (macrostructure, microstructure, and dimensions), and finally occlusal/mechanical (forces and prosthetic design).6,7 

Until recently it was thought that the crucial variable for a therapeutically successful outcome was the no-loading healing period of the dental implant (delayed loading). For osseointegration to be properly accomplished, a stress-free environment should be established and the implant should be out of any kind of occlusion. The rationale behind this hypothesis was that mechanical factors interfere with the bone-implant interface, inducing micromovement, which prevents the bone deposition.8,9 

Until now, the immediate loading protocol has not been well investigated. More and wider randomized controlled studies are needed in order for the case for immediate loading to be evidence based.10 Initially, immediate loading of dental implants in the 1960s resulted in fibrous encapsulation, mobility, and, finally, loss of implants. In later studies, when immediate loading started to be governed by strict protocols, it was found to be effective.11 Ledermann12 published the first case report of a successful screw-type dental implant, which was loaded within 72 hours after the implant placement. Since then, immediate loading has been applied in cases of both full and partial edentulism.13,15 In these cases it has often demonstrated survival rates, predictability, and direct bone-to-implant contact comparable to conventionally loaded implants.16,19 

It seems that the success of immediate loading procedures is a matter of appropriate patient selection, loading conditions, implant (geometry and surface), and prosthesis design.7,20,22 However, due to the lack of understanding of the relationship between interface biomechanics and bone biology, it is difficult to predicatively comment on any of the previous factors.

Optimizing implant geometry in order to maintain a beneficial stress level at the bone-implant interface is a complex issue.23 There are many studies analyzing the stress distribution generated in the surrounding bone in order to arrive at the optimum shape and thread design.24,25 However, the macroscopic features of dental implants, such as length and diameter, have never been investigated with reference to immediate loading as parameters that could provide a healthy stress level at the bone-implant interface assuring a normal healing period during osseointegration.

The purpose of the present study is to compare the calculated stresses and strains on a single dental implant and its surrounding bone for different implant lengths and diameters prior to and after the phase of osseointegration. A qualitative evaluation of the results provided useful information about the appropriate selection of implants in terms of geometry according to the timing of loading.

Materials and Methods

In the present study, a two-dimensional finite elements analysis was preferred to a three-dimensional one because the results are equally accurate in a study limited to qualitative rather than quantitative evaluation of the cases.26 The whole modeling and solution process was performed using the ANSYS software program.

An initial model of a single implant-supported crown substituting a lower second premolar was developed with reference to a posterior cross-sectional area of both cortical and trabecular bone. The selected mandibular bone was replicated as a double-layered block, with dimensions vertical (yy) 18.75 mm and horizontal (xx) 11.25 mm. Trabecular bone was located in the lower part of this block and was clearly distinguished from cortical bone by attributing different materials properties, meaning that cortical and trabecular bone were not modeled as a unit. The length and diameter of the implant were assumed to be L = 10 mm and D = 3.75 mm. The implant threads were not modeled. The abutment length was defined at 4 mm in the yy direction and base and crest width were defined at 5.95 mm and 3.65 mm, respectively. The crown was modeled as a second premolar of the mandible (Figure 1). Since the primary concern of the study was to arrive at a qualitative comparison between the stress/strain values on the implant and its surrounding bone, the entire superstructure between the abutment and the crown was modeled as a homogeneous structure, ignoring, as was done in previous studies, the cement thickness and the metal framework.27,28 Several other studies have not been able to demonstrate any significant differences in the force absorption quotients of gold, porcelain, or resin prostheses.29,30 Thus, to preserve simplicity and to reduce computational time, it was assumed that the entire material properties of the superstructure would not have a significant effect on our results.

Figure 1.

Geometry of the initial model used in this study.

Figure 1.

Geometry of the initial model used in this study.

Subsequently, the initial model was modified in order to study the effects of implant length and diameter before and after osseointegration. Although the model contained three parameters—length, diameter, and the phase of osseointegration—the latter was not studied individually but always in combination with either the length or diameter of the implant. The finite element mesh of the initial model, consisting of 1707 nodes and 507 elements, was varied in line with modifications made to the model. The selected types of elements were target 169, contact 171, and plane 82. Constraints were applied at the outer surface of the bone in order to prevent free body motion. The loading condition was performed by the application of a static vertical force of 118.2 N to every node of the cusp, simulating the oblique direction of masticatory forces.31 The relative mechanical properties were attributed according to the materials and were selected based on previously published studies using finite element analysis (FEA).32,33 The material properties required for the structural analysis were Young's modulus and Poisson's ratio (Table 1).

Table 1.

Mechanical properties of the materials involved in this study

Mechanical properties of the materials involved in this study
Mechanical properties of the materials involved in this study

Implant length effect prior to and after osseointegration

Considering the length of the implant and the phase of osseointegration as independent variables, the implant diameter of the initial model was kept stable (3.75 mm). The influence of implant length was simulated using implants with lengths of 8 mm, 10 mm, 12 mm, and 14 mm. The influence of the phase of osseointegration was simulated assuming a different type of bond at the interface between bone and implant. Prior to osseointegration, the bone-implant interface was characterized by sliding of the entire surfaces, using different assumed coefficients of friction for cortical and trabecular bone.34,35 After the osseointegration, the contact surfaces of implant and surrounding bone were always bonded, with no sliding permitted (fixed bond). The influence of implant length prior to and after osseointegration was simulated by eight finite element models (models 1–8), as shown in Table 2.

Table 2.

Finite element models constructed for the investigation of implant length prior to and after osseointegration (Models 1–8)

Finite element models constructed for the investigation of implant length prior to and after osseointegration (Models 1–8)
Finite element models constructed for the investigation of implant length prior to and after osseointegration (Models 1–8)

Implant diameter effect prior to and after osseointegration

Considering the implant diameter and the phase of osseointegration as independent variables, the implant length of the initial model was kept stable (10 mm). The influence of diameter size was simulated using implants with diameters of 3 mm, 3.75 mm, 4.5 mm, and 5 mm. The influence of the phase of osseointegration was simulated as previously reported. The influence of implant diameter prior to and after osseointegration was also simulated by 8 additional finite element models (models 9–16), as shown in Table 3.

Table 3.

Finite element models constructed for the investigation of implant diameter prior to and after osseointegration (Models 9–16)

Finite element models constructed for the investigation of implant diameter prior to and after osseointegration (Models 9–16)
Finite element models constructed for the investigation of implant diameter prior to and after osseointegration (Models 9–16)

Results

The present study provides the stress/strain distribution on both the surrounding bone (cortical and trabecular) and implant. The influence of implant length and diameter prior to and after osseointegration was produced by evaluating the exhibited maximum von Mises stress values for the implant and the maximum von Mises strain values for the surrounding bone. Both the calculated stresses and strains are presented as a colored band, each color representing a particular stress/strain level in the deformed state. The von Mises stress and strain values for each model were compared with a reference model, in order to compare the effects of implant length and diameter qualitatively prior to and after osseointegration. The standard model being taken as the initial model prior to osseointegration (Model 2: L = 10 mm, D = 3.75 mm, prior to the osseointegration). The resulting values were computed as a percentage of the relative stress of the value for the reference model.

Implant length effect prior to and after osseointegration

Figures 2a through d present the stress state of the implant, while Figures 2e through h present the strain state of surrounding bone produced by finite element analysis of Models 1 through 4, respectively, for the same diameter but different lengths loaded during the healing phase. Table 4 shows the maximum von Mises stress and strain values for every implant length on implant and cortical/trabecular bone, respectively. The stress and strain distribution on the implant and peri-implant bone tissue of Models 5 through 8 is presented in Figures 3a through d and Figures 3e through h, respectively, for every implant length after the healing phase of osseointegration. Table 5 shows the maximum von Mises stress and strain values obtained for every model, after the phase of osseointegration.

Figure 2.

Maximum von Mises stresses and strains on implant and bone tissue respectively for the finite element Models 1 through 4.

Figure 2.

Maximum von Mises stresses and strains on implant and bone tissue respectively for the finite element Models 1 through 4.

Table 4.

Maximum von Mises stress and strain on implant and cortical/trabecular bone, respectively, prior to osseointegration (Models 1–4)

Maximum von Mises stress and strain on implant and cortical/trabecular bone, respectively, prior to osseointegration (Models 1–4)
Maximum von Mises stress and strain on implant and cortical/trabecular bone, respectively, prior to osseointegration (Models 1–4)
Figure 3.

Maximum von Mises stresses and strains on implant and bone tissue respectively for the finite element Models 5 through 8.

Figure 3.

Maximum von Mises stresses and strains on implant and bone tissue respectively for the finite element Models 5 through 8.

Table 5.

Maximum von Mises stress and strain on implant and cortical/trabecular bone, respectively, after osseointegration (Models 5–8)

Maximum von Mises stress and strain on implant and cortical/trabecular bone, respectively, after osseointegration (Models 5–8)
Maximum von Mises stress and strain on implant and cortical/trabecular bone, respectively, after osseointegration (Models 5–8)

Figures 2a through d and 3a through d show that the areas where maximum stress was produced appeared at the abutment-implant interface. The distribution of the von Mises stresses in the implant is similar for all the models both prior to and after osseointegration. Moreover, the calculated stress values in Tables 4 and 5 reveal that there was a tendency towards reduced maximum stress values in the implant with increasing implant length, prior to and after osseointegration. The plotting of relative stress (in terms of percentages of those in the reference model) on the implant against implant length for both osseointegration phases is shown in Figure 4. More specifically, the relative stress prior to osseointegration showed an increase of 4% when a shorter implant was used while use of longer implants (12 mm, 14 mm) led to reductions of 6.8% and 18.4%, respectively. After osseointegration, the use of short implants (8 mm, 10 mm) resulted in 6.8% and 11.8% stress decreases, respectively. Longer implants (12 mm, 14 mm) resulted in stress reductions of about 18.4% and 30.1%, respectively. All the maximum von Mises stresses on the implant for each implant length prior to osseointegration were higher than the measured von Mises stresses after osseointegration. Furthermore, the largest reduction was obtained for 14-mm implants for both phases.

Figures 4

and 5. Figure 4.  Relative stress (in percent) on implant with implant length for both osseointegration phases. Figure5. Relative strain (in percent) on trabecular and cortical bone with implant length for both osseointegration phases.

Figures 4

and 5. Figure 4.  Relative stress (in percent) on implant with implant length for both osseointegration phases. Figure5. Relative strain (in percent) on trabecular and cortical bone with implant length for both osseointegration phases.

The maximum developed strains on peri-implant bone tissue were found at the interface of cortical-trabecular bone, before and after the healing phase. Prior to the osseointegration, the strain distribution pattern inside the bony socket presented a gradual widening when the length of the implant was increased, while after osseointegration the strain distribution pattern was similar for all the models examined. Moreover, there was a similar tendency, for both trabecular and cortical bone, of strain decreasing when longer implants (12 mm, 14 mm) were used, for either phase of healing. In contrast, no difference in the strain values for both bone structures appeared when short (8 mm, 10 mm) implants were analyzed, for each healing phase. The plot of relative strain on bone tissue (expressed in percentages of the reference model) with implant length for both osseointegration phases is shown in Figure 5.

Prior to osseointegration, loading of the implants with lengths of 12 mm and 14 mm led to a relative strain reduction of 7.8% and 14.7% on the trabecular bone, while the reduction reached 58.9% and 61.6% in the cortical bone for the same implants. After the osseointegration, the obtained reduction for same implant lengths was 38.4% and 41.8% for the trabecular bone and 58.8% and 61% for the cortical bone, respectively. The highest reduction was obtained for the 14-mm implant for both healing phases. After the osseointegration, the maximum von Mises strain values for each implant length were higher for the cortical bone than the obtained strain values prior to osseointegration. The opposite was the case for the trabecular bone. It should also be noted that the difference in the calculated relative strain values for cortical bone was about 0.6%, while the difference in the obtained relative values for trabecular bone were 30% to 40%.

Implant diameter effect prior to and after osseointegration

Figures 6a through d and Figures 6e through h show the stress and strain field on implant and peri-implant bone for Models 9 through 12, respectively, due to the effect of implant diameter prior to osseointegration. The maximum von Mises values are presented in Table 6. The stress/strain patterns in the investigated structures caused by the variation of implant diameter after osseointegration (Models 13–16) are presented in Figures 7a through d and Figures 7e through h, respectively, while the maximum values obtained for the observed stress and strain on implant and bone tissue, respectively, are shown in Table 7.

Figure 6.

Maximum von Mises stresses and strains on implant and bone tissue respectively for the finite element Models 9 through 12.

Figure 6.

Maximum von Mises stresses and strains on implant and bone tissue respectively for the finite element Models 9 through 12.

Table 6.

Maximum von Mises stress and strain on implant and cortical/trabecular bone, respectively, prior to osseointegration (Models 9–12)

Maximum von Mises stress and strain on implant and cortical/trabecular bone, respectively, prior to osseointegration (Models 9–12)
Maximum von Mises stress and strain on implant and cortical/trabecular bone, respectively, prior to osseointegration (Models 9–12)
Figure 7.

Maximum von Mises stresses and strains on implant and bone tissue respectively for the finite element Models 13 through 16.

Figure 7.

Maximum von Mises stresses and strains on implant and bone tissue respectively for the finite element Models 13 through 16.

Table 7.

Maximum von Mises stress and strain on implant and cortical/trabecular bone, respectively, after osseointegration (Models 13–16)

Maximum von Mises stress and strain on implant and cortical/trabecular bone, respectively, after osseointegration (Models 13–16)
Maximum von Mises stress and strain on implant and cortical/trabecular bone, respectively, after osseointegration (Models 13–16)

According to Figures 6a through d and 7a through d, no difference in the developed stress field on implant structure was observed for the phase prior to and after osseointegration. The finite element analysis shows that the variation in diameter had a varying effect on stress/strain distribution, significantly different from the pattern produced by varying length. The relative stress (expressed in percentages of the reference model) on the implant, plotted against implant diameter, is shown in Figure 8. There was a tendency towards decreased stress on the implant with progressively larger diameter implants when the implants were loaded during the healing phase. The maximum reduction was obtained for the 5-mm–diameter implant (8.2%). On the contrary, when the implants were loaded after the osseointegration, the maximum von Mises stress pattern did not behave similarly with increasing diameter. Specifically, the least reduction was obtained for the 3.75-mm diameter implant, while the highest reduction occurred with the 4.5-mm diameter implant. However, the measured von Mises stress values for the implant were always lower compared with the measured values prior to osseointegration for each diameter.

Figures 8

and 9. Figure 8 . Relative stress (in percent) on implant with implant diameter for both osseointegration phases. Figure9. Relative strain (in percent) on trabecular and cortical bone with implant diameter for both osseointegration phases.

Figures 8

and 9. Figure 8 . Relative stress (in percent) on implant with implant diameter for both osseointegration phases. Figure9. Relative strain (in percent) on trabecular and cortical bone with implant diameter for both osseointegration phases.

The stress pattern generated in peri-implant bone tissue was also similar for all the models investigated, with the maximum von Mises stresses concentrated in the area around the upper part of implant, on the cortical-trabecular interface. The relative strain (expressed in percentages of the reference model) on bone tissue plotted against implant diameter is shown in Figure 9. During the healing phase, the reduction of implant diameter to 3 mm resulted in a strain reduction of about 2% and 56.1% for the trabecular and cortical bone, respectively—although the most marked intraosseous strain effect occurred with an implant diameter of 4.5 mm. Here the reduction was about 6.5% for trabecular and 58.4% for cortical bone. Further increase in implant diameter to 5 mm caused increased stress on the bone tissue, 0.1% and 54.9% for the trabecular and cortical bone, respectively. After osseointegration, all the strain values obtained in trabecular bone for each implant diameter were lower than those calculated for the same implant diameter during the healing phase. The maximum difference was obtained for the 5-mm implant. The calculated strain values for cortical bone were higher than those calculated during the healing phase, except the value exhibited by the 5-mm implant, which was lower after the end of healing phase. At this point, it must be noted that the cortical bone exhibited small relative differences between the two phases (1%–4%), while the trabecular bone exhibited much higher relative differences (30%–40%).

Discussion

FEA allows the estimation of the stress/strain state of extremely geometrically complex systems such as the dental implant–bone system. The more detailed the representation of its structural integrity, the more reliable the numerical results obtained. Thus, the prediction of dental implant success36,37 is increased. However, as with every other theoretical analysis, there are limitations stemming from the inadequacy of accurately representing the detailed geometry of the bone and implant superstructure, the boundary conditions, and the material properties of the structures involved, especially at the bone-implant interface.38 Due to these inadequacies, a comparative evaluation of the numerical results under the same limitations is preferable. In the same way, a qualitative description of the biomechanical behavior of the whole system, rather than an attempt at a quantitative analysis, is also preferred.39 

Under immediate loading conditions, finite element modeling is difficult to replicate due to the complex time-dependent situation existing at the bone-implant interface.40 However, a coefficient of friction is assumed at the bone-implant interface, representing a specific moment during the healing phase. On the other hand, a fixed bond is assumed as representing full osseointegration. Since the implant design influences force transmission and the stress/strain concentration in peri-implant bone,41 both implant length and diameter have been extensively studied in scientific literature. The implant diameter and length are responsible for microstrains, stresses, and eventually for micromotions generated at the bone-implant interface.42 According to the differentiation hypothesis demonstrated by Frost,43 this induced local mechanical environment regulates the proliferation and differentiation of the osteoblasts responsible for the peri-implant bone tissue formation. This mechanical environment may be beneficial for the bone-implant interface, within certain limits. A threshold for tolerated micromotion has been identified beyond which bone deposition cannot be achieved. Micromotion of less than 30 microstrains (μɛ) at the implant-bone interface does not interfere with osteogenesis,44 while an even wider range (50 μɛ–100 μɛ) has also been reported as not being detrimental.45 Furthermore, there is a physiologic spectrum of microstrains (500 μɛ–3000 μɛ) that promotes mature bone formation, while higher peak strains result in immature bone mineral formation and a fibroblastic cell pattern.46 

The necessity for simplification and the reduction of risk in surgical protocol when there is inadequate bone volume has led to the use of short and/or narrow implants.47,48 A research-based re-evaluation of this has begun with the investigation of the biomechanical performance of implant dimensions at the bone-implant interface.

Implant length effect prior to and after osseointegration

Until now, implant length has not been considered a significant factor contributing to osseointegration, because the applied stress is distributed mainly on cortical bone rather than on the rest of bone-implant interface, independent of implant length.49 Furthermore, implant length seems also to be a weak contributing factor to primary stability.50 In 2006, Misch et al tried to find the connection rationale between the high failure rates of posterior-placed short dental implants with the hypothesis that implant length does not influence success rates. Increased crown height, high bite forces, and bone density are the factors that affect the implant-bone interface and not the implant length.51 This is why the posterior sites of the jaw have been avoided for the application of immediate loading.52 Also, there are studies suggesting that the implant length cannot be considered in isolation, but only in conjunction with the height of the mandibular cross-section when considering the effect on strain concentration around an implant.23,53,54 

The present study indicates that the strain distribution pattern is independent of increased implant length prior to and after osseointegration. The maximum von Mises strains are concentrated at the trabecular-cortical interface for all the models considered, while the induced strains in the remaining bone-implant interface are always lower. These results are comparable to those reported by Lum49 and Himmlova et al.31 

The literature contains no studies defining with clarity the relationship between implant length and success rates. It has been reported that increasing implant length affects success rates up to a limit,49 while other studies report that implant length does not significantly affect survival rates,55,57 yet other studies correlate short implants either with increased failures58,59 or with similar outcomes to those reported with longer implants.60,62 Renouard et al, trying to explore the high failure rates of short implants, revealed that the surgical protocol used for short implant insertion did not include factors such as the evaluation of the bone quality and the implant surface.63 

As far as concerns the impact of implant length on immediate loading protocols, the only available data come from clinical experience and limited human studies.64 However, these results indicate the use of implants longer than 10 mm, and some authors suggest the use of even longer implants, equal to or longer than 14 mm.65,67 Ottoni et al in a controlled study reported 10 failed implants in the experimental group (immediate loading), while the control group (conventionally delayed loading) produced only one failure when inserting implants of various lengths (10–15 mm) with a standard diameter (3.75 mm, 4.5 mm). No statistical significant correlation was found between length and the cumulative survival rates, while the failures were significantly correlated with the insertion torque.68 

Histologic and histomorphometric reports validated the formation of mineralized tissue and the establishment of osseointegration, by counting the direct bone-to-implant contact around short implants, retrieved from both animals and humans.69,72 Degidi et al, making biopsies on immediate loaded short implants (8 mm, 9.5 mm) retrieved from humans after short periods of function, revealed newly formed bone lamellae, while the extent of the bone-to-implant contact was about 60% to 70%.73,74 A comparative study of the evaluation of the bone-to-implant contact between nonsubmerged immediate loaded and submerged implants revealed a higher percentage of contact for the immediate loaded implants.75 Varying degrees of integration have been obtained from retrieved transitional implants by evaluating the removal torque values.76 

In the present study, the results obtained from the correlation between implant length and intraosseous strains are in line with the results obtained from clinical studies, suggesting that by increasing implant length, lower strain status is induced at the implant-bone interface. However, it seems that the use of implants shorter than 10 mm does not imply a less desirable strain status. The generation of decreasing maximum von Mises strains for each increase in implant length led to the suggestion that implants longer than 10 mm should be preferred for both phases of healing phase. All the investigated models, in both healing phases, showed the greatest reduction when using an implant with a length of 14 mm.

Furthermore, it seems that the cortical bone undergoes almost the same strain deformation during each healing phase. In contrast, the deformation in trabecular bone presents the higher difference between the two phases, by undergoing significantly higher deformation prior to osseointegration. So, it can be assumed that phase of osseointegration affects the strain distribution in trabecular bone, independently of the examined design parameters. Despite this fact, the generation of different degrees of deformation at the bone-implant interface may not similarly affect each osseointegration phase. This is an area requiring further investigation.

In regard to the analysis of stress on the implant, it should be noted that the bone-implant interface is an area of great importance for implant survival and success, notwithstanding the significance of the implant-abutment interface for the vitality of implant-supported superstructure. This interface is associated with complications generated in the system, jeopardizing its predictability.77,78 Applied loading develops a highly deformed state at implant-abutment interface. Exceeding the proportional limit due to stress concentration may lead to joint opening.79 Many factors contribute to the mechanical integration at the implant-abutment interface80,81 although there is no study concerning the effect of length on the stress field in the implant.

The present study confirms that maximum stress concentration under loading is found at the implant-abutment interface. Incremental increase in implant length causes a gradual reduction of maximum von Mises stress at the abutment-implant interface, something observed for both healing phases—although loading of the implant after the phase of osseointegration produces a lower stress state on the overall superstructure.

Implant diameter effect prior to and after osseointegration

Apart from standard diameter implants (3.75 mm, 4 mm), extensive use of narrow (3 mm, 3.3 mm) and wide (5–7 mm) implants is now being made and even “mini” implants (<2.7mm) are available.82 Wide implants are preferred in cases where immediate placement, bone engagement, and initial stability are indicated,83,84 although the disadvantages of overinstrumentation and heat generation need to be taken into account.83 Narrow implants are preferred in cases where less than 5 mm of space is available or transitional implants are indicated but carry with them the handicap of lower fracture resistance.85 It has been reported that a 3.3-mm–diameter implant is about 25% more prone to fracture than a 3.75-mm implant.47 

The biomechanical rational behind the use of wide implants is the alleviation of the increased stress generated at the neck of the implant.31 This is supported by biomechanical studies using FEA, which report that the stress distribution around the neck of narrow implants is not comparable to wide ones.86 Against this must be set clinical studies evaluating potential vertical alveolar bone loss that are not in line with the biomechanical results and indicate that the pattern of marginal bone loss seems not to be significantly correlated with the diameter of the implant and its load-bearing capacity.47,57,87,88 

The literature contains studies attempting to correlate the implant diameter with survival rates, but the results are often contradictory. No correlation between the two parameters is revealed from several studies,57,89,90 while others demonstrate that the increased implant diameter (5 mm) is correlated with high failure rates. The high failure rates of wide-diameter implants are often associated with the presurgical/surgical protocol and the tendency of the compromised areas to be confronted with wide “rescue” implants.91 Clinical studies evaluating narrow implants fail to specify their clinical performance with clarity, although the combination of narrow and short implants seems to demonstrate the highest failures.92,95 

Regarding an immediate loading protocol, no critical diameter of the immediate loaded implant has been proposed and the obtained data are limited. Only Degidi et al associated an average increased risk with implants exceeding 5.25 mm in diameter.96 Previously, Lorenzoni et al, in a 1-year follow-up case series-study, had reported the 100% survival rates of immediate loaded implants with diameters 3.85 mm to 5.5 mm located in the anterior maxilla.97 

In the present study, the pattern of strain distribution seems to be similar for every diameter selected, both prior to and after the healing phase. The area of maximum von Mises stress concentration is identical for all the selected models and is located around the upper part of the implant. This means that the pattern of the generated field is independent of increased diameter for both healing phases.

The correlation between implant diameter and maximum von Mises strain values shows a different pattern for each phase of osseointegration without, however, permitting clear conclusions. Nevertheless, it seems that implants with a diameter of 4.5 mm have the best biomechanical performance when they are loaded prior to the end of osseointegration. Further increase to 5 mm results in greater strain values indicating that wider implants are not always preferable when the immediate loading protocol is applied. The cortical bone around conventionally loaded implants, for every diameter, shows biomechanical behavior similar to cortical bone around the immediate loaded implants of the same diameter. In contrast, trabecular bone presents a high relative difference between the two phases, being highly deformed prior to osseointegration. With the completion of osseointegration, increasing diameter up to 5 mm results in a gradual reduction of the strain values, indicating that wide implants should be selected when the rest of the requirements are fulfilled. Implants with a reduced diameter of 3 mm have a similar biomechanical performance for both healing phases, despite the fact that the calculated strain values are higher for the phase prior to osseointegration.

As far as the analysis of stress on the implant is concerned, it should also be noted that the abutment-implant interface is the most deformed area under loading. It has been hypothesized that wide diameter implants would experience less deformation at the implant-abutment interface than standard-diameter implants because of an increase in platform surface area. However, studies have revealed that 3.75-mm implants and 6-mm implants demonstrate similar fatigue patterns under certain cycles for the same abutment-implant interface, while the fatigue pattern is differentiated according to the type of the interface.98 All the models in this study, independent of the variable considered, present the factors conducive to higher stresses at the abutment-implant interface location. No clear conclusions can be drawn, however, on the basis of this study about the correlation between the stress distribution on an implant and its diameter. It seems that prior to osseointegration the use of progressively longer implants is accompanied by stress reduction. However, implants with diameters of 3.75 mm and 4.5 mm have almost the same biomechanical performance. Whereas, after osseointegration, the best biomechanical performance is achieved by the 4.5-mm–diameter implant, but no specific tendency can be observed between strain variability and increasing diameter. Of course, this lack of specificity is in accordance with the present literature. However, it is clear that for every implant diameter, the maximum von Mises stress values are lower for loading after the phase of osseointegration.

Conclusions

The results of this study suggest that:

  • Increasing implant length from 10 mm to 14 mm results in strain reduction on bone tissue during immediate (prior to osseointegration) and delayed (after osseointegration) implant loading. However, it seems that implants shorter than 10 mm do not alter the strain field.

  • No specific correlation has been identified between implant diameter and strain distribution on bone tissue. Within a certain range of implant diameters, strain reduction is observed. It seems that wide implants (>5 mm) should not be selected for immediate loading protocols.

  • Delayed implant loading results in significant strain reduction on trabecular bone, while almost no difference is observed for cortical bone, compared with immediate implant loading. It seems that the phase of osseointegration does not have an impact on cortical bone, while it significantly affects trabecular bone, something independent of the design parameter examined.

  • Bone tissue around the upper part of implant experiences maximum stress concentration during immediate and delayed loading for every implant length and diameter.

  • The abutment-implant interface experiences the maximum stress concentration prior to and after osseointegration.

  • Increased implant length results in stress reduction on the implant in both immediate and delayed loading. For a given implant length, the stresses are lower after the phase of osseointegration.

  • No specific correlation has been identified between implant diameter and strain distribution on an implant, although it is clear that there is a stress reduction for conventionally delayed loaded implants compared to immediate loaded implants.

  • Well-controlled load experiments in vivo are necessary for the estimation of the time-dependent reaction of bone tissue around dental implants.

Acknowledgments

This research is supported by the RTD PENED-2001 Programme of the General Secretariat for Research and Technology of Greece (http://www.gsrt.gr).

References

References
1
Brånemark
,
P. I.
,
U.
Breine
,
R.
Adell
,
B. O.
Hansson
,
J.
Lindström
, and
R.
Olsson
.
Intraosseous anchorage of dental prostheses. I. Experimental studies.
Scan J Plastic Rec Surgery.
1969
.
3
:
81
100
.
2
Albrektsson
,
T.
Direct bone anchorage of dental implants.
J Prosthet Dent.
1983
.
50
:
255
261
.
3
Brånemark
,
P. I.
Introduction to osseointegration.
In: PI. Brånemark, G. Zarb, T. Alberktsson, (eds).
Tissue-Integrated Prostheses. Osseointegration in Clinical Dentistry.
Berlin, Germany: Quintessence Publishing Co. Inc.
1985
.
11
76
.
4
Joos
,
U.
,
H. P.
Weismann
,
T.
Svuwart
, and
U.
Meyer
.
Mineralization at the interface of implants.
Int J Oral Maxillofac Surg.
2006
.
35
:
783
790
.
5
Neukam
,
F. W.
and
T. F.
Flemmig
.
Local and systemic conditions potentially compromising osseointegration.
Clin Oral Implants Res.
2006
.
17
:
160
162
.
6
De Vicente Rondriguez
,
J. C.
Dealyed loading in implantology.
Rev Esp Cir Oral y Maxilofac.
2005
.
27
:
271
286
.
7
Gapski
,
R.
,
H. L.
Wanh
,
P.
Mascarenhas
, and
N. P.
Lang
.
Critical review of immediate implant loading.
Clin Oral Implants Res.
2003
.
14
:
515
527
.
8
Szmukler–Moncler
,
S.
,
H.
Salama
,
Y.
Reingewirtz
, and
J. H.
Dubruille
.
Timing of loading and effect of micromotion on bone–dental implant interface: review of experimental literature.
J Biomed Mater Res Appl Biomater.
1998
.
43
:
192
203
.
9
Szmukler-Moncler
,
S.
,
T.
Testori
, and
J. P.
Bernard
.
Etched implants: a comparative surface analysis of four implant systems.
J Biomed Mater Res B Appl Biomater.
2004
.
69
:
46
57
.
10
Nkenke
,
E.
and
M.
Fenner
.
Indications for immediate loading of implants and implant success.
Clin Oral Implants Res.
2006
.
17
:
19
34
.
11
Drago
,
C. J.
and
R. J.
Lazzara
.
Immediate occlusal loading of osseotite implants in mandibular edentulous patient: a prospective observational report with 18-month data.
J Prosthodont.
2006
.
15
:
187
194
.
12
Ledermann
,
P. D.
Stegprothetische Versorgung des zahnlosen Unterkiefers mit Hilfe von plasmabeschichteten Titanschraubenimplantaten.
Deutsche Zahnärztliche Zeitschrift.
1979
.
34
:
907
911
.
13
Ericsson
,
I.
,
H.
Nilson
,
T.
Lindh
,
K.
Nilner
, and
K.
Randow
.
Immediate functional loading of Branemark single tooth implants. An 18 months' clinical pilot follow-up study.
Clin Oral Implants Res.
2000
.
11
:
26
33
.
14
Cannizzaro
,
G.
and
M.
Leone
.
Restoration of partially edentulous patients using dental implants with a microtextured surface: a prospective comparison of delayed and immediate full occlusal loading.
Int J Oral Maxillofac Implants.
2003
.
18
:
512
522
.
15
Chiapasco
,
M.
,
S.
Abati
,
E.
Romeo
, and
G.
Vogel
.
Implant-retained mandibular overdentures with Branemark system MKII implants: a prospective comparative study between delayed and immediate loading.
Inl J Oral Maxillofac Implants.
2001
.
16
:
537
546
.
16
Romeo
,
E.
,
M.
Chiapasco
,
A.
Lazza
,
P.
Casentini
,
M.
Ghisolfi
,
M.
Iorio
, and
G.
Vogel
.
Implant-retained mandibular overdentures with ITI implants.
Cln Oral Implants Res.
2002
.
13
:
495
501
.
17
Nkenke
,
E.
,
B.
Lehner
, and
K.
Weinzierl
.
et al
.
Bone contact, growth, and density around immediately loaded implants in the mandible of mini pigs.
Clin Oral Implants Res.
2003
.
14
:
312
321
.
18
Testori
,
T.
,
M.
del Fabro
,
F.
Galli
,
L.
Francetti
,
S.
Taschieri
, and
R.
Weinstein
.
Immediate occlusal loading the same day or the day after implant placement: comparison of 2 different time frames in totally edentulous lower jaws.
J Oral Implantol.
2004
.
30
:
307
313
.
19
Degidi
,
M.
,
A.
Scarano
,
G.
Iezzi
, and
A.
Piattelli
.
Histologic analysis of an immediately loaded implant retrieved after 2 months.
J Oral Implantol.
2005
.
31
:
247
254
.
20
Stanford
,
M.
Biomechanical and functional behavior of implants.
Adv Dent Res.
1999
.
13
:
88
92
.
21
Karabuda
,
C.
,
O.
Ozdemir
,
T.
Tosun
,
A.
Anil
, and
V.
Olgac
.
Histological and clinical evaluation of three different grafting materials for sinus lifting procedure based in 8 cases.
J Periodontol.
2001
.
26
:
1436
1442
.
22
Martinez
,
M.
,
P.
Davarpanah
,
R.
Missika
,
R.
Celleti
, and
R.
Lazzara
.
Optimal implant stabilization in low density bone.
Clin Oral Implant Res.
2001
.
12
:
423
432
.
23
Geng
,
J. P.
,
W.
Xu
,
K. B. C.
Tan
, and
G. R.
Liu
.
Finite element analysis of an osseointegrated stepped screw dental implant.
J Oral Implantol.
2004
.
30
:
223
233
.
24
Chun
,
H. J.
,
S. Y.
Cheong
,
J. H.
Han
,
S. J.
Heo
,
J. P.
Chung
,
I. C.
Rhyu
,
Y. C.
Choi
,
H. K.
Baik
, and
M. H.
Kim
.
Evaluation of design parameters of osseintegrated dental implants using finite element analysis.
J Oral Rehabil.
2002
.
29
:
565
574
.
25
Pierrisnard
,
L.
,
G.
Hure
,
M.
Barquins
, and
D.
Chappard
.
Two dental implants design for immediate loading: a finite element analysis.
Int J Oral Maxillofac Implants.
2002
.
17
:
353
362
.
26
Holmgren
,
E. P.
,
R. J.
Seckinger
,
L. M.
Kilgren
, and
F.
Mante
.
Evaluating parameters of osseointegrated dental implants using finite element analysis—A two-dimensional comparative study examining the effects of implant diameter, implant shape, and load direction.
J Oral Implantol.
1998
.
24
:
80
88
.
27
Hojjatie
,
B.
and
K. J.
Anusavice
.
Three-dimensional finite element analysis of glass-ceramic dental crowns.
J Biomech.
1990
.
23
:
1157
1166
.
28
Simsek
,
B.
,
E.
Erkmen
,
D.
Yilmaz
, and
A.
Eser
.
Effects of different inter-implant distances on the stress distribution around endosseous implants in posterior mandible: A 3D finite element analysis.
Med Eng Phys.
2006
.
28
:
199
213
.
29
Hobkirk
,
J. A.
and
K. J.
Psarros
.
The influence of occlusal surface material on peak masticatory forces using ossointegrated implant-supported prostheses.
Int J Oral Maxillofac Implants.
1992
.
7
:
345
352
.
30
Cibirka
,
R. M.
,
M. E.
Razzoog
,
B. R.
Lang
, and
C. S.
Stohler
.
Determining the force absorption on quotient for restorative materials used in implant occlusal surfaces.
J Prosthet Dent.
1992
.
67
:
361
364
.
31
Himmlová
,
L.
,
T.
Dostálová
,
A.
Kácovský
, and
S.
Konvicková
.
Influence of implant length and diameter on stress distribution: a finite element analysis.
J Prosthet Dent.
2004
.
91
:
20
25
.
32
Acka
,
K.
and
H.
Iplikcioglu
.
Finite element stress analysis of the effect of short implant usage in place of cantilever extensions in mandibular posterior edentulism.
J Oral Rehabil.
2002
.
29
:
350
356
.
33
Ishigaki
,
S.
,
T.
Nakano
,
S.
Yamada
,
T.
Nakamura
, and
F.
Takashima
.
Biomechanical stress in bone surrounding an implant under simulated chewing.
Clin Oral Impl Res.
2003
.
14
:
97
102
.
34
Rieger
,
M. R.
,
W. K.
Adams
,
G. L.
Kinzel
, and
M. O.
Brose
.
Finite element analysis of bone-adapted and bone-bonded endosseous implants.
J Prosthet Dent.
1989
.
62
:
436
440
.
35
Del Palomar
,
A. P.
,
A.
Arruga
,
J.
Cegonino
, and
M.
Doblare
.
A finite element comparison between the mechanical behaviour of rigid and resilient oral implants with respect to immediate loading.
Comput Methods Biomech Biomed Engineer.
2005
.
8
:
45
57
.
36
Weinstein
,
A. M.
,
J. J.
Klawitter
, and
S. D.
Cook
.
Finite element analysis as an aid to implant design.
Biomater Med Devices Artif Organs.
1979
.
7
:
169
175
.
37
Geng
,
J. P.
,
K. B.
Tan
, and
G. R.
Liu
.
Application of finite element analysis in implant dentistry: a review of the literature.
J Prosthet Dent.
2001
.
85
:
585
598
.
38
Van Oosterwyck
,
H.
,
J.
Duyck
, and
J.
Vander Sloten
.
et al
.
The influence of bone mechanical properties and implant fixation upon bone loading around oral implants.
Clin Oral Impl Res.
1998
.
9
:
407
418
.
39
Natali
,
A. N.
,
P. G.
Pavan
, and
A. L.
Ruggero
.
Analysis of bone-implant interaction phenomena by using a numerical approach.
Clin Oral Implants Res.
2006
.
17
:
67
74
.
40
Winter
,
W.
,
S. M.
Heckmann
, and
H. P.
Weber
.
A time-dependent healing function for immediate loaded implants.
J Biomech.
2004
.
37
:
1861
1867
.
41
Çehreli
,
M.
,
S.
Sahin
, and
K.
Akça
.
Role of mechanical environment and implant design on bone tissue differentiation: current knowledge and future contexts.
J Dent.
2004
.
32
:
123
132
.
42
Lee
,
J. H.
,
V.
Frias
,
K. W.
Lee
, and
R. F.
Wright
.
Effect of implant size and shape on implant success rates: a literature review.
J Prosthet Dent.
2005
.
94
:
377
381
.
43
Frost
,
H. M.
A 2003 update of bone physiology and Wolff's Law for clinicians.
Angle Orthod.
2004
.
74
:
3
15
.
44
Kawahara
,
H.
,
D.
Kawahara
,
M.
Hayakawa
,
Y.
Tamai
,
T.
Kuremoto
, and
S.
Matsuda
.
Osseointegration under immediate loading: biomechanical stress-strain and bone formation-resorption.
Implant Dent.
2003
.
12
:
61
68
.
45
Meyer
,
V.
,
H. P.
Wiesmann
,
T.
Fillies
, and
U.
Joos
.
Early tissue reaction at the interface of immediately loaded dental implants.
Int J Oral Maxillofac Implants.
2003
.
18
:
489
499
.
46
Meyer
,
U.
,
U.
Joos
, and
J.
Mythili
.
et al
.
Ultrastructural characterization of the implant/bone interface of immediately loaded dental implants.
Biomater.
2004
.
25
:
1959
1967
.
47
Comfort
,
M. B.
,
F. C. S.
Chu
,
J.
Chai
,
P. Y. P.
Wat
, and
T. W.
Chow
.
A 5-year prospective study on small diameter screw-shaped oral implants.
J Oral Rehabil.
2005
.
32
:
341
345
.
48
Misch
,
C. E.
Short dental implants: a literature review and rationale for use.
Dent Today.
2005
.
24
:
64
68
.
49
Lum
,
L. B.
A biomechanical rationale for the use of short implants.
J Oral Implantol.
1991
.
17
:
126
131
.
50
Miyamoto
,
I.
,
Y.
Tsuboi
,
E.
Wada
,
H.
Suwa
, and
T.
Iizuka
.
Influence of cortical bone thickness and implant length on implant stability at the time of surgery-clinical, prospective, biomechanical, and imaging study.
Bone.
2005
.
37
:
776
780
.
51
Misch
,
C. E.
,
J.
Steigenga
,
E.
Barboza
,
F.
Misch-Dietsh
,
L. J.
Cianciola
, and
C.
Kazor
.
Short dental implants in posterior partial edentulism: a multicenter retrospective 6-year case series study.
J Periodontol.
2006
.
77
:
1340
1347
.
52
Lekhom
,
U.
Immediate/early loading of oral implants in compromised patients.
Periodontol.
2000
.
33
:
194
203
.
53
Meijer
,
M. J. A.
,
L. H.
Kuiper
,
F. J. M.
Starmans
, and
F.
Bosman
.
Stress distribution around dental implants: influence of superstructure, length of implants, and height of mandible.
J Prosthet Dent.
1992
.
68
:
96
102
.
54
Petrie
,
C. S.
and
J. L.
Williams
.
Comparative evaluation of implant designs: influence of diameter, length, and taper on strains in the alveolar crest. A three-dimensional finite-element analysis.
Clin Oral Implant Res.
2005
.
16
:
486
494
.
55
Baelum
Implant therapy in periodontally compromised patients.
Clin Oral Implant Res.
1997
.
8
:
180
188
.
56
Gunne
,
J.
,
P.
Astrand
,
T.
Lindh
,
K.
Borg
, and
M.
Olsson
.
Tooth-implant and implant supported fixed partial dentures: a 10-year report.
Int J Prosthodont.
1999
.
12
:
216
222
.
57
Lemmerman
,
K. J.
and
N. E.
Lemmerman
.
Osseointegrated dental implants in private practice: a long-term case series study.
J Periodontol.
2005
.
76
:
310
319
.
58
Naert
,
I.
,
G.
Koutsikakis
,
J.
Duyck
,
M.
Quirynen
,
R.
Jacobs
, and
D.
van Steenberghe
.
Biologic outcome of implant-supported restorations in the treatment of partial edentulism. Part I: a longitudinal clinical evaluation.
Clin Oral Implants Res.
2002
.
13
:
381
389
.
59
Herrmann
,
I.
,
U.
Lekholm
,
S.
Holm
, and
C.
Kultje
.
Evaluation of patient and implant characteristics as potential prognostic factors for oral implant failures.
Int J Oral Maxillofac Implants.
2005
.
20
:
220
230
.
60
Fugazzotto
,
P. A.
,
G. R.
Beagle
,
J.
Ganeles
,
R.
Jaffin
, and
J.
Vlassis
.
Success and failure rates of 9 mm or shorter implants in the replacement of missing maxillary molars when restored with individual crowns: preliminary results 0–84 months in function. A retrospective study.
J Periodontol.
2004
.
75
:
327
332
.
61
Renouard
,
F.
and
D.
Nisand
.
Short implants in the severely resorbed maxilla: a 2-year retrospective clinical study.
Clin Implant Dent Related Res.
2005
.
7
:
104
110
.
62
Tawil
,
G.
,
N.
Abougaoude
, and
R.
Younan
.
Influence of prosthetic parameters on the survival and complication rates of short implants.
Int J Oral Maxillofac Implants.
2006
.
21
:
275
282
.
63
Renouard
,
F.
and
D.
Nisand
.
Impact of implant length and diameter on survival rates.
Clin Oral Implants Res.
2006
.
17
:
35
51
.
64
Attard
,
N. J.
and
G. A.
Zarb
.
Immediate and early implant loading protocols: a literature review of clinical studies.
J Prosthet Dent.
2005
.
94
:
242
258
.
65
Chiapasco
,
M.
,
C.
Gatti
,
E.
Rossi
,
W.
Haefliger
, and
T. H.
Markwalder
.
Implant-retained mandibular overdentures with immediate loading. A retrospective multicenter study on 226 consecutive cases.
Clin Oral Implants Res.
1997
.
8
:
48
57
.
66
Tarnow
,
D. P.
,
S.
Emtiaz
, and
A.
Classi
.
Immediate loading of threaded implants at stage 1 surgery in edentulous arches: ten consecutive case reports with 1- to 5-year data.
Int J Oral Maxillofac Implants.
1997
.
12
:
31
324
.
67
Horiuchi
,
H. K.
,
K.
Uchida
,
M.
Yamamoto
, and
M.
Sugimura
.
Immediate loading of Branemark system implants following placement in edentulous patients: a clinical report.
Int J Oral Maxillofac Implants.
2000
.
15
:
824
830
.
68
Ottoni
,
J. M. P.
,
Z. F. L.
Oliveira
,
R.
Mansini
, and
A. M.
Cabral
.
Correlation between placement torque and survival of single-tooth implants.
Int J Maxillofac Implants.
2005
.
20
:
769
776
.
69
Lazzara
,
R. J.
,
S. S.
Porter
,
T.
Testori
,
J.
Galante
, and
L.
Zetterqvist
.
A prospective multicenter study evaluating loading of osseotite implants two months after placement: one-year results.
J Esthet Dent.
1998
.
10
:
280
289
.
70
Degidi
,
M.
,
A.
Scarano
,
G.
Iezzi
, and
A.
Piattelli
.
Peri-implant bone in immediately loaded titanium implants: histologic and histomorphometric evaluation in human. A report of two cases.
Clin Implant Dent Relat Res.
2003
.
5
:
170
175
.
71
Nkenke
,
E.
,
M.
Fenner
,
E. G.
Vairaktaris
,
F. W.
Neukam
, and
M.
Radespiel-Troger
.
Immediate versus delayed loading of dental implants in the maxillae of minipigs. Part II: histomorphometric analysis.
Int J Oral Maxillofac Implants.
2005
.
20
:
540
546
.
72
Romanos
,
G. E.
,
T.
Testori
,
M.
Degidi
, and
A.
Piattelli
.
Histologic and histomorphometric findings from retrieved, immediately occlusally loaded implants in humans.
J Periodontol.
2005
.
76
:
1823
1832
.
73
Degidi
,
M.
,
G.
Petrone
,
G.
Lezzi
, and
A.
Piattelli
.
Histologic evaluation of 2 human immediately loaded and 1 titanium implants inserted in the posterior mandible and submerged retrieved after 6 months.
J Oral Implantol.
2003
.
29
:
223
229
.
74
Degidi
,
M.
,
A.
Scarano
,
G.
Iezzi
, and
A.
Piattelli
.
Histologic analysis of an immediately loaded implant retrieved after 2 months.
J Oral Implantol.
2005
.
31
:
247
254
.
75
Testori
,
T.
,
S.
Smukler-Moncler
, and
L.
Francetti
.
et al
.
Healing of Osseotite implants under submerged and immediate loading conditions in a single patient: a case report and interface analysis after 2 months.
Int J Per Res Dent.
2002
.
22
:
345
353
.
76
Simon
,
H.
and
A. A.
Caputo
.
Removal torque of immediately loaded transitional endosseous implants in human subjects.
Int J Oral Maxillofac Implants.
2002
.
17
:
839
845
.
77
Jemt
,
T.
,
U.
Lekholm
, and
K.
Grondahl
.
3-year follow-up study of early single implant restorations ad modum Branemark.
Int J Per Res Dent.
1990
.
10
:
340
349
.
78
Jemt
,
T.
and
U.
Lekholm
.
Oral implant treatment in posterior partially edentulous jaws: a 5-year follow-up report.
Int J Oral Maxillofac Implants.
1993
.
8
:
635
640
.
79
Cibirka
,
R. M.
,
S. K.
Nelson
,
B. R.
Lang
, and
F. A.
Rueggeberg
.
Examination of the implant–abutment interface after fatigue testing.
J Prosthet Dent.
2001
.
85
:
268
275
.
80
Boggan
,
R. S.
,
J.
Todd Strong
,
C. E.
Misch
, and
M. W.
Bidez
.
Influence of hex geometry and prosthetic table width on static and fatigue strength of dental implants.
J Prosthet Dent.
1999
.
82
:
436
440
.
81
Gratton
,
D. J.
,
S. A.
Aquilino
, and
C. M.
Stanford
.
Micromotion and dynamic fatigue properties of the dental implant–abutment interface.
J Prosthet Dent.
2001
.
85
:
47
52
.
82
Siddiqui
,
A. A.
,
M.
Sosovicka
, and
M.
Goetz
.
Use of mini implants for replacement and immediate loading of 2 single-tooth restorations: a clinical case report.
J Oral Implantol.
2006
.
32
:
82
86
.
83
Langer
,
B.
,
L.
Langer
,
I.
Herrmann
, and
L.
Jorneus
.
The wide fixture: a solution for special bone situations and a rescue for the compromised implant. Part 1.
Int J Oral Maxillofac Implants.
1993
.
8
:
400
408
.
84
Mahon
,
J. M.
,
B. K.
Norling
, and
R. D.
Phoenix
.
Effect of varying fixture width on stress and strain distribution associated with an implant stack system.
Implant Dent.
2000
.
9
:
310
320
.
85
Vigolo
,
P.
and
A.
Givani
.
Clinical evaluation of single-tooth mini-implant restoration: a five-year retrospective study.
J Prosthet Dent.
2000
.
84
:
50
54
.
86
Rieger
,
M. R.
,
W. K.
Adams
, and
G. L.
Kinzel
.
A finite element survey of eleven endosseous implants.
J Prosthet Dent.
1990
.
63
:
457
465
.
87
Morris
,
H. F.
,
S.
Winkler
,
S.
Ochi
, and
A.
Kanaan
.
A new implant designed to maximize contact with trabecular bone: survival to 18 months.
J Oral Implantol.
2001
.
27
:
164
173
.
88
Anner
,
R.
,
H.
Better
, and
G.
Chaushu
.
The clinical effectiveness of 6 mm diameter implants.
J Periodontol.
2005
.
76
:
1013
1015
.
89
Garlini
,
G.
,
C.
Bianchi
,
V.
Chierichetti
,
D.
Sigurta
,
C.
Maiorana
, and
F.
Santoro
.
Retrospective clinical study of Osseotite implants: zero- to 5-year results.
Int J Oral Maxillofac Implants.
2003
.
18
:
589
595
.
90
Romeo
,
E.
,
D.
Lops
,
E.
Margutti
,
M.
Ghisolfi
,
M.
Chiapasco
, and
G.
Vogel
.
Long-term survival and success of oral implants in the treatment of full and partial arches: a 7-year prospective study with the ITI dental implant system.
Int J Oral Maxillofac Implants.
2004
.
19
:
247
259
.
91
Ivanoff
,
C. J.
,
K.
Grondahl
,
L.
Sennerby
,
C.
Bergstrom
, and
U.
Lekholm
.
Influence of variations in implant diameters: a 3- to 5-year retrospective clinical report.
Int J Oral Maxillofac Implants.
1999
.
14
:
173
180
.
92
Spiekermann
,
H.
,
V. K.
Jansen
, and
E.
Richter
.
A 10-year follow-up study of IMZ and TPS implants in the edentulous mandible using bar-retained overdentures.
Int J Oral Maxillofac Implants.
1995
.
10
:
231
243
.
93
Lazzara
,
R.
,
A. A.
Siddiqui
,
P.
Binon
,
S. A.
Feldman
,
R.
Weiner
,
R.
Phillips
, and
A.
Gonshor
.
Retrospective multicenter analysis of 3i endosseous dental implants placed over a five-year period.
Clin Oral Impl Res.
1996
.
7
:
73
83
.
94
Zinsli
,
B.
,
T.
Sagesser
,
E.
Mericske
, and
R.
Mericske-Stern
.
Clinical evaluation of small-diameter ITI implants: a prospective study.
Int J Oral Maxillofac Implants.
2004
.
19
:
92
99
.
95
Saadoun
,
A. P.
and
M. G.
Le Gall
.
An 8-year compilation of clinical results obtained with Steri-Oss endosseous implants.
Compendium Cont Dent Ed.
1996
.
17
:
669
687
.
96
Degidi
,
M.
,
A.
Piattelli
, and
F.
Carinci
.
Immediate functional loading of edentulous maxilla: a 5-year retrospective study of 388 titanium implants.
J Periodontol.
2005
.
76
:
1016
1024
.
97
Lorenzoni
,
M.
,
C.
Pertl
,
K.
Zhang
,
G.
Wimmer
, and
W. A.
Wegscheider
.
Immediate loading of single-tooth implants in the anterior maxilla. Preliminary results after one year.
Clin Oral Implants Res.
2003
.
14
:
180
187
.
98
Hoyer
,
S. A.
,
C. M.
Stanford
,
S.
Buranadham
,
T.
Fridrich
,
J.
Wagner
, and
D.
Gratton
.
Dynamic fatigue properties of the dental implant–abutment interface: joint opening in wide-diameter versus standard-diameter hex-type implants.
J Prosthet Dent.
2001
.
85
:
599.
.

Author notes

B. Georgiopoulos, K. Kalioras, and C. Provatidis are at the Mechanical Design and Control Systems Division, School of Mechanical Engineering, National Technical University of Athens, 9 Iroon Polytechniou Street, 15773 Athens, Greece. Correspondence should be addressed to Dr. Provatidis (cprovat@central.ntua.gr).

M. Manda and P. Koidis are at the Department of Fixed Prosthesis & Implant Prosthodontics, School of Dentistry, Aristotle University of Thessaloniki, University Campus, 54124 Thessaloniki, Greece.