In the last article, I considered some of the general thought processes we need to go through before deciding whether or not to regenerate periodontal tissue in a previously diseased mouth with a non-responding tooth site.
Now I want to go into more detail about the specific nature of the process involved in successfully restoring the lost tissue. At this point I think it is pertinent to distinguish between guided bone regeneration (GBR) and periodontal regeneration (GTR). The former is a much simpler process because it involves only one tissue type. Secondly, assuming you can adequately cover the area with soft tissue during the healing phase, it is less susceptible to bacterial ingress than a relatively open healing periodontal site.
Periodontal regeneration is a highly complex process involving several tissue types that require ideal conditions as a prerequisite to regenerating. For the sporty amongst you, it is like choosing the right team players in the right positions who can then perform over the full length of a match to achieve the desired outcome, victory. Choose the wrong team and have adverse weather conditions and you are doomed to failure. For the literary amongst you, it order is words the wrong getting. You will simply not understand the message and fail to achieve the desired result, learning and wisdom.
The essential prerequisites for successful periodontal regeneration are:
1. A healthy clean mouth in a motivated patient who is willing to afford the necessary care where no better alternatives exist.
2. The exclusion of unwanted tissues. The concept of GTR was originally proposed in 1976 by Melcher, who believed the type of healing that occurred after periodontal surgery is determined by the cells that first repopulate the root surface.
Studies by Nyman et al and Gottlow et al suggest that the cells necessary for the regeneration of cementum, alveolar bone and periodontal ligament (PDL) are probably located in the PDL. A surgical procedure to prevent the apical migration of the epithelium (and hence the formation of a long junctional epithelium) from the surgical flap will allow the formation of a new attachment apparatus. In order to achieve this, a membrane is placed underneath the surgical flap to prevent the ingress of epithelial cells. Treatment of the first human tooth using the principle of GTR was reported by Nyman et al in 1982. After elevation of the surgical flap and root planing of the diseased tooth surface, a cellulose filter was placed over the defect and beneath the flap. After three months, histologic examination showed new cementum with inserting collagen fibres that extended coronally 5mm from the apical area of root planning. The Holy Grail.
We have considered the exclusion of unwanted tissue types in favour of cells from the periodontal ligament by covering the area with a physical barrier membrane. The membrane is placed over the defect and beneath the surgical flap to exclude epithelial cells. The choice of membrane is very important. Nyman, in his original human study, used a cellulose Millipore filter. Gottlow in 1984 used expanded polytetrafluoroethylene (ePTFE). These materials were chosen because they allowed the passage of liquid and nutrients to pass through but prevent the passage of cells. They were not originally designed for dental use. Since then there has been a considerable development in the membranes available for both GTR and GBR.
Membranes are divided into two basic types:
• Non-resorbable, e.g. ePTFE
• Resorbable, e.g. collagen, polylactic acid, polyglycolic acid.
So the desired properties for the membranes are:
• Tissue integration. The membrane must integrate with the surrounding tissue, thereby stabilising it and allowing it to protect the underlying healing and regenerating tissue. The membrane must protect the tissue and prevent micromovements that will result in the formation of connective tissue and not regeneration
• Cell occlusivity. The membrane must prevent the ingress of unwanted cells into the regenerating site, allowing the desired tissue types to form
• Clinical manageability. Regeneration procedures are often fiddly. It is essential to be able to place the membranes in such a way that they perform their desired function over a period of time. They must be accurately and stably placed and difficulty in their handling will potentially result in them failing to perform their task
• Spacemaking. The membranes must allow space for the new tissue to form. Collapse of the membrane, particularly in the early stages, will exclude the formation of new tissue with the resultant lack of regeneration
• Biocompatability. The membrane must be inert and not allow unwanted inflammatory or immune responses to interfere with the regeneration process.
A final desirable feature is that of resorbability. A non-resorbable membrane will require a second surgical procedure to allow its removal. This results in a second surgical procedure for the patient, added financial cost and resultant potential complications. Additionally, should a non-resorbable membrane become exposed during the healing phase then its removal is absolutely essential with the resultant failure to achieve regeneration. Resorbable membranes are more forgiving. Exposure does not necessitate removal and some regeneration, although a lesser amount will still potentially occur.
Some personal thoughts on membranes: I prefer to use resorbable membranes as they are more forgiving and avoid the need for a second surgical procedure. Some membranes are springy (have memory) and as a result can cause the sutured surgical flap to spring open. This is clearly undesirable, so I prefer membranes without memory. Finally, derivation of the membrane must be considered. Some membranes are derived from animal tendons and so moral, ethical and religious sensibilities must be taken into account before using them. Thoroughly consent your patients.