Automated facial landmark measurement using machine learning: A feasibility study.

STATEMENT OF PROBLEM: Information regarding facial landmark measurement using machine learning (ML) techniques in prosthodontics is lacking. PURPOSE: The objective of this study was to evaluate and compare the reliability, validity, and accuracy of facial anthropological measurements using both manual and ML landmark detection techniques. MATERIAL AND METHODS: Two-dimensional (2D) frontal full-face photographs of 50 men and 50 women were made. The interpupillary width (IPW), interlateral canthus width (LCW), intermedial canthus width (MCW), interalar width (IAW), and intercommissural width (ICW) were measured on 2D digital images using manual and ML methods. The automated measurements were recorded using a programming language (Python), and a convolutional neural network (CNN) model was trained to detect human facial landmarks. The obtained data from the manual and ML methods were analyzed using intraclass correlation coefficients (ICCs), the paired sample t test, Bland-Altman plots, and the Pearson correlation analysis (α=.05). RESULTS: Intrarater and interrater reliability values were greater than 0.90, indicating excellent reliability. The mean difference between the manual and ML measurements of IPW, MCW, IAW, and ICW was 0.02 mm, while it was 0.01 mm for LCW. No statistically significant differences were found between the measurements obtained by the manual and ML methods (P>.05). Highly significant positive correlations (P<.001) were obtained between the results of the manual and ML methods: (r=0.996[IPW], r=0.977[LCW], r=0.944[MCW], r=0.965[IAW], and r=0.997[ICW]). CONCLUSIONS: In the field of prosthodontics, the use of ML methods provides a reliable alternative to manual digital techniques for carrying out facial anthropometric measurements.

Assessing methodological quality in dental education research using MERSQI: Analysis of publications from two journals.

PURPOSE: The Medical Education Research Study Quality Instrument (MERSQI) has been used frequently to assess the methodological quality of medical education but not for dental education. The present study aimed to assess the methodological quality using MERSQI scores of articles published in the Journal of Dental Education (JDE) and the European Journal of Dental Education (EJDE). METHODS: A cross-sectional assessment of the quality of manuscripts published in 2012, 2017, and 2022 JDE and EJDE was conducted. MERSQI data, numbers of authors, first and corresponding author degrees, geographic origins, and funding information were also extracted for each included study. Descriptive and analytical statistics were conducted, and significance level was set at α < 0.05. RESULTS: Four hundred ninety-five articles met the inclusion criteria. The most common study design was a single-group cross-sectional or single-group posttest and conducted in one institution for all studied years. In all journals and years, studies were assessed mainly by participants. The study outcome was mostly satisfaction, attitudes, perceptions, opinions, and general facts. The total mean MERSQI score for each journal and year varied. Year and geographic origin significantly affected the total MERSQI score. Papers originating from Asia had the highest score, followed by South America, Europe, North America, Oceania, and Africa. CONCLUSION: MERSQI score is applicable to the assessment of the methodological quality of dental educational research. The MERSQI score for most of the domains was similar for both journals. The MERSQI score was affected by publication years and geographic origins.

Machine learning model to predict the width of maxillary central incisor from anthropological measurements.

PURPOSE: To improve smile esthetics, clinicians should comprehensively analyze the face and ensure that the sizes selected for the maxillary anterior teeth are compatible with the available anthropological measurements. The inter commissural (ICW), interalar (IAW), intermedial-canthus (MCW), interlateral-canthus (LCW), and interpupillary (IPW) widths are used to determine the width of maxillary central incisors (CW). The aim of this study was to develop an automated approach using machine learning (ML) algorithms to predict central incisor width in a young Turkish population using anthropological measurements. This automation can contribute to digital dentistry and clinical decision-making. METHODS: In the initial phase of this cross-sectional study, several ML regression models-including multiple linear regression (MLR), multi-layer-perceptron (MLP), decision-tree (DT), and random forest (RF) models-were validated to confirm the central width prediction accuracy. Datasets containing only male and female measurements, as well as combined were considered for ML model implementation, and the performance of each model was evaluated for an unbiased population dataset. RESULTS: Compared with the other algorithms, the RF algorithm showed improved performance for all cases, with an accuracy of 96%, which represents the percentage of correct predictions. The plot reveals the applicability of the RF model in predicting the CW from anthropological measurements irrespective of the candidate's sex. CONCLUSIONS: These results demonstrated the possibility of predicting central incisor widths based on anthropometric measurements using ML models. The accurate central incisor width prediction from these trials also indicates the applicability of the proposed model to be deployed for enhanced clinical decision-making.

Influence of ceramic thickness, background and cement shade on the translucency of zirconia reinforced lithium silicate and lithium disilicate ceramics.

Background: Although, the influence of cement and background shade on the final color and translucency of zirconia reinforced lithium silicate (ZLS) and lithium disilicate (LDS) ceramics has been previously investigated, there is still little data on the translucency of LDS and ZLS ceramics in decreased thickness (0.4 and 0.6 mm). The aim of this study was to investigate ceramic thickness', background and cement shades' effects on the zirconia reinforced lithium silicate (ZLS) and lithium disilicate (LDS) ceramics' translucency. Material and Methods: Totally 160 square-shaped A1 shade LDS and ZLS samples produced in 0.4 and 0.6 mm thicknesses were cemented with light and neutral shade resin cement on A2 and A3 shade composite resin backgrounds. The color notations of specimen were measured and translucency parameter (TP) values were calculated. Factorial ANOVA and Tamhane's T2 multiple comparison statistical analyzes were used. Results: Highest TP values (11.82±0.97) were obtained in ZLS specimens that were 0.4 mm in thickness, cemented on A2 background with light shade resin cement. While, the lowest TP values (9.60±0.55) were calculated in LDS samples that had 0.6 mm thickness, cemented on A3 background with neutral shade resin cement. Conclusions: Material type, thickness, and background shade affected TP values of specimens. The cement and background shade used might change the final translucency of ZLS and LDS ceramics that had 0.4 and 0.6 mm thickness. Key words:Ceramics, lithium disilicate, spectrophotometry, zirconia, dental materials.

Level of evidence and characteristics of clinical studies published in leading prosthodontics journals.

STATEMENT OF PROBLEM: Data on the level of evidence and the characteristics of studies published in peer-reviewed prosthodontic journals are lacking. PURPOSE: The purpose of this study was to investigate the characteristics and level of evidence (LOE) scores of studies published in 3 leading peer-reviewed prosthodontic journals. MATERIAL AND METHODS: Clinical studies published in the Journal of Prosthetic Dentistry (JPD), the Journal of Prosthodontics (JP), and the International Journal of Prosthodontics (IJP) in 2013 and 2020 were included in the analysis. Abstracts, letters to the editor, book reviews, and animal and laboratory studies were excluded from the investigation. For each study, design, type and LOE scores (Levels 1 to 5), publication year, impact factor (IF) of the journals, geographic origins of the first and corresponding authors, and funding status were recorded. Level 1 and Level 2 were defined as high evidence (HE), and Level 3, Level 4, and Level 5 were defined as low evidence (LE). Descriptive statistics and logistic regression analysis were performed (α=.05). RESULTS: Among the 439 studies included in the analysis, the proportion of HE and LE studies was 14.1% and 85.9%, respectively. According to univariate and multivariate analysis results, year of publication (P=.010 and P=.029), geographic origin of the corresponding author (P<.001), and funding status (P<.001 and P=.002) were significantly associated with the LOE of a study. However, the journal IF was not associated with LOE (P=.328). CONCLUSIONS: Although the number of HE studies in 3 leading prosthodontic journals has increased over time, the total number was still limited compared with LE studies. A further improvement in the overall LOE of clinical studies in prosthodontics is needed.

Effect of variations in facial flow curves on the perceptions of smile esthetics by laypeople.

STATEMENT OF PROBLEM: Information about the effect of the facial flow concept on the smile esthetic perception of laypeople is lacking. PURPOSE: The purpose of this study was to determine the effect of the facial flow concept on laypeople's perception of smile esthetics. MATERIAL AND METHODS: Frontal full-face images of a female volunteer were digitally altered to create commissural line and transverse occlusal plane inclinations, a dental midline shift, and facial asymmetries. A questionnaire was developed, and a single researcher asked 400 evaluators to rate the attractiveness of the different smiles by using a visual analog scale. The subsequent data were analyzed by using 3-factor repeated measures ANOVA and post hoc Bonferroni tests. RESULTS: Images with commissural line and transverse occlusal plane inclinations pointing toward the green side of the facial flow curve were found to be more attractive than those with inclinations pointing to the red side (P<.001). Asymmetric facial images with the dental midline coinciding with the facial flow curve had higher esthetic scores than those without (P<.001). Images that showed parallelism between the transverse occlusal plane and commissural line inclinations were perceived as more esthetic (P<.001). CONCLUSIONS: In an asymmetric face model, the degree and direction of commissural line and transverse occlusal plane inclinations and dental midline shift influenced the perceived attractiveness of a smile.

Tensile bond strength of soft and hard relining materials to conventional and additively manufactured denture-base materials.

PURPOSE: Studies comparing tensile bond strength of various soft and hard denture liner materials to conventionally and additively manufactured denture base resins are lacking. The purpose of this study was to investigate the tensile bond strength between chair- and laboratory-side soft and hard relining materials and denture-base materials produced by additive manufacturing and conventional methods. MATERIALS AND METHODS: A total of 120 dimethacrylate-based additively manufactured and polymethylmethacrylate (PMMA)-based conventionally fabricated dumbbell-shaped denture-base resins were produced. Heat-cured laboratory-side soft reline material, self-cured chair-side soft reline material, and self-cured chair-side hard reline material were attached to the denture bases. The tensile force was applied to the specimens with a universal testing machine at a crosshead speed of 5 mm/min. The obtained data were analyzed with two-way ANOVA and post hoc Tukey tests. The significance level was set at α = 0.05. RESULTS: The highest tensile bond strength values were obtained in the specimens from the conventionally manufactured base and self-cured chair-side hard reline material group, and the lowest was seen in the additively fabricated base and self-cured chair-side soft reline material group (p < 0.001). Conventionally manufactured base material's tensile bond strength was higher than that of additively fabricated resin, and self-cured chair-side hard reline material's strength was higher than that of laboratory-side and chair-side soft reline materials (p < 0.001). However, no significant difference emerged between laboratory-side and chair-side soft reline materials (p = 0.405). CONCLUSIONS: All the specimens used in the present study had tensile bonding stress values for clinical use. Both denture base resins provided an increased bond to the chair-side hard relining material, although an improved bond did not emerge for the chair-side and laboratory-side soft denture reline materials.

Evaluating the Effect of Ambient and Scanning Lights on the Trueness of the Intraoral Scanner.

PURPOSE: To determine the influence of different scanning and ambient light conditions on the trueness values of an intraoral scanning (IOS) device. MATERIAL AND METHODS: The present study was conducted among 20 complete dentate volunteers. After making complete maxillary arch impressions with vinyl polysiloxane material, type IV dental stone was poured, and working casts were obtained. Then, the models were digitized using a dental laboratory scanner (LS) and standard tessellation language (STL) files were acquired. Full arch digital scans of the volunteers were also performed using an IOS device with 2 ambient light conditions (RL: room light, 1003 lux, and ZL: zero light, 0 lux) and 2 scanning light modes (blue [B] and white [W]). Twenty digital scans per group at each light condition were consecutively obtained. Discrepancy between the digital scans and digitized working casts was analyzed using a 3D inspection software. The obtained data were analyzed using one-way ANOVA and Tukey tests (α = 0.05). RESULTS: Significant differences were obtained among different light conditions for the IOS device (p ˂ 0.0001, F = 42.958 for positive deviations and F = 29.278, for negative deviations). The room light and blue mode (RLB) condition had the lowest deviation values compared with the other light conditions, followed by room light and white mode (RLW), zero light and blue mode (ZLB), and zero light and white mode (ZLW; p =  0.008, p Ë‚ 0.0001, and p Ë‚ 0.0001, respectively). CONCLUSION: Lighting conditions are effective in assessing the trueness of the digital impressions made with an IOS device. RLB conditions are recommended for taking a digital impression.

Effects of gingival margin asymmetries on the smile esthetic perception of dental professionals and lay people.

OBJECTIVE: To determine the effects of different gingival margin asymmetries of anterior tooth on the smile esthetic perceptions of dentists, prosthodontists, periodontists and lay people. MATERIALS AND METHODS: A frontal close-up smile photo of a woman was used in this study. Image was digitally altered in order to create gingival margin asymmetries in left maxillary central, lateral incisors, and canines. Four stages of alterations were made in 0.5 mm increments. The final images were randomly assessed by 240 evaluators: 60 dentists, 60 prosthodontists, 60 periodontists, and 60 lay people. Questionnaire was carried out by a single researcher and each rater was asked to evaluate the attractiveness of the smile images by using the visual analog scale. Collected data were analyzed by using one-way ANOVA test with post hoc Scheffé test. RESULTS: Smiles with 0.5 mm gingival margin asymmetries were found to be more esthetic, while 2 mm gingival asymmetries were less esthetic (P ˂ .001). Lay people's esthetic scores were higher than other groups in all degrees of asymmetries (P ˂ .001). Esthetic scores of canine teeth were higher than, lateral, and central teeth (P ˂ .001). CONCLUSIONS: As the amount of asymmetries increased, esthetic scores decreased in all groups. Gingival margin asymmetries were less perceptible laterally. CLINICAL SIGNIFICANCE: This study may help dental professionals to understand which gingival asymmetries are found by patients as esthetic or unesthetic and guides them in their dental treatment, especially in the aesthetic zone.

The effect of restoration thickness and resin cement shade on the color and translucency of a high-translucency monolithic zirconia.

STATEMENT OF PROBLEM: Information regarding the influence of cements and material thickness on the final color of monolithic zirconia restorations is lacking. PURPOSE: The purpose of this in vitro study was to examine the effect of varying resin cement colors and material thicknesses on the color and translucency of a high-translucency monolithic zirconia and to compare these effects with those reported in similar studies that examined other dental zirconia materials. MATERIAL AND METHODS: Katana High Translucent (Kuraray) was used as a monolithic zirconia material. A total of 80 disk specimens (10 mm in diameter) were made in 4 different thicknesses of 0.5 mm, 1 mm, 1.5 mm, and 2 mm (n=20 per thickness). The color of the specimens (Commission Internationale de l'Eclairage [CIE] L*, a*, b* values) before cementation was measured using a spectrophotometer. Specimens within each thickness were further divided into 2 groups: transparent (n=10) and opaque (n=10). A transparent or opaque self-etch adhesive resin cement (Panavia V5) was then applied to each specimen. After cementation, the color was measured again. The translucency parameter (TP) and ΔE were calculated and evaluated with the color measurements by using descriptive statistics, correlation analysis, single specimen t test, 2-way ANOVA, and the Tukey Honestly Significant Difference (HSD) test. RESULTS: Statistically significant (P<.001) changes were found with the increasing thicknesses of the high-translucency zirconia specimens. The TP, L*, and b* values decreased, whereas the a* values increased. In both the transparent and opaque groups, statistically significant (P<.001) increases in L*, a*, and b* values and a significant decrease in TP were found with cementation. The lowest ΔE value (1.19 for 2 mm) was observed for monolithic zirconia-clear cement. The highest ΔE value (8.05 for the 0.5 mm) was observed for the monolithic zirconia and opaque cement combination. CONCLUSIONS: Material thickness and cement color affected the color and translucency of high-translucent monolithic zirconia, with effects similar to those observed with other monolithic zirconia materials.

Relationship between different points on the face and the width of maxillary central teeth in a Turkish population.

STATEMENT OF PROBLEM: Dentists may have difficulty determining the appropriate widths of the maxillary central incisors (CW) when restoring teeth for patients with edentulism. Anthropological measurements can help. PURPOSE: The purpose of this observational study was to evaluate the relationship between different anthropological distances on the face and the CW in a young Turkish population. MATERIAL AND METHODS: A total of 210 Turkish dental students without dental and facial deformities participated in this study. Two different digital photographs of their face (relaxed and smiling) were taken. The intercommissural width (ICW), intermedial canthus width (MCW), interlateral canthus width (LCW), interpupillary width (IPW), interalar width (IAW), and CW were measured. The t test, Pearson correlation analysis, and multiple linear regression analysis were performed to determine the relationship between facial measurements and CW (α=.05). RESULTS: A significant correlation was found between facial measurements (r=0.516[ICW], r=-0.534[IAW], r=-0.639[MCW], r=-0.599[LCW], and r=-0.683[IPW]) and CW in both sexes. All facial measurements, except ICW and IPW in women and MCW in men, had a significant effect on CW according to the multiple linear regression analysis. CONCLUSIONS: IAW and LCW can be used to determine CW in both sexes. The ICW and IPW can be specific anthropological measurements for men, and the MCW can be a specific anthropological measurement for women to determine CW.

An investigation of the esthetic indicators of maxillary anterior teeth in young Turkish people.

STATEMENT OF PROBLEM: Comprehensive studies evaluating the dimensions of anterior maxillary teeth in the Turkish population with respect to different esthetic parameters are lacking. PURPOSE: The purpose of this clinical study was to evaluate different proportions of teeth and compare them with current esthetic parameters such as the golden proportion, recurring esthetic dental proportion, and width-to-height ratio of central incisors and to evaluate whether the apparent contact dimension of maxillary anterior teeth follows the "50:40:30" rule. MATERIAL AND METHODS: A total of 150 Turkish dental students (81 men and 69 women) aged between 18 and 24 years participated in the study. Standardized digital photographs of the mouth were made from an anterior view. The width and length of the maxillary central incisor, apparent width of the maxillary lateral and canine teeth, and distances between contact areas of the maxillary incisor teeth were measured with software. Differences between the measured proportions and the determined esthetic parameters were assessed with the 1-sample t test (α=.05). RESULTS: The width and length proportions of the maxillary incisor teeth in both sexes were significantly different than the golden and recurring esthetic dental proportions. The width-to-height ratio for the maxillary central incisor was different from 80%, which is considered optimal, and the difference among these parameters was statistically significant (P<.001). The apparent contact dimensions on the right and left sides were not statistically significantly different (P>.05). However, the proportions did not fit the 50:40:30 ratio that has been defined as the esthetic proportion, and the differences were statistically significant (P<.001). CONCLUSION: Proportions among maxillary anterior teeth were found to be significantly different from the golden proportion and recurring esthetic dental proportion in both sexes. The proportions of apparent contact dimension were significantly different than the 50:40:30 ratio in both sexes. The width-to-height ratio for maxillary central incisor was significantly different from 80% in both sexes.