- Email: [email protected]
Incomplete seating of cemented crowns: A literature review
WEAR
RATES
UNDER
STRESS-REARING
CONDITIONS
en in viva zwischen amalgam und komposit. Dtsch Zahnarztl Z 1980;35:489-92. 3. Lutz F, Phillips RW, Roulet JF, Setcos JC. In viva and in vitro wear of potential posterior composites. J Dent Res 1984;63:91420. potential as a posterior 4. Lutz F, Imfeld T. Phillips RW. P-lo-its composite. Dent Mater 1985;1:61-5. 5. Hiirsted P, Borup J. In viva abrasion of Profile and Adaptic composite resins. &and J Dent Res 1984;92:249-52. 6. Lambrechts P, Braem M, Vanherle G. Accomplishments and expectations with posterior composite resins. In: Vanherle G, Smith DC, eds. Posterior composite resin dental restorative materials, Proceedings of International Symposium. Utrecht: Szulc Press, 1985;521. 7. Leinfelder K F. Evaluation of clinical wear of posterior composite resins. In: Vanherle G, Smith DC, eds. Posterior composite resin dental restorative materials. Proceedings of International Symposium. Utrecht: Szulc Press, 1985;507.
8.
Lutz F, Phillips RW. A classification and evaluation of composite resin systems. J PROSTHETDENT 1983;50:480-8. 9. Feilier AJ, de Gee AJ, Davidson CL. Curing contraction of composites and glass-ionomer cements. J PROSTHET DENT 1988;59:297-300. 10. Braem M, Lambrechts P, van Doren V, Vanherle G. The impact of composite structure on its elastic response. J Dent Res 1986; 65:648. Reprint requests to: DR. C. L. DAVIDSON UNIVERSITY OF AMSTERDAM
ACTA, LOUWESWEGG 1 1066 EA AMSTERDAM THE NETHERLANDS
Incomplete seating of cemented crowns: A literature review R. Pilo, D.M.D.,* H. S. Cardash, B.D.S., L.D.S., R.C.S, Eng.,** and M. Helft,, D.M.D.***
H. Baharav, D.M.D.,*
Tel Aviv Liniversity, The Maurice and Gabriela Goldschleger School of Dental Medicine, Tel Aviv, Israel
K
asloP said, “To fulfill the requirements for an ideal restoration, a casting must be made to fit the prepared tooth intimately.” It has long been recognized, however, that cast crowns do not seat completely when cemented. The more accurately the casting fits the prepared tooth, the more difficult it is for cement trapped between the crown and the occlusal surface of the tooth to escape.2Thus, a properly constructed fixed prosthesis may fail as a result of incomplete seating during cementation.) Most research on cementation of crowns relates seating failure to the thickness of the cement film. FACTORS AFFECTING THE FILM THICKNESS OF CEMENT In 1960, Jdrgensen4 investigated factors influencing the thickness of cement between the restoration and the prepared tooth. The optimum cementation force required to reduce the film thickness of cement was 5 kg for 1 minute. An increase in the powder/liquid ratio of the cement or an increase in the mixing temperature *Instructor, Department of Oral Rehabilitation. **Senior Lecturer, Department of Oral Rehabilitation. ***Head, Department of Oral Rehabilitation. THE JOURNAL
OF PROSTHETIC
DENTISTRY
increased the film thickness. The smaller the taper of the preparation (less than 10 degrees) the greater is the film thickness of cement when the occlusal surface of the crown is not perforated. WindelerS pointed out that the occlusal displacement of a veneer crown due to cement film thickness is a function of the sine of one half the taper angle of the preparation: film thickness at the axial walls Occlusal displacement = sine 1/ taper angle
FILM
THICKNESS
MEASUREMENTS
Dies with cemented crowns have been sectioned and the film thickness measured directly with a travelling microscope.6 Film thickness has also been measured indirectly by recording the distance between the margin of the casting and the finishing line of the preparation before and after cementation,’ or between reference marks on the casting and die.2,8s9The ADA specification for film thickness of type I zinc phosphate cement is 25 pm and for type II 40 pm. Most investigators found film thickness much higher than this on cemented crowns at the occlusal surface, ranging from 60 pm to 435 P.~-” The wide range may relate to different methods of measurement and experimental design of the models used. 429
PILO ET AL
THEORIES FOR rNCOMPLETE SEATING The failure of crowns to seat completely during cementation was explained by J~rgensen.*~‘*He suggestedthat when the crown carrying the cementis placed on the prepared tooth, cement accumulates on the occlusal surface. When pressure is applied to complete the seating of the crown, excesscement can escapeonly through the spaceat the cervical margin. As the crown approachesits final position this spacebecomessmaller, The flow of the noncompressible liquid cement is inhibited and seatingof the crown is resisted.Cement at the occlusalsurfacemust travel the greatestdistance and overcomefrictional resistancein order to escape.Hydrodynamic pressure causesthe cementto separatein solid and liquid phases.The solid particles form a massthat only allows passageof the thinner liquid, causing further separation and filtration of the cement. This phenomenon, called t~e~~trut~o~ processresults in a much higher film thickness than the ADA Specification No. 8 for zince phosphatecement. Hoard et al.19 investigated intracoronal pressures during crown cementation with zinc phosphatecement. Maximum pressurewas recordedat the occlusal surface of a die after 2 seconds;it reducedto zero after 1 minute. Less pressurereducing to zero was recordedat the cusp tip and at the axial walls, reducing to 25% after 1 minute. In a comparison of different cements,the more viscousthe cement, the greater was the hydraulic pressure that did not reduce to zero. Thus, it was concluded that internal back pressure plays a limited role in preventing the complete seating of a crown. Hoard et al.19 also suggested that the filtration process of J~rgensen4,‘*resulting in accumulation of cementparticles in various regions on the internal surface of the crown is responsible for increased film thickness of cement. DISCREPANCIES OF MARGINAL
FIT
Among the complications causedby incomplete seating of crowns are (1) creation of premature contacts;(2) alteration of contact areas with a;ijacent teeth; (3) a reduction in crown retention by 19% to 32Y0’~;and (4) discrepanciesof marginal fit of the crown. Crowns may fail becauseof cement wash-out at the margins.M Ill-fitting margins expose large amounts of cementto the oral fluids, &-easing the rate of deposition of plaque.21Dissolution of cementin oral fluids results in marginal leakage and a rough surface that accumulates debris and bacteria.= After setting, zinc phosphate cement has been shown to elute zinc, magnesium~ sodium, and phosphate ions into an aqueous solution.23 Osborne et al.24 in assessing clinical solubility and disintegration of cements,however, observedno correlation between in vivo and conventional in vitro tests. Swartz et al.25found that early exposure of zinc phosphate cementto water after setting increasedits solubil430
ity and suggestedcoating the exposedsurfacewith cavity varnish. The con~guration of the finishing line of the preparation affectsthe width of the band of cement exposedto oral fluids. Shoulder finishing lines showed an exposed cementline as great as the discrepancy of seating of the crown. When a chamfer finishing margin is used, the cement line decreasesaccording to its inclination. The exposedcement of a shoulderlesscrown remains minimal regardlessof the discrepancyof seating.26Gavelis et al.” confirmed that feathered edgesand shoulders and chamferswith parallel bevelshad the smallest marginal openings. ~lini~lly, there is no clear correlation between the thickness of the exposedband of cement at the crown margin and the amount of cement dissolvedby the oral fluids. Crowns present in the mouth for 8 to 15 years on teeth subsequently extracted for periodontal reasons were examined by us. In many caseswhere the crowns were grossly ill-fitting, no cement wash-out was observed.On the other hand, well-fitting crowns exhibited spacesbetween crown and tooth substanceindicating wash-out of cement.Thus, the marginal integrity of the crown may not be solely responsible for cement wash-out. Cement manipulation or environmental factors localized to the tooth and not necessarily present elsewhere in the mouth should be considered.Some of these factors are currently being researched by us. Venting, internal relief of the castings, and modified cementation techniques have been proposedto improve the marginal fit of cementedcrowns. VENTING A small hole prepared in the occlusal or axial surface of the restoration allows exit of excesscement during cementation.Cooper et al. l3found that venting of casting reduced the mean marginal opening by 45 pm. Similarly, Van Nortwick and Cettleman’ improved the vertical seating of crowns by 290 pm with venting. Kaufman et a1.15improved seating by 175 pm ,with venting and $howed that retention was increased by 19% to 32%. Dimashkieh and Davies6found that venting of crowns is less critical when the taper angle of the preparation is increased.In near parallel-sided prepared teeth, venting was necessary to avoid an excessive occlusal cement thickness. This study also showed that the time of final seating of 1 minute in nonvented crowns was reducedto 15 secondsin vented crowns. Venting, however, has someseriousdisadvantages:(1) an extra visit is necessaryto fill the vent hole; (2) the material used to fill the vent hole may wear or display marginal leakage;and (3) occlusalventing of ceramic or ceramometalcrowns may weaken the porcelain. Vent holes in crowns may be closedwith amalgam or composite. Bassett28described a technique of casting a pin that was sized to fill a hole made by a No. 699 bur. APRIL
1988
VOLUME
59
NUMBER
4
INCOMPLETE
SEATING
OF CEMENTED
CROWNS:
REVIEW
Sebergz9prepared a hole in the wax pattern and cast a matching Williams pin. The pin was seated in the vent hole immediat.ely after the escape of the cement.
INTERNAL
RELIEF
A space is, created between the casting and the prepared tooth to accommodate excess cement after closure of the marginal pathway of escape. Pascoe30 demonstrated that the margins of oversized castings fit better than undersized castings after cementation. The same effect can be obtained by relieving the internal surface of the crown. A number of methods exist to achieve internal reliePI-33.
1. Grinding the inside of the casting 2. Internal carving of the wax pattern 3. Etching the internal surface of the wax restoration with aqua regia 4. Electrochemical milling of the inside of the casting These methods have been rejected as inaccurate and inconsistent. It is impossible to obtain a uniform space for the cement. These methods cannot be used for ceramometal restorations. Recently researchers have obtained internal relief by cutting internal channels in prepared abutment teeth and in the internal surface of the crowns before cementation.34s37Mean marginal discrepancies of more than 200 pm were reduced to 30 pm by cutting axial channels 0.5 mm deep extending from the occlusal surface to within 1 mm of the cervical margin before cementation of the crowns.)” No significant difference was found after modification of the occlusal surface of the preparation. This technique causes loss of adaptation of tooth and casting only in discreet areas where channels are prepared. An effective method of obtaining internal relief is die spacing. Paint is applied to the die to within 0.5 to 1 mm of the finishing line of the preparation. Fusayama et alz6 reduced cement thickness under cemented crowns to 34 to 44 pm by coating the dies with nail polish or a 40 pm thickness of tinfoil. The results were superior to those obtained with occlusal venting. Eames et a1.,14using a 25 pm relief, decreased film thickness of cement to 45 pm in lo-degree tapered preparations and to 33 Km in 20degree tapered preparations, whereas venting achieved thicknesses of 64 pm and 63 pm, respectively. In contrast, Van Nortwick and Gettlemar9 obtained seating to within 52 pm by using a die spacer and 44 km by using venting. The optimum thickness of die spacer that will still allow maximurn retention is not known. Eames et a1.14 and Eliasson a:nd Lund3s suggest 25 pm. Fusayama et a1.26used 40 pm and implied that less than 30 pm was undesirable. Fusayama and Iwamotto39 found that the thickness of zinc phosphate cement necessary for optiTHE JOURNAL
OF PROSTHETIC
DENTISTRY
mum shear strength was 31 to 38 pm. However, Jfirgensen and Esbensen@concluded that 20 to 140 pm had only a moderate effect on retention. A clinically acceptable relief is considered to be 20 to 40 clm.33
THE CEMENTATION
TECHNIQUE
Three variations of the cementation technique have been used in an effort to obtain improved seating: vibration, the site of application of cement, and the magnitude of cementation pressure. Oliveira et a14’ found that vibration improved the fitting of MOD inlays by 16 pm and crowns by 27 pm. It is not stated how the vibration was applied except that it occurred before static pressure was applied. Van Nortwick and Gettleman* indicated that vibration applied horizontally while the cement was setting did not affect crown seating. Koyano et al.’ reported that the cement film was thinner when vibrating pressure was applied. Vertical vibration was slightly more effective than horizontal vibration but less comfortable to the patient. A subject that has yet to be fully investigated is the effect of the site of cement application on the seating of the crown. Ishikiriama et al.” found that cement painted on the inner walls of the crown promoted a better fit than when the crown was completely filled with cement. The flow pathway of cement and the amount of incomplete marginal seating of the restoration has been studied.42Cement was applied at various locations on the internal surface of the crown and on the prepared tooth. An incomplete marginal seating of 54 pm was found when cement was placed on the margins of the crowns compared with 106 pm when cement was applied on the apical half of the axial walls of the crowns. When cement was applied to the apical half of the axial walls of the prepared tooth, incomplete seating was 40 ,um and when applied to the margin of the preparation only, incomplete seating reduced to 10 pm. Fusayama and Iwamotto39 and Jfirgensen4 reported that the relationship between cement thickness and compressive load applied during cementation was in the form of a hyperbolic curve. The disagreement between them concerned the load above which the effect is minimal. Jdrgensen4 noted that an increase in load above 5 kg had little effect on the result. Fusayama et a1.26 reported that excessive amounts of pressure (15 to 50 kg) applied during cementation produced no significant difference in the thickness of cement on the shoulders of preparations. Grajower et a1.43reported that a pressure increase of 2 to 10 kg applied at the first try-on stage of cast full crowns caused an average apical movement by the crown of 63 pm. This is attributed to protrubances on the internal surface of the casting arresting the complete seating of the crown. On application of pressure, these protrusions created furrows in the axial surface of the prepared tooth. The average elevation of nonprecious 431
PILO ET AL
metal crowns caused by cementation was found to be 54 pm. This elevation corresponds to an effective minimum cement thickness of 4.7 pm at the axial walls. On application of pressure, protrusions on the casting surface could cause high localized pressure on the cement and might therefore penetrate the cement layer. The results of Grajower et a1.43indicate that the effective minimum cement thickness at the axial walls can be lower than 4 brn and that the possibility for metal-dentin contact in certain locations cannot be excluded. This raises a question as to the relevance of the ADA Specification No. 8. J#rgensen and EsbenserP believe that the ADA Specification No. 8 relates more to the viscosity of the cement than to the film thickness. Grajower et a1.43 suggest that studies regarding cementation and crown elevation be done on teeth instead of on dies because mechanical properties of the dentin may affect the results. The amount of incomplete seating of a cemented crown is equal to the film thickness of the cement at the occlusal surface. It is related to the cement thickness at the axial walls of the tooth preparation by the equation: Film thickness at occlusal surface =
film thickness at axial wall sine 1%the taper angle
The Jplrgensen filtration process explaining why the thickness of cement exceeds the ADA Specification No. 8 is based on two assumptions: (1) On placing the crown containing the cement on the prepared tooth, cement accumulates on the occlusal surface, and (2) hydrodynamic pressure develops within the cement as the marginal opening prevents cement escaping. In wellcontrolled circumstances, these two assumptions can be contradicted: (1) The amount of cement reaching the occlusal surface can be controlled and even totally prevented by applying cement only to specific areas of the crown or preparation. 42It is not yet clear whether complete elimination of cement at the occlusal surface is desirable inasmuch as an empty space may encourage microbial growth. (2) At the try-on stage of the crown, a space exists between it and the tooth preparation. If the volume of this space could be calculated and the correct amount of cement introduced into the space, hydrodynamic pressure would not develop. Controlling the amount of cement may well eliminate the filtration process of Jbrgensen. Windelers claims that the occlusal discrepancy is caused by excess cement that exceeds the space available for it and suggests the equation: Occlusal discrepancy =
film thickness on axial walls minus space available for cement sine 1%taper angle of the preparation
As shown by Grajower et al.43a film thickness as small as 4 pm can be reached at the axial walls. Research should continue to determine the correct amount of cement to place in the crown, the site of 432
application, and the amount of cementation pressure so that space between the axial wall and the crown will accommodate the available cement. The emphasis in the literature about incomplete seating of crowns during cementation has been placed on eliminating marginal discrepancy by venting and internal relief. More stress should be placed on the cementation technique as a means of solving the problem of incomplete seating. REFERENCES 1. Kasloff A. Casting techniques and some variables. J PROSTHET DENT 1961;11:533-6. 2. Jones MD, Dykema RW, Klein AI. Television micromeasurement of vented and non-vented cast crown marginal adaptation. Dent Clin North Am 1971;15:663-77. 3. Abelson J. Cementation of cast complete crown retainers. J PROSTHETDENT 1980;43:174-9. 4. Jdrgensen KD. Factors affecting the film thickness of zinc phosphate cements. Acta Odontol &and 1960;18:479-90. 5. Windeler AS. Powder enrichment effects on film thickness of zinc phosphate cement. J PROSTHETDENT 1979;42:299-303. 6. Dimashkieh MR, Davies EH. Measurement of the cement film thickness beneath full crown restorations. Br Dent J 1974; 137:281-4. 7. Koyano E, Iwaku M, Fusayama T. Pressuring techniques and cement thickness for cast restorations. J PROSTHET DENT 1978;40:544-8. 8. Van Nortwick NT, Gettleman L. Effect of internal relief, vibration, and venting on the vertical seating of cemented crowns. J PR~~THET DENT 1981;45:395-9. 9. Suthers MD, Wise MD. Influence of cementing medium on the accuracy of the remount procedure. J PROSTHET DENT 1982;47:377-83. 10. Ishikiriama A, Oliveira JF, Vieira DF, Mondelli J. Influence of some factors on the fit of cemented crowns. J PROSTHETDENT 1981;45:400-4. 11. Grieve AR. A study of dental cements. Br Dent J 1969;127:40510. 12. Fusayama T, Ide K, Kurosu A, Hosoda H. Cement thickness between cast restorations and preparation walls. J PROSTHET DENT 1963;13:354-64. 13. Cooper TM, Christensen GJ, Laswell HR, Baxter R. Effect of venting on cast gold full crowns. J PROSTHETDENT 1971;26: 621-6. 14. Eames WB, O’Neal SJ, Monteiro J, Miller C, Roan JD, Cohen KS. Techniques to improve the seating of castings. J Am Dent Assoc 1978;96:432-6. 15. Kaufman EG, Coelho HD, Cohn L. Factors influencing the retention of cemented gold castings. J PROSTHETDENT 1961; 11:487-502. 16. McLean JW, von Fraunhofer JA. The estimation of cement film thickness by an in uivo technique. Br Dent J 1971;131:107-11. 17. Moore JA, Barghi N, Brukl CE, Kaiser DA. Marginal distortion of cast restorations induced by cementation. J PROSTHET DENT 1985;54:336-40. 18. Jdrgensen KD. Structure of the film of zinc phosphate cements. Acta Odontol Stand 1960;18:491-7. 19. Hoard RJ, Caputo AA, Contino RM, Koenig EM. Intracoronal pressure during crown cementation. J PROSTHETDENT 1978; 40:520-5. 20. Grieve AR, Jones JC. Marginal leakage associated with four inlay cementing materials. Br Dent J 1981;151:331-4. 21. Orstavik D, Orstavik J. In vitro attachment of Streptococcus sanguis to dental crown and bridge cements. J Oral Rehabil 1976;3:139-44. APRIL 1988
VOLUME 59
NUMBER 4
INCOMPLETE
SEATING
OF CEMENTED
CROWNS:
REVIEW
Schwartzman B, Caputo AA, Schein B. Antimicrobial action of dental ceme:nts.J PROSTHE~DENT 1980;43:309-12. 23. Wilson AD, Abel G, Lewis BG. The solubility and disintegration test for zinc phosphate dental cements. Br Dent J 1974;137:313-7. 24. Osborne JW, Swartz ML, Goodacre CJ, Phillips RW, Gale EN. A method for assessing the clinical solubility and disintegration of luting cements. J PROSTHETDENT 1978;40:413-7. Swartz ML, Sears C, Phillips RW. Solubility of cement as related to l.ime of exposure in water. J PROSTHET DENT 1971;26:501-5. 26. Fusayama T, Ide K, Hosoda H. Relief of resistance of cement of full cast crowns. J PROSTHETDENT 1964;14:95-105. Gavelis JR, Morency JD, Riley ED, Sozio RB. The effect of various finishing line preparations on the marginal seal and occlusal sea,. of full crown preparations. J PROSTHET DENT 1981;45:138..45. Bassett RW. Solving the problems of cementing the full veneer cast gold crown. J PROSTHETDENT 1966;16:740-7. 29. Seberg DC. A simplified venting procedure for cementation of full veneer crowns. J Am Dent Assoc 1973;86:145-8. Pascoe DF. Analysis of the geometry of finishing lines for full crown restorations. J PROSTHETDENT 1978;40: 157-62. Hollenback GM. A practical contribution to the standardization of casting technique. J Am Dent Assoc 1928;10:5-9. 32. Bassett RW, Stauts BM. Evaluation of electromechanical milling (stripping) versus etching with aqua regia. J S Calif Dent Assoc 1966;34:478-80. Campagni WV, Preston JD, Rdsbick MH. Measurement of paint on die spacers used for casting relief. J PROSTHETDENT 1982;47:606-11. Brose MO, Woelfel JB, Rieger MR, Tanquist RA. Internal channel vents for posterior complete crown. J PROSTHETDENT 1984;51:755-60. Tjan .4HL, ,Sarkissian R, Miller GD. Effect of multiple axial grooves on the marginal adaptation of full cast gold crowns. J PROSTHETDENT 1981;46:399-403. 36. Miller GD, Tjan AHL. An internal escape channel. A simplified solution to the problem of incomplete seating of full cast-gold crowns. J Am Dent Assoc 1082;104:332-5.
22.
Webb EL, Murrary HV, Holland GA, Taylor DF. Effects of preparation relief and flow channels on seating full coverage castings during cementation. J PROSTHETDENT 1982;49:77780. 38. Eliasson ST, Lund MR. Improving marginal fit through finishing procedures. J Indiana State Dent Assoc 1974;53:13-7. 39. Fusayama T, Iwamotto T. Relationship between retaining force of inlays and film thickness of zinc oxyphosphate cement. J Dent Res 1960;39:756-60. 40. Jfirgensen KD, Esbensen AL. The relationship between the film thickness of zinc phosphate cement and the retention of veneer crowns. Acta Odontol Stand 1968;26:169-74. 41. Oliveira JF, Ishikiriama A, Vieira DF, Mondelli J. Influence of pressure and vibration during cementation. J PROSTHETDENT 1979;41:173-7. 42. Rimmer Y. The flow of zinc phosphate cement under a full coverage restoration according to the location of its application and its effect on the marginal adaptation. Thesis, Tel Aviv University, School of Dental Medicine, Tel Aviv, Israel, 1986. 43. Grajower R, Lewinstein I, Zeltser C. The effective minimum cement thickness of zinc phosphate cement for luted non-precious crowns. J Oral Rehabil 1985;12:235-45. 37.
Contributing
author
B. Ben-Shemen, D.M.D., Instructor, Department of Oral Rehabilitation, Tel Aviv University, The Maurice and Gabriela Goldschleger School of Dental Medicine, Tel Aviv, Israel Reprint requests to: DR. RAPHAEL PILO TEL AVIV UNIVERSITY THE MAURICE AND GABRIELAGOLDSCHLEGER SCHOLLOF DENTAL MEDICINE RAMAT AVIV 69978 TEL AVIV ISRAEL
Temperature rise produced by various visible light generators through dentinal barriers Anthony
H. I,. Tjan, Dr.Dent., D.D.S.,* and James R. Dunn, D.D.S.**
Loma Linda University, School of Dentistry, Loma Linda, Calif.
T
emperature changes that occur during dental procedures have been shown to produce odontoblastic and pulpal changes if a significant amount of heat is transferred to the tooth structure.‘-6 Zach and Cohen2 reported that a 5.5” C (10’ F) intrapulpal temperature rise in
Presented at Ihe American Academy of Restorative Dentistry, Chicago, Ill. *Professor and Director of Biomaterials Research, Department of Restorative Dentistry. **Assistant Professes, Department of Restorative Dentistry. THE JOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 1. Dentin disk embedded
in resin. 433
RATES
UNDER
STRESS-REARING
CONDITIONS
en in viva zwischen amalgam und komposit. Dtsch Zahnarztl Z 1980;35:489-92. 3. Lutz F, Phillips RW, Roulet JF, Setcos JC. In viva and in vitro wear of potential posterior composites. J Dent Res 1984;63:91420. potential as a posterior 4. Lutz F, Imfeld T. Phillips RW. P-lo-its composite. Dent Mater 1985;1:61-5. 5. Hiirsted P, Borup J. In viva abrasion of Profile and Adaptic composite resins. &and J Dent Res 1984;92:249-52. 6. Lambrechts P, Braem M, Vanherle G. Accomplishments and expectations with posterior composite resins. In: Vanherle G, Smith DC, eds. Posterior composite resin dental restorative materials, Proceedings of International Symposium. Utrecht: Szulc Press, 1985;521. 7. Leinfelder K F. Evaluation of clinical wear of posterior composite resins. In: Vanherle G, Smith DC, eds. Posterior composite resin dental restorative materials. Proceedings of International Symposium. Utrecht: Szulc Press, 1985;507.
8.
Lutz F, Phillips RW. A classification and evaluation of composite resin systems. J PROSTHETDENT 1983;50:480-8. 9. Feilier AJ, de Gee AJ, Davidson CL. Curing contraction of composites and glass-ionomer cements. J PROSTHET DENT 1988;59:297-300. 10. Braem M, Lambrechts P, van Doren V, Vanherle G. The impact of composite structure on its elastic response. J Dent Res 1986; 65:648. Reprint requests to: DR. C. L. DAVIDSON UNIVERSITY OF AMSTERDAM
ACTA, LOUWESWEGG 1 1066 EA AMSTERDAM THE NETHERLANDS
Incomplete seating of cemented crowns: A literature review R. Pilo, D.M.D.,* H. S. Cardash, B.D.S., L.D.S., R.C.S, Eng.,** and M. Helft,, D.M.D.***
H. Baharav, D.M.D.,*
Tel Aviv Liniversity, The Maurice and Gabriela Goldschleger School of Dental Medicine, Tel Aviv, Israel
K
asloP said, “To fulfill the requirements for an ideal restoration, a casting must be made to fit the prepared tooth intimately.” It has long been recognized, however, that cast crowns do not seat completely when cemented. The more accurately the casting fits the prepared tooth, the more difficult it is for cement trapped between the crown and the occlusal surface of the tooth to escape.2Thus, a properly constructed fixed prosthesis may fail as a result of incomplete seating during cementation.) Most research on cementation of crowns relates seating failure to the thickness of the cement film. FACTORS AFFECTING THE FILM THICKNESS OF CEMENT In 1960, Jdrgensen4 investigated factors influencing the thickness of cement between the restoration and the prepared tooth. The optimum cementation force required to reduce the film thickness of cement was 5 kg for 1 minute. An increase in the powder/liquid ratio of the cement or an increase in the mixing temperature *Instructor, Department of Oral Rehabilitation. **Senior Lecturer, Department of Oral Rehabilitation. ***Head, Department of Oral Rehabilitation. THE JOURNAL
OF PROSTHETIC
DENTISTRY
increased the film thickness. The smaller the taper of the preparation (less than 10 degrees) the greater is the film thickness of cement when the occlusal surface of the crown is not perforated. WindelerS pointed out that the occlusal displacement of a veneer crown due to cement film thickness is a function of the sine of one half the taper angle of the preparation: film thickness at the axial walls Occlusal displacement = sine 1/ taper angle
FILM
THICKNESS
MEASUREMENTS
Dies with cemented crowns have been sectioned and the film thickness measured directly with a travelling microscope.6 Film thickness has also been measured indirectly by recording the distance between the margin of the casting and the finishing line of the preparation before and after cementation,’ or between reference marks on the casting and die.2,8s9The ADA specification for film thickness of type I zinc phosphate cement is 25 pm and for type II 40 pm. Most investigators found film thickness much higher than this on cemented crowns at the occlusal surface, ranging from 60 pm to 435 P.~-” The wide range may relate to different methods of measurement and experimental design of the models used. 429
PILO ET AL
THEORIES FOR rNCOMPLETE SEATING The failure of crowns to seat completely during cementation was explained by J~rgensen.*~‘*He suggestedthat when the crown carrying the cementis placed on the prepared tooth, cement accumulates on the occlusal surface. When pressure is applied to complete the seating of the crown, excesscement can escapeonly through the spaceat the cervical margin. As the crown approachesits final position this spacebecomessmaller, The flow of the noncompressible liquid cement is inhibited and seatingof the crown is resisted.Cement at the occlusalsurfacemust travel the greatestdistance and overcomefrictional resistancein order to escape.Hydrodynamic pressure causesthe cementto separatein solid and liquid phases.The solid particles form a massthat only allows passageof the thinner liquid, causing further separation and filtration of the cement. This phenomenon, called t~e~~trut~o~ processresults in a much higher film thickness than the ADA Specification No. 8 for zince phosphatecement. Hoard et al.19 investigated intracoronal pressures during crown cementation with zinc phosphatecement. Maximum pressurewas recordedat the occlusal surface of a die after 2 seconds;it reducedto zero after 1 minute. Less pressurereducing to zero was recordedat the cusp tip and at the axial walls, reducing to 25% after 1 minute. In a comparison of different cements,the more viscousthe cement, the greater was the hydraulic pressure that did not reduce to zero. Thus, it was concluded that internal back pressure plays a limited role in preventing the complete seating of a crown. Hoard et al.19 also suggested that the filtration process of J~rgensen4,‘*resulting in accumulation of cementparticles in various regions on the internal surface of the crown is responsible for increased film thickness of cement. DISCREPANCIES OF MARGINAL
FIT
Among the complications causedby incomplete seating of crowns are (1) creation of premature contacts;(2) alteration of contact areas with a;ijacent teeth; (3) a reduction in crown retention by 19% to 32Y0’~;and (4) discrepanciesof marginal fit of the crown. Crowns may fail becauseof cement wash-out at the margins.M Ill-fitting margins expose large amounts of cementto the oral fluids, &-easing the rate of deposition of plaque.21Dissolution of cementin oral fluids results in marginal leakage and a rough surface that accumulates debris and bacteria.= After setting, zinc phosphate cement has been shown to elute zinc, magnesium~ sodium, and phosphate ions into an aqueous solution.23 Osborne et al.24 in assessing clinical solubility and disintegration of cements,however, observedno correlation between in vivo and conventional in vitro tests. Swartz et al.25found that early exposure of zinc phosphate cementto water after setting increasedits solubil430
ity and suggestedcoating the exposedsurfacewith cavity varnish. The con~guration of the finishing line of the preparation affectsthe width of the band of cement exposedto oral fluids. Shoulder finishing lines showed an exposed cementline as great as the discrepancy of seating of the crown. When a chamfer finishing margin is used, the cement line decreasesaccording to its inclination. The exposedcement of a shoulderlesscrown remains minimal regardlessof the discrepancyof seating.26Gavelis et al.” confirmed that feathered edgesand shoulders and chamferswith parallel bevelshad the smallest marginal openings. ~lini~lly, there is no clear correlation between the thickness of the exposedband of cement at the crown margin and the amount of cement dissolvedby the oral fluids. Crowns present in the mouth for 8 to 15 years on teeth subsequently extracted for periodontal reasons were examined by us. In many caseswhere the crowns were grossly ill-fitting, no cement wash-out was observed.On the other hand, well-fitting crowns exhibited spacesbetween crown and tooth substanceindicating wash-out of cement.Thus, the marginal integrity of the crown may not be solely responsible for cement wash-out. Cement manipulation or environmental factors localized to the tooth and not necessarily present elsewhere in the mouth should be considered.Some of these factors are currently being researched by us. Venting, internal relief of the castings, and modified cementation techniques have been proposedto improve the marginal fit of cementedcrowns. VENTING A small hole prepared in the occlusal or axial surface of the restoration allows exit of excesscement during cementation.Cooper et al. l3found that venting of casting reduced the mean marginal opening by 45 pm. Similarly, Van Nortwick and Cettleman’ improved the vertical seating of crowns by 290 pm with venting. Kaufman et a1.15improved seating by 175 pm ,with venting and $howed that retention was increased by 19% to 32%. Dimashkieh and Davies6found that venting of crowns is less critical when the taper angle of the preparation is increased.In near parallel-sided prepared teeth, venting was necessary to avoid an excessive occlusal cement thickness. This study also showed that the time of final seating of 1 minute in nonvented crowns was reducedto 15 secondsin vented crowns. Venting, however, has someseriousdisadvantages:(1) an extra visit is necessaryto fill the vent hole; (2) the material used to fill the vent hole may wear or display marginal leakage;and (3) occlusalventing of ceramic or ceramometalcrowns may weaken the porcelain. Vent holes in crowns may be closedwith amalgam or composite. Bassett28described a technique of casting a pin that was sized to fill a hole made by a No. 699 bur. APRIL
1988
VOLUME
59
NUMBER
4
INCOMPLETE
SEATING
OF CEMENTED
CROWNS:
REVIEW
Sebergz9prepared a hole in the wax pattern and cast a matching Williams pin. The pin was seated in the vent hole immediat.ely after the escape of the cement.
INTERNAL
RELIEF
A space is, created between the casting and the prepared tooth to accommodate excess cement after closure of the marginal pathway of escape. Pascoe30 demonstrated that the margins of oversized castings fit better than undersized castings after cementation. The same effect can be obtained by relieving the internal surface of the crown. A number of methods exist to achieve internal reliePI-33.
1. Grinding the inside of the casting 2. Internal carving of the wax pattern 3. Etching the internal surface of the wax restoration with aqua regia 4. Electrochemical milling of the inside of the casting These methods have been rejected as inaccurate and inconsistent. It is impossible to obtain a uniform space for the cement. These methods cannot be used for ceramometal restorations. Recently researchers have obtained internal relief by cutting internal channels in prepared abutment teeth and in the internal surface of the crowns before cementation.34s37Mean marginal discrepancies of more than 200 pm were reduced to 30 pm by cutting axial channels 0.5 mm deep extending from the occlusal surface to within 1 mm of the cervical margin before cementation of the crowns.)” No significant difference was found after modification of the occlusal surface of the preparation. This technique causes loss of adaptation of tooth and casting only in discreet areas where channels are prepared. An effective method of obtaining internal relief is die spacing. Paint is applied to the die to within 0.5 to 1 mm of the finishing line of the preparation. Fusayama et alz6 reduced cement thickness under cemented crowns to 34 to 44 pm by coating the dies with nail polish or a 40 pm thickness of tinfoil. The results were superior to those obtained with occlusal venting. Eames et a1.,14using a 25 pm relief, decreased film thickness of cement to 45 pm in lo-degree tapered preparations and to 33 Km in 20degree tapered preparations, whereas venting achieved thicknesses of 64 pm and 63 pm, respectively. In contrast, Van Nortwick and Gettlemar9 obtained seating to within 52 pm by using a die spacer and 44 km by using venting. The optimum thickness of die spacer that will still allow maximurn retention is not known. Eames et a1.14 and Eliasson a:nd Lund3s suggest 25 pm. Fusayama et a1.26used 40 pm and implied that less than 30 pm was undesirable. Fusayama and Iwamotto39 found that the thickness of zinc phosphate cement necessary for optiTHE JOURNAL
OF PROSTHETIC
DENTISTRY
mum shear strength was 31 to 38 pm. However, Jfirgensen and Esbensen@concluded that 20 to 140 pm had only a moderate effect on retention. A clinically acceptable relief is considered to be 20 to 40 clm.33
THE CEMENTATION
TECHNIQUE
Three variations of the cementation technique have been used in an effort to obtain improved seating: vibration, the site of application of cement, and the magnitude of cementation pressure. Oliveira et a14’ found that vibration improved the fitting of MOD inlays by 16 pm and crowns by 27 pm. It is not stated how the vibration was applied except that it occurred before static pressure was applied. Van Nortwick and Gettleman* indicated that vibration applied horizontally while the cement was setting did not affect crown seating. Koyano et al.’ reported that the cement film was thinner when vibrating pressure was applied. Vertical vibration was slightly more effective than horizontal vibration but less comfortable to the patient. A subject that has yet to be fully investigated is the effect of the site of cement application on the seating of the crown. Ishikiriama et al.” found that cement painted on the inner walls of the crown promoted a better fit than when the crown was completely filled with cement. The flow pathway of cement and the amount of incomplete marginal seating of the restoration has been studied.42Cement was applied at various locations on the internal surface of the crown and on the prepared tooth. An incomplete marginal seating of 54 pm was found when cement was placed on the margins of the crowns compared with 106 pm when cement was applied on the apical half of the axial walls of the crowns. When cement was applied to the apical half of the axial walls of the prepared tooth, incomplete seating was 40 ,um and when applied to the margin of the preparation only, incomplete seating reduced to 10 pm. Fusayama and Iwamotto39 and Jfirgensen4 reported that the relationship between cement thickness and compressive load applied during cementation was in the form of a hyperbolic curve. The disagreement between them concerned the load above which the effect is minimal. Jdrgensen4 noted that an increase in load above 5 kg had little effect on the result. Fusayama et a1.26 reported that excessive amounts of pressure (15 to 50 kg) applied during cementation produced no significant difference in the thickness of cement on the shoulders of preparations. Grajower et a1.43reported that a pressure increase of 2 to 10 kg applied at the first try-on stage of cast full crowns caused an average apical movement by the crown of 63 pm. This is attributed to protrubances on the internal surface of the casting arresting the complete seating of the crown. On application of pressure, these protrusions created furrows in the axial surface of the prepared tooth. The average elevation of nonprecious 431
PILO ET AL
metal crowns caused by cementation was found to be 54 pm. This elevation corresponds to an effective minimum cement thickness of 4.7 pm at the axial walls. On application of pressure, protrusions on the casting surface could cause high localized pressure on the cement and might therefore penetrate the cement layer. The results of Grajower et a1.43indicate that the effective minimum cement thickness at the axial walls can be lower than 4 brn and that the possibility for metal-dentin contact in certain locations cannot be excluded. This raises a question as to the relevance of the ADA Specification No. 8. J#rgensen and EsbenserP believe that the ADA Specification No. 8 relates more to the viscosity of the cement than to the film thickness. Grajower et a1.43 suggest that studies regarding cementation and crown elevation be done on teeth instead of on dies because mechanical properties of the dentin may affect the results. The amount of incomplete seating of a cemented crown is equal to the film thickness of the cement at the occlusal surface. It is related to the cement thickness at the axial walls of the tooth preparation by the equation: Film thickness at occlusal surface =
film thickness at axial wall sine 1%the taper angle
The Jplrgensen filtration process explaining why the thickness of cement exceeds the ADA Specification No. 8 is based on two assumptions: (1) On placing the crown containing the cement on the prepared tooth, cement accumulates on the occlusal surface, and (2) hydrodynamic pressure develops within the cement as the marginal opening prevents cement escaping. In wellcontrolled circumstances, these two assumptions can be contradicted: (1) The amount of cement reaching the occlusal surface can be controlled and even totally prevented by applying cement only to specific areas of the crown or preparation. 42It is not yet clear whether complete elimination of cement at the occlusal surface is desirable inasmuch as an empty space may encourage microbial growth. (2) At the try-on stage of the crown, a space exists between it and the tooth preparation. If the volume of this space could be calculated and the correct amount of cement introduced into the space, hydrodynamic pressure would not develop. Controlling the amount of cement may well eliminate the filtration process of Jbrgensen. Windelers claims that the occlusal discrepancy is caused by excess cement that exceeds the space available for it and suggests the equation: Occlusal discrepancy =
film thickness on axial walls minus space available for cement sine 1%taper angle of the preparation
As shown by Grajower et al.43a film thickness as small as 4 pm can be reached at the axial walls. Research should continue to determine the correct amount of cement to place in the crown, the site of 432
application, and the amount of cementation pressure so that space between the axial wall and the crown will accommodate the available cement. The emphasis in the literature about incomplete seating of crowns during cementation has been placed on eliminating marginal discrepancy by venting and internal relief. More stress should be placed on the cementation technique as a means of solving the problem of incomplete seating. REFERENCES 1. Kasloff A. Casting techniques and some variables. J PROSTHET DENT 1961;11:533-6. 2. Jones MD, Dykema RW, Klein AI. Television micromeasurement of vented and non-vented cast crown marginal adaptation. Dent Clin North Am 1971;15:663-77. 3. Abelson J. Cementation of cast complete crown retainers. J PROSTHETDENT 1980;43:174-9. 4. Jdrgensen KD. Factors affecting the film thickness of zinc phosphate cements. Acta Odontol &and 1960;18:479-90. 5. Windeler AS. Powder enrichment effects on film thickness of zinc phosphate cement. J PROSTHETDENT 1979;42:299-303. 6. Dimashkieh MR, Davies EH. Measurement of the cement film thickness beneath full crown restorations. Br Dent J 1974; 137:281-4. 7. Koyano E, Iwaku M, Fusayama T. Pressuring techniques and cement thickness for cast restorations. J PROSTHET DENT 1978;40:544-8. 8. Van Nortwick NT, Gettleman L. Effect of internal relief, vibration, and venting on the vertical seating of cemented crowns. J PR~~THET DENT 1981;45:395-9. 9. Suthers MD, Wise MD. Influence of cementing medium on the accuracy of the remount procedure. J PROSTHET DENT 1982;47:377-83. 10. Ishikiriama A, Oliveira JF, Vieira DF, Mondelli J. Influence of some factors on the fit of cemented crowns. J PROSTHETDENT 1981;45:400-4. 11. Grieve AR. A study of dental cements. Br Dent J 1969;127:40510. 12. Fusayama T, Ide K, Kurosu A, Hosoda H. Cement thickness between cast restorations and preparation walls. J PROSTHET DENT 1963;13:354-64. 13. Cooper TM, Christensen GJ, Laswell HR, Baxter R. Effect of venting on cast gold full crowns. J PROSTHETDENT 1971;26: 621-6. 14. Eames WB, O’Neal SJ, Monteiro J, Miller C, Roan JD, Cohen KS. Techniques to improve the seating of castings. J Am Dent Assoc 1978;96:432-6. 15. Kaufman EG, Coelho HD, Cohn L. Factors influencing the retention of cemented gold castings. J PROSTHETDENT 1961; 11:487-502. 16. McLean JW, von Fraunhofer JA. The estimation of cement film thickness by an in uivo technique. Br Dent J 1971;131:107-11. 17. Moore JA, Barghi N, Brukl CE, Kaiser DA. Marginal distortion of cast restorations induced by cementation. J PROSTHET DENT 1985;54:336-40. 18. Jdrgensen KD. Structure of the film of zinc phosphate cements. Acta Odontol Stand 1960;18:491-7. 19. Hoard RJ, Caputo AA, Contino RM, Koenig EM. Intracoronal pressure during crown cementation. J PROSTHETDENT 1978; 40:520-5. 20. Grieve AR, Jones JC. Marginal leakage associated with four inlay cementing materials. Br Dent J 1981;151:331-4. 21. Orstavik D, Orstavik J. In vitro attachment of Streptococcus sanguis to dental crown and bridge cements. J Oral Rehabil 1976;3:139-44. APRIL 1988
VOLUME 59
NUMBER 4
INCOMPLETE
SEATING
OF CEMENTED
CROWNS:
REVIEW
Schwartzman B, Caputo AA, Schein B. Antimicrobial action of dental ceme:nts.J PROSTHE~DENT 1980;43:309-12. 23. Wilson AD, Abel G, Lewis BG. The solubility and disintegration test for zinc phosphate dental cements. Br Dent J 1974;137:313-7. 24. Osborne JW, Swartz ML, Goodacre CJ, Phillips RW, Gale EN. A method for assessing the clinical solubility and disintegration of luting cements. J PROSTHETDENT 1978;40:413-7. Swartz ML, Sears C, Phillips RW. Solubility of cement as related to l.ime of exposure in water. J PROSTHET DENT 1971;26:501-5. 26. Fusayama T, Ide K, Hosoda H. Relief of resistance of cement of full cast crowns. J PROSTHETDENT 1964;14:95-105. Gavelis JR, Morency JD, Riley ED, Sozio RB. The effect of various finishing line preparations on the marginal seal and occlusal sea,. of full crown preparations. J PROSTHET DENT 1981;45:138..45. Bassett RW. Solving the problems of cementing the full veneer cast gold crown. J PROSTHETDENT 1966;16:740-7. 29. Seberg DC. A simplified venting procedure for cementation of full veneer crowns. J Am Dent Assoc 1973;86:145-8. Pascoe DF. Analysis of the geometry of finishing lines for full crown restorations. J PROSTHETDENT 1978;40: 157-62. Hollenback GM. A practical contribution to the standardization of casting technique. J Am Dent Assoc 1928;10:5-9. 32. Bassett RW, Stauts BM. Evaluation of electromechanical milling (stripping) versus etching with aqua regia. J S Calif Dent Assoc 1966;34:478-80. Campagni WV, Preston JD, Rdsbick MH. Measurement of paint on die spacers used for casting relief. J PROSTHETDENT 1982;47:606-11. Brose MO, Woelfel JB, Rieger MR, Tanquist RA. Internal channel vents for posterior complete crown. J PROSTHETDENT 1984;51:755-60. Tjan .4HL, ,Sarkissian R, Miller GD. Effect of multiple axial grooves on the marginal adaptation of full cast gold crowns. J PROSTHETDENT 1981;46:399-403. 36. Miller GD, Tjan AHL. An internal escape channel. A simplified solution to the problem of incomplete seating of full cast-gold crowns. J Am Dent Assoc 1082;104:332-5.
22.
Webb EL, Murrary HV, Holland GA, Taylor DF. Effects of preparation relief and flow channels on seating full coverage castings during cementation. J PROSTHETDENT 1982;49:77780. 38. Eliasson ST, Lund MR. Improving marginal fit through finishing procedures. J Indiana State Dent Assoc 1974;53:13-7. 39. Fusayama T, Iwamotto T. Relationship between retaining force of inlays and film thickness of zinc oxyphosphate cement. J Dent Res 1960;39:756-60. 40. Jfirgensen KD, Esbensen AL. The relationship between the film thickness of zinc phosphate cement and the retention of veneer crowns. Acta Odontol Stand 1968;26:169-74. 41. Oliveira JF, Ishikiriama A, Vieira DF, Mondelli J. Influence of pressure and vibration during cementation. J PROSTHETDENT 1979;41:173-7. 42. Rimmer Y. The flow of zinc phosphate cement under a full coverage restoration according to the location of its application and its effect on the marginal adaptation. Thesis, Tel Aviv University, School of Dental Medicine, Tel Aviv, Israel, 1986. 43. Grajower R, Lewinstein I, Zeltser C. The effective minimum cement thickness of zinc phosphate cement for luted non-precious crowns. J Oral Rehabil 1985;12:235-45. 37.
Contributing
author
B. Ben-Shemen, D.M.D., Instructor, Department of Oral Rehabilitation, Tel Aviv University, The Maurice and Gabriela Goldschleger School of Dental Medicine, Tel Aviv, Israel Reprint requests to: DR. RAPHAEL PILO TEL AVIV UNIVERSITY THE MAURICE AND GABRIELAGOLDSCHLEGER SCHOLLOF DENTAL MEDICINE RAMAT AVIV 69978 TEL AVIV ISRAEL
Temperature rise produced by various visible light generators through dentinal barriers Anthony
H. I,. Tjan, Dr.Dent., D.D.S.,* and James R. Dunn, D.D.S.**
Loma Linda University, School of Dentistry, Loma Linda, Calif.
T
emperature changes that occur during dental procedures have been shown to produce odontoblastic and pulpal changes if a significant amount of heat is transferred to the tooth structure.‘-6 Zach and Cohen2 reported that a 5.5” C (10’ F) intrapulpal temperature rise in
Presented at Ihe American Academy of Restorative Dentistry, Chicago, Ill. *Professor and Director of Biomaterials Research, Department of Restorative Dentistry. **Assistant Professes, Department of Restorative Dentistry. THE JOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 1. Dentin disk embedded
in resin. 433