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Author Dr. Rahul Nagrath,

ABSTRACT

Hemisection of molars may be a viable treatment option when there is vertical bone loss involving one root and the other root/roots are healthy so that the teeth are retained in whole or in part. Bio mechanical factors such as overload, leverage, torque and flexing induce abnormal stress concentration in a fixed partial denture. Stress concentration is found in the connectors of the prosthesis and this factor may play an important role in the failure of the prosthesis. The use of non rigid connector helps in relieving the stress and thus aids in the success of the FPD.

This paper describes a case report regarding replacement of missing second molar with hemisected first molar which is used as an abutment.

Key words : Hemisection, non rigid connector, proximal half crown, telescopic crown

Management of a hemisected molar– a case report

Introduction

Hemisection of molars is a viable treatment option when there is vertical bone loss involving one root and the other root/roots are healthy. Such teeth can be useful as independent units of mastication or as abutments in simple fixed bridges9. The use of non rigid connector in fixed partial denture reduces stress concentration on the abutment and increases the life span of the prosthesis. This case report describes the use of non rigid connector in FPD with a hemisected molar as an abutment.

Case Report

A 37 year old male visited the OPD of KDDC, Mathura with a chief complaint of pain in the left back region of his mouth since once week. He also had a missing tooth in the same region, which he wanted to get replaced. On examination the left mandibular first molar was sensitive to percussion and revealed Grade I mobility. On probing the tooth, there was a deep periodontal pocket in relation to the distal root of the tooth with a Class II furcation involvement. The left mandibular second molar was missing. On radiographic examination, severe vertical bone loss was evident surrounding the distal root. The bony support of mesial root was completely intact. (Figure 1)

Treatment

It was planned that for long term survival of the tooth, it was necessary that the molar be hemisected and the mesial root retained after endodontic therapy (Figure 2). This would also aid in maintenance of good hygiene and plaque control. Root canal therapy and periodontal therapy which included scaling was accomplished. Selective grinding of the occlusal surface was done to ensure that the forces were redirected along the long axis of the mesial root. The patient responded well to the treatment. After satisfactory tissue healing, restoration of the hemisected molar and replacement of the missing teeth were started.
Various treatment modalities for restoring the tooth and edentulous area were thought of which included removable partial denture, fixed partial denture, implant supported prosthesis. Implants were ruled out as the patient could not bear the expenses. The patient desired a fixed prosthesis, hence FPD was the best option considering the patients needs and for restoring the hemisected molar and the missing second molar.

It was planned to fabricate the FPD in two halves, mesial half and distal half. A non rigid connector (customized key, keyway) in the distal of hemisected molar joined both these halves to reduce stress on the abutment. The distal most abutment was the third molar, but it had an angulation of more than 30 degrees. After tooth preparation, a telescopic crown was first fabricated and cemented. A proximal half crown was planned as retainer on this telescopic crown to compensate for the discrepancy between the paths of insertion of the abutments. On the mesial side, it was deemed necessary to take advantage of a secondary abutment (second premolar) as the first molar had lost significant amount of its attachment surface area after hemisection.

Discussion

Various resection procedures described in the literature include root resection, root amputation, hemisection, radisection and bicuspidization. Hemisection denotes removal or separation of root with its accompanying crown portion of mandibular molars.

Indications for hemisection11

1. One or more roots of a molar may be removed to eradicate areas of the tooth that create problems in maintenance of good hygiene and plaque control10.

2. Severe vertical bone loss involving one root of a mandibular molar or one or two roots of a maxillary molar.

3. Furcation involvement that is not treatable by odontoplasty-osteoplasty.

4. Vertically or horizontally fractured roots or teeth.

5. Unfavorable root proximity.

6. Severe caries.

7. Internal or external resorption.

8. Inability to treat one root canal successfully.

9. Failure of an abutment in a long-span splint or FPD.


Contraindications for hemisection11


1. Closely approximated or fused roots.

2. Significantly decreased general osseous support or an increased crown/root ratio.

3. Remaining structure that will not provide adequate resistance against the forces of mastication.

4. Excessive loss of supporting root structure.

5. Inability to be treated endodontically.

In the case presented, the distal most abutment was the third molar which was utilized as a retainer. But the inclination of the tooth was more than 30 degrees. It was impossible to prepare the abutment tooth for a fixed partial denture along the long axis of the abutments and achieve a common path of insertion. Various treatment modalities have been described in the literature regarding the restoration of such teeth. Some of these include uprighting of the tooth by orthodontic treatment, proximal half crown, telescopic crown and coping10. In this case, a full crown preparation was made to follow the long axis of the tilted molar. An inner coping was made to fit the tooth preparation and was cemented (Figure 3).A proximal half crown which would serve as the retainer for the FPD was fabricated to fit over the coping. This restoration allowed for total coverage of the clinical crown while compensating for the discrepancy between the paths of insertion of the abutments.

It had become necessary to involve the second premolar as the secondary abutment as the hemisected molar had lost 32% of surface area 10 It was also imperative that the hemisected molar was called upon to bear the least amount of stress, hence a customized Non-Rigid Connector (key - keyway) was designed. The Non-Rigid Connectors are mainly used to relieve stress on the abutment, in cases of pier abutments and to accommodate malaligned FPD abutments.

There are many types of Non-Rigid Connectors which are used like the dovetails (key-key ways), split pontics (connector inside the pontic) or tapered pins. For this case, the wax pattern for the retainers (mesial half) was fabricated on the working cast. (Figure 4) A key way was formed of acrylic resin, which was then incorporated into the distal surface of the wax pattern of the hemisected first molar. The wax pattern for the pontic and the proximal half crown retainer (distal half) was then fabricated. An acrylic resin key was made and incorporated into the mesial of the pontic. The path of insertion of both the halves was such that the key fitted passively in the key way. The key was tried for placement into the keyway. The wax patterns were invested, burned out and cast. The fixed partial denture was hence fabricated in two parts - the mesial and distal half (Figure 5). The mesial two unit segment was cemented first followed by the distal two unit segment, immediately afterwards. Care was taken to ensure that no cement was placed in the keyway (Figure 6, Figure 7).

It has been reported that high stress values are located at the connectors, cervical regions of abutment teeth, root surfaces and apical aspects. 8,7,6 However, with the use of a Non-Rigid Connector, stress distribution patterns are reduced. Especially with the use of a nonrigid connector at the distal region of the pier abutment 1, the area of maximum concentration for the pier abutment was reduced. With this design type, there were no stress concentrations at the anterior abutment with posterior loading, and vice versa. 1

The current prosthetic guidelines for rehabilitation of hemisected molars suggests that the restoration emerges from the root with a zero degree emergence profile. This flat prosthetic contour at the gingival margin, produces a more hygienic, less plaque retentive region. 5,6

CONCLUSION

Hemisection of either a maxillary or mandibular molar is often a means of retaining teeth needed for restorative abutments or occlusal support. Use of non rigid connector in fixed partial denture is a viable treatment option to relieve stress on the weak abutment and also to accommodate malaligned abutments. The design and passive fit of the non rigid connector is critical in the success of the prosthesis.


PHOTOGRAPHS AND LEGENDS
Figure 1 - Pre operative radiograph showing vertical bone loss around distal root 36
Figure 2 - Vertical cut towards the bifurcation area 36
Figure 3 – Metal coping cemented on the third molar, hemisected molar(36) also can be seen (Occlusal view)
Figure 4 – Mesial half of the FPD with customized keyway in the distal of hemisected molar
Figure 5 – Complete FPD with the mesial and distal halves
Figure 6 – Mesial half cemented onto the abutments
Figure 7 – Complete FPD with the mesial and distal halves cemented restoring hemisected molar(36) and missing second molar (37) (Occlusal view)

References
  1. Selcuk Oruc, Oguz Eraslan, H. Alper Tukay, Arzu Atay. Stress analysis of effects of nonrigid connectors on fixed partial dentures with pier abutments. J Prosthet Dent 2008;99:185-192.
  2. Gregor M Kurtzman, Lee H Silverstein, Peter C Shatz. Hemisection as an alternative treatment for vertically fractured mandibular molars. Compendium February 2006;27: 2.
  3. Botelho MG, Dyson JE. Long-span, fixed-movable, resin-bonded fixed partial dentures: a retrospective, preliminary clinical investigation. Int J Prosthodont 2005;18:371-6.
  4. P.V Badwaik, A.J Pakhan. Non-rigid connectors in fixed prosthodontics: current concepts with a case report. JIPS 2005;5:2.
  5. Parmar G, Vashi P. Hemisection : A case-report and review. Endodontology, Vol. 15, 2003
  6. Moulding MB, Holland GA, Sulik WD. Photoelastic stress analysis of supporting alveolar bone as modified by nonrigid connectors. J Prosthet Dent 1988;59:263-74.
  7. Sutherland JK, Holland GA, Sluder TB, White JT. A photoelastic analysis of the stress distribution in bone supporting fixed partial dentures of rigid and nonrigid design. J Prosthet Dent 1980;44:616-23.
  8. Shillingburg HT Jr, Fisher DW. Nonrigid connectors for fixed partial dentures. J Am Dent Assoc 1973;87:1195-9.
  9. Basaraba N. Root Amputation and tooth hemisection.Dent Clin of N Amer 1969;13 : 1211.
  10. Shillinburg. Hobo, Whitsett, Jacobi. Fundamentals of fixed Prosthodontics, Third edition.
  11. Rosenstiel, Land, Fujimoto. Contemporary fixed prosthodontics. Third edition

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