Customized TMJ Implant: 16-year-old gets treated for Mandibular Cancer

By Dr. Gopinath AL

Temporo-mandibular joint (TMJ) disorder causes pain, stiffness, or lack of mobility in the joint, keeping one from using the jaw’s full range of movement. An open joint surgery with replacement of complete TMJ by artificial prosthesis is required in severe TMJ disorder that involves:

  • A lot of tissue or bone growth or the tumor that stops the joint from moving
  • Fusion of the joint tissue, cartilage, or bone (ankylosis)
  • Inability to reach the joint with arthroscopy

The most common complication of TMJ surgery is a permanent loss in range of motion.

Other possible complications include:

  • injury of facial nerves, sometimes resulting in partial loss of facial muscle movement or loss of sensation
  • damage to nearby tissue, such as the bottom of the skull, blood vessels, or anatomy related to your hearing
  • persistent pain or limited range of motion

Hence, it is important to understand the pre-op condition in detail and analyze the patient-specific surgical approach and customized prosthesis to restore TMJ as close as possible to the natural one.

Here is one such case of TMJ replacement by using advanced visualization, pre-surgical planning, and customized TMJ implant for the patient. A female patient of age 16 was diagnosed with cancer on the right mandible.

Dr. Gopinath AL, HOD, Dept of Oral-maxillofacial surgery – VS Dental College and hospital, approached our clinical engineers for a robust plan and precise reconstruction of the TMJ by using the patient-specific implant.

We mapped out to Visualize, Plan, and then execute.

Visualization:

In order to visualize the mandibular anatomy and its neighboring area, a high-resolution CT scan of adequate slice thickness and increment was used to 3D model the defect. The region of interest was well captured in the scan and replicated as a 1:1 digital model for understanding the defect and pathology. The idea is to provide a self-explanatory model and help the surgeon to make them visualize the information which usually remains hidden in conventional 2D CT images.

 

Planning:

Once the 3D modeling of the images (segmentation) was completed, the plan was to lay down the removal of the tumor followed by reconstruction using customized TMJ.

Key steps involved –

  • Tumor on the right mandible was to be removed including the condyle and hence, it was necessary to have the right occlusion when the TMJ is replaced.
  • A proper occlusion was achieved by virtually simulating the correct occlusion state taking references from the mandibular/maxillary teeth and re-positioning the healthy left condyle in the fossa. This helped design the customized TMJ for the patient ensuring the correct range of motion and jaw opening.

Then the healthy left mandible was mirrored to achieve the best clinical reference for reconstructing the body of the mandible

  • A surgical guide was designed to resect the mandible for perfect joint connection of the implant body to the healthy left mandible. A marking guide was also designed to ensure there is no bulge of the anterior flap of the implant.

  • Freeform design following the natural mandibular shape referred from the healthy side was made. To reduce the weight of the implant, there was a lattice structure provided inside the body, which also helps in osteointegration at the implant-bone contact surface.
  • Fossa was designed to ensure the proper range of motion of the implant and natural jaw opening, ensuring that the condyle doesn’t dislocate out of the fossa.

3D Printing:

Once the surgical plan was approved and finalized, the plan was translated to physical models to analyze the outcome. Pre-op, intermediate, and post-op models were printed. The patient-specific guides were 3d printed in biocompatible autoclavable material for realizing the planned cuts intra-operatively on the mandible. The customized implant was printed in medical-grade titanium with required finishing and post-processing techniques for better articulation.

 

Conclusion:

Preplanning the surgical approach and use of the customized surgical guides and patient-specific implant, helped in achieving accurate reconstruction, reduced intra-operative time, and faster recovery of the patient.

 

Dr. Gopinath AL
VS Dental College, India
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