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How to avoid problems with porcelain-fused-to-metal restorations
REPORTS OF COUNCILS AND BUREAUS
How to avoid problems with porcelain-fused-to-metal restorations
Council on Dental Materials and Devices
T h e p u rp ose o f this paper is to p rovid e a num ber o f recom m en d ation s as so lu tio n s to p rob lem s e n co u n tered w ith p orcelain -fu sed -to-m etal restora tio n s. T h e recom m en d ation s apply eq u ally to n o b le , p rec io u s, and b a se m atal sy ste m s. M an y o f th e se g u id elin es h a v e b een offered earlier a s so lu tio n s to p rob lem s w ith co n v en tio n a l gold allo y restoration s; h o w e v er , th ey are still ap p licab le to th e p o rcelain -fu sed -to-m etal sy ste m s. T h e fe w re fere n c es n o ted in this p aper are highly re co m m en d ed fo r m ore sp ecific inform ation.
Improving anatomical detail ■ To obtain optimum esthetic value
G u id elin es— O ptim um to o th red u ction fo r p re c io u s m etal restoration s is 1.5 m m . T h is a llo w s 0 .5 mm for m etal, ± 0 .2 m m fo r opaquing and ± 0 .8 m m for p orcela in . O ptim um to o th red u ction for b a se m etal restoration s is 1.3 m m . (F o r further inform ation, refer to re fere n c es 1-4.) □ P ro v id e the laboratory w ith d ia g n o stic c a s ts, or c o p ie s th ereo f, to b e u sed by the tec h n i cian as a referen ce visu a l aid o f p reo p era tiv e c o n d ition s during co n stru ctio n o f th e p ro sth esis. □ P ro v id e th e tech n icia n w ith d raw in gs, w h ere appropriate, o f an atom ical fea tu res that are not apparent o n th e stu d y c a sts. □ I f p o ssib le , h a v e restoration s returned from th e laboratory in th e b isq u e b ake form for try-in, final shaping, and o cc lu sa l adjustm ent. □ D eter m in e if th e an atom ic d etail on th e p ro s th esis is a ccu ra te. D is c u s s y o u r ev a lu a tio n w ith the laboratory tech n icia n .
Do □ M ak e full-arch d iagn ostic c a sts for b oth a rch es b efo re to o th preparation. □ U s e d ia g n o stic ca sts for trial w a x u p s, to o th arrangem ent sim u lations for p atien t ap p roval, and d isc u ssio n s w ith the laboratory ab ou t o p tio n s in restoration d esign . □ U n d erstan d the p h y sica l p rop erties o f ea ch p orcela in -to -m eta l sy stem p rescrib ed and o f th e restriction s im p osed on th e structural d e s ig n .1'3 B e sure th e tech n ician d e v e lo p s the sam e k n o w l ed g e. 818 ■ JADA, Vol. 95, October 1977
Improving shade matches
oo
■ G eneral T h e inform ation n e c e ssa r y to arrive at a near p erfect m atch o f ceram ic restoration sh a d es w ith natural teeth is p rob ably in clu d ed in th e literature o n c o lo r d iscrim ination p ra ctices. H o w e v e r ,
so m e o f th e essen tia l in form ation is q uite so p h is tica ted and has n ot y e t b een c o n d en sed for ea sy assim ilation b y d en tists and d en tal te c h n ic ia n s.5 8 S ev er a l fa cto rs related to su c c e ssfu l sh ad e m atch ing h a v e alread y b een id en tified and agreed on by m any w h o h a v e taken a sp ecia l in terest in d e v e l op ing reliab le sh ad e m a tch es. T h e fo llo w in g item s are p ra ctices y o u should co n sid er in attem p ting to a c h ie v e a true sh ade m atch.
■ In selecting shades Do □ U n d erstan d h ow eaich o f th e d im en sio n s o f co lo r en ters in to the se le c tio n , p rescrip tion , and d ev elo p m en t o f d esired sh a d e s.5'7 H u e refers to th e d ifferen t c o lo r fam ilies (red, b lu e, green , and so forth). C hrom a is the in ten sity or strength o f a g iv en h u e. V a lu e refers to a purity or saturation sc a le , th e am oun t o f gray in a color. □ F o r sh ad e d eterm in ation s, u se o ffic e lights w ith at le a st tw o k now n sp ectra, sin c e sh ad es appear d ifferen tly in d ifferen t ty p e s o f light e n v i ron m en ts. A d ayligh t sim u lated sp ectrum and an in d oor “ so ft ligh t” sp ectru m are g o o d c h o ic e s b e c a u se m ost p eo p le are freq u en tly in th e se ty p es o f ligh t en viron m en ts. M ajor re flec tiv e su rfaces, su ch as ceilin g s and w a lls, sh ou ld b e neutral w ith a M u n sell v a lu e o f se v en or eigh t (light gray) to av o id alteration o f the sp ectra. □ C om p are co lo r d iscrim ination cap ab ilities w ith th e tec h n icia n , th e d en tal a ssista n t, and at le a st three o th er p erson s k n ow n or e x p e c te d to h a v e “ n orm al” co lo r vision . □ E n cou rage p atients to w ea r o n ly natural sh ade c o s m e tic s to ap p oin tm en ts. M ask or re m o v e an y unnatural sh ade c o s m e tic s if th ey are w o rn , as th ey m ight interfere w ith sh ad e s e le c tion. □ O b ser v e and record the p a tien t’s e y e , hair, and skin colorin g b efore m aking sh ad e se lec tio n . □ U s e the sh ad e gu id e recom m en d ed for the p o rcelain b ein g u sed . I f ex te n d ed sh ad e gu id es m ade for oth er p rod ucts are u sed , b e sure the tech n ician u nd erstan ds their relation sh ip w ith the p o rcelain b ein g u sed . □ B e sure th e natural tee th and th e sh ad e guide tab are lightly m oisten ed w ith saliva. □ M ak e sev era l sh ade d eterm in ation s b efore to o th preparation. R ecord ea c h d eterm in ation sep a rately, w ith ou t referring to p rev io u s records. T h e final sh ad e se lec tio n sh ou ld b e b a sed on tw o or m ore earlier d eterm in ation s. I f th e d esired sh ade falls b e tw e e n tw o sh ade ta b s, c h o o s e the lighter sh ade. I f the sh ade is o ff, it w ill b e ea sier to
co rrect b y lo w tem perature staining than stripping and reapp lyin g p o rcelain to the castin g. □ O cca sio n a lly g la n ce at gray or green cardbord to p rev en t retinal c o lo r fa tig u e, w h ich resu lts in a lo ss o f co lo r a cu ity .
Do not □ E ntrust the sh a d e se le c tio n to an oth er p er so n u n le ss the co lo r p ercep tio n a cu ity o f the in d i vid ual has b een p ro v en to b e m ore reliable. □ U s e shade g u id es m ade for p la stic tee th , silica te ce m en ts, or oth er m aterials u nrelated to th e p orcelain being u sed . □ A ttem p t sh ade se le c tio n s u nder p oor ligh t ing co n d itio n s such as m ay e x ist on clo u d y d a y s, or w h en e y e s are fatigued.
■ In tooth preparation Do □ R ed u ce ab utm ent teeth su fficien tly to p ro v id e th e sp a ce for the m etal su bstru ctu re and fo r th e bulk o f p orcelain required to a ch ie v e the d e sired sh ade m atch w ith o u t o v erco n to u rin g th e cro w n s.
■ Communicating shade requirem ents to the dental technician Do □ In clu d e in the p rescrip tion su ch ch a ra cteris tics o f p atient as s e x , ag e, and hair, e y e , and skin co lo rs. □ S en d the dental tech n icia n the sh ade gu id e tab(s) u sed to d eterm in e th e appropriate sh a d e(s) for the p ro sth e sis. I f th e sh ad e tab is n ot an e x a c t m atch for th e natural to o th , in d icate h ow ch rom a, h u e, and v a lu e o f th e p o rcelain sh ould b e a d ju sted to obtain th e d esired sh ade m atch. □ S en d d ia g n o stic c a sts as v isu a l aids to in d i ca te th e lo ca tio n o f an y ch aracterizin g fea tu res, su ch as cra ck s, sta in s, or sim u lated resto ra tio n s. □ P ro v id e d raw ings to sh o w the d esired b o d y and in cisa l shade d istrib u tion s and th e lo ca tio n o f ch aracterizin g featu res n ot in d icated o n stu d y c a sts. □ A rrange to try in d ifficult restoration s b efo re the final g la ze is ap plied so that sh ad e ad ju stm ents can b e m ade b efo re th e in sertion date. S a n d b lasted sh ad e gu ide tabs w ill help in th e ev a lu a tio n o f the sh ad e m atch. □ E v a lu a te the a ccu ra cy w ith w h ich th e sh ad e p rescrip tion w as filled by the tech n icia n . D is c u s s the ev a lu a tio n w ith the tech n icia n .
REPORTS OF COUNCILS AND BUREAUS / JADA, Vol. 95, October 1977 ■ 819
■ In providing instructions to the labora tory
Avoiding high occlusion
Do
One of the principal complaints dentists have re garding fixed prostheses received from labora tories is the amount of occlusal adjustment re quired to restore centric occlusion. These com plaints occur even though restorations are re turned from the laboratory on an articulator in apparently perfect maxillomandibular relation ship. ■ In making impressions and occlusal reg istrations
□ Request master casts be mounted on adjust able articulators to enable refinement of occlusion in excursive movements (for a more refined ap proach see reference 4). □ Request the bisque bake restoration for try-in and occlusal adjustment. Do not
□ Allow the technician, without clearly de fined instructions, to adjust the occlusion by grinding tooth structure represented in oppo sing casts. ■ When seating the restoration
Do
Do
□ Make full-arch impressions. It is always dif ficult and sometimes impossible to align quadrant arch casts in centric occlusion. □ When taking lower impressions advise pa tients to maintain a minimal interarch distance after impression trays have been seated and while the impression material is setting (to prevent the production of lower casts with teeth occupying positions different than when the mandible is in rest position). Mandibular distortions occurring when the mouth is opened more than 28% of ca pacity can force mandibular teeth significantly out of the position that they normally occupy in cen tric.9
□ Make final adjustments before final cem entation. Do not
□ Use a cement mixture that is lumpy or too thick.
O btaining accurate-fitting restorations
D o not
■ To obtain proper marginal adaptation
□ Make impressions or occlusal registrations with materials that require exertion of forces that will push teeth out of their normal centric occlu sion positions. □ Allow the patient to bite or exert forces on the tray that might create internal stresses in the impression or move teeth out of their normal posi tions. ■ While structed
the
restoration
is
being
con
Do
□ Be sure the tooth preparation clearly defines the margins. □ Be sure impressions accurately record the margins. □ Recognize that margins in stone dies can be chipped when bur ditching is used to identify margin location. ■ To avoid distortion of impressions For all im pressions
Do
□ Place temporary restorations that incorpo rate edentulous areas and are in occlusion with opposing dentition. This will prevent proximal or occlusal shifting of teeth and stabilize the rela tionship and position of the dentition while the prosthesis is being constructed.
□ Customize all trays as much as possible to provide uniform space for the final impression material. □ Let acrylic resin custom trays cure for at least 24 hours before using them to take an im pression.
820 ■ REPORTS OF COUNCILS AND BUREAUS / JADA, Vol. 95, October 1977
□ Know the properties of the impression mate rials used. Materials appearing on the American Dental Association’s list of certified dental mate rials have specific physical requirements and handling characteristics. □ Follow the manufacturer’s instructions exactly. □ Have patients keep their mouths closed as much as possible while the impression material is setting (see page 820, “Avoiding high occlu sion,” the second item under “ In making im pressions and occlusal registrations” ). Do not
□ Use flexible trays. □ Remove from the mouth too soon.
Do not
□ Use impression material components in which ingredients exhibit separation or other signs of deterioration. T o obtain and m aintain accurate dies Do
□ Know the properties of the stone die mate rials used. The stone die materials appearing on the American Dental Association List of Cer tified Dental Materials have specific physical properties and handling characteristics. □ Be sure that the impression and die materials being used together are compatible. Do not
In handling agar and alginate im pression m ate rials Do
□ Pour impressions as soon as possible after removal from the mouth (no later than 15 min utes). These materials begin losing moisture through syneresis soon after setting. In the syneresis process, the gel contracts to force part of the liquid content to the surface of the impres sion. Dimensional changes accompanying the moisture loss cannot be prevented by storage in a saturated moisture environment. □ Check water temperature used for cooling agar impression before loading the tray. Water temperature during cooling should not be under 55° F.
□ Expose dies to water contact any longer than absolutely necessary after removal from the im pression. T o m aintain tooth relationships w hile restora tions are being constructed Do
□ Insert temporary restorations to restore all spaces and stabilize tooth position while the pros thesis is being constructed.
Avoiding porcelain fractures
In handling elastom eric im pression m aterials Do
□ Be sure each of the two materials used in a two-component single impression technique will set properly when proportioned and mixed ac cording to the instructions. □ In double impression techniques, relieve the initial impression to provide adequate space for final impression material. Inadequate space might create internal stresses in the tray material which would be released when the impression is with drawn causing distortion. □ In double impression techniques, bore holes through impression and tray materials to allow the final impression material to flow freely. This will help avoid overcompression which can contribute to distortion of the impression. □ Pour die material into the impression as soon after its removal from the mouth as possible.
■ When preparing abutm ent teeth and de signing the covering restorations Do
□ Adjust occlusion by selective grinding be fore tooth preparation to eliminate interferences that could apply undue stress during excursive movements. □ Remove tooth structure uniformly from the coronal surfaces of abutment teeth such that they will be contoured as miniatures of the original natural teeth. Porcelain can then be applied in uniform layers to minimize stress development during firing cycles. □ Reduce tooth structure to provide the re quired clearance for metal substructures strong enough to resist deformation under mastication forces.
REPORTS OF COUNCILS AND BUREAUS / JADA, Vol. 95, O ctober 1977 ■ 821
Do not
m etal su rface on ly.
□ D e sig n abutm ent restoration s to h ave sharp an gles at th e p orcelain -to-m etal ju n ction .
■ During postpreparation operations Do □ F o llo w su g g estio n s offered on page 820 u nder “ O btaining accurate-fitting re sto ra tio n s,” to en su re that o n ly m inim al seatin g fo rc es w ill be required. F o rcin g restoration s into p o sitio n m ay p rod u ce str e sse s w h ich w ill fracture p orcelain . □ F o llo w su g g estio n s o ffered on page 820 under “ A v o id in g high o c c lu s io n ,” to avoid e x c e s s iv e o c c lu sa l grinding w h ich m ight redu ce p orcelain th ic k n ess and th erefore strength.
■ Diagnosing causes of porcelain frac tures
Causes
— In co rrect d eg a ssin g o f m etal b y tech n icia n . — In co rrect p la cem en t o f m etal co n d itio n er by tech n icia n . □ F ractu re o f the m ajority o f th e p o rcela in fa c ing le a v in g slight am ount o f o p a q u e. Causes
— In co rrect p lacem en t o f m etal co n d itio n er by tech n icia n . — In co rrect firing o f op aq u e c o a t o f p o rcelain b y tech n icia n ; u sually the tem perature is to o lo w . — In a d eq u a te bulk o f m etal co n n ecto r. □ F ractu re o f p orcelain o n ly n o t ex p o sin g any m etal. Causes
W h en fracture or d islo d g em en t o f p orcelain fa c ing o cc u r s, the d en tist sh ould b e able to identify o n e o f the follo w in g apparent c a u se s o f th e failure and recom m en d ch an ges in future restoration s to th e appropriate person: □ F ractu re o f the total p orcelain facin g leaving
The Council appreciates the assistance of the following persons who helped in the preparation of this report: Nathan Ancer, CDT, Chicago; Frank Baasch, CDT and Blair Blase, CDT, both of Prairie View, III; Michael Bridge, CDT, Skokie, III; Capt. Gerald Eastwood, DC, USN, Great Lakes, III; Walter Gebhort, CDT, Chicago; Ted Gordon, DDS, CDT, Chicago; J. J. Harrington, DTC, USN, CDT, Great Lakes, III; Frank Hebert, CDT, Prairie View, III; Don Hesselgesser, CDT, Chicago; Eddie Jones, CDT, Fort Wayne, Ind; Ed ward Larsen, CDT, Chicago; Robert M. McConnell, CDT, American Dental Association, Chicago; Col. Wendell A. Meikle, DC, USN, Washington, DC; Joachim Nordt, CDT, Highland Park, III; Capt. Richard Prince, DC, USN, Great Lakes, III; Melvin Saxton, CDT, Chicago; Charles Schoenfeld, DDS, PhD, American Dental Associ ation, Chicago; Stanley Spiller, CDT, Chicago; Everett Starnes, CDT, Mt. Vernon, Ind; Edward Weaner, CDT, Chicago; Lance Wroblewski, CDT, and Stanley-Zygowicsz, CDT, both of Chicago.
— T raum a to cro w n s ca u se d b y o c c lu sio n or extern a l fo rce. — M eta l fram ew ork ca st to o sm all by th e te c h n ician . F ra m ew o rk s sh ould b e o n ly 1 m m to 1.5 m m le s s in co n to u r than the ev en tu a l cro w n or p o n tic.
1. Crown and bridge manual. Hartford, Conn, J. M. Ney Co., 1972, 139. 2. Tylman, S.D. Theory and practice of crown and fixed partial prosthodontics (bridge), ed 6. St. Louis, C. V. Mosby Co., 1970, p 1023. 3. Kornfeld, M. Mouth rehabilitation, voi 2. St. Louis, C. V. Mosby Co., 1974. 4. Dawson, P.E. Evaluation, diagnosis and treatment of occlusal problems. St. Louis, C. V. Mosby Co., 1974, p 133, 177. 5. Lemire, P.A., and Burk, B. Color in dentistry. Hartford, Conn, J. M. Ney Co., 1975. 6. Cornsweet, T.N. Visual perception. New York, Academic Press, 1970, p 135. 7. Subtractive color fixtures. New York, J. F. Jelenko and Co., 1976. 8. GE TP-119, Light and color. Cleveland, Lamp Business Div., General Electric Co., 1974. 9. Douglas, G.D. The cast restoration— why it is high. J Prosthet Dent 34:491 Nov 1975.
The Council on Dental Materials and Devices is interested in receiving your comments and suggestions on the information pre sented in its reports. Are the reports of use to you in your practice? Are reports of this nature beneficial to the dental profession? What general types of articles are most helpful? What format do you prefer? On what other topics would you like information published? Please send your comments to the Council on Dental Materials and Devices, 211 E Chicago Ave, Chicago, 60611.
822 ■ REPORTS OF COUNCILS AND BUREAUS / JADA, Vol. 95, October 1977
How to avoid problems with porcelain-fused-to-metal restorations
Council on Dental Materials and Devices
T h e p u rp ose o f this paper is to p rovid e a num ber o f recom m en d ation s as so lu tio n s to p rob lem s e n co u n tered w ith p orcelain -fu sed -to-m etal restora tio n s. T h e recom m en d ation s apply eq u ally to n o b le , p rec io u s, and b a se m atal sy ste m s. M an y o f th e se g u id elin es h a v e b een offered earlier a s so lu tio n s to p rob lem s w ith co n v en tio n a l gold allo y restoration s; h o w e v er , th ey are still ap p licab le to th e p o rcelain -fu sed -to-m etal sy ste m s. T h e fe w re fere n c es n o ted in this p aper are highly re co m m en d ed fo r m ore sp ecific inform ation.
Improving anatomical detail ■ To obtain optimum esthetic value
G u id elin es— O ptim um to o th red u ction fo r p re c io u s m etal restoration s is 1.5 m m . T h is a llo w s 0 .5 mm for m etal, ± 0 .2 m m fo r opaquing and ± 0 .8 m m for p orcela in . O ptim um to o th red u ction for b a se m etal restoration s is 1.3 m m . (F o r further inform ation, refer to re fere n c es 1-4.) □ P ro v id e the laboratory w ith d ia g n o stic c a s ts, or c o p ie s th ereo f, to b e u sed by the tec h n i cian as a referen ce visu a l aid o f p reo p era tiv e c o n d ition s during co n stru ctio n o f th e p ro sth esis. □ P ro v id e th e tech n icia n w ith d raw in gs, w h ere appropriate, o f an atom ical fea tu res that are not apparent o n th e stu d y c a sts. □ I f p o ssib le , h a v e restoration s returned from th e laboratory in th e b isq u e b ake form for try-in, final shaping, and o cc lu sa l adjustm ent. □ D eter m in e if th e an atom ic d etail on th e p ro s th esis is a ccu ra te. D is c u s s y o u r ev a lu a tio n w ith the laboratory tech n icia n .
Do □ M ak e full-arch d iagn ostic c a sts for b oth a rch es b efo re to o th preparation. □ U s e d ia g n o stic ca sts for trial w a x u p s, to o th arrangem ent sim u lations for p atien t ap p roval, and d isc u ssio n s w ith the laboratory ab ou t o p tio n s in restoration d esign . □ U n d erstan d the p h y sica l p rop erties o f ea ch p orcela in -to -m eta l sy stem p rescrib ed and o f th e restriction s im p osed on th e structural d e s ig n .1'3 B e sure th e tech n ician d e v e lo p s the sam e k n o w l ed g e. 818 ■ JADA, Vol. 95, October 1977
Improving shade matches
oo
■ G eneral T h e inform ation n e c e ssa r y to arrive at a near p erfect m atch o f ceram ic restoration sh a d es w ith natural teeth is p rob ably in clu d ed in th e literature o n c o lo r d iscrim ination p ra ctices. H o w e v e r ,
so m e o f th e essen tia l in form ation is q uite so p h is tica ted and has n ot y e t b een c o n d en sed for ea sy assim ilation b y d en tists and d en tal te c h n ic ia n s.5 8 S ev er a l fa cto rs related to su c c e ssfu l sh ad e m atch ing h a v e alread y b een id en tified and agreed on by m any w h o h a v e taken a sp ecia l in terest in d e v e l op ing reliab le sh ad e m a tch es. T h e fo llo w in g item s are p ra ctices y o u should co n sid er in attem p ting to a c h ie v e a true sh ade m atch.
■ In selecting shades Do □ U n d erstan d h ow eaich o f th e d im en sio n s o f co lo r en ters in to the se le c tio n , p rescrip tion , and d ev elo p m en t o f d esired sh a d e s.5'7 H u e refers to th e d ifferen t c o lo r fam ilies (red, b lu e, green , and so forth). C hrom a is the in ten sity or strength o f a g iv en h u e. V a lu e refers to a purity or saturation sc a le , th e am oun t o f gray in a color. □ F o r sh ad e d eterm in ation s, u se o ffic e lights w ith at le a st tw o k now n sp ectra, sin c e sh ad es appear d ifferen tly in d ifferen t ty p e s o f light e n v i ron m en ts. A d ayligh t sim u lated sp ectrum and an in d oor “ so ft ligh t” sp ectru m are g o o d c h o ic e s b e c a u se m ost p eo p le are freq u en tly in th e se ty p es o f ligh t en viron m en ts. M ajor re flec tiv e su rfaces, su ch as ceilin g s and w a lls, sh ou ld b e neutral w ith a M u n sell v a lu e o f se v en or eigh t (light gray) to av o id alteration o f the sp ectra. □ C om p are co lo r d iscrim ination cap ab ilities w ith th e tec h n icia n , th e d en tal a ssista n t, and at le a st three o th er p erson s k n ow n or e x p e c te d to h a v e “ n orm al” co lo r vision . □ E n cou rage p atients to w ea r o n ly natural sh ade c o s m e tic s to ap p oin tm en ts. M ask or re m o v e an y unnatural sh ade c o s m e tic s if th ey are w o rn , as th ey m ight interfere w ith sh ad e s e le c tion. □ O b ser v e and record the p a tien t’s e y e , hair, and skin colorin g b efore m aking sh ad e se lec tio n . □ U s e the sh ad e gu id e recom m en d ed for the p o rcelain b ein g u sed . I f ex te n d ed sh ad e gu id es m ade for oth er p rod ucts are u sed , b e sure the tech n ician u nd erstan ds their relation sh ip w ith the p o rcelain b ein g u sed . □ B e sure th e natural tee th and th e sh ad e guide tab are lightly m oisten ed w ith saliva. □ M ak e sev era l sh ade d eterm in ation s b efore to o th preparation. R ecord ea c h d eterm in ation sep a rately, w ith ou t referring to p rev io u s records. T h e final sh ad e se lec tio n sh ou ld b e b a sed on tw o or m ore earlier d eterm in ation s. I f th e d esired sh ade falls b e tw e e n tw o sh ade ta b s, c h o o s e the lighter sh ade. I f the sh ade is o ff, it w ill b e ea sier to
co rrect b y lo w tem perature staining than stripping and reapp lyin g p o rcelain to the castin g. □ O cca sio n a lly g la n ce at gray or green cardbord to p rev en t retinal c o lo r fa tig u e, w h ich resu lts in a lo ss o f co lo r a cu ity .
Do not □ E ntrust the sh a d e se le c tio n to an oth er p er so n u n le ss the co lo r p ercep tio n a cu ity o f the in d i vid ual has b een p ro v en to b e m ore reliable. □ U s e shade g u id es m ade for p la stic tee th , silica te ce m en ts, or oth er m aterials u nrelated to th e p orcelain being u sed . □ A ttem p t sh ade se le c tio n s u nder p oor ligh t ing co n d itio n s such as m ay e x ist on clo u d y d a y s, or w h en e y e s are fatigued.
■ In tooth preparation Do □ R ed u ce ab utm ent teeth su fficien tly to p ro v id e th e sp a ce for the m etal su bstru ctu re and fo r th e bulk o f p orcelain required to a ch ie v e the d e sired sh ade m atch w ith o u t o v erco n to u rin g th e cro w n s.
■ Communicating shade requirem ents to the dental technician Do □ In clu d e in the p rescrip tion su ch ch a ra cteris tics o f p atient as s e x , ag e, and hair, e y e , and skin co lo rs. □ S en d the dental tech n icia n the sh ade gu id e tab(s) u sed to d eterm in e th e appropriate sh a d e(s) for the p ro sth e sis. I f th e sh ad e tab is n ot an e x a c t m atch for th e natural to o th , in d icate h ow ch rom a, h u e, and v a lu e o f th e p o rcelain sh ould b e a d ju sted to obtain th e d esired sh ade m atch. □ S en d d ia g n o stic c a sts as v isu a l aids to in d i ca te th e lo ca tio n o f an y ch aracterizin g fea tu res, su ch as cra ck s, sta in s, or sim u lated resto ra tio n s. □ P ro v id e d raw ings to sh o w the d esired b o d y and in cisa l shade d istrib u tion s and th e lo ca tio n o f ch aracterizin g featu res n ot in d icated o n stu d y c a sts. □ A rrange to try in d ifficult restoration s b efo re the final g la ze is ap plied so that sh ad e ad ju stm ents can b e m ade b efo re th e in sertion date. S a n d b lasted sh ad e gu ide tabs w ill help in th e ev a lu a tio n o f the sh ad e m atch. □ E v a lu a te the a ccu ra cy w ith w h ich th e sh ad e p rescrip tion w as filled by the tech n icia n . D is c u s s the ev a lu a tio n w ith the tech n icia n .
REPORTS OF COUNCILS AND BUREAUS / JADA, Vol. 95, October 1977 ■ 819
■ In providing instructions to the labora tory
Avoiding high occlusion
Do
One of the principal complaints dentists have re garding fixed prostheses received from labora tories is the amount of occlusal adjustment re quired to restore centric occlusion. These com plaints occur even though restorations are re turned from the laboratory on an articulator in apparently perfect maxillomandibular relation ship. ■ In making impressions and occlusal reg istrations
□ Request master casts be mounted on adjust able articulators to enable refinement of occlusion in excursive movements (for a more refined ap proach see reference 4). □ Request the bisque bake restoration for try-in and occlusal adjustment. Do not
□ Allow the technician, without clearly de fined instructions, to adjust the occlusion by grinding tooth structure represented in oppo sing casts. ■ When seating the restoration
Do
Do
□ Make full-arch impressions. It is always dif ficult and sometimes impossible to align quadrant arch casts in centric occlusion. □ When taking lower impressions advise pa tients to maintain a minimal interarch distance after impression trays have been seated and while the impression material is setting (to prevent the production of lower casts with teeth occupying positions different than when the mandible is in rest position). Mandibular distortions occurring when the mouth is opened more than 28% of ca pacity can force mandibular teeth significantly out of the position that they normally occupy in cen tric.9
□ Make final adjustments before final cem entation. Do not
□ Use a cement mixture that is lumpy or too thick.
O btaining accurate-fitting restorations
D o not
■ To obtain proper marginal adaptation
□ Make impressions or occlusal registrations with materials that require exertion of forces that will push teeth out of their normal centric occlu sion positions. □ Allow the patient to bite or exert forces on the tray that might create internal stresses in the impression or move teeth out of their normal posi tions. ■ While structed
the
restoration
is
being
con
Do
□ Be sure the tooth preparation clearly defines the margins. □ Be sure impressions accurately record the margins. □ Recognize that margins in stone dies can be chipped when bur ditching is used to identify margin location. ■ To avoid distortion of impressions For all im pressions
Do
□ Place temporary restorations that incorpo rate edentulous areas and are in occlusion with opposing dentition. This will prevent proximal or occlusal shifting of teeth and stabilize the rela tionship and position of the dentition while the prosthesis is being constructed.
□ Customize all trays as much as possible to provide uniform space for the final impression material. □ Let acrylic resin custom trays cure for at least 24 hours before using them to take an im pression.
820 ■ REPORTS OF COUNCILS AND BUREAUS / JADA, Vol. 95, October 1977
□ Know the properties of the impression mate rials used. Materials appearing on the American Dental Association’s list of certified dental mate rials have specific physical requirements and handling characteristics. □ Follow the manufacturer’s instructions exactly. □ Have patients keep their mouths closed as much as possible while the impression material is setting (see page 820, “Avoiding high occlu sion,” the second item under “ In making im pressions and occlusal registrations” ). Do not
□ Use flexible trays. □ Remove from the mouth too soon.
Do not
□ Use impression material components in which ingredients exhibit separation or other signs of deterioration. T o obtain and m aintain accurate dies Do
□ Know the properties of the stone die mate rials used. The stone die materials appearing on the American Dental Association List of Cer tified Dental Materials have specific physical properties and handling characteristics. □ Be sure that the impression and die materials being used together are compatible. Do not
In handling agar and alginate im pression m ate rials Do
□ Pour impressions as soon as possible after removal from the mouth (no later than 15 min utes). These materials begin losing moisture through syneresis soon after setting. In the syneresis process, the gel contracts to force part of the liquid content to the surface of the impres sion. Dimensional changes accompanying the moisture loss cannot be prevented by storage in a saturated moisture environment. □ Check water temperature used for cooling agar impression before loading the tray. Water temperature during cooling should not be under 55° F.
□ Expose dies to water contact any longer than absolutely necessary after removal from the im pression. T o m aintain tooth relationships w hile restora tions are being constructed Do
□ Insert temporary restorations to restore all spaces and stabilize tooth position while the pros thesis is being constructed.
Avoiding porcelain fractures
In handling elastom eric im pression m aterials Do
□ Be sure each of the two materials used in a two-component single impression technique will set properly when proportioned and mixed ac cording to the instructions. □ In double impression techniques, relieve the initial impression to provide adequate space for final impression material. Inadequate space might create internal stresses in the tray material which would be released when the impression is with drawn causing distortion. □ In double impression techniques, bore holes through impression and tray materials to allow the final impression material to flow freely. This will help avoid overcompression which can contribute to distortion of the impression. □ Pour die material into the impression as soon after its removal from the mouth as possible.
■ When preparing abutm ent teeth and de signing the covering restorations Do
□ Adjust occlusion by selective grinding be fore tooth preparation to eliminate interferences that could apply undue stress during excursive movements. □ Remove tooth structure uniformly from the coronal surfaces of abutment teeth such that they will be contoured as miniatures of the original natural teeth. Porcelain can then be applied in uniform layers to minimize stress development during firing cycles. □ Reduce tooth structure to provide the re quired clearance for metal substructures strong enough to resist deformation under mastication forces.
REPORTS OF COUNCILS AND BUREAUS / JADA, Vol. 95, O ctober 1977 ■ 821
Do not
m etal su rface on ly.
□ D e sig n abutm ent restoration s to h ave sharp an gles at th e p orcelain -to-m etal ju n ction .
■ During postpreparation operations Do □ F o llo w su g g estio n s offered on page 820 u nder “ O btaining accurate-fitting re sto ra tio n s,” to en su re that o n ly m inim al seatin g fo rc es w ill be required. F o rcin g restoration s into p o sitio n m ay p rod u ce str e sse s w h ich w ill fracture p orcelain . □ F o llo w su g g estio n s o ffered on page 820 under “ A v o id in g high o c c lu s io n ,” to avoid e x c e s s iv e o c c lu sa l grinding w h ich m ight redu ce p orcelain th ic k n ess and th erefore strength.
■ Diagnosing causes of porcelain frac tures
Causes
— In co rrect d eg a ssin g o f m etal b y tech n icia n . — In co rrect p la cem en t o f m etal co n d itio n er by tech n icia n . □ F ractu re o f the m ajority o f th e p o rcela in fa c ing le a v in g slight am ount o f o p a q u e. Causes
— In co rrect p lacem en t o f m etal co n d itio n er by tech n icia n . — In co rrect firing o f op aq u e c o a t o f p o rcelain b y tech n icia n ; u sually the tem perature is to o lo w . — In a d eq u a te bulk o f m etal co n n ecto r. □ F ractu re o f p orcelain o n ly n o t ex p o sin g any m etal. Causes
W h en fracture or d islo d g em en t o f p orcelain fa c ing o cc u r s, the d en tist sh ould b e able to identify o n e o f the follo w in g apparent c a u se s o f th e failure and recom m en d ch an ges in future restoration s to th e appropriate person: □ F ractu re o f the total p orcelain facin g leaving
The Council appreciates the assistance of the following persons who helped in the preparation of this report: Nathan Ancer, CDT, Chicago; Frank Baasch, CDT and Blair Blase, CDT, both of Prairie View, III; Michael Bridge, CDT, Skokie, III; Capt. Gerald Eastwood, DC, USN, Great Lakes, III; Walter Gebhort, CDT, Chicago; Ted Gordon, DDS, CDT, Chicago; J. J. Harrington, DTC, USN, CDT, Great Lakes, III; Frank Hebert, CDT, Prairie View, III; Don Hesselgesser, CDT, Chicago; Eddie Jones, CDT, Fort Wayne, Ind; Ed ward Larsen, CDT, Chicago; Robert M. McConnell, CDT, American Dental Association, Chicago; Col. Wendell A. Meikle, DC, USN, Washington, DC; Joachim Nordt, CDT, Highland Park, III; Capt. Richard Prince, DC, USN, Great Lakes, III; Melvin Saxton, CDT, Chicago; Charles Schoenfeld, DDS, PhD, American Dental Associ ation, Chicago; Stanley Spiller, CDT, Chicago; Everett Starnes, CDT, Mt. Vernon, Ind; Edward Weaner, CDT, Chicago; Lance Wroblewski, CDT, and Stanley-Zygowicsz, CDT, both of Chicago.
— T raum a to cro w n s ca u se d b y o c c lu sio n or extern a l fo rce. — M eta l fram ew ork ca st to o sm all by th e te c h n ician . F ra m ew o rk s sh ould b e o n ly 1 m m to 1.5 m m le s s in co n to u r than the ev en tu a l cro w n or p o n tic.
1. Crown and bridge manual. Hartford, Conn, J. M. Ney Co., 1972, 139. 2. Tylman, S.D. Theory and practice of crown and fixed partial prosthodontics (bridge), ed 6. St. Louis, C. V. Mosby Co., 1970, p 1023. 3. Kornfeld, M. Mouth rehabilitation, voi 2. St. Louis, C. V. Mosby Co., 1974. 4. Dawson, P.E. Evaluation, diagnosis and treatment of occlusal problems. St. Louis, C. V. Mosby Co., 1974, p 133, 177. 5. Lemire, P.A., and Burk, B. Color in dentistry. Hartford, Conn, J. M. Ney Co., 1975. 6. Cornsweet, T.N. Visual perception. New York, Academic Press, 1970, p 135. 7. Subtractive color fixtures. New York, J. F. Jelenko and Co., 1976. 8. GE TP-119, Light and color. Cleveland, Lamp Business Div., General Electric Co., 1974. 9. Douglas, G.D. The cast restoration— why it is high. J Prosthet Dent 34:491 Nov 1975.
The Council on Dental Materials and Devices is interested in receiving your comments and suggestions on the information pre sented in its reports. Are the reports of use to you in your practice? Are reports of this nature beneficial to the dental profession? What general types of articles are most helpful? What format do you prefer? On what other topics would you like information published? Please send your comments to the Council on Dental Materials and Devices, 211 E Chicago Ave, Chicago, 60611.
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