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Prosthodontics

Authors: Dr. Rathika Rai, Dr. Menaga and Dr. R. Prabhu

ABSTRACT:

Modern Dentistry offers sophisticated treatment options for individual patients and tooth. Prosthodontists face the difficult task of judging the influence and significance of multiple risk factors of periodontal, endodontic, or prosthetic origin that can affect the prognosis of an abutment tooth. The process for deciding when to restore or extract a tooth is often a "gray area" based mostly on clinical experience and rough predications on the long-term prognosis of the tooth in question.

As a result, the clinician often makes decisions on "feelings" rather than clinical parameters. The restorative dentist may have placed all of the restorations on a particular tooth only to see them fail and ultimately need extraction. With the advent of widespread utilization of implants, the issue of retention of questionable teeth assumes a new dimension. The purpose of this review is to summarize the critical factors involved in deciding whether a questionable tooth should be treated and maintained, or extracted and possibly replaced by dental implants.

INTRODUCTION

Restoring function and esthetics for the partially edentulous patient is rewarding for both the patient and the prosthodontist. The options of replacing missing teeth are similar for both anterior and the posterior segments in a Dental arch. Restorative therapies using fixed dental prostheses (FDPs) or removable prostheses are required to replace missing teeth or tooth substance1. The maintenance of healthy oral structures plays a significant role in the success of such restorative therapies.

Commonly observed complications associated with a conventional fixed partial denture (FPD) include loss of retention and tooth fracture and the distal abutment of an FPD developed severe periodontal disease with mobility2. The recent success of dental implants has resulted in substantive changes in treatment strategies for removable dental prostheses (RDPs) when extension bases can be avoided, and for FDPs when there are caries-free or well restored adjacent teeth, which otherwise would have been prepared for abutments with a substantial loss of tooth structure3.

There is, however, considerable variation in treatment planning philosophy among clinicians when encountering patients with pulpally involved teeth and a questionable prognosis4. The greatest challenge in treatment planning is to assign an accurate prognosis and develop a predictable protocol. In the era of evidence-based dentistry, outcome studies have forced us to reexamine our treatment approaches and decide if superior treatment options such as implants should be pursued5.The diagnosis of an abutment is based on 3 parameters (periodontal, endodontic and restorative parameters6) and is always related to a certain prognosis.

An abutment is classified as good, questionable or hopeless3 based on its clinical and radiological assessment. As endosseous dental implants gain greater acceptance because of high success rates, the critical question is whether a tooth with a questionable prognosis should be managed conservatively in a traditional fashion or be strategically extracted in preparation for a dental implant5.As soon as restorative therapies are required, all facets of periodontal, endodontic, and restorative risks must be considered and possible implant contraindications evaluated3.

In most fields, the study of a phenomenon by a group of scientists that focus on just one research direction7. Similarly, there are very few studies where the relative importance of all risk factors has been analyzed multivariately8. The purpose of this article is to summarize the parameters involved in periodontal, endodontic and prosthodontic point of view, that are relevant for deciding whether to treat and maintain a questionable abutment or to extract it and possibly replace it with a dental implant and the role of implants as an abutment.

PERIODONTAL CONSIDERATIONS:

Dental replacements and the dental-periodontal support (the abutments) form an inseparable biomechanical complex. Thus, as the dentures distribute the forces to the abutments, the biological and morphological response of the structures of the oral and maxillary apparatus under the influence of these forces and biomechanical laws has to be assessed.

One of the main goals of dental prosthetics is to reestablish the balance between the two groups of forces with opposite direction that occur during chewing. The result of these forces actions is stress that can lead to a limit-situation (breaking) of the structure (prosthesis) that can no longer fulfill its purpose. Functional occlusal forces are the result of the contraction of masticatory muscles during the functions of the oral apparatus (chewing, swallowing, and speech)7. Reaction forces oppose the occlusal forces and maintain the teeth in their natural position, and also restore them to their initial position after the action of the functional forces stops9.

The crown-to-root ratio (CRR) represents the biomechanical concept of class I lever for evaluating abutment teeth. The ratio is defined as “the physical relationship between the portions of the tooth within the alveolar bone compared with the portion not within the alveolar bone, as determined radiographically.” The fulcrum or center of rotation, of the Class I lever is in the middle portion of the root that is embedded in alveolar bone.

The CRR may increase over time, primarily as a result of loss of alveolar bone support; the crown portion of the fulcrum (effort arm) would then increase, and the root portion (resistance arm) would decrease. The center of rotation moves apically, and the tooth is more prone to the harmful effect of lateral forces. The CRR definition has several inherent shortcomings. The ratio is based on linear measurements only. When clinically evaluating abutment teeth, the status of the alveolar bone height and the total supported root surface of the abutment tooth should be examined.

The CRR does not express the actual area of bone support, and therefore, might underestimate the severity of bone loss around the abutment. The radiographic evaluation of CRR should be based on periapical radiographs10. In periodontics, the classification of teeth as having a good, questionable, or hopeless prognosis is based on the amount of periodontal attachment loss (PAL) and residual probing pocket depth (PPD) or furcation involvement (F.I) 11.

The prognosis of an abutment is considered “good” if the probing pocket depth is less than or equal to 3mm with absence of bleeding on probing, periodontal attachment loss less than 25% and furcation involvement less than or equal to 1st degree (considered as good predictors for a stable situation)12. An abutment is considered “questionable” if the residual PPD is more than or equal to 6mm with presence of bleeding on probing, PAL loss of approximately 50% and FI with either degree II or III(predictive of further activity) 12.

Insufficient residual attachment is considered “hopeless” abutment3. Teeth with a good prognosis are maintained, those with a questionable prognosis are retreated, and hopeless teeth are extracted3. Ante’s law stated that CRR for an FPD abutment of 1:2 to be ideal, but in practice this is rarely observed and this ratio is based on studies of periodontally healthy subjects. Teeth with a normal amount of bone support should be used for abutments and teeth with loss of more than 1/3 of the periodontal support should be of questionable value.

A ratio of 1:1.5 has been suggested as an acceptable and desirable CRR for abutments, although a 1:1 ratio may be a minimum acceptable ratio when the periodontium is healthy and the occlusion is controlled. If the opposing occlusion is composed of tissue-supported prosthesis, a CRR greater than 1:1 might be adequate because of the diminished occlusal forces10.The mobility of natural teeth may increase when the supporting periodontium is lost. It is, therefore, important to reduce the deteriorating effects of the poor supporting tissues under physiologic loads in rehabilitating periodontally compromised dentition13.

This prognosis assessment is generallyperformed at different stages of periodontal therapy:first at baseline, then during reevaluation following the initial nonsurgical therapy and after the active phase of periodontal therapy, and then before the restorative treatment planning, including implant placement. The resulting prognosis implies a consecutive recommendation for the recall interval and additional treatment modalities, if required3. For periodontally involved abutment, the initial assessment does not adequately predict tooth survival, and a reevaluation 6-8 weeks following completion of active therapy (at the earliest) is required to adequately predict tooth prognosis, particularly when the questionable tooth is intended for incorporation as an abutment in an FDP14.

In a study to evaluate the periodontally compromised teeth, 14.4% of the teeth initially present in patients with moderate to severe periodontitis were extracted and approximately half of the extractions were performed during the phase of active therapy, and the other 49% occurred during the maintenance period of 11 years on average15.Patients with prosthodontic reconstructions who are under long-term supportive periodontal therapy were at higher risk for further tooth loss (especially the abutment tooth) than patients without prostheses16.Among periodontally compromised teeth, maxillary molars are the teeth most likely to be lost17.

This reduced efficacy of conventional periodontal therapy in molars is primarily related to complicating anatomical factors, such as furcation entrance diameters <1 mm or root concavities and bifurcation ridges inhibiting adequate personal plaque control and sufficient access to professional cleaning18. Degree I furcation involvement (FI) can be successfully treated by nonsurgical mechanical debridement and surgical treatment may be indicated for degree II and III FIs to eliminate the plaque-retentive morphology and to provide access for plaque removal by the patient and for professional maintenance19.

Surgical interventions include the apically repositioned flap with or without tunneling, and resective procedures, including hemisection and the amputation of 1 or 2 roots20. The prognosis of tunneled molars was found to be improved when regular periodontal maintenance and continuous exposure to fluoride were applied21. Carranza & Newman started that periodontally compromised abutment teeth are unsuitable because they can be “overstressed” from the additional forces applied to teeth supporting a fixed partial denture.

This may be attributed to the resistance to the impact of occlusal forces called as “shock absorber effect”22. On the contrary, there is evidence that teeth with compromised periodontal support can serve successfully as the fixed bridge abutments but, clinicians continue to avoid using periodontally compromised abutment teeth23. The degree of periodontal compromise in abutment teeth to be utilized in a fixed partial denture is however, restricted to grade 1 or 2 mobility22.Additional abutments are not required when periodontally compromised abutment teeth are splinted as there is an increase of stress was observed in periodontally compromised abutments22.

Itohet al24. believed that positive effects of fixed splinting of RPD abutments are more pronounced as the severity of the periodontal defect increases. The maximum acceptable C/R ratio for fixed splinting of a weak abutment to adjacent normal tooth was shown to be 1.65−225. Nyman and Lindhe26 showed that under normal circumstances, a C/R ratio of 1:1 is considered the minimum ratio that is acceptable for a FPD abutment.

Multiple rest seats can be used for sustaining vertical support while improving stress distribution in removable partial denture designs. In periodontally involved dentitions where some teeth have a questionable prognosis an effort should be made to place rest seats in a majority of the teeth involved with the framework. These rests should be placed as close to the long axis of the tooth as possible. In teeth with periodontal involvement this will greatly aid in stress distribution and minimize the potential damage from lateral forces.

Rest seats should have adequate bulk without interfering with the occlusion. To achieve adequate bulk in the rest seat and framework connector may mandate the preparation and restoration of the cingulum of anterior teeth or the proximal surfaces of posterior teeth27. In periodontally involved teeth it is desirable to reduce the torque producing traits of clasps to improve tooth longevity. Hansen et al suggest the use of .0032 nickel-chromium wire for this purpose. It can be bent for use as a circumferential or I-bar type clasp and attached to a replacement denture base should an abutment tooth be lost.

If the new abutment tooth has contour deficiencies that reduce the ability to gain retention on the replacement abutment, the tooth can be recontoured with burs or resin to provide optimal retention27.

ENDODONTIC CONSIDERATIONS:

One of the fundamental goals of dentistry is the retention of a patient’s natural dentition in a disease-free state. When a tooth has a pulpal involvement secondary to tooth fracture and carious lesion, the use of surgical and nonsurgical endodontic treatment has historically been a key ingredient in the attainment of this goal.Survival rates of restored endodontically treated teeth are of great importance. The practitioners believe that all endodontically treated teeth are brittle and require extensive restoration. Clinical prosthetic procedures range from a conventional filling to complete coronal coverage by placement of a complete crown or fixed dental prosthesis.

This situation is complex because fixed partial dentures (FPDs) can be short span, long span or cantilevered and can be made with rigid or nonrigid connectors. The literature on endodontically treated teeth as abutments for fixed and removable partial dentures is sparse. Reports have been primarily empirical statements because limited clinical studies have been performed28.The prognosis of endodontically treated abutment depends not only on the treatment itself, but also the prompt placement of coronal restorations that withstand the stress from the prosthesis retained by it.

In endodontic treatment, the classification of teeth as having a good, questionable, or hopeless prognosis are based on the presence or absence of clinical signs and symptoms and periapical radiolucency. The prognosis of an abutment is considered “good” if there are no clinical signs and absence of or decreasing radiolucency. An abutment is considered “questionable” if there no clinical signs but with persisting radiolucency. Symptomatic situation and presence of radiolucency with no further treatment feasible and extraction is the only choice is considered a “hopeless” abutment3.

Any endodontic treatment in a nonvital tooth with apical radiolucency starts with a 0% success rate, and several months or even years are required for complete healing of the periapical bony lesion. Hence, a reduction in size of the periapical radiolucency over 4 to 5 years is considered a sign of the healing process. Instead of just reporting “success” or “failure” for the outcome of root canal treatment (RCT), it would be better to evaluate it as “success/healed or healing,” which is equivalent to a good prognosis;“diseased/survival,” comparable with a questionable prognosis; and “failure,” corresponding to a poor prognosis29.

The preoperative absence of periapical radiolucency, RCT with no voids, RCT extending to 2 mm within the radiographic apex, and a satisfactory coronal restoration were found to improve the outcome of primary root canal treatment significantly30. Replacement of questionable teeth that can be saved by endodontic therapy with implants is rarely justifiable31.In a study evaluating the reasons for failure of endodontically treated teeth, prosthetic reasons dominated and explained almost 60% of the failures; 32% failed for periodontal reasons, while pure endodontic failures were rare and accounted for less than 10%. Prosthetic and periodontal failures mostly occurred after an average of 5 to 5.5 years, whereas endodontic failures were recognized within a 2-year period after RCT had been completed32.

Caution was suggested with the use of a pulpless tooth as an abutment for a removable partialdenture (RPD) especially when it is a rotation point foran extension RPD28. Others propose that anyendodonticallytreated tooth can be used as an abutment33.However, little information is available to evaluate endodontically treated teeth as abutments for fixed partial dentures (FPD) or RPDs28. It is felt that pulpless teeth must be adequately reinforced if they are to be subjected to the demands of greater stresses as abutments and “reinforcement” with a dowel is mandatory if these teeth are to be used as FPD or RPD abutments34.

In evaluating partial denture abutments and the resultant forces, it is necessary to differentiate between entirely tooth-borne and combination tooth-tissue-borne partial dentures35. Krol36 states: “In the fully tooth borne partial denture occlusal stresses are transmitted to bone by way of the periodontal ligament. It functions similarly to a fixed partial denture. The extension base partial denture, however, derives its support from two different tissues, teeth and edentulous ridge each having different degrees of displaceability. This often results in torquing stress on abutment teeth.” Kratochvil35 circumvents endodontically treated teeth as abutments for RPDs, especially when the tooth serves as a distal extension partial denture abutment. Krol36 concurs with this philosophy if the tooth was endodontically treated more than 10 years earlier.

Composite resin core or amalgam core with a prefabricated post is acceptable for single restorations but a cast dowel and core is necessary for abutments37.Dowel placement had limited influence on the success rate of FPD abutment teeth. Dowel placement is associated with a significantly higher success rate in RPD abutment teeth28.Perel and Muroff38 proposed that additional canals must be enlisted to fabricate a multi-posted post and core for posterior abutments. Prefabricated fiber posts are superior to the conventional post and core systems after 4 years of clinical service39. There was no significant difference in the long-term survival of complete crowns on vital abutments versus post and core complete crowns or in the survival of 3-unit FPDs on vital abutments versus those with at least 1 RCT abutment40.

PROSTHETIC CONSIDERATIONS:

An abutment with extensive damage is one that has lost substantial structure as a result of caries, previous restoration failures, fractures or even procedures related to endodontic treatment and achieving sufficient anchorage in the remaining clinical crown is often impossible. The extent of the remaining tooth structure is among the most important and critical factors in determining the prognosis of a damaged tooth used as an abutment.

Hence, this extensive loss of tooth structure necessitates complete-crown restorations with pulpal retention40. The dimensions of the crown dentin are considered important and it is suggested that a dentin thickness of less than 1mm increases the risk of failure41. The restoration of severely damaged coronal hard tissue and endodontically treated teeth is always a challenge in reconstructive dentistry. Improved restorative adhesive bonding techniques and materials have led some researchers to suggest that such teeth can be restored in a more conservative manner than was previously considered appropriate. Precautions are to be taken when such teeth when used as abutments for the prostheses.

From prosthetic perspective, the most decisive factor that classifies anabutment as having a good, questionable, or hopeless prognosis is based on the remaining coronal tooth substance and the strategic value of the respective tooth with regard to the residual dentition. The prognosis of an abutment is considered “good” whensufficient residual tooth substance with adequate retention and resistance (ideally, 4mm wall height with 15-20 degree convergence angle but with 1.5 to 2mm ferrule)42. An abutment is considered “questionable” when there is reduced retention and resistance form (less than 3mm wall height and/or more than 25 degree convergence angle. Insufficient residual tooth substance (less than 1.5mm with circular ferrule)43 and no crown lengthening or extrusion is feasible in an abutment is considered as “hopeless” abutment3.

Teeth that serve as FPD abutments bear greater stresses in function than single crown abutments34. Teeth serving as abutments for RPDs receive greater stresses in function than non abutment teeth44. Distal-extension partial denture abutment teeth withstand greater stresses than any other abutment tooth33. These stresses can fracture teeth weakened by endodontic therapy and dowel space preparation28.

The purpose of a core is to provide the compromised crown of the tooth with resistance, retention and geometric form for the final restoration. The core material fills the pulp chamber and replaces lost tooth structure prior to crown preparation. A variety of accepted materials may be used for the core superstructure. Dentin-bonded reinforced composite resins and amalgam is the materials of choice. Core materials should be distinguishable from tooth structure. Many reinforced composite materials are available in a variety of colors for this purpose 45.

Nayyar46 et al reported that amalgam coronal-radicular cores can be used to restore abutments for FPDs and RPDs. An invitro study by Steele and Johnson47 showed that composite or amalgam restorations with 3 surfaces (MOD), increases fracture resistance. The comparison between different adhesive systems for the reconstruction of Root canal treated premolars with MOD cavities have shown that dentin-bonding systems stabilize teeth particularly well, such that their fracture resistance was comparable to intact teeth48. The core material has little or no effect on the fracture resistance of the endodontically treated teeth in teeth with only 1 wall of the crown remains49. Crown preparation will further decrease fracture resistance when the tooth is used as an abutment for fixed or removable partial dentures50.

Atleast 1 to 2mm of sound tooth structure gingival core is essential for a well designed crown preparation and marginal adaptation. No matter how well the core materials are bonded to the tooth structure, the potential for leakage exists if the margins gingival to the core significantly enhances stability and increases retention. Resistance to root fracture and core fracture are also improved. When these objectives cannot be readily achieved due to deep cavities or tooth fractures, periodontal crown lengthening is indicated. In the case of the severely compromised endodontically treated tooth, crown lengthening ensures not only a properly restored tooth, but also allows for a sound biologic attachment of periodontal tissues 2 to 3mm apical to the crown45.

It must be noted that the criteria for ideal retention form were originally defined on the basis of in vitro studies investigating gold alloy restorations luted with zinc phosphate cement, while the use of adhesive cementation techniques potentially allows for greater flexibility 51. The next major factor in prosthetic considerations apart from the remaining tooth structure and the luting material used to cement the FPD, maintaining vitality of the abutment is also a important. According to a multivariate analysis of abutment failures (365 teeth with vital pulps, 122 root-filled teeth), other influencing factors besides root canal treatment were distal terminal position in the FDP, and advanced marginal bone loss, as initially assessed from radiographs 52.

An improved outcome for tooth-supported FPDs was achieved by using less compromised teeth as abutments, not necessarily extracting and replacing them, but placing implants in addition53. According to a review comparing the outcome of implant- and tooth supported restorations, there were no differences after 60 months, with a 95% success rate for implant restorations and 94% for conventionally fixed dental prostheses, while resin bonded FDPs had a somewhat lower success rate of 75% 54.

SPECIAL CONSIDERATIONS:

There are few clinical situations where the abutment is considered questionable merely by its position in the Dental arch, which is otherwise deemed healthy. Various treatment options have been suggested by researchers over the years but obtaining long term success has been a paramount to the Prosthodontist.

Pier abutments:

The prosthetic restoration of a partially edentulous ridge in the posterior region of the oral cavity, by means of a 5-unit fixed partial denture with a pier, is considered a challenging task. Pier abutment, also named intermediate abutment, is defined by the Glossary of Prosthodontic terms as a natural tooth located between terminal abutments that serve to support a fixed or removable dental prosthesis. It has been postulated that the tendency of the terminal abutments to intrude during function results in a teetering movement, where the pier acts as fulcrum. This movement will eventually result in debonding of the less retentive terminal retainer and invariably the failure of the prosthesis. The use of non-rigid connectors has been suggested to overcome this potential risk55.

Shillingburg et al56 determined that the matrix of a non-rigid connector (either a precision or semi-precision attachment) should be placed at the distal aspect of the pier retainer and the matrix in the distal pontic. Markley55 suggested that the non-rigid connector should be placed on one of the terminal retainers and emphasized that it should not be placed at the pier abutment because this would subject the relatively weak abutment to extreme loads. Adams57 advised placing one non-rigid connector at the distal side of the pier and adding one more at the distal of the anterior retainer.

Shillingburg et al56 contraindicated the use of a non-rigid connector in a posterior 5 unit FPD with a pier in some situations: (1) If the abutment teeth present significantly mobility, (2) If the span between the abutments is longer than 1 tooth, because the stresses transferred to the abutment tooth under the soldered retainer would be destructive and (3) If the distal retainer and pontic are opposed by a removable partial denture or edentulous edges while the 2 anterior retainers are opposed by natural dentition, possibly allowing the distal terminal abutment to supraerupt.

In a FPD with a pier abutment, almost 98% of posterior teeth tilt mesialy when subjected to occlusal forces even when a non-rigid connector is used. If the keyway of the connector is placed on the distal side of the pier abutment, mesial movement seats the key into the keyway more solidly. Placement of the keyway on the mesial side, however, causes the key to be unseated during its mesial movements58.

Tilted Abutments:

Placement of a fixed partial denture (FFD) can be complicated by misaligned abutment teeth. An unfavorably tilted abutment tooth is a common problem in prosthodontics. Such a tooth is unlikely to offer adequate retention or an adequate guide surface for a removable partial denture. Such malaligned abutments often disrupt the occlusal plane, possibly with premature or interceptive cuspal contact, and form a large cervical embrasure space between the prosthesis and abutment tooth. Misalignment is most frequently encountered when a mandibular first molar is to be replaced after the second and third molars have drifted and tilted mesially and lingually59.

Many treatment options were advocated. Use of orthodontic treatment to upright the mesially tipped molar has been suggested60. Although this approach is ideal, patients are often reluctant to commit the time and funds necessary for this extended and extensive treatment. It is possible to prepare the molar abutment with a path of insertion that is compatible with the premolar preparation, but this approach has several disadvantages. The risk of creating a mechanical exposure of the mesial pulp horn is increased and the retention and resistance of the molar prepared under these conditions are severely compromised61.

Rosenstielet al62 and Shillingburg et al63 have recommended the use of the mesial half crown as a retainer for tilted molars. A mesial half-crown retainer has several disadvantages: (1) The mesial half crown cannot be used if the molar has previously been restored on the distal surface. (2) Preparation of the molar could result in exposure of the mesial pulp horn. (3)The patient may object to the use of a cast-metal restoration. (4) Caries occurring on the unrestored distal surface of the second molar abutment after insertion of the prosthesis jeopardizes the restoration. Shillingburg et al63 have suggested use of a complete coping with retentive grooves and a telescopic mesial half crown for the molar retainer. The disadvantages included pulp exposure or an overcontoured retainer.

Shillingburg et al63 have suggested the use of a segmented FPD with a nonrigid attachment between the second premolar retainer and pontic. O'Connor et al64 have proposed a segmented FPD with a split pontic containing a nonrigid connector.

IMPLANT SUPPORTED PARTIAL DENTURES:

Dental implants are generally placed into relatively healthy surroundings. This is clearly a different situation from that presented with periodontally involved or endodontically treated teeth, which require a different type of treatment evaluation 3.Despite the fact that dental implants have been used widely for restoring complete and partial edentulous jaws, still there is debate on connecting the implant to the natural tooth 65.

Since there is a biomechanical challenge in connecting teeth to osseointe-grated implants, the use of rigid connectors (RCs) in TIFPs is not supported by Skalak66. To compensate for dissimilar mobility of natural teeth and implant systems, several specific methods have been suggested. Non rigid connectors (NRCs) act as stress breakers with the ability to separate the splinted units67. On the other hand, thanks to prosthesis and implant, rigid connectors have the inherent flexibility to modify dissimilar mobility characteristics68. There is no difference in using a rigid connector, non rigid connector in the distal surface of the tooth or in the mesial surface of an implant69.

This is clearly a different situation from that presented with periodontally involved or endodontically treated teeth, which require a different type of treatment evaluation. Following successful implant osseointegration, the prognosis is defined to be good when there is no bleeding on probing, suppuration or bone loss around the implant. The implant is considered questionable if there is bleeding on probing but without presence of bone loss and a mobile implant is considered as hopeless prognosis3.

Early implant failures occur primarily during the first weeks or months after implant placement and are frequently related to surgical trauma, complicated wound healing, insufficient primary stability, and/ or initial overload70.Late implantlosses occur after initially successfulosseointegration and are causedby microbial infection, overload, ortoxic reactions from implant surfacecontamination, such as from acidremnants. Microbial infection initiates periimplantmucositis. This correspondsto gingivitis and may progress intoperiimplantitis, which correspondsto periodontitis71. While periimplantmucositis is a reversible inflammatoryreaction in the soft tissues surroundingan implant, periimplantitis is aninflammatory reaction associatedwith loss of supporting bone aroundan implant in function72.

The preservation of gingival structures is critical and is most predictable when the questionable tooth is treated and maintained with a sound periodontium. As soon as tooth extraction is performed, most of the distinct fiber arrangements within the zone of connective tissue attachment are lost, particularly those inserting into the cementum73.

It was previously believed that implant placement in the fresh extraction socket (immediate implant placement) would prevent bone resorption and, hence, maintain the original shape of the ridge74. A recent clinical study has demonstrated, however, that irrespective of the placement of an implant, post-extraction bone remodeling occurs and results in horizontal and vertical bone loss75.There was no significant difference in the treatment outcomes comparing the teeth treated with Toot canal treatment and extracting the teeth and replacing it with implants76.

When developing a treatment plan, tooth prognosis is first assessed and all pretreatment requirements are considered, including periodontal treatment, RCT, posts and cores, crown lengthening, and/or orthodontic extrusion. Before the definitive restorative therapy is conducted, any questionable tooth is reevaluated in terms of periodontal stability, unaffected sensibility, or healing of periapical radiolucency following RCT.

As soon as multiple risk factors are identified for a tooth intended as an abutment for an FDP, complexity increases and the entire restoration is at higher risk. When, however, the questionable tooth is in a strategic position for a long-span FDP, extraction and a change in treatment plan with single units or short-span FDPs supported by implants or teeth may be considered. Clearly, the condition of the remaining dentition and the overall treatment plan will determine, at least in part, whether or not a questionable tooth is maintained 3.

SUMMARY:

With deficiencies in comparative studies and success being defined in very different ways both within and among the different treatment modes, with complications largely unexplained and psychosocial outcomes incompletely addressed, to summarize with the minimal literature:
 
  1. Teeth with reduced periodontal support can serve as abutments for FPDs or RPDs after successful periodontal treatment. Abutments in which radicular treatment such as radisection or hemisection are likely to fail as abutments.
  2. Clinically asymptomatic endodontically treated teeth with healing periapical radiolucency can be used as an abutment for FPDs and RPDs.
  3. Prefabricated posts have shown better results in reinforcing compromised teeth.
  4. From the restorative perspective, atleast 2 to 3 walls should be present for the core material to support the remaining tooth structure
  5. .
  6. Atleast 1 to 2mm of sound tooth structure gingival core is essential for a well designed crown preparation and marginal adaptation.
  7. When a long span of FPD is required with multiple questionable abutments, it is advisable to plan for multiple short span FPDs.
  8. Implant supported denture too shows short term promise but requires long term follow-up and results.
  9. Placement of non-rigid connectors in FPD’s provided better success rate in clinical situations with pier abutments.
  10. Segmented FPD’s are a well-established method recommended when tilted teeth are used as abutments.

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