The PTV had the negative values except failed implants, but there was no statistical meaning of the correlationship between the differences in the ISQ values and PTV.
Although a good interexaminer reliability was reported, a number of variables influenced the PTV. They could be increased or decreased by changes in the vertical measuring point on the implant abutment, the handpiece angulation and the horizontal distance of the handpiece from the implant. Therefore, the use of the resonance frequency analysis device seems to be safer in assessing reliable implant stability data, because variables during the standardized measurements are kept to a minimum.8
The ISQ values have been claimed to be useful for monitoring implant osseointegration during the healing phase.8
However, few studies describing normal ISQ values have been published. The implicit assumption is that implants undergoing osseointegration are supposed to increase their stability with time or at least maintain it (Meredith 1998).9
An ISQ level of 69 (range of 57 - 82) may describe the stability of a fully integrated implant.12
The RFA method, as a diagnostic tool, was not reliable in identifying mobile implants, however implant stability could be reliably determined for implants with an ISQ ≥ 47.16
In this study, no significant difference was found from implant stability (PTV, ISQ values) between various implant surfaces. But, as shown in - , the measured stability increased together with the healing process in all implants. The measured ISQ values did not change significantly or increase with time after 5 weeks. This means that the implants had reached a stable state. Clinically, the stability of a dental implant system increases as the bone contact increases. After the osseointegration process has stabilized, stability of the implant system is achieved; therefore the ISQ values reach a plateau.
Furthermore the lowest ISQ values were seen between 2 to 4 weeks after implant placement. Other study indicated that the initial resorption periods at implant surgery were found in the first 2 weeks.7
In an in vivo
study of de novo alveolar bone formation adjacent to endosseous implants, described a novel model to investigate different temporal phases of wound healing that result in osseointegration.17
In this animal model, new bone formation was noted at 1 week postplacement. Replacement of the original bone that was responsible for the initial stability of the implant at placement was well underway at the 2 week mark.
A rough estimate of comparative healing rates between dogs and humans would suggest that the events of wound healing and bone remodeling happen approximately 1.5 times sooner in dogs than would occur in the human. In this study during the process of healing, the ISQ values of the tested implants increased and reached a plateau at around 5 weeks. Although no human data are available from this study, the ISQ curve for humans can be predicted to reach a plateau at around 7 weeks or 8 weeks.
When the implants failed the ISQ values decreased. This is because the boundary condition of the implants was destroyed and, therefore, the contact area at the implant-bone interface was reduced.
In this study, we did final drilling till 3.3 mm to increase the initial fixation forces, so that the ISQ values after 8 weeks were higher than initial ISQ values. An implant with a better initial stability condition (i.e. with higher initial ISQ values) would result in a higher final ISQ values.4
Higher initial ISQ values had shorter simulated healing times.6
But, in one individual, the stability decreased in gap after one week was big because the initial fixation force was so great that there was the cortical bone ischemia. And the stability after 8 weeks was lower than initial stability.
In the histological findings there was no specific infection that meant the good osseointegration. In a study in vivo
, at 8 and 12 weeks, there were marked signs of remodeling within the wound chamber.17
Consequently in the histological view, it means that the implants of this study has no mechanical, functional problem on the loading after 8 weeks. But the histological view should be analyzed earlier because the ISQ values of the implants loading time meant the 5 or 6 weeks.
The process of osseointegration is affected by many factors, including surgical techniques and the conditions of the implant bed.3
Clinical observations have also indicated that the final healing time is affected by individual differences and operation conditions.18
The results given here also demonstrated that the initial ISQ values of implants vary with each individual. It could be concluded that from all difference tendency of this study, the variation of surgical situation (e.g. bone quality, bone quantity, insertion torque, heat generation etc) may be one of the major factors to estimate the clinical success. Therefore, the test implants were evaluated individually.
One of the implants was lost during the experimental periods. The x-ray view showed that the implants invaded the nerves in this study. It was assumed that produced paralysis then maintained for 8 weeks, and made overloaded the occlusal force. So it could be suggested that the reason of the visible failure of implants which produced clinical instability.
Also in this study, the implants were planted always same place with the same sequence so that could effect the results. The purpose of this study is not the comparison of the values according to the implant surfaces but the timing of the osseointegration. We wanted to find the changes of the stability of each implant so the problem of the places of implants was not considered.
It is well known that rapid ingrowth of bone into the threads during the initial healing period make sure better stability of the implants after the 1st surgery and also contributes to advance the long-term success.19
However, further study for the proper healing time and mechanics by the surface properties of implant is needed.