Stress breakers Introduction Stress force per unit area

Stress breakers

Introduction � Stress : force per unit area within a structure subjected to an external force or pressure. � Stress exerted against the teeth and must be within the adaptive capacities of the. or else the tissues may not be capable of compensation and adaptation and the result is tissue destruction.

� Various approaches are been made to distribute the stress or forces acting on a partial denture between the soft tissue and teeth. � The stress breaker is suggested as a means to allow the base to move slightly with less strain to the abutments.

Definition � A stress breaker is a device that allows some movement between the denture base or its supporting framework and the direct retainers [ intracoronal or extracoronal] �It is also called stress equalizer or stress director or articulated prosthesis

Aims of stress breaking �To direct occlusal forces in the long axis of the abutment teeth. �To prevent harmful loads being applied to the remaining natural teeth. � To share load as evenly as possible between the natural teeth and saddle areas. � To ensure that the load applied to the saddle area is distributed as evenly as possible � To provide greater comfort to the patient.

Guidelines for stress breaker � To decide whether to use a stress breaker or a rigid design �Rule 1: If the teeth are strong and the ridge is poor flat, knife edged, or narrow- use a rigid design. �Rule 2: If the teeth are weak e. g. , loss of supporting tissues so the mobility is plus or more and the ridge is strong, use a stress breaker.

Classification of stress breakers Stress-breakers can be classified according to their mode of action: � Type 1 - Those utilizing a hinge or moveable joint. � eg : hinges , sleeves and cylinders and ball and socket devices

�Type 2 - Those utilizing flexible connection. eg: wrought wire connectors , split major connectors.

Type 1 stress breaker � These can be used in association with either precision attachments or clasp units as toothbearing direct retainers. . � The hinge is usually of a rigid design, the soft tissue absorbs a minimum of load adjacent to the hinge and a maximum of load toward the distal of the ridge. The base is permitted movement in a vertical plane only. The movement may be unrestricted, or it may be controlled within definite limits by a stop arrangement built into the device.

. � The hinge type of device spares the tooth from all stresses that results from vertical movement of the base, but it is still subjected to all the lateral and torsional stresses

�E. g: the Swiss made Dalbo attachment and the Crismani attachment. � If the device works on a ball and socket principle, movement of the base is allowed in all planes and the tooth is relieved of all stress.

Dalbo attachment A- Dalbo extra-coronal precision attachment device

ASC 52 ATTACHMENT

Type 2 stress breakers � design having a flexible connection between the direct retainer and the denture base � wrought wire connectors, divided major connectors a moveable joint between two major connectors

Various types of type 2 stress breakers 1. Torsion bars/split bar major connectors: Used in the design of a lower partial denture carrying bilateral free- end saddles.

�Bars extend anteriorly from the clasp units on each side to join a lingual bar near the midline. � Flexibility can be controlled by varying the cross-section of the torsion bars, the method of construction (cast or wrought) and the material of construction

2. Partial division of connectors : � This principle can be applied in both upper and lower dentures. � a lingual plate may be partly divided by an anteroposterior slot. The upper portion of the plate is attached to the retainer unit on the abutment tooth and the lower portion is attached to the saddle� a degree of flexibility developed.

3. Mesial placement of occlusal rests: � This offers the simplest available approach to stress -breaking. � The degree of stress-breaking achieved is , much less than that available where more complex devices are employed.

Other types of stress breakers 12 -gauge chrome wire stress breaker The advantages : � The extension base moves vertically immediately and the resiliency of the wire quickly returns the base to its original position. � The rigidity of the 12 gauge wire avoids overloading the mucosa. � It is easy to splint teeth with this design. � The fabrication is relatively simple. Repairs are rarely needed.

Split palate stress breaker A stress breaker for a maxillary partial denture is often not necessary, has there is more alveolar ridge for support. In case of Kennedy class V, partial denture may be difficult to design, as the placement of a rest on the weak lateral incisor is not considered desirable. The left second molar would be required to absorb most of the load of mastication on the left side. In such cases a split palate stress breaker was designed.

Advantages 1. Since the horizontal forces acting on the abutment teeth are minimized, the alveolar support of these teeth is preserved. 2. By careful choice of the type of flexible connector, it is possible to obtain a balance of stress between the abutment teeth and the residual ridge. 3. Intermittent pressure of the denture bases massages the mucosa, thus providing physiologic stimulation, which prevents bone resorption and eliminates the need for relining

4. If relining is needed but not done, the abutment teeth are not damaged as quickly. 5. Splinting of weak teeth by the denture is made possible despite the movement of a distal extension base.

Disadvantages 1. The broken stress denture is usually more difficult to fabricate and therefore more costly. 2. Vertical and horizontal forces are concentrated on the residual ridge, resulting in increased ridge resorption. Many stress breakers designs are not well stabilized against horizontal forces. 3. If relining is not done when needed, excessive resorption of the residual ridge may result. www. indiandentalacademy. com 4. The effectiveness of indirect retainers is reduced or eliminated altogether.

5. The more complicated the prosthesis , the less it may be tolerated by the patient. 6. Flexible connectors may be bent and distorted by careless handling. 7. Repair and maintenance of any stress breaker is difficult, costly, and frequently required.