Intracorurtal pressure during crown cemmMon R J. Hoard, D.D.S.,* A. A. Caputo, Ph.D.,** R. M. Contino, D.D.S.,*** and M. E. Koenig”““’ University

of California,

School of Dentistry,

Los Angeles, Calif.

investigations to date have not dealt extensively with the role, duration, and magnitude of the intracoronal pressures which develop during the seating of full crowns. Although incomplete crown seating has been reported for over 40 years, Jorgensen’s recent work has advanced the most detailed explanation of this phenomenon.‘, ’ He stated that the great bulk of dental cement is at the occlusal surface during the initial phase of crown seating. As the crown is directed to a full marginal seat, the cement must escape through space at the marginal collar. The closer the crown approaches its ideal resting place, the smaller the space available for cement to escape. At this point the cement resists full seating of the crown because the narrow pathway for escape is closing down against the flow of the noncompressible liquid. Further, the cement at the occlusal surface must travel the greatest distance and overcome frictional resistance to escape cervically. The mixture of cement is affected by this movement and undergoes partial separation into its two basic phases, solid and liquid. The solid particles clump together, forming a sievelike mass which only allows passage of the thinner liquid, causing a further separation and filtration process to occur. Since it has been shown that venting aids in achieving a more complete seating of full crowns, it has been suggested that high cement viscosity and unrelieved hydraulic pressure are the main factors in determining cement film thickness.J a Previous studies to clarify the contribution of hydraulic pressure have lacked a satisfactory model system sensitive to

*Assistant Professor, Operative Dentistry, Univenity of California, Los Angeles, Calif. **Professor and Chairman, UCLA Biomaterials Science Section, Los Angela, Calif.; Formerly Bialental Research Engineer, Veterans Administration Hospital, Sepulveda, Calif. “*Private Practice, Pasadena, Calif. ****Engineering Technician, Dental Research. VA Hospital, Sepulveda, Calif.

520

NOVEMBER 1~8

VOLUME 40

NUMBER 5

‘1 / I I I ’

’I

140;

“I

DIE CONFIGURATION

Fig. 1. Diagrammatic representation of die configuration. the pressures that occur during crown cementation. It was the purpose of this investigation to develop a model system that would be suitable for assessing the role of intracoronal pressures during crown cementation.

MATERIALS AND METHODS A split die was fabricated from naval brass to the configuration of an ideal full crown molar preparatioh, with a 4-degree taper and chamfer margin (Fig. 1). Occlusal reduction was accomplished along planes similar to the occlusal reduction of cusp inclines of a natural tooth. The die was machined and burnished so that no seam was detectable under X 10 magnification (Figs. 2 and 3). In this way no artificial sluiceway was available to the cement during crown seating. A hollow sleeve was machined to receive the die with a 0.00%inch tolerance (Figs. 4 and 5). This die-sleeve combination was used to fabricate standard, reproducible wax patterns.

0022~3913/78/110520

+ Ofi$OO.600/0 0 1978 The C. V. Monby Co.

INTRACORONAL

PRESSURE

Fig. 2. Axial view of assembled split die. Fig. 4. Mold for fabrication of wax patterns.

Fig. 3. Ckclusal view of assembled split die. Five gold castings were made by a standardized method. The die was lubricated and placed into the mold sleeve. The heated wax was applied with a medicine dropper into the sleeve, and while the wax was still in the liquid stage, the cap was screwed snugly into place. The assembly was then chilled, the wax pattern and die were removed as one unit, and excess wax was removed. Then the pattern was sprued with a hollow plastic sprue with a reservoir 1 to 2 mm from the pattern. A hygroscopic investment material* was used. The investment was vacuummixed and poured into a casting ring containing a wet asbestos liner.5, 6 The casting ring was then immediately immersed in a 100” F water bath for 30 minutes. The ring was removed and placed in an oven at 800” F for 20 minutes and then held at 1,100” F for an additional 40 minutes. Casting was done on a Vat-o-castt machine using a Type III gold.$ The resulting crowns were cleaned and viewed at X20 magnification to confirm that they were free of surface nodules which would prevent correct seating on the die (Fig. 6). Semiconductor strain gauges5 were used as pressure-sensing elements. The gauges were mounted at the internal chamber wall at three locations of the *Beauty Cast, The Whip-Mix Corp., Louisville, Ky. tRickenbacber Manufacturing Co., Los Angeles, Calif. $Ncy Ore, Type III, The J. M. Ney Co., Bloomfield, Corm. IKulite Semiconductor Products, Inc., Ridgefield, N. J.

THE JOURNAL OF PROSTHETIC DENTISTRY

Fig. 5. Wax mold with die in place.

Fig. 6. Gold casting is seated on the die. die-the cusp tip, occlusal center, and axial wall (Fig. 7). The gauges served as transducers to measure the external pressure of the die wall. Each strain gauge was connected to a wheatstone bridge having a null balance strain gauge lead to a Brush 440 amplifier-recorder with a frequency response of -3dB at 1 kHz + 20%.* All tests were conducted using a chart speed of 25mm/minute. The millivolt response of the strain gauges which resulted from the pressure at the external wall was *BN.& Instruments, Cleveland, Ohio.

521

HOARD ET AL

LOCATION

OF GAUGES

Fig. 7. Location of gauges for pressure measurement. I, Cusp tip. 2, Center occlusal surface. 3, Axial wall. Fig. 9. Schematic of seating force direction.

Fig. 8. ExperimentaI arrangement for crown cementation depicting loading frame and casting seated on the die. monitored continuously for the duration of the crown-seating tests. Three cements were considered in this study. They were (1) zinc phosphate,* (2) polycarboxylate,t and (3) zinc oxide-eugeno1.g Zinc phosphate cement was mixed to a standard clinically acceptable consistency following the manufacturer’s specifications. Polycarboxylate cement was mixed using 1.5 parts of powder to 1 part of liquid.’ The two-paste zinc oxide-eugenol was mixed according to manufacturer’s specifications. Standardization of successive mixes was assured by proportioning the two components of each of the cements on a precision balance to an accuracy of rt 0.05 gm. *Fleck’s cement, Mizzy, Inc., Clifton Forge, Va. tPCA Cement, S. S. White Dental Co., Philadelphia, $Temp Bond, Kerr Mfg. Co., Romulus, Mich.

522

A special loading frame with a die-positioning device was constructed. This frame directs a predetermined weight through the long axis of the crowndie combination, allowing the crown to be directed by the cement flow rather than the crown dinxting the cement flow (Figs. 8 and 9). The testing sequence consisted of placing the mixed cement within the crown and seating the crown on the die with a 5 kg load’ while the recording system was documenting the pressureinduced output of the internal strain gauges. Crown seating was repeated 20 times for each cement to assure reproducibility of the measurements. Once the hydraulic pressure reached a stable state, as evidence by a flat line on the recorder, the crown was removed and the cement was dissolved before it set by the use of ultrasonic solution.* This prevented any alteration of the intaglio surface of the crowns, and each of the five crowns could be used again. RESULTS Prior to the test sequences with the cements, the crown was seated on the die with no cement under a 5 kg weight. No significant strain gauge output was recorded under these circumstances. This indicated that no sign&cant occlusal or axial contact occurred between the crown and the die. A characteristic of crown seatings, using all the cements under consideration, was a rapid increase of pressure to a peak, followed by a rapid decrease (Figs. 10 to 12). For all the cements, the peak

Pa. *Demon, L. R. Mfg. Co., Kcamy, N. J

NOVEMBER 1978

VOLUME 10

NUMBER 9

INTRACORONAL

PRESSURE

seconds Fig. 10. Gauge output (mV) during crown seating with zinc phosphate cement. Top, Gauge 1, cusp tip. Middle, Gauge 2, center occlusal surface. Botfom, Gauge 3, axial wall. pressures were reached within approximately 2 seconds. An uneven distribution of intracoronal peak pressure was recorded at various locations of the crown preparation. The total overall pressure was greatest for the zinc phosphate cement and least for the temporary zinc oxide-eugenol cement. The polycarboxylate cement caused pressures of intermediate intensity. A summary of the peak pressures for all crown seatings is presented in Fig. 13. The zinc phosphate cement produced the greatest peak pressure in the center of the occlusal surface and the least at the cusp tip and axial wall regions. The zinc oxideeugenol cement produced the greatest pressure at the axial walls and the least at the cusp tips. The polycarboxylate cement generated no significant pressure differences at the occlusal surface and axial walls. A lower pressure was recorded at the cusp tips. The nature of the release of pressure was different for the three cements. The three gauges recorded similar pressure decay curves for the zinc oxideeugenol cement. The pressure at each gauge location reduced to 0 in 10 seconds (Fig. 12). With the polycarboxylate cement the three pressure decay curves had similar shapes (Fig 11). The gauges at the

THE JOURNAL OF PROSTHETIC DENTISTRY

Fig. 11. Gauge autput (mV) during crown seating with polycarboxylate cement. Top, Gauge 1, cusp tip. Middle, Gauge 2, center occlusal surface. Bottom, Gauge 3, axial wall.

seconds Fig. 12. Gauge output (mV) during crown seating with zinc oxide-eugenol (ZOE) cement. Tap, Gauge 1, cusp tip. Middle, Gauge 2, center occlusal surface. Boftom, Gauge 3, axial wall.

523

HOARD

ET AL

center of the occlusal surface and axial wall had an initial sharp decrease followed by a more gradual decrease to 0 after an elapsed time of approximately 1.2 minutes. A markedly different behavior was manifested by the gauge at the occlusal tip. Zero pressure was observed at approximately 15 seconds. The pressure became negative at this time and leveled out at 1.2 minutes to a negative pressure equal to the initial positive peak pressure. With the zinc phosphate cement each of the three gauges exhibited a different response (Fig. 10). The pressure release rate was greater for the zinc phosphate than for the other two cements. The pressure at the center of the occlusal surface did not reduce to 0 but remained at a pressure approximately 10% of the peak pressure. The pressure at the axial wall leveled off to 25% of peak pressure. Each of these pressures was reached at approximately 1 minute. At the cusp tip, zero pressure was achieved at 24 seconds. As with the polycarboxlyate cement, a negative residual pressure was maintained.

ing may have been overestimated. Evidence for this was the short duration of peak pressures observed for all cements at all gauge locations. Consequently, it appears that after the initial resistance provided by the hydrostatic pressure, the distribution of intracoronal pressures provides a complex hydrodynamic situation. This leads to various localized filtration process conditions which affect the flow of the cement and hence the final seating of the crown. Jorgensen’ noted that as pressure was exerted on dental cement a separation of the particles from the liquid occurs. The separated particles then flow differently and can accumulate or clump together in various regions on the crown preparation interface. It is this accumulation or stacking together of the particles that results in an effective film thickness much greater than the ADA specification. Venting works because it affects the flow, limits the stacking of the particles, and relieves any small residual intracoronal pressure. It was observed that the cement fluidity has considerable influence on the intracoronal pressure distribution during crown seating. For example, the most fluid cement, zinc oxide-eugenol, showed intracoronal pressure reduced to 0 shortly after reaching peak pressures. The less fluid cements (zinc phosphate and polycarboxylate) reached higher peak pressures that did not reduce to 0. In fact, both positive and negative residual pressures resulted with these cements. One could then expect that cements mixed with higher powder-liquid ratio (,to obtain higher strength) would result in thicker consistency and higher peak pressures with accentuated residual pressures. The explanation for the negative residual pressure at the cusp tip is not clear at this time. The flow characteristics in the vicinity of the cusp tip (as influenced by the cement particle size, viscosity, etc.) may cause the development of negative pressure in this region.

DISCUSSION

SUMMARY

Zinc phosphate cement has an inherent film thickness that does not account for the much larger film thickness found between cemented crowns and the prepared tooth.’ The thickness and physical presence of the dental cements illustrates the nature of the problem. It must remain to aid in retention, but it also must be limited to allow complete seating and closure of the margin. The results of this study indicate that the direct role of hydrostatic pressure in opposing crown seat-

A model system was developed which recorded the intracoronal pressure during crown cementation at three locations simultaneously. Peak pressures and residual pressures were greatest with zinc phosphate cement. The zinc oxideeugenol cement generated the smallest amount of peak and residual pressures. The polycarboxylate cement exhibited an intermediate pressure intensity. The uneven intracoronal pressure in the cement suggests a complex flow pattern capable of developing the separation of

Fig. 13. Variations on peak pressure as function of cement type and gauge location.

524

NOVEMBER

1978

VOLUME

10

NUMBER

5

INTRACORONAL PRESSURE

phases that earlier work reported. However, the small residual pressure indicates that these internal back pressures appear to play a limited role in preventing a complete seating of a crown.

Fusayama, T.. Factors and technique of precision casting, Part 1. J PRO~THETDEW 9:468. 1958. Fusayama, T.. Factors and technique of prcx iston castinq. Part II. J PKOSTHFTDF.NT 9:4&i 19.X3. Kafalias, M. C:., Swartz, M. L., and Phillips, K W.: Etfect of manipulative variables on the propertics of rl polycarboxvlate cement. r\ustral Dent J 20:X. 19ii

REFERENCES I.

Jorgensen. K. D.: Factors affecting the film thickness of zinc phosphate cements. Acta Odontol Stand 18:479, 1960. 2. Jorgensen, K. D.: Structure of the film of zinc phosphate cements. Acta Odontol Stand 18:491, 1960. 3. Fusayama, T.. Ide, K.. and Hosada, H.: Relief of resistance of cement of full cast crowns. J PROSTHET DENT 14:95, 19tS. 4. Basset, R. W.: Solving the problems of cementing the full veneer cast gold crown. J PROSTHETDF.NT 16:740, 1966.

Ktplf rtqws1sIO. DR. RI~HAHI~ J. IIo~at) ~NIVF.RSI.IY Of ~ALWORNIA SCHOOL01: DENTISTRY Los Asct.~ts. (::\LI~. 90024

ARTICLES TO APPEAR IN FUTURE ISSUES Dowel form and tensile force Jerry

K. Johnson,

D.D.S.,

MS.,

and Joseph

S. Sakumura,

Ph.D

A study of the reproducibility of the functional dynamic impression technique Stig Karlsson,

D.D.S.,

and Bjorn

Hedegard,

D.D.S.,

denture space with a

D. Odont.

Application of various removable partial denture design concepts to a maxillary obturator prosthesis Gordon

E. King,

Swallowing W. R. E. Laird,

D.D.S.,

and William

D. Gay, D.D.S.

and denture occlusion M.D.S.

Anatomic comparison of arbitrary Frank

R. Lauciello,

D.D.S.,

Obturator-overdentures Michael

MacEntee,

and Marc

reference notch on Hanau articulators

Appelbaum,

D.D.S.

retained by nonrigid

attachments

L.D.S.

Retention of vital submerged roots under complete dentures: Report of 10 patients Martin

P. Masterson,

D.D.S.

Custom tray modifications John

W. McCartney,

for complete dentures

D.D.S.

THE JOURNAL OF PROSTHETIC DENTISTRY

525

Intracoronal pressure during crown cementation.

Intracorurtal pressure during crown cemmMon R J. Hoard, D.D.S.,* A. A. Caputo, Ph.D.,** R. M. Contino, D.D.S.,*** and M. E. Koenig”““’ University of...
2MB Sizes 0 Downloads 0 Views