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Evaluating bone defects and simulating corrections

Evaluating bone defects and simulating corrections using SimPlant planning software and stereolithographic models

Craig M. Misch, DDS, MDS Specialist in Prosthodontics and Oral & Maxillofacial Surgery, Sarasota, Florida, USA
 

Introduction

 

Most dental surgical planning software packages were basically focussed on planning implant positions taking into account the underlying bone quality and quantity, and aesthetic considerations. In later software versions, e.g. SimPlant 8, also other surgical aspects can be simulated, like sinus grafting. This case report describes the use of the SimPlant planning software and stereolithographic models for evaluation of bone defects and simulation of the possible onlay bone graft corrections. 

 

Case reports


The first case is a 17 year old female who suffered facial fractures and avulsion of three teeth in a bicycle accident. She unfortunately underwent a bone graft procedure that inadequately reconstructed the defect. The patient presented for regrafting of the maxillary defect for dental implant placement.

The bone augmentation was simulated in the SimPlant planning software. Starting from mandibular and maxillary alginate impressions, study casts were fabricated and mounted on an articulator. Denture teeth were selected and arranged for an aesthetic try in of a diagnostic set up. Following the confirmation of the diagnostic tooth set up, the denture teeth were returned to the working cast, and a diagnostic wax up was performed with pink baseplate wax to develop ideal alveolar and soft tissue contours.

 

An alginate impression was made of the diagnostic tooth and soft tissue wax up for fabrication of a master cast. A CT scan template was then fabricated on the master cast. The template was trimmed well beyond the cervical margins of the teeth in the bone defect area, to include the alveolar soft tissue contour. The template should also include natural teeth adjacent to the bone defect, resulting in a more stable positioning of the scan template in the mouth.

 

Barium sulfate was mixed with a carrier to obtain a radiopaque paint mixture, which was painted over the replacement teeth and extending over the alveolar ridge apical to the teeth. This allows an evaluation of the ideal soft tissue contour on the CT images. Following the scanning of the patient, wearing the pre-fabricated scan template, the raw CT scan data was reformatted into a SimPlant study. On the CT images, the clinician is able to visualise the discrepancy between the defective ridge and the ideal alveolar contour, by means of the radiopaque scan template. This provides valuable information on the reconstructive needs
of the patient. It is helpful in determining if hard and/or soft tissue augmentation is required. By simulating the needed augmentation in the SimPlant planning software, the volume of the augmentation can be determined. Donor sites for the harvest of bone grafts, such as the symphysis, ramus or iliac crest, may be selected based on the volume of augmentation that is needed.

 

On the CT images, the relationship between the ridge and the ideal prosthetic tooth positions is also visualised. Implants can be positioned in their ideal prosthetic position taking into account underlying bone quality and bone quantity and the planned augmentation.

 

By fabrication of a stereolithographic model based on the CT images, it is possible to pre-shape the bone graft, outside the patient.

 

The anterior maxilla of this patient was reconstructed with a pre-shaped corticocancellous bone graft from the iliac crest.
The second patient, a 25 year old male, suffered traumatic loss of three teeth. He presented for reconstruction of the maxillary defect for dental implant placement.
A radiopaque CT scan template was fabricated using the same method as described for the first patient.

The reconstructive needs of the patient were checked in the SimPlant planning software, and the volume of the needed augmentation was determined.

 

Based on the CT images, a stereolithographic model of the jaw was fabricated. The CT scan template, made on the master cast, was positioned onto the stereolithographic model, allowing a three dimensional evaluation of the ideal alveolar contours and the existing bone deficiency. A laboratory reconstruction was performed on the stereolithographic model. Cold cure acrylic (or light cure acrylic) was used to build up the bone to the proper dimensions indicated by the CT scan template. As a result, the acrylic reconstruction of the defect can be used as a bone grafting template.

 

The laboratory reconstruction of the defect can be removed from the model and evaluated, to determine suitable donor sites for the harvest of bone grafts. The stereolithographic modeland the bone graft templates can be used during surgery after cold sterilisation. Following reflection of the soft tissue flap over the bone defect, the
bone graft template were tried into place.

 

The template can be used to plan the ideal size and shape of the graft and to help three dimensionally shape the graft for close adaptation to the recipient bone. The shaped graft can be tried on the stereolithographic model, avoiding the need to take the graft in and out the mouth several times during surgery.

 

The anterior maxilla of the patient was reconstructed with pre-shaped bone grafts from the mandibular ramus and symphysis.

 

Conclusion

 

Surgical planning software, like SimPlant 8, and stereolithographic models based on the CT images, can help clinicians in realising better clinical and aesthetic results. Not only the planning of the implant positions, but also sinus grafting and bone augmentation can be evaluated and simulated using these tools. As avoiding surprises and complications during surgery, together with a clinically and aesthetically satisfying result for the patient, are the main objectives of each clinician, the SimPlant 8 planning software and stereolithographic models have to be considered as very helpful tools for successful surgery.

Email: misch@bonegraft.com

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