Identifying factors influencing orthodontic residency program selection

PURPOSE

The desirability of Orthodontic Residency remains high today relative to the past 30 years. This investigation seeks to re-assess factors influencing Orthodontic Residency program selection amidst contemporary challenges and changes, including increasing student debt, reduced residency stipends, and shifting practice models.

METHODS

This mixed-methods study consisted of interviews (qualitative) and surveys (quantitative). Fifteen final-year dental students and first-year orthodontic residents were interviewed one-on-one following a topic guide and then transcripts were analyzed using MAXQDA2022 to identify values, factors, and influences related to program selection and ranking. Qualitative findings and previous studies provided the basis for a survey distributed to residency applicants in 2020-22. Data were analyzed with bivariate and descriptive statistics with stratification by debt group.

RESULTS

Interviews (N = 15) elevated the importance of location, interview experience, program cost, and clinical education. Surveys (N = 239) identified the most desirable factors for program selection: satisfied residents, strong clinical training with multiple techniques, good interview impressions, low cost, high patient numbers, a strong reputation, and good clinical facilities with new technology. Less desirable factors include programs that are hospital-based, certificate-only, research-intensive, and require considerable after-hours work.

CONCLUSIONS

Clinical education and interview experiences are key for residency selection, consistent with prior studies, though program cost has grown in importance. Findings can help guide orthodontic programs in recruiting applicants and suggest a need to limit educational costs.

Preface to the 9th Biennial COAST Conference: Harnessing Technology and Biomedicine for Personalized Orthodontics

OBJECTIVE

The Consortium on Orthodontic Advances in Science and Technology (COAST) convened for its 9th biennial conference titled 'Harnessing Technology and Biomedicine for Personalized Orthodontics' to explore cutting-edge craniofacial research towards building the foundations for precision care in orthodontics.

SETTING AND SAMPLE POPULATION

Seventy-five faculty, scholars, private practitioners, industry, residents and students met at the UCLA Arrowhead Lodge on 6-9 November 2022 for networking, scientific presentations and facilitated discussions. Thirty-three speakers provided state-of-the-art, evidence-based scientific and perspective updates in craniofacial and orthodontic-related fields. The overall format included an Education Innovation Award Faculty Development Career Enrichment (FaCE) workshop focused on faculty career development, three lunch and learns, keynote or short talks and poster presentations.

MATERIAL AND METHODS

The 2022 COAST Conference was organized thematically to include (a) genes, cells and environment in craniofacial development and abnormalities; (b) precision modulation of tooth movement, retention and facial growth; (c) applications of artificial intelligence in craniofacial health; (d) precision approaches to Sleep Medicine, OSA and TMJ therapies; and (e) precision technologies and appliances.

RESULTS

The collective advances in orthodontics and science represented in the manuscripts of this issue fulfil our goal of laying solid foundations for personalized orthodontics. Participants elevated the need for stronger industry-academic research partnerships to leverage knowledge gained from large datasets with treatment approaches and outcomes; systematizing the potential of big data including through multi-omics and artificial intelligence approaches; refining the genotype: phenotype correlation to create biotechnology that will rescue inherited dental and craniofacial defects; evolving studies of tooth movement, sleep apnoea and TMD treatment to accurately measure dysfunction and treatment successes; and maximizing the integration of newer orthodontic devices and digital workflows.

CONCLUSIONS

Technological advances combined with those in biomedicine and machine learning are rapidly changing the delivery of health care including that in orthodontics. These advances promise to lead to enhanced customization, efficiencies and outcomes of patient care in routine orthodontic problems and in severe craniofacial problems, OSA and TMD.

Evaluating video-based lectures on YouTube for dental education

PURPOSE/OBJECTIVES

Multimedia presentations and online platforms are used in dental education. Though studies indicate the benefits of video-based lectures (VBLs), data regarding user reception and optimal video features in dental education are limited, particularly on Web 2.0 platforms like YouTube. Given increasing technology integration and remote learning, dental educators need evidence to guide implementation of YouTube videos as a freely available resource. The purpose of this study is to determine video metrics, viewership and format efficacy for dental education videos.

METHODS

First, a cross-sectional survey was conducted of viewers (N = 683) of the Mental Dental educational videos on YouTube. Analytics were evaluated for 677 200 viewers to assess audience demographics, retention and optimal video length. Second, a randomized crossover study was conducted of dental students (N = 101) who watched VBLs in either slideshow or pencast formats and were tested on content learning to compare format efficacy.

RESULTS

Most viewers of Mental Dental videos were dental students (44.2%) and professionals (37.8%) who would likely recommend the platform to a friend or colleague (Net Promoter Score = 82.1). Audience retention declined steadily at 1.34% per minute, independent of video length. Quiz performance did not differ between slideshow and pencast videos, with students having a slight preference for slideshows (P = 0.049).

CONCLUSIONS

Dental students and professionals use VBLs and are likely to recommend them to friends and colleagues. There is no optimal video length to maximize audience retention and lecture format (slideshow vs. pencast) does not significantly impact content learning. Results can guide implementation of VBLs in dental curricula.

Using a digital platform to establish odontometric variation based on race, gender and Angle classification

Orthodontists often encounter significant clinical challenges in the finishing stages of treatment due to a disproportion in interarch tooth size relationships. Despite the increasing presence of digital technology and concomitant focus on customized treatment approaches, there is a gap in the knowledge of how generating tooth size data using digital versus traditional methods may impact our treatment regime.

OBJECTIVE

This study aimed to compare the prevalence of tooth size discrepancies using digital models and a digitally based cast analysis in our cohort based on (i) Angle's Classification; (ii) gender and (iii) race.

MATERIALS AND METHODS

The mesiodistal widths of teeth in 101 digital models were assessed using computerized odontometric software. A Chi-square test was used to determine the prevalence of tooth size disproportions among the study groups. The differences between all three groups of the cohort were analysed using a three-way analysis of variance (ANOVA).

RESULTS

An overall Bolton tooth size discrepancy (TSD) prevalence of 36.6% was observed in our study cohort; 26.7% had an anterior Bolton TSD. No differences existed in the prevalence of tooth size discrepancies between male and female subjects as well as between the different malocclusion groups (P > .05). Caucasian subjects had a statistically significant smaller prevalence of TSD compared to Black and Hispanic patients (P < .05).

CONCLUSION

The prevalence results in this study illuminate how relatively common TSD is and underscores the importance of proper diagnosis. Our findings also suggest that racial background may be an influential factor in the presence of TSD.

Orthodontic patients and the information found on the web: a cross-sectional study

BACKGROUND

In recent years, the Web has become a source of medical information for patients, even though the information available online may be incorrect or qualitatively inadequate. Younger generations, immersed in a digital environment since a very tender age, are more likely to get informed online. This study aims to understand the relevance of online information for prospective orthodontic patients and to investigate the effects of digital research on patients' decision-making process, and it also aims to investigate potential generational differences between digital natives and digital immigrants.

MATERIALS AND METHODS

An anonymous questionnaire was developed to investigate patients' orthodontic-themed Web searches as well as the effects digital material had on their decision-making process. Before submitting the newly designed survey to patients, it was validated in a pilot study. Univariate analysis was applied to analyze the relationship between the demographic characteristics of respondents and their answers on the use of digital research for the decision-making process.

RESULTS

64.6% of the study population searched the Web for orthodontic information prior to their visit. Google was the most used platform regardless of patients' age. The perceived reliability of online sources varied significantly with age. Men displayed more trusting behavior towards their doctor than women. Prospective patients' satisfaction with affected patients' decision-making processes, and the perceived reliability of online sources of information had repercussions on the doctor-patient relationship.

CONCLUSIONS

Orthodontists should be aware that the majority of patients use the Internet as a source for orthodontic information, and that patients who are digital immigrants are more prone to trust the information found online. Patients who perceive the information found on the Web as either useful or reliable don't easily discard it, even if it is inconsistent with the orthodontist's opinion.

Validating clinical characteristic of primary failure of eruption (PFE) associated with PTH1R variants

BACKGROUND

Primary failure of eruption (PFE) is a hereditary condition, and linkage with variants in the PTH1R gene has been demonstrated in many cases. The clinical severity and expression of PFE is variable, and the genotype-phenotype correlation remains elusive. Further, the similarity between some eruption disorders that are not associated with PTH1R alterations is striking. To better understand the genotype-phenotype correlation, we examined the relationship between the eruption phenotype and PTH1R genotype in 44 patients with suspected PFE and 27 unaffected relatives. Sanger sequencing was employed to analyze carefully selected PFE patients. Potential pathogenicity of variants was evaluated against multiple genetic databases for function prediction and frequency information.

RESULTS

Mutational analysis of the PTH1R coding sequence revealed 14 different variants in 38 individuals (30 patients and 8 first-degree relatives), 9 exonic and 5 intronic. Their pathogenicity has been reported and compared with the number and severity of clinical signs. In 72.7% of patients with pathogenic variants, five clinical and radiographic criteria have been found: involvement of posterior teeth, involvement of the distal teeth to the most mesial affected, supracrestal presentation, altered vertical growth of the alveolar process and posterior open-bite. In cases with mixed dentition (3), the deciduous molars of the affected quadrant were infraoccluded.

DISCUSSION

The probability of an affected patient having a PTH1R variant is greater when five specific clinical characteristics are present. The likelihood of an eruption defect in the absence of specific clinical characteristics is rarely associated with a PTH1R mutation.

CONCLUSIONS

We report here that systematic clinical and radiographic observation using a diagnostic rubric is highly valuable in confirming PFE and offers a reliable alternative for accurate diagnosis.

A machine learning approach to determine the prognosis of patients with Class III malocclusion

INTRODUCTION

The conundrum of determining how to treat a patient with Class III malocclusion is significant, creating a burden on the patient and challenging the orthodontist. The objective of this study was to employ a statistical prediction model derived from our previous cephalometric data on 5 predominant subtypes of skeletal Class III malocclusion to test the hypothesis that Class III subtypes are associated with treatment modalities (eg, surgical vs nonsurgical) and treatment outcome.

METHODS

Pretreatment lateral cephalometric records of 148 patients were digitized for 67 cephalometric variables, and measurements were applied to a mathematical equation to assign a Class III subtype. Subjects were assigned to either a surgical or nonsurgical group depending on the treatment received. Treatment outcome was determined by facial profile and clinical photographs. Log binomial models were used for statistical analysis.

RESULTS

Subtype 1 (mandibular prognathic) patients were 3.5 × more likely to undergo orthognathic surgery than subtypes 2/3 (maxillary deficient) and 5.3 × more likely than 4/5 (combination). Subtype 1 patients were also 1.5 × more likely to experience treatment failure than subtypes 2/3 (maxillary deficient) and 4/5 (combination).

CONCLUSIONS

This assessment of a systematic method to characterize patients with Class III malocclusion into subtypes revealed that subtype 1 (mandibular prognathic) showed a likelihood to undergo orthognathic surgery while subtypes 2/3 experienced significantly lower treatment failure (in response to orthodontics alone). Further refinement of the equation may yield a reliable prediction model for earlier identification of surgical patients and also provide predictive power of Class III treatment outcomes.

Educational debt and the gender gap: Understanding factors influencing orthodontists' career decisions

INTRODUCTION

Orthodontic residents face challenges unparalleled to their predecessors, including competitive marketplaces, rising debt burdens, and changing demographics that have contributed to the shift in initial career choice from owner to employee. We aim to understand factors important to orthodontists at different career stages and the impact on job satisfaction through a sequential mixed methodology study.

METHODS

Semistructured interviews were conducted with 25 orthodontic residents and practitioners. A survey was developed from qualitative findings that explored career decision-making of orthodontic residents and practicing orthodontists, with descriptive and bivariate statistical analyses (n = 343 orthodontists and 185 residents).

RESULTS

Graduating orthodontic residents are choosing employment over ownership as their initial job, prioritizing high income to offset the educational debt. The majority of residents report thinking about their debt very often to all of the time and find it very to extremely stressful. Current residents have long-term goals of ownership, whereas practicing doctors of both genders became owners at equal frequencies. However, on average, women earn $119,000 less per year and report being the primary family caretaker more often than men.

CONCLUSIONS

Excellent patient care, work-life balance, and sufficient income are the most important drivers for career choices and job satisfaction for orthodontists of all ages. Despite debt, most residents and working orthodontists report a high level of job satisfaction and would recommend the field of orthodontics to others.

Preface to COAST 2018 Innovators' Workshop: Bridging the biology and technology gap in orthodontics and craniofacial care

OBJECTIVE

A third focused workshop explored how to transfer novel findings into clinical orthodontic practice.

SETTING AND SAMPLE POPULATION

Participants met at the Scottsdale Plaza Resort, 12-16 September 2018 for the Consortium for Orthodontic Advances in Science and Technology 2018 Innovators' Workshop. Thirty speakers and four lunch-hour focus group leaders shared and exchanged information with approximately 45 registered attendees.

MATERIAL AND METHODS

This Innovators' Workshop was organized according to five themed sessions which covered: (a) The relevance of genetics, biology and environment to therapeutic outcomes; (b) Application of bioinformatics in craniofacial research; (c) Regeneration with and for orthodontic treatment; (d) Technology in precision orthodontics; and (e) Muscle, joint, and airway: Growth, function and pain.

RESULTS

The papers that comprise this supplemental issue exemplify the important outcomes of the 2018 COAST Workshop. In addition, matters identified as important needs include improved understanding of neural, skeletal and muscle tissue crosstalk in early craniofacial growth; standardized methods for three-dimensional radiographic and surface landmark and reference plane identification, measurements and serial superimpositioning techniques for use in the clinic; sharing and making available existing data sets (eg, cone beam computed tomography images, genotype-phenotype data); evidence of the usefulness and effectiveness of new devices; guidelines of what to measure to characterize the airway; more information about the influences of the soft tissues on craniofacial morphology; and information about effective digital work flows applied to clinical and educational settings.

CONCLUSIONS

Progress in bridging the biology-technology gap has identified new needs for improvements in orthodontics and craniofacial care.

A novel nonsense PTH1R variant shows incomplete penetrance of primary failure of eruption: a case report

BACKGROUND

Aim of this work was to describe a rare inheritance pattern of Primary Failure of Eruption (PFE) in a small family with incomplete penetrance of PFE and a novel nonsense PTH1R variant.

CASE PRESENTATION

The proband, a 26 year-old man with a significant bilateral open-bite, was diagnosed with PFE using clinical and radiographic characteristics. DNA was extracted from the proband and his immediate family using buccal swabs and the entire PTH1R coding sequence was analyzed, revealing a novel heterozygous nonsense variant in exon 7 of PTH1R (c.505G > T). This variant introduces a premature stop codon in position 169, predicted to result in the production of a truncated and non-functional protein. This variant has never been reported in association with PFE and is not present in the Genome Aggregation Database (gnomAD). Interestingly, the c.505G > T variant has also been identified in the unaffected mother of our proband, suggesting incomplete penetrance of PFE.

CONCLUSIONS

In this study, we report a new PTH1R variant that segregates in an autosomal dominant pattern and causes PFE with incomplete penetrance. This underlines the diagnostic value of a thorough clinical and genetic analysis of all family members in order to estimate accurate recurrence risks, identify subtle clinical manifestations and provide proper management of PFE patients.

A new cyte in orthodontics: Osteocytes in tooth movement

Orthodontic tooth movement (OTM) relies on the orchestration of clinical and biologic events that include the application of clinical force followed by a cascade of cellular and molecular responses. Our understanding about OTM today has evolved from, and is largely based on historic studies. However, the advances in bone biology and clinical orthodontics today continue to pave the pathway towards an improved knowledge base, and state of the art therapeutics in OTM. Osteoblasts and osteoclasts have been the primary cells analyzed in OTM. However, the role of osteocytes, a cell previously thought to be static, should be considered in light of new findings in molecular biological research. Osteocytes are now known to be significant in controlling responses to mechanical forces and therefore may be central to both OTM and normal tooth eruption. In this review, we explore the biology of OTM by focusing specifically on the potential role of osteocytes. Evidence from recent studies reveal that osteocytes have a role in controlling the response to mechanical forces and OTM. We therefore propose that these findings and further research endeavours may shape the future of clinical applications-specifically enhanced outcomes in OTM.

Primary failure of eruption: Clinical and genetic findings in the mixed dentition

OBJECTIVE

To test the hypothesis that mutations in the parathyroid hormone 1 receptor ( PTH1R) include effects in both primary and permanent teeth.

MATERIALS AND METHODS

DNA was extracted from saliva samples of 29 patients (8 familial and 21 sporadic) who presented with clinical evidence of infraoccluded teeth, and their unaffected relatives (N = 22). Sequencing followed by mutational analysis of the coding regions of PTH1R gene was completed for all individuals (N = 29).

RESULTS

Eight of 29 cases revealed a heterozygous pathogenic variant in the PTH1R gene; five of eight variants represented distinct mutations based on comparison with the dbSNP, HGMD, and ESP databases. One mutation (c.1765 T>C p.Trp89Arg) was found to segregate within a family (n = 3). In silico analyses for all variants revealed a putative pathogenic effect. A genotype-phenotype correlation was reported as defined by a functional mutation in PTH1R and corresponding effects on one or more posterior teeth only; unilateral or bilateral involvement, infraoccluded primary teeth.

CONCLUSIONS

Novel mutations were reported in the PTH1R gene that included PFE-affected primary molars, thus providing the basis for using a genetic diagnostic tool for early diagnosis leading to proper management.

Nine Novel PAX9 Mutations and a Distinct Tooth Agenesis Genotype-Phenotype

Tooth agenesis is one of the most common developmental anomalies affecting function and esthetics. The paired-domain transcription factor, Pax9, is critical for patterning and morphogenesis of tooth and taste buds. Mutations of PAX9 have been identified in patients with tooth agenesis. Despite significant progress in the genetics of tooth agenesis, many gaps in knowledge exist in refining the genotype-phenotype correlation between PAX9 and tooth agenesis. In the present study, we complete genetic and phenotypic characterization of multiplex Chinese families with nonsyndromic (NS) tooth agenesis. Direct sequencing of polymerase chain reaction products revealed 9 novel (c.140G>C, c.167T>A, c.332G>C, c.194C>A, c.271A>T, c.146delC, c.185_189dup, c.256_262dup, and c.592delG) and 2 known heterozygous mutations in the PAX9 gene among 120 probands. Subsequently, pedigrees were extended, and we confirmed that the mutations co-segregated with the tooth agenesis phenotype (with exception of families in which DNA analysis was not available). In 1 family ( n = 6), 2 individuals harbored both the PAX9 c.592delG mutation and a heterozygous missense mutation (c.739C>T) in the MSX1 gene. Clinical characterization of families segregating a PAX9 mutation reveal that all affected individuals were missing the mandibular second molar and their maxillary central incisors are most susceptible to microdontia. A significant reduction of bitter taste perception was documented in individuals harboring PAX9 mutations ( n = 3). Functional studies revealed that PAX9 haploinsufficiency or a loss of function of the PAX9 protein underlies tooth agenesis.

Genetic Disorders of Dental Development: Tales from the Bony Crypt

PURPOSE OF REVIEW

The ebb and flow of genetic influence relative to the understanding of craniofacial and dental disorders has evolved into a tacit acceptance of the current genetic paradigm. This review explores the science behind craniofacial and dental disorders through the lens of recent past and current findings and using tooth agenesis as a model of advances in craniofacial genetics.

RECENT FINDINGS

Contemporary studies of craniofacial biology takes advantage of the technological resources stemming from the genomic and post-genomic eras. Emerging data highlights the role of key genes and the epigenetic landscape controlling these genes, in causing dentofacial abnormalities. We also report here a novel Glu78FS MSX1 mutation in one family segregating an autosomal dominant form of severe tooth agenesis as an illustration of an evolving theme, i.e., different mutations in the same gene can result in a spectrum of dentofacial phenotypic severity. The future of clinical therapeutics will benefit from advances in genetics and molecular biology that refine the genotype-phenotype correlation. Indeed, the past century suggests a continued convergence of genetic science in the practice of clinical dentistry.

Personalized and precision orthodontic therapy

OBJECTIVE

To bring together orthodontic stakeholders from academics, industry, and private practice for a series of thematically focused workshops to explore and develop the transfer of novel approaches into clinical orthodontic practice.

SETTING AND SAMPLE POPULATION

Twenty-seven invited speakers, eight poster presenters, and participants of the Consortium for Orthodontic Advances in Science and Technology (COAST) 2014 Innovators' Workshop at the Eaglewood Resort and Spa, Itasca, Illinois, September 11-14, 2014.

MATERIAL AND METHODS

Five themed sessions involving between 4-7 presentations followed by panel discussions were organized. The aims of the discussion sessions were to highlight important findings and consider the strength of evidence for these, indicate next steps and needed research or technological developments to move forward, and to weigh the expected benefits from these findings and steps to implement in clinical practice.

RESULTS

Among important areas for attention identified were need for multiscale and multispecies modeling and experimentation for interspecies translation of results; large-scale collaborative efforts within the profession to address the need for adequate sample sizes for future genetic studies of complex traits such as malocclusion; a consortium approach to improve new technologies such as intra-oral scanning and 3D imaging by establishing standards; and harnessing the growing body of knowledge about bone biology for application in orthodontics.

CONCLUSIONS

With increased awareness of the potential of current and emerging technologies, translation of personalized and precision approaches in the field of orthodontics holds ever-increasing promise.

Novel mutations in PTH1R associated with primary failure of eruption and osteoarthritis

Autosomal dominant mutations in PTH1R segregate with primary failure of eruption (PFE), marked by clinical eruption failure of adult teeth without mechanical obstruction. While the diagnosis of PFE conveys a poor dental prognosis, there are no reports of PFE patients who carry PTH1R mutations and exhibit any other skeletal problems. We performed polymerase chain reaction-based mutational analysis of the PTH1R gene to determine the genetic contribution of PTH1R in 10 families with PFE. Sequence analysis of the coding regions and intron-exon boundaries of the PTH1R gene in 10 families (n = 54) and 7 isolated individuals revealed 2 novel autosomal dominant mutations in PTH1R (c.996_997insC and C.572delA) that occur in the coding region and result in a truncated protein. One family showed incomplete penetrance. Of 10 families diagnosed with PFE, 8 did not reveal functional (nonsynonymous) mutations in PTH1R; furthermore, 4 families and 1 sporadic case carried synonymous single-nucleotide polymorphisms. Five PFE patients in 2 families carried PTH1R mutations and presented with osteoarthritis. We propose that the autosomal dominant mutations of PTH1R that cause PFE may also be associated with osteoarthritis; a dose-dependent model may explain isolated PFE and osteoarthritis in the absence of other known symptoms in the skeletal system.

The etiology of eruption disorders - further evidence of a 'genetic paradigm'

The clinical spectrum of tooth eruption disorders includes both syndromic and non-syndromic problems ranging from delayed eruption to a complete failure of eruption. A defect in the differential apposition/resorption mechanism in alveolar bone can cause conditions such as tooth ankylosis, primary failure of eruption, failure of eruption due to inadequate arch length and canine impaction. As our knowledge of the molecular events underlying normal tooth eruption has increased, so too has our understanding of clinical eruption disorders. The recent finding that one gene, parathyroid hormone receptor 1 (PTH1R), is causative for familial cases of primary failure of eruption (PFE) suggests that other disturbances in tooth eruption may have a genetic etiology. In this report, we evaluated the current terminology (ankylosis, PFE, secondary retention, etc.) used to describe non-syndromic eruption disorders, in light of this genetic discovery. We observed that some individuals previously diagnosed with ankylosis were subsequently found to have alterations in the PTH1R gene, indicating the initial misdiagnosis of ankylosis and the necessary re-classification of PFE. We further investigated the relationship of the PTH1R gene, using a network pathway analysis, to determine its connectivity to previously identified genes that are critical to normal tooth eruption. We found that PTH1R acts in a pathway with genes such as PTHrP that have been shown to be important in bone remodeling, hence eruption, in a rat model. Thus, recent advances in our understanding of normal and abnormal tooth eruption should allow us in the future to develop a clinical nomenclature system based more on the molecular genetic cause of the eruption failures versus the clinical appearance of the various eruption disorders.

Primary failure of eruption and PTH1R: the importance of a genetic diagnosis for orthodontic treatment planning

INTRODUCTION

Primary failure of eruption (PFE) is characterized by nonsyndromic eruption failure of permanent teeth in the absence of mechanical obstruction. Recent studies support that this dental phenotype is inherited and that mutations in PTH1R genes explain several familial cases of PFE. The objective of our study was to investigate how genetic analysis can be used with clinical diagnostic information for improved orthodontic management of PFE.

METHODS

We evaluated a family (n = 12) that segregated an autosomal dominant form of PFE with 5 affected and 7 unaffected persons. Nine available family members (5 male, 4 female) were enrolled and subsequently characterized clinically and genetically.

RESULTS

In this family, PFE segregated with a novel mutation in the PTH1R gene. A heterozygous c.1353-1 G>A sequence alteration caused a putative splice-site mutation and skipping of exon 15 that segregated with the PFE phenotype in all affected family members.

CONCLUSIONS

A PTH1R mutation is strongly associated with failure of orthodontically assisted eruption or tooth movement and should therefore alert clinicians to treat PFE and ankylosed teeth with similar caution-ie, avoid orthodontic treatment with a continuous archwire.

Genetic analysis of familial non-syndromic primary failure of eruption

OBJECTIVES

While some eruption disorders occur as part of a medical syndrome, primary failure of eruption (PFE) - defined as a localized failure of secondary tooth eruption - exists without systemic involvement. Recent studies support that heredity may play an important role in the pathogenesis of PFE. The objective of our human genetic study is to investigate the genetic contribution to PFE.

MATERIALS AND METHODS

Four candidate genes POSTN, RUNX2, AMELX, and AMBN) were investigated because of their relationship to tooth eruption or putative relationship to each other. Families and individuals were ascertained based on the clinical diagnosis of PFE. Pedigrees were constructed and analyzed by inspection to determine the mode of inheritance in four families. The candidate genes were directly sequenced for both unrelated affected individuals and unaffected individuals. A genome wide scan using 500 microsatellite markers followed by linkage analysis was carried out for one family.

RESULTS

Pedigree analysis of families suggests an autosomal dominant inheritance pattern with complete penetrance and variable expressivity. Sequence analysis revealed two non-functional polymorphisms in the POSTN gene and no other sequence variations in the remaining candidate genes. Genotyping and linkage analysis of one family yielded a LOD score of 1.51 for markers D13S272; D15S118 and D17S831 on chromosomes 13, 15 and 17 respectively.

CONCLUSIONS

While LOD scores were not significant evidence of linkage, extension of current pedigrees and novel SNP chip technology holds great promise for identification of a causative locus for PFE.

Mechanism and control of tooth eruption: overview and clinical implications

OBJECTIVES

To review pre- and post-emergent eruption, with particular emphasis on distinguishing isolated molar ankylosis from primary failure of eruption (PFE) and genetic considerations in eruption problems.

MATERIAL AND METHODS

Radiographic review of eruption failure patients; animal and human experiments; high precision observations of movements of erupting teeth.

RESULTS

In pre-emergent tooth eruption, the controlling element is the rate of resorption of overlying structures. A path is cleared, and then the erupting tooth moves along it. This has clinical importance in recognizing the cause of eruption problems, particularly PFE, in which all teeth distal to the most mesial involved tooth do not erupt or respond to orthodontics. In our study of by far the largest sample of PFE cases yet reported, familial cases of PFE accounted for approximately (1/4) of all cases examined. Candidate genes now are being evaluated. In post-emergent eruption, control seems to be light forces of long duration that oppose eruption, rather than heavy forces of short duration such as those during mastication. Studies of human premolars in their passage from gingival emergence to the occlusal plane show that in this phase eruption occurs only during a few hours in the early evening. The critical hours for eruption parallel the time that growth hormone levels are highest in a growing child. In this stage intermittent force does not affect the rate of eruption, but changes in periodontal blood flow do affect it.

Primary failure of eruption: Further characterization of a rare eruption disorder

INTRODUCTION

Posterior open bite has several possible causes, including primary failure of eruption (PFE) that affects all teeth distal to the most mesial involved tooth, mechanical failure of eruption (MFE) (primarily ankylosis) that affects only the involved tooth or teeth, and soft-tissue interferences with eruption (other).

METHODS

Radiographs and other clinical records for 97 cases of failure of posterior eruption submitted for consultation were analyzed to further characterize PFE and distinguish it from MFE.

RESULTS

Of the 97 cases, 38 were judged to be clear-cut PFE; 19 were diagnosed as MFE; 32 were classified as indeterminate failure because they were too young to be certain of the distinction between PFE and MFE; and 8 were placed in the "other" category. Two subtypes of PFE were observed. In type 1, eruption failure occurred at or near the same time for all teeth in an affected quadrant. In type 2, a gradient of the time of failure was present, so that some further development of the teeth posterior to the most mesial affected tooth was observed before eruption failure. A family history of eruption problems was noted in 10 of the 38 PFE subjects (26%), and a pedigree analysis was done for 4 families. This was consistent with autosomal dominant transmission.

CONCLUSIONS

The distinction between PFE and MFE is clinically important because it determines whether all posterior teeth, or only individual affected teeth, will not respond to orthodontic force. Certain diagnosis often requires progress radiographs so that the pattern of eruption of teeth distal to the most mesial affected tooth can be observed.

A longitudinal study of incremental expansion using a mandibular lip bumper

A retrospective study using models was performed to evaluate the incremental expansion that occurred during mandibular lip bumper therapy in 44 adolescent patients. The purpose was to determine whether expansion occurs evenly between appointments or whether it attenuates with treatment time. Dental cast measurements were made for arch width and arch length. Treatment duration was broken into near-equal time segments and compared. Results showed that about 50% of the total expansion achieved occurred within about the first 100 days. Forty percent of the total amount of expansion occurred during the next 200 days, with only about 10% of the total expansion occurring after the first 300 days. It is unnecessary to have the appliance in place for longer than 300 days. The percentage of expansion that occurred at each time segment was not related to whether the patient had concomitant maxillary expansion.

Mutational analysis of families affected with molar oligodontia

Oligodontia, the congenital absence of six or more permanent teeth, is a common developmental anomaly of human dentition whose genetic basis is poorly understood. We recently reported a nonsyndromic form of oligodontia involving mostly all permanent molars in a large kindred, caused by a frameshift mutation in exon 2 of the human PAX9 gene [3]. To better understand the genotype/phenotype correlation in non-syndromic familial oligodontia, we identified additional families with a similar pattern of molar oligodontia. We hypothesize that molar oligodontia is due to allelic heterogeneity involving different mutations in PAX9. To test this hypothesis, we performed pedigree analysis followed by mutational analysis. Pedigree analysis revealed that the oligodontia trait is inherited in an autosomal dominant fashion. Mutational analysis of PAX9 thus far excludes the presence of the previously identified frameshift mutation.

A novel mutation in human PAX9 causes molar oligodontia

Experimental and animal studies, as well as genetic mutations in man, have indicated that the development of dentition is under the control of several genes. So far, mutations in MSX1 and PAX9 have been associated with dominantly inherited forms of human tooth agenesis that mainly involve posterior teeth. We identified a large kindred with several individuals affected with molar oligodontia that was transmitted as an isolated autosomal-dominant trait. Two-point linkage analysis using DNA from the family and polymorphic marker D14S288 in chromosome 14q12 produced a maximum lod score of 2.29 at theta = 0.1. Direct sequencing of exons 2 to 4 of PAX9 revealed a cytosine insertion mutation at nucleotide 793, leading to a premature termination of translation at aa 315. Our results support the conclusion that molar oligodontia is due to allelic heterogeneity in PAX9, and these data further corroborate the role of PAX9 as an important regulator of molar development.