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Apparatus for simulating extraction forces
lilt. J. Oral Maxillofac. Surg. 1986: 15: 444-445 (Key words: ex/rac/ion. /ee/h; phantom)
Apparatus for simulating extraction forces RISTO LEHTINEN AND TARMO OJALA
Department of Oral Surgery. Institute of Dentistry. Turku. Finland
The extraction forces can be stimulated using a mean value indicator, extraction forceps and a phantom skull. The rocking and twisting moments occuring during "extraction" can be measured with strain gauges. Before beginning practical work on patients, dental students carried out simulated extractions of various teeth. The moments were significantly lower than forces needed for real extractions. When using the simulator, the students must be supervised by a teacher able to demonstrate the correct grips of forceps handles and the correct style in extraction. ABSTRACf -
( Accepted for publication 10 August 1985)
The number of teeth being extracted has been reduced, and dental students do not receive adequate experience of dental extraction. OJALA2• 3 has developed an apparatus that can measure the moments present during teeth extraction. The rocking and twisting moments occurring during extraction are measured with strain gauges attached to forceps handles. MACGREGOR & TmlLiNsoN I reported the use of strain gauges in extractions performed on patients. There have been no reports of previous use of this method on a phantom skull in teaching dental students.
by students in cavity preparation. The acrylic teeth are firm enough to withstand simulation and they remain in "alveolar sockets" after simulation. The subjects were 30 dental students, who had just been lectured on the basic principles of extractions. Before beginning practical work on patients, they carried out simulated extractions of various teeth. First, they were asked to apply the buccal and palatal rocking moment for 10 s with a force sufficient for the extraction of normal teeth. While simulating extraction, the students observe the mean value indicator. The authors have made earlier reports on the mean values for rocking moments and their duration in different tooth groups" s, and these values were used as control values. The statistical test used was the t-test.
Material and methods The mean value indicator was the same as that used in earlier studies" s. By the same apparatus, extraction forces can be simulated using a mean value indicator, extraction forceps and a phantom skull (Fig. I). The same phantom skull was used
Results and discussion The moments used by the students in simulating extraction in the lower jaw were (P< 0.001) significantly lower than those
EXTRACTION SIMULATION
445
supervised by a teacher able to demonstrate the correct grip of the forceps handles and the correct style in extraction. After the first attempt, the teacer must also give the correct moment values. The students found this way of teaching very demonstrative and felt that it gave them some idea of moment before treating patients. The apparatus is now commercially available and will be used for all students in our department. Fig. 1. The mean value indicator used in this study (left) and extraction forceps and phantom skull (right).
used by OJALA4 (Table I). Table I gives the values for buccal moments of the lower jaw only over a 10-s period. The lingual moments as wen as the moments for the upper jaw differed from the control figures·,s in the same way as the reported moments. When using the simulator, the students must be
Table I. The mean values of buccal rocking moments (J) in connection with the extraction of lower jaw teeth; control values are from OJALA'S' study Premolars s.d.
X students no. of cases control no. of cases
0.61
Molars s.d.
X
0.32
0.88
0.74
2.08
30 1.25
43
0.29 30 1.13 30
References I. MACGREGOR, A. J. & TmILINSON, G. E.: An apparatus for measuring the forces of dental extraction. Sr. J. Oral SlIrg. 1980: 17: 71-76. 2. OJALA, T.: Strain gauge measurements in connection with the extraction of teeth (I). Equipment and method. SIIOlll. HallllllQsliiiik. Toilll. 1971: 67: 325-332. 3. OJALA, T.: Strain gauge measurements in connection with the extraction of teeth (II). Equipment and method. Proc. Finn. Dent. Soc. 1972: 68: 181-183. 4. OJALA, T.: Rocking moments in extraction of teeth in the lower jaw. Int. J. Oral SlIrg. 1980: 9: 367-372. 5. OJALA, T. & LEHTINEN, R.: Rocking and twisting moments in extraction of teeth in the upper jaw. 1nl. J. Oral SlIrg. 1980: 9: 377-382. Address: Institute of Dentistry Unirersity of Turkll Lellllllinkiiisenkatll 2 SF-20520 TlIrku Finland
Apparatus for simulating extraction forces RISTO LEHTINEN AND TARMO OJALA
Department of Oral Surgery. Institute of Dentistry. Turku. Finland
The extraction forces can be stimulated using a mean value indicator, extraction forceps and a phantom skull. The rocking and twisting moments occuring during "extraction" can be measured with strain gauges. Before beginning practical work on patients, dental students carried out simulated extractions of various teeth. The moments were significantly lower than forces needed for real extractions. When using the simulator, the students must be supervised by a teacher able to demonstrate the correct grips of forceps handles and the correct style in extraction. ABSTRACf -
( Accepted for publication 10 August 1985)
The number of teeth being extracted has been reduced, and dental students do not receive adequate experience of dental extraction. OJALA2• 3 has developed an apparatus that can measure the moments present during teeth extraction. The rocking and twisting moments occurring during extraction are measured with strain gauges attached to forceps handles. MACGREGOR & TmlLiNsoN I reported the use of strain gauges in extractions performed on patients. There have been no reports of previous use of this method on a phantom skull in teaching dental students.
by students in cavity preparation. The acrylic teeth are firm enough to withstand simulation and they remain in "alveolar sockets" after simulation. The subjects were 30 dental students, who had just been lectured on the basic principles of extractions. Before beginning practical work on patients, they carried out simulated extractions of various teeth. First, they were asked to apply the buccal and palatal rocking moment for 10 s with a force sufficient for the extraction of normal teeth. While simulating extraction, the students observe the mean value indicator. The authors have made earlier reports on the mean values for rocking moments and their duration in different tooth groups" s, and these values were used as control values. The statistical test used was the t-test.
Material and methods The mean value indicator was the same as that used in earlier studies" s. By the same apparatus, extraction forces can be simulated using a mean value indicator, extraction forceps and a phantom skull (Fig. I). The same phantom skull was used
Results and discussion The moments used by the students in simulating extraction in the lower jaw were (P< 0.001) significantly lower than those
EXTRACTION SIMULATION
445
supervised by a teacher able to demonstrate the correct grip of the forceps handles and the correct style in extraction. After the first attempt, the teacer must also give the correct moment values. The students found this way of teaching very demonstrative and felt that it gave them some idea of moment before treating patients. The apparatus is now commercially available and will be used for all students in our department. Fig. 1. The mean value indicator used in this study (left) and extraction forceps and phantom skull (right).
used by OJALA4 (Table I). Table I gives the values for buccal moments of the lower jaw only over a 10-s period. The lingual moments as wen as the moments for the upper jaw differed from the control figures·,s in the same way as the reported moments. When using the simulator, the students must be
Table I. The mean values of buccal rocking moments (J) in connection with the extraction of lower jaw teeth; control values are from OJALA'S' study Premolars s.d.
X students no. of cases control no. of cases
0.61
Molars s.d.
X
0.32
0.88
0.74
2.08
30 1.25
43
0.29 30 1.13 30
References I. MACGREGOR, A. J. & TmILINSON, G. E.: An apparatus for measuring the forces of dental extraction. Sr. J. Oral SlIrg. 1980: 17: 71-76. 2. OJALA, T.: Strain gauge measurements in connection with the extraction of teeth (I). Equipment and method. SIIOlll. HallllllQsliiiik. Toilll. 1971: 67: 325-332. 3. OJALA, T.: Strain gauge measurements in connection with the extraction of teeth (II). Equipment and method. Proc. Finn. Dent. Soc. 1972: 68: 181-183. 4. OJALA, T.: Rocking moments in extraction of teeth in the lower jaw. Int. J. Oral SlIrg. 1980: 9: 367-372. 5. OJALA, T. & LEHTINEN, R.: Rocking and twisting moments in extraction of teeth in the upper jaw. 1nl. J. Oral SlIrg. 1980: 9: 377-382. Address: Institute of Dentistry Unirersity of Turkll Lellllllinkiiisenkatll 2 SF-20520 TlIrku Finland