BDS8228 Clinical partial prosthodontics- Principles of partial denture design and problems.__958b8fceb3bc7ff7c26e7ded30c16601.pdf

NEWGIZA UNIVERSITY BDS8228 Clinical partial prosthodontics: Principles of partial denture design and problems. Date:2023 NEWGIZA UNIVERSITY Aims The educational aims of this lecture are: • To explain the principles of partial denture design • To detail the problems related to the design of the...

NEWGIZA UNIVERSITY BDS8228 Clinical partial prosthodontics: Principles of partial denture design and problems. Date:2023 NEWGIZA UNIVERSITY Aims The educational aims of this lecture are: • To explain the principles of partial denture design • To detail the problems related to the design of the partial denture Objectives On completion of this lecture, the student should have: • An understanding of the forces acting on the partial denture and the design components that overcome them • An understanding of different partial denture designs and the problems related to each NEWGIZA UNIVERSITY Types of RPD according to support • Tooth Support • Mucosa support • Tooth-mucosa support NEWGIZA UNIVERSITY Possible Partial denture movements • Tissue-ward movements • Tissue-away movements • Horizontal movements: A) Lateral movements B) Antero-posterior movements. • Rotational movements I- Tissue-ward movements • Vertical forces acting in gingival direction tending to move the denture towards the tissues • They occur during Mastication, Swallowing • This function of the partial denture is called “Support” NEWGIZA UNIVERSITY NEWGIZA UNIVERSITY This Function Is Mainly Provided By: Properly designed supporting rests placed in rest seats, which are prepared on the abutment teeth, Rigid major connectors that are neither relieved from the tissues nor placed on inclined planes also provide support Broad accurately fitting denture bases in distal extension partial dentures. NEWGIZA UNIVERSITY II- Tissue-away movements • Vertical forces acting in an occlusal direction tending to displace and lift the denture from its position • It occurs due to a.The action of muscles acting along the periphery of the denture b.Gravity acting on upper dentures c.sticky food adhering to the artificial teeth or to the denture base. • This function of the partial denture is called “Retention” NEWGIZA UNIVERSITY This Function Is Mainly Provided By: 1. Mechanical Direct Retainers, Which Engage Undercuts On Abutment Teeth 2. physiologic forces on polished surfaces of denture bases 3. physical forces on fitting surfaces of denture bases III- Horizontal movements: A) Lateral movements • Horizontal forces developed when the mandible moves from side to side during function while the teeth are in contact • Lateral movements have a destructive effect on teeth leading to tilting, breakdown of the periodontal ligament and looseness of abutment teeth. • Bracing is Resistance to Lateral Movement of the Partial Denture NEWGIZA UNIVERSITY NEWGIZA UNIVERSITY This Function Is Mainly Provided By: a. Bracing clasp arms placed at or above the survey line of the tooth. b. Minor connectors in contact with axial (vertical) surfaces of abutment teeth c. Proximal plates d. Adequate extension of the flanges NEWGIZA UNIVERSITY Horizontal movements B) Antero-posterior movements • Horizontal forces which occur during forward and backward movement of the mandible during function while the teeth are in contact • There is natural tendency for the upper denture to move forward and for the lower to move backward. NEWGIZA UNIVERSITY NEWGIZA UNIVERSITY Horizontal movements B) Antero-posterior movements • • Forward movement of the upper denture could be resisted by: a. Anterior natural teeth. b. Palatal slope. c. Maxillary tuberosity. d. The natural teeth bounding the edentulous space. The backward movement of the lower denture could be resisted by a. The slope of the retromolar pad b. The natural teeth bounding the saddle area. c. Proximal plates. NEWGIZA UNIVERSITY IV. Rotational movement Indirect retainers are the Components of removable partial denture that are used to reduces the tendency for a removable partial denture to rotate in an occlusal direction about the fulcrum axis NEWGIZA UNIVERSITY Support Retention RPD Design Indirect Retention Bracing and stabilization Reciprocation NEWGIZA UNIVERSITY Problem of Class I NEWGIZA UNIVERSITY Different Displacement Between PDL & Mucosa Periodontal ligament (0.25mm) Mucosa 2.0mm) Support NEWGIZA UNIVERSITY NEWGIZA UNIVERSITY Problems of support associated with free-end saddles RPD is due to: 1. Lack of posterior abutment 2. Support is derived from both the residual ridge and abutment 3. Major support is obtained from the residual ridge 4. If resorption occurs and relining of the denture is neglected further bone resorption occurs with subsequent torque acting on the abutments. NEWGIZA UNIVERSITY ? ? ? ? ? ? ? ? ? ? ? ? NEWGIZA UNIVERSITY Management of class I Load reduction Distributing the load between the ridge and abutments Wide distribution of load NEWGIZA UNIVERSITY I. Load reduction • Leaving a tooth off the saddle • Replacing premolars with canines, and molars with premolars NEWGIZA UNIVERSITY I. Load reduction • Using narrow teeth bucco-lingually NEWGIZA UNIVERSITY II. Wide load distribution • Among the maximum possible area of the ridge (Maximum coverage) • Among larger number of teeth (rigid rests) NEWGIZA UNIVERSITY III. Load distribution • Varying the nature of connection between the clasp and the base • Anterior placement of the occlusal rest • Functional impression technique NEWGIZA UNIVERSITY Varying the nature of between the clasp and the saddle A. Gingivally Approaching clasps B. Stress Breaker NEWGIZA UNIVERSITY 1. Varying the nature of between the clasp and the saddle Using flexible clasps:  All gingivally approaching clasps  Occlusally approaching clasps  Reverse Aker clasp  Back action clasp  Reverse back action clasp  R.P.A.  Wrought wire clasps NEWGIZA UNIVERSITY R.P.A Rest. Proximal plate. Aker  I is a single arm clasp  It engages an undercut of 0.02 of an inch.  It is flexible clasp  Used in free end saddle cases  It is indicated in cases which we can’t use gingivally approaching clasps. Back action clasp (not common)  Single arm clasp (flexible)  Minor connector starts mesio-lingually to engages mesio-buccal undercut.  Rest is located distally.  Used in free end saddle and maxillary premolars and molars NEWGIZA UNIVERSITY NEWGIZA UNIVERSITY Reverse Back action clasp The same as the back action but starts at the mesiobuccal line angle to engage a mesiolingual undercut. Its occlusal rest is placed at the distal side of the abutment Used in lower premolars NEWGIZA UNIVERSITY II. Gingivally approaching clasps  The retentive arm terminal has different forms e.g. T, C, U or I. NEWGIZA UNIVERSITY II. Gingivally approaching clasps  Contraindication of GA clasp:  when buccal undercut is absent  cases with severe tissue undercut to avoid food or tissue trap.  shallow vestibule i.e. the base of the Ibar should be at least 3 mm from the gingival margin NEWGIZA UNIVERSITY R.P.I Rest. proximal plate. I Bar NEWGIZA UNIVERSITY Combination In Design Retentive arm Gingivally app. Bracing arm Occlusally app. NEWGIZA UNIVERSITY Combination In Material Retentive arm Bracing arm Wrought metal cast wire NEWGIZA UNIVERSITY Stress breaker (stress equalizers) • Using movable joint between the denture base and the RPD NEWGIZA UNIVERSITY 2. Placing the occlusal rest away from the distal extension base Changes the distal torque into mesial torque which is counteracted by the adjacent tooth buttressing effect NEWGIZA UNIVERSITY Anterior placement of occlusal rest • Disengagement of the clasp during tissue ward forces (elimination of the torque) NEWGIZA UNIVERSITY Anterior placement of the rest Increase the length of the arc of rotation, so the forces transmitted to the ridge are more vertical NEWGIZA UNIVERSITY Anterior placement of the rest The area of support is increased (decrease force /unit area) NEWGIZA UNIVERSITY 3. Functional impression • The mucosa is recorded in a compressed form, so the degree of tissue ward displacement is decreased intraorally NEWGIZA UNIVERSITY Strain on the residual ridge is minimized through: 1. Broad tissue coverage and maximum extension of the denture base 2. Fitness and intimate adaptation of the denture base to the tissue. 3. Muco-compression impression recording of the residual ridges. 4. Improving the condition of the residual ridge e.g. correction of abusive condition of tori and hyperplastic tissues. NEWGIZA UNIVERSITY Strain on the residual ridge is minimized through: 5. Use of small and narrow teeth 6. Harmonious occlusion Leaving a tooth off the saddle. 7. Placement of occlusal rests away from the saddle. 8. Providing Posterior Abutments i. Using an implant at the distal part of the ridge ii. Salvaging a hopeless badly decayed tooth (an overdenture abutments) NEWGIZA UNIVERSITY Strain on the abutment teeth is minimized through 1. Correct choice of the abutment Tooth with sufficient alveolar bone support and crown and root morphology 2. Placement of occlusal rests away from the saddle. 3. Correct choice of direct retainer (flexible clasping). 4. Using stress equalizing design 5. By placing additional rests NEWGIZA UNIVERSITY Problems of class II partial dentures NEWGIZA UNIVERSITY Designing class II partial dentures usually follow the same basic principles of class I partial dentures. The absence of a saddle on the other side of a class II partial denture complicates the Retention of the appliance. Problems of Class II NEWGIZA UNIVERSITY • Designing class II partial dentures usually follow the same basic principles of class I PD. As the problems resulting from absence of posterior abutment, which causes lack of proper posterior support and retention. • The absence of a saddle on the other side of a class II partial denture complicates the retention of the appliance. NEWGIZA UNIVERSITY I- Designing of class II partial dentures with no modifications 1. A double Aker clasp usually used on the dentulous side. 2. An indirect retainer should be provided to counteract rotation of the denture away from the tissues. NEWGIZA UNIVERSITY Un-modified class II NEWGIZA UNIVERSITY I- Designing of class II partial dentures with no modifications 1- Rigid clasping and rigid connection between the saddle and the retainer can be done in cases with:  Short edentulous span  Strong abutment with healthy periodontium.  Well formed edentulous ridge covered with firm mucosa NEWGIZA UNIVERSITY I- Designing of class II partial dentures with no modifications 2- Designs applying stress equalizing principles • This design is applied in long class II cases. • It includes either: i. Flexible clasps ii. Stress breaker NEWGIZA UNIVERSITY II- Designing of class II partial dentures with modification spaces: The clasps on abutments bounding the modification area provide: • Retention • bracing • indirect retention NEWGIZA UNIVERSITY Modified class II NEWGIZA UNIVERSITY Problem of Class III It is Either Modified Or not In both cases it will be treated with a bilateral PD NEWGIZA UNIVERSITY Does the modification area simplify or complicate the case? The presence of a modification area simplifies the problem to a great extent as the extension to the other side provides Cross arch stabilization Retention Support Aim is to achieve cross arch stabilization NEWGIZA UNIVERSITY Tooth born removable prosthesis is characterized by: 1. The base is usually made from metal as there is no need for relining or rebasing except if……….. 2. No indirect retainer is needed as no tissue away displacement is anticipated except if………………. 3. No stress breaking action is required from the clasp, and so rigid clasp arm could be used which provide splinting effect. 4. Only anatomic impression is required Conventional PD NEWGIZA UNIVERSITY Rest seats. • Near zone. Retentive clasps • All clasps may be used, especially rigid clasps. Clasps distribution However there should be support on all abutments Quadrilateral clasp configuration Tripod clasp configuration Denture base. NEWGIZA UNIVERSITY • Metallic denture base. • Combination denture base in cases of anterior saddle, and long span ridge. Indirect retention • No need for indirect retention. Unilateral PD NEWGIZA UNIVERSITY Problems of unilateral PD 1. Instability. 2. Permits only a limited distribution of load. 3. Could be aspirated or swallowed NEWGIZA UNIVERSITY The following criteria must be fulfilled to go for a Unilateral partial denture: 1. 2. 3. Very short edentulous span. Criteria of the abutment teeth: • Long roots. • Not have extreme root taper. • Long clinical crown. • Nearly parallel BL surfaces. • No gingival recession. • Exhibits minimal mobility. • Presence of suitable buccal and lingual undercuts. No excessive occlusal stresses. The clinical crown of abutment tooth must be long enough and with nearly parallel B and L surfaces to resist rotational forces. NEWGIZA UNIVERSITY Design considerations in unilateral PD 1. Provide B and L cusp contact during working occlusion Stability. 2. Wide box shaped occlusal rest Bracing and retention. 3. Double bracing double retention. 4. Maximum extension of the flanges. NEWGIZA UNIVERSITY Class IV Problems NEWGIZA UNIVERSITY Class IV Problems • usually follow the same basic principles of class I partial dentures and are considered as free-end partial dentures. • As the edentulous area that crosses the midline lies anterior to the abutments So, the Potential problems of Class IV is: 1. The incising action tends to displace the PD in an anterosuperior (Upper) or antero-inferior (Lower) direction. 2. Usually, the anterior teeth are placed in a less ideal relation to the residual ridge to satisfy the esthetic demands which tends to magnify the stresses. 3. Poor esthetics with the use of anterior clasp NEWGIZA UNIVERSITY Long span. Short span. Rest seats NEWGIZA UNIVERSITY Short span • Near zone. (mesial) • Cingulum rests. Long span. • Far zone (distal). • Occlusal rest. Long span is considered free end saddle. Retentive clasps • R.P.I or gingivally approaching clasp. For flexibility and esthetics. • Reverse aker • Double aker may be used in the posteriors Denture base Combination denture base, for esthetics. NEWGIZA UNIVERSITY Major connector. • Antro-posterior palatal strap. Maxillary major connector. • Full palatal coverage. Maxillary major connector. • Horseshoe Maxillary major connector. • Lingual plate Mandibular major connector. NEWGIZA UNIVERSITY Indirect retention. • As far posteriorly as possible. • Occlusal rests. • Posterior strap of the antro-posterior strap maxillary major connector. NEWGIZA UNIVERSITY Aims The educational aims of this lecture are: • To explain the principles of partial denture design • To detail the problems related to the design of the partial denture Objectives On completion of this lecture, the student should have: • An understanding of the forces acting on the partial denture and the design components that overcome them • An understanding of different partial denture designs and the problems related to each NEWGIZA UNIVERSITY Reading List Students are advised to read details at: • Removable partial dentures, Nicholas J A Jepson, 2004: Chapter 6 • Removable partial prosthodontics, Alan B Carr & David T Brown, 2011: Chapter 11 • Stewart's Clinical Removable Partial Prosthodontics NEWGIZA UNIVERSITY Thank You