Accuracy of Static Computer-assisted Implant Surgery in Distal Free-end Scenarios

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 transfer of the virtual implant planning to the mouth of the patient, based on the use of a surgical guide. 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 3.58º (SD = 0.2).

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.A prospective, controlled and blinded quasi-experimental study was carried out involving 27 patients with 76 implants distributed into two groups according to the surgical guide manufacturing approach used: conventional (control group \[CG\]) or CAD-CAM (test group \[TG\]). The implants were planned virtually with the planning software, and the surgical guides were manufactured. Fully guided implant placement was carried out, and the deviations were measured along with other secondary variables as potential confounding factors.

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 secure optimum esthetic and biological outcomes, affording long-term stability of the soft and hard tissues.

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 planning of the implants. 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. This simplifies the workflow, which can reduce the costs of smaller rehabilitations.

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.These data justify further research in humans, focusing on fully sCAIS, in order 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. 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.

A prospective, controlled, examiner- and statistician-blinded, parallel-arm quasi-experimental study was carried out at the University of Valencia (Valencia, Spain). Two groups were established according to the surgical guide design involved: conventional (control group \[CG\]) or CAD-CAM (test group \[TG\]).

Eligibility Criteria:
Inclusion Criteria:

* Indication of fixed prosthesis over at least two consecutive implants.
* Sufficient residual crest for placing at least two implants 4.1 mm in diameter and 8 mm in length.
* Mature bone and healthy soft tissues.
* Implants placed via fully guided surgery.
* Age \> 18 years.
* Good general health.
* Non-smokers or smokers of \< 10 cigarettes/day (pipe smokers excluded).
* Oral hygiene index \< 3 and bleeding index \< 25%.
* Pre- and post- CBCT scan for analysis of accuracy.
* Periapical radiographs at loading and after one year.

Exclusion Criteria:

* Contraindications to implant therapy
* Locations with acute infection.
* Pregnant or nursing women.
* Lack of follow-up.