Accuracy of 3d Printed Dentures Clinical Trial
Official title:
Accuracy of 3D Printed Maxillary Complete Dentures Compared With Conventional Complete Dentures: Non-Randomized Control Trial
Conventional complete dentures have been used for almost a century as a treatment choice for edentulous patients, despite of their inaccuracy & dimensional changes during manufacturing. Recently, new manufacturing techniques like RP/3D printing (rapid prototyping) has progressed in the dental field including prosthodontics, does the 3D printed complete denture show more accuracy than conventional ones?
Conventional complete dentures have been used as a clinically accepted prosthetic treatment
for completely edentulous patients for almost a century. [1] One of its advantages is ability
to customize teeth arrangement and to check each step of the preceding steps before the
delivery stage.
Conventional complete dentures fabrication consist of several steps of recording,
transferring, evaluating, and creating artificial substitutes for patient's teeth and gingiva
which must be in harmony with patient's mouth and face. All this steps demand high
experience, artistic, and skillful operator and technician.
However denture processing results in polymerization shrinkage of the resin (due to flask
cooling), and distortion of the denture base (due to stress release after denture base
removal from the stone cast), and decreasing the accuracy and denture adaptation. [2] These
dimensional changes increase the gap between the denture base and underlying mucosa,
resulting in an ill-fitting denture.[3] Denture adaptation and fitting plays a crucial role
in complete denture retention (by physical means), stability, and patient comfort. [4]
Also, flask closure must be done under considerable pressure to ensure metal-to-metal contact
between the halves of the flask to confine the resin inside the mold with no excess.[5] In
addition to the inherent processing shrinkage and/or expansion properties of the acrylic
resin.[6] Researchers tried to overcome these disadvantages by changing the technique of
polymerization of the resin, by using of microwave energy, dry heat, and visible light.[7]
But unfortunately researchers found that, Discrepancies in the base adaptation shown by
several techniques are not easily corrected after complete denture processing.[8] Denture
base adaptation to the stone cast is usually not satisfactory, especially in the midline
section of the central portion of the posterior border.[9] To overcome the previous
disadvantages computer aided manufacturing technology was applied to complete dentures. Some
advantages of digitally fabricated complete dentures are 1) reduced number of patient visits;
2) superior strength and fit of dentures; 3) omitting multiple error-introducing steps such
as impression, waxing, and casting.[10] 4) reduced cost for patient and clinician; 5) easy
denture duplication (due to stored digital data); 6) standardization of clinical research on
complete dentures and implant-retained overdentures.
To fabricate physical prototype (model) there are two different approaches: subtractive and
additive manufacturing.
Subtractive manufacturing is based on milling the denture from a larger blank by a computer
numeric controlled (CNC) machine. The input data for this method are principally from an
optical or contact probe digitizer, which can only capture the external surface data of the
anatomy and not the internal tissue surface of the object.
Although CAD/CAM dentures have many advantages compared to conventional ones, but the CAD/CAM
protocol introduces additional steps (like scanning, software modeling, and milling) in the
fabrication process that can lead to inaccuracies.[11] Another disadvantage of CAD/CAM is its
inability to reproduce fine details by milling .[12] Additive manufacturing is the process
that creates objects from 3D model data, in an additive layer by layer manner.[13] The
additive systems used in dentistry are stereo-lithography, selective laser sintering or
melting, and 3D printing.
The main advantage of additive technology is the ability to create minor details (undercuts,
voids, complex internal geometries) in the proposed model. In addition to Incremental
vertical object build-up, no material wastage, large objects produced, passive production
(i.e., no force application), and ability to print multiple materials at the same time (in
case of 3D printing). [15] A clinical study was done to compare the accuracy values of
maxillary conventional heat-polymerized trial denture bases with those RR printed ones and
the results were as follows: Mean deviation was (-0.0051mm), (SD, 0.19mm).[16]
In the same study authors used ratings from 100-mm VAS in 10 patients and 20 prosthodontists
comparing conventional and RP methods and the results were as follows:
Patients comparing overall satisfaction: P=0.59, prosthodontists comparing overall
satisfaction: P=0.87 The term selective laser sintering is used to describe the fabrication
of a pattern from ceramics or polymers while selective laser melting describes pattern
fabrication from metal.[14] The laser beam locally raises the temperature close to the
melting point of the metal particle, to avoid complete melting. The platform is slightly
immersed in the powder, and powder thickness is controlled by a cylinder rolling on the
powder pool. After each new powder layer application, the laser melting process is repeated
until the 3D object is completed.
Stereo lithography technology consists of photosensitive resin bath, a model-building
platform, and ultraviolet laser for curing. To fabricate the desired model the layers are
cured successively, and bonded together from bottom to top. As the first layer is polymerized
the model-building platform is brought down inside the bath, and another layer of resin is
added and cured. This process continues until the desired model is completed.
In 3D printing system the material is extruded from a nozzle that solidifies as soon as it is
deposited on the manufacturing platform. The layer pattern is achieved through horizontal
nozzle movement and interrupted material flow. This is followed by vertical movement for the
sequential layer deposition.
The captured 3D data of model slice into cross-sections by a certain thickness. Inputting the
processing parameters based on the contour information of each layer sheet allows for the
automatic generation of the numerical code. Finally, a 3D object consisting of a series of
layers is formed by stacking. This technology can receive CAD data directly and create new
samples or models quickly without need for molds, cutting tools, or tooling fixtures.
Thanks to this technology, wasting less material, employing less human power, decreasing
treatment time at the chair side, decreasing treatment cost, and lowering the rates of
contamination, is possible.
In this study, a combination of conventional technique and RP will be used to fabricate
complete dentures to overcome the polymerization shrinkage which results from conventional
processing.
Explanation for choice of comparators:
Heat processed denture base is the treatment of choice for most of edentulous patients and it
is considered as the golden standard and the main comparator for the new techniques. But
using Heat Cured Acrylic resin would require many laboratory steps which introduce several
errors.[14] Meanwhile, the introduction of rapid prototyping method with high accuracy which
eliminates some of the laboratory steps was the reason for choosing it to compare it with the
conventional method
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