A laboratory silicone for preclinical training in ear prosthesis.

This article describes an industrial elastic silicone as a material for the laboratory fabrication of ear prosthesis. It has been tested for toxicity in lab animals by the SGS India Pvt. Ltd and approved as a material to pass the parameter of abnormal toxicity. This material therefore can be safely recommended for laboratory exercise to fabricate facial prosthesis. The high cost of the maxillo facial silicone materials prohibits their use for facial prosthesis in pre-clinical training of post-graduate students in maxillofacial prosthodontics. For this reason, pre-clinical laboratory exercise in facial prosthesis is inadequate. A few institutions use polymethyl methacrylate resins which are rigid and do not have elastic characteristics of silicone, which is used for facial defects. This cost-effective industrial silicone material which mimics the elastic and color characteristics of the conventional silicones can be recommended for preclinical exercises.

Maxillo facial training is an integral part of postgraduate curriculum in prosthodontics. With the increase in oral malignancy, facial tumors and trauma to face the post-surgical rehabilitation of the facial defects remains the responsibility of the prosthodontists. For the purpose of prosthetic rehabilitation, biologically accepted materials such as poly methyl methacrylate, poly vinyl chloride, poly urethane and silicone are used.[12] Silicones are generally the preferred material by the patient because of its light weight, flexibility and lifelike appearance.

A structured preclinical training in the fabrication of facial prosthesis is imperative for post-graduate students to acquire clinical dexterity in fabrication of facial prosthesis. Since the cost of the current silicones is prohibitive, the laboratory phase of fabricating facial prosthesis is very limited and minimal. This material offers sufficient scope to the postgraduate student to train himself in the modulation and staining of various facial prosthesis such as auricular, nasal and orbital prosthesis. This material is akin to the silicone, which is later used for patient work.

Material description

Curing type – Acetoxy

Color – Tranlucent

Density – Approximately 1.04 g/cc

Skin formation time – Approximately 5 min at 30°C

Curing time – Approximately 24 h. for 2 mm thickness at 30°C

Movement accommodation – Approximately 15%

Tensile strength – Approximately 0.61 N/mm2

Elasticity – Approximately 260%

Fabrication of Ear Prosthesis

Step 1: Ear impression is made using irreversible hydrocolloid alginate and custom made wax rim. wet gauze pieces are layered on top of alginate for the interlocking of the plaster to be poured [Figure 1].

Figure 1

Making of ear impression

Step 2: Undercut areas in the impression are identified and blocked out with wax. Die stone is poured [Figure 2].

Figure 2

Block out impression partly with wax and cast poured

Step 3: working model is retrieved from the impression carefully and base trimmed [Figure 3].

Figure 3

Working model with dental stone prepared

Step 4: Custom tray using soft tray sheets prepared. A complete ear cast is made by making alginate impression for a person related to the patient [Figure 4].

Figure 4

Custom tray using soft tray sheets prepared for complete ear cast

Step 5: Skin tone of the patient is matched to the oil colors. It is mixed and added to the silicone material [Figure 5].

Figure 5

Colors mixed with silicone

Step 6: Silicone material is dispensed to the under cuts of the custom tray and filled completely [Figure 6].

Figure 6

Material dispensed with syringe into soft sheet custom tray

Step 7: Separating medium is applied on working cast and under cuts are filled with silicone material. It is pressed against the soft sheet custom tray carrying the silicone material [Figure 7].

Figure 7

Silicone filled tray pressed against working cast

Step 8: Prosthesis is tried on the model and trimmed before insertion on patient [Figure 8].

Figure 8

Prosthesis tried on the model

Discussion

Over a period of time various materials such as wood, leather, polyurethane and polyvinyl chloride have been used to produce esthetic properties to prosthesis, but silicone has proved to be the material of choice because of its lifelike effects and flexibility.[3] Methyl methacrylate resin is been used as a maxillo-facial material, but its use is limited due to its rigidity. The flexibility and staining of silicone are the requirements of a maxilla-facial prosthesis materials.[456] This industrial silicone has the property of elasticity and has the potential to incorporate stains and colors to mimic natural skin.[78] Its toxicity has been tested and for laboratory purpose it is an acceptable material.

Conclusion

The advantage of this industrial silicone material is the low cost factor, soft nature, flexibility, easy to fabricate and having good esthetic property and it will be an ideal material for the post-graduate student to train himself and acquire skills during his pre-clinical training program, which includes maxilla facial prosthodontics. Since the cost is not prohibitive and as this material is quite similar to the current silicones, it can be recommended.