The relationship between implant stability quotient values and implant insertion variables: a clinical study

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1 J o u r n a l o f Oral Rehabilitation Journal of Oral Rehabilitation ; The relationship between implant stability quotient values and implant insertion variables: a clinical study K.-J. PARK*, J.-Y. KWON*, S.-K. KIM*, S.-J. HEO*, J.-Y. KOAK*, J.-H. LEE, S.-J. LEE, T.-H. KIM &M.-J.KIM* *Department of Prosthodontics and Dental Research Institute, Seoul National University Dental Hospital, School of Dentistry, Seoul National University, Seoul, Department of Mathematical Sciences, College of Natural Sciences, Seoul National University, Seoul, Department of Prosthodontics, Asan Medical Center, College of Medicine, University of Ulsan, Ulsan, Department of Orthodontics, School of Dentistry, Seoul National University, Seoul, Korea and Division of Restorative Science, Removable Section, Herman Ostrow School of Dentistry, University of Southern California, Los Angeles, CA, USA SUMMARY The aim of this study was to determine whether resonance frequency analysis can be integrated into the routine clinical evaluation of the initial healing of dental implants. In addition, this study was designed to verify whether there was a correlation between implant stability quotient (ISQ) values, maximum insertion torque values, angular momentum and energy, and to evaluate the importance of different clinical factors in the determination of ISQ values and maximum insertion torque values at implant insertion. Two different implant designs of 81 dental implants in 41 patients were evaluated using ISQ values. Maximum insertion torque values were obtained during the placement procedure. Two new methods were used to calculate the angular momentum developed due to implant installation as well as the energy absorbed by the bone. A linear correlation between ISQ values and maximum insertion torque values at the initial implant surgery was found (P <0Æ01). There was a correlation between ISQ values and angular momentum (P <0Æ05), although ISQ values and energy did not show a significant linear correlation at the initial surgery (P > 0Æ05). There was a correlation between maximum insertion torque values, each part s angular momentum, and their energies during installation (P <0Æ01). The sequence of the variables that influenced ISQ values was implant location, design, diameter, and gender of the patient. The results of this experiment suggest that both ISQ values and new methods to calculate angular momentum and energy can help to predict implant stability. KEYWORDS: implant, insertion torque, implant stability quotient, angular momentum, energy Accepted for publication 26 July 2011 Introduction The achievement and maintenance of implant stability are prerequisites for long-term positive outcomes of osseointegrated implants. Implant stability is the key to clinical success (1). Therefore, the application of simple, clinically applicable non-invasive tests to assess implant stability and osseointegration is considered highly desirable. So far, many tests have been suggested through methods of percussion, radiography, resonance frequency analysis, placement resistance, reverse torque and vibration in the sonic and ultrasonic ranges (2, 3). Recently, a clinical instrument was developed to analyse resonance frequency. With the introduction of resonance frequency analysis, it is now possible to measure the degree of implant stability at any time during implant treatment and loading (4). It is also possible to identify the risk of implants failure before they become loose (5). The clinical instrument that was developed to analyse resonance frequency utilises a new unit of measurement called the implant stability quotient (ISQ) which represents bone-implant contact (6 9). The ISQ unit replaces hertz, which are dependent on doi: /j x

2 152 K.-J. PARK et al. the transducer used, and is recorded as a number between 1 and 100, with 100 representing the highest degree of stability (9). ISQ levels for successfully integrated implants are reported to range from 57 to 82 (10); however, there is continued controversy about ISQ values. Friberg et al. (6) reported that the highest correlation was found when comparing the mean torque values of the upper crestal portion with the resonance frequency values at implant placement. On the other hand, Cunha et al. (11) reported that there was no correlation between ISQ values and insertion torque. Therefore, new concepts to assess implant stability were used in this study. New methods to calculate angular momentum and energy during implant installation were developed (12, 13). Angular momentum represents the load on the implant during insertion, while energy represents the energy absorbed by bone during the initial implant surgery. This concept of energy may be helpful for analysing the insertion process in real time. The aim of this study was to determine whether resonance frequency analysis can be integrated into the routine clinical evaluation of the initial healing of dental implants. In addition, this study was designed to verify whether there was a correlation among ISQ value, maximum insertion torque value, angular momentum, and energy and to evaluate the importance of various clinical factors in the determination of ISQ values and maximum insertion torque values at implant insertion. Materials and methods Patients Forty-one patients (16 females and 25 males; mean age of 52Æ7 age) who visited the Prosthodontic Department and Periodontic Department at Seoul National University Dental Hospital in Seoul, Korea and scheduled implant placement surgery were included in this study. All were accurately informed about the procedures and signed an informed consent form. The study was approved by the Ethics Committee of the Seoul National University Dental Hospital (Seoul, Korea, CRI06010). At the screening appointment, the subject s medical and dental histories were reviewed, and inclusion exclusion criteria were confirmed. Table 1. The variables used in this study Variable Implants (n = 81) Gender Female 27 Male 54 Jaw location Maxilla 36 Mandible 45 Spatial location Anterior 11 Posterior 70 Implant design External 59 Internal 22 Implant length (mm) 11Æ5 34 >11Æ5 47 Implant diameter (mm) 4 40 >4 41 Implants A total of 81 dental implants and two different (external or internal type) implant designs were evaluated by using ISQ values. In this study, the external types were Brånemark implants * and the internal types were ITI implants. For each implant, the gender of the patient, implant location, anterior posterior location, design, length and diameter were recorded (Table 1). Measurement of insertion torque The implants were placed using an ELCOMED instrument with a calibrated torque of 50 N cm at a determined rpm. Upon implant placement, data was recorded onto a smartcard of the ELCOMED instrument. Insertion torque was measured by the motor during implant insertion and was recorded in N cm (Fig. 1). The process was performed internally in the ELCOMED unit. The maximum insertion torque value is the peak insertion torque reached in the final stage of implant placement into the prepared site. Whether to apply bone drill and pre-tapping drill was judged subjectively. *NobelBiocare, Göteborg, Sweden. Straumann, Waldenburg, Switzerland. W&H Dentalwerk, Bürmoos Gmbh, Austria.

3 ISQ VALUES AND INSERTION VARIABLES 153 Torque (Ncm) Insertion Torque Region 35: ITI Dental Implant System 8 Hz, Speed: 30 rpm, Maximum torque: 50-0 N cm Time (s) Fig. 1. An example of an insertion torque graph obtained from this study. Measurement of ISQ values This study was designed to measure implant stability using a resonance frequency analyzer (RFA) at the time of implant placement. All measurements were performed by a single dentist. The RFA device was placed by hand tightening onto the implant fixture with a torque of 5 10 N cm. The ISQ values were twice measured parallel and perpendicular to the alveolar ridge of the jaw, and a high level of repeatability was achieved. The ISQ value for each time point was the mean of the ISQ values taken in the two orientations. Table 2. Measurement values and definitions used in this study Measurement value Unit Definition Maximum insertion torque N cm The maximum torque value during the implant insertion procedure Angular momentum N cm s Load developed on the implant during the initial insertion based on the maximum insertion torque values. The angular momentum values were assessed by plotting the insertion torque graph into the program Total insertion energy J Energy absorbed by the bone at the maximum torque value during implant insertion Torque(N cm) Calculation of angular momentum and energy developed with implant installation Techniques to calculate the energy and angular momentum developed with implant installation had previously been developed (12, 13). They were established in the Java program with special permission from the Industrial Property Office of South Korea. First, the insertion torque data from the smartcard of the ELCOMED device was input into the program. The program then automatically calculated the angular momentum and energy used during the initial surgery. The definitions of measurements are described in Table 2. If a system consisted of several particles, the total angular momentum about an origin could be obtained by adding (or integrating) all of the angular momentum values of the constituent particles (Fig. 2). Osstell Mentor; Integration Diagnostics AB., Götenborg, Sweden. Smartpeg; Integration Diagnostics AB., Gemlestadsvägen, Sweden. Fig. 2. The angular momentum and mean torque. Time(s) The angular momentum (load on the implant) values were assessed by plotting an insertion torque graph into the first program. The total angular momentum and angular momentum of the crestal, middle and apical thirds of the implant during implant installation were measured. According to the work-kinetic energy theorem and the first law of thermodynamics, work applied to an isolated system is defined as the energy variation in the system. Thus, energy variation can be calculated by

4 154 K.-J. PARK et al. determining the amount of work applied to a system. The energy required to insert an implant was determined by plotting the insertion torque values against the angular displacement values of the implant in radians (14). The energy values were determined by plotting the insertion torque graph into the second program. The total energy and the energy of each implant section were calculated. Theoretical basis of the energy index In physics, work is calculated by measuring the displacement in the direction of the force: W ¼ ~F ~S; where W is work, ~F is the force vector, and ~S is the displacement vector. A small portion of work which occurs within a brief instance can be measured using the following formula: dw ¼ ~F d~s; where dw is work, ~F is the force vector, and ~ ds is the small displacement vector. Thus, power (P) can be calculated using the following formula: p ¼ dw dt ¼ ~F d ~S dt ¼ ~F ~v: In rotational motion, the small displacement vector between time t and time t +lt is as follows: D~r ¼ ~rðt þ DtÞ ~rðtþ Dh ^x ~rðtþ; Where ^x is a unit vector for the angular velocity vector, lh is the small angular change and ~rðtþis the displacement vector during time t. In rotational motion, the velocity vector is as follows: ~v ¼ d ~r dt ¼ lim D~r ¼ ~x ~r; Dt!0 Dt where ~x is the angular velocity vector. Thus, in rotational motion, power can be calculated using the following formula: p ¼ dw ¼ ~F ~v ¼ ~F ð~x ~rþ: dt The above formula can be changed to use a vector identity as follows: p ¼ ~F ð~x ~rþ ¼ ~F ð~r ~xþ : ¼ ð~f ~rþ~x ¼ð~r ~FÞ~x In rotational motion, torque is defined as ~s ¼ ~r ~F; where ~s is the torque vector, ~r is the displacement vector and ~F is the force vector. Using the torque vector in rotational motion, power P can be expressed as Z p ¼ ~s ~x: In rotational motion, applied work W can be calculated using the following formula: Z W ¼ p dt Z : ¼ ~s ~x dt In the process of implanting the final implant fixture, the angular velocity is steadily maintained. In that case, the above formula can be changed to Z W ¼ ~x ~s dt: Most of the implants presented torque-time values. For instance, the ELCOMED device presented the data and programs shown in Fig. 1. Energy, generated in the process of implanting the implant fixture, can be calculated in the case of applying the above-changed formula to such data in accordance with a simple program. Statistical analysis The influence of each parameter on the ISQ value was analysed using Pearson s correlation (quantitative variables). A stepwise multiple regression test was performed to determine the magnitude sequence of the variables that influenced the ISQ value and the maximum insertion torque values. One-way ANOVA was performed to determine the most critical part of the implant, that which requires greater insertion energy than those of the other parts. Kaplan Meier survival analysis was carried out to find survival rate.

5 ISQ VALUES AND INSERTION VARIABLES 155 Results Variables correlated with ISQ value High ISQ values were achieved in most of the jaw regions. Of the 81 implants, 53 implants (75Æ7%) showed an ISQ value of 65 or higher and 61 implants (91Æ4%) showed an ISQ value of 60 or higher. Table 3 shows a correlation between the ISQ value and the maximum insertion torque value at the initial implant surgery (P < 0Æ01, r = 0Æ427). Table 3 also shows a correlation between the ISQ value and the total angular momentum (P < 0Æ05, r = 0Æ257). Variables correlated with ISQ value and maximum insertion torque value Table 4 shows that the maximum insertion torque value had a linear correlation with the energy and Table 3. Correlation of the variables with the ISQ value Mean value vs. ISQ (Pearson s correlation coefficient) ISQ 71Æ29 Maximum insertion 31Æ17 0Æ427 ** torque (N cm) Total energy (J) 4Æ62 0Æ216 Total angular 166Æ40 0Æ257 * momentum (N cm s) Mean torque (N cm) 9Æ51 0Æ202 **P <0Æ01, *P <0Æ05. Table 4. The variables correlated with the ISQ value and the maximum insertion torque value Mean value vs. Maximum insertion torque value (Pearson s correlation coefficient) vs. ISQ value Angular momentum to the 20Æ60 0Æ328 ** 0Æ121 apical third (N cm s) Angular momentum to the 51Æ51 0Æ511 ** 0Æ188 middle third (N cm s) Angular momentum to the 90Æ28 0Æ699 ** 0Æ277 * coronal third (N cm s) Energy to the apical third (J) 0Æ60 0Æ356 ** )0Æ005 Energy to the middle third (J) 1Æ44 0Æ513 ** 0Æ147 Energy to the coronal third (J) 2Æ59 0Æ780 ** 0Æ272 * **P <0Æ01, *P <0Æ05. Table 5. Energy values acquired with implant insertion depth Area Total Apical third Middle third Coronal third angular momentum of each part of the implant. The most critical part of the implant was the coronal third (Table 5). Variables influencing ISQ value and maximum insertion torque Table 6 shows the sequence of variables that influence the values of ISQ and maximum insertion torque. This sequence was implant location (maxilla or mandible), design (external or internal type), diameter, and gender of the patient. Implants in the mandible showed higher ISQ values than did those in the maxilla (P <0Æ01), and ISQ values were higher for the external type of implants compared to those of the internal type (P < 0Æ01). As the implant diameter increased, the ISQ value also increased (P < 0Æ01). The sequence of variables that influenced the maximum insertion torque value was implant location, design, and gender location. Implants in the mandible showed higher maximum insertion torque values than did those in the maxilla (P <0Æ01), while male patients exhibited higher maximum insertion torque values than did females (P < 0Æ01). Maximum insertion torque values were higher with the external implant type compared to those of the internal type (P <0Æ01). Survival rate Energy mean value (J) 0Æ87 0Æ60 0Æ82 1Æ18 Survival analysis for the patients has been carried out. Although it is not a significantly long-term study, the cohort study was performed for 10Æ5 to 52Æ3 months data. As a result of the Kaplan Meier survival analysis, 6 persons were lost to follow-up, 79 implants were censored, and 2 implants were failed. One implant failed in 10Æ5 months, and the other case in 50 months. The result shows very high rate of success. It also shows that the most failure cases occurred in the maxilla.

6 156 K.-J. PARK et al. Table 6. Stepwise multiple regression tests to determine the sequence of variables that influence the ISQ and maximum insertion torque values Dependent variable Independent variables b Significance Adjusted R-squared ISQ value Implant location (maxilla, mandible) )0Æ385 0Æ000 ** 0Æ351 Implant design (external, internal type) )0Æ317 0Æ000 ** Diameter 0Æ411 0Æ001 ** Gender (male, female) )0Æ318 0Æ004 ** Maximum insertion torque Implant location (maxilla, mandible) )0Æ477 0Æ000 ** 0Æ349 Gender (male, female) )0Æ390 0Æ000 ** **P <0Æ01. Implant design (external, internal type) )0Æ334 0Æ002 ** Discussion The need for a clinical diagnostic tool to detect early changes in and the stabilities of dental implants have increased with the use of immediate and or early loading concepts. The development of a clinical instrument based on measurements of resonance frequency of a small transducer attached to an implant fixture has several promising applications. Insertion torque and removal torque have been considered as efficient methods for determining implant stability (15). The maximum insertion torque may be due to the impingement of the implant flange on the crestal cortical bone, bottoming out of the implant at the base of the prepared bone channel, and engagement of the implant. The resistance of the bone to this compression generates a rapid increase in insertion torque (16). In this study, maximum insertion torque values were explored as a reference to determine implant stability. There was a direct relationship between ISQ value and the maximum insertion torque (P <0Æ05, r =0Æ427). This indicates that resonance frequency analysis may be a useful tool in identifying implants with a sufficient degree of stability. ISQ values corresponded to angular momentum (P < 0Æ05), but no linear correlation was observed between ISQ value and energy at the initial implant surgery (P > 0Æ05). Maximum insertion torque values corresponded to the energy and angular momentum of each part of the implant (P <0Æ01). This study showed that ISQ value was related to implant location (maxilla or mandible), design, diameter and gender of the patient. Implant location mainly influenced the ISQ value and maximum insertion torque value, with higher ISQ values observed in the mandible compared to those of the maxilla. The data also supported results of clinical studies on higher implant survival in the mandible. Differences between implants in the mandible and maxilla can also be explained in terms of bone density, since maxillary bone is often softer due to lesser amounts of cortical bone (17). During the study, it was at the discretion of the surgeons whether to apply bone drill and pre-tapping. Bone density assessment has always been one of the most important parameters for predicting long-term success in dental implant therapy (18, 19). Bone quality is important to decide preparation and conditioning of the implant site, i.e. use of cortical bone drill, pretapping the implant site in the crestal area, which may have an influence on the final results. During the study, the bone drill and pre-tapping drill were applied in most of the mandible, not in the maxilla. So both factors have been confounded with the variable whether the implant was placed in the maxilla or mandible. No-tapping cases are dominant in the maxilla, whereas pre-tapping cases in mandible. Most failure occurred in maxilla and no-tapping cases. Implant stability did not show significant difference between the pre-tapping and no-tapping groups. However, maximum insertion torque and ISQ show statistically different according to the jaw location (P < 0Æ01). Previous literatures reported that measuring bone density with panorama or CT is necessary before using a tapping drill (16, 20). Some investigators emphasised the importance of the clinicians tactile sensation during the initial drilling. In other words, the previous studies could have been influenced by the clinicians discretion of whether to pretap the site or not (21, 22). Stepwise multiple regression tests showed higher ISQ values in the external type compared with those of the internal type, in wide diameters compared to narrow

7 ISQ VALUES AND INSERTION VARIABLES 157 diameters, and in males compared to females. There were no significant linear correlations between ISQ value and anterior posterior location or implant length. When comparing different implant systems, differences in ISQ value should not be misinterpreted as differences in the stability or degree of osseointegration. Several factors influence ISQ values including the stiffness of the implant bone interface, the stiffness of the bone itself, and the stiffness of the implant components. Furthermore, there is a strong correlation between supracrestal implant height and ISQ value. External type implants are placed on the level of the crestal bone, while internal type implants have a 3-mm supracrestal shoulder. If the ISQ values of internal type implants are corrected for the height of the implant shoulder, about nine ISQ values could be added to the present measurements, resulting in similar ISQ values to those reported for external type implants (16). Thus, it appears that it is not possible to compare the stabilities of various implant systems using standardised RFA-ISQ values during the early phases of healing. Each system should be separately calibrated and evaluated to define acceptable ISQ values for ideal implant stability. After the initial implant surgery, bone must undergo remodelling at the implant bone interface to integrate the two materials. If trauma is very high at that time, the stress will be increased. Therefore, it is necessary to decrease the surgical trauma and the amount of initial bone remodelling at implant placement. Causes of trauma include thermal injury and micro-fracture of bone during implant placement. Excessive surgical trauma and thermal injury may leads to osteonecrosis and result in fibrous encapsulation around implant. Therefore to minimise factors related to thermal injury and surgical trauma when considering immediate load to the implant interface is prudent (23). One goal for an immediate loaded implant prosthesis system is to decrease the risk of occlusal overload and its resultant increase in the remodelling rate of bone. Under these conditions the surgical regional acceleratory phenomenon mat replace the bone interface without the additional risk of biomechanical overload. The lower the stress applied to the bone, the lower the strain in the bone (23). In this study, the stress represents the energy applied to the bone. Calculating the energy used during implant insertion is complex. A technique using insertion torque data to calculate the energy used in bone cutting was recently invented. This energy is related to torque path 2 path 1 Fig. 3. The diagram of developed torques during implant installation. the load in the bone. In general, the energy is divided into mechanical load and heat on the bone. However, the overall energy used during insertion is an overestimation of the energy imparted to the bone since energy is also lost in the generation of heat within the hand piece, in the generation of noise, and to friction between the components of the hand piece and motor (24). Nonetheless, if the energy is excessive, the bone will exhibit slow healing or necrosis. With new methods, the stabilities of implants in normal implant procedures can be estimated. Using the insertion torque graph, the corresponding angular momentum and energy were determined. When practitioners decide loading time, it is necessary to consider maximum insertion torque, ISQ value and bone strain. As seen in Fig. 3, the total energy applied to bone can be different on where maximum insertion torque values are same. Even in the case of implant with rigid fixation on good quality bone, the additional torque to secure or evaluate fixation of implant in bone may increase the strain on the interface and the amount of remodelling, which can eventually damage the strength of bone implant interface. So the references, i.e. energy and strain, can be also helpful for practitioners to decide when to load and whether implant would be successful or not. However, further research is required to find the appropriate level of energy. With this program, the stress on the bone and the amount of bone remodeling required could be estimated. These new methods might be a basis for the design of new implants that exhibit higher implant t

8 158 K.-J. PARK et al. stability and lower damage to the bone during surgery. Other intriguing finding was that the most critical part of the implant that requires the greatest insertion energy was the coronal third of the implant. The acquired energy in each part increased with increased insertion depth. These new methods might be a basis for the design of new implants that exhibit higher implant stability and lower damage to the bone during surgery. These findings correspond to the results of Friberg et al. (6) who measured bone density in the marginal, middle, and apical parts of maxilla implants. Subsequent RFA measurements showed a correlation between implant stability and the density of the marginal bone, but not at other parts of the implant site. The authors concluded that marginal bone properties were the main determinants of the RFA measurements. In the case of the energy index, the shape of the implant can be improved so that the energy index can be reduced and a standard for the rotational speed of the implant can be established. For example, in Fig. 3, paths 1 and 2 indicate the same maximum insertion torque values since both cases have the same insertion torque. It is predetermined that path 1 confers less osseous damage compared to that of path 2 since the total energy is less for path 1. Likewise, as the bone is not remodelled as much as in path 2, the stability of the implant in path 1 is expected to be improved. The ideal situation is that in which the insertion torque value is high and the energy is low; however, with recent surgical techniques a correlation exists. If the insertion torque is too high, the bone will be damaged. Therefore, the energy values should be lowered even though the insertion torque will also lowered. To minimise the production of friction heat when placing implants, the adapted surgical protocol must be followed. The developed Java program can be used to obtain the energy produced with implant placement, which can then be used, in combination with the resonance frequency analysis technique, to predict implant success. A further research is needed to find the appropriate level of energy. We view that review of our ISQ, angular momentum, and energy values can be helpful to decide appropriate loading time. Information available at the time of implant insertion might be a scientific basis to decide appropriate timing for loading and even enable immediate loading. Through a long-term cohort study, we would be able to find more accurate guidance of ISQ, angular momentum and energy values to define the most appropriate loading time. A further research is needed. Acknowledgments This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology ( ). References 1. Sennerby L, Meredith N. Resonance frequency analysis: measuring implant stability and osseointegration. Compend Contin Educ Dent. 1998;19: , 2; quiz Meredith N. A review of nondestructive test methods and their application to measure the stability and osseointegration of bone anchored endosseous implants. Crit Rev Biomed Eng. 1998;26: Turkyilmaz I. A comparison between insertion torque and resonance frequency in the assessment of torque capacity and primary stability of Branemark system implants. J Oral Rehabil. 2006;33: Tozum TF, Bal BT, Turkyilmaz I, Gulay G, Tulunoglu I. Which device is more accurate to determine the stability mobility of dental implants? A human cadaver study. J Oral Rehabil. 2010;37: Tozum TF, Guncu GN, Yamalik N, Turkyilmaz I, Guncu MB. The impact of prosthetic design on the stability, marginal bone loss, peri-implant sulcus fluid volume, and nitric oxide metabolism of conventionally loaded endosseous dental implants: a 12-month clinical study. J Periodontol. 2008; 79: Friberg B, Sennerby L, Meredith N, Lekholm U. A comparison between cutting torque and resonance frequency measurements of maxillary implants. A 20-month clinical study. Int J Oral Maxillofac Surg. 1999;28: Meredith N, Book K, Friberg B, Jemt T, Sennerby L. Resonance frequency measurements of implant stability in vivo. A cross-sectional and longitudinal study of resonance frequency measurements on implants in the edentulous and partially dentate maxilla. Clin Oral Implants Res. 1997;8: Meredith N, Alleyne D, Cawley P. Quantitative determination of the stability of the implant tissue interface using resonance frequency analysis. Clin Oral Implants Res ;7: Barewal RM, Oates TW, Meredith N, Cochran DL. Resonance frequency measurement of implant stability in vivo on implants with a sandblasted and acid-etched surface. Int J Oral Maxillofac Implants. 2003;18: Balleri P, Cozzolino A, Ghelli L, Momicchioli G, Varriale A. Stability measurements of osseointegrated implants using Osstell in partially edentulous jaws after 1 year of loading: a pilot study. Clin Implant Dent Relat Res. 2002;4:

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