The virtual planning eliminates some laboratory steps and reduces the errors associated to manual procedures. Thanks to the digital method, the setup is faster and more repeatable because the procedure is standardized and the teeth are moved with completely measurable parameters and values [1] . Three-dimensional cephalometry using standardized CT scanning protocols has the advantage that all measurements are life-sized scale (1:1), which allows both cross-sectional and longitudinal comparison of 3D distances, linear projective, and orthogonal measurements [12] . Three-dimensional imaging provides information and images of craniofacial structures free from perspective distortion, with none of the magnification or superimposition associated with 2D images [9] .

The repeatability of this procedure would reduce human error in cephalometric analysis, in face-bow record and the assembly on the articulator. According to Xu et al. [13] , the most common error that occurred in the articulator procedure was in reproducing the angle between the occlusal and the horizontal planes. A variable errors in terms of replicating the angulation of the occlusal plane were ranged from 1˚ to 20˚. This procedure caused excessive or insufficient movement in the vertical and sagittal direction. Quast et al. [14] found that in most cases, the angle in the sagittal dimension was higher in the articulator-based model than in the computer-based model. The angle in the transverse dimension was as often under- as over-represented. The type of malocclusion, skeletal class, vertical relationship, and degree of asymmetry, had no significant impact on the amount of error. Metzger et al. [12] reported that rotational and translational movements of the plaster models were insufficiently controlled during the model surgery stage. Ho et al. [15] also compared three-dimensional planning of the final digital occlusion with the conventional dental cast approach. They found that the proposed intraoral scan and setup process of the final digital occlusion was reliable and accurate.

Another advantage of virtual planning is that the clinician can evaluate how well the guides fit the dental arches without repeating alginate impression to evaluate presurgical results and without causing unfavorable phenomena such as jiggling movements [9] .

Prediction of surgical and orthodontic outcome also integrate the soft tissue envelope and photographic 3D images [16] . The ability to accurately simulate the response of soft tissues to planned surgical movements can be a viable tool for communication with patients and evaluating treatment options [17] [18] . The development of simulation software also provides the aesthetic standards for different populations (aesthetic-centered virtual planning) [8] .

According to Chen et al. [4] , the VSP technique showed clinically significantly greater precision for soft tissue prediction in the sagittal plane than the traditional technique. However, Elshebiny et al. [17] found that Dolphin 3D software had limitations in predicting midface soft tissue changes in patients who received a double-jaw surgery. Franto-nasal angle differences might be due Le Fort I osteotomies that can rotate the base of the nose superiorly after maxillary impactions or advancements, and widening of the alar bases with a tendency for the tip of the nose to rotate downward and back.

Therefore, only approximate results can be expected for the soft tissue. Virtual planning may be helpful to simulate the result after surgery, especially the position of the lips after orthognathic surgery, but has a lower precision when compared to the bones [19] . In some cases, soft tissue remodeling disharmony could occur after hard tissue changes [20] .

Virtual surgery is a very powerful tutorial and communication tool for colleagues, trainees, and patients [19] . VSP has better visualization than articulator model surgery and can provide additional information and details about the case, as well as the potential problems that are supposed to occur during the operation [13] . The virtual simulation also facilitates communication between the different members of the treatment team especially the orthodontist and the maxillofacial surgeon. This is particularly useful when orthodontist and surgeon are separated by long distances as they can quite easily perform simulations together by computer and exchange comments, and even make “live” modifications [2] .

Another advantage of digital planning is the improvement of data management, as all the information is stored in the computer [13] .

A useful advantage of 3D planning is that it increases the knowledge of the anatomy of each particular patient because the surgical procedure has been performed several times before on “the same” virtual patient [19] . Virtual planning enables an accurate surgical plan, executed with precision during the real surgery and helps deciding the osteotomy line in surgical procedures, even when no cutting or positioning guides are made [9] [21] . It also allows orthodontists and surgeons to review the possible surgical options, which might produce more accurate and stable surgical outcome compared to conventional surgical planning [22] [23] .

The comparison between VSP and TSP techniques showed a similar surgical accuracy for hard tissue in the sagittal plane, although the VSP technique was significantly more accurate in certain reference areas, especially in the anterior area of the maxilla. Both the VSP and TSP techniques had significantly better surgical accuracy for the maxilla than for the mandible. Accuracy in the coronal plane was regarded as the main disadvantage of the TSP technique, especially for the diagnosis and treatment of patients with asymmetric deformity [4] . Thus, the 3D planning was especially relevant for the correction of facial asymmetries [5] .

Fawzy et al. [8] assessed the effect of the deformity pattern on the VSP applicability. Some aspects in planning, such as rotational movement of the maxillaemandibular complex around the Y axis (Yaw movement), were more predictable using the 3D virtual planning. Less VSP applicability was found in cleft-related dentofacial deformities compared to the noncleft group. This could be attributed to restricted movement of the maxillary segment because of scar tissue resulting from the primary cleft repair. Data analysis also revealed no significant difference in the VSP applicability between surgery-first and orthodontic-first groups.

VSP-driven workup was effective and accurate when comparing pre-treatment and post-treatment cephalometric measurements complications [11] . Growth and relapse considerations were factored into the plan. VSP allowed a virtual run through of different scenarios to arrive at the best overall treatment choice. Hence, 3D planning improved efficiency, accuracy and reproducibility in orthognathic surgery which reduced complications and reoperations [19] [24] .

Park et al. [25] found that the time investment in VSP was significantly smaller than that in conventional surgical planning, and the difference was greater in group I (Le Fort I osteotomy and bilateral sagittal split osteotomy) than in group II (only bilateral sagittal split osteotomy). According to Xu et al. [13] , VSP planning took about three hours, while articulator model surgery required double the time of VSP.

Although the VSP technique requires more time for software planning, but it has an advantage in terms of time saving when considering the entire preoperative process [4] . Accompanied by the use of an accurate computer-aided splint, the VSP technique could effectively reduce the operative time [26] . These findings are significant because a prolonged operative time is closely correlated with increased postoperative complications [11] .

Many studies compared the cost reduction between VSP and conventional planning. They revealed that the total cost of the VSP was similar to that of the traditional technique [4] [25] . Resnick et al. [26] found that VSP for bimaxillary orthognathic surgery was even less expensive than standard planning. However, high spending was required to buy machines and software, and patients had to pay more money, which was the most considered factor of VSP [13] [27] .