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.

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.

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.

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.

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.

Labial cervical vertical groove (LCVG) distribution and morphometric characteristics.

OBJECTIVE: Labial cervical vertical groove (LCVG), a dental anomaly found at the cervical region of upper permanent incisors, can be of esthetic, periodontal and prosthetic concern. The aim of this study was to define the prevalence and characteristics of LCVG. DESIGN: Of the 1250 examined subjects, 66 exhibited an LCVG. This group (age 19.7+/-11.4 years) was then compared with a matched No-LCVG (control) group of 49 subjects (age 17.9+/-5.7 years). Six LCVG characteristics were examined: distribution, severity and location of LCVG in central (I(1)) and lateral (I(2)) permanent maxillary incisors, Angle's classification, gender and presence of LCVG in siblings. RESULTS: Total LCVG prevalence was 5.3% (single 3.76%; multiple 1.53%), found predominantly in I(1) (93.9%) compared with I(2) (p=0.001). The anomaly presented mostly as a single configuration (71.21%); double configuration was predominantly homological bilateral, i.e., I(1)+I(1), or I(2)+I(2) (88%). LCVG in I(2) was mainly associated with multi-configuration (75%). The severe form occurred only in I(1). A mid-crown LCVG allocation was distinctive in I(1) (62.2%, p=0.001) and mesial-crown in I(2) (66.7%, p=0.038). LCVG was found mostly in males (p=0.045). In the LCVG group 16.7% were siblings. CONCLUSIONS: LCVG primarily involved I(1) in single configuration as the target assaulted tooth and secondarily I(2) mostly as a multi-configuration. The genetic impact on LCVG formation was primarily supported by the high prevalence in siblings and secondarily by the favourable occurrence in males, exclusive pattern of allocation within the crown and high occurrence of bilateral double-configuration LCVG.

Periodontal healing following orthodontic movement of rat molars with intact versus damaged periodontia towards a bony defect.

The aim of this research was to determine whether orthodontic tooth movement influences periodontal healing. In 16 male Wistar rats, 12 week of age, a bony defect was created mesial to both maxillary first molars, not including the attachment apparatus (group 1), and in 15 animals, the defect included the periodontal ligament (group 2). In both groups, the right first molar was moved mesially (orthodontic side) for 2 weeks followed by a 1-week retention period; the contralateral molar was not moved (control side). Histomorphometric analysis was performed. The results within and between the different treatment groups and sides were statistically compared by t-test and analysis of variance with repeated measures on logarithmic transformation. Junctional epithelium was significantly larger at the control than at the orthodontic side of both groups (P = 0.024), and significantly larger in group 2 than in group 1 (P < 0.001). A significantly (P = 0.034) larger pocket depth was found at the control side in group 1. Supracrestal connective tissue was larger at the control than at the orthodontic side for both groups and significantly larger in group 2 than in group 1 (P = 0.004). Root resorption was found infrequently only at the orthodontic side in both groups (five out of 31 cases). The principal findings suggest favourable effects of orthodontic tooth movement on restraining epithelial apical down-growth and decreasing pocket depth. Orthodontic treatment could not completely avoid formation of a long epithelial attachment. Therefore, periodontal regenerative surgery might be indicated prior to orthodontic tooth movement. Orthodontic movement, shortly after periodontal surgery, had no detrimental effect on periodontal soft tissue healing or on diminished but non-inflamed periodontal tissues.

Gene profile in periodontal ligament cells and clones with enamel matrix proteins derivative.

AIM: Evaluate enamel matrix proteins derivative effect on gene expression profiles in cultured human periodontal ligament cell population and its clones. MATERIAL AND METHODS: Human periodontal ligament (PDL) cells were explanted. Cell cloning was performed and clones classified into fibroblastic (FB) and mineralized tissue forming (MTF) according to their capacity to express alkaline phosphatase and form mineralized tissue. All cell cultures were grown for 7 days, with and without enamel proteins added to the medium. Following RNA extraction, expression profiling was performed by hybridization with a DNA micro-array. Selected genes differed from the control at a significant level smaller than p<0.01. RESULTS: Enamel proteins induced major qualitative changes in mRNA expression in all PDL cell populations, differently affecting the entire PDL cell population and its clones. In the entire PDL cell population, enamel proteins significantly enhanced PDL cell function, with a general effect on enhanced cell functional metabolism. CONCLUSIONS: Enamel proteins enhanced gene expression responsible for protein and mineralized tissue synthesis in the entire PDL population. In the MTF clones, nucleic acid metabolism, protein metabolism and signal transduction related genes were up-regulated, while in the FB clones, up-regulated genes were related to cell adhesion, nucleic acid metabolism and signal transduction.

Centric slide, bite force and muscle tenderness changes over 6 months following fixed orthodontic treatment.

OBJECTIVE: The postorthodontic change of the masticatory muscles was evaluated using three parameters: maximal voluntary bite force (MVBF), slide in centric (difference between maximal intercuspation and retruded contact position), and muscle sensitivity to palpation. MATERIALS AND METHODS: MVBF was measured with a custom-made rubber tube bite force device, centric slide with a digital caliper, and sensitivity to palpation of the masseter and temporalis muscles (scale 0-3) during application of standardized digital force (10 N). Data were collected at four time points: T0, before bracket removal; T1, immediately after bracket removal; T2, after 3 months of retention; and T3, after 6 months of retention. Patients (n = 41; 22 females, 19 males; mean age 17.4 +/- 5.4 years) were examined from T0 to T1 and from T1 to T2. Of these, 28 (15 females, 13 males) were followed at T3. RESULTS: Immediately after bracket removal (T0 to T1), MVBF increased significantly by 15%. Another significant increase (15.5%) was found 3 months posttreatment (T1-T2), and almost no increase (2%) at 6 months (T2-T3). The slide in centric remained within normal values during the three time points. A decline in sensitivity to palpation from T1 to T3 was found for both masseter and temporalis muscles. CONCLUSIONS: Neuromuscular adaptability begins within several minutes after bracket removal. A second stage of muscular adaptation occurs within 3 months of retention. These findings suggest that muscular adjustment occurs within a short period after orthodontic treatment.

Assessment of open and incomplete bite correction by incisor overlap and optical density of polyvinyl siloxane bite registration.

Open bite (OB) is a generalized term, which could incorporate subgroups that react differently to vertical correction. The objectives of the present study were to detect vertical treatment changes in incomplete bite (IB: inter-incisor overlap with no lower incisor contact with teeth or palate) and OB (no inter-incisor overlap) groups compared with a complete bite (CB: inter-incisor overlap with full lower incisor contact with teeth or palate) control group, to evaluate treatment response of the central and lateral incisors, and to study the vertico-sagittal interaction. Dental casts were taken at three time points, pre-treatment, post-treatment, and after one year of retention, from 54 Class II patients (22 males and 32 females with a mean age of 11 years 6 months) divided into three groups: CB (n = 21), IB (n = 18) and OB (n = 15). Measurements included incisor overlap (mm) and optical density (OD/mm2) of occlusal bite registration made of polyvinl siloxane. Both CB and IB groups demonstrated post-retention bite opening. However, bite opening in the CB group was three times greater than that in the IB group (e.g. lower lateral = -1.42 mm, 118 OD/mm2 versus -0.40 mm, 107 OD/mm2). Conversely, the OB group showed a significant (P < 0.001) bite closure (e.g. lower lateral = 1.30 mm, -377 OD/mm2). Overjet changes affected OD measurements, causing diversity in OD and millimetric measurements of the lateral incisors in the IB group. In conclusion, the OB group demonstrated a significant stable vertical correction; a post-treatment non-contact inter-incisor relationship was determined by a vertico-sagittal relapse; and full compensation of an IB was not possible.

Unequal outer and inner bow configurations: comparing 2 asymmetric headgear systems.

INTRODUCTION: Asymmetric headgear is used when different molar distalization forces (MDF) are needed on the right and left sides of the jaw to correct a Class II molar relationship. METHODS: We investigated 2 asymmetric headgear configurations, the outer-bow and the inner-bow, on cervical-pull headgear. In the first configuration, 5 hooks were soldered on 1 side of the outer bow at 10-mm intervals, making this side shorter; in the other, 4 stops (1.5 mm) were added to 1 side of the inner bow, making this side longer. The right and left MDF and the extraoral force (EF) were measured simultaneously with 2 fork transducers and a testing machine, respectively. RESULTS: A 40-mm difference between the long and short outer bows resulted in a 2.17-fold greater MDF on the long-side molar (7:3 ratio). The 3-4 stop configuration provided the optimal inner-bow arrangement, with stop/no-stop MDF ratios of 7:3 and 10:0, respectively, at 10 N EF. At low-to-medium EF levels, a unilateral MDF developed on the stop side with zero MDF on the no-stop side. The sum of the right and left MDF nearly equaled the EF in the outer-bow asymmetry and was 60% in the inner-bow setting; this suggests strong lateral forces in the latter. CONCLUSIONS: Clinically, for a bilateral unequal Class II relationship, the system of choice is outer-bow asymmetric headgear. For a unilateral Class II relationship with 1 side in a Class I molar relationship (Class II subdivision), inner-bow asymmetric headgear is recommended.

Skeletal and dental response to rapid maxillary expansion with 2- versus 4-band appliances.

PURPOSE: Banding a rapid palatal expansion (RPE) appliance to the 2 first molars has been proposed as an equivalent to the conventional 4-band RPE appliance. However, the dentoskeletal response to this treatment has not been evaluated. MATERIAL: Twenty-eight subjects (aged 8-20 years) who required maxillary expansion were matched by age and randomly assigned to either a 2-band or a 4-band RPE group. Skeletal and dental responses were measured from standardized anteroposterior cephalometric and occlusal radiographs and dental casts before treatment (T1), at the end of expansion (T2), and at 1 year postexpansion (T3). RESULTS: At T2, suture expansion was 2.5 times greater and arch perimeter was 6-fold larger in the 4-band than in the 2-band group. Both appliances displayed the typical "V" expansion of the suture and "reverse V" expansion of the dental arch. At T3, remineralization reduced the suture opening by 75%, but 95% to 99% of the dental reaction was maintained. The 2-band group demonstrated a significant inverse age-dependent correlation ( r = -0.795), with treatment failure beyond 12 years of age, whereas the 4-band group was age-independent. CONCLUSIONS: The greater the skeletal resistance, the smaller the sutural response but the greater the dental response to RPE therapy. Four-band RPE is indicated when severe anterior crowding is accompanied by a tapered arch form, and 2-band RPE is recommended in the mixed dentition when mild crowding occurs with posterior constriction.

Labial-cervical-vertical groove in maxillary permanent incisors--prevalence, severity, and affected soft tissue.

OBJECTIVES: To investigate the prevalence and severity of a labial-cervical-vertical groove (LCVG) in maxillary permanent incisors and its effect on the associated gingival tissue. METHODS: A total of 600 adolescents (293 boys and 307 girls, mean age 13.6+/-1.99 years) were randomly selected and examined for the presence of LCVG. The deformity was classified as mild, moderate, or severe according to predetermined criteria. Gingival coverage at the groove site was defined as normal, partial, and irregular. RESULTS: LCVG was found in 27 adolescents (4.5%). It was unilateral in 24 (89%) and bilateral in 3 (11%). The ratio of central to lateral incisors was 29:1. No sexual dimorphism or side prevalence were found. Mild LCVG was found in 22 incisors, moderate LCVG in 7 incisors, and severe LCVG in one incisor. Moderate LCVG was 5 to 6 times more susceptible to partial or irregular coverage of the gingival margin than mild LCVG. The gingival sulcus in teeth with LCVG demonstrated a significant (P = .001) increase in depth compared to non-LCVG teeth (1.55+/-0.90 mm vs 1.18+/-0.75 mm). CONCLUSIONS: An LCVG is a deformity confined predominantly to a single permanent maxillary central incisor. Its prevalence is not connected with gender. Most LCVGs are mild and often difficult to detect. However, the greater the severity, the more gingival irregularity is associated. This and the increase in sulcus depth in LCVG incisors are adverse predispositions for periodontal sequelae, calling for cautious oral hygiene maintenance.

In vivo debonding strength and enamel damage in two orthodontic debonding methods.

Bracket debonding strength related to diverse debonding methods and enamel damage has not been assessed in vivo. The study hypothetized a direct relationship between these three parameters. Debonding strength was measured clinically in the wings method and base method on 50 patients in a split mouth method using a calibrated debonding plier. Brackets from 30 of these patients were scanned in SEM and EDAX for adhesive remnant index and enamel calcium remnants. Base method debonding force was significantly greater than wings method (163.5+/-68.7 N, 106.1+/-66.2 N, respectively, p < 0.001). A positive adhesive remnant index score was found in both methods (68.7%, 66.7%, respectively). Debonding strength vs. adhesive remnant index or calcium index scores were not correlated. However, the latter two were significantly correlated (0.524 < R < 0.895, p < 0.031). Half of the debonding failures developed at the adhesive enamel interface. The results warnts the potential of enamel damage during debonding.

Maxillary incisor root resorption after rapid palatal expansion in Felis catus.

Root resorption after rapid palatal expansion (RPE) treatment was found in anchored teeth but has not been studied on non-anchored incisors. This study evaluated root resorption, root tipping, and root proximity of maxillary incisors after RPE treatment. Fourteen cats were divided into treated (n = 10) and untreated (n = 4) groups. The RPE treatment consisted of active, retention, and relapse phases, lasting 25, 60 and 60 d, respectively. Standardized occlusal radiographs were taken to measure tipping and root proximity before and after each treatment phase. Maxillary incisors were analysed histologically by fluorescent microscopy for root resorption. Data was analysed statistically with anova with repeated measures, t-test and Pearson's coefficient of correlation. Root resorption was confined to the first incisors and was 750-fold greater in the treated vs. the control group. Root tipping and root proximity were significantly greater (2.5- and 17-fold, respectively) in the first than in the second maxillary incisor and highly correlated with root resorption (r = -0.927 and 0.723, respectively). This suggests a cause (tipping and root proximity) and effect (root resorption) relationship. Data suggest that first maxillary incisor susceptibility to root resorption during RPE is associated with severe tipping and root proximity.