Scientific Foundation of BMP in Craniofacial Bone Regeneration

This report provides a comprehensive literature review on the application of Bone Morphogenetic Proteins (BMPs), particularly rhBMP-2, in craniofacial surgery for bone regeneration. It examines the rationale behind using BMPs, their biological mechanisms, and their effectiveness as grafting materials. The study focuses on clinical studies and animal trials, comparing the results of BMP use with other bone regeneration techniques like guided bone regeneration (GBR). The review covers the evolution of BMPs, from initial discoveries to current applications, emphasizing the potential to reconstruct large bone defects and minimize the need for secondary harvest sites. The methodology includes a search of Medline, Medpilot, and Cochrane Database of Systematic Reviews, with specific inclusion and exclusion criteria to ensure relevance. The report highlights the importance of selecting appropriate carrier systems for BMP delivery and discusses the challenges and advancements in the field, offering insights into future directions and clinical implications. The study also follows PRISMA guidelines for systematic reviews, ensuring a structured and rigorous approach to data analysis and presentation. This report is a valuable resource for maxillofacial surgeons, researchers, and students interested in the latest advancements in bone regeneration techniques.

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Bone Morophogenetic Protein Application as Grafting
Materials for Bone Regeneration in CraniofacialSurgery:
Current Application and Future Directions
Marco Cicciu`, DDS,PhD,Luca Fiorillo,DDS,Gabriele Cervino,DDS,PhD,
and Mutaz B.Habal,MD, FRCSC
Abstract: Rebuilding atrophied alveolar ridges can present a signifi-
cant challenge for the maxillofacial surgeons. A multitude of treatment
options including guided bone regeneration, onlay block grafting, and
distraction osteogenesis are today available as safe procedures.
The recent Food and Drug Administration approval of recombinant
human bone morphogenetic proteins (rhBMPs) has given clinicians an
added treatmentoption forreconstructing localized and large jaw
defects. Currently, several patients have been successfully treated with
the combination of bone graft and rhBMP-2 and the results have been
documented as predictable and safe by clinical and radiologic exam-
inations follow-up.In this study,a literature review was conducted
using Medline,Medpilot,and Cochrane Database ofSystematic
Reviews. It was concentrated on manuscripts and overviews published
in the last20 years (2000–2020).The key terms employed were
platelet-rich plasma, rhBMPs, and their combinations with the com-
mon scaffolds used for bone regeneration techniques. The results of
clinicalstudies and animaltrials were especially emphasized.The
statements from the literature were compared with authors’own
clinical data.
The potential to reconstruct these large bone defects with a growth
factorthus limiting oreven avoiding a secondary harvestsite is
exciting and it represents a new frontier in the field of surgery. This
study data confirm how there are excellentdocuments aboutthe
possible combination of using substitute materials and growth factor
for treating large and minor craniofacial bone defects.
Key Words: Bone regeneration,recombinant human bone
morphogenetic protein-2,tissue engineering
(J Craniofac Surg 2021;32: 787–793)
Rationale
Severalsurgicaltechniques and technologies aiming atbone
augmentation and osteointegration ofprosthetic implants in
the axialand body skeleton are continuously introduced.Thus,
orthopedics,oral/maxillofacial,and periodontalsurgeonsoften
confrontthe dilemma of selecting 1 technology or therapy over
the other.1 In orthopedics and maxillofacial surgery, novel tools and
techniques are being sought to improve the regeneration of bone
tissue.Numerous attempts have been made to enhance the osteo-
conductivity of titanium prostheses, including modifications in their
surface properties and coating with layers of calcium phosphate.
The decision-making process about the treatment choice for atro-
phic ridge reconstruction and the next dental implant positioning
becomes difficult and often it depends by the surgeons skills and
experience aboutthe treatmentdefects.The treatmentof severe
atrophies of the jaw is not so rare and clinicians had no references
both for the surgical technique decision, and for the graft material
choice.1–3
The investigationssupporting the clinicalevaluationsoften
focusjust on the statisticalsignificance ratherthan clinically
evaluate the significanteffectiveness of the biomaterials applied
to the surgicalprocedures.Moreover,the preclinicaldata are
usually referred to in vitro or clinical animal model observations,
and the clinical human study can be related with clinical reports or
surgical technical strategies.4
At the same way,in the last20 years,the number of dental
implants applied for oral prosthodontics procedures has increased
steadily worldwide, reaching about 1 million dental implantations
per year; but this procedure is related with adequate volume and
bone quality of the jaws.4 The use of dental implants for the oral
rehabilitation of fully and partially edentulous patients has greatly
broadened the scope of clinical dentistry, creating additional treat-
ment options in complex patients in which functional rehabilitation
was previously limited or inadequate. The predictability and long-
term success of dental implants have been well documented, both in
removable and fixed prostheses and their clinical success is con-
nected to the early osteointegration,so to the bone quality and
healing.In this field of knowledge and experience,the advent of
tissue engineering and specifically growth factors applied to max-
illofacialreconstruction procedure signed a fundamentalstep to
obtain bone tissue adequate in volume as wellin quality,with a
minimally invasive surgery.The main problem stillremains the
better choice of the ‘‘carrier’’ as well as the age of patients involved
in the surgery.5
About bone morhogenic proteins (BMPs) discoveries and their
clinical applications,firstly the Dr Marshal Urist investigated a
group ofproteins sequestered in bone and aptly named them
BMPs. Urist observed thatbone matrix preparations contained
BMPs that induced cartilage, bone, and marrow formation when
implanted intramuscularly in rodentmodels.6 The BMPs have
been studied extensively and represent a significant addition to
From the Department of Biomedicaland Dental Sciences and Morpholo-
gical and Functional Images,University of Messina, Messina, Italy.
Received May 6,2020.
Accepted for publication June 22,2020.
Address correspondence and reprint requests to Prof. Marco Cicciu`, DDS,
PhD,Department of Biomedical and Dental Sciences and Morpholo-
gical and Functional Imaging,University of Messina, Via Consolare
Valeria,98100 Messina, Italy; E-mail: [e-mail],
[e-mail]
The authors report no conflicts of interest.
Supplementaldigitalcontents are available forthis article.DirectURL
citations appear in the printed text and are provided in the HTML and
PDF versions of this article on the journal’s Web site (www.jcraniofa-
cialsurgery.com).
Copyright# 2020 by Mutaz B.Habal,MD
ISSN: 1049-2275
DOI: 10.1097/SCS.0000000000006937
SCIENTIFIC FOUNDATION
The Journalof CraniofacialSurgery Volume 32, Number 2, March/April2021 787

Copyright © 2021 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
our understanding of bone biology and development. The influ-
ence of BMPs may begin as early as at gestation and continues
throughout postfetal life,recapitulating processes in embryonic
bone formation.The BMPs actas growth and differentiation
factors, and as chemotactic agents. They stimulate angiogenesis,
migration, proliferation, and differentiation of stem cells from the
surrounding mesenchymal tissues into bone-forming cells in an
area of injury.7 – 9
The BMPs can be defined as multifunctionalgrowth factors
belonging to the transforming growth factor b superfamily. Family
members are expressed during limb development,endochondral
ossification,early fracture,and cartilage repair.The activity of
BMPs was firstidentified in the 1960s,buthuman BMPs were
unknown until their purification and cloning in the 1980s. To date,
about 15 BMPs family members have been identified and charac-
terized,but the most used in craniofacial surgery is currently the
recombinant human bone morphogenetic protein-2 (rhBMP-2).5,10
In the craniofacial surgery, to be efficacious at a biologic target
site, rhBMP-2 as well as other growth factors should be delivered
locally by a suitable carrier system. Numerous materials have been
tested fortheirefficiency in carrying rhBMP-2.Among these
materials,collagen,synthetic or naturalceramics,demineralized
bone matrix (DBM),and polyglycolic acid have been mostfre-
quently investigated.However,none ofthese carriermaterials
meets all of the requirements of an ideal osteoinductive system.11,12
Thanks to the improvementof surgicaltechniques and bio-
materials, it is now possible to regenerate portions of tissues that
have been lost,thanks to oral surgery techniques.Guided bone
regeneration (GBR) and guided tissue regeneration are surgical
procedures that use barrier membranes to direct the growth of new
bone and gingival tissue at sites with bone or gum volumes or sizes
for proper functioning,aesthetics,or insufficientimplant-pros-
thetic restoration.7 – 9
The GBR is similar to guided tissue regeneration, but is focused
on the development of hard tissues in addition to the soft tissues of
the periodontal attachment.At present,GBR is mainly applied in
the oral cavity to support growth of new hard tissue on an alveolar
ridge to allow stable positioning of dental implants. The bone graft
used in combination with membranes and otherbiomaterials of
differentderivation are now predictable surgicaltechniques.13,14
The bone is the 2nd most transplanted tissue after the blood,the
need for bone tissue transplantation occurs in the eventof major
trauma, in which there is nothing to do with a fracture, but with a
real bonegap, osteoporoticvertebralfractures,osteomyelitis,
bone gaps due notto trauma butto removalof tumors and bone
cysts.In these patients,the bone can be replaced with natural
autograft or autologous tissue, allograft or homologous, xenograft
or heterologous.13,14
As seen therefore, it is possible to use biomaterials of different
derivation,the osteoinductive properties typicalof these proteins
can act in synergy with osteoconductive biomaterials and improve
their characteristics, being this a highly debated topic in maxillofa-
cial surgery and dentistry, it was defined as the main objective of
this review.15
Objectives
Aim of this revision is to compare the recentresults of the
rhBMP-2 applicationin craniomaxillofacialreconstruction
defects,trying to highlightdata from recentliterature about
clinical effectiveness,patientsatisfaction,bonequality,and
long-term results.The main purpose of this review is therefore
to evaluate allthe randomized clinicaltrials published in the
literature and to examine the raw results,to understand the real
efficacy and safety of BMPs.
The Population-Intervention-Comparison-Outcome(PICO)
questions that summarize the aim of this review are:
In GBR need patients,whatis the effectof BMP on bone
features compared with no BMP use?
Does BMP influence bone quality and volume in patients who
needs oral bone regeneration?
METHODS
Protocol and Registration
Scientific protocols have been followed for the preparation of
this review.A search wasconducted in the systematic review
databasesto highlightsimilarstudiesor not.Subsequently the
systematic review has been registered on PROSPERO (international
database of prospectively registered systematic reviews in health
and social care, welfare, public health, education, crime, justice, and
internationaldevelopment,where there isa health-related out-
come).The PROSPERO is produced by Center for Review and
Dissemination and funded by the NationalInstitute forHealth
Research.The number and date of registration (under review) on
PROSPERO are as follows: number 183834 on May 2nd 2020.
The systematic review was conducted in accordance with the
Preferred Reporting Items for Systematic Reviews and Meta-Anal-
yses (PRISMA) statement, all the guidelines were followed (Check-
list/Flow diagram),the division into chapters and paragraphs was
respected. The analysis of the risk of bias and the setting up of the
research,including the drafting of the objective questions of the
systematic review, respected the PRISMA criteria, and in particular,
in the latter patient the PICO guidelines (Fig.1).
Eligibility Criteria
The full text of all studies of possible relevance was obtained for
assessment against the following inclusion criteria:
1. Study about bone regeneration techniques with and without use
of BMPs
FIGURE 1.Preferred Reporting Items for Systematic Reviews and Meta-Analyses
flow chart.
Cicciu` et al The Journalof CraniofacialSurgery Volume 32, Number 2, March/April2021
788 # 2021 Mutaz B.Habal,MD

Copyright © 2021 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
2. Study of patients’ side effect of BMPs
3. Clinical studies on BMPs use and control groups
4. Articles published in the last 20 years
The applied exclusion criteria for studies were as follows:
1. Studiesinvolvingsubjectswith other specific diseases,
immunologicdisorders,oncologicpatients,osteo-porosis,
and genetic diseases
2. Not enough information regarding the selected topic
3. No access to the title and abstract in English language or letters,
commentary,PhD thesis and editorials
4. Not randomized clinical trial (RCT) studies
Information Source
A literature review was conducted using Medline, Medpilot, and
Cochrane Database of Systematic Reviews.A hand search of the
reference lists in the articles retrieved was carried out to highlight
any additional publications and to improve the sensitivity.
Search
The review concentrated on manuscripts and overviews pub-
lished in the last 20 years (2000–2020). The key terms employed
were ‘‘bone morphogenetic proteins’’ and scaffolds used in combi-
nation.Statements from the literature with our own publications
have been compared. The search term was: ‘‘bmp[All Fields] AND
(‘‘mouth’’[MeSH Terms] OR ‘‘mouth’’[AllFields] OR ‘‘oral’’[All
Fields]) AND ‘‘bone regeneration’’[All Fields] in January 2020.
Study Selection
Two independent reviewers (LF and GC) of the University of
Messina singularly analyzed the results to selectinclusion and
exclusion criteria.They compared decisions and resolved differ-
ences through help of a 3rd expert reviewer (MC). For the stage of
reviewing of full-text articles, a complete independent dual revision
was performed. The results have been compared at the end of the
research with a 4th externalseniorreviewer(MH). A possible
disagreement regarding the inclusion of the studies was discussed
among the authors.
Data Collection Process
The firstphase of the research consisted in abstractreading,
which allowed us to make a firstscreening ofthe manuscript
eliminating those not concerning our research. Finally, the full text
of all studies was obtained and according to the expected inclusion/
exclusion criteria,articleswereselected and included in the
present review.
Data Items
After the firstliterature analysis,all articles were screened to
excludeirrelevantpublications,clinical reports,and thenon-
English language publications. Then, researches were not selected
based on data obtained from screening the abstracts. Some studies
included did not present sufficient data to conduct review, or data
were unclearor absent.The finalstage ofscreening involved
reading the full texts to confirm each study’s eligibility,based on
the inclusion and exclusion criteria.
Risk of Bias in Individual Studies
This type ofreview analyses allthe studies in the literature
in the last 20 years presenting a review of recent data about BMPs
effectsin bone regeneration.Regardlessof the resultsof the
studies taken into consideration,the evaluation was carried out
on the field of action of the analyses carried outby the studies.
Risk of bias analysis has been conducted according to PRISMA
guidelines.16–18
Summary Measures
Data were collected from results and arranged in the following
fields as seen in tables:
Supplementary DigitalContent,Table 2,http://links.lww.-
com/SCS/B749
Authorsand Year:authorsand yearof publication ofthe
selected study
Type of study: research type
Sample: sample size and type
Follow-up: follow-up of the RCT
Supplementary DigitalContent,Table 5,http://links.lww.-
com/SCS/B752
Authorsand Year:authorsand yearof publication ofthe
selected study
Group type: type of groups division and administrated drug
Methods: used method to evaluate outcomes
Raw data: results of the studies,and obtained measures
Statistical results: statistical analysis of the single study
Synthesis of Results
The results of individualstudies have been shown in Supple-
mentary Digital Content, Table 1, http://links.lww.com/SCS/B748.
In synthesisof resultsparagraph,individualresultshave been
manually summarized and main results have been highlighted in
temporal order.
Risk of Bias Across Studies
Risk of bias assessment (sometimes called ‘‘quality assessment’’
or ‘‘critical appraisal’’) helps to establish transparency of evidence
synthesis results and findings.A risk of bias assessmentis often
performed for each included study in your review.A risk of bias
analysis has been conducted according to PRISMA guidelines.
Additional Analyses
The Mann-Whitney U-testhas been performed between com-
parable results of individual studies to conduct a meta-analysis. The
Mann-Whitney U-test is a nonparametric test that allows 2 groups or
conditionsor treatmentsto be compared withoutmaking the
assumption that values are normally distributed.
RESULTS
Study Selection
From the first research, a total of 410 results were obtained from
the scientific databases.Subsequently these results,subjected to
screening and application of the inclusion and exclusion criteria,
were reduced as follows. Subsequently, only the articles published
in the last20 years were considered,for a totalof 394 results
remaining. Therefore, only the accessible and available data articles
(383)and subsequently the RCT with sufficientinformation to
conduct a review were considered (16).
Study Characteristics
Study characteristics have been shown according to Methods
section and they are in Supplementary Digital Content,Tables 2,
The Journalof CraniofacialSurgery Volume 32, Number 2, March/April2021 BMP Application as Grafting Material
# 2021 Mutaz B.Habal,MD 789

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http://links.lww.com/SCS/B749 and 3,http://links.lww.com/SCS/
B750.
Risk of Bias Within Studies
Risk of bias analysis for each study has been shown in Supple-
mentary Digital Content, Table 4, http://links.lww.com/SCS/B751
according to Methods section guidelines.
Results of Individual Studies
Results of individual studies have been shown in Supplementary
Digital Content, Table 5, http://links.lww.com/SCS/B752, accord-
ing to Summary Measures section.
Synthesis of Results
Results of the studies could be summarized as follows. Thoma
et al19 showed how there are no statisticaldifferences between
BMP-2 loaded xenogenic bone block and autogenous bone block on
outcomes of bone regeneration techniques. They conducted surgery
on 2 groups of 12 patients each. Ridge width decreased significantly
in both during 4 months time healing phases. Ridge width has been
evaluatedthoughta cone beam computedtomographyscan.
Authorsevaluatedthe buccalsoft-tissuecontourtoo, and it
appeared as slightly increased for both groups. Jo et al20 evaluated
differencesbetween an rhBMP-2 soaked absorbablecollagen
sponge (ACS)and hydroxyapatite (HA)particlesimmersed in
rhBMP-2 at a post extractive implant site; the site was surrounded
by a minimum of50% of alveolarbone.Groupsshowed no
statistical differences in bone height and width.Thoma et al21 in
this RCT on 24 patients,compared two treatment modalities with
xenogenic block loaded with rhBMP-2 and autogenous block in an
implant site regenerative surgery. Measure and histologic analyses
showed comparable resultsbetween techniques.Despite tissue
showed more mineralized componentin the controlgroup,this
group reported a higher morbidity.Shim et al22 used HA treated
with rhBMP-2 orbovine bone foralveolarridge preservation.
Difference in groups was statistically significant with better results
for test group. Nam et al23 studied differences between the use of
BMP-2 and bovine bone grafton alveolarridge augmentation.
There are no significantdifferencesbetween techniques.Kim
et al24 evaluated differences between Escherichia coli-produced
rhBMP-2 with a biphasic calcium phosphate carrier to deprotei-
nized bovine bone on human maxillary sinus floor augmentation.
According to authors,all sites healed with no complications,but
there were no differences between groups on radiographic analysis.
Kim et al,25in another study, evaluated differences in bone forma-
tion and safety between E coli-derived rhBMP-2 soaked with HA
granules and inorganic bovine bone xenograft.Despite soft tissue
and residualgraftshowed no significantdifferences,there was a
significant difference regarding bone formation; Authors obtained
these results through theirhistomorphometric analysis.Further-
more, there was no significant increase in the amount of rhBMP-2
antibody in the serum after the integration with the HA granules.
An interesting study of Marx and Harrell26investigated the role
of CD34þ cells during bone regeneration techniques. In their RCT,
authors investigated the use of 2 different grafts (shown in Results
of individual studies) on mandibular defects. Authors showed how
CD34þ cell counts above 200/mL were associated with a better
bone quality for the same amountof rhBMP-2.The oldestKim
et al27 study evaluated the effect of injectable DBM gel combined
and not with rhBMP-2. This study demonstrated how there were no
adverse effectin both groups and how there were no immune
response and no hematologic findings.Kim et al27 did not found
significant differences between groups. Coomes et al28 conducted
an RCT study comparing the bone regenerative propertiesof
rhBMP-2 with an ACS carrier to a sponge alone in postextraction
sites.Authors evaluated the possibility of dental implant rehabili-
tation without the need of additional augmentation. The test group
rhBMP-2 performed significantly better about clinicaland radio-
graphicalridge augmentation.Marx et al29 in an olderstudy,
evaluated the effectof rhBMP-2/ACS with crushed cancellous
freeze-dried allogeneic bone,and platelet-rich plasma versus the
effect of size-matched 100% autogenous grafts. Corinaldesi et al30
in their RCT study showed how rhBMP-7 with deproteinized bone
did not offer better results than deproteinized bone alone; on the
contrary,histologic and histomorphometric analysesof biopsy
specimens showed thatthere was significantly more new bone
on the controlside (19.9 [6.8]%)than on thetestside (6.6
[4.8]%).Despite of this,radiographic examination showed better,
butnotsignificant,results for testgroup.Triplettet al31 in their
prospective study evaluated the safety and effectiveness of rhBMP-
2 on ACS versus only the ACS on sinus floor augmentation.A
significantamountof new bone was formed by 6 months;the
rhBMP-2 group was significantly denser than that in the bone graft
group. No differences were found in the histologic analysis and the
regenerated bone was comparable to the native one.The success
rate for the rhBMP-2 on ACS group was 79%.Fiorelliniet al32
compared 2 differentconcentrations ofrhBMP-2 with an ACS
versus a collagen sponge alone. They showed how is it possible to
obtain the greaterbone augmentation ifa higherconcentration
(1.50 mg/mL)of rhBMP-2 is used forsocketpreservation after
tooth extraction.Bianchiet al33 conducted an RCT evaluating
computed tomography afterbone augmentation with 2 different
concentrations of rhBMP-2 in association with ACS or only an
ACS. This study presentsanalogieswith the previousone of
Fiorelliniet al.32 There was a statistically significantdifference
in bone formation between patients treated with a concentration of
1.5 mg/mL rhBMP-2 compared with each of the other groups; and
no statistical differences between groups.Jung et al34 in an RCT
evaluated the use ofxenogenic bone substitute and resorbable
collagen membrane with rhBMP-2 and without.There were sta-
tistically significant differences in defect height decreasing thanks
to the use of rhBMP-2,and histomorphologic analysis showed a
superior newly formed bone density at test sites than control sites.
Authorsalso showed how the surfacesof the bone substitute
particles were in direct contact with newly formed bone.
Risk of Bias Across Studies
The studies taken into consideration in this review are few, but
sufficient to conduct a meta-analysis.The evaluated studies have
investigated clinical trials evaluating the effect of rhBMP. The risk
of bias is defined as low. It is preferable to use simple approaches
for assessing validity that could be fully reported.
Additional Analysis
A Mann-Whitney U-test has been performed. The 9 studies that
measured rhBMP-2 outcomes (M ¼ 4.97) compared to the 9-study
control group (M ¼ 4.76) demonstrated not significant results. M stand
for mean (Supplementary Digital Content, Tables 6, http://links.lww.
com/SCS/B753 and 7, http://links.lww.com/SCS/B754).
Result 1: U-value
The U-value is 39.The criticalvalue of U atP < 0.05 is 17.
Therefore,the result is not significant at P < 0.05.
Result 2: Z-ratio
The Z-score is 0.0883. The P-value is 0.92828. The result is not
significant at P < 0.05.
Cicciu` et al The Journalof CraniofacialSurgery Volume 32, Number 2, March/April2021
790 # 2021 Mutaz B.Habal,MD

Copyright © 2021 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
DISCUSSION
Summary of Evidence
Thoma et al19showed how both rhBMP-2 loaded xenogenic and
autogenic bone blocksincreased the ridge width,but with no
differences between groups.They demonstrated how the impact
of hard tissue augmentation on the soft-tissue contour was minimal,
despite this is stilla debated topic.According to Jo etal,20 all
patients showed good healing,the delivery systems had a similar
efficacy on ridge preservation.Thoma etal21 concluded thatfor
implant site regeneration,autogenous bone provided more miner-
alized tissue and that there are no differences on ridge weight after
bone incremental.According to Shim etal,22 alveolar ridge was
preserved both with the use and not of rhBMP-2. In this investiga-
tion,the rhBMP-2/HA resulted in greater new bone formation at
3 months time aftersurgery.Nam etal23 concluded thatboth
evaluated techniquesprovide ridge augmentation,but with no
statisticaldifferencesbetweenthem. Authors believedthat
rhBMP-2/HA should be reserved forcomplicated bone defects.
According to Kim et al,24sinus augmentation with E coli-produced
rhBMP-2 carrying biphasic calcium phosphate carrierdid not
enhance bone regeneration at 24 weeks. Another Kim et al25study
suggested how low-dose E coli-derived rhBMP-2/HA was effective
in early stages for enhanced bone formation after maxillary sinus
floor augmentation without harmful adverse events. Kim et al27 in
their study showed that the application of rhBMP-2/DBM gel is safe
to use clinically forpreservation ofthe alveolarridge,and no
difference in the dimensionalchanges was observed between the
test group and the control ‘‘no rhBMP-2/DBM’’ group. According
to Coomes etal,28 rhBMP-2 used in combination with collagen
sponge in flapless extraction sites with buccal dehiscence is able to
regenerate the lost buccal bone, and to maintain ridge dimension at
leastfor 5 months.According to Marx etal,29 the composite
grafting technique resulted in less blood loss and shorter surgical
time butgreater and longer-lasting edema.This composite graft
represents an in situ tissue engineering conceptthatis able to
achieve results equivalentto autogenous grafts in large vertical
ridge augmentations without donor bone harvesting. Some authors
evaluated differences of the use of rhBMP-2 in different concen-
trations.Fiorellini et al32 demonstratedhow combinationof
rhBMP-2 and a common collagen sponge had positive effecton
new bone formation for dental implant placement. Bianchi et al33
demonstrated how, the higher concentration of rhBMP-2 in associ-
ation with ACS provided greater results on bone regeneration too.
According to Jung et al,34 the combination of the xenogenic bone
substitute mineralwith rhBMP-2 could enhance bone maturation
and regeneration,this protein has the potentialto improve and
accelerate GBR. Triplett et al31showed how rhBMP-2/ACS regen-
erated sites performed similarly to ACS after functionalloading.
Not only rhBMP-2 article was found during the results search.
Corinaldesiet al30 evaluated theeffectof rhBMP-7 in bone
regeneration,histologic analyses resulted in the formation of less
bone than treatment with deproteinized bovine bone alone.Marx
and Harrell26 studies evaluated how CD34þ cells play a primary
role during bone regeneration. The CD34 protein is a member of a
family of single-pass transmembrane sialomucin proteins that show
expression on early hematopoietic tissue and tissue associated with
the vessels.Cells expressing CD34 (CD34þ cells)are normally
found in the umbilical cord and bone marrow as hematopoietic cells
or in mesenchymalstem cells,they are also implicated in the
therapiesof spinalcord disease.With the sameamountof
rhBMP-2, the group with higher cell concentration obtains a bone
of clearly superiorquality,both on radiographic,clinical,and
histomorphometric examination. The CD34þ cell works as a central
signaling cell to mesenchymal stem cells and osteoprogenitor cells
in bone regeneration process. Furthermore, some studies on animals
showed thatthe addition of rhBMP-2 to the sites ofdistraction
osteogenesis improves soft tissue healing, and reduced graft expo-
sure and protecting the bone tissue healing.35 Differentstudies
reported patients when effectiveness of the rhBMP-2 action regard-
ing large defect reconstructions.36–38The formation of bone tissue
requires 3 main ingredients:the soluble osteoinductive signal,a
suitable insoluble substrate that acts as a support and can signal for
the formation of new bone tissue and a pool of mesenchymal cells
capable of capturing the signaland differentiating in osteoblasts.
All 3 components could be manipulated: the signal or morphoge-
netic signals that should be transmitted, the nature of the substrate,
the mesenchymalcells capable ofcontinuous differentiation.In
recent years, advances in cellular and molecular biology have made
it possible to clarify the fundamental mechanisms of bone healing,
the very meaning of the regenerative potential of the bone, opening
the way to bone tissue engineering.The signals responsible for
osteoinduction belong to a family of proteins,precisely rhBMPs.
The only rhBMPs on the market and approved by the Food and Drug
Administration are numbers 2 and 7.Otherproducts are being
studied by the Food and Drug Administration, such as rhBMP-XR,
basically represented by the BMP-9. These proteins belong to the
family of growth and differentiation factors known as transforming
growth factors b. The concept that bone induction depends on the
combined action ofBMPs and a complementary substrate is of
fundamentalimportance for therapeutic applications.For a local
release perspective, a carrier substrate is required to release BMPs
to specific receptors present on target cells in sufficient quantities to
evoke the desired therapeutic response. On the contrary, undiffer-
entiated mesenchymal cells adhere to a solid substrate to receive the
signal, proliferate and differentiate into bone-producing cells. The
substrate should therefore be able to receive the signal (BMPs) and
free it, but it should also act as a scaffold for the bone formation.
BMPs are not the only growth factors today.In fact,the platelet-
derived growth factors (PDGF) should be mentioned: in particular,
the use of PDGF-BB in combination with tricalcium beta-phosphate
carrier has given excellentclinicalresults in the regeneration of
periodontal bone defects of limited size. More recent works wanted
to test the regenerative potential of PDGF-BB in combination with
blocks of deproteinized bovine bone in difficult contexts,such as
the vertical increase of alveolar ridge. Even in this type of applica-
tion PDGF-BB has produced extremely promising results, proving
to be able to regenerate bone. It is certain that a specific geometric
configuration of the substrate is capable of promoting vascular and
mesenchymal invasion, hence osteogenesis. Soluble signals induce
morphogenesisand physicalforcesimparted by the geometric
topography of the substrate dictate biologic traits,building bone
induction and regulating the expression of selective gene products
according to the structure.The repetitive seriesof concavities
prepared on and within the substrate induces growth and rapid
invasion of the vessels and capillaries. These provide a continuous
flow of mesenchymal cells capable of differentiation and transfor-
mation into osteoblastic cells under the stimulus of BMPs. Osteo-
blasts are encouraged to migrate into pores with a diameter between
200 and 400 micron and it is on surfaces with these characteristics
thatmesenchymalcells also manage to express the osteogenic
phenotype.The concavities are in factequipped with geometric
memory,sincethey reproduce morphologic eventsthatoccur
during embryonic developmentand actas a ‘‘gate’’activating
the growth and differentiation of mesenchymalcells into osteo-
blasts.These evidences led to codify the conceptof geometric
induction of bone formation. The surface geometry of the substrate
influencescell morphology and the relationshipsbetween cell
structures,with enormous reflections on cellfunction,nucleus,
and gene expression. Different materials are cited as carriers, from
The Journalof CraniofacialSurgery Volume 32, Number 2, March/April2021 BMP Application as Grafting Material
# 2021 Mutaz B.Habal,MD 791

Copyright © 2021 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.
ACS, to deantigenized and deproteinized bovine bone, to hard tooth
tissues such as enameland dentin,or materials such as HA or
tricalcium betaphosphate. There is no evidence on which material
gives the best clinical results. In this sense, biomimetic biomaterials
could be cited,intelligentmatricescapable ofmimicking and
guiding tissue healing by dictating precise biologic traitsand
building bone induction.Certainly,the concavity represents an
idealmicroenvironmentalso in this sense because itprotects the
mesenchymal cells from excessive stress,allowing their adhesion
and proliferation, therefore the differentiation into osteoblasts.39–41
Thanks to these new surgicaltechniques and biomaterial,it is
therefore possible,in addition to increasing the predictability of
rehabilitations,also their safety.
Limitations
The main limitation of this study is given by the fact that it is not
possible to couple the single resultand carry outa univocal
statistical analysis, as the results come in the single result evaluated
using differentparameters.Only English-language articles were
considered and this may be a limitation.
There may also be a discrepancy in the results, which may also
caused by the very wide temporary range.
EDUCATIONAL MESSAGE AND CONCLUSIONS
Maxillofacialbone surgery techniques become increasingly pre-
dictable, thanks to the evolution of biomaterials. Certainly, BMPs
representan added factor,which could influence the success of
regeneration. From this systematic review, however, although there
are clinicaldifferencesin the resultsanalyzed,a statistically
significantdifference isnot demonstrated.In this study,only
manuscripts evaluating different dosages,distinctive carriers,and
peculiarBMPs application techniques were considered.Further
studies on these methods are needed to clarify the function of
BMPs, above allto evaluate the predictable value and the effec-
tiveness of different surgical techniques.
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