Bone Regeneration: Foundational Techniques and the PASS Principle

Implant dentistry has become a cornerstone of prosthetic and aesthetic restoration yet achieving ideal results hinges on one critical factor: the presence of adequate bone. Often, dental professionals face situations where bone must be regenerated to meet the necessary dimensions for successful implant placement. This challenge brings them to a crucial question: With numerous regenerative materials and techniques available, what’s the best approach?

In a recent educational online event hosted by Dentsply Sirona Regenerative Solutions, Dr. Sausha Toghranegar, a periodontist, delved into this topic to understand why vital bone so crucial and which techniques, tools, and principles⁴ create high amount of vital bone for implants to integrate successfully. We summarize his lecture in this article.

Understanding the Importance of Vital Bone

As discussed by Dr. Toghranger, the foundation of successful implant dentistry is vital bone, which possesses a robust blood supply and cellular activity that helps to maintain peri-implant tissues¹. Implants require this vital bone with sufficient blood supply as well as cellular activity to maintain the surrounding marginal bone¹. The process of developing this vital bone involves various techniques and materials that can enhance bone regeneration, ensuring a stable and functional foundation for dental implants¹.

Practical Techniques and Tools for Socket Grafting

Dr. Toghranger recommends various techniques for preserving and regenerating bone. Atraumatic extraction methods are essential to preserve existing blood supply and cellular activity. Using the right tools helps in atraumatic extraction, preserving vital bone², including:

• Periotomes with different angles²
• Serrated or diamond-coated forceps²
• Long, thin diamond burs²

These tools allow for the careful removal of teeth and other structures without damaging the surrounding bone, creating an optimal environment for bone regeneration².

Blood Clot Formation and Bone Healing

Dr. Toghranger provided guidance on the extraction process: once the tooth has been extracted and the socket cleaned, the natural healing process starts with blood clot formation, essential for bringing in nutrients and cells necessary for regeneration³. This is followed by:

1. Granulation tissue formation
2. Early woven bone development
3. Mature lamellar bone formation
4. After a period of several months, depending on the size of the defect and socket, alveolar ridge formation

When a tooth is extracted, the patient can suffer from dimensional changes and bone loss. Without using bone grafting, there may be horizontal and vertical depressions in the bone and soft tissue, which complicate aesthetic and functional outcomes^5-9.

As discussed by Dr. Toghranger, the foundation of successful implant dentistry is vital bone, which provides a continuous blood supply and cellular activity to ensure long-term success^1,4. Implants require this vital bone with sufficient blood supply as well as cellular activity to maintain the surrounding marginal bone¹. Some believe that slowly substituted bone grafts such as cortical FDBA (Freeze-Dried Bone Allograft) or DBBM (Deproteinized Bovine Bone Mineral) occupy too much of the peri-implant bone and therefore reduce the percentage of vital and vascularized hard tissue^17-19. The consequence may be the increased susceptibility to marginal bone loss as suggested by some researchers^17-19.

The process of developing this vital bone involves various techniques and materials that can enhance bone regeneration, ensuring a stable and functional foundation for dental implants¹. If the goal is to develop more vascularized and natural bone tissues, then reducing the residual graft remnants will allow for more space for vital tissues. The use of a collagen scaffold that will be replaced by tissue over six months fits this concept^20-21 .

The PASS Principles for Bone Regeneration

To address horizontal and vertical bone loss, Dr. Toghranegar recommends following these principles⁴, a guiding framework for successful bone regeneration developed by Dr. Hom-Lay Wang and his team, standing for⁴:

• P – Primary wound coverage
• A – Angiogenesis
• S – Space maintenance
• S – Stability

Dr. Toghranegar recommends these principles, as he believes they enable solid guided bone regeneration.

Primary Wound Coverage

According to Dr. Toghranegar, primary wound coverage is essential but can be flexible depending on the situation¹⁴. For example, in socket preservation, achieving primary closure might not always be necessary and could be counterproductive. Overly aggressive closure could lead to the loss of keratinized tissue, which is valuable for peri-implant health³.

Angiogenesis

Blood supply is the cornerstone of bone regeneration¹⁵. Without adequate blood flow, graft materials will not integrate properly, leading to potential failure. In the maxilla, the porous, cancellous bone facilitates blood supply, while in the mandible, particularly the posterior region, the denser cortical bone presents challenges. Techniques such as decortication, which involves creating holes in the cortical bone, can enhance blood supply to the graft site⁴.

Space Maintenance

Maintaining space is critical to ensure that bone cells have the environment needed to proliferate⁴. Dr. Toghranegar’s “cup concept” illustrates this: an intact socket is like a cup that can hold graft material, while a socket with a missing wall is like a broken cup, unable to retain the material. In such cases, additional measures are needed to maintain space and promote bone cell activity⁴.

Stability

The stability of the graft and wound is crucial for successful healing⁴. Just as a broken bone needs a cast to heal properly, bone grafts need to remain immobile. Any movement can lead to soft tissue healing instead of bone regeneration⁴. Ensuring the stability of the graft material against the surrounding structures is vital for the formation of robust bone³.

Conclusion

As explained by Dr. Toghranegr, the foundation of successful implant dentistry lies in the presence of vital bone, which requires careful preservation and regeneration¹. “The PASS principle offers a structured framework for achieving robust bone regeneration⁴. By adhering to these principles and utilizing advanced techniques, dental professionals can enhance implant dentistry outcomes, helping to provide more stable and functional results for their patients.”

References

1. Ibrahim Elgali et al. Guided bone regeneration: materials and biological mechanisms revisited; Eur J Oral Sci. 2017 Oct; 125(5): 315–337.

2. Gurpreet Singh  Lamba et al. Techniques for Atraumatic Extractions: A narrative review; Journal of Advanced Medical and Dental Sciences Research; Vol. 10, Issue 6; June 2022

3. Wood RA, Mealey BL. Histologic comparison of healing after tooth extraction with ridge preservation using mineralized versus demineralized freeze-dried bone allograft. J Periodontol. 2012 Mar;83(3):329-36. doi: 10.1902/jop.2011.110270. Epub 2011 Jul 12. PMID: 21749166.

4. Wang HL, Boyapati L. “PASS” principles for predictable bone regeneration. Implant Dent. 2006;15(1):8-17

5. Bertl, K., Kukla, E. B., Albugami, R., Beck, F., Gahleitner, A., & Stavropoulos, A. (2018). Timeframe of socket cortication after tooth extraction: A retrospective radiographic study. Clinical Oral Implants Research, 29(1), 130-138. 2023-06-28 13:22:56

6. Sundar Ramalingam, Chalini Sundar, John A. Jansen, Hamdan Alghamdi, Chapter 1 – Alveolar bone science: Structural characteristics and pathological changes, Editor(s): Hamdan Alghamdi, John Jansen, Dental Implants and Bone Grafts, Woodhead Publishing, 2020, Pages 1-22, ISBN 9780081024782,https://doi.org/10.1016/B978-0-08-102478-2.00001-5.

7. Gluckman, H., Pontes, C.C. and Du Toit, J., 2018. Radial plane tooth position and bone wall dimensions in the anterior maxilla: A CBCT classification for immediate implant placement. The Journal of Prosthetic Dentistry, 120(1), pp.50-56. 2023-06-28 13:23:38

8. Chappuis V, Engel O, Reyes M, Shahim K, Nolte LP, Buser D. Ridge alterations post-extraction in the esthetic zone: a 3D analysis with CBCT. J Dent Res 2013; 92: 1955-2015

9. Avila-Ortiz, G., Chambrone, L., & Vignoletti, F. (2019). Effect of alveolar ridge preservation interventions following tooth extraction: A systematic review and meta-analysis. Journal of Clinical Periodontology, 46, 195-223.

10. Diana Heimes et al. Buccal Bone Thickness in Anterior and Posterior Teeth—A Systematic Review; Healthcare (Basel). 2021 Dec; 9(12): 1663

11. Couso-Queiruga E, Stuhr S, Tattan M, Chambrone L, Avila-Ortiz G. Post-extraction dimensional changes: A systematic review and meta-analysis. J Clin Periodontol. 2021;48(1):126-144

12. Araujo MG, Silva CO, Misawa M, Sukekava F. Alveolar socket healing: what can we learn? Periodontol 2000. 2015; 68: 122-134

13. Avila-Ortiz G, Chambrone L, Vignoletti F. Effect of alveolar ridge preservation interventions following tooth extraction: a systematic review and meta-analysis. J Clin Periodontol. 2019; 46(21): 195-223

14. Lizette Llamosa-Cáñez. Microsurgery in Guided Bone Regeneration; Springer chapter 2022; pp 373-444

15. Hye-Jeong Jang and Jeong-Kee Yoon. The Role of Vasculature and Angiogenic Strategies in Bone Regeneration; Biomimetics 2024, 9(2), 75

16. Georg N. Duda et al. The decisive early phase of bone regeneration; Nature Reviews Rheumatology volume 19, pages78–95 (2023)

17. Shatta A, Bissada NF, Ricchetti P, Paes A, Demko C. Impact of Implant and Site Characteristics on the Pattern of Bone Loss in Peri-implantitis. Int J Oral Maxillofac Implants. 2019 Nov/Dec;34(6):1475-1481.

18. Kofina, Vrisiis & Demirer, Mutlu & Erdal, Barbaros & Eubank, Tim & Yildiz, Vedat & Tatakis, Dimitris & Leblebicioglu, Binnaz. (2020). Bone grafting history affects soft tissue healing following implant placement. Journal of Periodontology. 92. 10.1002/jper.19-0709.

19. Huang H, Ogata Y, Hur Y, Griffin T. (2012). Comparison of Peri-implant Bone Level In Augmented And Pristine Bone. Poster Session AADR/CADR Annual Meeting.

20. Casarez-Quintana A, Mealey BL, Kotsakis G, Palaiologou A. Comparing the Histological Assessment Following Ridge Preservation Using a Composite Bovine-derived Xenograft Versus an Alloplast Hydroxyapatite-sugar Cross-Linked Collagen Matrix. J Periodontol. 2022;1-10

21. Neiva R. Evolution of Biomaterials in Implant Dentistry Leads to Enhanced Tissue Quality. Compend Contin Educ Dent. 2022;43(7): 454-455

*Dr. Toghranegar receives financial support from Dentsply Sirona.

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