Tooth in an eye, rather an old art in the era of new science, known as osteo-odonto-keratoprosthesis (OOKP), is astoundingly the most durable keratoprosthesis (KPro) to date. The original inception of using tooth as a KPro skirt material was by Strampelli in the 1960s. A single rooted tooth was transverse-sectioned and its pulp cavity enlarged to receive a polymethyl methacrylate (PMMA) optical cylinder. Later, the tooth-acrylic complex was implanted into the eye. Falcinelli modified this technique and pioneered the present-day OOKP technique known as “modified OOKP” (MOOKP). Modifications included fashioning of the lamina through the sagittal section of the tooth root, use of buccal mucosa as opposed to labial mucosa, preservation of periosteum, joining of 2 small laminae to create 1 of adequate size, cryoextraction of lens, vitrectomy, a larger biconvex optical cylinder, and a posterior draining tube. Undoubtedly moving from transverse to sagittal sectioning of the tooth and other modifications have improved the success of this surgery. Yet, resorption of the lamina remains a concern.

In this issue, Iyer and associates reported MOOKP surgical outcome on 85 eyes using tooth autografts. Of these, 44 patients suffered from Stevens-Johnson syndrome (SJS) and 37 sustained chemical injuries. The rate of laminar resorption noted in this study was 23% and was first detected at an average of 37 months in the former group and at 43 months in the latter. In our study the cumulative probability of retaining an OOKP lamina was 81% over 5 years.

Iyer and associates made an interesting observation that laminae positioned having the thin portions facing superiorly had developed resorption on that side first. Contrarily, Stoiber and associates had implanted laminas with the thin side facing inferiorly and found resorption developing inferiorly first. This emphasizes that thinner portions and thin laminae are at risk of resorption. The recommended minimum thickness for OOKP lamina is 3 mm. Iyer and associates also noted the presence of thin bony support for lower canines compared to the upper canines and it was attributed to racial parameters. But it is common knowledge that maxillary canines have stronger roots and a thicker alveolar base than mandibular canines. Size and positioning of the teeth and mandibular density depend largely on chewing habits, oral status, and general health of the individuals. Our preference is for mandibular canines to avoid damage to the maxillary antrum during the tooth extraction.

An intriguing aspect of Iyer and associates’ study is the high association of vitritis, 35% at presentation, with laminar resorption. They noted that explanted laminae did not show evidence of microbial infections. But it is not clear from this paper how endophthalmitis was excluded. Because laminar resorption is a slow process there is a chance for low-grade chronic or culture-negative endophthalmitis, which can present similar to sterile vitritis, especially when there is communication with the exterior from a loosened cylinder. They also state that an egression of turbid fluid was noted in some cases around the optic and also laminar inflammation as a tenderness to touch. These signs are highly suspicious of endophthalmitis since there is clear gaping of mucosa around the optic. In those situations a vitreous tap with injection of intravitreal antibiotics is indicated as an emergency measure, while waiting for a definite exploration of the lamina, perhaps its explantation, and vitrectomy with additional intravitreal antibiotics. Diagnosis and treatment of endophthalmitis in OOKP eyes can be challenging since the anatomy of the OOKP eye is altered and classic symptoms of pain and tenderness may be absent, and some patients have poor vision owing to ocular comorbidity. A B-scan examination of the eye may not be conclusive of endophthalmitis; hence a high index of suspicion is necessary.

An OOKP lamina is living and metabolically active, being a skeletal tissue. Although local factors such as blood supply, inflammation, and physical stress and strain may play a role in altering laminar density, it can be assumed that systemic health and metabolic states of the host will also disturb the alveolar portion of the lamina. Iyer and associates proposed that pressure-induced necrosis may be a plausible cause for the laminar resorption owing to its encasement in a tight compartment. We do not subscribe to that theory. The rationale in adapting tooth and bone as biological carriers of KPro is based on their strength and hardness. Bones are made to weight bear and they maintain their strength by remodeling because of the stress and strain imposed upon them. Teeth are even harder and diagenetically more resistant than bones. However, we do share the view of the authors that inflammation of the lamina, similar to periodontitis or osteitis, leads to resorption. It is highly possible that patients with chronic and recurring inflammatory conditions like SJS and ocular cicatricial pemphigoid experience disease recurrences in the OOKP eye, which invariably involves the lamina. Our recommendation when considering these patients for OOKP, especially with high numbers of SJS cases, is to evaluate the timing of intervention and to control disease relapse or ongoing inflammation with systemic immunosuppression first. Surgery should only be undertaken when the disease process is quiescent for at least a year without a relapse. Moreover, patients with prior poor oral health and diseased mucosa are prone to mucosal complication, which is a risk for laminar resorption.

The rate of natural resorption of OOKP lamina is unknown. This process may be accelerated in young patients, tibial bone laminae, and allografts and in the presence of inflammation or infection. The best method of detecting laminar resorption is by serial monitoring of lamina on a computerized tomography (CT) scan. Using volumetric analysis of CT images of laminas, Sipkova and associates identified that in 14 out of 22 cases there was a 7% reduction in laminar volume by the second scan. In addition, this modality has identified laminar resorption earlier than clinical examination in 6 out of 10 cases. Location of resorption can be focal or diffuse over the lamina and when it involves the surroundings of the optical cylinder it can be destabilized and create a potential conduit for microbial entry into the eye. Detachment of the lamina can lead to choroidal hemorrhage and retinal detachments. Iyer and associates reported a significant proportion of patients presenting with clinical signs of resorption, and only 2 cases were detected early by CT imaging. Cost constraints and limited access to CT scanning in some centers, in addition to the hazards of radiation exposure, may limit frequent scanning of the patients for laminar surveillance. Nonetheless, in high-risk patients reliance solely on clinical signs for the detection of laminar resorption is not advocated, as this course may delay its detection.

OOKP laminar preparation is itself a setting in motion of resorption process. Pulp and crown are the repositories of dentine-secreting odontoblasts, and pulp is also the source of nourishment to the dentine. Both are removed from the tooth, and so is the capacity for dentine regeneration. Furthermore, resorption is enhanced owing to the surgical trauma to the alveodental ligament during laminar preparation. Triggers for laminar resorption cannot be revoked, and repeated stimuli could be cumulative. Patients and surgeons must therefore be prepared for nonpermanent visual restoration with the OOKP, as in other KPros.