Journal of Oral Rehabilitation, 1992, Volume 19, pages 245-252
Longitudinal study on torque transmitted from a denture base to abutment tooth of a distal extension removable partial denture with circumferential clasps K. O G A T A , A . ISUU and I. N A G A R E Department of Removable Prosthodontics, Okayama University Dental School, Okayama, Japan
Summary
Not only forees but also torque exerted on abutment teeth are important factors for planning the eonstruetion of distal extension removable partial dentures. The purpose of this study was to make longitudinal analysis of torque transmitted from denture base to a direct abutment tooth of these dentures with eireumferential elasps. The results are summarized as follows: (i) Vertical Max. MT (maximal mean value of torque) was decreased and beeame constant after one or one and half months of the insertion of new dentures, (ii) Lateral Max. MT in one subject was changed from the lingual direction to the buccal direetion while in another subject it was constant. (iii) In the vertieal direction, there were no remarkable differences of Max. MT and Ave. T (average value of torque) between subjects. Max. MT was 5-10 X lO^^^kgm ' in the downward. Ave. T was 2 - 3 x 10~''kgmss~' in the downward and 0-3 x 10~^kgmss~' in the upward. (iv) In the lateral direction, there were considerable differences of Max. MT and Ave. T between subjects. Max. MT was less than 2OxlO^^kgm. Ave. MT was 2 - 8 X 10~-\gmss''.
Introduction
Not only foree (vector of force) but also torque (moment of force) is transmitted to abutment teeth of removable, partial dentures. Torque exerted on abutment teeth may rotate, incline or displace them. As force directed toward tissue occurs on a distal extension denture base, rotational forces take place around distal oeelusal rest. Cast circumferential elasps ean place an extremely destructive distal tipping force or torque on the abutment tooth (Stewart et al., 1983). However there do not appear to be any dynamie in vivo studies on torque aeting on abutment teeth. The purpose of this study was to make a longitudinal analysis of torque exerted on a direct abutment tooth of distal extension removable dentures with eireumferential clasps.
Correspondenee: Dr K. Ogata, Department of Removable Prosthodontics, Okayama University Dental School, 2-5-1 shikata eho Okayama 700, Japan. 245
246
K. Ogata et al.
Materials and methods Subjects. Two subjects, 65 and 75 years of age, with dentulous in the maxilla, Kennedy Class I partially edentulous in the mandibular were selected for this experiment. Experimental apparatus. The experimental apparatus which was reported by Ogata et al. (1991) was used. It was made of two parts, one was the metal framework and the other was the denture base embedded with the transducers (Fig. 1). The metal framework had a steel bar which was connected with the framework parallel to the alveolar ridge and the Camper's plane. The denture base touched the steel bar only through the two loading points. Forces exerted on the denture base was conducted as follows; denture base -^ fixed part -^ loading points —» steel bar —* metal framework -^ abutment teeth. Two transducers, anterior transducer (Ant-Tr) and posterior transducer (Post-Tr) could detect lateral and vertical forces exerted on the loading point at same time. The signals from the transducers were amplified by the carrier amplifiers*. Moreover, vertical jaw movement was measured by the electric measuring apparatus of mandibular movementf, at same time. Analog signals from the apparatus were converted into digital signals (sampling clock period; 40ms), processed and stored on floppy discs using the signal processor^. Measurements. The subject was asked to sit in an upright position. Forces and vertical jaw movement were recorded during the following chewing activities; (i) chewing one dry-roasted peanut; (ii) chewing three pieces of carrot (6 x 6 x 6 mm); (iii) chewing two raisins; and (iv) chewing two pieces of sausage (10 x 10 x 10 mm). All subjects were asked to masticate on the transducer side. Forces were measured on several separate occasions up to 4 months from the insertion of new dentures.
Metal plate
Denture base / . . , /. * -r \ ^ Anterior transducer (Ant-Tr) Posterior transducer (Post-Tr) Stopper
Steel bar Loading point Fixed part Loading point Fig. I. A cross-section of the e.xperimental denture. * DPM-602A KYOWA Eleetronic Instruments Co., Ltd., Tokyo, Japan t Mandibular Kinesiograph K5AR, Myo-Tronies Research Inc., Seattle, WA, U.S.A. :|: 7T18, NEC San-ei Instruments Ltd., Tokyo. Japan
Torque exertion on abutment teeth
247
Analysis. Torque was evaluated on a direct abutment tooth. Torque around the vertical axis (lateral torque) (TL), torque around the lateral axis (vertical torque) (Tv), lateral force (FL) and vertical force (Fv) were calculated (Fig. 2). The direction of these forces corresponded to the movement of a terminal on the experimental dentures. Figure 3 shows the original waveforms and their processed waveforms which were computed from all sampling points of the original waveforms by the signal processor using the equations shown in Fig. 2. The maximal (peak) mean value of torque {Max. MT) of TL and Tv at the minimum of the interocclusal distance and its standard deviation were calculated from the peak level of all strokes of each processed waveforms. The integration value of torque (I) and time (T) from initiation of chewing to swallowing were obtained, and the average value of torque (Ave. T) was then calculated {Ave. T= I/T) (Fig. 4). Integration value was equal to the area which was surrounded with the waveform and the base line. The maximal (peak) mean value of force {Max. MF) and the average value of force {Ave. F) of FL and Fv were obtained in the same manner. Then, the average of Ave. T and Ave. F of measurements were obtained.
Buc.
(
Sagittal axis
c
Lateral axis
j
Fig. 2. Schematie presentation of torque and foree: A = loading point of Ant-Tr, P = loading point of Post-Tr; lateral foree ( = A L ) and vertical force (=Av) were deteeted by Ant-Tr, lateral foree ( = PL) and vertical force ( = Pv) were detected by Post-Tr; vertieal force (=Fv), lateral foree ( = F L ) , torque around the vertieal axis (lateral torque) ( = T L ) and torque around the lateral axis (vertieal torque) (Tv) were exerted on a direct abutment tooth.
248
K. Ogata et al. Processed data
Original data Lateral force
Torque
(x10"'kgm)
(N)
4
Buc. 2 0 0 Lin. 20-
10
20
30 (S)
(S) 30
20
10
Up 200 Down 20-
I 40Vertical force (N) 40-J Up 200Down 20-
Porce
Av 10
(S ) 30
20
rr|W||; ^
30 (S)
40 J
(N)
Pv
(N)
Up 20Down 2040-
10
20
n
1
T 30 (S)
Up 200 Down 20-
(S) 30
20
10
Fig. 3. Original data and proeessed data.
Max.MT Ave.T Baseline Ave.T Max.MT
L
: I
Fig. 4. Maximal (peak) mean value of torque {Ma.x. MT) was calculated from each processed waveforms. Average mean value of torque {Ave. T) was ealculated following the equation: Ave. T=\ (integration value)/T (time required for ehewing).
Torque exertion on abutment teeth
249
Results
Subject L Figure 5 shows the longitudinal changes of Max. MT and Max. MF in 1 Lateral Max i n l ddirection iti th day d subject 1. Max. MT was 10 x lO^-'kgm"' in the llingual on the of insertion of the new denture. As the period of wearing the denture proceeded, this value decreased, and changed to the buccal direction after 134 days. Vertical Max. MT decreased after 7 days, then became constant. The constant value was 2-5 X lO^^^kgm^' during chewing of food. Table 1 shows the average of Ave. T and Ave. F of all measurements in subject. 1. In the lateral direction, Ave. 7 was 1-8-2-9 (mean; 2-5) x 10~-^kgmss"' in the lingual and 0-5 x K r - \ g m s s ' in the buccal. In the vertical direction, Ave. 7 was 1-6-2-2 (mean; 1-9) x lO^^'kgmss ' in the downward and 0-3 x 10~-'kgmss"' in the upward. Ave. T in the lingual was 130% of it in the downward while Ave. F in the lingual was 60% of that in the downward. Subject 2. Figure 6 shows the longitudinal changes of Max. MT and Max. MF in subject 2. There are not remarkable changes of lateral Max. MT. The value of it was 10-20 X 10 ''kgm"' in the buccal direction. Vertical Max. MT decreased after 7 days, and the increase then became constant at a value of 5-10 x 10 \ g m ' in the
Max.MT Lateral
Peanuts
Carrot
20.
Raisin
20-,
40
120
§ IJ 10o I 20-
20-| 10-
20-|
(day) 10160
80
Sausage
40
80
160 120
1020-
10-
0
40
80
160 120
10-
0
40 80 120
0
40
160
1020-
20-
Vertical 80
120 160
Max.MP Lateral
Peanuts
Carrot
^ 20-,
20-
20-|
5 i 10- 0 8° 0-
10-
10-
11. 3
40 80
160 120
10-
I 20-
0
40 80 120
(day) 1020-
Sausage
Raisin
160
1020-
20-|
0
40 80 120
10-
160
r
0
40
80
0
40 80 120 160
120 160
1020-
Vertical
-^\'°]
20-
S §10- 0
10-
20-
40
80 120 160
0
40
80 120
20 n 10160 0
10-
10-
20-
20-
2C40 80 120 160
}^^~
Fig. 5. Longitudinal changes of Max. MT and Max. MF in subject 1.
10
250
K. Ogata et al.
Table 1. The average of Ave. T and Ave. F exerted on a direct abutment tooth in subjeet 1 Ave. F (N ss"^)
Ave. T { x l O - m kgss"^)
Peanuts Carrot Raisin Sausage
(
Lateral
Vertical
Lateral
Vertical
Bue.
Lin.
Down.
Up.
Bue.
Lin.
Down.
Up.
0-6 (0-8) 0-4 (0-4) 0-5 (0-4) 0-4 (0-2)
2-5 (1-4) 2-9 (1-5) 2-5 (1-7) 1-8 (0-7)
1-6 (0-7) 2-2 (0-9) 1-7 (0-7) 2-2 (0-5)
0-6 (0-3) 0-3 (0-1) 0-3 (0-1) 0-1 (0-1)
0-3 (0-4) 0-2 (0-2) 0-2 (0-1) 0-2 (0-1)
1-3 (0-7) 1-7 (1-2) 1-7 (1'5) 1-2 (0-6)
2-6 (1-4) 2-6 (1-5) 2-3 (1-4) 1-9 (0-7)
0-3 (0-3) 0-1 (0-1) 0-1 (0-1) 0-1 (0-1)
): S.D.
Table 2. The average of Ave. T and Ave. F exerted on a direct abutment tooth in subject 2 Ave. T (xlO -'k gm SS ') Vertieal
Lateral
Peanuts Carrot Raisin Sausage
Ave. F (N SS-') Lateral
Vertieal
Buc.
Lin.
Down.
Up.
Buc.
Lin.
Down.
Up.
8-2 (1-8) 7-7 (2-1) 8-0 (1-5) 6-8 (1-6)
0-1 (0-1) 0-2 (0-2) 0-2 (0-1) 0-2 (0-2)
2-2 (1-2) 2-5 (1-6) 2-8 (2-0) 1-8 (1-9)
0-3 (0-6) 0-2 (04) 0-3 (0-6) 0-3 (0-5)
5-4 (1-2) 4-8 (0-9) 4-6 (0-8) 3-8 (0-7)
0-1 (0-1) 0-1 (01) 01 (0-1) 0-1 (0-1)
3-2 (1-7) 3-3 (2-0) 3-6 (2-4) 2-7 (2-1)
0-1 (0-1) 0-1 (0-1) 0-1 (0-1) 0-1 (0-1)
): S.D.
downward direction. Table 2 shows the average of Ave. T and Ave. F of all measurements in subject 2. In the lateral direction, Ave. Twas 6-8-8-2 (mean; 7-7) x 10 kgm ss^' in the buccal and 0-2 x lO^'^kgmss"' in the lingual. In the vertical direction. 1-8-2-8 (mean; 2-3) x 10"^kgmss"' in the downward and 0 3 x 10 kgmss - 1 in the upward. Ave. T in the buccal was three or four times greater than downward while Ave. F in the buccal was one and one-half times greater than in the downward. Discussion The type of stress exerted on abutment teeth and edentulous mucosa was influenced by the design of dentures. In order to evaluate the design, it is desirable to assume that forces transmitted from denture base to metal framework is exerted only on a direct abutment tooth. If the design is simple, forces exerted on abutment teeth can
Torque exertion on abutment teeth
251
be calculated from a static point of view. However, if the design is complex, the results are likely to be groundless because they are based on many assumptions. Moreover, if the evaluation point such as a direct abutment tooth is determined, torque could be calculated as shown in Fig. 2. In Fig. 2, there are three kinds of torque around the lateral, vertical and sagital axes, and there are three directions of vectors of forces i.e. lateral, vertical and sagital. In this study, torque around the lateral and vertical axes, and vertical and lateral direction of forces were calculated from a static point of view using the results of the previous study (Ogata et al., 1991). The transducer of this study allowed the denture base to rotate slightly around the steel bar connected with the metal framework so as to eseape torque around the sagital axis. Lowe et al. (1970) computed the total daily potential energy (impulse of force) for swallowing force exerted on the flange of lower removable partial dentures. The impulse is an important factor, because a small value for such forces may not have mueh of an infiuenee on abutment teeth even if the stroke was of high magnitude. In this study, the average of torque and force were obtained. Max. MT and Max. ME as shown in Figs 5 and 6 were generated by oeelusal force. Therefore almost all oi Ave. Tin the lingual-downward (subject 1) or buccal-downward
Max.MT
S k 30 "o ^ 20 • ^ CO .5. 10
Sausage
Raisin
Carrot
Peanuts
Lateral
30-|
30-|
30-1
20-
20-
20-
10-
10-
0
0
40
80
120 160 (day)
0 0
40
80
120 160 10J 0
40
80
120 160
0
40
80
120 160
40
80
120 160
0
40
80
120 160
Vertical
Ifl
20-,
^ §10-
40
80 120 160
10-
40
80
120 160
10-
0
0-
10-
10-
2oJ
20-
Max.MF
i £5
Carrot
Peanuts
Lateral f 30-] ^ 20-
Raisin
30-| 20100
0 0
40
80
30 20100 0
120 160 (day)
Sausage
40
80
30-1
2010-
0
120 160
40
80
0
40
80
120 160
20-| 10- 0 120 160
40
80
120 160
120 160 10-
Vertical 0
40
80
120 160
20-
20-
10-
10-
0
40
80 120 160
0
40
80
S. § 1 0 -
10-
10-
10-
i 20-
20-
20-
20-
Fig. 6, Longitudinal changes of Max. MT and Max. MF in subjeet 2.
252
K. Ogata et al.
(subject 2) direction were generated by ocelusal force, and in the other directions were generated by tongue, cheeks or hps. In the vertical direction, the value of Ave. T generated by tongue, cheeks or hps was 10—20% of that generated by ocelusal force and the value of Ave. F generated by tongue, cheeks or lips was 5—10% of that generated by occiusal force in subjects 1 and 2. In the lateral direction, the value of Ave. T generated by tongue, cheeks or lips was 20% of that generated by occiusal force in subject 1 while the value was less than 3% in subject 2. The value of Ave. F generated by tongue, cheeks or hps was 15% of that generated by the occiusal force in subject 1 and the vahie was less than 2% in subject 2. It is suggested that not only occiusal force but also tongue, cheeks and hps contribute generating torque and forces exerted on abutment teeth. In order to reduce vertical torque exerted on an abutment teeth, a number of improvements in design of dentures have been proposed e.g. I-bar clasp system (Kratochvil, 1963; Krol, 1973) or attachments which allow the denture base to move vertically. (Preiskel, 1979). However lateral torque also needs to be considered; in the clinic it should be noted that the lateral torque transmitted to a abutment tooth was 1-3—4 times as much as that in the vertical. References Influence of occiusal rest position and clasp design on movement of abutment iccth. Jottrnal of Prosthcllc Dentistry. 13. 114. KKOL. A..I. (1973) Clasp design lor extension-base removable partial dentures. Journal of Prosthetic
KKATOCHVIL. F . J . ( 1 % 3 )
Dentistry. 29. 40,S.
LowH. R.D.. KYDD. W . L . & SMITH. D . E . (1970) Swallowing and resting forces related to lingual flange thickness in removable partial dentures. Journal of Prosthetic Dentistrv, 23. 279. Oci.viA. K. & SHIMI/U, K. (1991) Longitudinal study on forces transmitted from denture base to retainers of lower tree-end saddle dentures with Aker's elasps. Journal of Oral Rehabilitation. 18. 471. PKHSKI-L. H . W . (1979) Precision attachments in dentistry, third edition, pp. 109-155. Henry Kimpton Ltd. London. SriiWART. K.L.. RuoD. K.D. & KUEBKHK, W . A . (1983) Clinical removable partial prosthodontics, pp. 94-112. C.V. Mosby Company. St. Louis. Toronto and London.
Longitudinal study on torque transmitted from a denture base to abutment tooth of a distal extension removable partial denture with circumferential clasps K. O G A T A , A . ISUU and I. N A G A R E Department of Removable Prosthodontics, Okayama University Dental School, Okayama, Japan
Summary
Not only forees but also torque exerted on abutment teeth are important factors for planning the eonstruetion of distal extension removable partial dentures. The purpose of this study was to make longitudinal analysis of torque transmitted from denture base to a direct abutment tooth of these dentures with eireumferential elasps. The results are summarized as follows: (i) Vertical Max. MT (maximal mean value of torque) was decreased and beeame constant after one or one and half months of the insertion of new dentures, (ii) Lateral Max. MT in one subject was changed from the lingual direction to the buccal direetion while in another subject it was constant. (iii) In the vertieal direction, there were no remarkable differences of Max. MT and Ave. T (average value of torque) between subjects. Max. MT was 5-10 X lO^^^kgm ' in the downward. Ave. T was 2 - 3 x 10~''kgmss~' in the downward and 0-3 x 10~^kgmss~' in the upward. (iv) In the lateral direction, there were considerable differences of Max. MT and Ave. T between subjects. Max. MT was less than 2OxlO^^kgm. Ave. MT was 2 - 8 X 10~-\gmss''.
Introduction
Not only foree (vector of force) but also torque (moment of force) is transmitted to abutment teeth of removable, partial dentures. Torque exerted on abutment teeth may rotate, incline or displace them. As force directed toward tissue occurs on a distal extension denture base, rotational forces take place around distal oeelusal rest. Cast circumferential elasps ean place an extremely destructive distal tipping force or torque on the abutment tooth (Stewart et al., 1983). However there do not appear to be any dynamie in vivo studies on torque aeting on abutment teeth. The purpose of this study was to make a longitudinal analysis of torque exerted on a direct abutment tooth of distal extension removable dentures with eireumferential clasps.
Correspondenee: Dr K. Ogata, Department of Removable Prosthodontics, Okayama University Dental School, 2-5-1 shikata eho Okayama 700, Japan. 245
246
K. Ogata et al.
Materials and methods Subjects. Two subjects, 65 and 75 years of age, with dentulous in the maxilla, Kennedy Class I partially edentulous in the mandibular were selected for this experiment. Experimental apparatus. The experimental apparatus which was reported by Ogata et al. (1991) was used. It was made of two parts, one was the metal framework and the other was the denture base embedded with the transducers (Fig. 1). The metal framework had a steel bar which was connected with the framework parallel to the alveolar ridge and the Camper's plane. The denture base touched the steel bar only through the two loading points. Forces exerted on the denture base was conducted as follows; denture base -^ fixed part -^ loading points —» steel bar —* metal framework -^ abutment teeth. Two transducers, anterior transducer (Ant-Tr) and posterior transducer (Post-Tr) could detect lateral and vertical forces exerted on the loading point at same time. The signals from the transducers were amplified by the carrier amplifiers*. Moreover, vertical jaw movement was measured by the electric measuring apparatus of mandibular movementf, at same time. Analog signals from the apparatus were converted into digital signals (sampling clock period; 40ms), processed and stored on floppy discs using the signal processor^. Measurements. The subject was asked to sit in an upright position. Forces and vertical jaw movement were recorded during the following chewing activities; (i) chewing one dry-roasted peanut; (ii) chewing three pieces of carrot (6 x 6 x 6 mm); (iii) chewing two raisins; and (iv) chewing two pieces of sausage (10 x 10 x 10 mm). All subjects were asked to masticate on the transducer side. Forces were measured on several separate occasions up to 4 months from the insertion of new dentures.
Metal plate
Denture base / . . , /. * -r \ ^ Anterior transducer (Ant-Tr) Posterior transducer (Post-Tr) Stopper
Steel bar Loading point Fixed part Loading point Fig. I. A cross-section of the e.xperimental denture. * DPM-602A KYOWA Eleetronic Instruments Co., Ltd., Tokyo, Japan t Mandibular Kinesiograph K5AR, Myo-Tronies Research Inc., Seattle, WA, U.S.A. :|: 7T18, NEC San-ei Instruments Ltd., Tokyo. Japan
Torque exertion on abutment teeth
247
Analysis. Torque was evaluated on a direct abutment tooth. Torque around the vertical axis (lateral torque) (TL), torque around the lateral axis (vertical torque) (Tv), lateral force (FL) and vertical force (Fv) were calculated (Fig. 2). The direction of these forces corresponded to the movement of a terminal on the experimental dentures. Figure 3 shows the original waveforms and their processed waveforms which were computed from all sampling points of the original waveforms by the signal processor using the equations shown in Fig. 2. The maximal (peak) mean value of torque {Max. MT) of TL and Tv at the minimum of the interocclusal distance and its standard deviation were calculated from the peak level of all strokes of each processed waveforms. The integration value of torque (I) and time (T) from initiation of chewing to swallowing were obtained, and the average value of torque (Ave. T) was then calculated {Ave. T= I/T) (Fig. 4). Integration value was equal to the area which was surrounded with the waveform and the base line. The maximal (peak) mean value of force {Max. MF) and the average value of force {Ave. F) of FL and Fv were obtained in the same manner. Then, the average of Ave. T and Ave. F of measurements were obtained.
Buc.
(
Sagittal axis
c
Lateral axis
j
Fig. 2. Schematie presentation of torque and foree: A = loading point of Ant-Tr, P = loading point of Post-Tr; lateral foree ( = A L ) and vertical force (=Av) were deteeted by Ant-Tr, lateral foree ( = PL) and vertical force ( = Pv) were detected by Post-Tr; vertieal force (=Fv), lateral foree ( = F L ) , torque around the vertieal axis (lateral torque) ( = T L ) and torque around the lateral axis (vertieal torque) (Tv) were exerted on a direct abutment tooth.
248
K. Ogata et al. Processed data
Original data Lateral force
Torque
(x10"'kgm)
(N)
4
Buc. 2 0 0 Lin. 20-
10
20
30 (S)
(S) 30
20
10
Up 200 Down 20-
I 40Vertical force (N) 40-J Up 200Down 20-
Porce
Av 10
(S ) 30
20
rr|W||; ^
30 (S)
40 J
(N)
Pv
(N)
Up 20Down 2040-
10
20
n
1
T 30 (S)
Up 200 Down 20-
(S) 30
20
10
Fig. 3. Original data and proeessed data.
Max.MT Ave.T Baseline Ave.T Max.MT
L
: I
Fig. 4. Maximal (peak) mean value of torque {Ma.x. MT) was calculated from each processed waveforms. Average mean value of torque {Ave. T) was ealculated following the equation: Ave. T=\ (integration value)/T (time required for ehewing).
Torque exertion on abutment teeth
249
Results
Subject L Figure 5 shows the longitudinal changes of Max. MT and Max. MF in 1 Lateral Max i n l ddirection iti th day d subject 1. Max. MT was 10 x lO^-'kgm"' in the llingual on the of insertion of the new denture. As the period of wearing the denture proceeded, this value decreased, and changed to the buccal direction after 134 days. Vertical Max. MT decreased after 7 days, then became constant. The constant value was 2-5 X lO^^^kgm^' during chewing of food. Table 1 shows the average of Ave. T and Ave. F of all measurements in subject. 1. In the lateral direction, Ave. 7 was 1-8-2-9 (mean; 2-5) x 10~-^kgmss"' in the lingual and 0-5 x K r - \ g m s s ' in the buccal. In the vertical direction, Ave. 7 was 1-6-2-2 (mean; 1-9) x lO^^'kgmss ' in the downward and 0-3 x 10~-'kgmss"' in the upward. Ave. T in the lingual was 130% of it in the downward while Ave. F in the lingual was 60% of that in the downward. Subject 2. Figure 6 shows the longitudinal changes of Max. MT and Max. MF in subject 2. There are not remarkable changes of lateral Max. MT. The value of it was 10-20 X 10 ''kgm"' in the buccal direction. Vertical Max. MT decreased after 7 days, and the increase then became constant at a value of 5-10 x 10 \ g m ' in the
Max.MT Lateral
Peanuts
Carrot
20.
Raisin
20-,
40
120
§ IJ 10o I 20-
20-| 10-
20-|
(day) 10160
80
Sausage
40
80
160 120
1020-
10-
0
40
80
160 120
10-
0
40 80 120
0
40
160
1020-
20-
Vertical 80
120 160
Max.MP Lateral
Peanuts
Carrot
^ 20-,
20-
20-|
5 i 10- 0 8° 0-
10-
10-
11. 3
40 80
160 120
10-
I 20-
0
40 80 120
(day) 1020-
Sausage
Raisin
160
1020-
20-|
0
40 80 120
10-
160
r
0
40
80
0
40 80 120 160
120 160
1020-
Vertical
-^\'°]
20-
S §10- 0
10-
20-
40
80 120 160
0
40
80 120
20 n 10160 0
10-
10-
20-
20-
2C40 80 120 160
}^^~
Fig. 5. Longitudinal changes of Max. MT and Max. MF in subject 1.
10
250
K. Ogata et al.
Table 1. The average of Ave. T and Ave. F exerted on a direct abutment tooth in subjeet 1 Ave. F (N ss"^)
Ave. T { x l O - m kgss"^)
Peanuts Carrot Raisin Sausage
(
Lateral
Vertical
Lateral
Vertical
Bue.
Lin.
Down.
Up.
Bue.
Lin.
Down.
Up.
0-6 (0-8) 0-4 (0-4) 0-5 (0-4) 0-4 (0-2)
2-5 (1-4) 2-9 (1-5) 2-5 (1-7) 1-8 (0-7)
1-6 (0-7) 2-2 (0-9) 1-7 (0-7) 2-2 (0-5)
0-6 (0-3) 0-3 (0-1) 0-3 (0-1) 0-1 (0-1)
0-3 (0-4) 0-2 (0-2) 0-2 (0-1) 0-2 (0-1)
1-3 (0-7) 1-7 (1-2) 1-7 (1'5) 1-2 (0-6)
2-6 (1-4) 2-6 (1-5) 2-3 (1-4) 1-9 (0-7)
0-3 (0-3) 0-1 (0-1) 0-1 (0-1) 0-1 (0-1)
): S.D.
Table 2. The average of Ave. T and Ave. F exerted on a direct abutment tooth in subject 2 Ave. T (xlO -'k gm SS ') Vertieal
Lateral
Peanuts Carrot Raisin Sausage
Ave. F (N SS-') Lateral
Vertieal
Buc.
Lin.
Down.
Up.
Buc.
Lin.
Down.
Up.
8-2 (1-8) 7-7 (2-1) 8-0 (1-5) 6-8 (1-6)
0-1 (0-1) 0-2 (0-2) 0-2 (0-1) 0-2 (0-2)
2-2 (1-2) 2-5 (1-6) 2-8 (2-0) 1-8 (1-9)
0-3 (0-6) 0-2 (04) 0-3 (0-6) 0-3 (0-5)
5-4 (1-2) 4-8 (0-9) 4-6 (0-8) 3-8 (0-7)
0-1 (0-1) 0-1 (01) 01 (0-1) 0-1 (0-1)
3-2 (1-7) 3-3 (2-0) 3-6 (2-4) 2-7 (2-1)
0-1 (0-1) 0-1 (0-1) 0-1 (0-1) 0-1 (0-1)
): S.D.
downward direction. Table 2 shows the average of Ave. T and Ave. F of all measurements in subject 2. In the lateral direction, Ave. Twas 6-8-8-2 (mean; 7-7) x 10 kgm ss^' in the buccal and 0-2 x lO^'^kgmss"' in the lingual. In the vertical direction. 1-8-2-8 (mean; 2-3) x 10"^kgmss"' in the downward and 0 3 x 10 kgmss - 1 in the upward. Ave. T in the buccal was three or four times greater than downward while Ave. F in the buccal was one and one-half times greater than in the downward. Discussion The type of stress exerted on abutment teeth and edentulous mucosa was influenced by the design of dentures. In order to evaluate the design, it is desirable to assume that forces transmitted from denture base to metal framework is exerted only on a direct abutment tooth. If the design is simple, forces exerted on abutment teeth can
Torque exertion on abutment teeth
251
be calculated from a static point of view. However, if the design is complex, the results are likely to be groundless because they are based on many assumptions. Moreover, if the evaluation point such as a direct abutment tooth is determined, torque could be calculated as shown in Fig. 2. In Fig. 2, there are three kinds of torque around the lateral, vertical and sagital axes, and there are three directions of vectors of forces i.e. lateral, vertical and sagital. In this study, torque around the lateral and vertical axes, and vertical and lateral direction of forces were calculated from a static point of view using the results of the previous study (Ogata et al., 1991). The transducer of this study allowed the denture base to rotate slightly around the steel bar connected with the metal framework so as to eseape torque around the sagital axis. Lowe et al. (1970) computed the total daily potential energy (impulse of force) for swallowing force exerted on the flange of lower removable partial dentures. The impulse is an important factor, because a small value for such forces may not have mueh of an infiuenee on abutment teeth even if the stroke was of high magnitude. In this study, the average of torque and force were obtained. Max. MT and Max. ME as shown in Figs 5 and 6 were generated by oeelusal force. Therefore almost all oi Ave. Tin the lingual-downward (subject 1) or buccal-downward
Max.MT
S k 30 "o ^ 20 • ^ CO .5. 10
Sausage
Raisin
Carrot
Peanuts
Lateral
30-|
30-|
30-1
20-
20-
20-
10-
10-
0
0
40
80
120 160 (day)
0 0
40
80
120 160 10J 0
40
80
120 160
0
40
80
120 160
40
80
120 160
0
40
80
120 160
Vertical
Ifl
20-,
^ §10-
40
80 120 160
10-
40
80
120 160
10-
0
0-
10-
10-
2oJ
20-
Max.MF
i £5
Carrot
Peanuts
Lateral f 30-] ^ 20-
Raisin
30-| 20100
0 0
40
80
30 20100 0
120 160 (day)
Sausage
40
80
30-1
2010-
0
120 160
40
80
0
40
80
120 160
20-| 10- 0 120 160
40
80
120 160
120 160 10-
Vertical 0
40
80
120 160
20-
20-
10-
10-
0
40
80 120 160
0
40
80
S. § 1 0 -
10-
10-
10-
i 20-
20-
20-
20-
Fig. 6, Longitudinal changes of Max. MT and Max. MF in subjeet 2.
252
K. Ogata et al.
(subject 2) direction were generated by ocelusal force, and in the other directions were generated by tongue, cheeks or hps. In the vertical direction, the value of Ave. T generated by tongue, cheeks or hps was 10—20% of that generated by ocelusal force and the value of Ave. F generated by tongue, cheeks or lips was 5—10% of that generated by occiusal force in subjects 1 and 2. In the lateral direction, the value of Ave. T generated by tongue, cheeks or lips was 20% of that generated by occiusal force in subject 1 while the value was less than 3% in subject 2. The value of Ave. F generated by tongue, cheeks or hps was 15% of that generated by the occiusal force in subject 1 and the vahie was less than 2% in subject 2. It is suggested that not only occiusal force but also tongue, cheeks and hps contribute generating torque and forces exerted on abutment teeth. In order to reduce vertical torque exerted on an abutment teeth, a number of improvements in design of dentures have been proposed e.g. I-bar clasp system (Kratochvil, 1963; Krol, 1973) or attachments which allow the denture base to move vertically. (Preiskel, 1979). However lateral torque also needs to be considered; in the clinic it should be noted that the lateral torque transmitted to a abutment tooth was 1-3—4 times as much as that in the vertical. References Influence of occiusal rest position and clasp design on movement of abutment iccth. Jottrnal of Prosthcllc Dentistry. 13. 114. KKOL. A..I. (1973) Clasp design lor extension-base removable partial dentures. Journal of Prosthetic
KKATOCHVIL. F . J . ( 1 % 3 )
Dentistry. 29. 40,S.
LowH. R.D.. KYDD. W . L . & SMITH. D . E . (1970) Swallowing and resting forces related to lingual flange thickness in removable partial dentures. Journal of Prosthetic Dentistrv, 23. 279. Oci.viA. K. & SHIMI/U, K. (1991) Longitudinal study on forces transmitted from denture base to retainers of lower tree-end saddle dentures with Aker's elasps. Journal of Oral Rehabilitation. 18. 471. PKHSKI-L. H . W . (1979) Precision attachments in dentistry, third edition, pp. 109-155. Henry Kimpton Ltd. London. SriiWART. K.L.. RuoD. K.D. & KUEBKHK, W . A . (1983) Clinical removable partial prosthodontics, pp. 94-112. C.V. Mosby Company. St. Louis. Toronto and London.
