Results - Discussion - References.
Postoperative healing after insertion of the membrane was uneventful in all dogs except two. One dog showed necrosis of all four sites on the palate, whereas another dog showed necrosis on one side of the palate. New membranes were inserted into the second and fourth rugae posterior to the canine using the same surgical techniques described in the Material and Methods section, and subsequent healing was uneventful in those dogs. Evaluation of these later-placed samples were not different, so they were combined with the others. Histologic Analysis.
Membrane degradation rates were variable at different time periods and among dogs within the same time period. Six samples were unreadable, but their absence did not significantly affect the results. Scores ranged from 1 to 2 for all membranes at the 1-month time period. Scores ranged from 2 to 3 for all membranes at the 2-month time period, except for one A-H membrane that seemed to be intact and was given a score of 0. All membranes were given a score of 3 to 4 at both the 3 month and 4 month time periods, indicating almost total degradation after 3 months.
Blood vessel penetration varied among the samples. Blood vessels were found to be abundant in one of the BG samples at 3 months. Only two samples showed any signs of inflammation. BioGide.
The BG samples showed slight to moderate degradation at 1 month after insertion. Blood vessels ranged from none to moderate. No inflammation or giant cells were found. The BG samples at 2 months showed slight to moderate degradation. Blood vessels ranged from slight to moderate, whereas only slight inflammation was found in one sample. The BG samples at 3 months showed severe degradation. No inflammation was found in any samples. Blood vessels were found to be abundant in one of the BG samples at 3 months. BG samples at 4 months revealed severe degradation to completely absent. Blood vessels ranged from none to moderate, and no inflammation was found. AlloDerm Human-Derived.
The A-H samples showed slight to moderate degradation at 1 month. Blood vessels ranged from slight to moderate, whereas no inflammation was found in any of the samples. The A-H samples at 2 months ranged from intact and easily identifiable to severe degradation. No inflammation was found. Blood vessels ranged from none to moderate amounts. The A-H samples at 3 and 4 months ranged from severe degradation to absent. No inflammation was found. Blood vessels ranged from none to moderate. AlloDerm Porcine-Derived.
A-P samples showed slight to moderate degradation at 1 month. Slight inflammation was found in one sample. Blood vessels ranged from slight to moderate. A-P samples revealed moderate to severe degradation at 2 months. No inflammation was found with only a slight amount of blood vessels detected. A-P samples showed severe degradation to not identifiable at 3 and 4 months. No inflammation was seen. Blood vessels ranged from none to moderate. Statistical Analysis.
Statistical analysis was not performed. The n was too low to perform any meaningful statistical analysis, and this study was intended to be a descriptive study. DISCUSSION.
One of the pivotal issues concerning GTR and GBR is how long the barrier should stay in place. The amplifying divisions of periodontal ligament cells may be complete at 21 days47; how long these cells need to be protected after this has not been determined. Computer-assisted densitometric image analysis and clinical probing correlate weakly at 3 months and still only moderately at 12 months. Bragger et al. considered that all alveolar bone adjacent to sites exposed to GTR demonstrated a slow consolidation of the tissues represented by delayed mineralization compared with the changes in probing attachment levels. Sigurdsson et al41 used ePTFE membranes and showed that dogs produce no regeneration at 3 weeks, whereas at 8 weeks, 75% of the bone has repaired together with 40% of the cementum. If collagen barriers are completely resorbed before day 30, neocementum can be found in the healing area, but no new bone. However, 10 days duration seems long enough to avoid apical migration of the epithelium.
The collagen membranes used in this experiment have different characteristics, but similar purported resorption rates. Different animal models surely have an influence on the speed of resorption. Periodontal healing rates have not been classified among potential models, and the effects of their various metabolisms are still greatly unknown. This might explain why the polylactic acid membrane used by Gottlow in monkeys was still intact at 3 months and was considerably degraded in the rabbit model after the same length of time. It is quite possible that the collagen barriers studied in this project would not resorb as quickly in humans. Therefore, one needs to be careful when applying data found in this project to humans.
The length of time the membrane must stay in place is estimated very differently, depending on which materials researchers are utilizing. Because the cell-mediated breakdown of this material produces only a slight inflammatory reaction, if at all, there seems to be no contraindication to having a very slow biodegradation. However, clinical and histologic evaluations as those described above seem to demonstrate that premature removal or dissolution can be detrimental to the formation of cementum and/or bone.
Because research on bioresorbable membranes is in constant progress, it is often difficult to compare results with an identical product. Research concerning collagen membranes involves materials from many different origins. Apparently not only the degree of cross-linkage is important, but also the percent of collagen in the initial solution. Kodama et al49 studied the effects of three concentrations of atelocollagen and found that the highest concentration produced the best results. When freeze-dried cross-linked bovine collagen was tested by Hyder et al, it was found to be totally dissolved in bacterial collagenase 5 times slower than non–cross-linked collagen. Modifications of collagen membranes could include more crosslinking to slow down resorption rates.
Suggestions for future studies include evaluation of additional types of collagen membranes. A different model system that mimics the human in healing rates would provide better data. Evaluation with something that marks the membrane and truly distinguishes it from the surrounding tissues would make identification of the membrane easier.REFERENCES.
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