Reliability of a chairside CAD-CAM surgical guide for dental implant surgery on the anterior maxilla: An in vitro study.

PURPOSE: This study evaluated the reliability of the chair-side CAD-CAM surgical guide (CSG) in the anterior maxilla by comparing its accuracy with the laboratory 3D-printed surgical guide (3DSG) and manual surgical guide (MSG) concerning different levels of dentists' surgical experience. MATERIALS AND METHODS: Ten surgical guides of each type (MSG, 3DSG, and CSG) were fabricated on a control study model with missing right and left central incisors. Sixty implants were placed in 30 study models by two dentists (one inexperienced and one experienced) using three different types of surgical guides. Horizontal deviations at shoulder and at apex, vertical, and angular deviations were measured after superimposing the planned and placed implant positions in the software. Kruskal-Wallis and Mann-Whitney U tests were used to compare the accuracy of three types of surgical guides in each dentist group and the accuracy of each surgical guide between two dentists (α = .05). RESULTS: There were no significant differences in any deviations between CSG and 3DSG, apart from angular deviation, for both dentists' groups. Moreover, both CSG and 3DSG showed no significant differences in accuracy between the two dentists (P > .05). In contrast, MSG demonstrated significant differences from CSG and 3DSG and a significant difference in accuracy between the two dentists (P < .05). CONCLUSION: CSG provides superior accuracy to MSG in implant placement in the maxillary anterior region and is comparable to 3DSG at different levels of surgical experience, while offering the benefits of shorter manufacturing time and reduced patient visits.

The teaching of geriatric dentistry in South Korean dental schools.

OBJECTIVE: The purpose of this study was to investigate the curriculum of geriatric dentistry for undergraduates in Korean dental schools. BACKGROUND: For development purposes, it was necessary to compare geriatric dentistry education programmes in South Korea to programmes in the United States and Europe. METHODS: The most recent curriculum and related information on geriatric dentistry at the undergraduate level in all 11 dental schools in South Korea were collected by both official letter and e-mail. A symposium for gathering expert opinions to improve geriatric dentistry education in South Korea was also held. The collected data were analysed, and the expert opinions at the symposium were summarised. RESULTS: Six of 11 schools had a didactic course as compulsory and three schools as elective. The course was usually conducted as a form of integrated lectures, and the level of standardisation of lecture content was very low. There were no topics for older people who cannot access dental clinics due to functional frailty or disability. No dental school-affiliated hospitals had an independent department for geriatric dentistry. No schools provided clinical teaching for geriatric dentistry. There were no outreach programmes for geriatric dentistry. CONCLUSIONS: The educational curriculum for geriatric dentistry in South Korea was insufficient to cope with social and demographic changes. Curriculum content should include clinical practice education and needs to be focused on frail and dependent older adult patients. An essential educational curriculum and core competency for geriatric dentistry should be prepared.

Long-Term Comparison of Survival and Marginal Bone of Implants with and without Sinus Augmentation in Maxillary Molars within the Same Patients: A 5.8- to 22-Year Retrospective Study.

Maxillary sinus floor augmentation (MSFA) is widely used and considered a predictable procedure for implant placement. However, the influence of MSFA on implant survival and marginal bone loss (MBL) is still inconclusive. The purpose of this retrospective observational study is to evaluate the long-term genuine influence of MSFA on the survival and MBL of implants by comparing those with and without MSFA only in maxillary molars within the same patients. Thirty-eight patients (28 male and 10 female), with a total of 119 implants, received implants with and without MSFA, and were followed up for 5.8 to 22 years. Patient- and implant-related factors were assessed with a frailty model for implant survival and with generalized estimation equations (GEE) for MBL around the implant. No variables showed a statistical significance for implant failure in the frailty model. In GEE analysis for MBL, MSFA did not show any statistical significance. In conclusion, MSFA demonstrated no significant influence on implant failure and MBL in posterior maxilla in this study.

Long-term outcomes of the implants accidentally protruding into nasal cavity extended to posterior maxilla due to inferior meatus pneumatization.

BACKGROUND: There is limited information about inferior meatus pneumatization in terms of implant treatment for the posterior maxilla. PURPOSE: To demonstrate the clinical, radiologic, and nasal endoscopic outcomes of implants accidentally protruding into the nasal cavities with inferior meatus pneumatization in the posterior maxilla. MATERIALS AND METHODS: A total of 560 implants (324 patients) with transcrestal sinus augmentation in the posterior maxilla were screened. On panoramic radiographs, 132 implants (78 patients) appear to penetrate the sinus floor, but cone-beam computed tomography demonstrated that 26 implants (13 patients) penetrated the nasal floor due to inferior meatus pneumatization. Width of nasal and sinus cavities and extent of penetration were radiographically measured. Nasal endoscopy was performed. RESULTS: Two implants were lost during 13.81 ± 5.40 years due to peri-implantitis. However, no nasosinusal problem occurred in any patient. The nasal cavity was significantly larger in patients with implants penetrating the pneumatized inferior meatus than in those with implants penetrating the sinus floor (P< .05). Nasal endoscopy demonstrated that the apical portion of the implants was covered with thin mucosa without inflammation. CONCLUSION: Implants accidentally penetrating the pneumatized inferior meatus demonstrated high survival with no specific nasosinusal complications. Inferior meatus pneumatization should be considered for implant treatment in the posterior maxilla.

Long-Term Implant Survivability of an Implant Having Direct Contact with Cementum-Like Tissue in a Preexisting Mandibular Intraosseous Lesion with a 16-Year Longitudinal Follow-up.

This case report demonstrates long-term implant stability associated with focal cemento-osseous dysplasia (FCOD). The nature of the cementum-like tissue (CLT) of FCOD around the titanium surface of the implant is described clinically, radiologically, and histologically. A dental implant placed directly into the FCOD lesion was successfully integrated, and the stability was maintained for 15 years. However, at the 16-year follow-up, the implant and a sclerotic mass were removed due to peri-implantitis, and the entire specimen was evaluated with conventional histology and microcomputed tomography. The analysis revealed that the sclerotic mass attached to the implant was CLT that was free of any intervening soft tissue. The implant placed into the FCOD lesion achieved integration similar to that of conventional osseointegration. Rather than bone, the CLT was in direct contact with the titanium surface. The integrity of the union was maintained for up to 16 years.

Factors influencing long-term survival rates of implants placed simultaneously with lateral maxillary sinus floor augmentation: A 6- to 20-year retrospective study.

OBJECTIVES: To evaluate the long-term influence of residual bone height (RBH), sinus membrane perforation and the presence of voids on the survival of implants placed simultaneously with lateral maxillary sinus floor augmentation (MSFA). MATERIALS AND METHODS: A total of 207 patients (613 implants) who underwent MSFA from 1999 to 2003 and followed up until 2018 were included in this study. RBH and marginal bone loss were assessed using a series of panoramic and periapical radiographs. Cumulative survival rates (CSR) with log-rank tests and hazard ratios of implant failure according to RBH, membrane perforation, and the presence of voids were assessed. RESULTS: The overall 10-year and 20-year CSRs were 95% (95% CI: 84.95%-85.05%) and 85% (95% CI: 84.95%-85.05%), respectively. CSR was significantly higher for implants with ≥3 mm RBH (n = 260, 92.4%) than those with <3 mm RBH (n = 353, 78.8%) (p = .002). CSR of non-smoking group (n = 312, 90.0%) was higher than that of smoking group (n = 301, 77.1%) (p = .009). There was no significant difference in the hazard ratio of implant failure between the perforated membrane group (n = 245) and the non-perforated group (n = 368). In two out of 11 patients with voids, the inflammation of peri-implantitis progressed into voids, resulting in severe bone resorption. CONCLUSIONS: The survival of implants placed in <3 mm of RBH, even though it showed a lower CSR, could be considered acceptable. Neither sinus membrane perforation nor the presence of voids appeared to affect implant survival as long as supportive maintenance therapy with proper oral hygiene was provided.

Evaluating the oxysterol combination of 22(S)-hydroxycholesterol and 20(S)-hydroxycholesterol in periodontal regeneration using periodontal ligament stem cells and alveolar bone healing models.

BACKGROUND: Oxysterols, oxygenated by-products of cholesterol biosynthesis, play roles in various physiological and pathological systems. However, the effects of oxysterols on periodontal regeneration are unknown. This study investigated the effects of the specific oxysterol combination of 22(S)-hydroxycholesterol and 20(S)-hydroxycholesterol (SS) on the regeneration of periodontal tissues using in-vitro periodontal ligament stem cells (PDLSCs) and in-vivo models of alveolar bone defect. METHODS: To evaluate the effects of the combined oxysterols on PDLSC biology, we studied the SS-induced osteogenic differentiation of PDLSCs by assessing alkaline phosphatase activity, intracellular calcium levels [Ca2+]i, matrix mineralization, and osteogenic marker mRNA expression and protein levels. To verify the effect of oxysterols on alveolar bone regeneration, we employed tooth extraction bone defect models. RESULTS: Oxysterols increased the osteogenic activity of PDLSCs compared with the control group. The expression of liver X receptor (LXR) α and ß, the nuclear receptors for oxysterols, and their target gene, ATP-binding cassette transporter A1 (ABCA1), increased significantly during osteogenesis. Oxysterols also increased protein levels of the hedgehog (Hh) receptor Smo and the transcription factor Gli1. We further confirmed the reciprocal reaction between the LXRs and Hh signaling. Transfection of both LXRα and LXRß siRNAs decreased Smo and Gli1 protein levels. In contrast, the inhibition of Hh signaling attenuated the LXRα and LXRß protein levels. Subsequently, SS-induced osteogenic activity of PDLSCs was suppressed by the inhibition of LXRs or Hh signaling. The application of SS also enhanced bone formation in the defect sites of in-vivo models, showing equivalent efficacy to recombinant human bone morphogenetic protein-2. CONCLUSIONS: These findings suggest that a specific combination of oxysterols promoted periodontal regeneration by regulating PDLSC activity and alveolar bone regeneration.

Long-Term Clinical and Radiographic Observation of Periimplant Tissues After Autogenous Soft Tissue Grafts: A 15-Year Retrospective Study.

PURPOSE: The aim of this study was to evaluate the periimplant tissues after autogenous soft tissue graft (ASTG) during 15 years of follow-up. MATERIALS AND METHODS: The clinical parameters, dimension of keratinized mucosa (KM), and marginal bone loss of 50 patients with 127 implants were followed up and their relationships were assessed at 15-year follow-up. In addition, clinical and radiographic parameters of 11 patients who had both autogenous soft tissue grafted (n = 21 implants) and nongrafted (n = 21 implants) sides were compared. RESULTS: The thickness of the KM was related to the width of the KM (P < 0.01) and mucosal recession (P < 0.05); however, there was no significant association between marginal bone loss and dimension of the KM. The autogenous soft tissue grafted group showed statistically significantly lower modified bleeding index, wider and thicker KM than the nongrafted group. However, the modified plaque index, probing depth, and marginal bone loss did not show any significant differences between 2 groups. CONCLUSIONS: This 15-year follow-up study shows that the thickness or width of KM is not related to the marginal bone loss around implants. However, it seems that ASTG can be beneficial for preventing mucosal recession and soft tissue inflammation around dental implants.

Alveolar Ridge Preservation Using Allografts and Dense Polytetrafluoroethylene Membranes With Open Membrane Technique in Unhealthy Extraction Socket.

We evaluated the effectiveness of the open membrane technique using a high-density polytetrafluoroethylene (dPTFE) membrane with freeze-dried bone allografts in damaged sockets for alveolar ridge preservation (ARP). This retrospective study included 26 sites from 20 patients who had received ARP for the placement of dental implants. ARP was conducted using dPTFE membrane with allografts on the day of extraction without primary closure. When the membrane was removed after 4 weeks, the newly formed reddish tissue at the grafted site was checked (first outcome, clinical evaluation). Four months after membrane removal, a core biopsy was performed from the center of the grafted site before implant placement (second outcome, histomorphometric evaluation). Radiographic measurements of alveolar bone changes between implant prosthesis delivery and the 1-year follow-up were obtained (third outcome, radiographic evaluation). A total of 23 sites from 18 patients had no complications during the follow-up period. Three sites from two patients were excluded because of early membrane removal. Newly formed reddish tissue was found at 15 sites, and partially formed tissue was found at 8 sites. Although we were unable to harvest bone core from all sites, histomorphometric analysis in 11 patients indicated that the mean area of new bone was 28.48% ± 6.60%, that of the remaining graft particle was 27.68% ± 9.18%, and that of fibrous tissue was 43.84% ± 6.98%. The mean loss of marginal bone was 0.13 ± 0.06 mm at the mesial area and 0.15 ± 0.06 mm at the distal area, as assessed using radiographic evaluations. The results of this nonrandomized study suggest that this technique may be an appropriate procedure for ARP. Further studies with a control group and more subjectives can be designed based on this study.

Epidemiology of Implant Mortality Disparity Among Intraoral Positions and Prosthesis Types.

PURPOSE: To examine the disparity of single-crown implant failure with a similar loss of the splinted prosthesis in differing anatomical locations while controlling for other demographic and clinical variables that may confound the relationship between prosthesis types and implant loss. MATERIALS AND METHODS: A multicenter retrospective cohort study was designed to include patients treated with dental implants from 2003 to 2014. The variables included age, sex, systemic disease, bone graft, implant placement date, position of dental implant, length of dental implant, diameter of dental implant, loading time, type of prosthesis, type of opposing occlusion, latest check date, and survival or loss of the dental implant. The demographic and clinical variables' influence on the survival of dental implants was estimated by the Kaplan-Meier method. The position and diameter were adjusted for the accurate estimation of the relationship between the prosthesis type and survival of the dental implant with the Cox proportional hazard method. RESULTS: A total of 1,151 dental implants from 403 patients were ascertained. After adjusting for the confounding effect of position and diameter, single-crown prostheses were 38.1 (95% CI: 15.1-118) times more likely to be lost than the connected-type prostheses. For single-crown implants, the waiting time for osseointegration before loading was the highest for the maxillary molar position and the lowest for the mandibular molar position (P < .0001), while the most frequent implant loss occurred in the maxillary anterior area, and the second frequent area was the maxillary molar position; the lowest occurrence of implant loss was for the mandibular molar position. This disparity was statistically significant (P = .0271). CONCLUSION: Despite the high survival rates of endosseous implants as a whole, since the variation of implant loss was observed among the different anatomical positions for single-crown implants, special attention has to be given to the maxillary anterior and maxillary molar positions. A longer healing time assuming compensation for disadvantageous bone quality was not directly effective in increasing implant longevity in the vulnerable positions.

High-Frequency, Low-Intensity Pulsed Ultrasound Enhances Alveolar Bone Healing of Extraction Sockets in Rats: A Pilot Study.

Most studies of the beneficial effects of low-intensity pulsed ultrasound (LIPUS) on bone healing have used frequencies between 1.0 and 1.5 MHz. However, after consideration of ultrasound wave characteristics and depth of target tissue, higher-frequency LIPUS may have been more effective on superficially positioned alveolar bone. We investigated this hypothesis by applying LIPUS (frequency, 3.0 MHz; intensity, 30 mW/cm(2)) on shaved right cheeks over alveolar bones of tooth extraction sockets in rats for 10 min/d for 2 wk after tooth extraction; the control group (left cheek of the same rats) did not receive LIPUS treatment. Compared with the control group, the LIPUS group manifested more new bone growth inside the sockets on histomorphometric analysis (maximal difference = 2.5-fold on the seventh day after extraction) and higher expressions of osteogenesis-related mRNAs and proteins than the control group did. These findings indicate that 3.0-MHz LIPUS could enhance alveolar bone formation and calcification in rats.

Simultaneous Block Bone Grafting Using "L-Shaped Notch" Preparation in Mandible: Case Series and 1-Year Follow-up.

PURPOSE: A novel autogenous block bone grafting technique with simultaneous placement of dental implants is described for several cases of horizontal ridge augmentation. METHODS: Seven patients with a mandibular horizontal ridge that was inadequate for proper implant placement were included in this study. Simultaneous implant placement and autogenous block bone grafting was planned; we designed the "L-shaped notch" preparation of the recipient site for the additional fixation with only 1 screw. This new technique also required minimal size of autogenous block bone. RESULTS: In total, 11 implants and final restorations were delivered in 7 patients. The dehiscence defects were covered successfully (79.70 ± 5.58%; 2.26 ± 0.68 mm) at the uncover surgery. The marginal bone loss was 0.50 ± 0.26 mm on the mesial side and 0.58 ± 0.23 mm on the distal side. The outcomes were satisfactory clinically and radiographically during the 1-year follow-up. CONCLUSION: Although additional studies, with more than 7 patients, are needed to evaluate the L-shaped notch preparation, this was effective to accomplish horizontal ridge augmentation simultaneously with the placement of dental implants using the minimal size of autogenous block bone.

Extensive gingival necrosis and sequestration of the alveolar bone caused by methimazole-induced neutropenia and three-year follow-up.

PURPOSE: Methimazole is an anti-thyroid drug that can cause life-threatening neutropenia in rare situations. The aim of this case report is to describe a set of oral complications associated with methimazole-induced neutropenia and the healing of the gingiva after proper treatment. METHODS: A 31-year-old female patient hospitalized for systemic symptoms of sore throat and fever and showing extensive gingival necrosis with pain was referred to the Department of Periodontics from the Department of Endocrinology. Methimazole-induced neutropenia was diagnosed based on blood test results and her medical history. Methimazole was discontinued and a range of treatments was administered, including the injection of granulocyte colony stimulating factor. RESULTS: After systemic treatment, the gingiva began to heal as the neutrophil count increased. Approximately one year later, the gingiva had returned to a normal appearance. Twenty-one months after treatment, sequestra of the alveolar bone that had broken through the gingiva were removed. Periodic supportive periodontal treatment has been continued uneventfully. CONCLUSIONS: The oral manifestations of gingival necrosis and ulcerations, in combination with systemic symptoms such as fever and sore throat, are the critical signs presented in the early stages of drug-induced neutropenia. Therefore, dentists need to be aware of these oral complications in order to make an accurate diagnosis and to ensure that prompt medical intervention is provided.

Effects of increased low-level diode laser irradiation time on extraction socket healing in rats.

In our previous studies, we confirmed that low-level laser therapy (LLLT) with a 980-nm gallium-aluminum-arsenide diode laser was beneficial for the healing of the alveolar bone in rats with systemic disease. However, many factors can affect the biostimulatory effects of LLLT. Thus, we attempted to investigate the effects of irradiation time on the healing of extraction sockets by evaluating the expressions of genes and proteins related to bone healing. The left and right first maxillary molars of 24 rats were extracted. Rats were randomly divided into four groups in which extraction sockets were irradiated for 0, 1, 2, or 5 min each day for 3 or 7 days. Specimens containing the sockets were examined using quantitative real-time reverse transcription polymerase chain reaction and western blotting. LLLT increased the expressions of all tested genes, Runx2, collagen type 1, osteocalcin, platelet-derived growth factor-B, and vascular endothelial growth factor, in a time-dependent manner. The highest levels of gene expressions were in the 5-min group after 7 days. Five minutes of irradiation caused prominent increases of the expression of all tested proteins after both 3 and 7 days. The expression level of each protein in group 4 was higher by almost twofold compared with group 1 after 7 days. Laser irradiation for 5 min caused the highest expressions of genes and proteins related to bone healing. In conclusion, LLLT had positive effects on the early stages of bone healing of extraction sockets in rats, which were irradiation time-dependent.

Immobilization of alkaline phosphatase on solid surface through self-assembled monolayer and by active-site protection.

Retaining biological activity of a protein after immobilization is an important issue and many studies reported to enhance the activity of proteins after immobilization. We recently developed a new immobilization method of enzyme using active-site protection and minimization of the cross-links between enzyme and surface with a DNA polymerase as a model system. In this study, we extended the new method to an enzyme with a small mono-substrate using alkaline phosphatase (AP) as another model system. A condition to apply the new method is that masking agents, in this case its own substrate needs to stay at the active-site of the enzyme to be immobilized in order to protect the active-site during the harsh immobilization process. This could be achieved by removal of essential divalent ion, Zn2+ that is required for full enzyme activity of AP from the masking solution while active-site of AP was protected with p-nitrophenyl phosphate (pNPP). Approximately 40% of the solution-phase activity was acquired with active-site protected immobilized AP. In addition to protection active-site of AP, the number of immobilization links was kinetically controlled. When the mole fraction of the activated carboxyl group of the linker molecule in self-assembled monolayer (SAM) of 12-mercaptododecanoic acid and 6-mercapto-1-ethanol was varied, 10% of 12-mercaptododecanoic acid gave the maximum enzyme activity. Approximately 51% increase in enzyme activity of the active-site protected AP was observed compared to that of the unprotected group. It was shown that the concept of active-site protection and kinetic control of the number of covalent immobilization bonds can be extended to enzymes with small mono-substrates. It opens the possibility of further extension of the new methods of active-site protection and kinetic control of immobilization bond to important enzymes used in research and industrial fields.

Hesperetin alleviates the inhibitory effects of high glucose on the osteoblastic differentiation of periodontal ligament stem cells.

Hesperetin (3',5,7-trihydroxy-4-methoxyflavanone) is a metabolite of hesperidin (hesperetin-7-O-rutinoside), which belongs to the flavanone subgroup and is found mainly in citrus fruits. Hesperetin has been reported to be an effective osteoinductive compound in various in vivo and in vitro models. However, how hesperetin effects osteogenic differentiation is not fully understood. In this study, we investigated the capacity of hesperetin to stimulate the osteogenic differentiation of periodontal ligament stem cells (PDLSCs) and to relieve the anti-osteogenic effect of high glucose. Osteogenesis of PDLSCs was assessed by measurement of alkaline phosphatase (ALP) activity, and evaluation of the mRNA expression of ALP, runt-related gene 2 (Runx2), osterix (OSX), and FRA1 as osteogenic transcription factors, as well as assessment of protein expression of osteopontin (OPN) and collagen type IA (COLIA). When PDLSCs were exposed to a high concentration (30 mM) of glucose, osteogenic activity decreased compared to control cells. Hesperetin significantly increased ALP activity at doses of 1, 10, and 100 µM. Pretreatment of cells with hesperetin alleviated the high-glucose-induced suppression of the osteogenic activity of PDLSCs. Hesperetin scavenged intracellular reactive oxygen species (ROS) produced under high glucose condition. Furthermore, hesperetin increased the activity of the PI3K/Akt and ß-catenin pathways. Consistent with this, blockage of Akt or ß-catenin diminished the protective effect of hesperetin against high glucose-inhibited osteogenic differentiation. Collectively, our results suggest that hesperetin alleviates the high glucose-mediated suppression of osteogenic differentiation in PDLSCs by regulating ROS levels and the PI3K/Akt and ß-catenin signaling pathways.

Differences in implant stability associated with various methods of preparation of the implant bed: an in vitro study.

STATEMENT OF PROBLEM: It is difficult to achieve the primary stability necessary for immediate loading in the posterior maxilla because of thin cortical bone, low density trabecular bone, and inadequate bone height due to the presence of the maxillary sinus. PURPOSE: The purpose of this study was to examine the primary stability of dental implants placed by using different methods of preparation for in vitro monocortical and bicortical models of the posterior maxilla. MATERIAL AND METHODS: Sixty screw-shaped implants (4.0 × 10 mm) were inserted into solid rigid polyurethane blocks. The implants were divided into 6 groups (n=10) to test 2 variables: 1) location (monocortical or bicortical block) and 2) preparation method (standard preparation, underpreparation, or the osteotome technique). The insertion and removal torques were measured and resonance frequency analysis (RFA) was performed to determine the primary stability of each implant. Insertion and removal torque data were analyzed by 2-way ANOVA, followed by the post hoc Tukey HSD multiple comparison test. RFA data were analyzed by 2-way and 1-way ANOVAs and the Tukey HSD multiple comparison test (α=.05). The Pearson correlation analysis was also performed to examine correlations among the values. RESULTS: The preparation method had a significant effect on insertion torque, RFA value, and removal torque; however location had a significant effect only on the removal torque (P<.001). There was a significant interaction between location and preparation method for RFA values (P=.045) and a significant difference in standard preparation method according to the location (P=.039); however, there was no significant difference in underpreparation (P=1.00) and osteotome technique (P=1.00). Statistically significant correlations were found between insertion torque and RFA values (r=0.529, P< .001), insertion torque and removal torque values (r=0.517, P< .001), and removal torque and RFA values (r=0.481, P<.001). CONCLUSIONS: Underpreparation and bicortical fixation significantly increased implant stability and the osteotome technique decreased implant stability in synthetic bone models that mimicked the posterior maxillary region. The primary stability values had statistically significant correlations to each other.

Nicotinic acetylcholine receptor α7 and ß4 subunits contribute nicotine-induced apoptosis in periodontal ligament stem cells.

Nicotine, a major component of cigarette smoking, is the important risk factor for the development of periodontal disease. However, the mechanisms that underlie the cytotoxicity of nicotine in human periodontal ligament stem cells (PDLSCs) are largely unknown. Thus, the purpose of this study was to determine the cytotoxic effect of nicotine by means of nicotinic acetylcholine receptor (nAChR) activation in PDLSCs. We first detected α7 and ß4 nAChRs in PDLSCs. The gene expressions of α7 and ß4 nAChR were increased by nicotine administration. Nicotine significantly decreased cell viability at a concentration higher than 10(-5) M. DNA fragmentation was also detected at high doses of nicotine treatment. Moreover, the detection of sub G1 phase and TUNEL assay demonstrated that nicotine significantly induced apoptotic cell death at 10(-2) M concentration. Western blot analysis confirmed that p53 proteins were phosphorylated by nicotine. Under various doses of nicotine, a decrease in the anti-apoptotic protein Bcl-2, but an increase in p53 and cleaved caspase-3 protein levels, was detected in a dose-dependent manner. However, the apoptotic effect of nicotine was inhibited by the pretreatment of α-bungarotoxin, a selective α7 nAChR antagonist or mecamylamine, a non-selective nAChR antagonist. Finally, increases in the subG1 phase and DNA fragmentation by nicotine was attenuated by each nAChR antagonist. Collectively, the presence of α7 and ß4 nAChRs in PDLSCs supports a key role of nAChRs in the modulation of nicotine-induced apoptosis.