Original study - ZZI 02/2016

The influence of various implant types on peri-implant bone loss – a retrospective radiological evaluation

Background: Preserving marginal bone is crucial for good esthetic and functional results with implant-supported prosthetic restorations. However, several authors have reported remodeling of crestal bone and bone loss during the early stages following implant placement.

Objective: The objective of the present retrospective study was to review marginal peri-implant bone loss using radiographs collected by a dental oral surgery practice over a period of up to 17 3/4 years. It was hypothesized that no difference in bone loss would be found between the various dental implant types. The influence of implant-specific design features, prosthetic restorations, and the implant/abutment connection were investigated.

Materials and Methods: In this retrospective study, post-operative and follow-up radiographs of patients who had received implants in a private oral and maxillofacial practice over a 17 3/4-year period were digitized. Peri-implant bone-level changes were measured, and descriptive statistics computed.

Results: The study included 569 patients ranging in age from 14.8 to 84.4 years who received a total of 1434 implants, of which 173 images (12.1 %) were excluded because of lack of follow-up radiographs. A total of 3613 radiographs were taken of the remaining 1261 implants, which included 506 from Astra Tech Dental (40.1 %), 558 from Camlog (44.3 %), and 197 from DENTSPLY Friadent (15.6 %). The measurements were distributed evenly among upper and lower jaws. Marginal bone loss decreased markedly after the first 2 years, and significantly (p < 0.05) more bone loss was found in the upper jaw (mean = 0.91 mm, SD = ± 1.37) than in the lower jaw (mean = 0.79 mm, SD = ± 1.60). Bone cavities were smallest at single-tooth sites (mean = 0.74 mm, SD = ± 1.39) and in edentulous lower jaws. They were significantly greater (p < 0.05) around implants supporting bridges (mean = 0.96 mm, SD = ± 1.54). Short and thin implants induced less bone loss than long and thick ones (p < 0.05). Implants that had been placed in augmented areas incurred more bone loss overall than others during the course of observation, but the type of augmentation was crucial. Examination of the individual implant types revealed the most significant differences (p < 0.05). Regardless of the type of load, superstructure, augmentation or location, Camlog implants exhibited the largest bone cavities (mean = 1.25 mm, SD = ± 1.49), followed by DENTSPLY Friadent implants (mean = 1.16 mm, SD = ± 1.69), and Astra Tech dental implants (mean = 0.18 mm, SD = ± 1.07).

Conclusion: The implant/abutment connector geometry appeared to significantly influence the progression of bone loss.

Keywords: peri-implant; marginal bone; bone level; bone loss

Cite as: Knöfler W, Wostratzky M, Schmenger K: The influence of various implant types on peri-implant bone loss – a retrospective radiological evaluation. Z Zahnärztl Implantol 2016; 32: 114–129

DOI 10.3238/ZZI.2016.0114–0129

Introduction

An adequate amount of local bone ensures firm retention of the implants together with the superstructures they support and contributes to esthetic success by supporting the soft tissue. Particularly during the early stages following implant placement, the crestal bone is subjected to considerable remodeling processes due to restoration of the biologic width [8, 13]. According to the criteria for successful implant outcomes published by Albrektsson und Zarb [1] and modified [2, 30], 1.5 mm bone loss in the first year and 0.2 mm during subsequent years is considered acceptable. However, given the continued development of implant systems, the question arises as to whether these criteria still apply today [3].

In the ongoing discussion about factors impacting the peri-implant bone level [15], the most important influences include those specific to the implant system [9, 22], the surgical procedures and treatments, the types of prosthetic restoration [23], the moment in time at which restoration is carried out, localization of the implant site and patient-specific influences [28]. The specific factors for every implant system include parameters such as implant length and diameter [4, 24], the implant shape, whether the system includes one or two-piece implants and the implant/abutment connector geometry [12]. The roughness of the implant surface, the type of coating and distance between the implant/abutment connection and bone may be of significance [6, 7, 25, 27]. Particularly with two-piece implants, the connection between the implant and the abutment determines the future situation of the peri-implant bone. One-piece implants with bar-borne coverdentures were shown to cause less bone resorption than two-piece systems. Bone loss due to surgical exposure and placement of the superstructure was also observed [19].

Although prospective, controlled, randomized clinical studies produce the best proof of which of these factors influence crestal bone loss most, in dental practices success can only be evaluated with radiographs taken during recall appointments. The objective of the present study was to evaluate the influence of 3 manufacturers’ implants on peri-implant bone loss.

Material and methods

Study population and test method

This retrospective study collected data from patients provided with implants between March 29, 1995 and December 31, 2012. The data were collected from the patients’ records at Dr. Knöfler’s dental practice, Leipzig, Germany.

The patients were informed that their data were to be used for statistical evaluation. No data were collected other than those usually gathered during a check-up. The evaluation included all patients where at least one postoperative and a further check-up radiograph were available. All radiographs of these patients were digitized.

To ensure that they cooperated, all patients included in this study took part in a professional dental hygiene program.

Patients with bone diseases, non-regulated diabetes mellitus or severe, aggressive periodontitis were excluded. Further exclusion criteria were bisphosphonate treatment and smoking more than 20 cigarettes per day.

All implants with peri-implant diseases during the observation period, either with or without augmentation, and all other implants which would have failed for other reasons were excluded from the study, regardless of the cause of implant failure.

The implant types1 used in this study are shown in table 1.

Augmentation procedure

The various augmentation procedures employed during the study period included internal sinus lifting, bone compaction, bone splitting, alveolar ridge spreading, bone onlay grafting and even external sinus lifting.

Two or more radiographs of each patient were then measured as follows. On each digitized image a line (A) was drawn perpendicular to the implant axis (at a tangent to the implant tip). Then the following values were recorded: the distance from the apical implant tip to the implant platform (implant length = Li) and the lengths of the 2 lines parallel to it – one running from line A to the bony ridge and to the mesial of the implant (Lm) and one running from line A to the bony ridge and to the distal of the implant (Ld) (fig. 1).

For each radiograph the mean depth of the bony cavity (Dorg) was calculated with the following formula: Dorg(0, 1, ...n)= (Li(0, 1, 2 ...n) – [(Ld(0, 1, 2...n)+ Lm(0, 1, 2 ...n) )/2]) x Li org)/Li(0, 1, 2...n) represented the known implant length and Li the measured implant length. Use of this formula compensates for distortion of the radiograph images in comparison to reality. The mean depth of the bony cavity calculated from radiographs taken immediately after implant placement was designated Dorg0 and the depths calculated from images of the same patient taken later were designated Dorg1, Dorg2 etc.

Normally, bone loss data was available for several implants per patient. In addition, information on bone loss per implant at different times was available for many patients. Accordingly, the decision was taken to observe these data points separately, i.e. as if each element of information on bone loss taken at every point in time, stemmed from a different patient (“independent examination“). For this type of evaluation a dot was entered on the time diagram for every measurement and a scatter plot created. The progression was indicated by a curve surrounded by a cloud of dots.

As several implants were placed epicrestally, some supracrestally and a few subcrestally, an attempt was made to determine whether the depth of placement [(a) epicrestal, (b) supracrestal or (c) subcrestal)] led to differences in the progression of bone loss (fig. 2). For every implant, the bone loss values taken later were compared with the previous value and these values used for drawing another scatter plot.

Quantitative evaluation

2

The data were evaluated using the SAS 9.2 program (SAS Institute, Cary, North Carolina, U.S.A.). Mean values, standard deviations, median, minimum and maximum were used for variables with uniform distribution. With discretely distributed variables absolute and relative frequencies were specified.

In order to describe bone loss as a function of time (quantile regression, PROC quantile), non-parametric regression procedures were employed. Regression analysis of the implants which failed was not carried out as all implant failures were not included.

This enabled the time-dependent behaviour of the parameters tested to be shown more clearly in comparison to a scatter plot where the regression functions for a series of quantiles (5 %, 10 %, 25 %, 50 %, 75 %, 90 %, 95 %) of the variables undergoing examination were determined and shown as lines. With quantile regression, hypotheses on the basis correlation function were established. A polynomial of the third degree was used for the decade logarithm, with which the time-axis was compacted (compression of long time periods), to achieve uniform distribution along the time-axis.

With a different procedure for visualization only the calculated median value is shown, but with a confidence interval of 95 %. It is unlikely (p < 0.05) that the actual course (which should be mirrored by selection of this study population) will be outside this range.

Results

Records of 569 patients with a total of 1434 implants were evaluated. The patients included 263 men (46.2 %) and 306 women (53.8 %). Of the 1434 implants, at least one additional follow-up radiograph was available for 1261 implants (681 (54.0 %) placed in women and 580 (46.0 %) placed in men). A total of 3613 radiographs of the 1261 implants were available. Beyond the 1261 radiographs taken immediately after placement, an additional 780 (61.9 %) were taken within the first year, 335 (26.6 %) within the second year, 762 (60.4 %) between years 2 and 5, and 379 (30.1 %) between years 5 and 10. A further 96 (7.6 %) radiographs were taken more than 10 years after implant placement, bringing the total to 3613 radiographs.

Implant distribution

The implants were evenly distributed among the 4 jaw quadrants. However, bicuspids and molars predominated (34.7 %, 33.2 %), followed by incisors (22.4 %) and then canines (9.7 %). The distribution of implants according to indication is shown in table 2.

Implant types

The implant types were represented as follows: 506 (40.1 %) were Astra Tech Dental implants, 558 (44.3 %) were Camlog implants and 197 (15.6 %) came from DENTSPLY Friadent (tab. 3). Camlog and DENTSPLY Friadent products were further categorized into subgroups, according to their types of implant/abutment connection. Camlog implants were divided into Morse taper (Conelog) and internal connection (Camlog), whereas DENTSPLY Friadent were divided into internal connection (Frialit/XiVE) and transgingival systems (Frialoc/Xive TG). The distribution of these subgroups is depicted in table 4.

Bone loss – Progression

Depiction of the bone loss measurements in a diagram revealed a relatively large degree of variance. Delimitation using the quantiles showed that in each case, 95 % of the measurements were within the respective corridors. The median bone cavity depth on the immediately post-surgical radiographs was –0.107 mm, while after 17.5 years it was almost 2 mm. Most of the bone loss occurred during the first 2 years. After that, bone loss decreased to almost zero.

Although the distribution of implants in the upper and lower jaw was nearly identical (51.4 % and 48.6 % respectively), the resorption kinetics in the 2 jaws appeared to be different. More rapid bone loss was registered in the upper jaw than in the lower. Taking all implants into account, the majority of bone loss occurred during the first year (fig. 3). When the results of the individual indication classes (tab. 2) are transferred to a diagram, it is apparent that implants replacing lost support teeth to ensure continued functioning of the prosthesis (IBrep) and those placed in edentulous lower jaws (ELJ) caused less bone resorption than those placed for single crowns, bridges and in edentulous uppers.

Implant length and diameter

The implant length also appeared to have a noticeable influence on bone loss, with shorter implants exhibiting fewer signs of bone resorption than longer ones (fig. 4). This difference was significant (p < 0.05) for implants ? 9 mm. No significant differences were observed for implants > 9 mm. The diameter of the implants appeared to have a similar effect. The more slender the implants were, the smaller the bone cavity (fig. 5). A significant difference was also established when comparing the implants with a diameter ? 3.5 mm to all others, and this also applied to implants with a diameter exceeding 5.0 mm (p < 0.05). No significant differences were established when comparing implants with diameters ranging between 3.5 mm and 4.1 mm to those between 4.1 mm and 5.0 mm.

The influence of implant types

The results of this study revealed different bone loss situations for specific implant types. After 4 years, Camlog implants exhibited 2 mm mean bone loss, while DENTSPLY Friadent products did not reach this value, even after 10 years (fig. 6, 7). The Astra Tech Dental implants exhibited virtually no bone cavities (fig. 8). After 10 years, values were still below 0.5 mm.

Comparison between Camlog implants and the Conelog version highlighted a serious difference. Morse taper Conelog implants led to significantly (p < 0.05) fewer signs of bone loss than the tube-in-tube connected Camlog implants, even if the observation period is short (fig. 9).

A comparison of two-piece DENTSPLY Friadent products and one-piece Frialoc/Xive-TG implants showed that the latter exhibited significantly fewer signs of bone loss (p < 0.05) (fig. 10). However, the one-piece Frialoc/Xive-TG implants were placed exclusively in edentulous lowers, in accordance with the Ledermann principle [18]. Comparison of the results for the specific implant types in the upper and lower jaw revealed a similar pattern. However, the bone loss values for the lower jaw were noticeably lower than for the upper.

Augmentation procedures

A similar picture emerged when the implant type was examined for the effectiveness of augmentation. Although augmentation around Astra Tech Dental implants did lead to increased bone loss, it was only half as much as occurred around the Camlog and DENTSPLY Friadent products (fig. 11). Without augmentation, almost no loss was detected around Astra Tech implants. Significantly more bone loss was discovered around DENTSPLY Friadent implants, and even more around Camlog implants.

Discussion

Although follow-up studies covering up to 11 years are available for various implant systems, data for follow-ups of more than 11 years are rare [26]. The data presented in this article represent a large cross section of patients treated in one practice over a period of almost 18 years.

When looking at the bone loss irrespective of subgroups, mean bone loss of 1.2 mm was noted within the first year, 1.3 mm after 2 years, and 1.8 mm at the end of the observation period.

Taking into account the methodological limitations of the radiological measurements [14], these values exceed one of the generally accepted success criteria for butt joint implants, namely, bone loss not exceeding 1.5 mm in the first year and no more than 0.2 mm in subsequent years [1].

Most studies addressing the success rates of upper compared to lower implants have shown higher success rates in the lower jaw [26]. Along with bone quality, bone volume and different methods of preparation appear to influence implant success. Very few studies have indicated comparable bone loss in both the upper and lower jaws [11]. Loss rates in the present study were significantly higher in the upper jaw than in the lower jaw, irrespective of the factors examined.

The implant/abutment connector geometry appears to influence the development of marginal bone. Conical implant connections have been shown to be superior to flat ones due to their intrinsic platform switching [16]. The differences have partly been attributed to conical systems entrapping bacteria in the implant lumen and thus preventing inflammation. Another explanation for the reduced bone loss due to conical connections is that they are subjected to fewer micromovements. According to this explanation, reduced bone loss could be due to reduced load transmission and hence fewer irritations under loading in the implant area [20, 29]. In transgingival implant systems, the highest rates of remodeling occur 4 weeks after implant placement, while in two-piece systems, these rates occur 4 weeks after abutment placement.

Regardless of whether they were placed in the upper or lower jaw, the conical implant systems (ASTRA Tech implants, Conelog implants) examined in the present study showed significantly less bone loss than the butt joint systems (Camlog, Frialit/XiVE) and/or one-piece systems (Frialoc/XiVE TG). Whether these observations can be attributed to one of the explanations just discussed cannot be answered conclusively from the parameters examined here. However, as conical and one-piece connections achieve better results than butt joint connections, regardless of jaw; this suggests that the conical connection significantly influences peri-implant bone levels. These results correspond to those of Krebs et al. [17].

The impact of prosthetic restoration is another interesting factor because a distinction is usually made between bone loss at early and later stages once the implants have been loaded prosthetically [5]. In the present study, bone loss was lowest with implants placed for single crowns, ensuring that existing superstructures continue to function, increasing the number of existing abutments or restoring edentulous lower jaws, while it was significantly higher for those used for supporting bridges or restoring edentulous uppers.

To examine the role of implant length, another recent review compared short (< 10 mm long) implants placed for supporting fixed restorations with standard length implants (? 10 mm) [24]. The data of the 5 studies included in this review were subjected to a meta-analysis to assess the impact of the independent variable of implant length on median marginal bone loss. No significant differences in terms of marginal bone loss were found between the 2 subgroups. However, the authors pointed out that most of the studies did not include long-term data and were very heterogeneous. This may explain the significantly better performance of short (? 9 mm long) implants in the present study. Moreover, 119 of the 168 implants which were < 9 mm long in the present study were Astra or Conelog implants that experienced hardly any bone loss. Additionally the review article revealed a significant dependence of bone loss on implant-abutment connections, with internal connections judged to be superior to external connections.

A review by Renouard et al. [21] categorized implants with a diameter of ? 4.5 mm as “thick” implants. The authors were able to establish a trend of higher bone loss rates for them. A finite element analysis showed a significantly greater effect on the reduction of force on the crestal bone when the implant diameter was increased than when different implant lengths were used [4]. Regardless of the implant system used, our data showed smaller diameters (? 3.5 mm) to be superior to larger diameters. However, only 41 of the 202 implants with smaller diameters were Camlog implants. The others were one-piece or Astra Tech implants, thus favoring this size.

A study by Galindo-Moreno et al. [10] observed a significantly higher level of bone loss after 12 months for augmented bone than for non-augmented bone. During the observation period, implants placed in augmented bone sites incurred more bone loss on the whole than other implants. However, the type of augmentation was also important. Implants placed in augmentation sites with little or no increase in volume (sinus lifting, bone compaction and splitting, alveolar ridge spreading) incurred little bone loss, whereas those placed in conjunction with bone apposition or classical sinus lifting led to more bone loss. In the present study, the bone loss appeared to be determined by the connector geometry rather than the type of augmentation.

The clinical conclusions derived from results of the present study suggest that Morse taper implant/abutment connections led to significantly less bone loss around implants than butt joints. Other factors such as implant length and diameter as well as augmentation procedures may influence marginal bone loss in addition.

Conclusion

Irrespective of the type of load, restoration, augmentation, or location, measurement of successive radiographs of Astra Tech implants placed during almost 18 years in a dental practice showed the least amount of peri-implant bone loss, followed by DENTSPLY Friadent and Camlog implants. The implant/abutment connector geometry was shown to significantly influence the progression of bone loss symptoms.

Acknowledgements: Manuscript preparation and review was in part supported by DENTSPLY IH GmbH (Mannheim/Germany).

Conflict of interest: The author Wolfram Knöfler declares the following possible conflicts of interest as defined by the ICMJE: He specified that he received fees for running courses for Camlog, Astra Tech and Dentsply Friadent, expenses for the statistical computations from Dentsply Friadent/Dentsply Implants, traveling expenses from all engaged Companies.

Footnote

1 Dental practice on oral and maxillofacial surgery, implantology and aesthetic dentistry, Leipzig

2 Dental practice Dr. Eva Wostratzky & Dr. Stefan Wostratzky, Leipzig

3 Dentsply Implants, MannheimÜbersetzung: LinguaDent

1 Those makes were used which were commercially available until completion of data collection in April 2012.

2 The statistical calculations were carried out by ACOMED-Statistik, Leipzig, Germany.

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