297
printing thin layers below 0.1 mm thicknesses. In addition, the biocompatibility of
the silicone materials used in the study was unknown. The authors also reported that
direct printing can only be adjusted for an interim post-surgical prosthesis. Likewise,
medical grade silicone elastomers are needed which are not available in today’s
additive manufacturing technologies.
Most, if not all, studies have used 3D printing for the mold making or duplication
in the field of maxillofacial prosthodontics (Karayazgan-Saracoglu et al. 2009;
Watson and Hatamleh 2014). Few studies have demonstrated the direct silicone
printing, since the silicone printing technology must be developed due to complex
polymerization process (Jindal et al. 2016, 2018).
Two types of silicone elastomers have been used in maxillofacial prosthodontics
with respect to the type of polymerization: (1) the room temperature vulcanizing
(RTV) silicones, which are the most common due to their easy to use in the laboratory applications, and (2) high temperature vulcanizing (HTV) silicones, which
have excellent mechanical and physical properties compared to RTV silicones, in
addition to have high translucency (Polyzois et al. 1994). However, the main disadvantage of HTV silicones is their complex coloring process. Nonetheless, they have
the advantage of a working time of more than 30 min (Jindal et al. 2016). The commercial RTV silicones such as one- or two-part silicones, also known as one- or
two-component silicones, which are commercially available (Lontz 1990; Huber
and Studer 2002). Recently, platinum catalyzed silicone elastomers were introduced
and platinum based silicone elastomers are rapidly polymerized without a need of
heat, besides platinum catalyst could be react with other additives in the silicones
which might slow down the polymerization process (Lai and Hodges 1999; Jindal
et al. 2016). While 3D printable silicones are one-component RTV types, twocomponent RTV silicones are more common in use due to their biocompatibility
(Symes et al. 2012).
Jindal et al. (2016) reported that early production of a biocompatible maxillofacial silicones by 3D printing process. Although HTV silicones are not suitable for
3D printing, an experimental HTV silicone was used by Jindal et al. (2016) in the
presence of a heat catalyst (platinum carbonyl cyclovinylmethylsiloxane complex),
which was then replaced by a platinum catalyst to develop an ideal maxillofacial
silicone. They found that the mechanical properties varied with the different concentrations in the crosslinkers (catalysts) and the different length of the PDMS
chains (Jindal et al. 2016), as well as they reported that a concentration of the crosslinking agent (catalyst) at 5% was optimal for production of two-component printable maxillofacial RTV (room temperature vulcanizing) silicone elastomers.
Keeping this in view, Jindal et al. (2018) reported the properties of a novel twocomponent 3D-printable maxillofacial RTV-silicone elastomer containing a thixotropic agent. However, the addition of the thixotropic agent decreased the mechanical
strength of the 3D printable silicone compared to the commercial maxillofacial silicone elastomer (Jindal et al. 2018).
The most notable results from Jindal et al. (2016, 2018) were: (1) the addition of
a hear catalyst for the manufacture of a 3D printable silicone must be replaced with
12 Maxillofacial Silicone Elastomers in Dentistry
printing thin layers below 0.1 mm thicknesses. In addition, the biocompatibility of
the silicone materials used in the study was unknown. The authors also reported that
direct printing can only be adjusted for an interim post-surgical prosthesis. Likewise,
medical grade silicone elastomers are needed which are not available in today’s
additive manufacturing technologies.
Most, if not all, studies have used 3D printing for the mold making or duplication
in the field of maxillofacial prosthodontics (Karayazgan-Saracoglu et al. 2009;
Watson and Hatamleh 2014). Few studies have demonstrated the direct silicone
printing, since the silicone printing technology must be developed due to complex
polymerization process (Jindal et al. 2016, 2018).
Two types of silicone elastomers have been used in maxillofacial prosthodontics
with respect to the type of polymerization: (1) the room temperature vulcanizing
(RTV) silicones, which are the most common due to their easy to use in the laboratory applications, and (2) high temperature vulcanizing (HTV) silicones, which
have excellent mechanical and physical properties compared to RTV silicones, in
addition to have high translucency (Polyzois et al. 1994). However, the main disadvantage of HTV silicones is their complex coloring process. Nonetheless, they have
the advantage of a working time of more than 30 min (Jindal et al. 2016). The commercial RTV silicones such as one- or two-part silicones, also known as one- or
two-component silicones, which are commercially available (Lontz 1990; Huber
and Studer 2002). Recently, platinum catalyzed silicone elastomers were introduced
and platinum based silicone elastomers are rapidly polymerized without a need of
heat, besides platinum catalyst could be react with other additives in the silicones
which might slow down the polymerization process (Lai and Hodges 1999; Jindal
et al. 2016). While 3D printable silicones are one-component RTV types, twocomponent RTV silicones are more common in use due to their biocompatibility
(Symes et al. 2012).
Jindal et al. (2016) reported that early production of a biocompatible maxillofacial silicones by 3D printing process. Although HTV silicones are not suitable for
3D printing, an experimental HTV silicone was used by Jindal et al. (2016) in the
presence of a heat catalyst (platinum carbonyl cyclovinylmethylsiloxane complex),
which was then replaced by a platinum catalyst to develop an ideal maxillofacial
silicone. They found that the mechanical properties varied with the different concentrations in the crosslinkers (catalysts) and the different length of the PDMS
chains (Jindal et al. 2016), as well as they reported that a concentration of the crosslinking agent (catalyst) at 5% was optimal for production of two-component printable maxillofacial RTV (room temperature vulcanizing) silicone elastomers.
Keeping this in view, Jindal et al. (2018) reported the properties of a novel twocomponent 3D-printable maxillofacial RTV-silicone elastomer containing a thixotropic agent. However, the addition of the thixotropic agent decreased the mechanical
strength of the 3D printable silicone compared to the commercial maxillofacial silicone elastomer (Jindal et al. 2018).
The most notable results from Jindal et al. (2016, 2018) were: (1) the addition of
a hear catalyst for the manufacture of a 3D printable silicone must be replaced with
12 Maxillofacial Silicone Elastomers in Dentistry