Microplastics in Dentistry—A Review
165
2.2 BIS Phenol A from Orthodontic Appliances
In orthodontic appliances, there is an extensive use of polymers as polyurethanes for
elastomeric ligatures and chains, polycarbonates for esthetic brackets, polyamidebased wire sleeves, lip bumper appliances made of poly propylene. Bis Phenol A
is often used in the manufacture of dental resins as a precursor of BIS GMA or bis
phenol A Dimethacrylate. Sudies have shown that this BPA is a culprit in endocrine
dysfunctions causing peripubertal mammary gland development in mice, male feminization, and early puberty of females. Systemic intake of BPA can be through
ingestion, inhalation, and through the dental pulp [32].
Most of the times, the orthodontic appliances are worn for an average duration of
two years and the retainers are worn for an extended period. In the case of bonded
lingual retainers, a larger surface of the adhesive used for bonding is exposed to the
oral cavity and the thickness of the resin adhesive promotes incomplete polymerization. The leaching of materials from this resin can initiate adverse health effects.
Clinicians are encouraged to do a prophylaxis with pumice over the surface of these
resin adhesives to remove the uncured material [17]. Debonding of the brackets is a
major cause of exposure to resins for the dental personnel.
In vitro studies on residual TEGDMA released from adhesives have shown that
it can cause chromosomal anomalies by deleting DNA chain sequence. Also it
was observed that this resin adhesives mimic estrogenic activity after stimulated
debonding. Polycarbonate brackets degrade in the oral cavity and release BPA. It
was noticed that the polycarbonate base ceramic brackets release more amount of
umpolymerized resins than the ceramic brackets [29].
The orthodontic adhesives are exposed to the oral environment through the peripheral margins of bracket, through the fixed maxillary and mandibular retainers and
while removing the fixed appliances which involves removal of the adhesive by
grinding with burs [23]. The release of polymers from margins is less compared to
that from the fixed retainers which remain on the teeth either for a long duration
or entire lifetime [43]. The particles released during removal of the appliances is a
mixture of filler degradation products, polymer matrix pieces, and particles from the
wear of bur used. This aerosol can cause health hazards to both the patient as well as
the dentist. The Bis-GMA released can eventually lead to formation of BPA which
is a known endocrine disruptor [50].
Various in vitro studies done to estimate the release of BPA from orthodontic
adhesives show conflicting results. A study by [18] in an in vitro environment assessed
the release of BPA after various time intervals of 1 day, and weekly intervals of 1,
3, and 5 weeks. The study did not show any evidence of BPA release. However, the
authors mentioned that the results could not be extrapolated in an in vivo environment.
Another study by [49] attempted to correlate the distance between the light-curing
unit and the degree of conversion of the polymers. The study concluded that an inverse
relation exists between the distance of the curing unit and the rate of polymerization.
A reduction in the degree of polymerization was accompanied by an increased rate of
polymers into the oral environment. The estrogenicity of light cured and chemically
165
2.2 BIS Phenol A from Orthodontic Appliances
In orthodontic appliances, there is an extensive use of polymers as polyurethanes for
elastomeric ligatures and chains, polycarbonates for esthetic brackets, polyamidebased wire sleeves, lip bumper appliances made of poly propylene. Bis Phenol A
is often used in the manufacture of dental resins as a precursor of BIS GMA or bis
phenol A Dimethacrylate. Sudies have shown that this BPA is a culprit in endocrine
dysfunctions causing peripubertal mammary gland development in mice, male feminization, and early puberty of females. Systemic intake of BPA can be through
ingestion, inhalation, and through the dental pulp [32].
Most of the times, the orthodontic appliances are worn for an average duration of
two years and the retainers are worn for an extended period. In the case of bonded
lingual retainers, a larger surface of the adhesive used for bonding is exposed to the
oral cavity and the thickness of the resin adhesive promotes incomplete polymerization. The leaching of materials from this resin can initiate adverse health effects.
Clinicians are encouraged to do a prophylaxis with pumice over the surface of these
resin adhesives to remove the uncured material [17]. Debonding of the brackets is a
major cause of exposure to resins for the dental personnel.
In vitro studies on residual TEGDMA released from adhesives have shown that
it can cause chromosomal anomalies by deleting DNA chain sequence. Also it
was observed that this resin adhesives mimic estrogenic activity after stimulated
debonding. Polycarbonate brackets degrade in the oral cavity and release BPA. It
was noticed that the polycarbonate base ceramic brackets release more amount of
umpolymerized resins than the ceramic brackets [29].
The orthodontic adhesives are exposed to the oral environment through the peripheral margins of bracket, through the fixed maxillary and mandibular retainers and
while removing the fixed appliances which involves removal of the adhesive by
grinding with burs [23]. The release of polymers from margins is less compared to
that from the fixed retainers which remain on the teeth either for a long duration
or entire lifetime [43]. The particles released during removal of the appliances is a
mixture of filler degradation products, polymer matrix pieces, and particles from the
wear of bur used. This aerosol can cause health hazards to both the patient as well as
the dentist. The Bis-GMA released can eventually lead to formation of BPA which
is a known endocrine disruptor [50].
Various in vitro studies done to estimate the release of BPA from orthodontic
adhesives show conflicting results. A study by [18] in an in vitro environment assessed
the release of BPA after various time intervals of 1 day, and weekly intervals of 1,
3, and 5 weeks. The study did not show any evidence of BPA release. However, the
authors mentioned that the results could not be extrapolated in an in vivo environment.
Another study by [49] attempted to correlate the distance between the light-curing
unit and the degree of conversion of the polymers. The study concluded that an inverse
relation exists between the distance of the curing unit and the rate of polymerization.
A reduction in the degree of polymerization was accompanied by an increased rate of
polymers into the oral environment. The estrogenicity of light cured and chemically