# In Vitro Preliminary Evaluation of Bacterial Attachment on Grooved and Smooth Healing Abutments
## 4 Discussion  
The effect of depth grooves on healing abutments on bacterial adhesion has hardly been evaluated; the present in vitro study reveals, for the first time, their negative effect, by significantly enhancing bacterial adhesion. Previous reports have shown that surface modifications on dental implants and abutments play a relevant role in bacterial adhesion [3]. The chemical and physical surface characteristics of trans-gingival implant components significantly influence bacterial attachment. The control of bacterial infection in the peri-implant soft and hard tissues is critical for the long-term stability of implants supporting oral rehabilitation [4; 10; 21; 22]. There are no previous reports concerning the relationship of the healing abutment macro-morphology (machined or grooved), used in dental implant procedures, to clinical and microbiological parameters; however, it is clear that bacterial plaque negatively affects peri-implant tissue stability [22]. Our results demonstrate the significantly larger bacterial attachment of both strains in the grooved areas compared to in the smooth areas of the healing abutments, especially of _F.n_, which was 100 times larger. Our results are in accordance with those of [PERSON] et al. that showed the significant accumulation of pathogenic bacteria (_F. nucleatum_ and _A. actinomycetemmitans_) on moderate-roughness compared to minimal-roughness implant surfaces [23]. Peri-implantitis presents a heterogeneous microbiota, where perio-pathogenic bacteria such as _Porphylomonas gingivalis_ and Prevotella intermedius/nigrescens together with asaccharide anaerobic Gram-positive rods and other Gram-negative rods may be found [24]. The treatment of peri-implantitis is mainly based on different mechanical and physical means to remove biofilms from the implant surface [25]. Healing abutments are usually placed following a surgical intervention, such as implant placement or uncovering. In a recent randomized, controlled study, either micro-grooved or machined healing abutments were placed. After nonsurgical treatment and the reconstitution of oral hygiene measures, the incidence of peri-implant mucositis was found to be significantly lower at the non-grooved abutments [26]. Bacterial colonization, as found in this in vitro study, was enhanced in grooved healing caps. Bacterial accumulation following implant uncovering might induce pro-inflammatory events in the mucosa, jeopardizing optimal healing. Epithelial cell attachment may prevent the bacterial invasion of titanium surfaces; however, early bacterial colonization on these surfaces may, in turn, downregulate this effect. Peri-implant soft tissue clinical maturity is apparently established as early as four weeks  
Figure 7: _Porphylomonas gingivalis_ growth on the inner aspect of the grooved surface. Note the high bacterial count in this area (magnification, \(\times\) 2500). following implant placement in a one-stage surgical protocol, while the newly created peri-implant crevices are colonized by bacteria within two weeks [27]. Soft tissue healing and maturation around dental implants placed in a one-stage protocol may be at greater risk, since bacterial plaque can cause inflammation, which negatively affects osseointegration. In the present study, only two types of bacterial lines with known morphology were tested to avoid result masking from full plaque presenting wide morphologic variations. Since bacteria are present within the implant-abutment connection, one-stage dental implants become contaminated even during the first two postoperative weeks. These microorganisms can penetrate the sulcus around the fixtures and disrupt healing and osseointegration [28; 29; 30]. Using machined smooth abutments, as was demonstrated in the current study, may minimize bacterial adherence, which impairs osseointegration, especially in one-stage dental implants.