Three-Dimensional Observation of Enamel Cracks on Restored Teeth Using SS-OCT

Objectives: To three-dimensionally and non-invasively characterize enamel cracks on teeth restored with amalgam and composite-resins using swept-source optical coherence tomography (SS-OCT).
Methods: Twenty freshly extracted human molars with Class I amalgam restorations (n=10) and Class I composite-resin restorations (n=10), from patients age 30 to 55 years old, were used in the study. The restorations were small to medium-sized (does not exceed one-third of the buccolingual width of the tooth). These teeth were extracted due to failed restorations or periodontal disease. The teeth were observed for cracks on the functional and non-functional cusps. The cracks were analyzed using the classification from a previous three-dimensional OCT study on enamel crack patterns: Type 1 – superficial horizontal cracks; Type II – vertically (occluso-gingival) oriented cracks; and Type III – hybrid or complicated cracks, a combination of a Type I and Type III cracks (Segarra et al, 2017). Confocal laser scanning microscopy (CLSM) was done to validate the results of the OCT observation.
Results: More cracks were observed in teeth with amalgam restorations. These cracks were predominantly type I and III cracks and starts near the restoration. They were more defined, deeper and have fewer crack deflections. Cracks found in composite-resin restorations were shallower and showed more crack deflections. Small cracks were also noticed around the margins of the restorations probably due to polymerization shrinkage of the composite-resin. Regardless of the restorative material used, Type II cracks were more common in non-functional cusps.
Conclusions: Teeth with amalgam restorations exhibited predominantly Type II cracks which were more defined. Shallower cracks and more crack deflections were observed in composite-resin restored teeth. SS-OCT can be effectively used for the monitoring of enamel cracks of restored teeth.