- Email: [email protected]
Load transfer of posts and cores to roots through cements
Load transfer
of posts and cores to roots through
cements
James M. Leary, D.D.S., M.S.,* M. E. Jensen, D.D.S., PhD.,** and J. J. Sheth, B.D.S., M.S.*** University of Iowa, Collegeof Dentistry, Iowa City, Iowa This study evaluated differences in load transfer when cast posts are fixed to roots with different cements. Cast posts and cores were cemented with 40 endodontically prepared teeth by using four different cement mediums. The load exerted on the root surface through the post was evaluated using a strain gauge. The increased flexure after cementation was statistically analyzed. In conclusion, there was load transfer from post to root structure when posts were cemented, but no difference was found between cementation mediums. (J PROSTHET DENT 1989;62:298-302.)
0
ne persistent problem in clinical dentistry has been vertical root fractures of vital and pulpless teeth.lT8 The causes of vertical root fractures in endodontically treated teeth include volumetric expansion of endodontic posts due tc corrosion,s-ll inordinate force in seating castings,‘* 12,13stressfrom occlusal forces on posts,14zl5 and excessive force in lateral condensation of gutta percha.16Tl7 Cameron1 and Hiatt3 noted that fractures occurring in vital teeth were only in posterior teeth. However, vertical root fractures in endodontically treated teeth occurred in anterior and posterior teeth. The vertical fractures were related to a concentration of forces associated with guttapercha obturation,16* i7 and restoration with po~ta.e-~~Any tooth treated in a similar manner was subject to fractures with propagation of the fracture in a buccolingual direction.7pg Caputo et al.,‘8 determined with photoelastic analysis, that lateral stresses exerted on a root through a post and core were less with cemented posts. Perel and Murofflg agreed that the cement layer redistributed stress. Since then, various studies have been petformed on the restoration of pulpless teeth, examining variations in length,ss-2s diameter,” shape and surface configuration,25 and materials for construction and techniques of fabrication.223 26-2s Additional studies have been accomplished with luting agents and their effects on retention of various post designs.2s-34Diverse methods have been used in the previous studies to evaluate load and cementation. Recently, strain indicators have provided reliable information on the effect of applying small loads to the dental structure.35* 36 Whether load transfer occurs from the post to the dentin through the cementing medium appears subjugated by design and retention studies. This study determined whether load transfer from post to root structure differed
*Assistant Professor,Department of Family Dentistry. **AssociateProfessor,Dews Institute for Dental Research. ***Post-Doctoral Associke, Dows Institute for Dental Research. 1011112240
298
Fig. 1. Prepared specimen with post and core pattern.
Fig. 2. Prepared specimen with cast post and core and strain gauge glued to root surface.
according to the various cements used. If this load transfer exists, the stress might be redistributed throughout the entire root structure and alleviate specific regions of high stress distribution.37 Vertical root fractures associated with localized regions of stress concentration would also diminish.
MATERIAL
AND METHODS
Forty freshly extracted central incisors stored in distilled water with 0.1% thymol were selected for study. Each tooth possesseda root that was 12 mm in length from the cemen-
SEPTEMBER
is89
VOLUME
62
NUMBER
3
LOAD
TRANSFER
OF POSTS
AND
CORES
Fig. 3. Potted specimen next to mounting apparatus.
toenamel junction (CEJ) apically. In addition, each sample was inspected to ensure that the root surfaces were free of caries and without defects. The experimental design included four groups of 10, with each group representing a different cement and technique. The coronal structure of each specimen was prepared to within 2 mm of the CEJ, leaving a flat 14 mm of tooth structure. The canal was then instrumented with a No. 30 endodontic file (Kerr/Sybron Corp., Romulus, Mich.) and debrided of material. Patency was achieved with a No. 15 endodontic file (Kerr/Sybron Corp.) and irrigation. The canal was then enlarged by using a No. 3 Peeso (Union Broach Co., Long Island City, N.Y.) reamer and extended to a length 10 mm from the flattened tooth surface. This ensured a minimum of 4 mm of gutta-percha at the apex as suggested by Shillingburg. A No. 80 plastic endowel (Star Dental Co., Valley Forge, Pa.) was then used with Duralay (Reliance Dental Mfg. Co., Worth, Ill.) resin to make a pattern for a cast post and core. The pattern incorporated an antirotational design and the positive seat (Fig. 1).37PTM 88 (J. F. Jelenko, Armonk, N.Y.) metal was cast for the post and core in a lost-wax technique. The cast patterns were then adjusted in the tooth to ensure a passive, positive seat with minimal lateral stress during insertion and cementation. The final casting had a post 10 mm long that fit accurately into the root structure. In addition, it included a core 10 mm from the prepared tooth surface. The flat surface was the positive seat and the natural flare of the canal represented the antirotational design. A groove was placed on the facial surface of the core 6 mm from the tooth surface and core interface for future loading. A strain gauge (CEA-09--06‘2ww-350, Measurement Group Inc., Raleigh, N.C.) was glued to the midportion of the facial surface of each root (Fig. 2). The specimen was then potted in a l-inch diameter phenol ring (Buehler Ltd., Evanston Ill.) by using tray acrylic resin (Coe Laborato-
THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
ries, Chicago, Ill.) as a potting medium after inserting a piece of steel wire in the root apex to prevent vertical displacement. The ring containing the test specimen was inserted in a custom mounting apparatus (Fig. 3). The mounting apparatus with the specimen was immobilized on the horizontal base of a Ney (J. M. Ney Co., Hartford, Conn.) surveyor. A VishayEllis digital strain indicator (model VE-BOA, Measurement Group Inc.) was connected to the leads from the strain gauge. The half-arm wheatstone bridge system of the bonded strain gauge (Measurements Group Inc.) was calibrated before loading of the post and core system by following the manufacturer’s tecommendations. A 2.5 kg static weight was then placed on the vertical spindle of the surveyor, the spindle was lowered, and a force was exerted onto the core where the buccal groove was placed 6 mm from the core tooth interface. The application of the load was at a go-degree angle to the long axis of the specimen (Fig. 4). The force was repeated three times for each precementation and postcementation test with minimal lag time between applications of force. The load exerted on the root surface through the 10 mm long post was then recorded from the digital strain indicator (Fig. 5). The measurements in micro&rain units were noted before and after cementation. The 40 samples were randomly subdivided into four groups (A through D) of 10 samples for testing. The cements for each group were (A) tlomspan (L. D. Caulk Co., Milford, Del.) luting cement, (13)Comspan luting cement after pretreatment with Gluma (Bayer Dental, Leverkusen, W. Germany) dentin bond, (C) Flecks (Mizzy Inc., Clifton Forge, Va.) zinc phosphate, and (D) Ketaccem (ESPE Premier, Norristown, Pa.) glass ionomer. After the initial pretreatment loading of the uncemented posts, the casts were chemically etched with ETCH IT (American Dental Supply, Easton, Pa.) etchant according to the manufacturer. (Scanning electron micrographs from a pilot 299
LEARY,
JENSEN,
AND
SHETH
Fig. 4. Specimen loaded with 2.5 Kgm force.
Fig. 5. Test mechanism.
study revealed that the ETCH IT agent, provided the best etch patterns of the chemical etchants with the PTM 88 metal.) The etched posts were then cemented in a randomized manner, loaded again after 1 hour, and the flexure strain to the root surface recorded. A mean value for the precementation and postcementation strain between the four groups was computed following data collection, and the percent change was compared by analysis of variance (ANOVA). A paired t-test (SAS procedures) also compared the differences between the two test procedures within each test group. Since microstrain units are a relative value, the postcementation was expressed as a percentage change from precementation.
change (difference) in stress within each test group was computed and the percent change, including standard deviations from the mean (Table I), were evaluated and plotted on a graph (Fig. 6). The differences between the precementation and postcementation means were used in the computation of the paired t-test (Table II). A significant difference was found for the Comspan luting cement alone and Flecks zinc phosphate with this test. The data indicated an increase in stress to the root surface when the posts were cemented. An ANOVA of the percent change between the precementation and postcementation means (Table III) demonstrated that these percentage changes (increases) in postcementation stress were not significantly different within the four groups where
RESULTS The data were obtained from readings on a digital strain indicator. The loading procedure was repeated three times for each precementation and postcementation procedure and the three digital readings were averaged to establish a mean value. These mean values were used as a basis for the statistical analysis. All of the groups indicated a net increase in strain after the post was cemented. The mean
p < 0.05.
SUMMARY A definite increase in stress was exerted onto the root surface when noncemented posts were inserted. This finding was confirmed when a 2.5 kg force was applied to the cores, 6 mm from the tooth-core interface, and at 90 degrees to the long axis of the tooth. Stress measurements
SEPTEMBER
1989
VOLUME
62
NUMBER
3
LOAD TRANSFER
OF POSTS AND CORES
MATERIAL& A - Comspan B * Comspan with Giuma Pretreatment C - Ketec-cem D = Zinc Phosphate
60-
396
T
1
6. Percent of increase in stress to root structure after posts were cemented.
Fig.
Table I. Computed means, percent change, and standard deviations within each group
Table II. Summary of comparison (paired t-test) of precementation to postcementation changes within each group
change (microstrain units)
% Change
SD
+46.6 +83.9 +39.3 +87.3
13.6 23.4 13.4 21.4
1.9 30.2 23.8 18.2
Mean
Group
Comspan Comspan with Gluma Ketac-cem Zinc phosphate
Group
N
Mean change
SD
t
Pr > /tj
Comspan Comspan with Gluma Ketac-cem Zinc phosphate
10 10
46.6 83.9
25.07 108.10
-5.86 -2.45
0.0002* 0.0365
10 10
39.3 87.3
62.78 62.35
-1.98 -4.43
0.0789 0.0017*
*Significant at p < 0.01
also indicated that load transfer to the roots through the cement occurred and was verified by the paired t-test. An ANOVA revealed no statistical difference in stress exerted between the cements. Nevertheless, the trends displayed by the percentof-change graph indicated greater total load transfer when Comspan material with Gluma pretreatment material and Flecks zinc phosphate was used, compared with Comspan and Ketac-cem materials. This total load or stress transfer differs greatly from localized stress concentration. It is believed that the cement resulted in an even distribution of stress throughout the entire root surface and not in a localized region of high stress. It was predicted that different cements would improve internal adaptation of the posts with the roots. This closer adaptation would redistribute the stress uniformily throughout the entire internal circumference of the root without undue stress at a specific site. The effect would be a total overall stress increase without localized areas of high concentrations. Although more total stress to the root was
THE JOURNAL
OF PROSTHETIC
DENTISTRY
Table III. ANOVA summary chart for percent change within the groups Source
DF
Sum of squares
Mean square
Between samples Within samples Corrected total
3 36 39
0.081 1.688 1.770
0.027 0.047
*Significant
F-Value 0.58
Pr > F* 0.6323
at p < 0.05
measured when cemented posts were compared with noncemented posts, the stress was distributed throughout the entire root structure because of the cement. This finding was consistent with photoelastic studies by Caputo et a1.,18 which exhibited less concentraton of lateral stress exerted at specific points of the root structure. This finding also supported the studies of Perel and Muroff,lg who stated that a cement layer redistributed the stress.
301
LEARY,
REFERENCES 1. Cameron CE. The cracked tooth syndrome. J Am Dent Assoc 1976;93:971-5. 2. Silvestri AR. The undiagnosed split-root syndrome. J Am Dent Assoc 1976;92:930-5. 3. Hiatt WH. Incomplete crown-root fracture in pulpal-periodontal disease. J Periodontol 1973;44:369-79. 4. Ritchey B, Mendenhall R, Orban B. Pulpitis resulting from incomplete tooth fracture. Oral Surg 1957;10:665-70. 5. Sutton PNR. Greenstick fracture of the tooth crown. Br Dent J 1962;112:362-3. 6. Viener AE. Fractured teeth: a cause of odontalgia. Oral Surg 1965;20: 494-5. 7. Pitts DL, Natkin E. Diagnosis and treatment of vertical root fractures. J Endodont 1983;9:338-46. 8. Johnson WT, Leary JM. Vertical root fractures: diagnosis and treatment. Gen Dent 19%32:425-g. 9. Rud J, Omnell K. Root fractures due to corrosion. Stand J Dent Res 1970;78:397-403. 10. Peterson KB. Longitudinal root fracture due to corrosion of an endodontic post. J Can Dent Assoc 1971;37:66-8. 11. Mansson BA, Omnell KA, Rud J. Root fractures due to corrosion. Odont Rev 1969;203244-65. 12. Meister F, Lommel TJ, Gerstein H, Davies EE. Endodontic perforations which resulted in alveolar bone loss. Oral Surg 1979;47:463-70. 13. Wechsler SM, Vogel RI, Fishelberg B, Shovlin FE. Iatrogenic root fractures: a case report. J Endodont 1978;4:251-3. 14. Peters MCRB, Poor? HW, Farah JW, Craig RG. Stress analysis of a tooth restored with a post and core. J Dent Res 1983;62:760-3. 15. Harrington GW. The perio-endo question: differential diagnosis. Dent Clin North Am 1979;23:673-90. 16. Meister R, Lommel TJ, Gerstein H. Diagnosis and possible causes of vertical root fractures. Oral Surg 1980,49:243-53. 17. Harvey TE, White JT, Leeb IJ. Lateral condensation stress in root canals. J Endodont 1981;7:151-5. 18. Caputo AA, Standlee JP, Collard EW. The mechanics of load transfer by retentive pins. J PROSTHET DENT 1973;29:442-9. 19. Perel ML, Muroff FI. Clinical criteria for post and cores. J PROSTHET DENT 1972;28:405-11.
20. Leary JM, Aquilino SA, Svare CW. An evaluation of post length within the elastic limits of dentin. J PROSTHET DENT 1987;57:277-81. 21. Standlee JP, Caputo AA, Collard EW, Pollack MH. Analysis of stressdistribution by endodontic posts. Oral Surg 1973;33:952-60. 22. Lovdahl PE, Nicholls JI. Pin-retained amalgam cores vs cast gold dowel cores. J PROSTHET DENT 1977;38:507-14.
302
JENSEN,
AND SHETH
23. Nayyar A, Walton RE, Leonard LA. An amalgam coronal-radicular dowel and core technique for endodontically treated posterior teeth. J PROSTHET DENT 1980;43:511-5.
24. Ruemping DR, Lund MR, Schnell RJ. Retention of dowels subjected to tensil and torsional forces. J PROSTHET DENT 1979;41:159-62. 25. Lau VNS. The reinforcement of endodontically treated teeth. Dent Clin North Am 1976;20:313-28. 26. Ghan RW, Bryant RW. Post-core foundations for endodontically treated posterior teeth. J PROSTHET DENT 1982;48:401-6. 27. Sorensen JA, Martinoff JT. Intracoronal reinforcement and coronal coverage: a study of endodontically treated teeth. J PROSTHET DENT 1984;51:780-4.
28. Brandal JL, Nicholls JI, Harrington GW. A comparison of three restorative techniques for endodontically treated anterior teeth. J PROSTHET DENT 1987;58:161-5.
29. Standlee JP, Caputo AA, Hanson EC. Retention of endodontic dowels: effect of cement, dowel length, diameter and design. J PROSTHET DENT 1978;39:401-5.
30. Assif D, Ferber A. Retention of dowels using a composite resin as a cementing medium. J PROSTHET DENT 1982;48:292-6. 31. Krupp JD, Caputo AA, Trabert KC, Standlee JP. Dowel retention with glass-ionomer cement. J PROSTHET DENT 1979;41:163-6. 32. Judes H, Gordon M, Kusner W. Composite resin retained post and core. NY J Dent 1983;53:205-7. 33. Ben-Amar A, Contar G, Fitzig S, Urstein M, Liberman R. Retention of prefabricated posts with dentinal adhesive and composite. J PROSTHET DENT 1986;56:681-4.
34. Tjan AHL, Whang SB. Retentive properties of some simplified dowelcore systems to cast gold dowel and core. J PROSTHET DENT 198350: 203-6. 35. Douglas WH. Methods to improve fracture resistance of teeth. In: Vanher1 G, Smith DC. International symposium on posterior resin dental restorative materials. Minnesota Mining and Mfg Co, Peter Szule Publishing Co, 1985;433-41. 36. Jensen ME, Redford DA, Williams BT, Gardner F. Posterior etched porcelain restorations: an in-vitro study. Compend Contin Educ Dent 1987;8:615-22. 37. Shillingburg HT, Kessler JC. Restoration of the endodontically treated tooth. Chicago: Quintessence Pub1 Co, Inc, 198221, 52-4. Reprint requests to: DR. JAMES M. LEARY COLLEGE OF DENTISTRY UNIVEFSXI’Y OF IOWA IOWA CITY, IA 52242
SEPTEMBER
1939
VOLUME
62
NUMBER
3
of posts and cores to roots through
cements
James M. Leary, D.D.S., M.S.,* M. E. Jensen, D.D.S., PhD.,** and J. J. Sheth, B.D.S., M.S.*** University of Iowa, Collegeof Dentistry, Iowa City, Iowa This study evaluated differences in load transfer when cast posts are fixed to roots with different cements. Cast posts and cores were cemented with 40 endodontically prepared teeth by using four different cement mediums. The load exerted on the root surface through the post was evaluated using a strain gauge. The increased flexure after cementation was statistically analyzed. In conclusion, there was load transfer from post to root structure when posts were cemented, but no difference was found between cementation mediums. (J PROSTHET DENT 1989;62:298-302.)
0
ne persistent problem in clinical dentistry has been vertical root fractures of vital and pulpless teeth.lT8 The causes of vertical root fractures in endodontically treated teeth include volumetric expansion of endodontic posts due tc corrosion,s-ll inordinate force in seating castings,‘* 12,13stressfrom occlusal forces on posts,14zl5 and excessive force in lateral condensation of gutta percha.16Tl7 Cameron1 and Hiatt3 noted that fractures occurring in vital teeth were only in posterior teeth. However, vertical root fractures in endodontically treated teeth occurred in anterior and posterior teeth. The vertical fractures were related to a concentration of forces associated with guttapercha obturation,16* i7 and restoration with po~ta.e-~~Any tooth treated in a similar manner was subject to fractures with propagation of the fracture in a buccolingual direction.7pg Caputo et al.,‘8 determined with photoelastic analysis, that lateral stresses exerted on a root through a post and core were less with cemented posts. Perel and Murofflg agreed that the cement layer redistributed stress. Since then, various studies have been petformed on the restoration of pulpless teeth, examining variations in length,ss-2s diameter,” shape and surface configuration,25 and materials for construction and techniques of fabrication.223 26-2s Additional studies have been accomplished with luting agents and their effects on retention of various post designs.2s-34Diverse methods have been used in the previous studies to evaluate load and cementation. Recently, strain indicators have provided reliable information on the effect of applying small loads to the dental structure.35* 36 Whether load transfer occurs from the post to the dentin through the cementing medium appears subjugated by design and retention studies. This study determined whether load transfer from post to root structure differed
*Assistant Professor,Department of Family Dentistry. **AssociateProfessor,Dews Institute for Dental Research. ***Post-Doctoral Associke, Dows Institute for Dental Research. 1011112240
298
Fig. 1. Prepared specimen with post and core pattern.
Fig. 2. Prepared specimen with cast post and core and strain gauge glued to root surface.
according to the various cements used. If this load transfer exists, the stress might be redistributed throughout the entire root structure and alleviate specific regions of high stress distribution.37 Vertical root fractures associated with localized regions of stress concentration would also diminish.
MATERIAL
AND METHODS
Forty freshly extracted central incisors stored in distilled water with 0.1% thymol were selected for study. Each tooth possesseda root that was 12 mm in length from the cemen-
SEPTEMBER
is89
VOLUME
62
NUMBER
3
LOAD
TRANSFER
OF POSTS
AND
CORES
Fig. 3. Potted specimen next to mounting apparatus.
toenamel junction (CEJ) apically. In addition, each sample was inspected to ensure that the root surfaces were free of caries and without defects. The experimental design included four groups of 10, with each group representing a different cement and technique. The coronal structure of each specimen was prepared to within 2 mm of the CEJ, leaving a flat 14 mm of tooth structure. The canal was then instrumented with a No. 30 endodontic file (Kerr/Sybron Corp., Romulus, Mich.) and debrided of material. Patency was achieved with a No. 15 endodontic file (Kerr/Sybron Corp.) and irrigation. The canal was then enlarged by using a No. 3 Peeso (Union Broach Co., Long Island City, N.Y.) reamer and extended to a length 10 mm from the flattened tooth surface. This ensured a minimum of 4 mm of gutta-percha at the apex as suggested by Shillingburg. A No. 80 plastic endowel (Star Dental Co., Valley Forge, Pa.) was then used with Duralay (Reliance Dental Mfg. Co., Worth, Ill.) resin to make a pattern for a cast post and core. The pattern incorporated an antirotational design and the positive seat (Fig. 1).37PTM 88 (J. F. Jelenko, Armonk, N.Y.) metal was cast for the post and core in a lost-wax technique. The cast patterns were then adjusted in the tooth to ensure a passive, positive seat with minimal lateral stress during insertion and cementation. The final casting had a post 10 mm long that fit accurately into the root structure. In addition, it included a core 10 mm from the prepared tooth surface. The flat surface was the positive seat and the natural flare of the canal represented the antirotational design. A groove was placed on the facial surface of the core 6 mm from the tooth surface and core interface for future loading. A strain gauge (CEA-09--06‘2ww-350, Measurement Group Inc., Raleigh, N.C.) was glued to the midportion of the facial surface of each root (Fig. 2). The specimen was then potted in a l-inch diameter phenol ring (Buehler Ltd., Evanston Ill.) by using tray acrylic resin (Coe Laborato-
THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
ries, Chicago, Ill.) as a potting medium after inserting a piece of steel wire in the root apex to prevent vertical displacement. The ring containing the test specimen was inserted in a custom mounting apparatus (Fig. 3). The mounting apparatus with the specimen was immobilized on the horizontal base of a Ney (J. M. Ney Co., Hartford, Conn.) surveyor. A VishayEllis digital strain indicator (model VE-BOA, Measurement Group Inc.) was connected to the leads from the strain gauge. The half-arm wheatstone bridge system of the bonded strain gauge (Measurements Group Inc.) was calibrated before loading of the post and core system by following the manufacturer’s tecommendations. A 2.5 kg static weight was then placed on the vertical spindle of the surveyor, the spindle was lowered, and a force was exerted onto the core where the buccal groove was placed 6 mm from the core tooth interface. The application of the load was at a go-degree angle to the long axis of the specimen (Fig. 4). The force was repeated three times for each precementation and postcementation test with minimal lag time between applications of force. The load exerted on the root surface through the 10 mm long post was then recorded from the digital strain indicator (Fig. 5). The measurements in micro&rain units were noted before and after cementation. The 40 samples were randomly subdivided into four groups (A through D) of 10 samples for testing. The cements for each group were (A) tlomspan (L. D. Caulk Co., Milford, Del.) luting cement, (13)Comspan luting cement after pretreatment with Gluma (Bayer Dental, Leverkusen, W. Germany) dentin bond, (C) Flecks (Mizzy Inc., Clifton Forge, Va.) zinc phosphate, and (D) Ketaccem (ESPE Premier, Norristown, Pa.) glass ionomer. After the initial pretreatment loading of the uncemented posts, the casts were chemically etched with ETCH IT (American Dental Supply, Easton, Pa.) etchant according to the manufacturer. (Scanning electron micrographs from a pilot 299
LEARY,
JENSEN,
AND
SHETH
Fig. 4. Specimen loaded with 2.5 Kgm force.
Fig. 5. Test mechanism.
study revealed that the ETCH IT agent, provided the best etch patterns of the chemical etchants with the PTM 88 metal.) The etched posts were then cemented in a randomized manner, loaded again after 1 hour, and the flexure strain to the root surface recorded. A mean value for the precementation and postcementation strain between the four groups was computed following data collection, and the percent change was compared by analysis of variance (ANOVA). A paired t-test (SAS procedures) also compared the differences between the two test procedures within each test group. Since microstrain units are a relative value, the postcementation was expressed as a percentage change from precementation.
change (difference) in stress within each test group was computed and the percent change, including standard deviations from the mean (Table I), were evaluated and plotted on a graph (Fig. 6). The differences between the precementation and postcementation means were used in the computation of the paired t-test (Table II). A significant difference was found for the Comspan luting cement alone and Flecks zinc phosphate with this test. The data indicated an increase in stress to the root surface when the posts were cemented. An ANOVA of the percent change between the precementation and postcementation means (Table III) demonstrated that these percentage changes (increases) in postcementation stress were not significantly different within the four groups where
RESULTS The data were obtained from readings on a digital strain indicator. The loading procedure was repeated three times for each precementation and postcementation procedure and the three digital readings were averaged to establish a mean value. These mean values were used as a basis for the statistical analysis. All of the groups indicated a net increase in strain after the post was cemented. The mean
p < 0.05.
SUMMARY A definite increase in stress was exerted onto the root surface when noncemented posts were inserted. This finding was confirmed when a 2.5 kg force was applied to the cores, 6 mm from the tooth-core interface, and at 90 degrees to the long axis of the tooth. Stress measurements
SEPTEMBER
1989
VOLUME
62
NUMBER
3
LOAD TRANSFER
OF POSTS AND CORES
MATERIAL& A - Comspan B * Comspan with Giuma Pretreatment C - Ketec-cem D = Zinc Phosphate
60-
396
T
1
6. Percent of increase in stress to root structure after posts were cemented.
Fig.
Table I. Computed means, percent change, and standard deviations within each group
Table II. Summary of comparison (paired t-test) of precementation to postcementation changes within each group
change (microstrain units)
% Change
SD
+46.6 +83.9 +39.3 +87.3
13.6 23.4 13.4 21.4
1.9 30.2 23.8 18.2
Mean
Group
Comspan Comspan with Gluma Ketac-cem Zinc phosphate
Group
N
Mean change
SD
t
Pr > /tj
Comspan Comspan with Gluma Ketac-cem Zinc phosphate
10 10
46.6 83.9
25.07 108.10
-5.86 -2.45
0.0002* 0.0365
10 10
39.3 87.3
62.78 62.35
-1.98 -4.43
0.0789 0.0017*
*Significant at p < 0.01
also indicated that load transfer to the roots through the cement occurred and was verified by the paired t-test. An ANOVA revealed no statistical difference in stress exerted between the cements. Nevertheless, the trends displayed by the percentof-change graph indicated greater total load transfer when Comspan material with Gluma pretreatment material and Flecks zinc phosphate was used, compared with Comspan and Ketac-cem materials. This total load or stress transfer differs greatly from localized stress concentration. It is believed that the cement resulted in an even distribution of stress throughout the entire root surface and not in a localized region of high stress. It was predicted that different cements would improve internal adaptation of the posts with the roots. This closer adaptation would redistribute the stress uniformily throughout the entire internal circumference of the root without undue stress at a specific site. The effect would be a total overall stress increase without localized areas of high concentrations. Although more total stress to the root was
THE JOURNAL
OF PROSTHETIC
DENTISTRY
Table III. ANOVA summary chart for percent change within the groups Source
DF
Sum of squares
Mean square
Between samples Within samples Corrected total
3 36 39
0.081 1.688 1.770
0.027 0.047
*Significant
F-Value 0.58
Pr > F* 0.6323
at p < 0.05
measured when cemented posts were compared with noncemented posts, the stress was distributed throughout the entire root structure because of the cement. This finding was consistent with photoelastic studies by Caputo et a1.,18 which exhibited less concentraton of lateral stress exerted at specific points of the root structure. This finding also supported the studies of Perel and Muroff,lg who stated that a cement layer redistributed the stress.
301
LEARY,
REFERENCES 1. Cameron CE. The cracked tooth syndrome. J Am Dent Assoc 1976;93:971-5. 2. Silvestri AR. The undiagnosed split-root syndrome. J Am Dent Assoc 1976;92:930-5. 3. Hiatt WH. Incomplete crown-root fracture in pulpal-periodontal disease. J Periodontol 1973;44:369-79. 4. Ritchey B, Mendenhall R, Orban B. Pulpitis resulting from incomplete tooth fracture. Oral Surg 1957;10:665-70. 5. Sutton PNR. Greenstick fracture of the tooth crown. Br Dent J 1962;112:362-3. 6. Viener AE. Fractured teeth: a cause of odontalgia. Oral Surg 1965;20: 494-5. 7. Pitts DL, Natkin E. Diagnosis and treatment of vertical root fractures. J Endodont 1983;9:338-46. 8. Johnson WT, Leary JM. Vertical root fractures: diagnosis and treatment. Gen Dent 19%32:425-g. 9. Rud J, Omnell K. Root fractures due to corrosion. Stand J Dent Res 1970;78:397-403. 10. Peterson KB. Longitudinal root fracture due to corrosion of an endodontic post. J Can Dent Assoc 1971;37:66-8. 11. Mansson BA, Omnell KA, Rud J. Root fractures due to corrosion. Odont Rev 1969;203244-65. 12. Meister F, Lommel TJ, Gerstein H, Davies EE. Endodontic perforations which resulted in alveolar bone loss. Oral Surg 1979;47:463-70. 13. Wechsler SM, Vogel RI, Fishelberg B, Shovlin FE. Iatrogenic root fractures: a case report. J Endodont 1978;4:251-3. 14. Peters MCRB, Poor? HW, Farah JW, Craig RG. Stress analysis of a tooth restored with a post and core. J Dent Res 1983;62:760-3. 15. Harrington GW. The perio-endo question: differential diagnosis. Dent Clin North Am 1979;23:673-90. 16. Meister R, Lommel TJ, Gerstein H. Diagnosis and possible causes of vertical root fractures. Oral Surg 1980,49:243-53. 17. Harvey TE, White JT, Leeb IJ. Lateral condensation stress in root canals. J Endodont 1981;7:151-5. 18. Caputo AA, Standlee JP, Collard EW. The mechanics of load transfer by retentive pins. J PROSTHET DENT 1973;29:442-9. 19. Perel ML, Muroff FI. Clinical criteria for post and cores. J PROSTHET DENT 1972;28:405-11.
20. Leary JM, Aquilino SA, Svare CW. An evaluation of post length within the elastic limits of dentin. J PROSTHET DENT 1987;57:277-81. 21. Standlee JP, Caputo AA, Collard EW, Pollack MH. Analysis of stressdistribution by endodontic posts. Oral Surg 1973;33:952-60. 22. Lovdahl PE, Nicholls JI. Pin-retained amalgam cores vs cast gold dowel cores. J PROSTHET DENT 1977;38:507-14.
302
JENSEN,
AND SHETH
23. Nayyar A, Walton RE, Leonard LA. An amalgam coronal-radicular dowel and core technique for endodontically treated posterior teeth. J PROSTHET DENT 1980;43:511-5.
24. Ruemping DR, Lund MR, Schnell RJ. Retention of dowels subjected to tensil and torsional forces. J PROSTHET DENT 1979;41:159-62. 25. Lau VNS. The reinforcement of endodontically treated teeth. Dent Clin North Am 1976;20:313-28. 26. Ghan RW, Bryant RW. Post-core foundations for endodontically treated posterior teeth. J PROSTHET DENT 1982;48:401-6. 27. Sorensen JA, Martinoff JT. Intracoronal reinforcement and coronal coverage: a study of endodontically treated teeth. J PROSTHET DENT 1984;51:780-4.
28. Brandal JL, Nicholls JI, Harrington GW. A comparison of three restorative techniques for endodontically treated anterior teeth. J PROSTHET DENT 1987;58:161-5.
29. Standlee JP, Caputo AA, Hanson EC. Retention of endodontic dowels: effect of cement, dowel length, diameter and design. J PROSTHET DENT 1978;39:401-5.
30. Assif D, Ferber A. Retention of dowels using a composite resin as a cementing medium. J PROSTHET DENT 1982;48:292-6. 31. Krupp JD, Caputo AA, Trabert KC, Standlee JP. Dowel retention with glass-ionomer cement. J PROSTHET DENT 1979;41:163-6. 32. Judes H, Gordon M, Kusner W. Composite resin retained post and core. NY J Dent 1983;53:205-7. 33. Ben-Amar A, Contar G, Fitzig S, Urstein M, Liberman R. Retention of prefabricated posts with dentinal adhesive and composite. J PROSTHET DENT 1986;56:681-4.
34. Tjan AHL, Whang SB. Retentive properties of some simplified dowelcore systems to cast gold dowel and core. J PROSTHET DENT 198350: 203-6. 35. Douglas WH. Methods to improve fracture resistance of teeth. In: Vanher1 G, Smith DC. International symposium on posterior resin dental restorative materials. Minnesota Mining and Mfg Co, Peter Szule Publishing Co, 1985;433-41. 36. Jensen ME, Redford DA, Williams BT, Gardner F. Posterior etched porcelain restorations: an in-vitro study. Compend Contin Educ Dent 1987;8:615-22. 37. Shillingburg HT, Kessler JC. Restoration of the endodontically treated tooth. Chicago: Quintessence Pub1 Co, Inc, 198221, 52-4. Reprint requests to: DR. JAMES M. LEARY COLLEGE OF DENTISTRY UNIVEFSXI’Y OF IOWA IOWA CITY, IA 52242
SEPTEMBER
1939
VOLUME
62
NUMBER
3