Reopening of a school of dentistry in the era of COVID-19 pandemic, "Step-by-step" approach.

INTRODUCTION: The COVID-19 pandemic has a great impact on all aspects of higher education worldwide. In Iran, after several months of lockdown, all dental schools coped with the challenge of "reopening." School of Dentistry of Tehran University of Medical Sciences (TUMS) planned to facilitate the process of reopening using a "step-by-step" approach. The aim of this study was sharing our experiences of reopening of the school during the pandemic. METHODS: TUMS School of Dentistry planned a "step-by-step" approach of reopening of school to both provide infrastructure of online education for theoretical credits and reassure all staff and students about infection control for practical courses. Also, a two-section survey on students' satisfaction with a variety of aspects of reopening process and the clinical performance of students in different clinical courses was conducted. RESULTS: Findings showed 65.1% of the students, attended the survey, were satisfied with reopening of the school. Also, 86.4% were satisfied with the new online method of education for theoretical courses. Regarding personal protective equipment (PPE) provided for the students, 22.9% and 56.5% of them were satisfied and moderately satisfied, respectively. Additionally, 78.2% of the students were satisfied with the newly developed online assessment method. CONCLUSION: Although reopening of schools during COVID-19 pandemic seems enigmatic for all authorities and students, the "step-by-step" plan designed by TUMS School of dentistry including emotional and infrastructural prerequisites might be a reliable method for all people, who are in charge of management of dental school in uncertain crisis.

Biomechanical behavior of endocrown restorations with different cavity design and CAD-CAM materials under a static and vertical load: A finite element analysis.

STATEMENT OF PROBLEM: The influence of different restorative materials, the divergence angle, and the preparation design of the pulp chamber floor in endocrowns on stress distribution is unclear. PURPOSE: The purpose of this finite element analysis study was to evaluate the stress distribution and maximum von Mises stress values in endocrown restorations and remaining teeth. MATERIAL AND METHODS: An endodontically treated first mandibular molar was prepared with 2-mm occlusal reduction, a butt-joint margin, and a mesial box with a 4-mm buccolingual extension to receive an endocrown restoration. The model was then scanned, and the exported standard tessellation language file was designed according to the anatomic references by using a computer-aided design software program. The reference model was duplicated, and 27 variations were formed: restorations made of IPS e.max, Vitablocs MarkII, and Vita Enamic, as well as different divergence angles of 6, 12, and 16 degrees prepared with 3 variations of pulp chamber floor designs, keeping the natural form, adding a 1-mm glass ionomer pulp chamber base, and adding a 2-mm extension into the distal canal. Stress distribution under axial loading and maximum von Mises stress values were analyzed and calculated by using the Ansys software program. RESULTS: The endocrown restoration presented the lowest von Mises stress values when a 6-degree divergence angle was used with Vitablocs MarkII. However, in other layers such as enamel, resin cement, and pulpal floor, the lowest von Mises stress values were observed in IPS e.max restorative material when the divergence angle was increased to 16 degrees. No difference was found in the stress distribution pattern and maximum von Mises stress values in the alveolar bone or periodontal ligament. CONCLUSIONS: Endocrowns fabricated with lithium disilicate ceramics without intraradicular extension exhibited lower stresses on tooth structure. An increase in the divergence angle improved the stress distribution on tooth structure; however, sound dental tissue should not be removed to achieve better stress distribution.

A clinical comparison of digital and conventional impression techniques regarding finish line locations and impression time.

OBJECTIVE: This study compared digital and conventional impression techniques regarding impression time, frequency of adjustments, and adaptation of cobalt-chromium (Co-Cr) copings with supragingival and subgingival finish lines. MATERIALS AND METHODS: Thirty premolars prepared for single-unit metal-ceramic restorations with supragingival and subgingival finish lines (n = 15). Conventional impression and digital scan of prepared teeth were made. Using computer aided design/computer aided manufacturing (CAD/CAM) system the copings were produced by a milling machine from Co-Cr blocks and internal and marginal discrepancies were measured using silicone replica technique. Data were analyzed using repeated measures ANOVA and Mann-Whitney test (alpha = .05). RESULTS: The impression technique had a significant effect on the magnitude of gap (P < .001). The internal and marginal gaps in the digital technique (49.43 µ and 60.07 µ, respectively) were significantly lower than the values in the conventional method (91.88 µ and 96.96 µ, respectively-P < .001). Finish line positions had no significant effect on the fit and marginal gap of copings (P = .54 and .243, respectively). The mean impression time (19':27″ in conventional technique and 10':31″ in digital technique) was significantly shorter (P < .001) and the mean frequency of adjustments (2.2 times for conventional and 1.3 times for digital technique) was significantly lower in the digital technique (P < .001). The gingival biotype (thick or thin) had no significant effect on marginal and internal fit (P = .052 and .319, respectively). CONCLUSION: The digital technique was superior in terms of fit, impression time, and frequency of adjustments. Finish line positions had no significant effect on the fit of copings. CLINICAL SIGNIFICANCE: Using intraoral scanner promotes the fits of restorations in supragingival and subgingival finish lines.

The effect of conventional, half-digital, and full-digital fabrication techniques on the retention and apical gap of post and core restorations.

STATEMENT OF PROBLEM: Conventional cast metal posts and cores are fabricated using direct and indirect techniques, both of which need impression materials and considerable laboratory work. Digital techniques have the capacity to substitute for conventional methods in fabricating the posts and cores. However, the accuracy of restorations resulting from a digital workflow is unknown. PURPOSE: The purpose of this in vitro study was to compare the retention of posts and cores fabricated using full-digital, half-digital, and conventional techniques and to define the accuracy of each technique in terms of the apical gap. METHOD AND MATERIALS: Thirty newly extracted mandibular first and second premolar teeth were selected for this in vitro study. Impressions were made using direct acrylic resin patterns (conventional), indirect silicone impressions of the intracanal which scanned with a 3Shape laboratory scanner (half digital), and intracanal scan posts captured with an intraoral 3Shape scanner (full digital). Casting and milling were conducted for the conventional impression and digital scans. The obtained posts were cemented using zinc phosphate cement. A universal pullout test was used to measure retention at a crosshead speed of 0.5 mm/min. The apical gap of each post in the canals was defined with parallel digital radiography. The data were analyzed using the Kruskal-Wallis test (α=.05) and Mann-Whitney test at the adjusted α=.016. RESULTS: Significant differences were found among the conventional, full-digital, and half-digital techniques in terms of the apical gap (0.11, 0.29, and 0.66 mm; P<.001) and retention (171.6 ±1.9, 107.1 ±5.6 and 91.8 ±6.6 N; P<.001). The correlation between gap and retention in conventional (P=.43), full-digital (P=.09), and half-digital techniques (P=.06) was not statistically significantly different. CONCLUSIONS: The conventional technique was more accurate and resulted in higher retention than both the full- and half-digital techniques. However, the retention and gap of all the posts fell within clinical guidelines.

Effect of Implant Connection Type and Depth on the Seating Accuracy of Hand-Tightened Abutments.

PURPOSE: Improper seating of abutment on the implant is a common problem. This study investigated the effect of the type of implant/abutment interface on the complete seating of the abutments on the head of implants placed at different gingival depths. MATERIALS AND METHODS: Three implant systems with three different connections including straight external hexagon, butt-joint internal tri-lobed, and conical internal hexagon were used. Two gingival thicknesses (2 and 7 mm) were created using pink baseplate wax around the straight abutments seated on the implants. After placing the implants in acrylic blocks, the wax was replaced with the gingival mask material to simulate the gingival drape around the implant heads. Afterwards, 15 prosthodontists were asked to hand-tighten the straight abutments in the corresponding implant bodies relying only on their tactile sense. At the final stage, the gingival mask was removed, and the seating quality of the abutments on implant bodies was assessed visually. The effect of implant connection and depth on abutment seating accuracy was analyzed using Kruskal-Wallis and multiple-comparison tests. RESULTS: No significant difference was found regarding the effect of either depth or connection design on the accuracy of the abutment seating (p > 0.05); however, pairwise comparison of the combined effect of the depth and connection design was significant (p = 0.009). Accuracy of abutment seating on the Nobel Active implants at both 2 and 7 mm depths were significantly better than Replace system with 7 mm depth (p = 0.027). The same results were obtained in comparison between Nobel Active system at both 2 and 7 mm depths with Branemark system with 7 mm depth (p = 0.006). CONCLUSION: An increase in implant placement depth meant a decrease in accuracy of the abutment seating. The internal conical connection design showed the best result in abutment positioning in deep implants as compared with external and internal butt-joint connection designs.

Interim Prosthesis Options for Dental Implants.

Dental implants have become a popular treatment modality for replacing missing teeth. In this regard, the importance of restoring patients with function during the implant healing period has grown in recent decades. Esthetic concerns, especially in the anterior region of the maxilla, should also be considered until the definitive restoration is delivered. Another indication for such restorations is maintenance of the space required for esthetic and functional definitive restorations in cases where the implant site is surrounded by natural teeth. Numerous articles have described different types of interim prostheses and their fabrication techniques. This article aims to briefly discuss all types of implant-related interim prostheses by different classification including provisional timing (before implant placement, after implant placement in unloading and loading periods), materials, and techniques used for making the restorations, the type of interim prosthesis retention, and definitive restoration. Furthermore, the abutment torque for such restorations and methods for transferring the soft tissue from interim to definitive prostheses are addressed.

Does Ferrule Effect Affect Implant-Abutment Stability?

PURPOSE: This study investigated the influence of placing implant-supported crowns on the torque loss of the abutment screw before and after loading. MATERIAL AND METHODS: Twenty implant-abutment assemblies were randomly assigned to two groups. The first group was consisted of abutments with abutment-level finishing line (abutment-level), and in the second group the crown margin was placed on the implant shoulder (implant-level). Initial torque loss was recorded for all specimens. After 500000 cyclic load of 75 N and frequency of 2 Hz, post loading torque loss was recorded. Finite element model of each group was also modeled and screw energy, and stress were analyzed and compared between two groups. RESULTS: ANOVA for repeated measurements showed that the torque loss did not change significantly after cyclic loading (P=0.73). Crown margin also had no significant effect on the torque loss (P=0.56). However, the energy and stress of screw in abutment-level model (4.49 mJ and 22.74 MPa) was higher than implant-level model (3.52 mJ and 20.81 MPa). CONCLUSIONS: Although embracing the implant with crown produced less stress and energy in the abutment-implant screw, it did not have any significant influence on the torque loss of the screw.

Does Abutment Collar Length Affect Abutment Screw Loosening After Cyclic Loading?

A significant vertical space that is corrected with vertical ridge augmentation may necessitate selection of longer abutments, which would lead to an increased vertical cantilever. This study investigated the influence of different abutment collar heights on single-unit dental implant screw-loosening after cyclic loading. Fifteen implant-abutment assemblies each consisted of an internal hexagonal implant were randomly assigned to 3 groups: Group1, consisting of 5 abutments with 1.5 mm gingival height (GH); Group2, 5 abutments with 3.5 mm GH; and Group3, 5 abutments with 5.5 mm GH. Each specimen was mounted in transparent auto-polymerizing acrylic resin block, and the abutment screw was tightened to 35 Ncm with an electric torque wrench. After 5 minutes, initial torque loss (ITL) was recorded for all specimens. Metal crowns were fabricated with 45° occlusal surface and were placed on the abutments. A cyclic load of 75 N and frequency of 1 Hz were applied perpendicular to the long axis of each specimen. After 500 000 cycles, secondary torque loss (STL) was recorded. One-way ANOVA analysis was used to evaluate the effects of abutment collar height before and after cyclic loading. One-way ANOVA showed that ITL among the groups was not significantly different (P = .52), while STL was significantly different among the groups (P = .008). Post-hoc Tukey HSD tests showed that STL values were significantly different between the abutments with 1.5 mm GH (Group1) and with 5.5 mm GH (Group3) (P = .007). A paired comparison t-test showed that cyclic loading significantly influenced the STL in comparison with the ITL in each group. Within the limitations of this study, it can be concluded that increase in height of the abutment collar could adversely affect the torque loss of the abutment screw.

Comparative evaluation of impression accuracy of tilted and straight implants in All-on-Four technique.

PURPOSE: The aim of this in vitro study was to compare the accuracy of implant impressions in parallel and nonparallel implants of All-on-Four treatment plan. MATERIALS AND METHODS: A reference model containing 4 internal-connection implant analogs was fabricated according to All-on-Four treatment plan (2 anterior implants at 0 degree and 2 posterior implants at 30 degrees in relation to the perpendicular line). Twenty impressions of this model were made using open-tray impression technique. Impressions were poured with American Dental Association type 4 stone, and the positional accuracy of the implant replica heads in x-, y-, and z- axes was evaluated using a coordinate measuring machine. These measurements were compared with the obtained measurements from the reference model that served as control, and data were analyzed using independent test (α = 0.05). RESULTS: The results showed that the accuracy of the implant impressions did not show any significant difference between the tilted and straight implants except in y-coordinate (P = 0.012). CONCLUSION: Within the limitations of this study, the accuracy of the implant impressions did not differ for different implant angulations in All-on-Four treatment plan.

Stress distribution around maxillary anterior implants as a factor of labial bone thickness and occlusal load angles: a 3-dimensional finite element analysis.

The purpose of this study was to evaluate the influence of the stress/strain distribution in buccal bone of an anterior maxillary implant using 3 bone thicknesses under 5 different loading angles. Different testing conditions incorporating 3 buccal bone thicknesses, 3 bone compositions, and 5 loading angles of an anterior maxillary implant were applied in order to investigate the resultant stress/strain distribution with finite element analysis. The maximum equivalent stress/strain increased with the decreasing of loading angle relative to the long axis. In addition to loading angle, bone quality and quantity also influenced resultant stress distribution. Dental practitioners should consider combinations of bone composition, diameter, and load angulations to predict success or failure for a given implant length and diameter.

Accuracy of maxillary full-arch digital impressions of tooth and implant models made by two intraoral scanners.

OBJECTIVES: Limited studies are available on the accuracy of intraoral scanners (IOSs) for full-arch implant and tooth models. This study aimed to assess the accuracy of maxillary full-arch digital impressions of tooth and implant models made by two IOSs. MATERIALS AND METHODS: This in vitro, experimental study was conducted on two maxillary dentiform models: one with six prepared natural teeth and the other with six implants at the site of canine, first premolar, and first molar teeth, bilaterally. A highly accurate industrial scanner was used for actual measurements on the models that served as the reference scan. TS (Trios3) and CO (CEREC Omnicam) IOSs were then used to scan each model 10 times according to the manufacturer's instructions. All scans were saved in STL format. The GOM Inspect software was used according to the best-fit algorithm to compare the accuracy of measurements in the groups with the reference scan. The trueness and precision were calculated. Statistical analyses were carried out using SPSS by one-way analysis of variance and t-test (α = .05). RESULTS: TS showed a significantly higher trueness than CO for both tooth and implant models (p < .05). TS also revealed significantly higher precision than CO for the tooth model; however, the difference in precision for the implant model was not significant between the two IOSs (p > .05). CONCLUSIONS: TS showed higher accuracy than CO in both tooth and implant models.

Does implant staging choice affect crestal bone loss?

PURPOSE: The purpose of the present study was to compare the crestal bone loss around implants placed according to either a 1-stage or 2-stage implant installation procedure using a digital subtraction radiography technique. MATERIALS AND METHODS: In the present randomized clinical trial, screw-shaped tapered implants were inserted in the posterior mandible of patients needing fixed partial dentures. In each edentulous area, according to the randomization table, 1 implant was inserted using a 1-stage procedure (group 1) and 1 was placed using a 2-stage approach (group 2). The implants were temporized with the relined denture after 2 weeks. All implants were functionally loaded with fixed partial dentures after 3 months. Crestal bone loss (primary outcome variable) was measured using a digital subtraction radiography technique. Standardized radiovisiographs were taken after implant insertion, after fixed partial denture installation (3 months after surgery), and after 6 and 12 months of functional loading. The data were analyzed using the Wilcoxon signed ranks test (α = 0.05). RESULTS: Eleven patients (mean age 46.9 years, 3 women and 8 men) were included in the study. A total of 34 implants were inserted, 17 using a 1-stage protocol and 17 using a 2-stage protocol. Three months after implant placement, the 2-stage implants showed significantly more crestal bone loss (0.65 ± 0.71 mm) than the 1-stage implants (0.41 ± 0.53 mm; P = .02). However, after 6 and 12 months of functional loading, both groups showed comparable changes in bone level (P > .05). CONCLUSIONS: No differences were found between 1-stage and 2-stage implant placement in crestal bone loss after 1 year of functional loading.

Alveolar bone stress around implants with different abutment angulation: an FE-analysis of anterior maxilla.

OBJECTIVES: To comparatively assess the masticatory stress distribution in bone around implants placed in the anterior maxilla with three different labial inclinations. MATERIALS AND METHODS: Three-dimensional finite element models were fabricated for three situations in anterior maxilla: (1) a fixture in contact with buccal cortical plate restored by straight abutment, (2) a fixture inclined at 15 degrees, and (3) 20 degrees labially restored with corresponding angled abutment. A palatal bite force of 146 N was applied to a point 3 mm below the incisal edge. Stress distribution around the bone-fixture interface was determined using ANSYS software. RESULTS: The maximum compressive stress, concentrated in the labial crestal cortical bone, was measured to be 62, 108, and 122 MPa for 0-, 15-, and 20-degree labially inclined fixtures, respectively. The maximum tensile stress, concentrated in the palatal crestal cortical bone, was measured to be 60, 108, and 120 MPa for 0-, 15-, and 20-degree labially inclined fixtures, respectively. CONCLUSIONS: While all compressive stress values were under the cortical yield strength of 169 MPa, tensile stress values partially surpassed the yield strength (104 MPa) especially when a 20-degree inclination was followed for fixture placement.

Effect of static magnetic fields on the osseointegration of immediately placed implants: a randomized controlled clinical trial.

PURPOSE: The aim of this study was to evaluate the effects of static magnetic fields (SMFs) on the implants immediately placed in fresh extraction sockets. MATERIALS AND METHODS: Twenty patients who were in need of 20 fixed implant-supported single crowns in the anterior maxilla were included. After tooth extraction, screw-type implants were placed immediately into fresh extraction sockets and were randomly covered with either magnetic abutment (test group) or conventional healing abutment (control group). Radio frequency analysis (RFA) was conducted at implant placement and after 1, 2, and 3 months. Marginal bone level changes were recorded 1, 2, and 3 months postoperatively. RESULTS: The RFA measurements showed a significant higher stability for implants in test group than that of control group after 1 month (P = 0.04). At month 2, less crestal bone loss was found in the test group (P = 0.03). However, at month 3, there was no significant difference between the groups for both parameters (P > 0.05). CONCLUSION: SMFs caused more noticeable increase in implant stability and less bone loss during the initial weeks of healing.

Effect of Clinical Rotation Timing on Learning Quality of Dental Students.

Objective: Dental educational curricula are under constant modification and improvement. However, designing a comprehensive, efficient, and flexible curriculum is still challenging for the authorities. An efficient curriculum should obviate the educational needs of students and promote their knowledge and expertise for future practice. Time planning of clinical rotations is highly important for optimization of the learning process. This study aimed to compare the efficacy of two different timing models of clinical rotations, namely four versus two rotations in each semester. Materials and Methods: A total of 74 dental students and 54 faculty members of Tehran University of Medical Science that experienced both rotation models for two consecutive years (2018 and 2019) participated in this study. A questionnaire was designed to assess different aspects of the two timing-models. Results: A one-sample t-test indicated that students' and faculty members' mean perception were significantly better regarding the two-rotation program. Conclusion: This study indicated that changing the time planning of educational rotations can affect different aspects of education.

Fully Digital versus Conventional Workflows for Fabricating Posterior Three-Unit Implant-Supported Reconstructions: A Prospective Crossover Clinical Trial.

This study assessed the clinical variables influencing the success of three-unit implant-supported fixed dental prostheses (ISFDPs) fabricated using either fully digital or conventional workflows. The clinical trial evaluated 10 patients requiring three-unit ISFDPs in the posterior mandible. Maxillomandibular relation records, and digital and conventional impressions were obtained from each patient using an intraoral scanner (IoS) and polyvinylsiloxane (PVS), and the frameworks were fabricated using zirconia and cobalt-chromium, respectively. A 2 µm accuracy scanner scanned the conventional master casts and standard reference models. The stereolithography (STL) files of the digital and conventional impressions were superimposed on the standard model file, and the accuracy was calculated with the best-fit algorithm. The framework adaptation and passivity were assessed using the one-screw and screw resistance tests. The time required for occlusal adjustment of both types of reconstructions, including the duration of the whole treatment, was recorded. The aesthetic appearance of ISFDPs was rated by each patient and clinician using a self-administered visual analogue scale questionnaire and the FDI World Dental Federation aesthetic parameters, respectively. The sample size was based on the power calculation, and alpha was set at 0.05 for the statistical analyses. The impression accuracy, framework adaptation and passivity, and reconstructions aesthetics did not significantly differ between the digital and conventional approaches. The total fabrication time was significantly shorter using the digital workflow. Within the limitations of this clinical study, the fully digital workflow can be used for the fabrication of ISFDPs with a clinical outcome comparable to that of the conventional workflow.

Three-dimensional accuracy of implant and abutment level impression techniques: effect on marginal discrepancy.

Impression techniques should precisely represent the 3-dimensional status of implants to allow for the fabrication of passively fitting prostheses and subsequently the elimination of strain on supporting implant components and surrounding bone. The aim of this study was to compare the accuracy of an abutment level impression method with that of an implant level (direct and indirect) impression method using polyether impression material to obtain precise definitive casts and prostheses. A reference acrylic resin dentoform with 2 internal connection implants (Implantium) was made. A total of 21 medium-consistency polyether impressions of the dentoform, including 7 direct implant level, 7 indirect implant level, and 7 abutment level (after 2 straight abutments were secured), were made. Impressions were poured with American Dental Association (ADA) type IV stone, and the positional accuracy of the implant replica heads and abutment analogs in each dimension of x-, y-, and z-axes, as well as angular displacement (Δθ), was evaluated using a coordinate measuring machine. Noble alloy 3-unit castings were fabricated and seated on the abutments in 3 groups; marginal discrepancies were measured at 4 points between prostheses and abutments. Data were analyzed using Mann-Whitney U test, 1-way analysis of variance (ANOVA), and Kruskal-Wallis tests. In comparisons of different impression techniques, only significant statistical Δθ differences were noted between the abutment level method and other techniques (P < .001). Results of this study reveal that although the implant level impression method could better transfer the angular position of the implants (Δθ), the impression method could not affect Δy, Δx, and Δz coordinates of the implants or marginal discrepancy of the 3-unit fixed partial dentures (FPD).

Step-by-step oral rehabilitation of a generalized odontodysplastic patient with implant-supported prostheses: a clinical report.

This clinical report describes the rehabilitation of a 19-year-old girl diagnosed with generalized odontodysplasia. Ten implants were placed in the maxilla and mandible and metal-ceramic implant-supported fixed prostheses were fabricated for both arches. This treatment option seems to be favorable for patients with generalized odontodysplasia.

Reconstruction of a Mandibular Defect with Toronto Bridge Following Tumor Resection and Bone Graft: A Case Report.

Dental implants are highly recommended to improve the retention, stability, and support of prostheses in edentulous patients with large surgical defects. Depending on the size of the defect, a bone graft procedure might be necessary. However, due to limitations of bone grafts, some complications might negatively affect the prosthetic rehabilitation of the patient. This case report presents some of these prosthetic problems following surgical resection and autogenous bone graft procedures.

Dimensional Changes of 3-Unit Implant-Supported Zirconia Frameworks of Two CAD/CAM Systems from Scanning to Sintering.

OBJECTIVES: Internal fit of implant frameworks is an important factor determining the long-term success of dental implant restorations. This in-vitro study aimed to evaluate dimensional changes of implant-supported zirconia frameworks fabricated by two computer-aided design/computer-aided manufacturing (CAD/CAM) systems from scanning to sintering. MATERIALS AND METHODS: A master model of a three-unit fixed partial denture was fabricated with two implant abutments. In each CAD/CAM system (AmannGirrbach and Zirkonzahn), the master model was scanned 12 times, and data were saved as Standard Transformation Language files (scanning groups). Using semi-sintered zirconia, 12 real-size frameworks (milling groups) and 12 enlarged frameworks, were sintered (sintering groups) and made by each system. Dimensions of the master model and frameworks in each phase were measured. Dimensional changes (compared to the master model) were calculated. Data were analyzed using repeated measures analysis of variance, independent t-test, and paired sample t-test (α=0.05). RESULTS: Comparison of the two systems revealed that although dimensional changes were greater in the milling phase of Zirkonzahn, they were larger in the sintering phase of the AmannGirrbach system. Evaluation of fabrication phases revealed greater dimensional changes in the milling phase compared to the other phases in the Zirkonzahn system (P<0.05). However, in the AmannGirrbach system, the values were not significantly different between milling and sintering phases (P>0.05). CONCLUSION: Within the limitations of this study, the results showed that fabrication phases, CAD/CAM system type and abutment size had significant effects on dimensional changes.