Radiographic Bone Level Changes of Implant-Supported Restorations in Edentulous and Partially Dentate Patients: 5-Year Results Hadi Gholami, DDS, Dr Med Dent1/Regina Mericske-Stern, Prof Dr Med Dent2/ Gerda Kessler-Liechti, Dr Med Dent3/Joannis Katsoulis, PD Dr Med Dent, MAS4 Purpose: To evaluate and compare crestal bone level changes and peri-implant status of implant-supported reconstructions in edentulous and partially dentate patients after a minimum of 5 years of loading. Materials and Methods: All patients who received a self-tapping implant with a microstructured surface during the years 2003 and 2004 at the Department of Prosthodontics, University of Bern, were included in this study. The implant restorations comprised fixed and removable prostheses for partially and completely edentulous patients. Radiographs were taken immediately after surgery, at impression making, and 1 and 5 years after loading. Crestal bone level (BIC) was measured from the implant shoulder to the first bone contact, and changes were calculated over time (∆BIC). The associations between pocket depth, bleeding on probing (BOP), and ∆BIC were assessed. Results: Sixty-one implants were placed in 20 patients (mean age, 62 ± 7 years). At the 5-year follow-up, 19 patients with 58 implants were available. Implant survival was 98.4% (one early failure; one patient died). The average ∆BIC between surgery and 5-year follow-up was 1.5 ± 0.9 mm and 1.1 ± 0.6 mm for edentulous and partially dentate patients, respectively. Most bone resorption (50%, 0.7 mm) occurred during the first 3 months (osseointegration) and within the first year of loading (21%, 0.3 mm). Mean annual bone loss during the 5 years of loading was < 0.12 mm. Mean pocket depth was 2.6 ± 0.7 mm. Seventeen percent of the implant sites displayed BOP; the frequency was significantly higher in women. None of the variables were significantly associated with crestal bone loss. Conclusion: Crestal bone loss after 5 years was within the normal range, without a significant difference between edentulous and partially dentate patients. In the short term, this implant system can be used successfully for various prosthetic indications. Int J Oral Maxillofac Implants 2014;29:898–904. doi: 10.11607/jomi.3042 Key words: crestal bone level, edentulous, implant survival, partially dentate
O
sseointegrated implants have been used successfully to restore function to fully and partially edentulous patients. Modifications of implant design on both the macroscopic and microscopic levels have been implemented to improve implant success rates. Some clinical advantages have been reported for moderately rough surfaces in comparison with smooth or
1Postdoctoral
Student, Department of Prosthodontics, School of Dental Medicine, University of Bern, Switzerland. 2Director and Chair, Department of Prosthodontics, School of Dental Medicine, University of Bern, Switzerland. 3Assistant Professor, Department of Prosthodontics, School of Dental Medicine, University of Bern, Switzerland. 4 Associate Professor, Department of Prosthodontics, School of Dental Medicine, University of Bern, Switzerland. Correspondence to: Dr J. Katsoulis, Department of Prosthodontics, School of Dental Medicine, University of Bern, Freiburgstrasse 7, 3010 Bern, Switzerland. Fax: +41-31-632-49-33. Email: [email protected] ©2014 by Quintessence Publishing Co Inc.
rough surfaces.1 However, very few of the long-term best-documented oral implants from the major oral implant companies are still available on the market.2 In addition, little is known about the impact of the type of edentulism (partial or complete) on crestal bone level changes around implants. In 2001, a new implant system, Thommen (Thommen Medical), was released to the market. To date, few clinical studies have reported working with this implant system,3,4 although several other dental implant systems have been properly documented for 5 years or more.2 In a pilot study, clinical procedures, prosthetic complications, and required maintenance after 1 year of loading were shown to be comparable to other implant systems.3,4 According to the authors, osseointegration of Thommen implants was highly successful in a variety of patients, and their stability was very good, although some minor problems were identified with the instruments for prosthetic procedures. These instruments were subsequently improved, modified, or replaced. The system offers implants with different platforms and a low
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shoulder design that may provide favorable results in the esthetically demanding anterior maxilla.3 For the current study, the Element implant (Fig 1a), which has a cylindric screw design and a short machined neck of 1.0 mm, was selected. This implant type is more often indicated for completely edentulous mandibles, anterior fixed crowns, and short partial dentures, compared with the Contact (Fig 1b) implant, which has a root-form screw design and a longer machined neck of 1.5 mm. Furthermore, various abutments, healing caps, and a sophisticated screwdriver are available, making clinical application of the system easier. No differences in failure rates, complications, or bone levels were seen after 3 years between implants that were loaded immediately or early.5 A limited number of studies are available that have assessed longitudinally the survival and success rates of implants and various supporting restorations for 5, 10, or more years. Some studies were published in the 1990s; most discussed the Brånemark System (Nobel Biocare) and a few focused on ITI implants (Straumann).6–11 While some crestal bone loss of 1 to 2 mm in the initial phase after placement and during the first year of loading has been observed and described as a normal effect of the bone-remodeling process after the surgical trauma of implant placement, continuing bone loss should not occur or should not exceed 0.2 mm per year.6 A distinction between early and late implant failures was made and clinical manifestations were discussed by Esposito et al in 1999 and 2000.12,13 The reported prevalence of peri-implantitis with progressive crestal bone loss is between 0% and 14.4% in different populations with various study durations.14 Currently, there is little information available on the clinical long-term success of this specific implant system for different clinical indications. A comparison of survival and success rates between implants placed in partially and completely edentulous jaws has not been performed. Thus, the aim of the present study was to compare the success rate of the cylindric, mediumrough-surface Element implant (Thommen Medical) when used to support removable and fixed dental prostheses after a minimum of 5 years of functional loading. The hypothesis was that the crestal bone level of implants connected to rigid bars and fixed denture prostheses remains stable, fulfilling the success criteria, without any difference between partially and completely edentulous patients.
MATERIALS AND METHODS Patients and Implant-Prosthetic Treatment
During a 1-year period (2003 to 2004), the Thommen implant system (Thommen Medical) was used in a
a
b
Figs 1a and 1b (a) The SPI Element, with short polished collar, as used in this study; (b) SPI Contact, which features a relatively longer polished collar neck and a root-form design.
prospective pilot study for the treatment of partially and completely edentulous patients who had been referred to the Department of Prosthodontics, University of Bern.3,4 Signed informed consent was obtained from all patients stating that the patients accepted the treatment plan (placement and restoration of the implants) and agreed to cover the related costs and follow the maintenance program. Each patient was interviewed, and medical histories were thoroughly evaluated to ensure their good general health at the time. Patients were categorized as class I or II according to the American Society of Anesthesiologists classification.15 Adequate bone volume (height and width) was a prerequisite for placement of implants with a minimum length of 8 mm and minimum endosseous width of 3.5 mm. Exclusion criteria for the placement of implants were drug or alcohol abuse, psychiatric problems, history of heart attack within the previous 6 months, uncontrolled diabetes or insulin dependence, immunocompromised status, current chemotherapy or leukocyte disorders, any health conditions that would compromise a surgical procedure under local anesthesia, extraction at an implant site fewer than 6 months before implant placement, and the presence of irradiated bone, severe parafunctional habits, or severe atrophy that required bone augmentation before implantation.16 Light smokers (fewer than 10 cigarettes per day) were included in the study but were asked to participate in a smoking cessation program prior to implant therapy. The patients had partially or completely edentulous jaws, and the prosthetic indications comprised various reconstructions with fixed and removable prostheses in the maxilla or mandible. All patients enrolled in the study underwent the same clinical screening and pretreatment protocol prior to implant placement. The International Journal of Oral & Maxillofacial Implants 899
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Gholami et al
a
b
Figs 2a and 2b Digital measurements of crestal bone levels in relation to the known implant length for (a) interforaminal implants in the edentulous mandible and (b) single implants in a partially edentulous maxilla.
Active periodontal therapy consisting of motivation, instruction in oral hygiene practices, scaling and root planing, and periodontal surgery was performed until any periodontal disease had been appropriately controlled (no bleeding on probing [BOP] and no pockets deeper than 6 mm). Restoration therapy (for any caries lesions) was also carried out, and complete dentures were adapted or new provisional prostheses were delivered prior to placement of implants. Patients underwent implant placement surgery within a 12-month period that ended in 2004. The implants were placed according to the drilling protocol prescribed by the manufacturer and surgical guides. A standard healing period of 3 months for the mandible and 4 months for the maxilla was maintained. No provisional prostheses were connected to the implants during this time. The treatment was performed by different trained clinicians but under the supervision of the same instructor in the same clinical setting. Radiographs were obtained immediately after surgery, at the time of impression taking (loading), and 1 and 5 years after loading of implants with the definitive prostheses. Panoramic radiographs were used when implants were placed interforaminally in an edentulous mandible, while single periapical radiographs were obtained with film holders for all other indications. The surgical and prosthetic procedures were identical for all patients according to standard protocols, and standard instruments were used.
Follow-up Protocol
Five to 6 years after implant loading, all patients were recalled for an examination by one trained and calibrated investigator who had not been involved in the treatment. Peri-implant parameters were recorded, and radiologic crestal bone levels were assessed digitally (DBSWIN 4.5.2, Dürr Dental). Analog radiographs
were digitized with an adequate scanner (HP LaserJet 4000). Vertical changes in the bone level were measured on the mesial and distal sides of each implant, with the implant shoulder used as a reference point (Figs 2a and 2b). First bone-to-implant contact (BIC) was defined as the distance between the implant shoulder and the most coronal point of the implant in contact with the alveolar bone.17 This value was calculated for each implant in the series of radiographs and compared between surgery and follow-up appointments to determine the crestal bone level changes. The known length and size and typical design of the implants (distance of screw threads, implant shoulder) allowed for accurate reading of BIC by means of computer software that allowed calibration to adjust for distortion and magnification. Crestal bone changes were expressed as ∆BIC for the corresponding intervals and the overall observation time. When all patients were recalled for the final radiograph after 5 years of loading, clinical peri-implant parameters were recorded, namely pocket depth (PD) and BOP, using a graded probe (with markings at 3, 6, 9, and 12 mm). PD and BOP were measured at four sites (mesial, distal, buccal and lingual, in millimeters, for PD), and the presence or absence of BOP was reported as percentage of measured sites. Different criteria to determine implant success have been proposed by various authors using clinical and radiologic parameters.18–22 Survival of implants, meaning that the implant is still in function, is presented via life table analysis in the current study. A distinction was made between early failures (during the healing phase) and late failures (after loading with a provisional or definitive prosthesis). To clinically assess peri-implant health, various measurement parameters were defined, usually adopted from periodontology23,24 (eg, radiographic measurements8,25). The gold standard to
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Table 1 Cumulative Implant Survival Rate over 5 Years Implants
No. of dropouts
No. of failed implants
20
61
0
1
20
60
0
0
100%
98.4%
1 to 2 y
20
60
0
0
100%
98.4%
2 to 3 y
20
60
0
0
100%
98.4%
3 to 4 y
20
60
2
0
100%
98.4%
4 to 5 y
19
58
0
0
100%
98.4%
Time interval
No. of patients
Before loading 0 to 1 y
determine implant success is the measurement of radiologic crestal bone level changes on the mesial and distal sides of the implants. As proposed by Albrektsson et al,18 therefore, a bone loss equal to or less than 0.2 mm per year was defined as acceptable.
Statistical Analysis
All data were subjected to statistical analysis using SPSS software (version 18, SPSS). Descriptive statistics were used for patient demographics and calculation of ∆BIC. The cumulative survival rate was calculated for all implants placed. Nonparametric testing was performed to compare ∆BIC between groups. The Pearson correlation coefficient was used to assess the association between PD and ∆BIC.
RESULTS
98.4%
Cumulative survival rate 98.4%
Table 2 Demographic and Implant Information with Respect to Crestal Bone Level Changes (∆BIC) No. of No. of ∆BIC (mm) implants implants (mean ± SD) placed (20 at 5 y (19 (surgery patients) patients)* to 5 y) Dental status
Edentulous
38
35
1.5 ± 0.9
Partially edentulous
23
23
1.1 ± 0.6
Mandible Maxilla
26 35
24 34
1.5 ± 1.1 1.3 ± 0.7
Location Anterior Posterior
40 21
38 20
1.4 ± 0.9 1.3 ± 0.9
Gender
Male Female
30 31
28 30
1.5 ± 0.9 1.3 ± 0.9
Implant length
8 mm
5
5
1.2 ± 0.7
11 mm 14 mm
32 24
31 22
0.9 ± 0.7 1.7 ± 1.0
Jaw
Patients and Implants
A total of 20 patients (10 women and 10 men) received a total of 61 placed implants and were enrolled in the study. The mean age at the time of implant placement was 62.1 ± 7.2 years. Only two patients were younger than 50 years. The patients were similar in terms of gender, dental status, and number and distribution of implants. In one woman, one implant failed during the healing period, resulting in a 98.4% implant success rate after the entire observation period (Table 1). Thus, a total of 60 implants (34 in the maxilla, 26 in the mandible) were loaded and assessed radiographically from the beginning of the prosthetic treatment. In all, 16 implant overdentures (1 in the maxilla supported by four implants and 15 in the mandible on 33 implants) and 23 single crowns in the anterior and posterior regions of both arches were delivered to the patients. At the 1-year follow-up exam, all 20 patients were available with 60 implants, while at the 5-year follow-up two implants were lost to follow-up since one male patient with an implant-supported mandibular overdenture had died. Thus, a total of 58 implants in 9 men and 10 women completed a minimum of 5 years of observation.
No. surviving during interval
Implant 3.5 mm diameter 4.2 mm
26
25
1.5 ± 0.9
35
33
1.2 ± 0.8
Total*
61
58*
1.4 ± 0.9
*One implant in the posterior maxilla failed during the healing phase, and two implants were lost in the anterior mandible after 3 years (the patient died).
Crestal Bone Level Changes The loaded implants (n = 60) exhibited successful osseointegration without peri-implant radiolucency during the observation period. Table 2 demonstrates an overview of patients, implants, and mean ∆BIC after 5 years. The average ∆BIC in edentulous and partially dentate patients between surgery and the 5-year follow-up was 1.5 ± 0.9 mm and 1.1 ± 0.6 mm, respectively (Mann-Whitney U test, P = .071) (Table 3). The bone remodeling process in both partially dentate and edentulous patients was most pronounced during the period after surgery (50% of implants) and during the first year of loading (21%). Thereafter, from loading to the 5-year follow-up, the bone level changes showed a stable mean annual bone loss of < 0.12 mm (Fig 3). The International Journal of Oral & Maxillofacial Implants 901
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Gholami et al
Soft Tissue Parameters
Table 3 Mean Crestal Bone Level Changes over Time, with Percentages of Completed Bone Loss over Time Surgery– loading
Loading– 1y
1–5 y
Total
Edentulous
0.7 mm (46%)
0.4 mm (27%)
0.4 mm (27%)
1.5 mm (100%)
Partially edentulous
0.6 mm (55%)
0.2 mm (18%)
0.3 mm (27%)
1.1 mm (100%)
Total
0.7 mm (50%)
0.3 mm (21%)
0.4 mm (29%)
1.4 mm (100%)
DISCUSSION
Mean crestal bone level (mm)
0.0 –0.5 –1.0 –1.5
Partially edentulous
–2.0 –2.5 –3.0
Edentulous
–3.5 –4.0 Surgery Loading 1 y
2y
3y
4y
5y
Fig 3 Crestal bone level changes in edentulous and partially edentulous patients.
Edentulous Partially edentulous
>2 mm 1.5–2 mm Bone loss
The average PD was 2.58 ± 0.73 mm at the 5-year follow-up. Slightly increased PD values were found in patients who still had their natural teeth. When dental status and the jaw were considered together as a single effect, PD was deeper in the maxilla and in jaws still exhibiting natural teeth (P < .006). Thirty percent of all implants exhibited one or more sites with positive BOP, ie, 17% of all implant sites, with a higher frequency in female patients (P = .009). The Pearson correlation coefficient did not reveal correlations between PD and ∆BIC or between BOP and ∆BIC.
1–1.5 mm 0.5–1 mm 85% and 94% of implants had < 1.5 mm of bone loss, respectively (Fig 4). In all, six implants showed bone loss ≥ 2 mm after an observation time of 5 years.
The implant survival rate did not reach 100% in this study, since one implant failed during the healing period and two implants were excluded from the study. However, the survival rate can be considered satisfactory, especially taking into consideration the learning curve with the new implant system. The two implants in the patient who passed away did not show any signs of problems during the initial follow-up appointments. Although it appears that a sandblasted acid-etched implant surface may shorten the healing time and moderately roughened surfaces display a stronger bone response,1 in the present study standard healing times were used (3 months for the mandible and 4 months for the maxilla). Unlike other previously described conical implant systems,26,27 the present implants were not placed at the crestal bone level; rather, the machined 1-mm neck was left out of the bone. The mean level of supracrestal implant positioning is shown in Fig 3 (surgery). Furthermore, conical implants have a longer conical intrabony part. This was not the case with the cylindric implant used in the present study. Therefore, the pronounced loss of crestal bone of up to 3.6 mm was most likely a result of the collar length.26 Furthermore, this study26 had a mean follow-up time of 3 years for 19 implants and 5 years for only two implants, limiting the strength of the results. However, this increased bone loss was not observed with the present implant design. Currently, the present implant system has been in use for 11 years. The first generation of these implants, which was used in the present study, featured a sandblasted, acid-etched, medium-rough surface. The time point of measurements is crucial when comparing crestal bone level changes in different studies. In many studies, baseline was set as the day of reentry and loading.20,28–30 In the present study, the healing period was included in ∆BIC measurements, which resulted in 46% (edentulous) and 55% (partially dentate) higher total ∆BIC values in relation to total
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bone loss. There are different ways of reporting crestal bone loss in clinical studies, but only minor variations in the measured values have been seen. Standardized radiographs were not taken annually and the mean annual bone loss, as reported in the studies, is therefore an extrapolation, calculated over the entire observation time. If this type of reporting had been applied to the measurements in the present study, the annual crestal bone loss would be less than 0.1 mm. One long-term study reported only 0.05 mm of crestal bone loss per year for different types of implants in the edentulous mandible supporting fixed prostheses.28 In another long-term study on interforaminal ITI implants (Straumann) with plasma-sprayed surfaces, a mean crestal bone loss of 0.54 mm was found after an average observation period of 16.5 years31; this translates into an average of less than 0.1 mm of bone loss per year. Bone loss around implants in the edentulous maxilla within a time period of 5 or more years was less than 1 mm with ITI implants in another study; the healing period was not stated.29 A more recent retrospective study with three different implant systems reported > 2 mm crestal bone loss after an observation period of 4 years.30 That study used Straumann implants with a sandblasted/acid-etched surface, and no differences between the three implant systems were observed. It has been commonly reported that most bone remodeling occurs during the healing period and during the first year of loading. Factors such as surgical trauma, occlusal overload, biologic width, the implantabutment microgap, implant crest remodeling, and peri-implantitis are considered the causes of initial crestal bone loss around implants.32 Petrie and Williams in 200533 concluded that wide, long, nontapered implants were more likely to show favorable long-term results. Another study reported that implant length failed to affect the implant success rate in patients who had undergone maxillary sinus augmentation prior to implant surgery.34 One study of narrow-diameter (3.5-mm) implants failed to show a lower survival rate.35 The present data with these microstructured medium-rough implants showed a tendency toward the best results when the implants had a standard diameter of 4.2 mm and length of 11 mm. Subtraction radiography may be a highly precise method to evaluate crestal bone level changes,25 but clinical studies typically use periapical radiographs, whether traditional or, more recently, digital. The accuracy and reliability of oral radiographic methods have been studied in human cadavers and in animal models,28,36 with insignificant overall errors found. In the present study, film holders were used for radiographs, except for interforaminal implants in an edentulous arch, where a high mouth floor often prevented the use of film holders. Panoramic radiographs of good
quality were obtained and measurements were done using known implant dimensions as landmarks. Other indices, eg, the modified bleeding index according to Mombelli and Lang,23 have been used to evaluate peri-implant parameters in other studies; however, BOP and PD are easy to use and provide valid information. One limitation of the present study was the very small number of patients/implants and the heterogeneity of prosthetic indications. Thus, a multivariable regression analysis of 58 implants (or 116 sites) in 18 patients is questionable. PD of the implants was not associated with BIC, but PDs were significantly higher in the maxilla than in the mandible. This may be explained by the thick palatal mucosa in the maxilla. ∆BIC values for implants in partially dentate jaws had the tendency to be lower. One explanation may be that the crestal bone of healthy teeth contributed to the stability of the crestal bone at the adjacent implant sites. For single-tooth replacement with ITI implants, crestal bone loss from the time of crown placement up to 9 years was minimal (around 0.5 mm). All implant sites had healthy adjacent natural teeth with stable crestal bone. All patients were in good health, and major systemic problems or medications that could adversely affect osseointegration or the stability of the crestal bone were not present. Conclusions cannot be drawn for the implants that lost ≥ 2 mm of crestal bone, and it should be noted that these findings are still within the limits of normal variation. However, the number of implants was small and patients with different dental status and locations of implants were included. Therefore, the significance of these findings should not be overstated. However, the compliance of the patients involved during the observation period of 5 to 6 years was excellent. The hypothesis that mean crestal bone remains stable around the implants was confirmed, since crestal bone changes remained within the range of known success criteria.
CONCLUSIONS Within the limitations of the present study, it can be concluded that peri-implant parameters of the specific microstructured medium-rough implants were stable and the bone loss around implants was within the range designated by implant success criteria over 5 years of functional loading in partially and completely edentulous patients. Thus, the present implant system can be considered reliable, effective, and comparable to other systems in the short term for the rehabilitation of partially or completely edentulous patients. More studies with more implants and longer observation periods are needed to provide a higher level of evidence. The International Journal of Oral & Maxillofacial Implants 903
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ACKNOWLEDGMENTS The authors reported no conflicts of interest related to this study.
REFERENCES 1. Albrektsson T, Wennerberg A. Oral implant surfaces: Part 1— Review focusing on topographic and chemical properties of different surfaces and in vivo responses to them. Int J Prosthodont 2004;17:536–543. 2. Albrektsson T, Wennerberg A. Oral implant surfaces: Part 2— Review focusing on clinical knowledge of different surfaces. Int J Prosthodont 2004;17:544–564. 3. Kessler-Liechti G, Mericske-Stern R. [Anterior teeth esthetics with the SPI implant system]. Schweiz Monatsschr Zahnmed 2006;116:275–286. 4. Kessler-Liechti G, Mericske-Stern R. [The SPI implant system: Clinical experience and one-year results]. Schweiz Monatsschr Zahnmed 2006;116:258–267. 5. Merli M, Moscatelli M, Mariotti G, Piemontese M, Nieri M. Immediate versus early non-occlusal loading of dental implants placed flapless in partially edentulous patients: A 3-year randomized clinical trial. J Clin Periodontol 2012;39:196–202. 6. Adell R, Eriksson B, Lekholm U, Brånemark PI, Jemt T. Long-term follow-up study of osseointegrated implants in the treatment of totally edentulous jaws. Int J Oral Maxillofac Implants 1990;5:347–359. 7. Buser D, Mericske-Stern R, Bernard JP, et al. Long-term evaluation of non-submerged ITI implants. Part 1: 8-year life table analysis of a prospective multi-center study with 2359 implants. Clin Oral Implants Res 1997;8:161–172. 8. Zarb GA, Schmitt A. The longitudinal clinical effectiveness of osseointegrated dental implants: The Toronto study. Part I: Surgical results. J Prosthet Dent 1990;63:451–457. 9. Zarb GA, Schmitt A. The longitudinal clinical effectiveness of osseointegrated dental implants: The Toronto Study. Part II: The prosthetic results. J Prosthet Dent 1990;64:53–61. 10. Zarb GA, Schmitt A. The longitudinal clinical effectiveness of osseointegrated dental implants in anterior partially edentulous patients. Int J Prosthodont 1993;6:180–188. 11. Zarb GA, Schmitt A. The longitudinal clinical effectiveness of osseointegrated dental implants in posterior partially edentulous patients. Int J Prosthodont 1993;6:189–196. 12. Esposito M, Thomsen P, Ericson LE, Lekholm U. Histopathologic observations on early oral implant failures. Int J Oral Maxillofac Implants 1999;14:798–810. 13. Esposito M, Thomsen P, Ericson LE, Sennerby L, Lekholm U. Histopathologic observations on late oral implant failures. Clin Implant Dent Relat Res 2000;2:18–32. 14. Berglundh T, Persson L, Klinge B. A systematic review of the incidence of biological and technical complications in implant dentistry reported in prospective longitudinal studies of at least 5 years. J Clin Periodontol 2002;29(suppl 3):197–212. 15. Maloney WJ, Weinberg MA. Implementation of the American Society of Anesthesiologists Physical Status classification system in periodontal practice. J Periodontol 2008;79:1124–1126. 16. Mericske-Stern R, Grutter L, Rosch R, Mericske E. Clinical evaluation and prosthetic complications of single tooth replacements by nonsubmerged implants. Clin Oral Implants Res 2001;12:309–318. 17. Hermann JS, Schoolfield JD, Nummikoski PV, Buser D, Schenk RK, Cochran DL. Crestal bone changes around titanium implants: A methodologic study comparing linear radiographic with histometric measurements. Int J Oral Maxillofac Implants 2001;16:475–485.
18. Albrektsson T, Zarb G, Worthington P, Eriksson AR. The long-term efficacy of currently used dental implants: A review and proposed criteria of success. Int J Oral Maxillofac Implants 1986;1:11–25. 19. Albrektsson T, Zarb GA. Current interpretations of the osseointegrated response: Clinical significance. Int J Prosthodont 1993;6:95–105. 20. Buser D, Weber HP, Bragger U, Balsiger C. Tissue integration of one-stage ITI implants: 3-year results of a longitudinal study with Hollow-Cylinder and Hollow-Screw implants. Int J Oral Maxillofac Implants 1991;6:405–412. 21. Buser D, Weber HP, Lang NP. Tissue integration of non-submerged implants. 1-year results of a prospective study with 100 ITI hollow-cylinder and hollow-screw implants. Clin Oral Implants Res 1990;1:33–40. 22. Esposito M, Hirsch JM, Lekholm U, Thomsen P. Biological factors contributing to failures of osseointegrated oral implants. (I). Success criteria and epidemiology. Eur J Oral Sci 1998;106:527–551. 23. Mombelli A, Lang NP. Clinical parameters for the evaluation of dental implants. Periodontol 2000 1994;4:81–86. 24. van Steenberghe D, Klinge B, Linden U, Quirynen M, Herrmann I, Garpland C. Periodontal indices around natural and titanium abutments: A longitudinal multicenter study. J Periodontol 1993;64:538–541. 25. Bragger U, Hafeli U, Huber B, Hammerle CH, Lang NP. Evaluation of postsurgical crestal bone levels adjacent to non-submerged dental implants. Clin Oral Implants Res 1998;9:218–224. 26. Malevez C, Hermans M, Daelemans P. Marginal bone levels at Brånemark system implants used for single tooth restoration. The influence of implant design and anatomical region. Clin Oral Implants Res 1996;7:162–169. 27. Norton MR. Marginal bone levels at single tooth implants with a conical fixture design. The influence of surface macro- and microstructure. Clin Oral Implants Res 1998;9:91–99. 28. Carlsson GE, Lindquist LW, Jemt T. Long-term marginal periimplant bone loss in edentulous patients. Int J Prosthodont 2000;13:295–302. 29. Mericske-Stern R, Oetterli M, Kiener P, Mericske E. A follow-up study of maxillary implants supporting an overdenture: Clinical and radiographic results. Int J Oral Maxillofac Implants 2002;17:678–686. 30. Semper W, Heberer S, Nelson K. Retrospective analysis of barretained dentures with cantilever extension: Marginal bone level changes around dental implants over time. Int J Oral Maxillofac Implants 2010;25:385–393. 31. Ueda T, Kremer U, Katsoulis J, Mericske-Stern R. Long-term results of mandibular implants supporting an overdenture: Implant survival, failures, and crestal bone level changes. Int J Oral Maxillofac Implants 2011;26:365–372. 32. Oh TJ, Yoon J, Misch CE, Wang HL. The causes of early implant bone loss: Myth or science? J Periodontol 2002;73:322–333. 33. Petrie CS, Williams JL. Comparative evaluation of implant designs: Influence of diameter, length, and taper on strains in the alveolar crest. A three-dimensional finite-element analysis. Clin Oral Implants Res 2005;16:486–494. 34. Hurzeler MB, Kirsch A, Ackermann KL, Quinones CR. Reconstruction of the severely resorbed maxilla with dental implants in the augmented maxillary sinus: A 5-year clinical investigation. Int J Oral Maxillofac Implants 1996;11:466–475. 35. Zinsli B, Sagesser T, Mericske E, Mericske-Stern R. Clinical evaluation of small-diameter ITI implants: A prospective study. Int J Oral Maxillofac Implants 2004;19:92–99. 36. De Smet E, Jacobs R, Gijbels F, Naert I. The accuracy and reliability of radiographic methods for the assessment of marginal bone level around oral implants. Dentomaxillofac Radiol 2002;31:176–181.
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O
sseointegrated implants have been used successfully to restore function to fully and partially edentulous patients. Modifications of implant design on both the macroscopic and microscopic levels have been implemented to improve implant success rates. Some clinical advantages have been reported for moderately rough surfaces in comparison with smooth or
1Postdoctoral
Student, Department of Prosthodontics, School of Dental Medicine, University of Bern, Switzerland. 2Director and Chair, Department of Prosthodontics, School of Dental Medicine, University of Bern, Switzerland. 3Assistant Professor, Department of Prosthodontics, School of Dental Medicine, University of Bern, Switzerland. 4 Associate Professor, Department of Prosthodontics, School of Dental Medicine, University of Bern, Switzerland. Correspondence to: Dr J. Katsoulis, Department of Prosthodontics, School of Dental Medicine, University of Bern, Freiburgstrasse 7, 3010 Bern, Switzerland. Fax: +41-31-632-49-33. Email: [email protected] ©2014 by Quintessence Publishing Co Inc.
rough surfaces.1 However, very few of the long-term best-documented oral implants from the major oral implant companies are still available on the market.2 In addition, little is known about the impact of the type of edentulism (partial or complete) on crestal bone level changes around implants. In 2001, a new implant system, Thommen (Thommen Medical), was released to the market. To date, few clinical studies have reported working with this implant system,3,4 although several other dental implant systems have been properly documented for 5 years or more.2 In a pilot study, clinical procedures, prosthetic complications, and required maintenance after 1 year of loading were shown to be comparable to other implant systems.3,4 According to the authors, osseointegration of Thommen implants was highly successful in a variety of patients, and their stability was very good, although some minor problems were identified with the instruments for prosthetic procedures. These instruments were subsequently improved, modified, or replaced. The system offers implants with different platforms and a low
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Gholami et al
shoulder design that may provide favorable results in the esthetically demanding anterior maxilla.3 For the current study, the Element implant (Fig 1a), which has a cylindric screw design and a short machined neck of 1.0 mm, was selected. This implant type is more often indicated for completely edentulous mandibles, anterior fixed crowns, and short partial dentures, compared with the Contact (Fig 1b) implant, which has a root-form screw design and a longer machined neck of 1.5 mm. Furthermore, various abutments, healing caps, and a sophisticated screwdriver are available, making clinical application of the system easier. No differences in failure rates, complications, or bone levels were seen after 3 years between implants that were loaded immediately or early.5 A limited number of studies are available that have assessed longitudinally the survival and success rates of implants and various supporting restorations for 5, 10, or more years. Some studies were published in the 1990s; most discussed the Brånemark System (Nobel Biocare) and a few focused on ITI implants (Straumann).6–11 While some crestal bone loss of 1 to 2 mm in the initial phase after placement and during the first year of loading has been observed and described as a normal effect of the bone-remodeling process after the surgical trauma of implant placement, continuing bone loss should not occur or should not exceed 0.2 mm per year.6 A distinction between early and late implant failures was made and clinical manifestations were discussed by Esposito et al in 1999 and 2000.12,13 The reported prevalence of peri-implantitis with progressive crestal bone loss is between 0% and 14.4% in different populations with various study durations.14 Currently, there is little information available on the clinical long-term success of this specific implant system for different clinical indications. A comparison of survival and success rates between implants placed in partially and completely edentulous jaws has not been performed. Thus, the aim of the present study was to compare the success rate of the cylindric, mediumrough-surface Element implant (Thommen Medical) when used to support removable and fixed dental prostheses after a minimum of 5 years of functional loading. The hypothesis was that the crestal bone level of implants connected to rigid bars and fixed denture prostheses remains stable, fulfilling the success criteria, without any difference between partially and completely edentulous patients.
MATERIALS AND METHODS Patients and Implant-Prosthetic Treatment
During a 1-year period (2003 to 2004), the Thommen implant system (Thommen Medical) was used in a
a
b
Figs 1a and 1b (a) The SPI Element, with short polished collar, as used in this study; (b) SPI Contact, which features a relatively longer polished collar neck and a root-form design.
prospective pilot study for the treatment of partially and completely edentulous patients who had been referred to the Department of Prosthodontics, University of Bern.3,4 Signed informed consent was obtained from all patients stating that the patients accepted the treatment plan (placement and restoration of the implants) and agreed to cover the related costs and follow the maintenance program. Each patient was interviewed, and medical histories were thoroughly evaluated to ensure their good general health at the time. Patients were categorized as class I or II according to the American Society of Anesthesiologists classification.15 Adequate bone volume (height and width) was a prerequisite for placement of implants with a minimum length of 8 mm and minimum endosseous width of 3.5 mm. Exclusion criteria for the placement of implants were drug or alcohol abuse, psychiatric problems, history of heart attack within the previous 6 months, uncontrolled diabetes or insulin dependence, immunocompromised status, current chemotherapy or leukocyte disorders, any health conditions that would compromise a surgical procedure under local anesthesia, extraction at an implant site fewer than 6 months before implant placement, and the presence of irradiated bone, severe parafunctional habits, or severe atrophy that required bone augmentation before implantation.16 Light smokers (fewer than 10 cigarettes per day) were included in the study but were asked to participate in a smoking cessation program prior to implant therapy. The patients had partially or completely edentulous jaws, and the prosthetic indications comprised various reconstructions with fixed and removable prostheses in the maxilla or mandible. All patients enrolled in the study underwent the same clinical screening and pretreatment protocol prior to implant placement. The International Journal of Oral & Maxillofacial Implants 899
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Gholami et al
a
b
Figs 2a and 2b Digital measurements of crestal bone levels in relation to the known implant length for (a) interforaminal implants in the edentulous mandible and (b) single implants in a partially edentulous maxilla.
Active periodontal therapy consisting of motivation, instruction in oral hygiene practices, scaling and root planing, and periodontal surgery was performed until any periodontal disease had been appropriately controlled (no bleeding on probing [BOP] and no pockets deeper than 6 mm). Restoration therapy (for any caries lesions) was also carried out, and complete dentures were adapted or new provisional prostheses were delivered prior to placement of implants. Patients underwent implant placement surgery within a 12-month period that ended in 2004. The implants were placed according to the drilling protocol prescribed by the manufacturer and surgical guides. A standard healing period of 3 months for the mandible and 4 months for the maxilla was maintained. No provisional prostheses were connected to the implants during this time. The treatment was performed by different trained clinicians but under the supervision of the same instructor in the same clinical setting. Radiographs were obtained immediately after surgery, at the time of impression taking (loading), and 1 and 5 years after loading of implants with the definitive prostheses. Panoramic radiographs were used when implants were placed interforaminally in an edentulous mandible, while single periapical radiographs were obtained with film holders for all other indications. The surgical and prosthetic procedures were identical for all patients according to standard protocols, and standard instruments were used.
Follow-up Protocol
Five to 6 years after implant loading, all patients were recalled for an examination by one trained and calibrated investigator who had not been involved in the treatment. Peri-implant parameters were recorded, and radiologic crestal bone levels were assessed digitally (DBSWIN 4.5.2, Dürr Dental). Analog radiographs
were digitized with an adequate scanner (HP LaserJet 4000). Vertical changes in the bone level were measured on the mesial and distal sides of each implant, with the implant shoulder used as a reference point (Figs 2a and 2b). First bone-to-implant contact (BIC) was defined as the distance between the implant shoulder and the most coronal point of the implant in contact with the alveolar bone.17 This value was calculated for each implant in the series of radiographs and compared between surgery and follow-up appointments to determine the crestal bone level changes. The known length and size and typical design of the implants (distance of screw threads, implant shoulder) allowed for accurate reading of BIC by means of computer software that allowed calibration to adjust for distortion and magnification. Crestal bone changes were expressed as ∆BIC for the corresponding intervals and the overall observation time. When all patients were recalled for the final radiograph after 5 years of loading, clinical peri-implant parameters were recorded, namely pocket depth (PD) and BOP, using a graded probe (with markings at 3, 6, 9, and 12 mm). PD and BOP were measured at four sites (mesial, distal, buccal and lingual, in millimeters, for PD), and the presence or absence of BOP was reported as percentage of measured sites. Different criteria to determine implant success have been proposed by various authors using clinical and radiologic parameters.18–22 Survival of implants, meaning that the implant is still in function, is presented via life table analysis in the current study. A distinction was made between early failures (during the healing phase) and late failures (after loading with a provisional or definitive prosthesis). To clinically assess peri-implant health, various measurement parameters were defined, usually adopted from periodontology23,24 (eg, radiographic measurements8,25). The gold standard to
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Table 1 Cumulative Implant Survival Rate over 5 Years Implants
No. of dropouts
No. of failed implants
20
61
0
1
20
60
0
0
100%
98.4%
1 to 2 y
20
60
0
0
100%
98.4%
2 to 3 y
20
60
0
0
100%
98.4%
3 to 4 y
20
60
2
0
100%
98.4%
4 to 5 y
19
58
0
0
100%
98.4%
Time interval
No. of patients
Before loading 0 to 1 y
determine implant success is the measurement of radiologic crestal bone level changes on the mesial and distal sides of the implants. As proposed by Albrektsson et al,18 therefore, a bone loss equal to or less than 0.2 mm per year was defined as acceptable.
Statistical Analysis
All data were subjected to statistical analysis using SPSS software (version 18, SPSS). Descriptive statistics were used for patient demographics and calculation of ∆BIC. The cumulative survival rate was calculated for all implants placed. Nonparametric testing was performed to compare ∆BIC between groups. The Pearson correlation coefficient was used to assess the association between PD and ∆BIC.
RESULTS
98.4%
Cumulative survival rate 98.4%
Table 2 Demographic and Implant Information with Respect to Crestal Bone Level Changes (∆BIC) No. of No. of ∆BIC (mm) implants implants (mean ± SD) placed (20 at 5 y (19 (surgery patients) patients)* to 5 y) Dental status
Edentulous
38
35
1.5 ± 0.9
Partially edentulous
23
23
1.1 ± 0.6
Mandible Maxilla
26 35
24 34
1.5 ± 1.1 1.3 ± 0.7
Location Anterior Posterior
40 21
38 20
1.4 ± 0.9 1.3 ± 0.9
Gender
Male Female
30 31
28 30
1.5 ± 0.9 1.3 ± 0.9
Implant length
8 mm
5
5
1.2 ± 0.7
11 mm 14 mm
32 24
31 22
0.9 ± 0.7 1.7 ± 1.0
Jaw
Patients and Implants
A total of 20 patients (10 women and 10 men) received a total of 61 placed implants and were enrolled in the study. The mean age at the time of implant placement was 62.1 ± 7.2 years. Only two patients were younger than 50 years. The patients were similar in terms of gender, dental status, and number and distribution of implants. In one woman, one implant failed during the healing period, resulting in a 98.4% implant success rate after the entire observation period (Table 1). Thus, a total of 60 implants (34 in the maxilla, 26 in the mandible) were loaded and assessed radiographically from the beginning of the prosthetic treatment. In all, 16 implant overdentures (1 in the maxilla supported by four implants and 15 in the mandible on 33 implants) and 23 single crowns in the anterior and posterior regions of both arches were delivered to the patients. At the 1-year follow-up exam, all 20 patients were available with 60 implants, while at the 5-year follow-up two implants were lost to follow-up since one male patient with an implant-supported mandibular overdenture had died. Thus, a total of 58 implants in 9 men and 10 women completed a minimum of 5 years of observation.
No. surviving during interval
Implant 3.5 mm diameter 4.2 mm
26
25
1.5 ± 0.9
35
33
1.2 ± 0.8
Total*
61
58*
1.4 ± 0.9
*One implant in the posterior maxilla failed during the healing phase, and two implants were lost in the anterior mandible after 3 years (the patient died).
Crestal Bone Level Changes The loaded implants (n = 60) exhibited successful osseointegration without peri-implant radiolucency during the observation period. Table 2 demonstrates an overview of patients, implants, and mean ∆BIC after 5 years. The average ∆BIC in edentulous and partially dentate patients between surgery and the 5-year follow-up was 1.5 ± 0.9 mm and 1.1 ± 0.6 mm, respectively (Mann-Whitney U test, P = .071) (Table 3). The bone remodeling process in both partially dentate and edentulous patients was most pronounced during the period after surgery (50% of implants) and during the first year of loading (21%). Thereafter, from loading to the 5-year follow-up, the bone level changes showed a stable mean annual bone loss of < 0.12 mm (Fig 3). The International Journal of Oral & Maxillofacial Implants 901
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Gholami et al
Soft Tissue Parameters
Table 3 Mean Crestal Bone Level Changes over Time, with Percentages of Completed Bone Loss over Time Surgery– loading
Loading– 1y
1–5 y
Total
Edentulous
0.7 mm (46%)
0.4 mm (27%)
0.4 mm (27%)
1.5 mm (100%)
Partially edentulous
0.6 mm (55%)
0.2 mm (18%)
0.3 mm (27%)
1.1 mm (100%)
Total
0.7 mm (50%)
0.3 mm (21%)
0.4 mm (29%)
1.4 mm (100%)
DISCUSSION
Mean crestal bone level (mm)
0.0 –0.5 –1.0 –1.5
Partially edentulous
–2.0 –2.5 –3.0
Edentulous
–3.5 –4.0 Surgery Loading 1 y
2y
3y
4y
5y
Fig 3 Crestal bone level changes in edentulous and partially edentulous patients.
Edentulous Partially edentulous
>2 mm 1.5–2 mm Bone loss
The average PD was 2.58 ± 0.73 mm at the 5-year follow-up. Slightly increased PD values were found in patients who still had their natural teeth. When dental status and the jaw were considered together as a single effect, PD was deeper in the maxilla and in jaws still exhibiting natural teeth (P < .006). Thirty percent of all implants exhibited one or more sites with positive BOP, ie, 17% of all implant sites, with a higher frequency in female patients (P = .009). The Pearson correlation coefficient did not reveal correlations between PD and ∆BIC or between BOP and ∆BIC.
1–1.5 mm 0.5–1 mm 85% and 94% of implants had < 1.5 mm of bone loss, respectively (Fig 4). In all, six implants showed bone loss ≥ 2 mm after an observation time of 5 years.
The implant survival rate did not reach 100% in this study, since one implant failed during the healing period and two implants were excluded from the study. However, the survival rate can be considered satisfactory, especially taking into consideration the learning curve with the new implant system. The two implants in the patient who passed away did not show any signs of problems during the initial follow-up appointments. Although it appears that a sandblasted acid-etched implant surface may shorten the healing time and moderately roughened surfaces display a stronger bone response,1 in the present study standard healing times were used (3 months for the mandible and 4 months for the maxilla). Unlike other previously described conical implant systems,26,27 the present implants were not placed at the crestal bone level; rather, the machined 1-mm neck was left out of the bone. The mean level of supracrestal implant positioning is shown in Fig 3 (surgery). Furthermore, conical implants have a longer conical intrabony part. This was not the case with the cylindric implant used in the present study. Therefore, the pronounced loss of crestal bone of up to 3.6 mm was most likely a result of the collar length.26 Furthermore, this study26 had a mean follow-up time of 3 years for 19 implants and 5 years for only two implants, limiting the strength of the results. However, this increased bone loss was not observed with the present implant design. Currently, the present implant system has been in use for 11 years. The first generation of these implants, which was used in the present study, featured a sandblasted, acid-etched, medium-rough surface. The time point of measurements is crucial when comparing crestal bone level changes in different studies. In many studies, baseline was set as the day of reentry and loading.20,28–30 In the present study, the healing period was included in ∆BIC measurements, which resulted in 46% (edentulous) and 55% (partially dentate) higher total ∆BIC values in relation to total
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Gholami et al
bone loss. There are different ways of reporting crestal bone loss in clinical studies, but only minor variations in the measured values have been seen. Standardized radiographs were not taken annually and the mean annual bone loss, as reported in the studies, is therefore an extrapolation, calculated over the entire observation time. If this type of reporting had been applied to the measurements in the present study, the annual crestal bone loss would be less than 0.1 mm. One long-term study reported only 0.05 mm of crestal bone loss per year for different types of implants in the edentulous mandible supporting fixed prostheses.28 In another long-term study on interforaminal ITI implants (Straumann) with plasma-sprayed surfaces, a mean crestal bone loss of 0.54 mm was found after an average observation period of 16.5 years31; this translates into an average of less than 0.1 mm of bone loss per year. Bone loss around implants in the edentulous maxilla within a time period of 5 or more years was less than 1 mm with ITI implants in another study; the healing period was not stated.29 A more recent retrospective study with three different implant systems reported > 2 mm crestal bone loss after an observation period of 4 years.30 That study used Straumann implants with a sandblasted/acid-etched surface, and no differences between the three implant systems were observed. It has been commonly reported that most bone remodeling occurs during the healing period and during the first year of loading. Factors such as surgical trauma, occlusal overload, biologic width, the implantabutment microgap, implant crest remodeling, and peri-implantitis are considered the causes of initial crestal bone loss around implants.32 Petrie and Williams in 200533 concluded that wide, long, nontapered implants were more likely to show favorable long-term results. Another study reported that implant length failed to affect the implant success rate in patients who had undergone maxillary sinus augmentation prior to implant surgery.34 One study of narrow-diameter (3.5-mm) implants failed to show a lower survival rate.35 The present data with these microstructured medium-rough implants showed a tendency toward the best results when the implants had a standard diameter of 4.2 mm and length of 11 mm. Subtraction radiography may be a highly precise method to evaluate crestal bone level changes,25 but clinical studies typically use periapical radiographs, whether traditional or, more recently, digital. The accuracy and reliability of oral radiographic methods have been studied in human cadavers and in animal models,28,36 with insignificant overall errors found. In the present study, film holders were used for radiographs, except for interforaminal implants in an edentulous arch, where a high mouth floor often prevented the use of film holders. Panoramic radiographs of good
quality were obtained and measurements were done using known implant dimensions as landmarks. Other indices, eg, the modified bleeding index according to Mombelli and Lang,23 have been used to evaluate peri-implant parameters in other studies; however, BOP and PD are easy to use and provide valid information. One limitation of the present study was the very small number of patients/implants and the heterogeneity of prosthetic indications. Thus, a multivariable regression analysis of 58 implants (or 116 sites) in 18 patients is questionable. PD of the implants was not associated with BIC, but PDs were significantly higher in the maxilla than in the mandible. This may be explained by the thick palatal mucosa in the maxilla. ∆BIC values for implants in partially dentate jaws had the tendency to be lower. One explanation may be that the crestal bone of healthy teeth contributed to the stability of the crestal bone at the adjacent implant sites. For single-tooth replacement with ITI implants, crestal bone loss from the time of crown placement up to 9 years was minimal (around 0.5 mm). All implant sites had healthy adjacent natural teeth with stable crestal bone. All patients were in good health, and major systemic problems or medications that could adversely affect osseointegration or the stability of the crestal bone were not present. Conclusions cannot be drawn for the implants that lost ≥ 2 mm of crestal bone, and it should be noted that these findings are still within the limits of normal variation. However, the number of implants was small and patients with different dental status and locations of implants were included. Therefore, the significance of these findings should not be overstated. However, the compliance of the patients involved during the observation period of 5 to 6 years was excellent. The hypothesis that mean crestal bone remains stable around the implants was confirmed, since crestal bone changes remained within the range of known success criteria.
CONCLUSIONS Within the limitations of the present study, it can be concluded that peri-implant parameters of the specific microstructured medium-rough implants were stable and the bone loss around implants was within the range designated by implant success criteria over 5 years of functional loading in partially and completely edentulous patients. Thus, the present implant system can be considered reliable, effective, and comparable to other systems in the short term for the rehabilitation of partially or completely edentulous patients. More studies with more implants and longer observation periods are needed to provide a higher level of evidence. The International Journal of Oral & Maxillofacial Implants 903
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Gholami et al
ACKNOWLEDGMENTS The authors reported no conflicts of interest related to this study.
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