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Showing 19 results for Alikhasi

H. Siadat, A. Mirfazaelian , M. Alikhasi , M. Mohammad Alizadeh ,
Volume 20, Issue 4 (5 2008)

Background and Aim: An important criterion for success assessment of implant-supported prostheses is marginal fit. Vertical and horizontal discrepancy can result in loosening of the prosthetic screw, crestal bone resorption, peri-implantitis and loss of osseointegration. Despite careful attention to waxing, investing, and casting, marginal discrepancies are inevitable. The aim of this study was to evaluate the marginal gap and overhang in three casting methods with two different alloys in ITI implants.

Materials and Methods: In this experimental in vitro study 48 analog abutments were randomly divided into six groups as follows: 1) burn out cap + BegoStar, 2) impression cap + BegoStar, 3) conventional wax up + BegoStar, 4) burn out cap + Verabond2, 5) impression cap + Verabond2, 6) conventional wax up + Verabond2. Waxing was done in 0.7 mm thickness verified by a digital gauge and a putty index was made for all groups. Reamer was used for correction of the finish line after casting in all groups. Castings were seated on analog abutments and embedded in acrylic resin. Specimens were sectioned by isomet instrument and polished and cleaned by ultrasonic cleaner for 10 min. The marginal gap and overextended margins of castings were examined under a  Scanning Electron Microscope (SEM) (X200). The mean gap and margin overextension were calculated for each group. Data were analyzed by multivariate analysis and Bonferroni post-hoc test with p<0.05 as the level of significance.

Results: No significant difference in gap size was observed among the three casting methods with two alloys (P=0.056). The marginal gap was not different in the studied casting methods (P=0.092). Gold alloy crowns showed lower marginal gaps compared to base metal alloy crowns (P<0.001). No significant difference in overhang size was observed among casting methods with two alloys (P=0.093). Base metal alloy crowns showed less overhang compared to gold alloy crowns (P<0.001). There was a significant correlation between overhang and use of impression cap in base metal alloys (P<0.001).

Conclusion: Based on the results of this study, vertical discrepancy of frameworks made with gold alloy were less than those made with base metal alloy. Base metal alloy demonstrated less overhang. Conventional wax up or using burn out caps produced less horizontal discrepancy.

M. Panjnosh, H. Siadat, M. Alikhasi, M. Alihoseini,
Volume 22, Issue 2 (20 2009)

Background and Aim: It is well recognized that implant treatment is common worldwide, but the approach to success is not predictable because of bone loss that occurs around the implants. Also there are many factors affecting crestal bone loss around the implants that one of them is the surgical protocol of implant installation. The purpose of this investigation was to evaluate the amount of crestal bone loss around the Replace implants installed according to submerged and non- submerged treatment protocol.

Materials and Methods: In this study, 11 patients received 34 implants. In each patient (unilateral or bilateral mandible), one of the implants was placed with submerged procedure and in the other one non- submerged procedure was used. In a period of 3 months a temporary partial denture that covered the implants was used. After 3 months the submerged fixture was exposed, impression was performed and fixed prosthesis was fabricated. Loss of crestal bone at each implant was measured. These measurements have been done at surgical times, over a period of 3 months after implant installation and 6 months after the delivery of the fixed prosthesis. The measurement was done with digital subtraction radiography. Data was analyzed by Wilcoxon Signed Ranks test.

Results: Three months after implant placement, submerged groups showed statistically more crestal bone loss (0.65±0.71) than non-submerged (0.41±0.53) group (p=0.02). After 6 months the mean value of crestal bone loss in submerged group was 0.21±0.40 mm and in non submerged group was 0.29±0.49 mm. This data indicated no statistically significant difference between the two groups of implants (p>0.05).

Conclusion: Our results are in accordance with previously published studies and confirm that the value of crestal bone loss in submerged and non-submerged groups after 3 and 6 months were similar and in acceptable limit.

H. Siadat, R. Ghoveizi, A. Mirfazaelian, Gh. Ommati Shabestari, M. Alikhasi,
Volume 22, Issue 2 (20 2009)

Background and Aim: The aim of this clinical study was to determine the effectiveness of progressive loading procedures on preserving crestal bone height and improving peri-implant bone density around maxillary implants restored with single crowns by an accurate longitudinal radiographic assessment technique.

Materials and Methods: Eleven Micro-Thread Osseo Speed dental implants were placed in 11 subjects and permitted to heal for 6 weeks before surgical uncovering. Following an 8-week healing period, implants underwent a progressive loading protocol by increasing the height of the occlusal table in increments from adding acrylic resin to an acrylic crown. The progressively loaded crowns were placed in 2 mm infraocclusion for the first 2 months, light occlusion for the second 2 months, and full occlusion for the third 2 months. At forth 2 months, a metal ceramic crown replaced the acrylic crown. Digital radiographs of each implant were made at the time of restoration, then after 2, 4, 6, 8, and 12 months of function. Digital image analysis was done to measure changes in crestal bone height and peri-implant bone density.

Results: The mean values of crestal bone loss at 12 months were 0.11 ± 0.19 mm, and when tested with Friedman across the time periods, the differences were not statistically significant (p> 0.05). The mean values of bone density in the crestal, middle, and apical area were tested with Repeated Measure ANOVA across the time periods, the differences were statistically significant (p<0.05).

Conclusion: Progressive loading doesn’t cause crestal bone loss. The peri-implant density measurements of the progressively loaded implants show continuous increase in crestal, middle and apical peri-implant bone density by time.


M. Alikhasi, H. Siadat, A Monzavi, M. Naseri, S. Sheikhzadeh, F. Taghavi,
Volume 24, Issue 3 (21 2011)

Background and Aims: The bond strength between veneer ceramics and zirconia frameworks is the weakest component in the layered ceramics. Due to the possible effect of adding pigments to the core materials on the bond strength between core and veneer as well as the introduction of new ceramic materials in dentistry, the aim of this study was to compare the zirconia core-veneer microtensile bond strength using two ceramic veneers with or without coloring the core.
Materials and Methods: In this experimental study, 12 disc-shaped specimens were fabricated using a manually aided design- manually aided manufactured (MAD/MAM) zirconia core (Zirkonzahn). Two veneering ceramics of Ceram Kiss and Zirkonzahn ICE were also used to veneer the specimens. Half of the Zirkonzahn discs were remained white and the others were colored by shade A2.Then, the discs were cut into microbars (30 for each group) and the microtensile bond strength of the core-veneer was calculated. The specimens were assessed using scanning electron microscopy (SEM) and the data were analyzed using two-way ANOVA and Student's t-test.
Results: Significant differences with respect to veneer layer were found (P<0.001). No significant differences were seen among colored and uncolored cores (P=0.69).
Conclusion: According to the apparent effect of veneering ceramics on the core-veneer bond strength, careful selection of these agents is essential to achieve adequate bond strength between core and veneer to prevent delaminating and chipping failures of zirconia veneered restorations.

Marziyeh Alikhasi, Abbas Monzavi, Hakimeh Siadat, Bita Fathi,
Volume 25, Issue 2 (9 2012)

Background and Aims: Accurate recording of implant location is required to achieve passive fit and have the implants without stress concentration. The aim of this in-vitro study was to evaluate the dimensional and angular accuracy of open-tray and closed-tray impression techniques using polyether impression material and also to assess the surface detail reproduction of the tooth while impression making.

Materials and Methods: One reference metal model with 2 implants (Implantium) on the position of the maxillary second premolar and first molar and one molar tooth for evaluation of surface details was prepared. 27 polyether impressions of these models were made (9 using open-tray, 9 using closed-tray techniques and 9 were made just of the surface of the teeth without any implants). Impressions were poured with ADA type IV stone. Coordinate Measuring Machine was used for measuring the dimensional accuracy and video measuring machine for surface detail reproduction. All of these measurements were compared with the measurements on the reference model. Data were analyzed by and compared by T-test and One-way ANOVA.

Results: There was a significant statistical difference between open-tray and closed-tray techniques (P<0.001). There was no significant difference in the surface detail reproduction of open-tray and Closed-tray techniques and impression making with or without the implants (P>0.05).

Conclusion: The accuracy of open-tray impression technique was more than closed-tray technique. The surface detail reproduction of the tooth was not affected by impression technique.

Marzieh Alikhasi, Mahnaz Arshad, Hakime Siadat, Susan Rahimian,
Volume 25, Issue 3 (1 2012)

Background and Aims: Passive fit of prosthetic frameworks is a major concern in implant dentistry. Impression technique is one of the several variables that may affect the outcome of dental implants. The purpose of this study was to compare the three dimensional accuracy of direct and indirect abutment level implant impressions of ALL-ON-4 treatment plan.
Materials and Methods: A reference acrylic resin model with four Branemark fixtures was made according to All-On-4 treatment plan. Multiunit abutments were screwed into the fixtures and two special trays were made for direct and indirect impression techniques. Ten direct and ten indirect impression techniques with respective impression transfers were made. Impressions were poured with stone and the positional accuracy of the abutment analogues in each dimension of x, y, and z axes and also angular displacement (Δθ) were evaluated using a Coordinate Measuring Machine (CMM). Data were analyzed using T- test.
Results: The results showed that direct impression technique was significantly more accurate than indirect technique (P<0.001).
Conclusion: The results showed that the accuracy of direct impression technique was significantly more than that of indirect technique in Δθ and Δr coordinate and also Δx, Δy, Δz.

Abbas Monzavi, Reza Shabanpoor, Marzieh Alikhasi, Ghasem Omati Shabestari,
Volume 25, Issue 4 (9 2013)

Background and Aims: One of the decisive factors on the final esthetic results of implant treatment is the abutment material. Ceramic abutments are nowadays very popular in this regard. The purpose of this study was to compare the fracture resistance of three zirconia abutments with titanium abutment.

Materials and Methods: Four groups of abutments (five specimens in each) were prepared. The abutments were prefabricated titanium, prefabricated zirconia, zirconia-metal, and copy-milled zirconia abutment. After securing the abutments to the implant using a torque of 24 Ncm, they were mounted into a mounting jig using the 30º tilt. The force was applied on the assembly till the failure occured. Facture resistance and mode of failure were recorded for each specimen. The data were analyzed using One-way ANOVA.

Results: The mean values recorded for fracture resistance of different zirconia abutments varied between 426 to 688 N however, there was no significant differences among the groups (P=0.14). Body fracture was observed only in prefabricated zirconia abutments. Screw fracture and screw bending were the common failures observed in other groups.

Conclusion: Zirconia abutments of any type could be successfully used in regular plateform implants.

Marzieh Alikhasi, Roshanak Baghaie, Nasim Khosronejad, Pooya Aslani,
Volume 26, Issue 1 (3-2013)

Background and Aims: In response to esthetic demand of patients, ceramic abutments have been developed. Despite esthetic of zirconia abutments, machining accuracy of these abutments has always been a question. Any misfit in the abutment-implant interface connection can lead to detorque and screw loosening. The aim of this study was to compare torque loss value of manually aided design/manually aided manufacture (MAD/MAM) zirconia abutments with prefabricated titanium abutments.

Materials and Methods: Seven titanium abutments (Branemark RP, Easy abutment) and seven copy milled abutments which were duplicated from the prefabricated Zirkonzhan (ZirkonZahn, Sand in Taufers, Italy) were prepared. After sintering process of zirconia abutment, all abutments were fastened with a torque screw under 35 Ncm. Detorque measurements were performed per group pushing the reverse button of the Torque controller soon after screw tightening with values registered. The mean torque loss were calculated and compared using Student's t test.

Results: The mean of torque loss was 12.71 Ncm with standard deviation of 1.70 for prefabricated titanium abutments and 15.50 Ncm with standard deviation of 4.67 for MAD-MAM abutments. The difference between the two groups was not statistically significant (P=0.23).

Conclusion: Within the limitation of this study, MAD-MAM ceramic abutments could maintain the applied torque comparing to the prefabricated abutments.

Marzieh Alikhasi, Pooya Aslani,
Volume 26, Issue 2 (5-2013)

Background and Aims The purpose of this study was to evaluate the survival rate, mean bone loss and post operative complication of implants inserted in All-on-4 technique .

Materials and Methods: The literature was searched using keywords angled implant, All-on-4, tilted implant and graftless technique in the last 10 years (2001 to 2011) and clinical trial article that evaluated survival rate and mean bone loss around axial and tilted implants in All-on-4 technique was selected and evaluated.   A total of 73 articles were found by searching. After evaluation of titles and abstracts, finally 10 clinical trial, that were fully consistent with including criteria such as mean of bone loss and survival rate was selected and evaluated. 

Conclusion: Results showed that the survival rate (96-100%) and mean bone loss (0.34-1.9 mm) with All-on-4 technique in immediate loading is comparable with other implant support treatment plan. Comparison of implant survival and bone loss in axial and tilted implant in All-on-4 system is shown this treatment plan has consistent result with other conventional implant support prosthesis. Also, postoperative complication including fractures of the acrylic temporary prosthesis, detachment of the teeth, abutment or prosthesis screw loosening have been reported with All-on-4 technique. 

Marzieh Alikhasi , Razieh Khanmohammadi, Somayeh Niakan ,
Volume 26, Issue 3 (8-2013)

  Background and Aims: Along with the advances in dental materials and invention of new techniques for ceramic producion, the demand for the beauty and matching restoration’s color with patient’s natural teeth is growing. Nowadays, zirconia systems are the focus of attention. Despite their strength, one of the problems with such systems is the high opacity and failing to provide the favored color. Considering few studies about the influence of shading on Zirconia, the purpose of this in vitro study was to evaluate the effect of different shading of zirconia-based ceramics on the biaxial flexural strength .

  Materials and Methods: In this in vitro experimental study, Rainbow (Dentium, Korea) zirconia-based ceramics (the diameter of 15mm and 1mm in thick) were divided into four groups of 10 specimens. According to Vita shade guide system and manufacturer’s time recommendations (3 seconds), three groups of disc specimens were shaded to A3, B3 and D3 colors and other ten specimens remained uncolored as control group. The biaxial flexural strength test of discs was evaluated and the elements’ composition of colors was detected by Energy Dispersiue X-ray Microanalysisd (EDX). Finally, data were analyzed using one-way ANOVA and Post-hoc tests.

  Results: The biaxial flexural strength in non colored specimens, A3 shaded discs, B3 shaded, and D3 shaded specimens were determined 1061.93, 819.16, 1100.10, and 825.48 MPa respectively which was statistically significant among groups (P<0.001). The statistical analysis revealed that the highest strength in B3 and non colored groups which were significantly higher than A3 and D3. EDX analysis showed significant differences among different colored compositions.

  Conclusion: The biaxial flexural strength of zirconia cores are affected by shading and the specific selected color.

Marzieh Alikhasi, Hakimeh Siadat, Elaheh Beyabanaki,
Volume 26, Issue 4 (1-2014)

  Background and Aims: Making accurate impressions of prepared teeth when they are adjacent to dental implants is of great importance. In these situations, disregarding the selection of appropriate impression material and technique, not only can affect accuracy of transferring of the 3-dimentional spatial status of implant, but also can jeopardize the accurate recording of tooth. In the present study, the accuracy of two impression materials with taper impression copings for recording implant position and surface details was evaluated.

  Materials and Methods: One metal reference model with 2 implants (Implantium) and a preparation of three grooves on a tooth according to ADA no. 19 standard was fabricated. 10 medium- consistency polyEther (PE) impressions using custom trays and 10 polyVinyl Siloxane (PVS) putty wash impressions using prefabricated trays with conical impression coping were made. Impressions were poured with ADA type IV stone. A Coordinate Measuring Machine (CMM) evaluated x, y and angular displacement of the implant analog heads and also accuracy of groove reproduction were measured using a Video Measuring Machine (VMM). These measurements were compared to the ones from reference model. Data were analyzed using one-way ANOVA and T-test.

  Results: Putty wash PVS had less linear discrepancy compared with reference model (P > 0.001). There was no significant difference in the surface detail reproduction (P = 0.15).

  Conclusion: Putty wash PVS had better results for linear displacement compared with medium consistency PE. There was no significant difference in surface detail reproduction between the two impression materials.

Majid Sahebi, Marzieh Alikhasi, Farshad Movafegh, Vahideh Nazari,
Volume 29, Issue 1 (7-2016)

Background and Aims: In response to esthetic demand and use of zirconia abutments; detection of implant-abutment connection misfit is so important. The purpose of this study was to evaluate the sensitivity and specificity of radiographic images in the detection of abutment-implant connection misfit in zirconia and titanium abutments of three different implant connections.

Materials and Methods: One regular implant fixture of Branemark, Noble active and Replace systems were mount in acrylic models. Two pieces titanium and zirconium abutments were attached to the implants, once with correct adaptation and once with 0.5 mm spacer. Digital radiographic images were taken of 12 created states with zero degree vertical and horizontal inclination and evaluated by 10 specialists in implant treatment in two different time penods. Data were analyzed using Kappa analysis.

Results: Interclass Correlation Coefficients (ICC) of the agreement of answers in the first and second times were 97.4 and 97.5, respectively (P<0/001). Sensitivity of detecting gap in all groups was acceptable (95-100%) except titanium abutment in Noble active which was the lowest value (35%). Specificity of all groups were acceptable (80-95%) except zirconia abutments in Noble active and Replace with 45% and 30% values, respectively, and titanium abutments in Branemark had the highest value (95%).

Conclusion: The sensitivity of radiographic images in detection of abutment-implant connection misfit only in Noble active with titanium abutment was not acceptable. Specificity of radiographic images in the absence of gap in titanium abutments was more favorable.

Narges Ameri , Hakimeh Siadat, Ahmad Reza Shamshiri, Marzieh Alikhasi,
Volume 29, Issue 2 (11-2016)

Background and Aims: Marginal accuracy is a crucial factor influencing the clinical long-term reliability of implant-supported fixed dental prostheses (FDPs). The aim of this in vitro study was to evaluate the marginal fit of three-unit zirconia bridge frameworks fabricated using two different computer-aided design (CAD)/
computer-aided manufacturing (CAM) systems (AmannGirrbach and Zirkonzahn).

Materials and Methods: The master model of 3-unit FDP was made of two implant abutments (AmannGirrbach and Zirkonzahn) from canine to second premolar. Twelve frameworks were manufactured using each fabricating system from semi-sintered zirconia blanks, which had to be sintered for final density after milling. After manufacturing, the absolute marginal discrepancy in each abutment were determined by means of Video Measurement System (VMS). The data were analyzed, using independent and paired t test (P=0.05).

Results: For the premolar abutment, the absolute marginal discrepancy of frameworks fabricated by AmannGirrbach system was significantly greater than those of the other system (P=0.005). There was no significant difference between the marginal discrepancy of canine and premolar abutments (P>0.05).

Conclusion: Within the limitations of this study, it could be concluded that the marginal fit of zirconia FDPs was significantly dependent on the CAD/CAM system used, but the abutment size was not an effective factor.

Somayeh Zeighami, Hakimeh Siadat, Marzieh Alikhasi, Zeinab Saeidi,
Volume 30, Issue 1 (6-2017)

Background and Aims: Taking impression from angulated implants has always been a great challenge in clinic. In this regard, studies on sectional trays are very few. The aim of this study was to evaluate and compare the dimensional and angular accuracy of impressions using full arch and sectional trays.

Materials and Methods: Four implants (4.3 × 12 mm) (Implantium, Dentium) were placed in the first premolar and molar regions of a Kennedy class I mandibular acrylic model with 30° lingual angulation. Twenty open special trays (Full arch & Sectional) were made on the primary cast. The impressions were taken using vinyl polysiloxane (VPS) and were poured with type IV dental stone. The coordinate measuring machine (CMM) was used to measure the dimensional (Z, Y, X) and angular (θ) coordinates of implants. The data were analyzed using and t-test and SPSS 22. Software.

Results: The type of tray had no significant effect on the dimensional accuracy in X, Y and Z axes (P>0.05) and total linear displacement (r); However, it significantly affected the angular accuracy (∆q) (P<0.05).

Conclusion: Sectional tray yields less rotational displacement in impressions made of angulated implants.

Hakimeh Siadat, Amin Jabbari, Mohammad Taghi Baghani, Marzieh Alikhasi,
Volume 30, Issue 1 (6-2017)

Background and Aims: The exact placement of impression copings in making accurate prosthesis is very important. In some cases, the implants need to be placed deeply subgingival, which could reduce the direct vision and ultimately reduce the precision of impression copings and subsequently, delivered prosthesis. This would be the cause of multiple complications such as delivery of ill-fitting prosthesis. The aim of this study was to evaluate the effect of the dental implant placement depth on the accuracy of impression coping connection by students.

Materials and Methods: This in-vitro and experimental study was conducted by 50 senior dental students. Four implants at different depths (0, 2, 4 and 6 mm) were placed in a model. After learning how to mount impression coping on implants, the students were asked to mount impression copings on all four implants. The samples were examined by an experienced prosthodontist using a magnifier with 4x magnification. Data were analyzed by statistical Cochran test (P<0.05(.

Results: The proper adapting rate of transfer copings, in subgingival implants with the depth of 0, 2, 4 and 6 mm were 100%, 62%, 58% and 20%, respectively. Statistically significant differences were observed between all groups (P<0.001).

Conclusion: The results showed that there was an inverse relationship between the increasing depth of the implants in the gingiva and the dentist’s ability to connect the impression copings properly.

Somayeh Zeighami, Marzieh Alikhasi, Maryam Memarian, Moeen Hosseini Shirazi,
Volume 30, Issue 4 (1-2018)

Background and Aims: For the clinical success of implant-retained prostheses, fitness of matching components and stability of the applied torque to the implant-abutment assembly under dynamic occlusal loading is essential. The aim of this study was to evaluate the torque loss in Co-Cr castable abutments after cyclic loading.
Materials and Methods: 10 castable abutments were cast in Co-Cr alloy with similar size and height. Each specimen was mounted vertically on a separated implant using a 30 Ncm tightening torque. The detorque values of the abutments were evaluated after 10 min. The same tightening torque was applied to the abutments on their corresponding implants and cyclic loading was applied for 500,000 cycles to the implant-abutment assembly. The torque values after cyclic loading were recorded for each specimen. T-test analysis was conducted on scores from the groups.
Resultes: The results of this study showed that the percentage of torque loss in castable abutments was significantly increased after cyclic loading (P<0.001).
Conclusion: Misfit between the castable implant components can cause torque loss before and after cyclic loading. However, it is more appropriate to relate the results of this study to the screw loosening of the above mentioned abutments than judging their clinical performance.

Marzieh Alikhasi, Amirreza Hendi,
Volume 30, Issue 4 (1-2018)

Background and Aims: Loss of retention is one of the main reasons of failure in teeth restored with post and core. Several factors, including the type of cement can influence the retention of the posts. As zinc phosphate cement is considered as the standard for comparison this study performed to review articles evaluating the retention of cast posts cemented with zinc phosphate.
Materials and Methods: This systematic review was performed based on the PRISMA (Transparent Reporting of Systematic Reviews and Meta-analyses) guide. The question of this study was that how much is the amount of retention of cast posts cemented with zinc phosphate. Hence, a literature search was done in PubMed and Medline databases as well as Google scholar search engine using relevant keywords until 2016 limited to the English language. Articles were selected based on the inclusion and exclusion criteria, and were evaluated qualitatively.
Resultes: Internet search resulted in 1141 articles. Following the application of inclusion and exclusion criteria, 6 studies were included in this systematic review. The most common post material was nickel-chromium alloy. Retention of casting posts cemented by zinc phosphate was from 8.76 to 34.2 Kg and from 91 to 192.2 N.
Conclusion: Our review showed that the retention of cast posts cemented with zinc phosphate in controlled condition is moderate and factors including post material and length could influence the retention of the post.

Soudabeh Koulivand, Hakimeh Siadat, Safoura Ghodsi, Marzieh Alikhasi,
Volume 31, Issue 4 (1-2019)

Background and Aims: Despite the increasing application of intra-oral scanners, the effect of finish line position on gingival margins adaptation is still discussed. The purpose of this clinical study was to evaluate the fitness of cobalt-chromium copings obtained from intraoral scanning in two depth of finish lines.
Materials and Methods: Thirty teeth prepared for single premolar metal-ceramic crowns were included. Fifteen teeth had supragingival and fifteen had sub-gingival finish lines. Digital impressions were made using an intraoral scanner (Trios-3shape). Computer-aided design and computer-aided manufacture (CAD/CAM) cobalt-chromium copings were fabricated from the scan files. The copings were evaluated intraorally and after adjustments, the internal and marginal discrepancy were measured using silicone replicas and a stereomicroscopy. Internal and marginal discrepancies were analyzed using the Multivariate test (P<0.05).
Results: The mean internal and marginal gap were 52.1 and 56.27μ, for supragingival group and 49.72 and 62.98μ for subgingival group, respectively. The evaluation of finish line position showed no significant effect on obtained results (P>0.05).
Conclusion: CAD/CAM chrome-cobalt copings fabricated by digital impressions provided acceptable marginal and internal precision. However, the finish line position had no significant effect on the internal and marginal adaptation.

Marzieh Alikhasi, Narges Ameri, Hakimeh Siadat, Ahmad Reza Shamshiri, Mohammadreza Nejati,
Volume 32, Issue 1 (7-2019)

Background and Aims: Passive fitness of implant frameworks are important factors for long-term success of dental implant restorations. The aim of this in vitro study was to evaluate the dimensional changes of implant supported zirconia frameworks fabricated by Zirkonzahn CAD/CAM system during fabrication stages.
Materials and Methods: The master model of 3-unit FDP was made of two implant abutments. The master model was scanned 12 times and data were saved as STL files (scanning groups). Using semi-sintered zirconia,
12 real-size frameworks (milling groups) and 12 enlarged frameworks which were then sintered (sintering group) were made in this system. Dimensions of master model and specimens of each stage were measured. The dimensional changes in respect to master model were calculated. Data were analyzed using Repeated measures ANOVA, independent t-test, and paired sample t-test at α=0.05 of significance.
Results: The milling stage showed greater dimensional changes comparing to the other stages (P<0.05). At all stages, the dimensional changes of premolar abutment height were greater than canine (P<0.001).
Conclusion: Within the limitations of this study, the results suggested that the fabrication stages and size of abutments had significant effects on the dimensional changes of zirconia frameworks.

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