Clinical Factors Affecting the Accuracy of Guided Implant Surgery—A Systematic Review and Meta-analysis

The Journal of EVIDENCE-BASED DENTAL PRACTICE

ORIGINAL ARTICLE

CLINICAL FACTORS AFFECTING THE ACCURACY OF GUIDED IMPLANT SURGERY— A SYSTEMATIC REVIEW AND META-ANALYSIS WENJUAN ZHOU, DDS, PhDa,b,c, ZHONGHAO LIU, DDS, PhDa, LIANSHENG SONG, DDS, MSb, CHIA-LING KUO, PhDd, AND DAVID M. SHAFER, DMDb a

Department of Implant Dentistry, Yantai Stomatological Hospital, Binzhou Medical University, Yantai, China Division of Oral and Maxillofacial Surgery, UConn School of Dental Medicine, Farmington, CT, USA c Division of Conservative Dentistry and Periodontology, Competent Center of Periodontal Research, University Clinic of Dentistry, Medical University of Vienna, Vienna, Austria d CT Institute for Clinical and Translational Science, UConn Health, Farmington, CT, USA b

CORRESPONDING AUTHOR: Wenjuan Zhou, Division of Oral and Maxillofacial Surgery, UConn School of Dental Medicine, 263 Farmington Avenue, Farmington, CT 06030, USA. E-mail: [email protected]

KEYWORDS Dental implants, Computer-assisted, Guided surgery, Surgical guides, Accuracy

Conflict of Interest: The authors have no actual or potential conflicts of interest. Received 26 June 2017; accepted 17 July 2017

J Evid Base Dent Pract 2018: [28-40]

ABSTRACT Objectives To systematically review the current dental literature regarding clinical accuracy of guided implant surgery and to analyze the involved clinical factors. Material and Methods PubMed and Cochrane Central Register of Controlled Trials were searched. Metaanalysis and meta-regression analysis were performed. Clinical studies with the following outcome measurements were included: (1) angle deviation, (2) deviation at the entry point, and (3) deviation at the apex. The involved clinical factors were further evaluated. Results Fourteen clinical studies from 1951 articles initially identified met the inclusion criteria. Meta-regression analysis revealed a mean deviation at the entry point of 1.25 mm (95% confidence interval [CI]: 1.22-1.29), 1.57 mm (95% CI: 1.53-1.62) at the apex, and 4.1 in angle (95% CI: 3.97-4.23). A statistically significant difference (P , .001) was observed in angular deviations between the maxilla and mandible. Partially guided surgery showed a statistically significant greater deviation in angle (P , .001), at the entry point (P , .001), and at the apex (P , .001) compared with totally guided surgery. The outcome of guided surgery with flapless approach indicated significantly more accuracy in angle (P , .001), at the entry point (P , .001), and at apex (P , .001). Significant differences were observed in angular deviation based on the use of fixation screw (P , .001). Conclusions The position of guide, guide fixation, type of guide, and flap approach could influence the accuracy of computer-aided implant surgery. A totally guided system using fixation screws with a flapless protocol demonstrated the greatest accuracy. Future clinical research should use a standardized measurement technique for improved accuracy.

1532-3382/$36.00 ª 2017 Elsevier Inc. All rights reserved. doi: http://dx.doi.org/10.1016/ j.jebdp.2017.07.007

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INTRODUCTION

D

igital technology has been playing a more and more important role in dentistry for number of years, one of the most common used digitalized

The Journal of EVIDENCE-BASED DENTAL PRACTICE

dental technique is digital radiography, which provides dental professionals potentially a better way of diagnosis and treatment for dental desease.1-3 In the past several years, with the introduction of computed tomography (CT) and 3-dimensional (3D) printing into the field of implant dentistry, computer-aided design and computer-aided manufacturing (CAD/CAM) technology brought a great evolution of novel treatment concepts to dental implant treatment.4 CT and 3D implant planning software can not only provide clinicians with 3D information of patient’s anatomic structures, but also data regarding the patient’s final prosthesis, these digital data can be combined with the CAD/CAM technology and further lead to a digital workflow ending with the production of stereolithographic (STL) template via a prototyping system.5,6 The STL template can then be used to guide the position and direction of certain implants during surgery. By which, the whole surgical procedure is so called “guided dental implant surgery.”

In recent years, several studies have been performed on different factors affecting the accuracy of guided surgery,16,17 and systematic reviews6,18-20 have evaluated these studies very well, focusing on the accuracy, clinical advantages, survival rates, complications of computer-guided surgery, and the influence of using different types of guide. However, only limited and incomplete data were provided in clinical trials regarding the accuracy and influence of relevant clinical factors except for tissue of support.18 There are still no concerted standard parameters for the evaluation of deviation, which leads to diversity in results and, therefore, can hardly provide an effective indication for the clinical application of guided surgery.

According to the consensus statement published in 2009,7 the term “computer-guided surgery” is defined as the use of a static surgical guide that reproduces the virtual implant position directly from CT data and does not allow for intraoperative modification of the implant position. It has been demonstrated to be an established treatment,6 which reduces the probability of damage to the adjacent critical structures such as bones, nerves, adjacent tooth roots, and sinus cavities. The main advantage of guided surgery is the ability to plan and optimize the implant position in a restoration-driven placement manner. Moreover, computer-guided technique can help to decrease postoperative discomfort and allows for immediate function, as they enable implant placement with minimal surgical trauma. In addition, this technique offers an alternative to bone augmentation in situation of severely resorbed alveolar ridges, as they facilitate optimal position of implants in available bones.8-10 However, with the generalization of this technique, many doubts have risen on its usefulness and especially the accuracy.11-15

MATERIALS AND METHODS

Accuracy in guided implant surgery is defined as matching the planned position of the implant in the software with the actual position of the implant in the patient’s mouth.13 It reflects the accumulation of all deviations from imaging over the transformation of data into a guide, to the improper positioning of the latter during surgery,14 and the different types of errors include error during image acquisition and data processing, error during surgical template production, error during template positioning and movement of the template during drilling, and mechanical error caused by tolerance of surgical instruments. All errors, although seldom occurring, can be cumulative.

In the present study, we tried to review the current dental literature, focusing on the clinical accuracy of guided dental implant surgery, to analyze the involved clinical factors affecting the accuracy, and tried to find the most appropriate method for the evaluation of accuracy.

Protocol and Registration This review was registered at the International Prospective Register of Systematic Reviews (https://www.crd.york.ac.uk/ PROSPERO, registration number 42016050127). It was conducted in accordance with the guidelines of “Preferred Reporting Items for Systematic Review and Meta-analysis Protocols 2015 Statement.”21

Search Strategy for Identification of Studies Two Internet sources of MEDLINE-PubMed and Cochrane Central Register of Controlled Trials (CENTRAL) were used to search for eligible articles (published and online preview) in English, and this was complemented by a manual search of the references of all selected full-text articles. Publications from January 1, 1990, to October 31, 2016, were searched using the following search strategy: PubMed: ((((((((((((“Dental Implantation”[Mesh]) OR “Dental Implants”[Mesh]) AND “Surgery, Computer-Assisted”[Mesh]) OR “Computer-Aided Design”[Mesh]) OR dental implant navigation) OR digital dentistry) OR guided dental implant surgery) OR image-guided dental implant surgery) OR computer-guided dental implant surgery) OR dental stereo lithography) AND “Dimensional Measurement Accuracy”[Mesh]) OR dental implant deviation) OR dental implant precision) OR dental implant accuracy); Cochrane Central Register of Controlled Trials: dental implantation OR dental implant and dental navigation OR computer aided dental implant OR three-dimensional (3D) dental planning OR 3D dental planning OR computer-assisted dental implant OR dental stereo lithography OR guided dental implant placement OR dental surgical template OR dental guided surgery OR dental surgical guide AND dimensional

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measurement accuracy OR dental implant deviation OR dental implant precision OR dental implant accuracy.

Studies Selection and Data Extraction For inclusion in this study, the articles were selected according to the following criteria: (1) articles published in English; (2) clinical cohort studies; (3) the article title is related to the question, that is, studies reporting on the accuracy of static guided implant surgery performed in the partially or complete edentulous jaw; (4) studies in which quantitative results are provided (only studies providing exact information on the amount and direction of implant or osteotomy deviations were included); and (5) studies with a minimum sample size of 10. To evaluate the deviation, at least the following parameters should have been observed: deviation at the entry point, deviation at the apex, and deviation of the axis. Articles were additionally rejected after full-text analysis in the following situations: (1) expert opinions or literature reviews; (2) reports of techniques; (3) case series; (4) implants installed in areas of bone augmentation; (5) studies with zygomatic implants, pterygoid implants, or mini-implants for orthodontic purposes; and (6) studies using CT for implant planning without applying CAD/CAM surgical guide during surgery (mental navigation). Two reviewers retrieved the data independently and discussed with a third reviewer for the final selection of included studies. Except for the deviation of guided surgery; age, radiology method (CT or cone beam CT (CBCT)), position of guide (maxilla or mandible), fixation of guide (with or without fixation screw), type of guide (totally/fully guided or partially guided), and flap method (open flap or flapless) were further considered to be factors that would influence the accuracy of the outcome. For the assessment of bias risk in included studies, the adapted Newcastle-Ottawa Scale was used according to 2 previous systematic reviews.18,22 In brief, a maximum of 13 stars could be assigned for each included study; studies with 10-12 points indicated high methodological quality, 7-9 points indicated medium-level methodological quality, and others were considered as studies with low methodological quality.

Statistical Analysis The results of different studies were combined by metaanalysis assuming a random-effects model. Subgroup comparisons, for example, age groups and radiation methods, were performed in the framework of mixed-effects meta-regression. An omnibus test was used to test if there is mean difference between groups. If the result was significant, all possible pairwise comparisons were conducted with multiple testing adjustment by Tukey’s method. A P value

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less than 5% was deemed statistically significant. All the meta-regression analyses were performed using R 3.3.1. For the comparison of other involved clinical factors, metaanalysis was conducted using Review Manager, version 5.0 (The Nordic Cochrane Center, Denmark). Heterogeneity between studies was assessed with the I2 statistics ($50%) and Cochran’s Q test (P ,.001/95% confidence interval [CI]). P values and 95% CIs were calculated for each variable of interest. The level of significance was set at P # .05.

RESULTS The initial search yielded 1743 titles from PubMed and 208 from the Cochrane Central Register of Controlled Trials. After reviewing the abstract, 1906 were excluded and 45 were considered for further full-text screening. Finally, 14 articles (6 retrospective studies and 8 prospective studies) were included in this systematic review (Figure 1). The characteristics of the included articles are presented in Table 1; the review did not include studies with smokers and patients with periodontal disease or other systemic diseases to avoid selection bias. The risk of bias assessment showed that most observational studies included in this systematic review received 8-10 stars, which indicates a medium-level methodological quality,

Figure 1. Flow diagram of articles retrieved from databases.

u

Table 1. Characteristics of studies included for qualitative analysis.

Mean age (y)

Edentulism (no. of implants)

Jaw (no. of implants)

Guide system

Type of guide (no. of implants)

Type of flap (no. of implants)

Fix screw (no. of implants)

Angle deviation (degree)

Design

Rx

Patients/no. of implants

Ozan et al., 2009

Retrospective

CT

30/110

47

Fully; partially

Max. (58); Mand. (52)

Stent CAD

Total

Flapless (60); flap(50)

4.10

Cassetta et al., 2011

Retrospective

CT

10/111

54

Fully (94); partially (17)

Max. (68); Mand. (43)

SimPlant

Total

Cassetta et al., 2013

Retrospective

CT

12/129

55

Fully (112); partially (17)

Max. (78); Mand. (51)

SimPlant

Vieira et al., 2013

Retrospective

CBCT

14/62

Fully (62)

Max.; Mand.

Prospective

CBCT

10/Oct

42

Single (10)

CT

20/227

55

Study

Farley et al., 2013

Cassetta Retrospective et al., 2013a

–

Lateral deviation coronal (mm)

Lateral deviation apical (mm)

Depth deviation coronal (mm)

Depth deviation apical (mm)

Mean

SD

Mean

SD

Mean

SD

Mean

SD

Mean

SD

2.30 1.11

0.70

1.41

0.90

–

–

–

–

–

–

–

–

Flapless (93); Y (67); N (44) 4.68 flap(18)

2.98 1.52

0.61

1.97

0.86

1.20 0.63

–

–

Total

Flapless (111); flap (18)

Y (75); N (54)

4.78

2.89 1.57

0.63

2.06

0.88

1.23 0.60

–

–

Dental Slice

Total

Flapless (62)

Y (62)

1.89

0.46 1.79

0.81

2.21

1.50

–

–

–

–

–

–

–

Max. (3); Mand. (7)

iDent

Total

Flapless (10)

–

3.68

2.19 1.45

0.60

1.82

0.60

0.63 0.37

1.11

0.71

Fully (182); partially (45)

Max. (135); Mand. (92)

SimPlant

Y (111); N (116)

4.82

3.14 1.50

0.63

1.92

0.91

1.35 0.68

–

–

Fully (102)

Max. (64); Mand. (44)

SimPlant

Flapless (102)

Y (102)

3.38

1.11 0.78

0.32

0.83

0.33

–

–

–

Fully (17); partially (85)

Max. (62); Mand. (40)

Flap (102)

Y (102)

3.80

3.24 1.09

1.10

1.56

1.48

0.72 0.75

1.23

1.25

Fully (65); partially (20); single (9)

Max. (48); Mand. (46)

–

4.90

2.36 1.22

0.85

1.51

1.00

–

–

–

–

–

CT/CBCT

11/102

–

Lee et al., 2013

Retrospective

CT

48/102

52.9

Ersoy et al., 2008

Prospective

CT

21/94

43

Arisan et al., 2010

Prospective

CBCT

54/279

48.4

Fully; partially

Di Giacomo et al., 2011

Prospective

CBCT

12/60

60.3

Fully (60)

Stubinger et al., 2014

Prospective

CT

10/44

62.5

Fully (44)

Vasak et al., 2011

Prospective

CT

16/79

58

Fully; partially

Verhamme et al., 2015

Prospective

CBCT

30/104

Fully (104)

Total

OnDemand 3D Total (102)

–

–

21.20 0.70 21.24

–

0.68

–

–

–

–

0.69

1.03

–

–

–

–

0.66 0.95

Stent CAD

Total (94)

Flapless (41); flap (53)

Stent CAD SimPlant

Total (29); partial (30)

Flapless; flap

–

3.96

1.05 1.22

0.39

1.44

0.43

–

–

–

–

–

–

–

–

NTT

Partial (60)

Flapless (60)

Y (60)

6.53

4.31 1.35

0.65

1.79

1.01

–

–

–

–

–

–

–

–

Astra Tech AB

Total (44)

Flap (44)

Y (44)

2.39

0.97 0.71

0.399 0.77

0.382 0.43 0.297 0.52

–

–

Max.; Mand. Nobel Biocare

Total (79)

Y (79)

3.53

1.77 0.46

0.35

0.70

0.49

–

–

–

–

0.53 0.38

0.52

0.42

Nobel Biocare Total (104) Flapless (104)

Y (64); N (40)

2.819

–

1.587

–

0.60

–

0.751

–

–

0.843

–

– Max. (22); Mand. (38)

–

Max. (104)

–

1.368

CAD, computer-aided design; CT, computer tomography; CBCT, cone beam computer tomography; Max., maxilla; Mand., mandible; SD, standard deviation.

0.273

–

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Prospective

Total (111); Flapless (187); partial(116) flap (40)

N (110)

Mean SD Mean

Global deviation apical (mm)

SD

Arisan et al., 2013

–

Global deviation coronal (mm)

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and 4 studies had high-level methodological quality (Figure 2).

errors were 1.47 mm (95% CI: 1.40-1.53), 1.64 mm (95% CI: 1.14-2.14), and 1.27 mm (95% CI: 0.27-2.27).

Meta-regression analysis revealed an overall (14 studies, n 5 1513 implants) mean deviation at the entry point of 1.25 mm (95% CI: 1.22-1.29), 1.57 mm (95% CI: 1.53-1.62) at the apex, and the mean angular deviation is 4.1 (95% CI: 3.97-4.23). Seven studies (n 5 727 implants) reported a mean lateral error at the entry point of 1.05 mm (95% CI: 1.00-1.09), whereas the mean apical lateral deviation (4 studies, n 5 260 implants) was 0.91 mm (95% CI: 0.81-1.02). The mean depth deviation was 0.64 mm (95% CI: 0.53-0.74) at the entry point (3 studies, n 5 191 implants) and 1.24 mm (95% CI: 1.161.32) at the apex (4 studies, n 5 295).

P values from the omnibus test associated with age for angular deviation, deviation at the entry point, and deviation at the apex were 0.975, 0.789, and 0.658, respectively. None of the P values are statistically significant, which implies that there is no significant difference between age groups for the 3 deviations.

Effect of Age on the Accuracy of Guided Surgery Data on patients’ age were retrieved from 11 studies. Three age groups were created: 40-50 years (4 studies, n 5 493 implants); 50-60 years (5 studies, n 5 648 implants); and 60 years or older (2 studies, n 5 104 implants). The mean angular deviation was 4.15 (95% CI: 3.62-4.67) for the 40- to 50-year group, 4.32 (95% CI: 3.78-4.87) for the 50- to 60-year group, and 4.43 (95% CI: 0.37-8.48) for the 60 years or older group. The mean deviation at the entry point for the 3 age groups was 1.21 mm (95% CI: 1.15-1.26), 1.23 mm (95% CI: 0.81-1.64), and 1.03 mm (95% CI: 0.401.65), respectively, and their corresponding mean apical

Effect of Radiology Methods on the Accuracy of Guided Surgery For the influence of radiology techniques, 9 studies (n 5 946 implants) used CT for the guided surgery, whereas 6 studies (n 5 567 implants) used CBCT. The mean angular deviation was 4.02 (95% CI: 3.45-4.59) for the CT group and 3.86 (95% CI: 2.41-5.30) for the CBCT group. For deviation at the entry point, the CT group revealed a mean error of 1.10 mm (95% CI: 0.84-1.36), whereas the CBCT group presented a mean error of 1.31 mm (95% CI: 0.99-1.63). The mean deviation at the apex was 1.59 mm (95% CI: 1.52-1.66) and 1.54 mm (95% CI: 1.48-1.60), respectively, for CT and CBCT groups. The study of Arisan et al.23 had both CT and CBCT data. We conducted sensitivity analysis by including both data and excluding the CT data. The omnibus test P values for angular deviation, deviation at the entry point, and apical

Figure 2. Risk of bias of included studies. Stars were assigned to respective study, 10 studies received 8-10 stars that indicated a medium-level methodological quality, and 4 studies with more than 10 stars had high-level methodological quality.

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Figure 3. Deviation stratified by the guide position (maxilla vs mandible): (A) angular deviation; (B) deviation at the entry point; and (C) deviation at the apex.

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deviation were 0.738, 0.336, and 0.508 when including both data and were 0.654, 0.460, and 0.689 when excluding the CT data. Both gave consistent results and suggested that there is no significant difference in the accuracy between CT and CBCT.

Effect of the Guide Position Four studies (3 prospective studies and 1 retrospective study; n 5 274 implants) were reviewed for comparing the accuracy of guided surgery performed on the maxillary or mandible jaw. Statistically significant differences (P , .001) were found in the mean angular deviation between maxillary and mandible positions (MD: 0.89 [95% CI: 0.76-1.03]; Figure 3A). The global meta-analysis showed no statistical significance (P 5.06) in coronal accuracy when comparing the maxilla and mandible positions (MD: 20.17 [95% CI: 20.34 to 0.00]; Figure 3B), whereas differences in apical error between maxillae and mandibles were also not statistically significant (P 5 .8) (MD: 0.03 [95% CI: 20.20 to 0.27]; Figure 3C).

Influence of Guide Type (Totally Guide vs. Partially Guide) Only 2 studies (1 prospective and 1 retrospective study; n 5 215 implants) reported data comparison of totally and partially guided surgery protocols. The results of the prospective study showed that the angular deviation was significantly greater (P ,.001) in the partially guided surgery group, whereas the retrospective study showed no statistical difference (P 5 .35) in angular deviation when comparing the partially guided with totally guided surgery. Global meta-analysis indicated statistically greater accuracy (P , .001) in angle in the totally guided surgery group than the partially guided surgery group (MD: 21.16 [95% CI: 21.40 to 20.92]; Figure 4A). As for the deviation at the entry point and apex, the results showed significant greater error (P , .001) in the partially guided surgery group (MD: 20.53 [95% CI: 20.61 to 20.45] and MD: 20.65 [95% CI: 20.75 to 20.56], respectively) (Figure 4B-C).

Effect of Flap Approach Three studies (2 prospective studies and 1 retrospective study, n 5 190 implants) compared the effect of open-flap or flapless approach on the accuracy of guided surgery. A statistically significant greater reduction (P ,.001) in angle deviation (MD: 1.20 [95% CI: 0.90-1.50]) (Figure 5A) and coronal deviation (MD: 0.55 [95% CI: 0.45-0.65]) (Figure 5B) was reported in the guided surgery group with a flapless approach. For deviation at the apex, the outcome of the subgroup with retrospective study showed no statistical difference between flap and flapless groups (P 5 .07); however, the global analysis showed that the flapless group had significantly more accuracy (P , .001) than the open-flap group (MD: 0.66 [95% CI: 0.54-0.79]) (Figure 5C).

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Influence of the Guide Fixation To evaluate the influence of fixation on accuracy, only 2 retrospective studies (n 5 132 implants) were included. Significant differences (P , .001) were observed in the deviation of angle based on the use of fixation screw (MD: 21.30 [95% CI: 21.94 to 20.66]) (Figure 6A). No statistically differences were seen between fixed and unfixed guides in coronal deviation (P 5 .88) and apical deviation (P 5 .93) (Figure 6B-C).

DISCUSSION In this systematic review of the literature, the accuracy of guided implant surgery and the involved clinical factors were evaluated. At the time of this review, 4 other publications6,18-20 had reviewed literature regarding the accuracy; however, only limited and incomplete data were provided on clinical trials. In this meta-analysis, in addition to evaluation of the overall deviation of guided surgery, a comprehensive comparison of involved clinical factors was also performed to see whether these factors could influence the accuracy of the position of implants inserted with STL guides. The involved factors included age, radiology method, the position of guide (maxilla or mandible),24-27 type of guide (totally or partially guided),28,29 flap approach (open flap or flapless),25,27,28 and guide fixation (use of fixation screw or not).29,30 The effect of the type of tissue support has been well evaluated in another review,18 so we did not repeat the same work on the type of tissue support. In addition, during study selection, we found that the parameters used in clinical studies for evaluating deviation were diverse. Some of the studies reported 2D deviations with or without lateral and depth parameters, whereas other studies used 3D measurement. Some studies evaluated lateral and depth errors both coronally and apically, whereas others included data only at the entry point or at the apex. Moreover, calculation of these parameters was different. To standardize the measurement, only studies with data of at least global angular, coronal, and apical deviations were included; lateral and depth deviations at the entry point and the apex was reviewed separately. According to some plausible and straightforward measurement of deviation,20,31 global deviation was defined as the distance between the coronal/apical centers of the planned and placed implants, and angular deviation was calculated as the 3D angle between the longitudinal axes of both. Depth deviation was the coronal/ apical vertical distance between the planned and placed implants, and lateral deviation was the coronal/apical horizontal distance between the planned and placed implants. These should be taken into account as consensus parameters in further studies to standardize the research work. The results in this meta-analysis showed a mean deviation at the entry point of 1.25 mm, at the apex of 1.57 mm, and

The Journal of EVIDENCE-BASED DENTAL PRACTICE

Figure 4. Deviation stratified by the guide type (totally guided vs partially guided): (A) angular deviation; (B) deviation at the entry point; and (C) deviation at the apex. CI, confidence interval; Max., maxilla; Mand., mandible; SD, standard deviation.

angle of 4.1 . Meanwhile, the lateral coronal deviation retrieved from 7 studies26,29,30,32-35 was 1.05 mm, and lateral apical deviation retrieved from 4 studies26,33-35 was

0.91 mm. Coronal/apical depth deviation26,33,35,36 was 0.64 mm/1.24 mm. These results agree with previous review studies, which indicated that although guided implant

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Figure 5. Deviation stratified by the flap approach (flap vs flapless): (A) angular deviation; (B) deviation at the entry point; and (C) deviation at the apex. CI, confidence interval; Max., maxilla; Mand., mandible; SD, standard deviation.

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Figure 6. Deviation stratified by the fixation method (fixed vs unfixed): (A) angular deviation; (B) deviation at the entry point; and (C) deviation at the apex. CI, confidence interval; Max., maxilla; Mand., mandible; SD, standard deviation.

surgery has many advantages, the possible deviation errors with this technique that might cause damage to adjacent anatomic structures or lead to restoration misfit are not negligible. As we mentioned earlier, the deviation errors accumulate from every step of the procedure, so the involved clinical factors must be considered. Some authors17 reported smoking as an influencing factor, and others37 reported surgeon experience as an influencing factor. Factors such as CT scan method, guide position, type of guide, and so on were also reported in the literature.12,16,27,38,39 In this systematic review, we summarized these clinical factors, and several important findings were observed.

First, guided surgery performed on the mandible has a more angular accuracy than on the maxilla. Based on our daily practice, the possible explanation might be the bone anatomy and bone density; the structure of the mandible is straight with an arcuate shape, whereas the shape of maxilla is a circular curve, which restrains the angulation control. In addition, the mandible bone is denser. Another important finding was that the totally guided procedure was more precise than the partially guided procedure, which is because with the partially guided procedure, implants were inserted manually, thus leading to a greater error than implants inserted with a guide. Comparing the accuracy of guided surgery between the flapless and open-flap approaches, the results indicated that a flapless approach is more accurate than an open-flap approach. This can be

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explained by the fact that guided surgery required a more extensive flap than conventional surgery did18; repositioning of the guide during surgery is more difficult because of the possible interference of the reflected tissue.40,41 Finally, a guide with fixation screws showed greater reduction in angular deviation than a guide without fixation screws. The stability of STL template could be the explanation; a fixed surgical guide is more accurate than manual pressure or freehand placement to position the surgical guide.42 Regarding the effects of age and the radiology method, the meta-regressive analysis observed that age has no significant influence on accuracy. This result rejected our previous hypothesis that guided surgery performed on younger patients has greater accuracy because of high bone quality; dense bone cannot affect the angular deviation, regardless of the implant placement method.39 A possible explanation is that the subjects included in this study were at their middle age or older, in which stage individuals achieve peak bone mass, and after that, bone loss became more rapid than bone formation. Comparison of CT and CBCT revealed no significant difference for the influence on accuracy, which coincided with the results of the only study reporting on deviation comparison between CT- and CBCT-derived STL guides.23 Other factors such as smoking habit, the surgeon’s experience, surgery site in arch, guide system, and implant length were not analyzed in this review; the reason is that not enough eligible studies focusing on these factors were available. This fact reminds us of including these factors in further studies. As to the quality of included studies and potential bias, only prospective and retrospective clinical studies were included in this meta-analysis considering our daily clinical practice. Each study was analyzed using the Newcastle-Ottawa Scale to evaluate methodological quality, which showed moderate to high quality. To avoid or minimize possible selection bias, a standard protocol was employed, and exact inclusion and exclusion criteria were defined. In addition, the data from prospective and retrospective studies were analyzed separately in subgroups. Significant heterogeneity was observed when comparing some of the involved clinical factors. Possible explanations are as follows: the study designs were different, the included patients were diverse, and there were clinical variations. After sensibility analysis, one study26 including only 10 subjects with single missing tooth was recognized, but with low sensitive to the overall results. One obvious limitation of this review is the limited number of included studies, which impacts the results of this metaanalysis. These limitations remind us that additional clinical studies on accuracy are still needed to provide guideline for clinical work.

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CONCLUSION It can be concluded that the position of guide (maxilla or mandible), guide fixation (use of fixation screw or not), type of guide (totally or partially guided), and flap approach (open flap or flapless) influence the accuracy of computeraided implant surgery. Totally guided systems using fixed screws with a flapless approach had greater accuracy. To minimize the cumulative errors, clinicians can make a totally guided system with fixed screws as the first choice in daily practice, which can be made better with a flapless approach. Future clinical research work should be directed to use a standardized measurement for accuracy and to control all involved factors to improve the accuracy of guided implant surgery.

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41. Vieira DM, Sotto-Maior BS, Barros CA, Reis ES, Francischone CE. Clinical accuracy of flapless computer-guided surgery for implant placement in edentulous arches. Int J Oral Maxillofac Implants 2013;28:1347-51. 42. Arisan V, Karabuda CZ, Ozdemir T. Implant surgery using boneand mucosa-supported stereolithographic guides in totally edentulous jaws: surgical and post-operative outcomes of computer-aided vs. standard techniques. Clin Oral Implants Res 2010;21:980-8.