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Rotational path removable partial denture: An esthetic alternativeBy Raymond J. Byron Jr., DMDRobert Q. Frazer, DDSMichael C. Herren, DMDFeatured in General Dentistry, May/June 2007Pg. 245-250

Posted on Sunday, April 22, 2007

Raymond J. Byron Jr., DMD Robert Q. Frazer, DDS Michael C. Herren, DMD Missing teeth can be replaced using any of a number of methods. Patients may choose to replace missing teeth with a prosthesis that is either removable, fixed,or retained with implants. When it is necessary to replace anterior or posterior teeth, a properly designed and fabricated rotational path removable partial denturecan be both successful and esthetically pleasing to the patient. However, while a patients functional and esthetic needs can be met successfully, rotational pathremovable partial dentures can be more demanding for the laboratory technician to fabricate and for the dentist to seat in the mouth. Rotational path removablepartial dentures frequently are overlooked as a viable means of treating missing teeth. This article reviews the principles of rotational path removable partialdentures, as well as their categories, advantages, and disadvantages, in the hope that more dentists will consider them when the need arises. Received: September 19, 2006 Accepted: December 21, 2006 The goal for replacing missing teeth is to restore a patients function, stability, and esthetics. Modern dentistry offers many options for achieving this goal. Sinuslifts and bone augmentation offer more opportunities to replace missing teeth with implant-retained fixed and removable prosthetics. More than 700,000 dentalimplants are placed annually, although they are not always the treatment of choice.1 When patients choose removable prosthodontics to replace missing teeth, arotational path removable partial denture (RPD) may be the treatment of choice. Though rotational path RPDs are more complicated to design than fixedprosthodonticsand can be difficult to fabricate and (at times) to seata rotational path RPD can be successful.

This article discusses the rotational path RPD in terms of its principles, design, advantages, and disadvantages, as well as the difficulty encountered duringlaboratory fabrication. PrinciplesIn 1935, Humphreys reported that Hollenback had designed an RPD with a curved path of placement.2,3 It wasnt until 1978 that Garver revived the concept of arotary path of insertion of RPDs, describing a technique that was limited to a unilateral RPD with a fixed partial denture (FPD) contralaterally.4 In 1978, Kingproposed an RPD with a rotational path placement that primarily utilized a tooth-supported RPD to replace missing anterior and posterior teeth.5,6 Kings theorywas further clarified by Krol and Jacobson, who presented physiologic and engineering principles for use in the rotational path of insertion.7,8 According to Krol, aconventional RPD is seated in a single path of insertion, with every occlusal rest seated more or less simultaneously.8 By comparison, a rotational path RPD isseated in two segments; the segment that contains the centers of rotation is seated first before the RPD is rotated, positioning the second segment to the RPDsfinal seat.7,8 Stated differently, the RPD framework engages desirable proximal undercuts that are essential for retention during the first insertion path. At thatpoint, it rotates, utilizing conventional clasps for additional retention.

The flexible, conventional clasp is the most common form of direct retainer.5 The rotational path design uses a rigid portion of the RPD framework (known asthe rigid retainer or rigid retentive element) as the retentive component.9 The rigid portion of the RPD framework provides retention that is comparable to theflexible portion of conventional clasps. Once the undercuts are engaged, the framework is rotated to a fully seated position that allows conventional clasps toprovide further retention of the RPD framework, completing the second path of insertion.6 The principal advantage of a rotational path design is that the RPD



requires a minimal number of conventional clasps to ensure retention.9 In addition, the ro-tational RPD can improve the patients esthetic appearance (due toconventional clasps not showing) and decrease plaque retention.

CategoriesThere are three basic types of rotational path RPDs: anterior-posterior (AP), posterior-anterior (PA), and lateral. Jacobson and Krol narrowed the rotational paths totwo categories.9 Category I includes all prosthesis designs that first seat the rest that is associated with the rigid retainer. Once that first rest is seated, thesecond segment rotates into place and conventional clasps are engaged.5 The rotational centers are located at the end of unusually long rests.9 The rotationalcenters on each side of the arch determine the axis of rotation during final placement.10

Category I includes all PA and AP paths of insertion that replace posterior teeth.8 A PA rotational path partial can be used successfully in the mandibular archwhen the most distal molars are inclined mesially. Figure 1 illustrates a Category I rotational path RPD when a PA path or an AP path of placement is utilized. Fora PA path of placement, the end of the long occlusal rest contacts the molar first, creating the center of rotation. The rigid retainer engages the mesial undercut ofthe molar. The RPD is seated along the arc of rotation until the conventional clasps engage the mesiobuccal undercuts of the premolar. The minor connectordistal to the premolar must not engage the undercut, which is located between the arc and the distal surface of the premolar.

For an AP path of placement, the long occlusal rest first contacts the premolar, creating the center of rotation. The rigid retainer engages the distal undercut ofthe premolar. The RPD is rotated along an arc until the conventional clasps engage the distobuccal undercuts of the molar. The minor connector mesial of the



molar must follow the arc of rotation and should not engage any mesial undercut of the molar. Category II includes all lateral paths and AP paths that replace anterior teeth. The centers of rotation and the rigid retainers are found at the gingival extension

of minor connectors.5,9 These prostheses actually use a dual path of insertion, rather than a completely rotational path. To seat a Category II rigid retainer, asliding method must be used to make initial contact with the abutment tooth (Fig. 2). The path of insertion is a straight line from an incisal or occlusal direction tothe rotational centers. At that point, the conventional posterior or contralateral retainer is rotated into position from a conventional path of insertion. The initialstraight path of insertion along the mesial surfaces of the canines must be parallel with the cingulum rests to permit complete seating (Fig. 2).

Retainer design requirementsThe rigid retainer consists of a rest and a minor connector. The rest should be prepared to a depth of 1.52.0 mm.5,9,10 Preparing the rests to their proper depthprevents movement of the tooth and maintains intimate contact with the rigid retainer. Proper rest form also prevents the RPD framework from fracturing at thejunction where the rest and minor connector meet.9,10 The occlusal outline form of the rest preparations should be irregular or dovetailed and should extend tomore than half of the mesiodistal width of the occlusal surface (Fig. 3).5,9 When the RPD is seated, the long occlusal rests become the rotational centers andprovide similar bracing to reciprocating clasps.



The facial and lingual walls of a properly prepared rest should be nearly parallel to each other and both should be perpendicular to the long axis of the tooth. It

is extremely important for the walls of the rests to remain parallel bilaterally across the arch unless the teeth are both lingually and mesially inclined; in thesecases, the facial and lingual walls of the bilateral rest seats are prepared parallel to each other, which actually results in the rests not being parallel to the long axisof the abutment teeth (Fig. 4).10 A straight channel preparation (with its floor perpendicular to the long axis of the tooth) is preferred (Fig. 5).10 Under occlusalloading, the straight channel preparation exerts the smallest amount of tipping while still permitting slight movement of the tooth during function.



The rigid retainers are minor connectors that engage proximal undercuts located in the infrabulge area of abutment teeth, eliminating the need for conventional

retentive or reciprocating clasps. Guiding planes usually are not recommended for rotational path designs.5.9 Preparation of the abutment tooth may be requiredto enhance proximal undercuts. In some instances, natural dentition does not have the necessary shape to provide proper rest seats and/or proximal tooth



contours. In such cases, the best treatment is full metal or metal ceramic survey crowns fabricated in the dental laboratory. The basic requirements of claspdesign are satisfied by specially designed long rests in conjunction with the rigid retainer.9 Though rigid retainers are different from conventional direct retainers,they still are capable of satisfying the six biomechanical requirements of retention, support, stability, reciprocation, encirclement, and passivity.5

Laboratory considerationsRotational path RPDs are technique-sensitive and require a careful treatment plan. An experienced dental laboratory technician is needed to fabricate the metalRPD framework.8 As with any RPD, diagnostic and master casts must be surveyed by placing the cast on the surveyor at a zero-degree or neutral tilt. Undercutsfor the rigid retainers and conventional clasps are located when the cast is in a neutral tilt position.5,9-11

Dividers also should be used to design rotational path RPDs. One end of the divider tip is placed at the end of the long occlusal rest (the center of rotation)while the second tip is placed in the proximal undercut area and rotated occlusally. If the second tip can rotate freely toward the occlusal without being trappedproximally, the undercut and center of rotation are aligned properly.8 When the divider tip is trapped and unable to rotate freely, the undercut is incorrect and theproximal surface of the abutment tooth may need to be recontoured (Fig. 6).

The second abutment tooth that receives the conventional clasp for retention also must be analyzed to accommodate the rotational path. The first tip of the

divider is kept at the same position that was used to measure the first segment, the center of rotation. The second tip is extended to the marginal ridge of thesecond abutment tooth and rotated in an occlusogingival direction. As the divider rotates, the space that appears between the second abutment and the second tipwill require blockout to allow for full seating of the prosthesis as it rotates to its final position (Fig. 6). The minor connector should not rest inside this space. Afterthe rotation path is analyzed, the second abutment is surveyed (with a zero-degree cast tilt) to determine the proper undercut of the tooth that is to receive theconventional clasp.8

A divider is essential when planning multiple edentulous spaces to replace posterior teeth. The divider will determine the amount of blockout that is needed forthe multiple minor connectors. As edentulous space gets farther from the axis of rotation, the radius becomes straighter and the need for blockout is reduced. Asthe edentulous space gets closer to the axis of rotation, the curvature of the arc increases, more blockout is needed, and the RPD is more difficult to seat (Fig.7).5,12 When fabricating rotational path RPDs, an experienced dental laboratory technician is essential for blocking out undesirable undercuts.



For Category II designs, the cast first is surveyed at zero degrees to analyze the undercuts of the mesial surfaces of the anterior abutments and the

distobuccal undercuts of the posterior abutments. The retentive areas of the most anterior teeth should have an undercut of at least 0.010 in.1 A second tilt of thecast is required to identify the initial path of placement. This path is determined by adjusting the tilt of the cast upward anteriorly until the undercuts on the mesialsurface of the anterior abutment teeth are eliminated. The dental surveyor is used to ensure that the mesial undercuts are eliminated and that the cingulum restsare accessible during initial placement. During initial contact, the mesial rigid retainers and cingulum rests must contact the anterior abutment teeth almostsimultaneously.8,9

For the laboratorys convenience, the path of insertion for both the anterior/lateral rigid retainers and the posterior conventional retainers should be indicated bytwo separate tripod marks (Fig. 8).9 Using the analyzing rod of the surveyor, the land of the cast should be marked at the upward anterior tilt and the zero-degreetilt positions. It is important to mark the cast twice so that the dental laboratory technician will see where the path of insertion of the anterior rigid retainers and theconventional retainer of the posterior teeth are located.



Proper rest designs are important to ensure success of Category II partial dentures. The lingual rest of an anterior tooth (that is, canine) should be U-shaped in

appearance. In addition, it should extend to more that half the mesiodistal width of the tooth and should be prepared in enamel. From a proximal view, themaxillary cingulum rest should be shaped like an inverted V (Fig. 9).12 The proximal undercuts and rests must be parallel; otherwise, the rests will not seatcompletely. The surveyor must be used to confirm an absence of interference once the rests and rigid retainers are seated (Fig. 10).8



The dental laboratory technician must have a thorough knowledge of rotational path RPDs so that he or she may design the RPD framework correctly and

block out undesirable undercuts. Seating the RPD framework can be a challenge at times. Ideally, the tooth surface of the rigid retainers should not be relieved orfinished abrasively. Rigid retainers must make close contact with the undercuts of abutment teeth.9 If the RPD framework does not seat fully during its rotationalpath of insertion, the portion of the framework that is causing the interference should be meticulously reduced with a high-speed handpiece using a dental bur,diamond, or stone. If the anterior rigid retainers of a Category II AP RPD are cut back for esthetic reasons, there is a risk that retention will be lost in a worst-casesituation. Advantage and disadvantagesRetention, support, and stability are the principle requirements for successful RPD fabrication. A correctly fabricated rotational path RPD will not jeopardize theseprinciples.8 A rotational path RPD is an excellent alternative to an FPD for the anterior part of the mouth. Because anterior abutments do not require conventionalclasps, esthetics will improve and plaque accumulation will decrease. Rotational path RPDs are excellent for cases involving mesially inclined mandibular molars. In addition, a rotational path RPD with rigid retainers eliminates the possibility of losing RPD retention due to the distortion or breakage that can result from usingflexible conventional clasps.



The major disadvantage of the rotational path design is that it is technique-sensitive.9 Dental laboratory technicians must be skilled at placing the rigidretainers correctly via proximal undercuts and must be careful when finishing and polishing the final framework. All adjustments of the rigid retainers must becompleted chairside, using pressure indicator paste or other disclosing material. Adjustments must be conservative until the framework is seated completely. Excessive adjustments mean that the RPD framework must be remade if retention is lost, since rigid retainers cannot be adjusted like conventional clasps can. For the rotational path RPD to be successful, the dentist must have a thorough knowledge of rest design and proper blockout and also must communicate well withthe dental laboratory.

Rotational path RPDs are not recommended for distal extensions.13 Functional movement will cause undesirable torque on the anterior abutment teeth due tothe rigid retainers. The rotational path RPD can be considered for distal extensions, provided the residual ridges are firm and there is little or no displacement. A1987 study by Schwartz and Murchison reported that a spring clasp offered an alternative to a rigid retainer for creating anterior retention in distal extensionsituations.14 The metal RPD framework has a channel incorporated into its design in which a cast wrought wire spring clasp is soldered. Due to the spring claspsflexibility, this technique generates less torque to anterior abutment teeth but does not eliminate all torque.

SummaryRotational path RPDs improve esthetics by allowing dentists to replace missing teeth without placing a conventional clasp on every abutment tooth. They areuseful when molars are mesially inclined. It is important that dentists evaluate each patient carefully and survey casts meticulously to ensure success. Workingclosely with an experienced dental laboratory technician is a must. Chairside adjustments to rigid retainers should be made judiciously. Though they aretechnique-sensitive, a correctly designed rotational path RPD can be esthetically pleasing and retentive. AcknowledgementsIllustrations for this article were produced by Matthew H. Hazzard and Thomas J. Dole, Teaching and Academic Support Center, University of Kentucky. Author informationDrs. Byron and Frazer are full-time assistant professors, Division of Restorative Dentistry, College of Dentistry, University of Kentucky in Lexington, Kentucky. Dr.Herren is in private practice in Cynthiana, Kentucky. References1. Garcia LT. The use of a rotational-path design for a mandibular removable partial denture. Compend Contin Educ Dent 2004;25:552-567.2. Humphreys K. A unilateral removable bridge using a hook attachment. J S Calif Dent Assoc 1935;2:332-337.3. Humphreys K. Removable bridge using a hook attachment in a Tinker pontic. J S Calif Dent Assoc 1935;2:372-374.4. Garver DG. A new clasping system for unilateral distal extension removable partial dentures. J Prosthet Dent 1987;39:268-273.5. Jacobson TE. Rotational path partial denture design: A 10-year clinical follow-upPart I. J Prosthet Dent 1994;71:271-277.6. King GE. Dual-path design for removable partial dentures. J Prosthet Dent 1978;39: 392-395.7. Firtell DN, Jacobson TE. Removable partial dentures with rotational paths of insertion: Problem analysis. J Prosthet Dent 1983;50:8-15.8. Halberstam SC, Renner RP. The rotational path removable partial denture: The over-

looked alternative. Compendium 1993;14: 544-552.9. Jacobson TE, Krol AJ. Rotational path removable partial denture design. J Prosthet Dent 1982;48:370-376.10. Krol AJ, Finzen FC. Rotational path removable partial dentures: Part 1. Replacement of posterior teeth. Int J Prosthodont 1988;1: 17-27.11. Reagan SE, Dao TM. Oral rehabilitation of a patient with congenital partial anodontia using a rotational path removable partial denture: Report of a case.

Quintessence Int 1995;26:181-185.12. Krol AJ, Finzen FC. Rotational path removable partial dentures: Part 2. Replacement of anterior teeth. Int J Prosthodont 1988;1: 135-142.13. Aviv I, Ben-Ur Z, Cardash HS. An analysis of rotational movement of asymmetrical distal-extension removable partial dentures. J Prosthet Dent 1989;61:211-

214.14. Schwartz RS, Murchison DG. Design variations of the rotational path removable partial denture. J Prosthet Dent 1987;58:336-338.



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