Piezoelectric Alveolar Ridge-Splitting Technique with Simultaneous Implant Placement: A Cohort Study with 2-Year Radiographic Results Renzo Bassetti, Dr Med Dent1/Mario Bassetti, Dr Med Dent2/ Regina Mericske-Stern, Prof Dr Med Dent3/Norbert Enkling, PD Dr Med Dent4 Purpose: Extended grafting procedures in atrophic ridges are invasive and time-consuming and increase cost and patient morbidity. Therefore, ridge-splitting techniques have been suggested to enlarge alveolar crests. The aim of this cohort study was to report techniques and radiographic outcomes of implants placed simultaneously with a piezoelectric alveolar ridge-splitting technique (RST). Peri-implant bone-level changes (ΔIBL) of implants placed with (study group, SG) or without RST (control group, CG) were compared. Materials and Methods: Two cohorts (seven patients in each) were matched regarding implant type, position, and number; superstructure type; age; and gender and received 17 implants each. Crestal implant bone level (IBL) was measured at surgery (T0), loading (T1), and 1 year (T2) and 2 years after loading (T3). For all implants, ΔIBL values were determined from radiographs. Differences in ΔIBL between SG and CG were analyzed statistically (Mann-Whitney U test). Bone width was assessed intraoperatively, and vertical bone mapping was performed at T0, T1, and T3. Results: After a mean observation period of 27.4 months after surgery, the implant survival rate was 100%. Mean ΔIBL was –1.68 ± 0.90 mm for SG and –1.04 ± 0.78 mm for CG (P = .022). Increased ΔIBL in SG versus CG occurred mainly until T2. Between T2 and T3, ΔIBL was limited (–0.11 ± 1.20 mm for SG and –0.05 ± 0.16 mm for CG; P = .546). Median bone width increased intraoperatively by 4.7 mm. Conclusions: Within the limitations of this study, it can be suggested that RST is a well-functioning one-stage alternative to extended grafting procedures if the ridge shows adequate height. ΔIBL values indicated that implants with RST may fulfill accepted implant success criteria. However, during healing and the first year of loading, increased IBL alterations must be anticipated. INT J ORAL MAXILLOFAC IMPLANTS 2013;28:1570–1580. doi: 10.11607/jomi.3174 Key words: bone-level alteration, bone splitting, piezoelectric surgery, simultaneous implant placement
A
thin alveolar ridge is a frequently encountered barrier to standard implant placement. The pattern of bone resorption after tooth extraction is well known.1–4 Over a period of 4 to 12 months following tooth extraction, the buccolingual crestal bone dimension decreases by 3.1 to 5.9 mm (approximately 50% of
1 Assistant
Professor, Department of Prosthodontics, University of Bern, Switzerland. 2 Assistant Professor, Department of Periodontology, University of Bern, Switzerland. 3 Professor and Chair, Department of Prosthodontics, University of Bern, Switzerland. 4 Associate Professor, Department of Prosthodontics, University of Bern, Switzerland. Correspondence to: Dr Renzo Bassetti, Department of Prosthodontics, School of Dental Medicine, University of Bern, Freiburgstrasse 7, 3010 Bern, Switzerland. Fax: +41-31-632-49-33. Email:
[email protected] ©2013 by Quintessence Publishing Co Inc.
1570 Volume 28, Number 6, 2013
the original bone width).5–9 The changes in horizontal dimension are more pronounced in the molar regions than in the premolar areas and are even more distinct in the mandible than in the maxilla.9 There is a general consensus that a minimum of 6 to 7 mm of bone width is required for placement of an implant with a diameter of 3.5 to 4 mm using a standard surgical protocol.2,10–12 The minimum bone width of 1 to 1.5 mm required on both the buccal and lingual/palatal sides of an implant is important for a predictable outcome.13–15 If a distinctly reduced ridge width is identified (< 5 mm at the coronal and apical parts of the implant), two-stage surgical procedures using guided bone regeneration become necessary.16–20 A mixture of autogenous bone and allogenous material,21–24 autogenous block onlay grafts harvested intraorally or from the hip,25–28 or horizontal distraction osteogenesis can be applied. 29 Before implant placement, a healing time of several months is usually needed. Such procedures increase the treatment time and costs and negatively affect patient morbidity.26,30–33
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In cases of a very narrow ridge, some authors suggest alveolar ridge-splitting techniques (RST) or alveolar ridge expansion techniques with simultaneous implant insertion. The ridge expansion technique by means of hand osteotomes was introduced by Tatum and modified by Summers.34,35 These sets of instruments have gradually increasing dimensions and are applied to expand the implant site. Other clinicians prefer hand chisels instead of osteotomes to spread the alveolar ridge.13,14 Both procedures are recommended in soft bone (types 3 or 4) and allow positioning of implants simultaneously, but a minimum ridge width of 3 to 4 mm15,36 is a prerequisite. The limitations of these techniques arise from the presence of highly mineralized residual bone and the absence of a cancellous bone layer between the oral and buccal cortical plates. Two devices for cutting hard alveolar bone under adequate control have been described: microsaw devices15 and piezoelectric devices.36 Both may be used, regardless of bone quality.15,36 Additionally, with these devices, it is possible to prepare thinner cuts than with conventional burs.15 The aim of this observational study was to compare peri-implant bone-level alterations of implants placed with either an RST (with a split-flap design) or in native bone.
MATERIALS AND METHODS Patients and Implants During a 30-month period, seven patients (two men, five women; average age 54.3 ± 11.7 years) were consecutively admitted for implant treatment using RST (study group [SG]). Seven patients who received implant treatment without RST during the same time period served as a comparison group (control group [CG]). The CG patients were matched to the SG patients in terms of age (mean, 61.6 ± 13.3 years); gender; implant position; implant type (type of implant-abutment connection, implant surface, implant length, and implant diameter); implant number; and implant suprastructure. The SG and CG were each treated with 17 implants. Table 1 gives an overview of patients, implants, and prostheses. The inclusion criteria37 are presented in Table 2. Two initial situations are presented in Figs 1 and 2. The patients were informed in detail about possible risks and benefits of the treatment, and all provided informed consent. The study was performed in compliance with good clinical practices and the Declaration of Helsinki. This survey was part of a quality control assessment of the dental consultation and did not fall under the approval of an ethical review board (Ethical Committee of the Canton Bern [KEK], Switzerland).
Surgical Procedures RST procedures were carried out under local anesthesia (Ubistesin forte with adrenaline 1:100,000, 3M ESPE) and premedication with amoxicillin (Clamoxyl, GlaxoSmithKline AG), starting 1 hour preoperatively (3 × 750 mg) in both groups (SG, CG). Postoperative antibiotic medication was administered only in the SG (3 × 750 mg Clamoxyl for 7 days). In the SG, a full-thickness mucoperiosteal flap was released in the crestal area of approximately 3 mm in depth and then continued as a split-thickness mucosal flap in the vestibule. This preparation technique protected the periosteum on the buccal aspect of the thin ridge, permitting sufficient blood supply to the buccal plate. With the piezoelectric device (Piezon Master Surgery, EMS), a horizontal cut, 7 mm deep, was made on top of the alveolar ridge. In sites with types 1 and 2 bone, additionally, two vertical releasing cuts were made lateral to the first horizontal cut. In this area, the periosteum was also raised (Fig 3). Through the positioning of wedges (Fa. Zepf ) along the prepared bone split, the space between the lingual and buccal bone plates was gradually increased (Fig 4). The implant beds were carefully prepared with a minimum of drilling, and the corresponding implants were then inserted (Figs 5 and 6). Afterward, the remaining gap between the buccal and lingual bone walls created by the splitting technique was completely filled with xenogeneic hydroxyapatite particles (Bio-Oss Spongiosa granules, 0.25 to 1 mm, Geistlich Pharma) (Fig 7). Then, the split ridge was covered with a resorbable collagen membrane (Bio-Gide, Geistlich Pharma) to protect the graft. First, the periosteum was adapted to fix the membrane using a resorbable suture (Vicryl 4-0, Ethicon, Johnson & Johnson) (Fig 8). Then, by suturing the mucosal flap, the surgeon achieved tension-free soft tissue closure (Ethilon 4-0, Ethicon, Johnson & Johnson) (Fig 9). In CG patients, a full-thickness mucoperiosteal flap was always raised. A standard surgical protocol for implant placement was applied. All patients were instructed to rinse twice per day with chlorhexidine 0.12% (Meridol Perio, GABA) for 2 weeks postoperatively, starting the day of surgery. Sutures were removed postoperatively after 10 to 14 days in SG patients and 7 to 10 days in CG patients.
Prosthetic Phase After a minimum healing period of 3 months in SG sites and 6 weeks in CG sites, reentry surgery was performed with a miniature full-thickness flap. The surgical templates, which were used initially for the radiological implant planning and subsequently as orientation guide in the implant surgery, were used to identify the positions of the submerged implants. The International Journal of Oral & Maxillofacial Implants 1571
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Table 1
Overview of the Treated Patients SG Implant data Sex
Patient age at surgery (y)
1
F
2
M
Patient
3
F
Both groups
Site*
Length (mm)
Diameter (mm)
Reconstruction
Implant system
49
31 42
13 13
3.5 3.5
FPD
NRG
53
11
10
4.3
FPD
RRS
21
10
4.3 FPD
NRG
FPD MTB
SPI NRG
SC SC FPD
SBL NRG
63
4 5
M F
72 62
6 7
F F
19 62
11
13
4.3
22 35 13 23 44 14 15
13 11 10 10 13 12 10
3.5 4.0 4.3 4.3 4.3 3.3 3.5
14 11 21 24 25
10 10 10 10 10
3.5 3.5 3.5 3.5 3.5
*FDI tooth-numbering system. FPD = fixed partial denture; MTB = milled titanium bar; SC = single crown. NRG = NobelReplace Tapered Groovy implant + porous anodized TiUnite surface + internal tri-channel connection (Nobel Biocare); RRS = Replace R Select Tapered implant + porous anodized TiUnite surface + internal tri-channel connection (Nobel Biocare); SPI = SPI ELEMENT implant + sandblasted/acid-etched surface + internal-hexagon connection with reinforced collar (Thommen Medical); SBL = Straumann bone-level implant + chemically modified sandblasted/acid-etched titanium surface + conical internal connection (CrossFit) (Institut Straumann).
Table 2
Inclusion Criteria
Group
Criteria
SG
All patients were healthy or had well-controlled medical conditions. Indications to apply the RST were similar to those described by Holtzclaw et al37: A minimal horizontal bone width of ≥ 2 mm A minimal vertical bone height to vital structures of ≥ 10 mm The horizontal osteotomy maintains a minimum distance of 1 mm from the adjacent teeth. Nonconcave cross-sectional anatomy Indications for RST varied and included edentulous maxilla, lateral gap in the maxilla and mandible, and narrow anterior crest with missing front teeth in the mandible and maxilla (Figs 1 and 2).
CG
All patients were healthy or had well-controlled medical conditions. Bone height and width allowed for accommodation of implants with a diameter of at least 3.5 mm and a length of ≥ 10 mm. There was no need for local guided bone regeneration using grafting material and membranes.
After an additional 2-week period to allow healing of the soft tissue, impressions were taken with an open tray and a screwed impression coping procedure. According to the prosthetic indications, the definitive superstructures were placed in SG patients 4 to 8 months after surgery (Figs 10 and 11) and in CG patients 2 to 6 months after surgery. All patients were enrolled in a regular maintenance program that involved two scheduled visits per year. 1572 Volume 28, Number 6, 2013
Clinical Assessment The following parameters were recorded during follow-up: pain in the region of the implants, implant mobility (tested manually), probing depth (PD > 3 mm), bleeding on probing (BOP), and Plaque Index (PI).
Bone Width Alteration During Surgery The faciolingual dimension of the alveolar bone where the implants were inserted was measured twice
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CG Implant data Sex
Patient age at surgery (y)
1
F
64
2
M
74
Patient
3
F
56
4 5
M F
78 65
6 7
F F
19 75
Site*
Length (mm)
Diameter (mm)
Reconstruction
32 42
13 13
3.5 3.5
MTB FPD
11
13
4.3
22
13
4.3
11
13
4.3
22 35 13 23 45 24 15
13 11 13 13 13 12 13
4.3 4.2 4.3 4.3 4.3 3.3 4.3
13 11 21 23 25
13 10 10 13 10
3.5 4.3 3.5 3.5 4.3
FPD SC MTF SC SC FPD
Fig 1 Buccal view of missing teeth in the anterior mandible.
Fig 2 Edentulous maxilla with adequate height but advanced resorption of the labial plate.
intraoperatively (after mucosal flap release and after implant placement) by means of a slide gauge, 2 mm below the crest. The bone widths were measured to a precision of 0.1 mm.
Radiographic Examination
Bone Mapping At T0 (surgery/baseline), T1 (prosthesis delivery), and T3 (2 years after loading), the distance between the implant shoulder and the marginal bone crest was determined at four sides (mesial, buccal, distal, lingual) around all implants in SG by means of bone mapping using a periodontal probe. Measurements at T1 and T3 were performed under local anesthesia (Ubistesin forte with adrenalin 1:100,000, 3M ESPE) and after removal of the superstructures. Values were rounded to the nearest 0.5 mm.
Digital radiographs of the implant region (Figs 12 and 13) were taken in both groups at four time points: T0, T1, at 1 year after loading (T2), and T3. Dimaxis Pro software (version 4.3.2, Planmeca) was used to analyze the radiographs and measurements with a measurement precision of 0.01 mm. The region of interest on the radiographs was magnified using the software, and bone height measurements were calibrated based on the known implant length. The crestal bone level was assessed at mesial and distal sites of all implants with the implant shoulder as the reference point. The vertical implant bone level (IBL) was defined as the vertical distance between the microgap (implantsuperstructure connection) and the most coronal The International Journal of Oral & Maxillofacial Implants 1573
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Fig 3 Situation after use of the piezoelectric device and completion of the bone cuts (mandible).
Fig 6
Placement of implants (mandible).
Fig 8 The periosteum was sutured using horizontal mattress stitches to fix the membrane.
Fig 5 Placement of implants (maxilla).
Fig 7 The gap between the bone plates was filled with Bio-Oss Spongiosa granules (Geistlich Pharma).
Fig 9 Tension-free soft tissue closure was achieved using mattress and continuing sutures.
bone-to-implant contact. Independently, two blinded investigators experienced in dental radiology examined the radiographs twice. If the differences in the measurements between the two examiners were 0.1 mm or less, the mean of the four measurements was used. If the differences were greater than 0.1 mm, the examiners reanalyzed the specific implant together to reach a consensus. Changes in marginal bone levels over time were calculated as differences in the measured values (ΔIBL).
Statistical Analysis The primary hypothesis was that the application of RST leads to increased ΔIBL values compared to implants inserted in native bone. The secondary hypothesis stated that the success rates of implants placed by means of RST compared with implants inserted without augmentation procedures are similar. To test the primary hypothesis, ΔIBL values (T0 – T3) of SG and CG (ie, bone loss 2.5 years after implant 1574 Volume 28, Number 6, 2013
Fig 4 Expansion of the prepared bone slit by means of wedges (maxilla).
surgery) were compared (Mann-Whitney U test). The secondary hypothesis was evaluated using descriptive statistics: the ΔIBL values (T1 – T3) of SG and CG (ie, bone loss 2 years after loading) were compared. To determine implant success, the criteria of Albrektsson and Isidor were applied38; ie, no clinical problems (pus, suppuration, implant mobility, pain) and limited change in peri-implant crestal bone level, as assessed by radiographic follow-up: during the first year of loading ≤ 1.5 mm and annual additional bone loss thereafter ≤ 0.2 mm/year. The implant was used as the statistical unit. Prism software (version 4, GraphPad Software Firma) was used for statistical analysis.
RESULTS Two years after loading, the implant survival rate was 100% in both groups. The median value of the intra-
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Fig 10
Labial view of the definitive restoration in the maxilla.
Fig 12 Panoramic radiograph taken 2 years after loading (maxilla).
Fig 11 Labial view of the definitive restoration in the mandible.
Fig 13 Panoramic radiograph taken 2 years after loading (mandible).
Table 3 Alveolar Bone Width Alterations in the SG as Measured Intraoperatively by Means of a Slide Gauge Implant site*
Bone width after mucosal flap release (mm)
Diameter of the inserted implant (mm)
Bone width after implant placement (mm)
Increase in bone width (mm)
31 42 11 21 11 22 35 13 23 44 14 15 14 11 21 24 25
3.1 3.4 2.3 3.2 3.1 3.2 3.4 3.2 2.6 3.5 2.3 2.2 2.5 3.1 2.4 2.5 2.7
3.5 3.5 4.3 4.3 4.3 3.5 4.0 4.3 4.3 4.3 3.3 3.5 3.5 3.5 3.5 3.5 3.5
6.7 6.6 8.2 8.5 8.6 8.1 7.1 9.2 8.1 7.2 6.7 7.2 6.6 7.2 7.1 7.6 7.2
3.6 3.2 5.9 5.3 5.5 4.9 3.7 6.0 5.5 3.7 4.4 5.0 4.1 4.1 4.7 5.1 4.5
Mean ± SD
2.9 ± 0.4
3.8 ± 0.4
7.6 ± 0.8
4.7 ± 0.8
Median (IQR)
3.1 (0.8)
3.5 (0.8)
7.2 (1.3)
4.7 (1.5)
Patient 1 2 3 4 5
6 7
*FDI tooth-numbering system.
operatively achieved enlargement of faciolingual bone width in the SG was 4.7 mm (interquartile range [IQR] 1.5) (Table 3).
IBL values at the mesial and distal aspect of the implants were not significantly different between groups (P = .89) (Tables 4 and 5). Thus, the means of the mesial The International Journal of Oral & Maxillofacial Implants 1575
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Table 4
Changes in Peri-implant Marginal Bone Levels over Time in the SG ΔIBL (mesial)
ΔIBL (distal)
Time period
Mean
SD
Median
95% CI
Mean
SD
Median
95% CI
T0 to T1
–1.18
1.06
–1.08
–1.73; –0.64
–1.20
0.99
–1.14
–1.71; –0.69
T1 to T2
–0.65
0.98
–0.53
–1.16; –0.15
–0.53
0.91
–0.32
–1.01; –0.07
T2 to T3
–0.05
0.03
–0.05
–0.30; 0.20
–0.05
0.02
–0.05
–0.24; 0.15
T0 to T3
–1.66
1.08
–1.71
–2.22; –1.10
–1.69
0.90
–1.73
–2.16; –1.23
CI = confidence interval.
Table 5
Changes in Peri-implant Marginal Bone Levels over Time in the CG ΔIBL (mesial)
ΔIBL (distal)
Time period
Mean
SD
Median
95% CI
Mean
SD
Median
95% CI
T0 to T1
–0.94
0.57
–0.98
–1.24; –0.65
–0.93
1.14
–0.74
–1.51; –0.34
T1 to T2
–0.03
0.42
–0.02
–0.24; 0.19
–0.08
0.63
–0.10
–0.40; 0.25
T2 to T3
–0.06
0.20
–0.06
–0.16; 0.04
–0.04
0.15
–0.06
–0.12; 0.04
T0 to T3
–1.35
0.75
–0.76
–1.42; –0.65
1.04
1.04
1.01
–1.78; –0.51
CI = confidence interval.
Table 6
Overall Changes in Peri-implant Marginal Bone Levels ΔIBL ([M+D]/2) SG
ΔIBL ([M+D]/2) CG
Time period
Mean
SD
Median
95% CI
Mean
SD
Median
95% CI
P*
T0 to T1
–1.19
1.01
–1.09
–1.71; –0.67
–0.94
0.78
–0.75
–1.34; –0.54
.502
T1 to T2
–0.59
0.89
–0.3
–1.05; –0.14
–0.05
0.45
0.02
–0.51; –0.73
.022
T2 to T3
0.11
1.20
–0.07
–0.51; 0.73
–0.05
0.16
–0.05
–0.13; –0.03
.547
T0 to T3
–0.48
0.81
–0.42
–1.12; –0.08
–0.10
0.50
–0.03
–0.38; 0.32
.085
T0 to T1
–1.68
0.90
–1.64
–2.14; –1.21
–1.04
0.78
–1.04
–1.44; –0.64
.022
*Mann-Whitney U test. M = mesial; D = distal; CI = confidence interval.
and distal values were combined for further statistical analyses. Radiographically assessed bone-level alterations (ΔIBL T0 – T3) with a mean follow-up period of 27.4 months after surgery revealed statistically significant differences (P = .022) between the SG (–1.68 ± 0.90 mm) and the CG (–1.04 ± 0.78 mm) (Table 6). Thus, the primary hypothesis was accepted. In the CG, most bone loss occurred during the unloaded healing period after implant surgery; during implant loading, bone-level alterations were very limited. In the SG, similar bone loss as seen in the CG was observed during the healing phase. However, increased crestal bone loss occurred in the SG compared to the CG during the first year of loading (ΔIBL T1 – T2). Between T2 and T3, ΔIBL was limited to –0.11 ± 1.20 mm for the SG and –0.05 ± 0.16 mm for the CG (P = .546) (Fig 14). 1576 Volume 28, Number 6, 2013
The bone mapping approach, which provides a three-dimensional view of peri-implant bone changes, revealed a median bone alteration (ΔIBL T0 – T3) of 1.5 mm (IQR 1.0). Similar rates of bone loss were found mesially, distally, orally, and buccally (Table 7). After 24 to 30 months of loading, all implants were stable, and no signs of peri-implant infection were identified. In both groups, no pain was reported by any patient and no technical complications occurred. BOP was low, and neither group exhibited more than one BOP-positive side per implant. Two SG implants in the canine region of the maxilla exhibited a PD > 3 mm. These implants also showed marginal bone-level changes > 3.5 mm (ΔIBL T0 – T3). Bone-level alterations after implant loading revealed mean ΔIBL (T1 – T3) values in the SG of –0.48 ± 0.81 mm (95% confidence interval [CI] [–1.12;
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Table 7
Horizontal Bone Level, as Measured by Bone Mapping, in the SG at T 0, T1 , and T3 Distance between implant shoulder and marginal bone crest (mm)
Patient
T0
T1
T3
Implant site*
M
B
D
O
M
B
D
O
M
B
D
O
31 42 11 21 11 22 35 13 23 44 14 15 14 11 21 24 25
0 –1 0 1.5 –1 –1 –1 0.5 0 0 0 0 0 0 0 0 0
–1.5 0 0 0 0 0 –0.5 0 0 0 0 0.5 0.5 0 0 0.5 0.5
0 0 0.5 0 0 0 –1 0 0 –0.5 0 0 0 0 0 0 0
0 0 0 0 –0.5 0 0 0.5 0 0.5 0 0 0 0 0 0 0
–1 –0.5 –0.5 –1 –1 –0.5 –2 –2 –3 –1 0 –2 –2 –2 –1.5 –1.5 –1
–1 –1 –1 –1 –0.5 –1 –2 –2 –2.5 –1 –0.5 –2 –1.5 –1.5 –1.5 –1 –1
–1 –0.5 0 0 –0.5 0 –2 –2 –2.5 –1 0 –2.5 –2 –1.5 –2 –1.5 –1.5
–0.5 –0.5 0 –0.5 –1 0 –0.5 –1 –0.5 0 0 –0.5 –1 –1 –0.5 –1 –1
–1.5 –1 –0.5 –1.5 –2 –2 –1.0 –2 –3.5 –1.5 0 –1.5 –3.5 –2 –2 –1.5 –1.5
–1.5 –1.5 –2 –1.5 –2 –1.5 –3 –2.5 –2.5 –2 –1 –3 –2.5 –2.5 –3 –2.5 –2
–1.5 –0.5 –1 –1 –2 –1 –2 –2 –2 –2 0 –1.5 –3.5 –3 –2 –1.5 –2
–1 –1 –0.5 –0.5 –1 –0.5 –0.5 –1 –1 0 –1 –1 –1 –1.5 0 –1.5 –1
1 2 3 4 5
6 7
Mean ± SD Median (IQR)
0.04 ± 0.43
1.10 ± 0.74
1.58 ± 0.85
0 (0)
–1 (1)
1.5 (1)
*FDI tooth-numbering system. M = mesial; B = buccal; D = distal; O = oral.
–0.08]) and in the CG of –0.10 ± 0.50 mm (95% CI [–0.38; 0.32]). Thus, both groups fulfilled the success criteria; therefore, the secondary hypothesis was also accepted.
The 100% implant survival rate in both groups in this study demonstrates that the special surgical technique using piezosurgical instruments is successful for narrow bone ridges. Bearing in mind the limitations of this prospective cohort study, especially regarding the limited number of patients (n = 14) and the relatively short mean follow-up time of 27.4 months, implants placed by means of RST might have treatment outcomes similar to those placed by means of standard surgical procedures. These results are in accordance with published scientific data on implants placed using the RST. A 4-year follow-up study evaluating 54 patients and 68 implants showed a cumulative survival rate of 93.7%.39 A survival rate of 86.2% after 5 years was documented in a clinical study using 24 Brånemark System implants (Nobel Biocare) and 97 ITI implants (Straumann).40 A 5-year follow-up study with 329 implants reported survival rates of 88.5% to 99%, depending on the implant system.13 A survival rate of 91.9% after 2 years was reported in a recent retrospective study of 157 implants.41 Similar results have been reported for the expansion technique; Sethi and Kaus42 found a mean
–0.25 Median ∆ IBL (mm)
DISCUSSION
0.00
–0.50
SG CG
–0.75 –1.00 –1.25 –1.50 –1.75 T0
T1
T2
T3
Time points
Fig 14 Mean bone-level changes according to implant type at T0 (surgery), T1 (loading), T2 (1 year after loading), and T3 (2 years after loading).
implant survival rate after 5 years of more than 97%. In their prospective clinical study, 150 patients were treated with 449 implants, all of which were inserted in the maxilla.42 In a recent study of 230 implants that used ultrasonic bone surgery for bone splitting, a survival rate of 95.5% after 3 years was reported.43 Thus, the implant survival rate seems not to be negatively affected by the use of ridge expansion or RST. The International Journal of Oral & Maxillofacial Implants 1577
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Little is known about peri-implant crestal bone level alterations after RST. Thus, the primary endpoint of the present study was ΔIBL. ΔIBL was significantly higher in the SG than in the CG, as stabilization of the bone remodeling process appeared to be delayed after RST. It seems that the application of RST leads to increased ΔIBL values compared to implants placed in native bone, particularly during the first year of loading (Fig 14). However, after loading, the mean ΔIBL values of both groups were in line with the results of other clinical studies.44,45 The mean horizontal bone loss (–1.54 ± 0.85 mm), as assessed by means of bone mapping, between T0 and T3 was comparable with the overall radiographically examined mean ΔIBL (–1.68 ± 0.90 mm). That is, the overall bone loss values at the mesial and distal aspects of the implants seemed to be comparable with those at the buccal and oral aspects. In accordance with the criteria of Albrektsson and Isidor, implant treatment can be considered successful if the peri-implant bone loss within the first year after loading is 1.5 mm or less and if, during the following years, bone loss of no more than 0.2 mm occurs annually.38 The overall mean ΔIBL (–1.68 ± 0.90 mm) in the SG does not seem to meet this success criterion. However, in contrast to the success criteria of Albrektsson and Isidor, the baseline definition used in the present cohort study was the day of surgery and not the day of loading. Thus, the choice of baseline radiograph is crucial when describing crestal bone level changes around the implants,46 and the mean ΔIBL values of SG are in accordance with the published success criteria.38 Compared with published data,13,39,40,42,43 the present cohort study enrolled only a limited number of patients, but for comparison, a control group that matched the study group very closely was recruited. This enabled the authors to quantify the additional bone resorption that occurs after RST. Furthermore, the results of the statistical analysis would not be different if the patient had been used as the unit for statistical analyses instead of the single implant. The first clinical example (Fig 3) presents the insertion of two implants by means of RST in the mandible. As illustrated in Fig 3, the assumption that the right releasing cut has been applied too far away from the neighboring tooth is reasonable. When applying RST, the most important priority is avoiding fracture of the buccal bone wall. Therefore, especially in the mandible, where the bone is cortical (type 1), a cut that is as straight as possible should be used. Because of the curvature in this region, in this case a larger cut might have enhanced the risk of a fracture. Curved bone walls exhibit increased resistance toward bending compared to straight bone walls. Thus, higher forces must be applied when curved bone walls are separated after 1578 Volume 28, Number 6, 2013
splitting. Both implants were inserted according to a surgical template made during planning. The goal was not to insert the implants in the region of the releasing cuts. Thus, partial dentures with cantilevers on each side were projected. Cantilevers on fixed partial dentures lead neither to higher implant failure rates nor to more bone loss around supporting implants,47,48 although the stress level at the cervical region in the cortical bone seems to be higher than in a noncantilevered denture.49 However, to prevent excessive shear stresses, the cantilever length should not exceed 10 mm.50 Additionally, the predictability of complete soft tissue filling between an implant and a pontic (average soft tissue height: 5.75 mm) or between a tooth and a pontic (average soft tissue height: 6.75 mm)51 is greater than between a tooth and an implant (average soft tissue height: 4.5 to 5 mm).52,53 Therefore, the esthetic outcome is often improved through the use of pontics. Advantages of the piezoelectric alveolar RST are the high precision of micrometric cutting without pressure, the cavitation effect, and safety in relation to the soft tissue. Minimal bleeding enables optimal control of the surgical area. The device prevents overheating of bone tissue. A minor disadvantage is the slow cutting process. Various surgical bone-splitting techniques have been described. Some authors always raise a full-thickness flap (ie, a mucoperiosteal flap).37,43,54 However, other authors propose the preservation of the periosteum on the bone to minimize bone resorption (split-flap design, ie, a mucosal flap) during healing.36,42 The releasing of periosteum alone seems to cause a bone loss of ~0.5 mm.55 On the bone crest, where the horizontal cut was performed and in cases where releasing cuts were necessary, the periosteum was raised locally to ensure adequate visualization during the cutting process. Although the periosteum on the split bony walls was preserved at least partially in the SG, greater bone loss versus the CG could not be prevented. This enhanced bone remodeling might be a result of the surgical trauma and the deterioration of vascularization of the thin edges of the split bone during initial bone healing. The median alteration in bone width in SG was assessed intraoperatively (4.7 mm [IQR 1.5]). However, a limitation of this study was that changes during the healing and loading periods were not monitored. In the present study, the gap between the thin cortical layers was filled with grafting material and covered with a resorbable membrane. This approach is supported by a recent histologic study in dogs that showed a higher percentage of bone-to-implant contact and fewer changes in marginal bone levels around the implants 12 weeks after surgery if the gaps between the split bone walls were grafted and the sites covered with collagen membranes.56 Thus, the study
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outcome might be expected to be less favorable if a more invasive surgical procedure was used (eg, fullflap design, no filler, no membrane, use of burs or microsaws). Therefore, further clinical studies with larger cohorts and the use of cone-beam radiography before and at various time points after the application of RST to visually verify alterations in bone width are necessary to confirm the results of the present study.
CONCLUSION Using the piezoelectric ridge-splitting technique, implants can be inserted simultaneously with the augmentation procedure. This technique can be used in both arches. Considering the limitations of this prospective cohort study, after ridge splitting, during the healing phase and the first year of loading, a slightly more pronounced marginal bone loss should be anticipated compared to implant insertion in native bone. To anticipate this presumed increased marginal bone loss, the implant shoulder could be positioned 1 mm subcrestally to establish a future epicrestal position.
ACKNOWLEDGMENTS The study was supported by the authors’ own institutions. The authors declare that they have no conflicts of interest.
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