Response of regenerative tissues to plaque: a histological study in monkeys

Second Attempt of Guided Tissue Regeneration on a Previous Successfully Grafted Site with Periodontal Breakdown-A 5-Year Follow-up

Guided tissue regeneration (GTR) has been proven to promote attachment and regeneration of periodontal tissue. However, there is a 20 to 40% incidence of attachment loss on regenerated attachments reported in the literature. To my knowledge, this is the first case report on a second attempt in GTR on a previous successful grafted site with clinical attachment loss. A healthy 17-year-old Chinese male patient had GTR performed with xenograft particles and bovine resorbable membrane on his root-canal treated, fused upper right lateral incisor and upper right canine (#12-#13) in 2007. Probing depth on the mid-palatal region of #12-#13 was reduced to 4 mm and maintained for the next 4 years. But in the fifth year, probing depth increased to 11 mm with no endodontic symptoms, and a second attempt of GTR using the same materials was carried out. The probing depth at the surgical site was reduced to 4 mm and successfully maintained for another 5 years. Irregular maintenance and the presence of plaque retentive factor could have caused the clinical attachment loss on #12-#13. This case shows it is possible to attempt GTR on a previous successfully grafted site. GTR did not increase tissue resistance against periodontal breakdown. Hence, proper maintenance planning for GTR sites is important to prevent periodontal breakdown.

Do periodontal defects affect periodontal inflammation and destruction? Histological/microbiological changes and gene expression profiles of a pilot study in beagle dogs

BACKGROUND

The present study focused on the inflammatory disease progress after periodontal defect induction and aimed to specifically determine periodontal tissue responses following dental plaque accumulation by ligatures on a site with/without standardized periodontal defect induction.

METHODS

After 1 month from extraction of the adjacent teeth, semi-circumferential defects were surgically created in the unilateral second and fourth premolars (test group), whereas no defects were being induced at the contralateral sites (control group). One week later, silk was used to ligate the tooth cervix at both sites to encourage the accumulation of dental plaque. Four weeks later, the tissue samples were collected for histological/histomorphometric and microarray analysis. Microbiological analysis was performed before defect induction and at ligatures, and after 4 weeks of dental plaque accumulation.

RESULTS

Remarkable inflammation was clinically and histologically observed in both groups after plaque accumulation, and the intrabony type of periodontal defect exaggerated inflammatory cell infiltration into the connective tissue layer. Expression of genes related to inflammation such as IL-1 was highly up-regulated in test sites. However, these inflammatory infiltrations did not invade to a boundary of periodontal ligament and connective tissue attachment in both groups, and histomorphometric results corresponds to these observational results. Bacterial findings also showed no significant differences in detected microbiome compositions between control and test groups at three-time points.

CONCLUSION

Intrabony defect might exaggerate the plaque-induced inflammation in the aspect of inflammatory cell infiltration and the related gene expression, but both dental plaque and the pre-existing periodontal defect negligibly disrupt periodontal attachment and the underlying alveolar bone.

Experimental animal models in periodontology: a review

In periodontal research, animal studies are complementary to in vitro experiments prior to testing new treatments. Animal models should make possible the validation of hypotheses and prove the safety and efficacy of new regenerating approaches using biomaterials, growth factors or stem cells. A review of the literature was carried out by using electronic databases (PubMed, ISI Web of Science). Numerous animal models in different species such as rats, hamsters, rabbits, ferrets, canines and primates have been used for modeling human periodontal diseases and treatments. However, both the anatomy and physiopathology of animals are different from those of humans, making difficult the evaluation of new therapies. Experimental models have been developed in order to reproduce major periodontal diseases (gingivitis, periodontitis), their pathogenesis and to investigate new surgical techniques. The aim of this review is to define the most pertinent animal models for periodontal research depending on the hypothesis and expected results.

Long-term stability of periodontal conditions achieved following guided tissue regeneration with bioresorbable membranes: case series results after 6-7 years

OBJECTIVES

To evaluate the results of guided tissue regeneration (GTR) treatment of intrabony defects with bioresorbable membranes after 6-7 years, and to disclose factors that may influence the long-term outcome of the treatment.

METHODS

Twenty-five defects in 19 patients were treated by means of polylactic acid/citric acid ester copolymer bioresorbable membranes. At baseline and after 1 and 6-7 years, the following parameters were recorded: (1) probing pocket depth (PPD), (2) gingival recession (REC), (3) probing attachment level (PAL)=PPD+REC, (4) presence/absence of plaque (PI), (5) presence/absence of bleeding on probing (BOP). Smoking habits and frequency of dental-control visits were also recorded. Significance of differences between categorical variables was evaluated with McNemar's test, and between numerical variables with the t-test for paired observations. Generalized linear models were constructed to evaluate the influence of various factors on PAL gain and PPD changes from 1 to 6-7 years. Association of smoking, frequency of dental controls, oral hygiene, and BOP with sites losing > or =2 mm in PAL was evaluated with Fisher's exact test.

RESULTS

At baseline, a mean PPD of 8.7+/-1.1 mm and a mean PAL of 9.8+/-1.5 mm was recorded. Statistically significant clinical improvements were observed at 1 and 6-7 years after GTR treatment. An average residual PPD of 3.8+/-1.1 mm and a mean PAL gain of 3.8+/-1.4 mm were observed after 1 year. After 6-7 years the corresponding values were 4.7+/-1.3 and 3.6+/-1.4 mm, respectively. There were no statistically significant differences between the 1- and the 6-7-year values. At the 6-7-year control, only 16% of the sites had lost > or =2 mm (maximum 3 mm), of the PAL gain obtained 1 year after GTR treatment. None of the sites had lost all of the attachment gained 1 year after treatment. Smoking, frequency of dental controls, oral hygiene, and BOP did not seem to influence the change of PPD and PAL gain, or the stability of PAL gain (i.e. losing PAL or not) from 1 to 6-7 years from treatment.

CONCLUSION

Clinical improvements achieved by GTR treatment of intrabony defects by means of bioresorbable membranes can be maintained on a long-term basis.

Susceptibility of GTR-regenerated periodontal attachment to ligature-induced periodontitis. An experiment in the monkey

AIM

This study aimed to compare the susceptibility of guided tissue regeneration (GTR)-regenerated periodontal attachment to ligature-induced periodontitis with that of the pristine periodontium.

METHODS

Periodontal breakdown was produced in four monkeys by the placement of orthodontic elastics around experimental teeth (test teeth). During a flap operation, the root surfaces were scaled and planed, and a notch indicating the apical termination of scaling and root planing was made in the root surface. Following resection of the crowns and endodontic treatment, an e-PTFE membrane was adapted over the roots. Subsequently, the flaps were sutured to complete closure of the wound (submerged). At membrane removal after 5 weeks, the crowns of the contralateral teeth serving as controls were resected, and the roots treated endodontically during a flap operation. Artificial composite crowns were then placed on both test and control roots. After 3 months of tooth cleaning, cotton floss ligatures were placed passively around both test and control teeth for a period of 6 months. Two weeks later the animals were sacrificed.

RESULTS

Histological analysis demonstrated that the instrumented root surfaces of the test teeth were covered by newly formed cementum of the reparative, cellular, extrinsic and intrinsic fiber type, while the cementum on the controls was mainly acellular extrinsic fiber cementum. Histometric assessments demonstrated that similar attachment loss had occurred on test (1.0+/-0.5 mm) and control roots (1.0+/-0.4 mm) during the 6 months of ligature-induced plaque accumulation.

CONCLUSION

The results indicate that teeth with a periodontal attachment apparatus formed by GTR is not more susceptible to periodontitis than those with a pristine periodontium.

Clinical comparison of bioabsorbable barriers with non-resorbable barriers in guided tissue regeneration in the treatment of human intrabony defects

The purpose of the study was to compare the effects of guided tissue regeneration (GTR) with expanded polytetrafluoroethylene (ePTFE) non-resorbable barriers and polylactic acid bioabsorbable barriers in humans with intrabony defects due to periodontitis. Ten patients presented with 2 intrabony defects each. Mucoperiosteal flaps were performed. One of the defects was randomly assigned for placement of the ePTFE barrier over the roots and alveolar bone and the other defect with placement of the polylactic acid barrier. A minimum of 9 months after barrier placement, surgical reentry was performed. The data were evaluated by the Wilcoxon matched-pairs signed-ranks test and the Fisher exact test. Treatment with both types of barriers produced significant changes from baseline for all parameters, except in the ePTFE group for the amount of bony crest resorption (P = 0.055) and in the polylactic acid group for increased recession (P = 0.109). The results showed no significant differences between the barriers for any parameters: probing depth reduction (polylactic acid 2.60 +/- 1.90, ePTFE 2.80 +/- 1.40; P = 1.000); attachment gain (polylactic acid 1.40 +/- 1.43, ePTFE 1.90 +/- 1.29; P = 0.336); increased recession (polylactic acid 0.80 +/- 1.40, ePTFE 1.10 +/- 0.99; P = 0.531); amount of vertical bone fill (polylactic acid 1.60 +/- 1.84, ePTFE 2.00 +/- 2.49; P = 0.984); bony crest resorption (polylactic acid -1.30 +/- 1.06, ePTFE -1.30 +/- 1.63; P = 1.000); depth of bony defect reduction (polylactic acid 2.90 +/- 1.20, ePTFE 3.30 +/- 1.70; P = 0.750); width of bony defect reduction (polylactic acid 2.20 +/- 1.23, ePTFE 2.20 +/- 1.23; P = 0.875); or volumetric changes (polylactic acid 33.50 +/- 19.70 microl, ePTFE 34.00 +/- 18.40 microl; P = 0.750).

The use of biologic response modifiers in human clinical trials

To optimize regeneration of the periodontium, new cementum, periodontal ligament, and bone must be formed. Conventional periodontal surgery decreases the likelihood of continued progressive periodontal disease however, it does not lead to significant periodontal regeneration. In vitro studies have identified a class of biologic response modifiers loosely referred to as growth factors, which stimulate the cellular events of tissue regeneration. The most promising are mitogenic and differentiation factors. Based on promising results from animal studies, the application of growth factors to predictably stimulate periodontal regeneration is entering human clinical trials. This manuscript deals with several important considerations in testing biologic response modifiers in humans. Suggestions are made regarding the following parameters: 1) selection of the unit of measurement; 2) patient and lesion selection; 3) identification of controls; 4) selection of outcome parameters; 5) statistical approach; and 6) considerations in treatment regimens.

Resorption rates of 2 commercially available bioresorbable membranes. A histomorphometric study in a rabbit model

The respective resorption rates of recently commercialized collagen versus polylactic acid-citric acid ester membranes were compared. 16 rabbits were implanted with 2 mm x 4 mm pieces of membrane of both types in the alveolar mucosa just apically to the incisors on either side of the mouth. 1 animal was sacrificed on day 0, just after the operation. The others were sacrificed at 1, 2, 3, 5, 7, 9 and 12 weeks. The specimens were prepared for histologic examination. Observations showed that the cross-linked collagen membranes induced severe inflammation and were resorbed within 2 weeks. The polylactic acid-citric acid ester polymer barriers produced a much more moderate infiltrate and were still not totally resorbed at 12 weeks. Although resorption rates in the rabbit may not be similar to those observed in humans, it seems that the durability of the polymer barrier is more adequate for guided tissue regeneration than the cross-linked collagen.

The dynamics of microbial colonization of barrier membranes for guided tissue regeneration

The microbial colonization of expanded polytetrafluoroethylene membrane by putative periodontopathogens at 3 minutes of intraoral manipulation was determined in 42 patients with 42 mandibular posterior two- to three-wall defects. Twenty patients exhibited no periodontal pockets of > or = 5 mm, other than the study site, and low levels of pathogens (group A). Twenty-two patients revealed multiple periodontal pockets of 5 mm or more and numerous pathogens (group B). Within the preceding 3 months of regenerative surgery, group A patients had received apically positioned flap surgery with osseous recontouring (except for the study site), and group B patients had been enrolled in a non-surgical maintenance program. The subgingival microbiota was examined prior to regenerative therapy, and the membrane microbiota was examined at 3 minutes and at the time of removal at 6 weeks by culture, DNA probes, and phase-contrast microscopy. The mean initial defect depth was 7.4 mm for group A and 7.2 mm for group B. At 6 months, the difference in mean clinical attachment gain was statistically significant (P < 0.001; group A: 3.4 mm; group B: 1.4 mm). At 3 minutes, putative pathogens were detected in seven (16.7%) membranes in group B (group Binfected), and the associated sites gained only 0.6 mm in clinical attachment at 6 months. Clinical attachment gain was modeled as a linear function of the explanatory variables (r2 = 86%). The presence of Porphyromonas gingivalis detected by DNA probe at 3 minutes was associated with 1.5 mm less expected gain (P = 0.0002). Total microbial counts and the percentage of Peptostreptococcus micros and Capnocytophaga species at baseline, and of motile rods on the membrane surface facing the gingiva at 6 weeks, were statistically significant negative predictors of clinical attachment. For each week the membrane remained covered, an additional 0.5 mm gain could be expected (P = 0.002); and for every 10 sites that exhibited bleeding on probing, the clinical attachment gain was 0.6 mm less at the site of regeneration (P < 0.0001). The present results showed that putative pathogens may colonize membranes within 3 minutes of intraoral manipulation. The patient group treated with periodontal osseous surgery revealed the lowest levels of periodontal pathogens in the membranes and exhibited the most gain in clinical attachment.