Research Spotlight

Posted March 2nd 2021

Self-perception and self-representation preference between 2-dimensional and 3-dimensional facial reconstructions among dentists, dental students, and laypersons.

Marta Revilla-León, M.S.D.

Marta Revilla-León, M.S.D.

Revilla-León, M., Ashby, M.T., Meyer, M.J., Zandinejad, A. and Umorin, M. (2021). “Self-perception and self-representation preference between 2-dimensional and 3-dimensional facial reconstructions among dentists, dental students, and laypersons.” J Prosthet Dent.

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STATEMENT OF PROBLEM: Computer-aided design (CAD) software can merge the intraoral digital scan with patient photographs or 3-dimensional (3D) facial reconstructions for treatment planning purposes. However, whether an individual perceives a 3D facial reconstruction as a better self-representation compared with a 2-dimensional (2D) photograph is unclear. PURPOSE: The purpose of this observational study was to compare self-perception ratings and self-representation preference of the 2D and 3D facial reconstructions among laypersons, dental students, and dentists. MATERIAL AND METHODS: Three populations participated in the study: laypersons, dental students, and dentists (n=20, N=60). Facial and intraoral features were digitized by using facial and intraoral scanners, and a complete-face smile photograph was obtained. Two simulations were performed for each participant: 2D (2D group) and 3D (3D group) reconstructions. In the 2D group, a maxillary digital veneer waxing from the left to the right second premolars was produced without altering the shape, position, or length of the involved teeth. A software program (Dental Systems; 3Shape A/S) was used to merge the maxillary digital waxing with the full-face smile photograph. One image was obtained for each participant. In the 3D group, a dental software program (Matera 2.4; Exocad GmbH) was used to merge the intraoral and facial scans. Subsequently, 1 video of a 180-degree rotation of each 3D superimposition was obtained. Participants evaluated both superimpositions on a scale from 1 (least esthetically pleasing) to 6 (most esthetically pleasing). Finally, participants were asked which superimposition they preferred for a potential treatment outcome representation. RESULTS: All the ratings were esthetically pleasing (median group rating 5 or 6). When analyzed solely for differences across occupation groups, ratings for the 2D representation varied significantly across populations (Kruskal-Wallis chi-squared=13.241, df=2, P=.001), but the ratings for the 3D representation did not exhibit statistically significant differences (Kruskal-Wallis chi-squared=4.3756, df=2, P=.112). Ordinal logistic regression revealed no significant main effects but a significant effect of the population×image-type interaction on the esthetic rating. All participants felt well-represented in both the 2D and 3D representations. Also, 40% of dentists, 55% of dental students, and 50% of laypersons preferred the 3D reconstructions. Sex and occupation in general had no effect on the ratings. However, students tended to give higher ratings to the 3D representations of themselves. CONCLUSIONS: There is no evidence based on the current study that 2D and 3D representations were perceived differently, but representation preferences may depend on a person’s occupation. When individuals rated 3D visualization higher than 2D visualization, they strongly preferred the 3D visualization for representing the treatment outcome.


Posted March 2nd 2021

Fracture resistance of additive manufactured and milled implant-supported interim crowns.

Marta Revilla-León, M.S.D.

Marta Revilla-León, M.S.D.

Martín-Ortega, N., Sallorenzo, A., Casajús, J., Cervera, A., Revilla-León, M. and Gómez-Polo, M. (2021). “Fracture resistance of additive manufactured and milled implant-supported interim crowns.” J Prosthet Dent.

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STATEMENT OF PROBLEM: Interim dental prostheses can be fabricated by using subtractive or additive manufacturing technologies. However, the fracture resistance of implant-supported interim crowns fabricated by using vat-polymerization additive manufacturing methods remains unclear. PURPOSE: The purpose of this in vitro study was to evaluate the fracture resistance of anterior and posterior screw-retained implant-supported interim crowns fabricated by using subtractive and vat-polymerization direct light processing (DLP) additive manufacturing procedures. MATERIAL AND METHODS: An implant (Zinic Implant RP ∅4.0×10 mm) was placed in a 15×15-mm polymethylmethacrylate block. An implant abutment (ZiaCam, nonrotatory RP) was positioned on each implant. The virtual implant abutment standard tessellation language (STL) file provided by the manufacturer was imported into a software program (Exocad v2.2 Valletta) to design 2 anatomic contour crowns, a maxillary right central incisor (anterior group) and a maxillary right premolar (posterior group). Each group was subdivided into 2 subgroups depending on the manufacturing method: milled (milled subgroup) and additive manufacturing (additive manufacturing subgroup). For the milled subgroup, an interim material (Vivodent CAD Multi) and a milling machine were used to fabricate all the specimens (N=40, n=10). For the additive manufacturing subgroup, a polymer interim material (SHERAprint-cb) and a DLP printer (SHERAprint 30) were used to manufacture all the specimens at a 50-μm layer thickness and 45-degree build orientation as per the manufacturer’s instructions. Then, each specimen was cemented to an implant abutment by using composite resin cement (Multilink Hybrid Abutment HO) as per the manufacturer’s instructions. A universal testing machine was used for fracture resistance analysis, and the failure mode was recorded. The Shapiro-Wilk test revealed that data were normally distributed. One-way ANOVA and Tukey multiple comparison were selected (α=.05). RESULTS: One-way ANOVA revealed significant differences among the groups (P<.05). The anterior milled subgroup obtained a significantly higher fracture resistance mean ±standard deviation value of 988.4 ±54.8 N compared with the anterior additive manufacturing subgroup of 636.5 ±277.1 N (P<.001), and the posterior milled subgroup obtained significantly higher mean ±standard deviation of 423.8 ±68 N than the additive manufacturing subgroup of 321.3 ±128.6 N (P=.048). All groups presented crown fracture without abutment fracture. CONCLUSIONS: Manufacturing procedures and tooth type influenced the fracture resistance of screw-retained implant-supported interim crowns. Milled specimens obtained higher fracture resistance compared with the DLP additive manufacturing groups. The anterior group was higher than the posterior group.


Posted March 2nd 2021

Osteon: structure, turnover and regeneration.”

Xiaohua Liu, Ph.D.

Xiaohua Liu, Ph.D.

Chang, B. and Liu, X. (2021). “Osteon: structure, turnover and regeneration.” Tissue Eng Part B Rev.

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Bone is composed of dense and solid cortical bone and honeycomb-like trabecular bone. Although cortical bone provides the majority mechanical strength of a bone, there are few studies focusing on cortical bone repair or regeneration. Osteons (the Haversian system) form structural and functional units of cortical bone. In recent years, emerging evidences have shown that the osteon structure (including osteocytes, lamellae, lacunocanalicular network and Haversian canals) plays critical roles in bone mechanics and turnover. Therefore, reconstruction of the osteon structure is crucial for cortical bone regeneration. This article provides a systematic summary of recent advances in osteons including the structure, function, turnover and regenerative strategies. First, the hierarchical structure of osteons is illustrated and the critical functions of osteons in bone dynamics are introduced. Next, the modeling and remodeling processes of osteons at a cellular level and the turnover of osteons in response to mechanical loading and aging are emphasized. Furthermore, several bioengineering approaches that were recently developed to recapitulate the osteon structure are highlighted.


Posted March 2nd 2021

Comparison of optical performance among three dental operating microscopes: A pilot study.

Poorya Jalali, D.D.S.

Poorya Jalali, D.D.S.

Jalali, P., Kim, C. and Woodmansey, K.F. (2020). “Comparison of optical performance among three dental operating microscopes: A pilot study.” J Conserv Dent 23(4): 374-376.

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INTRODUCTION: Two important aspects of the dental operating microscope (DOM) that factor into its overall effectiveness are resolution and depth of field. Therefore, the objective of this study was to evaluate and compare the resolution and depth of field of DOMs from three well-known manufacturers using standardized test targets. MATERIALS AND METHODS: A resolution test, using the 1951 USAF Hi-Resolution Target (Edmund Optics, Barrington, NJ), and a depth of field test, using the Depth of Field Target 5-15 (Edmund Optics, Barrington, NJ), were performed by two calibrated observers. Three DOM systems such as Seiler IQ (Seiler Instrument Inc., St. Louis, USA), Global G-Series 6 step (Global Surgical Corp., St. Louis, USA), and Zeiss Extaro 300 (Carl Zeiss Meditec AG, Oberkochen, Germany) were used to compare the resolution and depth of field. RESULTS: The Zeiss Extaro 300 showed the highest maximum resolution and maximum DOF (64 lp/mm and 17mm, respectively). The Seiler IQ showed the lowest maximum resolution and maximum DOF (35.9 lp/mm and 11 mm, respectively). CONCLUSION: Within the limitations of this study, the Zeiss Extaro 300 was superior in terms of resolution and depth of field as compared to the other two DOMs.


Posted March 2nd 2021

Insights Into the February 2021 Issue of the JOE.

Gerald N. Glickman, M.S.

Gerald N. Glickman, M.S.

Azarpazhooh, A., Diogenes, A.R., Fouad, A.F., Glickman, G.N., Kishen, A., Levin, L., Roda, R.S., Tay, F.R. and Hargreaves, K.M. (2021). “Insights Into the February 2021 Issue of the JOE.” J Endod 47(2): 159-160.

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Welcome to the February 2021 issue of the JOE. Here, we share some of our favorite articles that are published in this issue of the Journal. We hope you look forward to reading these and other articles in the JOE.