Guided tissue regeneration with bioresorbable membranes in the treatment of extreme cases of intrabony defects

Introduction

Guided tissue regeneration (GTR) is considered to be one of the most predictable therapeutic approaches for reconstruction of lost periodontal attachment apparatus ^{(Karring et al., 1993)}. The GTR principle implies the use of a barrier membrane for covering the periodontal defects, thus allowing periodontal ligament (PDL) cells to selectively repopulate the detached root surfaces ^{(Nyman et al., 1982} ; ^{Gottlow et al., 1986} ; ^{Karring et al., 1993)}. In most histological and clinical studies on GTR non-bioresorbable barriers which must later be removed at a second surgical procedure have been used ^{(Gottlow et al., 1986} ; ^{Becker et al., 1988} ; ^{Caffesse et al., 1988} ; ^{Pontoriero et al., 1988}, ¹⁹⁹² ; ^{Cortellini et al., 1993)}. The use of non-bioresorbable membranes was often associated with membrane exposure and subsequent bacterial contamination producing inflammation and recession of the gingival margin ^{(Selvig et al., 1990}, ¹⁹⁹² ; ^{Newman, 1993} ; ^{Nowzari and Slots, 1994)}. Removal of the membrane at a second surgical procedure also involves the risk of damaging the newly formed immature tissue ^{(Greenstein and Caton, 1993)}. In order to avoid a second surgery different bioresorbable membranes with similar barrier properties as the non-bioresorbable membranes have been developed ^{(Greenstein and Caton, 1993} ; ^{Lundgren et al., 1994)}. Although animal and clinical studies have demonstrated that similar histological and clinical results can be obtained with non-bioresorbable and bioresorbable membranes, limited information is available concerning the possibilities and limits of GTR therapy with bioresorbable membranes ^{(Caffesse et al., 1994} ; ^{Christgau et al., 1995} ; ^{Cortellini et al., 1996} ; ^{Bouchard et al., 1997} ; ^{Hürzeler et al., 1997)}.

Therefore the aim of this study was to investigate the therapeutical outcomes of GTR therapy with bioresorbable membranes following the treatment of extremely deep intrabony periodontal lesions.

Materials and methods

Ten patients (4 males, 6 females) aged between 35 and 70 years were included in this study and signed informed consent. The criteria for inclusion in the study were : a) no systemic diseases, b) presence of at least one experimental site showing a clinical attachment loss of more than 12 mm associated with vertical bone loss, b) no or moderate mobility at the experimental tooth (mobile teeth were either splinted or included in bridge reconstructions), d) no endodontic problems in the experimental tooth, and e) a high level of oral hygiene (Pl I < 1) ^{(Silness and Löe, 1964)}.

Three months prior to surgery each patient was given thorough oral hygiene instruction, and full mouth supra- and subgingival scaling and root planing under local anaesthesia. The following clinical parameters were assessed by one calibrated investigator at the experimental site one week prior and twelve months after the surgical procedure using a manual periodontal probe (PCP 12, Hu-Friedy, USA) : probing pocket depth (PPD), gingival recession (GR), and probing attachment level (PAL) (^{fig. 1} and ⁷). All measurements were performed at six sites per tooth : mesiovestibular (mb), midvestibular (b), distovestibular (db), mesiolingual (ml), midlingual (l), distolingual (dl). The cemento-enamel junction (CEJ) was used as reference point. In cases where the CEJ was not visible, a restoration margin was used. Only the deepest site per tooth was included in the statistical analysis which was performed with the statistic program SPSS^® for Windows^® using the paired t-test. Bone changes were assessed using conventional radiographs taken with the long cone parallel technique ^{(Sewerin 1990)} (^{fig. 2}, ⁸, ⁹, ¹³, ¹⁴, and ¹⁵).

Surgical procedure

All defects were treated by the same surgeon at the Department of Periodontology, University of the Saarland. Under local anaesthesia, intracrevicular incisions were made and full-thickness mucoperiosteal flaps were raised at the vestibular and oral aspect of the experimental tooth. If necessary, vertical releasing incisions were placed in order to obtain optimal access to the defect. After removal of all granulation tissue, the root surfaces were thoroughly scaled and planed using hand and ultrasonic instruments (^{fig. 3}, ⁴ and ¹⁰). No osseous recontouring was performed. Following defect debridement and rinsing of the wound with sterile saline a bioresorbable barrier membrane (Resolut^®, Gore-Tex, Flagstaff, Arizona, USA) of an appropriate configuration was selected, trimmed and positioned in such a manner that the entire defect and an additional 2-3 mm of the surrounding bone were covered. The membranes were fixed to the neighbouring teeth with resorbable sutures (Dexon^® II, Davis & Geck, Inc., Manati, PR, USA) (^{fig. 5} and ¹¹). Finally the flaps were coronally repositioned and closed with vertical mattress sutures (^{fig. 6} and ¹²) All patients received antibiotics for one week after surgery (amoxicillin 3 x 375 mg/day). A strict infection control programme including rinsing with 0.1 % chlorhexidine twice a day for 8 weeks (Chlorhexamed^®, Blend a Dent, Mainz, Germany) and professional tooth cleaning every second week was carried out during the first 3 months after therapy. The sutures were removed 14 days following surgery. No subgingival intrumentation was performed during the first twelve months after surgery.

Results

At baseline the mean PPD of the selected defects was 12.9 ± 0.9 mm, the mean GR 1.4 ± 0.5 mm and the mean PAL 14.3 ± 0.5 mm (^{table I}). Healing was uneventfully in all cases. No allergic reactions against the membrane material, and neither suppuration nor abscesses were observed. However, exposure of the membrane material was observed in 4 cases within the first 3 weeks after surgery. It appeared that the exposed material disintegrated within a few days after exposure without any adverse reactions.

The clinical measurements 12 months after therapy revealed a significant reduction of probing pocket depth and gain of clinical attachment (^{table II} and ^{fig. 7}). The treated defects presented a mean PPD of 4.2 ± 1.0 mm and mean PAL of 8.9 ± 1.3 mm. The mean gingival recession was 4.7 ± 1.7 mm. The mean gain of PAL was 5.4 ± 1.4 mm and the mean PPD reduction 8.7 ± 0.8 mm. These changes were highly statistically significant (p < 0.0001). Although a radiological bone fill was observed to a ranging degree in all cases, a complete defect fill was never observed (^{fig. 8}, ¹³ and ¹⁵).

Discussion

The results of the present study have demonstrated that GTR periodontal therapy with a bioresorbable membrane (Resolut^®) may result in significant gain (mean 4-5 mm) of new connective tissue attachment in advanced intrabony defects. Bone formation was less conspicuous and varied considerably. The results from this study are comparable with those from other studies with different types of bioresorbable membranes ^{(Laurell et al., 1994} ; ^{Cortellini et al., 1996} ; ^{Becker et al., 1996)}. Most of the studies investigating the clinical outcomes in the treatment of intrabony defects with bioresorbable membranes have obtained a mean gain in PAL between 2.9 and 4.9 mm ^{(Laurell et al., 1994} ; ^{Cortellini et al., 1996} ; ^{Becker et al., 1996)}. Recent results with the Resolut^® bioresorbable membrane have demonstrated a gain in PAL between 2.9 and 4.6 mm ^{(Cortellini et al., 1996} ; ^{Becker et al., 1996)}. The greater gain in PAL observed in the present study may be explained by the very deep initial defect depths. Clinical studies have demonstrated that the PPD reduction and the PAL gain are proportional to the initial defect depth : the deeper the initial defect depth the greater the PPD reduction and PAL gain ^{(Cortellini et al., 1996} ; ^{Florès-de-Jacoby et al., 1994)}.

The most significant benefit of using bioresorbable membranes is the avoidance of the second surgical procedure ^{(Greenstein and Caton, 1993} ; ^{Cortellini et al., 1996)}. Histological and clinical studies have demonstrated that the newly gained immature tissue can be easily compromised as a result of incomplete flap coverage after removal of the non-bioresorbable membrane or due to infection ^{(Selvig et al., 1992} ; ^{Mombelli et al., 1993} ; ^{Tonetti et al., 1993} ; ^{Sander and Karring, 1995)}. These inconveniences might be reduced by the used of bioresorbable membranes. The lack of postoperative complications like complete exfoliation of the membrane or abscesses, as observed in the present study, has also demonstrated the good tissue integration properties of the membrane material. However, it is also very important to point out that although the treated defects displayed an advanced degree of periodontal attachment loss, only patients with a high level of oral hygiene and compliance with the maintenance program were included in the study. A careful patient selection and meticulous plaque control are always essential for the outcomes of any periodontal procedure and especially GTR therapy ^{(Tonetti et al., 1993}, ¹⁹⁹⁵ ; ^{Cortellini et al., 1994)}.

The fact that a complete radiological bone fill was not observed could be explained with a collapse of the membrane into the defect due to flap pressure or the not yet complete mineralization of the newly formed bone or both. The discrepancy observed between the amount of attachment gain and the amount of bone fill has also been reported in other studies ^{(Gottlow et al., 1986} ; ^{Christgau et al., 1995)}. Short-term clinical studies have also shown that radiologic bone changes after GTR therapy are rather difficult to assess ^{(Wenzel et al., 1992} ; ^{Christgau et al., 1995)}. Standardized conventional radiographs seem to be more reliable for the detection of short-term hard tissue changes after regenerative periodontal surgery than more complicated methods, as for example substraction radiographical techniques ^{(Wenzel et al., 1992)}.

In conclusion, the present study has shown that GTR therapy with bioresorbable membranes may lead to significant improvements of clinical attachment levels even in extremely advanced cases of intrabony defects. However, further histological and clinical studies are needed in order to determine the stability of the newly formed attachment and the reasons for the discrepancy between the gain of clinical attachment and the concomitant bone formation.

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