Abutment surface modifications
The speaker focused on the biology behind the interaction between soft tissue and implant-supported prostheses (fig 11).
State of the art
According to the concept of ‘biological width’ (Hermann et al., 2001), it is well known that supracrestal connective tissue is crucial for maintaining the vertical dimension of soft tissue around abutments and vertical bone levels around implants. Experimental and clinical research has demonstrated that soft tissue morphogenesis around abutments occurs between 8 and 12 weeks (Berglundh et al., 2007; Tomasi et al., 2014). In the sulcus, connective tissue is surrounded by epithelium that adheres to the abutment surface with a thin layer of proteoglycans (Iglhaut et al., 2014).
Some articles describe the pre-operative clinical characteristics of the soft tissue (Kan et al., 2010, Linkevicius et al., 2015). These articles describe thick and thin biotypes, but do not show any correlation between biotype and individual healing patterns. Regarding abutment material, a recent systematic review found no difference between titanium and zirconium abutments (Sanz-Sánchez et al., 2018).
Soft tissue integration has many variables: the host and their phenotype; the characteristics of the prosthetic material (aka ‘the guest’); the workflow we adopt; and the microbiome (‘the antagonist’).
There is no difference in the number of cells in thick and thin biotypes. Thick biotypes seem to have more extracellular matrix and a thicker lamina, which are involved in the formation of hyaluronic acid and other proteins potentially related to adhesion processes. Both phenotypes are determined by gene expression, and modulated by epigenetics via the synthesis of methyl and acetyl groups. These groups either deactivate or boost protein production respectively.
Some researchers have found that peroxisome proliferator-activated (PPA) receptors may be involved in soft tissue healing, which may explain why some cases heal correctly and others do not (Aghaei et al., 2016; Korbecki et al., 2019). When PPA receptor methylation was observed and highly expressed, even in thin biotypes, improved healing and increased connective tissue height was more likely. On the other hand, when there was no PPA receptor methylation or expression, a longer junctional epithelium and bone resorption was reported (fig 12–13).
The macro, micro and nano characteristics of abutment materials are important. Perhaps equally vital, however, is the timing of treatment. From the literature, it appears that clinicians have a strong influence over soft tissue healing during the prosthetic workflow stages (Tallarico et al., 2018).
In fact, repeated disconnection of abutments can disrupt tissue healing, and lead to a longer junctional epithelium (instead of connective tissue) being formed around the abutment. To prevent this from happening, the speaker proposed different strategies to maximise connective tissue adhesion to the abutment:
- Using an intra-surgical impression and ensuring the definitive abutment is ready at the time of re-opening
- An intermediate abutment can be used to transform bone-level implants in tissue-level implants
- A digital impression can also be taken at the time of implant placement, allowing the screw-retained crown to be prepared in advance of the second surgery
The macro morphology of the abutment also appears to influence soft tissue characteristics. A recent study comparing narrow and wide abutments found no differences regarding aesthetics or periodontal parameters, although narrow abutments showed less marginal bone loss (Canullo et al., 2019a). The speaker explained that the reason for this may be that connective fibres have more space and can better rearrange around the abutment, forming a stronger tissue seal.
Improved connective tissue healing was observed during early stages (3–6 months) in abutments with modified surfaces (Pesce et al., 2019). This is probably because tissue can be stabilised on the surface in a more coronal position, thus taking advantage of any grooves or surface irregularities (Piattelli et al., 2011). In the long term, however, rough surfaces did not seem to provide clinical advantages in soft tissue (unless used in cases involving ‘one abutment one time’ after bioactivation) (Canullo et al., 2019b).
Surface energy decreases over time, caused by atmospheric pollution and can even lead to new abutments becoming hydrophobic (Sawase et al., 2000; Canullo et al., 2013). Bioactivation of the abutment surface can improve cell adhesion quantitatively, in that a greater number of cells will be involved, and qualitatively, as a better arrangement of this adhesion can be achieved (Garcia 2017; Canullo et al., 2019c). Finally, bioactivation can be applied to a three-dimensional geometry of surfaces, leading to faster cell differentiation, clinically resulting in a larger band of connective tissue (Canullo et al., 2019d).
Bacteria compete with fibroblasts for space on the abutment surface (Neoh et al., 2012). When the abutment surface is decontaminated, fibroblasts can attach (even in cases involving rough surfaces) (Massucci et al., 2019). The speaker outlined a strict decontamination protocol which is recommended when placing the abutment and placing the prothesis.