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Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (≥9 mm) in atrophic posterior mandibles: a 5-year retrospective study
YIJOM-3748; No of Pages 8
Int. J. Oral Maxillofac. Surg. 2017; xxx: xxx–xxx http://dx.doi.org/10.1016/j.ijom.2017.07.005, available online at http://www.sciencedirect.com
Clinical Paper Dental Implants
Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study
F. Pieri1, C. Forlivesi1, E. Caselli2, G. Corinaldesi3 1 Private practice, Cesena, Italy; 2Private practice, Ancona, Italy; 3Department of Biomedical and Neuromotorial Science, University of Bologna, Bologna, Italy
F. Pieri, C. Forlivesi, E. Caselli, G. Corinaldesi: Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study. Int. J. Oral Maxillofac. Surg. 2017; xxx: xxx– xxx. ã 2017 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Abstract. This retrospective study compared the 5-year clinical and radiographic outcomes of short implants (6 mm) (short group), and standard-length implants (9 mm) placed after a vertical augmentation with autologous bone blocks (augmentation group), supporting partial fixed prostheses in the posterior mandible. Forty-five partially edentulous patients were enrolled in the study and evaluated after 5 years: 22 (51 implants) in the augmentation group and 23 (46 implants) in the short group. Eight surgical complications occurred in the augmentation group versus none in the short group (P = 0.003). One short implant failed before loading and one standard-length implant failed after 4 years because of peri-implantitis (P = 1.0). Eight biological and two prosthetic complications occurred in the augmentation group vs. three biological and three prosthetic complications in the short group (P = 0.09 and P = 1.0, respectively). A mean marginal bone loss of 1.61 1.12 mm in the augmentation group and 0.68 0.68 mm in the short group was found (P = 0.002). Within the limitations of this study, both techniques resulted in successful clinical results after 5 years, but short implants exhibited less surgical complications and marginal bone loss than standard-length implants placed in augmented bone.
0901-5027/000001+08
Key words: atrophic mandible; vertical augmentation; bone graft; short dental implants. Accepted for publication
ã 2017 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Pieri F, et al. Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.07.005
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The atrophic posterior mandible often poses a challenge to treatment with dental implants because the vertical and horizontal ridge resorption after tooth loss may preclude the placement of standard-length implants in the correct position and with ideal inclination. Various procedures to augment the native bone volume have been clinically tested, including onlay and inlay autologous bone grafts, alveolar nerve transposition, distraction osteogenesis and guided bone regeneration1–5. Unthese techniques are fortunately, associated with increased postoperative morbidity, higher costs, and higher risks of complications during the healing period that often deter patients from seeking implant therapy6,7. Thus, short implants with an intra-bony length of 8 mm or less could be a simpler, cheaper, and faster alternative to augmentation procedures, if they demonstrate to result in similar survival rates8,9. Some authors have reported that short implants did not have a good longterm prognosis when compared with standard-length implants in posterior jaws10, although the implant surface may have played a confounding role in the survival rates11. Other recent comparative clinical trials have documented that even short implants with a length of 5–6 mm may have a similar short-term survival rate compared with longer implants placed in augmented bone12,13. Nevertheless, very few data have been published comparing these two treatment approaches with an observation period longer than 3 years14,15. The aim of this retrospective study is to compare the clinical and radiographic outcomes of 6 mm short implants with those of 9 mm or longer implants placed following vertical ridge augmentation with autologous block bone grafts, for the partial fixed restoration of atrophic posterior mandibles after a follow-up period of 5 years. This study is reported following the STROBE (Strengthening the Reporting of Observational studies in Epidemiology) guidelines for reporting observational studies (http://www.strobe-statement.org/ ). Materials and Methods Patient selection
A retrospective chart review was performed for all patients who had implants placed in the atrophic posterior mandible between January 1, 2009, and February 1, 2012, in one private dental practice. Five years after implant placement, patients were contacted and invited for a compre-
hensive clinical and radiographic examination (including periapical radiographs of the implants and their restorations). Each patient gave informed consent to participate in the study. The study protocol was approved by the Ethics Committee of Area Vasta Romagna and IRST, and was conducted according to principles stated in the Helsinki Declaration. The following patient inclusion criteria were applied: (1) vertical bone atrophy in the posterior edentulous mandible (a residual bone height between 7 and 9 mm above the inferior alveolar nerve measured on a preoperative cone beam computed tomography (CBCT)); (2) treatment involving the placement of at least two short implants (6 mm) in the native bone or standard-length implants (9 mm) in ridges augmented with mandibular block bone grafts supporting a fixed partial denture; (3) delayed implant loading; (4) patients enrolled in a regular maintenance care programme; (5) a minimum followup period of 5 years from implant placement; (6) availability of a baseline periapical radiograph taken on the day of implant surgery. The patients were excluded if were diagnosed with systemic conditions known to alter bone metabolism, such as cancer requiring chemotherapy or facial radiotherapy, intravenous amino-bisphosphonates for metastatic bone diseases, uncontrolled diabetes mellitus, immunosuppression or immunodepression and smoking habit of more than 20 cigarettes per day (all pipe or cigar smokers were also excluded). Surgical protocol
All surgeries were performed by a single surgeon under local anaesthesia only or local anaesthesia with oral sedation (triazolam, 0.125 mg or 0.25 mg). All patients received prophylactic antibiotic therapy: 1 g of amoxicillin–clavulanic acid (or clindamycin 500 mg if allergic to penicillin) starting the night before the intervention, and twice per day for a total of 7 days, and pain medication (ibuprofen, 600 mg as needed every 6–8 hours). They were also asked to rinse with 0.2% chlorhexidine digluconate (every 12 hours starting 1 day preoperatively for 2 weeks).
were reflected to completely expose the atrophic ridge and identify the mental foramen. The exposed alveolar bone was cleaned of all soft tissue and several decortications holes were made using a small round bur. Bone harvesting was performed from the same side of the ramus with a piezoelectric surgical device (Piezosurgery, Mectron, Carasco, Italy). The block grafts were shaped according to the morphology of the defects and rigidly fixated to the residual bone with titanium miniscrews (Cizeta Surgicals, Bologna, Italy). Anorganic bovine bone particles (BioOss, Geistlich Pharma AG, Wolhusen, Switzerland) were added at the periphery and over the bone grafts. The reconstructed sites were then covered with a resorbable collagen membrane (Bio-Gide, Geistlich Pharmaceuticals). After careful periosteal releasing incisions in order to obtain absolute tension-free closure, the flaps were sutured in two layers with a combination of horizontal mattress and interrupted sutures. The sutures were removed after 3 weeks, and the patients were then checked at 2 months after surgery. Provisional removable prostheses were not allowed during the healing period. Four to five months after augmentation, a CBCT scan was retaken to plan implant placement. The flap outline was similar to the first surgery without vestibular releasing incisions. Following mucoperiosteal flap elevation and debridement, the bone block fixation screws were removed, and standard-length implants (Astra Tech OsseoSpeed, DENTSPLY Implants, Mannheim, Germany) were placed with the top of the platform flush with the facial alveolar crest (Fig. 1). Short implant group
After a crestal incision and flap reflection, implant osteotomy sites were prepared according to a standard drilling sequence. To minimize the risk of inferior alveolar nerve injury, the drills were used with adjustable stop devices that were always set at least 1 mm shorter than the radiographic working length above the canal. Two to three short implants (6 mm) (OsseoSpeed, DENTSPLY Implants) were placed in each patient (Fig. 2). Prosthetic protocol
Augmentation group
A midcrestal incision on the edentulous ridge was made. The incision was extended via the gingival sulcus of the adjacent tooth. Mesial and distal releasing incisions were performed, and full-thickness flaps
All implants in both groups were left submerged for 2–3 months. Definitive titanium–composite, or zirconia–ceramic FPDs were delivered 8–10 weeks after healing abutment connection; they were either screw-retained or cemented on cus-
Please cite this article in press as: Pieri F, et al. Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.07.005
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Atrophic posterior mandibles
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Fig. 1. Posterior mandibular atrophic site treated with a bone block augmentation and delayed standard-length implant placement. (A) Preoperative panoramic radiograph. (B) Preoperative cone-beam computed tomography scans. (C) Preoperative occlusal view of the atrophic left posterior mandible. (D) Fixation of the bone block graft harvested from the ramus with an osteosynthesis screw. (E) Particulate anorganic bovine bone graft around block graft. (F) Collagen membrane over the block graft. (G) Panoramic radiograph at 4 months from bone graft procedure. (H) Implant placement at mandibular left first and second molar positions. (I) Periapical radiograph at implant placement. (L) Five-year periapical radiograph demonstrates some crestal bone remodelling around both implants.
tomized computer-aided design/computer-aided manufacturing titanium abutments. All patients were kept under regular maintenance care and received full-mouth scaling every 6 months.
medical and dental history, a prosthodontic examination, and a peri-apical radiograph of all implants that fulfilled the inclusion criteria. The following outcome measures were assessed.
Outcome measures
Implant failure: defined as presence of any mobility of the individual implant and/or any situation dictating implant removal.
The 5-year follow-up examination was conducted by two investigators (C.F. and E.C.), and included an update of the
FPD failure: defined as planned FPD that could not be placed as planned due to implant failure(s), loss of the FPD secondary to implant failure(s), and replacement of the FPD for any reasons. Surgical complications: including haemorrhaging during and after surgery, soft-tissue dehiscence, infections, fistulae, sensory loss, and partial or total bone graft resorption.
Fig. 2. Posterior mandibular atrophic site treated with short dental implants. (A) Preoperative panoramic radiograph. (B) Preoperative cone beam computed tomography scans. (C) Occlusal view of the left posterior atrophic mandible. (D) Two 4 6 mm implants were placed in the second premolar and first molar positions. (E) Postoperative periapical radiograph. (F) Five-year periapical radiograph demonstrates stable bone levels for both implants.
Please cite this article in press as: Pieri F, et al. Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.07.005
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Biological complications: including peri-implant mucositis, and peri-implantitis. Peri-implant mucositis was defined as a heavily inflamed soft tissue without bone loss, and peri-implantitis was defined as a bone loss of more than 3 mm with suppuration, heavily inflamed tissues, or fistulas16. Prosthetic complications: including FPD detachment, screw loosening, and fracture of the screw, framework, or occlusal material. Peri-implant marginal bone levels (MBLs) were evaluated on digital periapical radiographs (Digora Optime; Soredex/Orion Corporation, Helsinki, Finland) taken at implant placement, implant loading, and 5 years after implant placement. For standardization, a film holder-beam aiming device (Dentsply Rinn, Elgin, IL, USA) was applied according to the long cone paralleling technique. The radiographs were taken with the film placed parallel to the implant axis and the radiographic beam directed perpendicular to the implant17. Customized positioners could not be used because of the retrospective character of the study. An imageanalysis software (Digora for Windows, ver. 2.1; Soredex/Orion Corporation) was used to measure the linear distance between the implant platform and the most coronal level of the bone deemed to be in contact with the implant surface with an on-screen cursor at 5 magnification. In cases where the implant platform was below the margin of the crestal bone, that is subcrestal, the value was considered as zero. To make calibrated measurements, an object of known size, the known diameter of the implant, was used. To adjust the measurements for any magnification error, the following equation was used to deter-
mine the correct MBLs: measured MBL (actual implant diameter/measured implant diameter)18. Relative mesial and distal bone height measurements were made to the nearest 0.01 mm and were averaged at a patient level. The change in MBL was calculated by subtracting the follow-up level from the baseline level at implant placement. Furthermore, at FPD placement, the crown/implant ratio was assessed for each implant, dividing the length of the restoration and the length of the implant. Radiographic measurements were performed by one experienced examiner (G.C.), who was calibrated and subjected to an intra-rater agreement test. Statistical analysis
All data analyses were performed using a statistical software package (GraphPad InStat, GraphPad Software Inc., San Diego, CA, USA). Descriptive statistics were expressed as a frequency and percentage, and means and standard deviations, as appropriate. The patient was the statistical unit of the analyses. Differences in the proportion of patients with failures and complications were compared between the groups using Fisher’s exact test. The Friedman test was used to detect intragroup differences, and Mann-Whitney test was used to detect between-group differences in MBL values. The level of significance was set at 0.05 for all comparisons. Results
The patient sample consisted of 45 patients from the 51 that were treated. Six patients were excluded from the study (2 in the augmentation group and 4 in the short group; 11.7% of patients) for the following reasons: one patient had been
treated with chemotherapy for malignant tumours during the follow-up period, one patient had moved away, and four patients failed to attend the examination for various reasons. Out of the final sample of 45 patients, 22 with 51 implants were of the augmentation group, and 23 with 46 implants were of the short implant group. In the augmentation group, 28 implants were 9 mm long, and 23 were 11 mm or longer; the diameter was 3.5 mm in 41 implants, and 4 mm in 10. In the short implant group, all implants were 6 mm long, and the diameter measured 4 mm. Patient and intervention characteristics are provided in Table 1. There were no apparent significant baseline imbalances between the two groups with the exception of less amount of native bone width in the augmentation group (4.72 0.63 mm versus 6.37 0.69 mm, P < 0.0001). Implant and prosthesis failures
The main results up to 5-year follow-up are summarized in Table 2. One implant failed in both groups, yielding a cumulative 5-year survival rate at patient level of 95.7% in the short implant group and 95.5% in the augmentation group. One FPD could not be made as planned in the short implant group because the last implant was found to be infected and mobile at abutment connection and was removed. It was the most distal implant and the patient was pleased with a shorter FPD and did not want to have it replaced. In the augmentation group, one implant (3.5 9 mm) in position 36 was removed (in a light smoker patient) because of excessive bone resorption (5 mm) after 4 years from placement. It was immediately replaced at removal with a 6-mm-long and 3.6-mm-diameter implant (Osseospeed,
Table 1. Patient and implant characteristics of the short implant group and augmentation group at the start of the study. Variable
Augmentation group (n = 22)
Short implant group (n = 23)
Mean age at placement (SD) No. of female patients No. of smokers (<20 cigarettes/day) No. of patients with periodontitis No. of patients with bruxism Preoperative mean bone height above the mandibular canal (SD) (mm) Preoperative mean residual bone width ( SD) (mm) Total no. of placed implants Mean number of implants in each patient (SD) Number of implants in premolar/molar position Mean implant height (SD) (mm) Mean implant diameter (SD) (mm) Mean crown/implant ratio
56.4 8.25 16 5 6 1 7.29 1.3 4.72 0.63 51 2.32 0.47 21/30 9.98 1.15 3.6 0.2 1.08 0.29
57.69 7.93 19 5 4 4 7.82 0.51 6.37 0.69 46 2.17 0.38 12/34 6 4 2.03 0.27
P-value 0.84a 0.45b 0.1b 0.49b 0.34b 0.32a <0.0001a 0.27a 0.13b
SD, standard deviation; FPD, fixed partial denture. a Mann–Whitney U test. b Fisher’s exact test.
Please cite this article in press as: Pieri F, et al. Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.07.005
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Table 2. Summary of the main clinical results after 5 years of follow-up (number of events and their descriptions in parenthesis). Implant failures Prosthesis failures Complications surgical biological prosthetic
Augmentation group (n = 22)
Short implant group (n = 23)
P-valuea
1 1 16 8 (5 partial graft resorptions, 3 transient lip paresthesiae) 8 (4 mucositis, 4 peri-implantatis) 3 (2 ceramic fractures, 1 decementation)
1 1 3 0
1.0 (NS) 1.0 (NS)
2 (2 mucositis, 1 peri-implantitis) 4 (1 ceramic fracture, 2 decementations, 1 abutment screw loosening)
0.09 (NS) 1.0 (NS)
0.003
NS, not significant. a Fisher exact test.
DENTSPLY Implants) in a distal position and a new FPD was made. On a patient basis, the differences in proportions of prosthesis and implant failures at patient level were identical and not statistically significant (P = 1.00). Complications
Before implant loading, eight surgical complications related to the block grafting procedure occurred in the augmentation group versus none in the short implant group. Three patients reported transient lower lip paraesthesia for a duration of 1–2 months after ramus harvesting and posterior mandibular reconstruction. Complete functional recovery was obtained in all cases. In five patients a partial graft resorption (<50%) occurred, which required supplementary bone augmentation at implant placement with
autologous bone particles harvested during implant osteotomy and a collagen membrane. There was a statistically significant difference in the number of surgical complications between the two groups (P = 0.003) (Table 2). After loading, biological complications occurred in eight patients of the augmentation group, and three patients of the short implant group. In total, four patients with eight implants in the augmentation group, and two patients with four implants in the short implant group were affected by periimplant mucositis, and were successfully managed by interceptive supportive therapy19, consisting of professional cleaning with titanium curettes, polishing using rubber cups and polishing paste, followed by 0.2% chlorhexidine mouth rinses, three times per day for 2 weeks. Four patients in the augmentation group and one patient of the short implant group had one to three
implants affected by peri-implantitis after 2–4 years from placement. These sites showed a severe bone loss of 3–6 mm and purulent exudate, and were treated by grafting the defect with granules of anorganic bovine bone (Bio-Oss, Geistlich Pharmaceuticals) or with resective surgery under systemic antibiotics (Fig. 3)20. At the 5-year follow-up evaluation, in four patients clinically healthy peri-implant soft tissues were re-established around implants with reduced but stable bone levels. In one patient of the augmentation group, one implant was removed after 4 years because of the progressive loss of marginal bone. The difference in proportions of patients experiencing biological complications between the two groups was not statistically significant (P = 0.09) (Table 2). Prosthetic complications in the augmentation group included minor ceramic
Fig. 3. Sequence of panoramic and periapical radiographs showing one of the patients treated with standard-length implants in augmented bone, which suffered from peri-implantitis. (A) Preoperative panoramic radiograph. (B) Postoperative panoramic radiograph. (C) Periapical radiograph just after implant placement. (D) Periapical radiograph at start of prosthetic loading. (E) Periapical radiograph at 1 year. (F) Periapical radiograph at 5 years that shows a stabilization of the bone crest around implants at a clearly reduced level after a surgical revision and an apical flap repositioning for the treatment of a peri-implantitis after 4 years.
Please cite this article in press as: Pieri F, et al. Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.07.005
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Table 3. Comparison of mean (SD) marginal bone levels (in mm) for the two groups between baseline (implant placement) and 1, and 5 years of follow-up. Baseline Year 1 Year 5 Bone level change baseline to 1 year Bone level change baseline to 5 years a b
Augmentation group (n = 22)
Short implant group (n = 23)
0.04 0.01 0.79 0.69b 1.65 1.13b 0.75 0.68 1.61 1.12
0.02 0.05 0.32 0.26b 0.7 0.69b 0.3 0.24 0.68 0.68
P-valuea
0.03 0.002
Mann–Whitney test. All changes from baseline statistically significant different (Friedman test, P < .0001).
veneer fractures at two FDPs, which could be simply polished, and the need for cementation of one FDP. Four prosthetic complications (one abutment screw loosening, two decementations, and one minor ceramic veneer fracture) were observed in the short implant group. There was no statistically significant difference with respect to prosthetic complications between the two groups (P = 1.0) (Table 2). Peri-implant marginal bone level changes
The two-way intra-class correlation coefficient was excellent (0.97) for radiographic intra-rater agreement analysis. Between and within group analysis of MBLs at patient level are presented in Table 3. Both groups gradually lost statistically significant amounts of marginal bone from implant placement to 5 years (P < .0001). There was a statistically significant difference between the two groups for peri-implant bone level changes at loading (P = 0.03), and 5 years (P = 0.002). A statistically significant difference was also observed in the number of patients with MBL change >1 mm at 5 years of follow-up: four (17.3%) in the short implant group versus 12 (54.5%) in the augmentation group (P = 0.02). Discussion
The objective of this retrospective study was to evaluate, after a 5-year follow-up, whether short (6 mm) implants could be a reliable alternative to a block bone-grafting procedure for placing standard-length (9 mm) implants when rehabilitating atrophic posterior mandibles with FPDs. Differences between treatments were found in the number of surgical complications and MBL changes, while for the number of implant and FPD failures, and biological and prosthetic complications, the differences were not statistically significant. When comparing the use of short implants and augmentation procedures, most authors agree that bone-grafting procedures are more technically demanding and related with higher
morbidity than placing short implants21. In a randomized clinical trial (RCT) by Felice et al.22 including 60 patients, no patient suffered from permanent damage of inferior alveolar nerve function, but more patients in the group that underwent inlay bone block augmentation suffered transient paraesthesia of the lower lip. In fact, 16 patients (57%) had transient postoperative paraesthesia vs. only two patients (7%) in the short implant group. Furthermore, four wound dehiscences occurred during graft healing in the augmentation group, while none occurred in the 7mm short implant group. Pen˜arrocha-Oltra et al.13, in a retrospective study of 37 patients, found five surgical complications (1 temporary hypoesthesia of the chin, and 4 wound dehiscences) in 20 augmented patients using mandibular block grafts versus none in 17 patients in the short implant group. The same trend was also observed in our study, with more surgical complications occurring when the most invasive procedure was used. The augmentation procedure not only was associated with more patients experiencing transient postoperative paraesthesia of the inferior alveolar nerve (3 patients vs. none in the short implant group), but there was also an insufficient remodelling of the bone graft associated to a partial resorption at the surgical re-entry in five patients. Consequently, implant placement was performed using a simultaneous bone augmentation procedure, with additional discomfort for the affected patients. The reason for this resorption is not fully understood23,24, but similar findings were described by Roccuzzo et al.25, and could be caused by an insufficient contact among the block grafts and the native bone or could be related to the extremely cortical nature of the mandibular blocks themselves. Evidence exists that combining a membrane with an autologous block graft may limit graft resorption, but this still occurs to a moderate extent26. Cases of inadequate vertical bone gain for placement of standard-length implants have been reported in most studies dealing on implants placed in vertically augmented
ridges in the posterior mandible. In a recent RCT by Esposito et al.12, in five out of 15 patients (33.3%) with bilateral atrophic mandibles, the planned 10-mmlong implants could not be placed, and shorter implants (7 and 8.5 mm) had to be used instead. Similarly, Pen˜arrocha-Oltra et al.13 were unable to place 10-mm-long implants in seven out of 20 patients (35%) subjected to block grafting procedures, and, therefore, shorter implants were used. Furthermore, almost half (21 out of 45) of the implants placed in grafted mandibles needed the addition of particulate bone graft to cover peri-implant dehiscences at implant placement. Also in the present study, the new bone obtained with the augmentation procedure did not allow to place implants longer than 9 mm in 28 out of 51 sites (55%). Previous comparative studies report similar long-term clinical and radiographic results for implant treatment in posterior mandibular atrophic sites treated with either block bone grafts or short dental implants. Felice et al.15 found no statistically significant differences for implant and FPD failures after 5 years, comparing 6.6 mm short implants and 10 mm or longer implants placed in augmented bone. In the same study, short implants lost a mean of 1.49 mm of peri-implant bone compared with 2.34 mm in the augmentation group, this being a statistically significant difference. Similar results were reported by Esposito et al.12 in another split-mouth RCT with 30 partially edentulous patients (15 mandibles and 15 maxillae), comparing 5-mm-long implants and 10-mm or longer implants placed in grafted bone. At the 3-year follow-up, one long implant failed versus two short implants in the same patient in posterior mandibles. Patients with mandibular implants showed a mean marginal bone resorption of 1.44 mm around short implants and 1.63 mm around long implants; the between-group difference in peri-implant bone loss was not statistically significant. In the present study, both procedures yielded similarly high 5-year implant and prosthesis survival rates (95.7% for
Please cite this article in press as: Pieri F, et al. Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.07.005
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Atrophic posterior mandibles short implant group and 95.5% for augmentation group), but short implants did it with only one surgical intervention, and in a shorter treatment time. The main potential risk with short implants is marginal bone loss over time, also considering the obvious higher crown/implant (C/I) ratios of the FPDs in the short group27, but our results are encouraging since short implants lost 0.93 mm less peri-implant marginal bone than standard-length implants placed in augmented bone. The explanation for this difference could be multifactorial, but at present the reasons might be essentially two: the first is that the slow revascularization process of the onlay bone blocks might have induced a more pronounced marginal bone remodelling around implants compare to native bone28; the second reason is that splinted restorations might have shared the occlusal loads and distributed the stresses more evenly between the implants than individual crowns, and mitigated the detrimental effects on peri-implant bone of high C/I ratio values29. Furthermore, four patients in the augmentation group versus only one in the short implant group suffered for peri-implantitis during the 5-year follow-up period and were considered at higher risk of premature implant failure30,31. It is most likely to be that this statistically significant between-group difference in the marginal bone loss would give rise to a clinical significance in the long-term period. Therefore, it is fundamental to wait for follow-ups up to 10 years, before being able to provided evidence-based recommendations on best therapeutic option. The results of the present study have to be interpreted with caution because of its limitations. Data were not recorded prospectively, but retrospectively and there was a moderate dropout rate among patients (n = 6; 11.7% of the sample). The residual bone width was not comparable at baseline between the two groups, because patients in the augmentation group showed on average about 1.5 mm less available alveolar bone width than that of the short implant group, as the surgeon systematically adopted the block grafting procedure in cases where the preoperative bone thickness was less than 6 mm. The different baseline bone dimensions and implant diameters might have confounded the results of this study. Among the strengths of this study, it is worth stressing that both techniques were tested in real clinical conditions and patient inclusion criteria were not particularly restrictive, therefore, the results of the
present study could be generalized to a larger population with similar characteristics. Within the limitations of this study, it was shown that short implants and standard-length implants placed in augmented bone using a block bone-grafting procedure are equally successful to support fixed partial restorations in the atrophic posterior mandible after a 5-year followup. However, short implants demonstrated a lower number of surgical complications and less marginal bone loss than standardlength implants placed in augmented bone. This increased resorption pattern of the augmented bone under physiological loading conditions must be confirmed by a long-term follow-up of 10 years. Funding
None. Competing interests
None. Ethical approval
The investigation was independently reviewed and approved by the Ethics Committee of Area Vasta Romagna and IRST (ref. no. 01imp). Patient consent
All patients gave consent for the surgery and the 5-year follow-up visit. References 1. Schwartz-Arad D, Levin L, Sigal L. Surgical success of intraoral autogenous block onlay bone grafting for alveolar ridge augmentation. Implant Dent 2005;14:131–8. 2. Jensen OT. Alveolar segmental sandwich osteotomies for posterior edentulous mandibular sites for dental implants. J Oral Maxillofac Surg 2006;64:471–5. 3. Fernandez Diaz JO, Naval Gias L. Rehabilitation of edentulous posterior atrophic mandible: inferior alveolar nerve lateralization by piezotome and immediate implant placement. Int J Oral Maxillofac Surg 2013;42: 521–6. 4. Garcia-Garcia A, Somoza-Martin M, Gandara-Vila P, Saulacic N, Gandara-Rey JM. Alveolar distraction before insertion of dental implants in the posterior mandible. Br J Oral Maxillofac Surg 2003;41:376–9. 5. Simion M, Jovanovic SA, Tinti C, Benfenati SP. Long-term evaluation of osseointegrated implants inserted at the time or after vertical ridge augmentation. A retrospective study on 123 implants with 1-5 year follow-up. Clin Oral Implants Res 2001;12:35–45.
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6. Aghaloo TL, Moy PK. Which hard tissue augmentation techniques are the most successful in furnishing bony support for implant placement. Int J Oral Maxillofac Implants 2007;22:49–70. 7. Nisand D, Picard N, Rocchietta I. Short implants compared to implants in vertically augmented bone: a systematic review. Clin Oral Implants Res 2015;26(Suppl. 11): 170–9. 8. Deporter D, Ogiso B, Sohn DS, Ruljancich K, Pharoah M. Ultrashort sintered porous-surfaced dental implants used to replace posterior teeth. J Periodontol 2008;79: 1280–6. 9. Pieri F, Aldini NN, Fini M, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012; 25:279–89. 10. Lemos CA, Ferro-Alves ML, Okamoto R, Mendonc¸a MR, Pellizzer EP. Short dental implants versus standard dental implants placed in the posterior jaws: a systematic review and meta-analysis. J Dent 2016;47: 8–17. 11. das Neves FD, Fones D, Bernardes SR, do Prado CJ, Neto AJ. Short implants — an analysis of longitudinal studies. Int J Oral Maxillofac Implants 2006;21:86–93. 12. Esposito M, Pistilli R, Barausse C, Felice P. Three-year results from a randomized controlled trial comparing prostheses supported by 5-mm long implants or by longer implants in augmented bone in posterior atrophic edentulous jaws. Eur J Oral Implantol 2014;7:383–95. 13. Pen˜arrocha-Oltra D, Aloy-Pro´sper A, Cervera-Ballester J, Pen˜arrocha-Diago M, Canullo L, Pen˜arrocha-Diago M. Implant treatment in atrophic posterior mandibles: vertical regeneration with block bone grafts versus implants with 5.5-mm intrabony length. Int J Oral Maxillofac Implants 2014;29:659–66. 14. Stellingsma K, Raghoebar GM, Visser A, Vissink A, Meijer HJ. The extremely resorbed mandible, 10-year results of a randomized controlled trial on 3 treatment strategies. Clin Oral Implants Res 2014;25: 926–32. 15. Felice P, Cannizzaro G, Barausse C, Pistilli R, Esposito M. Short implants versus longer implants in vertically augmented posterior mandibles: a randomized controlled trial with 5-year after loading follow-up. Eur J Oral Implantol 2014;7:359–69. 16. Roos-Jansaker AM, Lindahl C, Renvert H, Renvert S. Nine- to fourteen-year follow-up of implant treatment. Part II: presence of peri-implant lesions. J Clin Periodontol 2006;33:290–5. 17. Cassetta M, Driver A, Brandetti G, Calasso S. Peri-implant bone loss around platformswitched Morse taper connection implants: a prospective 60-month follow-up study. Int J Oral Maxillofac Surg 2016;45:1577–85.
Please cite this article in press as: Pieri F, et al. Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.07.005
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18. Abtahi J, Henefalk G, Aspenberg P. Randomized trial of bisphosphonate-coated dental implants: Radiographic follow-up after five years of loading. Int J Oral Maxillofac Surg 2016;45:1564–9. 19. Lang NP, Wilson TG, Corbet EF. Biological complications with dental implants: their prevention, diagnosis and treatment. Clin Oral Implants Res 2000;11(Suppl. 1):146– 55. 20. Renvert S, Polyzois I, Claffey N. Surgical therapy for the control of peri-implantitis. Clin Oral Implants Res 2012;23(Suppl. 6): 84–94. 21. Camps-Font O, Burguen˜o-Barris G, Figueiredo R, Jung RE, Gay-Escoda C, ValmasedaCastello´n E. Interventions for dental implant placement in atrophic edentulous mandibles: vertical bone augmentation and alternative treatments. A meta-analysis of randomized clinical trials. J Periodontol 2016;87:1444– 57. 22. Felice P, Pellegrino G, Checchi L, Pistilli R, Esposito M. Vertical augmentation with interpositional blocks of anorganic bovine bone vs. 7-mm-long implants in posterior mandibles: 1-year results of a randomized clinical trial. Clin Oral Implants Res 2010; 21:1394–403.
23. Chiapasco M, Zaniboni M, Rimondini L. Autogenous onlay bone grafts vs. alveolar distraction osteogenesis for the correction of vertically deficient edentulous ridges: a 2–4year prospective study on humans. Clin Oral Implants Res 2007;18:432–40. 24. Antoun H, Sitbon JM, Martinez H, Missika P. A prospective randomized study comparing two techniques of bone augmentation: onlay graft alone or associated with a membrane. Clin Oral Impl Res 2001;12:632–9. 25. Roccuzzo M, Ramieri G, Bunino M, Berrone S. Autogenous bone graft alone or associated with titanium mesh for vertical alveolar ridge augmentation: a controlled clinical trial. Clin Oral Implants Res 2007;18:286– 94. 26. Cordaro L, Torsello F, Morcavallo S, di Torresanto VM. Effect of bovine bone and collagen membranes on healing of mandibular bone blocks: a prospective randomized controlled study. Clin Oral Impl Res 2011; 22:1145–50. 27. Garaicoa-Pazmin˜o C, Sua´rez-Lo´pez del Amo F, Monje A, Catena A, Ortega-Oller I, Galindo-Moreno P, Wang HL. Influence of crown/implant ratio on marginal bone loss: a systematic review. J Periodontol 2014; 85:1214–21.
28. Chiapasco M, Casentini P, Zaniboni M. Implants in reconstructed bone: a comparative study on the outcome of Straumann1 tissue level and bone level implants placed in vertically deficient alveolar ridges treated by means of autogenous onlay bone grafts. Clin Implant Dent Relat Res 2014;16:32–50. 29. Bayraktar M, Gultekin BA, Yalcin S, Mijiritsky E. Effect of crown to implant ratio and implant dimensions on peri-implant stress of splinted implant-supported crowns: a finite element analysis. Implant Dent 2013;22: 406–13. 30. Atieh MA, Alsabeeha NH, Faggion Jr CM, Duncan WJ. The frequency of peri-implant diseases: a systematic review and meta-analysis. J Periodontol 2013;84:1586–98. 31. Roos-Jansa˚ker AM. Long time follow up of implant therapy and treatment of periimplantitis. Swed Dent J Suppl 2007;188: 7–66.
Address: Francesco Pieri Via Marinelli 43 47521 Cesena Italy E-mail: [email protected]
Please cite this article in press as: Pieri F, et al. Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.07.005
Int. J. Oral Maxillofac. Surg. 2017; xxx: xxx–xxx http://dx.doi.org/10.1016/j.ijom.2017.07.005, available online at http://www.sciencedirect.com
Clinical Paper Dental Implants
Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study
F. Pieri1, C. Forlivesi1, E. Caselli2, G. Corinaldesi3 1 Private practice, Cesena, Italy; 2Private practice, Ancona, Italy; 3Department of Biomedical and Neuromotorial Science, University of Bologna, Bologna, Italy
F. Pieri, C. Forlivesi, E. Caselli, G. Corinaldesi: Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study. Int. J. Oral Maxillofac. Surg. 2017; xxx: xxx– xxx. ã 2017 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Abstract. This retrospective study compared the 5-year clinical and radiographic outcomes of short implants (6 mm) (short group), and standard-length implants (9 mm) placed after a vertical augmentation with autologous bone blocks (augmentation group), supporting partial fixed prostheses in the posterior mandible. Forty-five partially edentulous patients were enrolled in the study and evaluated after 5 years: 22 (51 implants) in the augmentation group and 23 (46 implants) in the short group. Eight surgical complications occurred in the augmentation group versus none in the short group (P = 0.003). One short implant failed before loading and one standard-length implant failed after 4 years because of peri-implantitis (P = 1.0). Eight biological and two prosthetic complications occurred in the augmentation group vs. three biological and three prosthetic complications in the short group (P = 0.09 and P = 1.0, respectively). A mean marginal bone loss of 1.61 1.12 mm in the augmentation group and 0.68 0.68 mm in the short group was found (P = 0.002). Within the limitations of this study, both techniques resulted in successful clinical results after 5 years, but short implants exhibited less surgical complications and marginal bone loss than standard-length implants placed in augmented bone.
0901-5027/000001+08
Key words: atrophic mandible; vertical augmentation; bone graft; short dental implants. Accepted for publication
ã 2017 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Pieri F, et al. Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.07.005
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The atrophic posterior mandible often poses a challenge to treatment with dental implants because the vertical and horizontal ridge resorption after tooth loss may preclude the placement of standard-length implants in the correct position and with ideal inclination. Various procedures to augment the native bone volume have been clinically tested, including onlay and inlay autologous bone grafts, alveolar nerve transposition, distraction osteogenesis and guided bone regeneration1–5. Unthese techniques are fortunately, associated with increased postoperative morbidity, higher costs, and higher risks of complications during the healing period that often deter patients from seeking implant therapy6,7. Thus, short implants with an intra-bony length of 8 mm or less could be a simpler, cheaper, and faster alternative to augmentation procedures, if they demonstrate to result in similar survival rates8,9. Some authors have reported that short implants did not have a good longterm prognosis when compared with standard-length implants in posterior jaws10, although the implant surface may have played a confounding role in the survival rates11. Other recent comparative clinical trials have documented that even short implants with a length of 5–6 mm may have a similar short-term survival rate compared with longer implants placed in augmented bone12,13. Nevertheless, very few data have been published comparing these two treatment approaches with an observation period longer than 3 years14,15. The aim of this retrospective study is to compare the clinical and radiographic outcomes of 6 mm short implants with those of 9 mm or longer implants placed following vertical ridge augmentation with autologous block bone grafts, for the partial fixed restoration of atrophic posterior mandibles after a follow-up period of 5 years. This study is reported following the STROBE (Strengthening the Reporting of Observational studies in Epidemiology) guidelines for reporting observational studies (http://www.strobe-statement.org/ ). Materials and Methods Patient selection
A retrospective chart review was performed for all patients who had implants placed in the atrophic posterior mandible between January 1, 2009, and February 1, 2012, in one private dental practice. Five years after implant placement, patients were contacted and invited for a compre-
hensive clinical and radiographic examination (including periapical radiographs of the implants and their restorations). Each patient gave informed consent to participate in the study. The study protocol was approved by the Ethics Committee of Area Vasta Romagna and IRST, and was conducted according to principles stated in the Helsinki Declaration. The following patient inclusion criteria were applied: (1) vertical bone atrophy in the posterior edentulous mandible (a residual bone height between 7 and 9 mm above the inferior alveolar nerve measured on a preoperative cone beam computed tomography (CBCT)); (2) treatment involving the placement of at least two short implants (6 mm) in the native bone or standard-length implants (9 mm) in ridges augmented with mandibular block bone grafts supporting a fixed partial denture; (3) delayed implant loading; (4) patients enrolled in a regular maintenance care programme; (5) a minimum followup period of 5 years from implant placement; (6) availability of a baseline periapical radiograph taken on the day of implant surgery. The patients were excluded if were diagnosed with systemic conditions known to alter bone metabolism, such as cancer requiring chemotherapy or facial radiotherapy, intravenous amino-bisphosphonates for metastatic bone diseases, uncontrolled diabetes mellitus, immunosuppression or immunodepression and smoking habit of more than 20 cigarettes per day (all pipe or cigar smokers were also excluded). Surgical protocol
All surgeries were performed by a single surgeon under local anaesthesia only or local anaesthesia with oral sedation (triazolam, 0.125 mg or 0.25 mg). All patients received prophylactic antibiotic therapy: 1 g of amoxicillin–clavulanic acid (or clindamycin 500 mg if allergic to penicillin) starting the night before the intervention, and twice per day for a total of 7 days, and pain medication (ibuprofen, 600 mg as needed every 6–8 hours). They were also asked to rinse with 0.2% chlorhexidine digluconate (every 12 hours starting 1 day preoperatively for 2 weeks).
were reflected to completely expose the atrophic ridge and identify the mental foramen. The exposed alveolar bone was cleaned of all soft tissue and several decortications holes were made using a small round bur. Bone harvesting was performed from the same side of the ramus with a piezoelectric surgical device (Piezosurgery, Mectron, Carasco, Italy). The block grafts were shaped according to the morphology of the defects and rigidly fixated to the residual bone with titanium miniscrews (Cizeta Surgicals, Bologna, Italy). Anorganic bovine bone particles (BioOss, Geistlich Pharma AG, Wolhusen, Switzerland) were added at the periphery and over the bone grafts. The reconstructed sites were then covered with a resorbable collagen membrane (Bio-Gide, Geistlich Pharmaceuticals). After careful periosteal releasing incisions in order to obtain absolute tension-free closure, the flaps were sutured in two layers with a combination of horizontal mattress and interrupted sutures. The sutures were removed after 3 weeks, and the patients were then checked at 2 months after surgery. Provisional removable prostheses were not allowed during the healing period. Four to five months after augmentation, a CBCT scan was retaken to plan implant placement. The flap outline was similar to the first surgery without vestibular releasing incisions. Following mucoperiosteal flap elevation and debridement, the bone block fixation screws were removed, and standard-length implants (Astra Tech OsseoSpeed, DENTSPLY Implants, Mannheim, Germany) were placed with the top of the platform flush with the facial alveolar crest (Fig. 1). Short implant group
After a crestal incision and flap reflection, implant osteotomy sites were prepared according to a standard drilling sequence. To minimize the risk of inferior alveolar nerve injury, the drills were used with adjustable stop devices that were always set at least 1 mm shorter than the radiographic working length above the canal. Two to three short implants (6 mm) (OsseoSpeed, DENTSPLY Implants) were placed in each patient (Fig. 2). Prosthetic protocol
Augmentation group
A midcrestal incision on the edentulous ridge was made. The incision was extended via the gingival sulcus of the adjacent tooth. Mesial and distal releasing incisions were performed, and full-thickness flaps
All implants in both groups were left submerged for 2–3 months. Definitive titanium–composite, or zirconia–ceramic FPDs were delivered 8–10 weeks after healing abutment connection; they were either screw-retained or cemented on cus-
Please cite this article in press as: Pieri F, et al. Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.07.005
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Atrophic posterior mandibles
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Fig. 1. Posterior mandibular atrophic site treated with a bone block augmentation and delayed standard-length implant placement. (A) Preoperative panoramic radiograph. (B) Preoperative cone-beam computed tomography scans. (C) Preoperative occlusal view of the atrophic left posterior mandible. (D) Fixation of the bone block graft harvested from the ramus with an osteosynthesis screw. (E) Particulate anorganic bovine bone graft around block graft. (F) Collagen membrane over the block graft. (G) Panoramic radiograph at 4 months from bone graft procedure. (H) Implant placement at mandibular left first and second molar positions. (I) Periapical radiograph at implant placement. (L) Five-year periapical radiograph demonstrates some crestal bone remodelling around both implants.
tomized computer-aided design/computer-aided manufacturing titanium abutments. All patients were kept under regular maintenance care and received full-mouth scaling every 6 months.
medical and dental history, a prosthodontic examination, and a peri-apical radiograph of all implants that fulfilled the inclusion criteria. The following outcome measures were assessed.
Outcome measures
Implant failure: defined as presence of any mobility of the individual implant and/or any situation dictating implant removal.
The 5-year follow-up examination was conducted by two investigators (C.F. and E.C.), and included an update of the
FPD failure: defined as planned FPD that could not be placed as planned due to implant failure(s), loss of the FPD secondary to implant failure(s), and replacement of the FPD for any reasons. Surgical complications: including haemorrhaging during and after surgery, soft-tissue dehiscence, infections, fistulae, sensory loss, and partial or total bone graft resorption.
Fig. 2. Posterior mandibular atrophic site treated with short dental implants. (A) Preoperative panoramic radiograph. (B) Preoperative cone beam computed tomography scans. (C) Occlusal view of the left posterior atrophic mandible. (D) Two 4 6 mm implants were placed in the second premolar and first molar positions. (E) Postoperative periapical radiograph. (F) Five-year periapical radiograph demonstrates stable bone levels for both implants.
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Biological complications: including peri-implant mucositis, and peri-implantitis. Peri-implant mucositis was defined as a heavily inflamed soft tissue without bone loss, and peri-implantitis was defined as a bone loss of more than 3 mm with suppuration, heavily inflamed tissues, or fistulas16. Prosthetic complications: including FPD detachment, screw loosening, and fracture of the screw, framework, or occlusal material. Peri-implant marginal bone levels (MBLs) were evaluated on digital periapical radiographs (Digora Optime; Soredex/Orion Corporation, Helsinki, Finland) taken at implant placement, implant loading, and 5 years after implant placement. For standardization, a film holder-beam aiming device (Dentsply Rinn, Elgin, IL, USA) was applied according to the long cone paralleling technique. The radiographs were taken with the film placed parallel to the implant axis and the radiographic beam directed perpendicular to the implant17. Customized positioners could not be used because of the retrospective character of the study. An imageanalysis software (Digora for Windows, ver. 2.1; Soredex/Orion Corporation) was used to measure the linear distance between the implant platform and the most coronal level of the bone deemed to be in contact with the implant surface with an on-screen cursor at 5 magnification. In cases where the implant platform was below the margin of the crestal bone, that is subcrestal, the value was considered as zero. To make calibrated measurements, an object of known size, the known diameter of the implant, was used. To adjust the measurements for any magnification error, the following equation was used to deter-
mine the correct MBLs: measured MBL (actual implant diameter/measured implant diameter)18. Relative mesial and distal bone height measurements were made to the nearest 0.01 mm and were averaged at a patient level. The change in MBL was calculated by subtracting the follow-up level from the baseline level at implant placement. Furthermore, at FPD placement, the crown/implant ratio was assessed for each implant, dividing the length of the restoration and the length of the implant. Radiographic measurements were performed by one experienced examiner (G.C.), who was calibrated and subjected to an intra-rater agreement test. Statistical analysis
All data analyses were performed using a statistical software package (GraphPad InStat, GraphPad Software Inc., San Diego, CA, USA). Descriptive statistics were expressed as a frequency and percentage, and means and standard deviations, as appropriate. The patient was the statistical unit of the analyses. Differences in the proportion of patients with failures and complications were compared between the groups using Fisher’s exact test. The Friedman test was used to detect intragroup differences, and Mann-Whitney test was used to detect between-group differences in MBL values. The level of significance was set at 0.05 for all comparisons. Results
The patient sample consisted of 45 patients from the 51 that were treated. Six patients were excluded from the study (2 in the augmentation group and 4 in the short group; 11.7% of patients) for the following reasons: one patient had been
treated with chemotherapy for malignant tumours during the follow-up period, one patient had moved away, and four patients failed to attend the examination for various reasons. Out of the final sample of 45 patients, 22 with 51 implants were of the augmentation group, and 23 with 46 implants were of the short implant group. In the augmentation group, 28 implants were 9 mm long, and 23 were 11 mm or longer; the diameter was 3.5 mm in 41 implants, and 4 mm in 10. In the short implant group, all implants were 6 mm long, and the diameter measured 4 mm. Patient and intervention characteristics are provided in Table 1. There were no apparent significant baseline imbalances between the two groups with the exception of less amount of native bone width in the augmentation group (4.72 0.63 mm versus 6.37 0.69 mm, P < 0.0001). Implant and prosthesis failures
The main results up to 5-year follow-up are summarized in Table 2. One implant failed in both groups, yielding a cumulative 5-year survival rate at patient level of 95.7% in the short implant group and 95.5% in the augmentation group. One FPD could not be made as planned in the short implant group because the last implant was found to be infected and mobile at abutment connection and was removed. It was the most distal implant and the patient was pleased with a shorter FPD and did not want to have it replaced. In the augmentation group, one implant (3.5 9 mm) in position 36 was removed (in a light smoker patient) because of excessive bone resorption (5 mm) after 4 years from placement. It was immediately replaced at removal with a 6-mm-long and 3.6-mm-diameter implant (Osseospeed,
Table 1. Patient and implant characteristics of the short implant group and augmentation group at the start of the study. Variable
Augmentation group (n = 22)
Short implant group (n = 23)
Mean age at placement (SD) No. of female patients No. of smokers (<20 cigarettes/day) No. of patients with periodontitis No. of patients with bruxism Preoperative mean bone height above the mandibular canal (SD) (mm) Preoperative mean residual bone width ( SD) (mm) Total no. of placed implants Mean number of implants in each patient (SD) Number of implants in premolar/molar position Mean implant height (SD) (mm) Mean implant diameter (SD) (mm) Mean crown/implant ratio
56.4 8.25 16 5 6 1 7.29 1.3 4.72 0.63 51 2.32 0.47 21/30 9.98 1.15 3.6 0.2 1.08 0.29
57.69 7.93 19 5 4 4 7.82 0.51 6.37 0.69 46 2.17 0.38 12/34 6 4 2.03 0.27
P-value 0.84a 0.45b 0.1b 0.49b 0.34b 0.32a <0.0001a 0.27a 0.13b
SD, standard deviation; FPD, fixed partial denture. a Mann–Whitney U test. b Fisher’s exact test.
Please cite this article in press as: Pieri F, et al. Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.07.005
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Table 2. Summary of the main clinical results after 5 years of follow-up (number of events and their descriptions in parenthesis). Implant failures Prosthesis failures Complications surgical biological prosthetic
Augmentation group (n = 22)
Short implant group (n = 23)
P-valuea
1 1 16 8 (5 partial graft resorptions, 3 transient lip paresthesiae) 8 (4 mucositis, 4 peri-implantatis) 3 (2 ceramic fractures, 1 decementation)
1 1 3 0
1.0 (NS) 1.0 (NS)
2 (2 mucositis, 1 peri-implantitis) 4 (1 ceramic fracture, 2 decementations, 1 abutment screw loosening)
0.09 (NS) 1.0 (NS)
0.003
NS, not significant. a Fisher exact test.
DENTSPLY Implants) in a distal position and a new FPD was made. On a patient basis, the differences in proportions of prosthesis and implant failures at patient level were identical and not statistically significant (P = 1.00). Complications
Before implant loading, eight surgical complications related to the block grafting procedure occurred in the augmentation group versus none in the short implant group. Three patients reported transient lower lip paraesthesia for a duration of 1–2 months after ramus harvesting and posterior mandibular reconstruction. Complete functional recovery was obtained in all cases. In five patients a partial graft resorption (<50%) occurred, which required supplementary bone augmentation at implant placement with
autologous bone particles harvested during implant osteotomy and a collagen membrane. There was a statistically significant difference in the number of surgical complications between the two groups (P = 0.003) (Table 2). After loading, biological complications occurred in eight patients of the augmentation group, and three patients of the short implant group. In total, four patients with eight implants in the augmentation group, and two patients with four implants in the short implant group were affected by periimplant mucositis, and were successfully managed by interceptive supportive therapy19, consisting of professional cleaning with titanium curettes, polishing using rubber cups and polishing paste, followed by 0.2% chlorhexidine mouth rinses, three times per day for 2 weeks. Four patients in the augmentation group and one patient of the short implant group had one to three
implants affected by peri-implantitis after 2–4 years from placement. These sites showed a severe bone loss of 3–6 mm and purulent exudate, and were treated by grafting the defect with granules of anorganic bovine bone (Bio-Oss, Geistlich Pharmaceuticals) or with resective surgery under systemic antibiotics (Fig. 3)20. At the 5-year follow-up evaluation, in four patients clinically healthy peri-implant soft tissues were re-established around implants with reduced but stable bone levels. In one patient of the augmentation group, one implant was removed after 4 years because of the progressive loss of marginal bone. The difference in proportions of patients experiencing biological complications between the two groups was not statistically significant (P = 0.09) (Table 2). Prosthetic complications in the augmentation group included minor ceramic
Fig. 3. Sequence of panoramic and periapical radiographs showing one of the patients treated with standard-length implants in augmented bone, which suffered from peri-implantitis. (A) Preoperative panoramic radiograph. (B) Postoperative panoramic radiograph. (C) Periapical radiograph just after implant placement. (D) Periapical radiograph at start of prosthetic loading. (E) Periapical radiograph at 1 year. (F) Periapical radiograph at 5 years that shows a stabilization of the bone crest around implants at a clearly reduced level after a surgical revision and an apical flap repositioning for the treatment of a peri-implantitis after 4 years.
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Table 3. Comparison of mean (SD) marginal bone levels (in mm) for the two groups between baseline (implant placement) and 1, and 5 years of follow-up. Baseline Year 1 Year 5 Bone level change baseline to 1 year Bone level change baseline to 5 years a b
Augmentation group (n = 22)
Short implant group (n = 23)
0.04 0.01 0.79 0.69b 1.65 1.13b 0.75 0.68 1.61 1.12
0.02 0.05 0.32 0.26b 0.7 0.69b 0.3 0.24 0.68 0.68
P-valuea
0.03 0.002
Mann–Whitney test. All changes from baseline statistically significant different (Friedman test, P < .0001).
veneer fractures at two FDPs, which could be simply polished, and the need for cementation of one FDP. Four prosthetic complications (one abutment screw loosening, two decementations, and one minor ceramic veneer fracture) were observed in the short implant group. There was no statistically significant difference with respect to prosthetic complications between the two groups (P = 1.0) (Table 2). Peri-implant marginal bone level changes
The two-way intra-class correlation coefficient was excellent (0.97) for radiographic intra-rater agreement analysis. Between and within group analysis of MBLs at patient level are presented in Table 3. Both groups gradually lost statistically significant amounts of marginal bone from implant placement to 5 years (P < .0001). There was a statistically significant difference between the two groups for peri-implant bone level changes at loading (P = 0.03), and 5 years (P = 0.002). A statistically significant difference was also observed in the number of patients with MBL change >1 mm at 5 years of follow-up: four (17.3%) in the short implant group versus 12 (54.5%) in the augmentation group (P = 0.02). Discussion
The objective of this retrospective study was to evaluate, after a 5-year follow-up, whether short (6 mm) implants could be a reliable alternative to a block bone-grafting procedure for placing standard-length (9 mm) implants when rehabilitating atrophic posterior mandibles with FPDs. Differences between treatments were found in the number of surgical complications and MBL changes, while for the number of implant and FPD failures, and biological and prosthetic complications, the differences were not statistically significant. When comparing the use of short implants and augmentation procedures, most authors agree that bone-grafting procedures are more technically demanding and related with higher
morbidity than placing short implants21. In a randomized clinical trial (RCT) by Felice et al.22 including 60 patients, no patient suffered from permanent damage of inferior alveolar nerve function, but more patients in the group that underwent inlay bone block augmentation suffered transient paraesthesia of the lower lip. In fact, 16 patients (57%) had transient postoperative paraesthesia vs. only two patients (7%) in the short implant group. Furthermore, four wound dehiscences occurred during graft healing in the augmentation group, while none occurred in the 7mm short implant group. Pen˜arrocha-Oltra et al.13, in a retrospective study of 37 patients, found five surgical complications (1 temporary hypoesthesia of the chin, and 4 wound dehiscences) in 20 augmented patients using mandibular block grafts versus none in 17 patients in the short implant group. The same trend was also observed in our study, with more surgical complications occurring when the most invasive procedure was used. The augmentation procedure not only was associated with more patients experiencing transient postoperative paraesthesia of the inferior alveolar nerve (3 patients vs. none in the short implant group), but there was also an insufficient remodelling of the bone graft associated to a partial resorption at the surgical re-entry in five patients. Consequently, implant placement was performed using a simultaneous bone augmentation procedure, with additional discomfort for the affected patients. The reason for this resorption is not fully understood23,24, but similar findings were described by Roccuzzo et al.25, and could be caused by an insufficient contact among the block grafts and the native bone or could be related to the extremely cortical nature of the mandibular blocks themselves. Evidence exists that combining a membrane with an autologous block graft may limit graft resorption, but this still occurs to a moderate extent26. Cases of inadequate vertical bone gain for placement of standard-length implants have been reported in most studies dealing on implants placed in vertically augmented
ridges in the posterior mandible. In a recent RCT by Esposito et al.12, in five out of 15 patients (33.3%) with bilateral atrophic mandibles, the planned 10-mmlong implants could not be placed, and shorter implants (7 and 8.5 mm) had to be used instead. Similarly, Pen˜arrocha-Oltra et al.13 were unable to place 10-mm-long implants in seven out of 20 patients (35%) subjected to block grafting procedures, and, therefore, shorter implants were used. Furthermore, almost half (21 out of 45) of the implants placed in grafted mandibles needed the addition of particulate bone graft to cover peri-implant dehiscences at implant placement. Also in the present study, the new bone obtained with the augmentation procedure did not allow to place implants longer than 9 mm in 28 out of 51 sites (55%). Previous comparative studies report similar long-term clinical and radiographic results for implant treatment in posterior mandibular atrophic sites treated with either block bone grafts or short dental implants. Felice et al.15 found no statistically significant differences for implant and FPD failures after 5 years, comparing 6.6 mm short implants and 10 mm or longer implants placed in augmented bone. In the same study, short implants lost a mean of 1.49 mm of peri-implant bone compared with 2.34 mm in the augmentation group, this being a statistically significant difference. Similar results were reported by Esposito et al.12 in another split-mouth RCT with 30 partially edentulous patients (15 mandibles and 15 maxillae), comparing 5-mm-long implants and 10-mm or longer implants placed in grafted bone. At the 3-year follow-up, one long implant failed versus two short implants in the same patient in posterior mandibles. Patients with mandibular implants showed a mean marginal bone resorption of 1.44 mm around short implants and 1.63 mm around long implants; the between-group difference in peri-implant bone loss was not statistically significant. In the present study, both procedures yielded similarly high 5-year implant and prosthesis survival rates (95.7% for
Please cite this article in press as: Pieri F, et al. Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.07.005
YIJOM-3748; No of Pages 8
Atrophic posterior mandibles short implant group and 95.5% for augmentation group), but short implants did it with only one surgical intervention, and in a shorter treatment time. The main potential risk with short implants is marginal bone loss over time, also considering the obvious higher crown/implant (C/I) ratios of the FPDs in the short group27, but our results are encouraging since short implants lost 0.93 mm less peri-implant marginal bone than standard-length implants placed in augmented bone. The explanation for this difference could be multifactorial, but at present the reasons might be essentially two: the first is that the slow revascularization process of the onlay bone blocks might have induced a more pronounced marginal bone remodelling around implants compare to native bone28; the second reason is that splinted restorations might have shared the occlusal loads and distributed the stresses more evenly between the implants than individual crowns, and mitigated the detrimental effects on peri-implant bone of high C/I ratio values29. Furthermore, four patients in the augmentation group versus only one in the short implant group suffered for peri-implantitis during the 5-year follow-up period and were considered at higher risk of premature implant failure30,31. It is most likely to be that this statistically significant between-group difference in the marginal bone loss would give rise to a clinical significance in the long-term period. Therefore, it is fundamental to wait for follow-ups up to 10 years, before being able to provided evidence-based recommendations on best therapeutic option. The results of the present study have to be interpreted with caution because of its limitations. Data were not recorded prospectively, but retrospectively and there was a moderate dropout rate among patients (n = 6; 11.7% of the sample). The residual bone width was not comparable at baseline between the two groups, because patients in the augmentation group showed on average about 1.5 mm less available alveolar bone width than that of the short implant group, as the surgeon systematically adopted the block grafting procedure in cases where the preoperative bone thickness was less than 6 mm. The different baseline bone dimensions and implant diameters might have confounded the results of this study. Among the strengths of this study, it is worth stressing that both techniques were tested in real clinical conditions and patient inclusion criteria were not particularly restrictive, therefore, the results of the
present study could be generalized to a larger population with similar characteristics. Within the limitations of this study, it was shown that short implants and standard-length implants placed in augmented bone using a block bone-grafting procedure are equally successful to support fixed partial restorations in the atrophic posterior mandible after a 5-year followup. However, short implants demonstrated a lower number of surgical complications and less marginal bone loss than standardlength implants placed in augmented bone. This increased resorption pattern of the augmented bone under physiological loading conditions must be confirmed by a long-term follow-up of 10 years. Funding
None. Competing interests
None. Ethical approval
The investigation was independently reviewed and approved by the Ethics Committee of Area Vasta Romagna and IRST (ref. no. 01imp). Patient consent
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Address: Francesco Pieri Via Marinelli 43 47521 Cesena Italy E-mail: [email protected]
Please cite this article in press as: Pieri F, et al. Short implants (6 mm) vs. vertical bone augmentation and standard-length implants (9 mm) in atrophic posterior mandibles: a 5-year retrospective study, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.07.005