Abstract
Objective
This longitudinal pilot study aimed to morphologically and quantitatively investigate the progress of non-carious cervical lesions (NCCLs) by using swept-source optical coherence tomography (SS-OCT).
Methods
The samples examined comprised sets of NCCL epoxy resin replicas obtained from 10 lesions in 6 patients who attended annual dental visits over 4 or 5 years. SS-OCT images of the replicas were analyzed in terms of the maximum depth (D max ) and corresponding vertical width (VW) – using an image analyzer to estimate progression of the NCCLs over time.
Results
It was found that differences between wedge- and saucer-shaped lesions were morphologically distinguished well by the OCT images. There were significant differences in dimensions among D max , VW and horizontal width (HW). HW was the largest and D max was the smallest. Although no significant differences in absolute values of annual progression rates were found among D max, VW and HW, the percentage increase in D max was significantly greater compared to VW and HW. The ratios of D max to corresponding VW ranged from 0.49 to 1.01 for the wedge-shaped lesions and from 0.13 to 0.44 for saucer-shaped lesions, respectively.
Conclusions
The dimensional analysis demonstrated notable progression with large variations. The wedge-shaped lesions appeared to show greater D max values compared to the saucer-shaped lesions.
Clinical significance
With respect to the depth, the wedge-shaped lesions may progress at a greater rate compared to the saucer-shaped lesions.
1
Introduction
Non-carious cervical lesions (NCCLs), which are characterized by loss of hard tissue at the cemento-enamel junction in the absence of caries, are commonly encountered in dental practice . NCCLs are often restored due to hypersensitivity, poor esthetic appearance and prevention of further loss of tooth tissues . However, Lyttle et al. concluded that treatment for NCCLs may not be based on the correct diagnosis.
Generally, morphological features of NCCLs have been characterized as two distinct patterns, i.e. wedge-shaped lesions with sharp internal line angles and saucer-shaped lesions with more broad and rounded line angles . For the wedge-shaped lesion, Aw et al. introduced an angular scale of NCCLs, i.e. <45°, 45°–90°, 90°–135°, >135° as one of the parameters to characterize NCCL morphology. There is some suggestion that these morphological features of NCCLs are related to their etiology . Wedge-shaped lesions could be caused by abrasive factors such as incorrect tooth-brushing habits or tooth loading causing high stresses due to bruxism, which is called abfraction, whereas saucer-shaped lesions are generally shallow and could be caused by acid erosion . It is commonly accepted that initiation and progression of NCCLs have a multi-factorial etiology, but the relative contributions of the various etiological factors still remain unclear .
So far, most of the epidemiological surveys have been restricted to cross-sectional studies, where mostly visual inspection using scoring criteria of the Tooth Wear Index (TWI) was employed as a diagnostic tool . Estafan et al. further classified wedge-shaped lesions into 3 levels, mild (slight), moderate (<1 mm deep) and severe (≥1 mm deep). However, TWI is not suitable for quantitatively monitoring NCCL progression due to its large resolution. Very few studies have been published examining the longitudinal progression of NCCLs, where NCCL casts prepared by impression materials were obtained to record the 3-dimensional change over time . This method may overcome, to some extent, the problem of subjective diagnosis of NCCLs by visual inspection. Another group employed micro-computed tomography to characterize NCCL morphology in-vitro and examined the abfraction theory using extracted teeth .
Optical coherence tomography (OCT) uses low coherence interferometry to determine the echo time delay and magnitude of backscattered light reflected from a biological structure . This emerging diagnostic method can noninvasively obtain cross-sectional internal images of biological structures in real-time without use of x-ray irradiation. Swept-source OCT is the latest implementation of the technology, which has demonstrated superior sensitivity, higher scanning speed, and a higher signal-to-noise ratio over the conventional time-domain OCT . For instance, studies on detection and quantification of de-/remineralization in enamel and dentin have been performed both in-vitro and in-vivo . Other groups examined gap formation at the interface between the cavity floor and resin by OCT in-vitro . Wada et al. employed OCT to explore possible associations between NCCL size and other clinical observations such as occlusal wear, cracking, hypersensitivity and demineralization in-vivo .
A systematic review revealed that there were several prospective studies that dealt with progression of NCCLs . Recently, sets of NCCLs dental stone casts, which were annually prepared up to a maximum of 5 years from respective patients, were provided to our group to analyze NCCL progression using OCT. The purposes of this pilot study were to investigate the feasibility of OCT for NCCL morphological characterization and examine the progression over time by using the casts. The null hypotheses for this study were that OCT images do not clearly distinguish wedge- and saucer-shaped NCCLs, and the image analysis does not provide definitive data on the longitudinal changes in the dimensions of NCCLs. The other null hypothesis was that there is no association between morphology and progression rates of NCCLs.
2
Materials and methods
2.1
Preparation of plaster impression casts of dentitions and its epoxy resin replicas
A total of 26 subjects with NCCLs were recruited at Nagasaki University Hospital, Japan by one of the authors (SK) during the period between 2000 and 2005 to investigate the progression of NCCLs. This study was approved by the Ethics Committees of Nagasaki University School of Dentistry (No. 20). After careful removal of debris attached to tooth surfaces, silicone impressions (Exafine putty type, Injection type: GC Corp, Tokyo, Japan) of the NCCLs were taken and then poured up in improved dental stone (Fuji Rock: GC Corp). The stone casts were usually obtained every year for 4 or 5 years for each subject included in the study. These were transferred from Nagasaki University (NU) to Tokyo Medical and Dental University (TMDU) after collaboration between NU and TMDU was approved by the respective IRBs (No. 14070391 for NU and No. 959 for TMDU).
Ten sets of casts from 6 subjects, who fulfilled 4 or 5 years of observation and were randomly selected, were prepared for the current pilot study using OCT. Table 1 shows patients’ ages and gender, the tooth code with NCCL, and year of data acquisition. The gingival margins of the casts covering the hidden portions of NCCLs were trimmed to allow OCT visualization of the areas that would have been covered by gingival tissue on the casts. In order to avoid damaging the original casts, a further impression using silicone impression material (Duplicone: Shofu Inc., Kyoto, Japan) was taken to duplicate the lesions without under-cut area. Replicas were prepared using transparent epoxy resin (EpoxiCure: Buehler, Lake Bluff, Illinois, USA).
| Lesion | Subject | Tooth code | Age | Gender | 2000 | 2001 | 2002 | 2003 | 2004 | 2005 |
|---|---|---|---|---|---|---|---|---|---|---|
| L1 | S1 | 45 | 38 | F | ○ | ○ | ○ | × | ○ | × |
| L2 | S2 | 14 | 52 | F | ○ | × | ○ | × | ○ | × |
| L3 | S2 | 25 | 52 | F | ○ | ○ | ○ | × | ○ | × |
| L4 | S3 | 15 | 48 | M | ○ | × | ○ | ○ | ○ | ○ |
| L5 | S4 | 14 | 57 | F | × | ○ | ○ | ○ | ○ | ○ |
| L6 | S4 | 44 | 57 | F | × | ○ | ○ | ○ | ○ | ○ |
| L7 | S5 | 24 | 68 | F | ○ | ○ | ○ | × | × | ○ |
| L8 | S6 | 13 | 61 | F | × | ○ | × | × | ○ | ○ |
| L9 | S6 | 14 | 61 | F | × | ○ | ○ | × | ○ | ○ |
| L10 | S6 | 15 | 61 | F | × | ○ | × | × | ○ | ○ |
2.2
OCT image capturing of NCCL replicas
This study used Swept-Source Optical Coherence Tomography (SS-OCT: Santec OCT-2000 ® , Santec Co., Komaki, Japan, Fig. 1 a). The SS-OCT system incorporates a high-speed frequency swept external cavity laser, the wavelength ranges from 1260 nm to 1360 nm (centered at 1310 nm) at a 20-kHz sweep rate. Two-dimensional cross-sectional images were created from serial back-scatter (reflective) profiles along the surface. The axial and lateral resolutions of the system in air were 11 and 17 μm respectively. The system acquired an output of the NCCL image data (2000 × 1019 pixels) in 0.3 s including the processing time. The sensitivity of this SS-OCT and short-noise limited sensitivity were 106 dB and 119 dB respectively. The schematic presentation of SS-OCT laser optical circuit is available in the literature .
The epoxy resin replicas were fixed to a silicone holder placed on the stage ( Fig. 1 b) with the replica surface facing the scanning probe connected to the SS-OCT. The silicone holder was used to keep a line connecting the occlusal margin and the gingival margin at the center of the tooth in a mesiodistal direction parallel to both the surface and Y axis of the stage ( Fig. 1 b, c). The silicone holder was prepared for each set of NCCL epoxy resin replicas obtained from 10 lesions. In addition, the replica was placed so that the tooth axis was parallel to the scanning direction ( Fig. 1 c). The hand-held probe was set at a distance of 50 mm from the replica surface, with the scanning beam was oriented at 90 ° to the surface ( Fig. 1 b). To enable the repeatability of the OCT scan for different replicas prepared for each observation time from the same subject, the replicas were placed at the same orientation as accurately as possible.
2.3
Analysis of OCT image of NCCL replica
A typical two-dimensional OCT image of a NCCL is shown in Fig. 2 . The white cross-section outline is of the NCCL surface which is apparent owing to strong light reflection at the lesion surface. The b-scan was performed from the mesial to distal ends of the lesion at 500 μm intervals ( Fig. 1 c) and the NCCL was characterized in terms of the maximum depth (D max ) and the corresponding vertical width (VW) as shown in Fig. 2 . A custom code in the image analysis software (ImageJ ver.1.47 n; Wayne Rasband, NIH, Bethesda, MD, USA) was used to handle the raw data of the OCT scan. The horizontal width (HW) was measured with a Vernier micrometer (CD-S15C, Mitutoyo Corp. Tokyo Japan) manually because of the large width of HW that could not be measured by the current OCT system. In this study, as the representative data for a single NCCL sample, the D max value and the corresponding VW value were employed. The progression rates of the lesion were determined by the difference in dimensions of 3 parameters between baseline and respective recalls. The morphological features of the 10 NCCLs were subjectively categorized by the first author referring to the traditional classification i.e., wedge-shaped lesions with sharp internal line angles, saucer-shaped lesions with broad and round line angles and mixed-shape lesions . These analyses were performed for each observation year from the 10 lesions.
2.4
Statistical analysis
The Kruskal-Wallis test was used to compare the sizes, annual progression rates and the percentage increase between the 3 parameters by using SPSS statistical software (version 19.0, SPSS Inc., Chicago, Illinois, USA) at a significance level of 0.05.
2
Materials and methods
2.1
Preparation of plaster impression casts of dentitions and its epoxy resin replicas
A total of 26 subjects with NCCLs were recruited at Nagasaki University Hospital, Japan by one of the authors (SK) during the period between 2000 and 2005 to investigate the progression of NCCLs. This study was approved by the Ethics Committees of Nagasaki University School of Dentistry (No. 20). After careful removal of debris attached to tooth surfaces, silicone impressions (Exafine putty type, Injection type: GC Corp, Tokyo, Japan) of the NCCLs were taken and then poured up in improved dental stone (Fuji Rock: GC Corp). The stone casts were usually obtained every year for 4 or 5 years for each subject included in the study. These were transferred from Nagasaki University (NU) to Tokyo Medical and Dental University (TMDU) after collaboration between NU and TMDU was approved by the respective IRBs (No. 14070391 for NU and No. 959 for TMDU).
Ten sets of casts from 6 subjects, who fulfilled 4 or 5 years of observation and were randomly selected, were prepared for the current pilot study using OCT. Table 1 shows patients’ ages and gender, the tooth code with NCCL, and year of data acquisition. The gingival margins of the casts covering the hidden portions of NCCLs were trimmed to allow OCT visualization of the areas that would have been covered by gingival tissue on the casts. In order to avoid damaging the original casts, a further impression using silicone impression material (Duplicone: Shofu Inc., Kyoto, Japan) was taken to duplicate the lesions without under-cut area. Replicas were prepared using transparent epoxy resin (EpoxiCure: Buehler, Lake Bluff, Illinois, USA).
| Lesion | Subject | Tooth code | Age | Gender | 2000 | 2001 | 2002 | 2003 | 2004 | 2005 |
|---|---|---|---|---|---|---|---|---|---|---|
| L1 | S1 | 45 | 38 | F | ○ | ○ | ○ | × | ○ | × |
| L2 | S2 | 14 | 52 | F | ○ | × | ○ | × | ○ | × |
| L3 | S2 | 25 | 52 | F | ○ | ○ | ○ | × | ○ | × |
| L4 | S3 | 15 | 48 | M | ○ | × | ○ | ○ | ○ | ○ |
| L5 | S4 | 14 | 57 | F | × | ○ | ○ | ○ | ○ | ○ |
| L6 | S4 | 44 | 57 | F | × | ○ | ○ | ○ | ○ | ○ |
| L7 | S5 | 24 | 68 | F | ○ | ○ | ○ | × | × | ○ |
| L8 | S6 | 13 | 61 | F | × | ○ | × | × | ○ | ○ |
| L9 | S6 | 14 | 61 | F | × | ○ | ○ | × | ○ | ○ |
| L10 | S6 | 15 | 61 | F | × | ○ | × | × | ○ | ○ |
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