Frequency of undercuts and favorable path of insertion in abutments prepared for fixed dental prostheses by preclinical dental students

Marginal and Internal Fit of CAD/CAM Crowns Fabricated Over Reverse Tapered Preparations

“…Clinically achievable TOC recommendations range from 6° to 24° and have been quoted in textbooks, as being adequate . Unfortunately, aiming for low TOC angles is prone to preparation undercuts with a reported frequency ranging from 30.7% (experienced general dental practitioners, in vivo) to 59.1% (final year students, in vitro) . However, negative TOC angles or undecuts neither restrict the making of intraoral digital impressions nor are detrimental to their accuracy.…”

“…2,37 Unfortunately, aiming for low TOC angles is prone to preparation undercuts with a reported frequency ranging from 30.7% (experienced general dental practitioners, in vivo) 4 to 59.1% (final year students, in vitro). 3 However, negative TOC angles or undecuts neither restrict the making of intraoral digital impressions nor are detrimental to their accuracy. In addition, to overcome a minor undercut, the clinician usually removes (overprepares) more dental structure, until a tapered preparation is obtained.…”

“…In this regard, the total occlusal convergence (TOC) angle of a prepared tooth plays an important role in the retention (g/mm²) of dental restorations in a hyperbolic relationship, 1 with parallel axial walls providing maximum values, and highly converging walls providing the least; however, achieving parallel walls or optimal TOC angles (<10°) is a clinically challenging task, prone to preparation undercuts. [2][3][4] In fact, the reported frequency of undercuts in prepared teeth ranged from 30.7% (experienced general dental practitioners, in vivo) 4 to 59.1% (final year students, in vitro) 3 when attempting to achieve low TOC values. Therefore, more realistic TOC values are reported to be within the 10°to 22°range 2 with no apparent correlation to the operator's level of education or experience.…”

The bond shear strength of methacrylate materials used to reduce dental and alveolar undercuts

“…[1][2][3][4] It is a very important issue after a paralelometric analysis and affects the accuracy of the prosthesis. 5,6 Up to now, waxes, phosphate cements and silicone materials have been used to reduce undercuts. These materials did not provide sufficient precision of prosthetic devices, because they combined with the plaster model mechanically rather than chemically and, therefore, there was a need to replicate the plaster model.…”

A study on the machining accuracy of dental digital method focusing on dental inlay

“…8 Human teeth have few straight lines, and the dental arch is shaped like a curve. 9 Therefore, there may be an undercut region depending on the insertion direction, 10 which has limitations in being reproduced by the cutting method.…”