Quintessenz Journals

CLINICAL ARTICLE

277

Tommaso Grandi, Paolo Guazzi, Rawad Samarani, Giovanni Grandi

Immediate loading of four (all-on-4) post-extractive implants supporting mandibular cross-arch fixed prostheses: 18-month follow-up from a multicentre prospective cohort study Key words

full-arch prosthesis, immediate loading, post-extractive implants, tilted implants

Aim: To evaluate the outcome of immediately loaded mandibular cross-arch prostheses according to the ‘all-on-4’ concept supported by implants placed in fresh extraction sockets up to 18 months after loading. Materials and methods: In total, 47 patients with a mean age of 62.3 years (range 52 to 78) were rehabilitated with an immediately loaded fixed cross-arch prosthesis supported by four post-extractive implants. A total of 188 implants were inserted. Patients received a provisional fixed dental prosthesis with a metal framework within 48 hours after surgery and a permanent one 6 months later. The patients were evaluated clinically and radiographically at implant placement and at 6-, 12- and 18-month follow-up examinations. Results: At the 18-month follow-up, no implant failed and all restorations were stable. Peri-implant bone levels amounted to 0.31 ± 0.12 mm after 6 months, 0.58 ± 0.112 mm after 12 months and 0.7 ± 0.107 mm after 18 months. No significant differences in bone loss were found between axially placed and tilted implants at the 6-month (0.06 mm; P = 0.115), the 12-month (0.12 mm; P = 0.062) and the 18-month follow-up (0.08 mm; P = 0.146). Three patients had a fracture of the provisional restoration, but all of the definitive prostheses remained stable throughout the study period without any complications. Conclusions: Within the limits of this study, it can be suggested that immediately loaded mandibular cross-arch fixed dental prostheses can be supported by four post-extractive implants, however larger and longer follow-ups are needed. Conflict-of-interest statement: Dr Tommaso Grandi and Dr Paolo Guazzi serve as consultants for JDentalCare. This study was completely self-financed and no funding was sought or obtained, not even in the form of free materials.

Introduction The concept of immediate loading was first applied to the loading of multiple implants in the mandible for full-arch restorations, with predictable results1-3. Currently, the survival rates for implants that are

immediately loaded in mandibles vary between 80% and 100%4-6. Most of the studies published on immediate loading in the mandible have considered edentulous patients7. In many situations, clinicians are faced with partially edentulous patients who require extraction of their remaining teeth and

Eur J Oral Implantol 2012;5(3):277–285

Tommaso Grandi, DDS Department of Integrated Activities of Specialised Head-Neck Surgery, University of Modena and Reggio Emilia, Italy

Paolo Guazzi, DDS Private practice, Modena, Italy

Rawad Samarani, DCD, DES Assistant, Department of Periodontology, SaintJoseph University, Beirut, Lebanon

Giovanni Grandi, MDS University of Modena and Reggio Emilia, Italy Correspondence to: Tommaso Grandi Via Rua Muro 96 41121 Modena, Italy Tel: 00393337095223 Email: tommaso.grandi@ unimore.it

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All-on-4 placing of post-extractive implants

implant-supported cross-arch prostheses. These patients have to struggle with the challenge of wearing a conventional removable denture during the bone healing (4–6 months) after tooth extraction. Discomfort and social embarrassment make this approach not acceptable by many patients. From the patient’s perspective, it would be ideal to obtain a functional fixed prosthesis the same day of tooth extraction and implant placement, reducing discomfort, treatment time and costs, as long as the risk of implant failure is not increased. In three studies, the remaining teeth were extracted and implants inserted in healed sites and fresh sockets to provide full-arch restorations in the mandible8-10. The placement in healed or fresh extraction bone sites may not influence implant survival. In two studies, all of the implants supporting a cross-arch restoration were inserted in postextraction sites, but the evidence supporting such an approach is scarce11,12. Peñarrocha et al11 reported a 100% survival rate in 11 patients treated with immediate cross-arch restorations supported by postextractive implants. In a retrospective study, Mozzati et al12 showed that immediate loading of four implants immediately placed in extraction sockets is a valid treatment modality for the rehabilitation of the mandible. When rehabilitating totally edentulous mandibles with dental implants, there are many alternative options in terms of the number of implants and their positions. The development of protocols for immediate loading has switched focus from placing several implants to a few implants13. The use of fewer implants is supported by the results from implant load analyses demonstrating that four implants placed in the interforaminal area is an optimal number for a complete-arch prosthesis14. Moreover, the greater the number of implants, the greater the costs and difficulties in fabricating a precise metal framework that can be passively fixed on the implants13. According to the ‘all-on-four’ concept, two implants are inserted in an anterior position following the jaw anatomy direction and the other two implants are inserted just anterior to the foramina and tilted distally about 30 degrees relative to the occlusal plane3. By tilting the distal implants, a more posterior implant position can be reached, thereby reducing the cantilever. If these implants are inserted with a sufficient primary stability (insertion torque > 35 Ncm), the success rate is high in fully edentulous mandibles4,13,15.


The aim of this prospective study was to assess the clinical and radiographic outcome of immediately loaded mandibular cross-arch prostheses according to the ‘all-on-four’ concept supported by implants placed in fresh extraction sockets up to 18 months after loading. The secondary aim was to compare peri-implant marginal bone level changes between straight and tilted implants. This article reports preliminary data on implant survival and peri-implant bone loss. It is planned to follow up this patient cohort to the fifth year of function in order to evaluate the success of the procedure over time. The present article is reported according to the STROBE statement for improving the quality of reporting of observational studies (http://www. strobe-statement.org).

Materials and methods Study protocol This was a single cohort prospective study in which patients with partially edentulous mandibles in need of tooth extractions because of severe periodontal disease and/or caries were consecutively enrolled and treated. The investigation was conducted according to the principles embodied in the Helsinki Declaration for biomedical research involving human subjects. At the preliminary visit, all patients were duly informed about the nature of the study and about any possible alternative treatment. Before enrolment, written informed consent was obtained.

Selection criteria Candidates were patients of any race and gender with partially edentulous mandibles requiring extraction of the remaining teeth. All patients were subjected to a preliminary evaluation that included careful review of their medical and dental histories, detailed clinical examination, and evaluation of oral hygiene. Patients were consecutively included in the study provided that they fulfilled the following inclusion criteria: t at least 18 years of age t sufficient amount of bone volume in the intraforaminal area for placement of four implants at

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Fig 1 Preoperative orthopantomograph of patient to be rehabilitated in both jaws with implant-supported cross-arch dental prostheses in the same session.

Fig 2

least 11.5 mm in length and 3.7 mm in diameter. Bone dimensions were measured on preoperative computed tomography (CT) scans t adequate oral hygiene, i.e. Plaque Index16 ≤ 2.

tooth extraction (Figs 1 and 2). Preoperative photographs, impressions and careful aesthetic planning were performed. The diagnostic casts were mounted in an articulator and a diagnostic waxup was made in which the occlusion, aesthetic parameters and relation between the teeth and alveolar ridge (emergent profile) were evaluated. A surgical guide (duplicate of the diagnostic waxup) was constructed in transparent heat-processed acrylic resin. Prior to surgery, the patients underwent debridement and root scaling performed by a dental hygienist. Chlorhexidine digluconate 0.2% mouthwash (Curasepts, Curaden HealthCare s.r.l., Saronno MI, Italy) was prescribed starting 3 days before surgery and then daily for 7 days following surgery. Antimicrobial prophylaxis was obtained with 1 g of amoxicillin and clavulanic acid (Augmentin, Roche S.p.A., Milan, Italy) every 12 hours from the day before surgery to the sixth postsurgical day.

Exclusion criteria were: t systemic disease that could compromise osseointegration t subjected to irradiation in the head and neck area t treated or under treatment with intravenous amino-bisphosphonates t uncontrolled diabetes t substance abuse t heavy smoking (>20 cigarettes daily). The included patients were treated in three dental clinics by surgeons with considerable clinical expertise in immediate loading procedures. From March 2008 to July 2010, a total of 47 patients with partially edentulous mandibles in need of tooth extractions were rehabilitated with an immediately loaded fixed cross-arch mandibular prosthesis supported by four post-extractive implants. A total of 188 postextractive implants were inserted.

Presurgical preparation A careful clinical examination of the patients was performed assessing jaw size and relations, bone volume, and occlusal relations. The presurgical evaluation included periapical radiographs, orthopantomograms (OPTs) and CT scans to assess the possibility of placing four intraforaminal implants at the same stage as

Preoperative clinical view.

Implant placement On the day of surgery, the patient was treated under local anaesthesia using articaine with adrenaline (1:100,000). The remaining teeth were extracted while trying to preserve the integrity of the alveolar bone walls. Where present, all granulation tissues were removed. The alveolar bone walls were carefully sounded with a periodontal probe to confirm the absence of bone dehiscence. A mucoperiostal flap was raised at the ridge crest with relieving incisions on the buccal aspect in the molar area. The dental implant sites were identified along with the


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Fig 3 After tooth extraction, four post-extractive implants were placed in the mandible according to the ‘all-on-4’ protocol and healing caps were then positioned over the conical abutments.

Fig 4 The screw-retained provisional prostheses were delivered within 48 hours after surgery. No cantilevers were made to minimise fracture risk and excessive stress over the distal implants.

Fig 5 Periapical radiographs taken immediately after delivery of the provisional restoration.

a

b

ideal angulations as dictated by the surgical guide. After mucoperiosteal flap reflection and identification of the mental foramina, of paramount importance for positioning the tilted implant in a distal position, bone remodelling and flattening were performed. All patients received four tapered implants (JDEvolution®, JDentalCare, Modena, Italy) with internal connection and double acidetched treated surface. At first, the two distal tilted implants were placed. Operators were free to choose implant lengths (11.5, 13 or 15 mm) and diameters (3.7, 4.3 or 5 mm) according to clinical indications and preferences. The drill was inserted crestally in correspondence with the alveolar nerve foramen and tilted in order to reach a more posterior implant position, thereby reducing the cantilever. The distal implants were tilted to reach the emergence of the second premolar in the surgical guide. Thereafter, the two mesial implants were inserted. If there was a gap larger than 2 mm between implants and the surrounding bone, it was filled with 0.25 to 1 mm granules of anorganic bovine bone (Geistlich Bio-Oss, Geistlich Pharma AG, Wolhusen, Switzerland).


c

Care was taken to properly undersize the osteotomy to be able to obtain the best possible implant stability. Operators followed the drilling sequence recommended by the implant manufacturer. However, they underprepared with a drill of one size less than the one recommended at implant sites characterised by soft bone quality to obtain a high insertion torque. Final insertion torque was measured with a calibrated torque wrench (JDTorque®, JDentalCare). The wrench used was able to perform torque measurements within a range of 15 to 80 Ncm, with 5% precision. During the protocol-formulation phase, it was decided that implants should attain an insertion torque of at least 45 Ncm to be included in the study. If implants did not reach an insertion torque of at least 45 Ncm, patients were excluded from the study. Conical abutments were connected to the implants. On the distal implants, abutments with an inclination of 30 degrees relative to the implant axis were placed (n = 94) to allow for an optimal prosthetic screw access, while standard (n = 82) or 17 degree (n = 12) abutments were placed on the mesial implants. Abutment screws were tightened at 30 Ncm. After positioning the coping, the soft tissues were sutured

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Fig 6

Centric and lateral contacts were carefully checked.


281

Fig 7 Clinical view after delivery of both cross-arch final restorations 6 months after implant placement.

Fig 8 Periapical radiographs taken 18 months after implant placement.

a

b

with a 4-0 resorbable suture (Vicryl®, Johnson & Johnson Intl., St Stevens, Woluwe, Belgium) and an impression was taken by means of a polyether material (Impregum Penta™, 3M Italia S.p.A., Pioltello MI, Italy) directly on the coping. Healing caps were then positioned over the conical abutments (Fig 3).

Prosthetic procedure A 10-unit provisional fixed dental prosthesis was manufactured in the dental laboratory. The screwretained provisional prostheses were delivered within 48 hours after surgery (Figs 4 and 5). Screw-retained frameworks were cast in a non-precious alloy to rigidly splint the implants and to minimise the risk of provisional restoration fracture. Resin teeth were added and the prostheses were screwed onto the conical abutments using a standard torque of 15 Ncm. No cantilevers were used to minimise fracture risk and excessive stress over the distal implants. The prostheses had reduced occlusal surfaces with flat cusps; centric and lateral contacts were checked (Fig 6). A soft diet was recommended for the first month and oral hygiene instructions were given.

c

Patients were enrolled in an oral hygiene program with recall visits every 3 months for the entire duration of the study. All definitive screw-retained metal-resin prostheses were delivered 6 months after surgery (Figs 7 and 8).

Outcome measures Patients were recalled at 6, 12 and 18 months after surgery to assess the outcome measures that follow. The primary outcome measures were prosthesis and implant failure: t Prosthesis failure: a prosthesis was considered a failure if it needed to be replaced by an alternative prosthesis. t Implant failure: implant mobility and removal of stable implants dictated by progressive marginal bone loss or infection. The metallic handles of two instruments were used to assess implant stability. The stability of each individual implant was checked after removing the restorations at the delivery of the final restorations (6 months after implant placement), 12 months and 18 months after loading.


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Table 1


Patient characteristics.

Patients

47

Males

22

Females

25

Mean age at implant insertion

62.3

Age range

52–78

Smokers (less than 20 cigarettes/day)

11

Controlled diabetes

2

Hypertension

16

Opposing maxillary complete denture

8

Opposing fixed rehabilitation and natural teeth

27

Opposing removable prosthesis and natural teeth

12

The secondary outcome measures were biological and prosthetic complications and peri-implant bone changes: t Biological complications such as peri-implant mucositis (heavily inflamed soft tissue without bone loss), peri-implantitis (bone loss with suppuration or heavily inflamed tissues) and fistulas t Prosthetic complications such as fracture of the abutment screw or framework and detachment of resin teeth t Peri-implant marginal bone level changes evaluated on intraoral radiographs taken with the paralleling technique at implant placement, 6 months, 12 months and 18 months after loading. Particular attention was paid to position the radiographic film parallel to the implant and to align the X-ray beam perpendicular to the implant axis to minimise distortion of the implant threads. The measurements of bone level changes were made by an independent outcome assessor (GG), not involved in the treatment of the patients. Radiographs were scanned, digitized in JPG format, converted to TIFF format with a 600 dpi resolution and stored in a personal computer. Peri-implant marginal bone levels were measured using Image J 1.42 software (National Institutes of Health, Bethesda, MD, USA). The software was calibrated for every single image using the known implant diameter. Measurements of the mesial and distal crestal bone levels adjacent to each implant were made to the nearest 0.01 mm and averaged at patient level and then group level.


The measurements were taken parallel to the implant axis. Reference points for the linear measurements were the most coronal margin of the implant collar and the most coronal point of bone-to-implant contact.

Data analysis Statistical analysis was performed using the statistical package StatView (version 5.01.98, SAS Institute Inc, Cary, NC, USA). Significance was set at P < 0.05. The paired-samples t test was used to evaluate the bone level changes. The patient was the statistical unit of the analysis. Marginal bone loss around axially placed and tilted implants was compared using the paired-samples t test. Differences in bone level changes between different surgical operators were longitudinally analysed using the analysis of variance (ANOVA) test for repeated measures.

Results Fifty-six patients were screened for eligibility, but 9 patients were not included for the following reasons: 2 patients were excluded because of insufficient oral hygiene and 7 patients were hesitant to receive implant treatment for economic reasons. A total of 47 patients were considered eligible and were consecutively enrolled in the study. All patients were treated according to the allocated intervention, no dropout occurred up to 18 months after loading and the data of all patients were evaluated in the statistical analyses. Patients were recruited and treated from March 2008 to July 2010. All implants were successfully seated with an insertion torque of at least 45 Ncm. The main patient characteristics are presented in Table 1. Patients were generally healthy, though 16 patients had medication-controlled hypertension, 2 patients had controlled diabetes and 11 patients were smokers. The mean age of the patients at the time of surgery was 62.3 years (SD = 9.4; n = 47). Seating torque values and the dimensions (diameter and length) of the inserted implants are listed in Table 2. Measurements of insertion torque were averaged at patient level and then group level. Average insertion torque was 72.07 Ncm (SD 6.4).

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Table 2 Dimensions (diameter and length) and final seating torque of the inserted implants (n = 188).

Length

Diameter

Insertion torque (Ncm)

Table 3

283


Comparison of mean bone levels (means ± SD) at different time intervals.

11.5

64

13

82

Follow-up

Mean bone level (mm)

0-6 months

0-12 months

0-18 months

15

42

Baseline

-0.02 ± 0.12

0.33

0.6

0.72

3.7

66

6 months

0.31 ± 0.12

P < 0.0001

P < 0.0001

P < 0.0001

4.3

122

12 months

0.58 ± 0.11

45

5

18 months

0.7 ± 0.11

50

2

60

34

65

11

70

41

80

95

Apart from expected postoperative swelling and pain, there were no other immediate postsurgical complications. The resin portion of 3 (6.3%) of the provisional fixed dental prostheses fractured in 3 patients that had natural dentition or a fixed rehabilitation in the opposite arch. The complication was resolved after new resin was added in the lab and the occlusion was checked carefully chairside. Two patients had an episode of peri-implant mucositis and were treated with non-surgical debridement of the affected implants. All permanent fixed dental prostheses and implants remained stable through the 18-month follow-up period. The radiographic data are summarized in Table 3. The overall mean marginal bone levels at 0, 6, 12 and 18 months were -0.02 ± 0.12 mm, 0.31 ± 0.12 mm, 0.58 ± 0.11 mm and 0.7 ± 0.11 mm, respectively. A repeated measures ANOVA showed that there were no statistically significant differences in bone level changes among the three surgeons involved in the trial (P = 0.118). No significant differences in bone loss were found between axially placed and tilted implants at the 6-month (0.06 mm; P = 0.115), the 12-month (0.12 mm; P = 0.062) and the 18-month follow-up (0.08 mm; P = 0.146) (Table 4).

Discussion This prospective study aimed at evaluating the clinical and radiographic outcomes of four postextractive immediately loaded implants supporting

Time

Table 4 Axially placed versus tilted implants: comparison of mean bone levels (means ± SD) at different time intervals. Follow-up

Mean bone level (mm)

Baseline

Axially placed implants

-0.09 ± 0.24

6 months

0.27 ± 0.17

12 months

0.57 ± 0.13

18 months

0.68 ± 0.14

Axially placed vs tilted implants mean difference 0-6 months

0-12 months

0-18 months

0.06

0.12

0.08

0.06 ± 0.09

P = 0.115

P = 0.062

P = 0.146

0.36 ± 0.14

12 months

0.6 ± 0.16

18 months

0.74 ± 0.14

Baseline 6 months

Tilted implants

mandibular cross-arch fixed prostheses. Maló et al3 reported data on the prognosis of the ‘all-on-4’ protocol in edentulous mandibles or maxillae with hopeless teeth, but they did not investigate the clinical situations in which surgeons are forced to insert all four implants in post-extractive sockets due to the anatomical situation and space limitation. Our preliminary results indicate that such a technique may lead to an excellent prognosis, at least after 18 months of function. The high implant and prosthesis survival rate and the limited peri-implant bone remodelling observed in the present investigation may be a result of several factors, which include high implant primary stability, prosthetic design, and control of the occlusal forces. It was decided to load immediately only implants that achieved an insertion torque of at least 45 Ncm. To achieve high insertion torque, implant sites were underprepared to a varying degree according to bone quality. All the implants placed were inserted with an insertion


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torque ≥45 Ncm and 72.3% of the implants had an insertion torque ≥70 Ncm. The high insertion torque could be the result of the surgical technique used and also of the implant design. After tooth extraction, bone healing needs time and it was observed that after 4 months the consistency of the alveoli, even if filled with bone substitute, was still soft17. The screw-retained provisional prostheses were delivered within 48 hours after surgery. Screwretained frameworks were cast in a non-precious alloy to rigidly splint the implants and to prevent fracture of provisional restorations. The incidence of fracture of the provisional prostheses in the present study (6.3% of the total cases) was lower compared with that reported by Maló et al (30%)3 and similar studies (11% to 16%)2,18 in which acrylic provisional prostheses without a metal framework were delivered. This complication was observed in patients with a short face morphotype that had natural dentition or a fixed rehabilitation in the opposite arch. Our study reported an implant and prosthesis survival rate of 100%, which is consistent with previous studies in which all of the implants were inserted in fresh extraction sockets11,12. Lower success rates have been reported in the literature regarding implants immediately placed in fresh sockets, but most of these published studies involved single-tooth replacement19. The connection of implants may provide a safer transfer of load on each implant and so the placement in healed or fresh extraction bone sites may not influence implant survival when rehabilitating totally edentulous mandibles8-10. Regarding peri-implant marginal bone levels, 18 months after loading and using the bone levels at implant placement as baseline data, implants lost an average of 0.72 mm. The present data are similar to those observed of other implant systems used in similar conditions, considering a follow-up ranging between 12 and 24 months after loading. Studies reporting on four to six implants inserted in healed sites supporting cross-arch mandibular restorations have reported peri-implant marginal bone level changes


ranging from 0.57 to 1.52 mm4,8. Marginal bone level changes ranging from 0.55 to 2.03 mm were reported around post-extractive implants supporting cross-arch mandibular restorations9,12. Taking all these findings together, it is possible to suggest that four post-extractive implants placed according to the ‘all on 4’ protocol and immediately loaded may be sufficient to support a cross-arch fixed prosthesis in the mandible at least up to 18 months after loading, keeping in mind that the long-term prognosis is yet unknown. A limitation of the present investigation is the small sample size, but unfortunately the centres did not have the capacity to recruit more patients in a reasonable period. Randomised controlled trials with larger sample sizes and longer follow-ups are needed. The surgeons involved in the trial were experienced with post-extractive implants and immediate loading procedures and this factor might limit the extrapolation of the results. On the other hand, treatments were delivered under normal clinical situations, using relatively broad patient inclusion criteria. It would also be interesting to evaluate the efficacy of an alternative approach using only two implants as investigated recently by Cannizzaro et al13,20, which indicated good outcomes of two immediately loaded implants supporting a cross-arch fixed dental prosthesis up to 1 year after loading.

Conclusions Within the limits of this prospective cohort study, immediately loaded mandibular cross-arch fixed dental prostheses can be supported by four postextractive implants, provided that implants are inserted with at least 45 Ncm torque and that screw-retained metal frameworks are immediately used to rigidly splint the implants. These preliminary results must be confirmed by larger trials with longer follow-ups.

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