etentive
properties
Brett I. Cohen, PhD,a Barry Lee Musikant, South Hackensack, NJ.
of misaligned
Allan S. Deutsch, DMDb
DMD,b
post attachment
and
This study determined
the retention of different sizes of attachment sleeves when cemented in various alignments with the corresponding post heads. This experiment was divided into six groups of eight samples, except for group 6, which had 10 samples. The retention was measured in pounds using a universal testing machine. In all samples, the malalignment of the sleeve to its corresponding post head did not cause loss of retention compared with the control. In groups 1 and 3, an 0.26 mm offset was introduced and this resulted in increased retention for sleeves to the No. 2 and No. 3 cast post heads. These values for the 0.26 mm offset were statistically significant compared with the control. This cast post system offers the dentist a greater safety factor. (J PROSTHET DENT 1992;67:191-3).
he retention of an artificial crown to tooth structure or core material is critical for a successful restoration. Any simple technique that provides for a predictably high retention for a crown-to-tooth structure will be welcomed by the dental profession. In a previous publication1 the retention of the sleeve to the post head of the Flexi-Cast post system (Essential Dental Laboratories, South Hackensack, N.J.) was discussed. The shaft portion of the Flexi-Cast post is a prefabricated split post creating high retention of the post in the root, similar to the Flexi-post (Essential Dental Laboratories).2-5 This cast post system also includes a machined sleeve that is circumferentially grooved. The grooves are designed to precisely match a circumferentially grooved prefabricated post head. When the sleeve is cemented to the post head, the alignment of the sleeve grooves and the grooves in the post head results in improved retention of the sleeve to the post. The casting technique to this sleeve involves making an impression of the post head and then pouring a cast in epoxy. The sleeve is then inserted on the epoxy die of the post head and a core is cast to the sleeve. If an air bubble is inadvertently trapped in the impression at the flange of the post head and the impression is cast in epoxy, the die will have an excessive convexity of epoxy on the occlusal surface of the flange. This excess will prevent the sleeve from fully seating on the epoxy die. The effect of incomplete seating will be misalignment of the circumferential retention grooves of the sleeve with the circumferential grooves of the post head in the final casting. This investigation determined the retention after cementation of different size sleeves that were intentionally misaligned with the interlocking grooves of the post heads.
Wice-President
of Dental
Research,
Essential
Dental
Laborato-
ries.
bCo-director 10/l/29664
THE
JOURNAL
of Dental
Research,
OF PROSTHETIC
Essential
DENTISTRY
Dental
Laboratories.
Fig. 1. Sleeve and post grooves fully aligned (A). Sleeve and post grooves misaligned by 0.26 mm (B). Sleeve and post grooves misaligned by 0.56 mm (C).
MATERIAL
AND
METHOD
The specimens were divided into six groups; each group was made up of eight samples, except for group 6, which had 10 samples. Group 1 consisted of No. 2 cast posts with an 0.26 mm gap; group 2 was made up of No. 2 cast posts with an 0.56 mm gap; group 3 consisted of No. 3 cast posts with an 0.26 mm gap; group 4 was made up of No. 3 east posts with an 0.56 mm gap; group 5 consisted of fully seated No. 2 cast posts; and group 6 was made up of fully seated No. 3 cast posts. The sleeves were cemented to the post heads with zinc phosphate cement (Flecks cement, Mizzy, Inc., Clifton Forge, Va.) with either an 0.26 or an 0.56 mm cardboard separator to ensure a space between the grooves for the sleeve and the post head (Fig. 1). The cement was allowed to set for approximately 1 hour and then the spec-
191
COHEN,
Fig. 2. Vise grips of universal cement sleeve specimen.
Fig. 3. Enlargement from post head.
testing machine
of sleeve specimen
applied
to
before removal
imens were stored at 100% humidity for 1 week before testing. The cast post samples were mounted with special vise grips (Figs. 2 through 4) on a universal testing machine (Comten Industries, St. Petersburg, Fla.). Each post and sleeve combination was subjected to a tensile force at a crosshead speed of 0.25 in/min (0.635 cm/min), until retention failed or the sleeve was displaced from the post head. The data were analyzed as a 3 X 2 factorial analysis of variance (ANOVA). The two factors corresponded to alignment (staggered 0.26 mm, staggered 0.56 mm, and fully seated) and the type of post (Flexi-Cast No. 2 and No. 3). There were eight observations per cell, except in the fully seated Flexi-Cast post No. 3 cell, which had 10 observations. Duncan’s multiple range test was used to determine which alignment settings were different from one another.6
ESULT Failure occurred when the cemented sleeves were dislodged from their corresponding post heads under tensile
DEUTSCH,
AND
MUSIKANT
Fig. 4. Sleeve removed from post head, after failure. Zinc phosphate cement can be observed in grooves of post head.
loading. Table I provides a summary of the means and standard deviations for all of the groups. Table I also summarizes the retentive forces from an earlier study,l when the No. 2 and No. 3 sleeves were fully seated on their corresponding post head (groups 5 and 6). ANOVA revealed significant differences in mean retention between post types (p < 0.007) and between alignments (p < 0.009). No significant interaction term (which would have corresponded to a synergistic effect) was observed. Duncan’s multiple range test, as is often the case with multiple comparisons tests, did not clearly reveal which alignment settings differed from one another, although it appears that the 0.26 mm setting had a higher retention than the fully seated setting. Whether the mean retention for the 0.56 mm setting, which fell midway between the other two settings, was different is not clear. The retention of all the sleeves to the corresponding post head was greater than 130 pounds. As the post number and the size of the post and the head increased, there was a corresponding elevation in the retentive force needed to dislodge the sleeve.
DISCUSSION In this cast post system, retention is accomplished through cement interlocking into four circumferential matched grooves in both the head of the post and the sleeve cast into the crown. In group 1, when the grooves for the sleeve and the post head were staggered 0.26 mm (Fig. l), retention of the sleeve onto the post head increased from 137.1 pounds (group 5, fully seated) to 183 pounds and the difference was statistically significant. However, in group 2, when the staggered value for the grooves on the post head and sleeve was increased to 0.56 mm (Fig. I), it resulted in the same retention as in group 5 (fully seated). It appeared that most of the retention for these attachment sleeves was located in the first three retentive grooves. In group 3, an 0.26 mm offset was also introduced for the No. 3 cast post, and this raised the retention from 170.5
FEBRUARY
1992
VOLUME
67
NUMBER
2
RETENTION
OF MISALIGNED
ATTACHMENT
SLEEVES
pounds (group 6, fully seated) to 218.3 pounds. This elevation in retention was statistically significant. Likewise, when the offset was increased to 0.56 mm, the retention was the same as in group 6 or when the posts were fully seated. It appeared that most of the retention for the attachment sleeves was in the first three retentive grooves. It was hypothesized that the staggered conformations in groups 1 and 3 (Fig. 1) resulted in thinner film thicknesses of the zinc phosphate cement, with improved retention. Additional retention was probably realized by the machined parallelism of the post head and the matching sleeve. A new study is in progress to determine the effect on retention when the sleeve is cast in a casting. This approach should also enhance retention because of the improved fit of the margins of the crown. It appeared that despite the presence of a bubble of 560 pm (0.56 mm) or an offset sleeve on the epoxy die, the retention of the attachment was identical. This adaptation ability of the attachment to retain its retention with a misalignment provides the dentist with some latitude and confers increased patient safety. SUMMARY
AND
CONCLUSIONS
Flexi-Cast post sleeves No. 2 and No. 3 were luted with zinc phosphate cement to the corresponding post heads with a space to offset the interlocking grooves. 1. When the grooves of the sleeves and the cast post beads were offset 0.26 mm, the retention of the sleeves to the corresponding post head increased. This increase was statistically significant for the No. 2 and No. 3 cast post and sleeve combination. 2. When the stagger was increased to 0.56 mm, no loss of retention was observed. 3. There was no loss of retention attributed to sleeves
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
I. Mean and standard deviation for retention of sleeveto post head Table
Flexi-Cast No. 2 Mean
0.26 mm offset 0.56 mm offset
Fully seated
183.0 154.6 137.1
FlexMast
No. 3
SD
Mean
SD
29.61
218.3 187.6 170.5
56.64 29.42 58.90
22.57 43.09
that were not seated correctly on the corresponding post heads. 4. It appearedthat the system compensatedfor a clinical offset of 0.56 mm or 560ym in sleeveposition without a corresponding loss of retention. This margin of error provides the dentist with considerablelatitude and consequent greater safety for the patient. REFERENCES 1. Deutsch AS, Cohen BI, Musikant BL. Retentive properties of attachment sleeves for a new cast-post system. J PRO~THET DENT (In press) 2. Deutsch AS, Musikant BL, Cavallari J, Bernardi S. Retentive properties of a new post and core system. J PROSTHET DENT 1985;53:12-4. 3. Millstein PL, Yu H, Hsu CS, Nathanson D. Effects of cementing on retention of a prefabricated screw post. J PROSTHET DEWT 1987;57:171-4. 4. Brown JD, Mitchem JC. R&e&w properties of dowel post systems. Oper Dent 198’7;12:15-9. 5. Saunders RD, Lorey RE, Powers JM, Sloan KM. Comparison of five post-cement systems for tensile retentive capacity. J Dent Res 1988; 67:304.
6. Zar JH. Biostatistical 1974:151-4. Reprint
requests
analysis. Englewcod
Cliffs, NJ: Prentice-Hall
Inc,
to:
DR. BRETT I. COHEN 89 LEUKING ST. SOUTH HACKENSACK, NJ 07606
193
properties
Brett I. Cohen, PhD,a Barry Lee Musikant, South Hackensack, NJ.
of misaligned
Allan S. Deutsch, DMDb
DMD,b
post attachment
and
This study determined
the retention of different sizes of attachment sleeves when cemented in various alignments with the corresponding post heads. This experiment was divided into six groups of eight samples, except for group 6, which had 10 samples. The retention was measured in pounds using a universal testing machine. In all samples, the malalignment of the sleeve to its corresponding post head did not cause loss of retention compared with the control. In groups 1 and 3, an 0.26 mm offset was introduced and this resulted in increased retention for sleeves to the No. 2 and No. 3 cast post heads. These values for the 0.26 mm offset were statistically significant compared with the control. This cast post system offers the dentist a greater safety factor. (J PROSTHET DENT 1992;67:191-3).
he retention of an artificial crown to tooth structure or core material is critical for a successful restoration. Any simple technique that provides for a predictably high retention for a crown-to-tooth structure will be welcomed by the dental profession. In a previous publication1 the retention of the sleeve to the post head of the Flexi-Cast post system (Essential Dental Laboratories, South Hackensack, N.J.) was discussed. The shaft portion of the Flexi-Cast post is a prefabricated split post creating high retention of the post in the root, similar to the Flexi-post (Essential Dental Laboratories).2-5 This cast post system also includes a machined sleeve that is circumferentially grooved. The grooves are designed to precisely match a circumferentially grooved prefabricated post head. When the sleeve is cemented to the post head, the alignment of the sleeve grooves and the grooves in the post head results in improved retention of the sleeve to the post. The casting technique to this sleeve involves making an impression of the post head and then pouring a cast in epoxy. The sleeve is then inserted on the epoxy die of the post head and a core is cast to the sleeve. If an air bubble is inadvertently trapped in the impression at the flange of the post head and the impression is cast in epoxy, the die will have an excessive convexity of epoxy on the occlusal surface of the flange. This excess will prevent the sleeve from fully seating on the epoxy die. The effect of incomplete seating will be misalignment of the circumferential retention grooves of the sleeve with the circumferential grooves of the post head in the final casting. This investigation determined the retention after cementation of different size sleeves that were intentionally misaligned with the interlocking grooves of the post heads.
Wice-President
of Dental
Research,
Essential
Dental
Laborato-
ries.
bCo-director 10/l/29664
THE
JOURNAL
of Dental
Research,
OF PROSTHETIC
Essential
DENTISTRY
Dental
Laboratories.
Fig. 1. Sleeve and post grooves fully aligned (A). Sleeve and post grooves misaligned by 0.26 mm (B). Sleeve and post grooves misaligned by 0.56 mm (C).
MATERIAL
AND
METHOD
The specimens were divided into six groups; each group was made up of eight samples, except for group 6, which had 10 samples. Group 1 consisted of No. 2 cast posts with an 0.26 mm gap; group 2 was made up of No. 2 cast posts with an 0.56 mm gap; group 3 consisted of No. 3 cast posts with an 0.26 mm gap; group 4 was made up of No. 3 east posts with an 0.56 mm gap; group 5 consisted of fully seated No. 2 cast posts; and group 6 was made up of fully seated No. 3 cast posts. The sleeves were cemented to the post heads with zinc phosphate cement (Flecks cement, Mizzy, Inc., Clifton Forge, Va.) with either an 0.26 or an 0.56 mm cardboard separator to ensure a space between the grooves for the sleeve and the post head (Fig. 1). The cement was allowed to set for approximately 1 hour and then the spec-
191
COHEN,
Fig. 2. Vise grips of universal cement sleeve specimen.
Fig. 3. Enlargement from post head.
testing machine
of sleeve specimen
applied
to
before removal
imens were stored at 100% humidity for 1 week before testing. The cast post samples were mounted with special vise grips (Figs. 2 through 4) on a universal testing machine (Comten Industries, St. Petersburg, Fla.). Each post and sleeve combination was subjected to a tensile force at a crosshead speed of 0.25 in/min (0.635 cm/min), until retention failed or the sleeve was displaced from the post head. The data were analyzed as a 3 X 2 factorial analysis of variance (ANOVA). The two factors corresponded to alignment (staggered 0.26 mm, staggered 0.56 mm, and fully seated) and the type of post (Flexi-Cast No. 2 and No. 3). There were eight observations per cell, except in the fully seated Flexi-Cast post No. 3 cell, which had 10 observations. Duncan’s multiple range test was used to determine which alignment settings were different from one another.6
ESULT Failure occurred when the cemented sleeves were dislodged from their corresponding post heads under tensile
DEUTSCH,
AND
MUSIKANT
Fig. 4. Sleeve removed from post head, after failure. Zinc phosphate cement can be observed in grooves of post head.
loading. Table I provides a summary of the means and standard deviations for all of the groups. Table I also summarizes the retentive forces from an earlier study,l when the No. 2 and No. 3 sleeves were fully seated on their corresponding post head (groups 5 and 6). ANOVA revealed significant differences in mean retention between post types (p < 0.007) and between alignments (p < 0.009). No significant interaction term (which would have corresponded to a synergistic effect) was observed. Duncan’s multiple range test, as is often the case with multiple comparisons tests, did not clearly reveal which alignment settings differed from one another, although it appears that the 0.26 mm setting had a higher retention than the fully seated setting. Whether the mean retention for the 0.56 mm setting, which fell midway between the other two settings, was different is not clear. The retention of all the sleeves to the corresponding post head was greater than 130 pounds. As the post number and the size of the post and the head increased, there was a corresponding elevation in the retentive force needed to dislodge the sleeve.
DISCUSSION In this cast post system, retention is accomplished through cement interlocking into four circumferential matched grooves in both the head of the post and the sleeve cast into the crown. In group 1, when the grooves for the sleeve and the post head were staggered 0.26 mm (Fig. l), retention of the sleeve onto the post head increased from 137.1 pounds (group 5, fully seated) to 183 pounds and the difference was statistically significant. However, in group 2, when the staggered value for the grooves on the post head and sleeve was increased to 0.56 mm (Fig. I), it resulted in the same retention as in group 5 (fully seated). It appeared that most of the retention for these attachment sleeves was located in the first three retentive grooves. In group 3, an 0.26 mm offset was also introduced for the No. 3 cast post, and this raised the retention from 170.5
FEBRUARY
1992
VOLUME
67
NUMBER
2
RETENTION
OF MISALIGNED
ATTACHMENT
SLEEVES
pounds (group 6, fully seated) to 218.3 pounds. This elevation in retention was statistically significant. Likewise, when the offset was increased to 0.56 mm, the retention was the same as in group 6 or when the posts were fully seated. It appeared that most of the retention for the attachment sleeves was in the first three retentive grooves. It was hypothesized that the staggered conformations in groups 1 and 3 (Fig. 1) resulted in thinner film thicknesses of the zinc phosphate cement, with improved retention. Additional retention was probably realized by the machined parallelism of the post head and the matching sleeve. A new study is in progress to determine the effect on retention when the sleeve is cast in a casting. This approach should also enhance retention because of the improved fit of the margins of the crown. It appeared that despite the presence of a bubble of 560 pm (0.56 mm) or an offset sleeve on the epoxy die, the retention of the attachment was identical. This adaptation ability of the attachment to retain its retention with a misalignment provides the dentist with some latitude and confers increased patient safety. SUMMARY
AND
CONCLUSIONS
Flexi-Cast post sleeves No. 2 and No. 3 were luted with zinc phosphate cement to the corresponding post heads with a space to offset the interlocking grooves. 1. When the grooves of the sleeves and the cast post beads were offset 0.26 mm, the retention of the sleeves to the corresponding post head increased. This increase was statistically significant for the No. 2 and No. 3 cast post and sleeve combination. 2. When the stagger was increased to 0.56 mm, no loss of retention was observed. 3. There was no loss of retention attributed to sleeves
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
I. Mean and standard deviation for retention of sleeveto post head Table
Flexi-Cast No. 2 Mean
0.26 mm offset 0.56 mm offset
Fully seated
183.0 154.6 137.1
FlexMast
No. 3
SD
Mean
SD
29.61
218.3 187.6 170.5
56.64 29.42 58.90
22.57 43.09
that were not seated correctly on the corresponding post heads. 4. It appearedthat the system compensatedfor a clinical offset of 0.56 mm or 560ym in sleeveposition without a corresponding loss of retention. This margin of error provides the dentist with considerablelatitude and consequent greater safety for the patient. REFERENCES 1. Deutsch AS, Cohen BI, Musikant BL. Retentive properties of attachment sleeves for a new cast-post system. J PRO~THET DENT (In press) 2. Deutsch AS, Musikant BL, Cavallari J, Bernardi S. Retentive properties of a new post and core system. J PROSTHET DENT 1985;53:12-4. 3. Millstein PL, Yu H, Hsu CS, Nathanson D. Effects of cementing on retention of a prefabricated screw post. J PROSTHET DEWT 1987;57:171-4. 4. Brown JD, Mitchem JC. R&e&w properties of dowel post systems. Oper Dent 198’7;12:15-9. 5. Saunders RD, Lorey RE, Powers JM, Sloan KM. Comparison of five post-cement systems for tensile retentive capacity. J Dent Res 1988; 67:304.
6. Zar JH. Biostatistical 1974:151-4. Reprint
requests
analysis. Englewcod
Cliffs, NJ: Prentice-Hall
Inc,
to:
DR. BRETT I. COHEN 89 LEUKING ST. SOUTH HACKENSACK, NJ 07606
193
