Strain situation after fixation of three-unit ceramic veneered implant superstructures

The passive fit of superstructures used in implant prosthodontics is affected by several variables. The objective of this study was to quantify the strain development in various fixed partial dentures (FPDs), both in the condition as cast and after ceramic veneering. Five different types of three-unit FPDs (cementable/repositioning technique impression; cementable/pick-up technique impression; screw-retained/plastic cylinder; screw-retained/gold cylinder; screw-retained/bonded) with 10 samples each, representing commonly used FPD-types, were investigated before and after ceramic veneering. Two ITI implants were anchored in a measurement model simulating a real-life patient situation and strain gauges were mounted close to the implants. The strain development was recorded during cement setting and screw fixation. For statistical analysis, multivariate two-sample tests were performed with the level of significance set at P = 0.1. All FPDs revealed measurable amounts of strain. Neither the impression technique nor the fabrication modes for conventional screw-retained FPDs had a significant influence on strain development. Ceramic veneering caused an increase in strain development for the conventional bridge types. Furthermore, cementing appears to be able to compensate fabrication inaccuracies better than screw retention. The lowest strains were found in FPDs bonded to gold cylinders on the measurement model for metal frames and ceramic-veneered FPDs. Conventional procedures are unable to produce superstructures with an absolute passive fit. The technique of bonding superstructures to prefabricated components in the oral cavity seems to compensate for various shortcomings in superstructure fabrication.     

Static implant loading caused by as-cast metal and ceramic-veneered superstructures

STATEMENT OF PROBLEM: The passive fit of superstructures for implant-supported restorations is affected by each step of the fabrication process. In this context the question arises whether ceramic veneering would increase static implant loading. PURPOSE: The purpose of this study was to quantify the strain development of various fixed partial dentures (FPDs) both in the as-cast condition and after ceramic veneering. MATERIAL AND METHODS: Four different types (n = 10) of 5-unit FPDs (cementable, screw retained/plastic cylinder, screw retained/gold cylinder, screw retained/cemented) representing commonly used types of FPDs were investigated before and after ceramic veneering. Three implants were placed in a model simulating a patient situation, and strain gauges were mounted mesially and distally adjacent to the implants. The strain development was recorded during cement setting (provisional cement) and screw fixation. The data were analyzed statistically using multivariate 2-sample tests (alpha=.1). RESULTS: All FPDs revealed measurable amounts of strain. Neither the type of retention nor the mode of fabrication for conventional screw-retained FPDs had a significant influence on strain development. Ceramic veneering caused an increase in strain development for the conventional fixed partial dentures tested. The lowest strains were found in FPDs cemented to gold cylinders on the model for the metal frames and the ceramic-veneered FPDs. CONCLUSION: Conventional procedures were unable to produce superstructures with absolute passive fit. Ceramic veneering appeared to increase strain development and, thus, inaccuracy of the fit. The technique of cementing superstructures to prefabricated components directly on the implants may compensate for dimensional errors caused by impression making and superstructure fabrication.     

Influence of fixation mode and superstructure span upon strain development of implant fixed partial dentures.

PURPOSE: Implant-borne fixed partial dentures (FPDs) should fit passively in order to avoid complications ranging from screw loosening to loss of osseointegration. The aim of this study was to measure the strain development of three-unit and five-unit screw- and cement-retained implant-supported FPDs. Additionally, the influence of the parameters retention mechanism and FPD span were evaluated. MATERIALS AND METHODS: Three Straumann implants were anchored in a measurement model based on a real-life patient situation and strain gauges (SGs) were fixed mesially and distally adjacent to the implants and on the pontics of the superstructures. During cement setting and screw fixation of 40 implant FPDs (10 samples from each group: three-unit cementable; five-unit cementable; three-unit screw-retained; five-unit screw-retained), strain development was recorded. For statistical analysis, multivariate two-sample tests were performed with the level of significance set at p= 0.1. RESULTS: The mean strain values for the four FPD groups at the different SG sites ranged from 26.0 to 637.6 microm/m. When comparing the four groups, no significant differences in strain magnitude could be detected. Similarly, a comparison of the two FPD spans revealed no significant difference (p= 0.18 for cementable FPDs; p= 0.22 for screw-retained FPDs). A comparison of the two fixation modes also revealed no significant difference (p= 0.67 for three-unit FPDs; p= 0.25 for five-unit FPDs). CONCLUSION: FPD span and retention mechanism appear to have only a minor influence on strain development in implant FPDs. As implant-supported restorations have proven to be successful over time, the question arises as to whether an "absolute" passive fit is a prerequisite for successful implant restorations.     

In vitro study on passive fit in implant-supported 5-unit fixed partial dentures

PURPOSE: Fabrication and retention methods have an influence on the passivity of superstructure fit. The objective of the study was to quantify the strain development of various cemented and screw-retained fixed partial dentures (FPDs). MATERIALS AND METHODS: Forty samples of 4 different types of FPDs (10 of each type) were investigated. Each sample had 3 ITI implant abutments and 2 pontics. The 3 implants were anchored in a straight-line configuration in a measurement model simulating a real-life patient situation. Strain gauges were mounted close to the implants and on the pontics. The developing strains were recorded during cement setting and screw fixation. For statistical analysis, multivariate 2-sample tests were performed, with the level of significance set at P = .1. RESULTS: All FPDs investigated revealed a considerable amount of strain, with no significant difference between cement and screw retention. Furthermore, no significant difference was found between the conventional fabrication modes for screw-retained FPDs. The lowest strains were found in prostheses that were intraorally bonded onto gold cylinders. DISCUSSION: Because bonding of the superstructure in the oral cavity may compensate for impression and laboratory variables, restorations with the best possible passive fit can result from this retention technique. Before this technique can be recommended, the long-term stability of the adhesive layer should be investigated. CONCLUSIONS: As an absolute passive fit of superstructures is not possible using conventional clinical and laboratory procedures, and as clinical fit-evaluation methods often do not detect "hidden" inaccuracies, the more sensitive strain-gauge technique should be utilized for an objective accuracy test. Reference strain values from implant-supported prostheses that have served without complications could help define a "biologically acceptable fit.     

In Vivo Stress Behavior in Cemented and Screw-Retained Five-Unit Implant FPDs

PURPOSE: When fixing implant-supported fixed partial dentures (FPDs), it is important to achieve passive fit. The objective of the in vivo study presented was to quantify the strain development during the fixation of screw- and cement-retained FPDs. MATERIALS AND METHODS: After informed patient consent had been obtained (Ethics commission Approval No. 2315; FAU Erlangen-Nuremberg, Germany), four groups of five-unit FPDs (five samples per group) were fabricated and investigated in vivo. Group 1: Cementable, repositioning technique impression, burn out plastic coping; Group 2: Screwable, pickup technique impression, burn out plastic coping; Group 3: Screwable, pickup technique impression, cast to gold cylinder; Group 4: Screwable, pickup technique impression, bonded to gold cylinder. Two strain gauges (SG) were attached to the pontics of each bridge (SG-M and SG-D) to measure the strains that occurred during either the cementing or screw-in process. The final values were recorded for analysis. RESULTS: The mean strain values (microm/m) for each SG were: Group 1: SG-M 32 microm/m, SG-D: 89 microm/m; Group 2: SG-M 302 microm/m, SG-D: 197 microm/m; Group 3: SG-M 458 microm/m, SG-D: 268 microm/m; Group 4: SG-M 269 microm/m, SG-D: 52 microm/m. CONCLUSIONS: Although the bridges were clinically acceptable, none of them revealed a truly passive fit with zero microstrain. In contrast to conventional screw-retained bridges, cement retention seems to result in lower strain levels. Bonding bridge pontics to prefabricated implant components seems to allow both the retrievability of a screw-retained bridge and produce moderate strain values.     

Narrow-diameter implants as terminal support for occlusal three-unit FPDs: a biomechanical analysis

The purpose of this study was to examine force transmissions of narrow-diameter ITI implants when used as a terminal support for freestanding three-unit fixed partial dentures (FPD). Photoelastic and strain-gauged models of two 4.1-mm-diameter solid-screw implants; a 3.3-mm reduced-diameter implant and a 4.1-mm-diameter solid-screw implant; and a 3.3-mm-diameter narrow-neck implant and a 4.1-mm-diameter solid-screw implant supporting fixed prostheses were fabricated. A static force of 100 N was applied on both implants and on the pontic of the prostheses in separate load cases, and the generation of isochromatic fringes was observed and photographed in the field of a circular polariscope. The strain-gauge signals were digitized by a data-acquisition system and displayed in a computer by corresponding software at a sample rate of 10,000 Hz, and the principal strains were calculated. The use of narrow-neck and reduced-diameter implants resulted in an overall increase in stress and strain magnitudes around supporting implants in comparison with support from two standard solid-screw implants. Narrow-diameter ITI implants may be used to support FPDs for patients with low bite forces. In other clinical situations involving narrow-diameter implants, increasing the implant support is crucial to improve the biomechanical outcome of the treatment.     

Strain development in 3-unit implant-supported CAD/CAM restorations

PURPOSE: Passive fit is difficult to achieve in implant-supported restorations with existing superstructure fabrication techniques. The aim of the study presented was to investigate whether computer-generated fixed partial dentures (FPDs) based on optical impressions lead to less strain development than conventionally fabricated FPDs. MATERIALS AND METHODS: A measurement model with 2 implants was set up and strain gauges were attached to the model material mesially and distally adjacent to the implants. Two groups of conventional cementable restorations based on repositioning and pick-up impressions, respectively, and 1 group of CAD/CAM-generated FPDs based on optical impressions were fabricated (n = 10). Strain development during FPD fixation was recorded. In order to compare the different FPD groups with one another, a multivariate analysis of variance (MANOVA) was performed at a level of significance of alpha = .05. RESULTS: The mean strain development at the different strain gauge locations ranged from 80.38 microm/m to 437.11 microm/m. The 2 groups of conventionally fabricated FPDs showed no significant difference in terms of strain development (P = .07). The CAD/CAM-fabricated FPDs revealed a significantly lower strain development than those made from pick-up technique impressions (P = .01). No significant difference could be detected between the FPDs manufactured from repositioning technique impressions and the CAD/CAM-generated restorations (P = .19). CONCLUSION: Within the limitations of the study presented, it can be concluded that restorations fabricated on the basis of optical impressions demonstrate a level of fit which is at least as passive as that of conventional FPDs.     

In vitro strain gauge analysis of axial and off-axial loading on implant supported fixed partial dentures

The purpose of this study was to compare the in vitro strains on dental implants supporting cement-retained fixed partial dentures under axial and off-axial loading conditions. Ten implants incorporating strain gauges were placed in a certain configuration to simulate different clinical situations and were embedded in an experimental model. Two implant supported three-unit fixed partial dentures were fabricated on four groups of implants, and each group consisted of seven restorations. The prostheses were cemented with a temporary cement. Fifty N vertical load was applied on predetermined axial and off-axial loading locations on the prostheses. Strain indicator readings were recorded at a standardized time following each loading sequence. The point of load transfer affected strains on implants. For all prosthetic designs, off-axial loading generated more strain than axial loading on implants (P < 0.05). In comparison with axial loading, off-axial loading causes bending of the implants that may affect bone loss around the implant collar. Axial loading of implants should be provided by using wide diameter implants, narrow occlusal tables, and proper occlusal contacts on implant restorations.     

Different bone loading patterns due to fixation of three-unit and five-unit implant prostheses

BACKGROUND: It has been considered that implant prostheses ought to display passive fit. The objective of this finite element analysis (FEA) was to simulate the bone loading resulting from the fixation of implant-supported three and five-unit fixed partial dentures (FPDs). METHODS: Based on a patient case, six different FPD-groups were fabricated using either two or three implants for support. Strain gauges on the pontics of the prostheses were used for in vivo measurements. Based on the values obtained, bone loading models were simulated using three-dimensional finite element analysis and the results obtained were represented as von Mises equivalent stress. RESULTS: The mean strain (epsilon) values ranged from 15 micro epsilon to 170 micro epsilon for the three-unit FPDs and from 32 micro epsilon to 302 micro epsilon for the five-unit FPDs. FEA revealed von Mises stresses up to 30 MPa in the cortical area, while in trabecular bone values up to 5 MPa were observed. Static implant loading of similar magnitude can be provoked through 200 N axial load. CONCLUSIONS: Although the in vivo measured strain levels (epsilon) were of higher magnitude for the five-unit prostheses, FEA revealed bone loading of comparable magnitude for both three- and five-unit FPDs. Multi-unit prostheses may demonstrate greater inaccuracies compared with single implant restorations, but due to the absence of moment loading the multi-implant configuration appears to compensate for the higher strain development.     

Analysis of stress distribution in a screw-retained implant prosthesis

Four types of implant superstructures were screwed onto implant bodies, and the strains created around the implant bodies were compared and analyzed within the IMZ Implant System. Three IMZ implants were embedded in the center of a polyurethane block (30 x 40 x 30 mm), and a total of 16 superstructures was fabricated by 4 methods: 1-piece cast, 1-piece cast/split soldering, soldering, and passive fit. Six strain gauges were placed on the surface of the block 1 mm apart. Three embedded implants were numbered, and a fixed partial denture was placed on these implants and screwed by a torque wrench using 14.5 Ncm torque. This procedure was repeated 7 times for each fixed partial denture, and each created strain was measured when the last screw was tightened. In all fixed partial dentures, strains were produced around the implant bodies when screws retaining the prosthesis were tightened, and the strain was relieved with unscrewing. The magnitude of strain was greater with the 1-piece cast method or the section/solder method than with the soldering and passive-fit methods. Of the 2 soldering methods, when the screw on the middle implant was tightened before those on the terminal 2 implants, the magnitude of strain was lower with the soldering method than with the 1-piece cast/split soldering method. When the order of screw tightening was changed, there were significant differences in the magnitude of strain at each gauge with the soldering method. With the passive-fit method, no differences in the magnitude of strain attributable to the order of screw tightening could be detected. The magnitude of strain produced around a screw-retained implant prosthesis was significantly lower with the passive-fit method when compared to the other 3 fabricating methods. Furthermore, the implants prepared by the passive-fit method were not affected by the order of screw tightening.     

Passivity of fit and marginal opening in screw- or cement-retained implant fixed partial denture designs

The relationship of stress generation upon placement of cement-retained or screw-retained implant restorations has not been thoroughly investigated. Passivity of fit and marginal discrepancies of screw- and cement-retained implant fixed partial denture (FPD) designs were determined using a photoelastic model of a partially edentulous posterior mandibular arch with 3 screw-type implants. Buccal and lingual marginal openings, measured with a traveling microscope before cementation or screw tightening, revealed no statistical difference in adaptation between designs. Screw tightening caused a reduction in marginal opening (changes significant, P < .05). The opening with the cemented FPDs was similar before and after cementation. Photoelastic evaluation of the FPDs showed that cement-retained FPDs exhibited a more equitable stress distribution than did their screw-retained counterparts.     

Survival rates of IPS empress 2 all-ceramic crowns and fixed partial dentures: results of a 5-year prospective clinical study.

OBJECTIVE: The aim of this prospective clinical study was to evaluate the survival rates of IPS Empress 2 (Ivoclar Vivadent) all-ceramic crowns and fixed partial dentures (FPDs) after an observation period of up to 5 years. METHOD AND MATERIALS: Forty-three patients (19 women and 24 men) were included in this study. The patients were treated with a total of 58 adhesive bonded IPS Empress 2 restorations. A total of 27 single crowns were placed on molars and premolars, and 31 three-unit FPDs were placed in the anterior and premolar regions. Clinical follow-up examinations took place at 6, 12, 24, 36, 48, and 60 months after insertion. Statistical analysis of the data was calculated using the Kaplan-Meier method. RESULTS: Results of the 50-month analysis (interquartile range, 33 to 61 months) showed that the survival rate was 100% for crowns and 70% for FPDs. Six failures that occurred exclusively in the three-unit FPDs were observed. Framework fractures were recorded in three FPD units where the connector dimensions did not meet the manufacturer specifications. Only one FPD exhibited an irreparable partial veneer fracture, and 2 FPDs showed evidence of biologic failures. The accuracy of fit and esthetic parameters were clinically satisfactory for crowns and FPDs. CONCLUSION: The results of this 5-year clinical evaluation suggest that IPS Empress 2 ceramic is an appropriate material for the fabrication of single crowns. Because of the reduced survival rates, strict conditions should be considered before the use of IPS Empress 2 material for the fabrication of three-unit FPDs.     

On the role of number of fixtures, surgical technique and timing of loading

AIMS: The aims of this thesis were to analyze reduced number of implants supporting full arch fixed mandibular prostheses and fixed partial dentures (FPDs), non-submerged healing and early loading in the edentulous mandible. A further aim was to evaluate fit of Computer Numerical Controlled (CNC) milled I-Bridge frameworks. MATERIAL & METHODS: Paper I. One hundred and nineteen patients rehabilitated with full arch mandibular prostheses supported by four implants were evaluated after a mean follow-up of 4.4 years. Paper II. A total of 178 patients provided with FPDs supported by two (n=92) or three implants (n=122) of whom 123 were evaluated after a mean follow-up of 9.4 years. Paper III. Early and delayed loading of full arch mandibular prostheses were evaluated in 109 patients, 54 with delayed loading and 55 with early loading, with a mean follow-up of 3.6 years. Paper IV. Submerged and non-submerged implant placement for supporting fixed prostheses in the edentulous mandible were evaluated after five years in 29 patients. Paper V. The precision of fit of CNC-milled I-Bridge frameworks was evaluated using two different implant systems. RESULTS: Paper I. The five-year cumulative survival rate (CSR) for implants was 99.1% and for prostheses 100%. Mean bone loss from baseline to five-year follow-up was 0.5 mm. No indication could be found that the number of supporting implants influenced the prosthetic complications. Paper II. The five-year implant and prosthesis CSR was 97.7% for two-implant supported FPDs and 97.3% for three-implant supported FPDs. Mean bone loss at five years was 0.4 mm. Significantly more prosthetic and abutment screw loosening were seen in two-implant supported FPDs. Paper III. Five-year CSR for implants was 94.4% and 92.5% for prostheses in early loading, and 97.9% and 98.0% in the delayed loading group. More prostheses needed adjustment or replacement in the early group, but patients treated with early loading were more pleased with the treatment procedure. Paper IV. Five-year CSR survival rate was 99.4%. Three implants fractured in one patient. Mean bone loss at five years was 0.7 mm in submerged implants and 0.5 mm in non-submerged implants. Paper V. All frameworks demonstrated clinically acceptable fit with mean distortion values within 23 microm (x-axis), 26 microm (y), 4 microm (z- axis) and 34 microm (3-D) for all frameworks. Control frameworks displayed greater levels of distortion than frameworks produced in a strict test situation. CONCLUSION: A reduction of the number of supporting implants to four implants in full arch mandibular prostheses and two implants in three unit FPDs in partial edentulous jaws resulted in the same clinical outcome as when more implants are used. Non-submerged implant placement in the edentulous mandible was as predictable as submerged, but early loading of implant-supported mandibular prostheses incurred more prosthetic complications. Computer numerical controlled milled frameworks presented levels of precision of fit within limits considered to be clinically acceptable and superior to earlier published results on cast frameworks.     

Three‐Dimensional Image Correlation Analyses for Strains Generated by Cement and Screw‐Retained Implant Prostheses

Purpose: This study aimed to measure and compare strains generated by splinted implant crowns retained by cement or screws for two implants with applied load. Materials and Methods: A stereolithic resin model was printed using computed tomography data from a patient missing all mandibular molar teeth. Two 4 × 6 mm implants were consecutively placed in the left side. One set of splinted cement and screw‐retained crowns were made to fit the two implants. Image correlation technique was used for full‐field measurement of strains using an image correlation software and two synchronized high‐resolution digital cameras. A random dot pattern was applied to the model surface. Cameras recorded changes in random dot patterns as prostheses were loaded up to 400 N in vertical and oblique directions using a universal testing machine. Testing was repeated three times for cement and screw‐retained prostheses. An image correlation algorithm used the dot pattern to define correlation areas or virtual strain gauge boxes. Three‐dimensional coordinates of gauge box centers were determined for each recorded photograph and used to calculate strains. Strain distribution data were compared for major, minor, and von Mises strains for each loading condition, as well as peak and average strains for the field of view using an analysis of variance (α = 0.05). Results: Patterns and magnitudes of strain for cement‐ and screw‐retained splinted crowns were similar under vertical loading. Neither peak nor mean strains were significantly different for the two retention methods. For oblique loading, peak strains were lower for the screw‐retained crowns; however, there were no statistically significant differences between the two groups when strains were averaged throughout the entire field of view. Conclusions: Cement retention did not improve the magnitude of transferred strains for splinted implant crowns using either loading condition.     

Fixation of 5-unit implant-supported fixed partial dentures and resulting bone loading: a finite element assessment based on in vivo strain measurements

PURPOSE: It is believed that implant-supported fixed partial dentures (FPDs) should display passive fit. The objective of this in vivo-based finite element analysis (FEA) was to quantify the magnitude of bone loading occurring on account of the fixation of cemented or screw-retained 5-unit superstructures. MATERIALS AND METHODS: Based on a patient situation with 3 implants, 4 different groups of restorations with 10 samples each were fabricated. Strain gauges on the pontics of the restorations were used for in vivo measurements. Using the values obtained, bone loading in 3-dimensional FE models was simulated as von Mises equivalent stress. RESULTS: The in vivo measured mean strain values ranged from 32 microm/m to 458 microm/m at the different sites. FEA revealed stresses between 5 and 30 MPa in the cortical area, while in trabecular bone values ranging from 2 MPa to 5 MPa were observed. Stress of a similar magnitude was found for axial implant loading with 200 N. DISCUSSION: Assuming that the axial loading of a single implant with 200 N is within the realm of the bone's adaptation ability, it would appear that the amount of stress resulting from the fixation of superstructures alone does not constitute a risk. CONCLUSIONS: The level of precision of fit which can be obtained in superstructure fabrication would appear to suffice to produce restorations that do not cause bone damage.     

Role of implant configurations supporting three‐unit fixed partial denture on mandibular bone response: biological‐data‐based finite element study

Implant‐supported fixed partial denture with cantilever extension can transfer the excessive load to the bone around implants and stress/strain concentration potentially leading to bone resorption. This study investigated the effects of implant configurations supporting three‐unit fixed partial denture (FPD) on the stress and strain distribution in the peri‐implant bone by combining clinically measured time‐dependent loading data and finite element (FE) analysis. A 3‐dimensional mandibular model was constructed based on computed tomography (CT) images. Four different configurations of implants supporting 3‐unit FPDs, namely three implant‐supported FPD, conventional three‐unit bridge FPD, distal cantilever FPD and mesial cantilever FPD, were modelled. The FPDs were virtually inserted to the molar area in the mandibular FE models. The FPDs were loaded according to time‐dependent in vivo‐measured 3‐dimensional loading data during chewing. The von Mises stress (VMS) and equivalent strain (EQS) in peri‐implant bone regions were evaluated as mechanical stimuli. During the chewing cycles, the regions near implant necks and bottom apexes experienced high VMS and EQS than the middle regions in all implant‐supported FPD configurations. Higher VMS and EQS values were also observed at the implant neck region adjacent to the cantilever extension in the cantilevered configurations. The patient‐specific dynamic loading data and CT‐based reconstruction of full 3D mandibular allowed us to model the biomechanical responses more realistically. The results provided data for clinical assessment of implant configuration to improve longevity and reliability of the implant‐supported FPD restoration.     

Immediate implant loading following computer-guided surgery

Purpose

The aim of this study was to develop and apply a new method for easy intraoperative adjustment of a provisional fixed full-arch restoration, in order to allow immediate implant loading following computer-guided surgery, regardless of any implant positioning errors compared to the virtual planning.

Methods

In accordance with the NobelGuide™ protocol, a provisional restoration for immediate loading of six maxillary implants was prepared prior to surgery. Because small shifts between the planned and the actual implant positions were to be expected, the provisional restoration was not fabricated directly on temporary cylinders as a conventional one-piece superstructure, but was divided into two portions: six custom made abutments and a long span fixed restoration which were left unconnected. After implantation, the custom abutments were attached to the six implants to be immediately loaded, and the superstructure was cemented simultaneously to all abutments using dual cure resin cement. After the excess cement was cleaned and polished, the superstructure was then reseated. Passive fit was achieved between implants and the superstructure.

Conclusion

The superstructure described in this article can be easily seated and adjusted to accommodate any possible shifts in implant positioning occurring during computer-guided surgery. Through this method uneventful immediate implant loading can be achieved in a reasonable operative time.     

The influence of medial implant location in three-unit posterior cantilever fixed partial dentures on stress distribution in surrounding mandibular bone

This study examined the influence of medial implant location in three-unit posterior cantilever fixed partial dentures (FPDs) on stress distribution in mandibular bone surrounding two implants. A three-dimensional finite element model that included three-unit FPD and two cylindrical-type implants (4 mm in diameter and 10 mm in length) osseointegrated in the posterior mandible, was digitized. Five different models were created according to the medial implant location between the missing second premolar and the first molar location. The distal implant was fixed at the missing second molar location. Oblique bite force of 100 N at 30 degrees buccal to the vertical direction was directed on each of three artificial teeth, respectively and simultaneously, while the lower surface of the mandible was fixed. The maximum equivalent stress in the cortical and the trabecular bone generally increased as the medial implant shifted to a distal position. Under the simultaneous bite force, relatively low maximum stresses within the cortical bone: between 55 MPa and 57 MPa, were shown in the models with the medial implant placed within the range of one implant diameter from the most medial position, while higher maximum stresses: between 64 MPa and 73 MPa, were demonstrated with more distally placed medial implants. The results suggest that reasonably low mechanical stress in the surrounding bone may be assured when the medial implant is placed in the range between the missing second premolar position and one implant diameter distal from that location.     

Cantilever fixed prostheses utilizing dental implants: a 10-year retrospective analysis.

OBJECTIVE: The dental literature has been unclear about long-term success of fixed cantilever prostheses supported by dental implants. The disappointing results reported when cantilever fixed partial dentures (FPDs) are supported with natural teeth are not directly applicable to implant cantilever FPDs. This article reports on 10 years of implant-retained fixed prostheses primarily in the maxillary arch using the ITI dental implant system. METHOD AND MATERIALS: Sixty cantilever prostheses using 115 ITI dental implants on 36 patients were placed and monitored over a 10-year period. RESULTS: No implant fractures, abutment fractures, porcelain fractures, prosthesis fractures, soft tissue recession, or radiographic bone loss were recorded. All 60 cantilevered prostheses remain in satisfactory function. CONCLUSION: Positive, long-term results, using implant-retained cantilever FPDs can be achieved by: (1) using a rough surface implant of 4.1 mm or greater; (2) using an implant/abutment design that reduces stacked moving parts and reduces the implant-to-crowns ratio; and (3) using a cementable prosthesis design that eliminates the need for occlusal screw retention.     

Utilizzo implantare strategico del triangolo retrocanino con bypass del seno mascellare mediante espansori ossei e inserti piezoelettrici

Objectives

The study reports about two patients who received an implant rehabilitation device consisting in a three-unit fixed partial denture supported by two implants, one of which tilted. They were strategically placed in the retrocanine triangle after bypassing the maxillary sinus by the use of bone expanders and special piezoelectric inserts.

Materials and methods

Two patients were treated with this technique and received two implants each. The distal one was placed tilted in the retrocanine bone triangle through conic screw bone expanders and special piezoelectric inserts to avoid high demanding surgical skill sinus lift procedures. The mesial implant was axially placed with a piezoelectric preparation of the implant site. After a 6-month healing period, three unit, screw retained, fixed partial dentures were delivered. After one year of loading the rehabilitation implants were clinically and radiographically examined.

Results

After one year of loading all four implants were osseointegrated and the marginal bone reabsorption was in line with the traditional techniques. No biological or mechanical complications were found.

Conclusions

The synergy between these special piezoelectric inserts used for implant site preparation and conic screw bone expanders seems to offer a more gentle approach and a better bone compaction around the implants in comparison with the traditional technique. An implant-supported rehabilitation in the retrocanine triangle with delayed function on a three-unit fixed partial denture, avoiding sinus floor elevation procedures by using this modified technique, might be a less invasive technique, reducing costs and increasing benefits for the patients.