Bone regeneration in the presence of a synthetic hydroxyapatite/silica oxide-based and a xenogenic hydroxyapatite-based bone substitute material

TLDR: There is evidence that the synthetic hydroxyapatite/silica oxide granules provide comparable results with a standard xenogenic bovine mineral in terms of bone formation and defect bridging in non-critical size defects.

Abstract: Objectives: A comparison of synthetic hydroxyapatite/silica oxide, xenogenic hydroxyapatite-based bone substitute materials with empty control sites in terms of bone regeneration enhancement in a rabbit calvarial four non-critical-sized defect model Methods: In each of six rabbits, four bicortical calvarial bone defects were generated The following four treatment modalities were randomly allocated: (1) empty control site, (2) synthetic hydroxyapatite/silica oxide-based (HA/SiO) test granules, (3) xenogenic hydroxyapatite -based granules, (4) synthetic hydroxyapatite/silica oxide -based (HA/SiO) test two granules The results of the latter granules have not been reported due to their size being three times bigger than the other two granule types After 4 weeks, the animals were sacrificed and un-decalcified sections were obtained for histological analyses For statistical analysis, the Kruskal-Wallis test was applied (P<005) Results: Histomorphometric analysis showed an average area fraction of newly formed bone of 1232±1036% for the empty control, 1747±642% for the xenogenic hydroxyapatite -based granules group, and 212±532% for the group treated with synthetic hydroxyapatite/silica oxide -based granules Based on the middle section, newly formed bone bridged the defect to 3833±3755% in the empty control group, 5433±2212% in the xenogenic hydroxyapatite -based granules group, and to 79±1331% in the synthetic hydroxyapatite/silica oxide -based granules group The bone-to-bone substitute contact was 4638±1898% for the xenogenic and 5986±1492% for the synthetic hydroxyapatite/silica oxide-based granules group No significant difference in terms of bone formation and defect bridging could be detected between the two bone substitute materials or the empty defect Conclusion: There is evidence that the synthetic hydroxyapatite/silica oxide granules provide comparable results with a standard xenogenic bovine mineral in terms of bone formation and defect bridging in non-critical size defects To cite this article: 
Kruse A, Jung RE, Nicholls F, Zwahlen RA, Hammerle CHF, Weber FE Bone regeneration in the presence of a synthetic hydroxyapatite/silica oxide -based and a xenogenic hydroxyapatite -based bone substitute material

Figures

Fig. 5. Bone to bone substitute contact. The results of the histomorphometric analysis revealed no significant difference between the percentages of bone/bone substitute interface. The lines to the right of the values indicate the median of the group.

Fig. 2. Histological sections of the cranial defects in rabbits 4 weeks postoperatively: (A,B) No filling (empty) as a negative control, (C,D) xenogenic bone mineral as a golden standard, (E,F) as test material. Scale in millimeters. Original magnifications were 100 fold. Histological sections of the cranial defects in higher magnifications: (a, b) sintered bovine bone mineral, (c, d, e) synthetic hydroxyapatite/silica oxide granules; scales provided are 100 µm. Original magnifications were 300 fold. The areas shown with higher magnification are indicated.

Fig. 3. Bone tissue within the defect. The lines to the right of the values indicate the median of the group. No significant differences between the groups were observed.

Fig. 1. Picture of the operative site showing one example for defects before and after application of bone substitute materials. A: empty, B: sintered bovine bone mineral (DBBM) (0.25-1mm), C: Synthetic hydroxyapatite/silica oxide granules (HA/SiO) (0.25-1mm) D: Synthetic hydroxyapatite/silica oxide granules (1-3 mm) Please note that the size of the material (D) was much bigger than that of the other materials. Therefore these results are not reported here.

Fig. 4. Bony bridging is the percentage of the defect where new bone formation has occurred. The lines to the right of the values indicate the median of the group. No significant differences between the groups were observed.

Full text

ZurichOpenRepositoryand
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Year:2011
Boneregenerationinthepresenceofasynthetichydroxyapatite/silica
oxide-basedandaxenogenichydroxyapatite-basedbonesubstitutemateria
Kruse,A;Jung,RE;Nicholls,F;Zwahlen,RA;Hämmerle,CHF;Weber,FranzE
Abstract:Objectives:Acomparisonofsynthetichydroxyapatite/silicaoxide,xenogenichydroxyapatite-
basedbonesubstitutematerialswithemptycontrolsitesintermsofboneregenerationenhancementina
rabbitcalvarialfournon-critical-sizeddefectmodel.Methods:Ineachofsixrabbits,fourbicorticalcal-
varialbonedefectsweregenerated.Thefollowingfourtreatmentmodalitieswererandomlyallocated:(1)
emptycontrolsite,(2)synthetichydroxyapatite/silicaoxide-based(HA/SiO)testgranules,(3)xenogenic
hydroxyapatite-basedgranules,(4)synthetichydroxyapatite/silicaoxide-based(HA/SiO)testtwogran-
ules.Theresultsofthelattergranuleshavenotbeenreportedduetotheirsizebeingthreetimesbigger
thantheothertwogranuletypes.After4weeks,theanimalsweresacricedandun-decalciedsec-
tionswereobtainedforhistologicalanalyses.Forstatisticalanalysis,theKruskal-Wallistestwasapplied
(P<0.05).Results:Histomorphometricanalysisshowedanaverageareafractionofnewlyformedbone
of12.32±10.36%fortheemptycontrol,17.47±6.42%forthexenogenichydroxyapatite-basedgranules
group,and21.2±5.32%forthegrouptreatedwithsynthetichydroxyapatite/silicaoxide-basedgranules.
Basedonthemiddlesection,newlyformedbonebridgedthedefectto38.33±37.55%intheemptycontrol
group,54.33±22.12%inthexenogenichydroxyapatite-basedgranulesgroup,andto79±13.31%inthe
synthetichydroxyapatite/silicaoxide-basedgranulesgroup.Thebone-to-bonesubstitutecontactwas
46.38±18.98%forthexenogenicand59.86±14.92%forthesynthetichydroxyapatite/silicaoxide-based
granulesgroup.Nosignicantdierenceintermsofboneformationanddefectbridgingcouldbede-
tectedbetweenthetwobonesubstitutematerialsortheemptydefect.Conclusion:Thereisevidencethat
thesynthetichydroxyapatite/silicaoxidegranulesprovidecomparableresultswithastandardxenogenic
bovinemineralintermsofboneformationanddefectbridginginnon-criticalsizedefects.Tocitethis
article: KruseA,JungRE,NichollsF,ZwahlenRA,HämmerleCHF,WeberFE.Boneregenerationin
thepresenceofasynthetichydroxyapatite/silicaoxide-basedandaxenogenichydroxyapatite-based
bonesubstitutematerial.
DOI:https://doi.org/10.1111/j.1600-0501.2010.02039.x
PostedattheZurichOpenRepositoryandArchive,UniversityofZurich
ZORAURL:https://doi.org/10.5167/uzh-40370
JournalArticle
AcceptedVersion
Originallypublishedat:
Kruse,A;Jung,RE;Nicholls,F;Zwahlen,RA;Hämmerle,CHF;Weber,FranzE(2011).Boneregen-
erationinthepresenceofasynthetichydroxyapatite/silicaoxide-basedandaxenogenichydroxyapatite-
basedbonesubstitutemateria.ClinicalOralImplantsResearch,22(5):506-511.
DOI:https://doi.org/10.1111/j.1600-0501.2010.02039.x

1
Bone regeneration in the presence of a synthetic
hydroxyapatite/silica oxide based and a xenogenic hydroxyapatite
based bone substitute material
Kruse A
1
, Jung RE
2
, Nicholls F
3
, Zwahlen RA
1
, Hämmerle CHF
2
,
Weber FE
1*
1
University Hospital Zurich; Dept. of Cranio-Maxillofacial Surgery, Oral Biotechnology &
Bioengineering; Frauenklinikstrasse 24, 8091 Zürich; Switzerland
2
Department of Fixed and Removable Prothodontics and Dental Material Science, Dental
School, University of Zurich, Switzerland
3
University Hospital Zurich; ZKF; Zurich; Switzerland
* Corresponding author: FE Weber, University Hospital; Dept. of Cranio-Maxillofacial
Surgery, Oral Biotechnology & Bioengineering; Frauenklinikstrasse 24, 8091 Zürich;
Switzerland Tel: +41 44 255 5055, Fax: +41 44 255 4179
e-mail: franz.weber@zzmk.uzh.ch
Key words: bone substitute material, nano-crystalline hydroxyapatite, bone
regeneration

2
Abstract:
Objectives: Comparison of synthetic hydroxyapatite/silica oxide, xenogenic
hydroxyapatite based bone substitute materials with empty control sites in terms of
bone regeneration enhancement in a rabbit calvarial 4 non-critical sized defect
model.
Methods: In each of six rabbits, four bicortical calvarial bone defects were
generated. The following four treatment modalities were randomly allocated: (1)
empty control site, (2) synthetic hydroxyapatite/silica oxide based (HA/SiO) test
granules, (3) xenogenic hydroxyapatite based granules, (4) synthetic
hydroxyapatite/silica oxide based (HA/SiO) test 2 granules. The results of the latter
granules have not been reported due to their size being 3 times bigger than the other
two granule types. After four weeks, the animals were sacrificed and un-decalcified
sections were obtained for histological analyses.
For statistical analysis the Kruskan-Wallis test was applied (p<0.05).
Results: Histomorphometric analysis showed an average area fraction of newly
formed bone of 12.32±10.36% for the empty control, 17.47±6.42% for the xenogenic
hydroxyapatite based granules group, and 21.20±5.32% for the group treated with
synthetic hydroxyapatite/silica oxide based granules. Based on the middle section,
newly formed bone bridged the defect to 38.33±37.55% in the empty control group,
54.33±22.12% in the xenogenic hydroxyapatite based granules group, and to
79.00±13.31% in the synthetic hydroxyapatite/silica oxide based granules group. The
bone to bone substitute contact was 46.38±18.98% for the xenogenic and
59.86±14.92% for the synthetic hydroxyapatite/silica oxide based granules group.
No significant difference in terms of bone formation and defect bridging could be
detected between the two bone substitute materials or the empty defect.
Conclusion: There is evidence that the synthetic hydroxyapatite/silica oxide
granules provide comparable results to a standard xenogenic bovine mineral in terms
of bone formation and defect bridging in non critical size defects.
The substitution of autologous bone with synthetic materials to treat bone defects
represents still a challenge. Hydrated calcium phosphates, as hydroxyapatite, are
often used to develop synthetic bone substitutes due to their crystallographic
structures similar to bone (Hing et al. 2006). For extended bone defects autologous

3
bone is still the gold standard since hydroxyapatite based scaffolds need additions
like stem cells (Cancedda et al. 2007) and/or growth factors (Warnke et al. 2006) to
compete with them. For smaller defects, however, hydroxyapatite based scaffolds
improved by the addition of inorganic substances like silicon or by the application of
more sophisticated handling procedures omitting sintering yielding in a reduced
osteoconductivity (Henkel et al. 2006) might also serve the purpose.
In 1970 Carlisle (Carlisle 1970) found out that deficiency in silicon lead to abnormal
bone formation. Based on several other studies confirming this initial findings
(Schwarz & Milne 1972, Seaborn & Nielsen 2002), silicon has become an important
research topic in bone metabolism. Silicon is a major element in bioactive glass and
contributes to its enhanced bioactivity in vitro (Gao et al. 2001 , Gough et al. 2004)
with significant up-regulation of osteoblast proliferation and gene expression when
exposed to ionic dissolution products of bioactive glasses (Gao 2001, Hing et al.
2006, Xynos, et al. 2001).
In 2000, mimicking the postmenopausal state, Rico and co-workers (Rico et al. 2000)
detected in ovariectomized rats, that very high level of dietary silicon may abolish
bone mineral loss by increasing bone mineral content. A similar finding was stated in
2004 by Jugdaohsingh and co-workers (Jugdaohsingh et al. 2004) which suggested
in their Framingham Offspring Cohort study that higher dietary silicon intake in men
and younger women may have salutary effects on skeletal bone health, especially
cortical bone health.
In the course of the development of synthetic bone substitution materials many
researchers up to date have demonstrated in preclinical tests the benefits to early
bone ingrowth and repair through incorporation of silicon into porous HA (Hing et al.
2006, Patel et al. 2005, Seaborn & Nielsen 2002) or into calcium silicate ceramics
(Xu et al. 2008). Others confirmed the influence of silicon on cell proliferation ability

4
when compared to phase pure HA (Xu & Khor 2007) in vitro. In a recent paper Huang
and co-workers (Huang et al. 2008)
showed that internalization of mesoporous silica
nanoparticles induced a significant but transient osteogenic signal in human
mesenchymal stem cells.
During their synthesis process, most bone substitutes are sintered resulting in more
compact and less porous materials, where osteoconductivity might be reduced
(Gerike et al. 2006). The present test material is a non-sintered nano-crystalline
hydroxyapatite embedded in a highly porous silica gel matrix (HA/SiO). In order to
guarantee both high osteoinductive property and biodegradability, the granules are
loosely packed and present porosity between 60-80% (Werner et al. 2002). The gold
standard bone substitute material is a deproteinized bovine bone mineral (DBBM),
consisting of a mineral osseous matrix where the organic components have been
removed by pyrolysis (Spector 1994),
a procedure which also sinters the material.
Clinical outcomes of diverse procedures using DBBM are very well documented
(Esposito et al. 2006, McAllister & Haghighat 2007). Randomized clinical trials with
the synthetic non-sintered HA/SiO bone substitute material are not available yet but
several studies have been published recently. An immunohistochemical study on
biopsies from human jaws treated with the synthetic non-sintered HA/SiO bone
substitute material indicates that this material has osteoconductive and biomimetic
properties and is integrated into the host’s physiological bone turnover as early as
3.5 month postoperatively (Götz et al. 2008). A 3-year clinical and radiographic case
study on 13 patients showed successful outcome of implants placed in conjunction
with maxillary sinus floor augmentation using this synthetic hydroxyapatite/silica
oxide based material (Heinemann et al. 2009). Another preliminary histological study
with the same material shows sufficient bone formation in specimens harvested 6
months after sinus lifts were performed in severely resorbed maxillae (Canullo &