How implant and abutment design influence clinical outcomes
Clinical outcomes can be evaluated by a variety of diverse parameters. Does implant or abutment design matter in relation to the desired outcome? And what are the roles of biology, surgery and prosthodontics on clinical outcomes?
A retrospective study found that shorter abutments were associated with increased bone loss (Vervaeke et al., 2014). Short abutments are typically used when implants are positioned too high for the bone level and/or when the covering mucosa is thin. In these cases, bone remodelling can result in thread exposure. In a prospective randomized split mouth study it was confirmed that placing implants deeper, to allow 4 mm of soft tissue attachment, yielded an absence of thread exposure and less marginal bone loss (Vervaeke S, Matthys C, Nassar R, Christiaens V, Cosyn J, De Bruyn H. J Clin Periodontol. 2018 May;45(5):605-612. doi: 10.1111/jcpe.12871. Epub 2018 Feb 23). However, thread exposure has not yet been clearly associated with clinical peri-implantitis given the short term follow-up.
Preserving marginal bone
Implant macro design may also play an important role in bone loss. When the thread pitch is too high, bone loss increases and implant survival rates decrease; 0.6mm is considered the optimum inter-thread distance (Vandeweghe et al., 2012a).
Both machined and rough implant surfaces showed the same outcomes in immediate and conventional loading, regardless of design. Microthread necks did not make a difference to marginal bone level preservation (Van de Velde et al., 2010; Ravald et al., 2013).
Several changes have been made to macro designs in an attempt to improve primary stability. The surgical protocol should be adapted to each patient and their individual bone morphology. To this end, drills and steps for each procedure should be patient-guided instead of company-guided. The speaker cautioned that the learning curve when moving to another implant design should also be taken into account. Primary stability is a well-recognised benefit for immediate loading; but in delayed loading protocols, macro design modifications are not as important as we might think.
A recent study showed that implant-abutment interface does not influence pink aesthetic scores (PES) compared with other implant designs. The study did find that the interface appears to have a negative effect on marginal bone loss in flat-to-flat and platform switching designs compared with conical designs (Cooper et al., 2019). However, it should be noted that some features of the study may not have been well controlled, and so we cannot definitively conclude that conical designs are associated with less bone than other kinds of platforms.
It has been demonstrated that platform switched implants can better maintain marginal bone levels (Vandeweghe et al., 2012b). When used with correct biological implant placement approaches, according to soft tissue thickness, platform-switching may play an important role in compromised patients (smokers, periodontally involved patients, diabetics, etc) (fig 15–16).
Some implants have angle correction designs which allow us to position implants so that they are surrounded by bone, without an unfavourable prosthetic axis and allowing us to avoid fenestration. These implants are especially recommended in the anterior maxilla (Vandeweghe et al., 2012c; Vandeweghe et al., 2013). Results have shown that buccal bone performations requiring bone regenerative techniques are avoided when this angular connection within the implant is used, because the implant threads are completely covered by bone. However, crestal bone thickness was not as wide as simply placing the implant in a more palatal position. Angle-corrected implants have been also been the subject of a study investigating all-on-four implants (Van Weehaeghe et al., 2017).
Reverse tapered body
The speaker described another new implant design which has a wider apical half and thinner coronal half. This allows about 50% greater primary stability to be achieved in extraction sockets than conventional tapered implants with the same dimension, thus facilitating immediate loading. In combination with the angular connection within the implant, this furthermore improves the aesthetic outcome (fig 17–18).
Wider body implants
In the posterior area, immediate implant placement techniques may be improved by using an implant with a wider diameter than is conventional. With this design, implant geometry is optimised to engage the perimeter of the molar socket and fill it. In this way, remarkable primary stability can be achieved, allowing immediate loading in most cases (Hattingh et al., 2018) (fig 19).
Thin implants are being investigated in ‘fragile’ patients who are considered unsuitable for conventional implant designs. They can be placed in a minimally invasive way and, although the failure rate was around 16%, they have been shown to improve the quality of life of these patients with compromised bone volume (fig 20).
A recent clinical study made a quadruple comparison: implants with and without microthreads, and implants with external and internal connections. The same solid conical abutment was fitted in all groups at the moment of implant placement. After one year no differences were reported in bone remodelling, regardless of implant design (Glibert et al., 2018). Bone response does not seem to be influenced by these design factors; correct biological positioning of implants seems to be the main prognostic factor for preserving marginal bone.
Several studies have been conducted on abutment design and have come to the same conclusion: convex/concave and regular/curved abutments all show similar marginal bone loss levels and mucosal margin positions (Patil et al., 2014; Koutouzis et al., 2019). Additionally, abutment modifications do not affect the patient’s satisfaction with the aesthetic outcome (Patil et al., 2016, Patil et al., 2017).
The angle of the abutment emergence profile may influence marginal bone loss, but not the level of mucosa. Abutments with an angled emergence profile of more than 30º can encourage marginal bone loss and may also be considered a risk indicator for peri-implantitis. Further, convex profiles can pose an additional risk for bone‐level implants, but not for tissue‐level implants (Katafuchi et al., 2018) (fig 21).
These are the conclusions of the presentation:
- biology determines long-term clinical outcomes
- commercially driven dogmas are not scientifically proven
- there is not such a thing as ‘one implant for all indications’ – an individual approach is best for implant selection
- angled implants combine the best surgical option with the best prosthetic option
- site-specific implants are growing in popularity, as they can enlarge indications and enhance outcomes in compromised situations
- large emergence profiles and cemented restorations have a higher risk for peri-implant issues, so it is generally better to screw!
- it is not the engineering algorithms, but the clinical algorithms which will prevail