PIN INFLUENCEON FRACTURERESISTANCE
21. Pameijier CH, Segal E, Richardson J. Pulpal response to a glass ionomer cement in primafes. J PROSTHETDENT 1981;46:36-40. 22. Simmons JJ. The miracle mixture glass ionomer and alloy powder. Tex Dent 1983;100:6-12. 23. Van de Voorde A, Gerdt GJ, Murchison DF. Clinical uses of glass iota omer cement: a literature review. Quintessence 1988;19:53-61. 24. McLean JW. Alternative to amalgam alloys. Br Dent J 1984;157:432-3. 25. McLean JW, Gasser O. Glass-cermet cements. Quintessence Int 1985;16:333-43. 26. McLean JW. Glass ionomer cements. Br Dent J 1988;164:293-300. 27. Wilson AD. A survey of inorganic and polyelectrolyte cements. Br Dent J 1984;157:449-54. 28. Murray AJ, Nanos JA, Fontenot RE. Compressive strength of glass ionomer with and without silver alloy [Abstract]. J Dent Res 1986;65:193. 29. McKinney JE, Antonucci JM, Rupp NW. Wear and microhardness of a silver sintered glass ionomer cement. J Dent Res 1988;67:831-5. 30. Tjan AHL, Morgan DL. Metal-reinforced glass ionomers: their flexural and bond strengths to tooth substrates. J PROSTHETDENT 1988;59:13741. 31. Omura I, Yamauchi J, Harada I, Wasa T. Adhesive and mechanical properties of a new dental adhesive [Abstract]. J Dent Res 1984;62:233. 32. Pegoraro LF, Barrack G. A comparison of bond strengths of adhesive
33. 34. 35. 36. 37.
cast restorations using different designs, bonding agents, and luting resin. J PROSTHETDENT 1987;57:133-7. Abbasi J, Bertolotti RL, Lacy AM, Watanabe LG. Bond strengths of porcelain repair monomers [Abstract]. J Dent Res 1988;67:223. Hotz P, McLean JW, Sced I, Wilson AD. The bonding of glass ionomer cements to metal and tooth substrates. Br Dent J 1977;142:41-7. Sarkar NK, Thorjusen P, E1 Mallakh B, Traynham Y. Improved abrasion resistance in a new alloy reinforced glass ionomer [Abstract]. J Dent Res 1989;68:273. Mondelli J, Fonterrado V. The strength of class II amalgam restorations with and without pins. J PROSTHETDENT 1972;28:179-88. Lambert RL, Robinson FB, L!ndemuth JS. Coronal reinforcement with cross-splinted pin-amalgam restorations. J PROSTHET DENT i985; 54:346-9.
Reprint requests to:
DR. ELIZABETHC. KAO COLLEGEOF DENTISTRY OHIO STATEUNIVERSITY 305 W. 12TH AVE. COLUMBUS,OH 43210
T w i n - t a b l e s technique for occlusal rehabilitation: Part II--Clinical p r o c e d u r e s Sumiya Hobo, DDS, MSD, PhD a International Dental Academy, Tokyo, Japan, and University of California, School of Dentistry, Los Angeles Calif.
Molar disclusion is determined by the cusp-shape factor and the angle of hinge rotation, A n e w t w i n - t a b l e s technique has been introduced for d e v e l o p i n g molar disclusion by u s i n g two incisal tables. It is a r e l a t i v e l y uncomplicated technique and does not require Special equipment. The final prosthesis with the t w i n - t a b l e s technique e n s u r e s a restoration with a predictable posterior disclusion and anterior guidance in h a r m o n y with the condyle path. (J PROSTHET DENT 1991;66:471-7.)
A n t e r i o r g u i d a n c e is crucial in h u m a n occlusion b e c a u s e it i n f l u e n c e s m o l a r d i s c l u s i o n t h a t c o n t r o l s h o r i z o n t a l forces. M o l a r d i s c l u s i o n is d e t e r m i n e d b y a c u s p s h a p e f a c t o r a n d a n a n g l e of h i n g e r o t a t i o n . T h e m e c h a n i s m of m o l a r d i s c l u s i o n was r e v i e w e d in P a r t I. 1 I n P a r t II, t h e m e t h o d for c r e a t i n g m o l a r d i s c l u s i o n b y u s i n g a t w i n - t a b l e s t e c h n i q u e will b e d e s c r i b e d , T h i s n e w t e c h n i q u e d e v e l o p s a n t e r i o r g u i d a n c e to c r e a t e a p r e d e t e r mined, harmonious disclusi0n with the condylar path.
Presented at the American Academy of Fixed Prosthodontics meeting, Chicago, Ill. aDirector, International Dental Academy; Visiting Professor, University of California, School of Dentistry.
10/1/29419
THE JOURNAL OF PROSTHETICDENTISTRY
O n e incisal t a b l e is u s e d t o i n c o r p o r a t e a c u s p - s h a p e fact o r a n d t h e o t h e r is u s e d for t h e a n g l e of h i n g e r o t a t i o n . T h i s m e t h o d does n o t r e q u i r e special e q u i p m e n t a n d is a n u n c o m p l i c a t e d p r o c e d u r e s u i t a b l e for d a i l y p r a c t i c e . T h e m y s t e r y Of e s t a b l i s h i n g t h e o p t i m a l a n t e r i o r g u i d a n c e is also clarified, i n c l u d i n g a c c u r a t e d e v e l o p m e n t of a specific d e g r e e of d i s c l u s i o n d e s i r e d b y t h e d e n t i s t .
MEASUREMENT PATH
OF THE CONDYLAR
T h e c u s p - s h a p e f a c t o r a n d t h e a n g l e of h i n g e r o t a t i o n is derived primarily from the condylar path. To ensure an a c c u r a t e m e a s u r e m e n t , a p a n t o g r a p h or i n t e r o c c l u s a l r e c o r d s c a n b e u s e d for t h i s p r o c e d u r e . H o w e v e r , w h e n int e r o c c l u s a l r e c o r d s are used, t h e h o r i z o n t a l l a t e r a l c o n d y -
471
HOBO
Fig. 1. Diagnostic casts mounted on semiadjustable articulator.
Fig. 4. To make molars glide smoothly through maximum intercuspation, any interference that prevents even posterior contacts is removed. Areas are marked with indelible pen.
Fig. 2. Anterior portion of maxillary cast is easily made removable by using dowel pins.
Fig. 5. Wax is added to any surface on tooth that does not contact with opposing occlusal surfaces, until it has even contact.
Fig. 3. After anterior segment is removed, carbon occlusal paper is placed between maxillary and mandibular posterior teeth. Then articulator is moved to simulate forward, right, and left movement directions.
lar path reproduced is inaccurate, so the method of using the correlation between immediate side shift and the Bennett angle for adjusting the horizontal lateral condylar path is used. 2' 3 Two types of adjustable articulators are used clinically. A semiadjustable articulator creates only a straight condylar path whereas a fully adjustable articulator develops a curvature. Because a condylar path with a curve is more accurate and reflects a reliable anterior guidance, a fully adjustable articulator is preferred. The articulators duplicate the working condylar path in different ways. A semiadjustable articulator only develops a straight outward path and the sagittal deviation cannot be adjusted whereas a fully adjustable articulator reproduces the sagittal deviation of the working condylar path. According to a study of 50 adults, the working condyle travels straight laterally along the transverse horizontal axis.4, 5 When the working condyle follows this path during
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Fig. 7. Same procedures are repeated to complete two incisal tables. These tables are called incisal tables without disclusion. Fig. 6. If maxillary and mandibular casts interdigitate evenly, it indicates that cusp shape of molars has been established. Chemical-cure acrylic resin is placed on incisal table and resin is molded by moving articulator in all eccentric movements.
lateral movement with molar disclusion, the orbit formed at the incisal point is referred to as the neutral line. 6 The condylar path and anterior guidance are in harmony when the canine guidance coincides with the neutral line and the working condyle moves straight laterally. If they do not coincide, the working condyle deviates sagittally to compensate for the discrepancy. For the twin-tables technique, the working condylar path is set on the articulator to move directly outward along the transverse horizontal axis to produce a neutral line. A semiadjustable arcon-type articulator with a box-shaped fossa element mimics such a working condylar path. When a fully adjustable articulator is used, the working condylar path is reset to zero both in the frontal and the horizontal planes so that the working condyle moves straight outward. The working condyle that deviates clinically in different directions within the sagittal plane is called surtrusion, detrusion, protrusion, and retrusion. This deviation compensates for the difference between the neutral line and the actual anterior guidance. Setting the working condylar path of an articulator with a sagittal deviation incorporates the discrepancy. It is difficult to reproduce anterior guidance accurately on such an articulator because it incorporates the original reason for the sagittal deviation in the working condylar path. Nonworking and protrusive condylar paths, although unaffected by anterior guidance, can be reproduced in the usual manner. Readjustment of the working condylar path so that it moves straight outward does not interfere with reproduction of other condylar path elements. INCISAL
TABLE
WITHOUT
DISCLUSION
The study casts are initially prepared by making the anterior portion of the maxillary cast removable with dowel pins. The facebow and centric relation records are used to
THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 8. Resin cone must be placed toward back side of incisal pole (A). If cone is made similar to B, incisal pole crushes part of cone during movement.
mount the study casts on the articulator (Figs. i and 2). The anterior portion of the maxillary cast is removed to eliminate the effects of anterior guidance. The articulator is then moved in forward, right, and left directions (Fig. 3). With the anterior segmen t of the maxillary cast removed, the posterior teeth do not disclude during eccentric movements, but the molars should glide smoothly through maximum intercuspation. If there is an interference that prevents posterior contacts throughout eccentric movements, those contacts are removed and marked with an indelible pen (Fig. 4). The mark will be a reference for future intraoral occlusal adjustments. If there is an area where a tooth does not contact with the opposing occlusal surface, wax is added until it contacts evenly (Fig. 5). The missing teeth or tooth structure spaces are replaced with wax. If maxillary and mandibular casts interdigitate evenly during eccentric movement, it means that the cusp becomes parallel to the condylar path and the cusp shape of the molar has been harmoniously established. The cusp-shape factor is incorporated during this procedure.
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HOBO
Fig. 9. Three-millimeter thick plastic space is placed in nonworking-side fossa box to approximate lateral movement.
Fig. 11. When articulator is closed, incisal pin is directed laterally and upward. Resin cone is formed to record this position.
Fig. 10. Vinyl sheet 1 mm thick is placed on tip of mesiobuccal cusp of mandibular first molar on nonworking side.
Fig. 12. Three cones made at protrusive, right, and left lateral movements create angle of hinge rotation.
Chemical-cure acrylic resin is placed in a dough stage on the flat incisal table, and the resin is molded by moving the incisal pin through protrusive and lateral movements (Fig. 6). A second incisal table is prepared identically (Fig. 7). These incisal tables are referred to as incisal tables without disclusion. The molded incisal table coincides threedimensionally with the condylar path and molar cusp shape. If this table is used to create anterior guidance, a fully balanced occlusion will result.
the plastic spacers are inserted behind right and left condyles on the articulator, maxillary and mandibular casts are placed in a 3 mm protrusive Position. A vinyl sheet 1.1 mm thick is applied to the mesiobuccal cusp tips of right and left mandibular first molars, and the articulator is closed. This creates an average disclusion during protrusive movement of the mandible. The tip of the incisal pin is directed backward and upward from the incisal table. A brush is used to build chemical-cure acrylic resin into a cone between the incisal pin and incisal table. The cone marks the three-dimensional position of the tip of the incisal pin at a 3 mm protrusive movement with 1.1 mm molar disclusion. This creates the angle of hinge rotation required to produce the average disclusion during protrusive movement. The cone is placed toward the back side of the incisal pole similar to A in Fig. 8. If the cone is formed toward the tip of the incisal pole like B, when the incisal pin moves from P to C, the tip of the incisal pin crushes cone B. Because the
INCISAL
TABLE
WITH DISCLUSION
It is critical that anterior guidance is steeper than the condylar path to ensure molar disclusion. The rotation of the mandible resulting from the difference in inclinations is called the angle of hinge rotation. One of the incisal tables without disclusion is placed on the articulator so that the tip of the incisal pole contacts the incisal table in centric relation. Two 3 mm thick plastic spacers are prepared to approximate the protrusive movement position. When
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3
Fig. 13. Three resin cones are connected to form walls and triangular space between centric relation contact of incisal pin and top of wall is filled with newly mixed resin. Articulator is moved through all border movements to mold incisal table. This procedure produces incisal table with disclusion.
Fig. 14. Mounted maxillary and mandibular working casts and two incisal tables.
incisal pole has a definite size, as the center moves along the orbit P to C, the body of the pin interferes with the cone if placed in the pathway. It is critical to form the resin cones toward the outer edge of the path. The lateral movement can be simulated by placing a 3 mm thick plastic spacer behind one of the condyles on the articulator. A 1 mm thick vinyl sheet is positioned on the tip of the mesiobuccal cusp of the mandibular first molar on the nonworking side and a sheet 0.5 mm thick can be also positioned on the working side. When the articulator is closed, the incisal pin is directed laterally and upward. A
THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 15. Anterior portion of maxillary working cast is removed after wax outlines are completed. resin cone is inserted between the incisal pole and incisal table (Figs. 9 through 11). This same procedure is repeated for the other condyle, but one condyle at a time. This creates the angle of hinge rotation to ensure the average disclusion during lateral movement (Fig. 12). The three resin cones are connected with chemical-cure acrylic resin to make walls between the cones. The top of the wall must follow an imaginary line that connects the tips of the resin cones. After the walls are created, a triangular space remains between centric relation contact of the incisal pin and the top of the wall. This space is filled with a chemical-cure acrylic resin. The articulator is moved through all border and eccentric movements. The incisal table is easily molded because the ' centric contact and the three cone tips mark the beginning and end points for eccentric articulator movements (Fig. 13). The tip of the incisal pin has a hemispherical shape with a diameter of 8 mm and the total articulator movement is limited to 3 mm, restricted by the resin cone placement. This results in a molded surface that is one continuous concavity from the area where the incisal pin contacts in centric relation through all eccentric movements. This custom incisal table, called an incisal table with disclusion, incorporates a predetermined degree of disclusion. FABRICATION
OF RESTORATIONS
After preparations are completed, the intraoral interferences are removed by use of the previously marked diagnostic casts. An accurate final impression is made. The maxillary working cast is again made with a removable anterior segment using dowel pins. A facebow is used to transfer the maxillary working cast and a centric relation record is used to articulate the mandibular working cast (Fig: 14). The incisal table without disclusion is initially used in the articulator. The anterior portion of the maxillary working cast is removed and the posterior occlusal wax-up is completed (Figs. 15 and 16). The articulator should be guided by the incisal table and the condylar guidance
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HOBO
Fig. 16. Incisal table without disclusion and condylar path of articulator act as guides for even, gliding contacts in posterior occlusal wax-ups.
Fig. 17. After completion of posterior waxing, incisal table with disclusion is attached to articulator.
Fig. 18. Anterior segment is repositioned. Melted wax is added on lingual surfaces of anterior teeth; then articulator is closed and moved through all border movements to form anterior guidance.
476
Fig. 19. Restorations with incorporated predetermined disclusion on articulator.
Fig. 20. Disclusion is demonstrated with cemented restorations.
mechanism, and the eccentric movements of the maxillary and mandibular posterior teeth should glide evenly. This procedure develops a cuspal inclination parallel to the condylar path and creates the cusp-shape factor. The incisal table is changed on the articulator to the incisal table with disclusion (Fig. 17). The anterior segment is repositioned for waxing of the lingual surfaces of the maxillary anterior teeth. Melted wax is added to the lingual surfaces; then the articulator is closed and moved through all border movements. The wax is contoured by the incisal edges of the mandibular anterior teeth so that they contact evenly (Fig. 18). This procedure establishes the angle of hinge rotation and developes anterior guidance in harmony with the condylar path. Since the anterior guidance programmed in this manner is steeper than the condylar path and the molar cuspal inclinations, the posterior restorations provide a predetermined disclusion during eccentric movement (Figs. 19 and 20). As an alternative technique,
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VOLUME 66
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TWIN TABLES TECHNIQUE: P A R T II
it is possible to make only one incisal table without disclusion. After completion of the posterior occlusal wax-up, a sheet of vinyl can be placed on the wax crown to produce the incisal table with disclusion. This table is used to develop the maxillary lingual surface. The twin-tables technique can be used for a variety of prosthetic procedures including full mouth occlusal rehabilitation, posterior quadrant restorations, and anterior restorations. The following is an abbreviated description of the technique. 1. Record the condylar path by using a pantograph or interocclusal records. Set the working condylar path on the articulator so that the working condyle moves straight outward along the transverse horizontal axis. 2. Make the maxillary study cast with a removable anterior segment. M o u n t the casts to the articulator. Remove the maxillary anterior segment and move the articulator through eccentric movements to eliminate interferences that impede an even, gliding motion. This procedure results in an cusp-shape factor that harmonizes with the condylar path. 3. Insert a flat incisal table and mold chemical-cure resin by moving the incisal pin through eccentric movements. Repeat the procedure on a second table to complete two incisal tables without disclusion. 4. Use one of the incisal tables without disclusion on the articulator. Place two 3 m m spacers behind the condyles to simulate a protrusive position. Place a 1.1 m m thick spacer on the mesiobuccal cusp tip of the mandibular first molars; then close the articulator. Make a resin cone between the incisal pin and the incisal table to establish the angle of hinge rotation for an average disclusion during protrusive movement. 5. Next place one 3 m m spacer behind one condyle in the articulator. Place the 1 m m spacer on the nonworking side and a 0.5 m m spacer on the working side at the mesiobuccal cusp tip of the m a n d i b u l a r first molar to simulate a lateral movement position. Make a resin cone between the incisal pin and table. Repeat the procedure for the other condyle. This creates the angle of hinge rotation for an average disclusion during lateral movement. 6. Connect the three cones with additional resin to form walls. Add more resin, and direct the articulator through eccentric movements to complete the three-dimensional incisal table. This completes the incisal table with disclusion. 7. When making the final restorations, make the maxillary
T H E JOURNAL OF P R O S T H E T I C D E N T I S T R Y
cast with a removable anterior segment. Remove the anterior segment and use the incisal table without disclusion to wax the posterior occlusion through eccentric movements. This establishes the cusp-shape factor that forms the molar cuspal inclination parallel to the condylar path. 8. Use the incisal table with disclusion and reposition the anterior segment on the maxillary cast. Complete the anterior wax-up by moving the articulator through eccentric movements. This establishes the angle of hinge rotation and the posterior restorations will ensure a predetermined a m o u n t of disclusion. CONCLUSION Molar disclusion is determined by the cusp shape-factor and the angle of hinge rotation. A new twin-tables technique has been introduced for developing molar disclusion by use of two incisal tables. It is a relatively uncomplicated technique and does not require special equipment. The final prosthesis by use of the twin-tables technique results in a restoration with a predictable posterior disclusion and anterior guidance in harmony with the condylar path. I dedicate this article to the memory of the late Peter K. Thomas. I extend my appreciation to Dr. Lily T. Garcia for her assistance in completion of this article. REFERENCES 1. Hobo S. Twin-tables technique for occlusal rehabilitation. Part I: mechanismof anterior guidance.J PROSTHETDENT1991;66:299-303. 2. Hobo S. Formula for adjusting the horizontal condylar path of the semiadjustablearticulatorwith interocclusalrecords. Part I. Correlation betweenthe immediateside shift, the progressivesideshift, and the Bennett angle. J PROSTHETDENT1986;55:422-6. 3. Hobo S. Formula for adjusting the horizontal condylar path of the semiadjustablearticulatorwith interocclusalrecords. Part II. Practical evaluations.J PROSTHETDENT1986;55:582-8. 4. HoboS. A kinematicinvestigationof mandibularborder movementby means of an electronicmeasuringsystem. Part II. A study of the Bennett movement.J PROSTHETDENT1984;51:642-6. 5. HoboS. A kinematicinvestigationof mandibularborder movementby means of an electronicmeasuringsystem. Part III. Rotation center of lateral movement.J PROSTHETDENT1984;52:66-72. 6. HoboS, TakayamaH. Effectof canineguidanceon the workingcondylar path. Int J Prosthodont 1989;2:73-9. Reprint requests to: DR. SUMIYAHOBO INTERNATIONALDENTAL ACADEMY 1-25-18 SHOTOH, SHIBUYA-KU TOKYO 150 JAPAN
477
21. Pameijier CH, Segal E, Richardson J. Pulpal response to a glass ionomer cement in primafes. J PROSTHETDENT 1981;46:36-40. 22. Simmons JJ. The miracle mixture glass ionomer and alloy powder. Tex Dent 1983;100:6-12. 23. Van de Voorde A, Gerdt GJ, Murchison DF. Clinical uses of glass iota omer cement: a literature review. Quintessence 1988;19:53-61. 24. McLean JW. Alternative to amalgam alloys. Br Dent J 1984;157:432-3. 25. McLean JW, Gasser O. Glass-cermet cements. Quintessence Int 1985;16:333-43. 26. McLean JW. Glass ionomer cements. Br Dent J 1988;164:293-300. 27. Wilson AD. A survey of inorganic and polyelectrolyte cements. Br Dent J 1984;157:449-54. 28. Murray AJ, Nanos JA, Fontenot RE. Compressive strength of glass ionomer with and without silver alloy [Abstract]. J Dent Res 1986;65:193. 29. McKinney JE, Antonucci JM, Rupp NW. Wear and microhardness of a silver sintered glass ionomer cement. J Dent Res 1988;67:831-5. 30. Tjan AHL, Morgan DL. Metal-reinforced glass ionomers: their flexural and bond strengths to tooth substrates. J PROSTHETDENT 1988;59:13741. 31. Omura I, Yamauchi J, Harada I, Wasa T. Adhesive and mechanical properties of a new dental adhesive [Abstract]. J Dent Res 1984;62:233. 32. Pegoraro LF, Barrack G. A comparison of bond strengths of adhesive
33. 34. 35. 36. 37.
cast restorations using different designs, bonding agents, and luting resin. J PROSTHETDENT 1987;57:133-7. Abbasi J, Bertolotti RL, Lacy AM, Watanabe LG. Bond strengths of porcelain repair monomers [Abstract]. J Dent Res 1988;67:223. Hotz P, McLean JW, Sced I, Wilson AD. The bonding of glass ionomer cements to metal and tooth substrates. Br Dent J 1977;142:41-7. Sarkar NK, Thorjusen P, E1 Mallakh B, Traynham Y. Improved abrasion resistance in a new alloy reinforced glass ionomer [Abstract]. J Dent Res 1989;68:273. Mondelli J, Fonterrado V. The strength of class II amalgam restorations with and without pins. J PROSTHETDENT 1972;28:179-88. Lambert RL, Robinson FB, L!ndemuth JS. Coronal reinforcement with cross-splinted pin-amalgam restorations. J PROSTHET DENT i985; 54:346-9.
Reprint requests to:
DR. ELIZABETHC. KAO COLLEGEOF DENTISTRY OHIO STATEUNIVERSITY 305 W. 12TH AVE. COLUMBUS,OH 43210
T w i n - t a b l e s technique for occlusal rehabilitation: Part II--Clinical p r o c e d u r e s Sumiya Hobo, DDS, MSD, PhD a International Dental Academy, Tokyo, Japan, and University of California, School of Dentistry, Los Angeles Calif.
Molar disclusion is determined by the cusp-shape factor and the angle of hinge rotation, A n e w t w i n - t a b l e s technique has been introduced for d e v e l o p i n g molar disclusion by u s i n g two incisal tables. It is a r e l a t i v e l y uncomplicated technique and does not require Special equipment. The final prosthesis with the t w i n - t a b l e s technique e n s u r e s a restoration with a predictable posterior disclusion and anterior guidance in h a r m o n y with the condyle path. (J PROSTHET DENT 1991;66:471-7.)
A n t e r i o r g u i d a n c e is crucial in h u m a n occlusion b e c a u s e it i n f l u e n c e s m o l a r d i s c l u s i o n t h a t c o n t r o l s h o r i z o n t a l forces. M o l a r d i s c l u s i o n is d e t e r m i n e d b y a c u s p s h a p e f a c t o r a n d a n a n g l e of h i n g e r o t a t i o n . T h e m e c h a n i s m of m o l a r d i s c l u s i o n was r e v i e w e d in P a r t I. 1 I n P a r t II, t h e m e t h o d for c r e a t i n g m o l a r d i s c l u s i o n b y u s i n g a t w i n - t a b l e s t e c h n i q u e will b e d e s c r i b e d , T h i s n e w t e c h n i q u e d e v e l o p s a n t e r i o r g u i d a n c e to c r e a t e a p r e d e t e r mined, harmonious disclusi0n with the condylar path.
Presented at the American Academy of Fixed Prosthodontics meeting, Chicago, Ill. aDirector, International Dental Academy; Visiting Professor, University of California, School of Dentistry.
10/1/29419
THE JOURNAL OF PROSTHETICDENTISTRY
O n e incisal t a b l e is u s e d t o i n c o r p o r a t e a c u s p - s h a p e fact o r a n d t h e o t h e r is u s e d for t h e a n g l e of h i n g e r o t a t i o n . T h i s m e t h o d does n o t r e q u i r e special e q u i p m e n t a n d is a n u n c o m p l i c a t e d p r o c e d u r e s u i t a b l e for d a i l y p r a c t i c e . T h e m y s t e r y Of e s t a b l i s h i n g t h e o p t i m a l a n t e r i o r g u i d a n c e is also clarified, i n c l u d i n g a c c u r a t e d e v e l o p m e n t of a specific d e g r e e of d i s c l u s i o n d e s i r e d b y t h e d e n t i s t .
MEASUREMENT PATH
OF THE CONDYLAR
T h e c u s p - s h a p e f a c t o r a n d t h e a n g l e of h i n g e r o t a t i o n is derived primarily from the condylar path. To ensure an a c c u r a t e m e a s u r e m e n t , a p a n t o g r a p h or i n t e r o c c l u s a l r e c o r d s c a n b e u s e d for t h i s p r o c e d u r e . H o w e v e r , w h e n int e r o c c l u s a l r e c o r d s are used, t h e h o r i z o n t a l l a t e r a l c o n d y -
471
HOBO
Fig. 1. Diagnostic casts mounted on semiadjustable articulator.
Fig. 4. To make molars glide smoothly through maximum intercuspation, any interference that prevents even posterior contacts is removed. Areas are marked with indelible pen.
Fig. 2. Anterior portion of maxillary cast is easily made removable by using dowel pins.
Fig. 5. Wax is added to any surface on tooth that does not contact with opposing occlusal surfaces, until it has even contact.
Fig. 3. After anterior segment is removed, carbon occlusal paper is placed between maxillary and mandibular posterior teeth. Then articulator is moved to simulate forward, right, and left movement directions.
lar path reproduced is inaccurate, so the method of using the correlation between immediate side shift and the Bennett angle for adjusting the horizontal lateral condylar path is used. 2' 3 Two types of adjustable articulators are used clinically. A semiadjustable articulator creates only a straight condylar path whereas a fully adjustable articulator develops a curvature. Because a condylar path with a curve is more accurate and reflects a reliable anterior guidance, a fully adjustable articulator is preferred. The articulators duplicate the working condylar path in different ways. A semiadjustable articulator only develops a straight outward path and the sagittal deviation cannot be adjusted whereas a fully adjustable articulator reproduces the sagittal deviation of the working condylar path. According to a study of 50 adults, the working condyle travels straight laterally along the transverse horizontal axis.4, 5 When the working condyle follows this path during
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Fig. 7. Same procedures are repeated to complete two incisal tables. These tables are called incisal tables without disclusion. Fig. 6. If maxillary and mandibular casts interdigitate evenly, it indicates that cusp shape of molars has been established. Chemical-cure acrylic resin is placed on incisal table and resin is molded by moving articulator in all eccentric movements.
lateral movement with molar disclusion, the orbit formed at the incisal point is referred to as the neutral line. 6 The condylar path and anterior guidance are in harmony when the canine guidance coincides with the neutral line and the working condyle moves straight laterally. If they do not coincide, the working condyle deviates sagittally to compensate for the discrepancy. For the twin-tables technique, the working condylar path is set on the articulator to move directly outward along the transverse horizontal axis to produce a neutral line. A semiadjustable arcon-type articulator with a box-shaped fossa element mimics such a working condylar path. When a fully adjustable articulator is used, the working condylar path is reset to zero both in the frontal and the horizontal planes so that the working condyle moves straight outward. The working condyle that deviates clinically in different directions within the sagittal plane is called surtrusion, detrusion, protrusion, and retrusion. This deviation compensates for the difference between the neutral line and the actual anterior guidance. Setting the working condylar path of an articulator with a sagittal deviation incorporates the discrepancy. It is difficult to reproduce anterior guidance accurately on such an articulator because it incorporates the original reason for the sagittal deviation in the working condylar path. Nonworking and protrusive condylar paths, although unaffected by anterior guidance, can be reproduced in the usual manner. Readjustment of the working condylar path so that it moves straight outward does not interfere with reproduction of other condylar path elements. INCISAL
TABLE
WITHOUT
DISCLUSION
The study casts are initially prepared by making the anterior portion of the maxillary cast removable with dowel pins. The facebow and centric relation records are used to
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Fig. 8. Resin cone must be placed toward back side of incisal pole (A). If cone is made similar to B, incisal pole crushes part of cone during movement.
mount the study casts on the articulator (Figs. i and 2). The anterior portion of the maxillary cast is removed to eliminate the effects of anterior guidance. The articulator is then moved in forward, right, and left directions (Fig. 3). With the anterior segmen t of the maxillary cast removed, the posterior teeth do not disclude during eccentric movements, but the molars should glide smoothly through maximum intercuspation. If there is an interference that prevents posterior contacts throughout eccentric movements, those contacts are removed and marked with an indelible pen (Fig. 4). The mark will be a reference for future intraoral occlusal adjustments. If there is an area where a tooth does not contact with the opposing occlusal surface, wax is added until it contacts evenly (Fig. 5). The missing teeth or tooth structure spaces are replaced with wax. If maxillary and mandibular casts interdigitate evenly during eccentric movement, it means that the cusp becomes parallel to the condylar path and the cusp shape of the molar has been harmoniously established. The cusp-shape factor is incorporated during this procedure.
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Fig. 9. Three-millimeter thick plastic space is placed in nonworking-side fossa box to approximate lateral movement.
Fig. 11. When articulator is closed, incisal pin is directed laterally and upward. Resin cone is formed to record this position.
Fig. 10. Vinyl sheet 1 mm thick is placed on tip of mesiobuccal cusp of mandibular first molar on nonworking side.
Fig. 12. Three cones made at protrusive, right, and left lateral movements create angle of hinge rotation.
Chemical-cure acrylic resin is placed in a dough stage on the flat incisal table, and the resin is molded by moving the incisal pin through protrusive and lateral movements (Fig. 6). A second incisal table is prepared identically (Fig. 7). These incisal tables are referred to as incisal tables without disclusion. The molded incisal table coincides threedimensionally with the condylar path and molar cusp shape. If this table is used to create anterior guidance, a fully balanced occlusion will result.
the plastic spacers are inserted behind right and left condyles on the articulator, maxillary and mandibular casts are placed in a 3 mm protrusive Position. A vinyl sheet 1.1 mm thick is applied to the mesiobuccal cusp tips of right and left mandibular first molars, and the articulator is closed. This creates an average disclusion during protrusive movement of the mandible. The tip of the incisal pin is directed backward and upward from the incisal table. A brush is used to build chemical-cure acrylic resin into a cone between the incisal pin and incisal table. The cone marks the three-dimensional position of the tip of the incisal pin at a 3 mm protrusive movement with 1.1 mm molar disclusion. This creates the angle of hinge rotation required to produce the average disclusion during protrusive movement. The cone is placed toward the back side of the incisal pole similar to A in Fig. 8. If the cone is formed toward the tip of the incisal pole like B, when the incisal pin moves from P to C, the tip of the incisal pin crushes cone B. Because the
INCISAL
TABLE
WITH DISCLUSION
It is critical that anterior guidance is steeper than the condylar path to ensure molar disclusion. The rotation of the mandible resulting from the difference in inclinations is called the angle of hinge rotation. One of the incisal tables without disclusion is placed on the articulator so that the tip of the incisal pole contacts the incisal table in centric relation. Two 3 mm thick plastic spacers are prepared to approximate the protrusive movement position. When
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3
Fig. 13. Three resin cones are connected to form walls and triangular space between centric relation contact of incisal pin and top of wall is filled with newly mixed resin. Articulator is moved through all border movements to mold incisal table. This procedure produces incisal table with disclusion.
Fig. 14. Mounted maxillary and mandibular working casts and two incisal tables.
incisal pole has a definite size, as the center moves along the orbit P to C, the body of the pin interferes with the cone if placed in the pathway. It is critical to form the resin cones toward the outer edge of the path. The lateral movement can be simulated by placing a 3 mm thick plastic spacer behind one of the condyles on the articulator. A 1 mm thick vinyl sheet is positioned on the tip of the mesiobuccal cusp of the mandibular first molar on the nonworking side and a sheet 0.5 mm thick can be also positioned on the working side. When the articulator is closed, the incisal pin is directed laterally and upward. A
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Fig. 15. Anterior portion of maxillary working cast is removed after wax outlines are completed. resin cone is inserted between the incisal pole and incisal table (Figs. 9 through 11). This same procedure is repeated for the other condyle, but one condyle at a time. This creates the angle of hinge rotation to ensure the average disclusion during lateral movement (Fig. 12). The three resin cones are connected with chemical-cure acrylic resin to make walls between the cones. The top of the wall must follow an imaginary line that connects the tips of the resin cones. After the walls are created, a triangular space remains between centric relation contact of the incisal pin and the top of the wall. This space is filled with a chemical-cure acrylic resin. The articulator is moved through all border and eccentric movements. The incisal table is easily molded because the ' centric contact and the three cone tips mark the beginning and end points for eccentric articulator movements (Fig. 13). The tip of the incisal pin has a hemispherical shape with a diameter of 8 mm and the total articulator movement is limited to 3 mm, restricted by the resin cone placement. This results in a molded surface that is one continuous concavity from the area where the incisal pin contacts in centric relation through all eccentric movements. This custom incisal table, called an incisal table with disclusion, incorporates a predetermined degree of disclusion. FABRICATION
OF RESTORATIONS
After preparations are completed, the intraoral interferences are removed by use of the previously marked diagnostic casts. An accurate final impression is made. The maxillary working cast is again made with a removable anterior segment using dowel pins. A facebow is used to transfer the maxillary working cast and a centric relation record is used to articulate the mandibular working cast (Fig: 14). The incisal table without disclusion is initially used in the articulator. The anterior portion of the maxillary working cast is removed and the posterior occlusal wax-up is completed (Figs. 15 and 16). The articulator should be guided by the incisal table and the condylar guidance
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Fig. 16. Incisal table without disclusion and condylar path of articulator act as guides for even, gliding contacts in posterior occlusal wax-ups.
Fig. 17. After completion of posterior waxing, incisal table with disclusion is attached to articulator.
Fig. 18. Anterior segment is repositioned. Melted wax is added on lingual surfaces of anterior teeth; then articulator is closed and moved through all border movements to form anterior guidance.
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Fig. 19. Restorations with incorporated predetermined disclusion on articulator.
Fig. 20. Disclusion is demonstrated with cemented restorations.
mechanism, and the eccentric movements of the maxillary and mandibular posterior teeth should glide evenly. This procedure develops a cuspal inclination parallel to the condylar path and creates the cusp-shape factor. The incisal table is changed on the articulator to the incisal table with disclusion (Fig. 17). The anterior segment is repositioned for waxing of the lingual surfaces of the maxillary anterior teeth. Melted wax is added to the lingual surfaces; then the articulator is closed and moved through all border movements. The wax is contoured by the incisal edges of the mandibular anterior teeth so that they contact evenly (Fig. 18). This procedure establishes the angle of hinge rotation and developes anterior guidance in harmony with the condylar path. Since the anterior guidance programmed in this manner is steeper than the condylar path and the molar cuspal inclinations, the posterior restorations provide a predetermined disclusion during eccentric movement (Figs. 19 and 20). As an alternative technique,
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it is possible to make only one incisal table without disclusion. After completion of the posterior occlusal wax-up, a sheet of vinyl can be placed on the wax crown to produce the incisal table with disclusion. This table is used to develop the maxillary lingual surface. The twin-tables technique can be used for a variety of prosthetic procedures including full mouth occlusal rehabilitation, posterior quadrant restorations, and anterior restorations. The following is an abbreviated description of the technique. 1. Record the condylar path by using a pantograph or interocclusal records. Set the working condylar path on the articulator so that the working condyle moves straight outward along the transverse horizontal axis. 2. Make the maxillary study cast with a removable anterior segment. M o u n t the casts to the articulator. Remove the maxillary anterior segment and move the articulator through eccentric movements to eliminate interferences that impede an even, gliding motion. This procedure results in an cusp-shape factor that harmonizes with the condylar path. 3. Insert a flat incisal table and mold chemical-cure resin by moving the incisal pin through eccentric movements. Repeat the procedure on a second table to complete two incisal tables without disclusion. 4. Use one of the incisal tables without disclusion on the articulator. Place two 3 m m spacers behind the condyles to simulate a protrusive position. Place a 1.1 m m thick spacer on the mesiobuccal cusp tip of the mandibular first molars; then close the articulator. Make a resin cone between the incisal pin and the incisal table to establish the angle of hinge rotation for an average disclusion during protrusive movement. 5. Next place one 3 m m spacer behind one condyle in the articulator. Place the 1 m m spacer on the nonworking side and a 0.5 m m spacer on the working side at the mesiobuccal cusp tip of the m a n d i b u l a r first molar to simulate a lateral movement position. Make a resin cone between the incisal pin and table. Repeat the procedure for the other condyle. This creates the angle of hinge rotation for an average disclusion during lateral movement. 6. Connect the three cones with additional resin to form walls. Add more resin, and direct the articulator through eccentric movements to complete the three-dimensional incisal table. This completes the incisal table with disclusion. 7. When making the final restorations, make the maxillary
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cast with a removable anterior segment. Remove the anterior segment and use the incisal table without disclusion to wax the posterior occlusion through eccentric movements. This establishes the cusp-shape factor that forms the molar cuspal inclination parallel to the condylar path. 8. Use the incisal table with disclusion and reposition the anterior segment on the maxillary cast. Complete the anterior wax-up by moving the articulator through eccentric movements. This establishes the angle of hinge rotation and the posterior restorations will ensure a predetermined a m o u n t of disclusion. CONCLUSION Molar disclusion is determined by the cusp shape-factor and the angle of hinge rotation. A new twin-tables technique has been introduced for developing molar disclusion by use of two incisal tables. It is a relatively uncomplicated technique and does not require special equipment. The final prosthesis by use of the twin-tables technique results in a restoration with a predictable posterior disclusion and anterior guidance in harmony with the condylar path. I dedicate this article to the memory of the late Peter K. Thomas. I extend my appreciation to Dr. Lily T. Garcia for her assistance in completion of this article. REFERENCES 1. Hobo S. Twin-tables technique for occlusal rehabilitation. Part I: mechanismof anterior guidance.J PROSTHETDENT1991;66:299-303. 2. Hobo S. Formula for adjusting the horizontal condylar path of the semiadjustablearticulatorwith interocclusalrecords. Part I. Correlation betweenthe immediateside shift, the progressivesideshift, and the Bennett angle. J PROSTHETDENT1986;55:422-6. 3. Hobo S. Formula for adjusting the horizontal condylar path of the semiadjustablearticulatorwith interocclusalrecords. Part II. Practical evaluations.J PROSTHETDENT1986;55:582-8. 4. HoboS. A kinematicinvestigationof mandibularborder movementby means of an electronicmeasuringsystem. Part II. A study of the Bennett movement.J PROSTHETDENT1984;51:642-6. 5. HoboS. A kinematicinvestigationof mandibularborder movementby means of an electronicmeasuringsystem. Part III. Rotation center of lateral movement.J PROSTHETDENT1984;52:66-72. 6. HoboS, TakayamaH. Effectof canineguidanceon the workingcondylar path. Int J Prosthodont 1989;2:73-9. Reprint requests to: DR. SUMIYAHOBO INTERNATIONALDENTAL ACADEMY 1-25-18 SHOTOH, SHIBUYA-KU TOKYO 150 JAPAN
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