Ossiculoplasty : a new prosthesis. (A preliminary report).
The homograft incus is perhaps the most widely used graft material for ossiculoplasty in our country. However, it is not available to those without access to autopsy material and hence there is a need for an alternative graft material for ossiculoplasty.
The material should be inexpensive easily available, of the right consistency, relatively bio-inert and non-toxic. It should permit easy moulding and shaping, storage, sterilization and maintain its structure.
We selected the human tooth as a graft material for ossiculoplasty as it satisfies all the above criteria. The bio-inertness had to be tested and confirmed by animal experiments before use in the patients. We were encouraged by the fact that ivory has been used as implant material in cases of atrophic rhinitis.
The roots of healthy bicuspids and tricuspids obtained from the orthodontia department were cut off by a dental saw. They were stored in 70% alcohol, in the same manner as the homograft incus.
The bio-activity of the tooth root was tested by implanting it in a subcutaneous pouch on the thigh of a white mouse, the body of incus being used as a control implanted in the opposite thigh. The amount of foreign-body reaction evoked by the tooth root was much less than that evoked by the incus. After repeated experiments in animals, the tooth root was thought fit for use in tympanoplasty.
Shaping the tooth
The tooth root has a central root canal which permits a needle or straight pick to be passed through it for fixation during shaping [Fig. 1a]. Using a diamond paste burr, the root is moulded to the desired size and shape and stored in 70% alcohol.
Prior to surgery, the tooth root is washed thoroughly in an antibiotic solution. The final shaping of the tooth root is done after exposing the middle ear and assessing the ossicular chain defect. The root canal can be widened to fit snugly on the head of the stapes [ Fig. 1b].
The types of reconstruction done so far are shown in [Fig. 2]. Whenever the tooth root apposes the tympanic membrane, a small piece of autograft tragal cartilage is interposed between the root surface and the tympanic membrane graft as has been advocated with plastipore TORP AND PORP.
Of the 14 cases where the tooth was used as a prosthesis, eight cases were with central perforation and six with cholesteatoma. In the central perforation cases the posterior canal wall was always kept intact while in cholesteatomas an open mastoid cavity was kept draining to the outside. Temporalis fascia was used as inlay graft in all cases.
The temporalis fascia graft took well in 13 of the 14 cases while one case developed a small anterior perforation which healed subsequently. The tooth prosthesis was not rejected in any of the cases.
There was good hearing improvement in eleven cases with closure of the airbone gap to within 15 dB. Of the 3 cases which did not show satisfactory improvement one was re-explored after two months.
The tooth prosthesis used was too large and was producing a tenting of the tympanic membrane. It was covered with a layer of mucosa and there were no adhesions surrounding it so that the tympanic membrane could be easily lifted from it. The other two cases who have not improved are awaiting revision. The longest follow up is over 2 years and cases operated less than 3 months ago have not been included in this presentation.
The middle ear is a "privileged site" like the anterior chamber of the eye and the meninges and therefore tolerates a variety of graft materials that the otologist has taken the liberty to implant in it. The variety of material is proof enough that no single material is completely satisfactory in all situations. The homograft incus is the most popular ossicular prosthesis in our country. The more affluent countries use synthetic plastipore TORPS AND PORPS which under our economic conditions are rather expensive. Due to limited access to the homograft incus, many otologists have to look for some alternative which will give comparable results.
As with TORP AND PORP, it is advisable to interpose a piece of cartilage between the tooth and the tympanic membrane to avoid extrusion. It is technically easier to connect the footplate or the stapes head to the tympanic membrane rather than to the malleus and our results have shown equal hearing improvement with both these types of assemblies. This hearing gain is maintained without deterioration over long periods. The prosthesis removed at a revision operation showed no change of shape, size and structure and was seen to be covered with normal mucosa without adhesions. This confirms the stability of the tooth prosthesis in vivo as well as its bio-inert nature. The number of cases is small but we feel that our initial experience with this prosthesis is most satisfactory and we can now proceed to use it in a large number of cases to confirm this impression.
Thus, the tooth root satisfies all criteria of an ideal prosthesis for ossiculoplasty. It is well accepted in the middle ear with no evidence of rejection even when used with open mastoid cavities.
The hearing gain is comparable to that with the homograft incus, if not better. The gain is long lasting as the prosthesis is stable and remains without adhesions. A larger series with a longer follow up is needed to confirm our initial experience that the tooth root is an ideal ossicular prosthesis.
We are grateful to Dr. C. K. Deshpande, Dean, Seth G.S. Medical College & K.E.M. Hospital, Parel, Bombay 400012, for allowing us to publish the Hospital record in this paper.