The Use of Optical Coherence Tomography in Dental Diagnostics: A State-of-the-Art Review

Table 2

OCT in cariology and restorative dentistry in the last 5 years of publications.

Number	Reference number	Author	Title	Significance
(1)	[95]	Shimada et al.	Noninvasive cross-sectional imaging of proximal caries using swept-source optical coherence tomography (SS-OCT) in vivo	SS-OCT appears to be a more reliable and accurate method than bitewing radiographs for the detection and estimation of the depth of proximal lesions in the clinical environment.
(2)	[96]	Van Hilsen and Jones	Comparing potential early caries assessment methods for teledentistry	Although MID and CP-OCT were useful in detecting the presence of demineralization, examiners were not able to utilize these devices to adequately assess the depth of the demineralization. This study found that MID and CPOCT did not have markedly superior diagnostic values from simple CAM assessment for use in teledentistry.
(3)	[97]	Nazari et al.	3D assessment of void and gap formation in flowable resin composites using optical coherence tomography	The flowable composite with SDR (stress-decreasing resin) technology performed better than the conventional composite; however, bulk filling a 4 mm-deep cavity will compromise the sealing of the bonding interface regardless of the type of composite. OCT is a unique method of characterizing materials and their behaviors nondestructively and precisely.
(4)	[98]	Mandurah et al.	Monitoring remineralization of enamel subsurface lesions by optical coherence tomography	OCT signal attenuation demonstrated a capability for monitoring changes of enamel lesions during remineralization.
(5)	[99]	de Oliveira Mota et al.	Optical coherence tomography as an auxiliary tool for the screening of radiation-related caries	The OCT technique was able to characterize radiation-related caries, from a morphological point of view. Also demonstrated was its potential benefit for use in the clinical monitoring of radiation-related carious process.
(6)	[100]	Bista et al.	Nondestructive assessment of current one-step self-etch dental adhesives using optical coherence tomography	OCT is a unique tool to nondestructively evaluate the sealing performance of the restoratives through the cavity, provided that cavity walls have a certain minimum inclination with respect to the beam.
(7)	[101]	Park et al.	Assessment of interfacial defects at composite restorations by swept source optical coherence tomography	OCT imaging has the potential to nondestructively assess the interfacial adaptation of composite restorations and to detect internal defects in the layered composite material.
(8)	[102]	Marcauteanu et al.	Quantitative evaluation of dental abfraction and attrition using a swept-source optical coherence tomography system	A valuable tool in the evaluation of the dynamic evolution of ex vivo artificially induced abfractions and attritions is able to measure minute changes in the tooth morphology, having the potential to be employed as an effective tool for monitoring the temporal evolution of dental wear. OCT can offer the possibility of providing in vivo volumetric measurements and identification of fractural lines in dentine. The 2D and 3D pictures prove the OCT ability in the evaluation of dental abfractions and attritions. The system could measure a minimal volume of 2352 μm to 32,352 μm^3, where each volume is acquired as 25,000 A scans in 2.5 s.
(9)	[103]	Liu and Jones	Evaluating a novel fissure caries model using swept source optical coherence tomography	Despite correctly evaluating the depth, this work showed that the lesion width calculated from SS-OCT reflectivity images did not accurately predict the demineralized width. The relative reflectivity could not accurately determine the mineral density of the demineralized lesions. SS-OCT detected subsurface fissure demineralization and could be used to determine if the decay process was advancing toward the enamel-dentin junction.
(10)	[104]	Chan K. H. et al.	Use of 2D images of depth and integrated reflectivity to represent the severity of demineralization in cross-polarization optical coherence tomography	Calculated lesion depths from OCT were compared with lesion depths measured from histological sections examined using polarized light microscopy. The 2D images of the lesion depth and integrated reflectivity are well suited for visualization of early demineralization.
(11)	[105]	Chew et al.	Measuring initial enamel erosion with quantitative light-induced fluorescence and optical coherence tomography: an in vitro validation study	OCT and QLF were able to detect demineralization after 10 min of erosive challenge and could be used to monitor the progression of demineralization of initial enamel erosion in vitro.
(12)	[106]	Nakajima et al.	Detection of occlusal caries in primary teeth using swept source optical coherence tomography	The results obtained from SS-OCT and conventional visual inspections were compared with those of CLSM. SS-OCT detects both cavitated and noncavitated lesions. The magnitude of sensitivity for SS-OCT was higher than those for visual inspection (sensitivity of visual inspection and SS-OCT, 0.70 versus 0.93 for enamel demineralization, 0.49 versus 0.89 for enamel cavitated caries, and 0.36 versus 0.75 for dentin caries). Occlusal caries of a few clinical cases were observed using SS-OCT in vivo. SS-OCT has a great detecting potential for occlusal caries in primary teeth.
(13)	[107]	Rominu et al.	Zirconia enriched dental adhesive: a solution for OCT contrast enhancement. Demonstrative study by synchrotron radiation microtomography	The present study proved the capability of the OCT method in visualizing the morphology and integrity of zirconia-doped tooth adhesive fillings to be used for a further in vivo tool development.
(14)	[108]	Mandurah et al.	Characterization of transparent dentin in attrited teeth using optical coherence tomography	Physiological changes in transparent dentin that involve deposition of mineral casts in the dentinal tubules lead to lower attenuation of OCT signal. OCT has a potential role to detect transparent dentin on the surface of attrited teeth and can be used in the future as a clinical adjunct tool.
(15)	[109]	Ku et al.	Detection of early changes in caries lesion using QLF-D and OCT	The QLF-D and SS-OCT could detect subtle changes in mineral loss and lesion depth with respect to demineralized time. Furthermore, these devices were useful for monitoring changes in mineral amount and lesion depth.
(16)	[110]	Turkistani et al.	Sealing performance of resin cements before and after thermal cycling: evaluation by optical coherence tomography	OCT could be used for monitoring of composite inlays with several interfacial resin layers. The application of a direct bonding agent in the resin-coating technique improved interfacial sealing and durability of all resin cements.
(17)	[111]	Lee et al.	Automated assessment of the remineralization of artificial enamel lesions with polarization-sensitive optical coherence tomography	PS-OCT can automatically measure the changes in artificial enamel lesion structure and severity upon exposure to remineralization solutions.
(18)	[112]	Chan et al.	A method for monitoring enamel erosion using laser irradiated surfaces and optical coherence tomography	Irradiation of the enamel surface with a pulsed carbon dioxide laser at subablative intensities results in significant inhibition of erosion and demineralization under the acid challenge employed in this study. In addition, these results suggest that it may be feasible to modify regions of the enamel surface using the laser to serve as reference marks to monitor the rate of erosion in vivo.
(19)	[113]	Cara et al.	Evaluation of two quantitative analysis methods of optical coherence tomography for detection of enamel demineralization and comparison with microhardness	Both methods for signal analysis from OCT allowed detection of demineralization with good performance. The AUC-OCT approach enables obtaining a linear relation with the microhardness results, for a quantitative assessment of mineral loss in human teeth.
(20)	[114]	Oancea et al.	Assessment of the sealant/tooth interface using optical coherence tomography	Optical inspection and X-ray investigation revealed no defects, while SS-OCT assesses exactly the position, the nature, and the dimensions of each type of these defects.
(21)	[115]	Damodaran et al.	Development of an electro-optically tuned optical coherence tomography system for imaging dental lesions	The tuning range for LiNbO3 and KTP was found to be in the order of few micrometers whereas KTN (potassium tantalate niobate) using the quadratic electro-optic effect is expected to show scanning range of tens of micrometers. KTN based hybrid scanning for dental caries imaging is also planned.
(22)	[116]	Wada et al.	Clinical assessment of non carious cervical lesion using swept-source optical coherence tomography	SS-OCT results confirm that dentin mineral loss and occlusal attrition were associated with larger NCCLs and can be considered as an etiological fact or information and progress of these lesions.
(23)	[117]	Anadioti et al.	Internal fit of pressed and computer-aided design/computer-aided manufacturing ceramic crowns made from digital and conventional impressions	The combination of the digital impression and pressed crown produced the least accurate internal fit.
(24)	[118]	Bortolotto et al.	Failure analysis of adhesive restorations with SEM and OCT: from marginal gaps to restoration loss	When marginal imperfections, or noncontinuous margins, were detected by SEM, also imperfections beneath the surface could be observed at the tooth-restoration interface with OCT. Restoration loss occurred above the borderline of 50% of marginal gaps on enamel and dentin. Marginal discrepancies of adhesive restorations can propagate inside the cavity and lead to restoration loss.
(25)	[119]	Alsayed et al.	Optical coherence tomography for evaluation of enamel and protective coatings	The coatings showed different thicknesses (60–250 micrometers) and various levels of structural and interfacial integrity. OCT could detect a demineralization inhibition zone adjacent to the edge of the fluoride- and calcium-releasing material. Localized demineralization was occasionally observed under thinner coatings. Protection of susceptible enamel surfaces by thin resin-basedbioactive coatings provides protection from demineralization. OCT can be used to nondestructively monitor the integrity of such coatings, as well as enamel changes beneath and adjacent to them.
(26)	[120]	Espigares et al.	Assessment of natural enamel lesions with optical coherence tomography in comparison with microfocus X-ray computed tomography	The images obtained clinically in real time using the dental SS-OCT system are suitable for the assessment of natural subsurface lesions and their surface layer, providing comparable images to a laboratory high resolution μCT without the use of X-ray.
(27)	[121]	Sun et al.	Sensing of tooth microleakage based on dental optical coherence tomography	The results of this study show that microleakage can be detected with oral probing using SS-OCT in vivo. The calculated microleakage length was 401 μm and the width is 148 μm, which is consistent with the related histological biopsy measurements. The diagnosis of microleakage in teeth could be useful for prevention of secondary caries in the clinical treatment plans developed in the field of oral medicine.
(28)	[122]	Park et al.	Assessment of defects at tooth/self-adhering flowable composite interface using swept-source optical coherence tomography (SS-OCT)	Given the high proportion of adhesive defects with the experimental self-adhering flowable composite, its use as the definitive restorative material in class-V cavities must be critically scrutinized and clinical indications must be investigated further with in vitro and in vivo trials.
(29)	[123]	Milly et al.	Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization	Bioactive glass air-abrasion was used to precondition enamel white spot lesion. Preconditioning increased the average surface roughness of the lesion. An ultrathin, clinically insignificant layer was removed from the lesion surface. Preconditioning enhanced subsequent remineralization using bioactive glass.
(30)	[124]	Min et al.	Evaluation of penetration effect of resin infiltrant using optical coherence tomography	The OCT was the promising quantitative evaluation method for RI penetrated into EC. The OCT would be used as a nondestructive and real-time evaluation method for resin infiltrant penetrated into caries lesion on clinical procedure.
(31)	[125]	Sinescu et al.	Noninvasive quantitative evaluation of the dentin layer during dental procedures using optical coherence tomography	The study demonstrates the usefulness of OCT imaging in guiding such evaluations during dental procedures.
(32)	[126]	Majkut et al.	Validation of optical coherence tomography against micro-computed tomography for evaluation of remaining coronal dentin thickness	We used optical coherence tomography (OCT) and microcomputed tomographic (micro-CT) imaging to scan teeth after deep dentin caries removal. The remaining dentin thickness (RDT) at pulpal horns was measured and compared. A strong correlation was found in measurements between OCT and micro-CT imaging. It was possible to clearly visualize pulp horns with RDT up to 1.5 mm in thickness. A refractive index value of 1.54 is valid to convert optical readings of RDT by OC.
(33)	[127]	Turkistani et al.	Microgaps and demineralization progress around composite restorations	Microgaps forming at the margins of restorations depend on adhesives and significantly contribute to the progress of demineralization around the margins, while fluoride release may decrease the rate of progression.
(34)	[128]	Mota et al.	Optical coherence tomography applied to the evaluation of wear of composite resin for posterior teeth	90% of the restorations of both groups had fractures and/or points of stress concentration, considered niches for early dissemination of new fracture lines.
(35)	[129]	Barbosa et al.	Analysis of photodynamic cream effect in dental caries using optical coherence tomography	The OCT technique demonstrated that cream associated with laser showed the lowest quantitative enamel mineral loses after cariogenic challenge.
(36)	[130]	Makishi et al.	Assessment of current adhesives in class I cavity: nondestructive imaging using optical coherence tomography and microtensile bond strength	Sealing performance was measured in five adhesives by optical coherence tomography. Sealing and bond strength performance within individual specimens were correlated. Interfacial defects increased after thermal aging. Increased interfacial defects tended to decrease the bond strength. Two- and three-dimensional images were useful in assessing bonding performance.
(37)	[74]	Ibusuki et al.	Observation of white spot lesions using swept source optical coherence tomography (SS-OCT): in vitro and in vivo study	SS-OCT appears to be an effective tool for observation of the internal structure of WSLs, enabling quantitative assessment of WSL depth. Such data can be considered in the clinical management of white spot lesion.
(38)	[131]	Yoshimine et al.	Interfacial adaptation of composite restorations before and after light curing: effects of adhesive and filling technique	SS-OCT is a unique method to observe the pre-existing interfacial defects and gaps developed during polymerization, which were found to depend on both placement technique and applied adhesive.
(39)	[132]	Sampaio et al.	Effect of restorative system and thermal cycling on the tooth restoration interface—OCT evaluation	The self-etching adhesive system (CSE) showed better dentin marginal integrity after thermal cycling, compared with the etch-and-rinse (SB2), regardless of the type of resin composite used. Enamel was not affected even after thermal cycling.
(40)	[130]	Makishi et al.	Assessment of current adhesives in class I cavity: nondestructive imaging using optical coherence tomography and microtensile bond strength	Sealing performance was measured in five adhesives by optical coherence tomography. Sealing and bond strength performance within individual specimens were correlated. Interfacial defects increased after thermal aging. Increased interfacial defects tended to decrease the bond strength. Two- and three-dimensional images were useful in assessing bonding performance.
(41)	[133]	Borges et al.	Marginal and internal analysis of preheated dental fissure-sealing materials using optical coherence tomography	Preheated flowable composite provided the best marginal sealing of fissures and internal homogeneity of the material.
(42)	[134]	Dsouza et al.	Assessment of curing behavior of light-activated dental composites using intensity correlation based multiple reference optical coherence tomography	These results show that MR-OCT has the potential to measure the curing time and monitor the curing process as a function of depth. Moreover, MR-OCT as a product has potential to be compact, low-cost, and to fit into a smartphone. Using such a device for monitoring the curing of the resin will be suitable for dentists in stationary and mobile clinical settings.
(43)	[135]	Han et al.	Non-destructive evaluation of an internal adaptation of resin composite restoration with swept-source optical coherence tomography and micro-CT	Micro-CT and SS-OCT may be useful nondestructive methods for evaluating internal adaptation. The microleakage measured by micro-CT was lower than that of SS-OCT; however, the two measurements were relatively high-correlated. When adhesion depends mostly on the dentin surface, a two-step self-etch adhesive system should be considered for long-term longevity.
(44)	[137]	Tom et al.	Near-IR image-guided laser ablation of demineralization on tooth occlusal surfaces	Sequential near-IR reflectance images at 1500–1700 nm can be used to guide a 9.3 μm CO2 laser for the selective ablation of early demineralization on tooth occlusal surfaces.
(45)	[138]	Cassimiro-Silva et al.	Mitigation of enamel erosion using commercial toothpastes evaluated with optical coherence tomography	A significant increase in the mean roughness values was observed on eroded surface and also on treated surface as revealed by scanning electron microscopy. The use of SnF2/NaF toothpaste was the most effective method for reducing mineral loss. As quantitative methods, OCT and contact profilometry showed no statistical differences. OCT, which was used for this purpose for the first time, has the advantage of being noninvasive and therefore has the potential for clinical application.
(46)	[139]	Dao Luong et al.	Fractography of interface after microtensile bond strength test using swept-source optical coherence tomography	Testing MTBS samples at higher crosshead speeds induced more cracks in dentin. Lining with a flowable composite improved the bonding quality and increased the bond strength. SS-OCT can visualize interfacial cracks after restoration debonding.
(47)	[140]	Ito et al.	Assessment of occlusal fissure depth and sealant penetration using optical coherence tomography	The diagnostic power of SS-OCT was higher than that of visual inspection for fissure depth. Additionally, clear cross-sectional images of sealant penetration into fissures were observed with SS-OCT. SS-OCT can be used to evaluate fissure depth and monitor sealant penetration.
(48)	[141]	Han et al.	Internal adaptation of resin composites at two configurations: influence of polymerization shrinkage and stress	Internal adaptation in a high C-factor cavity was inferior to that in a low C-factor cavity for both conventional and bulk-filled composites. Internal adaptation, polymerization shrinkage, and stress were different among composite materials. Polymerization stress under the compliance-allowed condition showed significant correlations with internal adaptations in high and low C-factor cavities.
(49)	[142]	Horie et al.	Monitoring of cariogenic demineralization at the enamel–composite interface using swept-source optical coherence tomography	The carious demineralization around composite restorations was observed as a bright zone in SS-OCT during the process of bacterial demineralization. SS-OCT appears to be a promising modality for the detection of caries adjacent to an existing restoration.
(50)	[143]	Zhou et al.	Assessment of bacterial demineralization around composite restorations using swept-source optical coherence tomography (SS-OCT)	SS-OCT nondestructively detected demineralization around composite restorations and interfacial gaps created by S. mutans biofilm in this in vitro model.
(51)	[144]	de Moraes et al.	Progression of erosive lesions after Nd:YAG laser and fluoride using optical coherence tomography	The OCT technique is promising for diagnosing and monitoring erosive lesion damage; however, further in vitro and in vivo research is needed to improve its use.
(52)	[145]	Ueno et al.	Optical analysis of enamel and dentin caries in relation to mineral density using swept-source optical coherence tomography	Both enamel and dentin demineralization showed significantly higher IS200 and μμ than the sound tooth substrate from the sagittal scan. Enamel demineralization showed significantly higher IS200 than sound enamel, even with low levels of demineralization. In demineralized dentin, the μμ from the horizontal scan consistently trended downward compared to the sound dentin.
(53)	[146]	Sugita et al.	A pilot study to assess the morphology and progression of non-carious cervical lesions	The dimensional analysis demonstrated notable progression with large variations. The wedge-shaped lesions appeared to show greater Dmax values compared to the saucer-shaped lesions.
(54)	[147]	Schneider et al.	Imaging resin infiltration into non-cavitated carious lesions by optical coherence tomography	Resin infiltration can be increased by optimizing the etching process. Optical coherence tomography provides information about the process and degree of resin infiltration.
(55)	[20]	Holtzman et al.	Ability of optical coherence tomography to detect caries beneath commonly used dental sealants	Dentists were able to detect tooth decay beneath four commonly used dental sealants based on OCT images. Clinical investigations are now underway to determine the usefulness of this approach in vivo.
(56)	[12]	Kang et al.	Nondestructive monitoring of the repair of enamel artificial lesions by an acidic remineralization model using polarization-sensitive optical coherence tomography	This study demonstrated that PS-OCT can be used to nondestructively measure changes in lesion structure and severity upon exposure to an acidic remineralization model. This study also demonstrated that automated algorithms can be used to assess the lesion severity even with the presence of a weakly reflective surface zone.
(57)	[28]	Kang et al.	Nondestructive assessment of early tooth demineralization using cross-polarization optical coherence tomography	Cross-polarization OCT is ideally suited for the nondestructive assessment of early demineralization.
(58)	[58]	Nazari et al.	Effect of hydration on assessment of early enamel lesion using swept-source optical coherence tomography	In summary, the strong relationship found between DH and lesion extent indicates the potential of this method for assessment of early enamel lesion using SS-OCT. However, further studies on DH for evaluation of a wider range of demineralized lesions as well as remineralization, accompanied by a clinically relevant drying method are necessary to optimize the suggested methodology.
(59)	[60]	Shimada et al.	3D evaluation of composite resin restoration at practical training using swept-source optical coherence tomography (SS-OCT)	SS-OCT could detect the internal gaps and voids within the restorations in tomography images synthesized based on the backscatter signal from within the restoration. It is suggested that the SS-OCT is promising diagnostic modality, as well as educational imaging device for the detection of internal gaps in adhesive restorations.
(60)	[62]	Nakajima et al.	Noninvasive cross-sectional imaging of incomplete crown fractures (cracks) using swept-source optical coherence tomography	SS-OCT can clearly discriminate cracks, which appear as highlighted lines due to the scattering of light. The results obtained from the three scanning directions were correlated well with those of the histological sections.
(61)	[63]	Braz et al.	In situ gold nanoparticles formation: contrast agent for dental optical coherence tomography	The results show that the OCT technique, using in situ formed gold nanoparticles as contrast enhancers, can be used to visualize dentin structures in a noninvasive and nondestructive way.
(62)	[67]	Holtzman et al.	Assessment of early occlusal caries pre- and post-sealant application—an imaging approach	This study found that OCT-based imaging combined with a simple diagnostic algorithm accurately assessed the severity of natural early caries on occlusal surfaces in extracted teeth both in the absence and presence of dental sealant. The findings of this study support the clinical use of OCT imaging for assessment and monitoring progression of early noncavitated caries lesions on occlusal surfaces including areas under dental sealants.
(63)	[69]	Sugita et al.	A pilot study to assess the morphology and progression of non-carious cervical lesions	The dimensional analysis demonstrated notable progression with large variations. The wedge-shaped lesions appeared to show greater maximal values compared to the saucer-shaped lesions. With respect to the depth, the wedge-shaped lesions may progress at a greater rate compared to the saucer-shaped lesions.
(64)	[70]	Zhou et al.	Assessment of bacterial demineralization around composite restorations using swept-source optical coherence tomography (SS-OCT)	SS-OCT nondestructively detected demineralization around composite restorations and interfacial gaps created by S. mutans biofilm in this in vitro model.
(65)	[71]	Maia et al.	Evaluation of dental enamel caries assessment using quantitative light induced fluorescence and optical coherence tomography	Comparison of the percentage of alteration between optical properties of sound and artificial enamel caries regions showed that OCT processed images through the attenuation of light enhanced the tooth optical alterations more than fluorescence detected by QLF system. QLF versus OCT imaging of enamel caries: a photonics assessment.
(66)	[72]	Horie et al.	Monitoring of cariogenic demineralization at the enamel–composite interface using swept-source optical coherence tomography	The carious demineralization around composite restorations was observed as a bright zone in SS-OCT during the process of bacterial demineralization. SS-OCT appears to be a promising modality for the detection of caries adjacent to an existing restoration.
(67)	[73]	Damodaran et al.	Optical coherence tomography based imaging of dental demineralization and cavity restoration in 840 nm and 1310 nm wavelength regions	Results were comparable with that of the widely used 1310 nm OCT system. In the case of restoration with filler material, the 1310 nm OCT imaging displayed better imaging capacity due to lower scattering than 840 nm imaging.