Prospective Clinical Study on the Accuracy of Static Computer‐Assisted Implant Surgery in Patients With Distal Free‐End Implants. Conventional Versus 
Introduction The introduction and widespread use of cross‐sectional imaging in implant dentistry using cone‐beam computed tomography (CBCT) over the last decade has enabled clinicians to diagnose and evaluate the jaws in three dimensions before and after the insertion of dental implants, thus replacing computed tomography (CT) as the standard of care (Bornstein et al. ). Implant simulation software processes Digital Imaging and Communications in Medicine (DICOM) data obtained by CBCT and surface information, such as Standard Triangle Language (STL) or Polygon File Format (PLY), and affords a preoperative view of the anatomical structures. These technological advances have influenced the approach to implant treatment. One of the fields presently experiencing rapid development is static computer‐assisted guided surgery (sCAIS), which allows the transfer of the virtual implant planning to the mouth of the patient, based on the use of a surgical guide. Planning of the implants is made in the ideal prosthetic position based on a previous CAD‐CAM (computer‐aided design—computer‐aided manufacturing) wax‐up. sCAIS facilitates correct prosthetic emergence and therefore contributes to securing optimum esthetic and biological outcomes, affording long‐term stability of the soft and hard tissues (D'haese et al. ). These surgical guides can be manufactured using CAD‐CAM or conventional technologies in the laboratory, employing drilling machines or mechanical positioners. In the case of the conventional guide manufactured in the laboratory, the technician creates a radiological guide that is then converted into a surgical guide—the whole process being analogic, except for the planning of the implants. The planning software produces a series of values that are entered into the laboratory machine that prepares the holes for manufacturer sleeves (Behneke et al. ; Vercruyssen, Fortin, et al. ). At present, and with the development of digital workflows, CAD‐CAM procedures are used for both the design and manufacture of the surgical guide, using different processes (Khorsandi et al. ). This simplifies the workflow, which can reduce the costs of smaller rehabilitations. The simplified workflow enables the prosthodontist or surgeon to design the prosthetics and surgical guide digitally. The digitalization of manual procedures could probably reduce the deviations associated with manual non‐digital procedures (Skjerven et al. ), although there are no clinical studies to confirm this. An in vitro study (Matta et al. ) reported a 0.86 mm greater deviation in the xyz space with conventional manufacture compared to CAD‐CAM surgical guides, in 13 implants. In sCAIS there is a deviation between the virtually planned implant position and the actual position of the implant placed during surgery. A recent review analyzed only fully guided implants and recorded a mean coronal horizontal deviation (CHD) of 1.12 mm (standard deviation [SD] = 0.08), a mean apical horizontal deviation (AHD) of 1.41 mm (SD = 0.1), a mean vertical deviation (VD) of 0.12 mm (SD = 0.23), and a mean angular deviation (AD) of 3.58° (SD = 0.2) (Balaguer‐Martí et al. ). Surgical accuracy is conditioned by cumulative errors (Van de Velde, Sennerby, and De Bruyn ) that can occur from diagnosis to implant surgery, and by other characteristics such as the alveolar ridge morphology, type of edentulous space, and the guided surgery protocol, the use of sleeves or a sleeveless protocol, the drilling sequence, the use of keys or keyless systems, fully versus partially guided surgery, incorrect placement of the surgical guide, the number of guides, etc. (Dulla et al. ; Raabe et al. ). According to the recent literature (Putra et al. ), numerous factors can contribute to the accuracy of sCAIS and need to be controlled by the operator, but many of the published studies are in vitro (Chen et al. ; Sium‐Abel et al. ). Therefore, systems are being explored to simplify and minimize the number of steps in the surgical technique. Strict adherence to the system protocol is essential to avoid complications (Orentlicher et al. ), and sCAIS is associated with a learning curve that needs to be taken into account (Balaguer‐Martí et al. ). Clinical studies on accuracy published in the literature are heterogeneous, with differences in the systems used, the surgical technique, the type of surgical guide support, or the type of edentulism involved (Raico Gallardo et al. ; Tahmaseb et al. ; Balaguer‐Martí et al. ; Romandini et al. ). Fully sCAIS showed greater accuracy than partial sCAIS in previous studies (Bover‐Ramos et al. ). These data justify further research in humans, focusing on fully sCAIS, to reduce heterogeneity. Furthermore, a review of the literature revealed a lack of clinical publications on the accuracy of CAD‐CAM surgical guides compared to conventional guides, many of the published studies are in vitro (Matta et al. ; Sium‐Abel et al. ). Therefore, the aim of the present study was to compare the accuracy of CAD‐CAM and conventional guides in candidates for distal free‐end implant treatment and to analyze the effects of possible confounding factors inherent to the patient or the surgical technique employed. Intra‐ and postoperative complications of the surgical technique were also evaluated, as well as implant success and peri‐implant marginal bone loss. Hence, the null hypothesis of the study was the absence of any difference in accuracy between both guides. 

Material and Methods 2.1 Study Design and Population A prospective, controlled, examiner‐ and statistician‐blinded, parallel‐arm quasi‐experimental study was carried out at the University of Valencia (Valencia, Spain) during the period 2012–2019 (recruitment and follow‐up). The TREND guidelines for quasi‐experimental studies were followed (Tonetti and Palmer ; Fuller et al. ). The study protocol adhered to the Declaration of Helsinki on research involving human subjects, and was approved by the local Ethics Committee (reference no. H20190402125847). All subjects involved provided their informed consent prior to inclusion in the study. The study included patients referred to the Oral Surgery Department for rehabilitation with distal free‐end implants placed through fully sCAIS. The inclusion and exclusion criteria are indicated in Table . Two groups were established according to the surgical guide design involved: conventional (control group [CG]) or CAD‐CAM (test group [TG]). 2.2 Sample Size Calculation Clinically relevant aesthetic problems have been observed with deviations of more than 0.8 mm (SD = 0.44) with respect to planning (Fürhauser et al. ). For this effect size, an alpha error of 0.05 and a statistical power of 95%, the two‐tailed sample size calculation indicated the need for 18 patients in the study (9 in each group). For a power of 90%, the sample size was 16 patients. We decided to include a minimum of 20 patients to avoid dropout bias. Of the 64 candidates for participation in the study, 37 were excluded after radiographic examination. 2.3 Virtual Implant Planning In the CG, a radiological guide was manufactured by the technician. For this purpose, conventional impressions (Hydrogum 5; Zhermack, Italy) were obtained, and the master model was scanned with a desktop scanner (Imetric L1; Imetric 3D SA, Courtenay, Switzerland/3Shape D700, Copenhagen K, Denmark) to obtain an STL file of the patient arch, and the technician manufactured a radiological guide with barium facets at the distal free end. The guide was placed in the mouth, the fit was improved with photopolymerizing resin (Kiero Plast; Kuss Dental, Madrid, Spain), and the patient underwent a CBCT (NewTom GIANO 3D, fov 11 × 8 cm, Cefla SC, Imola, Italy) scan with the radiological guide in the mouth. coDiagnostix9 planning software (Dental Wings, Chemnitz, Germany) was used to superimpose the DICOM files of the CBCT and the STL file of the patient arch. In the TG, conventional impressions were obtained with the same material as in the CG, and the models were scanned with the desktop scanner. coDiagnostix9 planning software was used to superimpose the DICOM files of the CBCT and the STL file of the patient arch and the digital wax‐up performed in the laboratory. Once the three‐dimensional (3D) models were obtained, the implants in both groups were planned with a safety margin of 2 mm with respect to the neighboring anatomical structures (Tahmaseb et al. ), and with correct prosthetic emergence. The implant depth was 1–2 mm subcrestal. The sleeve height (distance between the implant shoulder and base of the sleeve) was chosen as 2, 4, or 6 mm to avoid interference with the soft tissues. All surgical computer simulations were performed by the same surgeon (BGM). 2.4 Manufacture of the Surgical Guide To manufacture the surgical guide in the CG, the gonyX device (Straumann; Straumann Group, Basel, Switzerland) was used to transform the radiological guide into a surgical guide by perforating the holes where the guide sleeves were to be positioned micrometrically. The sleeves were made of stainless steel and measured 5 mm in diameter and 5 mm in height (Straumann). In the TG, the surgical guide was computer‐aided designed by the same surgeon (BGM) using coDiagnostix9, leaving inspection windows to check correct fitting of the guide in the mouth, and followed by printing with Straumann Rapid Shape P20 and Straumann P Pro Surgical Guide Clear resin, and post‐processing (Shera, Flash‐Light Plus; Werkstoff‐Technologie GmbH, Lemförde, Germany). A calibration matrix from coDiagnostix was used to verify the sleeve diameter offset for the sleeve models which were used in the digital drill guide (hole 14). The offset to set the clearance between the guide and the patient's contact surface was 0.20 mm, the wall thickness of the surgical guide was 3 mm and large connectors were used for thickness to give more stability to the guide. The surgical guides had no bone fixation pins at the distal ends, and the laboratory adhered to the sleeves after printing. 2.5 Surgical Procedure and Prosthetic Rehabilitation and Follow‐Up The patients underwent supragingival scaling 1 week prior to implant surgery and received oral hygiene instructions. Implants were placed in mature bone (a minimum of 3 months after tooth extraction). All surgeries were performed under antibiotic premedication (amoxicillin 1 g, 1 h before surgery and every 12 h for 3 days) and local anesthesia (4% articaine with 1:100,000 epinephrine) (Inibsa, Lliça del Vall, Spain) by the same experienced surgeon (BGM). In all groups, the implant position was marked with ink through the surgical guide using a circular mucotome. Flapless implant surgery (punch technique) was performed if there was more than 5 mm of buccal keratinized mucosa from the marked zone to the mucogingival line. Finally, small mini‐flaps were raised to preserve the keratinized mucosa in cases where there was between 3–5 mm, or larger conventional full‐thickness flaps were created in the presence of < 3 mm. All implants were placed fully guided (Straumann Roxolid Bone Level) with the specific surgical kit for static computer‐assisted implant surgeries (Straumann), following the drilling sequence indicated by the software, with the implant positioned mesially first, and without removing the sCAIS implant mounters until all the implants were placed (Figure ). The diameter of the implants was 4.1 mm, and their length was selected depending on the height of the remaining bone. All the patients received postoperative oral hygiene instructions, and ibuprofen 600 mg every 8 h for 3 days after surgery was prescribed. After 3 months, the final screw‐retained CAD‐CAM ceramometal prostheses were fabricated. 2.6 Data Collection Calibration of the results was performed by the surgeons and examiners. The examiners and statisticians were blinded. The clinical and surgical parameters were recorded by the same examiner (JCB) at the Department of Oral Surgery: patient age and sex, smoking habits, dental hygiene, phenotype, interincisal distance, type of surgical guide, sleeve height, surgical procedure (incision, location, implant diameter and length, insertion torque in Ncm, Osstell value in ISQ) and intraoperative complications (surgical guide fitting, retention, drill access, guide fracture). Postoperative complications (infection, bleeding, edema, neurological alterations) were also recorded. The patients were asked to complete a questionnaire, with a visual analog scale (VAS) to rate pain and swelling during the postoperative period. At 12 months of follow‐up, we evaluated marginal bone loss, peri‐implant tissue (plaque scores, bleeding scores, probing depths and height of the attached mucosa), and success, based on the clinical and radiological criteria of (Buser, Weber, and Brägger ). 2.7 Image Fusion and Measurement of Deviation New CBCT scans were obtained in all patients 10 days after implant placement when the sutures were removed. The coDiagnostix9 application was used to match the pre‐ and postoperative CBCT images and to compare the axis positions of the planned and placed implants. The vertical, apical, and coronal horizontal deviations in millimeters (VD, AHD, and CHD), and the angular deviation in degrees (AD), were recorded between the long axis of the virtual planned and actual placed implant (Figure ). 2.7.1 Statistical Analysis A descriptive analysis was performed, calculating the mean, standard deviation (SD), and interquartile range (IQR). In the comparative/inferential analysis, hypothesis contrasts were made of the quantitative and qualitative variables. Multiple linear models were generated with generalized estimating equations (GEEs), as an extension of the generalized linear model (GLM), to adjust for the different confounding variables recorded, due to the dependent data. The coefficients of the confounding variables of the linear models were also registered. The significance level was set at α = 0.05, and statistical significance was considered for p < 0.05. The R Project for statistical computing package was used for data analysis (Team ). Both the examiners and the statistician were blinded to the assignment of the groups. 

Study Design and Population A prospective, controlled, examiner‐ and statistician‐blinded, parallel‐arm quasi‐experimental study was carried out at the University of Valencia (Valencia, Spain) during the period 2012–2019 (recruitment and follow‐up). The TREND guidelines for quasi‐experimental studies were followed (Tonetti and Palmer ; Fuller et al. ). The study protocol adhered to the Declaration of Helsinki on research involving human subjects, and was approved by the local Ethics Committee (reference no. H20190402125847). All subjects involved provided their informed consent prior to inclusion in the study. The study included patients referred to the Oral Surgery Department for rehabilitation with distal free‐end implants placed through fully sCAIS. The inclusion and exclusion criteria are indicated in Table . Two groups were established according to the surgical guide design involved: conventional (control group [CG]) or CAD‐CAM (test group [TG]). 

Sample Size Calculation Clinically relevant aesthetic problems have been observed with deviations of more than 0.8 mm (SD = 0.44) with respect to planning (Fürhauser et al. ). For this effect size, an alpha error of 0.05 and a statistical power of 95%, the two‐tailed sample size calculation indicated the need for 18 patients in the study (9 in each group). For a power of 90%, the sample size was 16 patients. We decided to include a minimum of 20 patients to avoid dropout bias. Of the 64 candidates for participation in the study, 37 were excluded after radiographic examination. 

Virtual Implant Planning In the CG, a radiological guide was manufactured by the technician. For this purpose, conventional impressions (Hydrogum 5; Zhermack, Italy) were obtained, and the master model was scanned with a desktop scanner (Imetric L1; Imetric 3D SA, Courtenay, Switzerland/3Shape D700, Copenhagen K, Denmark) to obtain an STL file of the patient arch, and the technician manufactured a radiological guide with barium facets at the distal free end. The guide was placed in the mouth, the fit was improved with photopolymerizing resin (Kiero Plast; Kuss Dental, Madrid, Spain), and the patient underwent a CBCT (NewTom GIANO 3D, fov 11 × 8 cm, Cefla SC, Imola, Italy) scan with the radiological guide in the mouth. coDiagnostix9 planning software (Dental Wings, Chemnitz, Germany) was used to superimpose the DICOM files of the CBCT and the STL file of the patient arch. In the TG, conventional impressions were obtained with the same material as in the CG, and the models were scanned with the desktop scanner. coDiagnostix9 planning software was used to superimpose the DICOM files of the CBCT and the STL file of the patient arch and the digital wax‐up performed in the laboratory. Once the three‐dimensional (3D) models were obtained, the implants in both groups were planned with a safety margin of 2 mm with respect to the neighboring anatomical structures (Tahmaseb et al. ), and with correct prosthetic emergence. The implant depth was 1–2 mm subcrestal. The sleeve height (distance between the implant shoulder and base of the sleeve) was chosen as 2, 4, or 6 mm to avoid interference with the soft tissues. All surgical computer simulations were performed by the same surgeon (BGM). 

Manufacture of the Surgical Guide To manufacture the surgical guide in the CG, the gonyX device (Straumann; Straumann Group, Basel, Switzerland) was used to transform the radiological guide into a surgical guide by perforating the holes where the guide sleeves were to be positioned micrometrically. The sleeves were made of stainless steel and measured 5 mm in diameter and 5 mm in height (Straumann). In the TG, the surgical guide was computer‐aided designed by the same surgeon (BGM) using coDiagnostix9, leaving inspection windows to check correct fitting of the guide in the mouth, and followed by printing with Straumann Rapid Shape P20 and Straumann P Pro Surgical Guide Clear resin, and post‐processing (Shera, Flash‐Light Plus; Werkstoff‐Technologie GmbH, Lemförde, Germany). A calibration matrix from coDiagnostix was used to verify the sleeve diameter offset for the sleeve models which were used in the digital drill guide (hole 14). The offset to set the clearance between the guide and the patient's contact surface was 0.20 mm, the wall thickness of the surgical guide was 3 mm and large connectors were used for thickness to give more stability to the guide. The surgical guides had no bone fixation pins at the distal ends, and the laboratory adhered to the sleeves after printing. 

Surgical Procedure and Prosthetic Rehabilitation and Follow‐Up The patients underwent supragingival scaling 1 week prior to implant surgery and received oral hygiene instructions. Implants were placed in mature bone (a minimum of 3 months after tooth extraction). All surgeries were performed under antibiotic premedication (amoxicillin 1 g, 1 h before surgery and every 12 h for 3 days) and local anesthesia (4% articaine with 1:100,000 epinephrine) (Inibsa, Lliça del Vall, Spain) by the same experienced surgeon (BGM). In all groups, the implant position was marked with ink through the surgical guide using a circular mucotome. Flapless implant surgery (punch technique) was performed if there was more than 5 mm of buccal keratinized mucosa from the marked zone to the mucogingival line. Finally, small mini‐flaps were raised to preserve the keratinized mucosa in cases where there was between 3–5 mm, or larger conventional full‐thickness flaps were created in the presence of < 3 mm. All implants were placed fully guided (Straumann Roxolid Bone Level) with the specific surgical kit for static computer‐assisted implant surgeries (Straumann), following the drilling sequence indicated by the software, with the implant positioned mesially first, and without removing the sCAIS implant mounters until all the implants were placed (Figure ). The diameter of the implants was 4.1 mm, and their length was selected depending on the height of the remaining bone. All the patients received postoperative oral hygiene instructions, and ibuprofen 600 mg every 8 h for 3 days after surgery was prescribed. After 3 months, the final screw‐retained CAD‐CAM ceramometal prostheses were fabricated. 

Data Collection Calibration of the results was performed by the surgeons and examiners. The examiners and statisticians were blinded. The clinical and surgical parameters were recorded by the same examiner (JCB) at the Department of Oral Surgery: patient age and sex, smoking habits, dental hygiene, phenotype, interincisal distance, type of surgical guide, sleeve height, surgical procedure (incision, location, implant diameter and length, insertion torque in Ncm, Osstell value in ISQ) and intraoperative complications (surgical guide fitting, retention, drill access, guide fracture). Postoperative complications (infection, bleeding, edema, neurological alterations) were also recorded. The patients were asked to complete a questionnaire, with a visual analog scale (VAS) to rate pain and swelling during the postoperative period. At 12 months of follow‐up, we evaluated marginal bone loss, peri‐implant tissue (plaque scores, bleeding scores, probing depths and height of the attached mucosa), and success, based on the clinical and radiological criteria of (Buser, Weber, and Brägger ). 

Image Fusion and Measurement of Deviation New CBCT scans were obtained in all patients 10 days after implant placement when the sutures were removed. The coDiagnostix9 application was used to match the pre‐ and postoperative CBCT images and to compare the axis positions of the planned and placed implants. The vertical, apical, and coronal horizontal deviations in millimeters (VD, AHD, and CHD), and the angular deviation in degrees (AD), were recorded between the long axis of the virtual planned and actual placed implant (Figure ). 2.7.1 Statistical Analysis A descriptive analysis was performed, calculating the mean, standard deviation (SD), and interquartile range (IQR). In the comparative/inferential analysis, hypothesis contrasts were made of the quantitative and qualitative variables. Multiple linear models were generated with generalized estimating equations (GEEs), as an extension of the generalized linear model (GLM), to adjust for the different confounding variables recorded, due to the dependent data. The coefficients of the confounding variables of the linear models were also registered. The significance level was set at α = 0.05, and statistical significance was considered for p < 0.05. The R Project for statistical computing package was used for data analysis (Team ). Both the examiners and the statistician were blinded to the assignment of the groups. 

Statistical Analysis A descriptive analysis was performed, calculating the mean, standard deviation (SD), and interquartile range (IQR). In the comparative/inferential analysis, hypothesis contrasts were made of the quantitative and qualitative variables. Multiple linear models were generated with generalized estimating equations (GEEs), as an extension of the generalized linear model (GLM), to adjust for the different confounding variables recorded, due to the dependent data. The coefficients of the confounding variables of the linear models were also registered. The significance level was set at α = 0.05, and statistical significance was considered for p < 0.05. The R Project for statistical computing package was used for data analysis (Team ). Both the examiners and the statistician were blinded to the assignment of the groups. 

Results 3.1 Sample Description Twenty‐seven patients were finally selected: 14 in CG and 13 in TG. Of these 27 patients, one was excluded from the analysis of deviations because all the implants had failed prior to the follow‐up CBCT scan. No patients were lost during follow‐up. The mean age of the patients was 61.3 years (SD = 8.8). There were 9 males and 18 females. The great majority of the patients (88.9%) were non‐smokers, and half of them brushed their teeth twice a day. The tooth adjacent to the defect had a thick gingival phenotype in 66.7% of the patients, with a similar proportion in both groups (CG and TG). There were no significant differences in age, sex, smoking habits, hygiene, phenotype, or interincisal distance between the two groups ( p > 0.05). A total of 76 implants were placed: 36 with conventional surgical guides and 40 with CAD‐CAM guides. A post‐hoc power calculation was done, because more than one implant was included per patient (ratio 2.8 implants per patient), and the statistical power had to be corrected to 60%. A molar site (73.7% of the cases) was more common than a premolar site. In addition, significantly more implants were placed in the molar region in the TG than in the CG (82.5% vs. 63.9%, respectively; p = 0.023). There were no significant differences in the location, arch, sleeve height, incision, and length of the implants between the two groups (Table ). Most implants (84.3%) were inserted with a torque of 30–40 Ncm. The mean ISQ value was 67.7. Implants placed with CAD‐CAM surgical guides had significantly higher torque ( p = 0.006) and ISQ values ( p = 0.044). There were no significant differences between the groups in terms of guide fitting and retention ( p > 0.05). Drill access through the guide was good in 69.7% of the implants. However, the distribution was not uniform in both groups, with poorer access in the TG group (94.4% good access in the CG group vs. 47.5% in the TG group) ( p = 0.014). Surgical guide fracture occurred in only one case (in the TG group), in the final moment of placing the second implant (Table ). There were no postoperative complications (infection, bleeding, edema, or sensory alterations), and pain and swelling were maximum during the first 2 days, and then gradually subsided ( p > 0.05) (Figure ). There were no significant differences between the groups in terms of pain ( p = 0.197) or swelling ( p = 0.098). 3.2 Accuracy of the Implants Coronal horizontal deviation (CHD) was found to be significantly greater in the implants placed with conventional surgical guides (1.52 mm) versus CAD‐CAM guides (1.04 mm) ( p = 0.004). Apical horizontal deviation (AHD) in turn was 1.67 mm versus 1.46 mm, respectively, the angular deviation (AD) was 2.87 versus 3.64, and the vertical deviation (VD) was −0.1 versus −0.05 mm, with no significant differences between the groups ( p > 0.05) (Figure ). After generating the multiple linear models and controlling for confounding variables (Table ), significantly greater accuracy in terms of CHD was observed in TG ( p = 0.04). In addition, a higher sleeve height and placement of the implant at the premolar level as opposed to the molar level improved accuracy ( p < 0.05). Implant placement in the zone of the first premolar resulted in 0.6 mm less CHD than when the implant was placed at the second molar level. For AHD, the surgical guide design did not affect accuracy after correcting for confounding variables ( p > 0.05). However, a shorter implant length, greater sleeve height, and placement of the implants at the premolar level were associated with significantly greater accuracy ( p < 0.05). Specifically, the use of 12 mm implants increased the deviation by 0.3 mm (95% confidence interval [95% CI] 0.5–0) compared to 8 mm implants, and placement at the second molar level increased the deviation by 0.4 mm (95% CI −0.7 to −0.1) compared to insertion at premolar level. The surgical guide design had no effect on angular deviation ( p = 0.692) after correcting for confounding variables, and implant placement at the premolar level reduced the deviation by 1.7° (95% CI −3 to −0.3) compared to placement at the second molar level ( p < 0.05). Vertical deviation was likewise not influenced by the type of surgical guide ( p = 0.813) or other confounding variables. 3.3 Bone Loss, Soft Tissues, and Success Rate At 1 year, the mean peri‐implant bone loss was 0.12 mm in both groups ( p > 0.05). The bleeding and plaque index scores showed no significant differences between groups ( p = 0.168, p = 0.437). The mean probing depth was < 3 mm and the CAD‐CAM surgical guides showed a comparatively lower probing depth, though the difference failed to reach statistical significance ( p > 0.05). The mean keratinized mucosa thickness of the implants after 1 year of loading was 2.7 mm, and 75% of the implants had > 2 mm of keratinized mucosa. The implant success rate was 92.1%, 90.7% in TG, and 100% in CG. All failures occurred in patients treated with CAD‐CAM guides (6 implants in 3 patients). Three of the failures occurred before the follow‐up CBCT scan in one patient because of postoperative infection with the presence of pus in the surgical area and swelling, causing the implants to be removed. Analysis of the linear models showed the variables with a statistically significant impact on the success rate to be implant length, drill access, and the type of flap ( p = 0.001, p = 0.033, and p = 0.011, respectively) (Table ). In this regard, short implants, with poor guide access and flapless surgery were associated with poorer success rates. The odds ratio (OR) corresponding to implant length was 12.9 in favor of the longer implants (2% failure rate) versus the shorter implants (20% failure rate). The OR corresponding to drill access was 0.13, with the probability of success decreasing an 87% when the access was poor. Lastly, the OR corresponding to the type of flap was 5.75, with a percentage success rate of 95.8% when mini‐flaps were used versus 80% when flapless surgery was done (Table ). According to the Fisher exact test, the difference in success rate between the groups was statistically significant ( p = 0.026) at the implant level. The difference was not significant at the patient level, however ( p = 0.098). 

Sample Description Twenty‐seven patients were finally selected: 14 in CG and 13 in TG. Of these 27 patients, one was excluded from the analysis of deviations because all the implants had failed prior to the follow‐up CBCT scan. No patients were lost during follow‐up. The mean age of the patients was 61.3 years (SD = 8.8). There were 9 males and 18 females. The great majority of the patients (88.9%) were non‐smokers, and half of them brushed their teeth twice a day. The tooth adjacent to the defect had a thick gingival phenotype in 66.7% of the patients, with a similar proportion in both groups (CG and TG). There were no significant differences in age, sex, smoking habits, hygiene, phenotype, or interincisal distance between the two groups ( p > 0.05). A total of 76 implants were placed: 36 with conventional surgical guides and 40 with CAD‐CAM guides. A post‐hoc power calculation was done, because more than one implant was included per patient (ratio 2.8 implants per patient), and the statistical power had to be corrected to 60%. A molar site (73.7% of the cases) was more common than a premolar site. In addition, significantly more implants were placed in the molar region in the TG than in the CG (82.5% vs. 63.9%, respectively; p = 0.023). There were no significant differences in the location, arch, sleeve height, incision, and length of the implants between the two groups (Table ). Most implants (84.3%) were inserted with a torque of 30–40 Ncm. The mean ISQ value was 67.7. Implants placed with CAD‐CAM surgical guides had significantly higher torque ( p = 0.006) and ISQ values ( p = 0.044). There were no significant differences between the groups in terms of guide fitting and retention ( p > 0.05). Drill access through the guide was good in 69.7% of the implants. However, the distribution was not uniform in both groups, with poorer access in the TG group (94.4% good access in the CG group vs. 47.5% in the TG group) ( p = 0.014). Surgical guide fracture occurred in only one case (in the TG group), in the final moment of placing the second implant (Table ). There were no postoperative complications (infection, bleeding, edema, or sensory alterations), and pain and swelling were maximum during the first 2 days, and then gradually subsided ( p > 0.05) (Figure ). There were no significant differences between the groups in terms of pain ( p = 0.197) or swelling ( p = 0.098). 

Accuracy of the Implants Coronal horizontal deviation (CHD) was found to be significantly greater in the implants placed with conventional surgical guides (1.52 mm) versus CAD‐CAM guides (1.04 mm) ( p = 0.004). Apical horizontal deviation (AHD) in turn was 1.67 mm versus 1.46 mm, respectively, the angular deviation (AD) was 2.87 versus 3.64, and the vertical deviation (VD) was −0.1 versus −0.05 mm, with no significant differences between the groups ( p > 0.05) (Figure ). After generating the multiple linear models and controlling for confounding variables (Table ), significantly greater accuracy in terms of CHD was observed in TG ( p = 0.04). In addition, a higher sleeve height and placement of the implant at the premolar level as opposed to the molar level improved accuracy ( p < 0.05). Implant placement in the zone of the first premolar resulted in 0.6 mm less CHD than when the implant was placed at the second molar level. For AHD, the surgical guide design did not affect accuracy after correcting for confounding variables ( p > 0.05). However, a shorter implant length, greater sleeve height, and placement of the implants at the premolar level were associated with significantly greater accuracy ( p < 0.05). Specifically, the use of 12 mm implants increased the deviation by 0.3 mm (95% confidence interval [95% CI] 0.5–0) compared to 8 mm implants, and placement at the second molar level increased the deviation by 0.4 mm (95% CI −0.7 to −0.1) compared to insertion at premolar level. The surgical guide design had no effect on angular deviation ( p = 0.692) after correcting for confounding variables, and implant placement at the premolar level reduced the deviation by 1.7° (95% CI −3 to −0.3) compared to placement at the second molar level ( p < 0.05). Vertical deviation was likewise not influenced by the type of surgical guide ( p = 0.813) or other confounding variables. 

Bone Loss, Soft Tissues, and Success Rate At 1 year, the mean peri‐implant bone loss was 0.12 mm in both groups ( p > 0.05). The bleeding and plaque index scores showed no significant differences between groups ( p = 0.168, p = 0.437). The mean probing depth was < 3 mm and the CAD‐CAM surgical guides showed a comparatively lower probing depth, though the difference failed to reach statistical significance ( p > 0.05). The mean keratinized mucosa thickness of the implants after 1 year of loading was 2.7 mm, and 75% of the implants had > 2 mm of keratinized mucosa. The implant success rate was 92.1%, 90.7% in TG, and 100% in CG. All failures occurred in patients treated with CAD‐CAM guides (6 implants in 3 patients). Three of the failures occurred before the follow‐up CBCT scan in one patient because of postoperative infection with the presence of pus in the surgical area and swelling, causing the implants to be removed. Analysis of the linear models showed the variables with a statistically significant impact on the success rate to be implant length, drill access, and the type of flap ( p = 0.001, p = 0.033, and p = 0.011, respectively) (Table ). In this regard, short implants, with poor guide access and flapless surgery were associated with poorer success rates. The odds ratio (OR) corresponding to implant length was 12.9 in favor of the longer implants (2% failure rate) versus the shorter implants (20% failure rate). The OR corresponding to drill access was 0.13, with the probability of success decreasing an 87% when the access was poor. Lastly, the OR corresponding to the type of flap was 5.75, with a percentage success rate of 95.8% when mini‐flaps were used versus 80% when flapless surgery was done (Table ). According to the Fisher exact test, the difference in success rate between the groups was statistically significant ( p = 0.026) at the implant level. The difference was not significant at the patient level, however ( p = 0.098). 

Discussion Although the accuracy of sCAIS has witnessed an overall improvement in the last decade, the variables that result in increased inaccuracies are still largely unknown. As the popularity of the sCAIS increases, the responsible introduction of its broad application requires knowledge of common variables and decision‐making points during treatment planning and execution (El Kholy, Janner, et al. ). The lack of clinical publications on the accuracy of CAD‐CAM surgical guides compared to conventional guides led to the present study comparing their accuracy in candidates for distal free‐end implant treatment. In addition, an evaluation was made of the influence of confounding factors inherent to the patient or the surgical technique employed. As secondary objectives, a study was made of the intra‐ and postoperative complications of the surgical technique, implant success, and peri‐implant marginal bone loss. A prospective clinical study with a quasi‐experimental design was carried out. Previous studies on the accuracy of conventional surgical guides versus CAD‐CAM guides involved in vitro designs (Koop et al. ; Matta et al. ; Sium‐Abel et al. ). In this regard, one of the main problems in placing distal free‐end implants in patients is that their limited oral aperture complicates access of the drill to the posterior zones—a problem that does not occur in the in vitro setting. In this study, surgical guides made with digital light processing (DLP) technology were used in the CAD‐CAM group. Le, Keßler, and Folwaczny , showed these guides to be superior to those made with conventional stereolithography (SLA) technology in terms of the accuracy of the 3D‐printed surgical guides when used for implant placement in free‐end scenarios. The baseline variables of the patients showed no significant differences between the CAD‐CAM surgical guide and the conventional guide groups. Therefore, despite the lack of randomization, the two groups may be considered to be homogeneous. Regarding the deviations analyzed, a postoperative CBCT study was made. Many published studies have used the same method for analyzing accuracy (Pimkhaokham et al. ), and at the start of the present study, it was the only registration procedure available. However, it is important to note that alignment of the pre‐ and postoperative CBCT scans can introduce additional errors in the measure of deviations. The main disadvantages of superimposing two CBCT datasets are the significant inaccuracies introduced by surface reconstruction from these datasets and potential errors such as motion and metal artifacts. The mean coronal horizontal deviation was 1.23 mm (SD = 0.60), while the mean apical horizontal deviation was 1.54 mm (SD = 0.57), the angular deviation was 3.34° (SD = 1.86), and the vertical deviation was −0.07 mm (SD = 0.43), which is consistent with the data found in the literature (D'haese et al. ; Bover‐Ramos et al. ; Park et al. ; Siqueira et al. ). A meta‐analysis by our group (Balaguer‐Martí et al. ), including only implants placed by fully sCAIS, yielded similar results. Thus, based on the data obtained, it is advisable to ensure a safety margin of at least 2 mm horizontally and vertically (Bover‐Ramos et al. ). The CAD‐CAM guides were found to be significantly more accurate than the conventional guides in relation to CHD. Specifically, the linear model showed a 0.6 mm greater deviation for the conventional guides compared to the CAD‐CAM guides ( p = 0.042). A possible explanation for this is that the digital procedure involves fewer cumulative errors in the design and manufacturing steps, and the CAD‐CAM surgical guides also had windows to check their correct placement during surgery. In the review published by Van Assche et al. , conventional guides showed greater accuracy than CAD‐CAM guides, though this was a relatively old review that included a single in vivo study in which the implants were placed with conventional guides (Behneke et al. ). Sium‐Abel et al.  did not find any difference in an in vitro study. The CAD‐CAM surgical guides offer additional advantages, such as easy and rapid design and manufacture, using machines less expensive than gonyX, and manufacture moreover can be performed in the dental clinic. However, the technique introduces new sources of error compared with the conventional procedure, such as the determination of the guide insertion axis, XY resolution, and layer height (Dalal et al. ). Most of the confounding factors recorded exerted no effect on accuracy or had so many categories that the linear model did not converge and could not be analyzed. The most relevant factor was the location of the implants, with premolar placement proving to be more accurate in terms of CHD, AHD, and AD than molar placement. This is consistent with the data reported in the literature (Vercruyssen, Cox, et al. ; Bencharit et al. ; Kessler, Le, and Folwaczny ). Kessler, Le, and Folwaczny , in an in vitro study using milled surgical guides, recorded greater deviation of implants replacing second molars than first molars. At the distal free‐ends, the surgical guides may flex due to a lack of support in the distal zone, which explains the greater accuracy at the premolar level (Putra et al. ). Putra et al.  recorded greater accuracy in terms of coronal deviation in bounded edentulous than distal extension spaces. For this reason, some authors in in vitro studies recommend the use of bony pins in such cases (Pessoa et al. ; Chen et al. ). El Kholy, Lazarin, et al. , in an in vitro study, recorded greater deviations at the distal free ends and noted that the deviation increased with the distance between the implant and the tooth adjacent to the distal end. In a more recent study, Park et al. , in free‐ending‐supported surgical guides, found that implants placed at the third or fourth closest sites to the most distal tooth had greater deviations than those placed at the first or second closest sites, in the vertical, platform, and apical aspects ( p = 0.015, p = 0.011, and p = 0.018, respectively). The presence of an oblique dense cortical layer at molar sites could also explain this increased deviation (Derksen et al. ). According to the linear model, greater implant length was associated with an increase in AHD, which is consistent with data found in the literature (D'haese et al. ; Koop et al. ; Tatakis, Chien, and Parashis ). This is because a longer length implies a greater free‐drilling‐distance (FDD), defined as the linear measurement from the bottom of the guided sleeve to the tip of the surgical drill (bottom of the osteotomy) (El Kholy, Janner, et al. ), and consequently, less control over the drilling of the bed, where the apical zone of the drill would show greater deviation (Koop et al. ). However, in contrast to the published in vitro or clinical studies (Van Assche and Quirynen ; Koop et al. ; Guentsch et al. ), a lower sleeve height was associated with greater CHD and AHD. The length of the implant seems to exert a greater influence on deviation than sleeve height. In the in vitro study published by El Kholy, Janner et al. , the evaluation of the impact of sleeve height as an individual variable on the 3D deviation values revealed no significant impact or direct correlation between sleeves of different heights and the 3D deviation values of the implants inserted with sCAIS. Lastly, the arch in which the implants were placed showed no differences in terms of accuracy, which is consistent with the results of the multicenter study carried out by Tallarico et al. . However, greater accuracy of implants placed in the maxilla was reported by Park et al. . The implant success rate at 1 year was 92.1%, which is comparable to the data reported (90.7%–100%) (Vercruyssen, Cox, et al. ; Pommer et al. ; Vasak et al. ). All implant failures occurred prior to prosthetic loading and were recorded in the CAD‐CAM surgical guide group. A greater number of implants were placed at the molar level, and there were significantly more cases of poor drill access in the CAD‐CAM group; this could account for the difference in success rate between the two groups. The difference in success between the groups was statistically significant at the implant level but not at the patient level. Peri‐implant marginal bone loss with both surgical guide types after 1 year of loading (0.21 mm) was less than that reported by other authors (0.4–1.7 mm) (D'haese et al. ; Laleman et al. ; Tatakis, Chien, and Parashis ; Gjelvold et al. ). As limitations of the present study, mention must be made of the lack of randomization. However, as a strength, it is the only in vivo study to compare the two techniques with fully guided surgery, and the groups were homogeneous. Furthermore, as mentioned, another possible limitation is the superimposing of two CBCT datasets (although this practice has been validated in the literature), resulting in significant inaccuracies, and the application of strict inclusion criteria (distal free ends without need for regeneration) that complicated patient recruitment. 

Conclusions sCAIS in distal free‐end scenarios with tooth‐supported surgical guides made in a digital workflow is a feasible treatment option. The deviations were similar to those reported in the literature, and the CAD‐CAM surgical guides showed less deviation than the conventional guides. The success rate was 92.1% and proved to be greater in the control group than in the test group (90.7% vs. 100% respectively). Further prospective, controlled clinical studies are needed to comparatively assess the true impact of confounding variables on the accuracy and success. 

García‐Mira Berta: supervision, validation, software, writing – original draft, writing – review and editing, conceptualization, methodology, funding acquisition, data curation. Canullo Luigi: writing – review and editing, conceptualization, supervision. Peñarrocha‐Diago Miguel: conceptualization, supervision, writing – review and editing. Balaguer‐Martí José Carlos: conceptualization, software, writing – original draft, formal analysis, funding acquisition, data curation, methodology, writing – review and editing. 

The authors declare no conflicts of interest. 

