Tosun T*, Stellini E**, Mazzoleni S**, Dağtekin G***, Favero GA**

Department of *Oral Implantology, Faculty of Dentistry, University of Istanbul, Turkey; Department of **Pedodontics, University of Padua, Italy; Department of ***Biostatistic and Public Health, Faculty of Medicine, University of Istanbul, Turkey

Key words: Implants, Guided bone regeneration, Bone augmentation

ABSTRACT

One of the major limits of the osseointegrated implant treatment is an insufficient bone quantity as an adequate volume of healthy bone should be available at possible recipient sites to expect a predictable long-term prognosis. When the analysis reveals that the anatomy of the alveolar ridge is insufficient at desired implant locations reconstructive surgery is needed . One augmentation technique is based on the principle of guided tissue regeneration using polytetrafluoroethylene ( PTFE ) barrier membranes, which was initially developed for periodontal regeneration.

There has been used GBR technique with 71 Guided Tissue Augmentation Material (GTAM) membranes in conjunction with 110 osseointegrated implants at the Dental Clinic of the University of Padua with the follow-up time from 3 to 0 years. The results indicate that guided bone regeneration is a recommendable technique for the treatment of extremely atrophied jaws with the osseointegrated implants.

A prerequisite for inserting dental implants is that a sufficient amount of bone is available in order to cover all parts of the implant and for the implant to support a prosthetic construction in a long term. In fact one of the main restrictive factors of osseointegrated implant therapy is the unfavorable anatomical condition of the edentulous bone crest.

The bone volume required for implant installment is at least 7mm vertically and 4mm in thickness.

But after tooth loss, alveolar ridge resorbtion often results in much smaller dimensions. Several authors suggested autologous bone grafting techniques, use of hydroxyapatite or tricalcium phosphate to permit osseointegrated implant insertion when anatomical conditions were not acceptable (1,2,8,19,20,21).

Autologous bone grafting therapy implies very invasive surgery to get tissue from the iliac ridge and the patient must be hospitalized. Use of alloplastic graft materials instead causes, mostly, the formation of hyper calcified fibrous tissues, thus not required for a future osseointegration (11,23,24).

Although the effectiveness of the guided tissue regeneration technique in the treatment of periodontal defects has been proven by several studies (3,18,22), only recently guided tissue regeneration has been applied to osseointegrated implants. Based on the results of the international research semipermeable membranes are presently used in osseointegrated implants to treat implant dehiscence or prior to fixture installation, into post-extraction sites and to augment bone volume in very thin alveolar crests (4,5,6,7,9,12,13). This procedure has been described by Buser et al. as Guided Bone Regeneration technique (GBR) (10).

The indications of GBR can be divided into two groups:

* the simultaneous approach: use of the technique as an augmentation prior to implant surgery in order to re-establish sufficient amount of bone in the area, which is judged as the upcoming implant site;

* the staged approach: use of the membrane technique in the treatment of localized bone defects around dental implants.

In this study there are described the indications and surgical technique of the applications of membranes in conjunction with implants in the extremely atrophied alveolar crests in order to obtain new bone around implant, and there are given the results of the follow-up from 3 to 0 years with the same technique.

MATERIALS – METHODS

The trial included 64 patients which were treated with 71 PTFE membranes (GoreTex Augmentation Material, W.L.Gore & Ass., Flagstaff, AZ) according to the guided bone regeneration principles in conjunction with osseointegrated dental implants between the years 1990 and 1993. There has been used Oval4 and Oval6 types of GTAM membranes. All patients were in good health, with regard to systemic or local contraindications to surgical treatment. All the surgical procedure has been made by one surgeon (G.A.Favero).

The patients were divided in two groups regarding the implant type, and each group into three subdivisions according the defect type and jaw:

The first group consist 30 patients, treated with 44 Branemark implants (Nobelpharma AB, Gothenburg, Sweden). The subdivisions of the first group are as follow :

I- periimplant fenestrations: 6 patients, 3 males and 3 females, ranging in age from 21 to 61 (average 4514.4), with 7 implants.

II- periimplant dehiscences on lower jaw :10 *patients, 5 males and 5 females, with ranging age from 35 to 57 ( mean 42.2±7.61 ) treated with 13 implants.

III- periimplant dehiscences on upper jaw : 15 *patients, 6 males and 9 females, from 35 to 73 years old ( average 48.5 10.2), having 24 implants.

*=In this group one patient had implants with periimplant dehiscences on both jaws. This was taken in consideration in the total calculations.

The second group included 34 patients which were treated totally with 66 Bonefit ITI – two part implants ( Inst. Straumann, Waldenburg, Switzerland ). The subdivisions of the second group are :

I- periimplant fenestrations : 6 patients, 2 males and 4 females, from 27 to 70 years old, with mean age 51±18.0, having 11 implants.

II- periimplant dehiscences on lower jaw : 8* patients, 5 males and 3 females, ranging in age between 14 and 65 years ( mean 46.8±15.2 ) with 13 implants.

III- dehiscences on upper jaw : 22* patients, 13 males and 9 females, ranging in age from 22 to 63 ( average 46.2±12.4 ), treated with 44 implants.

*=In this group one patient had different defect types in different implants; and another patient had both types of defects on the same implants. This has been take in consideration in the total calculations.

After the implant installation and after the removal of the membrane, the bone defects, where amount of implant surface was exposed, were measured by calibrated periodontal probe, in an apicocoronal direction. In the dehiscence type defects these measurements were made from the coronal aspect of the implant head to the bone crest, in the fenestrations along the long axis of the implant.

SURGICAL TECHNIQUE

The procedure to install the implant practically does not differ from the traditional surgery: the bone apical to the residual socket is drilled with special burrs according to the surgical protocol peculiar to the implant system chosen. The recipient site must not be pretapped before implant placement to secure adequate primary stabilization. But if there is very compact bone the use of tapping instrument is essential. An implant placed into an extraction socket or in a very thin crest must be immobile to achieve osseointegration. To cover adequately the recipient site, margins of the membrane should be extended at least 3mm beyond the border of bony defect to prevent fibro-epithelial ingrowth between membrane and bone tissue. Not to underestimate is the risk of ischemia of the mucosal flap which may result in retraction or necrosis of the flap and early exposure of the membrane. The more extended the material surface, the more affected the overlying mucosa. Therefore overlapping must not exceed 3mm beyond the defect margins. When placing membranes close to natural teeth 1-2mm must be left between material and tooth to enhance healing of the periodontal tissue. Prior to positioning the GTAM it must be removed completely soft tissues from the bone surface to prevent regeneration of the granulation tissues. The defect or space must be filled with a blood clot before wound healing can occur. In the cases with poor blood supply and where the coagulum is not sufficient it would be advantageous to decorticate the compact bone with around burr to increase fluid rate.

Initial stabilization of the membrane is important for the wound healing. Normally, material stability can be achieved by tucking the material under the periosteum or by anchoring it with the cover screw. The method used to maintain space in this study, is the use of titanium mini screws (Memfix, Inst. Straumann, Waldenburg, Switzerland) inserting them under the membrane. In some cases, same screws has been used to anchor the margins of the membrane to the adjacent bone.

To optimize post-operative healing, regardless to defect type, every attempt should be made to achieve primary closure of the flap over the material. This may require releasing of the periosteum to enhance the elasticity of the flap. Mattress, either vertical or horizontal are the suture of choice. Post-operative antibiotic therapy is indicated for a period of 7-10 days with 0.12% chlorhexidine rinse twice a day.

In order to eliminate the potential for long-term complications in the oral environment, membrane removal is recommended. Removal times ranging from 1 to 9 months have been reported. When a dental implant is involved, removal of the membrane as a part of second stage surgery seems logical. So in this study the GTAM’s were removed in the third month on the lower jaw and in the sixth month on the upper jaw.

STATISTICAL ANALYSIS

The range of age between groups was tested by using Student ‘s –t test. The same test was used also for statistical difference between first and second surgery on periimplant bone defects (dehiscences). Regarding fenestrations, there were used non-parametric tests. The Wilcoxon rank- sum test was used in testing of the differences of the means between the first and second surgery measurements for each group; Mann-Whitney U test was used for the implant system groups.

RESULTS

The range of age between groups and subdivisions was found to be insignificant (p>0.05).

The both types of bone defects were significantly (p<0.001) reduced in size by the membrane covering, compared to the initial conditions of the same sites.

There was no statistical differences between two implant systems (p>0.05), and also between upper and lower jaw results (p>0.05), except ITI Bonefit implants on dehiscences, with upper jaw’s significant new bone grown difference (p<0.05), which could be explained by different metabolic activity of the jaws.

Any of the 111 implants has been removed during the three year period. Unique problem observed was early exposure of the membranes, noticed on the 25 of 71 GTAM’s with 35.21% .

Implant System	n. of implants	Mean SD	Mean  SD ( in mm )
ITI Bonefit	n=11	2.23 0.79	0.32  0.25
Branemark	n=7	3.38  0.63	0.64  0.75

Fenestration measurements results: Differences between 1st. and 2nd. surgery on both implant systems are significant (ITI= p<0.01 ; Branemark= p<0.05 ; Wilcoxon-t). Difference between implant systems are insignificant (p>0.05 ; Mann-Whitney U test ).

Implant System		n. of implants	Mean ± SD	Mean  SD (in mm)
ITI Bonefit	upper jaw	n=44	3.23 ± 0.73	1.19  0.93
ITI Bonefit	lower jaw	n=13	3.77 ± 0.60	1.81  1.1
Branemark		n=24	3.98  0.91	1.40  0.93
Branemark	lower jaw	n=13	3.69 0.93	1.35  0.88

Dehiscence measurement results: Difference between 1st. and 2nd. surgery are statistically significant (p<0.001 for all jaws ; Student-t test ). Difference between implant systems on both jaws are insignificant (p>0.05 ; Student-t test ).

	n. of implants	Mean  SD (in mm)
upper jaw	n=24	1.40  0.93
lower jaw	n=13	1.35  0.88

Comparison of Branemark dehiscence results between upper and lower jaws: There is no statistically significant difference (p>0.05 ; Student-t test ).

		Mean  SD ( in mm )
upper jaw	n=44	1.19  0.93
lower jaw	n=13	1.81 1.1

Comparison of ITI Bonefit dehiscence results between upper and lower jaws: There is significant difference (p<0.05 ; Student-t ).

DISCUSSION

A substantial amount of information exist regarding the use of the Guided Tissue Regeneration concept in the treatment of advanced periodontal lesions (3,18,22). The use of an osteopromotive membrane technique in the field of oral implantology, aimed at exclusive creation of bone tissue, is a natural extension of the former technique (Guided Bone Regeneration)(10) . The results reported by several authors (4,5,7,9,10,12,13,14,15,16)with GBR to achieve augmentation of edentulous atrophic ridges in conjunction with implants are encouraging, and our results are in agreement with this studies. In this study it has been found significant difference on bone grown with membrane covering. So it seems that most of the contraindicated cases because of inadequate bone volume, would be successfully treated with screw type endoessous implants in combination with GBR. This study has demonstrated any statistical difference between two different implant systems which were proven osseointegrated with several studies by the international research.

So it would be recommendable use of the some scientifically proven osseointegrated implant systems for applications in the GBR technique.

However, this type of treatment has been limited to very small areas and the number of cases reported in the literature and long-term results are still to limited (7,13,15). In particular, some questions are still to be answered: which is the best method and material to be used in order to maintain the right distance between the membrane and the underlying bone tissue? Previous experience(14,16) with dehiscence defects have demonstrated a tendency for the material to collapse against the implant surface. Thus in the cases with a large space between implant and bony defect it should be filled with some augmentation material like autologous bone graft from retromolar area or demineralized human bone, or titanium mini-screws to prevent collapse of the GTAM. In this study the former one has been recommended as a simple and effective method for this aim and also to anchor the borders of GTAM to the bone. The hydroxyapatite is not indicated in this cases because of its impossibility to integrate with implants and very slow resorption capability.

Another problem to be solved is the early exposure tendency of the membrane(15,16). No studies have been reported in the literature so far to determine the exact time required to achieve complete mineralization of the new formed bone. Even the ideal quality and ability to bear the occlusal load by the regenerated supporting periimplant tissues are not known(6,13).

Nevertheless, both experimental and clinical data strongly support the potential of the membrane technique in the treatment of localized bone defects in conjunction with dental implants.

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