The transverse
strengths of three denture base resins
D o n n a L. D i x o n , D M D , a K a r l G. E k s t r a n d , D D S , P h D , b a n d L a r r y C. B r e e d i n g , D M D , M S E d c
University of Iowa, College of Dentistry, Iowa City, Iowa, and University of Kentucky, College of Dentistry, Lexington, Ky. Ten s p e c i m e n s each of (1) Lueitone 199, short- and long-cured, (2) Accelar 20, and (3) Triad m a t e r i a l s w e r e b r o k e n u s i n g a 3-point load on an Instron U n i v e r s a l testing m a c h i n e after p r o c e s s i n g and air drying. Five s p e c i m e n s of each r e s i n also w e r e b r o k e n after storage in d e i o n i z e d distilled w a t e r at 37 ° C for 30, 60, and 90 days. Triad m a t e r i a l d e m o n s t r a t e d the l o w e s t t r a n s v e r s e s t r e n g t h s of all three m a t e r i a l s overall. H o w e v e r , Triad m a t e r i a l w a s unaffected by w a t e r storage. The other resins all s h o w e d d e c r e a s e d s t r e n g t h s w i t h w a t e r storage. (J PROSTHET DENT 1991;66:510-3.)
B e c a u s e it is recognized that factors such as rate of loading and moisture content affect the transverse strength of acrylic resins, 1, 2 a transverse testing machine, which permitted control of these factors, was developed and described in the early 1950s. 3 This testing machine used lead shot; therefore even specimen loading could not be ensured. Today this testing is done with predictability by means of an Instron machine (Instron Corp., Canton, Mass.) with constant loading. 4 Recently high-impact strength resins, rapid heat-polymerized resins, and light-activated resins have been introduced as alternatives to the conventional polymethyl methacrylate denture base material. This investigation recorded and compared the transverse strengths of these types of denture base resins both dry and after soaking in water for various time periods. 5
MATERIAL AND METHODS Three denture base resins were selected for testing: (1) a high impact strength resin (Lucitone 199, Dentsply, Intl., York, Pa.), short- and long-cured, (2) a rapid heatpolymerized resin (Accelar 20, Columbus Dental Co., St. Louis, Me.), and (3) a light-activated resin (Triad, Dentsply, Intl.). A stainless steel mold was made with five breakaway compartments, each 65 × 10 × 3 mm, to fabricate specimens from the various resins. A polyvinylsiloxane impression (Reprosil, L.D. Caulk Co., Milford, Del.) was made of the mold and a cast was formed subsequently from the impression using improved dental stone.
aAssistant Professor, Department of Prosthodontics, University of Iowa, College of Dentistry. bAssistant Clinical Professor, Department of Prosthodontics, University of Iowa, College of Dentistry. CAssociate Professor, Department of Restorative Dentistry, University of Kentucky, College of Dentistry. 10/1/25050
510
F i g . 1. Assembly for testing transverse strength of den-
ture base resins. Table I. Calculated mean transverse
strengths within
each resin group N
Mean (MPa)
Resin
Group
Time
SD
Lucitone short-cure
1
Dry Wet
- - 10 30 5 60 6 90 5
94.73 8.47 87.64 12.77 81.95 15.96 87.52 5.48
Lucitone long-cure
2
Dry Wet
- - 10 30 5 60 5 90 5
96.26 81.06 84.83 86.25
Accelar 20
3
Dry Wet
- - 10 30 5 60 5 90 5
81.98 10.90 78.98 11.90 74.13 6.61 77.55 4.96
Triad
4
Dry Wet
- - 10 30 5 60 5 90 5
49.96 50.43 49.96 52.61
5.76 5.20 3.82 3.59
6.98 6.79 9.49 6.45
OCTOBER1991 VOLUME66 NUMBER4
TRANSVERSE STRENGTHS OF DENTURE BASE RESINS
Mean Strengths (MPa) 100 959085807570656055504540 Dry
30
60
90
Time (Days) ~Group
1
---Group
2
--o Group 3
--- Group 4
F i g . 2. Mean resin transverse strengths (MPa) over time.
T a b l e II. Two-factor ANOVA for mean transverse strengths Sum of
Source
Model Error Corrected total Group Time Group/time
elf
15 85 100 3 3 9
squares
Mean square
26713.812 1780.921 6264.809 73.704 32978.621 24856.422 1109.329 748.062
T a b l e III. S u m m a r y of ANOVA comparison of mean transverse strengths for each resin group by time
P r > F*
Resin group
24.16
0.0001
1
112.42 5.02 1.13
0.0001 0.0030 0.3525
F value
THE JOURNAL OF PROSTHETIC DENTISTRY
Sum of squares
Mean square
P r > F*
Model 3 646.242 215.414 Error 22 2691.677 122.349 Corrected 25 3337.918 total
1.76
0.1841
2
Model 3 967.063 322.354 Error 21 516.361 24.589 Corrected 24 1483.424 total
13.11
0.0001
3
Model 3 217.671 72.557 Error 21 1907.529 90.835 Corrected 24 2125.199 total
0.80
0.5084
4
Model 3 2 6 . 4 1 5 8.805 Error 21 1149.243 54.726 Corrected 24 1175.658 total
0.16
0.9214
*Significant at p < 0.05.
Lucitone 199 was used in making 25 specimens and cured for 9 hours at 168 ° F; another 25 specimens were made from this same resin with the short-cure method (11/2 hours at 168 ° F and i/2 hour at 212 ° F). Additional stone molds were used to form 25 specimens from Accelar 20 resin (processed for 20 minutes at 212 ° F). All resins were measured, mixed, and processed according to manufacturers' instructions. Because of the required curing m e t h o d for T r i a d resin, it was necessary to use the stainless steel mold for preparation of these 25 specimens. The uncured T r i a d denture base resin was inserted in each compartment, a Plexiglas cover was placed over the mold, and the entire assembly was placed in the T r i a d visible-light-curing unit (Dentsply, Intl.). The resin specimens were allowed to cure initially for 5 minutes. The mold was removed from the unit and the compartments wer e disassembled, releasing the resin specimens. They were then t u r n e d over and replaced in the curing unit for 5 minutes to complete the curing cycle. Ten specimens of each cured resin were deflasked and
df
F value
Source
*Significant at p < 0.05.
allowed to remain at room temperature; 15 specimens were deflasked and placed in deionized distilled water at 37 ° C. The samples were broken using an Instron Universal testing machine and a transverse testing rig similar to t h a t described by Stafford and H a n d l e y 4 (Fig. 1), with a 50 kg load cell and a crosshead speed of 0.5 cm/minute. The dry specimens were allowed to remain in the air at room temperature for at least 24 hours before testing. Five specimens of each resin also were broken with the same testing apparatus after 30, 60, and 90 days of water storage. The
511
DIXON, EKSTRAND, AND BREEDING
T a b l e IV. Summary of ANOVA comparison of mean transverse strengths for each time period by resin group Time
Dry
30
Source
df
Sum of squares
Mean square
F value
Pr > F*
Model 3 13853.378 4617.793 67.85 0.0001 Error 36 2450.034 68.056 Corrected 39 16303.412 total Model 3 4074.128 1358.043 14.37 0.0001
days
T a b l e V. Duncan's multiple range test for comparison
of mean transverse strengths for each resin group b y time Resin group
1 2 3 4
Dry (MPa)
94.73 96.26 81.98 ] 49.96i
30 days (MPa)
87.64} 81.06] 78.98 ! 50.431 /
60 days (MPa)
81.95 ] 84.83 1 74.13 49.961
90 days (MPa)
87.52 86.25 77.551 52.61 I
Vertical linesjoin valuesthat are not statistically differentat p < 0.05level. Error 16 Corrected 19 total
60 Model 3 days Error 17 Corrected 20 total 90 Model 3 days Error 16 Corrected 19 total
1511.696 5585.825
94.481
3839.215 1279.738 11.66 0.0002
of mean transverse strengths for each time period by resin group
1866.529 109.796 5705.744 3937.037 1312.346 48.10 436.550 4373.587
T a b l e VI. Duncan's multiple range test for comparison
Time period
Group 1 (MPa)
Group 2 (MPa)
Group 3 (MPa)
Group 4 (MPa)
0.0001
27.284
Dry 30 days 60 days 90 days
94.73 I 87.64 I 81.95 87.52
96.26 81.05 84.83 86.25
81.981 78.981 74.13 I 77.55 I
49.96 50.43 49.96 52.61
*Significant at p < 0.05.
Vertical linesjoin valuesthat are not statistically differentat p < 0.05level.
transverse strength of each resin measured at each time period was calculated with the following formula:
after water sorption has occurred. The water appears to act as a plasticizer for these resins. 6 Stafford and Smith 7 believed that a 30-day storage in water was necessary to maximize the effect. The present study continued water storage up to 90 days to determine whether this effect was indeed complete by the 30-day time period. It was observed that only the Lucitone 199 resin long-cured specimens showed significant decreases in transverse strengths from dry to 30 days in water storage. The Accelar 20 resin showed little change; Lucitone 199 short-cured resin specimens exhibited an intermediate change. The chemical formulation of the Accelar 20 resin, necessary for rapid cure without porosity, may have some effect on the amount of plasticizing caused by water sorption. Variations in the transverse strength values for all of these resins during 30, 60, and 90 days of water storage were not statistically significant, but interestingly all three resins began to increase in transverse strength values from 60 to 90 days. Longer storage would be needed to observe whether this trend would continue. The Triad denture base resin is composed of a matrix of urethane dimethacrylate plus small amounts of microfine silica with a filler of acrylic resin beads. Braden 9 found that an experimental microfine composite filling material based on urethane dimethacrylate resin showed less water uptake than existing proprietary materials. This finding could help explain the lack of effect of water storage noted with the Triad resin. The Triad resin specimens exhibited significantly lower transverse strength values at each time measurement.
3p1/2 3 x load X length S=~ or S = 2 x width X thickness 2 RESULTS
The transverse strength values for each material and test condition are summarized in Table I and graphically displayed in Fig. 2. The results of two-factor analysis of variance ( p < 0.05) are presented in Table II. The results indicate an effect for both group and time, whereas time and group interaction was not significant. The results of onefactor analysis of variance ( p < 0.05) for each group by time and each time by group are given in Tables III and IV. The Duncan's multiple range test was performed and the results are displayed in Tables V and VI. Only the Lucitone 199 resin long-cured samples showed a significant decrease in transverse strength from dry conditions to water storage. Lucitone 199 short-cured resin and Accelar 20 resin samples showed a decrease in transverse strength. However, this decrease was not statistically significant. The Triad resin specimens showed almost no change in transverse strength under any of the experimental conditions. However, at each measurement time, the Triad resin specimens exhibited significantly lower transverse strength values than the other resins. DISCUSSION
Previous studies 68- have shown a decrease in transverse strengths for polymethyl methacrylate denture base resins 512
OCTOBER 1991 VOLUME 66 NUMBER 4
TRANSVERSESTRENGTHSOF DENTURE BASE RESINS
CLINICAL
IMPLICATIONS
The results indicate that the transverse strength of Triad denture base resin is significantly lower than the heat polymerized brands Lucitone 199 and Accelar 20. Clinically, a resin material exhibiting a lower transverse strength may be more prone to fracture during function as a denture base than would a resin with a higher transverse strength. This potential for fracture may increase with use because of the water sorpti0n for some types of materials. CONCLUSION 1. Lucitone long-cured resin significantly decreases in transverse strength from dry to 30 days in water storage. 2. Accelar 20 resin shows minimal decrease in transverse strength from dry to 30 days in water storage. 3. The transverse strength of Triad resin was significantly lower than the other resins during all the time periods measured but was unaffected by water storage. 4. Changes in transverse strengths for all materials from 30 to 90 days of water storage were small and not statistically significant.
REFERENCES 1. Sweeney WA, Paffenbarger GC, Caul HJ, Sweeney WT. American Dental Association specification No. 12 for denture base resin: second revision. J Am Dent Assoc 1953;46:54-66. 2. Sweeney WT, Paffenbarger GC, Beall JR. Acrylic resins for dentures. J Am Dent Assoc 1942;29:7-33. 3. Sweeney WT, Caul H J, Gneug W. A transverse testing machine for denture resins. J Am Dent Assoc 1954;49:174-6. 4. Stafford GD, Handley RW. Transverse bend testing of denture base polymers. J Dent 1975;3:251-5. 5. Craig RG, ed. Restorative dental materials. 8th ed. St Louis: CV Mosby, 1989:512-3. 6. Gilbert AS, Pethrick RA, Phillips DW. Acoustic relaxation and infrared spectroscopic measurements of the plasticization of polymethyl methacrylate by water. J Appl Polymer Sci 1977;21:319-30. 7. Stafford GD, Smith DC. Some studies of the properties of denture base polymers. Br Dent J 1968;125:337-42. 8. Stafford GD, Bates JF, Huggett R, Handley RW. A review of the properties of some denture base polymers, J Dent 1980;8:292-306. 9. Braden M. Water absorption characteristics of dental microfine composite filling materials, II. Experimental materials. Biomater 1984;5:3735.
Reprint requests to: DR. DONNAL. DIXON COLLEGE OF DENTISTRY UNIVERSITYOF IOWA IOWACITY, IA 52242
An a n a l y s i s of the r e l a t i o n s h i p b e t w e e n m a n d i b u l a r a l v e o l a r bone loss and a low F r a n k f o r t - m a n d i b u l a r plane a n g l e J o h n W. U n g e r , D D S , a C h a r l e s W. E l l i n g e r , DDS, MS, b a n d J o h n C. G u n s o l l e y , D D S , M S c
Medical College of Virginia, School of Dentistry, Richmond, Va., and University of Kentucky, College of Dentistry, Lexington, Ky. A group of c o m p l e t e denture p a t i e n t s w a s studied to d e t e r m i n e the effect of a l o w F r a n k f o r t - m a n d i b u l a r plane angle on the loss o f r e s i d u a l ridge h e i g h t in the mandible. M e a s u r e m e n t s w e r e m a d e from tracings of c e p h a l o m e t r i c films. The Iow-FMA group did not e x p e r i e n c e s t a t i s t i c a l l y g r e a t e r a m o u n t s of a l v e o l a r ridge loss w h e n c o m p a r e d w i t h the group w i t h an FMA larger than 20 d e g r e e s . The loss of r e s i d u a l ridge h e i g h t for both groups f o l l o w e d a l i n e a r r e l a t i o n s h i p from y e a r 5 to y e a r 20. There w a s s o m e indication that the r e s i d u a l ridge h e i g h t w a s s m a l l e r initially in the Iow-FMA group. The r e l a t i v e effect of the loss of r e s i d u a l ridge height, c o m b i n e d w i t h s m a l l e r r e s i d u a l ridge height originally, indicates that the l o w - F M A p a t i e n t s are m o r e l i k e l y to h a v e a n a t o m i c deficiencies and p r o b l e m s w i t h c o m p l e t e d e n t u r e s a s s o c i a t e d w i t h this l a c k o f m a n d i b u l a r r e s i d u a l ridge height. (J PROSTHET DENT 1991;66:513-6.)
Supported by United States Public Health Service Research Grant No. R01 009401 from the Department of Health, Education, and Welfare. aAssociate Professor and Chairman, Department of Removable Prosthodontics, Medical College of Virginia, School of Dentistry. bprofessor, Department of Oral Health Practice, University of Kentucky, College of Dentistry. CDirector, Officeof Applied Research, Medical Collegeof Virginia, School of Dentistry. 10/1/25051 THE JOURNAL OF PROSTHETIC DENTISTRY
A l v e o l a r bone loss can have a profound effect on the success of complete denture treatment and is encountered most often in the mandible. A troublesome aspect of this problem is the wide variation frequently observed in the extent and amount of bone loss. The ability to predict which patients are likely to suffer great amounts of bone loss would be of importance to both patient and dentist. Reference has been made in the literature to a connection between residual ridge loss and a low 513
strengths of three denture base resins
D o n n a L. D i x o n , D M D , a K a r l G. E k s t r a n d , D D S , P h D , b a n d L a r r y C. B r e e d i n g , D M D , M S E d c
University of Iowa, College of Dentistry, Iowa City, Iowa, and University of Kentucky, College of Dentistry, Lexington, Ky. Ten s p e c i m e n s each of (1) Lueitone 199, short- and long-cured, (2) Accelar 20, and (3) Triad m a t e r i a l s w e r e b r o k e n u s i n g a 3-point load on an Instron U n i v e r s a l testing m a c h i n e after p r o c e s s i n g and air drying. Five s p e c i m e n s of each r e s i n also w e r e b r o k e n after storage in d e i o n i z e d distilled w a t e r at 37 ° C for 30, 60, and 90 days. Triad m a t e r i a l d e m o n s t r a t e d the l o w e s t t r a n s v e r s e s t r e n g t h s of all three m a t e r i a l s overall. H o w e v e r , Triad m a t e r i a l w a s unaffected by w a t e r storage. The other resins all s h o w e d d e c r e a s e d s t r e n g t h s w i t h w a t e r storage. (J PROSTHET DENT 1991;66:510-3.)
B e c a u s e it is recognized that factors such as rate of loading and moisture content affect the transverse strength of acrylic resins, 1, 2 a transverse testing machine, which permitted control of these factors, was developed and described in the early 1950s. 3 This testing machine used lead shot; therefore even specimen loading could not be ensured. Today this testing is done with predictability by means of an Instron machine (Instron Corp., Canton, Mass.) with constant loading. 4 Recently high-impact strength resins, rapid heat-polymerized resins, and light-activated resins have been introduced as alternatives to the conventional polymethyl methacrylate denture base material. This investigation recorded and compared the transverse strengths of these types of denture base resins both dry and after soaking in water for various time periods. 5
MATERIAL AND METHODS Three denture base resins were selected for testing: (1) a high impact strength resin (Lucitone 199, Dentsply, Intl., York, Pa.), short- and long-cured, (2) a rapid heatpolymerized resin (Accelar 20, Columbus Dental Co., St. Louis, Me.), and (3) a light-activated resin (Triad, Dentsply, Intl.). A stainless steel mold was made with five breakaway compartments, each 65 × 10 × 3 mm, to fabricate specimens from the various resins. A polyvinylsiloxane impression (Reprosil, L.D. Caulk Co., Milford, Del.) was made of the mold and a cast was formed subsequently from the impression using improved dental stone.
aAssistant Professor, Department of Prosthodontics, University of Iowa, College of Dentistry. bAssistant Clinical Professor, Department of Prosthodontics, University of Iowa, College of Dentistry. CAssociate Professor, Department of Restorative Dentistry, University of Kentucky, College of Dentistry. 10/1/25050
510
F i g . 1. Assembly for testing transverse strength of den-
ture base resins. Table I. Calculated mean transverse
strengths within
each resin group N
Mean (MPa)
Resin
Group
Time
SD
Lucitone short-cure
1
Dry Wet
- - 10 30 5 60 6 90 5
94.73 8.47 87.64 12.77 81.95 15.96 87.52 5.48
Lucitone long-cure
2
Dry Wet
- - 10 30 5 60 5 90 5
96.26 81.06 84.83 86.25
Accelar 20
3
Dry Wet
- - 10 30 5 60 5 90 5
81.98 10.90 78.98 11.90 74.13 6.61 77.55 4.96
Triad
4
Dry Wet
- - 10 30 5 60 5 90 5
49.96 50.43 49.96 52.61
5.76 5.20 3.82 3.59
6.98 6.79 9.49 6.45
OCTOBER1991 VOLUME66 NUMBER4
TRANSVERSE STRENGTHS OF DENTURE BASE RESINS
Mean Strengths (MPa) 100 959085807570656055504540 Dry
30
60
90
Time (Days) ~Group
1
---Group
2
--o Group 3
--- Group 4
F i g . 2. Mean resin transverse strengths (MPa) over time.
T a b l e II. Two-factor ANOVA for mean transverse strengths Sum of
Source
Model Error Corrected total Group Time Group/time
elf
15 85 100 3 3 9
squares
Mean square
26713.812 1780.921 6264.809 73.704 32978.621 24856.422 1109.329 748.062
T a b l e III. S u m m a r y of ANOVA comparison of mean transverse strengths for each resin group by time
P r > F*
Resin group
24.16
0.0001
1
112.42 5.02 1.13
0.0001 0.0030 0.3525
F value
THE JOURNAL OF PROSTHETIC DENTISTRY
Sum of squares
Mean square
P r > F*
Model 3 646.242 215.414 Error 22 2691.677 122.349 Corrected 25 3337.918 total
1.76
0.1841
2
Model 3 967.063 322.354 Error 21 516.361 24.589 Corrected 24 1483.424 total
13.11
0.0001
3
Model 3 217.671 72.557 Error 21 1907.529 90.835 Corrected 24 2125.199 total
0.80
0.5084
4
Model 3 2 6 . 4 1 5 8.805 Error 21 1149.243 54.726 Corrected 24 1175.658 total
0.16
0.9214
*Significant at p < 0.05.
Lucitone 199 was used in making 25 specimens and cured for 9 hours at 168 ° F; another 25 specimens were made from this same resin with the short-cure method (11/2 hours at 168 ° F and i/2 hour at 212 ° F). Additional stone molds were used to form 25 specimens from Accelar 20 resin (processed for 20 minutes at 212 ° F). All resins were measured, mixed, and processed according to manufacturers' instructions. Because of the required curing m e t h o d for T r i a d resin, it was necessary to use the stainless steel mold for preparation of these 25 specimens. The uncured T r i a d denture base resin was inserted in each compartment, a Plexiglas cover was placed over the mold, and the entire assembly was placed in the T r i a d visible-light-curing unit (Dentsply, Intl.). The resin specimens were allowed to cure initially for 5 minutes. The mold was removed from the unit and the compartments wer e disassembled, releasing the resin specimens. They were then t u r n e d over and replaced in the curing unit for 5 minutes to complete the curing cycle. Ten specimens of each cured resin were deflasked and
df
F value
Source
*Significant at p < 0.05.
allowed to remain at room temperature; 15 specimens were deflasked and placed in deionized distilled water at 37 ° C. The samples were broken using an Instron Universal testing machine and a transverse testing rig similar to t h a t described by Stafford and H a n d l e y 4 (Fig. 1), with a 50 kg load cell and a crosshead speed of 0.5 cm/minute. The dry specimens were allowed to remain in the air at room temperature for at least 24 hours before testing. Five specimens of each resin also were broken with the same testing apparatus after 30, 60, and 90 days of water storage. The
511
DIXON, EKSTRAND, AND BREEDING
T a b l e IV. Summary of ANOVA comparison of mean transverse strengths for each time period by resin group Time
Dry
30
Source
df
Sum of squares
Mean square
F value
Pr > F*
Model 3 13853.378 4617.793 67.85 0.0001 Error 36 2450.034 68.056 Corrected 39 16303.412 total Model 3 4074.128 1358.043 14.37 0.0001
days
T a b l e V. Duncan's multiple range test for comparison
of mean transverse strengths for each resin group b y time Resin group
1 2 3 4
Dry (MPa)
94.73 96.26 81.98 ] 49.96i
30 days (MPa)
87.64} 81.06] 78.98 ! 50.431 /
60 days (MPa)
81.95 ] 84.83 1 74.13 49.961
90 days (MPa)
87.52 86.25 77.551 52.61 I
Vertical linesjoin valuesthat are not statistically differentat p < 0.05level. Error 16 Corrected 19 total
60 Model 3 days Error 17 Corrected 20 total 90 Model 3 days Error 16 Corrected 19 total
1511.696 5585.825
94.481
3839.215 1279.738 11.66 0.0002
of mean transverse strengths for each time period by resin group
1866.529 109.796 5705.744 3937.037 1312.346 48.10 436.550 4373.587
T a b l e VI. Duncan's multiple range test for comparison
Time period
Group 1 (MPa)
Group 2 (MPa)
Group 3 (MPa)
Group 4 (MPa)
0.0001
27.284
Dry 30 days 60 days 90 days
94.73 I 87.64 I 81.95 87.52
96.26 81.05 84.83 86.25
81.981 78.981 74.13 I 77.55 I
49.96 50.43 49.96 52.61
*Significant at p < 0.05.
Vertical linesjoin valuesthat are not statistically differentat p < 0.05level.
transverse strength of each resin measured at each time period was calculated with the following formula:
after water sorption has occurred. The water appears to act as a plasticizer for these resins. 6 Stafford and Smith 7 believed that a 30-day storage in water was necessary to maximize the effect. The present study continued water storage up to 90 days to determine whether this effect was indeed complete by the 30-day time period. It was observed that only the Lucitone 199 resin long-cured specimens showed significant decreases in transverse strengths from dry to 30 days in water storage. The Accelar 20 resin showed little change; Lucitone 199 short-cured resin specimens exhibited an intermediate change. The chemical formulation of the Accelar 20 resin, necessary for rapid cure without porosity, may have some effect on the amount of plasticizing caused by water sorption. Variations in the transverse strength values for all of these resins during 30, 60, and 90 days of water storage were not statistically significant, but interestingly all three resins began to increase in transverse strength values from 60 to 90 days. Longer storage would be needed to observe whether this trend would continue. The Triad denture base resin is composed of a matrix of urethane dimethacrylate plus small amounts of microfine silica with a filler of acrylic resin beads. Braden 9 found that an experimental microfine composite filling material based on urethane dimethacrylate resin showed less water uptake than existing proprietary materials. This finding could help explain the lack of effect of water storage noted with the Triad resin. The Triad resin specimens exhibited significantly lower transverse strength values at each time measurement.
3p1/2 3 x load X length S=~ or S = 2 x width X thickness 2 RESULTS
The transverse strength values for each material and test condition are summarized in Table I and graphically displayed in Fig. 2. The results of two-factor analysis of variance ( p < 0.05) are presented in Table II. The results indicate an effect for both group and time, whereas time and group interaction was not significant. The results of onefactor analysis of variance ( p < 0.05) for each group by time and each time by group are given in Tables III and IV. The Duncan's multiple range test was performed and the results are displayed in Tables V and VI. Only the Lucitone 199 resin long-cured samples showed a significant decrease in transverse strength from dry conditions to water storage. Lucitone 199 short-cured resin and Accelar 20 resin samples showed a decrease in transverse strength. However, this decrease was not statistically significant. The Triad resin specimens showed almost no change in transverse strength under any of the experimental conditions. However, at each measurement time, the Triad resin specimens exhibited significantly lower transverse strength values than the other resins. DISCUSSION
Previous studies 68- have shown a decrease in transverse strengths for polymethyl methacrylate denture base resins 512
OCTOBER 1991 VOLUME 66 NUMBER 4
TRANSVERSESTRENGTHSOF DENTURE BASE RESINS
CLINICAL
IMPLICATIONS
The results indicate that the transverse strength of Triad denture base resin is significantly lower than the heat polymerized brands Lucitone 199 and Accelar 20. Clinically, a resin material exhibiting a lower transverse strength may be more prone to fracture during function as a denture base than would a resin with a higher transverse strength. This potential for fracture may increase with use because of the water sorpti0n for some types of materials. CONCLUSION 1. Lucitone long-cured resin significantly decreases in transverse strength from dry to 30 days in water storage. 2. Accelar 20 resin shows minimal decrease in transverse strength from dry to 30 days in water storage. 3. The transverse strength of Triad resin was significantly lower than the other resins during all the time periods measured but was unaffected by water storage. 4. Changes in transverse strengths for all materials from 30 to 90 days of water storage were small and not statistically significant.
REFERENCES 1. Sweeney WA, Paffenbarger GC, Caul HJ, Sweeney WT. American Dental Association specification No. 12 for denture base resin: second revision. J Am Dent Assoc 1953;46:54-66. 2. Sweeney WT, Paffenbarger GC, Beall JR. Acrylic resins for dentures. J Am Dent Assoc 1942;29:7-33. 3. Sweeney WT, Caul H J, Gneug W. A transverse testing machine for denture resins. J Am Dent Assoc 1954;49:174-6. 4. Stafford GD, Handley RW. Transverse bend testing of denture base polymers. J Dent 1975;3:251-5. 5. Craig RG, ed. Restorative dental materials. 8th ed. St Louis: CV Mosby, 1989:512-3. 6. Gilbert AS, Pethrick RA, Phillips DW. Acoustic relaxation and infrared spectroscopic measurements of the plasticization of polymethyl methacrylate by water. J Appl Polymer Sci 1977;21:319-30. 7. Stafford GD, Smith DC. Some studies of the properties of denture base polymers. Br Dent J 1968;125:337-42. 8. Stafford GD, Bates JF, Huggett R, Handley RW. A review of the properties of some denture base polymers, J Dent 1980;8:292-306. 9. Braden M. Water absorption characteristics of dental microfine composite filling materials, II. Experimental materials. Biomater 1984;5:3735.
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An a n a l y s i s of the r e l a t i o n s h i p b e t w e e n m a n d i b u l a r a l v e o l a r bone loss and a low F r a n k f o r t - m a n d i b u l a r plane a n g l e J o h n W. U n g e r , D D S , a C h a r l e s W. E l l i n g e r , DDS, MS, b a n d J o h n C. G u n s o l l e y , D D S , M S c
Medical College of Virginia, School of Dentistry, Richmond, Va., and University of Kentucky, College of Dentistry, Lexington, Ky. A group of c o m p l e t e denture p a t i e n t s w a s studied to d e t e r m i n e the effect of a l o w F r a n k f o r t - m a n d i b u l a r plane angle on the loss o f r e s i d u a l ridge h e i g h t in the mandible. M e a s u r e m e n t s w e r e m a d e from tracings of c e p h a l o m e t r i c films. The Iow-FMA group did not e x p e r i e n c e s t a t i s t i c a l l y g r e a t e r a m o u n t s of a l v e o l a r ridge loss w h e n c o m p a r e d w i t h the group w i t h an FMA larger than 20 d e g r e e s . The loss of r e s i d u a l ridge h e i g h t for both groups f o l l o w e d a l i n e a r r e l a t i o n s h i p from y e a r 5 to y e a r 20. There w a s s o m e indication that the r e s i d u a l ridge h e i g h t w a s s m a l l e r initially in the Iow-FMA group. The r e l a t i v e effect of the loss of r e s i d u a l ridge height, c o m b i n e d w i t h s m a l l e r r e s i d u a l ridge height originally, indicates that the l o w - F M A p a t i e n t s are m o r e l i k e l y to h a v e a n a t o m i c deficiencies and p r o b l e m s w i t h c o m p l e t e d e n t u r e s a s s o c i a t e d w i t h this l a c k o f m a n d i b u l a r r e s i d u a l ridge height. (J PROSTHET DENT 1991;66:513-6.)
Supported by United States Public Health Service Research Grant No. R01 009401 from the Department of Health, Education, and Welfare. aAssociate Professor and Chairman, Department of Removable Prosthodontics, Medical College of Virginia, School of Dentistry. bprofessor, Department of Oral Health Practice, University of Kentucky, College of Dentistry. CDirector, Officeof Applied Research, Medical Collegeof Virginia, School of Dentistry. 10/1/25051 THE JOURNAL OF PROSTHETIC DENTISTRY
A l v e o l a r bone loss can have a profound effect on the success of complete denture treatment and is encountered most often in the mandible. A troublesome aspect of this problem is the wide variation frequently observed in the extent and amount of bone loss. The ability to predict which patients are likely to suffer great amounts of bone loss would be of importance to both patient and dentist. Reference has been made in the literature to a connection between residual ridge loss and a low 513
