Polarization-Sensitive Optical Coherence Tomography to Detect Crown Margin Gaps

Objectives: Dentists lack the diagnostic instruments that can quantitatively evaluate the marginal integrity between teeth and fabricated crown margin finish lines. Polarization-sensitive optical coherence tomography (PS-OCT) is a non-invasive and non-ionizing technique that measures the magnitude of reflected backscattered light utilizing a near infrared laser. PS-OCT may potentially be used to measure and evaluate crown margin gaps before and after delivery of crowns.
Methods: A feltspathic porcelain crown was fabricated for a prepared acrylic tooth model using a CEREC^® milling device. The crown was luted to the prepared die with intentional slight marginal openings. A 4mm marginal area at the midline of the facial and the lingual surfaces and a 2mm marginal area along the midline of the mesial and distal crown margins were measured. Minim pins were placed below the crown margins and used as reference points. Marginal gap slices of 50µm were manually measured with the PS-OCT device and validated against 90µm manually measured slices measured with the micro-CT. Statistical analyses were conducted to compare the results.
Results: The mean marginal gap reading for all surfaces with both devices was greater than 160µm. The facial measurements showed no significant difference between the two devices (P>0.05). All four areas measured by the PS-OCT resulted in smaller mean measurements with the smallest marginal gap difference between devices occurring on the facial at 10.4µm and the largest difference occurring on the mesial at 53.4µm. The lingual and distal were 29.4 and 37.4µm, respectively.
Conclusions: Although PS-OCT and micro-CT measurements differed on three of four surfaces, from a clinical perspective the marginal gap differences were not large enough to be clinically relevant. PS-OCT may serve as a valuable tool to quantitatively assess the integrity of crown margins.