Partial veneer crown preparation

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Partial veneer crown preparation

  1. 1. THE PARTIAL VENEER CROWN, INLAY AND ONLAY PREPARATIONS *summarized from Contemporary Fixed Prosthodontics/lec note (POSTERIOR) PARTIAL VENEER CROWN PREPARATIONS a. max premolar ¾ c b. max molar ¾ c c. man ¾ d. max premolar 7/8 c e. modification of ¾ c - mand premolar modified ¾ c (reversed ¾ c) - proximal ½ crown - ¾ c with promixal boxes A. MAX PREMOLAR ¾ CROWN - preserve buccal surface - preparation refer page 289 (fig 10-3) & page 315 (summary) indications 1. strong clinical crown of average length or longer contraindications 1. short teeth 2. high caries index 2. intact buccal surface not in 3. extensive destruction need of contour modification and well supported by sound 4. poor alignment tooth structure 5. bulbous teeth 3. no conflict between axial 6. thin teeth relationship of tooth & proposed p.o.p 7. retainers for long 4. restore posterior teeth that span FDPs have lost moderate amounts of tooth struc 5. use as retainers for FDP advantages disadvantages 1. conservative 1. less retentive 2. easy access to margins 2. limited adjustment of path of withdrawal 3. less gingival involvement than complete cast crown 4. easy escape of cement and good seating 5. verification of seating simple 6. electric vitality test can be done 7. less pulpal & periodontal insult 8. easy access to supragingival margin 9. easy access to oral hygiene PREPARATIONS : 1) occlusal reduction : 1. func cusp – 1.5mm non-func cusp/central groove – 1mm * (both should less 0.2mm – for finishing) 2. place depth of groove - use tapered carbide/ narrow diamond 3. verify groove depth with periodontal probe 4. assess amount of occlusal reduction by ; - max intercuspation - all excursive movement of mandible 2) axial reduction : 1. place grooves for axial alignment at ; - center of lingual surface - mesioling & distoling line angles 2. assess groove by probe 3. remove tooth struc 4. place cervical chamfer 5. reduce proximal wall 6. resulting flange must // to linguoaxial preparation 7. place chamfer cervically ; - to provide 0.6mm of clearance with adj tooth & axial wall - allowing prox groove 4mm occlusocervically 8. common error ; - incline the p.o.p towards buccal - this reduces retention 3. some display of metal
  2. 2. - leads to excessive metal display 9. prox groove should // to p.o.p 10. place flare on buccal side of groove ; - to remove unsupported tooth struc 3) groove placement : 1. use tapered carbide bur 2. position bur against interproximal flange // to p.o.p 3. make groove perpendicular to axial surface 4. ideal criteria for groove ; - resist lingual displacement of probe - wall of grooves no undercut - walls should be flared buccally 5. remove last lip of unsupported tooth struc with a chisel - minimize risk of damage of adjacent tooth 4) bucco-occlusal contrabevel : 1. is a connection of mesial & distal flares 2. follow buccal cusp ridges 3. use diamond/carbide bur 4. aim – remove unsupported enamel - protect buccal cusp tip from chipping 5. place heavier bevel/chamfer/occusal offset if require multiple functions 6. if bevel is placed ; - should remain within curvature of cusp tip rather than extend onto buccal wall 5) occlusal offset : 1. aim – for additional bulk to ensure rigidity of restoration - for struc durability of ant partial veneer crown 2. v-shaped groove from proximal grooves along buccal cusp 3. use carbide bur 4. width – 1mm wide ledge 6) finishing : 1. round all sharp line angles 2. use fine-grit diamond/carbide 3. reevaluate flares ; - no undercut - should be straight - smooth - sufficient clearance between flares n adjacent tooth (min : 0.6mm) - dont extend mesial flare beyond transitional line angle
  3. 3. B. MAX MOLAR ¾ CROWN 1. same as premolar preparation except : a. some additional leeway may exist for groove placement because ; - more tooth struc on molars than premolars - molars less prominent/less visible in dental arch C. MAN ¾ CROWN - refer note doc 1. 2. 3. 4. 5. 6. occlusal reduction func cusp bevel occlusal shoulder axial reduction prox grooves prox flare D. MAX MOLAR 7/8 CROWN - refer page 294 (fig 10-17) Functions : 1. proximal groove - retention & resistance - struc durability 2. occlusal reduction - struc drability 3. axial reduction - retention & resistance - struc durability - periodontal preservation 4.func cusp bevel - struc durability 5. occlusal offset - struc durability 6. proximal flare - marginal integrity 7. facial finishing bevel - marginal integrity
  4. 4. MODIFICATION OF POST ¾ CROWN a. mand premolar modified ¾ c b. proximal ½ c c. ¾ crown with proximal box A. MAND PREMOLAR MODIFIED ¾ CROWN - aka reversed ¾ crown - more often on premolars than molars - preserves lingual surface - differs from max molar ¾ crown in 2 aspects : * require additional retention as mand teeth have shorter crown * axial surface that is not prepared include func cusp - grooves at lingual side of proximal surfaces indications 1. to restore mand molars with damaged buccal surfaces and intact lingual surfaces 2. used in teeth with severe lingual inclination which are to be used as bridge abutments PREPARATIONS : 1) occlusial reduction 1. place 0.8mm depth grooves ; - on buccal inclines of ling cusp (non-func cusp) place 1.3mm grooves ; - on ling inclines of buccal cusp (func-cusp) 2. reduce occlusal surface 2) axial reduction 1. place grooves on lingual surface - // to p.o.p and long axis of tooth 2. prepare mesial half 3. reduce distal surface 4. chamfer finish line dont extend too far cervically - unnecessarily reduced distobuccal line angle - decrease resistance form 3) finishing 1. place mesial & buccal groove 2. place distal groove 3. place mesial flare 4. connect mesial & buccal grooves with heavy chamfer func cusp - allow 1.5mm occlusal clearance 5. common error - when chamfer meets mesial flare B. PROXIMAL HALF CROWN 1. 2. 3. it is a ¾ crown which has been rotated 90 degrees distal surface rather than buccal surface has been left intact indicated in mesial tilted tooth C. ¾ CROWN WITH PROXIMAL BOXES 1. 2. has 30% more retention than standard preparation with grooves indications - when max premolar less than optimal length is to be used as a bridge
  5. 5. (ANTERIOR) PARTIAL VENEER CROWN PREPARATIONS - refer page 317 (summary) indications contraindication advantages disadvantages 1. strong clinical crown of average length or longer 1. short teeth 1. conservative of tooth struc 1. less retentive 2. non-vital teeth 2. easy access to margins for finishing 2. llimited adjustment of p.o.p 2. intact labial surface which - not need contour modification - supported by sound tooth struc 3. no disrepancy between axial relationship of tooth and proposed p.o.p of FDP 3. high caries index 4. extensive destruction 3. some display of metal 3. less gingival involvement 4. not indicated on non-vital 4. easy escape of cement and teeth 5. poor alignment with p.o.w of good seating FDP 5. easy verification of complete 6. cervical caries seating 7. bulbous teeth 6. electrical vitality can be done 8. thin teeth A. MAX CANINE ¾ CROWN - involves proximal and lingua surfaces - leaves facial surface intact - refer page 230 (fig 10-24) PREPARATIONS : 1) incisal & lingual reduction 1. remove enough enamel - to allow 1mm of metal thickness 2. design of incisal bevel - should prevent contact between opposing teeth & incisal margin 3. preserve original configuration of facial surface 4. place depth groove for both incisal bevel & lingual reduction - makes 45 degrees with long axis of tooth 5. use football/wheel-shaped diamond 6. ligual reduction should not extend onto cingulum 2) axial reduction & groove placement 1. determine p.o.p first 2. mesiodistally - should // to long axis of tooth 3. buccolingually - should // to middle 1/3 or incisal 2/3 of facial surface 4. place slightly exaggerated chamfer on ligual aspect & guiding groove in the middle of lingual wall - enhance retention & resistance 5. resulting in proximal flange 6. place proximal flares 3) incisal offset & lingual pinhole 1. means of reinforcement for preserving casting's integrity 2. incisal offset is a connection of mesial & distal grooves - resistance against lingual displacement - v-shaped - has sufficient dentin to prevent metal display - should follow normal configuration of incisal edge - transition into procimal flares should be smooth & continuous - use inverted-cone diamond/carbide 3. pinhole - in cingulum area - improve retention 7 resistance form - prepared in 5 stages - flares common area for undercut
  6. 6. B. PINLEDGE PREPARATIONS MAX CENTRAL INCISOR PINLEDGE - refer page 303 (fig 10-34) indications contraindications advantages disadvantages 1. undamaged anterior teeth in caries-free mouth 1. large pulps 1. minimal tooth reduction 2. thin teeth 2. min margin length 1. less retentive than complete cas crown 3. nonvital teeth 3. min gingival involvement 4. carious involvement 4. optimum access for margin finishing and hygiene 2. to modify of lingual contour of max ant teeth or modification of occlusion 3. ant splinting 4. low caries activity 5. labial surface remains intact 6. bulbous teeth 1. 2. 3. 4. 5. 6. 7. 5. probs with proposed p.o.p of FDP 5. adequate retention 6. poor oral hygiene 7. when optimum retention is needed used as single restoration only lingual surface is prepared used as retainer for FDP use to splint periodontally compromised teeth pin extend to a depth of 2mm into dentin - to provide retention & resistance highly esthetic restorations easier plaque control due to - short margin length - largely supragingival margin location 2. alignment can prove difficult 3. technically demanding 4. not usable on nonvital teeth
  7. 7. INLAYS & ONLAYS CLASS II INLAY PREPARATION - refer page 319 (summary) indications contraindications advantages disadvantages 1. small carious lesion in otherwise sound tooth 1. high caries indiex 1. superior material properties 2. poor plaque control 2. longevity 1. less conservative than amalgam 3. small teeth 3. no discoloration from corrosion 2. adequate dentinal support 3. low caries rate 4. patients's request for gold instead of amalgam or composite resin 4. adolescents 5. MOD restorations 4. least complex cast restoration 2. may display metal 3. gingival extension beyond ideal 4. wedge retention 6. poor dentinal support necessitating a wide preparation PREPARATIONS : 1) occlusal analysis 1. assess occlusal contact relationship 2. margin of restoration not too close to a centric contact - avoid damaging stresses at gold-ename junction 3. apply rubber dam - good visibility & moisture control are essential during tooth preparation & caries excavation 2) outline form 1. penetrate central groove - just to a depth of dentin - about 1.8mm - use small round/tapered carbide - // to p.o.p 2. extend occlusal outline through central groove - use tapered carbide - bur // to p.o.p 3. depth – just into dentin (1.8mm) 4. buccolingual width - should be conservative 5. make dovetail or pinhole on the proximal - for resistance to proximal displacement 6. extend outline proximally - undermining the marginal ridge - stop at height of contour of ridge 7. make proximal box - advance bur cervically to carious lesion - then lingually and buccally - bur should // to original unprepared prox surface - create convex axial wall in the box - width of gingival floor of box ; 1mm mesiodistally 8. completed inlay will require min of 0.6mm of prox clearance - to allow impression to be made - also can make prox flares & gingival bevels 9. round the sharp line angles 3) axiogingival groove & bevel placement 1. prepare small, well-defined groove at junc of axial & gingival walls at the base of prox box - to enhance resistance form - prevent distortion of wax pattern during manipulation 2. place 45 degrees gingival margin bevel - use thin, tapered carbide/fine-grit diamond - hold instrument // to gingival 1/3 of prox surface of adjacent tooth - bur not tilting bucally & lingually to p.o.p to avoid undercut 3. prepare proximal bevels on the bucall & lingual walls - use tapered bur 4. place occlusal bevel - to improve marginal fit - allow finishing
  8. 8. 5. smoth the preparation MESIO-OCCLUSAL DISTAL (MOD) ONLAY PREPARATION - same as inlay preparation but has 2 additional steps ; a. occlusal reduction b. func cusp ledge - refer page 321 (summary) indications contraindications 1. worn or carious teeth 2. 1. high caries index intact buccal & lingual cusps 2. poor plaque control 3. MOD amalgam requiring 3. short clinical crown replacement 4. extruded teeth 4. low carues rate 5. patients's request for gold instead of amalgam advantages disadvantages 1. support of cusps 1. lacks retention 2. high strength 2. less consrvative than amalgam 3. longevity 3. may display metal 4. gingival extension beyond ideal 5. lesions extending beyong transitional line angles PREPARATIONS : 1) outline form 1. prepare occlusal outline - use tapered carbide bur - 1.8mm deep 2. remove existing amalgam restorations 3. extend outline mesially & distally to the height of contour of marginal ridge 4. place MOD boxes - by advancing bur gingivally then bucally & lingually - leave thin section of enamel to prevent damage to adjacent tooth 5. make min clearance of 0.6mm 6. round sharp line angles 2) Caries excavation 1. remove any remaining caries - use excavator/round bur - low-speed handpiece 2. place cement base - to restore excavated tissue 3) occlusal reduction 1. place depth grooves on func cusps - 1.3mm deep - allow 0.2mm for smoothing 2. place depth grooves on non-func cusps - 0.8mm deep - allow 0.2mm for smoothing 3. connect grooves to form occlusal reduction 4) functional cusp ledge 1. prepare 1.0mm func cusp ledge - use cylindrical carbide bur - to give restoration bulk in a high-stress area - to prevent deformation during function 2. ledge should be placed 1mm apical to opposing centric contacts 3. ledge extends into proximal boxes 4. round any sharp line angles 5) margin placement 1. make bevel on all margins - must be smooth & continuous 2. place gingival bevel - use thin carbide/diamond - 45 degrees to p.o.p 3. bevel the non-func & func cusps - to give additional bulk at the margin 4. recheck occlusal clearance 5. smoothening pae.

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