REVIEW
Receptor technology – cell binding to P-15: a new method ofregenerating bone quickly and safely-preliminary
histomorphometrical and mechanical results in sinus ﬂoor
augmentations
Andreas H. Valentin1,2 and J. Weber3
1Institute for Oral Surgery, Mannheim, Germany, 2Nippon Dental University, Niigata, Japan and
3Dentsply Friadent GmbH, Mannheim Germany(Received for publication on March 12, 2004)

Abstract. Modern implantology involves the application and optimization of bone engineering biomaterials and scaffolds to achieve predictability in quality and quantity of the regeneration result andto avoid the high morbidity factor of the present gold standard. In this respect, acceleration of (woven)bone formation and completeness of the regeneration result seems to be an reasonable attempt bymultiplication of the whole cascades by duplicating all phases of cell binding, migration, proliferationand differentiation. Collagen I is an extracellular matrix protein with multiple main binding domains
for osteogenic progenitor cells and therefore plays a crucial role in osteogenesis. PepGen P15 is theﬁrst man engineered collagen I binding domain for potential osteoblasts and is able to multiply thecomplete regeneration cascade. The article explains the principles of micromolecular receptor enginering and its application in sinus ﬂoor augmentations as a preliminary report. It presents the ﬁrst
clinical and histomorphometrical results of this new technology in sinus ﬂoor elevations. The future
potential of individual bone regeneration will be discussed. (Keio J Med 53 (3): 166–171, September
2004)
Key words: biomimetic environment, osteogenic differentiation, receptor engineering

Introduction
Today, the goal of all dental and orthodontic surgery
is complete oral rehabilitation. Sufﬁcient bone volume
is a particularly important factor in the long-term success rate of dental implant treatment. In many cases
current surgical techniques in combination with the useof autogenous bone or bone grafting materials makeit possible to provide sufﬁcient bone for an implant
placement. However, due to its high morbidity the gold
standard has increasingly been regarded as critical. In
addition, bone grafting and bone regeneration materials
have evolved on a micromolecular basis in recent years
and could offer effective alternatives in the future. In allcases the bone-inducing cell, the osteoblast, is the center of interest.

Osteoblasts develop from inactive mesenchymal
progenitor cells by differentiation. The differentiation
process proceeds in combination with a variety of genetic and hormonal factors. Although most of thesesubstances are known (Babx 1, Cbfa 1, Osf 2, Dlx 5,
Ihh, BMP, leptin)1 the full interplay and mutual inﬂuences of the complex mechanisms and cascades have
not yet been thoroughly studied. For this reason it is
not surprising that experiments on inﬂuencing bone
growth with single factors have run into difﬁculties.
Clinically relevant results can often be obtained only
by increasing the concentration by a factor of several
thousand. On one hand, this unphysiological concentration increase interferes with the stoechiometry of
the biochemical processes. The results must also beviewed with scepticism because of their unpredictabil-

Presented at the 1346th Meeting of the Keio Medical Society in Tokyo, February 11, 2004.
Reprint requests to: Dr. Andreas H. Valentin, Institute for Oral Surgery, 07, 13 Planken, D-68161, Mannheim, Germany
166

Keio J Med 2004; 53 (3): 166–171

167

Fig. 2 Recombinant P15 binding domain on PepGen P 15 substratesimulate a collagenous biomimetic environment for the cells. Cellsurface integrin receptor contacts Peppen P15 particle and the natural
osteogenic differentiation process is triggered in the same way.

Fig. 1 Cell surface receptor contacts P15 binding domain in humancollagen I initiating the natural osteogenic differentiation process.

ity, particularly with reference to the effectiveness of
the applied highly concentrated substances. Their decomposition and intermediate products are in somecases still biologically active. In contrast to the above,
cell binding is scientiﬁcally documented as the precursor of the differentiation cascade of osteoblasts.
All local cells are in a three-dimensional extracellular matrix interconnected via collagen ﬁbers. Cells
move over them by haptotaxis. In this environment cellto-cell and cell-to-matrix interactions are mediated byhighly speciﬁc receptors.2
A short (766-GTPGPQGIAGQRGVV-780) sequence of collagen 1 a 1 – forming the major component of the organic components of bone at 85% – hasbeen identiﬁed as a cell binding domain for mesenchymal progenitor cells.3 The binding of osteoblastprogenitor cells at this domain initiates their proliferation and differentiation (Fig. 1). The connection of theextracellular matrix (ECM) is initiated here by integrin
receptors on the cellular membrane. The integrins
transfer the information via an ‘‘outside-in signaling’’

two-dimensional “classical” defect healing

Fig. 3process, which represents a transmembrane hierarchyof molecular responses such as receptor clustering andrecruiting of signal and cytoskeleton proteins to focal
adhesion.4
This amino acid sequence (P-15) can be produced inany desired quantity by synthetic processes. Since it isirreversibly bound to a carrier (Osteograf/N), it can bea substitute for the physiological collagen. A binding
to this synthetically manufactured analogue (PepGen
P-151, Dentsply FRIADENT, Mannheim, Germany)
triggers the same differentiation cascade of target cells
as the binding to the corresponding domains of thecollagen (biomimetics) (Fig. 2).
This cellular response could be demonstrated in various studies. Contrary to the use of conventional, biologically inert grafting materials, signiﬁcantly higher cellproliferation rates have been observed on materials
coated with P-15.5,6 They allow for immediate activation of all osteoblast progenitor cells, while physiologically a collagen network forms ﬁrst. This is theprerequisite for a multifocal formation of new bone,where unlike the classical defect healing process thebone is not organized exclusively starting from the vitalbone walls (Fig. 3). The result is accelerated formationof new, highly vascularized bone of very high quality.

three-dimensional, multifocal defect healing
after filling the defect with PepGen P-15

Various methods of defect healing with the use of micromolecular receptors.

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Valentin AH and Weber J.: Bone Regeneration with PepGen P15

Clinical Results
The receptor technology for bone remodeling in theform of the grafting material PepGen P-151 (DENTSPLY Friadent, Mannheim, Germany) has been available since 1999. Originally developed as a material foruse in periodontics,7,8 in 2000 the indications wereextended to include all other intra-oral rehabilitations.9
Today this material is widely used in the most various
indications. To ﬁll large defects PepGen P-151 is mostly
mixed with other bone grafting materials. This means
there are still enough receptor cells for cell attachment
but the total material cost is reduced.
Two examples from a continuing study that is investigating the application of PepGen P-151 in sinus
ﬂoor augmentation are described here. They not only
demonstrate histologically and histomorphometricallythe advantages of using the synthetic receptor but also
show the primary stability of the implants that canbe placed in the newly grafted bone. The histologicalresults described in the literature are in some cases notcoherent and are contradictory, with many different andunknown variables generally making it difﬁcult to compare the results of the study.
In a study on bone regeneration conducted byWheeler et al. in 2000,10 between 11% and 19% newly
formed bone was found regardless of the graftingmaterial used (hip bone, intra-oral bone, alloplastic
material (Interpore 200)). Surprisingly, this study demonstrated that the histological results with the use of
autogenous bone were in some cases worse than withpurely alloplastic materials.
The grafted sinus ﬂoor had the greatest volume ofbone growth from the primary woven bone formation
during the implant and prosthetic loading phase. The
woven bone is successively converted to lamellar bone.
According to the study conducted by Sartori et al. in
200311 the bone growth suddenly increases by a factor
of almost three after the ﬁrst year of prosthetic loading
and then continues to increase slowly until the tenthyear. The prerequisite for this bone growth is the comprehensive and qualitatively high-value primary boneformation (formation of woven bone) in the ﬁrst six totwelve months. Again this depends on the individual
regeneration potential and bioactivity of the graftingmaterial used, the number of bone-forming cells andthe number of collagen binding sites in the graftingmaterial.
In our ongoing study, the primary sinus ﬂoor augmentation was ﬁlled with a mixture of PepGen P-151(30%) to ‘‘improve the quality and accelerate the regeneration’’ and BioOss (0.5–1.0 gr., 70%) as a spacer
in a two-stage process. The implants were placed after
three, six or twelve months depending on the height of
the alveolar ridge. The bone cylinders retrieved withthe trephine drill (Brasseler Co., Lemgo, Germany; diameter 3.1 mm) during implant placement was histologically and histomorphometrically examined in thelaboratory.
Case 1The 65-year-old patient presented in our practice,where the examination showed a cyst in region 26 andextreme bone atrophy in the left lateral maxillary. The
residual alveolar height (RAH) was 0.5 mm. The patient desired a ﬁxed denture but refused an autogenous
bone transplant.
The pre-operative orthopantomograph clearly shows
the poor initial situation in the left lateral maxillary.
As a result of the cystic process only a very thin corticallamella remains adjacent to the maxillary sinus; theregenerative potential of the reduced alveolar ridge ispoor. The sinus ﬂoor was vertically augmentated withthe classical ‘‘window technique’’ with vertical graftingin the region of the cystic lesion. The cortical line separating the osseous lamella and the synthetic graftingmaterial can be clearly seen.
As a result of the poor initial situation an extended
healing period of 12 months was decided. The material removed with the trephine drill during implant
placement was initially ﬁxed in an ascending alcohol
series, then embedded in TECHNOVIT 7200, andsubsequently stained with toluidine blue for the histomorphometry. The histomorphometric measurement
result showed of 49.03% by volume formation of newbone in the regeneration material. The histomorphometric evaluation was performed by the University ofFreiburg, Germany. Two sections of the biopsy were
fabricated and the percentual volumes of bone andbone substitute material was determined and meanvalues of the two results were taken.
The histological view of the newly formed wovenbone shows not only complete vascularization of theregeneration material but also almost complete conversion of the ﬁller material BioOss. The ossiﬁcation
centers are in the immediate vicinity of the dark
Osteograf N particles.
Case 2
The 37-year-old patient had a primary sinus ﬂoor
augmentation and immediate implant placement in region 24 in the left maxilla. The residual alveolar ridge
height in the grafted region was 1–4 mm.
Figures 8 to 10 show the procedure for sinus ﬂoor
elevation. The greater residual alveolar ridge heightcompared to case 1 allowed a primary healing period of
six months.
The implant was placed analogously to case 1. FigureKeio J Med 2004; 53 (3): 166–171

169

Figs. 4 and 5 Pre-operative and post-operative orthopantomograph after removal of teeth, cystectomy and simultaneous sinus ﬂoor elevation
with PepGen P-151 and BioOss.

10 shows the bone core harvested from region 27. The
thin and paler region as residual alveolar ridge can beclearly seen in the top section without a microscope,
while the large lower segment is newly formed bone.
The XiVE implants (DENTSPLY Friadent, Mannheim, Germany) were threaded in place by machinein region 26 (diameter 5.5, L 13) and region 27 (di-ameter 5.5, L 13) and the insertion torque was measured simultaneously to assess the ﬁnal primary stability(FRIOS UNIT E, DENTSPLY Friadent, Mannheim,
Germany) Slightly different torque measurements wereachieved for the two implant positions, although both ofthem were well above the normal values in the area ofsinus ﬂoor elevation. Implant in area 26 reached a top

Fig. 6 Sinus lift and subsequent implant placement after 12 months
healing period with no signs of the cortical line. The loss of volume of
the grafting material appears to be clinically minor.

Fig. 7 Histological view of the trephined material with persistent
new bone, complete vascularization and generally incorporated spacer(BioOss).

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Valentin AH and Weber J.: Bone Regeneration with PepGen P15

Fig. 8View of the ‘‘Underwood septa’’.

torque value of 46.9 Ncm and implant in area 27 scoredat 39.9 Ncm.
Discussion
Clinical results and scientiﬁc documentation haveshown that predictable positive results can be achieved
with augmentation using bone grafting materials of themost varied types and origins. Today, the desire foraccelerated regeneration is at the center of scientiﬁcinterest.
The ﬁrst osteoconductive factor was discovered as
early as 1965 and named the ‘‘bone morphogenetic
protein’’.12 In 1979 osteoconductive glycoproteins
could be extracted from bone.13 However, because thecomplex interactions of the effective mechanisms of all
non-cellular growth factors are still not fully explained,bone can be induced only with greatly increased, unphysiological concentrations of these substances. The
questions that arise as a result of the biochemical stoechiometry and the decomposition and intermediate
products remain largely unanswered or have not beenFig. 9 Filling the new sinus with PepGen P-151 and BioOss mixture
after immediate implant placement in region 24 and soft tissue management with FRIADENT EsthetiCap.

Fig. 10

Bone core from region 27 after six months healing time.

considered. For this reason, the only practical method
so far is activation of mesenchymal stem cells, which are
directly differentiated to osteoblasts. This is enabled
by a peptide (P-15) bound to a carrier, which could
be identiﬁed as a cell-binding domain of the collagen 1
a 1 in scientiﬁc studies. The biological potential that
supports bone formation has been demonstrated by invitro studies as well as in clinical applications. The receptor technology has proven to be a practical and costefﬁcient method of accelerating bone regeneration. In
clinical use, it is signiﬁcant that the implants reach a
sufﬁcient primary stability in the ‘‘synthetically’’ grownbone. This primarily depends on the thickness of theresidual alveolar ridge, and also on the strength andcomplete regeneration of the grafting material. The
values measured were in some cases extremely high,Keio J Med 2004; 53 (3): 166–171

even in the weak site of the displaced sinus ﬂoor, and iscomparable with the DI bone of the mandible. This is
impressive, because the alveolar ridge had a residual
vertical height of 0–1 mm. The torque achieved in region 27 is solely attributable to the synthetic graftingmaterial. The long-term success rate in the grafted region is determined by the fastest possible and optimum
attachment of this area to the vascularization of thesubstrate. The complete vascularization of the graftingmaterial is an excellent sign of quality and an indication
for the vitality of the woven bone and the functionalityof the osteoblasts. Initial histological evaluations indicate that more bone is present in the regenerated
material as a result of the multiplication of the boneregeneration induced by the PepGen P-151, and thefunctional and force-oriented secondary integration of
the implants can proceed much more effectively during
the prosthetic loading phase. The constant volume is theimmediate result of the cell potentiating effect andthe complete vascularization of the grafted material.
While with autogenous transplants a volume loss of 30–
50% is recorded, with PepGen P-151 the volume loss
is approximately 5–10% only. This is the result of
the high inorganic proportion, the lower cellular conversion and the ﬁbrin contraction during the maturation
process.
Conclusion
Using the triggering mechanisms of a recombinantcollagen binding domain,14,15 complete bone regeneration cascades may be multiplied successfully leading toa faster and more predictable regeneration result in sinus ﬂoor augmentations.16
PepGen P15 simulates a biomimetic cell-attractive
environment for osteogenic cells and controls the stoechiometric processes of the bone regeneration cascades.
Clinically bone regeneration in sinus ﬂoor augmentations seems to be enhanced. The histologically examined biopsies show a complete vascularization and anincreased number of osteogenic cells. Previous attempts
in micromolecular bone regeneration focussed mainly
on highly concentrated protein deliveries (mitogenes,
morphogenes), vector techniques, mesenchymal stem
cell therapy using various types of scaffolds with various
success. In opposite to the above mentioned methods,
receptor engineering seems to be a promising, less expensive and more practical treatment option for a morenatural and stoechiometric correct bone regeneration.
Statistical results are still requested to verify theclinical beneﬁts. This is the focus of our ongoing study
in sinus ﬂoor augmentations which will be published in
the next article.

171

References
1. Ducy P, Schinke T, Karsenty G: The osteoblast: a sophisticatedﬁbroblast under central surveillance. Science 2000; 289: 1501–
1504
2. Bhatnagar RS, Qian JJ, Wedrychowska A, Sadeghi M, Wu YM,
Smith N: Design of biomimetic habitats for tissue engineeringwith P-15, a synthetic peptide analogue of collagen. Tissue Eng
1999; 5: 53–65
3. Bhatnagar RS, Qian JJ, Gough CA: The role in cell binding of abeta-bend within the triple helical region in collagen alpha 1 (I)chain: structural and biological evidence for conformational tautomerism on ﬁber surface. J Biomol Struct Dyn 1997; 14: 547–
560
4. Sastry SK, Horwitz AF: Integrin cytoplasmic domains: mediatorsof cytoskeletal linkages and extra- and intracellular initiatedtransmembrane signaling. Curr Opin Cell Biol 1993; 5: 819–831
5. Bhatnagar RS, Qian JJ, Gough CA: The role in cell binding of abeta-bend within the triple helical region in collagen alpha 1 (I)chain: structural and biological evidence for conformational tautomerism on ﬁber surface. J Biomol Struct Dyn 1997; 14: 547–
560
6. Turhani D, et al: Osteocalcinexpression in ‘‘Tissue Engineering’’
hergestellten Biokomposits. Z Zahnärztliche Impl 2003; 19: 153–
158
7. Yukna RA, Callan DP, Krauser JT, Evans GH, AichelmannReidy ME, Moore K, Cruz R, Scott JB: Multi-center clinicalevaluation of combination anorganic bovine-derived hydroxyapatite matrix (ABM)/cell binding peptide (P-15) as a bonereplacement graft material in human periodontal osseous defects. 6-month results. J Periodontol 1998; 69: 655–663
8. Yukna RA, Krauser JT, Callan DP, Evans GH, Cruz R, Martin
M: Multi-center clinical comparison of combination anorganic
bovine-derived hydroxyapatite matrix (ABM)/cell binding peptide (P-15) and ABM in human periodontal osseous defects. 6month results. J Periodontol 2000; 71: 1671–1679
9. Krauser JT, Rohrer MD, Wallace SS: Human histologic and histomorphometric analysis comparing OsteoGraf/N with PepGen
P-15 in the maxillary sinus elevation procedure: a case report.
Implant Dent 2000; 9: 298–302
10. Wheeler SL, Holmes RE, Calhoun CJ: Six-year clinical and histologic study of sinus-lift grafts. Int J Oral Maxillofac Implants
1996; 11: 26–34
11. Sartori S, Silvestri M, Forni F, Icaro Cornaglia A, Tesei P, Cattaneo V: Ten-year follow-up in a maxillary sinus augmentation
using anorganic bovine bone (Bio-Oss). A case report with histomorphometric evaluation. Clin Oral Implants Res 2003; 14:
369–372
12. Urist MR: Bone: formation by autoinduction. Science 1965; 150:
893–899
13. Urist MR, Mikulski A, Lietze A: Solubilized and insolubilizedbone morphogenetic protein. Proc Natl Acad Sci USA 1979; 76:
1828–1832
14. Qian JJ, Bhatnagar RS: Enhanced cell attachment to anorganicbone mineral in the presence of a synthetic peptide related tocollagen. J Biomed Mater Res 1996; 31: 545–554
15. Bhatnagar R, Qian JJ, Wedrychowsa A, Smith N: Constructionof biomimetic environments with a synthetic peptide analogue ofcollagen. Material Research Society Symp Proc 1998; v. 530
16. Krauser JT, Rohrer MD, Wallace SS: Human histologic and histomorphometric analysis comparing OsteoGraf/N with PepGen
P-15 in the maxillary sinus elevation procedure: a case report.
Implant Dent 2000; 9: 298–302