Displacement comparison of CAD-CAM titanium and zirconia abutments to implants with different conical connections.

PURPOSE: To compare the displacements of CAD-CAM zirconia and titanium abutments into different internal connection systems after torquing. METHODS: OsseoSpeed EV and OsseoSpeed TX implants (n=10) were placed in resin blocks. Zirconia and titanium abutments (n=5) were first hand tightened and then tightened to the recommended torque (20Ncm for TX and 25Ncm for EV). Displacements of abutments between screw tightening by hand and torque driver was measured using three-dimensional digital image correlation (3D DIC) technique. Displacements were measured in U (front/back), V (into/outward), W (right/left) directions and 3-dimensionally (3D). ANOVA with restricted maximum likelihood estimation method was used to analyze the data. Bonferroni-corrected t tests was used to determine the statistical differences (α=0.05). RESULTS: 3D displacement of zirconia and titanium abutments was significantly greater in OsseoSpeed EV implant (P<0.001). Displacement of zirconia and titanium abutments was not significantly different within implant systems, 3D (P≥0.386) and in each direction (P≥0.382). In U and V directions, zirconia and titanium abutments displaced significantly more towards negative in OsseoSpeed EV implant (P<0.019). Within the OsseoSpeed TX system, abutments displaced significantly more in V direction compared to the U and W (P≤0.005), and within the Osseospeed EV system, abutment displacements were significantly different amongst directions and displacements in V were the greatest (P<0.001). CONCLUSION: Abutments displaced more in the implant that required higher torque values to tighten the abutment. The amount of displacement in both systems was clinically small. Abutment material did not affect the magnitude of displacement.

Comparison of 3D displacements of screw-retained zirconia implant crowns into implants with different internal connections with respect to screw tightening.

STATEMENT OF PROBLEM: Internal conical implant-abutment connections without horizontal platforms may lead to crown displacement during screw tightening and torque application. This displacement may affect the proximal contacts and occlusion of the definitive prosthesis. PURPOSE: The purpose of this in vitro study was to evaluate the displacement of custom screw-retained zirconia single crowns into a recently introduced internal conical seal implant-abutment connection in 3D during hand and torque driver screw tightening. MATERIAL AND METHODS: Stereolithic acrylic resin models were printed using computed tomography data from a patient missing the maxillary right central incisor. Two different internal connection implant systems (both ∼11.5 mm) were placed in the edentulous site in each model using a surgical guide. Five screw-retained single zirconia computer-aided design and computer-aided manufacturing (CAD-CAM) crowns were fabricated for each system. A pair of high-resolution digital cameras was used to record the relationship of the crown to the model. The crowns were tightened according to the manufacturers' specifications using a torque driver, and the cameras recorded their relative position again. Three-dimensional image correlation was used to measure and compare crown positions, first hand tightened and then torque driven. The displacement test was repeated 3 times for each crown. Commercial image correlation software was used to extract the data and compare the amount of displacement vertically, mesiodistally, and buccolingually. Repeated-measures ANOVA calculated the relative displacements for all 5 specimens for each implant for both crown screw hand tightening and after applied torque. A Student t test with Bonferroni correction was used for pairwise comparison of interest to determine statistical differences between the 2 implants (α=.05). RESULTS: The mean vertical displacements were statistically higher than the mean displacements in the mesiodistal and buccolingual directions for both implants (P<.001). Mean displacements in all directions were statistically significant between iterations for both implants (P<.001). No statistically significant differences were found for displacements between implants at different directions and at different iterations (P>.05). CONCLUSIONS: Within the limitations of this in vitro study, screw-retained zirconia crowns tended to displace in all 3 directions, with the highest mean displacement in the vertical direction at iteration 1. However, the amount of displacement of crowns between the 2 different implants was statistically insignificant for all directions and iterations.

A load-to-fracture and strain analysis of monolithic zirconia cantilevered frameworks.

STATEMENT OF PROBLEM: The dimensions of implant-supported fixed cantilevered prostheses are important to prevent mechanical and biological complications. Information on the optimum thickness and cantilever length for improving the strength of zirconia cantilevered frameworks is limited in the literature. PURPOSE: The purpose of this in vitro study was to investigate the effect of cantilever length and occlusocervical thickness on the load-to-fracture and strain distribution of zirconia frameworks. MATERIAL AND METHODS: Twenty-seven rectangular prism-shaped specimens (6 mm thick buccolingually) were fabricated using a computer-aided design and computer-aided manufacturing (CAD-CAM) milling technique. The specimens were prepared in 9 groups (n=3) according to their vertical dimensions (6×6 mm, 8×6 mm, and 10×6 mm) and cantilever loading distance (7 mm, 10 mm, and 17 mm). All specimens were heat treated in a porcelain furnace and thermocycled for 20000 cycles before the tests. Each framework was secured using a clamp attached to the first 20 mm of the framework. A 3-dimensional image correlation technique was used for a full-field measurement of strain during testing. A load-to-fracture test was used until the specimens fractured. Maximum force and principal strain data were analyzed by 2-way analysis of variance using the maximum likelihood estimation method (α=.05). RESULTS: No statistically significant effects (P>.05) were found for occlusocervical thickness and cantilever length or between them on the strain distribution. The results showed that the effect of occlusocervical thickness and cantilever length was significant on the load to fracture (P<.001). No statistically significant interaction was observed between the 2 factors (P>.05). CONCLUSIONS: Increased occlusocervical thickness and decreased cantilever length allowed the cantilever to withstand higher loads. The occlusocervical thicknesses and cantilever lengths of zirconia frameworks tested withstood the maximum reported occlusal force. The properties of components in the implant-abutment framework assembly should be considered in the interpretation of these results.

Strain analysis of 9 different abutments for cement-retained crowns on an internal hexagonal implant.

STATEMENT OF PROBLEM: Many aftermarket abutments for cement-retained crowns are available for the tapered screw-vent implant. Aftermarket abutments vary widely, from stock to custom abutments and in materials such as zirconia, titanium, or a combination of the two. How these aftermarket abutments perform under occlusal loads with regard to strain distribution is not clear. PURPOSE: The purpose of this in vitro study was to measure and compare the different strains placed upon the bone around implants by 9 different abutments for cement-retained crowns on an implant with an internal hexagonal platform. MATERIAL AND METHODS: Nine 4.1×11.5-mm tapered screw-vent implants were placed into a 305×51×8-mm resin block for strain measurements. Five abutment specimens of each of the 9 different abutments (N=45) were evaluated with 1 of the 9 implants. Monolithic zirconia crowns were then fabricated for each of the 9 different abutments, the crowns were cyclically loaded (maximum force 225 N) at 30 degrees, twice at a frequency of 2 Hz, and the strain was measured and recorded. The strain to the resin block was determined using a 3-dimensional digital image correlation (3D DIC) technique. Commercial image correlation software was used to analyze the strain around the implants. Data for maximal and minimal principal strains were compared using analysis of variance with a Tukey-Kramer post hoc test (α=.05). RESULTS: Strain measurements showed no significant differences among any of the abutments for minimal (compression) principal strains (P>.05). For maximal (tensile) principal strains, the zirconia abutment showed the highest, and the patient-specific abutment showed the second-highest strain around the implant, with the zirconia being significantly greater than all abutments, with the exception of the patient-specific abutment, and the patient-specific abutment being significantly greater than the straight contoured abutment in titanium and also zirconia (P<.05). CONCLUSIONS: The name brand patient specific titanium and Atlantis zirconia abutments conferred the most tensile strain to the implants. When selecting an abutment for a cement-retained crown on a tapered screw-vent implant, practitioners should consider the abutment material and the manufacturer of the abutment because not all abutments that fit in an individual implant transmit the strains in the same way.

Displacement of Implant Abutments Following Initial and Repeated Torqueing.

PURPOSE: To measure and compare the three-dimensional (3D) position of nine different abutments manufactured by different manufacturers after repeated torqueing on an internal-hexagon implant. MATERIALS AND METHODS: Nine tapered implants were placed into an acrylic resin block. Five specimens each of nine different abutments (n = 45) were placed into one of nine implants. The abutments were handtightened and then torqued to the manufacturer-recommended torque of 30 Ncm. After 10 minutes, 30 Ncm of torque was reapplied. Another 10 minutes elapsed before testing was completed. Images were recorded in 12-second intervals. The spatial relationship of the abutments to the resin block was determined using 3D digital image correlation. Commercial image correlation software was used to analyze the displacements. Mean displacements for the abutments were calculated in three dimensions and overall for both torque applications. Statistical comparisons were done with a t test and a step-down Bonferroni correction. RESULTS: The overall 3D displacement of the Atlantis Titanium abutment after the second applied torque was significantly greater than that of two of the eight other abutments. Displacement in all three dimensions for the Atlantis Titanium abutment changed direction between the first and second torque applications. All abutments moved further in the same direction except for the Atlantis Titanium abutment, which moved back toward its original hand-tightened position horizontally after the second torque application. CONCLUSION: Re-torqueing of abutments after a 10-minute interval leads to minor displacement of varying degrees between the abutment and a tapered implant. A potential effect of embedment relaxation and/or manufacturing errors should be taken into consideration when selecting an abutment for a cement-retained crown on a tapered implant. Accordingly, clinicians may benefit from adjusting cement-retained implant crowns after re-torqueing the abutments to prevent potential occlusal and interproximal contact problems.

Three-Dimensional Displacement of Nine Different Abutments for an Implant with an Internal Hexagon Platform.

PURPOSE: Clinicians need to know whether there are any differences among the many abutment options available for restoring a particular implant. This study aims to compare nine abutments for one implant system for positional changes between hand tightening and torqueing. MATERIALS AND METHODS: Nine Tapered Screw-Vent (TSV) implants were placed into a resin block. Five specimens of nine different abutments (n = 45) were tried in one of the nine implants. Initially, the abutments were torqued to 20 Ncm to represent hand tightening. Abutments were tightened to 30 Ncm using a torque driver as recommended by the manufacturer for final seating. Images were recorded in 12-second intervals for approximately 10 minutes after the torque was applied. The spatial relationship of the abutments to the resin block was determined using three-dimensional digital image correlation. Commercial image correlation software was used to analyze the displacements. Mean displacements for the nine different abutments were calculated in all three dimensions and for overall displacement in space. A t test with a step-down Bonferroni correction was used for a pairwise comparison of each abutment's mean displacements to the other abutments to determine statistical differences (α = .05). RESULTS: The Atlantis titanium, Inclusive titanium, and Legacy zirconia abutments showed mean displacements that were statistically significantly higher than other abutments in the horizontal direction. The overall three-dimensional displacement of the Atlantis titanium abutment after an applied 30-Ncm torque was significantly higher than that of six of the other eight abutments (P < .0144). CONCLUSION: Within the limitations of this in vitro study, the Zimmer PSA demonstrated less displacement between hand tightening and torqueing than the Atlantis titanium or Inclusive titanium abutments when used to restore a TSV implant.

Load to failure of different titanium abutments for an internal hexagon implant.

STATEMENT OF PROBLEM: Several aftermarket abutments are available for a commonly used internal hexagonal connection implant. However, their load to failure performance is unknown when compared with the manufacturer's abutment. PURPOSE: The purpose of this in vitro study was to conduct a load to failure comparison of 5 different titanium abutments (manufacturer's and aftermarket) for cement-retained restorations used on an implant with an internal hexagon connection. MATERIAL AND METHODS: Five implants (Tapered Screw-Vent, 4.1×11.5 mm; Zimmer Dental) were individually secured in a loading apparatus, and 3 abutment specimens of each of the 5 different titanium abutments (Atlantis, AstraTech TiDesign, Legacy Straight Contoured, Inclusive Custom, and Zimmer PSA) (n=15 total) were loaded at a 30-degree angle until fracture of the implant abutment complex. Data for load to fracture were compared with analysis of variance and a Tukey-Kramer post hoc test (α=.05). RESULTS: Significant differences were noted between the fracture loads of some abutment pairs; Atlantis-AstraTech TiDesign, Atlantis-Legacy Straight Contoured, AstraTech TiDesign-Legacy Straight Contoured, Inclusive Custom-AstraTech TiDesign, and Inclusive Custom-Legacy Straight Contoured (P<.05). The highest overall resistance to fracture was achieved by the Legacy Straight Contoured Abutment, which was significantly greater than all other aftermarket abutments (P<.05). Tested abutments fractured at an average of 649.17 N. The Zimmer PSA abutment was the only abutment that showed no fracture of any of the components before implant failure. CONCLUSION: When comparing manufacturer's versus aftermarket brands, the manufacturer's abutment (Zimmer PSA) was the only abutment without fracture of any of the components. Aftermarket brands experienced screw fractures, which could result in further clinical prosthetic complications. The clinical implications of these findings need further investigation.

Load to failure of different zirconia abutments for an internal hexagon implant.

STATEMENT OF PROBLEM: Various zirconia abutment designs are available to restore implant systems. Fracture resistance is one of the criteria involved in selecting among these options. PURPOSE: The purpose of this in vitro study was to measure and compare load to failure for 5 zirconia abutments for an internally hexagon implant. MATERIAL AND METHODS: Five 4.1×11.5-mm Zimmer tapered screw-vent implants were individually secured in a loading apparatus, and 3 specimens of each of the 5 different abutments (Zimmer Contour with a Ti ring, anatomic-contour Atlantis-Zr, anatomic-contour Inclusive-Zr, anatomic-contour Astra Tech ZirDesign, Legacy Straight Contoured abutment with Ti core) (N=15) were loaded at a 30-degree angle until the implant abutment complex failed. Data for load to failure were compared with analysis of variance and a Tukey-Kramer post hoc test (α=.05). RESULTS: The custom anatomic-contour abutment (Inclusive) showed the lowest load to fracture, and the stock anatomic-contour (AstraTech ZirDesign) the second lowest load to fracture. These were significantly lower than all other abutments (P<.05). The highest overall fracture strength was of a zirconia abutment with a titanium core-hexagon (Legacy Straight Contoured), which was significantly greater than all other abutments (P<.05). Anatomic-contour zirconia abutments fractured at an average of 275 N compared with the average fracture load of 842 N for zirconia abutments with titanium component (P<.05). CONCLUSION: The stock zirconia abutment with a titanium ring and the zirconia abutment with a titanium core-hexagon (Legacy Straight Contoured) had significantly greater fracture resistance than that of any of the 1-piece anatomic-contour zirconia abutments tested.

Displacement of screw-retained splinted and nonsplinted restorations into implants with conical internal connections.

PURPOSE: Variable abutment displacement could potentially affect proximal contacts, incisal edge position, or occlusion of implant-supported prostheses. This study aimed to measure and compare displacements of splinted and nonsplinted restorations into implants featuring internal conical connections as screws were tightened by hand or by torque driver. MATERIALS AND METHODS: A stereolithic resin model was printed using computed tomography data from a patient missing mandibular left first and second molars. Two 5.0 × 11-mm implants were placed in the edentulous site using a surgical guide. Two sets (splinted and nonsplinted) of gold screw-retained prostheses were made indirectly to fit the implants in the stereolithic model representing the patient. The axial position of the crowns relative to a fixed location on the model was recorded following hand tightening using the three-dimensional image correlation technique and image correlation software. A pair of high-resolution digital cameras provided a synchronized view of the model during the experiment. Relative crown positions were again recorded after tightening with a torque driver to 25 Ncm. Testing was repeated randomly three times for each set of crowns. Displacement data after torque tightening were compared using a factorial analysis of variance with JMP 9.0 software (SAS) followed by a Tukey-Kramer post hoc test (α = .05). Interproximal contacts were evaluated using an 8-µm tin foil shim after tightening by hand and torque driver. RESULTS: Displacements for splinted and nonsplinted restorations differed only in a buccal direction. The nonsplinted crowns displaced significantly more than splinted crowns. Discernible differences were observed for the tin foil shim when dragged through proximal contacts following hand versus torque tightening. CONCLUSION: Differences between screw tightening by hand or torque driver should be taken into consideration during laboratory and clinical adjustments to prevent esthetic and functional complications.

Pilot study of 3D image correlation photogrammetry to assess strain and deformation of mouthguard materials.

BACKGROUND/AIM: The purpose of this investigation was to conduct a pilot study to evaluate the use of 3D image correlation photogrammetry (3DIC) in comparing strain characteristics of three commercially available mouthguard materials in the actual form of a mouthguard. MATERIAL AND METHODS: 3DIC was used to measure strain and deformation on the surface of a mouthguard and a resin model. A computed tomographic scan of a maxilla of a patient was used to fabricate a resin test model. Three mouthguard materials were tested: conventional ethylene vinyl acetate; Proform TM, a thermoplastic material; and Polyshok TM, an EVA product containing polyurethane. Three mouthguards of each of the three materials were fabricated and fitted to the acrylic model for testing. A speckle pattern was applied to the external surfaces of each of the mouthguards. Static mechanical tests using a servohydraulic load frame at 10, 25, and 50 pounds of force were applied to the mouthguards while on the resin model. Strains were measured in both the horizontal (x) and vertical (y) axes using (3DIC). Measured strains were analysed by 4-way anova. RESULTS: For all three materials tested, the difference in strain between two measured directions (X and Y) was found to be statistically significant for all regions evaluated. The analysis indicated that each direction, region, and load was involved in a statistically significant effect (P < 0.001). Statistical differences in the strain were noted with the highest strain region being closest to the applied load for all three materials. Differences in strains in two directions were found to be significant for the materials studied (P < 0.001). CONCLUSIONS: 3DIC is useful in evaluation of mouthguard materials in the actual form of a mouthguard. Materials, along with larger sample sizes, may improve confidence levels of the results. Further testing is indicated before clinical claims can be made.

Displacement of screw-retained single crowns into implants with conical internal connections.

PURPOSE: Internal conical implant-abutment connections without platforms may lead to axial displacement of crowns during screw tightening. This displacement may affect proximal contacts, incisal edge position, or occlusion. This study aimed to measure the displacement of screw-retained single crowns into an implant in three dimensions during screw tightening by hand or via torque driver. MATERIAL AND METHODS: A stereolithic acrylic resin cast was created using computed tomography data from a patient missing the maxillary right central incisor. A 4.0- × 11-mm implant was placed in the edentulous site. Five porcelain-fused-to-metal single crowns were made using "cast-to" abutments. Crowns were tried on the stereolithic model, representing the patient, and hand tightened. The spatial relationship of crowns to the model after hand tightening was determined using three-dimensional digital image correlation (3D DIC), an optical measurement technique. The crowns were then tightened using a torque driver to 20 Ncm and the relative crown positions were again recorded. Testing was repeated three times for each crown, and displacement of the crowns was compared between the hand-tightened and torqued states. Commercial image correlation software was used to analyze the data. Mean vertical and horizontal crown displacement values were calculated after torqueing. The interproximal contacts were evaluated before and after torquing using an 8-µm aluminum foil shim. RESULTS: There were vertical and horizontal differences in crown positions between hand tightening and torqueing. Although these were small in magnitude, detectable displacements occurred in both apical and facial directions. After hand tightening, the 8-µm shim could be dragged without tearing. However, after torque tightening, the interproximal contacts were too tight and the 8-µm shim could not be dragged without tearing. CONCLUSION: Differences between hand tightening and torque tightening should be taken into consideration during laboratory and clinical adjustments to prevent esthetic and functional complications.

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.

Comparison of strains for splinted and nonsplinted screw-retained prostheses on short implants.

PURPOSE: Because the evidence regarding the efficacy of splinting short implants on strain distribution is limited, this study aimed to measure and compare the strains generated by splinted and nonsplinted screw-retained implant crowns for short implants with internal connections. MATERIAL AND METHODS: Computed tomographic scan data of a patient missing all mandibular molar teeth were digitized using a software program, and stereolithography was then used to produce an acrylic resin cast. Two 4- x 6-mm implants were placed in the left side. One set of splinted crowns and one set of nonsplinted crowns were made to fit the two implants using screw retention. Three-dimensional image correlation was used for full-field measurement of strains and provided a synchronized stereo view of the cast during the experiment. Cameras recorded changes in random dot patterns that had been applied to the surface of the cast as the prostheses were loaded up to 400 N in vertical and oblique directions using a universal testing machine. Testing was repeated three times for splinted and nonsplinted crowns. An image correlation algorithm used the dot pattern to define correlation areas. Coordinates of these areas were determined for each recorded photograph and used to calculate the strains. Strain distribution data were compared for maximum and minimum principal strains. RESULTS: Qualitative data showed evidence of increased load sharing for splinted, screw-retained prostheses regardless of the direction of the load applied. However, the only statistically significant difference between the two prosthesis types occurred for peak maximum principal strain under oblique loading. CONCLUSIONS: Splinting short implants may provide a more even strain distribution during functional loading. Clinical corroboration of these findings is needed.

Comparison of strains for splinted and nonsplinted implant prostheses using three-dimensional image correlation.

PURPOSE: This study aimed to analyze and compare strain distribution patterns for splinted and nonsplinted restorations for dental implants with an internal conical connection. MATERIALS AND METHODS: Two stereolithic acrylic resin models were created using computed tomographic scan data from a patient missing all mandibular molar teeth. Two implants were placed in the right side of two mandibular models using a computer-generated surgical guide and appropriate protocol. The first model received 5 x 13-mm implants, and the second received 5 x 11-mm implants. Three splinted and three nonsplinted sets of gold screw-retained prostheses were created to fit the implants on each of the two stereolithic models. The 3D image correlation technique was used for full-field measurement of strains using commercial image correlation software and a pair of high-resolution digital cameras, which provided a synchronized stereo view of the models during the experiment. Static loads of up to 203 N were applied in vertical and oblique directions. Strain distribution data were compared for major and minor strains. A mixed-models analysis of variance was done to evaluate all main effect and two-way interactions for each strain, and P values were corrected for multiple comparisons using the step-down Bonferroni adjustment. RESULTS: Evidence of increased load sharing for the splinted prostheses compared to the nonsplinted prostheses was shown. Strain distribution data represented by the ratio of anterior and posterior peak strains were not statistically different for the splinted and nonsplinted prostheses for either implant length. CONCLUSIONS: Splinted prostheses generated more uniform strain distributions; however, the strain distribution data were not statistically different from that seen for the nonsplinted prostheses. This suggests that splinting may not be significant for internally connected implants when the crown-to-implant ratio is less than 1. However, clinical corroboration of these findings is required.