Accuracy of Static Guided Implant Surgery: 3D-printed vs Milled Surgical Guides

1. SCIENTIFIC BACKGROUND AND RATIONALE

   Traditionally, implant placement has been based on bone availability, with the implant industry focused primarily on enhancing implant survival by increasing the chances of osseointegration. In contrast, the position of the final prosthetic rehabilitation was considered of secondary importance. In certain instances, this approach may result in biological, prosthetic, and aesthetic complications. In contemporary dentistry, evaluating the success of implant therapy transcends the mere evaluation of implant survival and involves a comprehensive assessment that takes into consideration the long-term stability of soft and hard peri-implant tissues, access for oral hygiene, aesthetic demands, occlusal and functional dynamics, implant loading potential, and minimal invasiveness.

   Digital-based planning and guided surgery can maximize the chances of placing implants in an ideal prosthetic position. Different types of guided surgery have been described in the literature: (1) Static cast-based partial guidance, which considers the final prosthetic position without considering bone morphology and in which bone bed preparation and implant placement are free-handed. (2) Static computer-based partial guidance, in which the underlying bone morphology is considered in manufacturing the surgical guide, and that can be used for the initial, partial, or complete osteotomy, but implant placement is still free-handed. (3) Static computer-based full guidance that entails the utilization of a pre-made surgical template, involving both complete osteotomy preparation and implant placement guided by a prosthetically driven surgical guide; and (4) Dynamic guidance, that allows real-time guidance during drilling, with the implant position dynamically displayed on computed tomography data. Dynamic guides are associated with higher economic costs and pose challenges in in their clinical implementation, and consequently, static guides are more frequently utilized. The type of support for the guide can be categorized into three groups: mucosal-supported, tooth-supported (may be combined with mucosal-supported), or bone-supported.

   Implant surgical guides can be produced through two manufacturing processes: subtractive and additive manufacturing. The subtractive approach involves milling the surgical guide from a larger polymer block through a computer-numeric controlled machine. The additive approach is based on 3D printing the guide by sequential layering. In general, additive processes are more frequently employed, due to reduced expenses, the production of more guides per printing session, and minimal waste.

   Recent systematic reviews have demonstrated that static fully guided surgery has higher accuracy to achieve the planned position than free-handed and partially guided implant placement . Indeed, different RCTs have reported higher chances of obtaining a prosthetically correct implant position allowing for screw-retained restorations, lower mean depth deviation, lower angular deviation, as well as three-dimensional body deviations when using static guidance with respect to free-handed implants.

   However, there is no conclusive evidence on the differences in accuracy when comparing static guides fabricated either through an additive or a subtractive process.

2. STUDY OBJECTIVES The primary aim of this study is to determine whether there are any differences on the accuracy of implant placement using two different types of static surgical guides: 3D-printed vs. milled. The null hypothesis is that there will be no differences in the accuracy of implant placement when comparing 3D-printed and milled surgical guides.

   The primary objective of this investigation will be to evaluate the accuracy of implant placement defined in terms of differences in precision and trueness (ISO 5725-2) between the planned and the final implant position, when comparing 3D-printed and milled surgical guides.

   As secondary objectives the following outcomes will be evaluated: peri-implant health outcomes (bleeding on probing, suppuration, probing depth), plaque index, implant survival, implant success, surgery-related outcomes (time, difficulty [VAS scale], and wound healing index), and patient-reported outcomes measures.

   2.1 Clinical relevance A correct implant position is important for the long-term success of implant therapy. Static computer-assisted implant placement is an alternative to free-hand surgery that has shown higher accuracy in reaching an appropriate implant position. However, data on the accuracy associated to the use of either milled or 3D-printed implant surgical guides is limited.

3. MATERIALS AND METHODS

3.1. Study design Two-arm, double-blind (examiner, and patient), single-center parallel randomized controlled trial.

3.2. Trial centers This study will be carried out in the clinic of the Postgraduate of Specialization in Periodontology and Implant Dentistry at the Complutense University of Madrid (Spain)

3.4. Intervention / Study Procedures 3.4.1. Screening and Baseline Procedures All potential study participants will be screened for eligibility according to the inclusion and exclusion criteria and will be informed about the study procedures.

3.4.2. Informed Consent Written informed consent must be obtained from each patient prior to performing any study procedure or assessment. Before enrolling a subject, the Investigator will explain the study protocol, procedures, and objectives to the subject and/or legal guardian or legally authorized representative. When the subject understands and is willing to participate in the clinical trial, he/she must sign and date the IRB-approved Informed Consent Form (ICF). The ICF describes the study and the potential discomforts, risks, and benefits of participating. One copy of the consent form will be provided to the subject, and one copy will be maintained with the subject's permanent medical records. The study site personnel must also enter the date the informed consent was signed in the subject's source documentation or medical record.

3.4.3. Randomization Each patient will be randomized into the milled or 3D-printed group according to a balanced distribution system via a computer-generated table of random numbers. Allocation concealment will be kept during the surgery by means of opaque envelopes so that the patient is blinded, and it will be kept until the moment of data analysis by an independent researcher not involved in the execution of the clinical interventions. Opaque sealed envelopes will be opened at the milling center once the 3D implant planning has finished, been checked, and sent.

3.4.4. Pre-study phase and guide fabrication Upon inclusion in the study, all potentially eligible patients (all patients meeting primary inclusion criteria) will receive oral hygiene instructions (OHI) according to their individual needs. Patients with residual dentition with signs of periodontitis will also receive periodontal therapy.

After this, all eligible patients will be re-evaluated according to their compliance with oral hygiene procedures (secondary exclusion criteria) to establish their inclusion in the trial.

• A preoperative intraoral scan of the receptor arch and a cone-beam computed tomographic scan of the arch of interest will be acquired to digitally plan implant placement. A blinded investigator with experience in implant dentistry will perform the virtual planning for all cases based on a prosthetic-driven implant position using the Medconnect software platform (Archimedes).
• The digital planning will consist of 3-dimensional radiographical measurements on DICOM data to assess the optimal position of the implant(s) based on digital wax-up. An STL file will be used to construct the surgical guide (S0). At this stage, if additional bone regeneration procedures are needed to achieve the ideal position of the implant(s), the surgical planning will be aborted, and other options will be offered to the patient. Transalveolar sinus floor elevation up to 2 mm will be allowed. The surgical guide will be designed aiming primarily for tooth support or mixed (tooth and mucosal) support. Cases where this cannot be achieved will be excluded.
• Once this process has ended, patients will be randomized as described previously to receive milled guides (anaxCAM PMMA Clear blanks, Anaxdent, Germany) (CORiTEC 150i PRO miller, Imes-icore®, Germany) or 3D-printed guides (E-Guide resin, EnvisionTEC®, Germany) (D4K Pro printer, EnvisionTEC®, Germany) performed by the same commercial manufacturing center (Archimedes, Spain). All guides will be designed with guide sleeves.
• Finally, the guide will be post-processed and sterilized according to the manufacturer's recommendations.
• Before the day of surgery, the surgical guides will be tested for fit and stability through tactile inspection. In poorly fitted guides, new intraoral and CBCT scans will be obtained to repeat the digital planning phase.

3.4.5. Surgical procedure

• All implant surgeries will be performed under local anesthesia by one of five calibrated, experienced surgeons who have not been involved in the digital planning of the implant position.
• All implants will be bone-level Klockner Vega® implants (Klockner Implant System, Spain), ranging from 3.5 to 4.5 mm in diameter and 8 to 12 mm in length.
• The selection of performing a flapless or a full thickness mucoperiosteal flap will be determined before surgery by measuring the availability of keratinized mucosa. A flapless technique will be selected for cases where at least 2mm of surrounding keratinized mucosa can be ensured around the whole implant. If performing a flap, a crestal design will be used to assure that at least 2 mm of keratinized mucosa is left on the buccal and lingual flaps.
• Implant bed preparations and insertions will be done through the 3D surgical guides following the manufacturer's protocol (Sniper Guide System, Klockner Implant System, Spain). All implants will be placed 1-1.5 mm subcrestally.
• A transmucosal healing abutment and interrupted non-resorbable 5/0 sutures will be placed.

3.4.6. Postoperative care Patients will be instructed to rinse postoperatively for 1 min with 0.12% CHX + 0.05% CPC (Perio-aid treatment®) three times a day for 2 weeks. Patients will also be allowed to take Ibuprofen 600mg every 8 hours as needed. If necessary, Paracetamol 650mg will be intercalated. Patients will be asked to keep a record of the medication taken (type of medicine, frequency, and number of days).

Patients will be instructed to refrain from performing regular oral hygiene in the surgical area immediately after the surgery for one week. Smokers will be asked to limit (and possibly quit) smoking to no more that 5 cigarettes per day.

Sutures will be removed after 7 days, and self-performed biofilm control in the surgical area will be reinstituted with the use of a soft toothbrush. At one month, patients will be instructed to start routine self-performed oral hygiene procedures and will receive supragingival polishing with an air polishing device (Airflow® EMS) and a subgingival non-abrasive powder (Erythritol, Plus Powder®, EMS).

Three months after surgery, digital impressions will be taken at the implant level for single unit restorations or at the abutment level (Permanent) for multiple unit restorations. If intermediate abutments are used, the day of digital impression will be screwed and not removed anymore. Titanium bases will be used to cement zirconia CAD-CAM restorations at the laboratory, which will be then screw at the implant or the abutment the day of loading. To standardize the prosthetic designs, all the restoration will be fabricated at the same laboratory (Symmetrya, Oporto). Functional loading will be considered as the baseline visit for the subsequent follow-up. Professional prophylaxis and OHI will be performed at 6 and 12 months using ultrasonic and air polishing devices (Prophylaxis Airflow Master Piezon® EMS) and a subgingival non-abrasive powder (Erythritol, Plus Powder®, EMS).

3.4.7. Concomitant interventions/medications Locally. Dental or periodontal procedures, as required by the subject and as deemed necessary by the attending clinician, will be allowed before and during the trial.

Systemically. All necessary and not delayable concomitant interventions/medications will be allowed before and during the study. In case of incompatible concomitant systemic interventions/medications (e.g., bisphosphonates) assessed before the inclusion in the trial, the patient will not be included (see systemic exclusion criteria). In case the same treatments have been started after the patient inclusion but before the surgical treatment, the patient will be excluded from the trial (see "withdrawal criteria"). In case such treatments have been started after the surgical treatment, the patient will be retained in the study. Eventually, emergency medical care will always be allowed.

3.6. Statistical analysis

3.6.1. Sample Size Determination of the sample size was based on the mean deviation aft the implant platform between the static group and the dynamic group reported on previous studies: Putra et al., 2022, using the mean (SD) of the angular deviation between planned and implant insertion in G*Power (Version 3.1.9.7 software, Heinrich-Heine University, Dusseldorf, Germany). The effect size was estimated at 0.914, the significance level was set at 0,05 and the power at 0.80. The minimum required sample size resulted in 20 patients per group, but will be increased by 20%, expecting any possible dropouts. Thus, the final sample size will be adjusted to 48 patients, 24 in each group.

3.6.2. Statistical analysis Statistical analyses will be presented both at patient- and implant-level. Data will be reported as mean and SD unless otherwise specified (e.g., n [%]). Shapiro-Wilk goodness-of-fit test and histograms will be used to determine the normal distribution of the quantitative variables. Non-normally distributed variables will be additionally presented as medians and interquartile range (IQR). All analyses will be performed using the intention-to-treat population, and the last observation carried forward approach (LOCF) will be used for missing values.

The primary outcome will be accuracy as a compound parameter, where four different aspects will be measured: angular deviation, coronal deviation, apical deviation, and depth deviation. To assess the performance of the intervention, Students' t-test or Mann-Whitney U tests will be used for quantitative outcomes. Data on categorical outcomes will be compared using Chi-square test or Fisher-exact test. The secondary outcomes identified as relevant through the bivariant analysis will be included in a regression model, considering the accuracy as the primary outcome variable, which will be adjusted for confounding variables and factors such as the operators experience, type of surgical stent, etc.

Statistical significance will be set at p\<0.05. The analysis will be performed using IBM SPSS Statistics (version 29.0.1.1, IBM Corporation, New York, NY, USA).