Patients who present with resection of the mandible or maxilla pose some challenging and complex partial denture design problems. The objective is to design and RPD which effectively retains the obturator prosthesis without subjecting the abutment teeth to pathologic stress which may limit their lifespan.   This program of instruction reviews the basic principles of partial denture design as they apply to these unique defects.

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Maxillofacial Prosthetics – Maxillofacial Defects and RPD Design — Course Transcript

  • 1. Principles of RPD Design in Patients with Defects of the Maxilla and Mandible John Beumer III DDS, MS Division of Advanced Prosthodontics, Biomaterials, and Hospital DentistryThis program of instruction is protected by copyright ©. No portion ofthis program of instruction may be reproduced, recorded or transferredby any means electronic, digital, photographic, mechanical etc., or byany information storage or retrieval system, without prior permission.
  • 2. Principles of RPD designv Major connectors must be rigid.v Occlusal rest must direct occlusal forces along the long axis of the teeth.v Guide planes are employed to enhance stability and bracing.v Retention must be within the limits of physiologic tolerance of the periodontal ligament.v Maximum support is gained from the adjacent soft tissue denture bearing surfaces.v Designs must consider the needs of cleansibility.
  • 3. Maxillary DefectsProblems complicating RPD design v Multiple axis of rotation v Compromised support on the defect side v Lack of cross arch stabilization because of the loss of palatal structures on one side v Long lever arms v Forces of gravity become more significant
  • 4. Movement of the prosthesis and the length of the lever armv Potential exists for substantial movement as compared to the normal patients.v Length of lever arms are much greater than seen in conventional prosthodontics. Clinical significance: There is greater risk of overloading abutment teeth with inappropriate partial denture designs.
  • 5. Preservation of teethv RPDdesigns must anticipate and accommodate the movements of the prosthesis during function, without exerting pathologic stresses on the abutment teeth. Clinical significance: If the RPD designs do not conform to this idea there is risk that abutment teeth may be overloaded leading to their premature loss.
  • 6. Multiple axis of rotationFulcrum lines are dynamic and once the sites ofocclusal rests are selected, the axis of rotation isdependent upon the site of load application Load #1 – Fulcrum line A – B Load #2 – Fulcrum line C – D Load #3 – Fulcrum line E – F
  • 7. Abutments adjacent to the defectThese teeth are subject to more vertical and lateralforces and are more frequently lost thanabutments in other positions. Why? v The defect offers little support. v The long lever arms magnify the occlusal forcesClinical significance: Design and position of rests on these teeth mustdirect forces along the long axis of the teeth. In some patientssplinting these teeth to adjacent teeth may be useful; in others it is bestto use these teeth as overdenture abutements.
  • 8. Abutments adjacent to the defect v Rest position and contourThese rests all have one factor in common – they permitengagement of the tooth in a “positive” manner anddirect occlusal forces along the long axis of the tooth.
  • 9. Rest position and contours v Incisal rests are contraindicated on teeth adjacent to the defect. In this patient the incisal rest on the cuspid will disengage when an occlusal force is applied posteriorly
  • 10. Rest position and contoursAnterior teethadjacent to thedefect must have“positive”cingulum rests.
  • 11. Rest position and contours v Incisors – Splinting and cingulum rests. We recommend that incisors adjacent to the defect be splinted together with full veneer crowns and cingulum rests be developed within their contours. Note hygiene access
  • 12. Bolus manipulation v Patients soon learn to confine the bolus on the dentate side but they will incise on the defect side. Therefore, in most radical maxillectomy defects, clinically the most significant axis of rotation will be similar to the C-D axis seen in this defect. However, in this patient the A-B axis is the most important.
  • 13. Retainersv “I” bars are almost always used on the abutment tooth adjacent to the defect. Why?vMaximum natural cleansing vMinimal tooth contactaction vExact placement of retentionvPassive functional contactmovement of an extension vMinimal Interference withprosthesis natural tooth contourvBetter esthetics
  • 14. Retainersv “Suprabulge retainers are used posteriorly Why? •Better bracing (stability) provided by this type of retainer.
  • 15. Stability and Bracing v Lingualplate v Suprabulge retainersMore bracing isrequired in maxillaryresection defects andso suprabulgeretainers are use onposterior teeth andlingual plating isfrequently employed.
  • 16. Support – Palatal shelf area availableOne of these patients had a favorable defect and ample palatalshelf area. The other does not. Partial denture designs can beconservative for the patient on the left. Little bracing isrequired and fewer retainers are necessary. The oppositewould true for patient on the right – more retainers and morebracing are required.
  • 17. Master Impressionsv Impressions for the RPD framework v Stock tray with reversible hydrocolloidv Altered cast impressions of the defect v Bordermolding with dental compound v Wash impression materials vElastic materials vs thermoplastic wax
  • 18. Clinical proceduresv Impression for the RPD frameworkv Physiologic adjustment of partial denture frameworkv Altered cast impressions of the defectv Centric relation recordsv Trial denturesv Processingv Delivery and followup
  • 19. Master Impresssions Impressions for RPD frameworksA stock tray is used. Periphery wax is used to extendthe tray into the defect and onto the soft palate.Undercuts on themedial side of thedefect should beblocked out.Otherwise theresidual palatal The completed impressioncontours will be records the contours ofdistorted upon residual tissues, dentition,remmoval of the tray. and the defect
  • 20. Master cast and RPD framework
  • 21. Verify and physiologically adjust the RPD frameworkFramework try-in appointment:a) Verify accuracy of fitb) Physiologically adjust frameworkc) Occlusal adjustment of framework
  • 22. Physiologic adjustment of RPD frameworksRouge and chloroform is still themost effective means. Guideplanes and minor connectors Note where the rouge hasshould be carefully evaluated. been rubbed away from the distal guide plane (arrow). This area needs adjustment. Silicone type indicatorsare effective, but muchmore expensive.
  • 23. Physiologic adjustment of partial denture frameworks Another framework. Note the areas in need of adjustment (arrows). Adjustments are made with a high speed air rotor.
  • 24. Completed RPD with ObturatorSpeech and swallowing are restored to normal and masticationcan be accomplished effectively on the unresected side.
  • 25. Completed RPD with Obturator
  • 26. a c d Completed RPD – Obturator
  • 27. Completed RPD – Obturator
  • 28. Completed RPD – Obturators
  • 29. Completed RPD – Obturator
  • 30. Completed RPD – Obturators
  • 31. Completed RPD – Obturators
  • 32. Completed RPD – Obturators
  • 33. c Completed RPD – Obturators
  • 34. Mandibulectomy DefectsProblems regarding RPD design v Compromised support v Unilateral forces of occlusion v Angular path of closure tends to displace the prosthesis laterally towards the defect side. v Frontal plane rotation
  • 35. RPD design – Lateral discontinuity defectsvStability (bracing), resistance to displacement towards theresected side as a consequence of the angular path of closure,is enhanced by the lingual plate and the “I” bar.vBracing can be enhanced by adding an extra retainer toengage the first premolar. This retainer should not be in anundercut.
  • 36. RPD design – Lateral discontinuity defectsSupport is maximized by covering the retromolar padand extending onto the buccal shelf. Theseextensions are best refined with an altered castimpression.
  • 37. RPD designs Lateral discontinuity defectsDouble “I” bars and thepolished surface of thedenture on the nonresectedside prevent the prosthesisfrom being displaced laterallytowards the defect sideduring mastication.
  • 38. RPD designs – Lateral discontinuity defects v Physiologic adjustment Numerous studies have shown that occlusal forces are distributed more favorably to abutment teeth when RPD castings are physiologically adjusted.
  • 39. RPD designs – Lateral discontinuity defects Altered cast impressions l Note the contours of the polished lingual surface. The lingual flange on the resected side enhances stability. Maximal development of this extension, plus an accurate imprint of the imprint of the tongue on the polished surface should be made when making the altered cast impression.
  • 40. Patient is status post composite resection for acarcinoma of the right tonsil. The tonsillar bed was reconstructed with a myocutaneous flap. Tongue bulk and mobility were close to normal.The remaining anterior teeth were restored with PFM’s withcingulum rests. The premolar was also restored with a PFMand a rest was placed on the mesial.
  • 41. Altered cast impressions were madeOcclusion: Cusp angles of the maxilla are flattened and the central fossarounded out. The mandibular buccal cusps engage the central fossa ofthe maxillary teeth – a variation of the “lingualized” concept.
  • 42. Completed and inserted restoration Note flattened cusp angles and rounded central fossa Note the frontal plane rotation
  • 43. Restored lateral defects Partial denture design – Lateral defects where continuity has been retained or restoredNote the multiple axis of Patients tend to use therotation. The axis depends dentate side forupon the point of load mastication.application.
  • 44. BracingPatients with unilateraldentition and largeedentulous spaces suchas in this case, requireadditional bracing. Here,in addition to the bracingeffect of the proximalplates on the 2nd molarand the 1st premolar,bracing is provided byplating the lingualsurfaces of the remainingdentition.
  • 45. Restored lateral defects Purpose of the prosthesis l Lip support and esthetics l Prevent maxillary teeth from supererupting
  • 46. Restored lateral discontinuity defects
  • 47. Restored lateral discontinuity defects
  • 48. Completed RPD
  • 49. Anterior defectsContinuity was restoredwith a free graft. Continuity was maintained and a skin graftContinuity was retained and the used to resurface the exposed mandiblewound was closed primarily in these two patients The primary deficiency is the lack of support in the anterior extension area. The anterior extension of the prosthesis restores lip contours, and lip seal rather than facilitating mastication.
  • 50. Anterior defectsl Partial denture design – Anterior defects Axis of rotation
  • 51. Anterior defectsNote distal rests and mesial guide planes
  • 52. l Completed prosthesis. Its primary benefit isLack of support anteriorly.
  • 53. a b c d l Completed RPD
  • 54. Principles of RPD designv Occlusal rest must direct occlusal forces along the long axis of the teeth.v Major connectors must be rigid.v Guide planes are employed to enhance stability and bracing.v Retention must be within the limits of physiologic tolerance of the periodontal ligament.v Maximum support is gained from the adjacent soft tissue denture bearing surfaces.v Designs must consider the needs of cleansibility.
  • 55. v Visit ffofr.org for hundreds of additional lectures on Complete Dentures, Implant Dentistry, Removable Partial Dentures, Esthetic Dentistry and Maxillofacial Prosthetics.v The lectures are free.v Our objective is to create the best and most comprehensive online programs of instruction in Prosthodontics