|Year : 2018 | Volume
| Issue : 2 | Page : 69-76
Factors influencing implant stability
K Vidya Hiranmayi
Department of Periodontics, Dr. Syamala Reddy Dental College, Hospital and Research Centre, Bengaluru, Karnataka, India
|Date of Web Publication||17-Dec-2018|
Dr. K Vidya Hiranmayi
Senior Lecturer, Department of Periodontics, Dr. Syamala Reddy Dental College, Hospital and Research Centre, Bangalore, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Implant stability reflects implant osseointegration in that it requires certain objectives to be met during implant installation and healing. The main determinants of implant stability are the mechanical properties of bone tissue at implant site irrespective of how well the implant is engaged with bone tissue. Stability can be classified into two types as follows: primary stability that is measured immediately after implant placement, secondary stability which is measured after the healing of bone around the implant. Primary stability is a mechanical phenomenon, whereas secondary stability occurs through a cascade of events, such as bone deposition and remodeling at the bone implant interface. Many factors influence the primary and secondary stabilities of the implants which include implant design, implant surface topography, bone quality, and patient-related factors. Hence, it is essential to comprehend the multitude of factors that persuade the implant stability and to analyze the outcome of implant therapy.
Keywords: Bone density, implant design, primary implant stability, secondary implant stability
|How to cite this article:|
Hiranmayi K V. Factors influencing implant stability. J Dent Implant 2018;8:69-76
| Introduction|| |
Implant stability reflects implant osseointegration in that it requires certain objectives to be met during implant installation and healing. The main determinants of implant stability are the mechanical properties of bone tissue at the implant site irrespective of how well the implant is engaged with bone tissue. Good primary stability is positively associated with secondary stability. Secondary stability gradually increases by 4 weeks following implant placement and requires 3–6 months of the non-loaded healing period to achieve optimum stability. Branemark's protocol recommends complete healing of alveolar bone after tooth extraction followed by implant placement with submerged healing for 3–6 months. During this period, several factors can affect the prognosis of implant placed in alveolar bone like the quality and quantity of alveolar bone, implant design, surface properties of implants, primary stability, occlusal load, and marginal bone loss.
Stability can be classified into two types as follows: primary stability that is measured immediately after implant placement, secondary stability which is measured after the healing of bone around the implant. Primary stability is a mechanical phenomenon that occurs due to interlocking of bone to implant immediately after implant placement, whereas secondary stability occurs through a cascade of events, such as bone deposition and remodeling at the bone-implant interface., Various methods are developed to assess implant stability such as histologic analysis, radiographs, percussion test, reverse torque test, cutting torque resistance analysis, periotest, and resonance frequency analysis (RFA) () device. Many factors influence the secondary stability of implants which include implant surface topography, bone quality, and patient-related factors.,
| Bone Quality and Quantity|| |
Bone density is a major determinant of implant stability measurement. A positive correlation exists between bone density and implant stability values. Implant stability is higher in the denser bone of mandible than in maxilla. Poor bone quality and quantity are the main risk factors for implant failure.
Women showed significantly higher implant stability values than men, and higher implant stability quotient (ISQ) values were noticed for anterior implants than posterior implants. RFA is a useful clinical method to predict bone-implant contact% values and RFA is used to examine implant stability which further predicts the degree of osseointegration. Higher stability was recorded in type 2 than in type 4 bone by Kashi et al. in 2015.
Implants with a progressive thread design placed at 10° angulation had higher primary stability than other implant angulations. Placement of tapered implant design using tapered drills resulted in higher primary implant stability than control implants that were placed using subtle taper and straight drills suggesting the impact of drilling protocols on primary stability in different bone densities. There was a statistically significant increase in implant stability and bone density values during the 6th month observation period suggesting a correlation between bone density estimated by cone-beam computed tomography and stability of dental implants estimated by resonance frequency device osstell ISQ.
| Implant Design|| |
Implant design modifications over the implants also influenced implant stability values. Cylindrical wide body and parallel design implants were replaced by tapered implants to enhance esthetics, assist implant placement between adjacent teeth and to provide a degree of compression of cortical bone in an implant site with inadequate bone. Retention grooves at the neck design or microthreads assist in distributing stress, reducing the extent of bone loss and thereby preserving the crestal bone through time of the function. Thread design decreases compression of crestal bone and preserves it. Implant stability was influenced by implant design and bone level.
Reasons for high primary stability could be attributed to implant features such as those implants with a body that has a conical shape as it matches the drill thereby ensuring primary fixing rather cylindrical shape. Symmetrical, spiral-shaped thread design, and microrings at the cervical part of implant are preferred as it enhances contact with surrounding cortical plate. Threads at various levels of height on implant surface that allows greater secondary implant stabilities even in soft bone by preventing further bone resorption.
In a study conducted by Marković et al., self-tapping implants did achieve significantly higher primary stability compared to nonself-tapping implants. This could be explained by the intimate bone-to-implant contact resulting from the compressive threads and the minute lateral displacement exerted on bone tissue during implant insertion, whereby loose bone trabeculae are pushed closer together. Thus, “local” bone contained in the pitch regions (between two adjacent implant threads) becomes denser. By improving the characteristics of the local bone in these regions– the bone responsible for primary stability– the implant receives firmer support consequently resulting in increased primary stability.
Regarding primary implant stability measurements, data retrieved from the available literature indicates a higher RFA exhibition in conical implants compared to the cylindrical ones.,, Contradictory results to the results of these studies, however, have also been reported.,
In a study conducted by Brouwers et al. (2009) cylindrical implants exhibited a higher RFA compared to tapered implants. Similarly, Bilhan et al. (2010) observed superiority of cylindrical implants. According to the authors, this superiority was related to the different mechanical engagement achieved by these two different implant macro designs. Tapered implants do not use the apical half of drilled bone for stability like the cylindrical implants and the stability obtained from tapered implants is all at the cervical part that may create a risk for loosening in the apical part (Bilhan et al., 2010). Despite the controversy over the effectiveness of different implant designs in implant stability, the superiority of tapered implants in specific clinical applications has been well emphasized by Markovic et al. Another clinical advantage of this implant is that it can be placed in all regions where the placement of a regular-diameter implant is planned and without any risks of damaging the roots of neighboring teeth. With the use of this implant, there is also a possibility of decreasing the horizontal defect dimension between the implant and bone, although complete elimination of the vertical/horizontal alveolus defect buccolingually appears impossible for all type of implants test.
Toyoshima et al. conducted a study to evaluate the primary stability of two hybrid self-tapping implants compared to one cylindrical nonself-tapping implant with respect to drilling protocols in an ex vivo model. Pushout value of hybrid self-tapping implants was higher than nonself-tapping implants. Hybrid self-tapping implants could achieve higher primary stability which predicts them for use in low-density bone.
O'Sullivan et al. designed a study to analyze the influence of implant taper on the primary and secondary stability of osseointegrated titanium implants. One pair of 10 mm (EXP 1) primary taper and control implants. The primary taper results in better primary stability compared to standard Branemark implants. The tapered design did not cause any negative bone tissue reactions, and all implants gained stability during the healing period.
| Implant Surface Characteristics|| |
Various surface modifications have been attempted for enhancing osseointegration of dental implants such as chemical treatments and deposition of calcium phosphate coatings with fluoride and zinc ions. Characteristics of titanium implant surfaces have been modified by additive methods like titanium plasma spraying to alter macrotopography and subtractive methods like blasting and acid etching to alter the microtopography.
Four categories of bioactive agents may be applied to coat the titanium implant surface, namely, (1) biocompatible ceramics, (2) bioactive proteins and growth factors such as Bone morphogenic proteins, transforming growth factor-β, fibroblast growth factor (FGF)-2, platelet-derived growth factor, insulin-like growth factor, arginylglycylaspartic acid peptides, (3) ions, and (4) polymers. A bioactive surface forms a favorable substrate for the osseous deposition to occur and actively participates in the osseointegration process due to the reaction between the chemically modified surface coating and surrounding bone.
The texture of an implant surface, surface roughness and surface energy can influence bone to implant interface and mechanical stability. The altering surface topography of an implant enhances implant stability. Surface modified, oxidized, sandblasted implants showed greater stability than machined implants. Rough implant surfaces present a larger surface area thereby allowing firmer mechanical link to surrounding tissues.,
Acid etched and sandblasted implant surface promotes long-lasting osseointegration, optimizes tissue response and stimulates early bone deposition. Studies have demonstrated that sandblasted implant surfaces promote peri-implant osteogenesis by enhancing growth and metabolic activity of osteoblasts. Surface topography and roughness like sandblasting and acid etching positively influence the healing process by promoting cellular response and cell surface interactions.
Implant surface coatings also influence primary stability like the oxide layer of thickness 10–12 μ and anodized surface are active throughout the implant enhances active bone growth that quickly promotes mechanical (primary) stability. This multilayer surface allows bony tissue to grow deeper and in between micropores.
Microporous structure grows through the entire thickness of the oxide layer. Titanium oxide film is enriched with calcium hydroxyapatite (HA) that enhances cell viability, cellular, and tissue response that benefits osseointegration. Jung et al. evaluated the secondary stability of micro thickness HA-coated, tapered implants without measuring primary stability.
Sul et al. conducted an experimental study to investigate whether oxide properties of titanium implants influenced bone tissue responses after an in vivo implantation time of 6 weeks and to investigate which oxide properties are involved in such bone tissue responses. Implants that had an oxide thickness of approximately 600, 800, and 1000 nm demonstrated significantly stronger bone responses in the evaluation of removal torque values than did implants that had an oxide thickness of approximately 17 and 200 nm. However, there was no difference between implants with oxide thicknesses of 17 and 200 nm. It was concluded that oxide properties of titanium implants, which include oxide thickness, micropore configurations and crystal structures greatly influence the bone tissue response in the evaluation of removal torque values.
Pimentel Lopes de Oliveira et al. conducted a randomized controlled clinical split-mouth trial to compare anodized implant surfaces and implant surfaces modified by acid etching regarding primary and secondary stability. ISQ analysis revealed that the acid etched (AC) group showed statistically higher values than the anodized (ANO) group.
Nagayasu-Tanaka et al. conducted a study was to examine the effect of basic FGF-2 on the osseointegration of dental implants with low primary stability. This study demonstrates that FGF-2 promoted new bone formation around the dental implants and subsequent osseointegration, resulting in promotion of the stability of implants with low primary stability.
Implant length and diameter also influence implant stability. Longer implants showed higher stability than shorter implants. Higher stability with increased implant diameter and reduced stability in smaller size diameter implants can be attributed to the fact that in the coronal part there is less friction during insertion.
The relationship between implant diameter and ISQ values has been well emphasized though in previous studies (Zix et al., 2005).,, Many authors advocate that since wider implants are more appropriately engaged with buccal and lingual cortical plates and offer a larger surface for osseointegration, they should exhibit more primary and secondary stability.,
The wider implants are not always, the more stable ones. Although narrow platform (NP) implants demonstrated the least implant stability, regular platform (RP) and wide platform (WP) implants did not have any significant influence in terms of implant primary stability. Similarly, in a study by Bilhan et al. (2010) no significant differences were observed in the primary stability of implants of 3.8 mm and 4.6 mm in diameter. Data reported by other investigators (Shiffler K 2016 and Renouard F 1999) also suggest that implants of >4 mm in diameter do not exhibit significant differences.,
Since ISQ values in RP and WP implants did not show any significant differences, Barikani et al. (2014) suggested to use RP implants to preserve further thickness of bony walls. With regard to NP implants, the results of the same study indicated that their effect was more prominent in low bone quality sites. Inserted in these sites, NP implants were the least stable. Accordingly, the authors suggested to avoid using NP implants in cases of low bone quality, or alternatively perform bone reconstruction methods (guided bone regeneration) to enhance accommodation of larger implants. Perhaps, NP implants would be more safely indicated only for the anterior region of the mandible and the premolar sides in the maxilla where implants are imposed to mild occlusal loads (Barikani et al., 2014).
In general, however, optimum increase in length and diameter of implants should be seriously considered to achieve high primary stability of implants placed in low bone quality, as well as in cases of implant placement in fresh extraction sockets in posterior regions, where the use of wider implants compensates for the defect size and engages as much cortical bone as possible.
With regard to secondary stability, one should expect that given the same architecture, wider-diameter implants also result to be more stable than thinner ones because they can potentially engage a larger amount of osseointegrated interface. This hypothesis was tested in an experimental study conducted by Veltri et al., who proved that a strong positive correlation exists between ISQ values expressing secondary stability and the simulated bone-implant contact. Contradictory relations between implant diameter and secondary stability found in different studies (Zix et al.) may be partially attributed to the clinical variability of trabecular architecture determining the bone-implant contact. It is likely that a correlation between diameter and secondary stability might be established only in larger samples that could compensate for the above-mentioned variability.
Lekholm et al., 1994 stated that most of the failed implants were 7mm or 10 mm in length. Long implants are necessary for successful osseointegration to ensure greater surface area for bone contact. The lower stability for the long implants may be explained by the longer drilling time for placement of long implants resulted in overpreparation of the implant site. It, therefore, seems that implant length is not always an effective factor influencing RFA measurements and consequently implant stability, and placing a great deal of emphasis on the use of the longest implant applicable is not always the best decision (Rokn et al., 2011).,,
After a thorough investigation of Barikani et al. (2014), the only parameter that seems to increase the length factor's influence on stability measurements is the bone type. Although implant length did not have any significant influence on primary stability when there was a high bone quality on the implant side, in cases of insufficient bone quality, an increase in implant length increased implant primary stability (Barikani et al., 2014). Therefore, the researchers concluded that in low-quality bone types with an inadequate bone height, bone augmentation should be performed instead of placing short implants.
Vidyasagar et al. analyzed dental implant stability at Stage I and II surgery relative to length, diameter, arch location as measured using RFA.
Some surgical techniques for implant site preparation have been advocated that influences implant primary and secondary stability values. The variety of techniques for implant placement are: (1) undersized drilling technique, (2) osteotome technique, (3) Piezoelectric bone surgery, (4) flapless implant placement, and (5) Osseodensification using Densah burs. The undersized drilling surgical technique increases lateral compression during insertion resulting in higher stability. Modification of conventional techniques such as the use of small final drill diameter and bone condensing techniques increased the implant stability. Despite the increasing research in recent years, so far there has been little investigation into the influence of implant bed preparation techniques on RFA values., Quesada-García et al. (2012) compared ISQ for implants placed in beds prepared according to the bone condensing or the bone drilling technique, with or without irrigation. The more commonly used technique for dental implant placement is the conventional bone-drilling one. However, some authors have suggested superior outcomes following a bone-condensation technique where the bony walls of the implantation site are progressively condensed to compensate for a lower bone quality when needed (Marković et al., 2013).
Data reported by Marković et al. (2013), indicate that compared to bone-drilling technique, bone-condensing technique significantly increased primary implant stability in low-density bone regardless of the macro design of the implant used. This increased stability could be due to changes in the micromorphology of peri-implant trabecular bone caused by apico-lateral condensation.
Stacchi conducted a study to longitudinally monitor changes in implant stability using different site preparation techniques: twist drills versus piezosurgery during the first 90 days of healing. Ultrasonic implant site preparation resulted in a limited decrease of ISQ values and in an early shifting from a decreasing to increasing implant stability, when compared to the traditional drilling technique.
Krafft T et al (2013) evaluated the efficacies in using osteotomes for implant bed preparation, their effect on material properties of bone and primary implant stability as compared to conventional implant bed preparation using burs. Use of osteotomes led to higher implant stability values for all the parameters studied except in trabecular bone. Dos Santos et al. (2009) conducted an investigation to assess the influence of design and surface morphology on the primary stability of implants. The insertion torque and RFA were used to measure the primary stability as an indicator of osseointegration in an immediate/early loading protocol.
Ostman et al. conducted a study to evaluate primary stability by RFA and correlate its measurements with surgical technique, implant design and patient.
Öncü and Alaaddinoğlu conducted a study to compare the stability of dental implants inserted in a one stage protocol with or without platelet-rich fibrin (PRF). Therapeutic applications of PRF led to faster titanium implant osseointegration, which improves implant stability.
Al-Juboori and Al-Jubooriconducted a study to compare the effects of the flapless (FL) and full-thickness flap techniques on implant stability. Therefore, the study proves that periosteum preservation during the FL procedure will speed up bone remodeling and result in early secondary implant stability as well as early loading.
Osseodensification introduced by Salah Huwais 2013, a novel surgical technique that creates an autograft layer of condensed bone at the periphery of the implant bed by the aid of specially designed burs rotating in a clockwise and anticlockwise direction. osseodensification burs have been designed to work in a non-subtractive manner, work in a non-cutting mode due to negative rake angle then expand the osteotomy and smoothly compacting bone in the periphery. Podaropoulos osseodensification is a new promising procedure for enhancing bone density around dental implants and increase primary stability since the achievement of primary stability is of utmost importance for osseointegration. Trisi et al. evaluated the efficacy of osseodensification technique and stated that this procedure enhances bone density, ridge width, and implant secondary stability. Lahens et al. assessed the effect of osseodensification method on initial stability and early osseointegration of endosteal implants with conical or parallel wall design. He stated that higher primary implant stability values for osseodensification were observed relative to regular drilling technique regardless of implant geometry. Bone to implant contact ratio was also higher when osseodensification technique was used than regular drilling techniques. This could be attributed to densification of autologous bone debris at the bone walls.
A strong correlation exists between implant stability and time as a function of an increased stiffness resulting from new bone formation and remodeling. The increase or decrease in implant stability can be extrapolated to the changes occurring at the bone-implant interface during the early healing phase. In the initial bone remodeling phase, bone, and necrotic material are resorbed by osteoclastic activity, which is reflected by a reduction in ISQ value. After this, phase new bone apposition is initiated by osteoblastic cells.
One stage and immediately loaded implants have demonstrated an initial decrease of implant stability which reverses after 3 months due to healing and remodeling process of new bone. The slow increase of implant stability between the time of implant placement and 3–4 months has been reported by Cochran et al. This process of increase in stability has a correlation with strengthened bone formation concept around believing that deposition of lamellar bone into grids in human woven bones begins at the 6th week and continues till 18th week. Zix and Kessler L. concluded that a mean ISQ value of 64.5 ± 7.9 was found to be representative of stable implants at any given point of time. After the implant placement till the time of loading, implants show variation in stability. Barewal 2003 proposed that implant stability is minimum between 3 and 8 weeks following implant placement, irrespective of the type of bone.
According to Sennerby and Roos, ISQ value of about 60–70 indicates clinical success, whereas values <45 are indicative of implant failure. A similar attempt was made by authors to determine the minimum implant stability that would enable functional loading and success without jeopardizing implant outcome. However, such thresholds still lack sufficient evidence. There are varied opinions regarding the exact timing of the greatest change in post insertion stability of an implant.
Positioning of the Osstell implant stability quotient probe and implant stability quotient values
Literature with regard to implant stability measured by the Osstell device in different directions is very scarce.,,,, The manufacturer recommends the use of two directional measurements that are approximately perpendicular to each other to secure the highest and lowest ISQ values., However, the physical presence of the adjacent teeth may complicate the clinical measurements in the mesiodistal direction. The contact-free metal peg allows magnetic RFA assessments from any direction, but results of such studies have shown wide variability with Park JC et al. disputing that ISQ values are reproducible irrespective of instrument positioning showing a slight difference with ISQ values being higher when measured mesiodistally.,, This wide discrepancy suggests that the measurement of the stiffness of the bone/implant complex in one direction by the use of RFA reflects the stability of an implant only partially because implant–bone fusion occurs at 360° around a fixture and implant stability is a general reflection of this fusion.,
| Conclusion|| |
This literature review highlights the importance of the various factors influencing both primary and secondary stability. Successful implant integration is essential for achieving triumphant primary stability. Bone quality and quantity, implant geometry, and surgical technique adopted may significantly influence implant initial stability and overall success rate of dental implants. The extent of implant stability may also depend on the situation of the surrounding tissues. Impaired primary implant stability has been shown to jeopardize the osseointegration process. Although there are many techniques to measure implant stability that have been extensively used in clinical research for the past two decades. Nonetheless, from available literature, there is still a lack of precise information on the correlation between implant stability values and the short- and long-term implant outcomes. Different authors have attempted to establish thresholds for primary and secondary stability and highlighted the factors influencing to predict higher risks for implant failure. Only repeated measurements over a longer period would have clinical significance and prognostic value.
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Conflicts of interest
There are no conflicts of interest.
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