Coral
Scientific Name(s): Phylum Coelenterata (Cnidaria)
Common Name(s): Coral
Medically reviewed by Drugs.com. Last updated on Aug 1, 2022.
Clinical Overview
Use
Coral is used in cosmetic and reconstructive surgery (eg, bone graft surgery, maxillofacial surgery) and as a substrate for new bone growth. There are limited, relatively older studies available; larger quality studies are required to support use for any indication.
Dosing
Coral is implanted, not administered as a drug; therefore, there is no specific dose.
Contraindications
Contraindications have not been identified.
Pregnancy/Lactation
Avoid use. Information regarding safety and efficacy in pregnancy and lactation is lacking.
Interactions
None well documented.
Adverse Reactions
Adverse reactions from coral have not been reported.
Toxicology
No data.
Source
Corals are a broad group of marine invertebrate animals (phylum Coelenterata) that deposit a mineral skeleton as they grow, eventually producing coral reefs. Corals used for medical application are limited to a select number of genera. Goniopora and Porites appear to be used most commonly. Other commonly used coral genera include Acropora, Lobophyllia, Polyphyllia, Pocillopora, and Foraminifera. Areas of harvest include the Caribbean Sea, the New Caledonia island area of the Pacific Ocean, the Red Sea, the east coast of Africa, the Gulf of Thailand, the coast of Hainan Island, and the coastline of Australia.(Chou 2013, Demers 2002)
History
Coral has a history of use as a building material, as cutting tools, and as the basis of jewelry and amulets. It was not until the mid-1980s that its value in surgery was fully recognized. The natural material derived from the matrix of sea coral serves as an effective substrate for the growth of new bone in areas damaged by trauma or requiring reconstruction. Coral may be more durable than bone and appears to eliminate some of the complications inherent in traditional bone graft surgery.(Demers 2002, Jimenez 2016, Loty 1990) The remineralizing ability of coral calcium from fossilized coral sources on teeth has been explored.(Abdelnabi 2020)
Chemistry
Coral polyps absorb calcium ions and carbonic acid present in seawater to produce aragonite crystals of calcium carbonate, representing 97% to 99% of the coral exoskeleton. The remainder is made up of various elements, including magnesium (0.05% to 0.2%), sodium (0.4% to 0.5%), traces of potassium (0.02% to 0.03%), strontium, fluorine, and phosphorus in the phosphate form. The oligoelements in coral are known to play a critical role in the bone mineralization process and in the activation of enzymatic reactions with osteoid cells. Strontium contributes to the mineralization process and protects calcification. Fluorine is present 1.25 to 2.5 times more in coral than in bone, and is thought to help bone formation through its effect on osteoblast proliferation.(Demers 2002)
The main differences between natural coral and bone are the organic content and mineral composition. One-third of bone is made up of organic components compared with 1% to 1.5% of coral. The mineral content of bone is mainly hydroxyapatite and amorphous calcium phosphate associated with calcium carbonate, while coral is essentially calcium carbonate. Most of the elements found in bone can be found in coral, but in different concentrations.(Demers 2002)
Although the structural and mineral composition of coral is very similar to that of bone, coral is not implanted in its natural state. Following its harvest, coral is treated chemically together with heat and high pressure to convert the calcium carbonate matrix to hydroxyapatite (calcium phosphate hydroxide). Hydroxyapatite is the normal mineral portion found in bone.(Choi 2017, Sivakumar 1996)
Similar to hydroxyapatite, dental enamel is also composed of 96% of minerals by weight and generally consists of 20 to 40 nm of hydroxyapatite nanoparticles. Due to their chemical similarities, hydroxyapatite nanoparticles have been considered as an enamel substitute, such that localized enamel repair may be achieved through the use of an analogue compound that may prevent further demineralization.(Abdelnabi 2020)
Uses and Pharmacology
Natural coral has a porous structure that offers a substantial surface exchange area. The size and interconnectivity of the coral pores are critical factors in the rate of coral resorption and in the role of coral in bone regeneration. The pores of the processed coral exoskeletal matrix range from 150 to 600 microns in diameter, with interconnecting pore sizes averaging approximately 260 microns in diameter.(Green 2013, Ripamonti 1992, Zeng 1991) These dimensions are in the range for normal bone, making coral an excellent base for the spread of new bone growth. Sea coral has several advantages over human bone. Coral does not require the surgical removal of a bone matrix from elsewhere in the patient's body (eg, hip) for grafting, it retains its shape well, and it provides a long-lasting matrix that closely resembles natural bone.(Hippolyte 1991, Smith 1989)
In coral, mechanical properties are mainly influenced by the direction and growth of the polyps as well as the porosity of the skeleton. Corals have better mechanical properties in the direction of their growth, but overall, those growing vertically as opposed to horizontally have a better resistance to mechanical strains. Mechanical integrity can be maintained if the appropriate rate of coral resorption is matched to the bone formation rate of each implant site. Goniopora and Porites have an open porosity of 80% and 50%, respectively, resembling that of spongy bone where the pores are interconnected both longitudinally and transversally. This allows for a rapid vascularization as well as the invasion and apposition of newly formed bone. The 3-dimensional structure, porosity, pore interconnections, and composition of commonly used natural coral confer its osteoconductive capacity and make it suitable for hard tissue regeneration. Its osteoconductive capacity allows cell attachment and growth through the scaffold of the material, characteristic of a good support for cells. The initial invasion of coral by blood and bone marrow cells with subsequent vascularization is a determinant factor for bone regeneration. Research has clearly demonstrated that coral is only osteoconductive and is not an osteoinductive material.(Demers 2002)
Coral possesses all the principal properties of an adequate bone graft substitute, except for a lack of osteoinductivity and osteogenesis, which can be provided with the addition of growth factors, such as bone morphogenetic proteins and bone marrow cells. The addition of growth factors or bone marrow cells to coral grafts generally improves bone formation when compared with the implantation of coral alone. Coral scaffolds act as good carriers of growth factors and good supports for cell transplantation onto a bony site. Animal models have shown increased osteogenesis when using an appropriate osteoinductive protein, such as bone morphogenetic protein.(Demers 2002)
Bone graft/implant
Coral has been used clinically as a bone graft substitute to treat a wide range of bone-related problems. The applications tested include for spinal fusion, fracture repair caused by trauma, replacement of harvested iliac bone and treated bone tumors, and filling bone of defects, mainly in periodontal and cranial-maxillofacial areas. Overall, reported results appear satisfactory, with infection rates ranging from 0% to 11%, which is comparable with rates when autologous bone is used for treatment.(Demers 2002)
Clinical data
In a retrospective review, 20 patients with mechanical low back pain consistent with discogenic pain symptomology, each with loss of disc height and disc dehydration consistent with degenerative disc disease on magnetic resonance imaging, received anterior lumbar interbody fusions using a coralline hydroxyapatite bone graft. The mean preoperative disability score of 64% was reduced to 35% at latest follow-up. Clinical success was demonstrated in 16 patients who reported pain relief of 50% or more. The authors concluded that coralline hydroxyapatite performed similarly to autograft and allograft as the anterior component in an instrumented circumferential lumbar fusion model. The major drawback to its use is that it has no osteoinductive properties. The implant is osteoconductive, requiring a large interface directly with the bone in order for fusion to occur.(Thalgott 2002)
Another study showed that natural coral blocks placed in the iliac crest defect resorbed centripetally and were smaller than 50% of their original size, on average, at the end of approximately 2 years. None of the coral blocks resorbed completely. Coral served as a scaffold for soft tissue and to some extent for bone ingrowth, but the original form of the iliac crest was not achieved.(Vuola 2000)
In a small study of 11 patients with infrabony defects, bone defects healed rapidly following reconstruction with coral microgranules. Biopsies at 8 and 18 months showed good bone formation around the coral particles.(Issahakian 1989)
One study proposes that the method of particulate coral hydroxyapatite sheltered by titanium mesh is a promising solution in handling alveolar bone augmentation failure. However, more cases are needed for further research to form an efficient treatment procedure.(Zhou 2018)
Remineralization of tooth enamel
Experimental data
An ex vivo study using sound enamel disc specimens obtained from 35 extracted human molars demonstrated that the topical application of coral calcium gel significantly improved calcium remineralization compared to untreated controls using an artificial caries demineralization model. Specifically, the specimens that received 20% coral calcium alone or combined with argon laser exhibited 48.64% and 47.49% remineralization, respectively, compared to 7.26% for controls (P<0.001 for each comparison). These remineralization rates were also significantly higher than the other 7 test groups: coral calcium 10% or 30% alone or combined with argon laser, or coral calcium 10%, 20%, or 30% combined with hydroxyapatite (P<0.001 for each). Remineralization rates ranged from 33.04% to 39.06% for the other 7 test groups.(Abdelnabi 2020)
Dosing
Coral is implanted and not administered as a drug; therefore, there is no specific dose.
Pregnancy / Lactation
Information regarding safety and efficacy in pregnancy and lactation is lacking.
Interactions
None well documented.
Adverse Reactions
Infection rates are comparable with rates when autologous bone is used for treatment. Coral has been used clinically as a bone graft substitute to treat a wide range of bone-related problems. The applications tested include for spinal fusion, fracture repair caused by trauma, replacement of harvested iliac bone and treated bone tumors, and filling bone of defects, mainly in periodontal and cranial-maxillofacial areas. Overall, reported results appear satisfactory, with infection rates ranging from 0% to 11%, which is comparable with rates when autologous bone is used for treatment.(Demers 2002)
Toxicology
A 6- to 24-month follow-up of patients who received coral implants showed good tolerability and no deleterious host responses.(Zeng 1991) Data are not sufficient to confirm the benefit of coral products in assisting bone growth in severely damaged weight-bearing bones.
No immunologic or giant cell reaction has been reported surrounding bulk implants. The implants are initially mechanically weaker than the host bone, but with host tissue invasion, the strength of the implant increases proportionally with the amount of tissue ingrowth. From the mid-1980s to the late 90s, bulk implants of coralline hydroxyapatite have been used successfully to reconstruct metaphysical defects, but they are not recommended for comminuted diaphyseal defects because of incomplete incorporation and a lack of remodeling, which compromises the ultimate mechanical strength of the diaphysis. The poor initial strength and nonconforming handling properties of coralline implants also constitute a disadvantage with respect to their use as cortical diaphyseal implants.(Cornell 1998)
References
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