Incisors Research Articles

Association between molar incisor hypomineralisation and tooth agenesis: a cross-sectional study in Brazilian children and adolescents.

The aim of the present was to assess the association between MIH and tooth agenesis (TA) in orthodontic patients from the Federal University of Rio Grande do Norte, Natal, Brazil. A cross-sectional study was performed to evaluate the presence of MIH and TA in a sample of 371 pretreatment orthodontic records from patients aged 9-18years. Statistical analyses were performed using the Chi-square and Fisher's exact tests, and logistic regressions. There was a statistically significant association between the prevalence of tooth agenesis and MIH. A higher percentage of third molar agenesis, maxillary premolar agenesis, and mandibular second premolar agenesis was observed among children with MIH-affected teeth. Patients with MIH had a 2.43 times greater chance of third molar agenesis, and a 5.88 times higher likelihood of mandibular premolar agenesis. There is a weak association between MIH and TA. Furthermore, the presence of hypomineralised molars increases the risk of tooth agenesis.

Efficacy of Bone Anchored Pendulum Appliance Over Conventional Pendulum Appliance during Molar Distalization in the Orthodontic Management of Class II Malocclusion : A Systematic Review

Background: Pendulum appliance used commonly used to achieve molar distalization in the management of borderline class II malocclusion is associated with mesial tipping of the maxillary premolars and proclination of maxillary incisors post-distalization, resulting in round tripping and increased treatment time. Bone Anchored Pendulum Appliance (BAPA) is one of the modifications of the pendulum that could effectively prevent anchorage loss. Aim: To evaluate the effectiveness of Bone Anchored Pendulum Appliance(BAPA) over the Conventional Pendulum Appliance(CPA) for the distalization of maxillary molar in the management of Class II malocclusion. Materials and Methods: A web search was done in Google Scholar, MEDLINE, Web of Science, LILAC and COCHRANE Library databases using PRISMA guidelines. The search included RCTs and Non RCTs (Both Prospective and Retrospective studies) comparing distalization achieved by BAPA with CPA in Class II malocclusion. The Risk of bias was assessed using the ROBINS - I tool. Results: Of the initial 745 articles, 5 studies met the inclusion criteria and were included to the systematic review. The BAPA showed between 4.8 -6.4 mm of molar distalization and between 9 °-11.3° of distal tipping of molars while the distalization achieved with CPA was between 2mm -6.4mm with 6.67° -14.50° of distal tipping. While CPA groups showed mesial tipping of premolars, distal tipping of premolars was observed with the BAPA appliances. Conclusions: BAPA were found to significantly reduce anterior anchorage loss, distalise the premolars and molars. There is moderate evidence that BAPA provides greater distalization with reduced incidence of unwanted tooth movements.

Where do all the ewes go? Ewe culling and mortality in 34 sheep flocks in New Zealand

ABSTRACT Aims To describe rates of and reasons for culling and mortality of ewes between breeding and mid-lactation on New Zealand sheep farms; to investigate associations of these variables with farm demographic variables; and to describe rates of and reasons for culling of ewes at weaning. Methods Participants were a convenience sample of 34 farms from across New Zealand. Demographic data were initially collected for each farm via a questionnaire administered in-person to the flock owner or manager. During approximately 8 months from breeding to mid-lactation, ewe tally, culling and mortality data were collected and used to calculate various parameters related to flock performance and to investigate associations. During the main ewe-culling event at weaning, ewe-culling data were collected from 29/34 flocks participating in the study. Results There was considerable variation between flocks, but the between-flock mean replacement percentage was 29.2 (SD 5.0)%. Overall, a between-flock mean of 10.5 (SD 4.6)% of ewes presented for breeding were culled or dead/missing by mid-lactation and thus did not rear any lambs. Additionally, from 27 flocks that reported data on ewes’ success at rearing lambs, a between-flock mean of 3.9 (SD 2.5)% of ewes that remained alive at mid-lactation failed to rear any lambs, resulting in an overall between-flock mean loss of 23.1 (SD 6.3) potential lambs per 100 ewes. Two-thirds of ewe mortalities between breeding and mid-lactation occurred during the lambing period. Model results showed flocks with higher pregnancy scanning percentages had lower rates of culling and mortality between breeding and mid-lactation. However, apart from farm contour, from breeding to mid-lactation there were no associations for culling and mortality with farm size, flock size, number of ewes per labour unit, whether ewe hoggets (7–9 months of age) were presented for breeding, or duration of the breeding period. A between-flock mean of 16.5 (SD 8.3)% of ewes present at weaning were culled, and among mixed-age ewes, the most common reasons for culling at this time were age, incisor teeth defects and udder defects. Conclusions To reduce unnecessary ewe culling and mortality, attention should be focused on maximising conception rates, ensuring judicious culling decisions, optimising body condition score, and identifying farm-specific causes of death over the lambing period to facilitate targeted intervention strategies. Clinical relevance Identifying why and when ewes exit flocks, and comparing it with the data presented here, will facilitate the development of flock-specific interventions to reduce ewe culling and mortality. Abbreviations BCS: Body condition score; NI: North Island; SI: South Island

Orthodontic management of severe inversely impacted maxillary central incisors: a case series.

Abnormal positioning and dislocation of the central incisor can disturb tooth eruption. Generally, inversely impacted maxillary central incisors do not erupt naturally. Performing traction and applied extrusion of an inversely impacted maxillary central incisor with a high inclination angle of the crown is challenging. This study aimed to examine the possibility of orthodontic treatment for severely inversely impacted maxillary central incisors in a series of case studies. The inclination angle of the tooth crown, curvature of the tooth root, and length of the formed tooth root were measured using radiography. The teeth were then fenestrated and traction was applied using a lingual arch appliance with elastics. The average crown axis inclination was 113°, the degree of root curvature was 97.3°, and the root formation was 36.1%. Although the crown axis inclination and root curvature were severe, all the incisors were aligned in the correct position as vital teeth through surgical and orthodontic treatments. Traction should be performed in the early period of incisor development when root formation is not progressing, regardless of the tooth angle.

3D Printed Dual Reduction Guide: A Feasible Alternative for Conservative Gingivectomy and Minimally Invasive Preparation for Ceramic Veneers.

This case report describes a digital workflow for designing and 3D printing a guide with the dual purpose of gingivectomy and tooth preparation in the esthetic zone, to be followed by cementation of ceramic veneers under rubber dam isolation. The patient's primary concern was to improve her smile. After clinical evaluation, our recommendation was for a minimal gingivectomy to match the gingival zenith for both central incisors, to be followed by ceramic laminate veneers. A digitally designed and 3D printed guide was used for gingivectomy and tooth preparation for the ceramic veneers. Ceramic veneers were cemented under rubber dam isolation to maximize bonding properties. A single guide can be digitally designed and 3D printed to perform controlled gingivectomy and minimally invasive tooth preparations. The outcome of the gingivectomy improved the gingival architecture for central incisors, and the ceramic veneers fulfilled the patient's esthetic demands.

Comparing Three-dimensional Radiologic Outcomes Between Early Versus Late Secondary Alveolar Bone Grafting.

Secondary alveolar bone grafting (SABG) during mixed dentition is the standard of care for patients with complete cleft of lip and palate. Early SABG (E-SABG; 4 to 7y) occurs before the eruption of lateral incisors, whereas late SABG (L-SABG; 8 to 12y) occurs before the eruption of maxillary permanent canines. This study compares outcomes of E-SABG versus L-SABG among patients with unilateral cleft of lip and palate (UCLP). A prospective cohort study was conducted evaluating nonsyndromic patients with UCLP who underwent SABG from April 2018 to January 2020, 48 consecutive patients with UCLP were included. Preoperative and 6 to 10-month postoperative cone beam computed tomography imaging were obtained to assess graft and periodontal outcomes. Among 48 patients with UCLP, of which 21 were in the E-SABG group (6.9 ± 1.1y), and 28 were in the L-SABG cohort (10.4 ± 1.6y). The initial alveolar cleft width is significantly smaller in the E-SABG cohort compared with the L-SABG cohort (5.1 ± 1.5 versus 6.5 ± 2.0mm, P = 0.008). Compared with the L-SABG cohort, the E-SABG cohort had higher rates of bony bridge formation (77.3% versus 65.4%, P= 0.367), thicker bony bridges (5.7 ± 2.1 versus 3.9 ± 1.5mm, P= 0.004), lower Bergland scores [1.5 (interquartile range: 1 to 2) versus 2.25 (interquartile range: 1.5 to 3.5), P= 0.026], and greater alveolar bone coverage (79.8 ± 16.7% versus 67.9 ± 18.1%, 0.024). The authors' findings suggest that patients who undergo E-SABG at ∼7 years may have better graft outcomes and benefits to the periodontal bone support on cleft-adjacent incisor compared with L-SABG at 11 years.

Orthodontic-Surgical Management of Triple Impacted Mesiodens and Maxillary Incisors - A Case Report

Abstract Rationale: Mesiodens are supernumerary teeth located in the pre-maxilla between the two central incisors with a prevalence rate of 0.15–1.9%. An impacted mesiodens may cause delayed eruption of permanent incisors, ectopic eruption, pathological disturbances and malalignment of teeth. Patient Concerns: The patient complained of missing upper front teeth associated with pain in the same region for two weeks. Diagnosis: Upon clinical and radiographic examination, it was diagnosed as triple impacted mesiodens with impacted permanent maxillary central incisors. Treatment: The clinicians in the study approached the issue by surgical removal of the impacted mesiodens and orthodontic treatment for extrusion of the impacted permanent maxillary central incisors. Outcomes: The patient was relieved of the pre-operative concerns and followed up regularly for the eruption of permanent maxillary central incisors. Take-away Lessons: The authors advocate the importance of timely diagnosis and proper management of such rare pathologies.

Evaluation of a New Technique of Gingival Smile Reduction after Hyaluronic Acid Infiltration: A Cohort Study Focusing on Gingival Exposure and Patient-Oriented Outcomes.

A gummy smile is the visualization of more than 3 mm of gingiva above the maxillary incisors. This study aimed to evaluate the long-term effects on aesthetics and patient satisfaction of a new hyaluronic acid infiltration technique in reducing the gummy smile. Fifty patients with gummy smiles were treated using hyaluronic acid infiltration points by applying 0.1 mL per injection at specific points. Post-treatment evaluations were performed one week, one month, three months, six months, and 12 months later. A questionnaire assessed patient satisfaction, willingness to recommend the treatment, and side effects (pain and bruising during and after treatment). An average reduction of 2.5 mm in gingival exposure during smiling was observed. After one week, the reduction was constant. At six months, 40% of the original gingival exposure was recovered, and recovery was complete at 12 months. Patient satisfaction was 82.1%, and 100% of patients would recommend the treatment. Bruising, swelling, and pain decreased to 0% from the first month. In conclusion, this technique is a safe and effective option to improve the smile's appearance with minimal complications.

Reconstructing confidence: Fiber reinforced reattachment of a fractured maxillary lateral incisor – A clinical case report

AbstractA broken smile can be more than just a physical injury—it can impact self-esteem and confidence. This case highlights the successful reattachment of a fractured upper front tooth in a 32-year-old female following a recent fall. The comprehensive treatment strategy involved immediate root canal therapy to relieve pain, followed by a gingivectomy and osteotomy to correct the subgingival fracture and restore the biologic width. Advanced techniques, including fiber post and core reconstruction reinforced with ribbond fiber, were used to stabilize and support the tooth structure. The final touch is done with a layer of composite for optimal function and aesthetics. This holistic approach not only revived the patient's smile but also rejuvenated her confidence and psychological well-being.

Exploring the Learning Curve of Dental Implant Placement Using a Task-Autonomous Robotic System Among Young Dentists From Different Specialties-A Pilot Module Study.

The learning curve effect of dynamic computer-assisted implant surgery (D-CAIS) was observed among inexperienced novice surgeons. The learning curves can provide valuable information for novice surgeons and valid comparisons between new and conventional techniques. Recently, robotic computer-assisted implant surgery (R-CAIS) has shown promise as a novel dental implant surgical technique for both partially and edentulous patients. However, its learning curve remains unknown. The aim of this study was to explore the learning curve of dental implant placement surgery with a task-autonomous robotic system among young dentists with different specialties. Four young dentists (mean age: 25.3 ± 1.5 years at the beginning of their first attempt) with equal representation of males and females and with different specialties participated in this study. None of the participants had prior experience in R-CAIS. Each operator placed eight implants over eight attempts using a semi-active task-autonomous robotic system. Among the eight implants, four were straight lateral incisor implants, and four were 30°-tilted premolar implants. The implants were placed in each dental quadrant of the maxillary and mandibular jaw modules. The operation time was recorded. Coronal, apical, and angular deviations between the planned and actual sites of implant placement were measured by merging preoperative and postoperative cone-beam computed tomography (CBCT) scans. The data were analyzed with repeated-measures ANOVA (α = 0.05). The mean time for implant placement was associated with the number of attempts (p < 0.01). The time taken for the second attempt was significantly shorter than that of the first attempt (33.26 vs. 30.47 min; p < 0.001) then it plateaued. Three-dimensional (3D) angular (p = 0.31), coronal deviation (p = 0.26), and apical deviation (p = 0.06) did not differ significantly among attempts. The mean values and standard deviations of 3D coronal deviation, 3D apical deviation, and 3D angular deviation were 0.71 ± 0.31 mm, 0.72 ± 0.30 mm, and 0.94 ± 0.58°, respectively. Neither the position of the jaw (p > 0.59) nor the tilt angle of the implant (straight or 30°-tilted, p > 0.85) was related to implant placement accuracy. Dentists quickly learned the basic workflow of R-CAIS and thus facilitated the clinicians in the mastery of implant placement on edentulous jaw modules, leading to a comparable operating speed and high precision. Moreover, the accuracy of placement of straight and tilted implants in both the maxilla and mandible with R-CAIS was satisfactory.

Microsurgical Treatment of a Large Through-and-Through Periapical Lesion with Apicomarginal Defect using Guided Tissue Regeneration (GTR): A Case Report of a Two-Year Follow-Up

In case of a long-term periapical lesion, destruction of both vestibular and oral cortical plates is sometimes observed and even a through-and-through periapical lesion occurs. The success of the treatment decreases when an apicomarginal defect is added to the through-and-through periapical lesion. Large periapical lesions should be treated initially by orthograde root canal therapy. When the signs and symptoms of the infection don’t recede after the treatment, then surgical approaches should be considered. In this case report, a 22-year-old female with previously initiated therapy was referred for an endodontic microsurgery of tooth 22 (i.e., upper left lateral incisor). After the endodontic treatment the patient was referred to the oral surgeon for apicoectomy with augmentation of the bone defect. The sinus tract in the apex area of the tooth 22 remained active since the surgical intervention. Endodontic microsurgery and guided tissue regeneration were performed. The article presents diagnostic data, namely pre- and post-operative images of cone beam computed tomography (after 2 years), as well as pre-, intra- and post-operative clinical images. All pre- and intraoperative procedures and stages are detailed. In particular, separation of platelet-rich fibrin (PRF) from venous blood, retrograde preparation with an ultrasonic tip and a device using a dental operating microscope and the use of a collagen membrane. After two-year follow-up, radiographic examination revealed significant bone reconstruction and clinical signs and symptoms were absent. The patient hasn’t reported any symptoms since. The paper also analyzes scientific sources on the use of PRF and collagen membranes in bone defects of the jaws. Attention is also paid to the formation of a flap during operations of this type. The main six success factors in the treatment of such complex cases are highlighted. Rethinking the previously performed surgery (apicoectomy) in this patient, attention was paid to the main five factors that could contribute to the failure.

Sex determination and odontometric dimensions - A study of a North Indian population.

Sex determination is an indispensable parameter in identifying unknown deceased individuals. It can narrow down the chances of possible matches by 50%, providing a crucial lead in personal identification. In cases of commingled, decomposed, fragmented, charred and unidentifiable corpses, the importance of dental morphometrics cannot be overlooked due to the resistance of teeth to post-mortem degradation. Addressing this quality of teeth, a descriptive cross-sectional study was conducted in a North Indian population to evaluate sexual variations in dental dimensions and to identify the most sexually dimorphic dental dimension. The study included 207 participants (114 females and 93 males) in the age group of 21 to 45 years. Dental casts were prepared after obtaining informed consent from the participants and ethical clearance from the institute's ethical committee. Six odontometric dimensions, namely incisor-incisor distance, inter canine distance, combined width of central incisors, inter-premolar distance, inter-molar distance, and dental arch height of each participant were recorded on the dental casts using standard procedures. Analysis of the data elucidated the existence of statistically significant sexual dimorphism in the dental dimensions of the participants. The results of the discriminant function analysis show a sex determination accuracy of 68.1%, with a cross-validation accuracy of 65.2%. The study found the incisor-incisor distance to be the most sexually dimorphic trait, making it the best predictor of sex in the present population. The results of the present study may be helpful in sex determination and personal identification from dental remains in medico-legal and disaster victim identification cases.

Comprehensive Management of an Impacted Maxillary Central Incisor: A Case Report

Comprehensive Management of an Impacted Maxillary Central Incisor: A Case Report

TREATMENT OF TOOTH AVULSION: A CASE REPORT

Dental trauma (DT) refers to injuries caused by impacts to the teeth and/or the hard and soft tissues within or outside the oral cavity. Among the various types of DT, avulsion, characterized by the complete displacement of the tooth from its socket. The success of treatment depends on timely management and proper professional care during and after reimplantation in preserving the tooth in the oral cavity. This study describes a case report of an avulsion of the upper left central incisor (21) that underwent reimplantation. The patient, a 10-year-old boy, had a history of bicycle fall, presenting with extraoral injuries to the cheek and chin, lip abrasions, and avulsion of tooth 21. The tooth was stored in milk and reimplanted 30 minutes after the accident. Clinical and radiographic examinations showed no bone fractures but revealed mobility of teeth 11 and 12 and avulsion of tooth 21. Treatment included cleaning, repositioning of the avulsed tooth, stabilization with a semi-flexible splint, and administration of antibiotics and analgesics. Endodontic therapy with mechanical instrumentation was successfully initiated after 20 days. This case highlights the importance of proper tooth storage and timing of reimplantation, leading to the restoration of patient’s aesthetics, chewing function, and self-esteem.

Digital-assisted diagnosis and orthodontic management of an impacted mandibular lateral incisor: a case report

BackgroundThe impaction of mandibular lateral incisors presents significant aesthetic and functional challenges in orthodontics, including Bolton ratio discrepancies and anterior occlusal anomalies. The increasing preference for nonextraction treatment further complicates space management within the dental arch. However, the advent of digital-assisted orthodontic technologies, particularly advanced digital simulations, has revolutionized the precision and effectiveness of diagnosis and treatment planning. These technologies enable clinicians to strategically leverage natural jaw development and create the necessary space for the alignment of impacted teeth without resorting to extraction.Case presentationThis case report details the treatment of a 12-year-old male with an impacted mandibular lateral incisor, which resulted in both aesthetic concerns and functional impairments, alongside Class II malocclusion. By employing a digital-assisted diagnostic approach, including comprehensive digital simulations, we meticulously evaluated the feasibility of a nonextraction treatment plan. The strategy centred on harnessing the patient’s mandibular growth potential to expand the available space naturally. The treatment involved surgical exposure of the impacted tooth, followed by precise orthodontic traction guided by continuous digital monitoring. The integration of digital tools throughout the treatment process was crucial in achieving successful eruption and alignment of the impacted tooth, thus restoring optimal aesthetics and function without the need for extraction.ConclusionThis case highlights the transformative impact of digital-assisted technologies in the management of complex orthodontic cases, such as impacted mandibular lateral incisors. The successful integration of these advanced tools with a nonextraction treatment approach underscores their potential to significantly enhance clinical outcomes. Digital technologies not only improve the accuracy and effectiveness of treatment but also facilitate a multidisciplinary approach that elevates the standard of patient care in addressing complex orthodontic challenges.

Artificial Intelligence in Aesthetic Dentistry: Is Treatment with Aligners Clinically Realistic?

Smile aesthetics are increasingly prioritized in dental practice, with accurate orthodontic assessment and treatment planning being crucial for optimal outcomes. This study evaluates Invisalign® SmileView™ (SV), an AI-based tool that simulates post-treatment smiles, focusing on its ability to present potential orthodontic outcomes to patients. Background/Objectives: This research aims to study whether SV can simulate predictable orthodontic results and if it makes anatomical modifications to the teeth. Additionally, it will evaluate whether SV displays smiles that conform to the orthodontic criteria described in the literature. Finally, the study will analyze whether the software can align the dental with the facial midline. Methods: A total of 51 subjects were recruited in Madrid, Spain. The operator took a frontal photograph of the subjects with a social smile (T0), following the application’s instructions. Subsequently, the subjects followed the steps to modify their smile (T1), resulting in a new image of the subject with a different smile. The following variables were collected, analyzed, and compared with the standards defined in the literature: smile width, vertical exposure of the maxillary central incisor, width of the maxillary central and lateral incisors, proportion of the maxillary lateral incisor width to the central incisor, anterior gingival exposure level, position of the upper and lower dental midlines relative to the facial midline. Results: 58% of the sample showed dental expansion, with an excessive expansion (&gt;5 mm) observed in 8%. In the maxillary arch, 5.9% of incisors exceeded predictable aligner movement (&gt;1.5 mm), with 3.9% showing excessive extrusion and 2% excessive intrusion. For the lateral incisors, the mesiodistal size was reduced less than 0.5 mm in 31.4% of cases, with excessive interproximal reduction (&gt;0.5 mm) in 5.9%. Additionally, 62.7% of cases would require multidisciplinary treatment due to an increase in size. SV centered the upper midline in 77.9% of these cases. Among the sample, the upper midline was initially centered in 74.5% of subjects, and SV maintained it centered in 84.2% of these subjects. Conclusions: SV tends to generate simulations of broader smiles, which are mostly achievable through aligner treatments, from an orthodontic perspective, and showed high predictability regarding the vertical movements of the incisors that can be achieved with aligners. Moreover, it adjusted the mesiodistal size of the upper incisors in its simulations and demonstrated the ability to identify and correct deviations of the dental midlines relative to the facial midline.

Correlation of Tongue Dimensions and Posture with Lower Central Incisor Inclination and Alveolar Bone Thickness in Skeletal Class I and II Malocclusion: A CBCT Study

Background: In this study, Cone-Beam Computed Tomography (CBCT) was used to assess the dimension and posture of the tongue, as well as Alveolar Bone Thickness (ABT) and labiolingual inclination of mandibular central incisors in order to look for any correlations. Methods: A total of 200 CBCT images of skeletal Class I and II individuals were studied. Each group of malocclusion was divided into three subgroups: low-angle, normal-angle, and high-angle. Buccal and lingual alveolar bone thickness (BT &amp; LT), and the Inclination of Mandibular Plane Angle (IMPA) were measured and compared by using T-test. The spearman rank correlations test analyzed the correlations between dental variables and tongue measurements (p&lt;0.05). Results: Significant weak correlations were identified between dental variables and tongue measurements. In Cl I malocclusion, IMPA and Tongue Length (TGL) were found to be significantly correlated with a correlation value of 0.324 (p=0.001). In Cl II malocclusion, there was a significant correlation between BT3 and TGH. About BT3, there was a significant correlation with D4’ and a negative correlation with D5’. Further comparison among vertical subgroups revealed the same results. Conclusion: Class I patients with superior tongue posture may have thicker lingual alveolar bone around mandibular incisors and Class II patients showed that thicker labial alveolar bone of lower incisor and thinner alveolar bone at the lingual side may be associated with a superior position of the posterior portion of the tongue.

A 3D finite element analysis of biomechanical effects on teeth and bone during true intrusion of anteriors using miniscrews

The primary objective of this study was to investigate the biomechanical effects and stresses on bone, periodontal ligament (PDL), cementum and displacement along X-, Y- and Z-axis during true intrusion of incisors using mini-implants with Finite Element Analysis; the secondary objective of the study was to find out the best method for anterior intrusion in clinical practice to treat anterior deep bite malocclusions. A 3D finite element method was used to simulate true anterior intrusion with sliding mechanics using mini-implants. Two groups were modelled with mini-implants placed distal to lateral incisors for Model1, and below the anteriornasalspine (ANS) for Model2, to achieve intrusion. von Mises stress, principal stress on PDL and alveolar bone, displacements in all 3 planes were determined. Amongst the modalities compared in the present study, the stresses on bone and PDL were showing best behavior for mini-implants placed distal to lateral incisors (Model1). The teeth showed controlled tooth movement in Model1. Maximum stress was found in the cortical bone and in the PDL. Nature of the stress changed from compressive to tensile from cervical area to root apex, concentrating mainly at the apical area. Amongst the modalities compared, the best controlled tooth movements for anterior intrusion to treat anterior deep bite malocclusions, was for mini-implants placed distal to lateral incisors (Model1).

Three-dimensional analysis of force distribution on maxillary dentition while distalization of first and second molars simultaneously with clear aligners

Objective: To explore the force distribution on the maxillary dentition when the first and second molars distalized simultaneously with different step sizes using clear aligners in vitro in order to provide a theoretical basis for the rational design of molar distalization. Methods: Clear aligners were designed to simultaneously distalize the maxillary first and second molars bilaterally, with rectangular attachments placed on the buccal surfaces of the first and second premolars, as well as the second molars. Based on different step sizes, the aligners were divided into three groups: Group A (0.15 mm per step), Group B (0.20 mm per step), and Group C (0.25 mm per step). Ten aligners were fabricated for each group using 0.76 mm thick polyethylene terephthalate glycol (PET-G) sheets. A three-dimensional force measurement system was used to measure the forces exerted on each tooth by the aligners, the first and second molars served as the target teeth and the remaining teeth as anchorage teeth. The three-dimensional force data were compared among the three groups. Results: In the mesiodistal direction, the forces on the central and lateral incisors were relatively small among all three groups, with no statistically significant differences (P>0.05). However, significant differences were observed in the forces on the canines, first premolars, second premolars, first molars, and second molars (P<0.05). The distal forces on the second molars in Groups B and C were (6.13±1.45) N and (6.83±1.58) N, respectively, significantly higher than that in Group A [(3.51±1.01) N] (P<0.05). The distal force on the first molars in Group C [(6.62±0.89) N] was significantly higher than that in Groups A and B (P<0.05). The mesial reactive forces on the first and second premolars in Groups B and C were significantly higher than those in Group A (P<0.05). The mesial reactive force on the canines in Group C [(-2.98±1.33) N] was significantly higher than that in Group A [(-1.69±0.68) N] (P<0.05), while there were no significant differences between Groups B and C in the forces on the canines, first premolars, and second premolars (P>0.05). In the buccolingual direction, there were no statistically significant differences in the forces on the central and lateral incisors among three groups (P>0.05), but significant differences were observed in the forces on the canines, second premolars, and second molars (P<0.05). The buccolingual forces on the canines, second premolars, and second molars in Group B were (-0.56±0.54), (-2.07±0.95), (1.13±0.55) N, respectively, significantly higher than those in Group A (P<0.05), but there were no significant differences compared to Group C (P>0.05). Compared to the mesiodistal and buccolingual forces, the vertical forces on the target and anchorage teeth were relatively small in all three groups. Conclusions: When using 0.76 mm thick PET-G sheets to fabricate clear aligners for simultaneous molar distalization, a step size of 0.20 mm per step is recommended. To prevent buccal tipping of the molars during distalization, it is advisable to design lingual displacement for the molars and buccal displacement for the adjacent anchorage teeth to counteract the unfavorable forces, with attachments placed on the primary anchorage teeth.

A comparative study of shade-matching performance using intraoral scanner, spectrophotometer, and visual assessment

This study aimed to explore the clinical applicability of the shade-matching function in intraoral scanners. This study measured the tooth colors of maxillary anterior dentitions of 83 adults using visual matching, a spectrophotometer, and a scanner according to two color systems: VITA Classical (VC) and VITA 3D-Master (V3D). Agreement between each method was assessed by weighted Cohen’s kappa coefficient (KW, α = 0.05). For V3D, the overall agreement between the scanner and spectrophotometer (KW = 0.498) was higher than that between the scanner and visual matching (KW = 0.473). Similarly, the agreement between the scanner and spectrophotometer (KW = 0.283) was higher than that between a scanner and visual matching (KW = 0.140) for VC. Regarding tooth position, the highest agreement between the scanner and spectrophotometer was observed on the right central incisor (KW = 0.542) for V3D. Tooth color measurement with a scanner was comparable to that with a spectrophotometer, especially on the central incisors when using the VITA 3D-Master system. A scanner could serve as an alternative to a spectrophotometer for shade selection. However, color matching should still be visually verified.