Abutment Ppt p3v6y

CONTENTS - Introduction - Definitions - Ideal Requirements - Contraindication - Clinical examination of an abutment - Diagnostic casts - Radiographic examination. - Evaluation of roots and their ing tissues. - Crown - root ratio - Root configuration - Periodontal ligament area - Examination of crown of the tooth. - Biomechanical consideration

Special considerations Pier abutment Tilted molar abutment Abutment for the cantilever FPD -Endodontically treated teeth as abutments. -Questionable abutments -Detection of loose abutments. Abutments for removable partial dentures Abutments for immediate over denture -Summary

INTRODUCTION: The need for replacing missing teeth is obvious to the patient when the edentulous space is in the anterior segment of the mouth, but it is equally important in the posterior region too. Missing teeth can be replaced by one of the following prosthesis types. 1) Removable denture Complete Partial denture 2) Tooth ed fixed Partial denture 3) Implant ed fixed Partial denture . It is not uncommon to combine two types in the same arch, such as a RPD and a FPD. When a missing tooth is to be replaced, the majority of patients prefer a FPD. The usual configuration for a FPD utilizes an abutment tooth on each end of the edentulous space to the prosthesis. If the abutment teeth are periodontally sound, the edentulous span is short and straight and the retainers are well designed and executed.

DEFINITION :

 Abutment : A tooth, portion of a tooth/root or an implant used for and retention of fixed or removable prosthesis.  Intermediate abutment: An abutment located between abutments, that form the end of the prosthesis. Multiple abutments: Abutments splinted together as a unit to serve as and retention of a fixed prosthesis.

IDEAL REQUIREMENTS:

 An abutment should be a vital tooth.  However a tooth that has been endodontically treated and is asymptomatic, with radiographic evidence of a good seal and complete obturation of canal, can be used as an abutment.  The tooth must have some sound, surviving coronal tooth structure to insure longevity.  The ing tissues surrounding the abutment teeth must be healthy and free from inflammation.  The optimum crown - root ratio for a tooth to be utilized as a FPD abutment is 1:2. A ratio of 2:3 is considered adequate. A ratio of 1:1 is the minimum ratio that is acceptable for a prospective abutment.  Abutment root should be broader labiolingually than mesiodistally.

CONTRAINDICATION:

Teeth that have been pulp capped in the process of preparing the tooth should not be used as FPD abutments, Unless they are endodontically treated. Because there is a risk that they will require endodontic treatment later, with the resultant destruction of the retentive tooth structure. CLINICAL EXAMINATION OF AN ABUTMENT:     

Each abutment tooth should be examined for Dental caries Decalcification, mobility, erosion Abrasion Attrition and Sensitivity or fractures

DIAGNOSTIC CASTS:

Articulated diagnostic casts can provide good information for detecting and diagnosing the problems. The length of the abutment tooth can be accurately gauged to determine the preparation designs. The true inclination of the abutment teeth will also become evident. Mesiodistal drifting, rotation and faciolingual displacement of prospective abutment teeth can also be clearly seen.

RADIOGRAPHIC EXAMINATION: OPG and IOPA s are taken  Radiographs should be examined carefully for signs of caries, both on unrestored proximal surfaces and recurring around previous restorations.  Presence of periapical lesions and quality of previous endodontic treatments can be evaluated.  General alveolar bone levels, with particular emphasis on prospective abutment teeth should be observed.  The crown root ratio of the abutment can be calculated.  The length, configuration and direction of those roots should also be examined.  Widening of PDL ligament can be detected.  An evaluation can be made of the thickness of the cortical plate of bone around the teeth and trabeculation of the bone.  The presence of retained root tips beside the abutment tooth can also be detected through radiograph.

EVALUATION OF THE ROOTS AND THEIR ING TISSUES: The ing structures around abutment teeth must be healthy. Normally the abutment teeth should not exhibit mobility since they will be carrying an extra load. Roots and their ing tissues can be evaluated for the following factors.

1) The crown root ratio: This ratio is a measure of the length of tooth occlusal to the alveolar crest of bone compared with the length of root embedded in the bone. The ideal crown root ratio for a tooth to be utilized as a FPD abutment is 1:2, however 2:3 ratio is considered adequate. However there are situations in which a crown root ratio greater than 1:1 might be considered adequate. If the opposing tooth is artificial tooth, occlusal force will be diminished, with less stress on the abutment teeth. For the same reasons, an abutment tooth with a less than desirable crown root ratio is more likely to successfully a FPD if the opposing occlusion is composed of mobile, periodontally involved teeth

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2) Root configuration: This is an important point in the assessment of abutments suitability from a periodontal standpoint.  Roots that are broader labiolingually than they are mesiodistlally are preferable to roots that are round in cross section.  Multirooted posterior teeth with widely separated roots will offer better periodontal than roots that converge, fuse or generally present a conical configuration. ?The tooth with conical roots can be used as an abutment for a short span FPD, if all other factors are optimal A single rooted tooth with some curvature in the apical 3rd of the root is preferable to the tooth that has a nearly perfect taper.

Type of tooth Maxi. Central-------------------Maxi. Lateral-------------------Maxi. Cuspid-------------------Maxi. 1st Bi cuspid------------Maxi. 2nd Bi cuspid-----------Maxi. 1st molar----------------Maxi. 2nd molar---------------Mandibular central------------Mandibular lateral-------------Mandibular cuspid-------------Mandibular 1st Bi cuspid-----Mandibular 2nd Bi cuspid----Mandibular 1st molar----------Mandibular 2nd molar----------

Average surface area in Sq mm

204 179 273 234 220 433 431 154 168 268 180 207 431 426

Periodontal ligament area: Another consideration in the evaluation of prospective abutment teeth is the root surface area, or the area of PDL attachment of the root to the bone. Larger teeth have a greater surface area and are better able to bear added stress. Jepsen in 1963 conducted a study to measure the root surface of the abutment and a method for X-Ray determination of root surface area. He reported that the average root surface areas of various teeth were as follows.

Factors modifying Ante’s law: Condition existing 1. Bone loss from PDL disease---2. Medial or distal tipping or changes in axial inclination 3. Migration of abutment teeth decreasing mesiodistal length of edentulous area 4. Less than favourable opposing arch relationships producing increasing occlusal loads 5. Endodontically restored teeth as abutments with root resection 6.Arch from situations creasing greater leverage factors 7.Tooth mobility created after osseous surgery

Probable modification Increase number of abutments Increase number of abutments Decrease number of abutments

Increase number of abutments

Increase number of abutments Increase number of abutments Increase number of abutments.

EXAMINATION OF CROWN OF THE TOOTH:

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In this we should examine for Crown condition Crown strength Crown size Crown shape Crown surface area Crown appearance Degree of eruption Pulp

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Crown condition: If the crown is carious and heavily filled it is always desirable to remove the caries and an existing filling and then rerestore. ii) Crown strength: Caries existing restorations or endodontic treatment may have weakened abutment crown. So the extend of caries either primary or secondary caries must be known before type of retainer selection. iii) Crown size : Any tooth which has less than 4mm inter proximal height from the marginal ridge to the gingival attachments is unsuitable for extra coronal restorations. Pins and posts may be used for extra retention in case of short crowns. veneer. Full veneer crown retainers may overcome the problems of discolored abutment crown.

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Degree of eruption : This is the most important factor to determining the amount of retention available. The preparation can be nearly ideal with minimum convergence. viii)

Pulp : The size of the pulp can be assessed by radiograph chance of exposure of pulp is more particularly in lower first molar where the mesiobuccal horn often remains large.

BIOMECHANICAL CONSIDERATIONS : Bending or deflection of the FPD varies directly with the cube of the length and inversely with the cube of the occlusogingival thickness of the pontic

Compared with a FPD having a single tooth pontic span, a 2 tooth pontic span will bend 8 times as much. A 3-teeth pontic will bend 27 times as much as a single pontic. Double abutments are sometimes used as a means of overcoming problems created by unfavorable crown root ratios and long spans. There are several criteria for the secondary abutments.

A secondary abutment must have at least as much root surface area and as favorable a crown root ratio as the primary abutment. A canine can be used as a secondary abutment to a first premolar primary abutment, but it would be unwise to use a lateral incisor as a secondary abutment to a canine primary abutment. When the pontic flexes, tensile forces will be applied to the retainers on the secondary abutments. Also there should be sufficient crown length and space between adjacent abutments to prevent impingement on the gingiva under the connector

When pontics lie outside the interabutment axis line, the pontics act as a lever arm, which can produce a torquing movement. This is a common problem in replacing 4 maxillary incisors with a FPD. This can be best accomplished by gaining additional retention. i.e., the first pre molars sometimes are used as secondary abutments for a maxi. 4 pontic canine to canine FPD. Because of the tensile forces that will be applied to the premolar retainers, they must have excellent retention.

Special considerations : 1)Pier abutments : An edentulous space can occur on both sides of a tooth, creating a bone, free standing abutment called as pier abutment.

Studies in periodontometry have shown that the faciolingual movement ranges from 56-108 µm and intrusion is 28 µm. Teeth in different segments of the arch move in different directions. These movements can create stresses in a long span bridge that will be transferred to the abutments.

It has been stated that, forces are transmitted to the terminal retainers as a result of the middle abutment acting as a fulcrum, causing failure of the weaker retainer. In this situation rigid restoration is not indicated. The non rigid connector has been suggested as a solution to this problem. A non-rigid FPD transfers shear stress to ing bone rather than concentrating it in the connectors. It minimizes mesiodistal torquing of the abutments while permitting them to more independently.

The location of the stress breaking device in the fine unit fix abutment restoration usually is placed on the middle abutment, since placement of it on either of the terminal abutments could result in the pontic acting as a lever arm.

2. Tilted molar abutments: Another problem that occurs with some frequency is the mandibular 2nd molar abutment that has tilted mesially. It is impossible to prepare the abutment teeth for a FPD along the long axes of the respective teeth and achieve a common path of insertion.

A helical up righting spring is inserted into a tube on the banded molar and activated by hooking it over the wire on the anterior segment. The average treatment time required is 3 months.

If the tilting is slight, the problem can be solved by recontouring the mesial surface of the 3rd molar. If the tilting is severe, the treatment of choice is the uprighting of the molar by orthodontic treatment. Up righting is best accomplished by the use of a fixed appliance. Both premolars and the canine are banded and tied to a ive stabilizing wire.

There are other treatment options.  A proximal half crown sometimes can be used as a retainer on the distal abutment.

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A telescope crown and coping can also be used as a retainer on the distal abutment. A full crown preparation with heavy reduction is made to follow the long axis of the tilted molar. An inner coping is made to fit the tooth preparation and the proximal half crown that will serve as the retainer for the FPD is fitted over the coping. ·

The non rigid connector is another solution to the problem of the tilted FPD abutment.

3 Abutment for the cantilever FPD: A cantilever FPD is the one that has an abutment or abutments at one end only, with the other end of the pontic remaining unattached When a cantilever pontic is employed to replace a missing tooth, forces applied to the pontic have an entirely different effect on the abutment tooth.

Prospective abutment teeth for cantilever FPDs should be evaluated with an eye toward lengthy roots with a favorable configuration, long clinical crowns, good crown root ratios and healthy periodontium.

A cantilever can be used for replacing a maxillary lateral incisor. There should be no occlusal on the pontic in either centric or lateral excursions. The canine must be used as abutment, and it can serve in the role of solo abutment only if it has a long root and good bone .

A cantilever pontic can also be used to replace a missing first premolar For this purpose, full veneer retainers are required on both the second premolar and the first molar. These teeth must exhibit excellent bone .

4. Endodontically treated teeth as abutments:

Endodontically treated teeth should not be used as abutments for distal extension RPDs. They are more than 4 times as likely to fail than pulp less teeth not serving as abutments. Pulp less FPD abutment teeth fail nearly twice as often as single teeth. There is no contra-indication to use pulp less tooth as a part of bridge if there is a satisfactory root filling.

QUESTIONABLE ABUTMENTS : Classification of questionable abutments in FPD : The following outline is presented as a guideline for identification of teeth that are difficult to use as an abutment for FPD. CLASSIFICATION : I)GENERAL DISORDERS: A) Mineralization 1) Amelogenisis imperfecta 2) Dentinogenisis imperfecta 3) Hypo calcification 4) Ectodermal dysplasia 5) Discoloration due to drugs like tetracycline 6) Flouridosis 7) Internal resorption.

Skeletal B) Congenital and growth deformities 1) Malformed dentition 2) Malposed teeth 3) disparities of maxillomandibular relationships 4) Oligodontia II) LOCAL PROBLEMS ASSOCIATED WITH QUESTIONABLE ABUTMENTS: A) Poly carious tooth B) Periodontally involved teeth C) Occlusal plane correction D) Endodontically treated teeth 1) Previously treated teeth 2) Currently treated teeth E) Tilted teeth F) Attrition, abrasion, or erosion

Detection of loose abutment : A loose abutment can be detected by pulling occlusally on the splint or bridge, then drying the gingival margins and pressing the appliance into place. If saliva comes out, that shows that the abutment is loose. Another clinical sign is a foul odor about which the patient complains or with the operator detects in an otherwise clean mouth. Abutments for removable partial dentures : The requirements of an abutment for a RPD are not as strong as those for a FPD abutment. Tipped teeth ading edentulous spaces and prospective abutments with divergent alignments may tend themselves more readily to utilization as RPD rather than FPD abutments.

Periodontally weakened primary abutments may serve better in retaining a well-designed RPD than in bearing the load of a FPD. Teeth with short clinical crowns or teeth that are just generally short usually will not be good FPD abutments. An insufficient number of abutments may also be a reason for selecting a removable rather than a FPD

ABUTMENTS FOR IMMEDIATE OVERDENTURE: Preparing cast abutments: Procedure:  Mark the abutment on the cast indicating the amount of the tooth to be reduced.  Shorten the cast abutment with a bur.  The abutment should be shortened so that a minimum space of 2-3 mm exists between the abutment preparation and the opposing tooth. The abutment is prepared on the cast, removing stone from the facial, proximal and lingual surfaces. Approximately 60% of the reduction should come from the facial surface and about 40% from the lingual surface. The basic purpose of the prepared cast abutment is to form an indentation in the Overdenture that will be occupied by the natural abutment tooth. Then the Overdenture is constructed in conventional manner

Effect of abutment mobility, site, angle of impact on retention of fixed partial denture: By Richard Jacobi , T. Shillinburg JPD. 1985; 54: 178/183. The study included three positions of impacting dowel in relation to fixed partial denture. They were as follows. Position A : Force was directed apically at an angle of 900 to occlusal plane into fossa farthest from pontic area and centered 3mm distal to long axis of abutment die. Position B : Force was at 900 to occlusal plane, but directed in to the fossa closest to pontic area and centered 1.5 mm mesial to long axis of die. Position C : Force was directed 450 to occlusal plane and centered on lingual wall of fossa far from pontic area.

Each group was submitted to a mobility of 0.04mm, 0.08 mm and 0.16 mm. 0.08mm was considered normal by the authors. They observed that retention of fixed partial denture decreased when abutment teeth were mobile. The authors concluded that : 1) Crowns that anchor rigid prosthesis to mobile teeth require greater retentive ability. 2) Occlusal impacts are best with stood when they fall on the areas of fixed partial denture over and between center of rotation of abutments.

Designs of removable partial dentures that are appropriate to aid in ing teeth with secondary occlusal traumatism. JPD 1947:6; 587 / 584. 1) BAR RESTS A bar rest is basically an occlusal rest that s the prepared occlusal central fossa of a tooth or group of teeth. When a bar rest is seated on a prepared tooth, it provides resistance to movement of ed tooth from lateral and or vertical forces. This is best suited to stabilize mobile teeth when there is no distal extension base.

2) Multiple I-bar stabilization These are useful for lateral stabilization of mobile teeth. If there is no distal-extension base, then I-bar stabilizers can be positioned to a 0.01 inch infrabulge undercut. If there is adequate retention from other clasps, then I bar stabilizers may be positioned occlusally to the supra bulge. If there is a distal-extension base, then only those Ibar stabilizers that are distal to fulcrum line (occlusal rest) can engage the 0.01 inch undercut. Once adequate retention is achieved all other I bar stabilizers need only on suprabulge of mobile teeth. Regardless of whether I bar stabilizer engages an undercut or not, it should be plate.

3) Swing lock removable partial dentures This is alternative treatment for a partially edentulous patient designated for full-mouth extractions and complete dentures or for over dentures. After extensive periodontal therapy, certain situations require splinting or some other form of stabilization. In these cases, the swing lock removable partial denture can provide stabilization through control of posterior occlusal forces and through anterior and sometimes posterior splinting.

The removable partial denture as a periodontal prosthesis. DCNA vol. 28 No.2 April 1984.

Components parts of a removable partial denture that may affect the periodontal condition directly or indirectly are the following: Major connector, minor connector, extra coronal direct retainer (rest, retentive), proximal plate, indirect retainers, denture base.

Major connector 1) They should be rigid and should not damage the periodontal of abutment teeth. 2) They should not impinge on free marginal tissue and must never depend on gingival margin for . 3) Highly polished major connectors are more desirable, to decrease plaque accumulation

4) When periodontally compromised anterior teeth require stabilization, a special design of major connector should be used for splinting teeth together. A lingual plate should extend to the middle third of the lingual surface at mandibular anterior teeth and coronal border should follow the natural curvature of the cingulam surface.

Minor connector By ing guiding planes, these aids in distributing, forces to the abutments and in immobilizing the prosthesis against lateral movement. Any space less than 5mm between two vertical minor connectors will have a tendency to accumulate food and plaque in the area. Minor connectors associated with bar clasp arms should be located over keratinized gingiva and should not interfere with movement of alveolar mucosa and frena. If adequate attached gingiva does not exist on respective, mucogingival procedures such as free grafts or pedicle grafts should be instituted to prevent gingival irritation and possible future loss of periodontal attachment.

Direct retainers The circumferential clasp changes the contour of the tooth and interferes with the normal flow of food over surfaces of tooth. Thus allowing marginal gingiva to lose physiologic stimulation. 1) Wrought wire clasps reduces stress on abutment teeth as compared with a cast circumferential clasp. 2) A periodontally acceptable clasp arm should cover a minimum of tooth surface.

3) A retentive arm should be tapered uniformly from its point of attachment at the clasp body to its tip, to minimize damage to periodontal ligaments of abutment tooth.

Clayton – Jaslow 1971, showed that circumferential clasps even with wrought wire retentive clasp arms sometimes exert more force on abutment teeth beyond that required for orthodontic movement. This force causes increased mobility of abutment teeth after initial placement of the removable partial denture. A rest on mesial side of abutment teeth in distal extension removable partial dentures will transfer the chewing forces more perpendicular to ridges than distal occlusal rests. The gingival mucosa of abutment tooth will be better protected when mesial occlusal rests are used. The abutment tooth has more tendencies to rotate mesially, which will be protected by other teeth in front of abutment tooth.

Movement of abutment teeth and damage to the periodontal ligament is related to many elements such as 1)

Location of rests.

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Extension of removable partial denture base.

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Contour and rigidity of direct retainers.

TEBROCK et al 1979 (JPD 41: 511, 1979). studied three clasping systems – circumferential with distal rests, 18 gauge wrought wire clasp and the distal rest, and a buccal I-bar retentive clasp arm. They concluded that there was no significant mobility of abutment tooth during 4-week test period with each clasping system. However, any mobility during increases were in a buccal direction only. There was never a change in lingual mobility of abutment.

SHOKET 1969 (JPD 21: 267, 1969), studied four types of retainers and reported that greatest degree of destructive distal stress on abutments occurred with removable partial dentures with circumferential clasps and precision attachments.

The role of occlusion for the stability of fixed bridges in patients with reduced periodontal tissue . Suture Nyman, Jan Lindhe. J.Clin. Perio. 1975; 2; 53/66 The present investigation reports how occlusion may be utilized to establish and maintain stability of fixed bridges in patients with markedly reduced periodontal tissue . The material consisted of 20 adult patients, age 27-69, with advanced periodontal breakdown often in combination with extensive loss of teeth. After periodontal treatment, patients were rehabilitated with fixed bridges whose stability was evaluated once a year for 2-6 years.

The results show that permanent stability of bridge work can be obtained in patients where there is a minimum of remaining periodontal tissue even in combination with marked hyper mobility of individual abutment teeth.

The stability was achieved by proper treatment of diseased periodontal tissues, and establishment of stable occlusion in the intercuspal position. When there was a risk of bridge mobility on excursive movements of mandible, balancing s were established for prevention of migration, tilting and increasing mobility.

SUMMARY

 The success of prosthesis depends on the many foundational steps taken to prepare it. The proper handling, of abutment teeth is one of these important foundational steps that either enhances or detracts from the eventual value of the prosthesis.  When the conditions are proper like, crown contour, retention and criteria of good preparation techniques and design are met, sound abutment considerations will also be a strong link in the success of the prosthesis. Devan stated that preservation is most important than replacement. In daily practice when we come across abutments which are mobile or have the history of periodontitis they should not be advised for extraction. Treatment planning should be done in such a way so that these mobile teeth can be used as abutments with all precautionary measures to reduce the amount of occlusal forces acting on these mobile abutment teeth.

REFERENCES 1) Tylman’s theory and practice of fixed prosthodontics. 8th ed.

2) Shillinburg. Fundamentals of Fixed prosthodontics. 3rd ed. 3) Rosenstiel, Land, Fujimoto.Contemporary Fixed prosthodontics. 3rd ed. 4) The removable partial denture as a periodontal prosthesis. DCNA vol. 28 No.2 April 1984.

5) BDJ 2001: vol 191 No. 11, 597-604 6) Fixed bridge prosthodontics. D H .Roberts-2rd ed

7) JPD 41: 511, 1979. 8) JPD 21: 267, 1969.

9) The role of occlusion for the stability of fixed bridges in patients with reduced periodontal tissue . Suture Nyman, Jan Lindhe.. J.Clin. Perio. 1975; 2; 53/66. 10) Designs of removable partial dentures that are appropriate to aid in ing teeth with secondary occlusal traumatism. JPD 47:6; 587 / 584 11) Effect of abutment mobility, site, angle of impact on retention of fixed partial denture: By Richard Jacobi , T. Shillinburg JPD. 1985; 54: 178/183.