Application of intraoral scanner to identify monozygotic twins

A Systematic Review of the Use of Intraoral Scanning for Human Identification Based on Palatal Morphology

A common application for intraoral scanners is the digitization of the morphology of teeth and palatal rugae. Palatal scans are most commonly required to fabricate complete dentures and immediate transitional dentures and serve as a reference point for assessing orthodontic results. However, they are also frequently included by accident, even though the main purpose of intraoral scanning is to reconstruct dentition using computer-aided manufacturing (CAM). The literature shows that the identification of disaster victims has frequently involved palatal rugae impressions. As the skull provides sound insulation, the rugae are resistant to heat, chemicals, and stress. Antemortem data might be difficult to find during a forensic inquiry, particularly in disaster victim identification cases. In contrast with DNA and fingerprints, there is a greater likelihood of having a dental record that contains palatal scans. With specialized software, the scans can be exported as open stereolithography (STL) files. Considering that a full case consumes up to about 100 MB of hard drive space, long-term storage should not be an issue compared to a plaster model. Additionally, dentists widely use online databases to exchange data for smile design, implant registration, and orthodontic purposes. This will produce a digital database that grows quickly and is readily usable for forensic investigations. The uniqueness of forensic features is frequently challenged; however, palatal morphology's unique trait could make it possible as it is characteristic of individuals as well as the most distinguishing factor. This review will highlight how rugae, palatal morphology, mirroring, superimposition, and geometrics can serve in forensic identification.

Reproducibility of the digital palate in forensic investigations, a two-year retrospective cohort study of twins

OBJECTIVES

The palatal scans of the same individuals were compared after two years to assess forensic reproducibility. The effect of orthodontic treatment, the comparison area and the digitization approach were investigated.

METHODS

The palate was scanned in 20 pairs of monozygotic twins by an intraoral scanner (IOS) three times to assess repeatability. They were rescanned two years later by two different IOSs. An elastic impression and a plaster model were also made and scanned by a laboratory scanner (indirect digitization). Mean absolute distance between scans was compared after best-fit alignment. Scans from the two sessions were compared to evaluate the combined effect of aging, orthodontic treatment and different digitization methods (forensic reproducibility). Additionally, the scans of different digitization methods from the second session were compared (technical reproducibility). The between-siblings difference was compared in the two sessions to evaluate the effect of aging on palatal morphology.

RESULTS

The anterior palatal area showed significantly better repeatability and forensic reproducibility than the whole palate (p<0.001), but orthodontic treatment had no effect. Indirect digitization produced lower forensic and technical reproducibility than IOSs. For IOSs, repeatability (22 µm) was significantly (p<0.001) better than either forensic (75-77 µm) or technical reproducibility (37 µm). No significant changes were observed from the first to the second session in the between-sibling comparison. The closest between-sibling value (239 µm) considerably exceeded the highest forensic reproducibility value (141 µm).

CONCLUSIONS

Reproducibility is acceptable between the different IOSs, even two years apart, but is poor between IOS and indirect digitization. The anterior palate is relatively stable in young adults.

CLINICAL SIGNIFICANCE

Intraoral scanning of the anterior palatal area has superior reproducibility, regardless of the IOS brand. Therefore, the IOS method could be suitable for identifying humans through anterior palatal morphology. However, the digitization of elastic impressions or plaster models had low reproducibility, preventing their application for forensic purposes.

Palatal asymmetry assessed by intraoral scans: effects of sex, orthodontic treatment, and twinning. A retrospective cohort study

BACKGROUND

Symmetry is critical in perceived attractiveness, especially in female faces. The palate determines the teeth' alignment and supports facial soft tissues. Therefore, the study aimed to assess the effects of sex, orthodontic treatment, age, and heritability on the directional, anti-, and fluctuational asymmetry in the digital palatal model.

METHODS

The palate of 113 twins, 86 female and 27 male subjects, with and without previous orthodontic treatment, were scanned by the Emerald (Planmeca) intraoral scanner. Three lines were constructed horizontally in the digital model, one between the right and left first upper molars and two between the first molars and incisive papilla. Two observers calculated the left and right angles between the mid-sagittal plane and molar-papilla lines. The intraclass correlation coefficient was used to assess the inter-observer absolute agreement. The directional symmetry was determined by comparing the mean left and right angles. The antisymmetry was estimated from the distribution curve of the signed side difference. The fluctuating asymmetry was approximated from the magnitude of the absolute side difference. Finally, the genetic background was assessed by correlating the absolute side difference between monozygotic twin siblings.

RESULTS

The right angle (31.1 degrees) was not significantly different from the left one (31.6 degrees). The signed side difference followed a normal distribution with a mean of -0.48 degrees. The absolute side difference (2.29 degrees, p < 0.001) was significantly different from zero and negatively correlated (r=-0.46, p < 0.05) between siblings. None of the asymmetries was affected by sex, orthodontic treatment or age.

CONCLUSIONS

The palate illustrates neither directional asymmetry nor antisymmetry, indicating that most people's palates are symmetric. However, the significant fluctuating asymmetry suggests that some subject has considerable asymmetry but is not influenced by sex, orthodontic treatment, age, and genetics. The proposed digital method is a reliable and non-invasive tool that could facilitate achieving a more symmetrical structure during orthodontic and aesthetic rehabilitation.

TRIAL REGISTRATION

The Clinicatrial.gov registration number is NCT05349942 (27/04/2022).

DNA and protein analyses of hair in forensic genetics

Hair is one of the most common pieces of biological evidence found at a crime scene and plays an essential role in forensic investigation. Hairs, especially non-follicular hairs, are usually found at various crime scenes, either by natural shedding or by forcible shedding. However, the genetic material in hairs is usually highly degraded, which makes forensic analysis difficult. As a result, the value of hair has not been fully exploited in forensic investigations and trials. In recent years, with advances in molecular biology, forensic analysis of hair has achieved remarkable strides and provided crucial clues in numerous cases. This article reviews recent developments in DNA and protein analysis of hair and attempts to provide a comprehensive solution to improve forensic hair analysis.

Forensic Identification: Dental Scan Data Sets of the Palatal Fold Pairs as an Individual Feature in a Longitudinal Cohort Study

The INTERPOL standard for the identification of unknown individuals includes the established primary characteristics of fingerprint, DNA, and teeth. Exposure to noxious agents such as fire and water often severely limits the availability of usable material such as fingerprints. In addition to teeth, the protected oral cavity also houses palatal fold pairs, which are the subject of this study to demonstrate individuality and consequently support identification. Material and Methods: In this cohort study, 105 participants' palates were scanned twice with a dental intraoral scanner (Omnicam SIRONA®) over a 3 month period and were then analyzed using a matching program. The intraindividual and interindividual differences were determined, and the mean values and standard deviations were calculated and presented. Results: The intraindividual differences are highly significantly lower than the interindividual differences (p < 0.0001). Conclusions: Within the limitations of this study, the results suggest that palatal rugae pairs can be considered a highly individual feature and could be considered an identification feature in a young and healthy population.

Gingival shape analysis using surface curvature estimation of the intraoral scans

Background

Despite many advances in dentistry, no objective and quantitative method is available to evaluate gingival shape. The surface curvature of the optical scans represents an unexploited possibility. The present study aimed to test surface curvature estimation of intraoral scans for objective evaluation of gingival shape.

Methods

The method consists of four main steps, i.e., optical scanning, surface curvature estimation, region of interest (ROI) definition, and gingival shape analysis. Six different curvature measures and three different diameters were tested for surface curvature estimation on central (n = 78) and interdental ROI (n = 88) of patients with advanced periodontitis to quantify gingiva with a novel gingival shape parameter (GS). The reproducibility was evaluated by repeating the method on two consecutive intraoral scans obtained with a scan-rescan process of the same patient at the same time point (n = 8).

Results

Minimum and mean curvature measures computed at 2 mm diameter seem optimal GS to quantify shape at central and interdental ROI, respectively. The mean (and standard deviation) of the GS was 0.33 ± 0.07 and 0.19 ± 0.09 for central ROI using minimum, and interdental ROI using mean curvature measure, respectively, computed at a diameter of 2 mm. The method’s reproducibility evaluated on scan-rescan models for the above-mentioned ROI and curvature measures was 0.02 and 0.01, respectively.

Conclusions

Surface curvature estimation of the intraoral optical scans presents a precise and highly reproducible method for the objective gingival shape quantification enabling the detection of subtle changes. A careful selection of parameters for surface curvature estimation and curvature measures is required.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-022-02322-y.

Evaluation of the stability of the palatal rugae using the three-dimensional superimposition technique following orthodontic treatment

OBJECTIVES

To determine the uniqueness and stability of the palatal rugae after orthodontic treatment.

METHODS

Cast models of untreated subjects (n=50) were obtained twice at intervals of 8-30 months. Cast models of patients who received non-extraction (n=50) and extraction (n=50) orthodontic treatment were obtained before and after treatment at intervals of 11-41 months and 14-49 months, respectively. All 300 cast models were scanned digitally. The palatal rugae were manually extracted and transformed into 3D point clouds using reverse engineering software. An iterative closest point (ICP) registration algorithm based on correntropy was applied, and the minimum point-to-point root mean square (RMS) distances were calculated to analyze the deviation of palatal rugae for scans of the same subject (intrasubject deviation [ISD]) and between different subjects (between-subject deviation [BSD]). Differences in ISD between each group and the deviation between ISD and BSD of all 150 subjects were evaluated.

RESULTS

Significant differences were found in the 150 ISD and 1225 BSD in each group, as well as the 150 ISD and 11175 BSD across all groups. The mean values of ISD in untreated, non-extraction and extraction group were 0.178, 0.229 and 0.333 mm, respectively. When the first ruga was excluded in the extraction group, the mean ISD decreased to 0.241 mm, which was not significantly different from that in the non-extraction group (p=0.314).

CONCLUSIONS

Orthodontic treatment can influence the palatal rugae, especially in cases of extraction. Furthermore, variation mainly existed in the first ruga in cases of extraction. However, palatal rugae are still unique and may be used as a supplementary tool for individual identification.

CLINICAL SIGNIFICANCE

This study indicates that palatal rugae might be applied in the evaluation of orthodontic tooth movement and forensic individual identification. The registration algorithm based on correntropy provides a credible, precise, and convenient method for palatal rugae superimposition.