Marginal Adaptation of Implant-Supported Metal-Ceramic Crowns Fabricated With Gold Cylinders

Purpose The purpose of this investigation was to determine the mean marginal discrepancy of metal-ceramic crowns fabricated with gold cylinders and cemented on implant abutments. These discrepancies were then compared with those measured previously for implant-supported ceramic crowns. Materials and Methods Fifteen Nobel BioCare CeraOne abutments were connected to implant fixtures embedded in acrylic resin blocks. Marginal discrepancies were determined for gold cylinders, gold cylinders plus ceramic alloy (metal frameworks), completed metal-ceramic crowns, and cemented metal-ceramic crowns using a stereomicroscope equipped with a video camera linked to a computer. A Hotelling's T² test (p .05) was used to evaluate potential differences in mean marginal discrepancies among groups. Results The mean marginal discrepancies were: 1) gold cylinders, 7.56 ± 2.73 μm; 2) metal frameworks, 6.21 ± 1.34 μm; 3) metal-ceramic crowns, 11.06 ± 3.21 μm; and 4) zinc-phosphate cemented crowns, 31.47 ± 6.65 μm. No significant difference between gold cylinders and metal frameworks was found. Mean marginal discrepancies for metal-ceramic crowns were significantly greater than discrepancies for cast gold cylinders. Cemented-crown mean marginal discrepancy was significantly greater than all other means. Conclusions Cemented metal-ceramic crowns fabricated using proprietary gold cylinders exhibited well-fitting margins (31.47 μm).     

Randomized controlled clinical trial of customized zirconia and titanium implant abutments for canine and posterior single-tooth implant reconstructions: preliminary results at 1 year of function

Objectives: The aim of this study was to test whether or not customized zirconia abutments exhibit the same survival rates in canine and posterior regions as titanium abutments, and to compare the esthetic result of the two abutment types. Material and methods: Twenty‐two patients with 40 implants in posterior regions were included and the implant sites were randomly assigned to 20 customized zirconia and 20 customized titanium abutments. All‐ceramic (AC) and metal–ceramic (MC) crowns were fabricated. In all except two cases, the crowns were cemented on the abutments using resin or glass‐ionomer cements. Two zirconia reconstructions were screw retained. At baseline, 6 and 12 months, the reconstructions were examined for technical and biological problems. Probing pocket depth (PPD), plaque (Pl) and bleeding on probing (BOP) were assessed and compared with natural control teeth. Furthermore, the difference of color (ΔE) of the peri‐implant mucosa and the gingiva of control teeth was evaluated by means of a spectrophotometer (Spectroshade). The data were analyzed with Student's unpaired t‐test, ANOVA and regression analyses. Results: Twenty patients with 19 zirconia and 12 titanium abutments were examined at a mean follow‐up of 12.6±2.7 months. The survival rate for reconstructions and abutments was 100%. No technical or biological problems were found at the test and control sites. Two chippings (16.7%) occurred at crowns supported by titanium abutments. No difference was found regarding PPD (meanPPD_ZrO2 3.4±0.7 mm, mPPD_Ti 3.3±0.6 mm), Pl (mPl_ZrO2 0.2±0.3, mPl_Ti 0.1±1.8) and BOP (mBOP_ZrO2 60±30%, mBOP_Ti 30±40%) between the two groups. Both crowns on zirconia and titanium abutments induced a similar amount of discoloration of the soft tissue compared with the gingiva at natural teeth (ΔE_ZrO2 8.1±3.9, ΔE_Ti 7.8±4.3). Conclusions: At 1 year, zirconia abutments exhibited the same survival and a similar esthetic outcome as titanium abutments.     

Prefabricated zirconium dioxide implant abutments for single‐tooth replacement in the posterior region: evaluation of peri‐implant tissues and superstructures after 12 months of function

Aim: In the present study, prefabricated abutments made of zirconium dioxide Y‐TZP (tetragonal zirconia polycrystals) were inserted into the posterior region under controlled clinical conditions. The aim was to test whether abutments made of zirconium dioxide are suitable for this indication. Investigation parameters included reactions of peri‐implant tissue and the structural integrity of the all‐ceramic superstructures on the implants. Results after 12 months in function are reported in this article. Material and methods: Forty implants of the XiVE^® S plus screw‐type implants (DENTSPLY Friadent) were inserted into the posterior region of 24 patients. After the healing period, the implants were provided with all‐ceramic abutments made of zirconium dioxide Y‐TZP (FRIADENT^® CERCON^® Abutment; DENTSPLY Friadent). All‐ceramic crowns (CERCON^® smart ceramics; DENTSPLY DeguDent) were used as superstructures and cemented using the conventional method. The following parameters were used to document the state of soft tissue: modified plaque index (mPI), sulcus fluid flow rate (SFFR, Periotron; Oraflow Inc), modified sulcus bleeding index (mSBI) and pocket depth (ST). Mesial and distal bone levels were determined on radiographs during the prosthetic treatment and at the 12‐month recall. The Periotest^? (Medizintechnik Gulden) was used to determine implant stability. Results: All implants could be followed up after 12 months in function. In the presence of good oral hygiene (mPI: 0.5), the parameters SFFR (18) and mSBI (0.5) were indicative of stable and healthy soft tissue. ST was highest at the distal points of measurement (2.3 mm) and was generally at a low level. Compared with the baseline situation, proximal bone defects were reduced from ?1.1 to ?1 mm during the 12‐month period of functioning. The mean Periost^? values at the 12‐month recall were ?1.9 in the maxilla and ?3.8 in the mandible. Neither implant loss nor crown fractures occurred. Chipping of parts of the veneering ceramic was registered in four cases (10%). Conclusion: After 12 months of wear, no mechanical failure was registered in any of the all‐ceramic abutments. On clinical investigation, the peri‐implant hard and soft tissues were largely healthy and devoid of inflammation. To cite this article:
Nothdurft F, Pospiech P. Prefabricated zirconium dioxide implant abutments for single‐tooth replacement in the posterior region: evaluation of peri‐implant tissues and superstructures after 12 months of function.
Clin. Oral Impl. Res. 21 , 2010; 857–865.
doi: 10.1111/j.1600‐0501.2009.01899.x     

The effect of mechanical cycling and different misfit levels on Vicker's microhardness of retention screws for single implant-supported prostheses

Purpose: The aim of this study was to evaluate the effect of mechanical cycling and different misfit levels on Vicker's microhardness of retention screws for single implant‐supported prostheses. Materials and Methods: Premachined UCLA abutments were cast with cobalt‐chromium alloy to obtain 48 crowns divided into four groups (n = 12). The crowns presented no misfit in group A (control group) and unilateral misfits of 50 μm, 100 μm, and 200 μm in groups B, C, and D, respectively. The crowns were screwed to external hexagon implants with titanium retention screws (torque of 30 N/cm), and the sets were submitted to three different periods of mechanical cycling: 2×10⁴, 5×10⁴, and 1×10⁶ cycles. Screw microhardness values were measured before and after each cycling period. Data were evaluated by two‐way ANOVA and Tukey's test (p < 0.05). Results: Mechanical cycling statistically reduced microhardness values of retention screws regardless of cycling periods and groups. In groups A, B, and C, initial microhardness values were statistically different from final microhardness values (p < 0.05). There was no statistically significant difference for initial screw microhardness values (p > 0.05) among the groups; however, when the groups were compared after mechanical cycling, a statistically significant difference was observed between groups B and D (p < 0.05). Conclusions: Mechanical cycling reduced the Vicker's microhardness values of the retention screws of all groups. The crowns with the highest misfit level presented the highest Vicker's microhardness values.     

Fracture Strength and Failure Mode of Maxillary Implant-Supported Provisional Single Crowns: A Comparison of Composite Resin Crowns Fabricated Directly Over PEEK Abutments and Solid Titanium Abutments

Background: Polyetheretherketone (PEEK) temporary abutments have been recently introduced for making implant‐supported provisional single crowns. Little information is available in the dental literature on the durability of provisional implant‐supported restorations. Purpose: The objectives of this study were to evaluate the fracture strength of implant‐supported composite resin crowns on PEEK and solid titanium temporary abutments, and to analyze the failure types. Material and Methods: Three types of provisional abutments, RN synOcta Temporary Meso Abutment (PEEK; Straumann), RN synOcta Titanium Post for Temporary Restorations (Straumann), and Temporary Abutment Engaging NobRplRP (Nobel Biocare) were used, and provisional screw‐retained crowns using composite resin (Solidex) were fabricated for four different locations in the maxilla. The specimens were tested in a universal testing machine at a crosshead speed of 1 mm/minute until fracture occurred. The failure types were analyzed and further categorized as irreparable (Type 1) or reparable (Type 2). Results: No significant difference was found between different abutment types. Only for the position of the maxillary central incisor, composite resin crowns on PEEK temporary abutments showed significantly lower (p < 0.05) fracture strength (95 ± 21 N) than those on titanium temporary abutments (1,009 ± 94 N). The most frequently experienced failure types were cohesive fractures of the composite resin crowns (75 out of 104), followed by screw loosening (18 out of 104). According to reparability, the majority of the specimens were classified as Type 1 (82 out of 104). Type 2 failures were not often observed (22 out of 104). Conclusions: Provisional crowns on PEEK abutments showed similar fracture strength as titanium temporary abutments except for central incisors. Maxillary right central incisor composite resin crowns on PEEK temporary abutments fractured below the mean anterior masticatory loading forces reported to be approximately 206 N.     

Marginal Discrepancy of All-Ceramic Crowns Cemented on Implant Abutments

Purpose The purpose of this investigation was to determine the mean marginal discrepancy of all-ceramic crowns cemented on implant abutments. Materials and Methods Five Brånemark CeraOne abutments were connected to implant fixtures embedded in acrylic resin blocks. The marginal discrepancy was measured using a video camera connected to a digitizing board at four locations on each abutment for five samples in each of the following groups: all-ceramic caps (caps), all-ceramic crowns (crowns), and all-ceramic crowns cemented with zinc phosphate cement (cemented crowns). Results The mean marginal discrepancies were as follows: caps, 99.0 μm (SD, 16); crowns, 117.8 μm (SD, 20); and cemented crowns, 168.8 μm (SD, 23). Statistically significant differences were found between all three groups at the 99% level of confidence. In addition there were two significant differences between abutments. Conclusions Subgingival marginal discrepancies of the magnitude measured in this study have been shown to cause periodontal problems. It is probable that the marginal discrepancy of CeraOne restorations, as tested, can be improved. Efforts should be made to enhance the marginal accuracy of these restorations.     

Effect of virtual cement gap settings on the marginal fit of cemented resin-ceramic crowns on implant abutments

Statement of problemAgreement on the perfect virtual cement space value for computer-aided design and computer-aided manufacturing (CAD-CAM) implant-supported resin-ceramic crowns with the best marginal adaptation is lacking. The range of cement gap settings in some CAD design software programs is wide (0 to 200 μm), and manufacturer recommendations regarding the best cement gap setting for certain types of ceramics is not specific.PurposeThe purpose of this in vitro study was to evaluate the effect of virtual cement gap settings on the marginal fit of cemented resin-ceramic crowns on implant abutments.Material and methodsThirty implant analogs and matching stock abutments were coupled and implanted into autopolymerizing acrylic resin blocks. Three groups (n=10) of resin-ceramic molar crowns with 3 different virtual cement space settings (40, 60, and 100 μm) were designed by using a CAD design software program. The crowns were cemented over their corresponding abutments under a static load by using a specially designed cementing device. A scanning electron microscope was used to measure the mean vertical marginal gap (MG) for each group, where a total of 120 measurements for each of the 3 groups (12 sites per crown and 10 crowns per group) were evaluated. One-way analysis of variance and the post hoc Tukey pairwise comparison tests were used to analyze the data (α=.05).ResultsA significant difference (P<.001) was found between the MG values of the resin-ceramic implant-supported crowns fabricated by using the 3 cement space settings. The smallest MG was obtained with the 60-μm setting as compared with the 40-μm and 100-μm settings.ConclusionsA limited inverse relation was found between the MGs of CAD-CAM-fabricated resin-ceramic implant-supported crowns and the cement gap settings in the exocad software program. The smallest MGs were obtained when a 60-μm cement space value was used (P<.001).     

The Effects of Abutment Wall Height, Platform Size, and Screw Access Channel Filling Method on Resistance to Dislodgement of Cement-Retained, Implant-Supported Restorations

PURPOSE: Factors affecting the retention of fixed prostheses to natural abutments are well understood. In contrast, little is known concerning factors influencing the retention of fixed prostheses cemented to implant abutments. The purpose of this study was to investigate the effect that varying implant abutment wall height, platform size, and screw access channel filling method has on the retention of castings cemented to implant abutments using TempBond. MATERIALS AND METHODS: Four 15 degrees preangled abutments (Nobel Biocare Replace Select Esthetic) of each platform size--narrow (NP), regular (RP), and wide (WP)--were used. In each group of abutments the screw access axial wall was either unadjusted, one-third removed, two-thirds removed, or completely removed. The screw access channels were either fully or partially filled with Memosil, a vinyl polysiloxane impression material. For each abutment a casting was constructed that incorporated an attachment to allow removal. Castings were cemented to abutments with TempBond. The tensile force required to separate the cemented castings from the abutments was measured using an Instron Universal load-testing machine. RESULTS: The mean peak removal force for comparable abutments was significantly different ( p < 0.05): (1) where the screw access channel was completely filled with Memosil compared with those partially filled with Memosil; (2) with platform sizes--WP > RP > NP; (3) with alteration of axial wall height--1/3 removed > unadjusted = 2/3 removed > total wall removal. CONCLUSIONS: The retention of castings cemented to implant abutments with TempBond is influenced by the wall height, platform size, and the filling modality of the screw access channel.     

Fracture behavior of straight or angulated zirconia implant abutments supporting anterior single crowns

The aim of the study was to evaluate the influence of artificial aging on the fracture behavior of straight and angulated zirconia implant abutments (ZirDesign?; Astra Tech, Mölndal, Sweden) supporting anterior single crowns (SCs). Four different test groups (n?=?8) representing anterior SCs were prepared. Groups 1 and 2 simulated a clinical situation with an ideal implant position (left central incisor) from a prosthetic point of view, which allows for the use of a straight, prefabricated zirconia abutment. Groups 3 and 4 simulated a situation with a compromised implant position, requiring an angulated (20°) abutment. OsseoSpeed? implants (Astra Tech) 4.5 mm in diameter and 13 mm in length were used to support the abutments. The SCs (chromium cobalt alloy) were cemented with glass ionomer cement. Groups 2 and 4 were thermomechanically loaded (TCML?=?1.2?×?10⁶; 10,000?×?5°/55°) and subjected to static loading until failure. Statistical analysis of force data at the fracture site was performed using nonparametric tests. All samples tested survived TCML. Artificial aging did not lead to a significant decrease in load-bearing capacity in either the groups with straight abutments or the groups with angulated abutments. The restorations that utilized angulated abutments exhibited higher fracture loads than the restorations with straight abutments (group 1, 280.25?±?30.45 N; group 2, 268.88?±?38.00 N; group 3, 355.00?±?24.71 N; group 4, 320.71?±?78.08 N). This difference in load-bearing performance between straight and angulated abutments was statistically significant (p?=?0.000) only when no artificial aging was employed. The vast majority of the abutments fractured below the implant shoulder.     

Influence of implant abutment angulations on the fracture resistance of overlaying CAM-milled zirconia single crowns

Background: An in vitro study was performed to assess the effect of three implant abutment angulations and three core thicknesses on the fracture resistance of overlaying computer‐aided manufacturing (CAM) milled zirconia (Cercon^® system) single crowns. Methods: Three groups, coded A to C, with different implant abutment angulations (group A/0°, group B/15° and group C/30° angulation) were used to construct 15 crowns for each angulation. Forty‐five overlay restorations were milled using the Cercon^® system with zirconium core thicknesses of 0.4, 0.6 and 0.8 mm using five crowns for each angulation. The final restorations were prepared and stored in distilled water at mouth temperature (37 °C) for 24 hours prior to testing. The restorations were cemented using Temp Bond^®. The load required to break each crown and the mode of failure were recorded. All the results obtained were statistically analysed by the ANOVA test (level of significance p < 0.05). Tested crowns were examined using a stereomicroscope at 40X and selected crowns (five randomly selected from each group were further examined by scanning electron microscopy) to reveal the zirconia–ceramic interface and to determine the fracture origin. Results: Implant abutment angulations significantly (p < 0.05) reduced the fracture resistance of overlaying CAM‐milled zirconia single crowns. The fracture loads of Cercon^® crowns cemented onto abutment preparations with a 30° angulation were the lowest of the groups tested. The core thickness (0.4 to 0.8 mm) did not significantly (p > 0.05) affect the fracture resistance of the CAM‐milled zirconia single crowns. SEM showed that the origin of the fracture appeared to be located at the occlusal surfaces of the crowns and the crack propagation tended to radiate from the occlusal surface towards the gingival margin. Conclusions: The implant angulation of 30° significantly (p < 0.05) reduced the fracture resistance of overlaying CAM‐milled zirconia single crowns. Reducing the core thickness from 0.8 mm to 0.4 mm did not affect (p > 0.05) the fracture resistance of overlaying CAM‐milled zirconia single crowns.     

Influence of scanner,powder application,and adjustments on CAD-CAM crown misfit

Statement of problem

The manufacturers of computer-aided design and computer-aided manufacturing (CAD-CAM) systems emphasize that new technologies can improve the marginal fit of dental crowns. However, data supporting this claim are limited.

Marginal adaptation of all-ceramic crowns on implant abutments

Background: Studies focusing on the marginal accuracy of all‐ceramic crowns on implant abutments are in short supply. Purpose: This study evaluated the marginal accuracy of all‐ceramic crowns on different implant abutments. Materials and Methods: Ninety‐six standardized maxillary central incisor crowns (48 alumina and 48 zirconia) were fabricated for each of the six test groups (n = 16) (Ti1, titanium abutments–alumina crowns; Ti2, titanium abutments–zirconia crowns; Al1, alumina abutments–alumina crowns; Al2, alumina abutments–zirconia crowns; Zr1, zirconia abutments–alumina crowns; Zr2, zirconia abutments–zirconia crowns). The crowns were adhesively luted using a resin luting agent. The marginal gaps were examined on epoxy replicas before and after luting as well as after masticatory simulation at 200× magnification. Results: The geometrical mean (95% confidence limits) marginal gap values before cementation, after cementation, and after masticatory simulation were group Ti1: 39(37–42), 57(53–62), and 49(46–53); group Ti2: 43(40–47), 71(67–76), and 64(59–69); group Al1: 57(54–61), 87(85–90), and 67(65–69); group Al2: 66(63–69), 96(90–101), and 75(72–78); group Zr1: 54(51–57), 79(76–82), and 65(63–67); and group Zr2: 64(60–68), 85(80–91), and 75(70–81). The comparison between non‐cemented and cemented stages in each group demonstrated a significant increase in the marginal gap values after cementation in all groups (p < .001), while the comparison between cemented and aged stages in each group showed a significant decrease in the marginal gap values in groups Al1, Al2, and Zr1 (p < .0001). This reduction was not significant for groups Ti1, Ti2, and Zr2 (p > .05). Conclusion: The marginal accuracy of all tested restorations meets the requirements for clinical acceptance.     

Bone substitute as an on‐lay graft on rat tibia

Objectives: To investigate the capacity of Cerament^®, an injectable bone substitute, to guide bone generation from a cortical surface. Materials and method: Cerament^® was applied to the cortical surface of rat tibiae and investigated histologically after 3, 6 and 12 weeks, using a procedure similar to that performed in sham‐operated rats. Results: In both groups, the thickness of the bone cortex increased significantly from 473±58 μm (mean±SD) at day 0 to 1193±255 μm (Cerament^®) and 942±323 μm (sham) after 3 weeks. In the Cerament^® group, the new bone thickness remained constant (1258±288 μm) until the end of the experiment at 12 weeks, while the sham group demonstrated a return to initial cortical thickness (591±73 μm) at 12 weeks. The newly formed bone in the Cerament^® group was highly trabecular after 3 weeks but attained a normal trabecular structure of the cortex after 12 weeks. Conclusion: Cerament^® may guide bone generation from an intact cortical bone surface. Although bone remodeling speed may differ between rats and humans, our study indicates that Cerament^® may become a useful alternative to autologous bone, both to fill defects and to increase bone volume by cortical augmentation. To cite this article:
Truedsson A, Wang J‐S, Lindberg P, Gordh M, Sunzel B, Warfvinge G. Bone substitute as an on‐lay graft on rat tibia. Clin. Oral Impl. Res. 21 , 2010; 424–429.
doi: 10.1111/j.1600‐0501.2009.01875.x     

Fracture behaviour of implant–implant- and implant–tooth-supported all-ceramic fixed dental prostheses utilising zirconium dioxide implant abutments

This in vitro study investigated the fracture behaviour of implant–implant-supported and implant–tooth-supported all-ceramic fixed dental prostheses (FDP) using zirconium dioxide implant abutments (FRIADENT® CERCON® abutments, DENTSPLY Friadent). Six different test groups (n?=?8) were prepared. Groups 1, 2, 4, and 5 represented an implant–implant-supported FDP condition, whereas groups 3 and 6 simulated an implant–tooth-supported FDP condition. The second right premolar of the mandible was replaced with a pontic tooth. In groups 2 and 5, implant abutments were individualised by circumferential preparation. XiVe® S plus screw implants (DENTSPLY Friadent) that were 4.5 mm (first molar) and 3.8 mm (first premolar) in diameter and 11 mm in length and metal tooth analogues with simulated periodontal mobility, representing the first right premolar, were mounted in a polymethyl methacrylate block. The FDPs were cemented with KetacCem (3 M Espe GmbH, Germany). Groups 4, 5, and 6 were thermomechanically loaded (thermal and mechanical cycling (TCML)?=?1.2?×?10⁶; 10,000?×?5°/55°) and subjected to static loading until failure. Statistical analysis of data obtained for the force at fracture was performed using non-parametric tests. All samples tested survived TCML. In the implant–implant-supported groups, circumferential abutment preparation resulted in a tendency to lower fracture forces compared to groups with unprepared abutments (group 1, 472.75?±?24.71 N; group 2, 423.75?±?48.48 N; group 4, 647.13?±?39.10 N; group 5, 555.86?±?30.34 N). The implant–tooth-supported restorations exhibited higher fracture loads (group 3, 736.25?±?82.23 N; group 6, 720.75?±?48.99 N) than the implant–implant-supported restorations which did not possess circumferentially individualised abutments. Statistically significant differences were found when comparing the non-artificially aged groups. Implant–tooth-supported FDP restorations did exhibit an increased fracture load compared to implant–implant-supported FDP restorations.     

Resonance frequency measurements in vivo and related surface properties of magnesium-incorporated, micropatterned and magnesium-incorporated TiUnite®, Osseotite®, SLA® and TiOblast® implants

Objective: To investigate implant stability using resonance frequency measurements of topographically changed and/or surface chemistry‐modified implants in rabbit bone. Material and methods: Six groups of microstructured, screw‐shaped titanium implants: two oxidized, cation‐incorporated experimental implants [Mg implants and MgMp implants with micropatterned thread flanges (80–150 μm wide and 60–70 μm deep)] and four commercially available clinical implants (TiUnite^®, Osseotite^®, SLA^®, and TiOblast^®) were installed in 10 rabbit tibia for 6 weeks. The surface properties of the implants were characterized in detail using several analytical techniques. Implant stability was measured using a resonance frequency analyzer (Osstell^?). Results: Surface characterization of the implants revealed microstructured, moderately rough implant surfaces varying 0.7–1.4 μm in S_a (mean height deviation), but with clear differences in surface chemistry. After 6 weeks, all implants showed statistically significantly higher increases in implant stability. When compared with one another, MgMp implants showed the most significant mean implant stability quotient (ISQ) value relative to the others (P≤0.016). In terms of increment (ΔISQ) in implant stability, MgMp implants showed a significantly greater value as compared with Osseotite^® (P≤0.005), TiOblast^® (P≤0.005), TiUnite^® (P≤0.005), SLA^® (P≤0.007), and Mg implants (P≤0.012). In addition, transducer direction dependence of resonance frequency analysis (RFA) measurements was observed such that the differences in the mean ISQ values between longitudinal and perpendicular measurements were significant at implant placement (P≤0.004) and after 6 weeks (P≤0). Conclusion: The present study found that implant surface properties influence RFA measurements of implant stability. Surface chemistry‐modified titanium implants showed higher mean ISQ values than did topographically changed implants. In particular, cation (magnesium)‐incorporated micropatterns in MgMp implants may play a primary role in ΔISQ.     

Comparison of the effects of cement removal from zirconia and titanium abutments: An in vitro study

Statement of problem

Excess cement around dental implants is a significant cause of peri-implant inflammation. Research has focused on approaches to cement removal, the type of cement used, and the different instruments used for cement removal with titanium abutments. However, data comparing zirconia with titanium abutments are lacking.

Evaluation of the marginal precision of one-piece complete arch titanium frameworks fabricated using five different methods for implant-supported restorations

Objective: The aim of the present work was to compare the marginal precision of titanium frameworks for a complete arch‐fixed prosthesis fabricated using five different methods. Methods: A prospective study was designed. Fifteen titanium frameworks for totally edentulous upper or lower jaws, each supported by five to nine implants, were assigned to five study groups, so as to have three frameworks in each group for each technique: (1) lost wax technique frameworks, (2) cast titanium sovrastructures laser welded to prefabricated titanium copings, (3) Procera ^® Implant Bridge, (4) Cresco Ti System^? and (5) CAM StructSURE^® Precision Milled Bar. The microgap between the framework and the shoulders of implant analogues was measured on the master cast with a stereomicroscope at a magnification of 100 × at four different locations, yielding a total of 364 data points on 91 implants. Data were analyzed using an ANOVA and a Tukey post hoc test (P=<0.05). Results: The mean values for the microgap were 78 μm (SD±48) for lost wax technique frameworks, 33 μm (SD±19) for cast titanium sovrastructures laser welded to titanium copyings, 21 μm (SD±10) for the Procera ^® implant bridge, 18 μm (SD±8) for the Cresco Ti System^? and 27 μm (SD±15) for the CAM StructSURE^®. The differences among the mean values were statistically significant (P<0.01 or P<0.05). The comparisons among groups 3, 4, and 5 and between groups 2 and 5 were not significant (P>0.05). Conclusion: The computer‐aided procedures analyzed in the present study were able to produce a precision‐fitting framework, with no significant differences among them and, at the same time, showed a greater precision compared with the traditional casting methods or with the use of prefabricated titanium copings. However, it should be noted that, even if group 2 frameworks were not as accurate as groups 3 and 4, cast titanium sovrastructures laser welded to prefabricated titanium copings showed significantly better marginal precision than the frameworks produced with the lost wax technique.     

Accuracy of digital and conventional impression techniques and workflow

Objectives

Digital impression techniques are advertised as an alternative to conventional impressioning. The purpose of this in vitro study was to compare the accuracy of full ceramic crowns obtained from intraoral scans with Lava C.O.S. (3M ESPE), CEREC (Sirona), and iTero (Straumann) with conventional impression techniques.

Materials and methods

A model of a simplified molar was fabricated. Ten 2-step and 10 single-step putty-wash impressions were taken using silicone impression material and poured with type IV plaster. For both techniques 10 crowns were made of two materials (Lava zirconia, Cera E cast crowns). Then, 10 digital impressions (Lava C.O.S.) were taken and Lava zirconia crowns manufactured, 10 full ceramic crowns were fabricated with CEREC (Empress CAD) and 10 full ceramic crowns were made with iTero (Copran Zr-i). The accessible marginal inaccuracy (AMI) and the internal fit (IF) were measured.

Results

For AMI, the following results were obtained (mean?±?SD): overall groups, 44?±?26 μm; single-step putty-wash impression (Lava zirconia), 33?±?19 μm; single-step putty-wash impression (Cera-E), 38?±?25 μm; two-step putty-wash impression (Lava zirconia), 60?±?30 μm; two-step putty-wash impression (Cera-E), 68?±?29 μm; Lava C.O.S., 48?±?25 μm; CEREC, 30?±?17 μm; and iTero, 41?±?16 μm. With regard to IF, errors were assessed as follows (mean?±?SD): overall groups, 49?±?25 μm; single-step putty-wash impression (Lava zirconia), 36?±?5 μm; single-step putty-wash impression (Cera-E), 44?±?22 μm; two-step putty-wash impression (Lava zirconia), 35?±?7 μm; two-step putty-wash impression (Cera-E), 56?±?36 μm; Lava C.O.S., 29?±?7 μm; CEREC, 88?±?20 μm; and iTero, 50?±?2 μm.

Conclusions

Within the limitations of this in vitro study, it can be stated that digital impression systems allow the fabrication of fixed prosthetic restorations with similar accuracy as conventional impression methods.

Clinical relevance

Digital impression techniques can be regarded as a clinical alternative to conventional impressions for fixed dental restorations.     

In vitro influence of ultrasonic stress, removal force preload and thermocycling on the retrievability of implant-retained crowns

Objectives: The main goals of this in vitro study were to evaluate the influence of thermocycling, ultrasonic stress and the removal force preload on the retrievability of cemented implant crowns using a clinical removal device (Coronaflex) and evaluating the tensile strength using a universal testing machine (UTM). Methods: Thirty‐six crowns were cast from a Co–Cr alloy for 36 tapered titanium abutments (5° taper, 4.3 mm diameter, 6 mm height, Camlog, Germany). The crowns were cemented with a glass‐ionomer (Ketac Cem) or a polycarboxylate (Durelon) cement, followed by 3 days of storage in ionized water without thermocycling or 150 days of storage with 37,500 thermal cycles between 5°C and 55°C. Before removal, the crowns were subjected to ultrasonic stress for 0, 5 or 10 min with a contact pressure of either 50 or 500 g. The Coronaflex was used with a removal force preload of 50 or 400 cN, respectively, applied on the point of loading. Scanning electronic microscopy (SEM) was used to evaluate the impact of the removal on the abutment screws. Results: Crowns cemented with the glass‐ionomer cement were significantly easier to remove with the Coronaflex or the UTM than crowns cemented with the polycarboxylate cement (P≤ 0.05). Ultrasonic stress showed no significant impact on the retrievability regardless of the contact pressure or duration applied (P>0.05). No significant differences could be found for both cements when removed with the Coronaflex or the UTM (P>0.05) after thermocycling was applied. A removal force preload of 400 cN resulted in significantly reduced removal attempts in comparison with 50 cN for both cements (P≤ 0.05). Conclusions: Ultrasound and thermal cycling did not result in reduced cement strength, but to retrieve the crowns, the full impact of a removal instrument has to be applied. Ketac Cem can be used as a “semipermanent” solution, whereas Durelon might serve for permanent cementation. None of the abutment screws showed signs of wear caused by the removal process. To cite this article :
Mehl C, Harder S, Schwarz D, Steiner M, Vollrath O, Kern M. In vitro influence of ultrasonic stress, removal force preload and thermocycling on retrievability of implant retained crowns.
Clin. Oral Impl. Res. 23 , 2012; 930–937
doi: 10.1111/j.1600‐0501.2011.02236.x     

The implant-abutment interface of alumina and zirconia abutments

Background: Although ceramic and titanium abutments are widely used in clinical practice, the mechanical characterization of the implant‐abutment interface for ceramic abutments has not been evaluated after the dynamic loading. Purpose: The purpose of this study was to assess the implant‐abutment interface after the dynamic loading of titanium, alumina, and zirconia abutments. Materials and Methods: Fifteen aluminum oxide, zirconium oxide, and titanium abutments were manufactured by the Procera System® (Nobel Biocare AB, Göteborg, Sweden) and were connected to Ø 3.75 × 13‐mm regular platform implants (MK III, Nobel Biocare AB) secured in a 30° inclined plane. A mechanical testing machine applied compressive dynamic loading between 20 and 200 N at 1 Hz on a standard contact area of copings cemented on abutments for 47.250 cycles. The measurements of microgaps at the implant‐abutment interface from the labial, palatinal, mesial, and distal surfaces of each specimen were undertaken by scanning electron microscope analyses prior to and after the experiments. The data of the microgaps before and after the dynamic loading were statistically assessed using the Wilcoxon signed rank test and the Kruskal–Wallis variance analysis (α = 0.05). Results: Coping fracture, abutment fracture, or abutment screw loosening or fracture was not detected in any specimen during the entire test period. After the dynamic loading, the titanium abutment control group revealed an increased microgap (3.47 µm) than zirconia (1.45 µm) and alumina (1.82 µm) groups at the palatinal site (p < .05). The mean measurement values at different measurement sites of specimens within and between each abutment group were similar (p > .05). Conclusion: Owing to their comparable microgap values at the implant‐abutment interface after the dynamic loading, ceramic abutments can withstand functional forces like conventional titanium abutments.