Fresh-Socket Implants of Different Collar Length: Clinical Evaluation in the Aesthetic Zone Roberto Crespi, MD, MS;* Paolo Capparè, MD, DMD;† Elisabetta Polizzi, DH;‡ Enrico Gherlone, MD, DMD§
ABSTRACT Background: The aim of this clinical study was to compare clinical evaluations of implants in the aesthetic zone with smooth collars of different length. Materials and Methods: Sixty-six patients requiring extractions of one, two, or three teeth in the aesthetic zone of the maxilla were enrolled in this study. Ninety-four implants were positioned and were loaded immediately after tooth extraction. Forty-seven implants with a short smooth collar of 0.5 mm (SCI) and 47 implants with a long smooth collar of 1.8 mm (LCI) were utilized in this study and were placed using a nonsubmerged approach. Clinical (gingival index, modified plaque index, modified bleeding index, probing depth, gingival recession) and intraoral digital radiographic parameters were measured at baseline and after 6, 12, 24, and 36 months of healing to evaluate crestal bone loss levels over time. Results: After a follow-up period of 36 months, a survival rate of 100% was reported. The SCI group showed a mean bone loss of 1.07 1 0.38 mm at 12 months and 1.09 1 0.38 mm at 36 months. The LCI group showed a mean bone loss of 0.46 1 0.14 mm at 12 months and 0.53 1 0.12 mm at 36 months. After the 36-month follow-up period, both groups showed stable bone levels over time. Statistically significant differences were found between groups (p < .05). No statistically significant differences were found between SCI and LCI groups with regard to clinical parameters over time. Conclusions: This study revealed significant differences in radiographically observed marginal bone loss between the two types of implant with different smooth-collar lengths, but no differences in gingival vestibular margin outcome were observed. KEY WORDS: bone level, fresh-socket implant, gingival margin, immediate loading, smooth collar
INTRODUCTION
crowns placed on implants immediately), reporting a survival rate of 100% with minimal crestal bone loss. A sufficient width of keratinized masticatory mucosa is mandatory for gingival preservation in implant treatment; there is a significant association between subgingival restorations and gingival inflammation in areas with minimal keratinized gingiva in patients with poor plaque control.1–5 The characteristics of the periimplant soft tissue, including fill and contour, gingiva level, color, and texture, are also critical for final implant aesthetics6–8; hence, the accurate evaluation of bone and soft tissues around extraction sockets represents a key concern in immediate implant placement.9 Aspects of bone level to assess include the locations of the implant platform and of microgaps (implant-abutment interface) between implant components in relation to the alveolar crest.10–12 Using nonsubmerged dental implants, Weber and colleagues13 reported a mean bone loss of 0.6 mm within the first year of placement, without any
Aiming to avoid alveolar bone collapse and to attain an excellent aesthetic profile with regard to the soft tissues around implant-supported prosthetic restorations, several researchers1–3 have recently attempted placing dental implants with immediate loading in fresh extraction sockets (occlusal load applied to temporary *Clinical professor, Department of Dentistry, Vita Salute University, San Raffaele Hospital, Milan, Italy; †adjunct professor, Department of Dentistry, Vita Salute University, San Raffaele Hospital, Milan, Italy; ‡ adjunct professor, Department of Dentistry, Vita Salute University, San Raffaele Hospital, Milan, Italy; §full professor and chairman, Department of Dentistry, Vita Salute University, San Raffaele Hospital, Milan, Italy Corresponding Author: Dr. Roberto Crespi, Department of Dentistry, Vita Salute University, San Raffaele Hospital, Via Olgettina N.48, 20123 Milano, Italy; e-mail: [email protected] © 2014 Wiley Periodicals, Inc. DOI 10.1111/cid.12202
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significant changes found during yearly follow-up visits up to 5 years. The same radiographic results were reported by Buser and colleagues14 in an 8-year clinical study following one-stage nonsubmerged dental implants with smooth collars, suggesting the importance of the lack of a microgap at the bone crest level, which led to less crestal bone loss during healing and resulted in a more favorable crown-to-implant-length ratio. Increasingly, screw-type implants are being utilized, following the same one-stage nonsubmerged approach.15–17 This approach offers the clinical advantage of a one-stage procedure but still leaves a microgap near the crestal bone level, with bone resorption during the first month of healing.10 The presence or absence of a microgap and its location with respect to the bone alveolar crest may provide a significant influence on the amount of peri-implant bone remodeling.18 With a onepiece, nonsubmerged implant system and the rough/ smooth border placed at the crest, it was found that the biologic width was similar to that of natural teeth and that the gingival margin was in a more stable coronal position as compared with a two-piece system with the microgap located at the crest. Furthermore, placing the microgap at or below the alveolar crest resulted in a significant apical displacement of the crestal bone along the junctional epithelial attachment and a more apical location of the gingival margin.18 The aim of this clinical study was to compare clinical evaluations in aesthetic zones of implants with different smooth collar length. MATERIALS AND METHODS Patient Selection Between October 2008 and September 2010, 66 patients (41 women and 25 men) with a mean age of 52.4 years (range 29 to 70 years) were included in this study. All selected patients required extractions of one, two, or three teeth in the aesthetic zone of the maxilla for root fractures, caries, endodontic lesions or periodontal disease. Implants were positioned and loaded immediately after tooth extraction. The patients included in this clinical study were treated by one oral surgeon (RC) and one prosthetic specialist (EG) in the Department of Dentistry, San Raffaele Hospital. The following inclusion criteria were adopted: good health, no chronic systemic disease, presence of all four bony walls of the alveolus, presence of at least 4 mm of bone beyond the root apex, and a keratinized gingiva of
3 mm in width.4,5 Exclusion criteria were the following: presence of dehiscence or fenestration of the residual bony walls, coagulation disorders, signs of acute infection around alveolar bone at the surgical site, heavy smoking (more than 10 cigarettes per day), alcohol or drug abuse, and bruxism. The study protocol was approved by the local institutional review committee, and all patients consented to immediate implant loading and participation in the study by signing an informed consent form. Surgical Protocol One hour prior to surgery, the patients received 1 g amoxicillin (Zimox, Pfizer Italia, Latina, Italy), and they continued to receive 1 g twice a day for a week after the surgical procedure. Surgery was performed under local anesthesia (mepivacaine 20 mg/ml with adrenaline 1:80 000; Optocain, Molteni Dental, Scandicci, Italy). Ninety-four maxillary teeth in the incisor, canine, and first premolar regions were extracted, maintaining the integrity of the socket (Table 1) and avoiding buccal and palatal flaps; a periodontal probe (Hu-Friedy PGFGFS, Hu-Friedy, Chicago, IL, USA) was used to verify the integrity of the four walls of the fresh sockets. None of the experimental sites showed fenestration or dehiscence; no regenerative procedures were performed for any site. The implant site was prepared with a standard drill following the palatal bony walls as guide, and the apical portion of the implant was always placed at least 4 mm beyond the root apex; no countersinking was used. The quality of alveolar bone was determined during surgery for each site and in most cases was classifiable as quality 2 or 3 according to Lekholm and Zarb’s classification.19 The 47 titanium implants in the short-collar implant (SCI) group (Outlink, Sweden & Martina, Padua, Italy) had rough titanium plasma-spray surfaces, bodies with a progressive thread design, short smooth
TABLE 1 Implant Dimensions and Distribution for SCI and LCI Groups Teeth
SCI
LCI
Total
Incisors Canines First premolars Total
22 11 14 47
25 5 17 47
47 16 31 94
Implants of Different Collar Length
3
Each patient received from one to three dental implants, according to the number of extraction sites, from the same implant group, randomly selected by lot from a closed envelope. When resonance frequency analysis predicted an implant stability quotient > 60, immediate loading of the implants was performed with implant insertion torque 3 35 Ncm. No flap was raised in any of the cases (Figure 2). Chlorhexidine 0.20% mouthwash was prescribed twice daily for the next 15 days. Maintenance Protocol Immediately after surgery, all patients received metal temporary abutments, and temporary crowns were cemented. All temporary crowns were in full contact in centric occlusion, making the occlusal surfaces flat and reducing horizontal relations. All patients followed a soft diet (avoiding bread and meat) for 2 months. Figure 1 Two different types of implants. A, Implant with short smooth collar (0.5 mm in length). B, Implant with long smooth collar (1.8 mm in length).
collars of 0.5 mm, and external-hexagon implant/ abutment junctions (Figure 1A). Thirty-two of the implants had diameters of 4.10 mm, and the other 15 implants had diameters of 3.75 mm; all implants were 13 mm in length (Table 2). The implant platforms were inserted at the level of the alveolar crest. The 47 titanium implants in the long-collar implant (LCI) group (Advanced, Ticino Forniture Dentali, Novara, Italy) had long smooth collars of 1.8 mm, external-hexagon junctions, and rough titanium plasma-spray surfaces (Figure 1B). Thirty-four implants had diameters of 4.20 mm, and the other 13 implants had diameters of 3.80 mm; all implants were 13 mm in length (see Table 2). The smooth collars of the implants were left supracrestal, leaving the implant platforms at tissue level.
TABLE 2 Number of Implants according to Dimensions Diameter × Length (mm)
SCI LCI
4.2 × 13
4.1 × 13
3.75 × 13
3.8 × 13
Total
0 34
32 0
15 0
0 13
47 47
Follow-Up Evaluation Follow-up visits were performed by a dental hygienist (EP) twice a year after implant insertion. The following clinical parameters were checked: gingival index (GI);20 modified plaque index (mPI);20 modified bleeding index (mBI), measured around the four surfaces of the implants;21 and probing depth (PD), measured at four points (mesiobuccal, midbuccal, distobuccal, and midlingual) to the nearest millimeter with a pressuresensitive probe (Hu-Friedy PGF-GFS), using a standardized force of 0.35 N. The gingival recession was calculated as the distance between the soft tissue margin and the supragingivally located top of the abutment, measured to the nearest millimeter using the periodontal probe.22 The width of keratinized mucosa at the midbuccal point was measured from the mucogingival junction to the free gingival margin using a periodontal probe. Baseline levels were measured at the time of placement of the prosthesis. Clinical evaluations were performed by one examiner (EP), who was trained before the start of the study with respect to the various assessments included in the study. Intraexaminer variation was evaluated by means of double assessments in 10 patients. The mean difference between pairs of linear assessments varied between 0.14 and 0.17 for the various variables. In 84–88% of the sites, the measurements were identical. No difference > 1 mm was recorded.
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Figure 2 A, Fresh-socket implant with short collar in right central location. B, Clinical aspect of immediate temporary crown. C and D, Final restoration 3 years later. E, Fresh-socket implant with long collar in left central placement. F, Clinical aspect of immediate temporary crown. G and H, Final restoration 3 years later.
Success criteria for implant survival were the following: implant stability, absence of a radiolucent zone around the implants, no mucosal suppuration, and no pain. Radiographic Assessments Intraoral digital radiographic examinations (Schick CDR, Schick Technologies, New York, NY, USA) were conducted at baseline and after 6, 12, 24, and 36 months of healing. The periapical radiographs were taken perpendicularly to the long axis of the implant using the long-cone parallel technique, with an occlusal template being used to measure the marginal bone level. A radiologist twice measured the changes in marginal bone height over time; he marked the reference points and measured lines on the screen interactively (the numeric values of measurements were obtained using Schick CDR software). Implant height (a known quantity) was used for calibration. The distances between the implant
platform and the most coronal points of contact between the bone and the mesial and distal parts of implants were considered. Differences in bone level were measured using Schick CDR software. The intraexaminer error was calculated by comparing the first and second measurements in a paired t-test with a significance level of 5%. No statistical difference was found between measurements (p > .05). Statistics SPSS 11.5.0 (SPSS Inc., Chicago, IL, USA) was used for all statistical analyses. Clinical parameters (GI, mPI, mBI, PD) were calculated for each implant and were reported as mean 1 standard deviation at 3-year followup. Gingival recession values were calculated for each implant and were reported as mean 1 standard deviation at 6-month, 2-year, and 3-year follow-ups. Radiographic bone level values (mesial, distal, and mean bone loss) were calculated for each implant and were reported
Implants of Different Collar Length
as mean 1 standard deviation at 12-, 24-, and 36-month follow-ups. To compare the differences in radiographic values and clinical parameters between the two groups at every time point, a two-tailed Student’s t-test was conducted (p < .05 was considered the threshold for statistical significance). RESULTS
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TABLE 4 Radiographic Results (SCI Group) Time Point
Mesial Bone Loss (mm)
Distal Bone Loss (mm)
Mean Bone Loss (mm)
Survival Rate
12 months 1.04 1 0.35 1.10 1 0.42 1.07 1 0.38 100.00% 24 months 1.06 1 0.39 1.10 1 0.44 1.08 1 0.41 100.00% 36 months 1.07 1 0.21 1.11 1 0.56 1.09 1 0.38 100.00%
Survival After a 36-month follow-up period, an implant survival rate of 100% was reported. There was no patient withdrawal in either group. Minor swelling of the gingival mucosa was present during the first few days after surgery; no mucositis or flap dehiscence with suppuration was found. The final ceramic-fused-to-metal restorations were cemented 6 months after implant placement. No pain or final-prosthesis mobility was registered at 36-month follow-up. Clinical Parameters At 3-year follow-up, GI was 0.68 1 0.10 for the SCI group and 0.74 1 0.13 for the LCI group; mPI was 1.18 1 0.11 for the SCI group and 1.15 1 0.13 for the LCI group; mBI was 0.36 1 0.04 for the SCI group and 0.40 1 0.03 for the LCI group; and PD was 2.71 1 0.33 for the SCI group and 2.80 1 0.22 for the LCI group. There were no statistically significant differences (p > .05) between SCI and LCI in GI, mPI, mBI, or PD. Mean gingival recession values are shown in Table 3. In both groups, up to 60% of gingival recession occurred within the first 6 months, and recession rates stabilized over time (little increase for the LCI group). No statistically significant differences (p > .05) were found between groups for gingival recession values. Radiographic Evaluation Radiographic results were reported at 12, 24, and 36 months from implant placement (Tables 4 and 5). A
comparison of radiographic bone levels between the two groups of implants showed a relationship between the amount of bone remodeling with time and the location of the rough/smooth border with respect to the original alveolar crest. The SCI group showed a mean bone loss of 1.07 1 0.38 mm at 12 months from implant placement; subsequent follow-up radiographs reported no changes in peri-implant bone levels. In the LCI group, the mean distance from the implant platform to the bone crest at implant placement was 1.60 1 0.12 mm, leaving the 1.8 mm smooth collar supracrestal. The amount of bone loss at the 12-month time point for the implants in the LCI group was 0.46 1 0.14 mm, with subsequent follow-up radiographs showing virtually no change in peri-implant bone levels. For both groups, following this initial bone remodeling, bone levels at yearly follow-up visits were virtually unchanged, remaining stable over time. Statistically significant differences were found between values for the SCI and LCI groups at 12, 24, and 36 months (p < .05). DISCUSSION Although there were significant differences in radiographically observed marginal bone loss between the two types of implant with different smooth-collar lengths, no differences in gingival vestibular margin were observed.
TABLE 5 Radiographic Results (LCI Group) TABLE 3 Mean Gingival Recession Values for SCI and LCI Groups (N = 94 Implants) Time Point
SCI
LCI
6-month follow-up (mm) 0.21 1 0.17 0.19 1 0.11 2-year follow-up (mm) 0.21 1 0.15 0.22 1 0.10 3-year follow-up (mm) 0.20 1 0.16 0.23 1 0.12
p Value
.480 .934 .280
Time Point
Mesial Bone Loss (mm)
Distal Bone Loss (mm)
Mean Bone Loss (mm)
Survival Rate
12 months 0.43 1 0.11 0.50 1 0.17 0.46 1 0.14 100.00% 24 months 0.48 1 0.13 0.53 1 0.16 0.50 1 0.14 100.00% 36 months 0.50 1 0.11 0.56 1 0.13 0.53 1 0.12 100.00%
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The radiographic results for both groups showed that bone loss occurred mainly between the time of implant placement and the time when the final prosthesis was placed on the implant. Subsequent to that, little bone change was noted up to the 3-year follow-up.23 One factor that may influence bone loss in the initial period after implant placement may be interruption of the vascular supply and continuity of the bony structure during preparation of the implant site, resulting in an acute inflammatory response. Subsequently, the woundhealing process is initiated, during which the trabecular and cortical bone around the implant is demineralized, resulting in bone loss.18 Aside from surgical damage, the area near the coronal portion of the implant may be damaged by the use of impression materials, the placement of the temporary abutment with the crown, and the placement of the final prosthesis. All these clinical procedures may interfere in the healing process around the implant, resulting in significant amounts of inflammation and bone demineralization.24 As reported by Hermann and colleagues25,26 the areas around implants with collars showed less bone loss than those around implants without collars inserted at the level of the alveolar crest. The distance between the implant platform and bone crest prevented clinical procedures interfering in the healing process and preserved the biologic width over time. Hartman and Cochran18 placed the same one-piece implants using a nonsubmerged procedure at locations other than the alveolar crest. They found that a physiologic dimension appears to exist between the bone and the implant-crown interface around one-piece implants that is established early and maintained over time. These findings show that the amount of initial bone remodeling around these onepiece dental implants is dependent on the positioning of the rough/smooth border of the implant in the apicocoronal dimension. In the SCI group, where the implant platforms were inserted near the level of the alveolar crest, a bone loss of 1.07 1 0.38 mm was observed, while in the LCI group, the bone loss was lower at 0.46 1 0.14 mm. The bone level also remained essentially unchanged throughout the study period. This outcome suggests that placing implants with the same type of connection at different levels at the bone crest can lead to different levels of bone loss after 12 months and that these levels can be maintained over time. The 1.8 mm length of the implant collar may preserve the biologic width as described by Cochran and
colleagues,27 as the data suggest that a biologic width exists around unloaded and loaded nonsubmerged onepart titanium implants and that this is a physiologically formed and stable dimension as is found around teeth. The biological rationale for bone remodeling that occurs at a specific distance from the microgap may be explained by bacterial contamination of the interface, forming a niche for bacterial colonization and subsequent demineralization.28,29 However, these clinical results need to be confirmed over a longer period of time to verify biological tissue stability around implants with a 1.8 mm collar. With regard to the gingival recession values of the peri-implant mucosa, no differences were reported between the two groups. In both groups, up to 60% of gingival recession occurred within the first 6 months, after which the rate stabilized over time, as apical displacement of the soft tissue margin mainly took place during the first 6 months of observation. It has been suggested that the recession of the peri-implant soft tissue margin may largely be the result of a remodeling of the soft tissue in order to establish the “appropriate biological dimensions” of the peri-implant soft tissue barrier, that is, the required dimension of epithelial–connective tissue attachment in relation to the faciolingual thickness of the supracrestal soft tissue.22 The same clinical results were reported in a study by Den Hartog and colleagues30 where all implants were inserted into healed extraction sites, and the aesthetic outcome of single-tooth implants in the aesthetic zone with different neck designs was evaluated. Although there was a significant difference in marginal bone loss between the different implant neck designs, there were no differences in aesthetic outcome. The authors concluded that the aesthetics of single-tooth implants in the maxillary aesthetic zone appear to be independent of the implant neck designs applied but dependent on the need for preimplant surgery. The small amount of gingival recession reported in the present study may be explained by the presence of a 3 mm width of keratinized gingiva,4 as gingival recession is not related to the position of the implant but only to the width of keratinized mucosa, as shown in a study where implants were placed in fresh sockets in the same patients but with different widths of keratinized gingiva, and recession was observed around implants with minimal keratinized gingiva.31 The outcome with regard
Implants of Different Collar Length
to keratinized mucosa was evaluated in a retrospective study on long-term maintenance of dental implants with regard to the type of implant prostheses,32 and results suggested that the amount of keratinized gingiva was not significantly correlated with any clinical parameters related to prosthetic restorations, either fixed or removable. On the other hand, the presence of keratinized mucosa was shown to be significantly advantageous in maintenance of soft tissue health. An interesting finding was that the average bone loss around posterior implants was 3.5-fold higher than that around anterior implants in the presence of an adequate amount of keratinized mucosa. Similar results were reported in a clinical study of 307 mandibular dental implants placed in 73 completely edentulous patients and followed over a period of 5 years.33 In patients maintaining good oral hygiene and receiving regular implant maintenance therapy, implants with a reduced width of
ABSTRACT Background: The aim of this clinical study was to compare clinical evaluations of implants in the aesthetic zone with smooth collars of different length. Materials and Methods: Sixty-six patients requiring extractions of one, two, or three teeth in the aesthetic zone of the maxilla were enrolled in this study. Ninety-four implants were positioned and were loaded immediately after tooth extraction. Forty-seven implants with a short smooth collar of 0.5 mm (SCI) and 47 implants with a long smooth collar of 1.8 mm (LCI) were utilized in this study and were placed using a nonsubmerged approach. Clinical (gingival index, modified plaque index, modified bleeding index, probing depth, gingival recession) and intraoral digital radiographic parameters were measured at baseline and after 6, 12, 24, and 36 months of healing to evaluate crestal bone loss levels over time. Results: After a follow-up period of 36 months, a survival rate of 100% was reported. The SCI group showed a mean bone loss of 1.07 1 0.38 mm at 12 months and 1.09 1 0.38 mm at 36 months. The LCI group showed a mean bone loss of 0.46 1 0.14 mm at 12 months and 0.53 1 0.12 mm at 36 months. After the 36-month follow-up period, both groups showed stable bone levels over time. Statistically significant differences were found between groups (p < .05). No statistically significant differences were found between SCI and LCI groups with regard to clinical parameters over time. Conclusions: This study revealed significant differences in radiographically observed marginal bone loss between the two types of implant with different smooth-collar lengths, but no differences in gingival vestibular margin outcome were observed. KEY WORDS: bone level, fresh-socket implant, gingival margin, immediate loading, smooth collar
INTRODUCTION
crowns placed on implants immediately), reporting a survival rate of 100% with minimal crestal bone loss. A sufficient width of keratinized masticatory mucosa is mandatory for gingival preservation in implant treatment; there is a significant association between subgingival restorations and gingival inflammation in areas with minimal keratinized gingiva in patients with poor plaque control.1–5 The characteristics of the periimplant soft tissue, including fill and contour, gingiva level, color, and texture, are also critical for final implant aesthetics6–8; hence, the accurate evaluation of bone and soft tissues around extraction sockets represents a key concern in immediate implant placement.9 Aspects of bone level to assess include the locations of the implant platform and of microgaps (implant-abutment interface) between implant components in relation to the alveolar crest.10–12 Using nonsubmerged dental implants, Weber and colleagues13 reported a mean bone loss of 0.6 mm within the first year of placement, without any
Aiming to avoid alveolar bone collapse and to attain an excellent aesthetic profile with regard to the soft tissues around implant-supported prosthetic restorations, several researchers1–3 have recently attempted placing dental implants with immediate loading in fresh extraction sockets (occlusal load applied to temporary *Clinical professor, Department of Dentistry, Vita Salute University, San Raffaele Hospital, Milan, Italy; †adjunct professor, Department of Dentistry, Vita Salute University, San Raffaele Hospital, Milan, Italy; ‡ adjunct professor, Department of Dentistry, Vita Salute University, San Raffaele Hospital, Milan, Italy; §full professor and chairman, Department of Dentistry, Vita Salute University, San Raffaele Hospital, Milan, Italy Corresponding Author: Dr. Roberto Crespi, Department of Dentistry, Vita Salute University, San Raffaele Hospital, Via Olgettina N.48, 20123 Milano, Italy; e-mail: [email protected] © 2014 Wiley Periodicals, Inc. DOI 10.1111/cid.12202
1
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significant changes found during yearly follow-up visits up to 5 years. The same radiographic results were reported by Buser and colleagues14 in an 8-year clinical study following one-stage nonsubmerged dental implants with smooth collars, suggesting the importance of the lack of a microgap at the bone crest level, which led to less crestal bone loss during healing and resulted in a more favorable crown-to-implant-length ratio. Increasingly, screw-type implants are being utilized, following the same one-stage nonsubmerged approach.15–17 This approach offers the clinical advantage of a one-stage procedure but still leaves a microgap near the crestal bone level, with bone resorption during the first month of healing.10 The presence or absence of a microgap and its location with respect to the bone alveolar crest may provide a significant influence on the amount of peri-implant bone remodeling.18 With a onepiece, nonsubmerged implant system and the rough/ smooth border placed at the crest, it was found that the biologic width was similar to that of natural teeth and that the gingival margin was in a more stable coronal position as compared with a two-piece system with the microgap located at the crest. Furthermore, placing the microgap at or below the alveolar crest resulted in a significant apical displacement of the crestal bone along the junctional epithelial attachment and a more apical location of the gingival margin.18 The aim of this clinical study was to compare clinical evaluations in aesthetic zones of implants with different smooth collar length. MATERIALS AND METHODS Patient Selection Between October 2008 and September 2010, 66 patients (41 women and 25 men) with a mean age of 52.4 years (range 29 to 70 years) were included in this study. All selected patients required extractions of one, two, or three teeth in the aesthetic zone of the maxilla for root fractures, caries, endodontic lesions or periodontal disease. Implants were positioned and loaded immediately after tooth extraction. The patients included in this clinical study were treated by one oral surgeon (RC) and one prosthetic specialist (EG) in the Department of Dentistry, San Raffaele Hospital. The following inclusion criteria were adopted: good health, no chronic systemic disease, presence of all four bony walls of the alveolus, presence of at least 4 mm of bone beyond the root apex, and a keratinized gingiva of
3 mm in width.4,5 Exclusion criteria were the following: presence of dehiscence or fenestration of the residual bony walls, coagulation disorders, signs of acute infection around alveolar bone at the surgical site, heavy smoking (more than 10 cigarettes per day), alcohol or drug abuse, and bruxism. The study protocol was approved by the local institutional review committee, and all patients consented to immediate implant loading and participation in the study by signing an informed consent form. Surgical Protocol One hour prior to surgery, the patients received 1 g amoxicillin (Zimox, Pfizer Italia, Latina, Italy), and they continued to receive 1 g twice a day for a week after the surgical procedure. Surgery was performed under local anesthesia (mepivacaine 20 mg/ml with adrenaline 1:80 000; Optocain, Molteni Dental, Scandicci, Italy). Ninety-four maxillary teeth in the incisor, canine, and first premolar regions were extracted, maintaining the integrity of the socket (Table 1) and avoiding buccal and palatal flaps; a periodontal probe (Hu-Friedy PGFGFS, Hu-Friedy, Chicago, IL, USA) was used to verify the integrity of the four walls of the fresh sockets. None of the experimental sites showed fenestration or dehiscence; no regenerative procedures were performed for any site. The implant site was prepared with a standard drill following the palatal bony walls as guide, and the apical portion of the implant was always placed at least 4 mm beyond the root apex; no countersinking was used. The quality of alveolar bone was determined during surgery for each site and in most cases was classifiable as quality 2 or 3 according to Lekholm and Zarb’s classification.19 The 47 titanium implants in the short-collar implant (SCI) group (Outlink, Sweden & Martina, Padua, Italy) had rough titanium plasma-spray surfaces, bodies with a progressive thread design, short smooth
TABLE 1 Implant Dimensions and Distribution for SCI and LCI Groups Teeth
SCI
LCI
Total
Incisors Canines First premolars Total
22 11 14 47
25 5 17 47
47 16 31 94
Implants of Different Collar Length
3
Each patient received from one to three dental implants, according to the number of extraction sites, from the same implant group, randomly selected by lot from a closed envelope. When resonance frequency analysis predicted an implant stability quotient > 60, immediate loading of the implants was performed with implant insertion torque 3 35 Ncm. No flap was raised in any of the cases (Figure 2). Chlorhexidine 0.20% mouthwash was prescribed twice daily for the next 15 days. Maintenance Protocol Immediately after surgery, all patients received metal temporary abutments, and temporary crowns were cemented. All temporary crowns were in full contact in centric occlusion, making the occlusal surfaces flat and reducing horizontal relations. All patients followed a soft diet (avoiding bread and meat) for 2 months. Figure 1 Two different types of implants. A, Implant with short smooth collar (0.5 mm in length). B, Implant with long smooth collar (1.8 mm in length).
collars of 0.5 mm, and external-hexagon implant/ abutment junctions (Figure 1A). Thirty-two of the implants had diameters of 4.10 mm, and the other 15 implants had diameters of 3.75 mm; all implants were 13 mm in length (Table 2). The implant platforms were inserted at the level of the alveolar crest. The 47 titanium implants in the long-collar implant (LCI) group (Advanced, Ticino Forniture Dentali, Novara, Italy) had long smooth collars of 1.8 mm, external-hexagon junctions, and rough titanium plasma-spray surfaces (Figure 1B). Thirty-four implants had diameters of 4.20 mm, and the other 13 implants had diameters of 3.80 mm; all implants were 13 mm in length (see Table 2). The smooth collars of the implants were left supracrestal, leaving the implant platforms at tissue level.
TABLE 2 Number of Implants according to Dimensions Diameter × Length (mm)
SCI LCI
4.2 × 13
4.1 × 13
3.75 × 13
3.8 × 13
Total
0 34
32 0
15 0
0 13
47 47
Follow-Up Evaluation Follow-up visits were performed by a dental hygienist (EP) twice a year after implant insertion. The following clinical parameters were checked: gingival index (GI);20 modified plaque index (mPI);20 modified bleeding index (mBI), measured around the four surfaces of the implants;21 and probing depth (PD), measured at four points (mesiobuccal, midbuccal, distobuccal, and midlingual) to the nearest millimeter with a pressuresensitive probe (Hu-Friedy PGF-GFS), using a standardized force of 0.35 N. The gingival recession was calculated as the distance between the soft tissue margin and the supragingivally located top of the abutment, measured to the nearest millimeter using the periodontal probe.22 The width of keratinized mucosa at the midbuccal point was measured from the mucogingival junction to the free gingival margin using a periodontal probe. Baseline levels were measured at the time of placement of the prosthesis. Clinical evaluations were performed by one examiner (EP), who was trained before the start of the study with respect to the various assessments included in the study. Intraexaminer variation was evaluated by means of double assessments in 10 patients. The mean difference between pairs of linear assessments varied between 0.14 and 0.17 for the various variables. In 84–88% of the sites, the measurements were identical. No difference > 1 mm was recorded.
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Clinical Implant Dentistry and Related Research, Volume *, Number *, 2014
Figure 2 A, Fresh-socket implant with short collar in right central location. B, Clinical aspect of immediate temporary crown. C and D, Final restoration 3 years later. E, Fresh-socket implant with long collar in left central placement. F, Clinical aspect of immediate temporary crown. G and H, Final restoration 3 years later.
Success criteria for implant survival were the following: implant stability, absence of a radiolucent zone around the implants, no mucosal suppuration, and no pain. Radiographic Assessments Intraoral digital radiographic examinations (Schick CDR, Schick Technologies, New York, NY, USA) were conducted at baseline and after 6, 12, 24, and 36 months of healing. The periapical radiographs were taken perpendicularly to the long axis of the implant using the long-cone parallel technique, with an occlusal template being used to measure the marginal bone level. A radiologist twice measured the changes in marginal bone height over time; he marked the reference points and measured lines on the screen interactively (the numeric values of measurements were obtained using Schick CDR software). Implant height (a known quantity) was used for calibration. The distances between the implant
platform and the most coronal points of contact between the bone and the mesial and distal parts of implants were considered. Differences in bone level were measured using Schick CDR software. The intraexaminer error was calculated by comparing the first and second measurements in a paired t-test with a significance level of 5%. No statistical difference was found between measurements (p > .05). Statistics SPSS 11.5.0 (SPSS Inc., Chicago, IL, USA) was used for all statistical analyses. Clinical parameters (GI, mPI, mBI, PD) were calculated for each implant and were reported as mean 1 standard deviation at 3-year followup. Gingival recession values were calculated for each implant and were reported as mean 1 standard deviation at 6-month, 2-year, and 3-year follow-ups. Radiographic bone level values (mesial, distal, and mean bone loss) were calculated for each implant and were reported
Implants of Different Collar Length
as mean 1 standard deviation at 12-, 24-, and 36-month follow-ups. To compare the differences in radiographic values and clinical parameters between the two groups at every time point, a two-tailed Student’s t-test was conducted (p < .05 was considered the threshold for statistical significance). RESULTS
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TABLE 4 Radiographic Results (SCI Group) Time Point
Mesial Bone Loss (mm)
Distal Bone Loss (mm)
Mean Bone Loss (mm)
Survival Rate
12 months 1.04 1 0.35 1.10 1 0.42 1.07 1 0.38 100.00% 24 months 1.06 1 0.39 1.10 1 0.44 1.08 1 0.41 100.00% 36 months 1.07 1 0.21 1.11 1 0.56 1.09 1 0.38 100.00%
Survival After a 36-month follow-up period, an implant survival rate of 100% was reported. There was no patient withdrawal in either group. Minor swelling of the gingival mucosa was present during the first few days after surgery; no mucositis or flap dehiscence with suppuration was found. The final ceramic-fused-to-metal restorations were cemented 6 months after implant placement. No pain or final-prosthesis mobility was registered at 36-month follow-up. Clinical Parameters At 3-year follow-up, GI was 0.68 1 0.10 for the SCI group and 0.74 1 0.13 for the LCI group; mPI was 1.18 1 0.11 for the SCI group and 1.15 1 0.13 for the LCI group; mBI was 0.36 1 0.04 for the SCI group and 0.40 1 0.03 for the LCI group; and PD was 2.71 1 0.33 for the SCI group and 2.80 1 0.22 for the LCI group. There were no statistically significant differences (p > .05) between SCI and LCI in GI, mPI, mBI, or PD. Mean gingival recession values are shown in Table 3. In both groups, up to 60% of gingival recession occurred within the first 6 months, and recession rates stabilized over time (little increase for the LCI group). No statistically significant differences (p > .05) were found between groups for gingival recession values. Radiographic Evaluation Radiographic results were reported at 12, 24, and 36 months from implant placement (Tables 4 and 5). A
comparison of radiographic bone levels between the two groups of implants showed a relationship between the amount of bone remodeling with time and the location of the rough/smooth border with respect to the original alveolar crest. The SCI group showed a mean bone loss of 1.07 1 0.38 mm at 12 months from implant placement; subsequent follow-up radiographs reported no changes in peri-implant bone levels. In the LCI group, the mean distance from the implant platform to the bone crest at implant placement was 1.60 1 0.12 mm, leaving the 1.8 mm smooth collar supracrestal. The amount of bone loss at the 12-month time point for the implants in the LCI group was 0.46 1 0.14 mm, with subsequent follow-up radiographs showing virtually no change in peri-implant bone levels. For both groups, following this initial bone remodeling, bone levels at yearly follow-up visits were virtually unchanged, remaining stable over time. Statistically significant differences were found between values for the SCI and LCI groups at 12, 24, and 36 months (p < .05). DISCUSSION Although there were significant differences in radiographically observed marginal bone loss between the two types of implant with different smooth-collar lengths, no differences in gingival vestibular margin were observed.
TABLE 5 Radiographic Results (LCI Group) TABLE 3 Mean Gingival Recession Values for SCI and LCI Groups (N = 94 Implants) Time Point
SCI
LCI
6-month follow-up (mm) 0.21 1 0.17 0.19 1 0.11 2-year follow-up (mm) 0.21 1 0.15 0.22 1 0.10 3-year follow-up (mm) 0.20 1 0.16 0.23 1 0.12
p Value
.480 .934 .280
Time Point
Mesial Bone Loss (mm)
Distal Bone Loss (mm)
Mean Bone Loss (mm)
Survival Rate
12 months 0.43 1 0.11 0.50 1 0.17 0.46 1 0.14 100.00% 24 months 0.48 1 0.13 0.53 1 0.16 0.50 1 0.14 100.00% 36 months 0.50 1 0.11 0.56 1 0.13 0.53 1 0.12 100.00%
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Clinical Implant Dentistry and Related Research, Volume *, Number *, 2014
The radiographic results for both groups showed that bone loss occurred mainly between the time of implant placement and the time when the final prosthesis was placed on the implant. Subsequent to that, little bone change was noted up to the 3-year follow-up.23 One factor that may influence bone loss in the initial period after implant placement may be interruption of the vascular supply and continuity of the bony structure during preparation of the implant site, resulting in an acute inflammatory response. Subsequently, the woundhealing process is initiated, during which the trabecular and cortical bone around the implant is demineralized, resulting in bone loss.18 Aside from surgical damage, the area near the coronal portion of the implant may be damaged by the use of impression materials, the placement of the temporary abutment with the crown, and the placement of the final prosthesis. All these clinical procedures may interfere in the healing process around the implant, resulting in significant amounts of inflammation and bone demineralization.24 As reported by Hermann and colleagues25,26 the areas around implants with collars showed less bone loss than those around implants without collars inserted at the level of the alveolar crest. The distance between the implant platform and bone crest prevented clinical procedures interfering in the healing process and preserved the biologic width over time. Hartman and Cochran18 placed the same one-piece implants using a nonsubmerged procedure at locations other than the alveolar crest. They found that a physiologic dimension appears to exist between the bone and the implant-crown interface around one-piece implants that is established early and maintained over time. These findings show that the amount of initial bone remodeling around these onepiece dental implants is dependent on the positioning of the rough/smooth border of the implant in the apicocoronal dimension. In the SCI group, where the implant platforms were inserted near the level of the alveolar crest, a bone loss of 1.07 1 0.38 mm was observed, while in the LCI group, the bone loss was lower at 0.46 1 0.14 mm. The bone level also remained essentially unchanged throughout the study period. This outcome suggests that placing implants with the same type of connection at different levels at the bone crest can lead to different levels of bone loss after 12 months and that these levels can be maintained over time. The 1.8 mm length of the implant collar may preserve the biologic width as described by Cochran and
colleagues,27 as the data suggest that a biologic width exists around unloaded and loaded nonsubmerged onepart titanium implants and that this is a physiologically formed and stable dimension as is found around teeth. The biological rationale for bone remodeling that occurs at a specific distance from the microgap may be explained by bacterial contamination of the interface, forming a niche for bacterial colonization and subsequent demineralization.28,29 However, these clinical results need to be confirmed over a longer period of time to verify biological tissue stability around implants with a 1.8 mm collar. With regard to the gingival recession values of the peri-implant mucosa, no differences were reported between the two groups. In both groups, up to 60% of gingival recession occurred within the first 6 months, after which the rate stabilized over time, as apical displacement of the soft tissue margin mainly took place during the first 6 months of observation. It has been suggested that the recession of the peri-implant soft tissue margin may largely be the result of a remodeling of the soft tissue in order to establish the “appropriate biological dimensions” of the peri-implant soft tissue barrier, that is, the required dimension of epithelial–connective tissue attachment in relation to the faciolingual thickness of the supracrestal soft tissue.22 The same clinical results were reported in a study by Den Hartog and colleagues30 where all implants were inserted into healed extraction sites, and the aesthetic outcome of single-tooth implants in the aesthetic zone with different neck designs was evaluated. Although there was a significant difference in marginal bone loss between the different implant neck designs, there were no differences in aesthetic outcome. The authors concluded that the aesthetics of single-tooth implants in the maxillary aesthetic zone appear to be independent of the implant neck designs applied but dependent on the need for preimplant surgery. The small amount of gingival recession reported in the present study may be explained by the presence of a 3 mm width of keratinized gingiva,4 as gingival recession is not related to the position of the implant but only to the width of keratinized mucosa, as shown in a study where implants were placed in fresh sockets in the same patients but with different widths of keratinized gingiva, and recession was observed around implants with minimal keratinized gingiva.31 The outcome with regard
Implants of Different Collar Length
to keratinized mucosa was evaluated in a retrospective study on long-term maintenance of dental implants with regard to the type of implant prostheses,32 and results suggested that the amount of keratinized gingiva was not significantly correlated with any clinical parameters related to prosthetic restorations, either fixed or removable. On the other hand, the presence of keratinized mucosa was shown to be significantly advantageous in maintenance of soft tissue health. An interesting finding was that the average bone loss around posterior implants was 3.5-fold higher than that around anterior implants in the presence of an adequate amount of keratinized mucosa. Similar results were reported in a clinical study of 307 mandibular dental implants placed in 73 completely edentulous patients and followed over a period of 5 years.33 In patients maintaining good oral hygiene and receiving regular implant maintenance therapy, implants with a reduced width of
