Accuracy evaluation of surgical guides in implant dentistry by non-contact reverse engineering techniques

Abstract

Objective

In the paper laser scanning was used to evaluate, by indirect methods, the accuracy of computer-designed surgical guides in the oral implant supported rehabilitation of partially or completely edentulous patients.

Materials and methods

Five implant supported rehabilitations for a total of twenty-three implants were carried out by computer-designed surgical guides, performed with the master model developed by muco-compressive and muco-static impressions. For all cases the surgical virtual planning, starting from 3D models obtained by dental scan DICOM data, was performed. The implants were inserted on the pre-surgical casts in the position defined in the virtual planning. These positions were acquired by three-dimensional optical laser scanning and compared with the laser scans of the intraoral impressions taken post-operatively.

Results

The comparison between the post-surgical implant replica positions and the positions in the pre-operative cast, for the five patients, shows a maximum distance in the range 1.02–1.25 mm, an average distance in the range 0.21–0.41 mm and a standard deviation in the range 0.21–0.29 mm.

Significance

The results of this research demonstrate accurate transfer of implant replica position by virtual implant insertion into a pre-operative cast and a post-operative cast obtained from impressioning. In previous studies the evaluation of the implant positions have required a post-surgical CT scan. With the indirect methods by laser scanning technique, proposed in the paper, this extra radiation exposure of the patient can be eliminated.

Introduction

The number of patients asking for fixed implant-supported rehabilitations has increased considerably in the past few years .

Today implant-supported reconstructions to restore the stomatognathic system, in terms of function and esthetics, after tooth loss or aplasia, is considered to be a routine procedure with high success rates .

Historically, standard radiographic imaging techniques (intraoral and panoramic) were available for investigation of potential implant sites.

Nowadays three-dimensional computed tomography (CT) and cone beam CT (CBCT) systems allow a more reliable treatment planning than when only two-dimensional data were available .

From the CT data (DICOM format – digital imaging and communications in medicine ), the three-dimensional reconstruction of surgical sites is obtained . This allows the virtual implant planning driven by restorative considerations and the successive fabrication of surgical guides by means of CAM (computer aided manufacturing) or RP (rapid prototyping) techniques.

The developments in computer-aided planning by means of the use of 3D virtual models have drastically modified the interventional possibilities in implant dentistry, changing the traditional invasive surgical protocol, with a flapless procedure eventual immediate loading .

The clinical steps involved are determined by different morphological conditions: the bone quantity and quality, the sensitive anatomical structures.

Although computer-guided implant dentistry is an upcoming technology with the potential for more predictive and less invasive implant placement, its performance has to be critically evaluated, because it is already in clinical practice.

Transfer of the virtual three-dimensional implant planning to the surgical field is the most critical point in the procedure.

The aim of this paper is to evaluate the accuracy of the surgical guides, analysing the deviations between the virtual planning and the in vivo location of the implants.

In the previous studies the accuracy in computer- aided implant surgery was usually evaluated by means of post-surgical CT scan to verify the implant positions .

In the paper an indirect method for the accuracy evaluation, using a laser scanning technique is described. This method allows to reduce the radiation exposure eliminating the extra radiations of post-surgical computed tomography scan.

Materials and methods

Patients selection

The data of five patients, three men and two women with different implant-prosthetic rehabilitative requirement, were used for this study.

Two patients had a total mandibular edentulous dentition, one patient a total maxillary edentulous dentition, one patient a single intercalated mandibular edentulous dentition and one patient a bilateral distal maxillary edentulous dentition.

In order to preserve the keratinized gingival, in the case of thin biotype, only the patient exhibiting single intercalated edentulous dentition was rehabilitated using an approach with flap,

The mean patient age was 52 years (between 35 and 60 years). Table 1 shows the distribution of the implant sites.

Table 1
Patients and distribution of the implant sites.
Patient 1 Patient 2 Patient 3 Patient 4 Patient 5
46 12-14-16 22-24-26 14-15-16 24-25-26 32-34-36 42-44-46 32-35-42 45

Inclusion criteria for the patients were:

  • Absence of relevant systemic diseases in contradiction for osteo-integrate implant rehabilitations.

  • Presence of adequate bone volumes for the implant placement without regenerative techniques.

  • If smokers no more than 10 cigarettes for day.

On the basis of a panoramic radiograph, it was decided to continue the treatment-planning phase of selected patients by means of a CT scan of the maxilla that the patient carried out with radiographic stents produced from self-curing resin mixed with barium sulphate powder in a ratios of 3:1.

In order to avoid unwanted dental overlaps and to stabilize the radiographic stents during the CT examination, some stabilizers were made using extra-hard wax of 10 mm height, which patient bites between the dental arches during CT examination ( Fig. 1 ).

Fig. 1
Occlusal check in extra-hard wax with radiographic stents during CT examination.

Virtual pre-surgical planning computed tomography – based

The virtual pre-surgical planning was applied (Implant 3D software by Media Lab, Italy) to have a detailed 3D analysis in the implant placement ( Fig. 2 ).

Fig. 2
Virtual pre-surgical planning.

The planning was possible through the interpretation of DICOM images of the CT examination.

The virtual data were used to fabricate the surgical guides using a Ray Set machine (Biaggini Medical Devices, Italy) ( Fig. 3 ) that orients, in accordance with the parameters from virtual analysis, the resin or plaster master model, in order to place in it, in a correct three-dimensional manner, the implant analogs ( Fig. 4 ).

Fig. 3
Ray set machine.

Fig. 4
Master model is oriented and drilled to place in it the implant analogs.

Then both surgical stents with a resinous framework like of total removable dentures (stents for exclusive mucosal support), and surgical stents with a metal core like a skeleton (stents at the exclusive dental support) can be made.

Simulation of implant surgery on casts and reverse engineering acquisitions

From the 3D virtual planning, the data of implant positions were transferred to the master model and the analog implants were inserted and fixed in it ( Fig. 5 ).

Fig. 5
Simulation of implant surgery on pre-surgical cast.

A reverse engineering (RE) system, D700 Scanner (by 3Shape, Denmark) was used to acquire, for each patient, the three-dimensional virtual shape of the master model with the analogs ( Fig. 6 ) with the aim to obtain the 3D CAD model, useful for the successive evaluation of the accuracy of the implants position.

Fig. 6
Shape acquisition of the pre-surgical cast with implant analogs.

Implant surgery

Twenty-three conical implants have been used with lengths between 9 and 13 mm (EXACTA WP, Biaggini Mediacal Devices).

On the basis of periodontal biotype a flapless approach was chosen, in the case of thick biotype, and an approach with flap in the case of thin biotype, in order to preserve the keratinized gingiva.

The number of implants, the length and type of surgical approach, are summarized in the Table 2 .

Table 2
Number and length of implants and type of surgical approach.
Flapless With flap
Implantlenght 9 mm 1 0
Implantlenght 11 mm 1 0
Implantlenght 13 mm 22 1

All implants have received the provisional immediate load within 48 h post-surgery. In the case of the individual intercalated edentulous patients the prosthesis was attached through the abutment millable prosthesis screwed with a torque of 30 N cm, and using a cemented resin crown.

In Fig. 7 implant surgery is shown.

Fig. 7
Implant surgery.

Laser scans of post-surgical casts

For each patient, a post-surgical cast was realized.

The three-dimensional shape of these casts was acquired by means of 3Shape’s D700 Scanner and the 3D CAD models ( Fig. 8 ), useful for the accuracy evaluation of the implants position, were obtained.

Fig. 8
CAD model of a post-surgical cast.

Materials and methods

Patients selection

The data of five patients, three men and two women with different implant-prosthetic rehabilitative requirement, were used for this study.

Two patients had a total mandibular edentulous dentition, one patient a total maxillary edentulous dentition, one patient a single intercalated mandibular edentulous dentition and one patient a bilateral distal maxillary edentulous dentition.

In order to preserve the keratinized gingival, in the case of thin biotype, only the patient exhibiting single intercalated edentulous dentition was rehabilitated using an approach with flap,

The mean patient age was 52 years (between 35 and 60 years). Table 1 shows the distribution of the implant sites.

Nov 28, 2017 | Posted by in Dental Materials | Comments Off on Accuracy evaluation of surgical guides in implant dentistry by non-contact reverse engineering techniques
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