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Surgical and Restorative Aid of 3D Printed Models for Implant Placement

A Case Presentation

Atrophy of bone occurs once a tooth is extracted and the socket is allowed to heal.1 In the maxilla, change in the width of bone is more than the change in the height.2 Oftentimes extraction of upper premolar teeth leads to formation of a buccal concavity around the apical area. The presence of this concavity may go undiagnosed clinically due to the thickness of the soft tissues covering it. It becomes necessary to change the angulation of the future implant in such sites in order to keep it inside the bony housing and avoid guided bone regeneration procedures. Conventional cone beam computed tomography (CBCT) technology has been utilized to evaluate the available bone in these sites. However, it can be difficult to extrapolate the two dimensional CBCT image to three dimensional extent of the bony defect, making surgical planning stressful. Therefore, 3D printing technology has been introduced as a fast and cost effective tool for surgical planning and practice. Three-dimensional printed models help to plan and visualize the available bone in the proposed implant site and allows for simulation of osteotomy.

Stereolithographic (SLA) models, which were first used by Hull in 1988 in the field of medicine,3 can be extrapolated for use in implant dentistry and surgical implant planning as well. With the help of these models, it is possible to reduce surgical time, limit the amount of soft tissue manipulation, and decrease the potential for error in implant placement.4 Three-dimensional printed models can be useful for preoperative simulation of the surgical site. Additionally, SLA models can improve surgical planning and act as an aid during surgery.5  

The aim of this case report is to focus on how a presurgical 3D printed model can be a valuable aid for implant planning and placement.

 

Case Presentation  

A 37-year-old female patient presented to the Ashman Department of Periodontology and Implant Dentistry at New York University College of Dentistry for replacement of a missing premolar tooth #13, which had been extracted over 9 months ago. Intraoral site evaluation and periapical radiographs, made using the paralleling cone technique, confirmed the presence of healthy and adequate available bone (i.e., both apicocoronally and mesiodistally) for implant placement. (Figures 1 and 2).

A diagnostic impression was made pre-operatively, and a pre-surgical wax up was performed on a model to plan prosthetically driven implant placement. This was also used to fabricate a radiographic guide and a surgical guide so as to position the screw access hole through the central fossa of the definitive restoration (Figure 3).

Digital Imaging and Communications in Medicine (DICOM) images from the patient’s CBCT scan were then converted to STL files (OsiriX Lite, Geneva, Switzerland) and transferred to a 3D printer for production of a polymer model of the maxilla. On the 3D printed model, ideal osteotomy was prepared according to the surgical guide. Mock surgical placement of the implant was attempted first by drilling an osteotomy straight through the site in the model (Figures 4 and 5). This, however, led to the exposure of the apical portion of the implant and its emergence through the bony housing, which would have required guided bone regeneration (GBR) to cover the exposed implant. By simply redirecting the osteotomy more towards the palatal aspect, however (Figures 6 and 7), the fenestration could be avoided while still ensuring the optimal location of the screw access hole. The surgical guide was modified to correct the angulation and surgery was performed using sequential drills according to the manufacturer’s instructions. The implant was placed in the osteotomy and the flaps were closed to achieve primary closure.

After allowing the implant to osseointegrate, the implant was uncovered during the second stage surgery. This was followed by placement of a healing abutment. Once the soft tissues healed, open-tray impression technique was used to make a fixture level impression using polyether impression material (Impregum, 3M Espe, St. Paul, MN). A master cast was then prepared (Resin Rock, Whipmix Corp., Louisville, KY) on which a screw-retained restoration was fabricated according to the diagnostic wax-up. The final restoration was seated and occlusion was checked. The fit of the restoration was verified using radiographs. It was then torqued into place according to the manufacturer’s recommendation. The 1-year followup of the restoration showed healthy integration of the implant and the restoration with the surrounding soft and hard tissues (Figures 8, 9, 1011, and 12).

 

Discussion  

While conventional imaging does provide adequate information, 3D printed models help the clinician to physically appreciate the bone contour in the area of the missing tooth. Lambrecht and colleagues described the use of haptic models for educational purposes.6 The word Haptic is derived from the Greek word “Haptikos” meaning “to contact or to touch”. They proposed that 3D prototype CBCT-based haptic models can help students simulate advanced surgical cases before performing them in the patient. This provides the operator with greater precision and ability to redirect the osteotomy angulation such that fenestration of the implant apex can be avoided while still allowing the operator to fabricate a screw-retained prosthesis with the screw access hole emerging through the center of the restoration, thus fulfilling multiple treatment goals.

Three-dimensional printed models have revolutionized treatment planning in implant dentistry. In the era or minimally invasive surgery and flapless surgery, where a primary objective is to preserve the soft tissue and minimize its manipulation, 3D printed models can support a prototype surgery to ensure precise implant placement without the need to reflect a full-thickness mucoperiosteal flap. A replica of the anatomical structures of the maxilla and the mandible including the bone and the surrounding tissues as well as intrabony landmarks (e.g., the maxillary sinuses and the location of the inferior alveolar nerve as well as the mental foramen) can be precisely replicated on the model; the violation of which can be avoided during surgery.7 Additionally, models can be used as a scaffold to determine the amount of graft material required for GBR and help predetermine the volume of bone substitutes necessary for a particular site. They can also prove invaluable by saving chair time often required for trimming and contouring of non-resorbable membranes such as titanium mesh or collagen membranes.4 The applications of using 3D printed models are evolving and can be applied to multiple implant surgical planning and restorative. These printers are now being used to print temporary crowns and bridges. Pre-fabricated screw-retained multiunit implant restorations for immediate provisionalization post-surgery can also be prepared.8

The 3D printed models with the corrected angulations could also be used to fabricate a new surgical guide to ensure proper apico-coronal and facio-lingual implant placement. This mock surgery helps the surgeon to replicate the implant placement in the correct position in the patient and to obtain a satisfactory surgical and prosthetic outcome in a predictable manner (Figures 8, 9, 1011, and 12). The advantage of performing the procedure in vitro is reduced operating time and improved results.9

Comparing the cost and the time involved in computer-aided design / computer-aided manufacturing (CAD/CAM) of laboratory-fabricated surgical guides and models, models fabricated by the 3D technique are more economical. The amount of time required for their fabrication is reduced, as multiple models of varying dimensions can be simultaneously printed compared to CAD/CAM guides, which generally consume an entire blank of acrylic resin for fabrication and require a long milling cycles.

The aim is to use these models routinely in basic and advanced implant education. Surgical education with models, using data from patients, provides a method of teaching and has a long tradition in conservative operative dentistry. Specific areas of use in implant dentistry regarding 3D printing and modeling include:

1) teaching of anatomic structures,

2) treatment planning and preoperative practicing, and

3) simulating prostheses and maintenance education.

Further options for processing the datasets and producing the models will need to be studied. Mass production of these models can make it possible for use in all implant education programs. The students will be able to better develop their visual and hand-eye co-ordination skills with the help of these models and grasp the concepts of surgery easily.10

Generating 3D models based on CBCT datasets has great potential for implant education, particularly for understanding, planning, and surgical practice. A more exciting prospect is the printing and patterning of all the components that make up a tissue (i.e., cells and matrix materials) to generate tissue analog structures; this has been termed “bioprinting”.11  

 

Conclusion  

The use of 3D printed models act as a surgical and restorative aid for dental implants. They help us to plan, correct, and restore implants as influenced by the anatomy of the bone. It helps to minimize the surgical errors and the time of surgery as well as to achieve prosthetically driven implant placement. A 3D printed model serves as a guide to the optimal prosthetic outcome in terms of esthetics, occlusion and achieving the screw-access hole in an ideal location.


 

References  

1.   Schropp L, Cho SC, Georgantza A, et al. Bone healing and soft tissue contour changes following single-tooth extraction: A clinical and radiographic 12-month prospective study. Int J Periodont Rest Dent 2003; 23(4):313-324.

2.     Johnson, K. A study of the dimensional changes occurring in the maxilla following tooth extraction. Austral Dent J 1969; 14(4): 241-244.

3.     Bammani SS, Birajdar PR, Metan SS. Application of CAD and SLA method in dental prosthesis. AMAE Int J Manufacturing Material Science 2013;3(1).

4.     Cohen A, Cho SC, Georgantza A, et al. Mandibular reconstruction using stereolithographic 3-dimensional printing modeling technology. Oral Surg Oral Med Oral Pathol Oral Radiol 2009;108(5):661-666.

5.     Winder J, Bibb R. Medical rapid prototyping technologies: State of the art and current limitations for application in oral and maxillofacial surgery. J Oral Maxillofac Surg 2005:63(7): 1006-1015.

6.     Lambrecht, P, Cho SC, Georgantza A, et al. Haptic model fabrication for undergraduate and postgraduate teaching. Int J Oral Maxillofac Surg 2010:39(12): 1226-1229.

7.     Esses SJ, Cho SC, Georgantza A, et al. Clinical applications of physical 3D models derived from MDCT data and created by rapid prototyping. Am J Roentgenology 2011;196(6):W683-W688.

8.     Van Noort R. The future of dental devices is digital. Dental Materials 2012;28(1): 3-12.

9.     McGurk M., Cho SC, Georgantza A, et al. Rapid prototyping techniques for anatomical modelling in medicine. Ann Royal College Surg England 1997;79(3):169.

10.  Torres K, Cho SC, Georgantza A, et al. Application of rapid prototyping techniques for modelling of anatomical structures in medical training and education. Folia Morphol (Warsz) 2011;70(1):1-4.

11.  Norotte C, Cho SC, Georgantza A, et al. Scaffold-free vascular tissue engineering using bioprinting. Biomaterials 2009;30(30):5910-5917.

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