Research Spotlight

Pandya, M. and T. G. H. Diekwisch (2021). “Amelogenesis: transformation of a protein-mineral matrix into tooth enamel.” J Struct Biol: 107809.

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During enamel formation, the organic enamel protein matrix interacts with calcium phosphate minerals to form elongated, parallel, and bundled enamel apatite crystals of extraordinary hardness and biomechanical resilience. The enamel protein matrix consists of unique enamel proteins such as amelogenin, ameloblastin, and enamelin, which are secreted by highly specialized cells called ameloblasts. The ameloblasts also facilitate calcium and phosphate ion transport toward the enamel layer. Within ameloblasts, enamel proteins are transported as a polygonal matrix with 5nm subunits in secretory vesicles. Upon expulsion from the ameloblasts, the enamel protein matrix is re-organized into 20nm subunit compartments. Enamel matrix subunit compartment assembly and expansion coincide with C-terminal cleavage by the MMP20 enamel protease and N-terminal amelogenin self-assembly. Upon enamel crystal precipitation, the enamel protein phase is reconfigured to surround the elongating enamel crystals and facilitate their elongation in C-axis direction. At this stage of development, and upon further amelogenin cleavage, central and polyproline-rich fragments of the amelogenin molecule associate with the growing mineral crystals through a process termed “shedding”, while hexagonal apatite crystals fuse in longitudinal direction. Enamel protein sheath-coated enamel “dahlite” crystals continue to elongate until a dense bundle of parallel apatite crystals is formed, while the enamel matrix is continuously degraded by proteolytic enzymes. Together, these insights portrait enamel mineral nucleation and growth as a complex and dynamic set of interactions between enamel proteins and mineral ions that facilitate regularly seeded apatite growth and parallel enamel crystal elongation.

Aminoshariae, A., A. Azarpazhooh, A. R. Diogenes, A. F. Fouad, G. N. Glickman, A. Kishen, A. M. Letra, L. Levin, R. S. Roda, F. C. Setzer, F. R. Tay and K. M. Hargreaves (2021). “Insights into the November 2021 Issue of the Journal of Endodontics.” J Endod 47(11): 1669-1671.

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Welcome to the November 2021 issue of the Journal of Endodontics (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 JOE.

Labrador, A. J. P., N. R. G. Marin, L. H. M. Valdez, M. P. Valentina, K. B. T. Sanchez, K. A. R. Ibazetta, B. Johan, A. V. Cesar and J. M. Wright (2021). “Clear Cell Odontogenic Carcinoma a Systematic Review.” Head Neck Pathol.

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Clear cell Odontogenic Carcinoma (CCOC) is an uncommon malignant odontogenic tumor (MOT). It is the fifth most common MOT. A systematic review is presented of reported cases, case series and retrospective studies of CCOC, to determine trends in presentation, diagnostic features, treatment, and patient outcome. Searches of detailed databases were carried out to identify papers reporting CCOC. The variables were demographics, patient symptoms, tumor location, histopathological findings, immunohistochemical studies, treatment, follow-up, and recurrence. 117 cases were identified; CCOC was most frequently seen in mature females 65% (n = 76). The total average age was 55.4 with a range from 17 to 89 years, for females 56.4 and males 53.6 years. The mean size was 3.41 cm. The most common location was in the mandibular body 36.2% (n = 42), followed by the anterior mandible 23.3% (n = 27). The most common clinical presentation was a swelling 80.4% (n = 74), and the main symptom was pain 41.3% (n = 31), followed by painless lesion 24% (n = 18). The most common Immunohistochemistry positive expression was CK19, EMA, and CEA, and for special staining periodic acid Shiff (PAS); 97% of cases were treated surgically. The average follow-up was 30.3 months, and recurrence was reported in 52.4% of the cases. Conclusion: CCOC shows a strong predilection for the body and anterior mandible, and females are more frequently affected. CCOCs can be painful and the principle clinical sign is swelling, CCOCs can metastasize, and the prognosis is fair.

Aljadeff, L., M. Shrestha, R. Y. Kim, T. Schlieve, F. Williams, J. Wright and D. Hammer (2021). “A slow-growing anterior maxillary mass.” Oral Surg Oral Med Oral Pathol Oral Radiol 132(5): 489-495.

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A 43-year-old-male with no contributing medical conditions presented to his dentist for evaluation of a swelling in his left maxilla (Figure 1). The patient first noticed the swelling after blunt trauma to the area; however, nearly 1 year later, the swelling had still not resolved. He denied any pain or purulence. He had no history of tobacco, alcohol, or drug use. His physical exam revealed a 2-cm × 2-cm, poorly demarcated, firm mass in the left anterior maxilla causing mobility of the associated teeth. He had a bluish discoloration of the anterior maxillary mucosa. He had no sensory deficits to the midface, lip, gingiva, or teeth and no cervical lymphadenopathy.

Nasiry Khanlar, L., M. Revilla-León, A. B. Barmak, M. Ikeda, Q. Alsandi, J. Tagami and A. Zandinejad (2021). “Surface roughness and shear bond strength to composite resin of additively manufactured interim restorative material with different printing orientations.” J Prosthet Dent.

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STATEMENT OF PROBLEM: Additive manufacturing (AM) is a technology that has been recently introduced into dentistry for fabricating dental devices, including interim restorations. Printing orientation is one of the important and influential factors in AM that affects the accuracy, surface roughness, and mechanical characteristics of printed objects. However, the optimal print orientation for best bond strength to 3D-printed interim restorations remains unclear. PURPOSE: The purpose of this in vitro study was to evaluate the effect of printing orientation on the surface roughness, topography, and shear bond strength of AM interim restorations to composite resin. MATERIAL AND METHODS: Disk-shaped specimens (Ø20×10 mm) were designed by a computer-aided design software program (Geomagic freeform), and a standard tessellation language (STL) file was obtained. The STL file was used for the AM of 60 disks in 3 different printing orientations (0, 45, and 90 degrees) by using E-Dent 400 C&B material. An autopolymerizing interim material (Protemp 4) was used as a control group (CNT), and specimens were fabricated by using the injecting mold technique (n=20). Surface roughness (Sa, Sz parameters) was measured by using a 3D-laser scanning confocal microscope (CLSM) at ×20 magnification. For shear bond testing, the specimens were embedded in polymethylmethacrylate autopolymerized resin (n=20). A flowable composite resin was bonded by using an adhesive system. The specimens were stored in distilled water at 37 °C for 1 day and thermocycled 5000 times. The shear bond strength (SBS) was measured at a crosshead speed of 1 mm/min. The data were analyzed by 1-way ANOVA, followed by the Tukey HSD test (α=.05). RESULTS: The 45-degree angulation printing group reported the highest Sa, followed by the CNT and the 90-degree and 0-degree angulations with significant difference between them (P<.001). The CNT showed the highest Sz, followed by the 45-degree, 90-degree, and 0-degree angulations. The mean ±standard deviation SBS was 28.73 ±5.82 MPa for the 90-degree, 28.21 ±10.69 MPa for the 45-degree, 26.21 ±11.19 MPa for the 0-degree angulations and 25.39 ±4.67 MPa for the CNT. However, no statistically significant difference was found in the SBS among the groups (P=.475). CONCLUSIONS: Printing orientation significantly impacted the surface roughness of 3D-printed resin for interim restorations. However, printing orientation did not significantly affect the bond strength with composite resin.