Ultrasound-guided arthrocentesis for condylar head fracture: a technical report.

OBJECTIVES: Double puncture arthrocentesis (DPA) of the temporomandibular joint (TMD) is considered an effective preservative option for managing mandibular condylar head fractures. However, the procedure is commonly performed by a traditional "blind" method using anatomical characteristics. In the present study, an ultrasonography (US) device was applied for the treatment of a case with a fractured mandibular condyle. METHODS: A 79-year-old female was diagnosed right side condylar head fracture complaining pain of right TMD and reduced mouth opening range: inter-incisor distance of 20 mm. Since the fracture position was high and inoperable, the decision was made to perform DPA of the TMD. The US probe was positioned parallel and slightly oblique to the major axis of the mandibular ramus. Both the posterior and anterior insertions into the joint space were performed according to the axis mentioned above, which enabled the operator to visualize the entirety of the needle. RESULTS: The device offered safety and ensured accuracy by providing real-time visual aid to the surgeon. The procedure provided an early increase in the inter-incisor distance (31 mm) and pain relief. CONCLUSIONS: Hence, for the preservative treatment of mandibular condylar head fractures, based on the present study, we recommend US-guided arthrocentesis as a safe, feasible, and effective therapeutic option instead of the conventional "blind" method.

Clinical evaluation of bone quality of particulate cancellous bone and marrow, and implant prosthetic rehabilitation.

This study aimed to subjectively evaluate bone quality in the particulate cancellous bone and marrow (PCBM) graft area and to assess the survival rates of implants. A retrospective review was conducted based on patient age, sex, diagnosis, reconstructed site, number of implants, prosthetic type, and duration of follow-up. Images from computed tomography (CT) before implant insertion were obtained and used in this study. We selected a 4.0-mm diameter × 8.0-mm length region of interest in the implant placement area, and measured the CT attenuation value. No significant correlations were seen between CT attenuation values and implant survival rates in the maxilla and mandible. On the other hand, CT attenuation values and implant survival rates were significantly lower in patients with malignancy than in non-malignant cases. Placing implants in PCBM grafted bone requires a full understanding of bone quality before surgery and drilling to ensure primary stability, along with consideration of soft tissue management and maintenance programs.

Factors influencing delayed referral of oral cancer patients from family dentists to the core hospital.

Background/purpose: Most oral cancer (OC) cases are identified by family dentists in Japan. However, a significant number of patients with OC in Japan are referred to core hospitals at advanced stages. Therefore, identifying the factors that contribute to delayed referrals from family dentists to core hospitals is crucial for detecting OC in its earlier stages. The aim of this retrospective study was to identify the risk factors for referral delays from family dentists to core hospitals. Materials and methods: The study included 63 patients with OC who were referred by family dentists to the Yamagata University Hospital between 2010 and 2022. The clinical parameters related to referral delays were retrospectively investigated using letters of reference provided by the family dentists and patient charts. Backward multiple regression analysis was performed to identify the relationships between the length of referral delay and potential risk factors. Additionally, backward multivariate logistic regression analysis was performed to examine the independent association between referral delays of >4 weeks and several clinical parameters. Results: Multiple regression analysis revealed that misdiagnosis of malignant lesions by family dentists (P = 0.047) was significantly associated with longer referral delays. Additionally, misdiagnosis of malignant lesions by family dentists was also an independent risk factor for referral delays of >4 weeks (odds ratio, 10.387; P = 0.006). Conclusion: Misdiagnosis of malignant lesions by family dentists was a significant risk factor for referral delays from family dentists to core hospitals. Our results will motivate family dentists to improve their ability to diagnose OC.

Salivary metabolites as potential predictive biomarkers for lung surgery complications: a retrospective cross-sectional study.

PURPOSE: Saliva is often used as a tool for identifying systemic diseases because of the noninvasive nature of its collection. Moreover, salivary metabolites can be potential predictive factors for postoperative survival. We conducted the present study to establish whether salivary metabolites can function as predictive biomarkers for lung surgery complications. METHODS: Unstimulated salivary samples were collected from 412 patients before lung surgery. Salivary metabolites were analyzed comprehensively by capillary electrophoresis mass spectrometry. Clinical data with the discriminatory ability of biomarkers were assessed to predict lung surgery complications using multivariate logistic regression analysis. The primary endpoint was the risk factors for postoperative complications of Clavien-Dindo grade ≥ III. RESULTS: Postoperative complications of Clavien-Dindo grade ≥ III developed in 36 patients (8.7%). There was no postoperative 30-day mortality. Male sex (odds ratio [OR], 3.852; 95% confidence interval CI 1.455-10.199; p = 0.007) and salivary gamma-butyrobetaine (OR, 0.809; 95% CI 0.694-0.943; p = 0.007) were identified as significant risk factors for postoperative complications of Clavien-Dindo grade ≥ III. CONCLUSION: Salivary metabolites are potential noninvasive biomarkers for predicting postoperative complications of lung surgery.

Synergistic effect of zoledronate and compressive force suppresses proliferation and differentiation of human gingival fibroblasts.

We investigated the effects of zoledronate (ZA) and compressive force, separately and in combination, on the proliferation and differentiation of human gingival fibroblasts (HGFs) to verify the mechanism underlying medication-related osteonecrosis of the jaw (MRONJ). The addition of 100 µM ZA markedly inhibited cell proliferation. Expression of type I collagen, fibroblast growth factor 2, and connective tissue growth factor genes, was decreased by ZA and compressive force. Similar results were observed for collagen expression by using Sirius red staining. These results, together with clinical findings that MRONJ is more common in cases with excessive mechanical stress on the oral mucosa, suggest that bisphosphonates such as ZA and mechanical stress may act in conjunction as risk factors for the development of MRONJ by affecting homeostasis of the oral mucosal tissues, including HGFs.

Associations between subjective well-being, number of teeth, and self-rated mastication in Japanese adults: A cross-sectional study.

This cross-sectional study aimed to investigate the risk factors for low levels of subjective well-being (SWB) in the general population of Japan, specifically, the impact of the number of teeth and self-rated mastication. The surveyed population consisted of individuals aged between 40 and 79 years from Yamagata prefecture, Japan. A postal self-administered questionnaire survey of respondents lifestyles, medical history, oral health, and dietary intake, was conducted from 2017 to 2021. We included 6846 participants to confirm the independent associations between SWB and several parameters using multivariate ordinal logistic regression analysis to estimate adjusted odds ratios and 95% confidence intervals. Individuals with < 20 teeth and poor mastication ability had a 1.3-fold risk for low levels of SWB compared with individuals with ≥ 20 teeth with good mastication ability (adjusted odds ratios = 1.300, 95% confidence intervals = 1.043-1.621, P = .020). There were no differences between individuals with good mastication ability, regardless of the number of remaining teeth. Our study emphasizes not only the importance of having ≥ 20 teeth and good mastication ability for high levels of SWB but also the importance of restoring mastication ability using some form of prosthesis, to facilitate a high level of SWB when the number of remaining teeth is < 20.

Measures of oral health-related quality of life in patients with bone graft and implant prosthetic rehabilitation at the anterior of mandible/maxilla among young and middle-aged adults: a retrospective pilot study.

OBJECTIVES: Dental implants are believed to contribute to improved masticatory function and oral health-related quality of life (OHRQOL), but the details remain unclear. The aim of this study was to evaluate the clinical outcomes of dental implant prosthetic rehabilitation after bone graft at the anterior mandible/maxilla based on OHRQOL, particularly in young and middle-aged patients. METHODS: This retrospective study included 11 patients who received bone grafts at the anterior mandible/maxilla and dental implant surgery. Chewing function score and OHRQOL (using the Oral Health Impact Profile-14 questionnaire) were evaluated before and after completion of an implant-retained bridge or removable implant-supported denture. RESULTS: Chewing function score tended to improve slightly after dental implant prosthetic rehabilitation, but none of the observed differences were significant. In the assessment of OHRQOL, relatively worse domain scores before completion of dental implant prosthetic rehabilitation were seen for Functional limitation, Psychological discomfort, and Psychological disability. Conversely, Social disability seemed relatively unaffected by tooth loss. All domain scores and total scores for items other than Physical disability and Social disability were significantly improved after completion of dental implant rehabilitation. CONCLUSIONS: Tooth loss in the anterior region may not significantly affect chewing function score, but can have a significant impact on OHRQOL. Bone grafts and dental implant prosthetic rehabilitation can resolve these problems, and the results of this study will benefit both patients and medical professionals in terms of treatment planning and informed consent.

Association of health behaviors, dietary habits, and oral health with weight gain after 20 years of age in community-dwelling Japanese individuals aged 40 years and older: a cross-sectional study.

OBJECTIVES: This cross-sectional study investigated the factors associated with weight gain ≥ 10 kg after 20 years of age in the general Japanese population, with a focus on the number of teeth. MATERIALS AND METHODS: We included individuals aged ≥ 40 years from Yamagata prefecture, Japan from 2017-2021. A postal survey was conducted using a self-administered questionnaire; 5,940 participants were included in the final analysis. The questionnaire included items on lifestyle factors, medical history, physical and mental conditions, oral health, and dietary intake. A multivariate logistic regression analysis was used to identify independent associations between weight gain ≥ 10 kg after 20 years of age and various parameters; adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were estimated. RESULTS: Less than 20 teeth, male sex, drinking habit frequency, eating very fast or fast, and a higher frequency of eating-away-from-home were significant factors associated with weight gain ≥ 10 kg after 20 years of age; individuals with < 20 versus > 20 teeth exhibited a 1.35-fold higher OR (95% CI 1.15-1.59; p < 0.01). CONCLUSIONS: Our results suggest that having < 20 teeth may affect weight gain ≥ 10 kg after 20 years of age. However, owing to the cross-sectional study design, causality could not be determined. Therefore, maintaining healthy lifestyle behaviors to avoid tooth loss may also affect weight gain ≥ 10 kg after 20 years of age. CLINICAL RELEVANCE: Having < 20 teeth has the potential to affect long-term weight gain after 20 years of age.

Salivary metabolomics for oral leukoplakia with and without dysplasia.

PURPOSE: Oral leukoplakia (OL) is a common potentially malignant oral disorder. Therefore, there is a need for simple screening methods for OL before its transformation into oral cancer. Furthermore, because invasive open biopsy is the sole method to determine if an OL lesion is dysplastic, there is also a clinical need for non-invasive methods to differentiate dysplastic OL from non-dysplastic OL. This study aimed to identify salivary metabolites that can help differentiate patients with OL from healthy controls (HC) and also dysplastic OL from non-dysplastic OL. MATERIAL & METHODS: Whole unstimulated saliva samples were collected from patients with OL (n = 30) and HCs (n = 29). The OL group included nine patients with dysplastic OL and 20 with non-dysplastic OL. Hydrophilic metabolites in the saliva samples were comprehensively analyzed through capillary electrophoresis mass spectrometry. To evaluate the discrimination ability of a combination of multiple markers, a multiple logistic regression (MLR) model was developed to differentiate patients with OL from HCs and dysplastic OL from non-dysplastic OL. RESULTS: Twenty-eight metabolites were evidently different between patients with OL and HCs. Finally, three metabolites (guanine, carnitine, and N-acetylputrescine) were selected to develop the MLR model, which resulted in a high area under curve (AUC) of the receiver operating characteristic (ROC) to differentiate patients with OL from HCs (AUC = 0.946, p < 0.001, 95% confidential interval [CI] = 0.889- 1.000). Similarly, two metabolites were evidently different between patients with dysplastic and non-dysplastic OL. Finally, only one metabolite (7-methylguanine) was selected in the MLR model, which revealed a moderate discrimination ability for dysplastic and non-dysplastic OL (AUC = 0761, p = 0.027, 95% CI = 0.551-0.972). CONCLUSION: Our candidate salivary metabolites showed potential not only to discriminate OL from HC, but also to discriminate dysplastic OL from non-dysplastic OL.

Analgesic effect of a lidocaine-ropivacaine mixture for extraction of impacted mandibular third molars: a randomized controlled trial.

OBJECTIVES: The painless postoperative period can be significantly prolonged by using long-acting local anesthetics such as ropivacaine, though these local anesthetics are known for their slower onset of action. To compensate for this, a mixture of short-onset (e.g., lidocaine) and long-acting local anesthetics is used. However, the efficacy of such an anesthetic cocktail has not been elucidated in the field of oral and maxillofacial surgery. MATERIALS AND METHODS: To address the research purpose, this prospective randomized controlled trial included 56 patients scheduled for impacted mandibular third molar extraction. All patients received the inferior alveolar nerve block (IANB) using either 2% lidocaine with epinephrine or a 1:1 mixture of 2% lidocaine with epinephrine and 0.75% ropivacaine. RESULTS: Patients anesthetized using the lidocaine-ropivacaine mixture showed significantly prolonged postoperative analgesia and pain control than those anesthetized using lidocaine only. CONCLUSIONS: IANB using a lidocaine-ropivacaine mixture can provide prolonged postoperative anesthesia and pain control with extraction of mandibular third molars. CLINICAL RELEVANCE: This method can be a noteworthy addition to existing methods of local anesthesia for the extraction of mandibular third molars. Trial registration number University Hospital Medical Information Network (No. UMIN000044315).

Evaluation of radiographic characteristics and surgical removal of 147 mesiodens.

The aim of this study was to evaluate the radiographic characteristics and surgical removal of mesiodens among patients who had attended the Department of Dentistry, Oral and Maxillofacial-Plastic and Reconstructive Surgery of the Faculty of Medicine, Yamagata University. This study included 121 patients in the final analysis. We retrospectively reviewed medical records including patient age, sex, mesiodens number, direction, position, opportunity for detection, surgical approach and operating time. The 121 patients comprised 82 males and 39 females. Mean age was 7.6 ± 3.1 years (range, 4-35 years). The total number of mesiodens among these 121 patients was 147. Ninety-six patients had one mesiodens, 24 patients had two mesiodens and 1 patient had 3 mesiodens. Seventy-nine mesiodens were detected while taking X-rays for routine dental examination and/or orthodontic treatment at their family dental/orthodontic clinic. Mean operating time for removal of the 147 mesiodens was 32.2 ± 18.1 min. Among the 96 patients with one mesiodens, mean operating time for removal of the mesiodens was 30.7 ± 16.5 min. Operating time for removal of a mesiodens tended to be prolonged with increased distance from the alveolar crest. Early detection of mesiodens on routine radiographic check-ups and surgical planning considering patient age, crown direction, position of the mesiodens will contribute to improved treatment of mesiodens.

Reconstruction After Hemimandibulectomy With a Plate and Soft-Tissue Free Flap Followed by a Titanium Mesh and Particulate Cancellous Bone and Marrow Harvested From Bilateral Posterior Ilia: A Case Report.

A particulate cancellous bone and marrow (PCBM) graft combined with titanium (Ti-) mesh tray has become one of the most popular mandibular reconstruction methods. The technique has been applied to the mandibular discontinuity defects after segmental mandibulectomy. To the best of our knowledge, there are no reports on using the technique after hemimandibulectomy, during which a wide mandibular resection, including the condyle, is performed. Here, we first report a case of mandibular reconstruction after hemimandibulectomy, using a plate and soft-tissue free flap, followed by a Ti-mesh and PCBM harvested from the bilateral posterior ilia, which was successful. This case report first revealed how bone resorption occurred clinically in mandibular reconstruction using PCBM and Ti-mesh tray after hemimandibulectomy. We also revealed the high predictability of the mandibular reconstruction using PCBM and Ti-mesh tray after hemimandibulectomy. Our report also provides a guiding principle to overcome the limitation of mandibular reconstruction using PCBM and Ti-mesh tray after hemimandibulectomy. However, our manuscript has limited evidence, being a case report.

Association of the number of teeth and self-rated mastication with self-rated health in community-dwelling Japanese aged 40 years and older: the Yamagata cohort study.

Self-rated health (SRH) is a predictive factor for health-related prognoses such as mortality. This study aimed to comprehensively investigate the risk factors for poor SRH in the general population of Japan, focusing on the combination of the number of teeth and self-rated mastication. Individuals aged at least 40 years in Yamagata Prefecture, Japan, were surveyed from 2017 to 2021. The participants answered a self-administered postal survey on lifestyle factors, medical history, physical and mental conditions, oral health, and dietary intake, and 6739 participants were included. Multivariate logistic regression analysis showed that individuals with less than 20 teeth and who bite tightly on one side or neither side were at a 1.422- and 1.952-fold significantly higher risk, respectively, of poor SRH than individuals with at least 20 teeth and who bite tightly on both sides. Moreover, individuals who had less than 20 teeth but could bite tightly on both sides did not have a significant risk compared to those who had at least 20 teeth and could bite tightly on both sides. Regarding individuals with more than 20 teeth, there was no difference between those who could and could not bite tightly on both sides, although the odds ratios for poor SRH tended to increase for those who could bite on one side or neither side. Our results emphasize the importance of having at least 20 teeth without periodontal disease and oral rehabilitation using a type of prosthesis for SRH, even with less than 20 teeth.

Association between the duration of antibiotic prophylaxis and surgical site infection after orthognathic surgery in Japan.

PURPOSE: This study aimed to evaluate the risk factors for surgical site infection (SSI) after orthognathic surgery, focusing on the duration of prophylactic antibiotic administration in Japan. STUDY DESIGN: The study included 181 patients who underwent orthognathic surgery at the Department of Oral and Maxillofacial Surgery of Yamagata University Hospital between 2012 and 2021. The clinical parameters of SSI were retrospectively investigated using patient charts. Logistic regression analysis was used to estimate the odds ratios (ORs) with 95% confidence intervals (CIs) for risk factors for SSI after orthognathic surgery. RESULTS: Nineteen patients (10.5%) were complicated with SSI. Male sex (OR, 3.638; 95% CI, 1.316-10.058) and an antibiotic prophylaxis duration ≤3 days (OR, 12.718; 95% CI, 1.639-98.673) were independent risk factors for SSI after orthognathic surgery. CONCLUSION: Extended-term antibiotic prophylaxis was more effective for prevention of SSI after orthognathic surgery than short-term in this study.

Salivary Metabolomics for Oral Cancer Detection: A Narrative Review.

The development of low- or non-invasive screening tests for cancer is crucial for early detection. Saliva is an ideal biofluid containing informative components for monitoring oral and systemic diseases. Metabolomics has frequently been used to identify and quantify numerous metabolites in saliva samples, serving as novel biomarkers associated with various conditions, including cancers. This review summarizes the recent applications of salivary metabolomics in biomarker discovery in oral cancers. We discussed the prevalence, epidemiologic characteristics, and risk factors of oral cancers, as well as the currently available screening programs, in India and Japan. These data imply that the development of biomarkers by itself is inadequate in cancer detection. The use of current diagnostic methods and new technologies is necessary for efficient salivary metabolomics analysis. We also discuss the gap between biomarker discovery and nationwide screening for the early detection of oral cancer and its prevention.

Development of a highly sensitive Prussian-blue-based enzymatic biosensor for L-carnitine employing the thiol/disulfide exchange reaction.

This is the first report of conducting proof-of-concept study for amperometric acetyltransferase-based L-carnitine sensor by employing the thiol/disulfide exchange reaction. The carnitine acetyltransferase (CrAT) catalyzes the reaction between acetyl-CoA and L-carnitine to produce CoA which is difficult to detect directly by electrochemical methods owing to steric hindrance and electrostatic effect of CoA. The thiol/disulfide exchange reaction between CoA and cystamine was mediated in the enzymatic reaction to produce electrochemically detectable low molecular weight of cationic cysteamine. The sensor exhibited high sensitivity and selectivity for L-carnitine in the concentration range 0.28-50 µM with a limit of detection of 0.28 µM. This is a promising strategy for L-carnitine sensing in point-of-care testing applications.

A Cross-Sectional Survey on the Association between Dental Health Conditions and University Personality Inventory Scores among University Students: A Single-Center Study in Japan.

This study examined the association between dental health conditions and scores on the University Personality Inventory (UPI) among university students in Japan. Participants were freshmen at Yamagata University between 2010 and 2019. Dental check-ups, including dental caries, periodontal disease, malocclusion, and temporomandibular disorders (TMD), and mental health screening using the UPI were performed; 12,433 students were included in the final analysis. A logistic regression analysis was performed to confirm the association between dental health conditions and >30 UPI scores, which indicate the need to consult mental health professionals. Overall, students who required treatment for TMD had a 3.165-fold higher risk of >30 UPI scores (OR = 3.165, 95% CI = 1.710−5.857). Periodontal disease and TMD in male participants (periodontal disease: OR = 1.329, 95% CI = 1.108−1.595; TMD: OR = 3.014, 95% CI = 1.107−8.204) and TMD in female participants (OR = 2.938, 95% CI = 1.340−6.445) were significant risk factors for >30 UPI scores. Students requiring treatment for TMD were at risk of obtaining >30 UPI scores. Although our study has several limitations, students with subjective symptoms (e.g., disturbance in opening the mouth) should take the UPI test or in some cases consult mental health professionals.

Bone marrow space volume of the mandible influencing intraoperative blood loss in bilateral sagittal split osteotomy: A pilot Study.

The aim of this study was to investigate whether the bone marrow space volume of the mandible affects blood loss during bilateral sagittal split osteotomy (BSSO). Sixteen patients who underwent BSSO in our hospital were included in this study. Bone marrow space volume of the mandible was measured by analyzing images from computed tomography. Blood loss during BSSO was measured by weighing gauze, measuring suctioned blood, and adjusting for the volume of irrigation solution used during BSSO. Mean blood loss during BSSO for the 16 patients was 200.5 ml, and patients were divided into: Group I, with less than mean blood loss; and Group II, with greater than mean blood loss. Total bone marrow space volume was significantly greater in Group II (12,450.7 ± 2644.3 mm3) than in Group I (9130.3 ± 3005.8 mm3; P<0.05). A correlation between bone marrow space volume and blood loss during BSSO was suggested, and these results are beneficial for surgeons planning and preparing the orthognathic surgery.

Differential diagnosis of lung cancer and benign lung lesion using salivary metabolites: A preliminary study.

BACKGROUND: Saliva is often used as a biomarker for the diagnosis of some oral and systematic diseases, owing to the non-invasive attribute of the fluid. In this study, we aimed to identify salivary biomarkers for distinguishing lung cancer (LC) from benign lung lesion (BLL). MATERIALS AND METHODS: Unstimulated saliva samples were collected from 41 patients with LC and 21 with BLL. Salivary metabolites were comprehensively analyzed using capillary electrophoresis mass spectrometry. To differentiate between patients with LCs and BLLs, the discriminatory ability of each biomarker was assessed. Furthermore, a multiple logistic regression (MLR) model was developed for evaluating discriminatory ability of each salivary metabolite. RESULTS: The profiles of 10 salivary metabolites were remarkably different between the LC and BLL samples. Among them, the concentration of salivary tryptophan was significantly lower in the samples from patients with LC than in those from patients with BLL, and the area under the curve (AUC) for discriminating patients with LC from those with BLL was 0.663 (95% confidence interval [CI] = 0.516-0.810, p = 0.036). Furthermore, from the MLR model developed using these metabolites, diethanolamine, cytosine, lysine, and tyrosine, were selected using the back-selection regression method. The MLR model based on these four metabolites had a high discriminatory ability for patients with LC and those with BLL (AUC = 0.729, 95% CI = 0.598-0.861, p = 0.003). CONCLUSION: The four salivary metabolites can serve as potential non-invasive biomarkers for distinguishing LC from BLL.

High Parity Is an Independent Risk Factor for Tooth Loss in Women: A Community-Based Takahata Study in Japan.

Risk factors for tooth loss have been widely examined previously. However, no previous study has comprehensively investigated the risk factors, including lifestyle-related specific factors (parity, oral health habits, and socioeconomic status), for fewer than 20 teeth among women in the general population in Japan. This cross-sectional study explored the association of these risk factors, especially parity, with having fewer than 20 teeth among Japanese women. A self-reported questionnaire including items on lifestyle-related risk factors (parity, oral health, diet [e.g., alcohol and sucrose consumption]) and socioeconomic status was sent by post to female residents (age ≥ 40 years) of Takahata town, Yamagata Prefecture, in 2005. Multivariate logistic regression analysis including 3,854 eligible participants was performed to investigate the association between various factors (including parity) and having fewer than 20 teeth. The results indicated that, compared with nulliparous women, women with two, three, and four completed pregnancies had 2.485-, 2.844-, and 4.305-fold increased risk of having fewer than 20 teeth, respectively. Our study is the largest-scale study of the general female population in Japan and the first study to comprehensively investigate risk factors (parity, oral health status, and socioeconomic status) for fewer than 20 teeth. We thus found that higher parity, especially, two or more, was independent risk factors for having less than 20 teeth among Japanese women. In conclusion, the present study emphasizes the importance of good oral health habits in women, especially, during pregnancy and in the postpartum period, to maintain 20 or more teeth.