Objective To study the influence of implant depth and scanning rod lengths on the accuracy of digital impression for single-tooth implant restoration of the mandibular posterior teeth.Methods Five standard dental cast models with missing right mandibular first molar(46)were prepared with the subgingival implant depths of 0,1,3,5 and 7 mm.ITI RC and ITI RC H11 scanning rods were connected to the replacement body and placed into the seating tract for scanning.The reference data were obtained using a 3D dental scanner,and the experimental data were obtained by 10 scans of each model using a digitized intraoral scanner.Geomagic Wrap 2021 was used to analyze the model data to test the trueness and precision of the models.Results The trueness did not differ significantly among the groups(P>0.05).The implant depth of 1 mm achieved the highest impression precision(66.81±2.45 μm),and the depth of 0 mm resulted in a significantly lower precision(95.60±3.04 μm)than the depth of 1 and 3 mm.Starting from the subgingival depth of 1 mm,the precision of the scan decreased progressively with the increase of the implant depth.At the subgingival implant depth of 5 or 7 mm,the use of an extended rod significantly improved the scan precision.Conclusion For single-tooth implant restoration of the mandibular posterior teeth,the implant depth can substantially affect the accuracy of digital impression,which decreases as the implant depth increases.For a deep implant,the use of a longer scanning rod can improve the scanning accuracy.

Methylation modification is one of the most common epigenetic modification regulation in eukaryotes, including histone methylation, DNA methylation, RNA methylation, etc., which plays an important regulatory role in physiological processes and pathologic occurrence and development. Tooth root development is carried out by both epithelial and mesenchymal cells and involves a variety of cell-molecular interactions. In recent years, a large number of studies have found that methylation plays a key role in the regulation of tooth root development and expands the mechanism network of tooth root development. In this paper, we review the role and mechanism of methylation modification during root development.

Objective To study the influence of implant depth and scanning rod lengths on the accuracy of digital impression for single-tooth implant restoration of the mandibular posterior teeth.Methods Five standard dental cast models with missing right mandibular first molar(46)were prepared with the subgingival implant depths of 0,1,3,5 and 7 mm.ITI RC and ITI RC H11 scanning rods were connected to the replacement body and placed into the seating tract for scanning.The reference data were obtained using a 3D dental scanner,and the experimental data were obtained by 10 scans of each model using a digitized intraoral scanner.Geomagic Wrap 2021 was used to analyze the model data to test the trueness and precision of the models.Results The trueness did not differ significantly among the groups(P>0.05).The implant depth of 1 mm achieved the highest impression precision(66.81±2.45 μm),and the depth of 0 mm resulted in a significantly lower precision(95.60±3.04 μm)than the depth of 1 and 3 mm.Starting from the subgingival depth of 1 mm,the precision of the scan decreased progressively with the increase of the implant depth.At the subgingival implant depth of 5 or 7 mm,the use of an extended rod significantly improved the scan precision.Conclusion For single-tooth implant restoration of the mandibular posterior teeth,the implant depth can substantially affect the accuracy of digital impression,which decreases as the implant depth increases.For a deep implant,the use of a longer scanning rod can improve the scanning accuracy.