E f f e c t o f a g i n g on t e m p o r a r y c e m e n t r e t e n t i o n in v i t r o P. L. M i l l s t e i n , D. Nathanson,

D . M . D . , M . S . , * E. H a z a n , D.M.D., M.S.D.***

D.M.D.,**

and

Boston University, Goldman School of Graduate Dentistry, Boston, Mass. Retention of restorations cemented with temporary cement varies. Some cements a r e a d h e s i v e a n d o t h e r s a r e w e a k in r e t e n t i o n . In a d d i t i o n , c e m e n t r e t e n t i o n m a y v a r y o v e r t i m e . T h i s s t u d y d e t e r m i n e d (1) t h e r e t e n t i v e p r o p e r t i e s o f f o u r t e m p o r a r y c e m e n t s , a n d (2) t h e e f f e c t s o f a g i n g on t e m p o r a r y c e m e n t r e t e n t i o n . C y l i n d r i cal amalgam cores and mated stainless steel retainers with a 0.05 mm cement s p a c e w e r e u s e d in t h e s t u d y . C o r e s w e r e c e m e n t e d i n t o t h e r e t a i n e r s a n d s t o r e d in 1 0 0 % h u m i d i t y at 3 7 ° C u n t i l t e s t e d . R e t e n t i o n w a s m e a s u r e d b y a p p l y i n g a c o m p r e s s i v e f o r c e to t h e c o r e s t h r o u g h a r o d in a n I n s t r o n m a c h i n e . H a l f t h e samples were tested after 1 week and half were tested after 6 weeks. The results i n d i c a t e a s i g n i f i c a n t d i f f e r e n c e in r e t e n t i v e v a l u e a m o n g t h e f o u r c e m e n t s , i n c l u d i n g a s i g n i f i c a n t d e c r e a s e in r e t e n t i o n f o r o n e c e m e n t o v e r t h e 6 - w e e k a g i n g p e r i o d . (J PROSTHET DENT 1 9 9 1 ; 6 5 : 7 6 8 - 7 1 . )

T

h

e

primary function of t e m p o r a r y cements is to act as an interim cementing media for provisional or fixed restorations. 1 T e m p o r a r y cements may be medicated and are often used for tooth sedation as well as for retention. 2 The properties of t e m p o r a r y cements vary as to flow, setting time, film thickness, and retention. 3 The t e m p o r a r y cement should set quickly and provide sufficient retention for the t e m p o r a r y restoration to be properly held during function. Retention should be low enough t h a t removal of the restoration is possible after a specific time. A t e m p o r a r y cement should not become more retentive over time. This phenomenon is sometimes encountered in the clinical setting when restorations cemented with t e m p o r a r y cement for long periods of time become difficult to remove. Dental cement retention may be empirically related to a compressive strength index. 4 The greater the compressive strength, the greater the retention. However, this index may not account for retention in all cements, nor does it include the aging factor. Aging refers to possible physical or chemical change in the cement over time t h a t m a y lead to an increase or decrease in retention. Other than opinions arbitrarily relating cement retention to its compressive strength, there is little information concerning the retentive properties of different t e m p o r a r y cements. Comprehensive information concerning retention would be advantageous to dentists so t h a t they could choose a cement for a specific purpose. To gain more insight into t e m p o r a r y cementation, a study was designed to mea-

T a b l e I. Mean separation force of t e m p o r a r y cements

Group

x

SD

x

SD

1-Cav~ek 2-Freegenol 3-Temp-Bond 4-B + T

17 80 ~09 148

8 6 3 9

6 85 63 143

4 4 9 12

sure cement retention and the effects of aging in vitro. Four commonly used t e m p o r a r y cements were examined: (1) Cavitek (Kerr Co., Romulus, Mich.) two-paste eugenolcontaining cement of low compressive strength, which may be used to cement crowns for up to 1 week; (2) T e m p - B o n d (Kerr Co.) two-paste eugenol-containing cement with a moderate compressive strength of approximately 71 kg/ cm 2, which exhibits good mixing and handling properties and is used for periods of up to 1 month; (3) B & T ZOE (L.D. Caulk, Milford, Del.) powder-liquid reinforced zinc oxide-eugenol cement, which has a relatively high compressive strength of 140 kg/cm 2 and is primarily used for long-term cementation because the more powder one adds to the mix the stronger and more retentive the mix becomes; and (4) Freegenol (G.-C. Int., Scottsdale, Ariz.) two-paste noneugenol t e m p o r a r y cement with a low compressive strength of 30 kg/cm 2, which is used as an alternative to eugenol-containing cements for periods of up to 1 month. MATERIAL

Presented in part at the International Association for Dental Research meeting, Montreal, Que., Canada. *Associate Clinical Professor, Department of Biomaterials. **Former student of prosthodontics. ***Professor and Chairman, Department of Biomaterials. 10/1/27550

768

6 Weeks

1 Week

AND

METHODS

Variations in the retentive properties of t e m p o r a r y cements and the effects of aging on cement retention were evaluated with the use of precision cores and retainers. Cylindrical amalgam cores measuring 6 x 6 m m were made by condensing T y t i n high-copper amalgam (S.S. White Dental Mfg. Co., Philadelphia, Pa.) in aluminum J U N E 1991

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Fig. 1. Schematic drawing of core fabrication.

......

i

iiiiiii!i!i! .....

COMPRESSIVE ROD

,,.,.°.....,

,,,..,..% ......

:::::::::::: ::::::::::::

CORE

,.._...........¢

METAL CASTING

iiiiiiiHIlllllllllllll!iiiiJiiii , BASE

F i g . 2. Schematic drawing of test and measurement system.

molds coated with Teflon (Du Pont, Wilmington, Del.) material (Fig. 1). The amalgam was mixed and packed according to the manufacturer's instructions and the hardened cores were separated from the mold and stored in 100% h u m i d i t y at 37 ° C. Sharp edges and corners were removed from all cores by use of a laboratory handpiece and an abrasive cutting instrument. The cores were then cleaned with distilled water in an ultrasonic bath. Metal cylindrical retainers 12 m m in width and 6 m m in height were machined from a cast rod of Rexillium III alloy (Jeneric Industries, Inc., Wallingford, Conn.). A cylindrical space 6.1 m m in diameter was machined in the center of each cylinder to assure t h a t an amalgam core could be placed in each retainer, leaving a uniform cement space of 0.05 mm. The inner surface of the cylinder was sandTHE J O U R N A L OF P R O S T H E T I C D E N T I S T R Y

blasted with a fine-grain aluminum oxide abrasive to assure adequate surface contact on cementation. Retainers were cleaned with a detergent in an ultrasonic b a t h and washed in acetone. Cores and retainers were divided into four groups of 10 samples per group according to the brand of cement used: group 1, Cavitek; group 2, Freegenol; group 3, Temp-Bond; and group 4, ZOE B & T. Mixing included dispensing equal amounts of paste and accelerator for the paste-dispensed cement and using the manufacturer's recommended a m o u n t of powder and liquid for B & T cement. The cements were mixed on paper pads at room t e m p e r a t u r e (25 ° C). Mixed cement was applied to the internal surface of the retainers and external surfaces of the core with a plastic instrument. Cores were seated in the retainer by use 769

M I L L S T E I N , HAZAN, A N D N A T H A N S O N

f:omgk.

[ .

100

Fig. 3. Histogram shows mean separation forces of four temporary cements after 1-week and 6-week cementing periods. of finger pressure. Complete seating was assured by the open-ended design of the retainers. Mixing and insertion times did not exceed 60 seconds per retainer. Excess cement was removed when set. One half of the number of samples were cemented for 1 week and half were cemented for 6 weeks before testing. The samples were stored in 100% humidity at 37 ° C until tested. Each core-retainer assembly was seated in a specially machined base, which was placed in an Instron machine (Fig. 2). The cores were forced out of the retainers with a hardened steel compression rod at 0.02 cm/minute crosshead speed. Peak separation loads were recorded.

RESULTS Mean separation forces were calculated (Table I and Fig. 3). The four treatment groups were compared at the two time intervals by use of a two-way analysis of variance. Statistically significant differences (p < 0.001) were found among the groups when the different types of cement were compared. Differences among the specific groups were further identified with a Newman-Keuls test. As anticipated, Cavitec cement had the lowest retention values and B + T cement had the highest values. Significant differences between the two time intervals were evident for Temp-Bond cement (p < 0.001). Temp-Bond cement was significantly more retentive after 1 week than at 6 weeks. All other cements were statistically equivalent at the two time intervals.

DISCUSSION Temporary cements with a moderate-to-high compressive strength are recommended for cementation of acrylic 770

or metalized temporary crowns, whereas cements with a low compressive strength are suggested for temporary cementation of permanent restorations. The reason is that permanent restorations offer a better overall fit than temporary restorations and are therefore more retentive upon cementation. Stronger, more retentive temporary cements are indicated with loose fitting temporary crowns to prevent premature dislodgment. However, in spite of precautionary measures, temporary cement is sometimes so retentive that removal of a permanent restoration is not possible. Also, at times the removal of a temporary crown is not possible without destroying the restoration or injuring the underlying substructure. Use of a cement implies a working knowledge of its properties. Compressive strength provides dentists with an arbitrary means for assessing crown retention of temporary cements. The greater the compressive strength, the more retentive is the cement. This empirical type of assessment was only partially substantiated in this study. Cavitek cement, which is a low-compressive strength type, was least retentive whereas B & T ZOE cement with a relatively high compressive strength was most retentive. Temp-Bond cement with a moderate compressive strength of 71 kg/cm 2 after 24-hour storage required a separation force of approximately 110 pounds after 1 week, whereas Freegenol cement, with a low compressive strength of 30 kg/cm2 after 24 hours required a separation force of 80 pounds after 1 week. After a 6-week time interval, the separation force for Freegenol cement increased slightly to approximately 85 pounds whereas that of Temp-Bond cement significantly decreased to approximately 63 pounds. The index was not predictable for these two cements. The basic reason for this

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lack of predictability is not fully understood but could relate to other properties of the cement, such as solubility and effect of time. Aging is an important factor in the testing of permanent and temporary cements. It is important for temporary cements in assessing the durability of cement retention over time. Knowledge concerning cement retention would enable dentists to assess their clinical needs and avoid the situation where either the restoration falls off prematurely or cannot be removed by conventional means. The type of cement selected could depend on its retention value and estimated cementation time. Theoretically such information could be made available with a time-retentive index for temporary cements. SUMMARY

the four cements and one cement became significantly less retentive over time.

REFERENCES 1. The Dental Advisor. Ann Arbor, Mich: Dental Consultants, Inc, March 1985; Vol 2, p 6. 2. O'Brien WJ Ryge G. An outline of dental cements and their selection. Philadelphia: WB Saunders Co, 1978:152-70. 3. Craig RG. Restorative dental materials. 7th ed. St Louis: CV Mosby Co, 1985:178-84. 4. Dentists desk reference. 1st ed. Chicago: American Dental Association, 1981:79.

Reprint requests to: DR. PHILIP MILLSTEIN GOLDMAN SCHOOLOF GRADUATEDENTISTRY BOSTON UNIVERSITYMEDICALCENTER 100 E. NEWTON ST. BOSTON, MA 02118

In this study, retention of four temporary cements was studied at 1- and 6-week intervals. Retention varied with

E f f e c t o f a d i l a c e r a t e d r o o t on s t r e s s d i s t r i b u t i o n to t h e t o o t h and supporting tissues E m i n e C e l i k , D . D . S . , M.S., Ph.D.,* a n d E r g u n A y d i n l i k , D . D . S . , M.S., P h . D . * *

Hacettepe University, Faculty of Dentistry, Ankara, Turkey The configuration of the root of a p r o s p e c t i v e a b u t m e n t tooth has a significant influence on its potential l o a d - b e a r i n g capacity. D i l a c e r a t i o n is an a n g u l a t i o n in the root or crown. This a b n o r m a l i t y m a y also affect the s t a b i l i t y and l o n g e v i t y o f an abutment. Finite e l e m e n t s t r e s s a n a l y s i s w a s u s e d to i n v e s t i g a t e the effect o f a root dilaceration on s t r e s s distribution to the tooth and its supporting structures. A n o r m a l and a d i l a c e r a t e d s i n g l e - r o o t e d tooth under three loads (axial, distooblique, and m e s i o - o b l i q u e ) w e r e a n a l y z e d and compared. The results indicated that a dilaceration concentrates the s t r e s s e s in the supporting structures and m a y be t a k e n into c o n s i d e r a t i o n as a r i s k factor in a b u t m e n t selection. (J PROSTHET DENT 1991;65:771-7.)

T h e root form of a prospective abutment tooth has a significant influence on its potential effectiveness. Multirooted teeth with divergent or curved roots are stronger abutment teeth than single-rooted teeth or multirooted teeth whose roots are fused. 1 Shillingburg et al. 2 stated that the crown-root ratio of abutment teeth can be calculated, and the length, configuration, and direction of those roots should also be examined. They also pointed out that single-rooted teeth with evidence of irregular configuration or with some curvature

*Assistant Professor, Department of Prosthodontics. **Professor, Department of Prosthodontics. 10/1/27919

THE JOURNAL OF PROSTHETIC DENTISTRY

in the apical third of the root are preferable to the tooth that has a nearly perfect taper. On the other hand, according to Tylman, 3 if the position of the tooth is such that the root will not receive forces in line with its long axis, this condition may exclude its use as a fixed partial denture abutment. Dilaceration is an angulation or a sharp bend or curve in the root or crown of a formed tooth (Fig. 1). The condition is thought to be caused by trauma during the period in which the tooth is forming, with the result that the position of the calcified portion of the tooth is changed and the remainder of the tooth is formed at an angle. 4 The curve may occur anywhere along the length of the tooth, sometimes at the cervical portion, at other times midway along the root, or even just at the apex of the root, depending on the amount of root formed when the injury occurred. 4

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Effect of aging on temporary cement retention in vitro.

Retention of restorations cemented with temporary cement varies. Some cements are adhesive and others are weak in retention. In addition, cement reten...
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