Porcelain jacket crown

A brief definition, classification, tooth preparation, fabrication, finishing and cementation of full porcelain/ceramic jacket crowns

1. Porcelain Jacket Crown Hazim Ahmed Elbasha

2. Definition and Overview Complete/All Porcelain Jacket Crown is an esthetic dental prosthesis made of ceramic (porcelain) for replacing the outer layers of the tooth. They are made to match natural tooth structure accurately in terms of color, surface texture, and translucency . R ecently , improved materials and techniques are attempted by to overcome disadvantages inherent in that traditional method ( higher, adhesion to tooth structure, higher strength, etc.)

3. Definition and Overview Since it is made entirely from ceramic, it is the weakest type of crown restorations, more susceptible to fracture, and it is the least conservative type of crowns. Most of the time it used as single restoration on upper or lower anterior. The attempted development of higher strength have followed two paths: 1- One approach is to use a high-strength but nonesthetic ceramic core material and veneered with a lower strength esthetic porcelain, and 2- The development of a ceramic that combines good esthetics with high strength .

4. Types of All Porcelain Jacket Crowns

5. T he Classification that seems to be most significant clinically is whether the all-ceramic restoration from a given system can be etched and bonded or cemented . The three ceramic materials that can be etched and bonded are the traditional hand-stacked feldspathic porcelains , the leucite-reinforced glass-ceramics , and the lithium disilicate–reinforced glass- ceramics . The glass-ceramic restorations can be designed and fabricated as one-piece (monolithic) restorations, or they can act as core materials with more translucent porcelains layered for esthetic enhancement. The Cemented all-ceramic restorations are fabricated with high-strength core materials and veneered with weaker but more translucent porcelains to establish the desired contours and esthetic result . They are the alumina-reinforced ceramic , zirconia- reinforced ceramic , (Sometimes combined together or modified).

6. Bonded Ceramic Restorations (Indirect Bonded Restorations) T hese are the most conservative option, requiring the least amount of tooth reduction while at the same time offering the most esthetic potential . T here are minimal demands for retention and resistance form in the tooth preparation. They do not require features such as increased axial wall length, grooves, or boxes solely for the purpose of retaining the restoration. Retention and resistance are accomplished through the bonding process and rely much less on mechanical retention. The materials that can be etched with hydrofluoric acid and bonded with resin cements are the conventional hand-stacked feldspathic porcelains , highly filled glass-ceramics , and lithium disilicate glass-ceramics .

7. Feldspathic Porcelain Restorations The same type of porcelain veneered on metal substructures to produce porcelain fused to metal restorations, And on high-strength ceramic core restorations. Previously the most commonly used in porcelain restorations, replaced by (leucite- and lithium disilicate–reinforced ). the most esthetic and requires the least amount of tooth reduction of any available restoration. These veneers can be fabricated to a minimum thickness of (0.5 mm). Built with refractory die or a platinum foil matrix foundations. the translucency or opacity as well as color modifications can be built internally. Require high experience, difficult to built and to modify the shade, opacity and translucency. fragile(limited to anterior).

8. Highly Filled Glass-ceramic Restorations Produced with the familiar wax-up, investment, and burnout technique used in dental laboratories. formed within the glass matrix of feldspathic porcelain throughout various temperature cycles (one heating cycle only). Used in the CAD/CAM prosthodontic restorations (feldspathic ceramic and highly filled leucite-reinforced ceramic). Recommended for anterior full coverage and veneer applications inlay, onlay, and full coverage restorations for premolars and molar inlays and onlays (still prone to fracture in molars PJCs).

9. L ithium disilicate– reinforced material (e.max) E.max is available in both pressed ceramic (e.max Press) and CAD/CAM (e.max CAD). Has higher durability, now It is recommended all single-unit applications and certain three-unit anterior fixed partial dentures where there is adequate bulk in the connector area . Available in blocks with varying translucency (high Chroma gingival neck shade on one side of the block to a dentin shade in the center of the block to an enamel translucency on the opposite side of the block ).

10. Cemented Restorations (High-strength Core Restorations) The high-strength core restorations are composed of a substructure of ceramic veneered with feldspathic porcelain for esthetics. These cores are made of alumina, zirconia, or a combination of the two.

11. Alumina-reinforced Substructures The first high-strength core ceramic was a glass-infiltrated alumina A suspension of finely ground material (slip) mixed to a thin, creamy consistency is brushed onto the die in a method called slip casting. Recommended for both anterior and posterior single-unit restorations and selected three-unit anterior fixed partial dentures(before the advent of zirconia substructures). Available for CAD/CAM prosthodontic restorations

12. Zirconia-reinforced Substructures the strongest tooth-colored substructure materials available to date . fabricated using CAD/ CAM technology . The final esthetic results with zirconia-reinforced restorations are achieved by the addition of a hand-stacked veneer of feldspathic porcelain or a veneer of pressed ceramic Recommend for any single-unit restorations and most posterior, as well as anterior, fixed partial dentures I ncidence of substructure failure has been extremely low .

13. Tooth Preparation

14. Preparation requirements A shoulder of 1.5mm width is used as gingival finishing line to provide a flat seat to resist the force directed from incisal. Incisal edge should be flat and prepared with slight inclination lingually. All sharp angles should be slightly rounded to reduce the danger of stress concentration and fracture PJC should be avoided on teeth with edge to edge occlusal relation.

15. Armamentarium Handpiece Coarse-grit flat-end tapered diamond Coarse-grit football-shaped diamond Fine-grit flat-end tapered diamond CP-11/12 binangle chisel

16. Technique Depth-orientation grooves are placed on the labial and incisal surfaces with the coarse-grit flat- end tapered diamond before any reduction is done to accurately gauge the depth of reduction done on the labial surface . The bur is held parallel to the gingival one-third of the labial surface. A second set of two grooves is made parallel to the incisal two-thirds of the uncut labial surface.

17. Incisal reduction is done with the coarse-grit flat-end tapered diamond so that it will be possible for instruments to reach the finish line area of the preparation in subsequent steps. Approximately 1.5 to 2.0 mm of tooth structure is removed.

18. The tooth structure still remaining between the depth orientation grooves on the incisal portion of the labial surface is planed away The gingival portion of the labial surface is reduced with the coarse-grit flat-end tapered diamond. This reduction extends around the labioproximal line angles and fades out on the lingual aspects of the proximal surfaces.

19. Lingual reduction incisal to the cingulum is done with the coarse-grit football-shaped diamond, with care taken not to overreduce the junction between the cingulum and the lingual wall (apical to the cingulum ). Overshortening the lingual wall will reduce the retention of the preparation.

20. Reduction of the lingual axial surface is done with the coarse-grit flat-end tapered diamond

21. All of the axial walls should be smoothed with a fine-grit flat-end tapered diamond, accentuating the shoulder at the same time

22. All sharp angles should be rounded over at this time. The CP-11/12 modified binangle chisel is used to smooth the shoulder, removing any loose enamel rods at the cavosurface angle. Care must be taken not to create undercuts in the axial walls where they join the shoulder.

23. Types of finishing lines used for all ceramic crown Shoulder all around has been advocated as gingival finishing line to be use with this crown. The depth and contour of shoulder is established with the tip of flat end tapered fissure bur. Sharp angles should be rounded to avoid creation of point of stress concentration.

24. Fabrication

25. Tooth preparation for all-ceramic restorations should provide a minimum overall reduction of 1.0 mm to allow for a minimum thickness of core material. However, 1.5 mm on the facial and 1.5 to 2.0 mm on the occlusal aspects are preferred. All line and point angles should be rounded. The finish line is a radial shoulder that is 1.0 mm wide on the facial and 0.5 to 0.7 mm wide in other areas. A study comparing the marginal adaptation of In-Ceram crowns with varying finish lines found that all three of the configurations tested (chamfer, 50-degree shoulder, and 90- degree shoulder) yielded acceptable results

26. Following the impression of the prepared tooth, a master cast with removable dies is constructed . The dies are trimmed, and any undercuts are blocked out

27. Cement spacer is applied to the dies, with a distance of 0.5 to 1.0 mm maintained from the finish line

28. An addition silicone impression material is used to duplicate the master cast

29. the cast is poured in a specially formulated stone.

30. After the duplicate dies are trimmed, the finish line is marked

31. A sealant is applied to act as a surface wetting agent, decreasing absorption of liquid slip by the die

32. An ultrasonic device (Vitasonic, Vident) is used for the preparation of the alumina slip material. Liquid , alumina powder, and an additive are combined and mixed on a vibrator until they become a homogenous mass.

33. The slip is rapidly applied with a synthetic brush, building up the desired coping configuration. The die readily absorbs the fluid, aiding the condensation of alumina particles. The consistency of the applied slip materials resembles wax and carves easily

34. A scalpel and other carving instruments are used for initial shaping of the coping. The completed alumina coping is allowed to dry for 30 minutes. Then a liquid stabilizer is applied to the framework to facilitate correction after firing.

35. The framework is sintered in a furnace designed for long-duration firing. During the 10-hour firing cycle, temperatures reach 1,120°C. When the cycle reaches its maximum temperature, the copings are held at 1,120°C for 2 hours to allow the development of alumina crystals. During the sintering process, the duplicate dies shrink, making the removal of the copings extremely easy

36. Final shaping of the framework is accomplished with rotary stones and diamond burs. Glass infiltration provides the coping with its final shade, translucency, and strength. The desired shade of glass powder is mixed with distilled water. The mixture is generously applied to the coping, leaving a small area uncovered to facilitate an escape of air as the glass fills the porosities

37. The coping is set on platinum foil to fire the glass infiltrate. The infiltration firing cycle at 1,100°C requires 4 hours for single crowns and 6 hours for fixed partial denture frameworks.

38. When infiltration is complete, excess bulk of glass is removed with diamond burs. The coping is then air abraded.

39. Following glass infiltration, conventional porcelain is added to the coping, restoring the correct anatomical form and occlusal function. The incisal area is cut. Incisal porcelain is added back to restore full contour. After the necessary correction bakes, the crown is glazed and ready for cementation.

40. Cementation and Finishing

41. Crown Finishing To avoid fracture, only gentle forces should be used for inserting and testing ceramic restorations . Broad, relatively flat surfaces are best reduced extraorally with a large, smooth-cutting Busch Silent Stone (Pfingst), while grooves and ridges are reshaped with smaller pointed diamond stones and green stones.

42. It is best to postpone minor grinding adjustments on thin veneers and inlays until after they are permanently bonded to the tooth . Roughened ceramic surfaces are smoothed with clean white stones and polished with rubber wheels of progressively finer grit Porcelain also may be reglazed after it is polished

43. At try-in, the patient is asked to moisten the ceramic and adjacent teeth with saliva. The shade is evaluated under incandescent, fluorescent, and natural light. To minimize the effects of metamerism, it is better to accept a shade that matches reasonably well under all lighting conditions than one that matches perfectly under natural light but appears discolored under artificial light. The patient should be allowed to look at the completed restoration in a wall mirror and approve it before cementation

44. Crown Cementation Ceramic crowns may be cemented with zinc phosphate, glass ionomer, or a dual-polymerizing resin cement. Ceramic crowns that have been etched internally and bonded with a composite resin cement are 50% stronger than similar crowns cemented with zinc phosphate cement.

45. The crown should be clean, etched, and silaned. Any organic debris is removed with ethanol or acetone, and then the restoration is placed in an ultrasonic cleaner. Further cleaning can be accomplished by applying liquid phosphoric acid etchant.

46. The crown is rinsed and then dried with compressed air. The tooth preparation is cleaned with a rubber cup and flour of pumice, washed, and dried . A thin layer of cement is applied to the internal surfaces of the crown. The crown is seated, and excess cement is removed from the marginal areas with an explorer and a clean brush. A slight excess is left to avoid ditching the cement at the margin. The curing light is aimed at marginal areas from facial, lingual, and occlusal directions. For cements, 6 minutes should be allowed for autopolymerization. Bulky margins or premature occlusal contacts are adjusted with a fine diamond stone. Occlusal surfaces are polished with wheels from a porcelain adjustment kit.

47. References: Contemporary Fixed Prosthodontics, 4th edition Fundamentals of Fixed Prosthodontics, 4th Edition