Keywords hydroxyapatite - 3D printing - alveolar ridge augmentation - dimensional accuracy
- binder jetting technique - bone block grafts
Introduction
Synthetic graft has emerged as an alternative to traditional autogenous bone harvesting
in dental and maxillofacial procedures. While autogenous bone block grafts remain
the gold standard for bone augmentation, they are associated with several drawbacks,
including patient morbidity, technical complexity, and time-consuming procedures.[1 ]
[2 ] These limitations have driven the search for alternative bone graft materials that
can provide comparable outcomes with reduced patient burden.
Xenografts, typically derived from bovine or porcine sources, are natural in origin.[3 ]
[4 ] They maintain much of the original bone's structure and composition, including the
mineral content and collagen matrix. This similarity to human bone often allows for
excellent biocompatibility and osteoconductive properties.[5 ] The natural origin of xenografts may contribute to their steady and predictable
bone density increase over time.[6 ] Hydroxyapatite (HA), a synthetic composite material, has gained prominence in the
field of bone regeneration.[7 ] Its chemical structure closely resembles that of natural alveolar bone, making it
an excellent candidate for bone substitution. HA was developed to replicate the inorganic
components of bone tissue in a controllable, manufactured form.[8 ] This synthetic nature allows for precise control over its composition, porosity,
and degradation rate, optimizing bone regeneration.[8 ]
HA belongs to the family of calcium phosphate biomaterials, widely used for the treatment
of bone defects due to their osteoconductive properties and biocompatibility. Its
advantages include strong bioaffinity and osteoconductive properties, which create
a favorable environment for osteoprogenitor cells to proliferate and differentiate
into bone-forming cells.[9 ] However, properties such as pore size, configuration, and sintering temperature
significantly influence HA's performance.[10 ] When designed with an optimal pore size and shape, HA can provide a three-dimensional
(3D) structure for bone ingrowth while maintaining mechanical durability.[10 ] However, HA still has certain limitations. Traditional sintering-based manufacturing
techniques can lead to slow resorption rates. Despite these challenges, ongoing research
continues to improve HA's properties and performance making it a valuable tool in
bone augmentation, repair, and regeneration procedures.[11 ]
Recently, 3D printing technology has revolutionized the field of bone grafting by
offering a personalized and efficient approach. Advanced imaging techniques, such
as cone-beam computed tomography (CBCT), allow clinicians to generate a detailed 3D
model of the patient's alveolar bone and the specific area requiring grafting. This
digital model is then used to design and fabricate a customized bone graft using biocompatible
materials such as HA or polylactic acid, ensuring a precise fit tailored to the patient's
anatomical needs.[12 ]
Previously, we have developed a 3D-printed HA (3DHA), as a potential alternative to
autogenous bone grafts. The 3DHA bone graft is fabricated using a binder jetting technique
with low-temperature phosphorization, designed to serve as a bone substitute for alveolar
ridge augmentation before implant placement.[13 ]
[14 ] A key advantage of this 3DHA lies in the integration of 3D printing technology,
which enables the fabrication of grafts in precise shapes and sizes tailored to alveolar
defects. In addition, its resorbability supports tissue regeneration and promotes
new tissue ingrowth.[15 ]
[16 ]
[17 ]
While the use of 3DHA in bone regeneration has been reported, studies quantitatively
integrating high-resolution dimensional accuracy analysis with initial clinical outcomes
are still limited. In clinical applications, the success of 3D-printed bone block
grafts depends on various factors including their fit to the recipient site defect.
Several methods are available for analyzing scaffold structure.[18 ] One of the most effective techniques is micro-CT (µCT), which allows detailed visualization
of bone architecture and provides a 3D assessment of scaffold morphology.[19 ] µCT offers high-resolution imaging and is widely accessible for evaluating bone
graft integrity and internal structure.[20 ] To assess the accuracy of 3D-printed grafts, 3D analysis software was used to compare
the printed bone graft scan with the original virtual design through superimposition
techniques.[21 ] This method enables precise evaluation of fabrication accuracy, particularly for
materials with irregular or complex geometric shapes.[22 ] Recently, 3D assessment techniques have been introduced in prosthetic dentistry
for applications such as evaluating the fit of dental crowns and metal frameworks
for removable partial dentures.[23 ]
[24 ] However, limited data exist on the accuracy of this tool in prosthetic dentistry,
highlighting the need for further research in this area.
This pilot study aims to evaluate the dimensional accuracy of 3DHA bone block grafts,
manufactured using the binder jetting technique, by assessing their internal fit to
the target defect and comparing the 3D deviation between the printed grafts and their
virtual designs. Clinical application was preliminary conducted in eight patients,
where the optimized 3DHA grafts were assessed for their efficacy in augmenting alveolar
ridge defects. This study uniquely advances the field by demonstrating quantitative
dimensional accuracy alongside initial clinical outcomes, establishing both the technical
precision and translational feasibility of this approach.
Materials and Methods
Study Workflow
This study utilized a four-step approach to evaluate dimensional accuracy and fit
(gap between the 3DHA graft and the ridge defect), including: (1) designing the 3DHA
graft based on individual patient CBCT scans; (2) scanning the fabricated 3DHA graft
using μCT; (3) assessing the dimensional accuracy of the printed graft; and (4) analyzing
the gap between the 3DHA graft and the intended ridge defect ([Fig. 1A ]).
Fig. 1 (A ) Study workflow to analyze printing accuracy, fitness, and gap of three-dimensional
(3D)-printed hydroxyapatite (3DHA) grafts: (a) 3D discrepancy between the virtual
3DHA design and the microcomputed tomography (µCT)-scanned 3DHA is illustrated using
color maps to show deviation patterns, (b) STL files of the scanned 3DHA obtained
from μCT were aligned with the STL files of patients' defects. The marginal gap was
measured 1.25 mm from the marginal edge (blue area), while the internal gap was measured
in the remaining internal graft region, excluding the 1.25-mm margin (green area).
(B ) Assessment of bone volume and dimensional changes at 6 months postaugmentation through
superimposition of STL files from μCT-scanned 3DHA and 6 months cone-beam computed
tomography (CBCT) scans: (a) bone volume changes, (b) dimensional changes.
Clinical data were collected to evaluate changes in bone volume and dimensions. The
STL data sets from μCT (initial bone engraftment) and CBCT (6 months postaugmentation)
were analyzed to quantify these changes ([Fig. 1B ]). No calibration or cross-validation was performed to account for the differences
between these imaging modalities in voxel size, resolution, and reconstruction algorithms.
3DHA Bone Block Graft Design
CT scans of the patients were obtained with ethical approval from the Human Research
Ethics Committee of Thammasat University (Science) (COA no. 039/2562). The eight alveolar
ridge defects were located in the anterior maxilla (3 cases), premolar maxilla (4
cases), and posterior mandible (1 case). Digital Imaging and Communications in Medicine
(DICOM) files from the scans were imported into a dental implant planning software
(DentiPlan, NECTEC, Thailand) and then converted into STL files. These STL files were
further processed using 3D design software (Geomagic Freeform, 3D Systems, United
States) and a professional haptic device (The Touch Haptic Device, 3D Systems) to
create customized 3D bone block grafts. The 3DHA grafts were manufactured layer-by-layer
by a binder jetted 3D printer (Projet160, 3D Systems) operating at a resolution of
300 × 450 dpi and a layer thickness of 0.1 mm. Calcium sulfate-based powder (Visijet
PXL Core, 3D Systems) and a water-based binder (Visijet PXL Clear, 3D Systems) were
employed as raw materials. During printing, the binder selectively adhered the powder
particles at designated regions to form the structure, which solidified through evaporation,
eliminating the need for additional curing. No postprocessing was performed. After
the grafts were printed, they were soaked in 1 M disodium hydrogen phosphate solution
(Sigma Aldrich, United States) at 100°C for 48 hours, resulting in conversion to HA
structure. This technique preserved the original dimensions of the grafts and avoided
the shrinkage typically associated with sintering. The 3DHA possesses a porosity of
82.09 ± 3.00% and demonstrate a compressive strength of 7.32 ± 0.54 N. Finally, all
3DHA grafts were dried and sterilized using ethylene oxide gas.[17 ]
Microcomputed Tomography
The 3DHA were scanned using μCT scanner (SkyScan 1275, Bruker, Kontich, Belgium) to
assess their 3D morphology and architecture of 3DHA. Each 3DHA was securely mounted
on a holder table for scanning. The scanning procedure was performed using an X-ray
source potential of 70 kV, a current of 129 μA, 8W, and a voxel size of 6 μm. X-ray
transmission through the 3DHA samples was acquired over a full 360-degree rotation,
with an exposure time of approximately 30 minutes per sample.
All projection image data were reconstructed using NRecon software (NRecon V.2, Skyscan,
Bruker) to generate 3D images, which were visualized using CTvox software (CTvox,
Skyscan, Bruker). The volume of interest of the 3DHA was then analyzed using CTAn
software (CTAn, Skyscan, Bruker) and converted into STL files for further evaluation
([Fig. 2 ]).
Dimensional Accuracy Assessment
The geometric dimensions (width, length, height) of the 3DHA bone block graft virtual
design and μCT-scanned models were measured using a dimensional bounding box, aligned
to the global coordinate axis ([Supplementary Fig. S1 ]).
Measurements were recorded in millimeter (mm) using Geomagic FreeForm (3D Systems).
The relative percentage differences between the virtual design and μCT-scanned models
were calculated using the following formula:
The virtual 3DHA, designed using the Geomagic FreeForm software (3D Systems), was
imported into the analysis program (Geomagic Control X, 3D Systems) as reference data.
The scanned 3DHA, obtained by μCT, was then superimposed on the reference data using
initial alignment followed by best-fit alignment. The accuracy of the 3DHA was analyzed
by calculating the root mean square (RMS) of the total graft area (overall) as well
as dividing into three sections: marginal, contour, and internal area each consisting
of 40 points (point-to-surface). A 3D analysis was performed to assess the deviation
between the scanned 3DHA and the reference model.
The measurement data were evaluated using the intraclass correlation coefficient at
95% confidence interval to determine the level of accuracy of the printed 3DHA graft
within the same tested groups. The standard error of repeated measurement was less
than 0.002 mm. For the 3D analysis, the differences between the superimposed data
were analyzed using the 3D compare function in the inspection software, which generated
color surface maps. A maximum critical value of ± 0.10 mm and maximum nominal values
of ± 0.01 mm were set for color spectrum.
All points within the scanned graft of the reference data and all points within the
scanned 3DHA were calculated to determine the RMS values as follows:
X
1 in this equation is the data point of reference (virtual design) i , X
2 is the data point of study group i (μCT-scanned models), and n is the number of all measurement points.
To better illustrate accuracy differences, a color difference map was generated using
a ± 0.1 mm range (divided into 20 color segments) within the 3D inspection software.
In the color map, the red zone (0.01–0.1 mm) represents a positive error, indicating
that the scanned 3DHA data was larger than the reference or positive error in the
printing process. Conversely, the blue zone (−0.1 to −0.01 mm) indicates a negative
error, meaning the scanned 3DHA was smaller than the reference or there was shrinkage
in the printing process. The green zone (±0.1 mm) reflects exceptional accuracy with
meticulous precision ([Fig. 1Aa ]).
Gap Analysis
The STL files of the scanned 3DHA obtained from μCT were aligned with the STL files
of patients' defects. The mean gap distances between the internal area of the scanned
3DHA and the defect (surface-to-surface area) were assessed using Geomagic software.
The internal fit evaluation was performed in two areas consisting of the marginal
and internal area. The marginal gap was measured at a distance of 1.25 mm from the
marginal edge (blue area). The internal gap was measured at the internal graft area,
excluding the 1.25 mm margin (green area), as shown in [Fig. 1Ab ].
Bone Volume and Dimensional Changes
The CBCT scan (DentiiScan 2.0, NSTDA, Thailand) was taken at 6 months postaugmentation
(voxel size 0.2 mm, field of view [FOV] [diameter × height] 6 × 6 cm2 , focal spot 0.5 mm, 70 kVp). The DICOM data set was converted to an STL file data
set. For the baseline data, the initial graft from μCT was reconstructed using CTAn
software (CTAn, Skyscan, Bruker) and converted into STL format, then merged with the
preoperative bone defect model. The initial μCT model with the defect was superimposed
onto 6-month CBCT model. To determine the bone volume changes, the 6-month CBCT volume
was subtracted from the initial μCT volume and volume changes were calculated in mm3 using Geomagic FreeForm software ([Fig. 1Ba ]).
Dimensional changes were analyzed by measuring the 3D horizontal ridge alterations
between the baseline μCT and the 6-month postaugmentation CBCT data in mm using Geomagic
Control X software ([Fig. 1Bb ]).
Clinical Relevance
Eight patients who required dental implant therapy with horizontal bone defect were
enrolled in this study between June 2019 and December 2020 at the Faculty of Dentistry,
Thammasat University Hospital. The clinical protocol was registered in the Thai Clinical
Trials Registry (Study ID: TCTR20190704004) and approved by the Human Research Ethics
Committee of Thammasat University (Science) (COA no. 039/2562). Written informed consent,
outlining the details and purpose of the study, was obtained from all patients.
Statistical Analysis
Statistical analysis was performed using GraphPad Prism 9.0.0 (GraphPad, California,
United States). Descriptive statistics were presented as mean and standard deviation
(SD). The mean of geometric data for the 3DHA virtual design and scanned µCT was presented
as width, length, and height in millimeters (mm). The relative differences were expressed
as percentages. 3D comparison between the µCT scan of 3DHA and the virtual design
was presented as mean RMS data (mm). Reliability was assessed using the intraclass
correlation coefficient. The Shapiro–Wilk test was applied to determine the normal
distribution of the RMS (mm) data for 3D analysis of each surface. A repeated-measures
one-way analysis of variance (ANOVA) followed by multiple comparisons test was used
to evaluate the RMS data for accuracy assessment of all-eight-graft at: (1) the overall
area, (2) marginal area, (3) inner area, and (4) contour areas. A paired t -test was used to analyze bone volume changes between the initial μCT and 6-month
postaugmentation CBCT. A p -value of < 0.05 was considered statistically significant.
Results
Geometric Data Analysis of 3DHA
The STL files illustrated the 3DHA virtual design ([Supplementary Fig S2A ]) and scanned µCT model ([Supplementary Fig S2B ]) for each defect (defects 1 to 8). The geometric measurements, including width,
length, and height, are presented as mean ± SD in [Table 1 ]. The data revealed that µCT values were lower than the corresponding 3DHA-designed
dimensions across all defects. The relative differences were minimal for width (–2.72%)
and height (–3.26%), while a greater difference was observed in length (–7.24%).
Table 1
Geometric data of 3DHA virtual design and scanned µCT, presented as width, length,
and height in millimeters (mm) along with the relative differences in percentages
Defect
Width (mm)
Length (mm)
Height (mm)
Design
µCT
Relative difference
Design
µCT
Relative difference
Design
µCT
Relative difference
1
6.89
6.73
–2.32%
16.82
16.28
–3.21%
9.06
8.89
–1.88%
2
6.74
6.56
–2.67%
7.73
7.01
–9.31%
10.94
10.61
–3.02%
3
5.73
5.62
–1.92%
12.06
11.01
–8.71%
8.94
8.61
–3.69%
4
5.45
5.13
–5.87%
8.83
8.2
–7.13%
11.18
11
–1.61%
5
8.98
8.78
–2.23%
7.92
7.13
–9.97%
10.59
10.22
–3.49%
6
8.71
8.43
–3.21%
10.24
9.25
–9.67%
11.62
11.04
–4.99%
7
7.53
7.45
–1.06%
10.46
9.86
–5.74%
9.34
8.9
–4.71%
8
7.81
7.62
–2.43%
12.93
12.39
–4.18%
10.87
10.58
–2.67%
Mean ± SD
7.23 ± 1.28
7.04 ± 1.28
–2.72%
10.87 ± 3.03
10.14 ± 3.09
–7.24%
10.32 ± 1.04
9.98 ± 1.02
–3.26%
Abbreviations: 3DHA, three-dimensional-printed hydroxyapatite; µCT, microcomputed
tomography; SD, standard deviation.
3D Comparison Between the Virtual 3DHA Design and the µCT Scanned 3DHA
The 3D color maps illustrated the deviation pattern between the virtual 3DHA design
and the µCT-scanned 3DHA. The deviation pattern exhibited a heterogeneous distribution.
Shrinkage (negative RMS value) of 3DHA was observed in the marginal area. The accuracy
(precision by RMS value) was highest in the inner and outer areas.
The overall accuracy of 3DHA, measured by the RMS value (mean ± SD), mm, for n = 8, was 0.19 ± 0.04 mm. The mean distance value for the 40-point measurement in
the marginal area was –0.22 ± 0.25 mm, indicating shrinkage, as represented by light
blue to dark blue in the color map. In the internal area, the mean distance value
was –0.08 ± 0.18 mm, with green to light blue regions reflecting precise 3DHA printing.
The contour area had a mean distance value of 0.03 ± 0.11 mm, also depicted in green
to light blue, further confirming printing accuracy ([Fig. 3 ]), see also [Supplementary Table S1 ]. The intraclass correlation coefficient for these measurements ranged from 0.87
to 0.99, indicating an almost perfect agreement.
Fig. 2 Three-dimensional (3D)-printed hydroxyapatite (3DHA) grafts were scanned using microcomputed
tomography (A ) and subsequently analyzed with CTAn software (CTAn, Skyscan) to generate STL files
for further evaluation (B ).
Fig. 3 Measurement of 40 points on the marginal (A ), internal (B ), and contour (C ) areas of three-dimensional (3D)-printed hydroxyapatite (3DHA). In the color map,
red indicates a positive deviation, showing that the scanned 3DHA was larger than
the reference model. Blue (−0.1 to −0.01 mm) indicates a negative deviation, where
the scanned 3DHA was smaller than the reference. Green (±0.1 mm) represents areas
of high-dimensional accuracy, reflecting the precision of the printing process.
The Shapiro–Wilk test was used to assess the normality of all data. The data distribution
met the assumption of log-normality for all measured values (α = 0.05). A repeated-measures ANOVA revealed a statistically significant difference
in RMS values for the overall, margin, inner, and contour regions of the graft. The
multiple comparisons test also showed that the overall RMS differed significantly
(p < 0.0001) from the margin, inner, and contour regions of the graft, as presented
in [Supplementary Table S2 ].
Gap Distances Between 3DHA and Defect Site
The mean gap distance between the 3DHA and defect site was 0.14 ± 0.39 mm. Minimal
or no gap at the marginal area of the graft (0.19 ± 0.22 mm), while the gap distances
between the 3DHA and defect at the internal area (0.37 ± 0.12 mm), [Supplementary Table S3 ]. The gap at the marginal interest area and cross-sectional plane at the middle part
of 3DHA are illustrated in [Supplementary Figs S3 ] and [S4 ], respectively.
In conclusion, the fit between the 3DHA graft and the defect site was shown to be
accurate at the marginal area, but the differences were not statistically significant
(p = 0.1094). According to a previous study,[17 ] the marginal gaps error between 200 and 300 µm (0.2–0.3 mm) was clinically acceptable.
Clinical Results
The 3DHA bone block graft, when placed into the patient's defect, showed a good fit
with the recipient side wall. The 3DHA did not require any trimming or adjustment,
demonstrating its suitability for the defect site, [Supplementary Fig S5 ].
Bone Volume and Dimensional Changes
Bone volume changes at 6 months postaugmentation showed an increase from the initial
graft volume measured by µCT (164.4 ± 37.87 mm3 ) to the volume measured by CBCT at 6 months postaugmentation (169.2 ± 39.38 mm3 ). This change approached, but did not reach, statistical significance (p = 0.0538). The mean dimensional change was 0.30 ± 0.14 mm, [Table 2 ].
Table 2
Bone volume and dimensional changes between initial graft and 6 months
Defect
Initial graft volume by µCT (mm3 )
6 mo
Postaugmentation by CBCT (mm3 )
Dimensional changes (mm; mean ± SD)
1
201.2705
207.22
0.33 ± 0.04
2
117.9857
119.89
0.16 ± 0.07
3
161.0382
167.29
0.38 ± 0.07
4
143.555
150.11
0.41 ± 0.16
5
122.0555
124.89
0.16 ± 0.04
6
201.8797
209.81
0.54 ± 0.16
7
150.8579
152.6
0.13 ± 0.05
8
216.3364
221.4
0.30 ± 0.04
Mean ± SD
164.4 ± 37.87
169.2 ± 39.38
0.30 ± 0.14
Abbreviations: µCT, microcomputed tomography; CBCT, cone-beam computed tomography;
SD, standard deviation.
Discussion
This study mainly focuses on the 3D printing of HA for clinical applications. The
use of bioceramic materials, particularly HA, as bone grafts can vary in mechanical
properties due to factors such as pore size, graft size, interconnecting layers, and
the manufacturing process. The traditional method for producing HA involves sintering
at high temperatures, which results in lower bioactivity, slower resorption rates,
reduced specific surface area, and lower porosity. In contrast, HA produced using
low-temperature techniques exhibits higher bioactivity, faster bioresorption, greater
specific surface area, and increased porosity.[25 ]
[26 ]
[27 ] Furthermore, 3DHA features microporosity that improves water permeability and enhances
surface area topography. This nanohydroxyapatite scaffold gradually degrades or is
resorbed over time, creating space for new bone formation.[13 ]
[26 ] Due to the few studies of 3D bone printing accuracy, this study was focused on the
accuracy evaluation of 3DHA bone graft after printing, compared with the original
design, and some applications to the clinic.
The accuracy of 3D printing refers to how closely the dimensions of a printed scaffold
match its original model, as represented by nominal values. In this study, the first
method to evaluate dimensional accuracy involves geometric measurements of width,
length, and height from the STL data of 3DHA after printing, compared with the original
computed design, due to the irregular shape of 3DHA. Therefore, dimensional accuracy
is crucial for assessing a machine's reliability in producing objects that meet expected
specifications. This study investigates how the 3D printing process affects the dimensional
accuracy of scaffolds manufactured using this technology. The original design was
created using computer software, and the scaffolds were analyzed after the 3D printing
process; subsequently, they were scanned using µCT imaging. The results indicate that
the scaffolds experienced a shrinkage of approximately 2 to 7% compared with the original
design after printing. The shrinkage of the grafts occurred in all dimensions (width,
length, and height), as shown by the negative values of the percentage of relative
difference: –2.72% for width, –7.24% for length, and –3.26% for height. The greatest
shrinkage was observed in length, likely because the largest side of the graft is
more susceptible to printing errors.
The other method to evaluate the dimensional accuracy is 3D comparison from Geomagic
Control X software with superimposition algorithms in the automated best-fit alignment
to present the 3D differences between the original graft design and the printed graft.
The advantages of this program were reliable, reproducible, and easy to present in
color maps to analyze the interested area. The mean values of difference shown in
RMS in the interested area of overall, margin, inner, and contour area were 0.19 ± 0.04,
–0.22 ± 0.25, –0.08 ± 0.18, and 0.03 ± 0.11 mm, respectively. RMS of overall differed
significantly from margin (p < 0.0001), inner (p < 0.0001), and contour (p < 0.0001). The mean of RMS was a negative value, which means shrinkage of the graft
after printing at the margin and the inner of the graft. But these lower values are
clinically acceptable.[28 ]
The evaluation of the printed grafts positioned at the defect site revealed that the
mean gap measurement in the marginal and internal areas was 0.19 ± 0.22 mm and 0.37 ± 0.12 mm,
respectively. The comparison of the fitness between the 3DHA graft and the defect
site indicated that the gap distances in the marginal areas were not statistically
significant (p -value = 0.109). Other studies on the gap error of printed prostheses have suggested
that the marginal gaps of 200 to 300 µm (0.2–0.3 mm) are considered clinically acceptable.
The accuracy of 3DHA may vary based on the initial resolution of the 3D image from
patients' CBCT and the method used for manufacturing. It is possible to refine the
bone defect model according to the patient's bone surface. Customized 3D bone printing
from these models allows for the precise placement of bone defects and provides good
marginal adaptation.
This dimensional analysis showed superior adaptation at the marginal regions compared
with internal zones, with significantly reduced gap measurements at the periphery.
Enhanced marginal integrity is crucial for graft stabilization and optimal integration
at the recipient site without the need for using fixation pins. In all cases, the
scaffolds exhibited precise conformity to defect topography, eliminating the necessity
for intraoperative adjustments or modifications. Conversely, traditional autogenous
or allograft bone blocks require substantial intraoperative manipulation and reshaping
to achieve proper defect adaptation, directly increasing surgical duration and consequent
patient morbidity.[1 ]
[29 ]
Large-volume alveolar ridge augmentation, especially vertical ridge augmentation,
is a challenging surgical procedure due to the lack of support from adjacent bony
walls.[12 ] In this study, the 3D-printed bone block graft was used exclusively for horizontal
ridge augmentation, with 3DHA precisely adapted to the bony walls of the defects.
The 3D printing technique was applied to areas involving no more than three teeth.
Consequently, the use of 3D-printed bioresorbable scaffolds for bone augmentation
in clinical settings has been limited.
This study demonstrated changes in bone volume and dimensional changes using both
µCT and CBCT imaging techniques. Both methods provided a 3D morphology of the bone
graft but with different resolution. One study found that CBCT can be used for a clinically
reliable assessment of alveolar bone quality, achieving accuracy and reliability levels
comparable to those of µCT.[30 ]
[31 ] Additionally, another study concluded that CBCT provides comparable accuracy to
high-resolution µCT when assessing trabecular structures in the mandible.[32 ]
[33 ] In a comparison of the accuracy of 3D-printed models of the mandible derived from
CBCT systems with different FOVs, it was discovered that smaller voxels provided the
highest precision and greater accuracy in reconstructing maxillofacial landmarks.[34 ] This study indicated that while CBCT is a feasible tool for such studies, the differences
in resolution between CBCT and µCT still limit the interpretation of results.
The 3DHA in this study demonstrated greater resorption than sintered HA, which is
typically characterized by limited resorption capacity.[14 ]
[26 ] The additional xenograft of a 1-mm layer over the 3DHA was used to protect against
bone resorption. The results showed differences in graft volume between the initial
measurement from µCT (164.4 ± 37.87 mm3 ) and a follow-up measurement at 6 months postaugmentation using CBCT (169.2 ± 39.38 mm3 ). Furthermore, the factors influencing volumetric changes are likely not derived
from the original bone block graft itself but may be influenced by the overlay of
the xenograft and platelet-rich fibrin (PRF) membrane. These findings demonstrate
the feasibility of gaining bone volume after augmentation.
Another study on 3D-printed titanium mesh for treating alveolar ridge defects found
that the size of the bone defect did not affect the printing accuracy.[35 ] This was attributed to the rigid properties of the mesh, as there was minimal variation
in defect sizes among the groups, which involved the loss of one to five teeth. While
this study used bioceramic materials or nanohydroxyapatite as bone graft substitutes,
the mechanical properties of these materials can influence dimensional changes over
time.
To address this situation, 3DHA were designed with an outer cortex that has a thickness
of 2 mm, enhancing the mechanical performance of the printed parts. These constructions
feature a macroporous structure that mimics the natural porosity of alveolar bone,
allowing for improved blood supply and nutrient transport into the bone graft. The
clinical dimensional stability of the 3DHA bone block graft after 6 months shows that
the mean changes in dimensional contour were 0.30 ± 0.14 mm. These minimal contour
changes in the ridge defect following the bone graft may be attributed to the addition
of a 1-mm layer of xenograft, which was incorporated to slow down the resorption of
the graft.[29 ]
To enhance the success of bone augmentation, a collagen membrane (RTM collagen membrane,
Cytoplast) was used to cover the contour of 3DHA due to its long resorption period
of 26 to 38 weeks and lower risk of exposure compared with nonresorbable membranes.[36 ]
[37 ] Additionally, PRF is derived from a patient's own blood and contains a high concentration
of platelets and leukocyte cytokines.[38 ] This concentrate is rich in growth factors, including platelet-derived growth factors,
transforming growth factor, vascular endothelial growth factor, insulin-like growth
factor, and epidermal growth factor.[39 ] PRF has been proposed for various applications in dentistry, such as alveolar ridge
reconstruction, sinus lift procedures, and extraction socket preservation.[40 ]
[41 ] However, the effectiveness of PRF for bone regeneration remains uncertain.[42 ]
[43 ]
[44 ] The clinical protocol in this study involved the use of PRF due to its positive
effects on soft tissue healing, as in the previous study.[17 ]
This study has several limitations that warrant consideration. First, the small sample
size of eight patients and the relatively short follow-up period of 6 months reduce
the statistical power and limit the generalizability of the findings concerning the
efficacy of the 3DHA bone block graft. Second, the simultaneous utilization of xenografts
and PRF membranes alongside the 3DHA graft introduces potential confounding factors,
making it challenging to isolate the specific effects of the 3DHA material on bone
volume and dimensional changes. Third, methodological variability arises from the
use of different imaging modalities to assess graft dimensions: baseline measurements
were obtained via µCT, while follow-up evaluations employed CBCT. The inherent differences
in voxel size, resolution, and image reconstruction between µCT and CBCT could introduce
measurement bias, affecting the accuracy of longitudinal comparisons. Finally, the
absence of a control group encompassing other grafting materials, such as autogenous
and allogenic grafts, restricts direct comparative analysis and limits the interpretation
of the 3DHA graft's performance.
Conclusion
This pilot study demonstrated the feasibility of producing customized binder-jetted
HA block grafts with submillimetric accuracy, which could be placed clinically without
intraoperative modification. The workflow highlights the innovative application of
binder jetting in graft fabrication, offering a high degree of customization and accuracy.
Although volumetric changes observed over 6 months were small and not statistically
significant, the results indicate stability during the early healing phase. To establish
clinical reliability and confirm the long-term advantages of this approach, larger
controlled studies with standardized volumetric and histological outcomes are warranted.
