In NMC, the ventilation crosscut was in shape of the semiarch
with the dimension of 4300 mm in height and 5000 mm in width, and accordingly, the supporting set, with 1000 mm inverse arch in the floor, was shown in (Figure 1(a)).
The mechanical model of the VBS proved that the KS after break was essentially a semiarch
structure, despite it looking like a rock beam.
The rotating angle [[alpha].sub.1] of the main block [P.sub.a] was larger than the angle [[alpha].sub.2] of the rear block, and the block [P.sub.a] contacted with adjacent blocks at the hinged ends, and then a semiarch
of stress formed in the main block.
A young patient aged 43 presented with pain symptoms arising during mastication at the level of the left maxillary and mandibular semiarches
. X-rays showed granulomas with vertical bone reabsorption, rhizolysis, and extensive exposure of molar furcation (Figure 1).