Introduction
Mandible is a bone that forms the boundary of the oral cavity and, along with muscles of mastication and peri-oral musculature it forms the lower third of the face.1 Any mandibular defect jeopardizes the form, function and esthetics of an individual. However, marginal mandibular defect does not severely affect the esthetics but function is hampered. It results in loss of teeth along with resection of alveolar bone leaving inferior border of mandible intact. This case report describes the rehabilitation of Class I Subdivision A mandibular defect 2, 3 with cast partial denture using semi-precision attachment and arranging teeth in neutral zone.
Case Report
A 28 years old male patient was referred to the department of dental surgery for rehabilitation of post mandibulectomy residual defect. History of the patient revealed that he had undergone segmnetal mandibulectomy for the treatment of odontogenic keratocyst 1 year back. Intra oral examination revealed presence of right mandibular second premolar, and first and second molars on the same side. Remaining all mandibular teeth were resected along with alveolar bone leaving inferior cortex intact resulting in continuity defect (Figure 1). The wound was closed by split thickness skin graft over the resected mandible.
To rehabilitate marginal mandibular defects, the treatment options available are: (a) fixed dental prosthesis b) Implant supported prosthesis c) surgical reconstruction followed by implant supported prosthesis (d) removable partial denture. 4, 5 As implant supported prosthesis is the first choice of treatment, to evaluate availability of bone, CBCT was done (Figure 2). It revealed inadequate bone to place dental implants and the crown height space of approximately 24mm. The patient was given the choice of surgical reconstruction of mandible but this option was declined. So, the treatment plan was formulated to rehabilitate the patient with removable cast partial denture.
Procedure
The patient was explained about the treatment plan. The diagnostic impressions were made to obtain diagnostic casts and treatment planning was done. The remaining three teeth were prepared to receive full coverage three unit single piece metal crowns with chamfer finish line. Impression was made in polyvinyl siloxane addition silicone putty and light body by two step dual stage impression technique. Impression was poured in type IV dental stone.
Wax patterns in blue inlay wax with rest seats on molars were designed with favorable undercuts for direct retainers. The castable male component of semi-precision attachment was attached on the mesial surface of wax pattern of second premolar. The whole assembly was casted and luted with glass ionomer cement to the prepared teeth. Alginate impression was made of the luted assembly and the remaining resected mandible. Cast was poured in type 3 dental stone. Designing was done for the cast partial denture. Cast partial denture was fabricated with hollow first premolar (Figure 3) to receive the female component of semi-precision attachment. Cast partial denture framework was tried in and functional impression of edentulous area was made using functional relining method. According to functional impression the master cast was altered and altered master cast was obtained.
Again, with the framework, bite registration was done and orientation jaw relation was recorded with face-bow. The wax rim over the framework was replaced with impression compound, which was softened in warm water and placed in patient’s mouth. Patient was instructed to carry out functional movements of tongue, cheeks and lips to determine the netural zone. After functional molding of impression compound, addition silicone putty index was made around impression compound. Impression compound was removed and wax rim was fabricated according to the putty index. Teeth arrangement was done in neutral zone, try-in was done and polished surface of the denture was recorded by placing zinc oxide eugenol paste and again asking the patient to carry out functional movement. Acrylization of the partial denture was done. Denture was again tried in the patient’s mouth to evaluate the stability and retention.
The female component was attached over male component in the mouth and it was picked up in the hollow first premolar with the help of self cure acrylic resin. After complete setting of the acrylic resin, denture was removed and resin was finished. Cast partial denture along with semi-precision attachment was inserted and post insertion instructions were given (Figure 4). Patient was followed up after 7 days and minor adjustments were done. High level of clientele satisfaction was achieved.
Discussion
Marginal mandibulectomy defects generally poses rehabilitation challenges due to less number of remaining teeth, loss of vestibular depth, restricted functional movements of tongue and peri-oral musculature. 6 The post resection wound is closed by split thickness skin graft, which provides better foundation for the denture to rest over it instead of movable oral mucosa. 7 So, to achieve adequate retention and stability of partial denture, additional measures are taken like use of multiple abutments incorporation of precision or semi-precision attachments along with direct retainers. 8 In this case semi-precision attachment was used to provide retention as well as allows minor movements of the prosthesis for broad stress distribution 9 over the teeth as well as split thickness skin graft covered residual mandibular bone.
Stability of denture is very important for efficient functioning of the prosthesis. 10 To accomplish adequate stability, arranging teeth in the neutral zone is essential, especially when very few teeth are remaining. 11 The neutral zone in mouth is the place where the forces by peri-oral musculature is balanced and equally opposed by forces applied by tongue. Arranging teeth in this zone establishes stability of the denture and prevent its dislodgement.
Conclusion
This case report lays emphasis on using semi-precision attachments and application of neutral zone technique in marginal mandibulectomy patients. It helps in achieving adequate retention and stability of the denture and also restores the form, function, esthetics and psycho-social well being of the patient.
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