Potential application of dental stem cells in regenerative reconstruction of oral and maxillofacial tissues: a narrative review.

Background and Objective: Oral and maxillofacial (OMF) defects caused by congenital conditions, injuries, ablative surgery for benign and malignant head & neck tumor, can often lead to OMF deformities and malfunctions in speech, mastication/chewing, and swallowing as well as have deleterious psychological effects and socioeconomic burdens to patients. Due to the unique complex 3D geometry of the head and neck region, reconstruction and rehabilitation of OMF defects remain a major challenge for OMF surgeons.The purpose of this narrative review is to update the information on the biological properties and functions of mesenchymal stem cells derived from various dental tissues (dental-MSCs) and their potential application in tissue engineering (TE) and regenerative reconstruction of OMF tissues. Methods: A data-based search was performed by using PubMed database whereby articles published between 2000 and 2021 in English were included in the search with the following key words: dental stem cells, OMF reconstruction, OMF TE and regeneration. Key Content and Findings: Currently, the advancement in stem cell biology, biomaterial science, and TE technology has demonstrated the significant potential application of stem cell-based therapy in regenerative reconstruction and rehabilitation of OMF defects. However, no stem cell-based product or device has been translated into clinical application to replace microsurgical free tissue transfer, the current mainstay of care in the reconstruction of OMF defects. Conclusions: Currently, microsurgical free tissue transfer remains the gold standard mainstay of care for the reconstruction of OMF defects due to their abundant blood supply and flexibility for transplantation. However, several major challenges, such as the limited availability, the requirement of a second surgery, donor site morbidity, and the risk of free flap failure, have promoted the development of novel approaches. Due to the advancement in stem cell biology, biomaterial science, and TE technology, stem cell-based regenerative therapy is emerging as a promising therapeutic approach for a variety of diseases, including regenerative reconstruction and rehabilitation of OMF defects. In this narrative review, we update on the characteristics and biological functions of mesenchymal stem cells derived from various dental tissues (dental-MSCs) and their released cell-free products, extracellular vesicles (EVs). We also highlighted their potential application in TE and regenerative reconstruction of OMF defects in animal models and clinical studies and the potential challenges in this field.

High-Dose-Rate Brachytherapy for Primary Treatment of Refractory Proliferative Verrucous Leukoplakia of the Hard Palate.

Oral proliferative verrucous leukoplakia (PVL) is a rare, progressive form of leukoplakia with a high rate of malignant transformation. No therapies are known to lower the rate of malignant transformation and prevent a recurrence. An 84-year-old patient with a years-long history of symptomatic PVL of the hard palate refractory to CO2 laser ablation presented to the radiation oncology clinic for consideration of non-surgical management. High dose rate brachytherapy was used to deliver 36 Gy in 12 fractions to the hard palate using an Ir-192 source with a custom-molded applicator. By three months of follow-up, the patient had complete regression of the PVL and resolution of acute mucositis. With 18 months of follow-up, the patient remains disease- and symptom-free without toxicities of treatment. High dose rate surface applicator brachytherapy is a feasible and potentially effective treatment for oral PVL, yielding durable control with low long-term toxicity.

Efficacy of Alveolar Vertical Distraction Osteogenesis and Autogenous Bone Grafting for Dental Implants: Systematic Review and Meta-Analysis.

PURPOSE: The aim of this study was to assess the efficacy of alveolar vertical distraction osteogenesis and autogenous bone grafting in terms of bone gain, bone resorption, and implant survival and success rates and investigate the relationship between bone gain and resorption after alveolar vertical distraction osteogenesis. MATERIALS AND METHODS: A systematic search was done using MEDLINE, EMBASE, the Cochrane Library, and KoreaMed from inception to April 30, 2014. Supplementary manual searches of published full-text articles were also performed. RESULTS: Searches of four electronic databases and manual searches resulted in 1,538 articles. After selection, four studies were included in the systematic review and meta-analysis. The difference in bone gain at the end of distraction or bone grafting was statistically significant (weighted mean difference [WMD] 1.86, 95% CI 0.03 to 3.69, P = .05; heterogeneity: I(2) = 78%, P = .01). However, there was not a statistically significant difference between alveolar distraction osteogenesis and onlay bone grafting (WMD 0.30, 95% CI -0.99 to 1.59, P = .065). Bone resorption between the end of treatment and the time of implant placement was not statistically significant (WMD -0.12, 95% CI -1.10 to 0.85, P = .80; heterogeneity: I(2) = 78%, P = .01). A simple equation related to bone gain and resorption after alveolar vertical distraction was induced from these results. CONCLUSION: There was not a statistically significant difference between alveolar distraction osteogenesis and onlay bone grafting in terms of bone gain and bone resorption.

An anatomical study of the risorius in Asians and its insertion at the modiolus.

PURPOSE: Detailed explanations of the insertion, interaction patterns, and arrangement of the risorius muscle fibers at the modiolus have still not been clearly shown. The aim of this study is to clarify the arrangement of the risorius muscle by means of topographic examination, and to evaluate the anatomical variations in its attachments and pattern of shape to other perioral muscles, and eventually to understand the various features of the facial animation of Asians. MATERIALS AND METHODS: Eighty embalmed Korean and Thai adult hemifaces from cadavers of both genders were dissected in this study. Detailed dissection at the modiolus revealed the insertion of the risorius muscle in relation to its attachments and fiber interaction forms. RESULTS: When categorized into three common anatomical types--zygomaticus risorius (ZR), platysma risorius (PR), and triangularis risorius (TR). PR was most common with 45 % (36 cases) frequency. Risorius muscle also inserted into the modiolus in three distinct layers in relation to the depressor anguli oris: superficial, flush, and deep. Superficial attachment was most commonly found with 56.3 % (45 cases) frequency. CONCLUSIONS: These results will provide critical information for future planning and performing of reconstructive, reanimation, and cosmetic surgical procedures for cases such as developmental defect, facial trauma, facial muscle paralysis, and restoring the natural personal appearances.

Measurement of total occlusal convergence of 3 different tooth preparations in 4 different planes by dental students.

STATEMENT OF PROBLEM: Total occlusal convergence of crown preparation is an important didactic and clinical concept in dental education. PURPOSE: The purpose of this study was to compare the discrepancy between the total occlusal convergence of dental students' typodont crown preparations and the ideal range (4 to 10 degrees) in 3 different regions of the mouth and in 4 different planes of the teeth. MATERIAL AND METHODS: The dental students of the Class of 2012 at Harvard School of Dental Medicine were asked to prepare typodont teeth for crowns on 3 different teeth, the maxillary left central incisor (ceramic), mandibular left first molar (complete metal), and mandibular left first premolar (metal ceramic), during their third year preclinical summative examination and the Comprehensive Clinical Examination in their fourth year. Eighteen students prepared 3 teeth in their third and fourth years, whereas 19 students participated only in their fourth year, for a total of 55 sets of 3 teeth. By using custom fit die bases to reproduce the position, a novel procedure of measuring each tooth was accomplished in 4 different planes: the faciolingual, mesiodistal, mesiofacial-distolingual, and mesiolingual-distofacial. The total occlusal convergence of each image was measured with a computer screen protractor. The gingival 2 mm of the axial wall was used to determine the taper of each wall. Linear mixed model analysis was used to estimate and compare the total occlusal convergences of different teeth and planes (α=.05). Bonferroni corrections were used to adjust for post hoc multiple comparisons. RESULTS: The mean total occlusal convergence varied by tooth and plane (2-way interaction; P<.001). For the first molar, dental students excessively tapered in all 4 planes; the model-predicted 99% CIs for the total occlusal convergence were as follows: faciolingual (12.7, 19.4), mesiodistal (14.0, 19.3), mesiofacial-distolingual (13,4, 19.4), and mesiolingual-distofacial (13.7, 19.1). For the central incisor, 99% CIs for the total occlusal convergence were (15.9, 24.4) for the faciolingual measurement, providing strong evidence of excessive tapering, and (4.1, 8.0) for the mesiodistal measurement, which was within the ideal total occlusal convergence range. The mesiofacial-distolingual and mesiolingual-distofacial planes in the central incisor and all 4 planes in the first premolar had mean total occlusal convergences that exceeded 10 degrees; however, excessive tapering could not be statistically established, because their CIs included values within the ideal range. CONCLUSIONS: The present study found significant evidence of excessive tapering in a study comparing the total occlusal convergence values of crown preparations with those of the ideal preparation for 3 different teeth in 4 different planes. The total occlusal convergence for the molar preparations had the highest mean values.

A systematic review of screw- versus cement-retained implant-supported fixed restorations.

PURPOSE: To systematically evaluate the survival and success of screw- versus cement-retained implant crowns. MATERIALS AND METHODS: The authors performed an electronic search of nine databases using identical MeSH phrases. Systematic evaluation and data extraction of the articles from 1966 through 2007 were completed by three reviewers and two clinical academicians. The major outcome variable was implant or crown loss, and the minor outcome variables were screw loosening, decementation, and porcelain fracture. Random effects Poisson models were used to analyze the failure and complication rates. RESULTS: The initial search produced 26,582 articles. Of these, 577 titles and subsequently 295 abstracts were available for evaluation, with 81 full texts meeting the criteria for review. Data were extracted from 23 level one and two research studies. Fleiss' kappa interevaluator agreement ranged from almost perfect to moderate. Major failures included 0.71 screw-retained and 0.87 cement-retained failures per 100 years. Minor failures included 3.66 screw loosenings, 2.54 decementations, and 0.46 porcelain fractures per 100 years. CONCLUSION: There is no significant difference between cement- and screw-retained restorations for major and minor outcomes with regard to implant survival or crown loss. This is important data, as clinicians use both methods of restoration, and neither is a form of inferior care.

Bond strength of the porcelain repair system to all-ceramic copings and porcelain.

PURPOSE: The purpose of this study was to investigate the shear bond strength of the porcelain repair system on alumina and zirconia core ceramics, comparing this strength with that of veneering porcelain. MATERIALS AND METHODS: Veneering ceramic (n = 12), alumina core (n = 24), and zirconia core (n = 24) blocks measuring 10 × 5 × 5 mm(3) were fabricated. Veneering ceramic blocks were used as the control. Alumina and zirconia core blocks were divided into 2 groups (n = 12 each), and a slot (2 × 2 × 4 mm(3)) filled with veneering ceramics was prepared into one of the alumina and zirconia core groups (n = 12). Followed by surface treatments of micro-abrasion with 30 µm alumina particles, etching with 35% phosphoric acid and silane primer and bond, composite resin blocks (2 × 2 × 2 mm(3)) were built up and light polymerized onto the treated surfaces by 3 configurations: (a) composite blocks bonded onto veneering ceramic surface alone, (b) composite blocks bonded onto alumina core or zirconia core surfaces, (c) a 50% surface area of the composite blocks bonded to veneering ceramics and the other 50% surface area of the composite blocks to alumina core or zirconia core surfaces. The shear bond strength of the composite to each specimen was tested by a universal testing machine at a 0.5 mm/min crosshead speed. The shear bond strength was analyzed by unpaired t-tests for within the configuration groups and ANOVA for among the different configuration groups. RESULTS: When the mean shear bond strength was compared within groups of the same configuration, there were no statistically significant differences. Comparison of the shear bond strength among groups of different configurations revealed statistically significant differences. The mean shear bond strength of composite onto 100% veneering ceramic surface and composite onto 50% veneering 50% all-ceramic cores was statistically higher than that of composite onto 100% all-ceramic cores; however, the differences of the shear bond strength of composite bonded only onto the veneering ceramic surface were not statistically significant from those of 50% surface area of composite bonded onto all-ceramic cores. CONCLUSION: No statistically significant differences in the bond strength of a porcelain repair system to alumina and zirconia copings were observed. Increasing the surface of veneering ceramics to a porcelain repair system improved the repair material's bond strength.

In vivo measurements of human gingival translucency parameters.

The aim of this study was to evaluate the relationship between gingival translucency and peri-implant mucosa. A total of 22 peri-implant sites in 16 patients who required tooth replacement in the esthetic zone were included. Color measurements were obtained using a spectrophotometer and customized colored abutments. Mucosal thickness measurements were taken incrementally 0.5 mm from the facial gingival margin on sectioned casts. A statistically significant difference in gingival translucency was observed beginning at 1.5 mm. A negative correlation was observed between the thickness and translucency parameter (TP) (r = -0.64), with TP values decreasing as the gingival thickness increased. The gingival translucency was correlated with the thickness of the peri-implant mucosa and distance from the facial gingival margin.

A 10-year survey of US deans: trends, challenges, and mentoring in prosthodontics. Part 2.

PURPOSE: Part 2 of this survey reports on the 2009 survey findings distributed to the deans of US dental schools. A national, electronic survey of 58 dental school deans was distributed by e-mail to evaluate an interest in specialty training, an interest in specialty training in prosthodontics, faculty shortage issues, predoctoral curriculum in prosthodontics, ideology regarding dental specialties, and the administrative position of prosthodontics within the schools. MATERIALS AND METHODS: The survey data were transferred to an online spreadsheet program for statistical analysis (Key Survey, Inc. http://www.keysurvey.com, Braintree, MA). The opinions of dental school deans were viewed as legitimate indicators of change within predoctoral and postdoctoral prosthodontic education. Statistical analysis was carried out using Statistica Version 9.1 (Statsoft, Tulsa, OK). RESULTS: Of the 58 deans, 42 deans responded, for a 72.4% response rate. Twenty-three deans reported an increase in the number of students seeking specialty training after dental school. Only three deans reported a decrease in those seeking specialty training. In the 2009 survey, 45% the deans responded that there was an increased interest in prosthodontics. One or more open faculty positions in prosthodontics existed at 24 (59%) of the dental schools, and 30 (71%) offered at least one incentive or a variety of incentives to recruit faculty. The 2009 respondents to the deans' survey revealed predoctoral student exposure to prosthodontists was high, and exposure to advanced education in prosthodontics students was low. A survey of internal school programs that might have an impact on an increased interest in prosthodontics revealed the presence of a predoctoral mentoring program for prosthodontics in 36 (88%) of the institutions. The clinical curriculum included treatment of a variety of cases including complex cases as defined by a diagnostic classification system. The 2009 survey respondents reported an increase in the number of schools where prosthodontics is a separate entity or department. CONCLUSION: Deans reported an increased interest in prosthodontics in the 2009 survey. Open faculty positions in prosthodontics existed in the majority of dental schools, and most schools offered incentives to recruit faculty. The survey of deans found a very high level of exposure of dental students to full-time prosthodontists and a very low exposure level to students enrolled in advanced education in prosthodontics. The establishment of mentoring programs in prosthodontics was reported by most deans, and the predoctoral curriculum included treating complex cases. Most deans stated that dual-specialty training in prosthodontics and periodontics would be beneficial. The 2009 survey reported an increase in the number of departments of prosthodontics in US schools.

Increasing predoctoral dental students' motivations to specialize in prosthodontics.

This study provides data about factors that influence dental students' decision of which specialty to pursue and describes program changes in prosthodontics designed to expand student interest in a prosthodontics training program. Of 176 current and recently graduated students at Harvard School of Dental Medicine, 167 responded to the e-mail survey for a 94.9 percent response rate. Using the Pearson chi-square analysis, we analyzed nine factors to determine their contribution to these students' choice of specialty. Two factors, lecture and faculty/mentoring, were highly significant (p<0.006) regarding impact on the students' introductory experience with prosthodontics. When choosing a specialty, 44 percent of all students ranked "enjoyment of providing the specialty service" as the most important factor. Students wishing to specialize in prosthodontics, however, ranked four significant factors: enjoyment of providing the specialty service (p<0.037, p<0.057); faculty influence (p<0.0002, p<0.0001); length of program (p<0.039, p<0.006); and cost of program (p<0.023, p<0.004). Respondents also ranked the nine American Dental Association-recognized specialties regarding their perceptions of future salary and impact on the dental profession. They ranked prosthodontics fourth for future salary and fifth for impact on the profession. At the same time that this study was being conducted, key changes were being made in the graduate prosthodontics program; those appear to have had a positive impact on students' interest in pursuing prosthodontics as a specialty.

Ten-year survey of program directors: trends, challenges, and mentoring in prosthodontics. Part 1.

PURPOSE: This study consisted of two parts. Part 1 was a survey of US program directors, and Part 2 reports on the survey findings distributed to the deans of US dental schools. Both surveys evaluated observations of trends in prosthodontic education. The first survey (2005) of program directors and deans was published in 2007. This second survey was conducted in 2009. The 2009 survey provided 10-year data on trends in prosthodontics as reported by program directors. MATERIALS AND METHODS: A national e-mail survey of 46 program directors was used to collect enrollment data for years 1 to 3 of prosthodontics training for US and international dental school graduates, the total number of applicants and applications considered, and the trends over time of applicants to prosthodontics for US dental school graduates and for international graduates. In addition, the program directors were asked to rank 13 key factors that may have contributed to any changes in the prosthodontic applicant pool. Program directors were also asked for information on student financial incentives and whether their programs were state or federally funded, and whether their sponsoring institution was a dental school. RESULTS: Of the 46 program directors, 40 responded, for an 87% response rate. Respondents reported that 66% of their enrollees were graduates of US dental schools. Between 2000 and 2009 the applicant pool in prosthodontics nearly doubled, with 50% of the program directors reporting an increase in US-trained applicants, 42.5% reporting no change, and only 7.5% reporting a decrease. Using the Spearman correlation for the 10-year survey, there was a positive, statistically significant correlation that society's demand for a higher level of training and credentialing and interest in prosthodontics among dental students contributed to an increase in the number of US dental graduates applying to prosthodontic programs. Only four programs offered no financial packages to offset tuition. The remaining 36 respondents reported some financial package. Among the respondents, there were 23 state-sponsored programs and 6 sponsored by private universities; the remaining 9 were sponsored by hospitals or federal agencies. CONCLUSIONS: A nearly doubled applicant pool and more US-trained applicants to prosthodontics ensure a much more competitive applicant pool for our specialty. In the 2009 survey, program directors reported that factors such as society's demand for a higher level of training and credentialing, interest in prosthodontics among US dental students, advances in implant, esthetic, and reconstructive dentistry, literature pertaining to the need of prosthodontists for the future, marketing of prosthodontics as a career, and the dollar value of prosthodontic training have all had some impact on increasing the mentored applicant pool to prosthodontic training in the United States.

In vitro study of the correlation between the simulated clinical and radiographic examination of microgaps at the implant-abutment interface.

OBJECTIVES: To analyze the diagnostic value of the clinical and radiographic investigation of the interface of two-piece implant systems under the variables crevice size of the microgap, clinical experience, radiograph exposure time, prosthesis design, and type of evaluation. METHOD AND MATERIALS: A simulated mandibular cast with five screw-retained implants (Straumann) providing three different prosthesis designs displayed artificially created proximal, visually inaccessible microgaps of unequal sizes or junctions without any measurable gap formation. Three groups of 15 investigators each with a different degree of clinical experience evaluated the implant-abutment interfaces of the cast clinically and radiographically. The investigation was conducted on the basis of a scoring form adapted from the receiver operating characteristic (ROC) 5-choice method. Radiographs were prepared in two exposure times (0.1 second, 0.2 second) for each junction. Radiographs of the initial situation without any measurable gap formation were shown as a control and to detect false-positive scores for each gap size. A 10-point SEM measurement of the junctions served for standardization purposes. Statistical methods included ROC analysis, kappa analysis, and a regression analysis (alpha = .05). RESULTS: Gaps greater than 150.9 microm (P < .001) were detected 227% more frequently and gaps greater than 189.7 microm 292% more frequently via radiographic examination. Kappa values were adequate for the radiographic examination and unsatisfactory for clinical examination. Prosthetic superstructure and exposure time did not adversely affect the diagnosis. Clinical experience improved the detection of microgaps significantly. CONCLUSION: A relationship between the size of microgaps and the examiners' ability to detect them can be established. Whereas tactile examination alone is not accurate enough, radiographic analysis affiliated with a certain degree of clinical experience possesses features for an adequate clinical management of restoration defects.

Angle closure in younger patients.

PURPOSE: Angle-closure glaucoma is rare in children and young adults; only scattered cases associated with specific clinical entities have been reported. We evaluated the findings in patients aged 40 or younger with angle closure in our database. DESIGN: Retrospective noncomparative case series. PARTICIPANTS: Our database was searched for patients aged 40 years or younger with angle closure. Data recorded included age at initial consultation, age at the time of diagnosis, gender, slit-lamp examination, gonioscopy, ultrasound biomicroscopy (from 1993 onward), clinical diagnosis, and therapy. Patients with prior incisional surgery were excluded, as were patients with anterior chamber proliferative mechanisms leading to angle closure. RESULTS: Sixty-seven patients (49 females, 18 males) met entry criteria. Mean age at the time of consultation was 34.4 +/- 9.4 (standard deviation) years (range, 3-68 years). Diagnoses included plateau iris syndrome (35 patients); iridociliary cysts (8 patients); retinopathy of prematurity (7 patients); uveitis (5 patients); isolated nanophthalmos (3 patients); relative pupillary block (2 patients); Weill-Marchesani syndrome (3 patients); and 1 patient each with Marfan syndrome, miotic-induced angle closure, persistent hyperplastic primary vitreous, and idiopathic lens subluxation. CONCLUSIONS: The etiology of angle closure in young individuals differs from the older population and is typically associated with structural/developmental ocular anomalies rather than relative pupillary block. After laser iridotomy, these eyes should be monitored for recurrent angle closure and the need for additional laser or incisional surgical intervention.

Rosai-Dorfman disease. Extranodal sinus histiocytosis in three co-existing sites. A case report.

A 73-year-old woman presented with mild anterior uveitis, ipsilateral optic neuropathy, and ipsilateral skin nodules. A compressive mass at the level of the orbital apex and sphenoid wing was found on cranial magnetic resonance imaging. Biopsy of the skin nodules revealed histopathologic evidence of sinus histiocytosis with massive lymphadenopathy, or Rosai-Dorfman disease (RDD). Systemic investigations failed to show any massive lymphadenopathy, making this a case of extranodal RDD. This is a salient case in that it proposes three simultaneous and separate sites of involvement by extranodal RDD. It also exemplifies that RDD should be a suspect diagnosis even in the absence of lymphadenopathy.

Angle closure in younger patients.

PURPOSE: Angle-closure glaucoma is rare in children and young adults. Only scattered cases associated with specific clinical entities have been reported. We evaluated the findings in patients in our database aged 40 or younger with angle closure. METHODS: Our database was searched for patients with angle closure who were 40 years old or younger. Data recorded included age at initial consultation; age at the time of diagnosis; gender; results of slit-lamp examination, gonioscopy, and ultrasound biomicroscopy (from 1993 onward); clinical diagnosis; and therapy. Patients with previous incisional surgery were excluded, as were patients with anterior chamber proliferative mechanisms leading to angle closure. RESULTS: Sixty-seven patients (49 females, 18 males) met entry criteria. Mean age (+/- SD) at the time of consultation was 34.4 +/- 9.4 years (range, 3-68 years). Diagnoses included plateau iris syndrome (35 patients), iridociliary cysts (8 patients), retinopathy of prematurity (7 patients), uveitis (5 patients), isolated nanophthalmos (3 patients), relative pupillary block (2 patients), Weill-Marchesani syndrome (3 patients), and 1 patient each with Marfan syndrome, miotic-induced angle closure, persistent hyperplastic primary vitreous, and idiopathic lens subluxation. CONCLUSION: The etiology of angle closure in young persons is different from that in the older population and is typically associated with structural or developmental ocular anomalies rather than relative pupillary block. Following laser iridotomy, these eyes should be monitored for recurrent angle closure and the need for additional laser or incisional surgical intervention.