tite ceramic YakkiW

w-m

Taizo Ham&a,

, abEhn SWaab DW!t, PftD”

Stinrori,

crowns

DDS, PhD,a and

Hiroshima University, School of Dentistry, Hiroshima, Japan Thirty-three cast&& ag9tite ceramic crowns were constructed for 26 patients. The crowns were clfnically evaluated for anatomic form, mairginal adaptation, cavosurface m&&al &se&r&on, surface roughtless, and color match for a period of 2 years at rwu!ar in&rvaI.s. Resalts &owed that all restoration had satisfactory anatomic fdrm; ali but one exhibited good marginal adaptation. Slight abrasion was noticed at the f=netiWg cusps and ail but three of the restorations demonstrated excellent color matching. (d PROSTHET DENT 1991$6:754-S.)

H

is the main inorganic structural ydroxyapatite element of natural tooth enamel. This compound has not yet been synthesized. However, restorative materials with qualities similar to those of hydroxyapatite could make restorations resemble natural teeth. Various materials, including castable glass ceramics made of LisO-ZnO-Si02, LisO-SiOs, and SiOs-KsO-MgO-MgFs have been developed, but these lack the crystalline structure of the enamel of natural teeth.t-g Cerapearl (Kyocera Corporation, Kyoto, Japan), a castable apatite ceramic material, has qualities similar to those of natural tooth enamel.4 With this material, crystals of apatite are formed after crystallization. In this study, 33 crowns of this material were made for 26 patients. Photographs at ~1 magnification were made at four intervals: baseline, 3 months, 1 year, and 2 years. The results were evaluated according to the U.S. Public Health criteria of Cvar and Ryge.5 This study evaluated the clinical results of these crowns.

MATERIAL

Age (years)

21-30 31-40 41-50 51-60 61-70 Total

Table II.

W0Ulen

Men

7 1 0 1 1

Total

10 3 5 2

3 2 5 1 5 16

ii

2 26

Restored teeth

Tooth Incisor First premolar Second premolar First molar Second molar Total .--__

Maxilla

5 7 7 4 0 23

Mandible

Total

0 1 1 6 2 itI -----.

5 8 8 10 2 33

AND MEI’HODS

Twenty-six patients 16 to 68 years of age (mean 39.9 years) were selected from patients at the Department of Prosthodonties, Hiroshima University (Tables I and II). Only patients in whom tooth length and occlusal clearance were adequate for retention and strength of complete ceramic crowns were selected. The composition of the castable apatite ceramic by weight is: 44.6% CaO, 34% SiO2, 16.2% P205, and 4.6%, MgO. It contains glass powder distributed in a vitreous or noncrystalline state. The teeth that were to receive castable apatite ceramic crowns were prepared with a shoulder measuring 1 to 1.5 mm placed 0.5 mm subgingivally. The axial walls inclined 3 degrees to the long axis of the tooth. All line angles were rounded. Working dies were made with improved artificial stone

RLecturer, Department of Prosthetic Dentistry. hProfessor and Chairman, Department of Prosthetic Dentistry. lollnl%34 754

Table I. Age and sex of patients

(Die Stone, Columbus Dental, Columbus, Ohio). Silicone impression material (Exaflex, G-C Dental Industrial Corp., Tokyo, Japan) was used for all impressions. The wax pattern was prepared with inlay wax on the working die. The diameter of the sprue (Ready casting wax, G-C Dental Industrial Corp.) was 2.5 mm and it was attached to a large cusp. The wax pattern was located in the center of the investment ring. Investment material (CP mold, Kyocera Corp.) was mixed at a ratio of 0.23 (liquid powder) in a vacuum mixer. The wax was eliminated in an automatic furnace (CP ring 301, Denken Corp., Kyoto, Japan). The ring was heated to 300’ C at the rate of loo C per minute and raised to 800° C at the rate of 15’ C per minute where it was maintained for 1 hour (Fig. 1, A). The temperature was then decreased to 600’ C at the rate of 10’ C per minute where it was maintained for 20 minutes to prevent the castable apatite ceramic glass from fusing to the investment. The material was cast at 1510’ C with the help of an automatic casting machine (CP cast 701, Denken Corp.). The casting unit was rotated to 85 Kg/cm2 for casting (Fig. DECEMBER

1991

VOLUME

66

NUMBER

6

EVALUATION

OF APATITE

CERAMIC

Fig. 1. Equipment for castable apatite ceramic crown. A, CP-Ring 301, burnout of wax pattern and annealing; B, CP-Cast 701, casting; C, CP-Crystal 501, crystallization and shading (staining).

1,B) . Annealing was done 1 hour after casting. This procedure released the inner stress of the castable apatite ceranlit crowns. The annealing was done in the automatic furna Ice (CP ring 301, Denken Corp.). The ring was heated THE

J OURNAL

OF PROSTHETIC

DENTISTRY

to 700° C where it was maintained for 1 hour. The terntperature was then gradually decreasedat the rate of 30” CLper minute. After annealing, the investment was removec1 by sandblasting (aluminum beads, 25 to 50 pm), 2.5 to 3.5 Kg/ 755

NAHARA,

SADAMORI,

AND RAMADA

Fig. 2. Oral photographs and radiographs of upper second premolar after castable apatite ceramic crown was cemented. A, Condition of mouth before treatment; B, 3 months later; C, 2 years later. cm2 (Pencil blast, Yoshida Works, Osaka, Japan), and ultrasonic cleaning (UT 52, Sharp Corp., Tokyo, Japan). The sprue was removed with a diamond disk. The annealed crown was subsequently invested for crystallization. The investment powder (P) (CP crystal mold, Kyocera Corp.) was mixed with distilled water (W) at the ratio of 0.35 P/W. Crystallization was performed in the automatic furnace !CP crystal 501, Denken Corp.). This furnace can actuate various thermal schedules and the temperatures strictly follow directions. The annealed crown was heated to 800° C at the rate of 30“ C per minute and then raised to 900° C at the rate of 5OC per minute where ‘is,6

it was maintained for 1 hour to complete crystallization (Fig. 1, C). After crystallization, the investment was removed with the fingers, sand blasting, and ultrasonic cleaning. The resultant glass ceramic material contained crystallized apatite. This material possessedhigh-bending and compressive strengths to the value of 300 and 870 MPa, respectively. The crystallized crown was adjusted to establish the desired contact area, occlusal height, and anatomy on the working cast. Shade selection was attained with Vita Lumin Vacuum shade guide (Vita Zahnfabrik, H. Rauter Gmbh & Co., Bad Slickingen, W. Germany). Fine adjustment in color tone was necessary. At first, DECEMBER

1991

VOLUME

66

NUMBER

6

EVALUATION

OF APATITE

Table

Ratings for each castable apatite ceramic crown during 2 years of study

III.

CERAMIC

Category

Rating

Anatomic form

Marginal adaptation

Cavosurface marginal discoloration

Surface roughness

Color match

Alpha Bravo Charlie Alpha Bravo Charlie Alpha Bravo Charlie Alpha Bravo Charlie Alpha Bravo

Charlie

Baseline

3 Months

1 Year

2 Years

33

33

33

-

33

-

-

-

32 1

32 1

32 1

32 1

-

-

-

-

33

33

33

-

33

-

-

-

33

28

28 5

28 5

-

-

-

-

30 3

30 3

30 3

-

30 3

-

-

5

-

N =33.

base powder was painted on the surface of the crown and baked in the automatic furnace (CP crystal 501, Denken ’Corp.). Thereafter, ceramic powder for staining was painted

on the crown and baked. The baking schedule was as follows: the crown was heated to 800’ C at the rate of 50” C per minute, where it was maintained for 5 minutes and then lowered to 300° C at the rate of 251~C per minute. All of the crowns were made according to the instructions of the manufacturer. The crowns were cemented with resin cement (Panagraph Super Cement, Nibonshiken Corp., Tokyo, Japan) according to the instructions of the manufacturer. The crowns were held during cementing by finger pressure for 10 minutes. Color photographs (magnified xl) (Medical Nikkor, Nikon Corp., Tokyo, Japan) and radiographs were made at the baseline and at 3 months, 1 year, and 2 years (Fig. 2). A baseline evaluation was made within 1 week after cementation. Two investigators working independently examined the restorations for anatomic form and marginal integrity by using a mouth mirror, an explorer, and radiographs6 The U.S. Public Health Service System was used for the examinations5 RESULTS The results of the clinical evaluations are summarized in Table III. Anatomic form. All of the restorations had a satisfactory anatomic form at all observations. At 2 years, the restorations were rated Alpha for anatomic form. Marginal adaptation. All of the restorations except one were rated Alpha for the four observations. One restoration was rated Bravo for all periods. Cavosurface marginal discoloration. None of the restorations exhibited cavosurface marginal discoloration. All of restorations were classified as Alpha at the end of the study. The restorations which showed slightly unacTHE

JOURNAL

OF PROSTHETIC

DENTISTRY

ceptable marginal gingivae at baseline from 3 months to 2 years. Surface roughness. All restorations were graded Alpha at the baseline. Five restorations were rated Bravo at the S-month examination. The rating remained constant with little change. Slight abrasion was found at the working cusps of the occlusal surface of some restorations. Color matching. All but three of the restorations had excellent color match and rated Alpha for the entire 2-year period. The three exceptions were rated Bravo. In general, there was little change in color match at the 2-year period. Fig. 2 illustrates a typical result. The castable apatite ceramic crown was prescribed for a devitalized maxillary second premolar to improve esthetics. The patient was a 24-year-old man. The preparation required a dowel and core. All of the procedures were completed by one dentist. The laboratory procedures conformed to the manufacturer’s directives. All examinations at the four time periods were rated Alpha. DISCUSSION The consistent Alpha rating for anatomic form reflected the resistance to wear of the castable apatite ceramic crowns. The normal occlusal attrition did not exposesmall areas of dentin. All except one restoration showed satisfactory marginal adaptation at each time of evaluation. There was no recurrent caries. No significant changes were found in the marginal gingiva from the baseline to 2-year period, thereby suggesting that the restorations had no deleterious effect on the marginal gingiva. This phenomenon confirms the biocompatibility of the material. Redness and swelling of the marginal gingiva observed in a few patients at the baseline were due to poor oral hygiene. Surface roughness of all of the restorations was acceptable at the time of baseline evaluation. However, at the 757

NAHARA.

cusps of five restorations, the readings had declined to BB a res&t of attrition. The resistance of .a*@-~Wic crowns to attrition was clinically cotlqaB&b$o that of enamel. In color matching, all but three restorations were rated Alpha from the baseline to the 2-year period. The Bravo rating for the three restorations was the result of surface staining. Thisis not surprising in view of the surface texture. At 2 years, all restorations had acceptable color matching. SUMMARY

AND

CONCLUSIONS

All restorations resisted wear. All had good marginal adaptation, except for one where the explorer caught when drawn acrossthe margin. cavosurface marginal stains were not visible. Surface roughness and color match were rated Alpha or Bravo at each evaluation point. There were no sig&&cant differences among the restorations, as could be seen-from the consistent results.

758

SADAMORI,

AND HAMADA

REFERZNCES 1. S&o RB, Riley EJ. The shrink-free ceramic crown. J &XTHET DENT 1983;49582-7. 2. Riley EJ;Sozio RR, Shklar G, Krech K. Shrink-free ceramic crown versus ceramometat: a comparative study in dogs. J PROSTHETDENT 1983;49:766-71. 3. Schaerer P, S&o T, Woblmend A. A comparison of the marginal fit of three cast ceramic systems.J PR~~THETDENT 198&50-.534-42. 4. Hobo S, Iwata T. Castable apatite ceramicsae a new biocompatihle restorative material. I. Theroretical considerations. Quintessence Publ, 1985;135-41. 5. Davis RD, Mayhen RB. A clinical comparison of three anterior restorative resins at 3 years. J Am Dent Assoc 1966;112:659-63. Reprint requests to: DR. YUKINOFU NAHARA SCHOOL OF DENTISTRY HIROSHIMA UNIVERSITY KASUMI l-2-3 MINAMI-KU, HIROSHIMA 734 JAPAN

CEMBER 1091 VOLUME 66 NUMBER 6

Clinical evaluation of castable apatite ceramic crowns.

Thirty-three castable apatite ceramic crowns were constructed for 26 patients. The crowns were clinically evaluated for anatomic form, marginal adapta...
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