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ORIGINAL RESEARCH Table of Contents   
Year : 2007  |  Volume : 18  |  Issue : 4  |  Page : 168-172
Clinical assessment of primary stability of endosseous implants placed in the incisor region, using resonance frequency analysis methodology: An in vivo study

Department of Prosthodontics and Implantology, Meenakshiammal Dental College, Chennai, India

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Date of Submission30-Oct-2006
Date of Decision30-Apr-2007
Date of Acceptance02-May-2007


Aim: To evaluate the effect of immediate loading on the primary stability of endosseous implants placed in the anterior incisor region by mapping the stability, using resonance frequency analysis, over a period of time.
Materials and Methods:
A total of eight implants (Zimmer Screw-Vent) were placed in four patients. The Osstell™ resonance frequency analyzer was used to determine the primary stability at baseline (day 1), 15 th day, 30 th day, 60 th day, and 90 th day for each of the eight implants. Analysis of data was done using SPSS (Statistical Package for Social Science; version 4.0.1).
Results: All implants showed adequate initial stability at baseline with an ISQ > 50. Implant nos. 1, 3, 4, 7, and 8 showed a high initial stability at baseline (ISQ > 65), following which a decrease in the stability was recorded during the 15 th day, 30 th day, and 60 th day. By the 90 th day, the stability values were nearly equivalent to those obtained at baseline. The highest mean stability value was recorded on the day of implant placement. The lowest mean stability recording was obtained on the 30 th day after implant osteotomy. By the 90 th day, the mean stability value was nearly equivalent to that obtained at baseline.
Conclusions: Within the limitations of this study, it can be concluded that immediate loading of implants placed in the maxillary and mandibular incisor region does not seem to have an adverse effect on the osseointegration of implants, which achieved a high primary stability. The use of the resonance frequency analyzer as a tool to monitor the variation in the stability of the implants over a period of time has been validated.

Keywords: Immediate loading, implant stability quotient, primary stability, resonance frequency analysis

How to cite this article:
Ramakrishna R, Nayar S. Clinical assessment of primary stability of endosseous implants placed in the incisor region, using resonance frequency analysis methodology: An in vivo study. Indian J Dent Res 2007;18:168-72

How to cite this URL:
Ramakrishna R, Nayar S. Clinical assessment of primary stability of endosseous implants placed in the incisor region, using resonance frequency analysis methodology: An in vivo study. Indian J Dent Res [serial online] 2007 [cited 2019 Sep 17];18:168-72. Available from:

   Introduction Top

The use of endosseous implants to restore lost dentition has proved to be a successful treatment modality, providing the patient with a near natural replacement. Implants have become the treatment of choice in many, if not most, situations when missing teeth require replacement. Though the stringent protocol developed by the Swedish physician and researcher Per Ingvar Branemark that required the undisturbed and unloaded healing of the bone surrounding the implants for a specified period of time prior to the prosthesis application was widely accepted, an immediate implant loading protocol has been reported in literature of recent years [1],[2],[3],[4],[5],[6] with success rates of up to 100% after 2 years of follow-up.

One of the unraveled parameters predicting osseointegration is micromotion at the implant-tissue interface not surpassing the threshold of 50 to 150 microns during the postimplantation healing phase. [7] The most important prerequisite for immediate loading of implants is the achievement and maintenance of a high implant stability. The primary implant stability at placement is a mechanical phenomenon related to the quality and quantity of bone at the recipient site, the type and design of implant used, and the surgical technique employed. The secondary implant stability is the increase in stability attributable to bone formation and remodeling at the implant-tissue interface and in the surrounding bone. [8]

To evaluate the initial bone quality and the degree of osseointegration various methods have been used; these include histologic and histomorphometric observations, [9],[10],[11],[12] percussion tests, removal torque analysis, [13] pull-and push-through tests, [14] and the Periotest. [15]

The limitations exhibited by these traditional methods led to the development of a nondestructive and a noninvasive technique to evaluate the condition of the implant-tissue interface by Dr. Neil F Meredith in 1996; [16] it was called 'resonance frequency analysis.' This technique has been widely used in medical research and is accepted as a candidate parameter for the early assessment of the implant-bone interface.

The reasons for seeking new concepts for prosthetic restoration on dental implants are lack of comfort and the social limitations of the patients during the osseointegration phase. Hence, the aesthetic zone was chosen for this study.

The aim of this in vivo study was to evaluate the effect of immediate loading on the primary stability of endosseous implants placed in the anterior incisor region by mapping the stability over a period of time, using resonance frequency analysis.

The objectives of this study were:

  1. To analyze the development of the primary stability of immediately loaded implants by repeated resonance frequency measurements on the 1 st day, 15 th day, 30 th day, 60 th day, and 90 th day after implant placement.
  2. To compare the difference in the stability values at different time intervals.
  3. To evaluate whether immediate loading has any adverse effect on the primary stability of endosseous implants placed in the incisor region.
  4. To determine whether the measurement of implant stability is of use in predicting the optimum healing period of immediately loaded implants.

   Materials and Methods Top

The study sample consisted of a total of 8 implant sites in five patients aged between 25 to 50 years, who presented with missing maxillary or mandibular incisors. The medical status of the patients with regard to current and previous medical and dental history and medication was noted and only ASA classification P1 (normal, healthy) patients were included in the study. Only patients with sufficient alveolar bone volume at the implant site of >5.5 mm width labiolingually and >15 mm height, and Type I-III bone quality, were included. Patients who had severe clenching habit, bruxism, or other parafunctional habits; those 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. Complete blood count and blood chemistry studies were done. 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 quality of the bone, the morphology and the skeletal relationships were evaluated. The available bone height, width (bone mapping), 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 planning. The ability to perform plaque control was assessed for each patient prior to entry into the surgical phase.

Resonance frequency analyzer

Resonance frequency analysis technique is a bending test of the bone implant system, in which a microscopic bending force is applied by exciting the transducer fixed rigidly onto the implant fixture. Osstell™ resonance frequency analyzer (Integration Diagnostics, Sweden), intended for measuring the stability of implants in the oral cavity and craniofacial region, was used in this study. It is a reliable indicator for identifying stable implants with certainty. [17] Following the attachment of the transducer to the implant fixture, the measurements were made using an autoclavable stylus, enabling the instrument to be used in sterile conditions. This instrument has a graphic display panel showing the ISQ (implant stability quotient) value, that denotes the stability and the stiffness at the implant-tissue interface. The ISQ value is scaled from 1 to 100.

RFA value measurement

As a determinant of the remodeling at the implant-tissue interface in this study, the implant stability values were determined at baseline (day 1), 15th day, 30th day, 60th day, and 90 th day for each of the eight implants. This data would reveal the variation in the primary stability of the implant during the stage of osseous remodeling and osseointegration.

Implant and kit

The Zimmer Screw-Vent implant system (Zimmer Inc., USA) was used in this study. All implants used were 3.3 mm in diameter, 13 mm in length, self tapping, and threaded. Thus, the implant size and diameter were standardized for all implantation sites.

Surgical phase

All patients were premedicated prior to the procedure and their vital signs monitored prior to the commencement of the surgery. Under local anesthesia, a full thickness mucoperiosteal flap was raised in the anterior region 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. The Osstell transducer was then rigidly attached to the fixture and the baseline ISQ value was the recorded, following which 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. Postsurgical intraoral periapical radiograph was taken to assess the implant position. Postsurgical instructions were delivered and instructions regarding home care and medications were given.

Postoperative medication

Cap. Novamox (amoxicillin) 500 mg b.d. for 3 days

Tab. Ibuprofen t.d.s. for 3 days

Rexidin (2% chlorhexidine) mouthwash t.d.s. for 15 days

Review and suture removal

On the 7th day after implant placement, the patients were recalled and implant site healing was assessed, following which the sutures were removed.

Prosthetic phase

On the 7th day, the sutures were removed and the abutment was connected to the implant fixture. A perforated stock tray of suitable size, coated with tray adhesive, was used to make the impression of the abutment, using addition silicone of putty consistency. On curing, the impression was removed and disinfected. The abutment was then detached from the fixture and the implant analogue connected to the abutment rigidly. The abutment was then repositioned into the impression along with the analogue and the model poured, using type IV Die Stone.

Laboratory phase

The model was then retrieved from the impression, disinfected, and the abutment milled in order to mimic a prepared crown with relative parallelism. In the laboratory, the metal ceramic restoration and an acrylic resin provisional were then fabricated. The acrylic resin provisional had a guiding slot in the palatal / lingual side in order to facilitate the attachment and detachment of the abutment to the implant fixture, without inducing unwanted stresses.

Prosthesis loading

All implants were loaded with the acrylic provisional before the 15 th day after implant osteotomy. Definitive prosthesis was conferred 90 days after baseline.

Follow-up and evaluation

RFA values were noted at baseline, 15 th day, 30 th day, 60 th day, and 90 th day after implant placement. Intraoral periapical radiographs were taken at baseline, 1 month, 2 month, and 3 month time intervals.

Statistical analysis

The statistical package SPSS (Statistical Package for Social Science, version 4.0.1) was used for statistical analysis. Mean and standard deviation were estimated from the sample from each time point. The mean changes between two time points were compared by Student's paired t test. In the present study, P<0.05 was considered as significant.

   Results Top

All implants showed adequate initial stability at baseline with an ISQ value greater than 50 [Table - 1].

The highest mean stability value was recorded on the day of implant placement. The lowest mean stability recording was obtained at 1 st month after implant osteotomy. By the 3 rd month, the mean stability value was nearly equivalent to that obtained at baseline [Table - 2].

The results of the Student's paired t test are tabulated [Table - 3].

   Discussion Top

The long-term experience of using osseointegrated implants for prosthetic rehabilitation of the edentulous patient shows that high success rates can be predictably achieved if certain preconditions are fulfilled. The most important prerequisite is achievement and maintenance of implant stability. Implants of different designs, placed in different bone qualities, reach different degrees of stability which, according to the clinical findings, seems to determine their future clinical performance, since a relationship between bone densities (quality), implant length, and failure have been demonstrated. [18],[19] Moreover, recent clinical work has demonstrated that implants can be subjected to immediate/early loading with predictable results if certain preconditions, such as high bone density and primary stability, are fulfilled. [20],[21]

A thorough evolution of the implant design, dimensions, surgical techniques, and the biomechanical condition of the prosthesis, led to clinical practice shifting more towards immediate loading of oral implants. This reduction of proposed treatment time has important psychosocial and economic implications for patients and has led to an increasing interest among clinicians and researchers.

Initial implant stability obtained after implant insertion is regarded as critical for the prognosis of the implant. At placement, knowledge of primary stability may also serve as a guide to making a decision regarding the choice of the treatment protocol: immediate, early, or delayed loading. The measurement of secondary stability, after initial healing, may confirm a successful healing and facilitate decision-making with implants that demonstrate low stability.

The use of RFA makes it possible to individualize implant treatment with regard to healing periods, type of prosthetic construction, and whether one- or two-staged procedures should be used. Moreover, since measurements can be repeated over time, changes of implant stability during loading can be monitored. Implants with falling stability due to overload can thereby be detected before failure and rescued.

The ISQ value obtained is determined by three main factors:

  1. The design of the transducer itself
  2. The stability of the implant- the stiffness of the implant-tissue interface
  3. The effective length above the bone level

    The stiffness of the implant-tissue interface is the most important factor and describes the stability of the implant.

In this study, implants with a high primary stability (ISQ > 65) appeared to maintain a similar level of stability or to decrease somewhat in ISQ with time. Implants with a lower primary stability (ISQ 50-60) appeared to display an increase in ISQ with time. One implant showed a low primary stability (ISQ = 50), with a minor fall in the value during the first month healing period, but the value subsequently increased after the second month and showed a high stability by the third month. The decrease in the ISQ value during the osseous remodeling stage is consistent with the findings reported by Frieberg et al. [22]

Implant stability above 65 ISQ should be regarded as optimal, above which few failures should be expected. It is more difficult to establish a lower limit under which a high rate of failure occurs. In general, ISQ values of 50 to 60 are seen in softer bone (maxilla) and 60 to 80 in denser bone (mandible). A value below 45 should be looked upon as a warning sign and measures to increase the primary stability should be considered. Primary stability can be improved by adapting the surgical technique and by implant selection. For instance, the use of thinner drills and wider and tapered implant designs will result in a high primary stability. This improvement is due to lateral compression of the bone trabeculae and an increase of the interfacial bone stiffness. A high ISQ value achieved after such a procedure should not be relied upon as an indication for immediate loading, since this value may decrease over time as a result of mechanical relaxation. This means that a high 'manipulated' ISQ value after using thinner drills and wider and tapered implants describes a temporary increase of stiffness rather than the true load-bearing capacity of the bone-implant complex. However, the improved primary stability achieved by applying an adapted surgical technique may contribute to lower implant failure rates in soft bone because of the reduced risk of micromotions at the interface during healing. One way to improve the secondary stability would be to extend the healing period to 9-12 months. [23]

A decreasing ISQ value can serve as an 'early warning.' It is important to know if a sudden decrease is due to loss of marginal bone or demineralization of the interface bone. It is therefore important to analyze such implants with radiography. If marginal bone loss is seen, this is the reason for the decrease of ISQ. This is probably less alarming than if no marginal bone loss is seen, since the latter would indicate demineralization of the interface.

It is known that reduced bone volume, softer quality of bone, and excessive occlusal loads are the risk factors to be considered for implants to be loaded immediately. [7] Low resonance frequency levels after one and two months indicated an increased risk for the future failure of the implants. [24]

The results confirm the findings from Friberg et al. that implants with low primary stability show increased stability with time . [22] The observations also suggested that a healing period would not result in a higher secondary stability for implants with an already high primary stability, which implies that such implants may be immediately loaded.

Although surface texturing of implants does directly contribute to initial implant stability, it may reduce the risk of stability loss and consequently facilitate wound healing (secondary osseointegration). The implants used in this study (Zimmer Implant system, USA) incorporate a microstructured, threaded, SLA-treated surface with a screw-vent design. Stegaroiu et al. showed that all three superstructure materials, namely highly filled composite resin, acrylic resin, and gold alloy, had the same influence on the force transmitted to a bone stimulant that surrounded a single implant. [25] Hence, in this study, acrylic provisional crowns were cemented to load the implants immediately.

   Conclusions Top

Within the limitations of this study, it can be concluded that immediate loading of implants placed in the maxillary and mandibular incisor region did not seem to affect the osseointegration of the implants which showed a high primary stability. The use of the RFA as a tool to monitor the variation in the stability of the implants over a period of time has been validated since the readings correlated with the physiology of osseous remodeling after implant placement. Further studies need to be carried out to assess the potential for immediate loading in the posterior region of the oral cavity using the RFA methodology as a determinant.

The assessment of the change in the primary stability will be of benefit in predicting the optimum healing period of immediately loaded implants.

   References Top

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Correspondence Address:
R Ramakrishna
Department of Prosthodontics and Implantology, Meenakshiammal Dental College, Chennai
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0970-9290.35826

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  [Table - 1], [Table - 2], [Table - 3]

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