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Geometric study of incisal guide pin opening
Geometric David
study of incisal guide pin opening
A. Kaiser, D.D.S., M.S.D.,*
University
of Texas
Health
Science
and Ernst Schelb, D.D.S.**
Center,
Dental
School,
San Antonio,
A
newly made gold crown on a second molar may open the incisal guide pin of the articulator when placed on its die in the master cast. If the incisal pin opening is 1.5 mm, the amount of occlusal adjustment required on this second molar crown is less than 1.5 mm. The purpose of this geometric study was to determine the opening at the second molar and the incisal edges with a given opening at the incisal guide table.
Tex.
Hinge Axis
METHOD The second molar, incisors, and the incisal guide pin were placed 2, 4, and 6 inches, respectively, from the hinge axis (Fig. 1). The opening on the 2, 4, and 6 inch arcs (assume a straight line) was determined as the tan
Fig. 1. Second molar is diagrammatically located 2 inches from hinge axis of articulator, incisors 4 inches, and incisal guide pin 6 inches.
8 = g . Assume that 8 = 10 degrees and angle ab is a right angle. Calculations will then be: a = 2, 4, 6 inches
2 inches
l‘an
0
=
-b
0.17633
l’an
10 degrees
= =
0.03526
=
~00291 b 2 inches b b 4 inches
= ‘1
(1.17633
4 inches
6 inches
Ratio
Cl.7052
= ,,'
(1.17633
=
1.0578
=
h 6 inches b”
.500
=!
./66 -I
-I
,333
Therefore, if b = 1 mm, then b’ = 2 mm, and b’ ’ = 3.33 mm. This means that a given 1.5 mm opening at the incisal guide pin will give 1.5 mm X 0.333 = 0.5 mm opening at the second molar, and 1.5 mm X 0.666 = 1 mm opening at the incisal edges. A 0.5 mm opening will give 0.2 and 0.3 mm, respectively, and a 1 mm opening will give 0.3 and 0.6 mm, respectively. When the occlusal surface of the casting is adjusted in the articulator, the above ratios of 0.333 and 0.666 can be used to predict the amount of adjustment or a simple 3 : 2 : 1 ratio. Re~mll W9WJl\ lot
*Associate **Assistant
THE
Professor, Professor,
JOURNAL
Department Department
OF PROSTHETIC
of Restorative of Restorative
DENTISTRY
Dentistry. Dentistry
DR. DAVIII A. KAISER UNIVERSITY OF TEXAS HEALTH DENTAL SCHOOL SAN ANTONIO, TX 78284
SCIENCE CENTER
495
study of incisal guide pin opening
A. Kaiser, D.D.S., M.S.D.,*
University
of Texas
Health
Science
and Ernst Schelb, D.D.S.**
Center,
Dental
School,
San Antonio,
A
newly made gold crown on a second molar may open the incisal guide pin of the articulator when placed on its die in the master cast. If the incisal pin opening is 1.5 mm, the amount of occlusal adjustment required on this second molar crown is less than 1.5 mm. The purpose of this geometric study was to determine the opening at the second molar and the incisal edges with a given opening at the incisal guide table.
Tex.
Hinge Axis
METHOD The second molar, incisors, and the incisal guide pin were placed 2, 4, and 6 inches, respectively, from the hinge axis (Fig. 1). The opening on the 2, 4, and 6 inch arcs (assume a straight line) was determined as the tan
Fig. 1. Second molar is diagrammatically located 2 inches from hinge axis of articulator, incisors 4 inches, and incisal guide pin 6 inches.
8 = g . Assume that 8 = 10 degrees and angle ab is a right angle. Calculations will then be: a = 2, 4, 6 inches
2 inches
l‘an
0
=
-b
0.17633
l’an
10 degrees
= =
0.03526
=
~00291 b 2 inches b b 4 inches
= ‘1
(1.17633
4 inches
6 inches
Ratio
Cl.7052
= ,,'
(1.17633
=
1.0578
=
h 6 inches b”
.500
=!
./66 -I
-I
,333
Therefore, if b = 1 mm, then b’ = 2 mm, and b’ ’ = 3.33 mm. This means that a given 1.5 mm opening at the incisal guide pin will give 1.5 mm X 0.333 = 0.5 mm opening at the second molar, and 1.5 mm X 0.666 = 1 mm opening at the incisal edges. A 0.5 mm opening will give 0.2 and 0.3 mm, respectively, and a 1 mm opening will give 0.3 and 0.6 mm, respectively. When the occlusal surface of the casting is adjusted in the articulator, the above ratios of 0.333 and 0.666 can be used to predict the amount of adjustment or a simple 3 : 2 : 1 ratio. Re~mll W9WJl\ lot
*Associate **Assistant
THE
Professor, Professor,
JOURNAL
Department Department
OF PROSTHETIC
of Restorative of Restorative
DENTISTRY
Dentistry. Dentistry
DR. DAVIII A. KAISER UNIVERSITY OF TEXAS HEALTH DENTAL SCHOOL SAN ANTONIO, TX 78284
SCIENCE CENTER
495