In the present case, placement of a fixed prosthetic device by means of implants was selected for prosthetic treatment following extensive resection of the mandible due to an oral tumor. A simulation was performed to determine the optimal implant sites, and secondary reconstruction was carried out for the bone growth necessary for the implants. As a result, an appropriate occlusal relationship at the mandibular defect site was created.
To date, there have been numerous reports of cases of implant treatment for mandibular defects following mandibulectomy. In most of these, however, reconstruction using fibular bone and a plate was performed followed by implant therapy on the grafted bone, which is by no means sufficient for implants. In the present case, the desirable implant placement sites were considered in advance by envisaging the final appearance and occlusal status, after which sufficient bone volume was made up by secondary reconstruction. This allowed placement of the implant device at the optimal implant site. Guided bone regeneration (GBR), in which regeneration of bone tissue into areas of insufficient bone tissue is promoted, is routinely performed for implant treatment at many dental clinics [7]. However, in cases such as the present one with an extensive mandibular defect, and reconstruction is carried out with a cutaneous flap that has different properties from normal alveolar ridge mucosa, adjustment of the volume of the cutaneous flap and careful control of the volume of grafted bone are needed in the secondary reconstruction. An approach that combines specialists in oral surgery and specialists in prosthetics collaborating together needs to be put in place.
In the present case, a plan with the aim of restoring not only the patient’s appearance, but also her masticatory function, which were lost as a result of mandibulectomy, was drawn up. There are numerous methods available for evaluating a patient’s masticatory function, but it is important that the evaluation is objective and quantitative. In the present case, the method of evaluating the degree of comminution using gummy jelly intended for measurement of masticatory ability was used. In this method, the gummy jelly is freely chewed 30 times, and the degree of comminution is visually evaluated by comparing it against a score table. [8] Since this method allows anyone to easily evaluate masticatory performance, it is often used not just for clinical evaluations, but also in other settings, such as epidemiological research [9, 10]. In the present case, occlusion in the right molar region was established before the prosthetic treatment, so that a certain degree of masticatory function was retained. The patient herself stated that she somehow managed to eat by biting with the rear teeth on the right side. However, her masticatory performance improved from a pre-treatment score of 4 to a post-treatment score of 6, and she stated that, after the prosthetic treatment, she was able to chew food into small pieces and that meals took less time. Thus, it is essential to establish occlusion with a balance between both sides in the molar region to ensure smooth masticatory function, and this was achieved in the present case. Maximum bite force was also evaluated in the present case as an objective indicator of masticatory performance using the Dental Prescale system. In this method, a film for measuring occlusal force is placed between the upper and lower teeth, and the contact status of the teeth and the total pressure exerted by the teeth under maximum occlusal pressure at the maximal intercuspal position are evaluated [11]. It has been shown that maximum bite force correlates strongly with masticatory performance [12]. The establishment of occlusal support on the left side and the ability to exert occlusal pressure on the bilateral molars resulted in an improvement in maximum bite force, leading to improved masticatory performance.
When judging the results of dental treatment, it is important to evaluate the subjective level of satisfaction, as well as objective measures of oral function. In the present case, oral health-related QOL was evaluated as an indicator of the subjective level of satisfaction. The results showed that oral health-related QOL improved after the prosthetic treatment. Various other scales in addition to the OHIP-14 have been developed for evaluating oral health-related QOL, including the OHIP-49 [13] and the General Oral Health Assessment Index (GOHAI) [14], and these are widely used in clinical and research settings. The OHIP-14 is a short version of the OHIP-49, and it was used for the present case, because, in addition to being convenient to use, its reliability and validity have been reported [15]. Since improvement was seen following prosthetic treatment not just in the objective measure of masticatory function, but also in the subjective level of satisfaction, it is clear that the results of the prosthetic treatment in the present case were good.
In the present case, restoration-driven implant treatment was performed in a patient following segmental mandibulectomy for a mandibular tumor, with a good outcome. In addition, it was possible to visualize and accurately judge the effects of the treatment by conducting objective evaluation of masticatory function and subjective evaluation of the patient’s level of satisfaction before and after the prosthetic treatment. Planning the treatment measures with a focus on the final prosthetic vision while making use of the expertise of specialists from different fields, as in the present case, can lead to improvement of oral function in patients with extensive mandibular defects. At the same time, the soft tissue around implant was skin graft, which is completely different with normal oral mucosa. In this case, we did not perform mucosal transplantation such as free gingival graft or vestibuloplasty. Therefore, strict maintenance protocol including professional care and oral hygiene instruction is applied to this patient. It thinks to be better to obtain the keratinized tissue around implant to ensure better cleanability around implant prosthesis if applicable.