The Influence of Plastic Light Cure Sheaths on the Hardness of Resin Composite

Abstract

SUMMARYObjective: This study investigated the influence of a disposable light cure sheath on both the surface hardness and hardness at varying thicknesses of resin composite.Methods: A series of resin composite discs (Spectrum) were fabricated with varying depths up to 6 mm. The light curing units used were a standard halogen unit (Elipar Trilight) and an LED unit (Elipar Freelight 2). Recommended curing times from the manufacturer were followed. The disposable light-curing sheath (Cure Sleeve) was used with both light-curing units. Two additional groups without the sheath were employed as controls. Each specimen (n=4) was subjected to hardness testing to evaluate hardness from 0 mm to 5 mm thick. A 200g load was applied for 10 seconds using a Vickers diamond indenter and six indentations were obtained from each specimen. Statistical analysis was performed using two-way ANOVA.Results: The LED without a sheath achieved the highest surface hardness value (47.2 VHN ± 5.5). There was no significant difference between the groups regarding surface hardness (p>0.05). As the thicknesses of the resin composite increased, the hardness values decreased in all groups. The LED light curing unit, in combination with a sheath, demonstrated the lowest hardness values at a 5 mm thickness of resin composite (p<0.05). Conclusion Clinical RelevanceDisposable sheaths are now recommended as a method of cross infection control when light curing resin composite. However, these sheaths may affect the depth of cure of the resin composite, resulting in a compromise of the mechanical properties of the restorative material.ical properties of the resin composite. However, the use of the light cure sheaths still provided an acceptable depth of cure when used following the 2 mm increment rule. It was not until 3 mm that the use of the light cure sheaths compromised the hardness results. It is recommended that the curing depth should not exceed 2 mm, regardless of light curing method.

Distance and protective barrier effects on the composite resin degree of conversion

“…[13] The effects of curing distance on the %DC values of composite resins are controversial. [4513] Nevertheless, findings in the present study support the theory that polymerization is affected by curing distance[912] in cases of low irradiance levels, such as those emitted by the ultra LED. Despite its inferior power density performance, restoration quality obtained in this investigation using the ultra LED at a distance of 5 mm was acceptable.…”

“…[7] This may decrease light incidence,[36101112] although we recorded a reduction lower than 4% [Table 1]. Curing light units generally provide the minimum light intensity recommended (280-300 mW/cm 2 ),[9] but it may become insufficient with the use of protective barriers on light output.…”

“…[612] However, these studies have not investigated their use in conjunction with different curing distances and effects on irradiance and %DC of the resin. The distance from tip to the composite is an important element for analysis, given that some cavities do not allow close approximation.…”

Effect of a multi-layer infection control barrier on the micro-hardness of a composite resin

“…In this study, the micro-hardness was tested immediately after the light curing procedure because the occlusal adjustment, finishing and polishing of the composite resin restorations are usually performed just after light curing the composite resin in clinical situations. Stress created by these procedures can have a detrimental effect on the tooth-restoration interface, such as the premature breakdown of the restoration at the margin 2,22,24 .…”

“…Disposable barriers are convenient, non-invasive, and prevent contact between the oral tissues and the light guide. These types of barriers also eliminate the risk of damaging the light guide during autoclaving or disinfection 10,19,22,27 . Among various infection control barriers, the plastic wrap has the least effect on the LCU power density 19,27 .…”