1. Introduction
Osseointegration of implants and alveolar bone is essential for implants to withstand masticatory pressure and function [
1,
2,
3]. Osseointegration of implants is defined as close contact, with no intervening soft tissue, between the titanium surface of the implant and the alveolar bone [
2]. Osseointegration classically occurs after 3 to 6 months with machined or turned titanium implant surfaces, but it may occur more rapidly with enhanced surfaces [
3]. Furthermore, variables affecting implant osseointegration include the volume and density of the alveolar bone, the type of implant surface, patient age, and whether bone grafts were carried out [
3,
4].
Recently, due to developments in implant surfaces, a procedure that allows application of a functional load faster than the traditional osseointegration period has been introduced in many studies. In South Korea, where an aging society is progressing and implant treatment is available through insurance for patients over 65 years of age, implant placement is frequently performed, even in elderly patients over the age of 80 years. Since the differentiation rate of osteoblasts decreases with increasing age, older patients should be given a longer period for osseointegration [
1,
2,
3,
4]. In addition, clinical data on the implant osseointegration period according to the volume and density of the alveolar bone, and whether bone is transplanted, are also needed. It is of utmost importance to quantify implant stability at various time points and to determine establish the timing of loading [
3,
4].
Therefore, the measurement of implant stability is even more necessary now, and two types of widely used non-invasive diagnostic methods have been developed and examined: resonance frequency analysis (RFA) and damping capacity analysis (DCA) [
5]. In RFA, a method used by the Osstell ISQ Mentor (Osstell, Göteborg, Sweden), the stiffness of the implant-bone interface is outputted from the resonance frequency that is the response to oscillations applied to the implant-bone system [
6]. One DCA system device, Periotest M (Siemens AG, Bensheim, Germany) has been utilized to assess the mobility of natural teeth and is maintained to have the potential to reliably evaluate the stability of the implant-bone interface [
7,
8]. Recently, the new DCA system device, Anycheck (Neobiotech, Seoul, Korea) has been released; it is a measuring device that uses percussion, and has improved accuracy and reduced patient discomfort by reducing the intensity of the percussion [
9]. This system evaluates the duration of contact between a impacting rod and a healing abutment. It strikes the healing abutment 6 times over 2 seconds and converts the duration into implant stability test (IST) values [
9]. This system strikes a healing abutment by less force than Periotest M does and has the function that allows it to stop automatically that stability is low to protect the implant [
9]. However, little is known about the factors affecting the IST values or the reliability of the device.
Multiple previous studies have reported on the correlation between RFA and DCA device results indicating the stability of the same implant. An
in vitro study presented the strong correlation between the results from RFA and DCA devices [
9,
10,
11]. However,
in vivo studies presented the relatively lower correlation between the results from RFA and DCA devices [
12,
13]. The different results under experimental and clinical conditions suggest that there are clinical factors which affect the reliability of implant stability measuring devices. In the experimental condition implant stability can be examined without any obstacles and the device can be positioned in relation to the implant in an ideal way. Clinically, examination of the stability of the implant in the oral cavity may have access difficulties due to the cheek, tongue, and contralateral teeth. These obstacles may unfavorably influence the factors needed for accurate measurement of implant stability, including exact contact between implant and device, the angle of the device to the implant, and the angle of the device against gravity. In addition, in the clinical condition, the accessibility and angle of the device is influenced by the location of the implant in the oral cavity (anterior/ posterior, left/ right, and mandible/ maxilla).
Therefore, reliable implant stability measurement is required to evaluate the degree of osseointegration according to the implant placement site. However, there are few prospective clinical studies evaluating implant stability, and measuring device reliability, according to the implant placement site and post-implantation duration in older patients. Therefore, the aim of this in vivo study was to evaluate implant stability, and the reliability of different measuring devices, according to the implant placement site in the oral cavity and the duration of implantation in patients over 65 years. Additionally, one RFA device (Osstell), and two DCA devices (Periotest and Anycheck) were used to examine implants located in the maxillary right posterior, maxillary anterior, maxillary left posterior, mandibular right posterior, mandibular anterior, and mandibular left posterior positions.
The null hypotheses were that 1) the implant placement site and duration of implantation in the oral cavity does not affect implant stability and measuring device reliability in patients over 65 years, and 2) a correlation of 1 is shown by the three measuring devices.
3. Results
Implant stability measurement was performed using various devices. Mean values and standard deviations of ISQ, PTV, and IST among the groups, according to post-implantation duration, are shown in
Figure 3. For all the ISQ, PTV, and IST results, the implant stability results at the 2-month follow-up and before the final restoration delivery were significantly higher than those at the time of implant surgery. The significant differences in ISQ, PTV, and IST among the groups, according to post-implantation duration, are shown in
Supplementary Table 1. Paired sample t-tests were performed to ascertain whether there were differences according to post-implantation duration (
Supplementary Table 1). For the ISQ, there were statistically significant differences between the second and fifth visits, second and sixth visits, and fifth and sixth visits (
P<.05). For the PTV, there were statistically significant differences between the second and fifth visits, second and sixth visits, and the fifth and sixth visits (
P<.05). For the IST, there were significant differences at all points except those between the second and third visits, second and fourth visits, third and fourth visits, and fourth and fifth visits (
P<.05).
Figure 3.
Analysis of implant stability measurements made with different devices according to the duration. A) ISQ, B) PTV, and C) IST. ISQ, implant stability quotient; PTV, Periotest value; IST, implant stability tester value. 1V, first visit; 2V, second visit; 3V, third visit; 4V, fourth visit; 5V, fifth visit; 6V, sixth visit; 7V, seventh visit.
Figure 3.
Analysis of implant stability measurements made with different devices according to the duration. A) ISQ, B) PTV, and C) IST. ISQ, implant stability quotient; PTV, Periotest value; IST, implant stability tester value. 1V, first visit; 2V, second visit; 3V, third visit; 4V, fourth visit; 5V, fifth visit; 6V, sixth visit; 7V, seventh visit.
Mean values and standard deviations of implant stability measurements made with different devices according to dental implant placement site and duration are shown in
Figure 4. For the ISQ, there were statistically significant differences according to the post-implantation duration for each location of the inserted implants between the second and fifth visits, second and sixth visits, and sixth visits and the fifth visit (
Supplementary Table 2).
Figure 4.
Analysis of implant stability measurements made with different devices according to dental implant placement site and duration. A) ISQ, B) PTV, and C) IST. ISQ, implant stability quotient; PTV, Periotest value; IST, implant stability tester value. A, maxillary right posterior; B, maxillary anterior; C, Maxillary left posterior; D, mandibular right posterior; E, mandibular anterior; F, mandibular left posterior. 1V, first visit; 2V, second visit; 3V, third visit; 4V, fourth visit; 5V, fifth visit; 6V, sixth visit; 7V, seventh visit.
Figure 4.
Analysis of implant stability measurements made with different devices according to dental implant placement site and duration. A) ISQ, B) PTV, and C) IST. ISQ, implant stability quotient; PTV, Periotest value; IST, implant stability tester value. A, maxillary right posterior; B, maxillary anterior; C, Maxillary left posterior; D, mandibular right posterior; E, mandibular anterior; F, mandibular left posterior. 1V, first visit; 2V, second visit; 3V, third visit; 4V, fourth visit; 5V, fifth visit; 6V, sixth visit; 7V, seventh visit.
The result of Pearson’s correlation between the mean ISQ, mean PTV, and mean IST results are presented in
Table 5. Correlation coefficients (r) are evaluated as: very strong (0.80 ≤ r ≤ 1.00), strong (0.60 ≤ r ≤ 0.79), moderate (0.40 ≤ r ≤ 0.59), weak (0.20 ≤ r ≤ 0.39), very weak (0.00 < r ≤ 0.19), and no correlation (r = 0) for both positive and negative values [
16,
17]. At the second visit, the r between the ISQ and PTV result was -0.208, verifying the weak negative correlation (
P=.049). The r between the ISQ and IST result was 0.567, verifying the moderate positive correlation (
P<.001). Additionally, the r between the PTV and IST result was -0.490, verifying the moderate negative correlation (
P<.001). At the fifth visit, the r between the ISQ and PTV result was -0.298, verifying the weak negative correlation (
P=.001). The r between the ISQ and IST result was 0.367, verifying the weak positive correlation (
P=.003). Additionally, the r between the PTV and IST result was -0.701, verifying the strong negative correlation (
P<.001). At the sixth visit, the r between the ISQ and PTV result was -0.252, verifying the weak negative correlation (
P=.005). The r between the ISQ and IST result was 0.503, verifying the moderate positive correlation (
P<.001). Additionally, the r between the PTV and IST result was -0.479, demonstrating the moderate negative correlation (
P<.001). The result of Pearson’s correlation between the sixth visit and seventh visit IST values are shown in
Figure 5. The r between the values measured in the healing abutment states and the values measured in the prosthesis delivered states was 0.414, demonstrating a moderate positive correlation (
P <.001).
Table 5.
Results of Pearson’s correlation between the mean ISQ, PTV, and IST values.
Table 5.
Results of Pearson’s correlation between the mean ISQ, PTV, and IST values.
Value |
2V |
5V |
6V |
|
Correlation coefficient |
Size of Correlation |
P-value |
Correlation coefficient |
Size of Correlation |
P-value |
Correlation coefficient |
Size of Correlation |
P-value |
ISQ-PTV |
-.208 |
weak |
.049* |
-.298 |
weak |
.001* |
-.252 |
weak |
.005* |
ISQ-IST |
.567 |
moderate |
<.001* |
.367 |
weak |
.003* |
.503 |
moderate |
<.001* |
PTV-IST |
-.490 |
moderate |
<.001* |
-.701 |
strong |
<.001* |
-.479 |
moderate |
<.001* |
Figure 5.
The results of Pearson’s correlation between the mean sixth and seventh visit values of IST.
Figure 5.
The results of Pearson’s correlation between the mean sixth and seventh visit values of IST.
The results of all groups for the implant stability values between the locations of implants and the positions of arch in Osstell ISQ Mentor, Periotest M and Anycheck are showed in
Supplementary Table 3. The ISQ results showed statistically significant differences at the fifth (
P=.016) and sixth visits (
P=.042). In the PTV results, there were no significant differences in the correlations between the locations of the implants at all the visits (
P>.05). In the IST results, there was a statistically significant difference only at the sixth visit (
P=.044) in the correlations between the locations of implants.
The results of all groups for IST results between different locations and implant materials in Anycheck are presented in
Supplementary Table 4. There was no significant difference in the correlations between the values measured in the healing abutment states and the values measured in the prosthesis delivered states (
P>.05).
4. Discussion
In the present study, the accuracy of implant stability measurement devices were evaluated under clinical conditions affecting the reliability of the devices. In addition to the results from the devices, the valid impacts and the angle formed by the handpiece with the horizontal plane were measured to analyze the reasons for inaccurate results. The results showed that the implant placement site and the post-implantation duration in the oral cavity affected implant stability and the reliability of the measuring devices in patients over 65 years of age.
Devices for evaluating implant stability are either RFA or DCA and each device has distinct characteristics depending on their operating principles. A DCA device is convenient for measurement without an additional process if a healing abutment is installed; more factors during measuring should be controlled to derive accurate results compared to RFA devices [
18]. According to previous studies, the PTV is influenced by the length of the fixture and the healing abutment, the position and direction of percussion, and the angle of the handpiece [
19,
20].
Between the DCA devices, Periotest M was significantly affected by the position of artificial bone model impact error, while Anycheck showed consistently low impact error in this study. The results showed that Anycheck was able to provide a relatively stable measurement under unfavorable access conditions. Anycheck measured while in contact with the implant, the device does not move minutely during measurement, and it is possible to measure stably at the desired position. However, Periotest M is unstable because it is measured at a certain distance from the implant. Faulkner
et al. reported that Periotest M was very sensitive to the angulation of the handpiece and to the position at that the Periotest M impacted the abutment [
21]. A small change in the angle of the handpiece from 90 degrees to the abutment may cause a PTV difference between 2.5 and 4.0 as the rod hits an inconsistent point of abutment [
22,
23]. In addition, the variation in PTV was approximately 1.5 or 1 to 2 PTV depending on the height of the striking point per millimeter [
21,
22].
Some studies have investigated conflicting results for both RFA and DCA systems. Lee
et al. investigated the strong correlation (0.981) between the ISQ and IST in an
in vitro study [
9], while a systematic review showed a weak correlation (-0.294) between the ISQ and PTV [
11]. Additionally, the correlating ISQ and PTV readings of the buccal surface during implant installation were moderately negatively statistically significantly correlated (-0.466) between the two types of device for all 80 patients in the randomized clinical trial by Andreotti
et al [
10]. In this study, there were weak negative statistically significant correlations: -0.208 at 2V, -0.298 at 5V, and -0.252 at 6V, between ISQ and PTV. There were moderate positive statistically significant correlations: 0.567 at 2V, 0.367 at 5V, and 0.503 at 6V, between ISQ and IST. The results of this study are similar to the reported correlations in previous studies [
10,
11]. A factor that can affect the results is when using the DCA device clinically, the examiner is limited by patient cooperation, space, and access, unlike the laboratory study, that standardized models for measurement permit certain conditions. Thus,
in vivo analyses have additional sources of error, that could result in reduced accuracy of measurement. The results presented the weak or moderate statistically significant correlation between the three measuring devices.
Several studies have presented the strong correlation between ISQ and PTV, while others have presented no correlation [
24,
25,
26,
27]. Because of the discrepancies, standardized implant stability values have not yet been proved and analyses have been performed by other analytic methods, such as the measurement of insertion torque and radiographic and clinical examinations. There were moderate to high negative statistically significant correlations: -0.490 at 2V, -0.701 at 5V, and -0.479 at 6V, between PTV and IST. There was a moderate positive statistically significant correlation coefficient of 0.414 between the 6V and 7V, in IST (
P<.001).
Some studies have investigated that both the Osstell ISQ and Periotest devices could reliably evaluate the stability of implant [
6,
25,
28]. Lachmann
et al. maintained that both the Osstell ISQ and Periotest presented acceptable reliability in expecting the implant stability in an
in vitro study [
6]. Also Pang
et al. reported the strong correlation between the ISQ and PTV post-surgery and 2 months later [
25]. An animal study showed the strong correlation between ISQ and PTV [
27]. Additionally, some studies demonstrated that although both the Osstell ISQ and Periotest devices were useful for analyzing the stability of implant, the Osstell ISQ was more accurate than the Periotest systems, presenting high reliability [
29,
30]. However, some studies have found conflicting results for both the Osstell ISQ and Periotest systems [
10,
27]. Considering the controversy, both the Osstell ISQ and Periotest were evaluated with the Anycheck in this study [
27].
There are well known inconveniences and limitations of the Osstell ISQ and Periotest systems. The Osstell ISQ is the non-invasive system that could evaluate implant stability, based on the structural analysis principle [
31]. This system could be fairly reliable when the bone-implant interface is rigid and the implants have achieved osseointegration. However, when the implant-bone interface is doubtful or is not rigid, the ISQ results tend to change [
32,
33]. Additionally, use of the Osstell ISQ is needed removal of the upper fixture component, and the smart-peg connection, when evaluating implant stability and this could cause limitations and inconvenience. Long-term study on Periotest have presented that it could objectively measure implant stability.
34,35 However, some studies have reported that the devices lack sensitivity [
36,
37]. This is because the Periotest, schemed for natural dentition, evaluates the wide dynamic range. However, the range used for evaluating implant stability is limited [
26]. Other studies have showed that the even narrower range of -4 to -2 or -4 to +2 is required for clinically osseointegrated implants [
38,
39]. Moreover, PTV was unable to identify implants with borderline stability or those in the process of osseointegration [
40]. PTVs have also been criticized for vulnerability to operator variables and lack of resolution [
41,
42]. The IST results were consistent with ISQ results. Additionally, the IST results range from 1 to 99. Usage of the Anycheck does not need unscrewing of the healing abutment and the procedure is therefore easier than that of the Osstell ISQ.
This clinical study investigated the reliability of each device by comparing RFA and DCA devices with different measurement principles. The results presented the effect of the implant placement site and the post-implantation duration in elderly patients on the reliability of each measuring device. In addition, an attempt was made to accurately obtain the angle the handpiece would make with the ground and the number of effective strokes when measuring stability with Anycheck.
However, the limitation of this in vivo study was that the reliability of Anycheck was based on the correlations with the other systems and the agreement rate of each device was not evaluated in this study. Additionally, the design of the study could not compare the systems with the implant osseointegration and further large-scale in vivo studies are needed for clinical use. Additional studies are also needed to ascertain the reliability of the Anycheck system through analysis of the patient’s face shape, mouth size, and 3D structure of the oral cavity. In addition, the factors that may affect the measured values, such as soft tissue, bone quality, bone density, patient opening, and saliva, cannot be excluded during clinical use. Therefore, further in vivo studies are required to estimate the accuracy and accessibility of the devices in clinical use.