Effects of maxillofacial prosthetic treatment on oral health-related quality of life and masticatory ability of patients with head and neck tumors

Abstract

Purpose: Using multivariate analysis, this study investigated the effectiveness of maxillofacial prosthetic treatment in relation to oral health-related quality of life (OHR-QoL), masticatory ability (food intake status score and gum-jelly test score) and related factors in patients who had undergone surgery for head and neck tumors.

Methods: The study cohort comprised 112 patients who underwent surgical resection and prosthetic treatment among 224 patients with head and neck tumors seen at the Maxillofacial Prosthetics Clinic of Tohoku University Hospital in a 2-year period. Correlations between OHR-QoL, food intake status score, and gum-jelly test score (criterion variables), and age, sex, maxillary defect, tongue/soft tissue defect, reconstructive surgery, and chemoradiotherapy (explanatory variables) were investigated, and the data were examined statistically.

Results: Maxillary defect, tongue and soft palate tissue defect, and chemoradiotherapy were identified as factors that hindered the effectiveness of maxillofacial prosthetic treatment for improvement of the OHR-QoL, food intake status score, and gum-jelly test score. On the other hand, reconstructive surgery was a factor that facilitated the improvement of OHR-QoL and masticatory ability with maxillofacial prosthetic treatment.

Conclusion: The factors identified to be related to the success or failure of maxillofacial prosthetic treatment suggest the importance of combining prosthetic intervention with surgical reconstruction.

Introduction

In recent years, the number of patients with head and neck tumors in Japan has increased markedly due to the increased average life expectancy of the population. According to the National Cancer Center, 23,671 patients had oral and pharyngeal cancer in 2019, representing a 4.5-fold increase over the past 33 years [National Cancer Center. Statistical information by cancer type: oropharyngeal cancer. Cancer incidence NCR (2016-2019)]. On the other hand, with the development of treatment methods such as surgery, radiotherapy, and chemotherapy, and the implementation of multidisciplinary treatment, the 5-year survival rate is now >63% [National Cancer Center. Center for Cancer Control and Information Services, Monitoring of Cancer Incidence Japan - Survival (2009-2011)]. However, even if patients achieve a permanent cure and morphological/functional preservation, many experience dysphagia, dyslalia, or a decline in their oral health-related quality of life (OHR-QoL) after treatment, and these are major challenges for dentists responsible for postoperative rehabilitation. Maxillofacial prosthetic treatment is an effective form of dental rehabilitation that utilizes maxillofacial prostheses to restore shape and function in patients who have lost some of their teeth, maxillar/mandibular bone, or face as a result of surgery for head and neck tumors. Treatment planning that considers the final prosthetic restoration to reestablish the patient’s oral function is desirable from the outset, and team medical care based on multidisciplinary collaboration should be the basic policy.

Since 2009, Tohoku University Hospital has been a clinical and research facility for all related departments of Tohoku University. Medical-dental and interprofessional collaborations have created special treatment teams made up of members of departments such as the head and neck cancer boards, center for dysphagia, and cleft lip and palate center [1]. A clinical path and a collaborative medical care system have been established, covering a wide range of specialized fields from diagnosis to rehabilitation of patients with head and neck tumors through medical and dental collaboration. In addition, the institution has created an accurate clinical database of patients, allowing clinical evaluations while minimizing dropouts. However, development of a multidimensional prosthetic treatment plan needs to consider the postoperative recovery of oral function and verify the efficacy of maxillofacial prosthetic treatments using subjective and objective evaluations. Despite sufficient assessment of the effectiveness of maxillofacial prosthetic treatment in clinical settings, only a few studies have conducted longitudinal analysis using an accurate database based on a clinical practice system involving medical–dental collaboration. Moreover, such studies had only small numbers of participants, and were mostly case reports. For example, Aimaijiang et al. examined masticatory function and OHR-QoL after surgery for head and neck cancers and reported that surgery type influenced masticatory function and OHR-QoL after maxillofacial prosthetic treatment; however, they did not conduct adequate longitudinal evaluation in the postoperative period [2]. Said et al. also reported that masticatory function and OHR-QoL were improved by wearing maxillary dentures; however, their study covered only patients who underwent partial maxillectomy [3]. In a OHR-QoL evaluation of maxillofacial prosthesis treatment, Hagio et al. mentioned that the OHR-QoL improved in cases involving both maxillary and mandibular defects; however, the evaluation parameters were limited to the morphology of jaw defects [4].

Thus, the present prospective cohort study investigated cases included in a database of patients with head and neck cancers for whom dentistry played a role in the treatment. Through multivariate analysis, the study aim was to verify the efficacy of maxillofacial prosthetic treatment by examining its benefits in terms of OHR-QoL, masticatory ability (food intake status score and gum-jelly test score) and related factors in patients with head and neck tumors. The null hypothesis tested was that the OHR-QoL and mastication ability of patients who underwent surgery for head and neck tumors would not be influenced by maxillofacial prosthetic treatment, and that no related factors would be found.

Materials and Methods

The protocol for this longitudinal cohort study was approved by the Ethics Committee of Tohoku University Graduate School of Dentistry, Japan (No. 24-10: Outcome study of maxillofacial prosthetic treatment). The study was performed in accordance with the principles of the Declaration of Helsinki, and all participants provided informed consent.

Participants

Among 224 patients with head and neck tumors who visited the Maxillofacial Prosthetics Clinic of Tohoku University Hospital in a 2-year period beginning in April 2019, 156 patients with defects requiring prostheses were selected. Of these patients, 112 (60 men and 52 women; mean age, 68.56 ± 14.98 years) received dental intervention before and after surgery and agreed to participate in this study. The flow of patient selection is shown in Fig. 1. Patients who had two or more cancers or recurrent cancer, patients who received chemotherapy but not surgery, patients who received radiotherapy alone, and patients who received chemoradiotherapy alone were excluded. Moreover, patients who could not eat without prosthetics in place and who had a risk of aspiration were also excluded. The power of the sample size was determined using G*Power statistical software. At least 55 patients in total were required for detection of a significant difference (80% power, two-sided 5% significance level), based on previous assumptions.

Fig. 1 Flow diagram of participant selection

Evaluation methods

OHR-QoL

In this study, the Oral Health Impact Profile (OHIP-49), a questionnaire-based measure of OHR-QoL, was used as a subjective self-assessment tool by patients. This questionnaire is useful for surveys of patients with prostheses for defects [5,6] and consists of 49 questions. Answers to each question were scored as: “very often” (4 points), “fairly often” (3 points), “occasionally” (2 points), “hardly ever” (1 point), or “never” (0 points). A total score was then calculated for each patient. Lower scores indicate higher OHR-QoL.

Food intake status score

The food intake status was evaluated using Sato’s questionnaire [7]. Questionnaires were administered by a dentist who was not involved in the prosthetic treatment. Each patient was asked to complete a questionnaire as to whether specific foods were “easy to masticate”, “difficult to masticate”, or “impossible to masticate”. Masticatory ability was represented as the percentage of foods that were reported as “easy to masticate” among 20 food items. The masticatory ability score ranges from 0 to 100. A higher score indicates better masticatory ability.

Gum-jelly test score

A gum-jelly test was performed to objectively evaluate masticatory ability. In this test, the participants were allowed to chew freely 2 g of gum-jelly containing glucose (Glucorum, GC Corp., Tokyo, Japan) for 20 s on the main chewing side, followed by gargling with 10 mL of water. Masticatory ability was represented as the amount of glucose eluted after mastication measured by Gluco Sensor GS-II N (GC Corp.). A higher score also indicates better masticatory ability.

Assessment methods

OHR-QoL, food intake status score, and gum-jelly test score were assessed before surgery, after surgery, and after prosthetic treatment. The assessment schedule is shown in Fig. 2. Preoperative assessment was performed during the initial visit of the participants to the Maxillofacial Prosthetics Clinic, and postoperative assessment was performed within 4 weeks after surgery. Post-prosthetic assessment was performed 12 weeks after the participants had been fitted with prostheses, and the time by which the participants had accustomed themselves to the prostheses was taken into consideration. The interval between the preoperative assessment and post-prosthetic assessment was defined as ≤48 weeks for all participants to eliminate as far as possible the influence of natural healing on recovery of oral function. In this study, the 48-week period covering the preoperative period, postoperative period, and period after prosthetic treatment was defined as the perioperative period. Patients with a risk of aspiration were excluded. Post-prosthetic treatment assessments were performed with the patients wearing the maxillofacial prostheses. In addition, patients with severe radiation-induced oral mucositis were assessed only after the symptoms had subsided.

Fig. 2 Schedule for evaluation methods: OHR-QoL, food intake status score, and gum-jelly test score

Analysis methods

Comparison of changes in evaluation scores within periods

The change in evaluation scores from the preoperative to the postoperative period was defined as Term1 (T1), the change from the postoperative to the post-prosthetic period as Term2 (T2), and that from the preoperative to the post-prosthetic period as Term3 (T3). The changes in values within a given period for all the participants at T1, T2, and T3 were calculated using the following formulae:

1. •   Changes in values within period T1 = postoperative assessment value − preoperative assessment value
2. •   Changes in values within period T2 = post-prosthetic assessment value − postoperative assessment value
3. •   Changes in values within period T3 = post-prosthetic assessment value − preoperative assessment value

The median of the change in value was used to minimize any bias in OHR-QoL, food intake status score, and gum-jelly test score. The three groups were compared. The Kruskal-Wallis test was employed for statistical testing, and any difference was considered statistically significant when the P-value was <0.05.

Exploration of influencing factors

Changes in the OHR-QoL, food intake status score, and gum-jelly test score at T1, T2, and T3, and factors influencing these changes were investigated. These parameters were set as objective variables. The changes in evaluation scores within a period at T1, T2, and T3 as the objective variables translated to categorical variables as OHR-QoL (1 = improved, 0 = worse), food intake status score (1 = improved, 0 = worse), and gum-jelly test score (1 = improved, 0 = worse). Candidates for explanatory variables include age ( ≥65/<65 years), sex (male/female), maxillary defect (yes/no), mandibular defect (yes/no), tongue and soft palate tissue defect (yes/no), reconstructive surgery (yes/no), and chemoradiotherapy (yes/no). Of these variables, those with significant differences (P < 0.05) by the Mann-Whitney U test were set as explanatory variables after removal of those with strong correlations. Consequently, the following four explanatory variables were set: maxillary defect (yes/no), tongue and soft palate tissue defect (yes/no), reconstructive surgery (yes/no), and chemoradiotherapy (yes/no). Multiple logistic regression analysis was performed, with the significance level set at P < 0.05. All obtained analytical models were confirmed to have a high degree of fitness (P < 0.05) by the Hosmer-Lemeshow test. IBM SPSS Statistics version 25 (IBM, Armonk, NY, USA) was used for statistical analysis.

Results

Profiles of the study participants

The distribution of the 112 participants is presented in Table 1, which also shows the cases corresponding to each explanatory variable set in the exploration of influencing factors. Three cases of tongue cancer were included in mandibular defect cases because the patients underwent partial resection of the mandible at the time of tongue cancer removal and maxillofacial prostheses were placed. A palatal augmentation prosthesis (PAP) was placed in the remaining 20 tongue cancer cases because the resection area was limited to the tongue without maxillary defects. As regards tongue and soft palate tissue defects, 10 of the patients with maxillary gingival cancer had maxillary defects including the soft palate, and 14 of the patients with mandibular gingival cancer underwent partial tongue resection alongside mandibulectomy. Some patients underwent reconstructive surgery using a free anterolateral thigh flap and rectus abdominis musculocutaneous flap.

Table 1 Profile of the study participants

		Maxillary gingival cancer n = 24	Mandibular gingival cancer n = 26	Tongue cancer n = 23	Oral flower cancer n = 12	Pharyngeal cancer n = 13	Buccal mucosa cancer n = 14
Age	≧65/<65	14/10	12/14	7/16	8/4	6/7	8/5
Sex	male/female	8/16	16/10	16/7	4/8	5/8	11/3
TNM classification	T1N0/1	2/2	3/3	4/5	2/2	1/1	1/3
	T2N0/1	4/5	6/4	2/4	1/2	4/3	2/2
	T3N2a/2b	7/4	4/6	4/4	3/2	2/2	3/3
Staging	Stage Ⅰ/ Ⅱ	4/9	6/10	9/6	4/3	2/7	4/3
	Stage Ⅲ/Ⅳ	7/4	4/6	4/4	3/2	2/2	4/3
Location of jaw defect	maxilla/mandible	24/0	0/26	0/3	0/12	13/0	9/5
Tongue/soft tissue defect	presence/absence	10/14	14/12	23/0	9/3	13/0	1/13

Comparison of changes in values within periods

In the Kruskal-Wallis test, the OHR-QoL, food intake status score, and the gum-jelly test scores within a period showed statistically significant differences. Therefore, the null hypothesis was rejected.

OHR-QoL

The median changes in the values of all participants at T1, T2, and T3 are shown in Fig. 3. The OHR-QoL score was increased at T1, indicating a deterioration of QoL. At T2 and T3, the scores were decreased, indicating an improvement of QoL. Significant differences were observed among the three groups (P < 0.05).

Fig. 3 Median change in the values of OHR-QoL at T1, T2, and T3

Food intake status score

The median changes in the values for all participants at T1, T2, and T3 are shown in Fig. 4. The food intake status scores were decreased at T1, increased at T2, and unchanged at T3. Significant differences were observed among the three groups (P < 0.05).

Fig. 4 Median change in the values of food intake status score at T1, T2, and T3

Gum-jelly test score

The median changes in the values for all participants at T1, T2, and T3 are shown in Fig. 5. The gum-jelly test scores were decreased in T1, increased in T2, and slightly increased in T3. Significant differences were observed among the three groups (P < 0.05).

Fig. 5 Median change in the values of gum-jelly test score at T1, T2, and T3

Exploration of influencing factors

Significant differences were found in four factors at T1, T2, and T3: maxillary defect (yes/no), tongue and soft palate tissue defect (yes/no), reconstructive surgery (yes/no), and chemoradiotherapy (yes/no). Multiple logistic regression analysis was performed using the OHR-QoL, food intake status score, and gum-jelly test score as objective variables and the above four factors as explanatory variables. Therefore, the null hypothesis was rejected.

At T1, presence of a maxillary defect was a significant influencing factor for a deteriorated OHR-QoL and food intake status score. No significant influencing factors for the gum-jelly test score were found (Table 2). At T2, the maxillary defect, and tongue and soft palate tissue defect were significant influencing factors for a deteriorated OHR-QoL, whereas reconstructive surgery was a significant influencing factor for improved OHR-QoL. Presence of a maxillary defect was a significant influencing factor for a low food intake status score whereas chemoradiotherapy was a significant influencing factor for a low gum-jelly test score (Table 3). At T3, presence of a maxillary defect was a significant influencing factor for a low food intake status score. No significant influencing factors were found for the OHR-QoL and gum-jelly test score (Table 4).

Table 2 Correlation between objective variables (improved/worsened) and explanatory variables at T1

Explanatory variables	Oral health-related QoL (Hosmer-Lemeshow test: P = 0.325)
	Partial regression coefficient	Standard error	Wald Χ2	P	Odds ratio	95%CI (lower-upper)
Maxillary defect (presence/absence)	1.351	0.264	9.922	0.023*	1.98	1.88-3.63
Tongue/soft tissue defect (presence/absence)	0.323	0.031	7.781	0.102	0.98	0.96-0.99
Reconstructive surgery (with/without)	0.725	0.582	0.62	0.386	1.05	0.84-1.30
Chemotherapy/radiotherapy (with/without)	0.451	0.914	5.212	0.792	1.08	1.03-1.06
	Food intake status score (Hosmer-Lemeshow test: P = 0.124)
Maxillary defect (presence/absence)	−0.882	0.235	9.922	0.002*	2.33	1.46-3.54
Tongue/soft tissue defect (presence/absence)	−2.25	0.225	7.781	0.366	1.02	0.96-0.99
Reconstructive surgery (with/without)	−1.94	0.528	0.62	0.482	1.23	1.04-1.33
Chemotherapy/radiotherapy (with/without)	−0.88	0.772	5.212	0.712	1.06	1.20-1.25
	Gum-jelly test score (Hosmer-Lemeshow test: P = 0.315)
Maxillary defect (presence/absence)	−0.098	0.077	2.267	0.422	1.04	1.04-1.08
Tongue/soft tissue defect (presence/absence)	−1.932	0.082	3.919	0.092	1.07	1.02-1.08
Reconstructive surgery (with/without)	−1.723	0.059	0.72	0.153	1.18	0.96-1.20
Chemotherapy/radiotherapy (with/without)	−0.451	0.397	5.745	0.637	0.89	1.02-1.06

Stepwise multiple logistic regression analysis:*P < 0.05

Table 3 Correlation between objective variables (improved/worsened) and explanatory variables at T2

Explanatory variables	Oral health-related QoL (Hosmer-Lemeshow test: P = 0.442)
	Partial regression coefficient	Standard error	Wald Χ2	P	Odds ratio	95%CI (lower-upper)
Maxillary defect (presence/absence)	1.612	0.512	12.215	0.032*	1.87	1.23-3.01
Tongue/soft tissue defect (presence/absence)	2.251	0.317	13.721	0.001*	2.26	1.51-3.33
Reconstructive surgery (with/without)	−1.892	0.51	7.241	0.042*	1.98	1.88-3.02
Chemotherapy/radiotherapy (with/without)	0.421	0.041	0.927	0.462	1.12	1.03-1.24
	Food intake status score (Hosmer-Lemeshow test: P = 0.297)
Maxillary defect (presence/absence)	−3.241	0.039	13.512	0.042*	2.26	1.34-3.05
Tongue/soft tissue defect (presence/absence)	0.821	0.411	6.218	0.251	1.2	1.02-1.08
Reconstructive surgery (with/without)	1.042	0.451	0.526	0.349	1.04	0.96-1.02
Chemotherapy/radiotherapy (with/without)	1.522	0.653	4.213	0.622	1.03	0.88-1.33
	Gum-jelly test score (Hosmer-Lemeshow test: P = 0.340)
Maxillary defect (presence/absence)	1.024	0.441	3.55	0.429	0.89	0.98-1.02
Tongue/soft tissue defect (presence/absence)	0.892	0.621	7.232	0.71	1.05	0.87-1.39
Reconstructive surgery (with/without)	0.554	0.325	12.341	0.772	1.1	1.02-1.42
Chemotherapy/radiotherapy (with/without)	−2.851	0.025	11.15	0.009*	1.99	1.24-3.75

Stepwise multiple logistic regression analysis:*P < 0.05

Table 4 Correlation between objective variables (improved/worsened) and explanatory variables at the T3

Explanatory variables	Oral health-related QoL (Hosmer-Lemeshow test: P = 0.429)
	Partial regression coefficient	Standard error	Wald Χ2	P	Odds ratio	95%CI (lower-upper)
Maxillary defect (presence/absence)	2.15	0.421	0.982	0.491	1.12	0.98-1.02
Tongue/soft tissue defect (presence/absence)	0.841	0.339	9.231	0.783	1.03	0.96-1.22
Reconstructive surgery (with/without)	−0.271	0.302	13.223	0.302	1.34	1.62-1.80
Chemotherapy/radiotherapy (with/without)	0.882	0.529	11.056	0.205	1.19	0.80-1.20
	Food intake status score (Hosmer-Lemeshow test: P = 0.126)
Maxillary defect (presence/absence)	−2.412	0.024	13.88	0.024*	1.98	0.82-2.96
Tongue/soft tissue defect (presence/absence)	−1.921	0.257	6.399	0.522	0.89	0.87-1.44
Reconstructive surgery (with/without)	−0.887	0.322	0.921	0.104	1.02	0.82-1.12
Chemotherapy/radiotherapy (with/without)	−0.676	0.529	13.22	0.382	1.03	1.02-1.08
	Gum-jelly test score (Hosmer-Lemeshow test: P = 0.332)
Maxillary defect (presence/absence)	−1.01	0.582	0.63	0.422	1.03	0.96-1.04
Tongue/soft tissue defect (presence/absence)	−1.422	0.225	7.33	0.781	1.13	0.88-1.20
Reconstructive surgery (with/without)	−0.882	0.196	13.67	0.301	0.99	1.02-1.10
Chemotherapy/radiotherapy (with/without)	−0.451	0.263	15.29	0.4	1.21	1.04-1.18

Stepwise multiple logistic regression analysis:*P < 0.05

Discussion

The importance of multidisciplinary treatment including maxillofacial prosthetics for head and neck tumors has been increasing annually. However, its standardization is not easy because of the diversity of patient conditions, primary disease types, treatment methods, and prognosis. Clinical pathways are useful for standardizing medical care and enhancing the medical environment through multidisciplinary cooperation, and the hospital has employed a clinical pathway for head and neck cancers based on medical-dental collaboration. After patients are referred to the Division of Perioperative Oral Health Management, case conferences are held at the Center for Dysphagia and the Head and Neck Cancer Board, which involves staff from multiple divisions such as the Department of Otolaryngology-Head and Neck Surgery, Department of Oral, and Maxillofacial Surgery, Department of Medical Oncology, and Department of Plastic and Reconstructive Surgery, and maxillofacial prostheses are fabricated at the Maxillofacial Prosthetics Clinic [1]. Thus, a well-developed collaborative practice system that encompasses the progression from diagnosis to rehabilitation has been established. Under this system, the management of accurate clinical data for patients with head and neck cancers allowed high-quality clinical assessment in this study.

In this study, any bias in the number of cases corresponding to each disease, each stage diagnosis, and stage classification based on the TNM classification was small (Table 1). Therefore, the effects of these diversities on functional recovery were also small. The influence of spontaneous healing would have been eliminated because all cases were assessed during the total evaluation period without dropping out (Fig. 2). The effect of rehabilitation for dysphagia should be considered a confounding factor for maxillofacial prosthetics; however, all patients during the hospitalization period received standardized eating function therapy performed by professionals at Tohoku University Hospital. Therefore, the presence or absence of eating function therapy was thought to have little effect on recovery of oral function. Undeniably, the type of surgical procedure affects postoperative functional recovery. For example, the size and configuration of the defect would influence the masticatory function of patients who underwent maxillectomy with obturator prostheses [8], and the size of the defect and modality of tongue reconstruction would similarly influence the masticatory function of patients who underwent glossectomy [9,10]. In this study, neck dissection surgery was performed in patients with N1, N2a, or N2b disease. Postoperative sequelae after neck dissection may affect the degree of improvement in oral function [9,10,11].

In the analysis for this study, a simple comparison of the evaluation average values among the preoperative, postoperative, and post-prosthetic phases was not possible because the degree of damage varies greatly depending on the primary site and surgical procedure in patients with head and neck tumors. To correct for the difference in the clinical conditions of the patients, the median change in evaluation values between each phase (T1, from preoperative to postoperative; T2, from postoperative to post-prosthetic; T3, from preoperative to post-prosthetic) for each patient were used as the analyses index to determine the trend of effectiveness of maxillofacial prosthetic treatment in all patients. Thus, the degree of postoperative recovery of oral function may vary depending on the surgery type. According to Shpizer et al., who reported on cases of tongue cancer, the extent of postoperative oral dysfunction is influenced by the area of the residual tongue and the modality of tongue reconstruction [12]. Andrades et al. analyzed maxillary defects and found a strong association between the resected area of the jawbone and postoperative oral function [13].

As shown in Fig. 3, the median changes in the OHR-QoL score increased at T1 significantly, whereas they decreased significantly at T2 and T3. That is, the OHR-QoL significantly deteriorated from the preoperative to the postoperative period but significantly improved in the post-prosthetic period as compared with the preoperative and the postoperative period. These results suggest that the OHR-QoL was improved by maxillofacial prosthetic treatment. It is inferred that effective maxillofacial prosthetic treatment was provided to all patients, contributing to the improvement in postoperative functional limitations, pain, and physical disability. However, the OHR-QoL of patients who received maxillofacial prosthetic treatment could not be improved to the same level as that in preoperative conditions because of the significant difference observed between T2 and T3. Thus, even if an effective prosthetic intervention that contributes to improvement of functional limitations, pain, and physical disabilities after surgery had been provided in all patients, complete improvement would appear to be difficult.

The use of multivariate analysis is necessary to clarify the effect of prosthetic intervention on the perioperative period of patients with head and neck tumors, and its validity needs to be verified if logistic regression analysis shows poor reproducibility in the presence of numerous explanatory variables. Therefore, this time, a research method that newly selected explanatory variables from the evaluation items in the database was employed, and stepwise regression was used for analysis in the selection method in order to eliminate confounding factors. To prioritize examining the effects of oral changes directly caused by cancer treatment before and after surgery, “disease type”, “TNM classification/staging”, “evaluation period”, and “whether and what kind of dysphagia rehabilitation was provided” from among the explanatory variables were excluded because of their strong correlation with each other in the stepwise method.

Presence of a maxillary defect was found to be a significant influencing factor for a deteriorated OHR-QoL at T1 and T2. A maxillary defect was also a significant influencing factor for a low food intake status score at T1, T2, and T3. In patients with maxillary defects, the jaw defect is sealed by a denture with an obturator in the jaw defect area where the oral and nasal cavities meet. This procedure aims to improve swallowing and articulatory functions. If the jaw defect is extensive, securing the retentive force of the denture and sealing the jaw defect region are difficult. In such cases, frequent adjustments of the prosthesis are necessary, which may reduce patients’ QoL. It has been reported that patients with maxillary defects have greater oral dysfunction and esthetic impairment than those with mandibular defects, and that their OHR-QoL tends to be lower [14,15,16]. These problems are caused by poor fitting of the denture, low cleanability, and difficulty in handling by the patient.

Presence of a tongue and soft palate tissue defect was a significant influencing factor for a deteriorated OHR-QoL at T2. In patients with tongue cancer, insufficient contact between the tongue and palate after glossectomy resulted in poor tongue pressure, resulting in dysphagia, and dyslalia. Hasegawa et al. [17] reported that the tongue pressure decreased markedly from 1 to 2 weeks to 4 weeks after surgery, and Hamahata et al. [16] reported that the tongue pressure 6 months after surgery was 94.5% of the preoperative tongue pressure in patients with partial glossectomy and 40.4% of the preoperative pressure in patients with hemiglossectomy. Okay et al. [18] reported the challenge of supplementing the function of the soft palate with prostheses in patients with soft palate defect. Preservation of soft palate function has been advocated for successful maxillofacial prosthetic treatment. Moreover, in this study, the use of a rigid denture base resin was unable to functionally compensate for the defective area of the highly mobile soft palate. In some cases, affording functional morphology using maxillofacial prostheses was difficult. Furthermore, chemoradiotherapy was a significant factor reducing the gum-jelly test score at T2. Various side effects such as oral mucositis, dry mouth, dysgeusia, hyperesthesia, and stomatitis occur with the initiation of chemotherapy [19,20]. One report has indicated that oral mucositis occurs in nearly 100% of patients who receive radiotherapy in a field that includes the oral cavity [21]. Xerostomia is irreversible and can cause radiation caries as a late effect. Since various adverse events including oral mucositis were also observed in the present patients, it was likely a factor that influenced the worsening gum-jelly test score.

On the other hand, reconstructive surgery was a significant factor influencing the OHR-QoL at T2. In some patients with tongue cancer, reconstruction secured a certain volume of the tongue following glossectomy, and this led to improvement of dysphagia and dyslalia. In patients with pharyngeal cancer, reconstruction improved velopharyngeal function. Prostheses were adjusted effortlessly in some patients because their velopharyngeal function did not need to be supplemented by a maxillofacial prosthesis. Postoperative contracture at the resection site was reduced by reconstruction in some patients with gingival cancer, mouth floor cancer, or buccal mucosa cancer, which facilitated securing of the denture space and created an oral environment conducive to fabrication of maxillofacial prostheses. Sreeraj et al. [22] examined patient satisfaction with maxillofacial prosthetic treatment after maxillectomy by comparing those who had received a denture prosthesis alone with those who had received a denture prosthesis combined with reconstruction. They reported that patient satisfaction was significantly higher in the latter group. These findings suggest that reconstructive surgery could help to improve OHR-QoL.

The food intake status score assessed using the food intake questionnaire, which is a subjective index, was decreased at T1, increased at T2, and almost the same at T3. Significant differences were found in both periods, confirming that prosthetic intervention significantly improved food intake, which in turn is an indicator of postoperative oral function. In addition, the food intake status scores in the maxillary defect and chemoradiotherapy groups showed a negative relationship, indicating a tendency similar to that for OHR-QoL. Conversely, the gummy jelly test score, an objective index, showed a significant change in value at T1, T2, and T3. Thus, fitting of a maxillofacial prosthesis significantly improved masticatory ability, and thus postoperative oral function. Only chemoradiotherapy was a significant factor reducing the gum-jelly test score at T2. These findings suggest that masticatory ability would differ depending on the objective or subjective evaluation index used.

It has been considered difficult to improve QoL and masticatory ability with maxillofacial prosthetics in patients with maxillary defects or tongue and soft palate tissue defects, and those who undergo chemoradiotherapy. However, the present study showed that reconstructive surgery contributed to improvement of QoL and oral function, suggesting that effective maxillofacial prosthetic treatment can improve the oral environment from a surgical perspective through medical-dental collaboration, providing a scientific basis for the importance of such collaboration in clinical practice. Identification of changes in oral function over time encompassing the preoperative, postoperative, and post-prosthetic periods may thus lead to improvement in the quality of maxillofacial prosthetic treatment in the perioperative period.

The limitations of this study included the wide variety of pathological conditions of patients with head and neck tumors. Moreover, it was difficult to investigate the effects and factors related to OHR-QoL and masticatory ability because the degree of impairment differed depending on the primary site, surgical method, and social and psychological backgrounds of the patients. The patients’ conditions were standardized as far as possible, and dentists at the same institution were involved in all aspects of the treatment, from the preoperative to postoperative and post-prosthetic stages. To eliminate confounding factors, variables were limited by stepwise variable selection, and multiple regression analysis was performed. Further research should be examining a model that adds – as explanatory variables – the number of remaining teeth and the presence or absence of occlusal support related to the original oral environment. Improvement of the quality of maxillofacial prosthetic treatment for patients with head and neck tumors is expected to contribute to not only morphological and functional recovery but also rehabilitation, which includes psychological and social support.

Within the limitations of this study, the following conclusions can be made:

1. •   Maxillary defects, tongue and soft palate tissue defects, and chemoradiotherapy were factors that prevented maxillofacial prosthetic treatment from improving OHR-QoL and masticatory ability.
2. •   Reconstructive surgery was useful for improvement of OHR-QoL and masticatory ability along with maxillofacial prosthetic treatment.

Conflicts of Interest

The authors declare that they have no conflicts of interest related to this study.

Funding

The authors report no financial or personal interest related to any products, services and/or companies presented in this study.

Acknowledgments

The authors thank Prof. Kenji Takeuchi, Division of Statistics and Data Science, Liaison Center for Innovative Dentistry, Tohoku University Graduate School of Dentistry, for his support in completing this study.

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