Orbital implant placement using a computer-aided design and manufacturing (CAD/CAM) stereolithographic surgical template protocol

Abstract

Surgical implant placement in the orbital region for the support of a prosthesis is challenging due to the thin orbital rim and proximity to vital structures. This article reports the use of a computer-aided design and manufacturing (CAD/CAM) stereolithographic surgical template protocol for orbital implant placement in four patients, who were followed-up for about 7 years. A total of 11 orbital implants were inserted, eight of these in irradiated bone. No intraoperative complications were noted in any of the patients and the implants were all inserted in the planned positions. The survival rate of implants placed in irradiated bone that received hyperbaric oxygen therapy was 62.5% (5/8). One implant failed in a burns injury patient at 74 months after functional loading. The overall survival of implants in the orbital region and the cumulative survival at 7 years was 63.6%. With regard to skin reactions around the abutments, 85% were grade 0, 13% were grade 1, and 2% were grade 2 according to the Holgers classification. The mean survival time of the first prosthesis was 49 months. High patient satisfaction was achieved with the implant-retained orbital prostheses.

The advent of skin-penetrating implants for the support of craniofacial prostheses has revolutionized the rehabilitation of patients with facial defects. When placed in an optimum position, implants will enhance the retention of the prosthesis and allow better aesthetics to be achieved.

Orbital defects may result from trauma or tumour resection. Surgical implant placement in the orbital region for the support of a prosthesis is challenging. Depending on the extent of resection or trauma, the span of orbital rim that remains is variable. Although ideally, three or four implants should be placed to support an orbital prosthesis, at times there is sufficient length of bone to accommodate only two implants. Bone in the orbital region is thin and irregular and there are adjacent structures that need to be avoided, e.g. air sinuses, neurovascular bundles, and cerebral tissues. Implant position and angulation significantly affect the aesthetics of the prosthesis and therefore precision is especially critical during surgical implant placement in this region.

Computer-aided design and manufacturing (CAD/CAM) has been utilized effectively in dental implant treatment for more than 15 years. Using this technology, patient-specific surgical guides are fabricated, which transfer preoperative three-dimensional (3D) planning to the operating room. In an in vitro study, Sarment et al. showed that the use of CAD/CAM surgical guides significantly increased the accuracy of dental implant placement compared to the use of conventional surgical guides.

More recently, 3D planning and CAD/CAM technology have been adopted for the guidance of craniofacial implant surgery. The expected benefits include a reduction of surgical complications such as injury to adjacent vital structures, improved accuracy of implant positioning, greater intraoperative predictability, shorter operation time, and better aesthetics of the prosthesis.

This article reports the long-term clinical outcomes as well as satisfaction of four patients treated according to a 3D planning and CAD/CAM stereolithographic surgical template protocol for orbital rehabilitation using implant-retained prostheses.

Materials and methods

The study protocol was reviewed and approved by the SingHealth Centralised Institutional Review Board. This was a prospective cohort study. Patients classified as American Society of Anesthesiologists (ASA) I or II, who had an orbital defect requiring rehabilitation with a prosthesis or a pre-existing adhesive-retained orbital prosthesis, were offered the opportunity to participate in the study by the maxillofacial prosthodontist. No subjects were excluded based on gender, race, or age criteria. Exclusions included patients who had received radiotherapy in the orbital region less than 6 months prior to the planned implant surgery, heavy smokers, patients with a history of alcohol or other drug abuse, pregnant patients, and those who had difficulty understanding the consent process or the questionnaire. Written consent was obtained from every consecutive patient who met the criteria and agreed to participate in the study.

Four patients with orbital defects were enrolled in the study at the National Dental Centre Singapore from 2005 to 2007. The patients received implants in the orbital region according to the CAD/CAM stereolithographic surgical template protocol described below. All four patients had previously worn an adhesive-retained orbital prosthesis for several years but were dissatisfied with the experience and had therefore decided to have it replaced with an implant-retained prosthesis.

Treatment protocol

Computed tomography (CT) scan

CT scanning was performed according to a standardized craniofacial protocol. The slice thickness and reconstructed slice increments were 1.0 mm. The images, in Digital Imaging and Communications in Medicine (DICOM) format, were reconstructed using a 512 × 512 matrix with a field of view of the entire skull.

3D implant planning

The CT data were uploaded to a Simplant Pro CMF module (Materialise, Leuven, Belgium) for 3D implant planning. On the 3D view, several points along the orbital rim were selected to form the orbital curve. The dissection view was then generated perpendicular to the bone surface. Axial and panoramic views were also available on the planning program. Vistafix implants (Entific Medical Systems) of 3.75 mm in diameter and either 3 mm or 4 mm in length were selected from the software implant library and placed virtually at suitable positions along the orbital rim. Appropriate abutments were chosen to fit the implants. The virtually placed implants were then checked on the multi-planar views for correct length, positioning, and angulation, and to ensure that they did not encroach on adjacent vital structures.

Fabrication of the stereolithographic surgical template

Once the 3D plan was completed and agreed by both the surgeon and prosthodontist, it was saved and sent by e-mail to Materialise (Leuven, Belgium) for the fabrication of customized stereolithographic templates. Two templates were fabricated for each patient, one with 2.75-mm access holes and another with 3.75-mm access holes.

Hyperbaric oxygen (HBO) therapy

Patients who had a history of radiotherapy in the orbital region underwent HBO therapy at 2.5 absolute atmospheric pressure for 90 min daily, 20 times before and 10 times after implant placement.

Orbital implant surgery

All patients were treated according to a two-stage procedure.

In stage I, an incision was made and subperiosteal dissection was done to expose the region of the bony orbital rim where implants were to be inserted (usually the superior-lateral and lateral aspects). The fit of the CAD/CAM stereolithographic stents was tested by seating them on the orbital rim. They should be stable when seated in the correct position. Using the first stent with 2.75-mm access holes, the implant sites were marked with a small round bur. Using the same stent, an implant site osteotomy was started using a 2.5-mm twist drill to the planned depth of 3 mm or 4 mm. The second stent with 3.75-mm access holes was then used for osteotomy with a 3.5-mm twist drill. Vistafix implants (Entific Medical Systems) of 3.75 mm in diameter and of the planned length, either 3 mm or 4 mm, were then inserted into the osteotomy sites. A total of two or three implants were placed. Cover screws were inserted. Closure was done in layers using 4–0 Vicryl for the periosteum and subcutaneous layers and 6–0 Prolene for the skin. Any intraoperative complications such as penetration of the dura mater were noted.

Stage II was performed 6 months after stage I surgery. An incision was made to expose the cover screws of the previously placed implants. A supraperiosteal dissection was done around the cover screws, leaving the periosteum intact and attached to the bone surface. The skin was thinned by excising the subcutaneous tissue. The cover screws were removed and healing abutments of the appropriate heights were inserted. The skin was contoured with a blade to fit around the abutments and then sutured down to the periosteum using 6–0 Prolene. Healing caps were inserted on top of the abutments. Tobramycin and steroid-soaked ribbon gauze was wrapped around the abutments to provide compression.

Prosthesis fabrication and issue

When the skin surrounding the healing abutments had healed to a point when prosthesis fabrication could begin, mini Magnabutments (Entific Medical Systems) were connected to the implants. Transfer magnets were placed over the abutments for impression taking using polyvinyl-siloxane impression material (Affinis; Coltène/Whaledent GmbH). From the master cast, an implant-retained orbital prosthesis was fabricated using magnets for retention. At the issue stage, the patients were instructed on the path of insertion and removal of the prosthesis. Home care maintenance of the prosthesis and soft tissues around the implants consisted of daily use of water and soap and mechanical cleaning around the abutments with a soft toothbrush and irrigation with chlorhexidine solution.

Review

The patients were reviewed every 6 months by both the surgeon and the maxillofacial prosthodontist. During these visits, patient compliance with the hygiene protocols was checked, and when necessary, the instructions were reinforced. Implant survival, any skin reaction around the abutments, and the condition of the prosthesis were recorded. Any other complications were also noted.

Treatment protocol

Computed tomography (CT) scan

CT scanning was performed according to a standardized craniofacial protocol. The slice thickness and reconstructed slice increments were 1.0 mm. The images, in Digital Imaging and Communications in Medicine (DICOM) format, were reconstructed using a 512 × 512 matrix with a field of view of the entire skull.

3D implant planning

The CT data were uploaded to a Simplant Pro CMF module (Materialise, Leuven, Belgium) for 3D implant planning. On the 3D view, several points along the orbital rim were selected to form the orbital curve. The dissection view was then generated perpendicular to the bone surface. Axial and panoramic views were also available on the planning program. Vistafix implants (Entific Medical Systems) of 3.75 mm in diameter and either 3 mm or 4 mm in length were selected from the software implant library and placed virtually at suitable positions along the orbital rim. Appropriate abutments were chosen to fit the implants. The virtually placed implants were then checked on the multi-planar views for correct length, positioning, and angulation, and to ensure that they did not encroach on adjacent vital structures.

Fabrication of the stereolithographic surgical template

Once the 3D plan was completed and agreed by both the surgeon and prosthodontist, it was saved and sent by e-mail to Materialise (Leuven, Belgium) for the fabrication of customized stereolithographic templates. Two templates were fabricated for each patient, one with 2.75-mm access holes and another with 3.75-mm access holes.

Hyperbaric oxygen (HBO) therapy

Patients who had a history of radiotherapy in the orbital region underwent HBO therapy at 2.5 absolute atmospheric pressure for 90 min daily, 20 times before and 10 times after implant placement.

Orbital implant surgery

All patients were treated according to a two-stage procedure.

In stage I, an incision was made and subperiosteal dissection was done to expose the region of the bony orbital rim where implants were to be inserted (usually the superior-lateral and lateral aspects). The fit of the CAD/CAM stereolithographic stents was tested by seating them on the orbital rim. They should be stable when seated in the correct position. Using the first stent with 2.75-mm access holes, the implant sites were marked with a small round bur. Using the same stent, an implant site osteotomy was started using a 2.5-mm twist drill to the planned depth of 3 mm or 4 mm. The second stent with 3.75-mm access holes was then used for osteotomy with a 3.5-mm twist drill. Vistafix implants (Entific Medical Systems) of 3.75 mm in diameter and of the planned length, either 3 mm or 4 mm, were then inserted into the osteotomy sites. A total of two or three implants were placed. Cover screws were inserted. Closure was done in layers using 4–0 Vicryl for the periosteum and subcutaneous layers and 6–0 Prolene for the skin. Any intraoperative complications such as penetration of the dura mater were noted.

Stage II was performed 6 months after stage I surgery. An incision was made to expose the cover screws of the previously placed implants. A supraperiosteal dissection was done around the cover screws, leaving the periosteum intact and attached to the bone surface. The skin was thinned by excising the subcutaneous tissue. The cover screws were removed and healing abutments of the appropriate heights were inserted. The skin was contoured with a blade to fit around the abutments and then sutured down to the periosteum using 6–0 Prolene. Healing caps were inserted on top of the abutments. Tobramycin and steroid-soaked ribbon gauze was wrapped around the abutments to provide compression.

Prosthesis fabrication and issue

When the skin surrounding the healing abutments had healed to a point when prosthesis fabrication could begin, mini Magnabutments (Entific Medical Systems) were connected to the implants. Transfer magnets were placed over the abutments for impression taking using polyvinyl-siloxane impression material (Affinis; Coltène/Whaledent GmbH). From the master cast, an implant-retained orbital prosthesis was fabricated using magnets for retention. At the issue stage, the patients were instructed on the path of insertion and removal of the prosthesis. Home care maintenance of the prosthesis and soft tissues around the implants consisted of daily use of water and soap and mechanical cleaning around the abutments with a soft toothbrush and irrigation with chlorhexidine solution.

Review

The patients were reviewed every 6 months by both the surgeon and the maxillofacial prosthodontist. During these visits, patient compliance with the hygiene protocols was checked, and when necessary, the instructions were reinforced. Implant survival, any skin reaction around the abutments, and the condition of the prosthesis were recorded. Any other complications were also noted.

Analyses

Implant survival

Implant survival was defined as the implant being clinically present. Two methods were used to calculate the percentage of implant survival, or survival rate. The first method determined the percentage of the total number of exposed implants that survived without regard to the survival time. The second method calculated the cumulative survival rates over time using a life-table analysis. The starting point for the latter analysis was stage I surgery and the endpoint was either implant failure or the last follow-up visit at which the implants were still noted to be present clinically.

Skin reaction

Any skin reaction around the abutments was recorded at each patient review visit and graded from 0 to 4, according to Holgers et al. : 0 = no reaction, 1 = reddish, 2 = moist, 3 = granulation, and 4 = infection.

Prosthesis survival

Prosthesis survival was defined as the prosthesis being present and worn by the patient. The survival time of each prosthesis was defined as the duration from the issue of the prosthesis to when it was replaced or to the last follow-up visit at which the prosthesis was still being worn by the patient. Prosthesis complications and the reasons for fabrication of a new prosthesis were recorded.

Patient satisfaction questionnaire

The Facial Prosthesis Patient Satisfaction Questionnaire was used to evaluate each patient’s perception and treatment satisfaction with their implant-retained prosthesis. This 18-item questionnaire covers five domains that ascertain patient satisfaction, perceptions of comfort, fit, and retention, usage, treatment value, and level of self-consciousness. It was also used to compare the patient’s experience with the new implant-retained prosthesis and their previous adhesive-retained prosthesis. All subjects responded to each of the 18 listed items on a five-point scale. The survey was conducted after the implant-retained prosthesis had been worn for 6 months.

Only gold members can continue reading. Log In or Register to continue

Jan 17, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Orbital implant placement using a computer-aided design and manufacturing (CAD/CAM) stereolithographic surgical template protocol
Premium Wordpress Themes by UFO Themes