Rotational path removable partail dentures PINHATHAI KANTAWONG

Rotational Path Removable Partial Dentures 1. Replacement of Posterior Teeth 2. Replacement of Anterior Teeth

Rotational Path Removable Partial Dentures Retention is obtained when a minor connector rotates into a proximal undercut. It’s maintained in intimate contact with the tooth surface by its rest, other components Clasps located away from the path of rotation. esthetics not affected.

Rotational Path Removable Partial Dentures Influence Factors Patient acceptance and coordination Presence of proximal undercuts The Iocation and number of edentulous areas The arch form

In Conventional removable partial denture … a path of placement perpendicular to the occlusal plane is commonly chosen

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

The perpendicular path is usually selected because … 1. The contours of the abutment frequently present flavorable undercuts 2. Guiding planes prepared more easily 3. The path of placement is easily repeatable 4. Many patients seat their prostheses under occlusal force, and clasp distortion is less

To compensate for the lack of proper tooth position or contours To compensate for the lack of proper tooth position or contours. A modified path of placement is established by changing the lateral or the anteroposterior tilt of the cast If they are slight, may be helpful, but if they are severe, the patient may have difficulty placing the prosthesis.

Rotational Path Removable Partial Dentures Differs from the conventional straight path. The straight path: seats all rests more or less simultaneously, even varies from perpendicular The rotational path : seats one portion first, allowing one or more of the rigid components access to undercut areas. Then the entire prosthesis is rotated into its final position.

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Rotational Path Removable Partial Dentures Replaces conventional clasps with rigid retentive units Consist of a rest and retentive component. Retentive component may be a minor connector, used on posterior teeth , or an extension from the minor connector, in anterior teeth .

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Categories of rotational path designs

Categories of rotational path designs There are two categories based on the location of the framework rotational centers and their most appropriate clinical applications. Category I : primarily used to replace missing posterior teeth. The rotational centers of the framework are located at the ends of the long rests of the rigid retainers.

The rotational centers on each side: the axis of rotation. The rotational centers seated first, then the entire prosthesis is rotated into place

Category II designs : primarily used to replace anterior teeth. Their rotational centers located gingivally as rigid extension

The rigid retainers is first placed along a straight path to gain access to the rotational centers, then the prosthesis is rotated into place

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Design Considerations for Replacing Posterior Teeth

Design Considerations for Replacing Posterior Teeth Path of placement The anterior or posterior portion is designed to seat first, depending on esthetic and periodontal

Usually in the maxillary arch for esthetic If the anterior portion of the prosthesis is placed first the path of placement is anteroposterior (AP). Usually in the maxillary arch for esthetic Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

This design eliminates clasps on the anterior abutments Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

If the posterior portion is placed first the path is termed posteroanterior (PA). Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

In mandibular , the PA path may be used to great advantage when molar abutments are tipped mesially Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Categories of rotational designs Category I AP rotational path replacing posterior teeth Category I PA rotational path replacing posterior teeth Category II AP rotational path replacing anterior teeth Category I and II Lateral rotational path replacing teeth unilaterally

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

PART 1 Rotational Path Removable Partial Dentures Replacement of Posterior Teeth

Design Considerations for Replacing Posterior Teeth Rest form of the rigid retainer Must be deep enough to allow a rest thickness of at least 1.5 mm for base metal alloys and 2 mm for noble metal alloys

The rest should extend more than half the mesiodistal dimension of the abutment tooth, and its facial and lingual walls should be nearly parallel

The walls of the rest seats should be parallel bilaterally across the arch.

Restseat : an asymmetric outline, such as dovetails, to provide the equivalent of adequate encirclement of a clasp Intimate contact of minor connectors and rests with tooth surfaces must be preserved.

An exception to this rule applies to molars that are severely tipped mesially. For these teeth, a straight channel rest, its floor perpendicular to the long axis of the tooth, exerts the least amount of tipping force under occlusal loading.

Surveying for posterior tooth replacement AP Path

Surveying for posterior tooth replacement AP path The AP rotational path is used when esthetics is concern. Often true in the maxillary arch If the contours of the more anterior abutment tooth permit the use of rigid retainers, the AP may be indicated.

Surveying for posterior tooth replacement 1. A divider is helpful in determining the amount of blockout needed - One point : placed on the axis, around which the framework will rotate into position. - The other point : placed at the most cervical portion of the same tooth.

- The cervical point of the divider is then rotated occlusally to determine if the undercut is too great Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Surveying for posterior tooth replacement 2. Determine the undercut is sufficient for the rigid retentive component -One point : placed at the terminal of the retentive clasp arm. -The other point is placed at the cervical third of the proximal surface of the tooth which the minor connector will be positioned.

If the point on the proximal surface binds when moving occlusally, the undercut is adequate

Another method is to survey all of the abutments at the same horizontal level.

Surveying for posterior tooth replacement 3. Determine the amount of blockout necessary to coincide with the arc of rotation -One point : placed on the axis of rotation which the partial denture will rotate into. -The other point is extended to the marginal ridge of the posterior abutment, then rotated cervically

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Surveying for posterior tooth replacement 4. Determine the proper undercut on the tooth to be clasped Conventional surveying is done with a 0°tilt. The occlusal plane should be to the base of the surveyor

Surveying for posterior tooth replacement PA Path

Surveying for posterior tooth replacement The PA path may be used when molar abutment teeth are to receive the rigid retainer. The surveying procedure is similar to the one described for the AP path.

PA path, the rigid retainer is located on the posterior abutment, and a conventional clasp is used on the more anterior abutment

Factors affecting the rotational path

Factors affecting the rotational path Multiple edentulous areas Shape of the arch Lingually tilted teeth Vertical height of the retentive clasp terminal Multiple rotational paths

Multiple edentulous areas As the number of minor connectors increases, so does the potential difficulty of rotating the partial denture framework into place. An adequate blockout must be planned for all minor connectors.

Multiple edentulous areas The further the minor connector is from the axis of rotation the straighter the arc it must follow. The closer the minor connector is to the axis of rotation the greater the curvature of the arc it must follow.

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Shape of the arch Radii used to assess the amount of blockout required must be extended perpendicularly from the rotational axis. A shorter radius requires more blockout A tapering arch has shorter radii requiring more blockout than a square arch

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Lingually tilted teeth Prevent placement of a rotating framework. The major connector may require excessive relief which can create a food trap and bother the patient's tongue.

Vertical height of the retentive clasp terminal The terminals of the retentive clasp arm, which the partial denture tends to rotate around when the prosthesis is displaced, must be properly located in relation to the retentive retainer to make this component functional.

Maxillary arch, if a steep anteroposterior occlusal curve is present and a molar clasped, the rigid retainer on the more anterior abutment may be non retentive.

Surveying the cast with the anterior and posterior abutments at the same horizontal Ievel The absence of an undercut for the rigid retainer will become apparent

Multiple rotational paths More than one rotational path may be used to seat a single RPD. This may be confirmed by constructing a template of the proposed design in autopolymerizing resin, using strips of carding wax to confine the resin All undesirable undercuts must be blocked out.

The template should be removed easily Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Removed carefully to avoid fracture the teeth If the template cannot be removed easily, it may indicate that the proposed design should not be used Sent to the laboratory as a guide in fabricating the framework.

CONCLUSIONS

Rotational RPD can be used to advantage in many different clinical situations. In particular, it may help esthetic problems Although it allows little tolerance for error, several articles have been published that analyze common problems and describe how they may be avoided. By taking the time to understand the rotational path concept, both dentist and laboratory technician

PART 2 Rotational Path Removable Partial Dentures Replacement of Anterior Teeth

The concept is applied to the replacement of missing anterior teeth using the anteroposterior (AP) rotational. The anterior portion is first placed along a straight path to gain access to tooth surfaces that provide the necessary undercuts after the partial denture is rotated into its final position.

The most critical factors are the development of adequate cingulum rest seats to prevent migration of the abutment teeth and maintain intimate contact between the tooth and the rigid retentive components.

Rigid retentive units consists of a rest and its retentive component. The retentive component may be - a minor connector : post teeth - an extension from the minor connector : ant teeth

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Rotational Path Designs Category I designs are primarily used to replace missing post teeth.

The rotational centers of the framework are Iocated at the ends of long rests of the rigid retainers

Category II designs are used primarily to replace missing anterior teeth. Their rotational centers are located gingivally as rigid extensions of the minor connectors.

The anterior part is placed first along a straight path, which gives the rigid retainers access to the centers of rotation and undercut areas as well as the rest seats of the anterior abutment teeth

The rotational path has a great esthetic advantage

Rest Form of the Rigid Retainer on Anterior Teeth Planning rest seats for a Category II AP the proximal surfaces used for retention and the walls of the rest seats must be so related as to permit an initial path of placement

The rest seat preparation on the incisors or canines may require a restoration to achieve an adequate rest seat

The floor of the rest seat preparation should be in the enamel to offer greater resistance to displacement of the restoration. The restoration serves primarily to prevent facial migration of the abutment.

Surveying for anterior tooth replacement

Surveying for anterior tooth replacement 1. The cast is surveyed with a zero-degree tilt to determine the adequacy of undercuts on the mesial surfaces of anterior abutments and distobuccal surfaces of the posterior abutment

The amount of undercut on the should be at Ieast 0.020 inch.

Surveying for anterior tooth replacement 2. the cast is tilted upward anteriorly until the undercuts on the mesail surfaces of the anterior abutments are eliminated

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

The analyzing rod is then used to determine whether access still exists for the rests to be seated .

Surveying for anterior tooth replacement From a mechanical standpoint, the second molars,if present and in normal alignment, generally make the best posterior abutments.

Surveying for anterior tooth replacement The shape of the arch is also a factor. -In a tapering arch, the distance from the fulcrum line to the incisal edges of the central incisors will be greater than in a square arch displacing the molar clasps with less force

Krol j: Rotational Path Removable Partial Dentures, The International of prosthodontic ,San Francisco, 1988.

Surveying for anterior tooth replacement If the undercut on the mesial surfaces of the anterior teeth is less than 0.020 inch and displacement of the anterior segment of the partial denture could likely occur in function,

The use of a modified molar clasp may be helpful. A clasp design with a rigid component on the distal surface of the molar abutment

Multiple Edentulous spaces

As the number of minor connectors increases, so does the potential difficulty of rotating the partial denture framework into place.

The block out required will assume a curvature coinciding with the arc of placement. '

Adjustment of the rigid retainer

The rigid retentive units must be in intimate contact with their corresponding tooth surfaces to prevent migration of the tooth and loss of retention. If does not seat completely use a disclosing material and stone burs

Movement results from a lack of contact To restore proper contact, a recent developed autopolymerizing acrylic denture base resin which bonds to framework alloys Beware undercut

Lateral rotational path

The lateral rotational path may be used when anterior or posterior teeth are unilaterally missing. Most unilateral partial dentures can employ either AP or PA path of placement Designed to be placed first on the side where the teeth are missing, then seated clasps on the contralateral side.

If lingual undercuts are used, the design concept is similar to a Category I

If proximofacial undercuts are used, the design concept is similar to a Category II

Distal extension partial dentures

Distal extension removable partial dentures ordinarily do not lend themselves to a rotational path of placement because the rigid retainer will usually torque the anterior abutment teeth during rotational movements in function

cannot be recommended

Summary Advantage -Minimizes number of clasps,reducing tooth coverage and plaque accumulation -Improve esthetics -Minimal tooth prep compared to a precision attachment or fixed prosthesis -May be used in absence of ling or facial undercut -Distortion of rigid retentive is unlikely

Summary Disadvantage -Adjustment is difficult -Less tolerance for error -Required well prepared rest seat