Journal of Dental Herald

Journal of Dental Herald www.dherald.in A Review Abutment Evaluation A Boon To Success Of Fixed Partial Denture Introduction Fixed prosthodontic treatment can range from the restoration of a single tooth to the rehabilitation of the entire occlusion. Single teeth can be restored to full function, and improvement in cosmetic effect can be achieved. Missing teeth can be replaced with prostheses that will improve patient comfort and masticatory efficiency, maintain the health and integrity of the dental arches, and, in many instances, elevates the patient s self-image. Every restoration must be able to withstand the constant occlusal forces to which it is subjected. This is to particular significance when designing and fabricating a fixed partial denture, since the forces that would normally be absorbed by the missing tooth are transmitted, through the pontic, connectors and retainers, to the abutment teeth. For example, to evaluate the significance of a simple full crown on a mandibular molar tooth in a patient with relatively normal occlusion, a full complement of teeth and normal bone support. We see that the following parameter of form and forces are within the control and responsibility of the operator: a) Number and area of occlusal contacts. b) Inclination and length of cusps. c) Axial contours. Journal of Dental Herald (April 2014) Issue:2, Vol.:1 E ISSN No. : 2348 1331 P ISSN No. : 2348 134X 1 2 3 4 5 Sharma Sumeet, Sethuraman Rajesh, Singh Harvinder, Singh Sarbjeet, Wazir Dev Nikhil 1 Senior lecturer, Department of Prosthodontics, Institute of Dental Sciences, Sehora, Jammu, India. 2 Professor, Department of Prosthodontics, K.M. Shah Dental College & Hospital, Vadodara, India. 3 Professor, Department of Prosthodontics,Institute of Dental Sciences, Sehora, Jammu, India. 4 Reader, Department of Oral Medicine & Radiology, Institute of Dental Sciences, Sehora, Jammu, India. 5 Professor & HOD, Department of Conservative & Endodontic, Institute of Dental Sciences, Sehora, Jammu, India. Abstract Fixed partial dentures transmit forces through the abutments to the periodontium. Failures are due to poor engineering, the use of improper materials, inadequate tooth preparation, and faculty fabrication. Of particular concern to dentists is the selection of teeth for abutment. They must recognize the force developed by the oral mechanism, and the resistance of the tooth and its supporting structures to them. Successful selection of abutments for fixed partial dentures requires sensitive diagnostic ability. Through knowledge of anatomy, ceramics, the chemistry and physics of dental materials, metallurgy, periodontics, phonetics, physiology, radiology and the mechanics of oral function is fundamental1. This article review diagnostic procedures and requisities for the selection of abutments. Key Words Biomechanics, FPD, Pontics, Retainer, Span length, Clinical crown, Anatomical crown. double as an FPD retainer. If several abutments in one arch require crowns, there is a strong argument for the selection of a [1] fixed partial denture rather than a removable partial denture. Diagnostic Casts Accurate diagnostic cast must be correctly oriented to the transverse hinge axis and the plane of occlusion on an articulator to permit eccentric movements similar to those that take place in the mouth. This procedure allows a simple evaluation of the occlusal relationships of the dental arches and the abutment teeth. Roentgenographic Examination Periapical and bite-wing films are most important in selection of abutment teeth. The primary purpose of roentgenograms is to disclose hidden areas and structures such as the root morphology, pulp outline, the periodontal ligament space, the alveolar bone, infrabony defects, residual roots, impacted or supernumerary teeth, and the extent of present or past caries. Definite rules of treatment planning cannot be formulated. However, an understanding of the favourable indications and reasonable limitations of abutments for fixed partial dentures [2] is essential. Abutment teeth are called upon to withstand the forces normally directed to the missing teeth, in addition to those usually applied to the abutments. If a tooth adjacent to an edentulous space needs a crown because of damage to the tooth, the restoration usually can Quick Response Code Address For Correspondence: Dr. Sumeet Sharma, Senior Lecturer, Department of Prosthodontics, Institute of Dental Sciences, Sehora, Jammu, India. Phone no. 09419148335. E-mail: drsumit02@gmail.com Factors Governing Abutment Selection Crown Gottlieb has suggested a special terminology, anatomic crown and clinical crown. He calls the enamel covered portion of the tooth the anatomic crown, and the cementum covered portion, the anatomic root. Clinically, that portion of the tooth which is actually erupted (exposed) is called the clinical crown, and the remainder of the tooth, which is still united with the investing tissues, the clinical root. Thus, it may be said that in youth the clinical crown is smaller than the anatomic crown, and in old age the clinical crown is greater than the anatomic. In certain mouths, all of anatomic crowns are exposed at the age of 40; in others, at least for some teeth, there is an epithelial attachment 038

the clinical ratio unless otherwise specified. [5] Jepsen compared root surface areas and radio-graphic root areas and established that they could be correlated within a 10% to 15% margin of error, thereby demonstrating the validity of radiographic evaluation. Workers usually recommend the use of Ante's Law when allowances for a 15% to 20% variation in computations of the pericemental area are made." Other textbooks proposed the use of actual crown-toroot ratio in determining prognosis. Presumably these are based on linear measurements from radiographs. A ratio of 1:2 was considered ideal. 1:1.5 was acceptable, and a crown-toto the enamel at 50 years or even later. Size of crown: The combined existing surface area of the periodontal ligaments of the abutment teeth should be equal or exceed the normal area of the periodontal ligament of the teeth [3] to be replaced. The surface area of the periodontal ligaments [4],[5] of normal teeth has been measured by several investigators. The total mesio-distal width of the cusps of abutments should equal or exceed the width of the cusps of pontics. Occlusal anatomy: Occlusal anatomy has an indirect influence on the loads transmitted to the teeth. The occlusal surfaces of natural posterior teeth have distinct cusps with many primary and supplemental ridges. The cusps are convex in both directions with grooves interspersed between the [6] rigdes. Stallard points out that worn-down teeth need more muscular power and longer and more masticatory strokes in order to chew food enough. Much of this force is directed at right angles to the long axis of the teeth. Buccolingual dimension of the teeth: The occlusal surface of the pontics should harmonize with the buccolingual dimension of the natural unmutilated teeth, and recreate the normal buccal and lingual form to the height of contour. Reducing the width of the pontics does not materially reduces the force transmitted to the abutments, but merely places heavier per unit stress on the restoration and produces conditions in the pontic. Roots The forces acting on a tooth are transferred to the supporting bone through the root. The shape of the root determines the ability of the abutment to transfer the masticatory load to the supporting bone. a) Number: Multirooted posterior teeth with widely separated roots will offer better periodontal support than roots that converge, fuse, and generally present a conical configuration. b) Size: Teeth with longer root are stronger abutment than compared to the shorter ones. c) Width: Roots with greater labio-lingual width are preferred. d) Shape: Roots with irregular curvature are preferred. Teeth with conical roots can be used for short span fixed partial dentures. Crown: root ratio: Poor crown-to-root ratio can result from improper dental treatment as well as from traumatic or pathologic changes that either increase the length of the clinical crown or decrease the length of the clinical root. In [7] 1955, Marshall-Day and associates found crestal loss of alveolar bone in 98% or more of a sample of individuals 35 years of age or older. In 1962, examination of a random sample of Americans revealed the increased prevalence of periodontitis and advanced tissue destruction associated with [8] older age groups. Mobility, as related to crown-to-root ratio, occurs when alveolar support is no longer adequate to withstand the forces encountered in the oral cavity. Tooth mobility becomes significant when the re-quirements of comfort and masticatory [9] function are compromised. Development of dental caries on exposed root surfaces is a potential problem. A recent study revealed increased amount of caries on exposed root surfaces [10] in the mandibular arch, most frequently in premolars. In these patients the prevalence of root surface caries did not correlate with the degree of oral hygiene or with evidence of previous coronal caries. "These data suggest that the incidence of root surface caries may be a function of diet rather than an inevitable sequelae of root exposure. The root surface concavities and increased surface area associated with exposed roots also complicate oral hygiene efforts, thus favoring an increased incidence of caries. Sensitivity from exposed root surfaces is also a common problem. A variety of techniques and substances are available for desensitization." Unfortunately, no one approach is uniformly successful. The early guidelines on crown-to-root ratio for abutment teeth were conservative, but they still serve as a standard in many [11] [11] texts. Ante's Law states that "The combined pericemental area of the abutment teeth should be equal to or greater in pericemental area than the teeth to be replaced." Removal of all teeth or roots that are "unfit" for further service was also recommended. Definition and measurement technique: The level of supporting bone is rarely coincident with the cementoenamel junction or dentogingival junction(fig. 1). Evaluation is best performed using the clinical crown-to-root ratio. Further use of the term crown-to-root ratio will refer to Figure 1 039

[12],[13] root ratio of 1:1 was considered minimal or doubtful. Crown-to-root ratio was also discussed in terms of the linear amount of bone loss although the importance of this approach varies with root form and length. Teeth exhibiting extensive bone loss, with pocket depth greater than 6 to 7 mm from the cementoenamel junction, are sometimes considered hopeless because of the compromises encountered in periodontal [13] [14] surgery. Tylman recommended that teeth with a normal amount of bone be used for abutments. However, he stated that teeth lacking one third to one half of their normal periodontal [15] attachment. Beube," discussing the retention or extraction of teeth, assigned a poor prognosis to teeth with only one third of the apical bone remaining, advanced mobility, and poor root [16] morphology. Goldman and Cohen * advocated the retention of teeth based on their ability to return to health and maintain themselves in function. Treatment considerations for teeth with poor crown-root ratio Plaque: Plaque control and adequate oral hygiene are of primary concern in teeth having poor crown-to-root ratio. Continued progression of periodontitis due to inadequate plaque control invites treatment failure. Examples are the addition of margins and solder joints and the exposure of less accessible, concave crown and root surfaces. Periodontal surgery: Periodontal surgery can affect the crown-to-root ratio. Complete: osseous resection of periodontal bony defects to create physiologic contours may [17] result in loss of surrounding bone. Selipsky " noted that the decreased mobility obtained in initial therapy was not compromised in the long-term (1 year) by definitive surgery within "clinically operable limits. Periodontal support regeneration: Regeneration of lost periodontal support is the most logical approach to improve poor crown-to-root ratio, and bone grafting is the most reliable [18] method. Ingber presented the rationale and technique of forced eruption as a method of treating one- and two-wall infrabony defects. Occlusal reduction: Reducing clinical crown length by occlusal reduction of extruded teeth is a valid approach to improving the crown-to-root ratio. Bohannan and Abrams discussed crown shortening in conjunction with intentional pulp extirpation. They noted an improved crown-to-root ratio but encountered complications. For each millimeter of posterior tooth reduction and resultant decrease in the vertical dimension of occlusion, an increase of 3 mm of anterior vertical overlap (overbite) will occur. Overdentures represent an extreme approach to crown shortening and crown-to-root ratio improvement, providing a new treatment alternative. Increasing stability: The mobility seen in teeth with poor crown-to-root ratio can be reduced by selectively grinding occlusal surfaces and minimizing horizontal forces in the [9] existing dentition. Teeth which have poor crown-to-root ratio and exhibit mobility can be retained through splinting. [19] Dawson emphasized the difficulty in maintaining good oral hygiene in splinted areas and suggested splinting only when it is needed. Restorative consideration: Cast restorations for teeth with poor crown-to-root ratios place greater demands on the dentist. Ideal margins of restorations are essential, since inflammation has been associated with restorations having excellent [19] margins. Design of the preparations for cast restorations are dictated by the anatomy of the root surfaces, which may necessitate endodontic therapy. Contours must be consistent with existing root contours and clinical crown form to permit essential hygiene. Extraction: Extraction must be considered as a treatment alternative. Removal or retention of molar teeth related to [17] furcation involvement was reviewed by Saxe and Carmen. These considerations also applied to teeth with poor crown-toroot ratio. These authors suggested that the indications for removal of problem teeth are (1) An unopposed terminal tooth in an arch. (2) A periodontally involved tooth with sound adjacent teeth providing other treatment alternatives. (3) A solitary distal abutment that exhibits mobility. Periodontal factor Inflammation: A diagnosis of periodontitis is not uncommon for the patient requiring prosthodontics because one or more teeth may already have been lost to periodontal disease. The goals of periodontal therapy for the prosthodontic patient are: to resolve the inflammation; convert periodontal pocket depths to clinically normal sulcular depths; establish physiologic gingival architecture; and provide an adequate zone of attached gingiva. Adequate oral hygiene is fundamental to the maintenance of a healthy periodontium. If surgical intervention is required to achieve therapeutic goals, approximately six to eight weeks of healing is recommended before the gingival termination of the tooth preparations is completed. Furcation invasions: Teeth with furcation invasions require special consideration. Margin placement: G.V. Black's original concepts of [20] "extension for prevention" have been modified. Broad extension of cavity preparations to place margins in "caries immune" areas is not universally advocated. The recommendation that all gingival finish lines be developed [20],[21] within the gingival crevice has been challenged. The gingivae are healthiest when margins are placed well [22] above (i.e., 1 to 2 mm) the gingival crest, and intracrevicular margin placement is not the universal solution to dental caries. [23] Biologic width: Histologic studies by Gargiulo, et al have demonstrated a band of soft tissue attach-ment between the base of the gingival sulcus and the alveolar crest that is composed of approximately 1 mm of junctional epithelium (attachment epithelium) and 1 mm of connective tissue fibers. This dento-gingival attachment, referred to as the "biologic [24] width" (Fig.2), has significant implications in treatment planning. The presence of caries, fractured root structure, or previous restorations apical to the gingival crest maypredispose to violation of the biologic width during tooth preparation. A short clinical crown may induce the dentist to overextend the preparation apically in an attempt to enhance [25] retention. Location in the arch Parfitt GJ (1960), have shown that the faciolingual movement ranges between 56-108 µm, and intrusion of 28 µm. Teeth in different segments of the arch move in different directions. Because of the curvature of the arch, the faciolingual 040

Figure 2 movement of an anterior tooth occurs at a considerable angle to the faciolingual movement of the molar(fig.3). ARCH CURVATURE: There is a common problem in replacing all four maxillary incisors with a fixed partial denture and the problem is more pronounced in the arch that is pointed in the anterior. This occurs because the pontics lie outside the interabutment axis line and thus acts as a lever arm, which can produce a torquing movement. In order to offset the torque, additional retention is obtained in the opposite direction of the lever arm and at a distance from the interabutment axis equal to the length of the lever arm. The first premolars sometimes are used as secondary abutments for a maxillary four-pontic canine to canine fixed partial denture. Because of the tensile forces that will be applied to the premolar retainers, they must have excellent retention(fig.3). Figure 3 Angulation A common problem that occurs with some frequency is the mandibular second molar abutment that has tilted mesially into the space formerly occupied by the first molar. It is impossible to prepare the abutment teeth for a fixed partial denture along the long axes of the respective teeth and achieve a common path of insertion. There is further complication if the third molar is present. It will usually have drifted and tilted with the second molar. Uprighting is best accomplished by the use of a [27] fixed appliance. Both premolars and canine are banded and tied to a passive stabilizing wire.a helical uprighting spring is inserted into a tube on the banded molar and activated by [27],[28] hooking it over the wire on the anterior segment. The [29] average treatment required is 3 months. A proximal half crown sometimes can be used as a retainer on the distal [33] abutment.(fig.4) This preparation design is simply a three- Figure 4 quarter down that has been rotated 90 degrees so that the distal surface is uncovered. A telescope crown and coping can also be [34] used al 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 it made to fit the tooth preparation, and the proximal half crown that will serve as the retainer for the fixed partial denture it fitted over the coping. Conclusion Competent treatment depends upon the careful examination of all available information, a definitive diagnosis, and a realistic treatment plan that offers a favourable prognosis. A comprehensive, sequential approach to treatment planning is essential. Planning for fixed prosthodontics must not be independent of other disciplines of dentistry. Hasty, segmented planning that ignores major aspects of needed treatments defies modern concepts of treating the whole patient rather than individual teeth. When planning and treating cases involving fixed prosthodontic restorations, it is important that all the applicable parameters are taken into account. The prosthodontist must not focus too much on the finer details of constructing a perfect restoration, or risk creating a failure because proper engineering principles was not used. If success is to be attained the prosthodontist must take into account the length of span, attachment apparatus, periodontal bone loss, inclination of teeth, position in the arch, opposing occlusion to examine and comes to a specific treatment planning and one must make use of modern diagnostic tools. One such indispersible tool at the hand of the operator is the radiograph. A thorough analysis of the radiograph often reveals that the abutment teeth may not satisfy the requirement of Ante s law. However, long term studies have proved that treatment regimen & maintainence can convert questionable abutments into ideal abutments. Radiographs are made, and pulpal health is assessed by evaluating the response to thermal and electrical stimulation. Existing restorations, cavity liners, and residual caries are removed, and a careful check is made for possible pulpal exposure. Teeth in which pulpal health is doubtful should be endodontically treated before the initiation of fixed prosthodontics. Although a direct pulp cap may be an acceptable risk for a simple amalgam or composite resin, conventional endodontic treatment is normally preferred for 041

cast restorations, especially when the later need for endodontic treatment would jeopardize the overall success of treatment. References 1. Shillingburg H.T, Hobo Sumiya, Whitsett L.D, Jacobi Richard, Brackett S.E. Fundamental of Fixed Prosthodontics, ed. 3, Quintessence Publishing Co, Inc.2010. 2. Johnston J.F., Phillips R.W., Dykema R.W. Modern Practice in Crown and Bridge Prosthodontics, ed. 2, Philadephiah,1965. W.B. Saunders Company, p. 5. 3. Reynold J.M. : Abutment Selection for fixed Presthodontics J. Prosthet Dent.. 19:483, 1968. 4. Ante, I.H: J. Canadian D.A. 2: 249-260, 1936. 5. Jespen, A: Root surface Measurement and A method for X- ray Determination of Root surface area, Acta. Odont. Scandinav. 21: 35-46,1965. 6. Stallard, H.: The Good Mouth- A syallabus on Oral Rehabilitation and Occlusion, University of California, San Fransisco, Calif., Vol.1, p- 13. 7. Marshall-Day, C.D., Stephens, R.G., and Quigley, L.F., Jr.: Periodontal disease: Prevalence and incidence. J. Periodontal 26: 185,1955. 8. Johnson, E.S., Kelly, J.E., and Vankirk, L.E.: Selected Dental findings for adults. National center for health. Statistics, Series 11, No. 7, Washington, D.C, 1965. U.S. Public Health Service. 9. Nyman, S. Lindhe. J, and Lundgren. D.: The role of occlusion for the stability of fixed bridges in patients with reduced periodontal tissue support., J. Clin. Periodontal, 2 : 53, 1975. 10. Sumney, D.L. Jordon, H.V., and Englander H.V.: The Prevalence of root surface caries in selected population. J.Periodontal 44: 500, 1973. 11. Ante, I.H.: The Fundamental Principles of Abutment, Mich. Dent. Soc Bull. 8: 14, 1926. 12. Johnston, J.E, Phillips, R.W., and Dykema, R.W: Modern Practice in Crown and Bridge Prosthodontics, ed. 3, Philedelphia, 1971, W.B Saunders Co. 13. Dykema, R.W: Fixed Partial Prosthodontics, J. Tenn Dent Assoc. 43: 309, 1962. 14. Tylman, S.D: Theory and Practice of Crown and Bridge Prosthodontics, ed.5, st. Louis,1965, The C.V. Mosby Company, p- 173. 15. Beube, F.E: Correlation of the degree of alveolar bone loss with other factors for determining the removal or retention of teeth. Dent. Clin. North Am. 13: 801,1969. 16. Goldman, H.M, and Cohen, D.W.: Periodontal Therapy, Ed. 5, St. Louis, 1973, C.V. Mosby. Co. 17. Prichard, J.F: Advanced Periodontal Disease. Surgical and Prosthetic Management, ed.2, Philadelphia, 1972, W.B Saunders Co. 18. Robert E. Penny., crown-to-root ratio: its significance in resforative Dentistry, J. Prosthet Dent Vol 42; Number, July 1979. 19. Dawson PE. Evaluation, Diagnosis and Treatment of occlusal Problems,ed 1 ST.Louis, 1974. 20. Blackwell, R.E. G.V. Black s operative Dentistry, Vol. II, ed.9, South Milwankee, 1955, Medico-Dental Publishing Co.P-110-111. 21. Reynold J.M.: Abutment Selection for fixed Presthodontics J. Prosthet Dent.. 19:483, 1968. 22. Romanelli, J.H.I. Periodontal considerations in tooth preparation for growth and Bridge, Dent Cli. NorthAm. 24:2,271-283, 1980. 23. Marcum, J.S. : The effect of crown marginal depth upon gingival tissue, J. Prosthet Dent. 17:2,271-283, 1980. 24. Glickman, I.: Clinical Periodontology, ed. 4, Philedelphia, 1972, W. B. Saunders Co., p- 879-898. 25. Miller, C.: A Clinical interpretation of tooth preparation and design of metal substructures for metal ceramic restorations. In Mclean, J.W., editor; Dental Ceramics, Chicago, 1983, Quintessence Publishing co, Inc., P-169-170. Source of Support : Nill, Conflict of Interest : None declared 042