J Oral Maxillofac 49:1074-1078,
Surg
1991
Does Prestretching StainlessHave Any Clinical Signific RICHARD H. HAUG, DDS,* JON P. BRADRICK,
DDS,g AND MAR%LYN S
Clinical parameters of prestretch and tensi,on forces plaeed on stainlesssteel wire by 20 oral and maxillofacial surgeons were obtained. Unstretched wire was clinically as tough or tougher than prestretohed wire of a similar gauge. Both prestretched and unstretched wires, twisted to their maximum, loosened when under tension. As the prestretch forces increased, the clinical strength of the wire diminished.
For decades, use of stainless-steel wire has been the foundation for management of facial trauma and reconstructive surgery by oral and maxillofacial surgeons, yet in 48 volumes of the ./our& of Oral and Maxillofacial Surgery, only two publications have dealt with the physical properties of this material.‘,’ We wished to ascertain the forces exerted by the surgeon when stretching wire and then to determine whether prestretched and unstretched wire differ in toughness and strength.
force placed on a wire when an arch bar is being ligated to the teeth (Fig 2). The data were recorded and used to determine the mean and SD for prestretch and tension forces. Sixty-centimeter lengths of 22- and 24-gauge stainless-steel wire (Miltex, Lake Success, NY) were then prestretched using the mean force, 1 SD below the mean, and 1 SD above the mean as determined from the surgeon population. Unstretched and prestretched groups of 22- and 24-gauge wire were then suspended from a ring stand. .A needle holder was attached to each wire at a distance of 5 cm from the ring. Weights were suspended from the needle holder, re,presenting the mean tension force, 1 SD below the mean, and I SD above the mean of the predetermined tension force. The wires were then twisted clockwise until they ,broke. The number sf turns per centimeter for 10 trials in each group was recorded. Another set of 22- and 24-gauge stait&ss-steel wires was prestretched at the mean force and at B SD below the mean and 1 SD above the mean, and samples were suspended from the ring stand as previously described. Weights representing the mean tension force were suspended 5 cm below the ring, and the wires were twisted clockwise, two turns less than the mean breaking point. Weigkts were then incrementally suspended until a breaking point was reached. The results of 10 trials in e.ach group were recorded. The means and SD for 10 trials in each group were derived. To test the toughness of a particular wire, two-way analysis of variance (ANOVA) was used to identify the effect of stretch force, tension force, and the interaction effect between them. If sigmficant effects were found (P < .05), one-way
Materials and Methods Twenty oral and maxillofacial surgeons were used to determine the clinical parameters of force exerted on wires during stretching. Each surgeon was asked to prestretch a 60-cm length of 22-gauge stainless-steel wire with wire holders. After this exercise, the surgeons were asked to exert the same amount of force across an identical 60-cm span using the same wire holders. This force was measured with a spring balance and recorded (Fig 1). Next, the surgeons were asked to exert tension upon a stationary spring balance designed to represent the
Received from Case Western Reserve University, Cleveland. * Assistant Professor of Surgery, Cleveland Metropolitan General Hospital, and the Case Western Reserve University. t Assistant Professor of Surgery, Cleveland Metropolitan General Hospital, and the Case Western Reserve University. $ Statistical Consultant, Case Western Reserve University. Address correspondence and reprint requests to Dr Haug: Oral and Maxillofaciaf Surgery, Cleveland Metropolitan General Hospital, 3395 Scranton Rd, Cleveland, OH 44109. 0 1991 American Association of Oral and Maxillofacial
Sur-
geons 0278-2391/91/4910-0008$3.00/O
1074
HAUG, BRADRICK,
AND SU
%075
FIGURE 1. Determination of clinical prestretching forces with a self-recording spring balance.
ANQVA was used to examine the differences among the levels of these significant effects. To test the strength of a particular wire after it was twisted at the mean tension force, one-way ANOVA was used to explore the differences of the four stretch treatments.
R&SNS
There was a high degree of variability in both the prestretch and tension forces exerted by the 20 surgeons (Fig 3). The mean prestretch force was 12.44 t 4.34 kg (range, 5.90 to 22.7 kg). The mean tension force was 3.55 + 1.03 kg (range, 2.73 to 5.06 kg). T~UGHE~ESS Toughness is a term used in evaluating biomaterials to define the property of being difficult to break.’ Our definition of clinical toughness was the number of turns per centimeter required to break
FIGURE 2. Stationary selfrecording spring balance designed to measure forces applied to wire during arch bar ligation.
the wire. A high degree of consistency was noted between aH subgroups in a particular gauge csf wire. The mean turns per centimeter for all prestretched 22-gauge wire showed remarkable consistency (Table I). Two-way ANBVA results showed no significant difference in toughness due to tension force [F(2,119) = .63, B < 541 and no interaction between stretch and tension forces [F(6, BWI = .83, P < ,561; however, there was a signifnc&nt difference due to stretch forces [F(3,119) = 18.72, P < .OOl]. There were no digerences between th;e three prestretched groups [F(2,89) = .W, P < 1B]. There was a difference between the unstretched group and the three prestretched groups [F(l,l19) = 57.73, P < .OOB].The magnitude of the difference was such that the uns&etched wire had a mean todghness of 5.48 F 0.20 turns per centimeter, whereas al4 of the prestretched groups had an average toughness of 5.10 1 0.26 turns per cehtimeaer. The mean turns per ceratimeter foFBpB_ a19 prestretched 24-gauge wire also showed remarkable consistency (Table 2). ‘Results of two-way ANOVA of the 24-gauge wire showed a significant difference in toughness due to stretch forces [F(3,$19> =
1076
SlTAPNLESS STEEL
PRESTRETCWING
FIGURE 3. and prestretch per surgeon, prestretch.
TF RH JS BS MH AH RH CS-EP
WIRE
Wire tension ,(in kilograms) 1, Tension; El,
JB JG RS RS RD RD SF JO MP ON A!
SURGEON 18.76, P < .OOl] and the interaction between tension and stretch forces [F(6,119) = 5.95, P < .001]; however, there was no significant difference due to tension force [F(2,119) = 0.56, P < .57]. The interaction effect signifies that the 24-gauge wire treated by the four stretch forces reacted differently to the three tension forces. Figure 4 indicates that the toughness of a 24gauge unstretched wire increased significantly as tension force increased, whereas the toughness of the prestretched wires, in general, decreased or remained constant as the tension force increased. The wire prestretched with a force 1 SD below the mean was the least tough among both unstretched and prestretched groups for every tension force. I.Jnstretched 24-gauge wire was tougher than its prestretched counterpart when the tension force was 1 SD above the mean; however, it was less tough than wire prestretched with a force of 1 SD above the mean, when the tension force was 1 SD below the mean (Fig 4). There were no significant differences between the unstretched wire and the wire prestretched with a force 1 SD above the mean and at
the mean when the tension force was at the mean [F(2,29) = 0.93, P < .41].
Table 1. Toughness of 22.Gauge Wire in Mean Turns per Centimeter
Table 2. Toughness of 24.Gauge Wire in Mean Turns per Centimeter
STRENGTH Strength is a term used in evaluating biomaterials that describes the maximal force required to fracture a structure.’ Our definition of strength was the weight required to break a near-maximally ,turned wire. In each of the 80 trials in this portion, of the study, the loop of wire adapted to the ring stand increased its circumferential length 20% to 30% before breaking when placed under tension. The results of one-way ANOVA showed a significant difference between the unstretched and prestretched groups for both 22-gauge wire [F(3,39) = 7.41, P < .OOl] and 24-gauge wire [F(3,39) = 166.79, P < .001]. The mean strength (in kilograms) for both the 22- and 24-gauge wire ~83 essentially the same for the unstretched wire and the wire prestretched with a force 1 SD below the mean (Tables 3 and 4). There was a significant difference between the prestretched groups for both 22gauge wire
Tension Force 1 SD Below Mean
Tension
Tension Force
1SD
1 SD Above Mean
Tension
Mean
Tension
Mean
Below Tension
1 SD Above Mean
Tension
Mean
Tension
Stretch Force
(2.52kg)
(3.55 kg)
(4.58 kg)
Stretch Force
(2.52 kg)
(3.55 kg)
(4.58 kgj
Unstretched Prestretched 1 SD below mean (8.10 kg) Prestretched mean (12.44 kg) Prestretched 1 SD above mean (16.78 kg)
5.43 % 0.18
5.60 -t 0.25
5.41 ? 0.15
6.63 AZ0.15
6.79 2 0.17
7.08 f 0.16
5.02 r 0.42
5.09 f 0.22
5.18 f 0.40
6.53 2 0.37
6.44 i 0.10
6.36 + 0.34
5.12 2 0.36
5.09 +- 0.17
5.05 -t 0.13
6.72 -t 0.09
6.67 f 0.13
6.73 * 0.09
5.09 +- 0.27
5.13 2 0.23
5.12 c 0.23
Unstretched Prestretched 1 SD below mean (8.10 kg) Prestretched mean (12.44 kg) Prestretched 1 SD above mean (16.78 kg)
6.92 ? 0.27
6.71 + 0.24
6.62 r 0.19
Values are mean 2 SD.
Values are mean 2 SD.
WAUG,
BRADRfCK,
1077
AND SU
FIGURE 4. Interaction plot of the stretch force and tension force to the toughness of the 24”gauge wire. e Prestretched 1 SD below mean; e prestretched mean; @3,unstretched; -&, prestretched B SD above mean.
a
6.4
IJ s
6.2 1 SD
(TlJrl-U/CITI)
Below
Mean
Mean
It is of interest that one of the materials most frequently used by oral and maxillofacial surgeons has received so little attention in the literature. kemmons and Ming in 19’77 provided a detailed discussion of the metallurgic properties of stainlesssteel wires and the rationale for and against prestretching’ ; however, their article was a literature review and provided no definite conclusions. In 1989, Colm and Farish provided an excellent dissertation on the physical properties of 25gauge stainless-steel wire and the changes that occur with prestretching.2 This study was based on a sample of six
prestretched wires and three controls, without a known degree of prestretching force. The results sf the study provided a description of the changes in physical properties for industrial application but not for the clinical setting. The clinical concerns about stamless-steel wire are breakage during application and loosening or breakage during fixation. More than 400 wires were twisted and broken during our pilot studies, and during this experiment some very clear observations and conclusions regarding the clinical properties of stamless-steel wire were made. When a chnical study is performed, the parameters de&red by the population to be investigated must be derived. Because the prestretching and tension forces obtained from the 20 oral and maxillofacial surgeons in our study showed great variation (Fig 39, differences in clinical effects could be expected. These differences were most obvious in determining the clinical strength (Table 3). Virtually no difference existed between the unstretched samples and the prestretched samples Ii SD below the mean force, whereas greater prestretching forces resulted in significant differences. Toughness in our study would represent the breaking of wires during application of arch bars or final tightening after direct bone wiring. Our study showed that unstretched wire 'wasas tough or tougher than prestretched wn-e of a similar gauge.
Table 3. Strength of 22-Gauge Wire After Mean Tewsion and Twisting
Table 4. Strength of 24.fhuge Mean Tension and Twisting
and 24-gauge wire Use of the Scheffe multiple comparison method to examine the difference between the prestretched groups’ mean strength shswed that the mean strength of the 22gauge wire prestretched with a force 1 SD above the mean was significantly different that that of wire prestretched with other forces. In addition, the strength of the 24-gauge wire differed significantly among al prestretched groups. In general, the mean strength decreased as the prestretching force increased, and the wire prestretcbed with a force 1 SD above the mean was significantly less strong than all other groups. [F(2,29)
[F(2,29)
=
=
11.78,
177.47,
P
Surg
1991
Does Prestretching StainlessHave Any Clinical Signific RICHARD H. HAUG, DDS,* JON P. BRADRICK,
DDS,g AND MAR%LYN S
Clinical parameters of prestretch and tensi,on forces plaeed on stainlesssteel wire by 20 oral and maxillofacial surgeons were obtained. Unstretched wire was clinically as tough or tougher than prestretohed wire of a similar gauge. Both prestretched and unstretched wires, twisted to their maximum, loosened when under tension. As the prestretch forces increased, the clinical strength of the wire diminished.
For decades, use of stainless-steel wire has been the foundation for management of facial trauma and reconstructive surgery by oral and maxillofacial surgeons, yet in 48 volumes of the ./our& of Oral and Maxillofacial Surgery, only two publications have dealt with the physical properties of this material.‘,’ We wished to ascertain the forces exerted by the surgeon when stretching wire and then to determine whether prestretched and unstretched wire differ in toughness and strength.
force placed on a wire when an arch bar is being ligated to the teeth (Fig 2). The data were recorded and used to determine the mean and SD for prestretch and tension forces. Sixty-centimeter lengths of 22- and 24-gauge stainless-steel wire (Miltex, Lake Success, NY) were then prestretched using the mean force, 1 SD below the mean, and 1 SD above the mean as determined from the surgeon population. Unstretched and prestretched groups of 22- and 24-gauge wire were then suspended from a ring stand. .A needle holder was attached to each wire at a distance of 5 cm from the ring. Weights were suspended from the needle holder, re,presenting the mean tension force, 1 SD below the mean, and I SD above the mean of the predetermined tension force. The wires were then twisted clockwise until they ,broke. The number sf turns per centimeter for 10 trials in each group was recorded. Another set of 22- and 24-gauge stait&ss-steel wires was prestretched at the mean force and at B SD below the mean and 1 SD above the mean, and samples were suspended from the ring stand as previously described. Weights representing the mean tension force were suspended 5 cm below the ring, and the wires were twisted clockwise, two turns less than the mean breaking point. Weigkts were then incrementally suspended until a breaking point was reached. The results of 10 trials in e.ach group were recorded. The means and SD for 10 trials in each group were derived. To test the toughness of a particular wire, two-way analysis of variance (ANOVA) was used to identify the effect of stretch force, tension force, and the interaction effect between them. If sigmficant effects were found (P < .05), one-way
Materials and Methods Twenty oral and maxillofacial surgeons were used to determine the clinical parameters of force exerted on wires during stretching. Each surgeon was asked to prestretch a 60-cm length of 22-gauge stainless-steel wire with wire holders. After this exercise, the surgeons were asked to exert the same amount of force across an identical 60-cm span using the same wire holders. This force was measured with a spring balance and recorded (Fig 1). Next, the surgeons were asked to exert tension upon a stationary spring balance designed to represent the
Received from Case Western Reserve University, Cleveland. * Assistant Professor of Surgery, Cleveland Metropolitan General Hospital, and the Case Western Reserve University. t Assistant Professor of Surgery, Cleveland Metropolitan General Hospital, and the Case Western Reserve University. $ Statistical Consultant, Case Western Reserve University. Address correspondence and reprint requests to Dr Haug: Oral and Maxillofaciaf Surgery, Cleveland Metropolitan General Hospital, 3395 Scranton Rd, Cleveland, OH 44109. 0 1991 American Association of Oral and Maxillofacial
Sur-
geons 0278-2391/91/4910-0008$3.00/O
1074
HAUG, BRADRICK,
AND SU
%075
FIGURE 1. Determination of clinical prestretching forces with a self-recording spring balance.
ANQVA was used to examine the differences among the levels of these significant effects. To test the strength of a particular wire after it was twisted at the mean tension force, one-way ANOVA was used to explore the differences of the four stretch treatments.
R&SNS
There was a high degree of variability in both the prestretch and tension forces exerted by the 20 surgeons (Fig 3). The mean prestretch force was 12.44 t 4.34 kg (range, 5.90 to 22.7 kg). The mean tension force was 3.55 + 1.03 kg (range, 2.73 to 5.06 kg). T~UGHE~ESS Toughness is a term used in evaluating biomaterials to define the property of being difficult to break.’ Our definition of clinical toughness was the number of turns per centimeter required to break
FIGURE 2. Stationary selfrecording spring balance designed to measure forces applied to wire during arch bar ligation.
the wire. A high degree of consistency was noted between aH subgroups in a particular gauge csf wire. The mean turns per centimeter for all prestretched 22-gauge wire showed remarkable consistency (Table I). Two-way ANBVA results showed no significant difference in toughness due to tension force [F(2,119) = .63, B < 541 and no interaction between stretch and tension forces [F(6, BWI = .83, P < ,561; however, there was a signifnc&nt difference due to stretch forces [F(3,119) = 18.72, P < .OOl]. There were no digerences between th;e three prestretched groups [F(2,89) = .W, P < 1B]. There was a difference between the unstretched group and the three prestretched groups [F(l,l19) = 57.73, P < .OOB].The magnitude of the difference was such that the uns&etched wire had a mean todghness of 5.48 F 0.20 turns per centimeter, whereas al4 of the prestretched groups had an average toughness of 5.10 1 0.26 turns per cehtimeaer. The mean turns per ceratimeter foFBpB_ a19 prestretched 24-gauge wire also showed remarkable consistency (Table 2). ‘Results of two-way ANOVA of the 24-gauge wire showed a significant difference in toughness due to stretch forces [F(3,$19> =
1076
SlTAPNLESS STEEL
PRESTRETCWING
FIGURE 3. and prestretch per surgeon, prestretch.
TF RH JS BS MH AH RH CS-EP
WIRE
Wire tension ,(in kilograms) 1, Tension; El,
JB JG RS RS RD RD SF JO MP ON A!
SURGEON 18.76, P < .OOl] and the interaction between tension and stretch forces [F(6,119) = 5.95, P < .001]; however, there was no significant difference due to tension force [F(2,119) = 0.56, P < .57]. The interaction effect signifies that the 24-gauge wire treated by the four stretch forces reacted differently to the three tension forces. Figure 4 indicates that the toughness of a 24gauge unstretched wire increased significantly as tension force increased, whereas the toughness of the prestretched wires, in general, decreased or remained constant as the tension force increased. The wire prestretched with a force 1 SD below the mean was the least tough among both unstretched and prestretched groups for every tension force. I.Jnstretched 24-gauge wire was tougher than its prestretched counterpart when the tension force was 1 SD above the mean; however, it was less tough than wire prestretched with a force of 1 SD above the mean, when the tension force was 1 SD below the mean (Fig 4). There were no significant differences between the unstretched wire and the wire prestretched with a force 1 SD above the mean and at
the mean when the tension force was at the mean [F(2,29) = 0.93, P < .41].
Table 1. Toughness of 22.Gauge Wire in Mean Turns per Centimeter
Table 2. Toughness of 24.Gauge Wire in Mean Turns per Centimeter
STRENGTH Strength is a term used in evaluating biomaterials that describes the maximal force required to fracture a structure.’ Our definition of strength was the weight required to break a near-maximally ,turned wire. In each of the 80 trials in this portion, of the study, the loop of wire adapted to the ring stand increased its circumferential length 20% to 30% before breaking when placed under tension. The results of one-way ANOVA showed a significant difference between the unstretched and prestretched groups for both 22-gauge wire [F(3,39) = 7.41, P < .OOl] and 24-gauge wire [F(3,39) = 166.79, P < .001]. The mean strength (in kilograms) for both the 22- and 24-gauge wire ~83 essentially the same for the unstretched wire and the wire prestretched with a force 1 SD below the mean (Tables 3 and 4). There was a significant difference between the prestretched groups for both 22gauge wire
Tension Force 1 SD Below Mean
Tension
Tension Force
1SD
1 SD Above Mean
Tension
Mean
Tension
Mean
Below Tension
1 SD Above Mean
Tension
Mean
Tension
Stretch Force
(2.52kg)
(3.55 kg)
(4.58 kg)
Stretch Force
(2.52 kg)
(3.55 kg)
(4.58 kgj
Unstretched Prestretched 1 SD below mean (8.10 kg) Prestretched mean (12.44 kg) Prestretched 1 SD above mean (16.78 kg)
5.43 % 0.18
5.60 -t 0.25
5.41 ? 0.15
6.63 AZ0.15
6.79 2 0.17
7.08 f 0.16
5.02 r 0.42
5.09 f 0.22
5.18 f 0.40
6.53 2 0.37
6.44 i 0.10
6.36 + 0.34
5.12 2 0.36
5.09 +- 0.17
5.05 -t 0.13
6.72 -t 0.09
6.67 f 0.13
6.73 * 0.09
5.09 +- 0.27
5.13 2 0.23
5.12 c 0.23
Unstretched Prestretched 1 SD below mean (8.10 kg) Prestretched mean (12.44 kg) Prestretched 1 SD above mean (16.78 kg)
6.92 ? 0.27
6.71 + 0.24
6.62 r 0.19
Values are mean 2 SD.
Values are mean 2 SD.
WAUG,
BRADRfCK,
1077
AND SU
FIGURE 4. Interaction plot of the stretch force and tension force to the toughness of the 24”gauge wire. e Prestretched 1 SD below mean; e prestretched mean; @3,unstretched; -&, prestretched B SD above mean.
a
6.4
IJ s
6.2 1 SD
(TlJrl-U/CITI)
Below
Mean
Mean
It is of interest that one of the materials most frequently used by oral and maxillofacial surgeons has received so little attention in the literature. kemmons and Ming in 19’77 provided a detailed discussion of the metallurgic properties of stainlesssteel wires and the rationale for and against prestretching’ ; however, their article was a literature review and provided no definite conclusions. In 1989, Colm and Farish provided an excellent dissertation on the physical properties of 25gauge stainless-steel wire and the changes that occur with prestretching.2 This study was based on a sample of six
prestretched wires and three controls, without a known degree of prestretching force. The results sf the study provided a description of the changes in physical properties for industrial application but not for the clinical setting. The clinical concerns about stamless-steel wire are breakage during application and loosening or breakage during fixation. More than 400 wires were twisted and broken during our pilot studies, and during this experiment some very clear observations and conclusions regarding the clinical properties of stamless-steel wire were made. When a chnical study is performed, the parameters de&red by the population to be investigated must be derived. Because the prestretching and tension forces obtained from the 20 oral and maxillofacial surgeons in our study showed great variation (Fig 39, differences in clinical effects could be expected. These differences were most obvious in determining the clinical strength (Table 3). Virtually no difference existed between the unstretched samples and the prestretched samples Ii SD below the mean force, whereas greater prestretching forces resulted in significant differences. Toughness in our study would represent the breaking of wires during application of arch bars or final tightening after direct bone wiring. Our study showed that unstretched wire 'wasas tough or tougher than prestretched wn-e of a similar gauge.
Table 3. Strength of 22-Gauge Wire After Mean Tewsion and Twisting
Table 4. Strength of 24.fhuge Mean Tension and Twisting
and 24-gauge wire Use of the Scheffe multiple comparison method to examine the difference between the prestretched groups’ mean strength shswed that the mean strength of the 22gauge wire prestretched with a force 1 SD above the mean was significantly different that that of wire prestretched with other forces. In addition, the strength of the 24-gauge wire differed significantly among al prestretched groups. In general, the mean strength decreased as the prestretching force increased, and the wire prestretcbed with a force 1 SD above the mean was significantly less strong than all other groups. [F(2,29)
[F(2,29)
=
=
11.78,
177.47,
P
