Ligaplants-Tissue Engineered Ligaments in Implant Dentistry

INTRODUCTION

Dental implants have become a popular and effective way to replace missing teeth and have changed the face of dentistry over the last 25 years. The boom in implant dentistry is attributed to a combination of various reasons like prolonged life span of aging individuals, failures associated with removable and fixed prostheses, advantages and predictable outcomes associated with use of implants.

Periodontal ligament is also known as desmodont, gomphosis, pericementum, dental-periosteum, alveolodental ligament or periodontal membrane. Apart from anchoring of tooth, PDL progenitor cells help in alveolar bone formation and remodeling. Now, implants are retained in oral cavity by virtue of osseointegration i.e direct contact between living bone and the surface of a load carrying implant at histological level. Osseointegrated implants are the ones which are currently in use because of their long term survival rate but they too pose problems as they lack periodontal ligament. Many strategies have been experimented to improve the osseointegrative property of the implant, for example -

• surface modification to improve the mechanical, physical, and chemical characteristics of the implant
• modification of shape and design of implant
• alteration of surface topography
• nanostructured surface coatings or
• addition of growth factors to implant surface.

Recent scientific research developed an implant with PDL, achieved by combination of the PDL cells with implant biomaterial and named it as LIGAPLANTS. There is very less literature available on Ligaplants. Keeping this in mind we reviewed the properties, procedure of obtaining ligaplants, advantages and disadvantages.

LIGAPLANTS

The combination of PDL cells with implant biomaterial is known as Ligaplants. Currently, replacement of lost teeth is done without considering the PDL and implants of inert biomaterial are directly inserted into jawbones. Localized bone loss around the implant fixture represents a clinical challenge especially in the cases of gingival recession where it may require further surgical interventions due to its modified tissue architecture. So, to overcome this problem, a implant system with tissue-inducing properties might be useful. Technically, implants with PDL maybe installed in the extraction socket of the missing tooth, thereby facilitating the surgical procedure. Natural implant anchoring might also be compatible with further growth and development.

Conclusively, ligaplants have the capacity to induce the formation of the new bone, when placed in sites associated with large periodontal bone defects. Implants with PDL are placed in the extraction socket of the missing tooth, thereby facilitating the surgical procedure. Natural implant anchoring might also be compatible with further growth and development of the alveolar bone housing, and it may allow tooth movements during orthodontic therapy. Ligaplants have the capacity to induce the formation of new bone, when placed in sites associated with large periodontal defects.2,3

PROPERTIES OF LIGAPLANTS

1. PDL cells distributes forces, elicited during masticatory function and other contact movements to the alveolar process via the alveolar bone proper.
2. It gives the tooth some movement in the socket by acting as a shock absorber.Proprioception is also provided by ligaplants.
3. It is also a home to vital cells such as osteoblasts, osteoclasts, fibroblasts, cementoblasts, and most importantly undifferentiated stem cells which are osteoconductive in nature.

PROCEDURE OF OBTAINING LIGAPLANTS

Tooth transplantation with double PDL stimulation is one of the best examples of its healing capacity. The donor tooth is extracted and immediately replanted in its original alveolus 14 days before transplantation This deliberate trauma triggers a healing process within the PDL, which includes cell proliferation and differentiation. The in vivo cell culture reaches its peak of activity after 14 days. Now, the transplantation of the tooth can be performed with millions of cells full activity attached to its root by new Sharpey’s fibres.

A similar cell culture around an artificial root using tissue engineering techniques is now used. To obtain ligaplants there are 3 steps-

1. Temperature responsive culture dishes preparation: Onto polystyrene culture dishes, N-isopropylacylamide monomer in 2-propanalol solution is spread. Then these dishes are subjected to electron beam irradiation with an Area Beam Electron Processing System. The dishes are then rinsed with cold water to remove ungrafted monomer and then sterilized with ethylene oxide.
2. Cell culture and cells: From an extracted tooth, human periodontal ligament cells are isolated. From the middle third of the root periodontal tissue is scraped with a scalpel blade after extraction. The harvested tissue is placed into culture dishes containing = Dulbecco’s modified Eagle’s minimal essential medium, supplemented with 10% fetal bovine serum and 100units/mL of penicillin-streptomycin. Then, these outgrowth cells are cultured to allow attachment of the cells to the dishes in a humidified atmosphere of 5% CO₂ at 37°C for 48 hours . The debris are eliminated by washing the dishes and the medium has to be changed three times per week. To harvest the cell sheet, human periodontal ligament cells are placed on temperature-responsive culture dishes (35 mm in diameter) at a cell density of 1x10⁵ and cultured at 37°C supplemented with 50mg/mL ascorbic acid 2-phosphate,10nM dexamethasone and 10nM ß-glycerophosphate that function as an osteodifferentiation medium.
3. PDL cells culturing in a bioreactor: A hydroxyappatite (HAP) coated titanium pin is placed in a hollow plastic cylinder leaving a gap of 3mm around the pin. Through the gap culture medium is continuously pumped. Single cells suspension, obtained from human, is seeded first into plastic vessels under a flow of growth medium for 18 days.