JCDA Express Issue 3 2013

The full-text articles featured in JCDA Express are available free of charge for a 1-month period.

Light Curing: Health and Safety Considerations

	In this edition of JCDA Express, Dr. Richard Price, professor and head of fixed prosthodontics in the department of dental clinical sciences at Dalhousie University's faculty of dentistry, brings forward 3 articles that focus on health and safety considerations related to light curing dental resins.
Dr. Richard Price

Introduction

• Proper light curing of the entire restoration is a basic requirement when placing resin-based dental restorations—it improves the physical properties of the resin and achieves better bond strength and colour stability. However, if done improperly, light curing can adversely affect patient health and safety.
• The first 2 articles presented here examine the leaching of chemicals from dental resins as a result of inadequate light curing. Undercuring may occur due to excessive distances between the light-curing tip and the resin, poor positioning of the light guide over the resin, use of inappropriate curing lights, or inadequate exposure times.
• The December 2012 cover story in the Journal of the American Dental Association reported increased salivary and urinary concentrations of bisphenol A (BPA) and other chemicals after placement of resin-based composite dental restorations.¹ This finding is concerning, given the adverse effects of BPA in humans, including impaired psychosocial health in children with increased exposure to bisGMA-based dental composite resins.²
• In March 2013, the American Dental Association published an excellent review of the risks to dental patients from BPA in dental resins.
• While the implications of increased BPA exposure are not yet fully understood, dentists should take steps to minimize patient exposure to all chemicals as a result of dental treatment. As shown below in the paper by Durner et al., it is not just BPA that is released from resins.
• The last article presents three instances of soft tissue burns after patients received routine dental care with a light-emitting diode (LED) curing light. It is important to remember that as curing lights become more powerful, the potential for iatrogenic thermal trauma increases.

Undercured Resin-Based Composites May Release More Chemicals into the Body

Durner J, Obermaier J, Draenert M, Ilie N. Correlation of the degree of conversion with the amount of elutable substances in nano-hybrid dental composites. Dent Mater. 2012;28(11):1146-53.

JCDA Clinical Pearl: This in vitro study demonstrated a strong inverse correlation between degree of conversion and the presence of eluted chemicals from resin-based composites, and emphasized the importance of adequate light exposure.

Key Points:

• This study compared the degree of conversion and the amount of elutable chemicals from three commonly used resin-based composites (Venus Diamond, TetricEvo Ceram and Filtek Supreme) as a function of light exposure time (5, 10, 20 and 40 s) using the FreeLight 2 (3M ESPE) LED curing light.
• In all groups, reducing the light exposure time resulted in a significant decrease in degree of conversion and increased the amount of eluates, such as camphorquinone, methacrylic acid (MAA), ethylene glycol dimethacrylate (EGA), 2-hydroxyethyl methacrylate (HEMA),  4-N,N-dimethylaminobenzoic acid ethylester (DMABEE), triethylene glycol dimethacrylate (TEGDMA), Tinuvin P, and bisphenol-A-polyetheylene glycol dimethacrylate (BisEMA), from resin-based composites.

Reasons for Recommending this Article: This study highlights the increased likelihood of elution of potentially toxic chemicals when 3 popular dental resins were undercured. Shorter curing times (5 and 10 s) resulted in a lower degree of conversion and higher amounts of eluted chemicals with toxic potential compared to longer curing times (20 or 40 s). Clinicians should also be aware that undercuring dental resins does not just increase release of BPA—other chemicals are released as well.

Undercured Orthodontic Adhesives May Release BPA into the Body

Sunitha C, Kailasam V, Padmanabhan S, Chitharanjan AB. Bisphenol A release from an orthodontic adhesive and its correlation with the degree of conversion on varying light-curing tip distances. Am J Orthod Dentofacial Orthop. 2011;140(2):239-44.

JCDA Clinical Pearl: The resin adhesive holding orthodontic brackets onto the teeth must be adequately cured. Careful attention should be given to the light curing tip distance because even a 5 mm distance between the light and the resin significantly reduces the degree of conversion and increases the release of BPA.

Key Points:

• This in vitro study examined the effect of using various light-curing tip distances (0, 5, and 10 mm) to cure an orthodontic adhesive resin (Transbond XT, 3M Unitek).
• The labial surface of the brackets was exposed for 40 seconds with a halogen curing light.
• The release of BPA was assessed up to 35 days after light curing.
• Specimens cured at 5 and 10 mm light curing tip distances were significantly less well cured and released significantly more BPA compared to those cured at 0 mm.

Reasons for Recommending this Article: Adequate light curing is relevant to both restorative dentistry and orthodontics. When bonding orthodontic brackets, clinicians must adequately cure the adhesive resin and yet take care not to overheat the pulp or gingivae. Also, children receive the most orthodontic treatment and are most susceptible to the adverse effects of BPA.

LED Curing Lights Can Burn the Soft Tissues

Spranley TJ, Winkler M, Dagate J, Oncale D, Strother E. Curing light burns. Gen Dent. 2012;60(4):e210-4.

JCDA Clinical Pearl: Clinicians should be aware that high power dental curing lights can cause soft tissue burns if used inappropriately. The resulting soft tissue burns resemble ulcers and may not be recognized as related to the light curing procedure. Clinicians should ensure the light is neither placed on, nor shone onto, the lip, tongue, or other intraoral tissues.

Key Points:

• Three clinical cases were reported where an LED curing light burned the lips of patients. Because the patients were anesthetized, the soft tissue burns were only recognized after the treatment had concluded.
• The presence of a rubber dam offered no protection to the soft tissues; the authors recommended placing gauze between the rubber dam and the soft tissues.
• The authors also recommended pausing 2 to 3 minutes after each 20 seconds of light exposure near soft tissues to allow adequate cooling of the tissues.

Reasons for Recommending this Article: These case reports highlight the potential danger to the soft tissues when using a high power curing light. Clinicians should not arbitrarily increase light exposure times beyond the manufacturer’s recommended exposure times without knowing what effect this will have on the soft tissues or pulpal health. Currently there is no practical method for dentists to know the increase in temperature caused by their curing light in the mouth. Patients, who are often anesthetized, cannot be relied upon to indicate if their tissues are getting too hot. However, dentists can shine the curing light on the back of their own hand for the same exposure times they use on their patients. This will provide some idea of the potential for burning oral tissues with their curing light.

Additional References

1. Kingman A, Hyman J, Masten SA, Jayaram B, Smith C, Eichmiller F, et al. Bisphenol A and other compounds in human saliva and urine associated with the placement of composite restorations. J Am Dent Assoc. 2012;143(12):1292-302.
2. Maserejian NN, Trachtenberg FL, Hauser R, McKinlay S, Shrader P, Tavares M, et al. Dental composite restorations and psychosocial function in children. Pediatrics. 2012;130(2):e328-38.