Periodontal Measurement Accuracy and Reliability Using Intraoral Ultrasound

Abstract

Intraoral ultrasonography (iUS) has emerged as a noninvasive, radiation-free imaging modality capable of real-time visualization of both soft and hard tissues, yet its clinical accuracy and reliability remain incompletely characterized. This study aims to evaluate the accuracy and reliability of periodontal parameters measured on intraoral ultrasonograms. An in-house customized 20-MHz ultrasound imaging system with a rotational head was used to image the periodontium. Ex vivo accuracy was assessed in 58 teeth from 3 cadaver specimens with high-resolution micro–computed tomography (µCT) as the gold standard. Two raters independently performed repeated measurements of alveolar bone level (ABL) and alveolar bone thickness (ABT) on 50 iUS images using a standardized anatomy-guided protocol. Intermethod agreement was quantified using intraclass correlation coefficients (ICCs), mean absolute differences (MADs), paired t tests, and Bland–Altman analysis. In vivo clinical reliability was evaluated in 19 adolescents undergoing orthodontic treatment, with 3 raters measuring the ABL, ABT, attached gingival thickness, and free gingival thickness on 134 iUS images. Ex vivo analysis demonstrated excellent iUS accuracy and consistency for ABL (MAD 0.18–0.31 mm, ICCs 0.94–0.96) and excellent accuracy and good agreement for ABT (MAD 0.05 mm; ICCs 0.87). Paired t tests revealed no significant differences between iUS and µCT measurements for either parameter (all P > 0.05). Bland–Altman analysis demonstrated excellent agreement with near-zero bias for both ABL and ABT, with narrow 95% limits of agreement across raters. In vivo measurements exhibited outstanding intrarater reliability (ICCs ≥ 0.84; MAD ≤ 0.10 mm) and good-to-excellent interrater reliability (ICCs ≥ 0.82; MAD ≤ 0.18 mm) for all parameters. The standardized, anatomy-guided protocol minimized operator dependency, enabling reproducible assessments across raters. These results demonstrate that iUS provides highly reproducible and reliable periodontal measurements in cadavers and healthy adolescents. Further studies in patients with moderate-to-severe periodontal disease are required to fully validate iUS for longitudinal monitoring.

Keywords

intraoral ultrasonography periodontitis malocclusion alveolar bone cementoenamel junction micro–computed tomography

Introduction

Accurate assessment of the periodontium is essential for diagnosis, treatment planning, and long-term management in periodontal and orthodontic practice. The periodontium comprising the gingiva, periodontal ligament, cementum, and alveolar bone forms the structural support of the teeth (Hughes 2015). Key clinical parameters such as alveolar bone level (ABL), alveolar bone thickness (ABT), gingival thickness, and sulcus depth, reflect periodontal stability and disease progression (Papapanou et al 2018). Precise evaluation of ABL and ABT is critical for diagnosing periodontitis, determining severity, and predicting future tissue breakdown (Evangelista et al 2010; Walter et al 2016). In orthodontics, compromised bone height or thickness increases the risk of dehiscence, fenestration, and gingival recession during tooth movement (Antoun et al 2017). Accurate characterization of alveolar and gingival dimensions also guides periodontal plastic surgery, implant placement, and endodontic microsurgery (von Arx et al 2007; Ferrus et al 2010; Holtzman et al 2021).

Periodontal probing remains the gold standard for soft-tissue evaluation (Eke et al 2020; Chung et al 2022), but it is invasive and operator dependent (Salvi and Lang 2004). Two-dimensional radiographs reliably assess interproximal bone (Corbet et al 2009; Christiaens et al 2018) yet cannot adequately visualize buccal and lingual cortical plates because of anatomical superimposition (Jeffcoat et al 1995; Shah et al 2014). Cone-beam computed tomography (CBCT) provides 3-dimensional evaluation of alveolar bone morphology and defects with improved spatial resolution (Sun et al 2015; De Grauwe et al 2019), but its use is limited by radiation exposure, cost, and reduced suitability for longitudinal monitoring, especially in younger patients (Ludlow et al 2006; Nguyen et al 2018; Shatskiy 2021).

Intraoral ultrasonography (iUS) has emerged as a noninvasive, radiation-free alternative that enables real-time visualization of soft and hard tissues and allows repeated measurements (Marotti et al 2013; Nguyen, Le, Kaipatur, and Major 2016; Nguyen, Le, Kaipatur, Zheng, et al 2016; Chan et al 2017; Barootchi et al 2020; Nguyen et al 2020; Nguyen et al 2021; Moore et al 2022; Betancourt et al 2023; Soltani et al 2023). Advances in compact, high-frequency transducers have improved intraoral accessibility, spatial resolution, and measurement reproducibility (Chan and Kripfgans 2020; Fu et al 2022; Le et al 2024).

Previous studies have demonstrated encouraging accuracy and reliability for periodontal assessment (Tattan et al 2020; Tanaka et al 2023). Ex vivo comparisons with CBCT showed mean ABL differences of 0.07 to 0.68 mm (Nguyen et al 2018), while a clinical adolescent study (Nguyen et al 2023) reported a mean ABL difference of −0.07 mm (95% limits of −0.47 to 0.32 mm) between iUS and CBCT. Corbea et al (2025) reported high intraclass correlation coefficients (ICCs; 0.885 to 0.894) for ABL compared with micro–computed tomography (µCT). Qi et al (2024) observed cementoenamel junction (CEJ) identification discrepancies of 1.7 to 2.1 mm using ultrasound versus visual/tactile reference methods. Regarding reliability, interrater ICCs of 0.76 to 0.83 (mean absolute difference [MAD] 0.12 to 0.18 mm) were reported for gingival and crestal bone parameters (Majzoub et al 2022), while Figueredo et al (2023) demonstrated intra- and interrater ICCs of 0.859 to 0.953 and 0.836 to 0.958, respectively, for ABL, ABT, and gingival thickness. Despite these advances, ultrasound-derived ABT has not been rigorously validated against high-resolution µCT. Moreover, no standardized anatomy-guided protocol ensures reproducible, beam orientation–independent measurement of ABL, attached gingival thickness (AGT), and free gingival thickness (FGT). Prior studies have also assessed either ex vivo accuracy or in vivo reliability, but not both, within a unified framework.

Therefore, this study aimed to (1) evaluate the ex vivo accuracy of ABL and ABT using µCT as the reference standard and (2) assess the in vivo reliability of ABL, ABT, AGT, and FGT in adolescents. We additionally introduce a standardized, anatomy-guided protocol for periodontal assessment using iUS.

Materials and Methods

Data Collection and Sample Preparation

Cadaver specimens

Three human cadavers (2 females, 1 male; mean age 69.0 ± 6.6 y) were provided for research purposes at the University of Alberta (Pro00147871). Teeth with ceramic restorations or metal crowns were excluded to prevent ultrasound-related artifacts (acoustic shadowing and signal attenuation) that could obscure periodontal landmarks and bias comparison with the µCT reference standard. To establish reproducible anatomical reference points, paired notches were created on the buccal surface of selected teeth using a dental handpiece with a 0.25-mm drill bit. Each incisor, canine, and premolar received 1 vertically aligned notch pair positioned along the long axis in the mid-buccal crown region, coronal to the CEJ and away from the alveolar bone crest (ABC) to avoid interference with periodontal measurements. These notches served as spatial reference landmarks for aligning corresponding ultrasound and µCT imaging planes. A total of 58 teeth from mandibles–maxillae cadaver specimens were identified as suitable for analysis. Although the cadaver dentitions exhibited age-related horizontal alveolar bone loss, teeth included for quantitative analysis demonstrated intact buccal cortical plates without gross vertical defects in the measurement regions.

Human participants

Nineteen adolescents (mean age 13.8 ± 1.3 y; range 11 to 16 y) undergoing orthodontic treatment were recruited from the Kaye Edmonton Dental Clinic between January and June 2021. The study was conducted under University of Alberta research ethics approval (Pro00099721). The inclusion and exclusion criteria were identical to those used in the previously published work (Kumaralingam et al 2025). A total of 134 B-mode ultrasound images, including central (n = 31) and lateral (n = 35) incisors, canines (n = 33), and premolars (n = 35) from both the maxillae and mandibles, were selected for reliability assessment.

Data Acquisition

Intraoral ultrasound imaging

All imaging was performed using a 20-MHz iUS probe operating in pulse-echo mode. The transducer had a 2 mm × 12.8 mm (elevation × lateral) active area housed within a 13-mm × 18-mm probe head. The system provided an axial resolution of approximately 150 µm and a lateral resolution of 300 µm, enabling high-definition visualization of soft and mineralized periodontal tissues. The axial resolution was derived from the spatial pulse length according to standard ultrasound definitions, rather than directly from wavelength (Le et al 2024). The probe head allowed ± 90° rotation to facilitate intraoral positioning. A custom in-house software interface (Fig 1A) enabled real-time adjustment of imaging parameters, including gain and imaging depth. Acquired B-mode images were exported in DICOM format at 1,920 × 1,080 pixels (display/export resolution), with consistent pixel spacing and depth calibration across all scans. The active acoustic field occupied only a portion of the exported frame; all quantitative measurements were performed exclusively within this acquisition region. A detailed description of the imaging system architecture, including the probe assembly, rotational mechanism, acoustic coupling configuration, and hardware–software integration, is provided in our previously published work (Le et al 2024). Imaging was standardized to the mid-buccal surfaces of selected teeth in both arches. Molars, palatal/lingual, or mesial/distal aspects were excluded due to limited posterior accessibility, probe dimensions (13 mm × 18 mm), and difficulty achieving reproducible long-axis alignment with consistent visualization of the CEJ and ABC. Molars were specifically excluded because their broader crowns, multirooted anatomy, and furcations limit reliable landmark identification within a single imaging plane, precluding accurate comparison with µCT measurements.

Acoustic coupling

For cadaver imaging, acoustic coupling was achieved using ultrasound gel pads (Aquaflex^®, Parker Laboratories Inc.) in combination with standard liquid ultrasound gel (Aquasonic 100, Parker Laboratories Inc.).

For in vivo clinical imaging, custom biocompatible gel pads were fabricated from medical-grade silicone gel (Elkem RT Gel 4317, Elkem Silicones). The cured silicone pads exhibited a soft elastic modulus of approximately 1 MPa, ensuring patient comfort while maintaining consistent acoustic coupling.

Ex vivo scanning protocol

Cadaver imaging was performed at room temperature (~25 °C) by a biomedical imaging scientist with >10 y of iUS experience. The transducer was aligned along the long axis of each tooth at the mid-buccal surface to capture the gingiva, CEJ, ABC, and reference notches within a single imaging plane (Fig 1B, C). Images were included in the accuracy analysis if all landmarks were clearly visible, with distinguishable interfaces and no motion artifacts or acoustic shadowing. A total of 50 B-mode images were selected, comprising central (n = 11) and lateral (n = 15) incisors, canines (n = 13), and premolars (n = 11).

µCT imaging

Following ultrasound acquisition, cadaver mandibles and maxillae were scanned using a high-resolution µCT system (MILabs BV U-CT UHR) with a theoretical hardware resolution of 4 µm. Scans were acquired at 190 µA and 55 kV and reconstructed to 30-µm isotropic voxels using proprietary software, then exported in DICOM format. Samples were freely positioned within the gantry without additional fixation. The selected voxel size balanced the signal-to-noise ratio, minimal reconstruction artifacts, and preserved sufficient spatial detail for intraoral measurements (Fig 1D) (Corbea et al 2025).

In vivo scanning protocol

Clinical imaging was performed by a trained oral clinician following Figueredo et al (2023). The transducer was aligned along the longitudinal axis at the mid-buccal surface. A 3-mm biocompatible silicone gel pad was used as the acoustic coupling delay line between the transducer and the oral mucosa while maintaining the region of interest within the optimal lateral focal zone (4–6 mm; Fig 1E). A single-use probe cover was applied, and all procedures were performed in accordance with standard clinical hygiene protocols. Reusable components were cleaned between participants according to institutional infection-control protocols. Probe orientation was adjusted as needed to maximize the visualization of periodontal structures (Fig 1F). A total of 134 images were acquired for reliability analysis.

Periodontal Parameter Measurements

A structured training and calibration protocol was implemented before measurements. All raters (R1, R2, and R3) had diagnostic imaging experience but no prior iUS-based periodontal measurement expertise. They were trained by a biomedical imaging scientist in periodontal anatomy, landmark identification, and standardized measurement procedures for ABL, ABT, AGT, and FGT. Raters independently measured a calibration set of 20 images over 1 wk. An experienced orthodontist (N.K.) provided reference measurements, and feedback ensured accuracy and consistency. For the main study, measurements were performed independently on randomized images, with raters blinded to prior values. Washout periods of 1 wk (ex vivo) and 2 wks (in vivo) were applied. Raters participated only after completing the training protocol.

For the ex vivo accuracy study, sagittal µCT slices corresponding to each iUS image were extracted using 3D Slicer (Fedorov et al 2012) (Fig 1G). Volumes were manually reoriented to align the coronal plane with reference notches, and sagittal planes were positioned through both notches on the iUS imaging plane (Fig 1D). Paired µCT-iUS images were then used for quantitative analysis.

Two parameters, ABL and ABT (Fig 2A–C), were measured on the paired µCT-iUS image by R1 and R2, each performing 2 measurements per modality with a 1-wk interval using identical digital tools in 3D Slicer.

For the in vivo reliability study, ABL, ABT, AGT, and FGT (Fig 2D–F) were measured on iUS images by R1, R2, and R3, each repeated twice with a 2-wk washout interval to minimize recall bias.

Parameter definitions were standardized as follows:

ABL: Linear distance between the CEJ and ABC.

ABT: Thickness of the alveolar bone 0.3 mm apical to the ABC, measured perpendicular to the cementum reference line (CRL) (Fig 2A–C). The CRL, drawn along the cementum surface above and below the ABC, provided a consistent baseline for measurements.

AGT: Gingival thickness at the level of the ABC, measured parallel to the ABT.

FGT: Free gingival thickness 2 mm coronal to the gingival margin, parallel to the AGT.

The ABT measurements were corrected for the difference between the assumed ultrasound mapping speed $(v_{m a p} = 1, 540 m / s)$ and the bone propagation speed ( $v_{A B} = 1, 665 m / s$ ; Klein et al 2008). When the thickness vector was oblique to the ultrasound beam, this velocity mismatch systematically underestimated thickness. A correction factor ( $v_{A B} / v_{m a p}$ ) was applied to account for both geometric and propagation speed–related distortion (refer to Le et al 2023).

Statistical Analysis

All analyses were conducted using SPSS Statistics v29 (IBM Corp.). Variables (ABL, ABT, AGT, and FGT) are reported as mean ± SD. Normality was assessed with the Shapiro–Wilk test. Statistical significance was set at P < 0.05. The statistical unit was the individual tooth (1 image per tooth); teeth were clustered within cadavers/participants, but analyses were performed at the tooth level without clustering adjustment. A priori performance targets were prespecified. For ex vivo validation, iUS measurements of ABL and ABT were hypothesized to show good-to-excellent agreement with µCT (ICC ≥ 0.85; MAD ≤ 0.5 mm). For in vivo reliability, ABL, ABT, AGT, and FGT were expected to demonstrate good-to-excellent intra- and interrater agreement (ICC ≥ 0.80; MAD ≤ 0.5 mm).

Ex vivo accuracy analysis

Measurement differences were quantified using MAD and SD for repeated iUS sessions within raters, between raters, and between iUS and µCT (see Appendix). Intermethod agreement between iUS and µCT was assessed using 2-way mixed effects, absolute agreement (ICC [3,1]), with 95% confidence interval (CI). ICCs were interpreted as poor (< 0.50), moderate (0.50 to 0.74), good (0.75 to 0.89), or excellent (≥0.90) (Koo and Li 2016). Bland–Altman (BA) analysis was performed to evaluate systematic bias, 95% limits of agreement (LOA), and potential outliers. Paired t tests tested for significant differences between modalities. Sample size calculations for ICC and paired t tests are provided in the Appendix.

In vivo reliability analysis

Interrater reliability was evaluated using single-measure ICCs from a 2-way random-effects, absolute agreement model (ICC [2,1]), based on the mean of 2 repeated measurements per rater. MADs and SDs were calculated for all parameters (ABL, ABT, AGT, FGT). Intrarater reliability was assessed using a 2-way mixed-effects, absolute agreement (ICC [3,1]) comparing repeated measurements within each rater. Minimum sample size requirements are detailed in the Appendix.

Results

Cadaver Study

Table 1 (section A) summarizes the mean values and MADs for ABL and ABT measured on iUS and µCT images by 2 raters. ABL measurements were highly consistent across raters and modalities: 4.40 ± 1.15 mm (R1, iUS) versus 4.39 ± 1.11 mm (R1, µCT), and 4.56 ± 1.21 mm (R2, iUS) versus 4.49 ± 1.18 mm (R2, µCT). ABT measurements showed similar agreement, ranging from 0.32 ± 0.12 mm (R2, iUS) to 0.35 ± 0.12 mm (R1, iUS), and from 0.30 ± 0.13 mm (R2, µCT) to 0.34 ± 0.14 mm (R1, µCT). SDs were comparable across raters and modalities, indicating consistent measurement performance. MAD values further confirmed reproducibility, with ABL-MADs of 0.18 ± 0.25 mm (R1) and 0.31 ± 0.27 mm (R2), and consistently low ABT-MADs of 0.05 mm for both raters (R1 and R2).

Table 1.

Descriptive Statistics and Intermethod Agreement for Ex Vivo (Cadaver) Study.

Section A: Mean Values and MADs
Parameter	Rater	n	US, Mean ± SD, mm	µCT, Mean ± SD, mm	MAD ± SD, mm
ABL	R1	50	4.40 ± 1.15	4.39 ± 1.11	0.18 ± 0.25
ABL	R2	50	4.56 ± 1.20	4.49 ± 1.18	0.31 ± 0.27
ABT	R1	50	0.35 ± 0.12	0.34 ± 0.14	0.05 ± 0.04
ABT	R2	50	0.32 ± 0.12	0.30 ± 0.13	0.05 ± 0.04
Section B: Intermethod Agreement and Paired t Tests
Rater	ABL			ABT
Rater	ICC [Lower, Upper]		Paired t Test	ICC [Lower, Upper]	Paired t Test
R1	0.96 [0.94, 0.99]		t₄₉ = 0.16, P = 0.87	0.87 [0.77, 0.92]	t₄₉ = 1.46, P = 0.15
R2	0.94 [0.90, 0.97]		t₄₉ = 1.26, P = 0.21	0.87 [0.73, 0.92]	t₄₉ = 1.58, P = 0.12

ABL, alveolar bone level; ABT, alveolar bone thickness; ICC, intraclass correlation coefficient; MAD, mean absolute difference; SD, standard deviation; µCT, micro–computed tomography; US, ultrasound.

Intermethod ICCs demonstrated excellent agreement for ABL (R1: 0.96 [0.94–0.99]; R2: 0.94 [0.90–0.97]) and good agreement for ABT (R1: 0.87 [0.77–0.92]; R2: 0.87 [0.73–0.92]; Table 1, section B). Paired t tests showed no significant differences between modalities (all P > 0.05). BA analysis (Fig 3) demonstrated excellent agreement with negligible systematic bias. For ABL, average mean differences were −0.01 mm (R1) and 0.03 mm (R2), with 95% LOA ranging from −0.65 to 0.63 mm and −0.74 to 0.80 mm, respectively. For ABT, the average mean difference was 0.01 mm for both raters, with 95% limits of −0.19 to 0.23 mm (R1) and −0.15 to 0.21 mm (R2). These results confirm strong concordance and clinical equivalence between iUS and µCT for ABL and ABT assessment.

Clinical Study

Table 2 (section A) summarizes the descriptive statistics for ABL, ABT, AGT, and FGT measured by 3 raters. The mean ABL ranged from 1.77 ± 0.47 mm to 1.89 ± 0.48 mm, ABT from 0.32 ± 0.09 mm to 0.34 ± 0.08 mm, AGT from 1.36 ± 0.41 mm to 1.41 ± 0.41 mm, and FGT from 0.82 ± 0.24 mm to 0.92 ± 0.25 mm.

Table 2.

Descriptive Statistics and Reliability of In Vivo (Human) Study.

	Section A: Mean Values of In Vivo Measurements by Rater
Rater	n	ABL, mm	ABT, mm	AGT, mm	FGT, mm
R1	134	1.77 ± 0.47	0.32 ± 0.09	1.38 ± 0.40	0.82 ± 0.24
R2	134	1.89 ± 0.48	0.34 ± 0.08	1.41 ± 0.41	0.92 ± 0.25
R3	134	1.77 ± 0.52	0.33 ± 0.08	1.36 ± 0.41	0.85 ± 0.24
	Section B: Intrarater Reliability and Measurement Agreement
Parameter	Analysis		MAD ± SD, mm		ICC [Lower, Upper]
ABL	R1_1 vs R1_2		0.09 ± 0.15		0.93 [0.91, 0.95]
	R2_1 vs R2_2		0.07 ± 0.06		0.99 [0.98, 0.99]
	R3_1 vs R3_2		0.10 ± 0.11		0.96 [0.94, 0.97]
ABT	R1_1 vs R1_2		0.03 ± 0.03		0.92 [0.88, 0.94]
	R2_1 vs R2_2		0.03 ± 0.02		0.90 [0.86, 0.93]
	R3_1 vs R3_2		0.03 ± 0.03		0.84 [0.78, 0.88]
AGT	R1_1 vs R1_2		0.04 ± 0.08		0.97 [0.96, 0.98]
	R2_1 vs R2_2		0.06 ± 0.09		0.96 [0.95, 0.97]
	R3_1 vs R3_2		0.06 ± 0.10		0.96 [0.94, 0.97]
FGT	R1_1 vs R1_2		0.05 ± 0.06		0.95 [0.92, 0.96]
	R2_1 vs R2_2		0.06 ± 0.05		0.95 [0.93, 0.97]
	R3_1 vs R3_2		0.06 ± 0.06		0.94 [0.91, 0.96]
	Section C: Interrater Reliability and Measurement Agreement
Parameter	Analysis		MAD ± SD, mm		ICC [Lower, Upper]
ABL	R1 vs R2 vs R3		0.18 ± 0.13		0.88 [0.82, 0.92]
ABT	R1 vs R2 vs R3		0.04 ± 0.02		0.82 [0.76, 0.86]
AGT	R1 vs R2 vs R3		0.07 ± 0.08		0.96 [0.94, 0.97]
FGT	R1 vs R2 vs R3		0.10 ± 0.07		0.86 [0.73, 0.92]

ABL, alveolar bone level; ABT, alveolar bone thickness; AGT, attached gingival thickness; FGT, free gingival thickness; ICC, intraclass correlation coefficient; MAD, mean absolute difference; SD, standard deviation.

Intrarater reliability was excellent for all parameters (Table 2, section B). MAD values did not exceed 0.10 mm. Intrarater ICCs were 0.93 to 0.99 for ABL, indicating excellent repeatability. ABT ICCs ranged from 0.84 to 0.92, reflecting good-to-excellent reliability, while AGT and FGT measurements consistently demonstrated excellent intrarater reliability with ICCs ranging from 0.94 to 0.97. These results reflect measurement repeatability within a single rater under controlled conditions.

Interrater reliability between different raters (Table 2, section C) showed MADs ranging from 0.04 ± 0.02 mm for ABT to 0.18 ± 0.13 mm for ABL, with intermediate MADs of 0.07 ± 0.08 mm for AGT and 0.10 ± 0.07 mm for FGT. Interrater ICCs demonstrated good-to-excellent agreement, with values of 0.88 for ABL, 0.82 for ABT, 0.96 for AGT, and 0.86 for FGT. These findings confirm strong interrater consistency and robust clinical reliability of iUS-based periodontal measurements in a multioperator environment.

Discussion

This study provides a comprehensive evaluation of iUS for quantitative periodontal assessment, combining high-resolution ex vivo validation with multirater in vivo reliability analysis. While previous studies have reported iUS accuracy and reliability (Figueredo et al 2023; Corbea et al 2025), our work extends these findings by using a distinct dataset, refined anatomical landmarks, and an anatomy-guided measurement protocol. We demonstrate (1) excellent ex vivo accuracy of iUS for ABL, (2) good-to-excellent accuracy for ABT relative to µCT, and (3) robust intra- and interrater reliability for ABL, ABT, AGT, and FGT. While µCT is unsuitable for routine clinical use due to its size, cost, and radiation exposure, it remains the preclinical gold standard for periodontal evaluation. Its high spatial resolution and superior tissue contrast provide a rigorous reference for accuracy validation, enabling quantitative benchmarking of other assessment modalities, including clinical probing and CBCT.

This investigation introduces 2 methodological innovations for iUS measurement. First, ABT, AGT, and FGT were quantified perpendicular to a cementum reference line, making measurements independent of transducer orientation, unlike prior studies, in which thickness was measured along the beam, increasing interrater variability (Figueredo et al 2023). Second, ABT values were corrected for the mismatch between ultrasound propagation speed in soft tissue and alveolar bone. These refinements enhance accuracy, reproducibility, and provide a standardized framework for future iUS applications.

Ex vivo analysis confirmed that iUS provides highly accurate ABL measurements, with intermethod ICCs > 0.94, BA mean differences near zero (~0.2% to 0.7% of mean ABL), and > 95% of paired measurements within ±0.8 mm, meeting clinical interchangeability criteria (Giavarina 2015). Variability was well below the 1- to 2-mm threshold used for periodontitis staging (Oringer et al 1998), ensuring reliable disease classification. ABT measurements showed good agreement (ICC 0.87), with mean differences of ~0.01 mm, MADs < 0.1 mm, and LOA ±0.23 mm, smaller than the 0.5 mm (Laugisch et al 2021) reproducibility of probing and below typical alveolar bone remodeling (≥0.5 to 1.0 mm; Koretsi et al 2018). Thus, iUS provides sufficient precision to detect subtle buccal cortical changes for periodontal and orthodontic monitoring without ionizing radiation, enabling real-time, longitudinal assessment. This positions iUS not only as a safe alternative for selected measurements but also as a complementary tool for dynamic periodontal monitoring. However, ABT values (~0.3 mm) approach the lateral resolution of the 20-MHz probe (~300 µm), and measurements in very thin cortical regions should be interpreted cautiously, particularly for changes < 0.3 mm.

The in vivo component further supports the clinical readiness of iUS. Intra- and interrater reliability were good-to-excellent across all parameters (ICCs: 0.82–0.99), with MADs consistently less than 0.18 mm. The standardized, anatomy-guided protocol minimized operator dependency, allowing even less experienced raters to achieve reliability comparable to or exceeding that reported in prior iUS studies.

Several limitations should be acknowledged. Ex vivo sample size was constrained by cadaver availability, lack physiological conditions such as perfusion, tissue hydration dynamics, and soft-tissue elasticity, which may affect acoustic propagation compared with in vivo settings. Periodontal phenotype was not formally classified in either cohort; given that gingival and ABT vary by biotype, this may influence measurement variability and limit generalizability. Findings are primarily applicable to healthy or minimally altered tissues. Further validation in patients with moderate-to-severe periodontitis or significant anatomical alterations is warranted. Reported reliability reflects structured training and calibration conditions; performance among untrained clinicians remains to be established. The use of a silicone gel pad (1 MPa) as an acoustic coupling medium may introduce soft-tissue acoustic contrast due to its stiffness different from gingival tissues, which will create reflections. In addition, care was taken to minimize applied pressure during imaging as this mechanical interaction may influence tissue morphology. The assumed acoustic velocity in alveolar bone ( $v_{A B} = 1, 665 m / s$ ) was based on previously reported in vivo measurements of jaw bone ultrasound transmission velocity (Klein et al 2008). However, sound speed may vary with bone density, anatomical location, and pathological conditions such as bone loss or decalcification, which may introduce uncertainty in ultrasound-based estimations and represents a limitation of the current approach. Finally, 2-dimensional B-mode imaging differs fundamentally from volumetric CBCT, potentially limiting comprehensive spatial assessment. Within these constraints, iUS demonstrates excellent accuracy for ABL, good-to-excellent accuracy for ABT, and outstanding intra- and interrater reliability for both hard- and soft-tissue measurements.

Author Contributions

J. Wang, T.H. Hoang, contributed to analysis, drafted and critically revised the manuscript; K.C.T. Nguyen, contributed to conception, data acquisition, analysis, and interpretation, critically revised the manuscript; L. Graf-Alexiou, contributed to analysis, drafted the manuscript; L. Kumaralingam, N.R. Kaipatur, contributed to analysis and interpretation, critically revised the manuscript; T.G. La, contributed to analysis and interpretation, drafted and critically revised the manuscript; M. Li, contributed to acquisition and interpretation, critically revised the manuscript; E.H.M. Lou, P.W. Major, contributed to interpretation, critically revised the manuscript; L.H. Le, contributed to conception and design, data analysis and interpretation, critically revised the manuscript. All authors gave final approval and agreed to be accountable for all aspects of the work.

Supplemental Material

sj-docx-1-jdr-10.1177_00220345261446952 – Supplemental material for Periodontal Measurement Accuracy and Reliability Using Intraoral Ultrasound

Supplemental material, sj-docx-1-jdr-10.1177_00220345261446952 for Periodontal Measurement Accuracy and Reliability Using Intraoral Ultrasound by J. Wang, K.C.T. Nguyen, L. Graf-Alexiou, T.H. Hoang, L. Kumaralingam, M. Li, T.G. La, N.R. Kaipatur, E.H.M. Lou, P.W. Major and L.H. Le in Journal of Dental Research

Footnotes

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was supported by the National Research Council of Canada Industrial Research Assistance Program (IRAP), MITACS, Alberta Innovates Accelerating Innovations into CarE (AICE) program (grant No. RES0056222) and NSFC Key International Joint Research grant (W2511001). The authors gratefully acknowledge Alberta Innovates, Canada, for the generous support of graduate studentships (T.H. Hoang, L. Kumaralingam), China Scholarship Council for the CSC scholarship (J. Wang), NSERC Undergraduate Student Research Award (L. Graf-Alexiou), and NSFC (National Natural Science Foundation of China). K.C.T. Nguyen also acknowledges the support of the Izaak Walton Killam Memorial Scholarship and an Alberta Innovates postdoctoral fellowship. DenSonics Imaging Inc. kindly provided the ultrasound imaging system. The authors acknowledge Dr. Maria Alexiou and Dr. Daniel Graf for providing the assistance of µCT imaging in the Biomedical Oral & Maxillofacial Research Unit (BOMRU), Mike Petryk School of Dentistry. The authors also thank Drs. Daniel Livy and Jason Papirny from Department of Surgery and Dr. Tom Stevenson from Mike Petryk School of Dentistry for providing and preparing the cadaver samples.

ORCID iDs

J. Wang

K.C.T. Nguyen

T.H. Hoang

L. Kumaralingam

M. Li

L.H. Le

Data Availability Statement

Deidentified numerical data and results underlying the figures in this article are publicly available at . Cadaver specimens and patient data cannot be made publicly available due to ethical and legal restrictions imposed by the University of Alberta review board and data use agreements.

A supplemental appendix to this article is available online.

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