Unraveling the molecular mechanisms that lead to supernumerary teeth in mice and men: current concepts and novel approaches

Non-syndromic supernumerary teeth and association with a self-reported family history of cancer

BACKGROUND

Supernumerary teeth are an alteration of dental developmental and result in the formation of teeth above the usual number. Epidemiologic studies suggested that patients with dentofacial anomalies and their family members may present an increased risk of developing cancer, including female breast cancer and gynecologic cancers. These observations indicate that genetic alterations that result in dental anomalies may be related to cancer development. Thus, the aim of the present study was to evaluate the association between supernumerary teeth and a family history of female breast cancer and gynecologic cancers.

METHODS

The diagnosis of supernumerary teeth was based on clinical and radiographic examinations. For data collection, a questionnaire asking for information regarding ethnicity, age, gender, and self-reported family history of cancer up to the second generation was used. Statistical analysis was performed using the Χ2 test and Fisher's exact test with an established α of 5%.

RESULTS

A total of 344 patients were included; 47 of them had one or more non-syndromic supernumerary teeth (not associated with any syndrome or cleft lip and palate) and 297 were control patients. Age, ethnicity, and gender distribution were not statistically different between the group with supernumerary teeth and the control group (p > 0.05). The supernumerary teeth were most commonly observed in the incisors area. Breast cancer (n = 17) was the most commonly self-reported type of cancer, followed by uterine cervical (n = 10), endometrial (n = 2), and ovarian (n = 1) cancers. Endometrial cancer was significantly associated with the diagnosis of supernumerary teeth (p = 0.017).

CONCLUSION

This study suggests that patients with supernumerary teeth possess a higher risk of having family members with endometrial cancer.

Tooth number abnormality: from bench to bedside

Tooth number abnormality is one of the most common dental developmental diseases, which includes both tooth agenesis and supernumerary teeth. Tooth development is regulated by numerous developmental signals, such as the well-known Wnt, BMP, FGF, Shh and Eda pathways, which mediate the ongoing complex interactions between epithelium and mesenchyme. Abnormal expression of these crutial signalling during this process may eventually lead to the development of anomalies in tooth number; however, the underlying mechanisms remain elusive. In this review, we summarized the major process of tooth development, the latest progress of mechanism studies and newly reported clinical investigations of tooth number abnormality. In addition, potential treatment approaches for tooth number abnormality based on developmental biology are also discussed. This review not only provides a reference for the diagnosis and treatment of tooth number abnormality in clinical practice but also facilitates the translation of basic research to the clinical application.

Sequencing analysis of exons 5 and 6 in RUNX2 in non-syndromic patients with supernumerary tooth in Kelantan, Malaysia

OBJECTIVE

The aim of this study is to do a sequencing analysis of RUNX2 in non-syndromic patients with supernumerary tooth.

MATERIALS AND METHODS

Fifty-three patients with supernumerary tooth were identified retrospectively from 1,275 radiographic reviews who attended the Hospital Universiti Sains Malaysia (USM) Dental Clinic. Informed consent was obtained from the patients prior to the study. Blood samples were collected from 41 patients and DNA extractions were performed out of which 10 samples were chosen randomly for PCR amplification using designated primers for RUNX2 followed by DNA sequencing analysis.

RESULTS

This study involved 28 male patients (68.3%) and 13 female patients (31.7%) with a gender ratio of 2.2:1 and mean age of 15.9 ± 6.2 years. DNA extraction yielded ~ 40 ng/μl of concentrated DNA, and each DNA sample had more than 1500 bp of DNA length. The purity ranged between 1.8 and 2.0. DNA sequencing analysis did not reveal any mutations in exons 5 and 6 of RUNX2.

CONCLUSION

This study did not reveal any mutations in exons 5 and 6 of RUNX2 in non-syndromic patients with supernumerary tooth.

CLINICAL RELEVANCE

Analysis of mutations in RUNX2 is important to enhance the understanding of tooth development in humans.

Tooth Repair and Regeneration: Potential of Dental Stem Cells

Tooth defects are an extremely common health condition that affects millions of individuals. Currently used dental repair treatments include fillings for caries, endodontic treatment for pulp necrosis, and dental implants to replace missing teeth, all of which rely on the use of synthetic materials. By contrast, the fields of tissue engineering and regenerative medicine and dentistry (TERMD) use biologically based therapeutic strategies for vital tissue regeneration, and thus have the potential to regenerate living tissues. Methods to create bioengineered replacement teeth benefit from a detailed understanding of the molecular signaling networks regulating natural tooth development. We discuss how key signaling pathways regulating natural tooth development are being exploited for applications in TERMD approaches for vital tooth regeneration.

Mesial hyperdontia in Sigmodontinae (Rodentia: Cricetidae), with comments on the evolution of the anteroconid in Myomorpha

Supernumerary teeth are common dental anomalies reported in rodents, mainly occurring distally to molars. We report the first case of mesial hyperdontia in wild-caught sigmodontine: a simplified tooth anterior to the right first lower molar in Neacomys amoenus. It affected the first molar morphology, which exhibits an underdeveloped mesial region with a reduced anterior conulid, a similar pattern observed in early known myomorph fossils, including lineages that still possess the last premolar. However, only lineages without premolar display an elongated first lower molar with a large anteroconid, as observed in extant Myomorpha. During the odontogenesis in myomorphs, the posteriormost vestigial diastemal tooth bud, located at the same locus of the last lower premolar, has its development arrested and merges with the cap of the first molar. This process might have contributed to the development of an increased anteroconid in this lineage. The abnormal Neacomys’ atavistic phenotype corroborates the hypothesis that the absorption of the primordium of the last lower premolar had played an important role in the development of first molar’s mesial region. Additionally, it also might have promoted the evolutionary transition from a reduced conulid into an enlarged anteroconid, as deduced from the fossil record and developmental evidence

Multiple supernumerary teeth in a likely syndromic individual from prehistoric Illinois

OBJECTIVE

This paper reports the first published case of a prehistoric human with five or more supernumerary teeth. Such cases are often neglected in paleopathology, in part due to a gap between the medicodental and anthropological literature leading to the view in anthropology that supernumerary teeth are curious anomalies rather than pathologies.

DESIGN

Reconstruction and pathological description of the skeletal remains were performed according to standard osteological protocols. Each supernumerary tooth was categorized based on its morphology, location, and orientation. The dental characteristics of the individual were compared to published norms for incidences of syndromic and non-syndromic supernumerary teeth and a differential diagnosis was subsequently performed.

RESULTS

Six supernumerary teeth and one deciduous tooth were identified. Additionally, the individual suffered from impacted teeth, dilacerated roots, and extensive sutural anomalies (including retention of the metopic suture into adulthood and an unusually high number of sutural bones). The morphology and location of the supernumerary teeth, in conjunction with the suite of other symptoms, are highly unusual among non-syndromic patients and therefore are indicative of a complex genetic disorder.

CONCLUSIONS

The individual reported here almost certainly suffered from a genetic disorder or syndrome resulting in extensive dental and sutural abnormalities. Despite a lack of post-cranial involvement, a tentative diagnosis of Cleidocranial Dysplasia was made on the basis that mutations in the RUNX2 gene may cause the dental symptoms without any pathology of the clavicle.

Diagnosis and Surgical Management of Nonsyndromic Nine Supernumerary Teeth and Leong's Tubercle

Nonsyndromic multiple supernumerary teeth (ST) and Leong's tubercle are a condition with a very low prevalence and a multidisciplinary approach is required to restore function and aesthetics. So, this case report aimed at presenting a rare case of nonsyndromic nine supernumerary teeth and Leong's tubercle in a pediatric patient, without any evident familial history, showing its diagnosis and surgical management.

Dental peculiarities in the silvery mole-rat: an original model for studying the evolutionary and biological origins of continuous dental generation in mammals

Unravelling the evolutionary and developmental mechanisms that have impacted the mammalian dentition, since more than 200 Ma, is an intricate issue. Interestingly, a few mammal species, including the silvery mole-rat Heliophobius argenteocinereus, are able to replace their dentition by the addition of supernumerary molars at the back of jaw migrating then toward the front. The aim here was to demonstrate the potential interest of further studying this rodent in order to better understand the origins of continuous dental replacement in mammals, which could also provide interesting data concerning the evolution of limited dental generation occurring in first mammals. In the present study, we described the main stages of the dental eruptive sequence in the silvery mole-rat and the associated characteristics of horizontal replacement using X-ray microtomography. This was coupled to the investigation of other African mole-rats which have no dental replacement. This method permitted to establish evidence that the initial development of the dentition in Heliophobius is comparable to what it is observed in most of African mole-rats. This rodent first has premolars, but then identical additional molars, a mechanism convergent to manatees and the pygmy rock-wallaby. Evidence of continuous replacement and strong dental dynamics were also illustrated in Heliophobius, and stressed the need to deeply investigate these aspects for evolutionary, functional and developmental purposes. We also noticed that two groups of extinct non-mammalian synapsids convergently acquired this dental mechanism, but in a way differing from extant mammals. The discussion on the diverse evolutionary origins of horizontal dental replacement put emphasis on the necessity of focusing on biological parameters potentially involved in both continuous and limited developments of teeth in mammals. In that context, the silvery mole-rat could appear as the most appropriate candidate to do so.

Idiopathic resorption of impacted mesiodentes: a radiographic study

BACKGROUND

Although a large number of mesiodentes are left in situ, only a few are found in radiographs from epidemiological studies of adult populations. This leads to the development of a hypothesis that mesiodentes may be resorbed and disappear over time. The aim of this study was to radiographically investigate the frequency of resorptions and pathologies in relation to mesiodentes left in situ.

METHODS

The study population consisted of 44 individuals, with 49 mesiodentes left in situ at an early age. The individuals were 18-38 years old when re-examined. The inclusion criteria were that the mesiodentes had been diagnosed in childhood and left in situ, and that each individual was over 18 years of age at the time of re-examination. Either digital or analogue intraoral radiographs were used at the re-examination and compared with earlier analogue radiographs.

RESULTS

Forty-one per cent of the impacted mesiodentes showed resorptions-from limited to nearly complete resorption. No pathologies in connection to the mesiodentes were found.

CONCLUSION

About half of the mesiodentes examined displayed resorption. No pathologies caused by the mesiodentes were recorded.

Modeling the dental development of fossil hominins through the inhibitory cascade

The inhibitory cascade is a mathematical model for interpreting the relative size of the occlusal surfaces of mammalian molars in terms of developmental mechanisms. The cascade is derived from experimental studies of mouse molars developed in culture, and has been tested and applied to the dentitions of rodents, ungulates, carnivores, and platyrrhines. Results from such applications have provided new information regarding the origins of plesiomorphic traits in mammalian clade and how derived morphologies may arise. In this study we apply the inhibitory cascade model to the postcanine dentition of a sample of Old World primates that includes fossil hominins. The results of this study suggest that the inhibitory cascade (i.e. M1 < M2 < M3 ) describes the relative sizes of the molar occlusal areas of Old World primates and is likely the plesiomorphic condition for this clade. Within that clade, whereas most Old World monkeys have a M1 < M2 < M3 pattern, most apes have a M1 < M2 ≈ M3 pattern. This modified cascade suggests that greater levels of inhibition (or less activation) are acting on the posterior molars of apes, thus facilitating the reduction of M3 s within the apes. With the exception of the baboon genus Papio, extant congeners typically share the same molar inhibitory cascade. The differences in the relative size relationships observed in the molar and premolar-molar cascades of the species included in the fossil hominin genus Paranthropus suggest that although large postcanine teeth are a shared derived trait within this genus, the developmental basis for postcanine megadontia may not be the same in these two Paranthropus taxa. Our results show that phenotypic characters such as postcanine megadontia may not reflect common development.

Odontomas and supernumerary teeth: is there a common origin?

The aim of the present work is to analyze all scientific evidence to verify whether similarities supporting a unified explanation for odontomas and supernumerary teeth exist. A literature search was first conducted for epidemiologic studies indexed by PubMed, to verify their worldwide incidence. The analysis of the literature data shows some interesting similarities between odontomas and supernumerary teeth concerning their topographic distribution and pathologic manifestations. There is also some indication of common genetic and immuno-histochemical factors. Although from a nosological point of view, odontomas and supernumeraries are classified as distinct entities, they seem to be the expression of the same pathologic process, either malformative or hamartomatous.

Under your nose: a rare finding during dissection provides insights into maxillary supernumerary teeth

BACKGROUND

A supernumerary tooth was found during anatomical dissection. The position of this tooth, still impacted in the maxilla, and the associated pathology make this a rare case.

METHODS

During dissection by dental students of the sagittally-sectioned head of a cadaver, a supernumerary tooth was identified in the mid-palatal area. Further dissection revealed a swelling with a thin bony covering related to the crown of the tooth. The maxilla was removed en bloc and radiographic examination, CT scanning, electron microscopy and histology were undertaken.

RESULTS

The tooth had a crenulated occlusal surface and a single root. It was 25 mm posterior to the root apex of the permanent upper central incisor. The swelling, confirmed by radiographs and CT imaging to be associated with the crown, occupied approximately one-third of the maxillary sinus. The 3D shape of the cystic lesion was visualized by a composite digital movie.

CONCLUSIONS

The crown form, position of the tooth and the associated dentigerous cyst suggested it was a palatally developing supernumerary premolar which had been displaced to the palatal midline by the expanding cyst. This rare case highlights the learning and teaching opportunities available during dissection, showing important variations in both development and clinical anatomy.

Isolation and culture of dental epithelial stem cells from the adult mouse incisor

Understanding the cellular and molecular mechanisms that underlie tooth regeneration and renewal has become a topic of great interest(1-4), and the mouse incisor provides a model for these processes. This remarkable organ grows continuously throughout the animal's life and generates all the necessary cell types from active pools of adult stem cells housed in the labial (toward the lip) and lingual (toward the tongue) cervical loop (CL) regions. Only the dental stem cells from the labial CL give rise to ameloblasts that generate enamel, the outer covering of teeth, on the labial surface. This asymmetric enamel formation allows abrasion at the incisor tip, and progenitors and stem cells in the proximal incisor ensure that the dental tissues are constantly replenished. The ability to isolate and grow these progenitor or stem cells in vitro allows their expansion and opens doors to numerous experiments not achievable in vivo, such as high throughput testing of potential stem cell regulatory factors. Here, we describe and demonstrate a reliable and consistent method to culture cells from the labial CL of the mouse incisor.

Characterization of mesenchymal progenitor cells in crown and root pulp from human mesiodentes

OBJECTIVE

Mesiodentes are usually found in the central position of the upper or lower jaw as supernumerary teeth. Here, we obtained 10 mesiodentes and three permanent teeth (PT) and separated the dental pulp (DP) from these into crown and root portions. We then characterized and compared the isolated crown portion-derived cells (crown cells) with root portion-derived cells (root cells) using a range of in vitro assays.

MATERIALS AND METHODS

Crown cells and root cells were examined for cell surface marker expression, colony-forming unit-fibroblast (CFU-F), cell proliferation, cell cycle characteristics and markers, and osteogenic and adipogenic differentiation.

RESULTS

The proportion of CD105-positive cells (CD105(+) cells) in the crown cells vs the root cells varied among the mesiodentes, but not among the PT. When there were more CD105(+) cells in the root cells than in the crown cells, the root cells showed higher CFU-F, proliferation capacity, and osteogenic differentiation capacity. In contrast, when the crown cells contained more CD105(+) cells than the root cells, the crown cells showed the higher CFU-F, proliferation capacity, and osteogenic differentiation capacity. In addition, the sorted CD105(+) cells showed higher CFU-F and proliferation capacity than the sorted CD105(-) cells.

CONCLUSION

These results indicated that proportion of CD105(+) cells is an effective means of characterizing DP-derived cells in mesiodentes.

Three-dimensional analysis of the early development of the dentition

Tooth development has attracted the attention of researchers since the 19th century. It became obvious even then that morphogenesis could not fully be appreciated from two-dimensional histological sections. Therefore, methods of three-dimensional (3D) reconstructions were employed to visualize the surface morphology of developing structures and to help appreciate the complexity of early tooth morphogenesis. The present review surveys the data provided by computer-aided 3D analyses to update classical knowledge of early odontogenesis in the laboratory mouse and in humans. 3D reconstructions have demonstrated that odontogenesis in the early stages is a complex process which also includes the development of rudimentary odontogenic structures with different fates. Their developmental, evolutionary, and pathological aspects are discussed. The combination of in situ hybridization and 3D reconstruction have demonstrated the temporo-spatial dynamics of the signalling centres that reflect transient existence of rudimentary tooth primordia at loci where teeth were present in ancestors. The rudiments can rescue their suppressed development and revitalize, and then their subsequent autonomous development can give rise to oral pathologies. This shows that tooth-forming potential in mammals can be greater than that observed from their functional dentitions. From this perspective, the mouse rudimentary tooth primordia represent a natural model to test possibilities of tooth regeneration.

Supernumerary lateral incisor

Supernumerary teeth are common in general population and occur frequently in patients with familial trait. However, it is rare to find supernumeraries in individuals with no associated disease or syndrome. Supernumerary teeth are found in any region of maxilla and mandible, with a predisposition for anterior maxilla. A case of endodontically involved supernumerary lateral incisor is described.

Genetic basis of non-syndromic anomalies of human tooth number

Teeth organogenesis develops through a well-ordered series of inductive events involving genes and BMP, FGF, SHH and WNT represent the main signalling pathways that regulate epithelial-mesenchymal interactions. Moreover, progress in genetics and molecular biology indicates that more than 300 genes are involved in different phases of teeth development. Mutations in genes involved in odontogenesis are responsible for many dental anomalies, including a number of dental anomalies that can be associated with other systemic skeletal or organic manifestations (syndromic dental anomalies) or not (non-syndromic dental anomalies). The knowledge of the genetic development mechanisms of the latter is of major interest. Understanding the mechanisms of pathogenesis of non-syndromic teeth anomalies would also clarify the role of teeth in craniofacial development, and this would represent an important contribution to the diagnosis, treatment and prognosis of congenital malformations, and the eventual association to other severe diseases. Future research in this area is likely to lead to the development of tests for doctors to formulate an early diagnosis of these anomalies.

Continuous dental replacement in a hyper-chisel tooth digging rodent

Contrary to their reptilian ancestors, which had numerous dental generations, mammals are known to usually develop only two generations of teeth. However, a few mammal species have acquired the ability to continuously replace their dentition by the constant addition of supernumerary teeth moving secondarily toward the front of the jaw. The resulting treadmill-like replacement is thus horizontal, and differs completely from the vertical dental succession of other mammals and their extinct relatives. Despite the developmental implications and prospects regarding the origin of supernumerary teeth, this striking innovation remains poorly documented. Here we report another case of continuous dental replacement in an African rodent, Heliophobius argenteocinereus, which combines this dental system with the progressive eruption of high-crowned teeth. The escalator-like mechanism of Heliophobius constitutes an original adaptation to hyper-chisel tooth digging involving high dental wear. Comparisons between Heliophobius and the few mammals that convergently acquired continuous dental replacement reveal that shared inherited traits, including dental mesial drift, delayed eruption, and supernumerary molars, comprise essential prerequisites to setting up this dental mechanism. Interestingly, these dental traits are present to a lesser extent in humans but are absent in mouse, the usual biological model. Consequently, Heliophobius represents a suitable model to investigate the molecular processes leading to the development of supernumerary teeth in mammals, and the accurate description of these processes could be a significant advance for further applications in humans, such as the regeneration of dental tissues.

Exogenous fibroblast growth factor 8 rescues development of mouse diastemal vestigial tooth ex vivo

Regression of vestigial tooth buds results in the formation of the toothless diastema, a unique feature of the mouse dentition. Revitalization of the diastemal vestigial tooth bud provides an excellent model for studying tooth regeneration and replacement. It has been previously shown that suppression of fibroblast growth factor (FGF) signaling in the diastema results in vestigial tooth bud regression. In this study, we report that application of exogenous FGF8 to the mouse embryonic diastemal region rescues diastemal tooth development. However, this rescue of diastemal tooth development occurs only in an isolated diastemal regions and not in the mandibular quadrant, which includes the incisor and molar germs. FGF8 promotes cell proliferation and inhibits apoptosis in diastemal tooth epithelium, and revitalizes the tooth developmental program, as evidenced by the expression of genes critical for normal tooth development. Our results also support the idea that the adjacent tooth germs contribute to the suppression of diastemal vestigial tooth buds by means of multiple signals.

Molecular genetics of supernumerary tooth formation

Despite advances in the knowledge of tooth morphogenesis and differentiation, relatively little is known about the aetiology and molecular mechanisms underlying supernumerary tooth formation. A small number of supernumerary teeth may be a common developmental dental anomaly, while multiple supernumerary teeth usually have a genetic component and they are sometimes thought to represent a partial third dentition in humans. Mice, which are commonly used for studying tooth development, only exhibit one dentition, with very few mouse models exhibiting supernumerary teeth similar to those in humans. Inactivation of Apc or forced activation of Wnt/β(catenin signalling results in multiple supernumerary tooth formation in both humans and in mice, but the key genes in these pathways are not very clear. Analysis of other model systems with continuous tooth replacement or secondary tooth formation, such as fish, snake, lizard, and ferret, is providing insights into the molecular and cellular mechanisms underlying succesional tooth development, and will assist in the studies on supernumerary tooth formation in humans. This information, together with the advances in stem cell biology and tissue engineering, will pave ways for the tooth regeneration and tooth bioengineering.

Supernumerary teeth vary depending on gender

The presence of supernumerary teeth (ST) is a dental developmental anomaly of patterning and morphogenesis. Its variability of morphology, location and developmental timing can shed light on its etiology. In this work we report ST patterns. Orthopantomograms of 1,166 pediatric subjects were examined and the morphology, location and timing of the formation of ST were determined. The frequency of supernumerary teeth in the studied population was 2.3% (n = 27). Twenty-five subjects presented one ST. Maxilla midline was the most commonly affected region (nine cases). We noted high incidence of conical morphology in the midline region. Only teeth with tuberculate morphology presented delayed formation. ST in the midline region occurred more often in males whereas ST in the incisor region were more common in females. In conclusion, ST patterns vary depending on gender.

Extreme oral manifestations in a Marfan-type syndrome

A 12-year-old girl with an otherwise typical Marfan syndrome (Ghent criteria fulfilled) presented with highly unusual oral manifestations consisting of supernumerary teeth and severe dental crowding. Pathological examination of the supernumerary teeth revealed an elevated number of pulpoliths. No mutation in the FBN1, TGFBR1 and TGFBR2 genes was identified despite exhaustive screening, suggesting that another gene defect could explain this association of marfanoid features with dental abnormalities.

Autosomal-dominant ankyloglossia and tooth number anomalies

Ankyloglossia is a congenital oral anomaly characterized by the presence of a hypertrophic lingual frenulum. It frequently accompanies X-linked cleft palate and is sometimes seen alone due to mutations in the gene encoding the transcription factor TBX22, while knockout of Lgr5 in the mouse results in ankyloglossia. The aim of the present study was to characterize the phenotype and to verify sequence variations in the LGR5 gene in a Brazilian family with ankyloglossia associated with tooth number anomalies. Twelve individuals of three generations were submitted to physical, oral, and radiographic examinations and molecular analysis. Eight had ankyloglossia with various degrees of severity. Six also had hypodontia in the lower incisor region; one had a supernumerary tooth in this region, and another had a supernumerary tooth in the lower premolar region. The characterization of this family determined an autosomal-dominant inheritance and excluded the LGR5 gene mutations as being involved in the pathogenesis of this condition.

Retrospective analysis of the factors influencing mesiodentes eruption

AIM

This study aimed to evaluate the factors that predict the spontaneous eruption of mesiodens.

DESIGN

From the records of 431 patients (346 boys and 85 girls, average age 8.8 years) who visited Samsung Medical Center from January 2002 to December 2006, 471 mesiodentes were reviewed. The eruption rate was investigated according to the width/length ratio, angulation, location, and shape determined from periapical or panoramic radiographs.

RESULTS

The regression model showed that the width/length ratio and angulation were important determinants influencing the eruption of mesiodentes (P < 0.001, Pearson's r = 0.619). The location of the mesiodentes also affected their eruption (P < 0.01). However, no significant relationship was detected between the shape and eruption rate of mesiodentes (P > 0.05).

CONCLUSIONS

A lower probability of spontaneous eruption existed when the tooth had a greater angulation, shorter length, and wider width. Spontaneous eruption occurs more often when the mesiodens is located between the permanent incisors.

Revitalization of a diastemal tooth primordium in Spry2 null mice results from increased proliferation and decreased apoptosis

An understanding of the factors that promote or inhibit tooth development is essential for designing biological tooth replacements. The embryonic mouse dentition provides an ideal system for studying such factors because it consists of two types of tooth primordia. One type of primordium will go on to form a functional tooth, whereas the other initiates development but arrests at or before the bud stage. This developmental arrest contributes to the formation of the toothless mouse diastema. It is accompanied by the apoptosis of the rudimentary diastemal buds, which presumably results from the insufficient activity of anti-apoptotic signals such as fibroblast growth factors (FGFs). We have previously shown that the arrest of a rudimentary tooth bud can be rescued by inactivating Spry2, an antagonist of FGF signaling. Here, we studied the role of the epithelial cell death and proliferation in this process by comparing the development of a rudimentary diastemal tooth bud (R(2)) and the first molar in the mandibles of Spry2(-/-) and wild-type (WT) embryos using histological sections, image analysis and 3D reconstructions. In the WT R(2) at embryonic day 13.5, significantly increased apoptosis and decreased proliferation were found compared with the first molar. In contrast, increased levels of FGF signaling in Spry2(-/-) embryos led to significantly decreased apoptosis and increased proliferation in the R(2) bud. Consequently, the R(2) was involved in the formation of a supernumerary tooth primordium. Studies of the revitalization of rudimentary tooth primordia in mutant mice can help to lay the foundation for tooth regeneration by enhancing our knowledge of mechanisms that regulate tooth formation.