Bone regeneration at Straumann® Bone Level implants with SLActive® surface – histological and clinical experiences

Drs. F. Schwarz, D. Ferrari, M. Wieland, and J. Becker discuss study results regarding Straumann Bone Level implants

A recent review paper3 has summarized the potential of hydrophilic surface modifications (Straumann® SLActive®) to support tissue integration of titanium dental implants.

One part of this review paper focused on the pattern of wound healing at dehisced implants. In particular, previous experimental studies performed in dogs have demonstrated that Straumann Soft Tissue Level implants with SLActive surface supported bone regeneration in acute-type buccal dehiscence defects at submerged implants without the additional use of guided bone regeneration or bone augmentation procedures.4 At 2 weeks, newly formed trabeculae of woven bone, originating from both the lateral walls and the bottom of the defect areas, started to invade the dehiscence area. After 12 weeks, SLActive implants were surrounded by firmly attached, parallel-fibered woven bone. The newly formed buccal aspects of the ridge reached the level of the corresponding oral aspects. In contrast, wound healing at SLA implants was predominantly characterized by the formation of dense connective tissue at 2 and 12 weeks, without significant increases in mean new bone height or bone-to-implant contact.4 Similar results were also observed at non-submerged Soft Tissue Level implants with SLActive.5 In particular, immunohistochemical analysis after 1 week of healing in dogs revealed pronounced proliferation of blood vessels adjacent to SLActive implants, even reaching the central compartment of the defect area. In contrast, at SLA implants, the primary meshwork of newly formed vascular structures was located at the bottom and lateral aspects of the defect area. Histological and immunohistochemical observations have pointed to greater stabilization of the blood clot at SLActive implant surfaces, thus promoting the in-growth of new blood vessels from the adjacent alveolar bone. Basically, the blood clot acts as a physical matrix that induces and amplifies the migration, proliferation and differentiation of endothelial cells, subsequently leading to improved angiogenesis.6 Osteogenic cells have also been observed to arise from pericytes adjacent to small blood vessels in connective tissue,7-9 thus explaining the improved bone formation at SLActive implants. At 8 weeks, non-submerged and submerged SLActive implants revealed significantly higher mean values of new bone height, area of bone formation, and bone-to-implant contact than corresponding SLA implants. However, within the SLActive groups, bone regeneration was significantly improved at submerged implants.5

Accordingly, it was concluded that SLActive titanium implants supported bone regeneration in acute-type buccal dehiscence defects, and a submerged healing process further improved the healing outcome.5 A similar pattern of bone regeneration was also observed when Soft Tissue Level implants with SLActive were combined with different types of barrier membranes or bone substitutes.10,11 Blood vessels and the subsequently formed woven bone invaded the defect area in a coronal direction, primarily along the surface of SLActive implants.

Recently, the Straumann Bone Level Implant was introduced as a two-part implant to support bone preservation for predictable esthetic results.12,13 Its specific macrodesign coupled with the SLActive surface might provide a promising environment to support bone regeneration even at advanced defect sites as observed with Straumann Soft Tissue Level implants with SLActive. Accordingly, the aim of a very recent experimental pilot study performed in dogs was to assess the influence of the defect size on bone regeneration at Straumann Bone Level implants with SLActive. Standardized (width: 4 mm; depth: 1–2 mm) buccal dehiscence-type defects of different sizes (i.e. height: 7–8 mm; 8–9 mm; and 10 mm) were surgically created following implant site preparation in the lower jaws of dogs. After 4 weeks of submerged healing without the additional use of bone-graft substitutes or barrier membranes, dissected blocks were processed for histomorphometrical analysis (i.e. coronal extent of newly formed bone in contact with the implant surface, area of new bone fill, percentage of bone-to-implant contact in the defect area, and percentage of linear defect fill).

In general, wound healing was regarded as uneventful at all sites. There were no signs of any wound infections or dehiscences. Irrespective of the initial defect size, histomorphometrical analysis revealed a significant increase of all parameters investigated. The mean percentage of linear defect fill varied between 54 and 65%. In all specimens, the newly formed woven bone extended along the bottom of the defect in a coronal direction and showed close contact to the titanium surface (Figures 1A–1F). These values were within the range of the data reported for either non-submerged/submerged Straumann Soft Tissue or Bone Level implants with SLActive (Table 1). In these studies, however, the defects had a moderate height of 4 mm.

Based on these findings, it might be suggested that Bone Level implants with SLActive surface have a high potential to support bone regeneration even at advanced buccal dehiscence-type defects. Even though the surgical creation of standardized defects in dogs is a commonly used model to evaluate bone regeneration at titanium implants, acute-type defects have a certain tendency to spontaneous healing. Accordingly, from a clinical point of view, the defect model employed in these animal studies on SLActive implants may not reflect the biological situation encountered at chronic-type defects.

So far, however, clinical experience suggests that a combination of Straumann Bone Level implants with SLActive and simultaneous guided bone regeneration provides a high level of predictability to support hard-tissue formation even at advanced defect sites (Figures 2A–2L). These findings are also in agreement with the results obtained previously with Straumann Soft Tissue Level implants with SLActive surface.

References

1. Department of Oral Surgery, Heinrich Heine University, Düsseldorf, Germany

2. Institut Straumann AG, Basel, Switzerland

3. Schwarz F, Wieland M, Schwartz Z, Zhao G, Rupp F, Geis-Gerstorfer J, Schedle A, Broggini N, Bornstein MM, Buser D, Ferguson SJ, Becker J, Boyan BD, Cochran DL (2008). Review: Potential of chemically modified hydrophilic surface characteristics to support tissue integration of titanium dental implants. J Biomed Mater Res B Appl Biomater

4. Schwarz F, Herten M, Sager M, Wieland M, Dard M, Becker J (2007). Bone regeneration in dehiscence-type defects at chemically modified (SLActive®) and conventional SLA titanium implants: a pilot study in dogs. J Clin Periodontol 34:78-86.

5. Schwarz F, Sager M, Ferrari D, Herten M, Wieland M, Becker J (2008). Bone regeneration in dehiscence-type defects at non-submerged and submerged chemically modified (SLActive®) and conventional SLA titanium implants: an immunohistochemical study in dogs. J Clin Periodontol  35:64-75.

6. Liu HM, Wang DL, Liu CY (1990). Interactions between fibrin, collagen and endothelial cells in angiogenesis. Adv Exp Med Biol 281:319-331.

7. Long MW, Robinson JA, Ashcraft EA, Mann KG (1995). Regulation of human bone marrow-derived osteoprogenitor cells by osteogenic growth factors. J Clin Invest 95:881- 887.

8. Reilly TM, Seldes R, Luchetti W, Brighton CT (1998). Similarities in the phenotypic expression of pericytes and bone cells. Clin Orthop 95-103.

9. Rickard DJ, Kassem M, Hefferan TE, Sarkar G, Spelsberg TC, Riggs BL (1996). Isolation and characterization of osteoblast precursor cells from human bone marrow. J Bone Miner Res 11:312-324.

10. Schwarz F, Herten M, Ferrari D, Wieland M, Schmitz L, Engelhardt E, Becker J (2007). Guided bone regeneration at dehiscence-type defects using biphasic hydroxyapatite + beta tricalcium phosphate (BoneCeramic) or a collagen-coated natural bone mineral (BioOss Collagen): an immunohistochemical study in dogs. Int J Oral Maxillofac Surg 36:1198-1206.

11. Schwarz F, Rothamel D, Herten M, Wustefeld M, Sager M, Ferrari D, Becker J (2008). Immunohistochemical characterization of guided bone regeneration at a dehiscence-type defect using different barrier membranes: an experimental study in dogs. Clin Oral Implants Res 19:402-415.

12. Jung RE, Jones AA, Higginbottom FL, Wilson TG, Schoolfield J, Buser D, Hämmerle CH, Cochran DL (2008). The influence of non-matching implant and abutment diameters on radiographic crestal bone levels in dogs. J Periodontol  79:260-270.

13. Buser D, Halbritter S, Hart C, Bornstein MM, Grütter L, Chappuis V, Belser UC. Early implant placement with simultaneous GBR following single-tooth extraction in the esthetic zone 12-month results of a prospective study with 20 consecutive patients. J Periodontol (in press).

14. Schwarz F, Ferrari D, Sager M, Wieland M, Becker J. Comparative study on bone regeneration in dehiscence-type defects at chemically modified hydrophilic (SLActive®) or nanostructured (NanoTite®) titanium implants. An experimental study in dogs (study finished).