Accuracy of a CAD/CAM-guided template for locating abutment screws for cement-retained implant-supported restorations

Accuracy of digitally fabricated drilling guide to form screw-access channels in cement-retained implant prostheses: A randomized clinical trial

STATEMENT OF PROBLEM

Accurate intraoral preparation of screw channels in cement-retained implant prostheses could be a treatment challenge for tilted or badly positioned implants.

PURPOSE

The purpose of this randomized clinical trial was to evaluate screw channel accuracy for retrieving cement-retained implant prostheses by using a digitally fabricated drilling guide.

MATERIAL AND METHODS

Twenty-four participants requiring removal of cement-retained implant prostheses were recruited and consecutively assigned to 1 of 2 groups. In the first group, drilling guides were fabricated by using an intraoral scan, computer-aided design (CAD), and 3D printing to facilitate screw channel preparation (guide group). In the second group, screw channel preparation was based on panoramic radiographs without a drilling guide (freehand group). Screw channel accuracy was evaluated with a 3D analysis and subsequently compared with the ideal shape of the screw channel for linear deviation at coronal and apical levels, angular deviation, surface loss deviation, and volume loss deviation. The ideal shape of the screw-access channel was based on the Ø2.2-mm cylinder image marked along the long axis of the implant. The Mann-Whitney U and Kruskal-Wallis tests were used for statistical analyses (α=.05).

RESULTS

The drilling guide group showed higher dimensional accuracy than the freehand group for angular deviation (9.45 degrees versus 15.69 degrees; P=.014) and surface loss deviation (7.40 mm versus 9.53 mm; P=.001), especially when the implant was tilted more than 30 degrees. The deviation values of the screw channels were not significantly different according to implant tilt in either group (P>.05).

CONCLUSIONS

Digitally fabricated drilling guides for intraoral preparation of screw channels in cement-retained implant prostheses can improve accuracy and provide a less-destructive screw channel.

Techniques for locating the screw access hole in cement-retained implant-supported prostheses: A systematic review

STATEMENT OF PROBLEM

Different techniques for retrieving cement-retained implant-supported prostheses have been described to minimize damage to the prostheses. Nevertheless, a classification of the described techniques remains ambiguous.

PURPOSE

The purpose of this systematic review was to review and classify the described techniques for recording and locating the screw access hole in cement-retained implant-supported prostheses.

MATERIAL AND METHODS

A bibliographic search was completed on MEDLINE/PubMed, Web of Science, Scopus, and Cochrane databases. A manual search was also conducted. The articles that described or evaluated techniques for recording and locating the screw access hole of cement-retained implant-supported prostheses were included. Two investigators independently assessed the quality assessment of the studies using the Revised Cochrane risk of bias tool for randomized trials. A third examiner was consulted to resolve the lack of consensus.

RESULTS

A total of 30 articles were included. The different methods were classified according to whether the screw access hole location was registered before or after cementation. The precementation techniques were classified into 4 subgroups: identification marks, photographic records, digital files, and precementation screw access hole location guides. The postcementation techniques were subdivided into 2 subgroups: radiographic records and postcementation screw access hole location guides.

CONCLUSIONS

Different techniques have been proposed to facilitate the location of the screw access hole in cement-retained implant-supported restorations. Although the evidence is scarce, studies seem to ascertain that some techniques, such as the use of drilling guides, orientation with cone beam computed tomography images, or holes made in the metal framework, can increase the retrievability of cement-retained implant-supported prostheses and decrease complications in the location of the screw access hole. The proposed classification summarizes precementation and postcementation techniques and provides a tool to decide the most suitable for each specific clinical situation.

A method of locating the abutment screw access channel with cone-beam computed tomography and a 3D-printed drilling guide

In managing loose abutment screws, locating precisely the position of the screw access channel is difficult. This technique describes the use of cone-beam computed tomography (CBCT) and surgical guide planning software to locate the screw access channel with the intention of retrieving a loosened cement-retained implant-supported prosthesis. The method minimizes damage to the abutment crown assembly.