From Rough Surface to Peri-implantitis, Hybrid Implants and Subcrustal Implant Placement: A Mini Review of Last Decade Research and Clinical Findings in Implant Dentistry

Continuous effort to safely apply occlusal load immediately, or as early as possible, led thru improved titanium surfaces to give more rapid osseointegration on a bigger implant surface (BIC). Around year 2000 increasing implant roughness became a key with a wish to inoculate active, bone growing factors in it. Surprisingly after few years a totally new phenomenon of progressive bone loss around implants was observed and coined ‘peri-implantitis’ as a parallel to ‘periodontitis’. Similar pathogens became a suspect however exposed rough surface is the main trigger. Retrospective studies of machined implants led to hybrid implant design on one hand and recommendations of subcrestal placement of fully rough implants on the other(Figure 1). Additionally, more emphasis has been put on surgical technique and timing.


Bacteria Comes Secondary
Further Albrektsson et al. Indicate that once severe marginal bone loss is developed, a secondary biofilm-mediated infection may follow as a complication to the already established bone loss. The extend of this infection and subsequent bone loss was related to the implant roughness by Albouy, Abrahamsson and Berglundh [2][3][4][5] in their experimental study of ligature induced peri-implantitis in dogs.

Machined Surface Limits Biofilm Formation and May Stop Periimplantitis
The researchers conclude that the amount of bone loss that occurred during the plaque accumulation period after ligature removal was significantly larger at implants with a rough (TiUnite surface) than at implants with a machined (turned) surface. The histological analysis revealed that the vertical dimensions of the lesion, the pocket epithelium and the apical extension of the biofilm were also significantly larger at rough implants. Another words, when the ligature was removed on machined implants the bone loss was stopped while it continued on the rough surface.

Has this Been Demonstrated Clinically on Patients with Periimplantitis?
Schwarz et al. [6] have quite extensively presented and published follow ups of periimplantitis treatment where they compared different methods of surface decontamination

Modern Research in Dentistry Abstract
Continuous effort to safely apply occlusal load immediately, or as early as possible, led thru improved titanium surfaces to give more rapid osseointegration on a bigger implant surface (BIC). Around year 2000 increasing implant roughness became a key with a wish to inoculate active, bone growing factors in it. Surprisingly after few years a totally new phenomenon of progressive bone loss around implants was observed and coined 'peri-implantitis' as a parallel to 'periodontitis'. Similar pathogens became a suspect however exposed rough surface is the main trigger. Retrospective studies of machined implants led to hybrid implant design on one hand and recommendations of subcrestal placement of fully rough implants on the other( Figure 1). Additionally, more emphasis has been put on surgical technique and timing.

MRD.000623. 5(5).2020
as an add-on to standard surgical treatment of implantoplasty. Although laser decontamination did not prove to be any better than saline solution in their study the overall treatment success of stopping progression of periimplantitis was achieved in over 80% of cases. The result therefore could only be attributed to standard implantoplasty which is grinding exposed contaminated surface of an implant with a dimond drill on high speed. The roughness of the surface after implantoplasty is very similar to machined surface and also interestingly among the implants treated there were no machined (Branemark) implants but only implants with rough surface.

Hybrid implants
The risk of rough surface to form biofilm has already been indicated in 1993 by Dennis P Tarnow [7] who already then suggested a hybrid implant with a machined titanium surface in the coronal half and a rough titanium surface in the apical half. 'This will theoretically allow for minimal plaque accumulation at the crest if the implant becomes exposed to the oral environment'. Tarnow's idea for hybrid implants have become materialised after 25 years by Massimo Simion [8] who has also demonstrated that the rough surface is not any better forming bone than 'old' machined surface (Figure 1).

Figure 1: A prototype of a 3-hybrid implant with surfaces dedicated to 3 different tissue compartments.
Additionally, implant coated with double covalent layer of hyaluronic acid and its geometry modified with vertical grove to shred more bone chips during insertion.

Machined vs Rough
Simion et al. [8] conclude that 'the surface roughness may not be a key factor for successful osseointegration of immediately or early loaded implants' and that 'osseointegration follows a similar healing pattern with machined and oxidized implant surfaces. This common healing healing pattern observed by Simion et al. [8] in their histologic study was early bone formation around the bone chips which appear to be foci of osteogenesis. They observed that the bone began to grow on an implant surface if there was a bone chip there irrespective of the surface: machined or rough.

Surgical Technique
Considering above findings and high incidence of periimplantitis reported in the last decade-surgical technique changed towards limiting the risk of rough implant surface exposure. This includes subcrestal placement of fully rough implants as well as minimally invasive approach with one-time abutment concept. Also, palatal implant positioning and preventive tissue augmentations are the present measures to limit the risk of periimplantitis.

Conclusion and Considerations of Future Trends
Hybrid implants open a new perspective of applying surfaces dedicated to different tissue compartments. As machined surface is best safe coronally, rough in the middle may still give convenient friction and primary implant stability. The question remains about the apical portion of an implant that interfaces bone marrow. What would the best surface be there for the stem cells to migrate, spread and differentiate? How soon will we have growth factors spread on the implant surface and will it work as we desire? Some laboratory experiments in the past showed however that even if we inoculated BMP inside the pores of titanium discs the bone would vigorously grow around but not stick to the disc. Pouring however growth factors (rh PDGF-BB) into an implant osteotomy contributed in observable increase in BIC which was presented by Myron Nevins and David Kim, researchers from Harvard School of Dental Medicine. So far we observe that raw and fresh titanium surface, free from air hydrocarbonate contamination, may be most active and therefore some implants stored in sterile saline solution. Another interesting option is surface coating with Hyaluronic Acid [9] double covallent layer knowing that hyaluronic acid is an inter-cellular matrix building compound and therefore may facilitate osseointegration, but this needs to be confirmed best with further histology studies. If we stick to what we know which is that bone chips are foci of new bone formation in the space between an implant and native bonewe shall benefit from it clinically by modifying implant geometry to create more bone chips and also adding bone chips into osteotomy.