- Email: [email protected]
Accuracy and comparative stability of three removable die systems
JOCHEN,
grain-size variations relate to differences in hardness. Nevertheless, the opposite result obtained for Rx-91 alloy specimens is perplexing. A microprobe analysis of the surface elements on specimens from each test group might provide an answer to both phenomena. Perhaps the trace elements account for these differences. Manufacturer’s variations in metal processing also may contribute to bond results and to hardness values. The rapid approach to cooling of castings has been used in a large number of clinical caseswith W-l alloy. No instances of hot tearing were observed with this alloy. Generally, the completed restorations presented fewer difficulties in fabrication and resulted in a better quality of material when the rapid-cooling method was used. SUMMARY
AND
AND
MATYAS
quenching resulted in higher bond strengths than for specimens that were bench-cooled to room temperature. However, bench-cooling Rx-91 alloy lead to higher bond strengths than did quenching. 3. For all of the alloys examined, quenching produced a smaller grain structure than did bench-cooling. 4. From the standpoint of the parameters tested and the saving of processing time, quenching of the silverpalladium ceramic alloys examined is the cooling procedure of choice for W-l and JP-5 alloys. REFERENCES Tylman SD, Malone WFP. Tylman’s theory and practice of fixed prosthodontics. 6th ed. St Louis: The CV Mosby Co, 1978. 2. Shillingburg HT Jr, Hobo S, Whitsett LD. Fundamentals of fixed prosthodontics. Chicago: Quintessence Publishing Co, 1981. 3. Crown and Bridge Construction, A Handbook of Dental Laboratory Procedures. New Rochelle, NY: JF Jelenko & Co, Inc, 1968. 4. Ceramco Technical Manual. East Windsor, NJ: Johnson & Johnson, 1976;Sec 4, p 2. 5. Craig RG. Restorative dental materials. 7th ed. St Louis: The CV Mosby Co, 1985. 6. Jochen DG, Caputo AA, Matyas J. Effect of metal surface treatment on ceramic bond strength. J PROSTHET DENT 1986;55:186-8. 1.
CONCLUSIONS
Cast metal specimens for three ceramic metals were subjected to two different types of cooling procedures after casting. One method involved the rapid cooling of the casting as soon as the red glow of the button disappeared. The other method allowed the castings to bench cool to room temperature. Hardness, bond strength, and microstructural determinations lead to the following conclusions. 1. Vickers hardness values for W-l and Rx-91 alloys for each cooling regimen were not significantly different. Statistically higher hardness values were obtained for the quenched specimens of JP-5 alloys compared with the bench-cooled specimens. 2. Cooling of W-l and JP-5 alloy specimens by
CAPUTO,
Reprint requests to: DR. ANGEM A. CAPUTO UNIVERSITYOF CALIFORNIA,Los ANCELE~ SCHOLLOF DENTISTRY Los ANGELES,CA 90024
Accuracy and comparative stability of three removable die systems L. M. Covo, D.C.D., M.S.,* G. J. Ziebert, L. V. Christensen, D.D.S.**** Marquette
University,
School of Dentistry,
D.D.S., MS.,**
Milwaukee,
Y. Balthazar,
D.D.S., M.S.,***
and
Wis.
T
he accurate duplication of prepared teeth and the maintenance of their relationships are essential for the construction of fixed partial prostheses. The fabrication of removable dies is an important step in the realization of the master cast, and it is necessary to know the existing systems available with their respective qualities and imperfections. Many methods for the indirect tech*Assistant Professor, Fixed Prosthodontics. **Professor and Chairman, Fixed Prosthodontics. ***Assistant Professor, Head of Clinical Division, Fixed Prosthodontics. ****Adjunct Assistant Professor (Clinical). 314
Fig.
1. Master
cast (occlusal view).
nique of constructing a working cast with removable dies have been reported in the literature,‘-’ and some investigators have experimentally established the accuracy and comparative stability of the different systems.‘@j4 MARCH
1988
VOLUME
59
NUMBER
3
COMPARISON
OF THREE
REMOVABLE
DIE SYSTEMS
Am Horizontal Measurements
a mesial -distal b> c = lingual-facial
d = gingival-occlusal
displacement displacement
displacement
D Vertical Measurements Fig. 2. Horizontal and vertical reference points for Accu-Trac system, Pindex system, and conventional techniques. This study evaluated the accuracy of three removable die systems: th.e Accu-Trac system (Whaledent International, New York, N.Y.), the Pindex system (Whaledent International),, and the conventional brass dowel pin positioning technique. Stability in three directions (mesial-distal, buccal-lingual, and vertical) was evaluated.
MATERIAL
AND METHODS
A master cast with three adjacent molar-sized preparations was made by using heat-cured acrylic resin (Hygienic Co., Akron, Ohio). Thirty impressions were made by using reversible hydrocolloid impression material (Thompson hydrocolloid impression material, Columbus Dental, St. Louis, MO.). Ten working casts in die stone (Vel-Mix, Sybron/Kerr, Romulus, Mich.) for each of the three removable die systems were made from the 30 impressions (Fig. 1). Accu-Trac system. This system consists of a plastic mold into which the appropriately trimmed cast is fitted and stabilized .with plaster or stone over an independent base. A magnetic indexer on the inferior surface of the tray permits easy repositioning of the master cast to the articulator. For this study, the first pour of yellow stone (Duroc, Ransom and Randolph Co., Toledo, Ohio) was allowed to set for 1 hour, and the trimmed master cast was positioned so that the occlusal surface of the dies was parallel to the base of the tray. Pindex system. This system, designed to drill parallel holes from the underside of the cast, permits the cementation of pins into each removable section. The Pindex system is composed of a precision drill mechanism THE JOURNAL
OF PROSTHETIC
DENTISTRY
(aligned drill and a light source) that locates each hole position and automatically stops when hole size and depth are achieved. For this study, a twin pin (Denerica Dental Corp., Northfield, Ill.) was cemented in place with cyanoacrylate adhesive (Perxnabond International Division, Englewood, N.J.). Cast sleeves were then fitted to each cemented pin, the underside of the cast was lubricated, and the base of yellow stone was then poured for each cast. Each cast, with its base, was trimmed so that the inferior and superior surfaces were flat and parallel to each other. Conventional system. A medium dowel pin (Universal Dowel Pin, The Ney Co., Bloomfield, Conn.) was positioned freehandedly over the central preparation immediately after the die-stone was poured. After the stone had set, two depressions were made buccally and lingually to the dowel pin with a No. 6 round bur. The construction and shaping of the base was the same as for the Pindex system. A traveling microscope (Gaertner Scientific Corp., Chicago, Ill.) measured the horizontal (mesiodistal and buccolingual) distances; a micrometer (Etalon, P. Roth, Rolle, Switzerland) measured the vertical distances. All horizontal measurements were made within 10m3mm, all vertical measurements within lo-’ mm. The points of reference are shown in Fig. 2. Each reference point was made with a ruler and a surgical blade. Two distances were measured mesiodistally (a and b in Fig. 2); one distance was recorded faciolingually (c in Fig. 2). The three systems were modified to include one fixed lingual reference point. With the Pindex and Conven315
COVO
ET AL
Table I. Average die displacements (mm), aa measured mesially and distally, buccally and lingually, and gingivally and occlusally on three systems Removable dye system Statistic
Fig. 3. Fixed lingual reference pin with removable die
in place (Pindex system and conventional techniques).
Mesial-distal ST SD SE cv Buccal-lingual K SD SE cv
Pindex
Dowel pin
0.024 0.016 0.003 67%
0.019 0.014 0.003 74%
0.019 0.014 0.003 74%
0.032 0.026 0.008 81%
0.032 0.026 0.008 81%
0.041 0.029 0.009 71%
0.001 0.001 0.000 100%
0.001 0.001 0.000 100%
Accu-Trac
Gingival-occlusal 0.003 ST SD 0.002 SE 0.001 cv 67%
?I = Mean; SD = standarddeviationof the mean; SE = standard CV = coefficient of variation.
error of the mean;
Fig. 4. Accu-Trac system with arm locked and a lingual reference point.
tional systems, a brass pin was cemented at the base of each cast and cut horizontally to be at the same level as the occlusal surface of the central removable die (Fig. 3). With the Accu-Trac system, a stone die with an occlusal reference point was cemented over the base of the tray, lingual to the central removable die and at the same horizontal level (Fig. 4). Two distances were measured vertically from two occlusal reference points located at the surface of the central removable die and at the base of the cast (d in Fig. 2). Each distance was measured three times and averaged to produce the baseline data. The sectioning of the dies was done with a jeweler’s saw to separate the central die from the adjacent preparations. Each die was removed and replaced on its base 30 times, mimicking laboratory procedures. With the Accu-Trac system, the independent locking arms were left open and only the central die was removed and repositioned. With the three systems, the dies and casts 316
were cleaned with a soft brush and compressed air before they were repositioned for measurements. Before- and after-sectioning measurements were made at the same reference points, giving a total of 900 measurements, and the differences were calculated. This produced a mean number for each die, indicating the magnitude of movement in both the horizontal and vertical planes. After homogeneity of variance (“maxtest) was established, data were analyzed by single-factor analysis of variance (ANOVA). Multiple comparisons between means were analyzed by the Tukey test. All significance levels below the 5% level were accepted as statistically significant (ii, < .05).
RESULTS The average die displacements, as measured mesiodistally, buccolingually, and occlusogingivally are shown in Table I. When the three removable die systems were compared in the horizontal plane (mesiodistally and buccolingually), no significant differences were found between the mean displacements (p > .25; Tables II and III). In a comparison of the occlusogingival displacements of the three systems, ANOVA demonstrated a significant difference between the mean vertical shifts ($ < .025; Table IV). Tukey’s multiple comparison test showed that the mean vertical die displacement of the Accu-Trac system was significantly larger than those of the Pindex and conventional dowel pin systems, by factors of 1.95 and 1.87 respectively (p < .05). There was no significant difference between the mean vertical die displacement of the Pindex and conventional dowel pin systems @I > .05). MARCH
1988
VOLUME
59
NUMBER
3
COMPARISON
OF THREE
REMOVABLE
DIE SYSTEMS
Table II. Summary of single-factor of mesial-distal
Table III. Summary of single-factor
ANOVA
of buccal-lingual
die displacement
Source of variation
ss
DF
MS
F
P
Total Groups Error
12933.94 335.91 12598.03
57 2 55
167.95 229.05
0.73
>0.25
~p0.05(1),2,55 = 3.18. SS = Sum of squares; DF = degrees of freedom; MS = mean square; F = F-ratio; P = significance level.
ANOVA
die displacement
Source of variation
ss
DF
MS
F
P
Total Groups Error
21183.87 601.87 20582.00
29 2 27
300.93 762.29
0.39
>0.25
‘0.05(1),2,27 = 3.35. SS = Sum of squares; DF = degrees of freedom; MS = mean square; F = F-ratio; P = significance level.
DISCUSSION
Table IV. Summary of single-factor
The small and insignificant deviations in the horizontal plane observed with the three systems may be explained by the fact that the central removable dies are locked securely into place in different ways. With the Accu-Trac system, three die-contact tracks prevent lateral shifting. With the Pindex system, the placement of the twin pin into its corresponding metal sleeve secures the die firmly into position, preventing any rotation. The conventional technique is also accurate because of the length and shape of the dowel pin and the depressions prepared at the base with a round bur, which help to hold the die in place. The vertical movement of the dies was in an upward direction with the Pindex system and the conventional technique. This might be explained by particles of debris that can be trapped in the key-way. Other factors that may interfere are the interface of the stone between the first and second pour and the position and orientation of the dowel pin in the conventional technique. Care should be given to remove any trapped particle of debris by using either acetone or chloroform, compressed air, a small brush, or a pipe cleaner. The results also show that the Pindex system and the conventional technique are acceptable. The conventional system also gjves acceptable results and does not require expensive apparatus. A downward (setting) shift of the removable dies was evident in the Accu-Trac system. This shift would result clinically in a slightly premature contact (supraocclusion) of the fabricated restoration with the opposing tooth. The higher values of the mean average shift show that this technique is less accurate than the others examined. This finding can possibly be explained by the frictional wear of the surfaces of the base of the dies against the tracks of the tray during the 30 removals and replacements of the dies. Although the magnet may allow an easy repositioning of the master cast on the articulator, the entire system seemed somewhat cumbersome.
of gingival-occlusal
ANOVA
die displacement
Source of variation
SS
DF
MS
F
P
Total Groups Error
242.25 33.65 208.60
59 2 57
16.82 3.65
4.60
<0.025
F0.05(1),2,57 = 3.18. SS = Sum of squares; DF = degrees of freedom; MS = mean square; F = F-ratio; P = significance level.
dies in the mesiodistal, bucco-lingual, and gingivoocclusal directions was compared. Under the conditions of this investigation, the following conclusions were drawn. 1. No significant difference was found in the shift of the removable die in a horizontal direction between any of the three systems. 2. No significant difference was found in the displacement of the removable die in the vertical direction with the Pindex system and the conventional dowel pin techniques. The slight displacement that did occur was in an upward direction. 3. A significant vertical displacement of the removable die in a downward direction was found with the Accu-Trac system compared with the other two systems. REFERENCES 1.
Balshi TJ, Mingledorff
EB. Matches, clips, needle, or pins. J
PROSTHET DENT 1975;34:467-72.
2.
3.
4.
Cowell TA, Moore J. New technic for sectional model production for inlay and bridgework. J Am Dent Assoc 1965;71:138790. Robinson FB, Block B. Dowel pin positioning technique for fixed partial denture working casts. J PROSTHET DENT 1981;46:2156. Rudd KD, Strunk RR, Morrow RM. Removable dies for crowns, inlays, and fixed partial dentures. J PROSTHET DENT 1970;23:337-45.
SUMMARY
AND CONCLUSIONS
A study was performed to evaluate three removable die systems: the Accu-Trac, the Pindex, and the conventional brass do,wel pin technique. The stability of the THE JOURNAL
OF PROSTHETIC
DENTISTRY
5.
Rudd KD, Morrow RM, Bange AA. Accurate casts. J PROSTHET
6.
Smith CD, Nayyar A, Koth DL. Fabrication of removable stone dies using cemented dowel pins. J PROSTHET DENT 1979;41:579-
DENT 1969;21:545-54.
81.
317
COVO
7. Stone TE, Welker WA. A-method for locating dowel pins in
ET AL
employed for constructing working dies from hydrocolloid impressions. J PROSTHETDENT 1956;6:87-93. 13. Miranda FJ, Dilts WE, Duncanson Jr MG, Collard EW. Comparative stability of two removable die systems. J PR~~THET DENT 1976;36:326-33. 14. Myers M, Hembree JH Jr. Relative accuracy of four removable die systems. J PR~~THET DENT 1982;48:163-5.
artificial stone casts. J PR~~THET DENT 1980;44:345-6. 8. Toreskog S, Phillips RW, Schnell RJ. Properties of die materials: a comparative study. J PR~.VHET DENT 1966;16:11931. 9. Troendle KB, Troendle GR Jr, Cavazos E Jr. Positioning dowel pins for removable dies. J PROSTHETDENT 1981;46:575-8. 10. Dilts WE, Podshadley AG, Ellison E, Neiman R. Accuracy of a removable die-dowel pin technique. J Dent Res 1971;50:124952. 11. Dilts WE, Podshadley.AG, Sawyer HF, Neiman R. Accuracy of four removable die techniques. J Am Dent Assoc 1971;83:10815. 12. Hohlt FA, Phillips RW. Evaluation of various methods
Reprint requests to: DR. GERALD J. ZIEBERT MARQUETTE UNIVFXSIT~ SCHOLLOF DENTBTRY MILWAUKEE, WI 53233
Retention of cast endodontic posts: Comparison of cementing agents Ryle A. Radke, D.D.S., * Rahmat A. Barkhordar, D.M.D.,** and Ralph E. Podesta, D.D.S.*** University
of California,
San Francisco,
School of Dentistry,
C
San Francisco,
ast metal restorations are commonly used to restore teeth severely damaged by caries or trauma. Often, castings cannot be adequately supported without an intermediate buildup with a suitable dowel and core. The bond strength of the cementing agent plays an important role in the longevity and success of the final restoration. Zinc phosphate cement is the most commonly used cementing agent and remains the comparison standard. A major problem, however, is its lack of adhesion to tooth structure.‘-’ Polycarboxylate and glassionomer cements possessadhesive properties not present in zinc phosphate cement. Glass-ionomer cement is less soluble in the mouth than zinc phosphate cement whereas the polycarboxylate cements are more soluble.5-8 Previous studies reported findings on the retentive property of cements on Para-Post (Whaledent International, New York, N.Y.) dowels.9-‘5 This study compared the relative retentive value of three commonly used cements and one composite.
MATERIAL
AND METHODS
Twenty freshly extracted human single-rooted teeth were embedded in epoxy resin blocks. The teeth were closely matched for size (Fig. 1). Each tooth was sectioned at the cementoenamel junction and the root *Associate Clinical Professor, Fixed Prosthodontics. **Assistant Professor, Endodontics. ***Assistant Clinical Professor, Fixed Prosthodontics.
318
Calif.
Table I. Values at failure of cemented posts Material
Mean (kg)
SD
Zinc phosphate cement (Flecks) Glass-ionomer cement (Ketac cem) Polycarboxylate cement (Durelon) Composite resin (Den Mat)
16.03
2.12
15.17
4.58
12.78
6.85
8.50
7.35
canal systems were cleansed and shaped to a size No. 60 endodontic file with copious irrigation of sodium hypochlorite solution. An 8 mm post space was prepared with the drill supplied by the Para-Post system for the 0.036~inch Para-Post dowel. This serrated parallel-sided form was selected because of its reported superior retentive design. 16-18The Para-Post dowel casting forms were made with a loop centered on the end of the post (Fig. 2) to serve as an attachment to the Instron (model 1122, Instron Corp., Canton, Mass.) testing machine (Fig. 3). The patterns were invested and cast in type III casting gold (Firmilay, J. F. Jelenko Co., New Rochelle, N.Y.). The cementing agents listed in Table I were mixed according to the manufacturers’ directions and introduced into previously dried root canal spaces with a
MARCH
1988
VOLUME
59
NUMBER
3
grain-size variations relate to differences in hardness. Nevertheless, the opposite result obtained for Rx-91 alloy specimens is perplexing. A microprobe analysis of the surface elements on specimens from each test group might provide an answer to both phenomena. Perhaps the trace elements account for these differences. Manufacturer’s variations in metal processing also may contribute to bond results and to hardness values. The rapid approach to cooling of castings has been used in a large number of clinical caseswith W-l alloy. No instances of hot tearing were observed with this alloy. Generally, the completed restorations presented fewer difficulties in fabrication and resulted in a better quality of material when the rapid-cooling method was used. SUMMARY
AND
AND
MATYAS
quenching resulted in higher bond strengths than for specimens that were bench-cooled to room temperature. However, bench-cooling Rx-91 alloy lead to higher bond strengths than did quenching. 3. For all of the alloys examined, quenching produced a smaller grain structure than did bench-cooling. 4. From the standpoint of the parameters tested and the saving of processing time, quenching of the silverpalladium ceramic alloys examined is the cooling procedure of choice for W-l and JP-5 alloys. REFERENCES Tylman SD, Malone WFP. Tylman’s theory and practice of fixed prosthodontics. 6th ed. St Louis: The CV Mosby Co, 1978. 2. Shillingburg HT Jr, Hobo S, Whitsett LD. Fundamentals of fixed prosthodontics. Chicago: Quintessence Publishing Co, 1981. 3. Crown and Bridge Construction, A Handbook of Dental Laboratory Procedures. New Rochelle, NY: JF Jelenko & Co, Inc, 1968. 4. Ceramco Technical Manual. East Windsor, NJ: Johnson & Johnson, 1976;Sec 4, p 2. 5. Craig RG. Restorative dental materials. 7th ed. St Louis: The CV Mosby Co, 1985. 6. Jochen DG, Caputo AA, Matyas J. Effect of metal surface treatment on ceramic bond strength. J PROSTHET DENT 1986;55:186-8. 1.
CONCLUSIONS
Cast metal specimens for three ceramic metals were subjected to two different types of cooling procedures after casting. One method involved the rapid cooling of the casting as soon as the red glow of the button disappeared. The other method allowed the castings to bench cool to room temperature. Hardness, bond strength, and microstructural determinations lead to the following conclusions. 1. Vickers hardness values for W-l and Rx-91 alloys for each cooling regimen were not significantly different. Statistically higher hardness values were obtained for the quenched specimens of JP-5 alloys compared with the bench-cooled specimens. 2. Cooling of W-l and JP-5 alloy specimens by
CAPUTO,
Reprint requests to: DR. ANGEM A. CAPUTO UNIVERSITYOF CALIFORNIA,Los ANCELE~ SCHOLLOF DENTISTRY Los ANGELES,CA 90024
Accuracy and comparative stability of three removable die systems L. M. Covo, D.C.D., M.S.,* G. J. Ziebert, L. V. Christensen, D.D.S.**** Marquette
University,
School of Dentistry,
D.D.S., MS.,**
Milwaukee,
Y. Balthazar,
D.D.S., M.S.,***
and
Wis.
T
he accurate duplication of prepared teeth and the maintenance of their relationships are essential for the construction of fixed partial prostheses. The fabrication of removable dies is an important step in the realization of the master cast, and it is necessary to know the existing systems available with their respective qualities and imperfections. Many methods for the indirect tech*Assistant Professor, Fixed Prosthodontics. **Professor and Chairman, Fixed Prosthodontics. ***Assistant Professor, Head of Clinical Division, Fixed Prosthodontics. ****Adjunct Assistant Professor (Clinical). 314
Fig.
1. Master
cast (occlusal view).
nique of constructing a working cast with removable dies have been reported in the literature,‘-’ and some investigators have experimentally established the accuracy and comparative stability of the different systems.‘@j4 MARCH
1988
VOLUME
59
NUMBER
3
COMPARISON
OF THREE
REMOVABLE
DIE SYSTEMS
Am Horizontal Measurements
a mesial -distal b> c = lingual-facial
d = gingival-occlusal
displacement displacement
displacement
D Vertical Measurements Fig. 2. Horizontal and vertical reference points for Accu-Trac system, Pindex system, and conventional techniques. This study evaluated the accuracy of three removable die systems: th.e Accu-Trac system (Whaledent International, New York, N.Y.), the Pindex system (Whaledent International),, and the conventional brass dowel pin positioning technique. Stability in three directions (mesial-distal, buccal-lingual, and vertical) was evaluated.
MATERIAL
AND METHODS
A master cast with three adjacent molar-sized preparations was made by using heat-cured acrylic resin (Hygienic Co., Akron, Ohio). Thirty impressions were made by using reversible hydrocolloid impression material (Thompson hydrocolloid impression material, Columbus Dental, St. Louis, MO.). Ten working casts in die stone (Vel-Mix, Sybron/Kerr, Romulus, Mich.) for each of the three removable die systems were made from the 30 impressions (Fig. 1). Accu-Trac system. This system consists of a plastic mold into which the appropriately trimmed cast is fitted and stabilized .with plaster or stone over an independent base. A magnetic indexer on the inferior surface of the tray permits easy repositioning of the master cast to the articulator. For this study, the first pour of yellow stone (Duroc, Ransom and Randolph Co., Toledo, Ohio) was allowed to set for 1 hour, and the trimmed master cast was positioned so that the occlusal surface of the dies was parallel to the base of the tray. Pindex system. This system, designed to drill parallel holes from the underside of the cast, permits the cementation of pins into each removable section. The Pindex system is composed of a precision drill mechanism THE JOURNAL
OF PROSTHETIC
DENTISTRY
(aligned drill and a light source) that locates each hole position and automatically stops when hole size and depth are achieved. For this study, a twin pin (Denerica Dental Corp., Northfield, Ill.) was cemented in place with cyanoacrylate adhesive (Perxnabond International Division, Englewood, N.J.). Cast sleeves were then fitted to each cemented pin, the underside of the cast was lubricated, and the base of yellow stone was then poured for each cast. Each cast, with its base, was trimmed so that the inferior and superior surfaces were flat and parallel to each other. Conventional system. A medium dowel pin (Universal Dowel Pin, The Ney Co., Bloomfield, Conn.) was positioned freehandedly over the central preparation immediately after the die-stone was poured. After the stone had set, two depressions were made buccally and lingually to the dowel pin with a No. 6 round bur. The construction and shaping of the base was the same as for the Pindex system. A traveling microscope (Gaertner Scientific Corp., Chicago, Ill.) measured the horizontal (mesiodistal and buccolingual) distances; a micrometer (Etalon, P. Roth, Rolle, Switzerland) measured the vertical distances. All horizontal measurements were made within 10m3mm, all vertical measurements within lo-’ mm. The points of reference are shown in Fig. 2. Each reference point was made with a ruler and a surgical blade. Two distances were measured mesiodistally (a and b in Fig. 2); one distance was recorded faciolingually (c in Fig. 2). The three systems were modified to include one fixed lingual reference point. With the Pindex and Conven315
COVO
ET AL
Table I. Average die displacements (mm), aa measured mesially and distally, buccally and lingually, and gingivally and occlusally on three systems Removable dye system Statistic
Fig. 3. Fixed lingual reference pin with removable die
in place (Pindex system and conventional techniques).
Mesial-distal ST SD SE cv Buccal-lingual K SD SE cv
Pindex
Dowel pin
0.024 0.016 0.003 67%
0.019 0.014 0.003 74%
0.019 0.014 0.003 74%
0.032 0.026 0.008 81%
0.032 0.026 0.008 81%
0.041 0.029 0.009 71%
0.001 0.001 0.000 100%
0.001 0.001 0.000 100%
Accu-Trac
Gingival-occlusal 0.003 ST SD 0.002 SE 0.001 cv 67%
?I = Mean; SD = standarddeviationof the mean; SE = standard CV = coefficient of variation.
error of the mean;
Fig. 4. Accu-Trac system with arm locked and a lingual reference point.
tional systems, a brass pin was cemented at the base of each cast and cut horizontally to be at the same level as the occlusal surface of the central removable die (Fig. 3). With the Accu-Trac system, a stone die with an occlusal reference point was cemented over the base of the tray, lingual to the central removable die and at the same horizontal level (Fig. 4). Two distances were measured vertically from two occlusal reference points located at the surface of the central removable die and at the base of the cast (d in Fig. 2). Each distance was measured three times and averaged to produce the baseline data. The sectioning of the dies was done with a jeweler’s saw to separate the central die from the adjacent preparations. Each die was removed and replaced on its base 30 times, mimicking laboratory procedures. With the Accu-Trac system, the independent locking arms were left open and only the central die was removed and repositioned. With the three systems, the dies and casts 316
were cleaned with a soft brush and compressed air before they were repositioned for measurements. Before- and after-sectioning measurements were made at the same reference points, giving a total of 900 measurements, and the differences were calculated. This produced a mean number for each die, indicating the magnitude of movement in both the horizontal and vertical planes. After homogeneity of variance (“maxtest) was established, data were analyzed by single-factor analysis of variance (ANOVA). Multiple comparisons between means were analyzed by the Tukey test. All significance levels below the 5% level were accepted as statistically significant (ii, < .05).
RESULTS The average die displacements, as measured mesiodistally, buccolingually, and occlusogingivally are shown in Table I. When the three removable die systems were compared in the horizontal plane (mesiodistally and buccolingually), no significant differences were found between the mean displacements (p > .25; Tables II and III). In a comparison of the occlusogingival displacements of the three systems, ANOVA demonstrated a significant difference between the mean vertical shifts ($ < .025; Table IV). Tukey’s multiple comparison test showed that the mean vertical die displacement of the Accu-Trac system was significantly larger than those of the Pindex and conventional dowel pin systems, by factors of 1.95 and 1.87 respectively (p < .05). There was no significant difference between the mean vertical die displacement of the Pindex and conventional dowel pin systems @I > .05). MARCH
1988
VOLUME
59
NUMBER
3
COMPARISON
OF THREE
REMOVABLE
DIE SYSTEMS
Table II. Summary of single-factor of mesial-distal
Table III. Summary of single-factor
ANOVA
of buccal-lingual
die displacement
Source of variation
ss
DF
MS
F
P
Total Groups Error
12933.94 335.91 12598.03
57 2 55
167.95 229.05
0.73
>0.25
~p0.05(1),2,55 = 3.18. SS = Sum of squares; DF = degrees of freedom; MS = mean square; F = F-ratio; P = significance level.
ANOVA
die displacement
Source of variation
ss
DF
MS
F
P
Total Groups Error
21183.87 601.87 20582.00
29 2 27
300.93 762.29
0.39
>0.25
‘0.05(1),2,27 = 3.35. SS = Sum of squares; DF = degrees of freedom; MS = mean square; F = F-ratio; P = significance level.
DISCUSSION
Table IV. Summary of single-factor
The small and insignificant deviations in the horizontal plane observed with the three systems may be explained by the fact that the central removable dies are locked securely into place in different ways. With the Accu-Trac system, three die-contact tracks prevent lateral shifting. With the Pindex system, the placement of the twin pin into its corresponding metal sleeve secures the die firmly into position, preventing any rotation. The conventional technique is also accurate because of the length and shape of the dowel pin and the depressions prepared at the base with a round bur, which help to hold the die in place. The vertical movement of the dies was in an upward direction with the Pindex system and the conventional technique. This might be explained by particles of debris that can be trapped in the key-way. Other factors that may interfere are the interface of the stone between the first and second pour and the position and orientation of the dowel pin in the conventional technique. Care should be given to remove any trapped particle of debris by using either acetone or chloroform, compressed air, a small brush, or a pipe cleaner. The results also show that the Pindex system and the conventional technique are acceptable. The conventional system also gjves acceptable results and does not require expensive apparatus. A downward (setting) shift of the removable dies was evident in the Accu-Trac system. This shift would result clinically in a slightly premature contact (supraocclusion) of the fabricated restoration with the opposing tooth. The higher values of the mean average shift show that this technique is less accurate than the others examined. This finding can possibly be explained by the frictional wear of the surfaces of the base of the dies against the tracks of the tray during the 30 removals and replacements of the dies. Although the magnet may allow an easy repositioning of the master cast on the articulator, the entire system seemed somewhat cumbersome.
of gingival-occlusal
ANOVA
die displacement
Source of variation
SS
DF
MS
F
P
Total Groups Error
242.25 33.65 208.60
59 2 57
16.82 3.65
4.60
<0.025
F0.05(1),2,57 = 3.18. SS = Sum of squares; DF = degrees of freedom; MS = mean square; F = F-ratio; P = significance level.
dies in the mesiodistal, bucco-lingual, and gingivoocclusal directions was compared. Under the conditions of this investigation, the following conclusions were drawn. 1. No significant difference was found in the shift of the removable die in a horizontal direction between any of the three systems. 2. No significant difference was found in the displacement of the removable die in the vertical direction with the Pindex system and the conventional dowel pin techniques. The slight displacement that did occur was in an upward direction. 3. A significant vertical displacement of the removable die in a downward direction was found with the Accu-Trac system compared with the other two systems. REFERENCES 1.
Balshi TJ, Mingledorff
EB. Matches, clips, needle, or pins. J
PROSTHET DENT 1975;34:467-72.
2.
3.
4.
Cowell TA, Moore J. New technic for sectional model production for inlay and bridgework. J Am Dent Assoc 1965;71:138790. Robinson FB, Block B. Dowel pin positioning technique for fixed partial denture working casts. J PROSTHET DENT 1981;46:2156. Rudd KD, Strunk RR, Morrow RM. Removable dies for crowns, inlays, and fixed partial dentures. J PROSTHET DENT 1970;23:337-45.
SUMMARY
AND CONCLUSIONS
A study was performed to evaluate three removable die systems: the Accu-Trac, the Pindex, and the conventional brass do,wel pin technique. The stability of the THE JOURNAL
OF PROSTHETIC
DENTISTRY
5.
Rudd KD, Morrow RM, Bange AA. Accurate casts. J PROSTHET
6.
Smith CD, Nayyar A, Koth DL. Fabrication of removable stone dies using cemented dowel pins. J PROSTHET DENT 1979;41:579-
DENT 1969;21:545-54.
81.
317
COVO
7. Stone TE, Welker WA. A-method for locating dowel pins in
ET AL
employed for constructing working dies from hydrocolloid impressions. J PROSTHETDENT 1956;6:87-93. 13. Miranda FJ, Dilts WE, Duncanson Jr MG, Collard EW. Comparative stability of two removable die systems. J PR~~THET DENT 1976;36:326-33. 14. Myers M, Hembree JH Jr. Relative accuracy of four removable die systems. J PR~~THET DENT 1982;48:163-5.
artificial stone casts. J PR~~THET DENT 1980;44:345-6. 8. Toreskog S, Phillips RW, Schnell RJ. Properties of die materials: a comparative study. J PR~.VHET DENT 1966;16:11931. 9. Troendle KB, Troendle GR Jr, Cavazos E Jr. Positioning dowel pins for removable dies. J PROSTHETDENT 1981;46:575-8. 10. Dilts WE, Podshadley AG, Ellison E, Neiman R. Accuracy of a removable die-dowel pin technique. J Dent Res 1971;50:124952. 11. Dilts WE, Podshadley.AG, Sawyer HF, Neiman R. Accuracy of four removable die techniques. J Am Dent Assoc 1971;83:10815. 12. Hohlt FA, Phillips RW. Evaluation of various methods
Reprint requests to: DR. GERALD J. ZIEBERT MARQUETTE UNIVFXSIT~ SCHOLLOF DENTBTRY MILWAUKEE, WI 53233
Retention of cast endodontic posts: Comparison of cementing agents Ryle A. Radke, D.D.S., * Rahmat A. Barkhordar, D.M.D.,** and Ralph E. Podesta, D.D.S.*** University
of California,
San Francisco,
School of Dentistry,
C
San Francisco,
ast metal restorations are commonly used to restore teeth severely damaged by caries or trauma. Often, castings cannot be adequately supported without an intermediate buildup with a suitable dowel and core. The bond strength of the cementing agent plays an important role in the longevity and success of the final restoration. Zinc phosphate cement is the most commonly used cementing agent and remains the comparison standard. A major problem, however, is its lack of adhesion to tooth structure.‘-’ Polycarboxylate and glassionomer cements possessadhesive properties not present in zinc phosphate cement. Glass-ionomer cement is less soluble in the mouth than zinc phosphate cement whereas the polycarboxylate cements are more soluble.5-8 Previous studies reported findings on the retentive property of cements on Para-Post (Whaledent International, New York, N.Y.) dowels.9-‘5 This study compared the relative retentive value of three commonly used cements and one composite.
MATERIAL
AND METHODS
Twenty freshly extracted human single-rooted teeth were embedded in epoxy resin blocks. The teeth were closely matched for size (Fig. 1). Each tooth was sectioned at the cementoenamel junction and the root *Associate Clinical Professor, Fixed Prosthodontics. **Assistant Professor, Endodontics. ***Assistant Clinical Professor, Fixed Prosthodontics.
318
Calif.
Table I. Values at failure of cemented posts Material
Mean (kg)
SD
Zinc phosphate cement (Flecks) Glass-ionomer cement (Ketac cem) Polycarboxylate cement (Durelon) Composite resin (Den Mat)
16.03
2.12
15.17
4.58
12.78
6.85
8.50
7.35
canal systems were cleansed and shaped to a size No. 60 endodontic file with copious irrigation of sodium hypochlorite solution. An 8 mm post space was prepared with the drill supplied by the Para-Post system for the 0.036~inch Para-Post dowel. This serrated parallel-sided form was selected because of its reported superior retentive design. 16-18The Para-Post dowel casting forms were made with a loop centered on the end of the post (Fig. 2) to serve as an attachment to the Instron (model 1122, Instron Corp., Canton, Mass.) testing machine (Fig. 3). The patterns were invested and cast in type III casting gold (Firmilay, J. F. Jelenko Co., New Rochelle, N.Y.). The cementing agents listed in Table I were mixed according to the manufacturers’ directions and introduced into previously dried root canal spaces with a
MARCH
1988
VOLUME
59
NUMBER
3