Your Questions

Q: Dr. Eppley, I am interested in knowing more about Mimix bone cement. Here are my questions:

1) What type of surgery is Mimix mainly used for? 

2) What is the biggest features of Mimix? Could Mimix be placed in any area of the cranial bone?

3) In Genioplasty are there any special techniques in using it?

4) Can Mimix be placed in the gap between a cranial bone flap and the native bone with titanium plating?

5) Can Mimix be used for small defect cranioplasty (less than 25 square cm) for pediatric patients

6) Have you ever experienced Mimix breaking after surgery?

7) Do you have any experience using Mimix on maxillofacial and mandibular bone?

A: Based on my extensive experience with Mimix bone cement in craniomaxillofacial surgery, the answer to your questions are as follows:

1) Mimix is used for two main cranial (skull) purposes: 1) inlay defects of the skull such as burr holes or larger skull defects and 2) as an onlay material for skull augmentation such as aesthetic forehead augmentation or to build up deficient skull contours. There are a wide variety of other maxillofacial uses which ranges from filling in small bone defects and as a contouring material, but the skull makes up the vast majority of its uses particularly as judged by volume used.

2) If one is looking for a natural method of bone reconstruction (hydroxyapatite is similar to bone in chemical composition) of the skull as opposed to using completely synthetic metallic materials. Mimix can be placed in any area of the skull. Since the skull is non-mobile and non-load bearing, it can be used in any location from the temporal fossa to the frontal sinuses.

3) When placing the material in a genioplasty as an interpositional filler, it is important that the implantation site is not too wet with blood. A very wet field interferes with the setting/curing of any hydroxyapatite cement.

4) As a general rule, no. if you are referring to using Mimix in conjunction with titanium plating for cranial flap fixation it can be done but there is little reason to do so directly underneath a fixation plate. It may be used for other bone gaps along the cranial bone flap if they are significant enough in width.

5) Filling in pediatric skull defects would be a common use for Mimix due to its advantages in the growing skull.

6) It is important when using any hydroxyapatite cement to ensure that there is no mobility of the surrounding bone. Mimix is not a bone fixation method, it is a bone graft substitute that must have good stability of the surrounding bone otherwise it may fracture. In my experience I have never seen Mimix fracture or pose a problem in this way but you have to know how and when to use it to avoid this potential concern.

7) Mimix in the maxillofacial region is used as an inlay method only to fill in small bone defects that might otherwise require a graft and into which a dental implant is not intended.

Dr. Barry Eppley

Indianapolis, Indiana

Q: Dr. Eppley, I am inquiring about a natural method for cranioplasty. I have a forehead defect including a hole through the bone from a prior craniotomy for a brain tumor. The size of the forehead defect measures about 9 x 2 cms and represents the area where the bone flap appears to have settled inward. Can I use my own bone to reconstruct this forehead defect area?

A: Cranial bone flaps, despite using rigid fixation, can heal inconsistently or undergo some resorption leaving an outer contour depression. There are multiple ways to do a cosmetic or reconstructive cranioplasty with a variety of materials, bone being one of the options. If the defect is small enough, one could use natural bone, in other words cranial bone grafts. While natural bone has understandable appeal, it is actually not the best way to do most cranioplasties. Besides having to harvest the bone (and creating another bone defect), bone grafts are notoriously unreliable and predisposed to incomplete or total bone resorption particularly when used as an onlay. The more reliable way to perform most cranioplasties is to use hydroxyapatite cements. They are structurally stable, do not resorb and can be shaped perfectly to any defect whether it is an inlay, onlay or a combined cranial defect. They are also composed of hydroxyapatite, a calcium phosphate mineral, which is highly biocompatible with natural bone. While bone will never truly grow into it and replace it, bone will bond directly to it. The type of forehead defect that you have would do well with a hydroxyapatite cement cranioplasty.

Dr. Barry Eppley

Indianapolis, Indiana

Q: Dr. Eppley, I noticed that you also do reconstruction using bone cements.I had sagittal split osteotomy a couple years back which left my face unbalanced and my mandibular angles too small. I’d like to restore balance to my face without the bottom face turning too square. I’m not keen on using plastic implants. So, does hydroxyapatite make a good material for restoring facial contours for the mandible? Unlike bone grafting, it doesn’t resorb, and is comparatively easy to mold.. or so I have read. 

A:  Of the many materials available for facial bone augmentation, hydroxyapatite has a long history dating back over twenty-five years as a granular bone onlay material. This is a syringe method where the granules are introduced through an open intraoral approach with limited dissection. They do not resorb and are relatively easy to place. Confining them to the desired location was always an issue but it can be an effective method. Hydroxyapatite today is better known as a bone cement and has been widely used for cranial reconstructions in infants as well as adults. It needs to be mixed and applied in an open method as the setting of the material is very technique sensitive. It is not use very often as a facial augmentation material as it works best when used in an inlay bone defect that has borders. would not use bone or hydroxyapatite cement as this material composition is too difficult and unpredictable to place outside of an open cranioplasty where its setting/curing is more assured.

Hydroxyapatite granules, and a very similar material known as HTR granules, can be used for a small amount or moderate amount of mandibular angle augmentation.  

Dr. Barry Eppley

Indianapolis, Indiana