Marginal
accuracy
and geometry
of cast titanium
copings
Ronald Blackman, DDS, MSD,a Ramon Baez, DDS,b and Nasser Barghi, DDS, MAC University
of Texas Health
Science Center, Dental School, San Antonio,
Tex.
The hiocompatihility of titanium with human tissue is well established; its potential as an alternate metal for crown restorations has yet to be fully investigated. This study measured the geometry and accuracy of coping margins cast in Ti, 99.5% chemically pure. Twenty castings with 45-degree facial and go-degree palatal margins were made by indirect technique with a commercial system using recommended procedures. They were then cemented with ZnPO4 cement. The coping and die assemblies were embedded in resin, sectioned longitudinally, and measured with a microscope at x50 power. Casting shrinkage was characteristic, particularly along the horizontal axis in the plane of the shoulder. Although horizontal linear shrinkage of 45-degree margins was greater than that for the go-degree form, the surface of marginal discrepancy was greatest with the go-degree configuration. (J PROSTHET DENT 1992;67:435-40.)
I deally,
cemented crown margins meet prepared tooth margins in perfect nondetectable junctions. In actuality, clinical perfection is equally difficult to achieve and difficult to verify. With this in mind, a small marginal gap, nominally approximately 50 pm, is usually deemed acceptable.lT 2 Margin-fit relationships have been measured and reported in a variety of ways.3-8The essence of concern is the space existing between the restoration and tooth preparation margins where both meet the oral environment. The crevice, or gap, can be viewed as physical roughness and as such is considered adverse to optimal gingival and periodontal health in the same way that calculus or a poorly finished amalgam margin would be judged.g-12 Special measurements of these gaps can be compared to a theoretical zero. Minimal dimensions for these spaces have not been determined clinically; consequently there are no existing standards. A very sharp focus on marginal gaps might also include restoration surface, cement surface, and cement interfaces as additional important biologic considerations. Crown margins are often subgingival, where biologic considerations are of great concern. In this respect, titanium (Ti) may prove to be an attractive alternative to popular base metal alloys containing known allergens. Ti might also provide physical and manipulative characteristics reminiscent of gold alloys favored in past years. Because Ti casting equipment is commercially available,
aAssociate Professor, Department of Restorative Dentistry. bAssociate Professor, Department of General Practice. cProfessor and Head, Division of Occlusion, Department of Restorative Dentistry.
10/l/32708
THEJOURNALOFPROSTHETIC
DENTISTRY
gaining biologic advantages from cast Ti could be a matter of learning to use a metal with a new set of rules. It is logical that we accommodate this technology and identify restorative procedures where cast Ti might satisfy clinical requirements. Using this approach we could derive immediate benefits and, at the same time, continue work on refinements that may lead to a broad application for Ti in dentistry. This project examined Ti crown margins having the least restrictive external angles-45 degrees and 90 degrees. These configurations are common to metal-ceramic crown copings made for butt shoulder or heavy chamfer preparations. A typical coping would have a lingual apron with a go-degree external angle and a facial veneer with an approximately 45-degree external angle. For this study, stylized metal-ceramic copings with these margin designs were cast in pure Ti, cemented onto their individual master dies, and sectioned longitudinally for microscopic measurements of marginal fit. These measurements allow comparison of Ti crown margins with those cast in other metals.
METHODS
AND MATERIAL
Twenty individual polyvinyl siloxane impressions were used to duplicate two steel stylized dies and create two sets of 10 epoxy resin (Type 9000, Zahn Dental Co., Taunton, Mass.) master dies. The two steel dies represent, both in form and size, teeth prepared for full-crown restorationsone a maxillary central incisor and the other a maxillary premolar (Fig. 1). A dental stone die (Die-keen, Miles, Inc., South Bend, Ind.) was made for waxing each crown coping. With the exception of the shoulder, each stone die received two coats of a die spacer (Dicer Die Spacer, Dentsply International, York, Pa.). Copings were waxed and cast in Ti, 435
BLACKMAN,
Anterior
/ Incisor
Stylized
BAEZ,
AND
BARGHI
Die and Coping Bimensions: Imgrh lingual apron
/ -
Posterior
Fig.
/ Premolar-IClolar
Styhd
Die and Coping
1. Anterior and posterior stylized die and coping configurations with dimensions.
99.5 7%chemically pure (CP), using the manufacturer’s instructions (Ohara Company, Osaka, Japan) (Fig. 1). The castings were recovered with the aid of a grit blaster using 25 pm aluminum oxide. After the margins were protected with lacquer, the castings were chemically milled with 5 % HF acid, 10 seconds. Using magnification, internal adjustments were made as required to fit the castings first to their stone dies. Next, with a light-bodied polyvinyl siloxane impression material (Absolute, low viscosity; Coe Laboratories, Inc., Chicago, Ill.) to facilitate the step, they were fitted to their individual resin dies. No adjustments were made to the casting margins. This restriction included the entire shoulder surface. All castings were luted with zinc phosphate cement to the resin master dies under a 15 kg static load. The crown and die assemblies were embedded in resin and sectioned through the long axes with a slow-speed diamond saw (Isomet Slow Speed Saw, Beuhler, Ltd., Lake Bluff, Ill.). Specimens were divided midfacially and midpalatally and cut surfaces were finished to 600-grit with abrasive paper removing saw-induced distortions. The space lost between specimen faces was approximately 0.4 mm. Measurements were made with a microscope at X50 power. (Gaertner M1142, Gaertner Scientific Corp., Chicago, Ill.) on both surfaces of each specimen. Recorded distances and reference points were also used to create computer images (scale 1:lOOO)for additional measurements.
Measurement
criteria
The following parameters, illustrated in Figs. 2 through 4, were used to create a basis for marginal gap space comparisons. 436
9o” ma@
lJmmmd55mm Shwlda l.Ommand IOmm DIG dumeta 6.5mmmdVOmm Arral dumckr 4.5mm and 7.0 mm [a~ shculdo] Oxlusal dmmcta
1. An external cement surface will develop (Fig. 2), line G-H, with the removal of excess cement and through erosion. Its form and position was determined by a circle interposed between the casting and master die margin (Fig. 3). This circle was sized to contact the casting surface at a point where it could be described as having changed from vertical to horizontal, point 0 (Fig. 3). At this point, a line M-N tangent to the casting curvature was drawn. Then, through point 0 and perpendicular to line M-N, a line was drawn to intersect the die shoulder, point P (Fig. 3). The circle diameter was the distance between 0 and P, and the line O-P divided the circle in half. The segment of the circle’s inner half between casting and die surfaces was considered the cement surface. 2. Forty-five degree margins, if complete, would extend horizontally to a point in line with the external die surface, fully covering the entire shoulder surface. Since these margins were characteristically short, a straight line was drawn joining casting and die margin curvatures, point a to point b (Fig. 4). This line together with those representing casting, cement, and die surfaces delineated the defect area. In those instances where line ab would not adequately describe a marginal deficiency, a straight line drawn tangent to the die margin at 45 degrees, point b, and was extended to intersect with the casting at point a. 3. Ninety-degree margins, instead of being square and completely restoring the surface, were usually rounded and globular (Fig. 4). Supramarginal irregularities continuous with an irregular margin often extended vertically for some distance before reaching the relatively smooth surface characteristic of the apron. The supramarginal surface was considered in the following manner. A straight line was APRIL
1992
VOLUME
67
NUMBER
4
CASTING
ACCURACY
OF TITANIUM
COPINGS
i ..___.
h-13. Mrulmum d~slance be~wccn casting and die external surfaces. cxcludmg margIn roundness [outside diskancc]. C 10 Il. smallcs~ distance between casting and die shoulder measured vertically [vertical distance] E-1:. maximum perpendukr distance between A-B and extcmal cement surface [depth]. A-H/l
accuracy
and geometry
of cast titanium
copings
Ronald Blackman, DDS, MSD,a Ramon Baez, DDS,b and Nasser Barghi, DDS, MAC University
of Texas Health
Science Center, Dental School, San Antonio,
Tex.
The hiocompatihility of titanium with human tissue is well established; its potential as an alternate metal for crown restorations has yet to be fully investigated. This study measured the geometry and accuracy of coping margins cast in Ti, 99.5% chemically pure. Twenty castings with 45-degree facial and go-degree palatal margins were made by indirect technique with a commercial system using recommended procedures. They were then cemented with ZnPO4 cement. The coping and die assemblies were embedded in resin, sectioned longitudinally, and measured with a microscope at x50 power. Casting shrinkage was characteristic, particularly along the horizontal axis in the plane of the shoulder. Although horizontal linear shrinkage of 45-degree margins was greater than that for the go-degree form, the surface of marginal discrepancy was greatest with the go-degree configuration. (J PROSTHET DENT 1992;67:435-40.)
I deally,
cemented crown margins meet prepared tooth margins in perfect nondetectable junctions. In actuality, clinical perfection is equally difficult to achieve and difficult to verify. With this in mind, a small marginal gap, nominally approximately 50 pm, is usually deemed acceptable.lT 2 Margin-fit relationships have been measured and reported in a variety of ways.3-8The essence of concern is the space existing between the restoration and tooth preparation margins where both meet the oral environment. The crevice, or gap, can be viewed as physical roughness and as such is considered adverse to optimal gingival and periodontal health in the same way that calculus or a poorly finished amalgam margin would be judged.g-12 Special measurements of these gaps can be compared to a theoretical zero. Minimal dimensions for these spaces have not been determined clinically; consequently there are no existing standards. A very sharp focus on marginal gaps might also include restoration surface, cement surface, and cement interfaces as additional important biologic considerations. Crown margins are often subgingival, where biologic considerations are of great concern. In this respect, titanium (Ti) may prove to be an attractive alternative to popular base metal alloys containing known allergens. Ti might also provide physical and manipulative characteristics reminiscent of gold alloys favored in past years. Because Ti casting equipment is commercially available,
aAssociate Professor, Department of Restorative Dentistry. bAssociate Professor, Department of General Practice. cProfessor and Head, Division of Occlusion, Department of Restorative Dentistry.
10/l/32708
THEJOURNALOFPROSTHETIC
DENTISTRY
gaining biologic advantages from cast Ti could be a matter of learning to use a metal with a new set of rules. It is logical that we accommodate this technology and identify restorative procedures where cast Ti might satisfy clinical requirements. Using this approach we could derive immediate benefits and, at the same time, continue work on refinements that may lead to a broad application for Ti in dentistry. This project examined Ti crown margins having the least restrictive external angles-45 degrees and 90 degrees. These configurations are common to metal-ceramic crown copings made for butt shoulder or heavy chamfer preparations. A typical coping would have a lingual apron with a go-degree external angle and a facial veneer with an approximately 45-degree external angle. For this study, stylized metal-ceramic copings with these margin designs were cast in pure Ti, cemented onto their individual master dies, and sectioned longitudinally for microscopic measurements of marginal fit. These measurements allow comparison of Ti crown margins with those cast in other metals.
METHODS
AND MATERIAL
Twenty individual polyvinyl siloxane impressions were used to duplicate two steel stylized dies and create two sets of 10 epoxy resin (Type 9000, Zahn Dental Co., Taunton, Mass.) master dies. The two steel dies represent, both in form and size, teeth prepared for full-crown restorationsone a maxillary central incisor and the other a maxillary premolar (Fig. 1). A dental stone die (Die-keen, Miles, Inc., South Bend, Ind.) was made for waxing each crown coping. With the exception of the shoulder, each stone die received two coats of a die spacer (Dicer Die Spacer, Dentsply International, York, Pa.). Copings were waxed and cast in Ti, 435
BLACKMAN,
Anterior
/ Incisor
Stylized
BAEZ,
AND
BARGHI
Die and Coping Bimensions: Imgrh lingual apron
/ -
Posterior
Fig.
/ Premolar-IClolar
Styhd
Die and Coping
1. Anterior and posterior stylized die and coping configurations with dimensions.
99.5 7%chemically pure (CP), using the manufacturer’s instructions (Ohara Company, Osaka, Japan) (Fig. 1). The castings were recovered with the aid of a grit blaster using 25 pm aluminum oxide. After the margins were protected with lacquer, the castings were chemically milled with 5 % HF acid, 10 seconds. Using magnification, internal adjustments were made as required to fit the castings first to their stone dies. Next, with a light-bodied polyvinyl siloxane impression material (Absolute, low viscosity; Coe Laboratories, Inc., Chicago, Ill.) to facilitate the step, they were fitted to their individual resin dies. No adjustments were made to the casting margins. This restriction included the entire shoulder surface. All castings were luted with zinc phosphate cement to the resin master dies under a 15 kg static load. The crown and die assemblies were embedded in resin and sectioned through the long axes with a slow-speed diamond saw (Isomet Slow Speed Saw, Beuhler, Ltd., Lake Bluff, Ill.). Specimens were divided midfacially and midpalatally and cut surfaces were finished to 600-grit with abrasive paper removing saw-induced distortions. The space lost between specimen faces was approximately 0.4 mm. Measurements were made with a microscope at X50 power. (Gaertner M1142, Gaertner Scientific Corp., Chicago, Ill.) on both surfaces of each specimen. Recorded distances and reference points were also used to create computer images (scale 1:lOOO)for additional measurements.
Measurement
criteria
The following parameters, illustrated in Figs. 2 through 4, were used to create a basis for marginal gap space comparisons. 436
9o” ma@
lJmmmd55mm Shwlda l.Ommand IOmm DIG dumeta 6.5mmmdVOmm Arral dumckr 4.5mm and 7.0 mm [a~ shculdo] Oxlusal dmmcta
1. An external cement surface will develop (Fig. 2), line G-H, with the removal of excess cement and through erosion. Its form and position was determined by a circle interposed between the casting and master die margin (Fig. 3). This circle was sized to contact the casting surface at a point where it could be described as having changed from vertical to horizontal, point 0 (Fig. 3). At this point, a line M-N tangent to the casting curvature was drawn. Then, through point 0 and perpendicular to line M-N, a line was drawn to intersect the die shoulder, point P (Fig. 3). The circle diameter was the distance between 0 and P, and the line O-P divided the circle in half. The segment of the circle’s inner half between casting and die surfaces was considered the cement surface. 2. Forty-five degree margins, if complete, would extend horizontally to a point in line with the external die surface, fully covering the entire shoulder surface. Since these margins were characteristically short, a straight line was drawn joining casting and die margin curvatures, point a to point b (Fig. 4). This line together with those representing casting, cement, and die surfaces delineated the defect area. In those instances where line ab would not adequately describe a marginal deficiency, a straight line drawn tangent to the die margin at 45 degrees, point b, and was extended to intersect with the casting at point a. 3. Ninety-degree margins, instead of being square and completely restoring the surface, were usually rounded and globular (Fig. 4). Supramarginal irregularities continuous with an irregular margin often extended vertically for some distance before reaching the relatively smooth surface characteristic of the apron. The supramarginal surface was considered in the following manner. A straight line was APRIL
1992
VOLUME
67
NUMBER
4
CASTING
ACCURACY
OF TITANIUM
COPINGS
i ..___.
h-13. Mrulmum d~slance be~wccn casting and die external surfaces. cxcludmg margIn roundness [outside diskancc]. C 10 Il. smallcs~ distance between casting and die shoulder measured vertically [vertical distance] E-1:. maximum perpendukr distance between A-B and extcmal cement surface [depth]. A-H/l
