Research Spotlight

Revilla-Leon, M., M. T. Ashby, M. J. Meyer, M. Umorin, J. J. Barrington and A. Zandinejad (2020). “Layperson and Dental Professional Perception When Evaluating Their Own Virtually 2D or 3D Simulated Esthetic Discrepancies.” J Prosthodont May 5. [Epub ahead of print].

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PURPOSE: To analyze the perceptions of laypersons, dental students, and dentists regarding disparities of the maxillary dental midline and the occlusal plane (OP) when analyzing their own 2D or 3D clinical simulation. MATERIAL AND METHODS: 20 participants per group volunteered (N = 60). Intraoral and facial scans, and a photograph were obtained from each participant. Two simulation groups were created: 2D and 3D groups, which were subdivided into two subgroups. In the first subgroup, the OP was modified by 1-degree increments without changing the maxillary midline. In the second subgroup, the OP was modified by the same increments, but the maxillary midline was altered to match the OP inclination. Participants were asked to rate the simulations on a 1-to-6 scale and a question survey. Ordinal logistic regression (OR) was used to analyze the ratings. RESULTS: Tilt of the OP had the strongest negative effect on the ratings which was further amplified by the dental midline inclination (OR = 0.122). Midline modification alone did not affect the ratings (OR = 0.744). 3D simulations had a stronger positive effect on the ratings compared to 2D simulations. For dental students, the positive rating effect of 3D simulations was similar to dentists. For laypersons, the positive rating effect of 3D simulations compared to the 2D simulations decreased relative to dentists. The survey revealed that 45% of the dentists, 80% of the students, and 50% of the laypersons preferred the 3D simulation. CONCLUSIONS: The type of dimensional representation affected the esthetic perception of all participants. 3D simulations obtained higher esthetic ratings for the same esthetic discrepancy than 2D simulations. However, all participants’ ratings decreased with increased tilt of the OP and were further decreased with the inclination of the dental midline.

Revilla-León, M., N. Al-Haj Husain, L. Ceballos and M. Özcan (2020). “Flexural strength and Weibull characteristics of stereolithography additive manufactured versus milled zirconia.” J Prosthet Dent May 17;S0022-3913(20)30087-1. [Epub ahead of print.].

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STATEMENT OF PROBLEM: Zirconia restorations can be processed by using stereolithography additive manufacturing (AM) technologies. However, whether additive manufactured zirconia could achieve flexural strength values comparable with those of milled zirconia is unclear. PURPOSE: The purpose of this in vitro study was to compare the flexural strength and Weibull characteristics of milled and additive manufactured zirconia. MATERIAL AND METHODS: A total of 40 zirconia bars (25×4×1.2 mm) were obtained by using 2 manufacturing procedures, subtractive (CNC group) (IPS e.max ZirCAD; Ivoclar Vivadent AG) and additive manufacturing (AM group) (3DMix ZrO(2); 3DCeram) technologies and assigned to 2 subgroups according to accelerating artificial aging procedures (mastication simulation): nonaged and aged (n=10). Flexural strength was measured in all specimens by using 3-point bend tests according to ISO/CD 6872.2 with a universal testing machine (Instron Model 8501; Instron Corp). Two-parameter Weibull distribution values, including the Weibull modulus, scale (m), and shape (0) were calculated. Flexural strength values were analyzed by using 2-way ANOVA and Student t statistical tests (α=.05). RESULTS: The manufacturing procedure (P<.001), the mastication simulating aging procedure (P<.001), and the interaction between them (P<.001) significantly affected flexural strength values. The CNC group exhibited statistically higher flexural strength values than those in the AM group when the specimens were tested before performing an aging procedure (P<.001) and after mastication simulation (P<.001). Moreover, mastication simulation produced a significant reduction in flexural strength for both the CNC group (P<.039) and the AM group (P<.001). CONCLUSIONS: The manufacturing process reported a significant effect on the flexural strength of the zirconia material tested. Mastication simulation as a means of accelerating artificial aging resulted in the significantly decreased flexural strength values of milled and additively manufactured zirconia material, with the Weibull moduli being significantly higher for the milled groups versus the milled specimens.

Patel, T., D. Vayon, S. Ayilavarapu, L. Zhu, S. Jensen and C. T. Lee (2020). “A comparison study: Periodontal practice approach of dentists and dental hygienists.” Int J Dent Hyg May 8. [Epub ahead of print.].

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OBJECTIVES: The aim of this study was to investigate periodontal practice methods of dentists and dental hygienists to compare their knowledge and treatment approach in managing periodontal disease. METHODS: An electronic survey was designed to assess and capture three aspects of data: (a) knowledge of periodontics; (b) practice approaches in non-surgical periodontal therapy; and (c) factors affecting clinical care. The survey was distributed to dentists and dental hygienists who graduated from the same dental school within 5 years (2012-2016). Results were analysed by chi-square test, Fisher’s exact test and logistic regression model. RESULTS: Out of total 117 participants, 111 of them reported their profession (n = 77 in the dental programme, n = 34 in the dental hygiene programme). The results showed no statistical difference in basic periodontal knowledge between dentists and dental hygienists (P = .12). Only 13% of the surveyed population identified appropriate recall intervals for periodontal maintenance and more dental hygienists reported periodontal re-evaluations being performed within their offices compared with dentists (91% vs 70%, P = .02). Almost half of the participants who reportedly performed periodontal re-evaluations (46%) charged for the re-evaluation procedure, despite it not being covered by dental insurance. More hygienists reported being familiar with and performing adjunct therapy compared to dentists in the study (P < .01). CONCLUSION: In general, dentists and hygienists in the study were found to have similar periodontal knowledge and practice approaches. However, differences in performing periodontal re-evaluation and adjunct therapy were significant. Further studies are needed to investigate clinical barriers that impact evidence-based periodontal care.

Olea-Vielba, M., D. Jareno-Garcia, M. M. Methani, I. Martinez-Klemm and M. Revilla-Leon (2020). “Accuracy of the Implant Replica Positions on the Complete Edentulous Additive Manufactured Cast.” J Prosthodont Apr 26. [Epub ahead of print].

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PURPOSE: To compare the implant replica position accuracy on a duplicated complete edentulous maxillary implant definitive cast made either using conventional procedures or material jetting additive manufacturing (AM) technology using a coordinate measuring machine (CMM). MATERIAL AND METHODS: A complete edentulous maxillary cast with 6 implant replicas was prepared. The definitive cast was duplicated using two manufacturing procedures namely conventional (CNV group) and additive manufacturing procedures (AM group). On the CNV, an AM Co-Cr framework and a custom AM custom tray with a polyether impression material were used to obtain an impression of the definitive cast at room temperature (23 degrees C). On the AM group, the definitive cast was digitized using a laboratory scanner. The standard tessellation language (STL) file was exported and used to manufacture the polymeric AM specimens using a multijet printer following manufacturer s recommendations. A new digital implant replica was located on each corresponding housing of each AM specimen. A total of 10 specimens per group was obtained. A CMM was selected to measure the position of each implant replica on the definitive cast, CNV, and AM specimens. Linear and angular discrepancies were computed for each specimen. Thus, the Mann Whitney U test was used to analyze the data (p = 0.05). RESULTS: There was no significant difference in x-, y-, and z- linear and XZ angular discrepancy between both groups. However, the AM group revealed a significantly higher median YZ angular discrepancy than the CNV group (p = 0.007). CONCLUSIONS: Material jetting AM technology demonstrated no significant difference in trueness and precision values of the linear and angular implant replica positions when compared to the conventional technique.

Jing, Y., Z. Wang, H. Li, C. Ma and J. Feng (2020). “Chondrogenesis Defines Future Skeletal Patterns Via Cell Transdifferentiation from Chondrocytes to Bone Cells.” Curr Osteoporos Rep 18(3): 199-209.

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PURPOSE OF REVIEW: The goal of this review is to obtain a better understanding of how chondrogenesis defines skeletal development via cell transdifferentiation from chondrocytes to bone cells. RECENT FINDINGS: A breakthrough in cell lineage tracing allows bone biologists to trace the cell fate and demonstrate that hypertrophic chondrocytes can directly transdifferentiate into bone cells during endochondral bone formation. However, there is a knowledge gap for the biological significance of this lineage extension and the mechanisms controlling this process. This review first introduces the history of the debate on the cell fate of chondrocytes in endochondral bone formation; then summarizes key findings obtained in recent years, which strongly support a new theory: the direct cell transdifferentiation from chondrocytes to bone cells precisely connects chondrogenesis (for providing a template of the future skeleton, classified as phase I) and osteogenesis (for finishing skeletal construction, or phase II) in a continuous lineage-linked process of endochondral bone formation and limb elongation; and finally outlines nutrition factors and molecules that regulate the cell transdifferentiation process during the relay from chondrogenesis to osteogenesis.