ABSTRACT
Mandibular deviation related to radical surgical treatment for excising cancer of the oral cavity will result in impaired functionality and facial asymmetry. There are several methods of rehabilitation, that can be distinguished in surgically or prosthetic. Regarding to prosthetic management, the use of an intraoral resin splint (guide-plane) permits retraining the patient's neuromuscular system to the centric position before definitive prosthetic rehabilitation. A new possibility for treating hemimandibulectomy patients is using an only one device both for physiotherapy and eating.

INTRODUCTION
Surgery management for neoplastic lesions of the oral cavity often requires resection involving several anatomical structures: the mandible, floor of the mouth, tongue, and also palate. ⁽¹⁾
Mandibular deviation due to loss of mandibular bone continuity in consequence of surgical treatment, and related altered muscle function will clinically result in facial asymmetry and malocclusion. ⁽¹⁾ The residual mandible deviates medially and superiorly, and it will be more or less evident depending on the location and extend of the resection, the amount of soft tissue and innervation involvement, the presence of remaining natural teeth (the mandibular erroneous movement is more evident in edentulous patients then in dentulous patients that have had a normal intermaxillary relationship). ^(1) (2) A corrective device named "guide flange prosthesis" is indicated to limit that clinical manifestation, also waiting for an eventual reconstructive surgical treatment, and it can be applied or immediately postoperatively as intermaxillary fixation or within 7 to 10 days after the resection as removable device, to restore mandibular function. ^(2) (3)
Some authors prefer to make irreversible hydrocolloid impressions of maxilla and mandible and a wax interocclusal record of centric relation before surgical resective procedure. ⁽⁴⁾
The basic rehabilitation objective is to re-educate mandibular muscles to re-establish an acceptable occlusal relationship (physio-therapeutic function) for residual emimandible, ⁽⁵⁾ so that patient could control adequately and repeatedly opening and closing mandibular movements; ⁽⁶⁾ this is the beginning of definitive prosthetic rehabilitation using a removable prosthesis of which artificial teeth could warrant a stable occlusion; for better results the prosthetic management can be completed combining an exercise program, that can be starter 2 weeks postsurgically and consists of the patient grasping the chin and moving the mandible away from the surgical side. ⁽²⁾ It is generally accepted that there are fewer problems with the rehabilitation of partially edentulous patients than completely edentulous patients. ⁽¹⁾
A review of the literature shows varying basic design of prostheses used, that can be mandibular-based or palatally-based anchored on natural teeth or denture flange. ^{(1) (2) (5) (7)}
The mandibular guide flange device for hemimandibulectomy patients presenting good natural teeth on the residual mandible fits generally over that teeth (base-plaque) and has a guide plane (flange splint) extending into the maxillary buccal vestibule, and which rides on the buccal surfaces of several of the maxillary teeth: this is the mechanical system preventing the mandible from turning toward the resected side. ^(6) (8)
The success of mandibular guidance therapy depends on early initiation of the same, the nature of the surgical defect, patient cooperation. This sort of therapy is most successful in patients whose resection involves only bone structures, and minimally tongue, floor of the mouth and contiguous soft tissues. The prognosis of mandibular guidance therapy also improves if radical neck dissection or radiation therapy are not applied. ⁽³⁾
Normally, patients can use a guide flange device all the day except for night and meals.
The purpose of this article is to describe a new therapic possibility for the prosthetic management of hemimandibulectomy patients, that foresees using only one device both for corrective mandibular movement therapy and masticatory function. This sort of device permits to use the same prosthesis both for eating and for mechanical correction of mandibular deviation.

CLINICAL REPORT
A 56-year-old male came to the Dental Prosthesis Service with outcomes of left mandibular portion hemimandibulectomy. No intermaxillary fixation was applied at surgical time.
From a dental point of view the patient presented within first right to first left mandibular premolar; the surgical side was besides the first left premolar. Both right and left first premolar and canine were gold-resin fixed partial dentures. The patient wore a mandibular removable partial prosthesis with two Ackers clasps both on first right and left premolar and two denture bases of which the left with one resin molar and the right with two resin molars. Right maxillary central, lateral and canine and left central incisive were also gold-resin fixed partial dentures while first left molar was natural element. The patient wore a maxillary removable partial denture made with an anterior-posterior band, circumferential clasp on the first left molar and simple clasps on the right canine and left central incisive with one rest on their palatine surface. Three resin premolars and two resin molars were on the right denture base, and resin lateral incisive, canine and first premolar were on the left denture base.
The patient showed a mandibular deviation toward the osseus defect side, so a modifying on mandibular removable partial prosthesis was scheduled to correct mandibular deviation movements. Occlusal contacts on right side were good when mandible was moved into centric occlusion position , so it was not necessary to replace artificial teeth.
A wax splint (Beauty Pink, Moyco Industries Inc., Philadelphia, U.S.A.) was realized solidly with buccal surface of right denture base, modeled in oral cavity to try patient for centric occlusion position and then processed in transparent resin (Leocryl, Leone S.p.A., Florence, Italy) using an hydromuffle for 15 min at 40°C and pressure of 6 bar (Ivomat IP3, Ivoclar Vivadent, Schaan, Liechtenstein). The modify consisted in placing two cylindrical rubbing attachments (Conod, Cendres & Métaux Italia S.r.L., Milan, Italy), of which male portion diameter was 1.8 mm. and total height 3.0 mm. and female portion base diameter was 2.4 mm. and total height 2.7 mm.. The two male portions, before made active with the own key, were soldered at the ends of a rectangular metal plaque (Pa-Ag-Au-Cu-Zn alloy) 10x5 mm. and 0.5 mm. thickness, that was then inserted into buccal surface of right denture base of mandibular removable partial prosthesis. The mandibular removable partial prosthesis, so modified, was positioned into oral cavity and the two analogues of female portions of two attachments were placed on male portions of attachments. Two cavities were realized on resin splint corresponding to position of attachments; cold resin curing (Vertex Self Curing, Vertex-Dental BV, Zeist, The Netherlands) was placed on it and then the resin splint was inserted in oral cavity. After resin curing, the resin splint with analogues inserted was removed from mandibular prosthesis and polished. The analogues were then replaced by definitive female portions.
After one week mandibular movements were yet greater improved. Check-ups were once a fortnight for three months. During some of these check-ups was necessary rebasing the resin splint with hard wax (Beauty Pink, Moyco Industries Inc., Philadelphia, U.S.A.) to fill the gap between lingual surface of splint and buccal surface of maxillary corresponding teeth. The gap was in function of intermaxillary relationship modification induced by prosthetic treatment.

DISCUSSION
The basic design of the guide flange prostheses used will depend greatly on the oral post-operative findings, so there are no types of appliances that will serve for every patient. ⁽⁸⁾ For this reason improvising for each patient is the better solution to obtain the best results. ⁽⁸⁾
However there are fundamental principles for the construction of a functional appliance:

• Every patient should maintain centric occlusion for mastication, and this may be accomplished by a guide plane; ⁽⁸⁾
  
• No one articulator can reproduce the hemimandible movements, therefore centric relation should be taken in that more comfortable and repeatedly for the patient; this position might be subject to change at a later date if mandibular control ability improves or differs. ⁽⁵⁾
  

• easy to make and repair;
  
• comfortable to wear, also without guide flange inserted;
  
• easy to clean;
  
• functional for patient's disease so that expected results are obtained.
  

Intra-oral view with mandibular removable partial prosthesis placed.

Intra-oral view with maxillary removable partial prosthesis placed.

The mandibular removable partial prosthesis on dental cast with a flexible repositioning key used to maintain the position of wax splint.

Intra-oral view of the metal plaque, on which were soldered the two male portions of precision attachments, inserted into buccal surface of right denture base of mandibular removable partial prosthesis.

The transparent resin splint with female analogues positioned.

The transparent resin splint with definitive female portions of attachments.

Definitive resin splint inserted on mandibular removable partial prosthesis.

The device placed into oral cavity.