|Year : 2020 | Volume
| Issue : 3 | Page : 142-146
Silicone prosthesis: A viable treatment option for rehabilitation of residual ocular defects
Rahul Bahri1, Poonam Prakash1, Kirandeep Singh1, Brig S K Bhandari2
1 Prosthodontics and Crown & Bridge, Armed Forces Medical College, Pune, Maharashtra, India
2 Dept of Dental Surgery & Oral Health Sciences, Armed Forces Medical College, Pune, Maharashtra, India
|Date of Submission||01-May-2020|
|Date of Acceptance||16-Jun-2020|
|Date of Web Publication||15-Oct-2020|
Dr. Poonam Prakash
Department of Dental Surgery and Oral Health Sciences, Armed Forces Medical College, Pune - 411 040, Maharashtra
Rehabilitation of a residual ocular defect is a challenge for prosthodontists as it needs utilization of favorable anatomical factors and modification of unfavorable conditions so as to meet the triad of form, esthetics, and comfort. During the World War II, the United States Naval Dental and Medical School introduced the use of methyl methacrylate for the fabrication of ocular prosthesis. Since then, it has been widely used in the form of stock eye shell and modified stock shell and for custom-made ocular prosthesis. Medical-grade room-temperature vulcanizing silicone and its various advancements over the years have revolutionized the science of maxillofacial rehabilitation. The use of this material for ocular prosthesis has been underexplored. It exhibits numerous advantages over the age-old poly methyl methacrylate such as absence of monomer, flexibility, and improved esthetics in terms of intrinsic coloration, making it more biocompatible and comfortable for the patient. This case report aims to highlight the fabrication of custom-made ocular prosthesis using medical-grade silicone with emphasis on the use of multi-specialty approach for the selection of the iris and the use of photographic grid for iris placement. Medical-grade silicone has been used successfully for the fabrication of eye prosthesis in animals achieving desirable biological, mechanical, and esthetic goals of the rehabilitation process.
Keywords: Digital imaging, ocular prosthesis, room-temperature vulcanizing silicone
|How to cite this article:|
Bahri R, Prakash P, Singh K, K Bhandari BS. Silicone prosthesis: A viable treatment option for rehabilitation of residual ocular defects. SRM J Res Dent Sci 2020;11:142-6
|How to cite this URL:|
Bahri R, Prakash P, Singh K, K Bhandari BS. Silicone prosthesis: A viable treatment option for rehabilitation of residual ocular defects. SRM J Res Dent Sci [serial online] 2020 [cited 2021 Jul 27];11:142-6. Available from: https://www.srmjrds.in/text.asp?2020/11/3/142/298261
| Introduction|| |
Loss or absence of an eye may be due to congenital defects, irreparable trauma, or surgical ablation following tumor. Ocular prosthesis is a maxillofacial prosthesis that artificially replaces an eye missing as a result of trauma, surgery, or congenital absence. Various materials have been used in the past, ranging from precious stones, bronze, copper, gold, to glass-porcelain introduced by Pare in the 16th century. Methyl methacrylate has long been used as a material of choice for stock shell or custom-made ocular prosthesis. Medical-grade silicone can be used as a viable option for ocular prostheses.
This case report aims to highlight fabrication of a custom-made ocular prosthesis with emphasis on the use of multi-specialty approach for iris selection, use of photographic grid for iris placement, and medical-grade silicone as an alternative material for the fabrication of ocular prosthesis. This material has only been tried in animal studies where it helped in successfully achieving biological, mechanical, and esthetic goals of the rehabilitation process.
| Case Report|| |
A 43-year-old patient reported to the department of oral surgery with chief complaint of ill-fitting, unaesthetic ocular prosthesis fabricated 3 years back. History revealed that he had met with an accident 8 years back, and his right eye was enucleated. After healing period of 3 months, a custom-made poly methyl methacrylate (PMMA) ocular prosthesis was fabricated. At present, the older prosthesis was unaesthetic in appearance and appeared overextended causing increased palpebral opening [Figure 1]. Local examination of the defect site revealed a healthy tissue bed with no signs of inflammation and apparently normal muscle function. Treatment options discussed with the patient were customized ocular prosthesis using PMMA and silicone. Since the patient was provided with three PMMA prostheses in the past, it was planned to rehabilitate the residual ocular defect with custom-made silicone ocular prosthesis, following multidisciplinary approach for iris selection using digital imaging technique, and informed consent was obtained.
|Figure 1: (a): Pre-operative defect site (rt); (b): Old prosthesis in-situ|
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Custom tray fabrication
For fabrication of custom impression tray, the impression of intaglio surface of existing prosthesis was made using putty consistency of polyvinyl siloxane (PVS) impression material (Zehrmack, Italy). Autopolymerizing acrylic resin (DPI, India) was flown into it and custom tray was fabricated. The tray obtained was smoothened with finishing burs (Shofu Dental Corporation, USA) to prevent any irritation to the tissue bed, and escape holes were made.
Impression and wax pattern fabrication
A hollow syringe cap (Dispovan, India) was attached to the center of the tray. The tray was checked for extension, orientation, and unrestricted movement of the tissue bed. The patient was made to sit upright with the head supported by the headrest, and a functional impression was made using light body consistency of PVS impression material (Betasil, Germany). Impression was examined for its extension and surface defects. Split mold assembly was fabricated using Type III gypsum material (Neelkanth, India), and wax pattern was made using white carving wax (2GM, India) [Figure 2].
|Figure 2: (a): Impression of defect site (b): Impression using Custom tray (c): Split mold|
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Multidisciplinary approach for iris selection and photographic grid for iris placement
The wax pattern was tried and adjusted according to the palpebral opening and iris–scleral display of the normal eye. For the selection of the iris, a multidisciplinary approach with the help of the department of ophthalmology was followed, in which a fundus camera (Carl Zeiss FF 450 Plus, Carl Zeiss Meditec, Inc., USA) was used to obtain a close image of the normal eye. The image obtained was printed on high-quality photographic sheet (Kodak 180 GSM, Eastman Kodak Company, India).
The other challenge was to accurately position the iris, for which a photographic grid was used. An image of the patient's face was captured using a Digital Single-Lens Reflex (DSLR) camera (Nikon D 5300 24.2 MP, Japan), and a life size print was obtained on a transparent millimeter graph paper to select the position of the iris superoinferiorly and mediolaterally [Figure 3]. Once the position of the iris was confirmed, the iris was secured in the wax pattern using the iris button technique. Trial was done to check the fit, support and contour of the prosthesis with eyes in open and closed position [Figure 4].
Shade selection and silicone processing
Wax pattern was subjected to flasking and dewaxing as per the conventional protocol. Room-temperature vulcanizing (RTV) silicone (Technovent M511 Platinum Silicone, South Wales, UK) was used. Scleral shade selection was done using customized shade tabs fabricated by adding different concentrations of synthetic inorganic pigments available as functional intrinsic white and blue shade to the base of RTV silicone and by using transparent plastic sheets to check the depth of color in daylight. Base and catalyst were mixed in a ratio of 10:1 using long strokes to ensure homogenous mix. Once appropriate shade was obtained by incorporating intrinsic stains, the silicone was packed in the flask and allowed to polymerize at ambient room temperature for 24 h [Figure 5]. The prosthesis retrieved was finished with silicone finishing burs, and the iris was secured in the position using silicone adhesive (Technovent, South Wales, UK) [Figure 6]. The prosthesis was inserted into the ocular bed and checked for extension and comfort, and postinsertion instructions were given [Figure 7]. At the first recall appointment (24 h), the patient experienced better comfort, esthetics, and a lighter prosthesis as compared to his previous experience [Figure 8]. The patient was kept on regular recall visits as per the standardized protocol, and specific instructions were given for the maintenance and disinfection of the prosthesis.
|Figure 5: (a): Medical grade RTV silicone base and catalyst (b): Intrinsic stains (c): Shade selection (d): Packing of silicone in specialized ocular flask|
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|Figure 6: (a): Application of silicone adhesive (b): Finishing of prosthesis (c): Finished Prosthesis (d): Tissue surface of finished prosthesis|
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| Discussion|| |
The novelty of the case report is to highlight the use of medical-grade silicone for the fabrication of ocular prosthesis in humans with favorable biological, mechanical, and esthetic outcomes.
The iris–scleral visibility, color, size, and position of the iris are the main factors that govern the esthetics of an ocular prosthesis. For iris selection, digital techniques such as use of DSLR camera have been highlighted to obtain desired esthetic outcomes. Fundus camera is an ophthalmic device used to obtain images of the back portion of the eye. It consists of a camera with a specialized microscope and a lamp to obtain the image from different directions. In this case, the image of the normal eye obtained on the screen was used for iris selection. Since it was taken from the same patient, the color, size, and cosmetic requirements were adequately met by the use of this technique.
Literature has mentioned various methods for accurate positioning of the iris with the use of standard measurements using anatomical landmarks, Vernier caliper, and graphic methods. In the case discussed, photographic grid techniques allowed exact positioning of the iris and selection of dimensions of the iris to mathematical accuracy.
Silicone has been used widely for the fabrication of maxillofacial prosthesis with the acceptable esthetic outcome. The ability of silicone to accept intrinsic stains and extrinsic characterization can help in achieving desirable scleral shade.
Biological and mechanical
Materials such as scleral polymer, IPS e-max press scleral veneer, and light-cured materials have been used for custom-made ocular prosthesis, although PMMA is most commonly used in clinical practice., To reduce the cytotoxic risk and residual monomer content in the finished prosthesis, long curing cycles, immersion in water bath, and reverse curing are recommended. da Silva et al. concluded that long polymerization cycle with 9 h immersion in heated water, followed by 30 min of boiling, reduces the monomer content.
Bartlett and Moore highlighted the use of medical-grade silicone rubber as it evokes less inflammatory response. Due to desirable physical properties of silicone, it has been used worldwide for the fabrication of maxillofacial prosthesis. Favorable properties include ease of manipulation, biocompatibility with low degree of toxicity, and ability to accept intrinsic stain. When adequately cured, they resist absorbing organic materials and permit adequate cleaning. Heat-vulcanized silicones (HTV) are not as elastic as RTV silicones and are not recommended for situations with mobile tissue bed. The most common disadvantages of silicone materials include low tensile strength, low shearing resistance in thinner portions, color degradation, instability when exposed to ultraviolet rays, humidity, pollution, and temperature variation.
Certain necessary instructions to be followed by the patient include frequent removal of the prosthesis, cleaning with mild soap solution, use of a spectacle to prevent ingress of foreign particles, frequent recall for examination of tissue bed, prosthesis to be kept away from fire, and disinfected at regular interval.
Mechanical properties of silicone include that it is lighter than PMMA, and the inorganic component allows flexibility and permits great freedom of motion and gentle to adjacent tissue which favors its use in intraocular conditions.
Silicone ocular prosthesis was invented and patented in 2008 by Singer and Singer Matthew, Memphis, TM, USA (US 2008/0046078 A1) in which the prosthesis included a white-tinted silicone for the posterior sclera portion formed using molding process. It also included an anterior iris portion and a protective transparent layer over the sclera and iris to provide depth to the prosthetic eye. However, its use in humans is yet underexplored in spite of it being a common material for the use in maxillofacial prosthetics. This serves as a successful alternative treatment option, however its longevity needs to be ascertained.
Silicones have been commonly used in the fabrication of orbital prosthesis; however, prefabricated PMMA shells have been utilized for the ocular portion of the same., Silicone ocular prosthesis has also been attempted in horses and dogs where they have shown superior cosmetic results., This case report highlights the use of medical-grade silicone for the fabrication of ocular prosthesis in humans where the soft and cushioning effect of material can be used to advantage for the patient over hard acrylic shell. This helps in achieving favorable biological, mechanical, and esthetic outcomes for successful rehabilitation.
| Conclusion|| |
Various materials have been used for maxillofacial rehabilitation to provide maximum comfort to the patient along with the restoration of esthetics and maintenance of form. The prosthetic impact of silicone ocular prosthesis lies in its ability to achieve biological, cosmetic, and mechanical advantages in terms of patient's preference, comfort, and overall success of the prosthesis. Medical-grade silicone serves as a viable alternative option which requires long-term follow-up and further evaluation for the longevity and acceptability for use in human beings.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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