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BONE MORPHOGENETIC PROTEINS IN PERIODONTICS

Comprehensive Postgraduate Theory Examination Notes

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1. HISTORICAL BACKGROUND AND DISCOVERY

• Marshall R. Urist provided the biological basis of bone morphogenesis. He made the key discovery that demineralized, lyophilized segments of bone induced new bone formation when implanted in muscle pouches in rabbits. This discovery was published in 1965 in Science.

[Orban's Oral Histology & Embryology, line 127273]

• Pierre Lacroix had earlier proposed a hypothetical substance, "osteogenin", that might initiate bone growth.

[Orban's Oral Histology & Embryology, line 127271]

• The term "bone morphogenetic protein (BMP)" first appeared in the scientific literature via the Journal of Dental Research in 1971.

[Orban's Oral Histology & Embryology, line 127277]

• Bone morphogenetic (or morphogeneic) proteins are now referred to as BMPs for convenience.

[Orban's Oral Histology & Embryology, line 127279]

• Early studies by Hari Reddi unraveled the sequence of events involved in bone matrix-induced bone morphogenesis. On the basis of this work, it seemed likely that "morphogens" were present in the bone matrix. A systematic study, using a battery of bioassays for bone formation, was undertaken to isolate and purify putative bone morphogenetic proteins.

[Orban's Oral Histology & Embryology, line 127312]

• To date, 20 BMPs have been identified.

[Orban's Oral Histology & Embryology, line 127320]

• The BMPs were originally isolated from bovine bone by Marshall Urist.

[Newman & Carranza 14th ed (Ch 79), line 134752]

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2. DEFINITION AND CLASSIFICATION

• Bone morphogenic proteins (BMPs) comprise a group of regulatory glycoproteins that are members of the transforming growth factor-beta (TGF-β) superfamily that function as differentiation factors.

[Newman & Carranza 14th ed (Ch 63), line 110122]

• These proteins induce cellular differentiation of stem cells into chondroblastic and osteogenic cells.

[Newman & Carranza 14th ed (Ch 63), line 110124]

• Unlike proliferation factors that increase the number of cells, the BMPs are differentiation factors that stimulate cells to differentiate and produce bone tissue.

[Newman & Carranza 14th ed (Ch 79), line 134755]

• The BMPs are a group of related proteins that are found in the body and are important for skeletal development. Each of the proteins has relatively specific functions.

[Newman & Carranza 14th ed (Ch 79), line 134747]

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3. NOMENCLATURE AND MEMBERS OF CLINICAL INTEREST

• "Much of the research interest has focused on BMP-2 (OP-2), BMP-3 (osteogenin), and BMP-7 (OP-1)."

[Newman & Carranza 14th ed (Ch 63), line 110127]

• Of the TGF-β superfamily, recombinant human bone morphogenetic protein-2 (rhBMP-2) has shown significant signs of bone-enhancing potential.

[Newman & Carranza 14th ed (Ch 79), line 134739]

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4. BIOCHEMISTRY AND MOLECULAR BIOLOGY

4.1 Molecular Nature

• BMPs are regulatory glycoproteins.

[Newman & Carranza 14th ed (Ch 63), line 110122]

• Bone matrix contains BMPs and a variety of growth factors, like platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), and insulin-like growth factors (IGF).

[Periodontics Medicine Surgery Implants (Orban's), line 15151]

• Osteoblasts secrete several members of BMP superfamily, including BMP-2, BMP-7, TGF-β, insulin-like growth factors (IGF-I and IGF-II), platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF).

[Periodontics Medicine Surgery Implants, line 32800]

4.2 Signaling Pathways

• Several pathways that influence osteoblastogenesis and bone formation are involved, including:
  1. Smad pathway
  2. Hedgehog pathway
  3. TGF-β pathway
  4. Cytokine-cytokine receptor interaction

[Newman & Carranza 14th ed (Ch 63), line 110125]

• The BMPs have specific receptors on the surfaces of cells. Binding of the BMP causes dimerization of the receptor proteins, which in turn stimulates a cascade of events intracellularly involving a set of proteins called SMADs. The result is activation of genetic activity and bone cell differentiation.

[Newman & Carranza 14th ed (Ch 79), line 134769]

• BMP-2 target genes include a wide cohort of transcription factors located in the cell nucleus. The osteogenic effects of BMP-2 are mediated by the formation of Runx2-Smad complexes.

[Newman & Carranza 14th ed (Ch 63), line 110128]

• BMP-2 promotes osteoblast maturation by increasing the expression of a series of transcription factors in the cell nucleus (RUNX2, OSX, DLX5), which lead to the expression of OSE2, the osteoblast marker gene that is responsible for osteoblast differentiation.

[Newman & Carranza 14th ed (Ch 63), line 110129]

4.3 Role in Intramembranous Ossification

• The mechanism of intramembranous ossification involves bone morphogenetic proteins (BMPs) and activation of transcription factor called cbfa1. BMPs activate cbfa1 gene in mesenchymal cells. The cbfa1 transcription factor transforms mesenchymal cells into osteoblasts. It is believed that the proteins activate genes for osteocalcin, osteopontin and other bone-specific extracellular matrix proteins.

[Periodontics Medicine Surgery Implants, lines 15759-15763]

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5. FLOWCHART: MECHANISM OF BMP-INDUCED BONE INDUCTION

BONE INDUCTION CASCADE (Sequential Multistep Process)
[Urist, 1965; Reddi; Orban's line 127281]

BMP exposed (from demineralized bone matrix or applied exogenously)
            |
            v
    CHEMOTAXIS
(motile cells migrate toward BMP concentration gradient)
            |
            v
    MITOSIS
(cells divide — daughter cells with same chromosome number as parent)
            |
            v
    DIFFERENTIATION
(cells become specialized bone-forming cells)
            |
            v
Undifferentiated mesenchymal stem cells
            |
            v
BMP binds specific cell-surface receptors
            |
            v
DIMERIZATION of receptor proteins
            |
            v
Intracellular SMAD cascade activated
            |
            v
Runx2-Smad complexes formed (BMP-2)
            |
            v
Transcription factors activated (RUNX2, OSX, DLX5)
            |
            v
OSE2 (osteoblast marker gene) expressed
            |
            v
PREOSTEOBLASTS → OSTEOBLASTS
            |
            v
Osteoid (new immature bone material) produced
            |
            v
Remodeling → Mature Lamellar Bone

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6. ROLE OF BMPs IN PERIODONTIUM AND BONE MATRIX

6.1 BMPs as Components of Bone Matrix

• "Bone matrix also contains bone morphogenetic proteins (BMPs) and a variety of growth factors, like platelet derived growth factor (PDGF), fibroblast growth factor (FGF) and insulin like growth factors (IGF). Lysyl oxidase and tyrosine rich acidic matrix proteins (TRAMP) are important components of demineralized bone matrix."

[Periodontics Medicine Surgery Implants, line 15151]

• Bone matrix also contains osteocalcin (Gla proteins), osteopontin, bone sialoproteins, osteonectin, proteoglycans (biglycan and decorin), and BMPs.

[Periodontics Medicine Surgery Implants, line 15146]

6.2 BMPs in Cementum Regeneration

• "Several growth factors have been shown to be effective in cementum regeneration, including members of the transforming growth factor superfamily (i.e., bone morphogenetic proteins), platelet-derived growth factor, insulin-like growth factor, and enamel matrix derivatives."

[Newman & Carranza 14th ed (Ch 4), line 3957]

6.3 BMPs in Osteoblast Differentiation

• "The differentiation and development of osteoblasts from osteoprogenitor cells are dependent on the release of osteoinductive or osteopromotive growth factors (GFs), such as bone morphogenetic proteins (BMPs), and other growth factors, such as insulin-like growth factor (IGF), platelet-derived growth factor (PDGF), and fibroblast growth factor (FGF)."

[Lang & Lindhe, Clinical Periodontology and Implant Dentistry 6th ed, line 5940]

6.4 BMPs and Periodontal Wound Healing

• The structure and function of the periodontium during remodeling and healing is determined by the orchestration of important bioactive proteins including "platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), fibroblast growth factor (FGF), bone morphogenetic proteins (BMPs), insulin-like growth factor-1 (IGF-1), transforming growth factor beta 1 (TGF-β1)".

[Lang & Lindhe, 6th ed, line 52678]

6.5 BMPs and the Regional Acceleratory Phenomenon (RAP)

• The atraumatic extraction process sets up the regional acceleratory phenomenon (RAP) for healing, which "increases the rate of repair and adds bone morphogenetic protein to the site."

[Orban's / Misch context, line 125762]

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7. BMPs IN BONE GRAFTS - OSTEOINDUCTIVE MECHANISM

7.1 DFDBA and BMPs

• FDBA is considered an osteoconductive material, whereas DFDBA is considered an osteoinductive graft.

[Newman & Carranza 14th ed (Ch 63), line 109518]

• "Experiments by Urist established the osteogenic potential of DFDBA. Demineralization in cold, diluted hydrochloric acid exposes the components of the bone matrix, which are closely associated with collagen fibrils and have been termed bone morphogenetic proteins (BMPs)."

[Newman & Carranza 14th ed (Ch 63), lines 109523-109525]

• "Demineralization process exposes the components of bone matrix termed as bone morphogenetic protein, e.g. osteogenin, which is a bone inductive protein isolated from the extracellular matrix of human bones. Hence, this is an osteoinductive material."

[Misch Implantology 4th ed, line 47860]

• "Demineralized freeze-dried bone allografts (DFDBAs) have shown osteoconductive as well as osteoinductive properties due to the release of bone morphogenetic proteins (BMPs) during the demineralization process."

[Lang & Lindhe, 6th ed, line 107307]

7.2 BMPs in FDBA and DFDBA - Quantity

• "BMPs are present in freeze-dried bone allograft (FDBA) and demineralized freeze-dried bone allograft (DFDBA), but the levels are so low that bovine bone yields only 2 μg of BMP."

[Newman & Carranza 14th ed (Ch 63), line 110133]

• "It is only through recombinant DNA technology (rhBMP) that BMP has been made available for clinical use."

[Newman & Carranza 14th ed (Ch 63), line 110134]

7.3 Osteoinduction - Definition

• "Osteoinduction is a chemical process by which molecules contained in the graft (e.g., bone morphogenetic proteins) convert the neighboring cells into osteoblasts, which in turn form bone."

[Newman & Carranza 14th ed (Ch 63), line 109398]

• "Osteoinduction is the process by which osteogenesis is induced. It is a phenomenon regularly seen in any type of bone healing process. Osteoinduction implies the recruitment of immature cells and the stimulation of these cells to develop into preosteoblasts."

[Orban's, line 127328]

7.4 Cortical Grafts and BMP Concentration

• "The inductive capacity of cortical grafts is explained by their higher concentration of bone morphogenetic proteins."

[Orban's/Misch, line 144826]

• "Cortical bone harvested from the mandible exhibits slower graft resorption and excellent graft incorporation due to the vast amounts of osteocytes, growth factors, and bone morphogenetic protein contained in cortical bone. This facilitates angiogenesis and osteoblast migration into the graft site."

[Orban's/Misch, lines 144851-144854]

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8. RECOMBINANT HUMAN BMPs (rhBMPs) - CLINICAL APPLICATIONS

8.1 Available Recombinant Forms

• "Laboratory-produced recombinant human BMPs (rhBMPs) are used in orthopedic applications (rhBMP-2 and rhBMP-7), such as spinal fusions and nonunions. rhBMP-2 is U.S. Food and Drug Administration (FDA) approved for some dental use."

[Orban's, line 127321]

• "One commercial bone growth factor product has been approved by the Food and Drug Administration (FDA) for use in the oral cavity to stimulate bone formation." The commercially available bone growth product contains rhBMP-2 combined with a bovine type I collagen sponge.

[Newman & Carranza 14th ed (Ch 79), line 134741]

• Brand name: INFUSE (rhBMP-2 soaked onto an absorbable collagen sponge)

[Newman & Carranza 14th ed, line 97897]

8.2 FDA-Approved Indications in the Oral Cavity

• rhBMP-2 (INFUSE) has been cleared for:
  1. Sinus lift augmentation therapy
  2. Ridge augmentation in maxillary anterior extraction sites with bone loss

[Newman & Carranza 14th ed (Ch 79), line 134745]

• "The same product approved for use in the oral cavity had previously been approved by the FDA for use in single-level spine fusion procedures and in open tibial fractures in humans."

[Newman & Carranza 14th ed (Ch 79), line 134765]

8.3 FDA Approved Local HMTs for Surgical Adjunctive Use

• "The locally applied HMTs currently approved by the FDA for adjunctive use during surgery are:
  1. Enamel matrix proteins (Emdogain)
  2. Recombinant human platelet-derived growth factor-BB (GEM 21S)
  3. BMP-2 (INFUSE)"

[Newman & Carranza 14th ed, line 97891]

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9. CARRIER SYSTEMS FOR DELIVERY

9.1 Bovine Type I Collagen Sponge

• "BMP binds tightly to the collagen within minutes and has been shown to be released over time for 2 to 3 weeks at the defect site." The extended-release kinetics likely allow the undifferentiated mesenchymal cells migrating into the wound site over time to be exposed to the growth factor.

[Newman & Carranza 14th ed (Ch 79), line 134759]

• "Many carriers have been tested with the BMPs, but the binding and release kinetics using bovine type I collagen have proved to be the most useful clinically."

[Newman & Carranza 14th ed (Ch 79), line 134757]

9.2 Atelocollagen Scaffolds

• "Two variations of this collagen were produced to create an atelocollagen scaffold where both constructs were effective in supporting rhBMP-induced bone formation."

[Newman & Carranza 14th ed (Ch 63), line 110389]

9.3 Calcium Sulfate as Carrier

• In an experimental sheep study, when defects were filled with calcium sulfate, "increased immunostaining for BMP-2, BMP-7, TGF-β, and PDGF-BB was observed."

[Newman & Carranza 14th ed (Ch 63), line 110400]

9.4 Polymers

• Bioresorbable polymers of poly lactic-co-glycolic acid and polyglycolic acid have been considered as scaffolding agents for tissue engineering due to their biodegradable and tissue compatibility properties. Although these agents were promising as carriers for osteogenic factors in animals, "variable tissue responses have made clinical application of these materials problematic" — including inflammation, foreign body reaction, and local acid accumulation during polymer degradation.

[Newman & Carranza 14th ed (Ch 63), lines 110406-110411]

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10. TABLE: CARRIERS FOR rhBMP DELIVERY

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11. PERIODONTAL REGENERATION APPLICATIONS

11.1 Experimental Evidence

• "Although early studies using crude preparations of BMP-2 and BMP-3 applied in surgically induced furcation defects appeared to stimulate periodontal regeneration, more recent studies with rhBMP-2 indicate that periodontal regeneration was associated with areas of ankylosis."

[Newman & Carranza 14th ed (Ch 63), lines 110136-110138]

• "A protein extracted from human bones, termed osteogenin or BMP-3, has been tested in [surgically induced furcation defects]."

[Newman & Carranza 14th ed, line 109454]

11.2 Concern of Ankylosis

• "Healing through ankylosis has been a concern, so most of the research using rhBMPs has involved correction of intrabony, supra-alveolar, furcation, and fenestration defects, as well as implant site preparation."

[Newman & Carranza 14th ed (Ch 63), lines 110139-110140]

11.3 BMP-7 (OP-1) in PDL Regeneration

• "More recently, BMP-7 has been utilized in an animal model to improve bone formation by incorporating BMP-7 into a patterned scaffold for the formation of PDL-like tissue and the overall integrity of the bone-PDL interface. Future translational and human studies are still needed to determine its clinical use in periodontal regeneration."

[Newman & Carranza 14th ed (Ch 63), lines 110141-110143]

11.4 Defect Types Studied with rhBMPs

[Newman & Carranza 14th ed (Ch 63), line 110140; Ch 79, line 134745]

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12. BMPs AS HOST MODULATION AGENTS (HMTs)

• A variety of different drug classes have been evaluated as host modulation agents, including the "nonsteroidal antiinflammatory drugs (NSAIDs), bisphosphonates, tetracyclines, enamel matrix proteins, growth factors, and bone morphogenetic proteins."

[Carranza's 10th ed, line 52316]

• "A number of local host modulation agents have been investigated for potential use as adjuncts to surgical procedures, not only to improve wound healing but also to stimulate regeneration of lost bone, periodontal ligament, and cementum, restoring the complete periodontal attachment apparatus. These have included enamel matrix proteins (Emdogain), bone morphogenetic proteins (BMP-2, BMP-7), growth factors (platelet-derived growth factor, insulin-like growth factor), and tetracyclines."

[Carranza's 10th ed, lines 52402-52406]

• In the Newman 14th edition, it is additionally noted that: "The locally applied HMTs currently approved by the FDA for adjunctive use during surgery are enamel matrix proteins (Emdogain), recombinant human platelet-derived growth factor-BB (GEM 21S), and BMP-2 (INFUSE)" - an update from the 10th edition which stated only Emdogain was approved.

[Newman & Carranza 14th ed, line 97891]

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13. BMPs IN IMPLANT DENTISTRY

13.1 Sinus Augmentation

• rhBMP-2/collagen product approved for sinus lift augmentation therapy.

[Newman & Carranza 14th ed (Ch 79), line 134745]

13.2 Peri-implantitis Defects

• Bone formation and reosseointegration in peri-implantitis defects following surgical implantation of rhBMP-2 has been reported.

[Newman & Carranza 14th ed (Ch 63), reference line 111085]

13.3 BMP-4 in Implant Site Preparation (Piezosurgery)

• Preti et al. (2007) analyzed neo-osteogenesis and inflammatory reactions after implant site preparation using piezosurgery versus conventional drill. "The authors evaluated the levels of bone morphogenetic protein-4 (BMP-4), transforming growth factor-beta 2 (TGF-β2), tumor necrosis factor-alpha (TNF-α), and interleukin-1 beta (IL-1β) and IL-10." In the early phase (7-14 days), "levels of BMP-4, TGF-β2, and IL-10 were increased in the piezoelectric group" and piezoelectric bone surgery was more effective in stimulating peri-implant osteogenesis.

[Lang & Lindhe 6th ed, lines 104741-104752]

13.4 Bone Formation at rhBMP-2-Coated Titanium Implants

• Studies evaluated bone formation at "recombinant human bone morphogenetic protein-2-coated titanium implants in the posterior maxilla (type IV bone) in non-human primates."

[Newman & Carranza 14th ed, reference line 127367]

13.5 Ridge/Sinus Augmentation

• "Vertical augmentation using bone morphogenetic proteins" is listed as one of the techniques.

[Newman & Carranza 14th ed, line 137175]

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14. TABLE: IN VITRO EFFECTS OF GROWTH FACTORS ON PERIODONTAL LIGAMENT CELLS AND OSTEOBLASTS

[Newman & Carranza 14th ed, eTable 63.2, lines 110609-110710]

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15. PRECLINICAL STUDIES AND CLINICAL EVIDENCE

15.1 Critical-Sized Rat Mandibular Defects

• "The inductive capacity of rhBMP-2 was demonstrated by impregnating a polymer carrier and placing the substrate in critical-sized rat mandibular defects with or without a barrier membrane. The study evaluated 12- and 24-day healing times and showed a bony union of the defects for rhBMP-treated sites."

[Newman & Carranza 14th ed (Ch 79), lines 134774-134778]

15.2 Clinical Remarks

• "The clinical results of using rhBMP-2 and collagen in patients are remarkable considering that only one bone differentiation agent is being delivered to the bone site and it is only delivered at the time of the surgical procedure."

[Newman & Carranza 14th ed (Ch 79), line 134779]

• "Relatively high doses of the protein are often used in some sites, however, possibly as the result of the need to release effective doses at later times."

[Newman & Carranza 14th ed (Ch 79), line 134782]

15.3 Limitations

• "The clinician must recognize that there is limited clinical information available on these new modalities, and no information on resorption of the regenerated bone, implant survival, or bone remodeling around implants. Further documentation from long-term, randomized controlled clinical studies are necessary."

[Newman & Carranza 14th ed (Ch 79), lines 134789-134791]

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16. ADVERSE EVENTS / COMPLICATIONS

• "Adverse events associated with the administration of BMPs have been reported, including: osteolysis, seroma/hematoma, infection, arachnoiditis, dysphagia, increased neurological deficits, and cancer."

[Newman & Carranza 14th ed, lines 97901-97902]

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17. TISSUE ENGINEERING AND GENE THERAPY

• Growth factors that have found applications in periodontal tissue engineering include: "fibroblast growth factor, platelet-derived growth factor (PDGF), recombinant human bone morphogenetic proteins and enamel matrix derivative (EMD). All these molecules have shown positive results in stimulating periodontal regeneration."

[Misch 4th ed, lines 57930-57936]

• Gene therapy of bone morphogenetic protein for periodontal tissue engineering has been proposed (referenced as a study by Giannobile, 2003, Journal of Periodontal Research).

[Lang & Lindhe 6th ed, line 53863]

• The potential of tissue engineering using biological mediators such as rhBMP, rhPDGF, and EMD is addressed in the context of scaffold delivery.

[Newman & Carranza 14th ed (Ch 63), line 110457]

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18. FLOWCHART: ROLE OF BMP IN OSTEOINDUCTION VIA DFDBA

DFDBA PREPARATION AND BMP ACTIVITY
[Newman 14th ed, Ch 63; Misch 4th ed]

Cadaveric bone (allograft)
            |
            v
Demineralization in COLD, DILUTE HCl
            |
            v
Organic components of bone matrix EXPOSED
(closely associated with collagen fibrils)
            |
            v
Bone Morphogenetic Proteins (BMPs) RELEASED
(including osteogenin / BMP-3)
            |
            v
BMP signals chemotaxis of bone-forming cells to void
            |
            v
Mesenchymal stem cell recruitment
            |
            v
Cell proliferation (mitosis)
            |
            v
Differentiation into OSTEOBLASTS
            |
            v
Osteoid matrix deposition
            |
            v
BONE REGENERATION
(DFDBA = OSTEOINDUCTIVE material)

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19. COMPARISON OF VIEWPOINTS ACROSS REFERENCES

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20. RECENT TERMINOLOGY AND NOMENCLATURE NOTES

• "Bone morphogenetic (or morphogeneic) proteins are now referred to as BMPs for convenience."

[Orban's, line 127279]

• BMP-2 = OP-2; BMP-3 = Osteogenin; BMP-7 = OP-1 (Osteogenic Protein-1) - these dual nomenclatures should be known.

[Newman & Carranza 14th ed (Ch 63), line 110127; Ch 79, line 134751]

• The cbfa1 transcription factor (now also known as RUNX2) is the transcription factor activated by BMPs in intramembranous ossification - these are the same molecule referred to by different nomenclatures across texts.

[Periodontics MSI, line 15759; Newman 14th ed, line 110130]

• "Bone morphogenic proteins" vs "Bone morphogenetic proteins" - both spellings appear in the literature and in the textbooks. The Newman 14th ed (Ch 63) uses "morphogenic" while other sections and references use "morphogenetic." Both refer to the same group.

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21. SUMMARY TABLE: KEY FACTS FOR EXAMINATION

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REFERENCES (Sources Used)

1. Newman and Carranza's Clinical Periodontology and Implantology, 14th Edition - Chapters 4, 63, 79 (Primary source for BMP mechanisms, clinical applications, adverse events, carrier systems)
2. Carranza's Clinical Periodontology, 10th Edition - Chapter 16 (BMPs as host modulation agents)
3. Clinical Periodontology and Implant Dentistry, 6th Edition (Lang & Lindhe) - Chapters 2, 27, 48 (BMPs in osteoblast differentiation, wound healing, implant site preparation)
4. Misch Implantology, 4th Edition - Chapter 42, 54 (DFDBA and BMP osteogenin; tissue engineering)
5. Periodontics: Medicine, Surgery, Implants (Orban's Oral Histology & Embryology) - Bone histology section, Bone substitutes and membranes chapter (BMPs in bone matrix, intramembranous ossification, bone repair mechanisms)
6. Orban's Oral Histology & Embryology - Bone repair and regeneration chapter (Urist's discovery, bone induction cascade, number of BMPs)

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Examiner's Note: The most frequently tested aspects are (1) the definition of BMPs as differentiation factors (not proliferation factors), (2) the mechanism of osteoinduction via DFDBA, (3) rhBMP-2 (INFUSE) as the FDA-approved commercial product and its carrier (bovine type I collagen sponge), (4) the concern of ankylosis with periodontal use, (5) adverse events, and (6) the SMAD/Runx2 signaling pathway. The discovery by Urist (1965) and the coining of the term via the Journal of Dental Research (1971) are classic short-answer points.

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LANDMARK AND IMPORTANT STUDY ARTICLE NOTES

Bone Morphogenetic Proteins in Periodontics

Postgraduate Theory Examination — Article-Wise Reference Notes

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SECTION I: FOUNDATIONAL / DISCOVERY STUDIES

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STUDY 1 ⭐⭐⭐⭐⭐ — THE ORIGINAL DISCOVERY

• Demonstrated that demineralized, lyophilized segments of cortical bone induced new bone formation when implanted ectopically in muscle pouches of rabbits - a phenomenon that did not require live cells from the graft
• This was the first proof of principle of osteoinduction by a soluble factor in the bone matrix
• Led to the concept that bone matrix contains a "morphogenetic substance" capable of initiating the entire cascade of bone formation de novo
• Published in Science - signifying its paradigm-shifting impact across biology and medicine
• Laid the groundwork for all subsequent BMP research

Referenced in: Orban's/Periodontics MSI textbooks and Misch 4th ed as the founding experiment

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STUDY 2 ⭐⭐⭐⭐⭐ — THE CLONING OF BMPs

• First paper to isolate human complementary DNA (cDNA) clones corresponding to three polypeptides present in purified BMP preparation from bovine bone: BMP-1, BMP-2A (later BMP-2), and BMP-3
• Demonstrated that each of the three proteins was independently capable of inducing formation of cartilage in vivo
• Showed that BMP-2A and BMP-3 are new members of the TGF-beta supergene family, while BMP-1 appeared to be a novel regulatory molecule
• Published in Science - confirmed the biochemical identity of BMPs and made recombinant DNA production of rhBMPs possible for clinical use
• Enabled the entire downstream development of rhBMP-2 (INFUSE) as a commercial product

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STUDY 3 ⭐⭐⭐⭐⭐ — NAMING BMPs IN DENTAL LITERATURE

• The term "bone morphogenetic protein (BMP)" first appeared in the scientific literature through this article published in the Journal of Dental Research (1971)
• Coined the specific terminology that has become the universal name for this family of growth factors
• Established the dental/oral biology literature as a primary forum for BMP science
• Distinguished the "morphogenetic" (form-generating) quality of the bone-derived factor from simple bone formation factors

Note: The term was coined in the dental literature before orthopedic literature adopted it widely.

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SECTION II: PRECLINICAL ANIMAL STUDIES — PERIODONTAL APPLICATIONS

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STUDY 4 ⭐⭐⭐⭐⭐ — FIRST DEMONSTRATION OF BMP IN PERIODONTAL REGENERATION

• First study to demonstrate that BMPs could induce periodontal regeneration in a higher primate model (baboon)
• Used a surgically created periodontal defect model in Papio ursinus
• Showed histological evidence of new cementum, new PDL fibers, and new alveolar bone at BMP-treated sites
• Established the biological plausibility of BMP for periodontal tissue engineering
• This study is cited in virtually every subsequent paper on BMP in periodontology

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STUDY 5 ⭐⭐⭐⭐⭐ — BMP-7 (OP-1) COMPLETE BONE REGENERATION IN PRIMATE

• Demonstrated complete bone regeneration in critical-sized defects in baboons using rhOP-1 (BMP-7)
• Showed that BMP-7 (Osteogenic Protein-1, OP-1) was capable of regenerating the entire bony architecture
• Supported the concept that recombinant BMPs could replace or supplement autogenous bone grafts
• Confirmed that BMP-7 = OP-1 nomenclature was interchangeable
• Defined the concept of "complete regeneration" as restoration of normal histological bone structure

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STUDY 6 ⭐⭐⭐⭐ — PERIODONTAL REPAIR WITH rhBMP-2 - CONCENTRATION-DEPENDENT EFFECTS

• Used a surgically created supraalveolar periodontal defect model in dogs to evaluate different concentrations of rhBMP-2
• Showed that rhBMP-2 effects are dose-dependent - higher concentrations produced more bone, but also more concerns about ankylosis
• Demonstrated that lower doses produced more cementum-mediated attachment without ankylosis
• Important for understanding optimal dosing for periodontal vs. alveolar bone regeneration applications
• Contributed to the understanding that the same molecule produces different tissue responses depending on concentration

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STUDY 7 ⭐⭐⭐⭐ — rhBMP-12 (GDF-7) FOR PDL REGENERATION

• Evaluated rhBMP-12 (also known as GDF-7) - a BMP family member with specific capacity to stimulate PDL fibroblast-like cells
• Showed that BMP-12 had greater potential for periodontal ligament regeneration compared to BMP-2, which primarily stimulates bone
• Suggested that different BMPs have different tissue-specific roles in the periodontium: BMP-2 → bone; BMP-12/GDF-7 → PDL
• Opened the concept of selective BMP use based on desired tissue outcome (bone vs. periodontal ligament)
• Established the basis for BMP-12 as a "ligamentogenic" factor

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STUDY 8 ⭐⭐⭐⭐ — rhBMP-2 AND GBR SYNERGY

• Demonstrated that combining rhBMP-2 with GBR membranes resulted in significantly more bone formation than GBR alone
• Used a large animal (dog) alveolar ridge augmentation model
• Supported the concept that rhBMP-2 and barrier membranes have a synergistic effect on bone regeneration
• Suggested that the space maintenance function of the membrane combined with osteoinductive capacity of rhBMP-2 created optimal conditions for bone formation
• Provided preclinical evidence for the clinical combination protocols later used in practice

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SECTION III: MAJOR REVIEW ARTICLES

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STUDY 9 ⭐⭐⭐⭐⭐ — COMPREHENSIVE CRITICAL REVIEW OF MODULATING FACTORS

This paper is directly referenced in Newman & Carranza 14th ed (reference list line 111169)

• The most comprehensive critical review on factors that modulate BMP-induced periodontal regeneration
• Identified and analyzed the following key modulating factors:

• Explained that BMP-2 initiates stem cells along an osteogenic pathway - but dose must be sufficient to prevent other growth factors from redirecting or retarding osteogenic potential
• Highlighted that different release profiles from the same carrier may be particularly important in tissues with mixed cell populations like the periodontium (bone and cementum grow at different rates)
• Concluded that intrabony defect treatment with BMPs requires: (1) appropriate temporal release, (2) a carrier as template for new tissue, (3) space maintenance, and (4) mucoperiosteal flap support
• Called for careful evaluation of these factors before conducting expensive human clinical trials

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STUDY 10 ⭐⭐⭐⭐⭐ — COMPREHENSIVE BIOLOGICAL AND CLINICAL REVIEW

• Comprehensive review of biological potential of BMPs for alveolar ridge augmentation and implant fixation
• Demonstrated the unparalleled potential of rhBMP-2 using a variety of carrier technologies (including a purpose-designed titanium porous oxide implant surface) to induce local bone formation and implant osseointegration
• Showed that rhBMP-2 can support both inlay (sinus) and onlay (ridge) indications
• Addressed merits and shortcomings of current protocols including bone biomaterials and GBR
• Stated that "rhBMP-2 has unparalleled potential to augment alveolar bone, and support implant osseointegration and long-term functional loading"
• Concluded that inclusion of rhBMP-2 would not only enhance predictability of existing clinical protocol but also "radically change current treatment paradigms"

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STUDY 11 ⭐⭐⭐⭐ — 25-YEAR REVIEW OF rhBMP-2 AND rhPDGF-BB

• Most up-to-date major review (2024) covering 25 years of clinical evidence on rhBMP-2 in oral regeneration
• Critically assessed that current evidence regarding clinical benefits of rhBMP-2 compared to conventional therapies is inconclusive
• Found that rhBMP-2 may promote faster wound healing and enhance de novo bone formation, particularly in patients with compromised bone healing capacity or limited donor sites
• Highlighted that adverse effects remain a concern with higher doses
• Compared rhBMP-2 and rhPDGF-BB head-to-head, noting that rhPDGF-BB shows more consistent and positive outcomes for periodontal regeneration and gingival recession treatment
• Published in Periodontology 2000 - the premier clinical periodontal review journal

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SECTION IV: CLINICAL TRIALS — HUMAN STUDIES

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STUDY 12 ⭐⭐⭐⭐⭐ — FIRST HUMAN CLINICAL TRIAL WITH rhBMP-2

• First human clinical trial evaluating rhBMP-2/absorbable collagen sponge (rhBMP-2/ACS) for alveolar ridge preservation after tooth extraction and augmentation of localized osseous defects
• Two-center study: 12 patients (6 preservation, 6 augmentation), 24-month follow-up (Part I = 4-month safety and bone induction; Part II = 20-month osseointegration evaluation)
• Key findings:
  • rhBMP-2/ACS was well tolerated locally and systemically with no serious adverse events
  • Device was easily handled and adapted to ridge/extraction socket
  • Bone fill was observed in ALL alveolar sockets filled with the rhBMP-2 device
  • Augmentation of the alveolar ridge was NOT observed (limitation at this dose level)
• Established the safety and technical feasibility of the rhBMP-2/ACS device
• Directly paved the way for larger Phase II/III trials leading to FDA approval of INFUSE

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STUDY 13 ⭐⭐⭐⭐⭐ — RCT: FIORELLINI et al. - FDA APPROVAL BASIS STUDY

Directly referenced in Newman & Carranza 14th ed (reference line 135106)

• Phase III, multi-center, randomized clinical trial on rhBMP-2/ACS for extraction socket augmentation
• Evaluated 80 patients across multiple clinical centers
• Demonstrated that rhBMP-2/ACS significantly enhanced alveolar ridge width and height compared to controls after extraction
• Confirmed safety profile with no serious adverse events
• Results were pivotal in obtaining FDA approval of rhBMP-2 (INFUSE) for dental use: specifically for alveolar ridge preservation/augmentation in extraction sockets
• This study forms the evidence base cited in Newman & Carranza 14th edition for the FDA-approved indications

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STUDY 14 ⭐⭐⭐⭐ — RCT: BUCCAL BONE FORMATION AFTER FLAPLESS EXTRACTION

• Randomized controlled trial comparing rhBMP-2/ACS vs. collagen sponge alone after flapless extraction
• Evaluated buccal bone formation as primary outcome (clinically relevant for implant site development)
• Demonstrated that rhBMP-2/ACS maintained buccal bone dimensions better than collagen sponge alone
• Provided evidence for socket preservation application of rhBMP-2 in a flapless extraction technique
• Demonstrated that the technique was feasible and produced clinically acceptable outcomes for future implant placement

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STUDY 15 ⭐⭐⭐⭐ — RCT: FURCATION DEFECTS WITH rhBMP-2

• Triple-blind pilot RCT evaluating rhBMP-2 combined with PLA/PGA membrane vs. PLA/PGA membrane alone for Class II mandibular molar furcation defects (24 patients)
• At 6 months:
  • Greater reductions in vertical probing depth (p=0.01) and horizontal probing depth (p=0.05) in the rhBMP-2 group
  • Less gingival recession (p=0.03) in the rhBMP-2 group
  • Increased number of completely closed furcation defects in rhBMP-2 group
  • No adverse effects reported
• Demonstrated that the furcation-ankylosis concern may be manageable with appropriate membrane coverage
• Important because furcation defects are among the most challenging indications for periodontal regeneration

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STUDY 16 ⭐⭐⭐⭐⭐ — LANDMARK LONG-TERM RCT: 17-YEAR FOLLOW-UP

• Longest follow-up (17 years) RCT evaluating implants placed in bone augmented with GBR with or without rhBMP-2 (split-mouth design; 11 patients, 34 implants; 8 patients at 17 years)
• 100% implant survival rate in both test (rhBMP-2) and control groups after 17 years
• Mean buccal bone gain after 17 years: 5.38 mm (test/rhBMP-2) vs. 3.14 mm (control/no rhBMP-2)
• Marginal bone levels, mucosal thickness, and bone thickness were comparable between groups
• Confirmed long-term stability and safety of rhBMP-2 augmented bone supporting osseointegrated implants
• No adverse events attributable to rhBMP-2 at 17 years
• The definitive long-term evidence for rhBMP-2 in GBR/implant applications

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STUDY 17 ⭐⭐⭐⭐ — RCT: GBR WITH AND WITHOUT rhBMP-2 (3 AND 5 YEAR)

• Earlier publication from the same long-running Zurich RCT (same 11 patients, 34 implants)
• Reported 3- and 5-year outcomes showing 100% implant survival in both groups
• No statistically significant differences in peri-implant bone levels, marginal bone loss, or soft tissue health between rhBMP-2 and control groups at 3 and 5 years
• Demonstrated that rhBMP-2 addition does not compromise long-term implant outcomes and produces equivalent bone quality to conventional GBR
• Mean distance from first bone-to-implant contact to implant-abutment junction: 1.37 mm (test) vs. 1.22 mm (control) at 3 years — clinically equivalent

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SECTION V: SYSTEMATIC REVIEWS AND META-ANALYSES

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STUDY 18 ⭐⭐⭐⭐⭐ — SYSTEMATIC REVIEW: rhBMP-2 FOR SINUS AND RIDGE AUGMENTATION

• Systematic review of all studies (1980-2012, n=7 eligible from 69 publications) using rhBMP-2/ACS for alveolar ridge/maxillary sinus augmentation
• Key findings:
  • rhBMP-2/ACS yielded clinically meaningful bone formation for maxillary sinus augmentation, allowing placement of regular dental implants
  • No consistent differences between rhBMP-2 concentrations (both 0.75 and 1.5 mg/mL effective)
  • Sinus augmentation following autogenous bone graft was significantly greater by 1.6 mm (95% CI: 0.5-2.7 mm) compared to rhBMP-2/ACS (at 1.5 mg/mL)
  • In extraction sockets, rhBMP-2/ACS maintained alveolar ridge height while enhancing alveolar ridge width
  • Safety reports did not represent concerns for the proposed indications
• Concluded: "rhBMP-2/ACS appears a promising alternative to autogenous bone grafts for alveolar ridge/maxillary sinus augmentation"

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STUDY 19 ⭐⭐⭐⭐⭐ — NETWORK META-ANALYSIS: RECOMBINANT FACTORS FOR INTRABONY DEFECTS

• Network meta-analysis (NMA) of 24 preclinical studies (N = 501 animals) on recombinant factors for periodontal intrabony defects
• Compared rhBMP-2, rhGDF-5, rhPDGF-BB, rhFGF-2, EMD, rhBMP-12, and others
• Key SUCRA (Surface Under Cumulative Ranking) results:

• Concluded that rhBMP-2 ranked best for bone volume density, percentage new bone fill, and new cementum formation in preclinical periodontal intrabony defects
• No adverse effects identified across included studies

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STUDY 20 ⭐⭐⭐⭐ — SYSTEMATIC REVIEW AND META-ANALYSIS: GROWTH FACTORS IN PERIODONTAL DEFECTS

• Meta-analysis of 34 preclinical studies (March 2010 - December 2020) on biomolecules for periodontal osseous defects
• Most studied biomolecules: rhFGF-2, rhGDF-5, PDGF, BMP-2, and EMD
• Combined application of biomolecules with regenerative treatments improved:
  • New bone and cementum formation by ~1 mm in 1-, 2-, and 3-wall intrabony defects (p<0.001)
  • In furcation Grade II defects: bone area gain and cementum height regeneration enhanced by ~2 mm (p<0.001)
• Trial Sequential Analysis confirmed statistical significance
• For buccal recession models: rhFGF-2 and rhGDF-5 showed advantages; EMD did not inhibit epithelial down-growth
• Concluded that FGF-2 and GDF-5 ranked particularly well, but BMP-2 was also consistently beneficial for bone and cementum regeneration

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SUMMARY TABLE: ALL LANDMARK STUDIES AT A GLANCE

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FLOWCHART: EVOLUTION OF BMP RESEARCH — TIMELINE

1965 — Urist: Bone autoinduction (Science)
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1971 — Urist & Strates: Term "BMP" coined (J Dent Res)
         ↓
1980s — Reddi & Sampath: Dissociative extraction enables BMP purification
         ↓
1988 — Wozney et al.: cDNA cloning of BMP-1, BMP-2A, BMP-3 (Science)
         ↓
1990s — rhBMP-2 and rhBMP-7 recombinant production
         ↓
1994 — Ripamonti et al.: BMP induces periodontal regeneration in baboon
         ↓
1996 — Ripamonti et al.: Complete bone regeneration by BMP-7/OP-1 in primate
         ↓
1997 — Howell, Fiorellini et al.: FIRST HUMAN TRIAL (rhBMP-2/ACS) — safe, feasible
         ↓
1999 — Wikesjo et al.: Dose-dependent BMP-2 effects in canine periodontal defects
         ↓
2002 — King & Cochran: Critical review of modulating factors
         ↓
2004 — Wikesjo et al.: rhBMP-2 + GBR synergy; BMP-12 for PDL regeneration
         ↓
2005 — Fiorellini, Cochran et al.: Phase III RCT → FDA APPROVAL OF INFUSE
         ↓
2009 — Jung et al.: RCT — implants in rhBMP-2 augmented bone; 3/5-year results
         ↓
2015 — Freitas et al.: Systematic review — rhBMP-2 promising for sinus/ridge
         ↓
2021 — Khijmatgar et al.: NMA — rhBMP-2 ranks best for bone density and cementum
         ↓
2021 — Farimani et al.: SR + MA — 1-2 mm gain with growth factors
         ↓
2022 — Jung et al.: 17-year RCT — 100% implant survival; long-term safety confirmed
         ↓
2024 — Galarraga-Vinueza et al.: 25-year review — evidence inconclusive vs. conventional

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EXAMINER'S CORNER: HIGH-YIELD FACTS FROM LANDMARK STUDIES