- Email: [email protected]
Dimensional stability of occlusal splints
Dimensional David
M.
stability
Bohnenkamp,
DDS,
of occlusal
splints
MP
Sheppard Air Force Base, Tex. Five fabrication techniques and two storage methods were used to construct and store specimens to investigate the dimensional stability of acrylic resin occlusal splints. A research model was developed to more closely approximate the tooth coverage limits of occlusal splints. Ten specimens were fabricated on individual stone casts for each of the five techniques. Four die pins were transferred to each specimen, and the distances between the inside diameters of the pins were measured over a 2-week period. After construction, initial measurement, and removal from the cast, each acrylic resin specimen was stored in either a wet or a dry environment. Measurements between pins were made and recorded at five time intervals. The sprinkle-on techniques resulted in less dimensional change than the dough application, the vacuumadapted resin sheet and dough application, and the heat-cured denture processing techniques. Acrylic resin specimens stored in a wet environment showed less distortion 2 weeks after fabrication. (J PROSTHET DENT 1996;75:262-8.)
N
o treatment for dental disease has been characterized by more variety of concept and technique than that of interocclusal stabilization appliance therapy. Various uses and fabrication methods for these occlusal appliances have been described in the literature.1-26 Several descriptions report improved accuracy of fit and increased durability when a particular technique to fabricate occlusal splints is used. The primary construction methods described over the past 40 years include dough application, heat-cured processing, vacuum-adapted resin sheet combined with dough application, and segmental sprinkle-on techniques. A review of the literature reveals several unsubstantiated claims for improved dimensional stability when a particular fabrication technique is used. Grupe and Gromekg described the fabrication of a completely toothsupported bruxism splint with autopolymerizing acrylic resin mixed in a dough. They stated that this technique “offers the possibility of an absolutely accurate fitting of such an appliance” and felt that many bruxism splints, up to that time, had proved to be orthodontic appliances. Ramfjord and Ash1 stated that “by far the best appliance for patients with dysfunctional symptoms is the occlusal splint.” They described making the occlusal splint from wax, and “if the occlusal splint is made from casts mounted on an articulator and the acrylic is heat-cured, it is fairly easy to fit the splint in the mouth.” Allen0 also presented
The views or opinions expressed herein are the personal views of the author and do not necessarily reflect the views of the United States Air Force. This study was submitted as part of a thesis in partial fulfillment of the requirements for the degree of Master of Science in Prosthodontics, The University of Texas Graduate School of Biomedical Sciences at San Antonio. aLieutenant Colonel, U.S. Air Force, and Director, Dental Laboratory Technician Training Program. 10/l/69603
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a technique for the construction of occlusal bite guards from a wax-up made on mounted casts. The waxed bite guard was invested and then processed in clear heat-curing acrylic resin. According to Allen, “no adjustment should be needed to insert the appliance in the mouth.” Becker et a1.14 described a technique for fabricating night guards with a vacuum-adapted resin sheet and clear acrylic resin placed manually over the occlusal portion of the resin sheet. The authors pointed out that most previously reported techniques for construction of night guards had involved forming the appliance in wax but noted that their technique “. . is fast; and that time-consuming chairside fitting and adjusting are not necessary to compensate for processing distortions” as with heat-cured acrylic resin. AdamsI proposed a technique that “had as one of its advantages the accuracy and predictability of construction and fit.” He vacuum-adapted a clear acrylic resin splint to form a template on the maxillary cast. Different waxes were added to the template to provide for a centric relation record. The entire waxed occlusal splint and a stone index were fitted into a reline jig. Autopolymerizing acrylic resin was used to replace the waxes. The occlusal splint was processed in 100” F water and under air pressure. Adams concluded that processing acrylic resin in water under compressed air produced occlusal splints that were dimensionally more accurate than heat- or air-cured acrylic resin. Gjerde et all9 presented a technique for fabrication of an occlusal splint that they said “provided for less dimensional change than previous heat-cured methods.” Abaseplate wax pattern was flasked and processed with autopolymerizing acrylic resin and the flasks were placed under 3500 pounds of pressure for 10 minutes. The authors concluded that when this method is used the appliance should routinely fit onto the maxillary teeth without difficulty. Rass and Tregaskes15 felt that occlusal splints should be fabricated with autopolymerizing acrylic resin with a one-
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Fig. 2. Plastic sleeve modified for insertion onto die pin. Plastic sleeve will be retained in stone cast.
Fig. 1. Computer designed search model with paralleled
and machined die pins.
aluminum
re-
segment sprinkle-on technique. They applied the sprinkle-on technique to the vertical portion of the palate and to the buccal and occlusal surfaces of the maxillary cast to add stability, retention, and strength to the occlusal splint. The authors cautioned that premature removal from the cast would result in warpage of the acrylic resin. Hartman and Sweptson21 described a three-segment sprinkle-on fabrication technique. Their technique was based on addition of separate sections of autopolymerizing acrylic resin to the cast. Each section was allowed to complete polymerization before the next section was applied. The authors felt that this step-by-step segmental technique “minimized warpage and ensured a more accurate fit of the prosthesis.” The success of an occlusal splint depends on how well it fits; thus dimensional stability during the construction process is critical. It is reasonable to assume that a fabrication technique should exist for removable acrylic resin occlusal splints that can minimize distortion, eliminate mechanical stress, and provide a precise fit. There is little scientific evidence to indicate optimum techniques, materials, or storage methods for occlusal splint fabrication.26 The purpose of this study was to design and construct an investigation to determine the effects of five fabrication techniques and two storage methods on the dimensional stability of removable acrylic resin occlusal splints.
MATERIAL
AND METHODS
An aluminum research model was designed on a computer and constructed with the average dimensions for a maxillary dentate arch.* Four 2.0 mm diameter cylindric depressions were placed on the occlusal surface of the re-
*Kuebker WA, personal communication,
March
1996
San Antonio, Tex., 1986.
search model in the canine and second molar regions. A surveyor was used to parallel the occlusal surface and to place die pins in the cylindric depressions. Polyvinyl siloxane impression material was used to secure the pins in centered and paralleled positions on the research model (Fig. 1). The aluminum research model, with four die pins in place, was positioned in a duplicating flask and impressed with irreversible hydrocolloid. Fifty-six grams of irreversible hydrocolloid was vacuum-mixed with 350 ml of distilled water for 45 seconds to produce a smooth, runny, bubble-free mixture for duplication. The impression material was allowed to set for 5 minutes. Plastic die pin sleeves were altered by shortening their length to coincide with the nontapered ends of the die pins. Each plastic sleeve was then removed and replaced on its accompanying die pin in a reversed position (Fig. 2). This allowed for the plastic sleeves to be securely retained in the fabricated stone cast. After the aluminum research model was removed from the impression material in the duplicating flask, the die pins with altered plastic sleeves were placed in the depressions of the impression. To complete the fabrication of each research cast, vacuum-mixed improved dental stone was carefully vibrated into the impression. The dental stone was allowed to set for 1 hour, at which time the completed research cast was withdrawn from the impression material. After the research casts were dried, each embedded die pin was removed, cleaned, and inverted to provide a retentive flange approximately 1.5 mm above the stone cast occlusal surface (Fig. 3). Vertical grooves were placed in the metal flange to prevent rotation of each pin within the specimen. The locations of the pins were designated A, B, C, and D (Fig. 4). The outline, thickness, and overall dimensions of all acrylic resin specimens were made to approximate each other, not only within each design set but also among all the designs. The design of each acrylic resin specimen ensured coverage of 3 mm of the lingual and occlusal surfaces and 3 mm of the facial and distal surfaces of the research cast arch form.
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Fig. 3. Die pin inverted in research cast. Vertical groove and metal flange provide antirotational and mechanical lock of pin to acrylic resin specimen.
EORNENKAMP
Fig. 4. Research designated
Five specific fabrication techniques were used to construct 50 removable acrylic resin specimens. Ten specimens were fabricated on individual stone research casts for each of the five fabrication techniques. The five fabrication techniques were: 1. Design 1 was a one-segment sprinkle-on technique of autopolymerizing acrylic resin. 2. Design 2 was a three-segment sprinkle-on technique of autopolymerizing acrylic resin. 3. Design 3 was an autopolymerizing acrylic resin mixed into a dough and manually adapted over a research cast. 4. Design 4 was a clear 0.060 inch resin sheet vacuumadapted over a research cast and autopolymerizing acrylic resin mixed into a dough and manually placed over the resin sheet. 5. Design 5 was two thicknesses of baseplate wax adapted over a research cast and duplicated in clear heat-curing acrylic resin according to standard laboratory procedures for processing complete dentures. After construction, initial measurement, and removal from the research cast, each specimen was stored in either a wet or dry environment for the duration of the study. Half the available specimens from each design group were selected and stored in water at room temperature. The remaining specimens were stored in air at room temperature. As a method to determine the dimensional stability of the specimens, the distances between the inside diameters of the four die pins were measured with a linear measuring microscope. These distances, labeled A-B, C-D, A-C, and B-D, represented anterior, posterior, left, and right dimensions, respectively, of the casts and specimens. Baseline measurements were made and recorded at the following time periods: initial measurement, on research cast; on cast, after fabrication of each specimen; 0 hours, specimen off cast; 24 hours, specimen stored wet or dry; 72 hours, specimen stored wet or dry; and 2 weeks, specimen stored wet or dry. Initial measurements for design 4 spec-
264
cast and acrylic resin pin locations A, B, C, and D.
specimen
with
imens were made with the resin sheet vacuum-adapted to each cast. Initial measurements for design 5 specimens were made with the baseplate wax adapted to each cast. A four-factor repeated-measures experimental design was used for this study. The four factors were design, storage condition, location of the measurements, and time intervals. The dependent measure was cumulative linear dimensional change as measured by subtracting the initial measurement from the measurement at each time period. A four-factor repeated-measures analysis of variance was used for statistical analysis. In the case of significant interactions, appropriate tests of simple primary effects with two-way and single-factor partitioning of variance were performed. All multiple pairwise comparisons were assessed with the Scheffe F ratio test. The level of significance was established at 0.05.
RESULTS The means and SDS of cumulative linear dimensional change across designs, locations, and time intervals for specimens stored in a wet or a dry condition are presented in Tables I and II. The design 1 fabrication technique provided for the least cumulative linear dimensional change over the measured time intervals, and the design 4 fabrication technique provided for the greatest cumulative linear dimensional change. The wet storage method resulted in less cumulative linear dimensional change for each design at each location at 2 weeks than the dry storage method did, except for design 1 at location C-D. The four-factor repeated-measures analysis of variance revealed that cumulative linear dimensional change significantly differed across designs, storage conditions, locations of the measurements, and time intervals (Table III). Because of significant interactions among design, location, and time and storage condition, location, and time, these
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DENTISTRY
Statistical means and SDS of cumulative linear dimensional change for wet storage condition On cast
0 Hours
24 Hours
72 Hours
2 Weeks
1
Design
A-B C-D
A-C B-D Design A-B C-D A-C B-D Design A-B C-D A-C B-D Design A-B C-D A-C B-D Design A-B C-D A-C B-D
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+0.018 (0.030) -0.007 (0.012) -0.021(0.006) -0.038 (0.014)
-0.015 -0.066 -0.048 -0.068
(0.046) (0.029) (0.011) (0.016)
-0.019 (0.012) -0.032 (0.0'76) -0.060 (0.017) -0.069(0.006)
+0.006 +O.olO -0.046 -0.067
(0.027) (0.076) (0.006) (0.016)
+0.043 +0.097 -0.048 -0.063
(0.025) (0.075) (0.007) (0.012)
-0.016 (0.022) -0.016 (0.014) -0.031(0.025) -0.013(0.017)
-0.080 (0.022) -0.115 (0.045) -0.065 (0.017) -0.040(0.014)
-0.078 (0.029) -0.144(0.067) -0.074(0.015) -0.051(0.018)
-0.074(0.044) -0.138 (0.074) -0.074(0.015) -0.045 (0.020)
-0.052 -0.074 -0.066 -0.042
(0.038) (0.056) (0.014) (0.015)
-0.069 (0.060) -0.039 (0.052) -0.095 (0.081) -0.086(0.043)
-0.161(0.054) -0.239 (0.053) -0.103 (0.079) -0.101(0.033)
-0.176(0.043) -0.323 (0.051) -0.100 (0.078) -0.098 (0.036)
-0.178 (0.043) -0.341(0.055) -0.095 (0.071) -0.100 (0.034)
-0.126(0.059) -0.182 (0.090) -0.076 (0.070) -0.076 (0.031)
-0.150 -0.075 -0.119 -0.105
-0.198 (0.046) -0.242 (0.085) -0.127 (0.033) -0.112(0.038)
-0.228 (0.048) -0.378(0.119) -0.127(0.02'7) -0.106 (0.033)
-0.225 (0.054) -0.430 (0.118) -0.127(0.038) -0.100 (0.024)
-0.184(0.060) -0.352 (0.101) -0.103 (0.031) -0.087 (0.030)
-0.156 -0.145 -0.063 -0.062
-0.164(0.031) -0.116(0.062) -0.065 (0.068) -0.054(0.059)
-0.163 -0.164 -0.067 -0.065
-0.145 -0.128 -0.059 -0.058
2
3
4
(0.015) (0.022) (0.026) (0.025)
5
-0.070 (0.043) +0.001(0.034) -0.054(0.072) -0.046(0.045)
(0.033) (0.069) (0.060) (0.050)
(0.036) (0.061) (0.063) (0.051)
(0.036) (0.047) (0.065) (0.051)
All values are in millimeters. Table
II. Statistical means and SDS of cumullative linear dimensional change for dry storage condition On east
Design A-B C-D A-C B-D Design A-B C-D A-C B-D Design A-B C-D A-C 3-D Design A-B C-D A-C B-D Design A-B C-D A-C B-D
0 Hours
24 Hours
72 Hours
2 Weeks
1
-0.002 -0.002 -0.029 -0.029
(0.017) (0.020) (0.030) (0.024)
-0.050 -0.057 -0.062 -0.059
(0.090) (0.025) (0.030) (0.012)
-0.04010.022) -0.039 (0.035) -0.078 (0.024) -0.077 (0.019)
-0.057(0.023) -0.036 (0.045) -0.085 (0.029) -0.085 (0.013)
-0.069 (0.034) -0.031(0.070) -0.105 (0.027) -0.102 (0.027)
-0.013 -0.002 -0.025 -0.005
(0.022) (0.014) (0.014) (0.015)
-0.069 -0.074 -0.056 -0.038
(0.025) (0.032) (0.010) (0.011)
-0.087 (0.021) -0.097 (0.036) -0.076 (0.010) -0.066(0.051)
-0.106(0.028) -0.115 (0.051) -0.091(0.013) -0.072 (0.014)
-0.127(0.034) -0.140 (0.045) -0.102(0.013) -0.08110.014)
-0.059 -0.084 -0.153 -0.096
(0.075) (0.046) (0.038) (0.066)
-0.148 (0.060) -0.280(0.085) -0.168t0.040) -0.147 (0.036)
-0.151(0.056) -0.269(0.143) -0.179(0.038) -0.146 (0.044)
-0.160 (0.062) -0.261(0.155) -0.183 (0.042) -0.159 (0.042)
-0.153 (0.056) -0.215 (0.144) -0.188CO.042) -O-162(0.037)
-0.145 (0.049) -0.093 (0.030) -0.160 (0.047) -0.188(0.026)
-0.214(0.062) -0.305(0.095) -0.162(0.039) -0.147 (0.063)
-0.246(0.072) -0.426(0.153) -0.166 (0.041) -0.129 (0.030)
-0.266 (0.090) -0.458(0.168) -0.175(0.042) -0.136 (0.036)
-0.278 (0.093) -0.468 (0.176) -0.184(0.043) -0.141(0.025)
-0.061(0.080) -0.037 (0.027) -0.107 (0.039) -0.075 (0.044)
-0.152 -0.227 -0.100 -0.078
-0.162 (0.090) -0.229(0.066) -0.107 (0.027) -0.089 (0.041)
-0.168(0.085) -0.236 (0.065) -0.124(0.029) -0.101(0.044)
-0.196 (0.080) -0.269 (0.095) -0.151(0.027) -0.129 (0.040)
2
3
4
5
(0.085) (0.059) (0.031) (0.043)
All values are in millimeters.
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Table
III.
OF PROSTHETIC
Four-factor
DENTISTRY
BOHNENKAMP
repeated-measures
SOIWX
Degrees
Design Condition Design x condition Location Design x location Condition x location Design x condition x location Subjects with groups Time intervals Design x time Condition x time Design x condition x time Location x time Design x location x time Condition x location x time Design x condition x location x time Time x subjects with groups *Significance
Table
of variance
at freedom
4 1 4 3 12 3 12 160 4 16 4 16 760 48 12 48 640
IV. Multiple
pairwise
Location A-B
Location C-D Location A-C
comparison
12354 -
12534
~-
12534
of squares
Mean
square
F ratio
3.312 0.240 0.045 0.872
0.828 0.240 0.011 0.291
67.376 19.541 0.912 23.663
1.129 0.018
0.094 0.006 0.009 0.012 0.218 0.010 0.033 0.001 0.044 0.010 0.002 0.001
7.655 0.491 0.723
0.107 1.966 0.872 0.155 0.130 0.155 0.522 0.483 0.025 0.039 0.393
21534
denotes
statistically
--
significant
analyses
Significance
level
0.0001” 0.0001” 0.4587 0.0001* 0.0001” 0.6888 0.7276
0.0001” 0.0001” 0.0001” 0.0001* 0.0001* 0.0001* 0.0001* 0.0800
355.377 15.765 53.153 1.599 70.953 16.417 3.351 1.315
0.001
of designs 0 Hours
24 Hours
72 Hours
12354 --
12354 --
12354 -
12534
-
-
12534
--
Location B-D
subsets
-
12534
12534
2 Weeks
12354 -
12354
-
-
-
12.532
12534
12534
25143
21543
21543
-
21534
--
listed in order of increasing
significant effects are only important when they are considered with respect to each other. Thus simple primary effects tests were performed. No significant interactions existed between storage condition and location across any of the time intervals. However, significant differences did exist for storage condition across two of the time intervals and for location across all the time intervals. Significant interactions existed between design and location across each of the time intervals. Multiple pairwise comparison analyses of the designs at each location at each time interval were analyzed (Table IV). Statistically significant subsets are underlined and listed in order of increasing dimensional change from left to right.
DISCUSSION It was surprising to find only one study in the literature that had compared materials or construction techniques used for acrylic resin occlusal splints. Steele et a1.26
266
Sum
at p < 0.05.
On cast
Underline
analysis
dimensional
change,
left to right,
at p < 0.05
reported that the intraoral fit and retention of interocclusal splints were apparently unaffected by the material used (heat-cured or autopolymerizing polymethyl methacrylate). They advised use of heat-cured acrylic resin to optimize mechanical properties and minimize processing faults when interocclusal splints are intended for longterm wear. In this investigation the sprinkle-on autopolymerizing acrylic resin fabrication techniques displayed less linear dimensional change than the other fabrication techniques at all locations across a 2-week interval. Also, the vacuumadapted resin sheet and acrylic resin dough application technique displayed more linear dimensional change than the other techniques at all locations across a 2-week interval, except for the dough application technique at location B-D at 24 hours, 72 hours, and 2 weeks. The design 4 specimens constructed were representative of those occlusal splints in the literature fabricated with a
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vacuum-adapted resin sheet and acrylic resin dough application technique. In particular, the design 4 specimens demonstrated more linear dimensional change than did design 5 specimens, which were constructed by the heatcured acrylic resin denture processing technique. Thus any claim of greater dimensional stability for the vacuumadapted resin sheet and acrylic resin dough application technique compared with the heat-cured denture processremains unsubstantiated. ing technique14, I7 No significant differences in linear dimensional change were noted among design 1 and 2 specimens at any locations at any of the time intervals. This finding suggests that the incorporation of three segmental stages in a sprinkle-on technique for autopolymerizing acrylic resin’l does not seem to offer any advantages for minimizing linear dimensional change compared with a one-segment sprinkle-on fabrication technique. The majority of studies that evaluated storage methods for acrylic resins have concluded that storage methods significantly affect dimensional stability.27-34 Acrylic resins increase in dimension on wetting and decrease in dimension on drying. In this study a significant difference in the linear dimensional change of the acrylic resin specimens was noted between storage conditions at only one of the time intervals. Specimens stored in a wet environment demonstrated significantly less linear dimensional change after 2 weeks than did specimens stored in a dry environment. After saturation in water for 2 weeks the anticipated expansion took place for specimens stored in a wet condition; this was most apparent at the posterior location C-D. In the case of the specimens fabricated by the one-segment sprinkle-on technique, the water immersion was sufficient to cause an expansion greater than the initial contraction and a final slight expansion occurred. This observation is in agreement with the findings reported by Craig4 and Ogle et al.23 On the basis of their observations, they suggested that this net positive dimensional change may cause autopolymerizing acrylic resin appliances to be slightly oversized. However, in this study net positive dimensional changes were observed only for the one-segment sprinkle-on specimens and not for the specimens fabricated by either the three-segment sprinkle-on technique or the dough application technique.
CLINICAL
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DENTISTRY
technician should be aware that fabrication techniques and storage methods may influence the dimensional stability of acrylic resin occlusal splints. When deciding to make a passive occlusal splint or active orthodontic appliance, certain criteria are considered. The magnitude of the cumulative linear dimensional changes of the specimens in this study varied widely, although it did not exceed 0.5 mm. Further clinical research is indicated to determine whether changes of this amount significantly affect the oral dynamics of these prostheses. Because adverse forces may be transmitted to teeth and supporting periodontal structures by occlusal splints, optimal design and fabrication based on the best available research may preserve the health of the teeth and periodontium.
SUMMARY Various design features and construction methods have been proposed to cope with the inherent problems of distortion of removable acrylic resin occlusal splints. By use of original research methods it appears that cumulative linear dimensional change may be evaluated to determine the relative dimensional stability of occlusal splints constructed by different techniques. The results of this study suggest the laboratory use of an autopolymerizing acrylic resin sprinkle-on fabrication technique and a wet storage method to minimize dimensional change before the clinical use of an acrylic resin occlusal splint.
CONCLUSIONS On the basis of the results of this study, the following conclusions were drawn. 1. No significant differenceinlinear dimensional change was revealed between the one- and three-segment sprinkle-on fabrication techniques. 2. The sprinkle-on fabrication techniques appeared to provide less linear dimensional change than the other fabrication techniques studied. 3. The vacuum-adapted resin sheet and dough application techniques provided the greatest linear dimensional change among the fabrication techniques studied. 4. All specimens stored in a wet environment demonstrated significantly less linear dimensional change 2 weeks after fabrication than did specimens stored in a dry environment,
IMPLICATIONS
When acrylic resin is used in a situation that requires dimensional precision, one of the properties that is given first consideration is stability. The accurate and precise fit of an occlusal splint in the mouth of a patient is of prime importance to the clinician. Consequently, any change in the dimensions of an occlusal splint, either during fabrication or storage before delivery to the patient, is of importance. Because acrylic resins exhibit certain unavoidable dimensional changes, the clinician and the laboratory
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I thank Drs. William A. Kuebker, William J. Thrash, Barry K. Norling, Kenneth D. Rudd, and Charles R. Dufort for their contributions to this study. REFERENCES 1. Ramfjord SP, Ash MM. Occlusion. 2nd ed. Philadelphia: WB Saunders, 1971:248-50. 2. Kornfkld M. Mouth rehabilitation: clinical and laboratory procedures. 2nd ed. St. Louis: CV Mosby, 1974;1:178-9. 3. McNeil1 C. Diagnostic and treatment appliances. In: Eismann HF,
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4. 5.
6.
7. 8. 9. 10. 11. 12. 13.
14. 15. 16. 17. 18. 19.
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OF PROSTHETIC
DENTISTRY
Rudd KD, Morrow RM, eds. Dental laboratory procedures: fuied partial dentures. St. Louis: CV Mosby, 1980;2:327-46. Craig RG. Restorative dental materials. 6th ed. St. Louis: CV Mosby, 1980:358-75. Okeson J. Biteguard therapy and fabrication: advances in occlusion. Boston: John Wright-PSG, 1982;14:220-6. (Postgraduate dental handbook series.) Wagner EP, Crandall SK, Oliver RB. Splints. In: Morgan DS, House LR, Hall WP, Vamvas SJ, eds. Diseases of the temporomandibular apparatus. 2nd ed. St Louis: CV Mosby, 1982:265-76. Friedman MH, Weisberg J. Temporomandibular joint disorders: diagnosis and treatment. Chicago: Quintessence, 1985:77-80. Stahl DG. A simplified procedure for fabricating a temporary removable acrylic bite plate. J Periodontol 1956;26:118-9. Grupe HE, Gromek JJ. Bruxism splint: technique using quick cure acrylic. J Periodontol 1959;30:156-7. Allen DL. Accurate occlusal bite guards. Periodontics 1967;5:93-5. Askinas SW. Fabrication of an occlusal splint. J PROSTHET DENT 1972;28:549-51. Shulman J. A technique for bite plane construction. J PROSTHET DENT 1973;29:334-9. Horn R. Economical construction of bite planes for symptomatic treatment of temporomandibular joint dysfunction. Quintessence Int 1973; 4:71-4. Becker CM, Kaiser DA, Lemm RB. A simplified technique for fabrication of night guards. J PROSTHET DENT 1974;32:582-9. Kass CA, Tregaskes JN. Occlusal splint fabrication. J PROSTHET DENT 1978;40:461-3. von Krammer RK. Constructing occlusal splints. J PROSTHET DENT 1979:41:105-B. Adams HF. Fabrication of a maxillary occlusal treatment splint. J PROSTHET DENT 1979;42:106-11. LundeenTF. Occlusal splint fabrication. JPROSTHETDENT 1979;42:58891. Gjerde K, Clark GT, Solberg WK, S&ho D. A technique for construction of a temporomandibular occlusal stabilization splint (orthotic appliance). Quintessence Dent Tech 1981;5:43-52. Rehany A, Stern N. The modified Hawley occlusal splint. J PROSTHET DENT 1981;48:536-41.
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21. Hartmann GE, Swepston JH. Mandibular stabilization prosthesis. J PROSTHET DENT 1982;48:215-9. 22. Bates RE, Lewis JE, Atkinson WB. Single-appointment occlusal splints. Gen Dent 1984;2:44-6. 23. Ogle RE, Sorensen SE, Lewis EA. A new visible light-cured resin system applied to removable prosthodontics. J PROSTHET DENT 1986;56: 497-506. 24. Haddix JE. A simplified technique for occlusal splint fabrication. J PROSTHET DENT 1987;57:249-51. 25. Shulman J, Zeno A. A new technique for making occlusal devices. J PROSTHET DENT 1990;63:482-5. 26. Steele JG, Wassell RW, Walls AW. A comparative study of the fit and retention of interocclusal splints constructed from heat-cured and autopolymerizedpolymethylmethacrylate. JPRosTHETDENT~~~~;~~:~~~30. 27. Sweeney WT, Paffenbarger GC, Beall JR. Acrylic resins in dentistry. J Am Dent Assoc 1942;29:7-33. 28. Skinner EW, Cooper EN. Physical properties of denture resins, I: curing shrinkage and water sorption. J Am Dent Assoc 1943;30:184552. 29. McCracken WL. Evaluation of activated methyl methacrylate denture base materials. J PROSTHET DENT 1952;2:68-74. 30. Skinner EW, Jones PM. Dimensional stability of self-curing denture base materials. J Am Dent Assoc 1955;51:426-31. 31. Mowery WE, Burns CL, Dickson G, Sweeney WT. Dimensional changes occurring in dentures during processing. J Am Dent Assoc 1960;61:41330. 32. Woelfel JB, Paffenbarger GC, Sweeney WT. Changes in dentures during storage in water and in service. J Am Dent Assoc 1961;62:643-57. 33. Goodkind RJ, Schuke RC. Dimensional accuracy of pour acrylic resins and conventional processing of cold-curing acrylic resin bases. J PROSTHET DENT 1970;24:662-8. 34. Stafford GD, Bates JF, Huggett R. A review of the properties of some orthodontic base polymers. J Dent Res 1983;11:294-305.
Reprintrequeststo: DR. DAVID M. BOHNENXANIP 372 GOLDEN EAGLE DR. BROOMFIELD, CO 80020
VOLUME
75
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M.
stability
Bohnenkamp,
DDS,
of occlusal
splints
MP
Sheppard Air Force Base, Tex. Five fabrication techniques and two storage methods were used to construct and store specimens to investigate the dimensional stability of acrylic resin occlusal splints. A research model was developed to more closely approximate the tooth coverage limits of occlusal splints. Ten specimens were fabricated on individual stone casts for each of the five techniques. Four die pins were transferred to each specimen, and the distances between the inside diameters of the pins were measured over a 2-week period. After construction, initial measurement, and removal from the cast, each acrylic resin specimen was stored in either a wet or a dry environment. Measurements between pins were made and recorded at five time intervals. The sprinkle-on techniques resulted in less dimensional change than the dough application, the vacuumadapted resin sheet and dough application, and the heat-cured denture processing techniques. Acrylic resin specimens stored in a wet environment showed less distortion 2 weeks after fabrication. (J PROSTHET DENT 1996;75:262-8.)
N
o treatment for dental disease has been characterized by more variety of concept and technique than that of interocclusal stabilization appliance therapy. Various uses and fabrication methods for these occlusal appliances have been described in the literature.1-26 Several descriptions report improved accuracy of fit and increased durability when a particular technique to fabricate occlusal splints is used. The primary construction methods described over the past 40 years include dough application, heat-cured processing, vacuum-adapted resin sheet combined with dough application, and segmental sprinkle-on techniques. A review of the literature reveals several unsubstantiated claims for improved dimensional stability when a particular fabrication technique is used. Grupe and Gromekg described the fabrication of a completely toothsupported bruxism splint with autopolymerizing acrylic resin mixed in a dough. They stated that this technique “offers the possibility of an absolutely accurate fitting of such an appliance” and felt that many bruxism splints, up to that time, had proved to be orthodontic appliances. Ramfjord and Ash1 stated that “by far the best appliance for patients with dysfunctional symptoms is the occlusal splint.” They described making the occlusal splint from wax, and “if the occlusal splint is made from casts mounted on an articulator and the acrylic is heat-cured, it is fairly easy to fit the splint in the mouth.” Allen0 also presented
The views or opinions expressed herein are the personal views of the author and do not necessarily reflect the views of the United States Air Force. This study was submitted as part of a thesis in partial fulfillment of the requirements for the degree of Master of Science in Prosthodontics, The University of Texas Graduate School of Biomedical Sciences at San Antonio. aLieutenant Colonel, U.S. Air Force, and Director, Dental Laboratory Technician Training Program. 10/l/69603
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a technique for the construction of occlusal bite guards from a wax-up made on mounted casts. The waxed bite guard was invested and then processed in clear heat-curing acrylic resin. According to Allen, “no adjustment should be needed to insert the appliance in the mouth.” Becker et a1.14 described a technique for fabricating night guards with a vacuum-adapted resin sheet and clear acrylic resin placed manually over the occlusal portion of the resin sheet. The authors pointed out that most previously reported techniques for construction of night guards had involved forming the appliance in wax but noted that their technique “. . is fast; and that time-consuming chairside fitting and adjusting are not necessary to compensate for processing distortions” as with heat-cured acrylic resin. AdamsI proposed a technique that “had as one of its advantages the accuracy and predictability of construction and fit.” He vacuum-adapted a clear acrylic resin splint to form a template on the maxillary cast. Different waxes were added to the template to provide for a centric relation record. The entire waxed occlusal splint and a stone index were fitted into a reline jig. Autopolymerizing acrylic resin was used to replace the waxes. The occlusal splint was processed in 100” F water and under air pressure. Adams concluded that processing acrylic resin in water under compressed air produced occlusal splints that were dimensionally more accurate than heat- or air-cured acrylic resin. Gjerde et all9 presented a technique for fabrication of an occlusal splint that they said “provided for less dimensional change than previous heat-cured methods.” Abaseplate wax pattern was flasked and processed with autopolymerizing acrylic resin and the flasks were placed under 3500 pounds of pressure for 10 minutes. The authors concluded that when this method is used the appliance should routinely fit onto the maxillary teeth without difficulty. Rass and Tregaskes15 felt that occlusal splints should be fabricated with autopolymerizing acrylic resin with a one-
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Fig. 2. Plastic sleeve modified for insertion onto die pin. Plastic sleeve will be retained in stone cast.
Fig. 1. Computer designed search model with paralleled
and machined die pins.
aluminum
re-
segment sprinkle-on technique. They applied the sprinkle-on technique to the vertical portion of the palate and to the buccal and occlusal surfaces of the maxillary cast to add stability, retention, and strength to the occlusal splint. The authors cautioned that premature removal from the cast would result in warpage of the acrylic resin. Hartman and Sweptson21 described a three-segment sprinkle-on fabrication technique. Their technique was based on addition of separate sections of autopolymerizing acrylic resin to the cast. Each section was allowed to complete polymerization before the next section was applied. The authors felt that this step-by-step segmental technique “minimized warpage and ensured a more accurate fit of the prosthesis.” The success of an occlusal splint depends on how well it fits; thus dimensional stability during the construction process is critical. It is reasonable to assume that a fabrication technique should exist for removable acrylic resin occlusal splints that can minimize distortion, eliminate mechanical stress, and provide a precise fit. There is little scientific evidence to indicate optimum techniques, materials, or storage methods for occlusal splint fabrication.26 The purpose of this study was to design and construct an investigation to determine the effects of five fabrication techniques and two storage methods on the dimensional stability of removable acrylic resin occlusal splints.
MATERIAL
AND METHODS
An aluminum research model was designed on a computer and constructed with the average dimensions for a maxillary dentate arch.* Four 2.0 mm diameter cylindric depressions were placed on the occlusal surface of the re-
*Kuebker WA, personal communication,
March
1996
San Antonio, Tex., 1986.
search model in the canine and second molar regions. A surveyor was used to parallel the occlusal surface and to place die pins in the cylindric depressions. Polyvinyl siloxane impression material was used to secure the pins in centered and paralleled positions on the research model (Fig. 1). The aluminum research model, with four die pins in place, was positioned in a duplicating flask and impressed with irreversible hydrocolloid. Fifty-six grams of irreversible hydrocolloid was vacuum-mixed with 350 ml of distilled water for 45 seconds to produce a smooth, runny, bubble-free mixture for duplication. The impression material was allowed to set for 5 minutes. Plastic die pin sleeves were altered by shortening their length to coincide with the nontapered ends of the die pins. Each plastic sleeve was then removed and replaced on its accompanying die pin in a reversed position (Fig. 2). This allowed for the plastic sleeves to be securely retained in the fabricated stone cast. After the aluminum research model was removed from the impression material in the duplicating flask, the die pins with altered plastic sleeves were placed in the depressions of the impression. To complete the fabrication of each research cast, vacuum-mixed improved dental stone was carefully vibrated into the impression. The dental stone was allowed to set for 1 hour, at which time the completed research cast was withdrawn from the impression material. After the research casts were dried, each embedded die pin was removed, cleaned, and inverted to provide a retentive flange approximately 1.5 mm above the stone cast occlusal surface (Fig. 3). Vertical grooves were placed in the metal flange to prevent rotation of each pin within the specimen. The locations of the pins were designated A, B, C, and D (Fig. 4). The outline, thickness, and overall dimensions of all acrylic resin specimens were made to approximate each other, not only within each design set but also among all the designs. The design of each acrylic resin specimen ensured coverage of 3 mm of the lingual and occlusal surfaces and 3 mm of the facial and distal surfaces of the research cast arch form.
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Fig. 3. Die pin inverted in research cast. Vertical groove and metal flange provide antirotational and mechanical lock of pin to acrylic resin specimen.
EORNENKAMP
Fig. 4. Research designated
Five specific fabrication techniques were used to construct 50 removable acrylic resin specimens. Ten specimens were fabricated on individual stone research casts for each of the five fabrication techniques. The five fabrication techniques were: 1. Design 1 was a one-segment sprinkle-on technique of autopolymerizing acrylic resin. 2. Design 2 was a three-segment sprinkle-on technique of autopolymerizing acrylic resin. 3. Design 3 was an autopolymerizing acrylic resin mixed into a dough and manually adapted over a research cast. 4. Design 4 was a clear 0.060 inch resin sheet vacuumadapted over a research cast and autopolymerizing acrylic resin mixed into a dough and manually placed over the resin sheet. 5. Design 5 was two thicknesses of baseplate wax adapted over a research cast and duplicated in clear heat-curing acrylic resin according to standard laboratory procedures for processing complete dentures. After construction, initial measurement, and removal from the research cast, each specimen was stored in either a wet or dry environment for the duration of the study. Half the available specimens from each design group were selected and stored in water at room temperature. The remaining specimens were stored in air at room temperature. As a method to determine the dimensional stability of the specimens, the distances between the inside diameters of the four die pins were measured with a linear measuring microscope. These distances, labeled A-B, C-D, A-C, and B-D, represented anterior, posterior, left, and right dimensions, respectively, of the casts and specimens. Baseline measurements were made and recorded at the following time periods: initial measurement, on research cast; on cast, after fabrication of each specimen; 0 hours, specimen off cast; 24 hours, specimen stored wet or dry; 72 hours, specimen stored wet or dry; and 2 weeks, specimen stored wet or dry. Initial measurements for design 4 spec-
264
cast and acrylic resin pin locations A, B, C, and D.
specimen
with
imens were made with the resin sheet vacuum-adapted to each cast. Initial measurements for design 5 specimens were made with the baseplate wax adapted to each cast. A four-factor repeated-measures experimental design was used for this study. The four factors were design, storage condition, location of the measurements, and time intervals. The dependent measure was cumulative linear dimensional change as measured by subtracting the initial measurement from the measurement at each time period. A four-factor repeated-measures analysis of variance was used for statistical analysis. In the case of significant interactions, appropriate tests of simple primary effects with two-way and single-factor partitioning of variance were performed. All multiple pairwise comparisons were assessed with the Scheffe F ratio test. The level of significance was established at 0.05.
RESULTS The means and SDS of cumulative linear dimensional change across designs, locations, and time intervals for specimens stored in a wet or a dry condition are presented in Tables I and II. The design 1 fabrication technique provided for the least cumulative linear dimensional change over the measured time intervals, and the design 4 fabrication technique provided for the greatest cumulative linear dimensional change. The wet storage method resulted in less cumulative linear dimensional change for each design at each location at 2 weeks than the dry storage method did, except for design 1 at location C-D. The four-factor repeated-measures analysis of variance revealed that cumulative linear dimensional change significantly differed across designs, storage conditions, locations of the measurements, and time intervals (Table III). Because of significant interactions among design, location, and time and storage condition, location, and time, these
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Table
I.
OF PROSTHETIC
DENTISTRY
Statistical means and SDS of cumulative linear dimensional change for wet storage condition On cast
0 Hours
24 Hours
72 Hours
2 Weeks
1
Design
A-B C-D
A-C B-D Design A-B C-D A-C B-D Design A-B C-D A-C B-D Design A-B C-D A-C B-D Design A-B C-D A-C B-D
JOURNAL
+0.018 (0.030) -0.007 (0.012) -0.021(0.006) -0.038 (0.014)
-0.015 -0.066 -0.048 -0.068
(0.046) (0.029) (0.011) (0.016)
-0.019 (0.012) -0.032 (0.0'76) -0.060 (0.017) -0.069(0.006)
+0.006 +O.olO -0.046 -0.067
(0.027) (0.076) (0.006) (0.016)
+0.043 +0.097 -0.048 -0.063
(0.025) (0.075) (0.007) (0.012)
-0.016 (0.022) -0.016 (0.014) -0.031(0.025) -0.013(0.017)
-0.080 (0.022) -0.115 (0.045) -0.065 (0.017) -0.040(0.014)
-0.078 (0.029) -0.144(0.067) -0.074(0.015) -0.051(0.018)
-0.074(0.044) -0.138 (0.074) -0.074(0.015) -0.045 (0.020)
-0.052 -0.074 -0.066 -0.042
(0.038) (0.056) (0.014) (0.015)
-0.069 (0.060) -0.039 (0.052) -0.095 (0.081) -0.086(0.043)
-0.161(0.054) -0.239 (0.053) -0.103 (0.079) -0.101(0.033)
-0.176(0.043) -0.323 (0.051) -0.100 (0.078) -0.098 (0.036)
-0.178 (0.043) -0.341(0.055) -0.095 (0.071) -0.100 (0.034)
-0.126(0.059) -0.182 (0.090) -0.076 (0.070) -0.076 (0.031)
-0.150 -0.075 -0.119 -0.105
-0.198 (0.046) -0.242 (0.085) -0.127 (0.033) -0.112(0.038)
-0.228 (0.048) -0.378(0.119) -0.127(0.02'7) -0.106 (0.033)
-0.225 (0.054) -0.430 (0.118) -0.127(0.038) -0.100 (0.024)
-0.184(0.060) -0.352 (0.101) -0.103 (0.031) -0.087 (0.030)
-0.156 -0.145 -0.063 -0.062
-0.164(0.031) -0.116(0.062) -0.065 (0.068) -0.054(0.059)
-0.163 -0.164 -0.067 -0.065
-0.145 -0.128 -0.059 -0.058
2
3
4
(0.015) (0.022) (0.026) (0.025)
5
-0.070 (0.043) +0.001(0.034) -0.054(0.072) -0.046(0.045)
(0.033) (0.069) (0.060) (0.050)
(0.036) (0.061) (0.063) (0.051)
(0.036) (0.047) (0.065) (0.051)
All values are in millimeters. Table
II. Statistical means and SDS of cumullative linear dimensional change for dry storage condition On east
Design A-B C-D A-C B-D Design A-B C-D A-C B-D Design A-B C-D A-C 3-D Design A-B C-D A-C B-D Design A-B C-D A-C B-D
0 Hours
24 Hours
72 Hours
2 Weeks
1
-0.002 -0.002 -0.029 -0.029
(0.017) (0.020) (0.030) (0.024)
-0.050 -0.057 -0.062 -0.059
(0.090) (0.025) (0.030) (0.012)
-0.04010.022) -0.039 (0.035) -0.078 (0.024) -0.077 (0.019)
-0.057(0.023) -0.036 (0.045) -0.085 (0.029) -0.085 (0.013)
-0.069 (0.034) -0.031(0.070) -0.105 (0.027) -0.102 (0.027)
-0.013 -0.002 -0.025 -0.005
(0.022) (0.014) (0.014) (0.015)
-0.069 -0.074 -0.056 -0.038
(0.025) (0.032) (0.010) (0.011)
-0.087 (0.021) -0.097 (0.036) -0.076 (0.010) -0.066(0.051)
-0.106(0.028) -0.115 (0.051) -0.091(0.013) -0.072 (0.014)
-0.127(0.034) -0.140 (0.045) -0.102(0.013) -0.08110.014)
-0.059 -0.084 -0.153 -0.096
(0.075) (0.046) (0.038) (0.066)
-0.148 (0.060) -0.280(0.085) -0.168t0.040) -0.147 (0.036)
-0.151(0.056) -0.269(0.143) -0.179(0.038) -0.146 (0.044)
-0.160 (0.062) -0.261(0.155) -0.183 (0.042) -0.159 (0.042)
-0.153 (0.056) -0.215 (0.144) -0.188CO.042) -O-162(0.037)
-0.145 (0.049) -0.093 (0.030) -0.160 (0.047) -0.188(0.026)
-0.214(0.062) -0.305(0.095) -0.162(0.039) -0.147 (0.063)
-0.246(0.072) -0.426(0.153) -0.166 (0.041) -0.129 (0.030)
-0.266 (0.090) -0.458(0.168) -0.175(0.042) -0.136 (0.036)
-0.278 (0.093) -0.468 (0.176) -0.184(0.043) -0.141(0.025)
-0.061(0.080) -0.037 (0.027) -0.107 (0.039) -0.075 (0.044)
-0.152 -0.227 -0.100 -0.078
-0.162 (0.090) -0.229(0.066) -0.107 (0.027) -0.089 (0.041)
-0.168(0.085) -0.236 (0.065) -0.124(0.029) -0.101(0.044)
-0.196 (0.080) -0.269 (0.095) -0.151(0.027) -0.129 (0.040)
2
3
4
5
(0.085) (0.059) (0.031) (0.043)
All values are in millimeters.
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1996
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Table
III.
OF PROSTHETIC
Four-factor
DENTISTRY
BOHNENKAMP
repeated-measures
SOIWX
Degrees
Design Condition Design x condition Location Design x location Condition x location Design x condition x location Subjects with groups Time intervals Design x time Condition x time Design x condition x time Location x time Design x location x time Condition x location x time Design x condition x location x time Time x subjects with groups *Significance
Table
of variance
at freedom
4 1 4 3 12 3 12 160 4 16 4 16 760 48 12 48 640
IV. Multiple
pairwise
Location A-B
Location C-D Location A-C
comparison
12354 -
12534
~-
12534
of squares
Mean
square
F ratio
3.312 0.240 0.045 0.872
0.828 0.240 0.011 0.291
67.376 19.541 0.912 23.663
1.129 0.018
0.094 0.006 0.009 0.012 0.218 0.010 0.033 0.001 0.044 0.010 0.002 0.001
7.655 0.491 0.723
0.107 1.966 0.872 0.155 0.130 0.155 0.522 0.483 0.025 0.039 0.393
21534
denotes
statistically
--
significant
analyses
Significance
level
0.0001” 0.0001” 0.4587 0.0001* 0.0001” 0.6888 0.7276
0.0001” 0.0001” 0.0001” 0.0001* 0.0001* 0.0001* 0.0001* 0.0800
355.377 15.765 53.153 1.599 70.953 16.417 3.351 1.315
0.001
of designs 0 Hours
24 Hours
72 Hours
12354 --
12354 --
12354 -
12534
-
-
12534
--
Location B-D
subsets
-
12534
12534
2 Weeks
12354 -
12354
-
-
-
12.532
12534
12534
25143
21543
21543
-
21534
--
listed in order of increasing
significant effects are only important when they are considered with respect to each other. Thus simple primary effects tests were performed. No significant interactions existed between storage condition and location across any of the time intervals. However, significant differences did exist for storage condition across two of the time intervals and for location across all the time intervals. Significant interactions existed between design and location across each of the time intervals. Multiple pairwise comparison analyses of the designs at each location at each time interval were analyzed (Table IV). Statistically significant subsets are underlined and listed in order of increasing dimensional change from left to right.
DISCUSSION It was surprising to find only one study in the literature that had compared materials or construction techniques used for acrylic resin occlusal splints. Steele et a1.26
266
Sum
at p < 0.05.
On cast
Underline
analysis
dimensional
change,
left to right,
at p < 0.05
reported that the intraoral fit and retention of interocclusal splints were apparently unaffected by the material used (heat-cured or autopolymerizing polymethyl methacrylate). They advised use of heat-cured acrylic resin to optimize mechanical properties and minimize processing faults when interocclusal splints are intended for longterm wear. In this investigation the sprinkle-on autopolymerizing acrylic resin fabrication techniques displayed less linear dimensional change than the other fabrication techniques at all locations across a 2-week interval. Also, the vacuumadapted resin sheet and acrylic resin dough application technique displayed more linear dimensional change than the other techniques at all locations across a 2-week interval, except for the dough application technique at location B-D at 24 hours, 72 hours, and 2 weeks. The design 4 specimens constructed were representative of those occlusal splints in the literature fabricated with a
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vacuum-adapted resin sheet and acrylic resin dough application technique. In particular, the design 4 specimens demonstrated more linear dimensional change than did design 5 specimens, which were constructed by the heatcured acrylic resin denture processing technique. Thus any claim of greater dimensional stability for the vacuumadapted resin sheet and acrylic resin dough application technique compared with the heat-cured denture processremains unsubstantiated. ing technique14, I7 No significant differences in linear dimensional change were noted among design 1 and 2 specimens at any locations at any of the time intervals. This finding suggests that the incorporation of three segmental stages in a sprinkle-on technique for autopolymerizing acrylic resin’l does not seem to offer any advantages for minimizing linear dimensional change compared with a one-segment sprinkle-on fabrication technique. The majority of studies that evaluated storage methods for acrylic resins have concluded that storage methods significantly affect dimensional stability.27-34 Acrylic resins increase in dimension on wetting and decrease in dimension on drying. In this study a significant difference in the linear dimensional change of the acrylic resin specimens was noted between storage conditions at only one of the time intervals. Specimens stored in a wet environment demonstrated significantly less linear dimensional change after 2 weeks than did specimens stored in a dry environment. After saturation in water for 2 weeks the anticipated expansion took place for specimens stored in a wet condition; this was most apparent at the posterior location C-D. In the case of the specimens fabricated by the one-segment sprinkle-on technique, the water immersion was sufficient to cause an expansion greater than the initial contraction and a final slight expansion occurred. This observation is in agreement with the findings reported by Craig4 and Ogle et al.23 On the basis of their observations, they suggested that this net positive dimensional change may cause autopolymerizing acrylic resin appliances to be slightly oversized. However, in this study net positive dimensional changes were observed only for the one-segment sprinkle-on specimens and not for the specimens fabricated by either the three-segment sprinkle-on technique or the dough application technique.
CLINICAL
1996
OF PROSTHETIC
DENTISTRY
technician should be aware that fabrication techniques and storage methods may influence the dimensional stability of acrylic resin occlusal splints. When deciding to make a passive occlusal splint or active orthodontic appliance, certain criteria are considered. The magnitude of the cumulative linear dimensional changes of the specimens in this study varied widely, although it did not exceed 0.5 mm. Further clinical research is indicated to determine whether changes of this amount significantly affect the oral dynamics of these prostheses. Because adverse forces may be transmitted to teeth and supporting periodontal structures by occlusal splints, optimal design and fabrication based on the best available research may preserve the health of the teeth and periodontium.
SUMMARY Various design features and construction methods have been proposed to cope with the inherent problems of distortion of removable acrylic resin occlusal splints. By use of original research methods it appears that cumulative linear dimensional change may be evaluated to determine the relative dimensional stability of occlusal splints constructed by different techniques. The results of this study suggest the laboratory use of an autopolymerizing acrylic resin sprinkle-on fabrication technique and a wet storage method to minimize dimensional change before the clinical use of an acrylic resin occlusal splint.
CONCLUSIONS On the basis of the results of this study, the following conclusions were drawn. 1. No significant differenceinlinear dimensional change was revealed between the one- and three-segment sprinkle-on fabrication techniques. 2. The sprinkle-on fabrication techniques appeared to provide less linear dimensional change than the other fabrication techniques studied. 3. The vacuum-adapted resin sheet and dough application techniques provided the greatest linear dimensional change among the fabrication techniques studied. 4. All specimens stored in a wet environment demonstrated significantly less linear dimensional change 2 weeks after fabrication than did specimens stored in a dry environment,
IMPLICATIONS
When acrylic resin is used in a situation that requires dimensional precision, one of the properties that is given first consideration is stability. The accurate and precise fit of an occlusal splint in the mouth of a patient is of prime importance to the clinician. Consequently, any change in the dimensions of an occlusal splint, either during fabrication or storage before delivery to the patient, is of importance. Because acrylic resins exhibit certain unavoidable dimensional changes, the clinician and the laboratory
March
JOURNAL
I thank Drs. William A. Kuebker, William J. Thrash, Barry K. Norling, Kenneth D. Rudd, and Charles R. Dufort for their contributions to this study. REFERENCES 1. Ramfjord SP, Ash MM. Occlusion. 2nd ed. Philadelphia: WB Saunders, 1971:248-50. 2. Kornfkld M. Mouth rehabilitation: clinical and laboratory procedures. 2nd ed. St. Louis: CV Mosby, 1974;1:178-9. 3. McNeil1 C. Diagnostic and treatment appliances. In: Eismann HF,
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4. 5.
6.
7. 8. 9. 10. 11. 12. 13.
14. 15. 16. 17. 18. 19.
20.
OF PROSTHETIC
DENTISTRY
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