Restoring the patient’s missing dentition secondary to partial mandibulectomy of KCOT is important to improve function and aesthetics. The patient presented with a significant loss of alveolar bone which makes the fabrication of rehabilitation prosthesis a significant challenge. A neutral-zone impression technique is helpful in determining the exact space to be restored without compromising aesthetics and it avoids functional muscle displacement that may displace the prosthesis. This article describes the neutral zone impression technique to record a patient's functional muscular movement in guiding the setting of acrylic teeth and denture flange in the neutral zone area. This technique is very useful for postsurgical cases with significant loss of alveolar bone.
Keratocystic odontogenic tumour (KCOT) is a benign intraosseous neoplasm which can occur in a unicystic or multicystic form and originate from odontogenic tissue [
KCOT surgical treatment may cause the patient to have functional and aesthetic problems. This is due to the aggressive surgical treatment performed by the surgeon which includes at least 2 mm surgical removal from the margin’s lesion. This is done to prevent recurrence as the lesion can infiltrate the head and neck bone. The overall rate of occurrences of postsurgical treatment of KCOT are 23.09% [
Rehabilitation of patient postsurgical segmental mandibulectomy gives significant challenges to a dentist. The patient may present with a significant loss in vertical and horizontal alveolar bone which will make the fabrication of rehabilitation prosthesis a setback. After a surgical procedure, the patient is left with a space that used to be occupied with teeth and alveolus. This loss in space will allow the tongue and buccal mucosa tissue to occupy the space which will make the neutral zone smaller. A problem may also arise since there is no alveolar ridge to serve as a guide in the placement of the prosthetic teeth during acrylic denture setting. Minute displacement in the functional space will compromise denture stability, disturb patient speech, and interfere with patient masticatory function.
Preferably, the loss in vertical and horizontal bone should be replaced with vascularized bone graft or alloplastic material, which may involve another surgery for the former graft. Most of the patients who have been diagnosed with this neoplasm are reluctant to undergo through the surgical and emotional stress from another surgery. So this method of rehabilitation by removable of a partial denture recorded in the neutral zone is an alternative for patients who refuse such emotional and physical stress. This method will also serve as an interim prosthesis before future implant treatment consideration.
The purpose of this paper is to highlight the importance of the neutral zone for a mandibular partial denture in the rehabilitation of partial mandibulectomy of KCOT. This ensures that the polished surface of the denture does not encroach the functional movement on the lingual and buccal musculature and eventually minimizes denture displacement.
A 29-year-old Pakistani male was referred to the Oral Surgery Department for rehabilitation of the left edentulous mandible secondary to partial mandibulectomy surgery. He had undergone two operations for the left body of a mandible keratocyst odontogenic tumour (KCOT). The patient has been diagnosed with (KCOT) in Pakistan, where he received his first surgical treatment. A second surgical partial mandibulectomy was attempted due to recurrence. He has been reviewed regularly and he requested to have a replacement of his missing teeth on the lower left side due to a difficulty in eating and the effect on his appearance (Figure
Facial profile at initial presentation.
Clinical examination reveals an asymmetrical face with a slightly depressed left lower body of the mandible on a class I skeletal pattern (Figures
Coronal view profile at initial presentation.
Intraorally, the oral hygiene was fair with the presence of mild gingivitis. The dentition on the maxillary arch was unrestored (Figure
Preoperative maxillary occlusal view.
Preoperative mandibular occlusal view, note the tongue occupying the edentulous area.
Preoperative right buccal view at maximum intercuspation.
Left buccal view at maximum intercuspation. Note the tongue occupying the edentulous space.
Preoperative frontal view with teeth at maximum intercuspation.
An orthopantomogram was taken to evaluate the remaining bony structure of the mandible (Figure
Orthopantomogram.
Primary impression was made using alginate (Kromopan, Lascod, Illinois, USA) to obtain a set of study cast. A special tray was constructed using a light-cured acrylic resin tray material (plaque photo; W + P Dental, Hamburg, Germany). After border moulding, a secondary impression was taken with a polyether impression (Impregum Penta Soft, 3M-ESPE, Minnesota, USA) and poured with type IV die stone (Vel-Mix, SDS, Kerr, Orange CA) for the construction of the lower cobalt-chrome partial denture frame (Figure
Cobalt-chrome frame constructed on the working model.
After the framework try-in procedure, the bite was registered with a block of wax (Figure
Wax bite record.
Functional impression obtained to record the neutral zone.
The obtained functional impression.
Putty index to serve as a guide for the arrangement of acrylic teeth.
Working model with bite registration mounted on an articulator.
The sectioned putty index showing space for teeth arrangement within the neutral zone.
Teeth arranged in the neutral zone.
Intraoral facial view at ICP.
Occlusal view of prosthesis intraorally.
Buccal views after prosthesis delivery.
The keratocystic odontogenic tumour (KCOT), once known as odontogenic keratocyst (OKC), is a benign unicystic or multicystic odontogenic tumour with an aggressive and infiltrative behavior. It is considered a neoplastic lesion due to its locally destructive behavior, with the basal layer of the KCOT budding through connective tissue [
Treatment of KCOT can be divided into conservative and aggressive treatment. Conservative treatment involves enucleation with curettage of marsupialization, which is usually a treatment reserved for a cyst-oriented lesion. Aggressive treatment is usually done using the ostectomy technique and chemical curettage with Carnoy’s solution of en bloc resection [
The patient’s left mandibular alveolar bone was completely removed and the basal bone was preserved (Figures
Several options were given to the patient regarding the rehabilitation of his left mandibular defect. An implant that retained fixed partial dentures is a promising option given its high success rate. Prior to that, the left body of the mandible needs to be augmented to restore the bone height and width to provide a sound platform for placement. This is to ensure that the implant is not subjected to a high-tipping force resulting from an increased coronal : root ratio in implant restoration. Since the recurrence rate of KCOT was high, it is wise to defer the implant treatment and observe for any sign of recurrence. The recurrence of KCOT can take place up to 5–7 years after treatment [
Postoperative photograph. Note that the collapse of the buccal cheek has been restored symmetrically.
In this patient, a partial denture needs to be constructed in a neutral zone, a space that is free of muscle movement. This space is a result of a balanced interaction between the tongue’s outward movement together with buccal mucosa and lip inward movement during this function [
Upon issue of the lower partial denture, the patient was very satisfied with the result. He was happy to have his lower lip and cheek restored to the original contour and was satisfied with his smile (Figure
In the present case, we demonstrate the construction of a removable partial denture recorded at a neutral zone resulting in an adequate restoration of a patient’s aesthetics and function with minimal displacement from the normal soft tissue movement. The neutral-zone impression technique also allows a dental technician to arrange the acrylic teeth in an area with minimal deviation. The marked loss of alveolar bone secondary to surgical removal can give difficulty to the technician to arrange acrylic teeth in the actual position, which can later cause discomfort to the patient and may result in partial denture instability.
The authors declare that there is no conflict of interest regarding the publication of this paper.