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Stress transmitted through mouth protectors
S tr e s s tra n s m itte d
th ro u g h
m o u th
W illiam C. Godwin, DDS, MS Robert G. Craig, PhD, Ann Arbor, Mich
B rittle lacquer coatings on m axillary models were used to evaluate the effectiveness of mouth pro tectors in protecting the teeth from strain as a re su lt of im pact blows. Among the mouth protectors found to be most effective are the mouth-formed ones.
In our previous paper,1 the physical properties of custom-made mouth protectors were described. This paper also reviews the surveys and studies conducted to evaluate the effectiveness of the various types of mouth protectors. The reports in the literature were not in complete agreement with respect to the superiority of mouth-formed or stock-tray and the custom-made protectors based on the incidence of injuries, although all of the mouth protectors studied reduced oral in juries. Also, the values for energy absorption and hardness of the custom-made protectors did not definitely indicate which material would transfer the lowest strain or stress to the teeth from an im pact on the protector.1 A brittle lacquer technic2 was used to study surface strain and stress in bone:!~5 and dental restorations6 under load. The purpose of this in vestigation was to use the brittle coating technic to evaluate the effectiveness of mouth protectors.
p ro te c to rs
The acrylic casts were sprayed first with a lac quer containing aluminum powder. After the aluminum lacquer dried, the casts were sprayed with the appropriate lacquert depending on the tem perature and humidity during testing. The sprayed casts then were allowed to dry in air for a half hour and dried overnight at 37 C. The casts were removed from the oven the next day, at least one hour before testing, and allowed to reach equilibrium at room temperature. The sensi tivity of the lacquer was about 800/x inches/inch. The mouth protector was placed carefully on the model, and the assembly was mounted secure ly to the base of an impact tester.^ The pendulum, to which a 0.75-inch diam eter ball bearing had been attached, was released at an angle 60° from the vertical position, and the ball was allowed to strike the mouth protector (Fig 1). The angle of rebound of the pendulum was measured in all instances except when the teeth were fractured and the pendulum arm was caught before a sec ond impact occurred. Each mouth protector was tested in three regions: the labial surfaces of the maxillary central incisors, and the right and left buccal interproximal regions between the second premolar and first molar. In all tests, the cast was mounted so that the ball would strike the mouth protector halfway between the gingival and occlu sal or incisal surfaces. Two of each type of mouth protector were tested by use of a total of 20 lacquer-coated casts for each mouth protector. After the impact of the pendulum, the mouth protector was removed from the cast, and the ex tent and position of cracking or flaking of the
Materials and methods Acrylic and dental stone maxillary casts were pre pared in a rubber mold.* Whenever possible, the mouth protectors were fabricated on the acrylic casts to be used during testing. When this could not be done because of processing procedures, the mouth protector was prepared on a stone cast and transferred to an acrylic cast for testing. 1316
Fig 1 ■ Brittle lacquer-coated model with mouth protector in position being struck by impact blow.
Fig 2 ■ Brittle lacquer crack pattern after impact to anterior portion of mouth protector. la c q u e r w as o b serv ed . T en sile stra in w as in d ic ated by c ra c k s in the lacq u er, a n d th e d ire c tio n o f th e s tra in w as n o rm a l to th e d ire c tio n o f th e crack s. C o m p re ssiv e stra in w as in d ic a te d b y are as w h e re th e la c q u e r h a d loo sen ed fro m th e cast. T h e cra ck s o r flakes a p p e a re d w hen th e su rfa ce stra in w as m o re th a n 8 0 0 ¡x inches/inch. C ra c k s in th e la c q u e r co v e rin g th e rig h t c e n tra l inciso r show th a t th e ten sile stra in w as in th e d ire c tio n o f th e lo n g axis o f th e to o th (F ig 2). Q u a lita tiv e g rad in g o f th e su rfa ce stra in w as e sta b lish e d b y c o m p a rin g th e a p p e a ra n c e o f th e la c q u e r co a tin g (F ig 3, 4). T h e g ra d in g ran g e d fro m A w ith th e le ast su rfa ce stra in tra n s fe rre d to
th e te e th o f th e m o d e l to E w ith th e g re a te st s u r face stra in tra n sfe rre d . A re a s w h ere flak in g o c c u rre d a re in d ic a te d by c ro ssh a tc h in g , a n d crack s are show n as lines. T h e m o u th p ro te c to rs th a t w ere u se d in the stu d y w ere p re p a re d in th e fo llo w in g m a n n er. A u ste n a l (A u s te n a l C o .): T h e m o u th p ro te c to r w as fo rm e d fro m a 6 -in c h sq u a re sh e e t on a sto n e ca st u n d e r h e a t a n d 3 0 lb/sq in p re ss u re by u se o f th e A u ste n a l M ic ro fo rm P ress. A fte r th e p r o te c to r w as co o led , th e excess m a te ria l w as trim m ed . D e fe n d e r (L a c to n a ): T h e tw o -lay e r silico n e sh e et fin g er w as p re sse d o n to an ac ry lic ca st u n til w ell ad a p te d . I t w as h e a te d o n a sto n e c a st fo r 20 m in u tes in an o v en a t 177 C an d tra n s fe rre d to an acry lic c a st a fte r it w as co o led to ro o m te m p e ra tu re. E sta n e (B. F . G o o d ric h C o .): E x p e rim e n ta l m a te ria ls 5 7 4 0 1 , 5 7 4 0 7 , a n d 5 7 4 0 1 0 w ere su p p lied in 6 -in ch sq u a re sh eets a n d w ere fa b ric a te d by th e m e th o d u sed fo r A u ste n a l m o u th p ro te c to rs. F e a th e rb ite (F e a th e rla x C o rp .): T h e p re fo rm e d h o rsesh o e tra y w as so ften e d in 9 6 to 9 9 C w ate r fo r 3 to 5 m in u tes a n d w as p ressed o n to th e a c ry l ic c a st by fin g er p re ssu re . T h e m o u th p ro te c to r w as co o led to ro o m te m p e ra tu re w h ile in p o s i tio n o n th e cast.
A N T E R IO R LINGUAL
LABIAL
POSTERIOR BUCCAL
A OCCLUSAL
f in ih ï A
B
Fig 3 ■ Types of brittle lacquer crack patterns seen after impact loading in posterior region.
Fig 4 ■ Types of brittle lacquer crack patterns seen after impact in anterior region.
Godwin—Craig: STRESS TRANSMITTED THROUGH MOUTH PROTECTORS ■ 1317
Gardex (The Hygiene D ental M anufacturing Co.): The latex was paini&l on the acrylic cast, air-dried for 18 hours at room temperature* heat ed to 71 C for one hour, and then removed from the cast before it was boiled in water for 15 minutes. Jectron (Austenal Co.): These m outh protectors were fabricated on stone casts by the Austenal Company and were trimmed to a horseshoe shape on receipt. Pro-Tex (Pro-Tex Inc.): A 4-inch square sheet was softened in 96 to 99 C water for 3 to 5 minutes and adapted onto the acrylic cast by fin ger pressure. The mouth protectors were allowed to cool on the cast and then were trimmed to shape. Shield (Roberts Dental M anufacturing Co., Inc.): Single powder and liquid units were mixed until uniform; when the dough consistency was reached, it was packed into the accompanying flexible tray. The filled tray was pressed onto the stone cast with finger pressure, and it remained on the cast until it was polymerized. Sta-Guard (Stalite, Inc.): A 5-inch square sheet was softened in 96 to 99 C water for 3 to 5 m in utes and was vacuum-formed7 on an acrylic cast, , cooled to room temperature under vacuum, and finally trimmed.
Results The thicknesses of the mouth protectors in the buccal and labial regions are listed in Table 1. The thickness in the buccal region varied from 1.0 to 4.0 mm and in the labial region from 1.1 to 5.3 mm. The Featherbite protectors were the thickest and the Estane materials were the thinnest of the mouth protectors. The thickness of the Gardex protectors varied from 1.4 to 1.9 mm, and the thickness of the Jectron protectors was about 1.6 mm. The remaining protectors had thicknesses of 2.1 to 2.8 mm. The percentage o f the impact energy absorbed by the mouth protectors mounted on the models is shown in Table 2. The thick latex mouth pro tector (Gardex) absorbed the lowest percentage of the im pact energy (50% to 60% ), and the Shield protector absorbed the greatest amount of the impact (92% ). The mouth protectors fabricated from polyurethane absorbed 80% to 85% of the impact whereas those fabricated from polyethylene-polyvinylacetate absorbed about 7 5 % . O f 1318 ■ JADA, Vol. 77, December 1968
Table 1 ■ A ve ra g e th ic k n e s s o f m outh p ro te c to rs . Buccal region mm
Labial region mm
Austenal
2.3
2.1
Defender
2.5
Estane 574010
2.2 1.2 1.2 1.0
Featherbite
4.0
5.3
Gardex, thin
1.4
1.7
Gardex, thick
1.7
1.9
Jectron
1.6
1.7
Pro-Tex
2.4
2.2
Shield
2.4
2.7
Sta-Guard
2.6
2.8
Mouth protector
Estane 57401 Estane 57407
1.1 1.4
1.1
Table 2 ■ Energy absorption of mouth protectors on models during im pact.* Buccal region Average %
Labial region Average %
Austenal
85
82
Defender
81
84
Estane 57401
81
80
Estane 57407
83
80
Estane 574010
83
81
Mouthguard
Featherbite
68
60
Gardex, thin
63
63
Gardex, thick
50
60
Jectron
85
79
Pro-Tex
77
80
Shield
92
92
Sta-Guard
72
78
•Percentage of energy absorption = EP—EF X100 where Ep= potene; tial energy and EF=energy of rebound. EF=WL (1 —cos 0) where W and L are the pendulum weight and length, respectively, and 0 is the rebound angle.
the tray-formed type, the Featherbite mouth p ro tector absorbed the least and the Shield protector the greatest amount of energy from the impact. It is apparent that there is no direct correlation between the amount of energy absorption and the thickness of the mouth protector. The distribution of the type of brittle lacquer crack pattern on the teeth of the models protected by the various mouth protectors is shown in Table 3. In most instances, different tests with the same mouth protector showed a range of crack pat
Table 3 ■ Percentage distribution of the type of lacquer crack patterns observed in various regions after impact loading. Impact in posterior region Buccal A
rack pattern
B
C
Impact in anterior region
A
D
B
C
Lingual
Labial
Occlusal D
A
B
D
c
D
E
A
B
0 20 10 50 20
0
0 10 40 50
C
E
1outh protector 20 15 30 35
5 20 30 45
Austenal Defender
85 15
0
0
Estane 57401
25 50 25
0
0
Estane 57407
10 40 40
Featherbite
10 50 30 10 0
100
10
0 40 60
50 15 25 10
Gardex, thick
Pro-Tex Shield Sta-Guard
0
60 25 15
0
0 15 40 45 60 25
1
Jectron
0
10 15 25 50 75 10 15
0
10 60 30
0
0
0 20 50 20 10
0 10 45 45
0
0
0 20 80
0 15
0 20 65
0
0
0 20 80
0
0 50 50
0
0
0
0 100
50 50
0
0
0
75
0
0
0
0 60 40
0
0
0 25 50 25
0
0
0 25
0
0
0
0 50 50
0
0
0 10 90
0
0 10 20 70
15 70 0
0 30 70
5
5 20 70
50
15 20 15
0 20 60 20
0
0 35 20 45
45
15 30 10
10 70 10 10
0
20 60 20
0
0
10 10 30 50
15
15 40 30
0 70 10 20
0
40 10 10 40
0
Anterior region
Posterior region
1.2
2.3 4.0
Estane 574010 Estane 57407
1.3 1.4
2
Estane 57401 Austenal Pro-Tex
1.4 2.0 2.2
4.7 3.0 3.7
3
Gardex, thin Gardex, thick Defender
2.6 2.7 3.3
2.6 4.3 4.9
4
Sta-Guard Shield Featherbite
3.5 3.9 4.1
3.0 3.4 3.7
2.6
*Five is the maximum and 1 is the minimum. tGroup 1 vs group 2, p>70% that they are the same; group 1 vs group 3, p<12% that they are the same; group 1 vs group 4, p<18% that they are the same; group 2 vs group 3, p<4% that they are the same; group 2 vs group 4, p<1% that they are the same; group 3 vs group 4, p>79% that they are the same.
0
0 15
0 15 85
Table 4 ■ Nonparam etric ranking of mouth protectors.* Mouth protectors
15
30 30 30 10
te rn s; th is r a n g e is in d ic a te d by th e p e rc e n ta g e o f ea ch ty p e o f p a tte rn o b ta in e d in 2 0 tests. In g e n e ra l, m o re se v ere c ra c k in g o f th e la c q u e r w as o b se rv e d in a n te r io r c o m p a re d w ith p o ste rio r r e gions. T h e v a rio u s m o u th p ro te c to rs w ere ra n k e d by assigning a n u m b e r to th e ty p e o f cra ck p a tte rn fo rm ed . T h e fra c tio n o f th e v ario u s types o f cra ck p a tte rn s w as m u ltip lie d by th e follow ing n u m b e rs assig n ed to th e ty p e o f c ra c k p a tte rn (A = 5 B = 4 , C = 3, D —2, E = l ) . T h e h ig h e st ra n k in g p o ssib le w as 5 a n d th e lo w est w as 1; a hig h r a n k in g in d ic a te d th a t a low stra in w as tra n sfe rre d to th e te e th o f th e m o d el. T h e ran k in g s ca lc u lated
Groupt
0
20 25 25 30
0
Jectron
0
0 40 60
Estane 574010
Gardex, thin
■
fro m c ra c k p a tte rn s in th e p o ste rio r a n d a n te rio r reg io n s a re sh o w n in T a b le 4 . T h e lo w est r a n k ings w e re fo u n d fo r th e p o ly u re th a n e m o u th p r o te c to rs (E stan e, Je c tro n , a n d A u ste n a l) w ith r a n k in g s fro m 1.2 to 2 .0 fo r th e tests in th e a n te rio r reg io n . T h e p o ly e th y le n e-p o ly v in y la ce tate m o u th p ro te c to rs h a d a w id e ra n g e o f v alu es w ith P ro T e x h a v in g a v a lu e o f 2 .2 a n d S ta -G u a rd h av in g a v a lu e o f 3.5 fo r th e tests in th e a n te rio r reg io n . T h e tray -ty p e m o u th p ro te c to rs (D e fe n d er, F e a th e rb ite , an d S h ield ) h a d th e h ig h e st ran k in g s, a n d th e la tte r tw o h a d h ig h e r ran k in g s in tests in th e a n te rio r reg io n c o m p a re d w ith th o se in th e p o ste rio r region. A m o d ifie d ra n k su m te st8 w as u se d w h en th e cells in T a b le 3 c o n ta in in g ze ro s w ere n o t c o u n ted . T h is te st w as a p p lie d to th e fo u r g ro u p s o f m o u th p ro te c to rs sh o w n in T a b le 4 ; th e p ro te c to rs a re a rra n g e d ac co rd in g to in c re a sin g ra n k b ased o n th e rea d in g s in th e a n te rio r reg io n s. T h e se re a d ings w ere selected b e c a u s e th ey w ere th o u g h t to b e m o re im p o rta n t in th e fu n c tio n o f m o u th p r o te cto rs. G ro u p s w ere c o n sid e re d th e sa m e if th e p ro b a b ility v a lu e w as g re a te r th a n 2 0 % ; th e te st in d ic a te d th a t m o u th p ro te c to rs in g ro u p 1 w ere d iffe re n t fro m th o se in g ro u p s 3 a n d 4 a n d th a t p ro te c to rs in g ro u p 2 w e re d iffe re n t fro m th o se in g ro u p s 3 a n d 4 . T h e m o u th p ro te c to rs in g ro u p 3 co u ld n o t b e d istin g u ish e d fro m th o se in g ro u p 4 . A s w o u ld b e ex p ected , th e m o u th p ro te c to rs w ith in each g ro u p co u ld n o t b e d istin g u ish ed .
Godwin—Craig: STRESS TRANSMITTED THROUGH MOUTH PROTECTORS ■ 1319
The low values for the Estane materials in tests in the anterior region may be related to their low thickness o f 1.1 to 1.4 mm. It should be noted that during tests in the anterior region with Estane 57407 and 574010 a third of the plastic casts broke and with Estane 57401 half of the casts broke. The only other tests in which a significant num ber of casts were broken involved the impact of the thin Gardex protector; a fourth of the casts broke during tests in the anterior region. Tests with Austenal and Pro-Tex protectors resulted in a tenth of the models being broken; the remainder of the m aterials protected the models from frac turing in the anterior region.
Discussion The results indicate that energy absorption or re bound tests are not adequate for the selection of the most efficient mouth protectors and that the brittle lacquer coating method provided more appropriate information for such selection. The mouth protectors were separated into two groups based on the ranking of the anterior measure ments of the brittle coating. The superior group included Gardex, Defender, Sta-Guard, Shield, and Featherbite mouth protectors; it was not pos sible, however, to distinguish between these m outh protectors. The mouth protectors were not tested at a con stant thickness but as they are used in practice. Thus, protectors as used rather than materials were evaluated by the ranking test. The thickness of the protector does influence the effectiveness of a single material, but the thicker Featherbite protector (5.3 mm) and the Shield protector (2.7 mm) provided about equal protection. The poly urethane materials were less desirable than the polyethylene-polyvinylacetate products, although increasing the thickness of the former should im prove their effectiveness. The latex mouth pro tector absorbed less energy than the polyethylenepolyvinylacetate types but were as effective in minimizing strain to the teeth. The results indi cated that a minimum thickness of 2 mm of latex should be used, although the rankings in the an terior region could not be distinguished. The prevention of strain and associated stress on the teeth by mouth protectors is not the only criterion for success since the appliance must be worn to be effective. The six highest rankings of the mouth protectors were obtained with thick nesses of 1.7 to 5.3 mm in the anterior region. 1320 ■ JADA, Vol. 77, December 1968
Mouth protectors In the lower range of thickness should provide adequate protection and should be acceptable to the athlete.
Summary Brittle lacquer coatings on maxillary models were used to evaluate the effectiveness of mouth protectors in protecting the teeth from strain as a result of impact blows. The strain transferred to the teeth of the model was evaluated by ranking the crack patterns produced in the lacquer. The results of the brittle coating did not cor relate with rebound or thickness values, and since it was a measure of the strain transferred to the teeth, it is a better estimate of the effective ness of the mouth protectors. By the brittle coat ing measurements, the protectors were separated into two groups; the superior set included the mouth-formed protectors, one latex protector, and one polyethylene-polyvinylacetate customm ade mouth protector. Included in the less ef fective groüp were the polyurethane protectors and one polyethylene polyvinylacetate mouth protector. The authors thank Dr. Kamal El-Ebrashi for assistance and discussion of statistical interpretation and Dr. John Ohlson for compiling the experimental data. This study was supported by Horace H. Rackham Faculty Research Grant, special project no. 69. Doctors Godwin and Craig are at the School of Dentistry, University of Michigan, Ann Arbor 48104. *Columbia Dentoform Rubber Mold no. R22, Columbia Dentoform Corp., New York. fstresscoat, MagnafluxCorp., Chicago. ic h a rp y 15-inch Pound Tester, Department of Engineer ing Shop, University of Michigan, Ann Arbor. 1. Craig, R.G., and Godwin, W.C. Physical properties of materials for custom-made mouth protectors. J Mich State Dent Assn 49:34 Feb 1967. 2. de Forest, A.V.; Ellis, G., and Stem, F.B., Jr. Brittle coating for quantitative strain measurements. J Appl Mech Trans 64A:184 Dec 1942. 3. Evans, F.G., and Lissner, H.R. “Stresscoat” deforma tion studies of the femur under static vertical loading. Anat Rec 100:159 Feb 1948. 4. Gurdjian, E.S., and Lissner, H.R. Deformation of the skull in head injury: a study with “stresscoat” technique. Amer J Surg 73:269 Feb 1947. 5. Huelke, D.F. Mechanics in the production of mandib ular fractures: a study with the “stresscoat” technique. I. Symphyseal impacts. J Dent Res'40:1042 Sept-Oct 1961. 6. Craig, R.G., and Peyton, F.A. Measurement of stresses in f ixed-bridge restorations using a brittle coating technique. J Dent Res 44:756 July-Aug 1965. 7. Godwin, W.C. Simplified mouth protector technic. Part II. J Mich State Dent Assn 44:227 July-Aug 1962. 8. Hoel, P.G. Elementary statistics, ed 2. New York, Wiley and Sons, 1966, pp 252-255.
th ro u g h
m o u th
W illiam C. Godwin, DDS, MS Robert G. Craig, PhD, Ann Arbor, Mich
B rittle lacquer coatings on m axillary models were used to evaluate the effectiveness of mouth pro tectors in protecting the teeth from strain as a re su lt of im pact blows. Among the mouth protectors found to be most effective are the mouth-formed ones.
In our previous paper,1 the physical properties of custom-made mouth protectors were described. This paper also reviews the surveys and studies conducted to evaluate the effectiveness of the various types of mouth protectors. The reports in the literature were not in complete agreement with respect to the superiority of mouth-formed or stock-tray and the custom-made protectors based on the incidence of injuries, although all of the mouth protectors studied reduced oral in juries. Also, the values for energy absorption and hardness of the custom-made protectors did not definitely indicate which material would transfer the lowest strain or stress to the teeth from an im pact on the protector.1 A brittle lacquer technic2 was used to study surface strain and stress in bone:!~5 and dental restorations6 under load. The purpose of this in vestigation was to use the brittle coating technic to evaluate the effectiveness of mouth protectors.
p ro te c to rs
The acrylic casts were sprayed first with a lac quer containing aluminum powder. After the aluminum lacquer dried, the casts were sprayed with the appropriate lacquert depending on the tem perature and humidity during testing. The sprayed casts then were allowed to dry in air for a half hour and dried overnight at 37 C. The casts were removed from the oven the next day, at least one hour before testing, and allowed to reach equilibrium at room temperature. The sensi tivity of the lacquer was about 800/x inches/inch. The mouth protector was placed carefully on the model, and the assembly was mounted secure ly to the base of an impact tester.^ The pendulum, to which a 0.75-inch diam eter ball bearing had been attached, was released at an angle 60° from the vertical position, and the ball was allowed to strike the mouth protector (Fig 1). The angle of rebound of the pendulum was measured in all instances except when the teeth were fractured and the pendulum arm was caught before a sec ond impact occurred. Each mouth protector was tested in three regions: the labial surfaces of the maxillary central incisors, and the right and left buccal interproximal regions between the second premolar and first molar. In all tests, the cast was mounted so that the ball would strike the mouth protector halfway between the gingival and occlu sal or incisal surfaces. Two of each type of mouth protector were tested by use of a total of 20 lacquer-coated casts for each mouth protector. After the impact of the pendulum, the mouth protector was removed from the cast, and the ex tent and position of cracking or flaking of the
Materials and methods Acrylic and dental stone maxillary casts were pre pared in a rubber mold.* Whenever possible, the mouth protectors were fabricated on the acrylic casts to be used during testing. When this could not be done because of processing procedures, the mouth protector was prepared on a stone cast and transferred to an acrylic cast for testing. 1316
Fig 1 ■ Brittle lacquer-coated model with mouth protector in position being struck by impact blow.
Fig 2 ■ Brittle lacquer crack pattern after impact to anterior portion of mouth protector. la c q u e r w as o b serv ed . T en sile stra in w as in d ic ated by c ra c k s in the lacq u er, a n d th e d ire c tio n o f th e s tra in w as n o rm a l to th e d ire c tio n o f th e crack s. C o m p re ssiv e stra in w as in d ic a te d b y are as w h e re th e la c q u e r h a d loo sen ed fro m th e cast. T h e cra ck s o r flakes a p p e a re d w hen th e su rfa ce stra in w as m o re th a n 8 0 0 ¡x inches/inch. C ra c k s in th e la c q u e r co v e rin g th e rig h t c e n tra l inciso r show th a t th e ten sile stra in w as in th e d ire c tio n o f th e lo n g axis o f th e to o th (F ig 2). Q u a lita tiv e g rad in g o f th e su rfa ce stra in w as e sta b lish e d b y c o m p a rin g th e a p p e a ra n c e o f th e la c q u e r co a tin g (F ig 3, 4). T h e g ra d in g ran g e d fro m A w ith th e le ast su rfa ce stra in tra n s fe rre d to
th e te e th o f th e m o d e l to E w ith th e g re a te st s u r face stra in tra n sfe rre d . A re a s w h ere flak in g o c c u rre d a re in d ic a te d by c ro ssh a tc h in g , a n d crack s are show n as lines. T h e m o u th p ro te c to rs th a t w ere u se d in the stu d y w ere p re p a re d in th e fo llo w in g m a n n er. A u ste n a l (A u s te n a l C o .): T h e m o u th p ro te c to r w as fo rm e d fro m a 6 -in c h sq u a re sh e e t on a sto n e ca st u n d e r h e a t a n d 3 0 lb/sq in p re ss u re by u se o f th e A u ste n a l M ic ro fo rm P ress. A fte r th e p r o te c to r w as co o led , th e excess m a te ria l w as trim m ed . D e fe n d e r (L a c to n a ): T h e tw o -lay e r silico n e sh e et fin g er w as p re sse d o n to an ac ry lic ca st u n til w ell ad a p te d . I t w as h e a te d o n a sto n e c a st fo r 20 m in u tes in an o v en a t 177 C an d tra n s fe rre d to an acry lic c a st a fte r it w as co o led to ro o m te m p e ra tu re. E sta n e (B. F . G o o d ric h C o .): E x p e rim e n ta l m a te ria ls 5 7 4 0 1 , 5 7 4 0 7 , a n d 5 7 4 0 1 0 w ere su p p lied in 6 -in ch sq u a re sh eets a n d w ere fa b ric a te d by th e m e th o d u sed fo r A u ste n a l m o u th p ro te c to rs. F e a th e rb ite (F e a th e rla x C o rp .): T h e p re fo rm e d h o rsesh o e tra y w as so ften e d in 9 6 to 9 9 C w ate r fo r 3 to 5 m in u tes a n d w as p ressed o n to th e a c ry l ic c a st by fin g er p re ssu re . T h e m o u th p ro te c to r w as co o led to ro o m te m p e ra tu re w h ile in p o s i tio n o n th e cast.
A N T E R IO R LINGUAL
LABIAL
POSTERIOR BUCCAL
A OCCLUSAL
f in ih ï A
B
Fig 3 ■ Types of brittle lacquer crack patterns seen after impact loading in posterior region.
Fig 4 ■ Types of brittle lacquer crack patterns seen after impact in anterior region.
Godwin—Craig: STRESS TRANSMITTED THROUGH MOUTH PROTECTORS ■ 1317
Gardex (The Hygiene D ental M anufacturing Co.): The latex was paini&l on the acrylic cast, air-dried for 18 hours at room temperature* heat ed to 71 C for one hour, and then removed from the cast before it was boiled in water for 15 minutes. Jectron (Austenal Co.): These m outh protectors were fabricated on stone casts by the Austenal Company and were trimmed to a horseshoe shape on receipt. Pro-Tex (Pro-Tex Inc.): A 4-inch square sheet was softened in 96 to 99 C water for 3 to 5 minutes and adapted onto the acrylic cast by fin ger pressure. The mouth protectors were allowed to cool on the cast and then were trimmed to shape. Shield (Roberts Dental M anufacturing Co., Inc.): Single powder and liquid units were mixed until uniform; when the dough consistency was reached, it was packed into the accompanying flexible tray. The filled tray was pressed onto the stone cast with finger pressure, and it remained on the cast until it was polymerized. Sta-Guard (Stalite, Inc.): A 5-inch square sheet was softened in 96 to 99 C water for 3 to 5 m in utes and was vacuum-formed7 on an acrylic cast, , cooled to room temperature under vacuum, and finally trimmed.
Results The thicknesses of the mouth protectors in the buccal and labial regions are listed in Table 1. The thickness in the buccal region varied from 1.0 to 4.0 mm and in the labial region from 1.1 to 5.3 mm. The Featherbite protectors were the thickest and the Estane materials were the thinnest of the mouth protectors. The thickness of the Gardex protectors varied from 1.4 to 1.9 mm, and the thickness of the Jectron protectors was about 1.6 mm. The remaining protectors had thicknesses of 2.1 to 2.8 mm. The percentage o f the impact energy absorbed by the mouth protectors mounted on the models is shown in Table 2. The thick latex mouth pro tector (Gardex) absorbed the lowest percentage of the im pact energy (50% to 60% ), and the Shield protector absorbed the greatest amount of the impact (92% ). The mouth protectors fabricated from polyurethane absorbed 80% to 85% of the impact whereas those fabricated from polyethylene-polyvinylacetate absorbed about 7 5 % . O f 1318 ■ JADA, Vol. 77, December 1968
Table 1 ■ A ve ra g e th ic k n e s s o f m outh p ro te c to rs . Buccal region mm
Labial region mm
Austenal
2.3
2.1
Defender
2.5
Estane 574010
2.2 1.2 1.2 1.0
Featherbite
4.0
5.3
Gardex, thin
1.4
1.7
Gardex, thick
1.7
1.9
Jectron
1.6
1.7
Pro-Tex
2.4
2.2
Shield
2.4
2.7
Sta-Guard
2.6
2.8
Mouth protector
Estane 57401 Estane 57407
1.1 1.4
1.1
Table 2 ■ Energy absorption of mouth protectors on models during im pact.* Buccal region Average %
Labial region Average %
Austenal
85
82
Defender
81
84
Estane 57401
81
80
Estane 57407
83
80
Estane 574010
83
81
Mouthguard
Featherbite
68
60
Gardex, thin
63
63
Gardex, thick
50
60
Jectron
85
79
Pro-Tex
77
80
Shield
92
92
Sta-Guard
72
78
•Percentage of energy absorption = EP—EF X100 where Ep= potene; tial energy and EF=energy of rebound. EF=WL (1 —cos 0) where W and L are the pendulum weight and length, respectively, and 0 is the rebound angle.
the tray-formed type, the Featherbite mouth p ro tector absorbed the least and the Shield protector the greatest amount of energy from the impact. It is apparent that there is no direct correlation between the amount of energy absorption and the thickness of the mouth protector. The distribution of the type of brittle lacquer crack pattern on the teeth of the models protected by the various mouth protectors is shown in Table 3. In most instances, different tests with the same mouth protector showed a range of crack pat
Table 3 ■ Percentage distribution of the type of lacquer crack patterns observed in various regions after impact loading. Impact in posterior region Buccal A
rack pattern
B
C
Impact in anterior region
A
D
B
C
Lingual
Labial
Occlusal D
A
B
D
c
D
E
A
B
0 20 10 50 20
0
0 10 40 50
C
E
1outh protector 20 15 30 35
5 20 30 45
Austenal Defender
85 15
0
0
Estane 57401
25 50 25
0
0
Estane 57407
10 40 40
Featherbite
10 50 30 10 0
100
10
0 40 60
50 15 25 10
Gardex, thick
Pro-Tex Shield Sta-Guard
0
60 25 15
0
0 15 40 45 60 25
1
Jectron
0
10 15 25 50 75 10 15
0
10 60 30
0
0
0 20 50 20 10
0 10 45 45
0
0
0 20 80
0 15
0 20 65
0
0
0 20 80
0
0 50 50
0
0
0
0 100
50 50
0
0
0
75
0
0
0
0 60 40
0
0
0 25 50 25
0
0
0 25
0
0
0
0 50 50
0
0
0 10 90
0
0 10 20 70
15 70 0
0 30 70
5
5 20 70
50
15 20 15
0 20 60 20
0
0 35 20 45
45
15 30 10
10 70 10 10
0
20 60 20
0
0
10 10 30 50
15
15 40 30
0 70 10 20
0
40 10 10 40
0
Anterior region
Posterior region
1.2
2.3 4.0
Estane 574010 Estane 57407
1.3 1.4
2
Estane 57401 Austenal Pro-Tex
1.4 2.0 2.2
4.7 3.0 3.7
3
Gardex, thin Gardex, thick Defender
2.6 2.7 3.3
2.6 4.3 4.9
4
Sta-Guard Shield Featherbite
3.5 3.9 4.1
3.0 3.4 3.7
2.6
*Five is the maximum and 1 is the minimum. tGroup 1 vs group 2, p>70% that they are the same; group 1 vs group 3, p<12% that they are the same; group 1 vs group 4, p<18% that they are the same; group 2 vs group 3, p<4% that they are the same; group 2 vs group 4, p<1% that they are the same; group 3 vs group 4, p>79% that they are the same.
0
0 15
0 15 85
Table 4 ■ Nonparam etric ranking of mouth protectors.* Mouth protectors
15
30 30 30 10
te rn s; th is r a n g e is in d ic a te d by th e p e rc e n ta g e o f ea ch ty p e o f p a tte rn o b ta in e d in 2 0 tests. In g e n e ra l, m o re se v ere c ra c k in g o f th e la c q u e r w as o b se rv e d in a n te r io r c o m p a re d w ith p o ste rio r r e gions. T h e v a rio u s m o u th p ro te c to rs w ere ra n k e d by assigning a n u m b e r to th e ty p e o f cra ck p a tte rn fo rm ed . T h e fra c tio n o f th e v ario u s types o f cra ck p a tte rn s w as m u ltip lie d by th e follow ing n u m b e rs assig n ed to th e ty p e o f c ra c k p a tte rn (A = 5 B = 4 , C = 3, D —2, E = l ) . T h e h ig h e st ra n k in g p o ssib le w as 5 a n d th e lo w est w as 1; a hig h r a n k in g in d ic a te d th a t a low stra in w as tra n sfe rre d to th e te e th o f th e m o d el. T h e ran k in g s ca lc u lated
Groupt
0
20 25 25 30
0
Jectron
0
0 40 60
Estane 574010
Gardex, thin
■
fro m c ra c k p a tte rn s in th e p o ste rio r a n d a n te rio r reg io n s a re sh o w n in T a b le 4 . T h e lo w est r a n k ings w e re fo u n d fo r th e p o ly u re th a n e m o u th p r o te c to rs (E stan e, Je c tro n , a n d A u ste n a l) w ith r a n k in g s fro m 1.2 to 2 .0 fo r th e tests in th e a n te rio r reg io n . T h e p o ly e th y le n e-p o ly v in y la ce tate m o u th p ro te c to rs h a d a w id e ra n g e o f v alu es w ith P ro T e x h a v in g a v a lu e o f 2 .2 a n d S ta -G u a rd h av in g a v a lu e o f 3.5 fo r th e tests in th e a n te rio r reg io n . T h e tray -ty p e m o u th p ro te c to rs (D e fe n d er, F e a th e rb ite , an d S h ield ) h a d th e h ig h e st ran k in g s, a n d th e la tte r tw o h a d h ig h e r ran k in g s in tests in th e a n te rio r reg io n c o m p a re d w ith th o se in th e p o ste rio r region. A m o d ifie d ra n k su m te st8 w as u se d w h en th e cells in T a b le 3 c o n ta in in g ze ro s w ere n o t c o u n ted . T h is te st w as a p p lie d to th e fo u r g ro u p s o f m o u th p ro te c to rs sh o w n in T a b le 4 ; th e p ro te c to rs a re a rra n g e d ac co rd in g to in c re a sin g ra n k b ased o n th e rea d in g s in th e a n te rio r reg io n s. T h e se re a d ings w ere selected b e c a u s e th ey w ere th o u g h t to b e m o re im p o rta n t in th e fu n c tio n o f m o u th p r o te cto rs. G ro u p s w ere c o n sid e re d th e sa m e if th e p ro b a b ility v a lu e w as g re a te r th a n 2 0 % ; th e te st in d ic a te d th a t m o u th p ro te c to rs in g ro u p 1 w ere d iffe re n t fro m th o se in g ro u p s 3 a n d 4 a n d th a t p ro te c to rs in g ro u p 2 w e re d iffe re n t fro m th o se in g ro u p s 3 a n d 4 . T h e m o u th p ro te c to rs in g ro u p 3 co u ld n o t b e d istin g u ish e d fro m th o se in g ro u p 4 . A s w o u ld b e ex p ected , th e m o u th p ro te c to rs w ith in each g ro u p co u ld n o t b e d istin g u ish ed .
Godwin—Craig: STRESS TRANSMITTED THROUGH MOUTH PROTECTORS ■ 1319
The low values for the Estane materials in tests in the anterior region may be related to their low thickness o f 1.1 to 1.4 mm. It should be noted that during tests in the anterior region with Estane 57407 and 574010 a third of the plastic casts broke and with Estane 57401 half of the casts broke. The only other tests in which a significant num ber of casts were broken involved the impact of the thin Gardex protector; a fourth of the casts broke during tests in the anterior region. Tests with Austenal and Pro-Tex protectors resulted in a tenth of the models being broken; the remainder of the m aterials protected the models from frac turing in the anterior region.
Discussion The results indicate that energy absorption or re bound tests are not adequate for the selection of the most efficient mouth protectors and that the brittle lacquer coating method provided more appropriate information for such selection. The mouth protectors were separated into two groups based on the ranking of the anterior measure ments of the brittle coating. The superior group included Gardex, Defender, Sta-Guard, Shield, and Featherbite mouth protectors; it was not pos sible, however, to distinguish between these m outh protectors. The mouth protectors were not tested at a con stant thickness but as they are used in practice. Thus, protectors as used rather than materials were evaluated by the ranking test. The thickness of the protector does influence the effectiveness of a single material, but the thicker Featherbite protector (5.3 mm) and the Shield protector (2.7 mm) provided about equal protection. The poly urethane materials were less desirable than the polyethylene-polyvinylacetate products, although increasing the thickness of the former should im prove their effectiveness. The latex mouth pro tector absorbed less energy than the polyethylenepolyvinylacetate types but were as effective in minimizing strain to the teeth. The results indi cated that a minimum thickness of 2 mm of latex should be used, although the rankings in the an terior region could not be distinguished. The prevention of strain and associated stress on the teeth by mouth protectors is not the only criterion for success since the appliance must be worn to be effective. The six highest rankings of the mouth protectors were obtained with thick nesses of 1.7 to 5.3 mm in the anterior region. 1320 ■ JADA, Vol. 77, December 1968
Mouth protectors In the lower range of thickness should provide adequate protection and should be acceptable to the athlete.
Summary Brittle lacquer coatings on maxillary models were used to evaluate the effectiveness of mouth protectors in protecting the teeth from strain as a result of impact blows. The strain transferred to the teeth of the model was evaluated by ranking the crack patterns produced in the lacquer. The results of the brittle coating did not cor relate with rebound or thickness values, and since it was a measure of the strain transferred to the teeth, it is a better estimate of the effective ness of the mouth protectors. By the brittle coat ing measurements, the protectors were separated into two groups; the superior set included the mouth-formed protectors, one latex protector, and one polyethylene-polyvinylacetate customm ade mouth protector. Included in the less ef fective groüp were the polyurethane protectors and one polyethylene polyvinylacetate mouth protector. The authors thank Dr. Kamal El-Ebrashi for assistance and discussion of statistical interpretation and Dr. John Ohlson for compiling the experimental data. This study was supported by Horace H. Rackham Faculty Research Grant, special project no. 69. Doctors Godwin and Craig are at the School of Dentistry, University of Michigan, Ann Arbor 48104. *Columbia Dentoform Rubber Mold no. R22, Columbia Dentoform Corp., New York. fstresscoat, MagnafluxCorp., Chicago. ic h a rp y 15-inch Pound Tester, Department of Engineer ing Shop, University of Michigan, Ann Arbor. 1. Craig, R.G., and Godwin, W.C. Physical properties of materials for custom-made mouth protectors. J Mich State Dent Assn 49:34 Feb 1967. 2. de Forest, A.V.; Ellis, G., and Stem, F.B., Jr. Brittle coating for quantitative strain measurements. J Appl Mech Trans 64A:184 Dec 1942. 3. Evans, F.G., and Lissner, H.R. “Stresscoat” deforma tion studies of the femur under static vertical loading. Anat Rec 100:159 Feb 1948. 4. Gurdjian, E.S., and Lissner, H.R. Deformation of the skull in head injury: a study with “stresscoat” technique. Amer J Surg 73:269 Feb 1947. 5. Huelke, D.F. Mechanics in the production of mandib ular fractures: a study with the “stresscoat” technique. I. Symphyseal impacts. J Dent Res'40:1042 Sept-Oct 1961. 6. Craig, R.G., and Peyton, F.A. Measurement of stresses in f ixed-bridge restorations using a brittle coating technique. J Dent Res 44:756 July-Aug 1965. 7. Godwin, W.C. Simplified mouth protector technic. Part II. J Mich State Dent Assn 44:227 July-Aug 1962. 8. Hoel, P.G. Elementary statistics, ed 2. New York, Wiley and Sons, 1966, pp 252-255.