A ten year retrospective study of 616 Brånemark implants in a private practice in Casablanca (Morocco)

Introduction

Restoring edentulous patients with fixed prostheses supported by osseointegrated implants ad modum Brånemark is a well accepted clinical procedure (^{Brånemark et al., 1985}). The technique has been documented extensively in edentulous patients (^{Brånemark et al., 1985} ; ^{Adell et al., 1981} and ¹⁹⁹⁰ ; ^{Cox and Zarb, 1987} ; ^{van Steenberghe et al., 1987} ; ^{Albrektsson et al., 1988} ; ^{Jemt, 1991} ; ^{Worthington et al., 1987}) all over the world with success rates that suggested predictable results if the technique was used properly. Implants have also been used in partially edentulous jaws with comparable success rate (^{Jemt et al., 1989} ; ^{Jemt, 1993} ; ^{van Steenberghe et al., 1990} ; ^{Lekholm et al., 1994} ; ^{Lekholm et al., 1999}). Furthermore, multicenter studies on single-tooth replacement have also shown good results (^{Laney et al., 1994} ; ^{Henry et al., 1996}). However, those results were found in countries advanced in oral health with a population conscious of hygiene, dental care and follow-up to assess whether this technique could be applied.

This study was driven by two goals :

- with an equivalent success rate for another type of population and in a less favorable environment ;

- to assess whether it could be applied with satisfactory results in a private practice.

As a matter of fact, this retrospective study has been conducted in Morocco, a country of 35 millions inhabitants, located in North West Africa, with a very young edentulous population.

Eventhough, no exhaustive epidemiologic studies were done here yet to prove it, there are ample evidence that aggressive periodontitis are more prevalent in Morocco than in any other part of the world. The broad spreading of this disease can be explained by a different microbiota and a lower host resistance. We are hence dealing with a population where prevalence of periodontitis and caries is very high and treatment is often tooth extraction.

So, after a 10 year experience in oral implantology in a private practice, it was relevant to undertake a first evaluation and to study retrospectively the implant survival rate. All the patients included in this study had some type of periodontitis from moderate to severe but no correlation was looked for between survival rate and type of periodontitis.

The primary objective of this retrospective study is the evaluation of the implant survival rate, in a private practice, for this type of population compared to the one of more advanced countries. In order to evaluate implant success, osseointegration should be obtained and also be maintained overtime. ^{Albrektsson et al. (1986)} have described the criteria that should be used to evaluate a success rate :

- absence of mobility ;

- absence of painful symptoms or paresthesias ;

- absence of peri-implant radiolucency during radiographic evaluation ;

- absence of progressive marginal bone loss ;

All these parameters should be maintained overtime.

Material and method

Six hundred and sixteen Brånemark implants (Nobel Biocare^®, Göteborg, Sweden) were placed in 188 patients (86 males and 102 females aged from 17 to 73 years) between Octobre 1991 and December 2000 by the same operator, a periodontist. The patients were either referred to the clinic by their dentist or contacted the clinic directly. Prosthetics was realized by different dentists. All patients had clinical oral examination, periodontal treatment, and periodontal and hygiene reevaluation before implant placement by the same operator.

Clinical examination

Hygiene evaluation : modified Greene and Vermillon index (^{Greene and Vermillon, 1964}) :

- 0 = plaque was absent ;

- 1 = supra-gingival plaque present ;

- 2 = supra-gingival calculus present ;

- 3 = sub-gingival plaque and calculus present.

Eighty-five percent of the patients had an index of 3, 10 % an index of 2 and 5 % and index of 1.

Pocket depth was evaluated on all the remaining teeth with 6 measurements per tooth :

- 20 % of the patients had periodontal pocket depth of 4 mm and less ;

- 55 % had periodontal pocket depth of 4 to 6 mm (moderate periodontitis) ;

- 25 % had periodontal pocket depth of 4 to 8 mm (advanced periodontitis). Among them, 8 % were localized or generalized aggressive periodontitis.

Bleeding on probing (modified Muhlemann index) (^{Muhlemann and Son, 1971}) was done to evaluate the inflammation degree and was notified as absent : 0 ; or present : 1. For the majority of the patients (85 %), bleeding on probing was present.

Mobility was measured with the handgrip of two dental instruments with 0 : no mobility, 1 : mobility of less than 1 mm in a horizontal plane, 2 : more than 1 mm and 3 : mobility both horizontally and vertically.

All these parameters were registered around remaining teeth before and after periodontal treatment, and at every follow-up visit around implants.

Radiologic examination

All patients had a full mouth series of x-rays (14 retroalveolar and 4 bite-wings) before any treatment decision. In addition, a CT scan was always prescribed in mandibular cases and in most of the maxillary cases (^{Swartz et al., 1987a} and ^b).

Occlusal analysis

Study models were done to study the intermaxillary relationship in the antero-posterior and vertical plane. Simulation were often done for the esthetic zones but always in complete maxillary arch to study lip support, smile line and vertical dimension, etc.

In the majority of partial cases and in all the completely edentulous patients (except for overdenture), a surgical guide was used for proper implant positioning.

Periodontal treatment

Before any treatment, all patients had oral hygiene instruction by the surgeon. Scaling and root planing were done when needed. After periodontal reevaluation, pocket of 5 mm and more were treated surgically. The goal was a periodontal health and a strict plaque control before any implant placement.

Implant surgery

A two stage surgical technique was performed as recommended by the Brånemark team. Prophylactic antibiotic therapy was prescribed : 2 g of amoxicilline the night before, followed by 2 g each day for 7 days. For patients who were allergic to penicillin, a combination of spiramycin and metronidazole was prescribed (3 IU of spiramycin and 500 mg of metronidazole each day for 7 days). For postoperative care, a mouthwash with chlorhexidine (0,12 %) was used after each meal. Patients were not allowed to wear their removable prosthesis for 10 to 15 days post-operative. At suture removal the prosthesis were then relieved and relined with soft acrylic to allow for proper healing of the implants.

The patients were then checked once a week until healing of the soft tissues, then once a month until the second stage surgery. The healing period was 3-4 months for the mandible and 6-8 months for the maxilla. No X-rays were taken during the healing period unless really necessary.

The mobility of the implant and lack of pain were tested at stage 2 implant surgery, at final prosthetic installation then at the yearly control if bone loss was noticed. A radiograph was taken at the abutment healing phase to check the bone level, at the final abutment phase to check the proper sitting of the abutment and at the completion of the prosthetic restoration. Another X-ray was taken once a year.

Results

Among the 188 patients, 12 % were completely edentulous, 61 % were partially edentulous and 27 % had only one missing tooth.

442 implants were used for 151 fixed partial rehabilitations, 107 implants were used for 14 complete bridges, 52 implants were used to replace single teeth, and 15 implants were used to stabilize 7 overdentures (^{table 1}). In the maxilla, 401 implants were placed (65,1 %), and 215 implants (34,9 %) were placed in the mandible (^{table 2}). Two third of the implants (75,5 %) were placed in posterior segments (^{table 3}). Analyzing the results, it was found that on the 188 patients :

- 1 died accidentally ;

- 16,57 % never showed up after prosthetic completion : 3 patients had left the country definitively (1,6 %) but kept informing us regularly, and the others were followed by their dentists because they were living outside Casablanca ;

- 36,68 % came back regularly for their recall the first two years after final prosthesis and then were followed irregularly by their dentist ;

- 53,07 % came regularly for their recalls (^{table 4}).

In order to enhance the analysis of this findings, patients who could not be followed were contacted by phone. A questionnaire was laid before them, its goal being to know whether the patient had any pain or discomfort, and if the prosthesis was stable. All patients except two were reached : the one that died and one that moved. Therefore, the results will be analyzed in the following way :

- early failure (implant failure occurred before the prosthesis was placed) ;

- late failure (implant failure occurred after prosthetic was placed) ;

- survival : the implant was in place but was not followed clinically and radiologically according to Albrektsson criteria. The survival rate was studied for the majority of the implants (592 instead of 595 that had the second stage surgery : 1 patient with 3 implants couldn't be reached but had been followed for 4 years). On the 592 implants, 350 implants were analyzed according to the subjective signs of the patient or his dentist's report : the prosthesis was stable and functional and without any pain ;

- success : the implant has fulfilled all the requirements for success and patient came back regularly for control. On the 592 implants, 242 were followed overtime clinically and radiographically and could be studied according to Albrektsson criteria of success. The results were the following : on the 616 implants, 6 were in the patient deceased accidentally, 595 had a second stage implant surgery.

Thirty implants among 595 had an early failure (5,0 %) and 11 implants had a late failure (1,84 %) which make the overall failure rate 6,89 %. So the total survival rate would be 93,11 %.

The analysis of the survival rate per maxillary arch points toward a total success rate of 97,12 % for the mandible and 90,04 % for the maxilla (^{table 5}).

On the 242 implants that were followed and that could be analyzed according to the Albrektsson criteria of success, 15 had an early failure and 5 had a late failure. The total success rate for those implants was of 91,74 % (^{table 6}). However, if a high risk patient who lost 5 implants is removed from the study, the total success rate increases up to 93,81 %.

Now, when the analysis of the stability of the prosthesis according to each the type is done, it is found that :

- on the 52 implants for single prosthesis, 2 were lost. One was in the first maxillary molar area and didn't osseointegrate the second time either, which suggests that a wrong implant site. The second was in the first maxillary incisor and a maryland bridge was chosen for esthetic reasons instead of another attempt of implantation because the bone loss on the buccal plate was too important. However, in some cases of bone loss on the buccal plate, a guided tissue regeneration was done (^{fig. 1}, ², ³and⁴);

- the prosthetic success rate for single restorations was 96,17 %. Three patients had a recession on a anterior tooth, but only two of them could be corrected with a successful connective tissue graft (^{fig. 5}, ⁶, ⁷, ⁸, ⁹, ¹⁰, ¹¹, ¹², ¹³ and ¹⁴) and one could be considered as an aesthetic failure ;

- on the 442 implants used for fixed partial bridges (^{fig. 15}, ¹⁶, ¹⁷, ¹⁸, ¹⁹ and ²⁰), only 1 implant didn't osseointegrate the second time and the fixed bridge is still in place with 2 implants instead of 3. This means a prosthetic success rate of 100 %. But 2 implants were not restored adequately because of the embrasure space ;

- on the 107 implants used for complete fixed rehabilitation, they were all on the maxillary arch (^{fig. 21}). All the failing implants did ossseointegrate the second time (^{fig. 22}, ²³, ²⁴, ²⁵, ²⁶ and ²⁷). Two implants could be considered as surviving because they lost more than 3 mm but they are still in place (^{fig. 28}, ²⁹ and ³⁰). Two implants migrated in the sinus. All the fixed bridges are holding in place which again gives us a prosthetic success rate of 100 % ;

- on the 15 implants used for overdenture, 2 were reimplanted successfully. So the prosthetic success rate for overdenture was also of 100 %.

Discussion

The results of this study confirm that it is possible to treat predictably edentulous patients with the Brånemark implant even in a population where initial dental hygiene is poor, provided that the oral environment is healthy and plaque control strictly performed. The total survival rate of 93,11 % is good enough knowing that 75,5 % of the implants were placed in posterior areas and that 65 % were placed in the maxillary arch which very often has a lower bone density than the mandibular arch. This survival rate is in accordance with what has been reported in the literature (^{Brånemark et al., 1985} ; ^{Adell et al., 1981} ; ^{Adell et al., 1990} ; ^{Cox and Zarb, 1987} ; ^{van Steenberghe et al., 1987} and ¹⁹⁹⁰ ; ^{Albrektsson et al., 1988} ; ^{Jemt et al., 1989}, ¹⁹⁹⁰ ; ^{Jemt, 1993} ; ^{Lekholm et al., 1994} ; ^{Lekholm et al., 1999} ; ^{Laney et al., 1994}).

The low success rate for the maxilla can be explained for 2 patients. One of them had an overdenture on 3 ball abutments in the maxilla. This patient lost 2 out of 3 implants. However, the implants replaced remained stable. A bar for overdenture was used instead of ball attachments. The failure could be explained not only by the poor bone density but also by the type of prostheses, as reported in the literature (^{Parel, 1986} ; ^{Enquist et al., 1988} ; ^{Johns et al., 1992} ; ^{Naert et al., 1988} ; ^{Hutton et al., 1995} ; ^{Jemt et al., 1996}).

Concerning the high level of failure with the second patient who had a severe type of periodontitis compounded by his nicotinism and alcoholism, some explanations could be put forward :

- immediate implant placement was performed at the time of extraction to prevent more bone loss. Immediate implant placement has shown good success rates (^{Krump and Bannett, 1991} ; ^{Gelb, 1993} ; ^{Tolman and Keller, 1991} ; ^{Rosenquist and Grenthe, 1996}) but the success rate was lower when the tooth was extracted for periodontal purposes ;

- the thorough extraction site curettage and the strong antibiotic regimen did not prevent him from having some episodes of infection. Indeed, the role of bacteria in this patient can't be neglected : a strong correlation has been found between certain type of periodontal pathogens and implant failures (^{Becker et al., 1990} ; ^{Gouvoussi et al., 1997}) ;

- there was also a strong correlation between implant failure and cigarettes smoking (^{Bain, 1993}). However, the failure rate could be drastically reduced provided that the patient goes into a smoking cessation protocol (^{Bain, 1996}). This same patient, who lost 5 over 6 implants accepted to stop smoking and was able to have successful implants and prosthesis with 18 months follow-up.

So, if the above mentioned patients are removed from our results, the survival rate will be even greater (93,82 %).

From a broader point of view, two more explanations could be put forward :

- the history of the disease on an implant site ;

- temporary prosthesis after implant placement.

As a matter of fact, a lot of patients could go for years with endodontic abscess. With this respect, the dentists play a key role also in trying to safeguard periodontally compromised teeth which makes treatment more difficult by using guided tissue regeneration techniques with membrane.

Last but not least, temporary prosthesis can also have a negative influence on healing and osseointegration. As a matter of fact, patients who could afford this type of treatment were very active socially ; they very seldom accepted to remain without their prosthesis for 10 to 15 days. Furthermore, the analysis of type of failure on the 30 implants that did not osseointegrated underlines the fact that 13 implants were under a removable type of temporary prosthesis.

Indeed, this type of prosthesis acts like an early loading, and over the maxillary bone this can be crucial for the osseointegration.

This retrospective study has shown that osseointegration is possible in this type of population when the environment is healthy and patients strictly selected. It should be relevant to go beyond this study by looking for a correlation between the implant survival rate and the type of periodontitis. This will help us know in advance the risk patient assuming a significant link is found.

In addition, it will be relevant to study the lifetime of every type of prosthesis even in absence of follow-up.

Demande de tirés à part

Chafika EL BELGHAMI-KADIRI : Centre dentaire Avicenne - 1, impasse Mimosa - Angle boulevard Ibn Sina - CASABLANCA - MAROC.

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