cement removal from restorations luted to titanium abutments

Cement removal from restorations luted to titanium abutments with simulated subgingival margins

John R. Agar, DDS, MA," Stephen M. Cameron, DDS, b James C. Hughbanks, DMD, c and M. Harry Parker, MS, DDS d The School of Dental Medicine, University of Connecticut Health Center, Farmington, Conn.; The U.S. Army Dental Activity, Fort Gordon, Ga.; and Hanau Dental Clinic Command, Hanau, Germany

Statement o f p rob l em. The process of removing excess cement from subgingival margins after cementation of restorations to implant abutments may lead to scratching of the abutments or incomplete cement removal. Purpose. The purpose of this study was to investigate and to compare the surfaces of abutments after the removal of three cements (glass ionomer, resin, and zinc phosphate) by use of three instruments (gold coated scaler, rigid plastic scaler, and stainless steel explorer). Material and methods. Six investigators removed zinc phosphate, glass ionomer, and resin cements with explorers, gold coated sealers, and rigid plastic sealers with a model simulating clinical conditions. The surface of Branemark abutments with cemented restorations were examined with a microscope at 20x for scratches and cement remnants. Results. Statistical analysis of the results were inconclusive about which combination of instrument and cement worked most effectively. Conclusion. A surprising amount of cement remnants and scratching of abutments was observed. Although the six investigators were experienced in prosthodontic and implant procedures, there was variation in the results of their cement removal. (J Prosthet Dent 1997;78:43-7.)

T h e smooth machined surface of ti tanium abutments (Fig. 1) should be maintained during and after placement of restorations. The effects o f several prophy- laxis techniques on the titanium surface of implant abutments have been investigated with both in vitro 1,2 and in vivo 3 studies. Cement ing implant supported fixed par- tial dentures and single crowns with subgingival margins requires removal o f excess cement by using an instrument in a scraping motion. This process has not been studied and it may lead to scratches or gouges and still

The views and opinions expressed do not necessarily reflect those of the Department of Defense.

Presented at the 77th annual meeting of the Academy of Prosth- odontics in Tucson, Arizona, May 1995.

Supported in part by a Cooperative Research and Development Agreement with Nobel Biocare USA, Inc.

~Associate Professor and Prosthodontic Graduate Program Director, School of Dental Medicine, University of Connecticut Health Center.

~Chief, Maxillofacial Prosthetics/Denta[ Oncology and Assistant Di- rector, Prosthodontic Residency Program, Fort Gordon, Ga.

'Commander, Hanau Dental Clinic Command, Hanau, Germany. dDirector, Prosthodontic Residency Program, U.S. Army Dental Ac-

tivity, Fort Gordon, Ga.

Fig. 1. New 3 mm abutment. (Original magnification 20x.)

allow cement remnants to remain. Roughened implant surfaces may lead to increased plaque accumulation, 4-7 impaired plaque removal, and compromised soft tissue compatibility. 8 Cement remnants may adversely affect the per iodont ium and lead to unesthetic inflamed gingival tissues.

JULY 1997 THE JOURNAL OF PROSTHETIC DENTISTRY 43

THE JOURNAL OF PROSTHETIC DENTISTRY AGAR ET At

Fig. 2. Experimental model design. Three implant replicas are embedded in acrylic resin block (purple) and soft tissue is simulated with polyvinyl siloxane (blue). Cast metal crown (gray') was cemented to retrievable abutment.

Fig. 3. Experimental model without crown. Depth of simulated sulcus, which is approximately 1.5 mm on facial and lingual surfaces, increases up to 3.0 mm at interproximaI re- gion.

The purpose of this study was to investigate and to compare the surfaces of abutments after the removal of three cements (glass ionomer, resin, and zinc phosphate) with three instruments (gold coated scaler, rigid plastic scaler, and stainless steel explorer).

M A T E R I A L A N D M E T H O D S

The cements used in this study wcre a glass ionomer (Ketac-Cem, ESPE-Premier, Norristown, Pa.), a resin (Panavia-21, J. Morita USA Inc., Tustin, Calif.) and a zinc phosphate (Fleck's, Mizzy, Inc., Cherry Hill, N.I. ). The cements were used according to manufacturers' specifications. The threc instrumcnts used were sealers fabricated from a soft base metal that has been layered in gold palladium and 24K gold (Implarette scalers,

Implant Innovations Inc. (3I), IMPK1 Kit, West Palm Beach, Fla.), plastic sealers (rigid plastic implant scaler, 31) and explorers (HuFriedy #3CH, HuFriedy Mfg. Co., Inc., Chicago, Ill.). Six clinicians who were experienced in prosthodontics and implant dentistry used each instrument on each cement.

The experimental model consisted of an acrylic resin block, 65 x 25 x 20 mm, holding three replica implants (PRA 020 Nobel Biocare, Chicago, Ill.) 7 mm apart on one end of the block (Fig. 2). Replica standard abutments were secured with replica abutment screws to the two outer implants and a 3 mm CeraOne abutment was secured to the center implant. Crown replicas were fabricated by turning a wax pattern on a lathe to an oc- clusal diameter of 7 mm and gradually tapering it to- ward the abutment. This pattern was duplicated for both the plastic replica crowns for the outside implants and the cast metal crowns for the center experimental unit. The gingiva (Fig. 3) was simulated by producing an ide- alized model with wax and duplicating it with a light body polyvinyl siloxane material (Extrude Wash, Kerr USA, Romulus, Mich.). The depth of the model's gingival sulcus varied f?om approximately 1.5 mm at the facial and lingual surfaces, and increased up to 3 mm at the interproximal area (Fig. 3). The sulcus had light re- lief to simulate the tissue of a patient wearing a slightly oversized interim restoration, as recommended for clinical practice. The contours of the gingival sulcus were developed with the aid of periodontists. A duplicating mold was fabricated and a new gingival model was made and used for each test.

The center crown replicas were fabricated by using wax patterns. A modified laboratory screw (UCLA laboratory and try-in screw WSP30, 3I) maintained an oc- clusal access opening to the CeraOne abutment screw. The patterns were cast in type III metal (Symphony, Jelenko, Armonk, N.Y.). A silicone plug was fabricated from a polyvinyl siloxane impression material (Reprosil, L.D. Caulk Division, Dentsply Internat ional Inc., Milford, Del.) by injecting the material into the screw access space of the abutment and crown. This allowed the material to polymerize, and then the plug was cut even with the top of the crown replica. The plug was placed in the CeraOne abutment to obturate the screw access space during cementation. The obturation of the access hole was further augmented with a multilayer tin- toil cover.

The selected cements were placed on all inside surfaces of the crown replicas after mixing, according to manufacturers' instructions. The castings were seated on the abutments with finger pressure and then held in place under a constant 27-+3 kg load on an Instron test- ing machine (Instron 4502, Instron Co., Canton, Mass.) until the cement had set. The investigators then at- tempted to remove the cement with the indicated instrument, working until they thought they had removed

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AGAR ET AL THE JOURNAL OF PROSTHETIC DENTISTRY

Table I. The mean and standard deviation of the total number of scratches for each instrument and cement per quadrant of the abutment

Explorer Plastic scaler Gold scaler Total

Zinc phosphate 7.45 (3.22) 7.10 (2.49) 7.00 (4.51) 7.18 (3.45)

Glass ionomer 12.20 (8.41) 12.70 (7.73) 8.70 (2.74) 11.20 (6.90)

Resin 6.45 (4.37) 10.00 (6.63) 7.70 (3.70) 8.05 (5.19)

Table I|. The mean and standard deviation in mm of the length of individual scratches for each instrument and cement per quadrant of the abutment


Zinc phosphate 1.54 (1.20) 1.30 (0,73) 1.40 (1,32) 1.41 (1.09)

Glass ionomer 1.51 (1.17) 1.32 (0.97) 1.27 (0.74) 1.37 (0.97)

Resin 1.26 (0.72) 1.41 (0.90) 1.48 (0.83) 1.39 (0.82)

Table III. The mean and standard deviation in mm 2 of the area of cement remnants for each instrument and cement per quadrant of the abutment and crown


Zinc phosphate 0.09 (0.17) 0.06 (0.10) 0.20 (0.34) 0.11 (0.24)

Glass ionomer 0.13 (0.24) 0.05 (0.06) 0.21 (0.65) 0.13 (0.40)

Resin 1.74 (3.51) 1.06 (2.19) 0.61 (1.45) 1.13 (2.52)

all of the cement. The abutments with the cemented crowns were removed and analyzed.

Each quadrant of the abutment and crown replica was e v a l u a t e d wi th an image p r o d u c e d t h r o u g h a Stereomaster microscope (Fisher Scientific, Norcross, Ca.) set at 20x, which was attached to a Dell Dimen- sion XPS P90 computer (Dell Computer Corp., Austin, Texas) that ran an imaging program capable o f linear and area measurements (Image-Pro Plus, Media Cyber- netics, Silver Spring, Md.). The number and cumulative length of the scratches present in each quadrant were calculated for each abutment. The total area o f cement remnants measured included the surfaces of the crown and abutment in each quadrant (Fig. 4).

R E S U L T S

Cementing of implant abutments proved to be a tech- nique sensitive procedure. Complex interactions precluded statistically significant conclusions concerning abutment scratches and cement remnants with the use of particular cements and instruments (Tables I through

Fig. 4. Measurements of area of resin cement remnants on surface of abutment and crown as recorded with computer (original magnification 20x). Green characters are for identifi- cation of each area measured. Instrument used for cement removal was explorer.

1.2

1.0

0.8

0.6

0.4

0~

~///////,2 I

®

Zinc Phosphate Glass Ionomer Resin

Fig. 5. Mean area in mm 2 of cement remnants per quadrant by cement type.

III). More cement remnants were left with resin cement (Fig. 5). Although all six investigators were experienced in prosthodontics and implant dentistry, there was variation in their techniques and success at cement removal.

D I S C U S S I O N

The six investigators stated that they believed they had removed all of the residual cement. They were sur- prised when they saw the amount o f cement that re- mained and by the degree o f roughness they created during cement debridement. There was variation in each person's approach to cement removal. Some investigators were more aggressive and used the instrument tips more than others. Several areas exhibited damage that indicated that attempts were made to remove cement that may not have existed where the bevel meets the collar of the abutment (Fig. 6).

Christensen 9 has shown that dentists have less ability to critically evaluate crown margins when they are visu- ally inaccessible. When a restoration has subgingival margins, as in this study, clinicians probably underesti-

~ULY 1997 45

THE JOURNAL OF PROSTHETIC DENTISTRY AGAR ET AL

Fig. 6. Swaging in area where bevel meets collar of this abutment and scratches made by explorer while attempting to remove glass ionomer cement in areas beneath simulated gingival.

Fig. 8. Example of swaging of abutment metal with side of stainless steel explorer during aggressive attempt at zinc phosphate cement removal.

Fig. 7. Extreme example of abutment scratches with tip of explorer during removal of resin cement.

mate damage to restorations and overestimate their ef- fectiveness in removing cement. Clinicians who cement crowns with subgingival margins do not have the op- portunity to examine the remnants they leave or roughness they create. All participants in this project regarded the results as a significant learning experience.

The investigators thought that the resin was the most difficult and zinc phosphate the easiest cement to remove. More cement remnants were left with resin cement (Fig. 5). Resin cement remnants could provide protection against scratching of the restorations and this may account for not having more scratching during at- tempted removal of this type of cement.

The nature of the observed scratches and gouges produced by the different instruments and investigators varied considerably. A profile analysis to measure the

Fig. 9. Typical multiple shallow scratches per stroke pattern seen when gold scaler was used for cement removal. Cement was glass ionomer.

character of the scratchcs would have been valuable, but the cement remnants precluded the use ofa profilometer.

Stainless steel explorers appeared to produce the deep- est scratches. The stainless steel explorers had sharp tips and they were hard compared with the relatively soft titanium of the abutment.l° These characteristics favored deep gouges with the tip (Fig. 7) or swaging of the metal when the side of the explorer was used aggressively during cement removal (Fig. 8).

Gold sealers appeared to produce multiple shallow scratches per stroke. When the tips of the gold sealers were used, they produced some gouges but these appeared broader and shallower than those made with the stainless steel explorers (Fig. 9), Gold fi'om the gold sealers was sometimes left on the titanium abutment surface and resin cement remnants.

46 VOLUME 78 NUMBER 1

AGAR ET AL THE JOURNAL OF PROSTHETIC DENTISTRY

Fig. 10. Typical multiple shallow scratches per stroke pattern seen when plastic scaler was used for cement removal. Ce- ment was resin.

The plastic scalers created multiple scratches per stroke that were more shallow than the stainless steel explorers (Fig. 10). The tips of these plastic sealers did not appear to cause gouging as deep as the other instruments.

C O N C L U S I O N S

This study demonstrated that dentists should be aware of potential problems when cementing restorations with subgingival margins. Clinicians may be leaving more cement remnants and /o r causing more scratches and gouges on restorations and abutments than they realize. Clinicians should be particularly careful when using resin cements. Stainless steel explorers probably should not

be used to remove cement from subgingival abutment margins.

REFERENCES

1. Fox SC, Moriarty JD, Kusy RP. The effects of scaling a titanium implant surface with metal and plastic instruments: an in vitro study. J Periodontol 1990;61:485-90.

2. RapleyJW, Swan RH, Hallmon WW, Mills MP. The surface characteristics produced by various oral hygiene instruments and materials on titanium implant abutments. Int J Oral Maxillofac Implants 1990;5:47-51.

3. McCollum J, O'Neal RB, Brennan WA, Van Dyke TE, Homer JA. The effect of titanium implant abutment surface irregularities on plaque accumulation in vivo./Periodontol 1992;63:802-5.

4. Waerhaug J. Effect of rough surfaces upon gingival tissue. J Dent Res 1956;35:323-5.

5. Swartz ML, Phillips RW. Comparison of bacterial accumulations on rough and smooth enamel surfaces. J Periodontol 1957;28:304-7.

6. Keenan MP, Shillingburg HT Jr, Duncanson MG, Wade CK. Effects of cast gold surface finishing on plaque retention. J Prosthet Dent 1980;43:168- 73.

7. Quirynen M, van der Mei HC, Bollen CM, Schotte A, Marechal M, Doombusch GI, et al. An in vivo study on the influence of the surface roughness of implants on the microbiology of supra- and subgingival plaque. I Dent Res 1993;72:1304-9.

8. Dmytryk J J, Fox SC, Moriarty JD. The effects of scaling titanium implant surfaces with metal and plastic instruments on cell attachment. J Periodontol 1990;61:491-6.

9. Christensen GJ. Marginal fit of gold inlay castings, j Prosthet Dent 1966;16:297-305.

10. Quirynen M, Bollen CM, Willems G, van Steenberghe D. Comparison of surface characteristics of six commercially pure titanium abutments. Int J Oral MaxiHofac Implants 1994;9:71-6.

Reprint requests to: DR. JOHN R. AGAR DEPARTMENT OF PROSTHODONTICS UCONN SCHOOL OF DENTAL MEDICINE 263 FARMINGTON AVE. FARMINGTON, CT 06032 10/1/82198

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cement removal from restorations luted to titanium abutments

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