Are chin and symphysis morphology facial type-dependent? A computed tomography-based study.

INTRODUCTION: The chin is a major determinant of the facial profile; hence, it plays a major role in orthodontics and orthognathic surgery. It is thus essential to follow and better understand its expression in different facial types. The major objectives of the current study were to characterize morphometrically the chin and symphysis and reveal their association with different facial types. METHODS: Computed tomography scans of the head and neck of 311 adults (163 males, 148 females; age range, 18-95 years) were classified into 3 facial types: short, average, and long. Height, width, projection, inclination, thickness, and area were measured on the chin and symphysis. RESULTS: The majority of the population (70%) manifested an average facial type; the other 30% were almost equally distributed between short and long facial types. The long facial type was more common among females and the short facial type among males. Chin projection, area, and size were significantly greater in short-faced patients. Chin width in males was similar for all facial types, whereas, in females, chin width was the widest in the short facial type and the narrowest in the long facial type. Symphysis height was significantly greater in long-faced patients in both sexes. The mandibular incisors' inclination relative to the mandibular plane was not significantly associated with the chin or symphysis morphology. CONCLUSIONS: Chin and symphysis morphology is facial type-dependent. Orthodontists and maxillofacial surgeons should be aware of the complex relationship between facial types and chin/symphysis size and shape when planning treatment.

Upper Lip Horizontal Line: Characteristics of a Dynamic Facial Line.

Background: Upper lip appearance received major attention with the introduction of diverse treatment modalities, including lip augmentation, rhinoplasty surgery, and dental treatment designed to support the upper lip. Our objectives were to define the prevalence and characteristics of the upper lip horizontal line (ULHL), which is a dynamic line appearing during a smile, in relation to gender, malocclusions, aging, and facial morphology. Methods: First, the prevalence and gender distribution of ULHL was examined from standardized en-face imaging at full smile of 643 randomly selected patients. Second, cephalometric and dental cast model analyses were made for 97 consecutive patients divided into three age groups. Results: ULHL appears in 13.8% of the population examined, and prevailed significantly more in females (78%). The prevalence of ULHL was not related to age nor to malocclusion. Patients presenting ULHL showed shorter upper lip and deeper lip sulcus. The skeletal pattern showed longer mid-face, shorter lower facial height and greater prevalence of a gummy smile. Conclusions: Female patients with short upper lip, concavity of the upper lip, and gummy smile are more likely to exhibit ULHL. The ULHL is not age-related and can be identified in children and young adults. Therefore, it should be considered when selecting diverse treatment modalities involving the upper lip.

Variation in Chin and Mandibular Symphysis Size and Shape in Males and Females: A CT-Based Study.

The chin is a unique anatomical landmark of modern humans. Its size and shape play an important role from the esthetic perspective. However, disagreement exists in the dental and anthropological literature regarding the sex differences in chin and symphysis morphometrics. The "sexual selection" theory is presented as a possible reason for chin formation in our species; however, many other contradictory theories also exist. This study's aims were therefore to determine how chin and symphysis size and shape vary with sex, and to discuss "sexual selection" theory as a reason for its formation. Head and neck computed tomography (CT) scans of 419 adults were utilized to measure chin and symphysis sizes and shapes. The chin and symphysis measures were compared between the sexes using an independent-samples t-test, a Mann-Whitney test, and the F-statistic. The chin width was significantly greater in males than in females (p < 0.001), whereas the chin height, area, and size index were significantly greater in females (p < 0.001). Symphysis measures did not differ significantly between the sexes. Size accounted for 2-14% of the chin variance and between 24-33% of the symphysis variance. Overall, the chin was found to be a more heterogeneous anatomical structure than the symphysis, as well as more sexually dimorphic.

Comparison of lateral photographic and radiographic sagittal analysis in relation to Angle's classification.

OBJECTIVE: The goal of this study was to compare sagittal jaw relationships derived from standardized profile photographs (soft tissue) to those derived from lateral cephalograms (hard tissue) with respect to Angle's classification of malocclusion. METHODS: A total of 110 randomly selected subjects (mean age: 13.75 ± 1.46 years) undergoing treatment (Postgraduate Program in Orthodontics at Tel Aviv University) were assigned to three groups based on Angle's classification (Class I: n = 30; Class II: n = 50; Class III: n = 30). Standardized profile-view photographs and lateral radiographs (cephalograms) were compared using 11 soft tissue and 8 skeletal measurements, respectively. RESULTS: Tragus, infra-orbital, nasion, A point, B point, and pogonion were found to be the most reliable soft tissue reference points. A similar pattern of diversity was found between the three groups of Angle's classification (Class I/II/III) for the photographic soft,-tissue and the radiographic skeletal measurements (e.g., soft tissue A'N'B' =11.43°/13.30°/8.85° and hard tissue ANB = 3.13°/4.64°/-1.31°). Soft tissue A'N'B' measurement provides complementary information to hard tissue ANB measurement. CONCLUSION: Analyzing profile photographs for evaluating sagittal jaw relationships is a practical tool in determining soft tissue harmony. Soft tissue measurements provide a sagittal differential diagnosis in relation to Angle's classification of malocclusion.

Rate and pattern of interproximal dental attrition.

Although occlusal and interproximal attrition occur because of diverse etiology and present dissimilar features, both progress with age. The objectives of this study were to reveal the rate and pattern of development of interproximal attrition facets (PAF) with age and to compare those with occlusal attrition (OA) changes. Five-hundred and ninety-four teeth were collected from 198 skulls (of adults, 20-71 yr of age). Three mandibular teeth [first premolar (P1), second premolar (P2), and first molar (M1)] were examined for PAF size and OA rate. Interproximal attrition and OA followed similar patterns of development until subjects reached 40-45 yr of age, after which they took different paths: PAF did not increase in size and were not as large as in younger groups, regardless of facet location, whereas OA continued to progress. The PAF changes with age differed between premolars and molars, unlike OA, which presented a similar rate for all teeth studied. Although OA scores presented significantly moderate correlations with age, PAF area size demonstrated low correlations with age. Low, but significant, correlations were found between the rate of OA and that of PAF. However, PAF and OA exhibited different patterns of development with age. Premolars and molars presented dissimilar development of PAF, which is probably caused by a unique attrition pattern in the molar teeth, different morphology, and force vectors.

Pattern of maxillary and mandibular proximal enamel thickness at the contact area of the permanent dentition from first molar to first molar.

INTRODUCTION: Proximal enamel thickness (PET) at the mesial and distal contact areas of the complete permanent dentition has not been previously reported. Anatomic investigation of PET is essential for interproximal reduction treatment. Our objectives were to measure the PETs of the complete maxillary and mandibular dentitions at the contact areas, to compare the PETs of adjacent teeth, and to evaluate the vertical position of each contact area. METHODS: We evaluated 720 extracted teeth; of these, 109 intact teeth were selected. The mesial and distal contact areas were demarcated, and each tooth was embedded in transparent epoxy resin. Blocks were prepared so that the 2 demarcated contact areas were exposed, and 6 measurements were taken and statistically analyzed. RESULTS: Both jaws showed the same PET pattern characterized by 5 features: PET increased progressively from incisor (0.63 mm) to first molar (1.48 mm). Per tooth, mesial and distal PET did not differ. Total maxillary (26.86 mm) and mandibular (24.52 mm) PETs were similar. Paired PETs at the interproximal interface were similar, with the exception of the lateral incisor-canine interfaces. From incisor to first molar, the contact area becomes located farther gingivally. CONCLUSIONS: The existing guideline of maximal 0.5-mm interproximal reduction per 2 adjacent teeth should be kept in the anterior region and could be increased to 1 mm in the posterior region, when an equal amount is removed.

Long- and short-term effects of headgear traction with and without the maxillary second molars.

INTRODUCTION: A quantitative assessment of maxillary first molar distalization with and without the maxillary second molar (M2) was carried out. METHODS: Fifty-six cervical headgear patients undergoing fixed appliance orthodontic treatment were divided into 2 groups: before (G - M2) and after (G + M2) eruption of the maxillary second molars (ages, 11.87 ± 1.20, and 13.05 ± 1.55 years, respectively). The tightness of the dental contact point (TDCP) and the space between the second premolar and the maxillary first molar were measured at 6 levels of headgear force (0-15 N) at 3 intervals 6 months apart (T0, T1, T2). RESULTS: Relationships were found between space and TDCP, time, and presence or absence of the maxillary second molar at T1 and T2 (P <0.001). The TDCP decreased and space increased with increase in initial headgear force. An increase in initial force beyond 6 to 9 N did not significantly increase the initial maxillary first molar distalization. The G - M2 TDCP and space measurements were similar to those of G + M2 at T2 with the eruption of the maxillary second molar. From T0 to T1, maxillary first molar distalization was greater in G - M2. In comparison with our previous headgear-alone study, initial distalization with a fully bonded appliance was reduced by 4-fold. CONCLUSIONS: Headgear therapy is more effective before the eruption of the maxillary second molar. Once it erupts, the distalization pace of the maxillary first molar is reduced, but it can nevertheless be pursued at a slower pace when the maxillary second molar is present.

Proximal attrition facets: morphometric, demographic, and aging characteristics.

Although interproximal attrition is considered to be limited in modern populations, it has important clinical implications. However, in contrast to occlusal attrition, proximal attrition receives limited scientific attention. The main purpose of the current study was to fill this void. Seven-hundred and sixty-five teeth were collected from 255 skulls of subjects 18-75 yr of age. For each individual, three mandibular teeth (the first and second premolars and the first molar) were examined for proximal attrition facets (PAFs). The results provide detailed information on the size, shape, and location of the facets according to age cohort, gender, and ethnicity. The validity of the method used to measure the facets was also examined. The major findings were as follows: PAFs are usually located on the upper half of the crown proximal aspect; in each tooth, the mesial facet is more lingually positioned and the distal facet is more buccally positioned; the majority of the facets are subrectangular in shape; the size of the facets tends to increase in an anteroposterior direction (from premolars to molars); and facet size and location are age- and sex-dependent and ethnicity-independent. It is our recommendation that dentists bear in mind that interproximal attrition is a dynamic, long-term process and needs to be considered in many clinical scenarios.

An ortho-surgical approach to severe impaction using bone crestal bridge: a case report.

Impaction of both mandibular canine and lateral incisor is a rare clinical finding which is often treated by way of surgical extraction. This decision is often taken because of the anatomical limitations presented by the mandible, and the horizontal position of the impacted teeth, which have occasionally transmigrated, placing them in close proximity to the roots of neighboring teeth and with a high risk for causing their resorption. In addition, this condition significantly increases the likelihood that the area involved will undergo gingival recession and loss of crestal bone if an unsophisticated ortho-surgical approach is undertaken. The present report describes a novel ortho-surgical technique which maintains the alveolar crestal bone and utilizes a lingual arch attached to the first molars with traction through tunneling with super-elastic springs. This combined approach eliminated the need for extraction of the impacted teeth, and accomplished their full alignment without any of the aforementioned side effects. Every dentist (general practitioners as well as specialists) should be aware of this procedure and refer patients to a specialist.

Efficacy of three hygienic protocols in reducing biofilm adherence to removable thermoplastic appliance.

OBJECTIVES: To examine the ability of a removable thermoplastic appliance (RTA) to adsorb hygienic solutions and inhibit bacterial growth and to examine the efficacy of three hygiene protocols in reducing bacterial biofilm adherence to RTA. MATERIALS AND METHODS: Solution adsorption and bacterial growth inhibition were examined in vitro using paper vs RTA discs. Subsequently, 11 patients treated with RTA (mean age, 29.1 ± 4.7 years) were assigned into a sequence of three hygiene protocols: regular RTA brushing (baseline), immersion RTAs in chlorhexidine mouthwash (CHX), and using a vibrating bath with cleaning solution (VBC). For each patient, 12 upper RTAs were examined (2 baseline RTAs, 5 CHX RTAs, and 5 VBC RTAs), for a total of 132 RTAs. All RTAs were stained with gentian violet, and biofilm presence was measured using a photodensitometer. RESULTS: The RTA discs did not adsorb CHX or cleaning solution. The later agent did not show antibacterial features. Baseline RTAs showed significant biofilm adherence (P < .001) on the posterior palatal side of the aligner and on the anterior incisal edge. CHX and VBC hygienic protocols significantly (P < .001) reduced baseline biofilm adherence by 16% and 50%, respectively. Hygienic improvement was maintained over 140 days when CHX and VBC were used. However, VBC was three times more efficient than CHX. CONCLUSIONS: This study highly recommends the use of a VBC protocol. Biofilm deposits on the RTA, especially on incisal edges and attachment dimples, could lead to inadequate tooth/RTA and attachment/RTA overlap and consequently impair tooth alignment.

Malocclusion in early anatomically modern human: a reflection on the etiology of modern dental misalignment.

Malocclusions are common in modern populations. Yet, as the study of occlusion requires an almost intact dentition in both the maxilla and mandible, searching for the ultimate cause of malocclusion is a challenge: relatively little ancient material is available for research on occlusal states. The Qafzeh 9 skull is unique, as its preserved dentition allowed us to investigate the presence and manifestations of malocclusion. The aim of this study was thus to examine the occlusal condition in the Qafzeh 9 specimen in light of modern knowledge regarding the etiology of malocclusion. We revealed a pathologic occlusion in the Qafzeh 9 skull that probably originated in the early developmental stage of the dentition, and was aggravated by forces applied by mastication. When arch continuity is interrupted due to misalignment of teeth as in this case, force transmission is not equal on both sides, causing intra-arch outcomes such as mesialization of the teeth, midline deviation, rotations and the aggravation of crowding. All are evident in the Qafzeh 9 skull: the midline deviates to the left; the incisors rotate mesio-buccally; the left segment is constricted; the left first molar is buccally positioned and the left premolars palatally tilted. The inter-arch evaluation revealed anterior cross bite with functional shift that might affect force transmission and bite force. In conclusion, the findings of the current study suggest that malocclusion of developmental origin was already present in early anatomically modern humans (AMH) (the present case being the oldest known case, dated to ca. 100,000 years); that there is no basis to the notion that early AMH had a better adjustment between teeth and jaw size; and that jaw-teeth size discrepancy could be found in prehistoric populations and is not a recent phenomenon.

Stem cells of the lamina propria of human oral mucosa and gingiva develop into mineralized tissues in vivo.

AIMS: To characterize the mineralized tissue formed constitutively in the supracalvarial region of scid mice by a primitive stem cell population (hOMSC) derived from the lamina propria of the human oral mucosa and gingiva. MATERIAL AND METHODS: Fibrin-hOMSC constructs were cultured for 14 days at which time point they were analysed for the expression of osteoblastic/cementoblastic markers and implanted between the skin and calvaria bones into scid mice. After 8 weeks, the animals were sacrificed and the implantation sites analysed. RESULTS: Two-week-old cultures of fibrin-hOMSC constructs expressed osteogenic/cementogenic markers at the gene level. Macroscopic and radiographic examinations revealed mineralized masses at the implantation sites of fibrin-hOMSC constructs. Histology, histochemistry and immunofluorescence showed mineralized masses consisting of avascular cellular and acellular matrices that stained positively for collagen, Ca, cementum attachment protein, cementum protein 1, bone sialoprotein, alkaline phosphatase, osteocalcin, amelogenin and ameloblastin. Positive anti-human nuclear antigen indicated the human origin of the cells. Atomic force microscopy depicted long prismatic structures organized in lamellar aggregates. CONCLUSIONS: Within the limitation of this study, the results indicate for the first time that fibrin-hOMSC constructs are endowed with the constitutive capacity to develop into mineralized tissues that exhibit certain similarities to cementum and bone.

The arrangement of the interproximal interfaces in the human permanent dentition.

OBJECTIVES: The interproximal interface (IPI) is the interface between two adjacent teeth, i.e., the site where forces are transmitted along the dental arch. We investigated the IPI arrangement of the human permanent dentition. Specifically, the IPI morphometrical characteristics were studied and interpreted within a biomechanical framework. SUBJECTS AND METHODS: A novel in vivo IPI measurement was developed based on diversity in transillumination of Polyvinyl siloxane impression of the interproximal region. The study group included 30 subjects, aged 27, ±4.0 years. Eleven parameters were examined in each of the 26 IPIs of the permanent dentition. RESULTS: The IPI showed intra-arch similarity and interarch diversity between the tooth groups. The IPI shape was predominantly oval (60-100%), yet kidney-shaped in some molars (22-40%). From incisors to molars: the IPI increased significantly (p < 0.001) in size (1.72 to 6.05 mm(2)), occupied more of the proximal wall (7.8-12%), changed its orientation from vertical to horizontal (88.66-14.80°), and was mainly located in the buccal-occlusal quadrant of the proximal wall, chiefly in the molar teeth. CONCLUSIONS: The IPI is a product of proximal wall attrition and is dictated by the mastication forces, number of cusps, and crown inclination. IPI arrangement counteracts the adverse crowding effect of the anterior component of the mastication forces. CLINICAL RELEVANCE: The IPI characteristics found in the present study provide guidelines for crown and proximal filling restorations to meet dental physiology requirements. Further, IPI determines correct tooth alignment and proximal wall stripping applied to resolve arch length deficiency.

Mandibular second molar impaction. Part I: Genetic traits and characteristics.

INTRODUCTION: Detection of mandibular second molar (MM2) impaction is imperative for orthodontic diagnosis and treatment. In this study, we examined a possible genetic trait in MM2 impaction in 2 populations and defined distinctive characteristics. METHODS: Initial panoramic radiographs of patients of Israeli (n = 3500) and Chinese-American (n = 3000) origin, aged 11 to 15 years, were examined. Twelve distinctive characteristics were compared between the unilateral impacted and the nonimpacted sides. RESULTS: A total of 120 subjects with MM2 impaction were found (1.8%). The Chinese-American population had a higher prevalence (n = 71, 2.3%) of MM2 impaction compared with the Israeli population (n = 49, 1.4%; P = 0.004). For the subjects with MM2 impaction, the Israelis had significantly (P = 0.039) fewer bilateral impactions (27%) than did the Chinese-Americans (45%). Mesially inclined impacted MM2s were more common (88% and 89%) in the Israeli and Chinese-American populations, respectively. The unilateral impacted side demonstrated reductions in the distance between the mandibular first molar and the ramus (P <0.001), the length of the mesial root of the MM2 (P <0.001), and the height between the MM2 and the mandibular third molar, and increases in the angulations of the MM2 (P <0.001) and the mandibular third molar (P <0.003). CONCLUSIONS: An autosomal genetic trait is present in MM2 impaction with greater penetrance in the Chinese-American population. Within developmental impediments, the deficient mesial root length of the MM2 is the primary impaction factor.

In-vivo von Mises strains during Invisalign treatment.

INTRODUCTION: The Invisalign (Align Technology, Santa Clara, Calif) force delivery system has not been investigated. Since forces are related to the strains developed on the aligner surface, the behavior of the maxillary incisor and premolar von Mises strains (IVM, PVM) were studied during biweekly wear of an aligner. METHODS: Maxillary aligners (n = 61) were examined from 3 patients requiring maxillary incisor retraction and stationary anchored premolars. Two series of maxillary aligners were manufactured. Series 1 was worn by the patient, and series 2 served for in-vivo measurements with 2 strain gauge rosettes bonded to each aligner on the vestibular sides of the incisor and the premolar. Measurements were taken at days 1, 2, 9, and 15. RESULTS: All aligners demonstrated a peak IVM strain at day 1 (P<0.001); it then decreased at day 2 and plateaued through day 15. No anchorage loss was found in 2 patients (IVM ≥ PVM), and a minute loss was evident in 1 patient (PVM>IVM). CONCLUSIONS: Each aligner should be worn close to 24 hours in the first 2 days, with the time subsequently reduced (remaining 12 days). Final aligners should be thicker or worn for longer period (eg, 3 weeks). In spite of the inherent anchorage property of the aligner, attachment reinforcement should be considered in demanding anchorage requirements.

Incremental growth of the maxillary tuberosity from 6 to 20 years-A cross-sectional study.

OBJECTIVES: Although the maxillary tuberosity (MT) is a major growth site of the maxilla, its time-related growth was not fully investigated. The objectives of the study were to evaluate the MT growth from 6 to 20 years of age defining the peak growth age and to assess time-related indicators. DESIGN: Panoramic radiographs from 189 patients were divided in a cross-sectional study into six age groups. A special panoramic analysis was developed including 18 parameters and 3 time-related indicators, i.e., chronological age, crown/root development stages of the maxillary second (M(2)) and third (M(3)) molars and eruption stages. RESULTS: From 6 to 20 years, the MT vertical growth was 5.17-fold greater than the horizontal. The horizontal growth covered 36% of the maxillary growth but was inadequate to secure space for third molar eruption despite a 51% increase in MT area. MT peak growth was between 8 and 9 years and 10-11 year. During these 14 years, the maxillary length increased by pneumatisation of the maxillary sinus (86%), growth of the MT (36%) and decrease of the anterior maxillary region (-22%). Of the 18 examined parameters, 83% showed dependency to the combination chronological age with M(2), M(3) crown/root development stage and 72% to the combination chronological age with M(2), M(3) eruption stage. CONCLUSION: MT growth peak occurs with initiation of root development of M(2) and shortly before M(2) eruption (8-9 years to 10-11 years). Dental time-related indicators adjunct with the chronological age provide an effectual system to define MT growth potential.

Duration of elastomeric separation and effect on interproximal contact point characteristics.

INTRODUCTION: The common protocol of a week-long duration of elastomeric separators to facilitate band placement usually causes discomfort. In this study, we examined the minimum separation time required to create an interproximal space >0.16 mm (band thickness), the interproximal changes over 24 hours after separator removal, and the mechanical characteristics of various separators. METHODS: Thirty subjects, ages 28.1 +/- 2.8 years, had an elastomeric separator placed between the mandibular second premolar and first molar (CP5-6) for 1, 4, 12, and 24 hours. After separator removal, CP5-6 was measured for space and tightness of dental contact point (TDCP) changes up to 24 hours after separator removal. The mechanical behaviors of 6 manufacturers' separators were compared. RESULTS: After 12 and 24 hours of separation, all patients demonstrated space >0.16 mm (P <.001). A significant negative correlation (R = -0.59 to -0.63; P = .001) was found between baseline TDCP and the space measured at separator removal. A biphasic viscoelastic recovery (82%-95%) to baseline tightness level occurred within 24 hours. Variation between manufacturers was low (9%). CONCLUSIONS: Separators should be placed a day before banding. The patient should arrive 3 to 4 hours before the appointment for separator replacement if the separator is lost. Rapid recovery after separation removal implies the biological soundness of elastomeric separation regardless of the manufacturer used.

Duration and anchorage management of canine retraction with bodily versus tipping mechanics.

OBJECTIVE: To compare tipping mechanics (TM) and bodily mechanics (BM) with respect to duration, angulation, and anchorage loss during canine retraction. MATERIALS AND METHODS: TM and BM brackets were bonded to the upper right and left canines, respectively, of 14 subjects requiring maxillary first premolar extractions. The upper canines were retracted with variable nickel titanium closed coil springs (F = 0.50 or 0.75 N) attached posteriorly to a Nance anchorage appliance through the first molars. Panoramic radiographs and dental casts were taken at five time points. Canine angulation was assessed with custom metallic jigs inserted into the vertical slots of the canine brackets prior to radiographic exposure. RESULTS: The canine crown contacted the second premolar after 102.2 +/- 106 and 99.0 +/- 80.0 days, and achieved root uprighting in 72.0 +/- 31.3 and 37.2 +/- 42.7 additional days with the TM and BM groups, respectively. Only the uprighting stage differed significantly between the two mechanics (P < .05). During retraction, tooth angulation differed significantly (P < .001) between the TM (6 degrees ) and BM (-0.8 degrees ) groups. Anchorage loss, as assessed by mesial molar movement, was 1.2 +/- 0.3 mm and 1.4 +/- 0.5 mm for the TM and BM groups, respectively. CONCLUSIONS: Bodily canine retraction occurred faster (38 days) than tipping due to a shorter duration of root uprighting. Anchorage loss (17%-20%) was similar for both retraction methods, ie, maximum anchorage could not be provided by the Nance appliance. Both TM and BM brackets had inadequate rotational control of the retracted canine.