Osseodensification- the ideal path to accomplish complete osseointegration

NTRODUCTION

Dental implants are increasingly used in the present times to provide comprehensive rehabilitation for edentulism. Osseointegration is defined as the direct anchorage of an implant by the formation of bony tissue around it without growth of fibrous tissue at the bone-implant interface.¹ It is achieved after surgical placement of an implant through bone modeling and remodeling process.^2,3 For successful osseointegration and functional prosthetic superstructure, it is crucial to obtain optimum primary stability at the time of implant placement. The factors determining primary implant stability are the qualitative and quantitative aspects of the bone at the implant site, the surgical protocol followed, macro and micro design of the implant.^4-7

Most implant failures occur due to lack of osseointegration which may be the result of insufficient initial contact with the surrounding bone.8 The importance of primary stability is that it avoids any micro movement during the initial bone remodeling (Coelho and Jimbo, 2014).⁹ The primary stability achieved is maximum at the time of implant insertion, which then gradually decreases over time.¹⁰ The rate of secondary stability is again dependent on the extent of bone remodeling. Thus this crucial factor namely bone remodeling rate is the key for the transition from primary to secondary stability and relies on the inherent patient and implant design factors.¹¹

The density of bone correlates with its quality and quantity of the implant interface.^5,12 Both the hard and soft tissue parameters namely; mineral density and collagen integrity will determine the bone strength. All the above mentioned factors accentuate the importance of preserving the bone bulk during osteotomy preparation so as to obtain long term clinical success.

Clinical Considerations

Over the years, several surgical techniques have been developed to preserve the existing bone volume and increase its density, especially for low density bone. Sennerby et al has suggested that primary implant stability might be improved in low density bone by omission of the stage of bone tapping. Other authors have suggested under preparation of the implant osteotomy site to improve primary stability.^12,13 A study by Degidi et al¹⁴ reported that a 10% of undersizing the implant osteotomy site with respect to the diameter of the implant could result in enhanced primary implant stability in poor quality bone. There is also stepped osteotomy technique wherein, the under preparation is restricted only in the apical area of the implant site.¹⁵

More aggressive surgical protocols in the form of bone condensation with osteotomes have been employed.¹⁶ Here cylindrical steel instruments are used along the osteotomic walls to improve the bone density. Though the use of the osteotomes in poor density bone causes fracture and condensing of bony trabeculae, there is no improvement in periimplant bone density (%BV) or implant stability.^17,18 In fact, it even causes delayed secondary healing due to obstruction of osseointegration process by the debris.¹⁹

In an attempt to tackle all of these pitfalls, which can occur during the conventional subtractive drilling technique, an innovative, biomechanical, non-excavation osteotomy preparation called as Osseodensification has been developed by Salah Huwais in 2013. It utilizes specifically designed densifying burs are called Densah burs.²⁰ These burs induce a compression wave at the point of contact (bone drill), producing a controlled bone deformation through the inherent nature of bone tissue viscoelasticity and viscoplasticity.^20-23

Fig. 1 Negative rake angle of osseodensification burs (additive drilling).

Fig. 2 Positive rake angle of conventional burs (subtractive drilling).

Fig. 3 Densification drill design.

Rake angle is an important parameter of the design of the drill and is of three types, namely, positive, negative and zero. The traditional cutting (subtractive) drills have a positive rake angle (Fig.2) that eliminates the bone residue at the osteotomy site. On the contrary, in the non-cutting (additive) drills osseodensification (OD), there is a negative rake angle that results in compaction of osteotomy site walls by the lateral displacement of bone, thereby increasing primary stability (Fig. 1 and 3).^20,24,25 The residual bone remnants act as nucleating surfaces for osteoblasts around the implant, functioning as autograft facilitator for osseointegration.^20,21,22

The principle of Osseodensification procedure

The densifying burs can be used with a standard surgical engine, at a speed range of 800-1500 rpm in dual mode. It can be used in the counterclockwise direction (Densifying mode) to densify bone (Fig. 5)or in the clockwise cutting direction (Cutting mode) as a drill to cleanly cut the bone if needed (Fig. 4) An apical pressure coupled with profuse saline irrigation is used at the point of contact, which creates a compression wave inside the osteotomy site. This compression wave with the fluting creates a densified layer along the walls and base of the osteotomy site, through compaction and autografting. This helps in the expansion of bony ridges also.

Fig. 4 Osseodensification burs in Clockwise motion (Cutting mode).

Fig. 5 Osseodensification burs in Counterclockwise motion (Densifying mode).

It is recommended that the burs should be used in a bouncing motion (in and out), which creates a rate-dependent stress and produces a rate-dependent strain subsequently. The profuse saline irrigation gently pressurizes the bone walls and facilitates increased bone plasticity and bone expansion.^20,21,25 Thus the advantages of this technique are:

• Preservation of the bone volume

• Hastens the healing process through conservation of the bone matrix and the cells

• Continuous replacement of the autogenous bone graft matrix along the surface of the dental implant

• Increased insertion torque and bone to implant contact percentage

• Ridge expansion

• Higher primary implant stability

Discussion

Successful osseointegration relies on clinical aspects of the implant site preparation like insertion torque and primary stability. It also depends on the histomorphic features like bone to implant contact percentage (BIC%), bone area fraction occupancy (BAFO) and the quality of bone.²⁷

A case report by Huwais S et al in 2015 on osseodensification where ridge expansion was performed, it was shown that radiographically the alveolar bone crest and the density of the bone was maintained over 2 year period and there was no collapse of the ridge.²⁶ Another similar case report a year later demonstrated that there was enhanced implant stability and efficient expansion of ridge in both the jaws post osseodensification.²¹

There are a few animal studies, one by Trisi et al, and a more recent one by Lahens et al where the bone volume percentage (BV%) around implants were assessed and osseodensification showed superior BV% and also reduced micromotion.^{22, 31} Bone to implant contact (BIC) and bone area fraction occupancy (BAFO) are a more precise measure for osseointegration and were evaluated in a study by Lopez et al(2017) and Oliviera et al (2018), the results showed an increase in these values.^21,28,30 A histomorphometric study by Slete et al compared osteotomy preparation using standard extraction drilling (SD), Summers osteotomes (SO), and osseodensification technique (OD) in porcine tibial bones. The BV% and BIC was found to be greatest in the osseodensification group.³²

As with any new technique, it is essential to study the adverse effects on the biologic tissues (i.e, bone). A study by Witek et al in 2018 showed no negative effects on the bone healing especially in the initial remodelling with osseodensification protocol both in the clockwise and counter clockwise direction.³³ It is absolutely necessary to keep the implant site cool with adequate coolants so as to prevent the ensuing cell death which can occur beyond 47˚C for one minute (critical temperature). Meyer et al has shown a decided difference in the temperature. There was a difference of only 3˚C rise in temperature in the osseodensification group but it was well within the range of safety.

A prospective study by Gasper et al where a total of 97 implants in 41 patients were placed exclusively in the maxilla.²⁹ More complicated clinical situations namely, narrow alveolar ridge with ridge expansion, alveolar ridge regeneration, sinus lift procedures prior to implant placement and full arch rehabilitation with immediate loading were included. There was a clear cut advantage in using this densification technique for osteotomy in terms of higher of insertion torque and implant stability post ridge expansion. Even after immediate loading in full arch, the values of for implant stability were greater. Contrary to the above studies, an in-vitro study in 2018 did not find any statistically significant difference between effects of osseodensification and conventional drilling on implant stability.³⁴ Although, there was no standardization in the thread designs of the various implants used.

A recent in vitro study by Alifarag et al comapared osseodensification techniquie with conventional drilling technique using biomechanical and histomorphometric analysis and observed extensive new bone formation in the Counterclockwise samples of osseodensification technique. They concluded that the significantly higher insertion torque and removal torque values observed for the osseodensification techniques were most likely due to the compaction-autografting and the formation of the autograft bone wall comprised of compacted native bone which was evident by the higher BIC and BAFO for the osseodensification group histomorphometrically.²⁴

A case report by Machado et al in 2018 reported a high ISQ value (ISQ > 70) in posterior maxilla with the osseodensification technique. They also demonstrated the corticalization of the surgical alveolus by the osseodensification technique in trans operative CBCT examinations and concluded that there was gain in primary stability and densification of osteotomy site trans and post clinical case of dental implant immediate loading using the technique of osseodensification .³⁵

In a case report by Gasper et al, osseodensification technique was employed for implant placement at site with reduced bone height, through a minimally invasive technique of sinus lift by crestal approach. It was concluded that osseodensification protocol can be applied for maxillary sinus lift by crestal approach in a simple, safe and predictable way with reduced morbidity.³⁶

Conclusion

Conventional osteotomy preparation is fraught with its own set of disadvantages. Thus, osseodnsification ia s novel, specialized ingenious technique which tackles all these disadvantages and converts them into advantages.it expands the ridge at the osteotomy site and provides a dense bony tissue. All of these contribute to an overall increased percent of bone volume and bone to implant contact, thus providing a reinforced primary stability. It could be a promising solution to commonly encountered low density bone which could be a hurdle to implant success. It is important to consider that this technique is mostly advocated to be used in a poor density bone (such as D4 in maxillary posterior region) where achieving good primary stability with conventional techniques is a challenge to the surgeon. However, in areas with higher bone density (such as D1 in mandibular anterior region), densification could lead to pressure necrosis around the osteotomy but there is need of further investigations for the same. Also long term studies should be conducted to assess success outcome of this technique.