|Year : 2014 | Volume
| Issue : 3 | Page : 169-175
Determination of implant stability by resonance frequency analysis device during early healing period
K Lakshmi Kanth1, D Narasimha Swamy1, T Krishna Mohan2, Chakrapani Swarna1, Sahitya Sanivarapu1, Mohan Pasupuleti3
1 Department of Periodontics, Sibar Institute of Dental Sciences, Takkellapadu, Guntur, Andhra Pradesh, India
2 Department of Prosthodontics, Sibar Institute of Dental Sciences, Takkellapadu, Guntur, Andhra Pradesh, India
3 Department of Periodontics, St. Joseph's Dental College and Hospital, Eluru, Andhra Pradesh, India
|Date of Web Publication||17-Sep-2014|
K Lakshmi Kanth
Department of Periodontics, Sibar Institute of Dental Sciences, Takkellapadu, Guntur - 522 509, Andhra Pradesh
Source of Support: None, Conflict of Interest: None
Aim: The aim of the present study is to evaluate the implant stability determined by Osstell Mentor® resonance frequency analysis unit during initial healing period with different bone density and whether resonance frequency analysis (RFA) can be integrated into the routine clinical evaluation to determine the implant stability.
Materials and Methods: To measure the implant stability, 24 patients with an age group of 20 yrs to 40 yrs were included in the study. In all patients implants were placed by one stage technique using life care dental implants. RFA was measured at the time of implant placement, 2, 4, 8, and 12 weeks by using Osstell Mentor® device. Bone density was classified according to Lekholm and Zarb index.
Results: The overall mean minimum RFA value at the time of implant placement was 66.25 + 9.6 which gradually decreased to 63.25 + 11.4 at 4 weeks and gradually increased to 68.50 + 10.2 after 3 months. Mandibular implants showed higher values ranging from 68 to 72 compared to maxillary implants which ranged from 62 to 65. Type II bone showed higher values than type III bone. Statistical analysis was done by SPSS software version 20.
Conclusion: RFA by using Osstell TM mentor device is a non-invasive intraoral method designed to reflect the bone/implant interface and hence may be useful in documenting clinical implant stability and outcome of implant treatments. This test has been proven reliable for detecting alterations in implant stability during early healing and is sensitive enough to identify differences in implant stability based on bone density at the implant recipient site.
Keywords: Dental implant, implant stability, implant stability quotient, osseointegration, resonance frequency analysis
|How to cite this article:|
Kanth K L, Swamy D N, Mohan T K, Swarna C, Sanivarapu S, Pasupuleti M. Determination of implant stability by resonance frequency analysis device during early healing period. J NTR Univ Health Sci 2014;3:169-75
|How to cite this URL:|
Kanth K L, Swamy D N, Mohan T K, Swarna C, Sanivarapu S, Pasupuleti M. Determination of implant stability by resonance frequency analysis device during early healing period. J NTR Univ Health Sci [serial online] 2014 [cited 2020 Apr 1];3:169-75. Available from: http://www.jdrntruhs.org/text.asp?2014/3/3/169/140936
| Introduction|| |
In 1969, Branemark, et al, demonstrated that direct contact between bone and titanium implant surface was possible, defining osseointegration as "direct structural and functional contact between live bone and the surface of a functionally loaded implant".  Osseointegration is accepted as a histological term denoting direct bone apposition on the implant surface with no interposition of soft tissue.
Clinical assessment of implant stability is based on mechanical rather than histological criteria. Implant stability is a measure of the clinical immobility of an implant, which is an indirect indication or a requisite characteristic of osseointegration. , It is achieved at two levels: Primary and secondary stability. Primary stability is achieved at the time of implant placement and is associated with bone density, length, width and type of implant and drilling technique. Secondary stability depends on bone formation and remodeling at the implant bone interface and is influenced by the implant surface and the wound healing time. 
During healing, as primary bone contact decreases, secondary bone contact increases. Primary and secondary stability in healed bone has typically been assessed clinically via tapping the implant in a lateral direction with two opposing mirror handles. Although this is a widely practiced clinical technique, there is little evidence in the literature to suggest that this method is valid. 
More recent methods have involved measuring cutting torque resistance and insertion torque values, both of which lack repeatability. Reverse torque that is invasive and destructive, hence, impractical in a clinical setting. , Other techniques such as Periotest and dental fine tester were primarily developed for use on natural teeth and are subjected to several variables and hence questionable for accuracy and reliability. Histomorphometric and histologic analysis of the bone implant interface, even though reliable, is not practical in a clinical setting.  The need for a user friendly, non-invasive, reliable, and clinically applicable technique to measure implant stability lead to the development of resonance frequency analysis (RFA) by Meridith and co-workers in 1996, which is based on vibration and a principle of structural analysis. 
RFA has gained popularity as it is a non-invasive diagnostic method that measures implant stability. The most recent version of Osstell® resonance frequency analysis system now features the Osstell Mentor® [Figure 1], a type of electronic tuning fork that automatically converts kHz to ISQ values.  It is a portable, hand-held device that uses the magnetic frequencies between the transducer (a magnetic peg or smart peg) and the resonance frequency analyzer. The transducer is a metallic rod with a magnet on top that is screwed onto an implant or an abutment with a force of 5-10 Ncm.
The magnet is activated by a magnetic pulse of approximately 1-ms duration from a wireless probe. After excitation, the peg vibrates freely, and the magnet induces an electric voltage in the probe coil. This voltage is the measurement signal sampled by the resonance frequency analyzer. The results of an RFA are expressed as an implant stability quotient (ISQ) on a scale from 1 to 100 which represents a standardized unit of stability.
In the early studies, the hertz was used as the measurement unit. Later, Osstell created the implant stability quotient (ISQ) as a measurement unit in place of hertz. Resonance frequency values ranging from 3,500 to 8,500 Hz are translated into an ISQ of 0 to 100. A high value indicates greater stability, whereas a low value implies instability. The manufacturer's guidelines suggest that a successful implant typically has an ISQ greater than 65. An ISQ <50 may indicate potential failure or increased risk of failure.
The aim of the present study is to determine the implant stability by using Osstell TM mentor RFA device during the healing period and the relation between RFA value and bone density.
| Materials And Methods|| |
This human clinical trial was designed as a prospective study to measure implant stability with an RF analyzer at the time of implant placement and up to 10 weeks post placement. The study population consists of 24 patients between the ages of 20 to 50 years who received HI-TEC implants [Life Care Devices Private Limited]. Patients who did not attend the follow up examination or implants without primary stability were excluded. Patients who had severe clenching habit, bruxism, or other parafunctional habits, who had already received or lost implants at the potential implantation site, heavy smokers and those who had undergone radiotherapy or chemotherapy were not included in the study.
Preliminary treatment planning was done using diagnostic casts on which a diagnostic wax up was done and a surgical and a prosthetic stent were fabricated. Diagnostic intraoral and panoramic radiographs were taken and the morphology and the skeletal relationship were evaluated. The available bone height, width and length were calculated. Informed consent was obtained from all the patients prior to commence of the study. After fulfillment of the inclusion criteria, all patients underwent an initial periodontal therapy consisting of motivation, oral hygiene instructions and scaling and root planing.
All implants were placed using a non-submerged technique, according to a strict surgical protocol following the manufacturer's instructions. Bone quality was categorized as type I, II, III, and IV at the time of surgery following the anatomic criteria proposed by Lekholm and Zarb. This determination was based upon the drilling resistance to site preparation during implant placement.
Under local anesthesia, a full thickness mucoperiosteal flap was raised and the underlying alveolar bone exposed for osteotomy. The surgical template was then positioned and the implant position marked in the crestal bone using a round bur attached to a straight handpiece. Sequential osteotomy was carried out using osteotomy drills and the implant was driven into the prepared implant bed with allowance of time for bone to get compacted.
During healing, RFA was performed starting with an assessment immediately following implant placement and then at weeks - 2, 4, 8, and 12 post operatively. RFA was performed using the Osstell TM mentor (Integration Diagnostics AB, Goteborg, Sweden) instrument on each implant by inserting a standardized abutment (Smartpeg TM , Integration Diagnostics AB, Goteborg, Sweden) of fixed length into each implant. The transducer probe (Osstell TM mentor probe) was held so that the probe tip was aimed at the small magnet on top of the Smartpeg TM at a distance of 2-3 mm. The probe was held still during the pulsing time until the instrument beeped and the displayed the ISQ value [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6].
The transducer was detached and the healing collar threaded into the fixture. The flaps were then approximated and sutured using 3-0 black braided silk. Post-surgical intraoral periapical radiograph was taken to assess the implant position. Post-surgical instructions were delivered and instructions regarding home care and medications were given.
Antibiotics and analgesics were prescribed for 3 days and 0.2% chlorhexidine mouth wash for 15 days. After 7 days after implant placement, the patients were recalled and the implant site healing was assessed following which the sutures were removed. Impression taking for the restorative phase was commenced at 10 weeks post-surgery and abutments were cemented applying 35 Ncm. The final restorations were seated after 12 weeks of healing.
| Results|| |
Twenty six patients with age ranging from 20 to 50 yrs participated in the study. Twenty four implants were inserted and healed uneventfully. Of these, two implants at the time of implant placement were found to have low ISQ values below 45. Those were not included in the study and left to heal for 6 months before loading. The remaining 24 implants showed satisfactory stability throughout the study.
RFA values were recorded at the time of implant placement (baseline value), 2, 4, 8 and 12 weeks postoperatively. The overall mean minimum RFA value at the time of implant placement was 66.25 + 9.6, which gradually decreased to 63.25 + 11.4 at 4 weeks and gradually increased to 68.50 + 10.2 after 3 months [Table 1] and [Table 2].
|Table 1: The Mean And Standard Deviation Of The Implant Stability Quotient Values At Different Time Points|
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|Table 2: Results of student paired t-test to test the significance of mean change in the Implant stability quotient at different time points|
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Bone quality was categorized as type II and type III at the time of surgery following the anatomic criteria proposed by Lekholm and Zarb. The mean RFA values of type II and type III bone at all the time intervals and of the maxillary and mandibular implants were shown in the graph [Graphs 1 and 2].
Statistical analysis was done by SPSS software version20.
| Discussion|| |
The development of clinical, preferably non-invasive diagnostic instruments with high sensitivity and reproducibility to detect early changes in implant stability during tissue integration of dental implants was desirable in the light of the propagation and the increasing popularity of implants placed immediately into extraction sockets and/or early loading protocols. In this respect, RFA is a clinical method capable of quantitative evaluation of primary implant stability in order to:
- Identify implants with too little stability and to take measure to improve it.
- Decide on healing approach (one stage/ two stages).
- Decide whether immediate/early loading may be suitable.
- Decide length of healing before loading (Normal or prolonged healing).
It appears that implants of every system will, with time, approach a similar level of stability, which for Branemark type implants seems to be an implant stability quotient of 65-75, and for Straumann type implants seems to be an implant stability quotient of 55-65. In the present study the values were within a range of 60-70. It seems reasonable to assume that this degree of stability at any time during the lifetime of an implant would indicate a safe level of stability. An implant stability quotient value below 55 (Branemark) or 45 (Straumann) should be regarded as a warning sign, and measures to increase implant stability should be considered. Primary stability can be improved by modifying the surgical technique and by selecting a wider, longer or tapered implant. For instance, the use of thinner drills and wider and tapered implants will increase primary implant stability. 
In the current study, most of the cases are of type II and type III bone qualities. Irrespective of type of bone, there is a significant decrease seen in ISQ readings at 4 weeks and gradually increased (but less than that of the baseline readings) postoperatively which was also noted by Barewal, et al.  This decrease in ISQ readings may be partially explained by the changes occurring at the implant - bone interface during the early healing phase. Primary stability of a dental implant obtained during surgical placement is purely mechanical and occurs due to fixation of a press-fit structure into a bony cavity. During the first weeks of healing, bone modeling and remodeling take place around the implant surface. This phase with the formation of lamellar bone from woven bone may cause a decrease in primary bone contact.  Roberts  extrapolated a wound healing process from a rabbit model, concluding that bone density undergoes significant changes during the early weeks following wound formation (0 to 6 weeks in humans) due to callus formation and lamellar compaction within the woven bone. Similarly, the plateau effect in implant stability after 6 weeks was noted by Cochran, et al,  and this phenomenon was correlated by the concept of enhanced bone formation around the implant surface.
Study on 122 implants in 31 patients revealed weakest implant stability at 3-6 weeks after placement. Ersanli, et al,  concluded that implant stability quotient value can be used to determine different healing phases and the stability of dental implants but implant stability quotient level should be calibrated for each implant system separately.
Huwiler and coworkers  found implant stability quotient values between 57 and 70 represents homeostasis and implant stability during their study on 34 Straumann implants. They were unable to find any correlation between implant stability quotient and the classification of bone characteristics given by Lekholm and Zarb in 1985. But in the present study, there is decreased in the ISQ value of type III bone than compared to type II bone. Results of study on 81 Branemark system implants in 23 patients by Glauser and co-workers  shows that failing implants showed a continuous decrease of stability until failure and this information may be used to avoid implant failure by unloading them.
Zix, et al,  did study with 120 maxillary International Team for Implantology (ITI) implants in 35 patients and found mean implant stability quotient was 52.5 + 7.9. They concluded that single RFA measurement of an implant does not allow of its current status. Repeated measurements over a longer period of time would be necessary. Same thing i.e. single reading using RFA is of limited clinical value as concluded by Aparicio and co-workers.  Lai, et al,  found primary stability to be affected by bone type. Their study on 104 ITI sand blasted large grit acid etched (SLA) implants shows significantly higher implant stability quotient value for type I bone than type IV bone. Similar results showing strong correlation between the bone density and implant stability quotient were found by Turkyilmaz and co-workers  in their study on human cadavers using 24 implants. In contrast, most recent study by Lai and co-workers  shows no difference in implant stability quotient values between type III and type IV bone at implant placement and follow up. They concluded that residual bone height, implant length and bone type did not seem to affect the implant stability in the clinical situation.
In contrast to previous studies one of the recent studies on 24 patients using 64 implants by Boronet, et al,  shows higher implant stability quotient values for women than men and for anterior implants than posterior fixtures. They got mean implant stability quotient value for all implants was 62.6 and lowest mean stability measurement was at 4 weeks for all bone types, i.e., 60.9.
| Conclusion|| |
RFA by using Osstell TM mentor device is a non-invasive intraoral method designed to reflect the bone/implant interface and, hence, may be useful in documenting clinical implant stability and outcome of implant treatments. This test has been proven reliable for detecting alterations in implant stability during early healing and to determine proper time for loading and is sensitive enough to identify differences in implant stability based on bone density at the implant recipient site.
Further studies, preferably randomized, prospective longitudinal studies are certainly needed to establish threshold ranges for implant stability and for implants at risk for losing stability for different implant system.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2]