Heat Generated by Different Light-Emitting Diode (LED) Curing Units and Their Effect on Pulp: An In Vitro Study

Excessive intensity of light emitted from light-emitting diode (LED) curing units used during orthodontic bonding procedures can induce thermal changes within the pulp chamber, potentially leading to pulpal inflammation or damage. The degree of this thermal effect may vary based on the type and power output of the curing light used. This study aimed to determine the amount of heat generated by different LED curing lights during orthodontic bonding and to evaluate the associated histopathological changes in pulpal tissue.

The study was conducted on 42 first maxillary premolars scheduled for extraction as part of fixed orthodontic treatment, with informed consent and ethical clearance. The samples were divided into six groups, namely, Group A: Ivoclar Bluephase (histological; Ivoclar Vivadent, Schaan, Liechtenstein), Group B: Woodpecker (histological; Guilin Woodpecker Medical Instrument Co., Ltd., Guilin, China), Group C: 3M Unitek (histological; 3M, Maplewood, MN), Group D: Ivoclar Bluephase (thermal) Group E: Woodpecker (thermal), and Group F: 3M Unitek (thermal). A thermocouple was utilized to assess temperature changes in the pulp chamber before and after the curing process. The histopathological evaluation involved fixing and staining specimens for microscopic examination to identify inflammatory changes. Intergroup analysis of histopathological findings was performed using the chi-square test, while intragroup analysis of pulp chamber temperature changes within the thermal groups was carried out using one-way analysis of variance (ANOVA). A p-value of < 0.05 was considered statistically significant.

No significant histological changes were observed in Groups A and C. Group B exhibited mild to moderate inflammation in six samples, characterized by vascular dilation and inflammatory cell infiltration, with a statistically significant intergroup difference (p = 0.047). Group E showed the highest temperature rise (2.586 ± 0.6744 °C), though the difference among groups was not statistically significant (p = 0.064). One-way ANOVA revealed significant variation in pre-curing (p = 0.001) and post-curing temperatures (p = 0.011), with 3M Unitek showing the highest values in both.

LED curing units with higher light intensity, such as the Woodpecker unit, generated greater heat in the pulp chamber, potentially leading to early inflammatory changes in pulpal tissue. While these changes were predominantly reversible, a sustained temperature rise exceeding 5.5°C may contribute to pulpal irritation.