Twin Block Research Articles

Effect of Clark’s twin block appliance and upper premolar extraction treatment modality on smile aesthetics in skeletal class II malocclusion: a retrospective cross-sectional study

ABSTRACT Introduction Treatment undertaken during growth has various advantages over camouflage treatment including an improved profile and treatment stability. The objective of this study was to compare pre- and post-treatment smile variables in class II malocclusion population treated via functional appliance or upper first premolar extraction. Materials and methods A cross-sectional study was conducted at a tertiary care hospital that included frontal closeup smile (FCS) pictures of 40 patients treated with Clark’s twin block (CTB) appliance and upper premolar extraction (UPE). Smile ratios were calculated, and improvement in smile aesthetics were scored on a visual analogue scale (VAS) by a panel of raters of laypersons, general dentists and orthodontists with 20 subjects in each panel. Friedman and Wilcoxon signed rank tests were used to determine differences between pre-, mid- and post-treatment smile variables. Independent t-test was used to measure differences in improvement of smile aesthetic scores, while simple and multiple linear regression analyses were used to determine any associations between smile aesthetic scores and variables. Results CTB group showed highly statistically significant differences for smile index (SIR), interlabial gap ratio (IGR), visible dentition width ratio (VDWR), archform ratio (AFR), mandibular incisal show ratio (MnIR) and smile arc ratio (SAR). On comparison of post-treatment smile variables between the two treatment groups, statistically significant differences were observed for buccal corridor ratio (BCR) (p = 0.01) and AFR ratios. Conclusions Higher smile improvement scores were seen with CTB treatment with orthodontists rating it higher than UPE. Improvement in maxillary incisal ratio causes an increase in smile aesthetic scores.

Evaluation of Skeletal and Dentoalveolar Changes in Patients With Class II Div 1 Malocclusion Treated With Twin Block Appliance.

Objective The study was focused on evaluating the change in mandibular morphology following the Twin Block appliance therapy and recording its effect on the maxilla and maxillary dentoalveolar complex. Also, the results of the Twin Block appliance between males and females were compared. Material and methods In this two-armed retrospective cephalometric study, 30 patients (mean age 12 years) treated with Twin Block appliance for the period of 8-12 months were chosen, and their records were obtained to analyze. These results were compared with 15 control subjects of the same age group chosen from the American Association of Orthodontics Foundation (AAOF) growth legacy collection: Michigan Growth Study Class II subjects. Cephalometric tracing was done, and data was processed for descriptive statistical analysis. Results Paired sample t-test and ANOVA test were performed to evaluate the differences in the pre-treatment (T1) and post-functional (T2) values. ∠ANB showed a mean difference of -4.71°±1.55° for males and 6.22°±6.78° for females, which is significant. The mandibular length (Co-Gn), for male subjects, the mean difference was 5.14±1.74 mm, and for female subjects, it was 6±2mm, which is highly significant; 49.88% of skeletal changes and 50.12% of dentoalveolar changes were reported to bring about Class II correction with Twin Block. Conclusion A successful increase in mandibular length was achieved using a Twin Block as a functional appliance. Also, the significant maxillary restraining effect was recorded. More skeletal changes were observed in males than females.

Correction of Skeletal Class II Malocclusion in a Growing Child Using Standard Twin Block: A Case Report

Mandibular defiiency in a Class II malocclusion is a frequently encountered condition that can be managed with myofunctional appliance in a growing child. An 11-year-old patient presented with a complaint of forwardly placed upper front teeth. The patient had a convex facial profie, acute naso-labial angle, deep mento-labial sulcus with lip trap. Clinically the patient showed positive VTO. The clinical fidings and cephalometric analysis indicated skeletal Class II jaw bases owing to prognathic maxilla and retrognathic mandible with Angle’s Class II division 1 malocclusion. CVMIshowed that the patient was in his growth phase. The treatment was done with a standard twin block appliance for 9 months followed by fied orthodontic treatment. The post functional phase showed correction of skeletal class II jaw base and marked improvement in the facial profie from convex to straight. It was later followed by fixed orthodontic treatment in the second phase upon completion of which bonded lingual retainer and wrap around retainers were given in the upper and lower arch. The total duration of the treatment was 23 months.

Efficacy of a modified twin block appliance compared with the traditional twin block appliance in children with hyperdivergent mandibular retrognathia: protocol for a single-centre, single-blind, randomised controlled trial

IntroductionCompensatory mouth breathing, caused by nasopharyngeal obstructive diseases, is the main cause of hyperdivergent mandibular retrognathia in children. Such deformities require effective growth guidance before pubertal growth peaks. The traditional...

Incline Correct: A Novel Device for Accurate Inclination of Twin Block Appliances

Retrognathic mandible is the most common feature in growing children with skeletal Class II malocclusion. This does not self-correct with growth. Functional appliances are known to exert beneficial effects to improve this skeletal pattern. Among several removable functional appliances, Twin Block is the most preferred. Twin Blocks are designed for full-time wear such that maximum benefit from functional forces can be obtained. The maxillary and mandibular bite blocks occlude at a 70° angle on complete closure. It is important to angulate the inclines at exactly 70°, as an increase in this angulation will require a conscious effort from the patient. Incline Correct is designed to accurately measure and construct inclines at 70° to the occlusal plane.

Salivary Biomarker Levels in Children with Sleep Problems Before and After Twin Block Therapy.

Disturbances in sleep have a wide-ranging effect on a child's life profoundly impacting the standard of living. The aim of this study was to investigate levels of Salivary Tumor Necrosis Factor-Alpha (TNF-α) and Malondialdehyde (MDA) in a group of children with class II malocclusion and sleep problems before and after twin block appliance therapy. Eleven children aged 8-12 years with skeletal class II malocclusion and at least one sleep disorder participated in the study. All children were subjected to a recording of their sleep history and a clinical and radiographic examination. Pre-treatment levels of salivary TNF-α and MDA were recorded. A twin block appliance was custom made and delivered to every child. After a minimum follow-up period of 9 months, all children were recalled for a re-evaluation of salivary biomarker levels. Levels of salivary biomarkers TNF-α and MDA significantly decreased in children following myofunctional therapy using a twin block appliance. The measurement of TNF-α and MDA could be used as an alternative and noninvasive method to evaluate prognosis of twin block therapy for children with sleep-disordered breathing (SDB).

Effects of twin-block appliance on upper airway parameters in OSA children with class II malocclusion and mandibular retrognathia: a CBCT study.

Correction of class II mandibular retrognathic skeletal malocclusion with twin-block appliance resulted in a significant increase in upper airway volume, MCA, anteroposterior and lateral distances of the MCA at the level of the oropharynx, MCA at the level of the hypopharynx and upper airway length, and a significant decrease in AHI, but it had no effect on nasopharynx parameters. • CBCT imaging has been shown to be an effective and precise diagnostic tool for analyzing the upper airways and craniofacial structures. • Twin block appliance may be an effective treatment modality in children with OSA. • Minimal cross-sectional area of upper ways may be the most relevant potential parameter when explaining how the upper airway anatomy plays role of in the pathogenesis of pediatric OSA. • Twin block appliance induced favorable changes in upper airway morphology (oropharynx area mainly) and respiratory parameters in OSA children with class II malocclusion.

Effect of twin block and forsus on Pharyngeal airway dimensions: A comparative study

The objective of this study was to evaluate and compare the effects of Twin Block and Forsus on the Posterior Airway Passage (PAP) and Posterior pharyngeal wall Thickness (PPWT) in the treatment of Class II division 1 malocclusion. This was a 2-arm parallel, randomized controlled trial. A total of 24 Class II division 1 malocclusion patients indicated for treatment with functional appliances were randomized and equally divided among Twin Block and Forsus (3M Unitek Corp, Monrovia, Calif) groups. Skeletal changes, PAP changes and PPWT were compared using Twin Block and Forsus. Block randomization was determined by a computer-generated random number table. Blinding was performed for both participants and data analyser. 24 patients were analysed and statistical analysis were carried out using Student’s t-test and T test of Equality of Means (P <0.05). Significant increase in oropharyngeal and hypopharyngeal dimensions with no dimensional changes of nasopharynx, dimensional changes in soft palate thickness and length, and decompensatory action in thickness in the posterior pharyngeal wall was seen with both the appliances. On intergroup comparison insignificant results were observed between both the appliances indicating similar effect on PAP and PPWT. Both Twin Block and Forsus are effective in improving PAP and PPWT while correcting Class II malocclusion.

Early Intervention of Skeletal Class II Malocclusion by Twin Block Appliance Therapy

Early Intervention of Skeletal Class II Malocclusion by Twin Block Appliance Therapy

Comparison of invisalign mandibular advancement and twin-block on upper airway and hyoid bone position improvements for skeletal class II children: a retrospective study

BackgroundThis study is to evaluate and compare the improvement of upper airway morphology and hyoid bone position in children with Class II mandibular retrusion treated with Invisalign mandibular advancement (MA) and Twin-Block (TB) appliances, utilizing cone beam computed tomography (CBCT).Methods32 children aged between 8 and 11.5 years old were included in this study, with an average age of 10.2 years old. These children were divided into two groups, MA and TB, with 16 children in each group. Changes in upper airway morphology and hyoid bone position before and after treatment were analyzed using CBCT.Results(1) Changes in upper airway before and after treatment: the oropharynx volume (Or-V), the oropharynx minimum cross-sectional area (Or-mCSA), the hypopharynx volume (Hy-V), and the hypopharynx minimum cross-sectional area (Hy-mCSA) in both the MA and TB groups increased after treatment, and the differences were statistically significant (P < 0.05) compared to pre-treatment status. (2) Changes in hyoid bone position before and after treatment: The distances between H point and third cervical vertebra (H-C3), H point and pogonion (H-RGN), H point and mandibular plane (H-MP), H point and Frankfort horizontal plane (H-FH), H and S point (H-S), and H point and palatal plane (H-PP) in both the MA and TB groups increased after treatment, and the differences were statistically significant (P < 0.05).ConclusionBoth MA and TB appliances effectively improved the structural narrowness of the upper airway and reduced respiratory resistance, thus improving breath quality. However, MA showed more effectiveness in improving the narrowest part of the hypopharynx compared to TB. Both appliances also promoted anterior downward movement of the hyoid bone, which opens the upper airway of the oropharynx and hypopharynx and helps the upper airway morphology return to normal range.

Skeletal Effect of Modified Twin Block with Clear Plates Versus Conventional Twin Block in Class II Malocclusions – a Randomized Controlled Trial of Functional Appliances

Purpose: The aim of this in-vivo study was to evaluate the skeletal changes of a modified Twin Block with clear plates versus a conventional Twin Block appliance in skeletal class II patients. Methods and Materials: A total of 32 patients with skeletal class II malocclusion contributing to mandibular retrognathism were involved. The sample was divided into two groups: group A: 16 patients will undergo to orthodontic treatment with modified Twin Block with clear plates; group B: 16 patients will undergo to orthodontic treatment with conventional Twin Block appliance. After 12 months of treatment a cephalometric radiograph was taken in central occlusion to study skeletal changes. Independent sample T-test was used for studying significance between groups. Results: There were significant differences in MP-SN; MP-SPP and SN-NPG values. While there were no statistically significant differences in SNA, SNB and ANB values. A significant difference was observed after 12 months of treatment for each group (P&lt;0.05). Conclusion: Modified Twin Block with clear plates is an effective alternative device to treat skeletal class II malocclusion with vertical growth pattern.

A service evaluation of patients requiring growth modification in a public service setting.

Aim To conduct a service evaluation of patients who had functional appliance treatment to correct Class II malocclusions in a public orthodontic clinic. To evaluate the effect of prioritisation and earlier treatment of these patients on treatment duration and patient compliance. Methodology The prioritised treatment group (PTG) had twin block appliances fitted when they were 11 or 12 years old. In comparison, the routine treatment group (RTG) had twin block appliances fitted when they were 13 or 14. Electronic patient records were screened to find a sample of 100 patients from each cohort. The number of compliance issues, functional appliance treatment duration, fixed appliance treatment duration and total treatment duration was recorded retrospectively from patient charts. Results While mean total treatment time was similar across the two cohorts, the PTG did have significantly shorter fixed appliance treatment durations than the RTG. The PTG was also found to have better compliance than the RTG. Conclusion Prioritising patients who require functional appliance treatment does not reduce total treatment duration. A correlation between earlier treatment, improved patient compliance, and a shorter course of fixed appliance therapy can be seen, which may prove clinically beneficial. Further research in this area would be valuable.

A Cephalometric Study of Pharyngeal Dimensions Following Twin Block Treatment

Objective: To assess and compare changes in pharyngeal airway widths (PAW) using lateral cephalograms before and after treatment with a removable twin block appliance. Methodology: Lateral cephalogram records were taken before (T0) and after (T1) the treatment of 50 Class II subjects (ANB&gt;40; 28 males, 22 females; mean age 12.6 years) using the removable twin block appliance. The study period spanned 12 months. Airway volumes, including upper airway width (UAW), middle airway width (MAW), and lower airway width (LAW), were compared between T0 and T1. The data were analyzed using SPSS statistical software via paired t-test. A p-value of ?0.05 was considered statistically significant. Results: A total of 50 patients were included in the study, and airway changes were analyzed at two different times prospectively (T0 and T1). The male-to-female ratio was 1:0.8 (44% females, 56% males). The mean upper airway width (UAW) at T0 and T1 was 14.04 mm and 15.3 mm, respectively. The mean middle airway width (MAW) at T0 and T1 was 8.8 mm and 11.8 mm, respectively, while the mean lower airway width (LAW) at T0 and T1 was 7.5 mm and 10.2 mm, respectively. The mean age was 12.6 years, and the mean BMI was 21. The mean SN-Md angle was 31.8 degrees. At T1, a significant increase in airway volume was observed in upper airway width (UAW), middle airway width (MAW), and lower airway width (LAW) (P=0.000). Conclusion: Treatment with the Twin Block Appliance in growing subjects resulted in an increase in the overall posterior pharyngeal airway volumes.

Conventional Twin-Block Versus Cervical Headgear and Twin-Block Combination: Therapeutic Effects on the Craniofacial Structures in Growing Subjects.

To compare the short-term effects of the conventional twin-block (TB) appliance and the cervical headgear TB (CHG-TB) appliance on craniofacial structures. The retrospective controlled study examined lateral cephalograms taken from 46 growing subjects. Individuals were divided into two groups according to the treatment. Group I consisted of 15 individuals (9 girls, 6 boys, mean age: 12.34±1.23 years) treated with the TB appliance and Group II consisted of 16 individuals (9 girls, 7 boys) treated with the CHG-TB appliance (mean age: 12.50±1.30 years). To distinguish the treatment effects of these appliances on growth, a control group of 15 untreated individuals (9 girls, 6 boys, mean age: 11.82±1.16 years) was included from the archives. Significant improvements were found in the interdental and maxillo-mandibular measurements in the treatment groups (p<0.001). Significant differences were observed in the SNA, SN/PP, and SN/GoGn values in the CHG-TB group compared to other groups (p<0.05). The mandible showed a significant downward movement in both treatment groups compared with the control group (p<0.001), while the change in SNB angle was statistically significant only in the TB group compared to the control group (p<0.05). Lower incisors showed significant proclination only in the TB group (p<0.05). The CHG-TB appliance was found to be more effective in limiting maxillary growth and preventing lower incisor proclination compared with the TB appliance, whereas the TB appliance was more effective in anterior mandibular movement.

Comparison of masticatory myofunctional rehabilitation combined with conventional functional appliances for the treatment of class Ⅱ, division 1 malocclusion. A retrospective cohort study

ObjectiveTo estimate the clinical efficacy of early masticatory myofunction rehabilitation combined with conventional functional appliances for the treatment of class Ⅱ, division 1 malocclusion in orthodontic children during the growing phase. Materials and methodA comparative retrospective cohort study, enrolled patients diagnosed with class Ⅱ/1 in the stage of late mixed or early permanent dentition. Patients were divided into a TBA group (Cohort 1): receiving Twin-block appliance treatment; and a MMR group (Cohort 2): receiving either early masticatory myofunction rehabilitation as adjunctive therapy combined with the same conventional functional appliances. The study variables were active (Phase 1) treatment duration, oral esthetic subjective impact score (OASIS), several cephalometric indices calculated from X-ray photographs, the maximum voltage (mV) and asymmetry index (AsI) of anterior temporalis (TA) and masseter muscles (MM) before and after treatment. Complications were also recorded. ResultsA total of 424 cases were enrolled. The mean treatment duration in the MMR group was 168.33 days (SD: 25.43) and 215.00 days (SD: 28.81) in the TBA group; mean difference: -46.67 days (95% CI: [-81.62, -11.71]), P<0.001. For the OASIS outcome measure, there was no statistically significant difference between the mean total scores for the MMR group (18.83±7.73) or TBA group (17.67±6.47) groups adjusted to include pre-treatment OASIS scores (P = 0.783). After treatment, sella-nasion-B point (SNB), mandibular incisor angle, maxillary base and mandibular base in both two groups were significantly increased, while AB plane angle (ANB), maxillary incisor angle, overjet and overbite were significantly decreased. The mV and AsI of TA and MM were also improved following treatment. However, no significant differences were observed between two groups. ConclusionOur results confirmed that early masticatory myofunction rehabilitation in combination with conventional TBA for patients in the growing phase was significantly effective in the management of class Ⅱ/1 in orthodontic treatment, which could significantly shorten the treatment duration and had the similar improvement in the cephalometry data, OASIS scores and masticatory muscles function when comparing to conventional TBA alone.

The effect of text message reminders on compliance with Twin Block appliances: A randomised controlled trial.

The aim of this study was to evaluate whether text reminders influence patient compliance with Twin Block appliances. The null hypothesis was that there was no statistically significant differences in Twin Block compliance between those who receive text reminders and those that do not. Single-blind parallel randomised controlled clinical trial. Health Service Executive (HSE) orthodontic outpatient clinic in Dublin, Ireland. A total of 59 patients aged 11-15 years with a 5a Index of Orthodontic Treatment Need (IOTN grade) starting treatment with Twin Block appliances. A computer-generated unstratified allocation sequence was used to randomise the participants into the control group (CG) or the text group (TG). Both groups were asked to wear their appliances full-time. In addition to the same verbal and written instruction received by the CG, the TG received text message reminders, every 3 days, to wear their appliances. The primary outcome measure was wear time reported by Theramon® sensors embedded in the appliances. Data on wear time were uploaded from the Theramon® sensors onto cloud software. Participants in both groups were asked to fill out wear diaries and submit these at each visit. Treating clinicians and the primary investigator were blinded to the allocation group. Participants were followed up for 4 months. Participants were not blinded to their treatment group. In total, 29 participants were allocated to the CG and 30 to the TG. The data for 53 participants were analysed, 24 from the CG and 29 from the TG. The median hours/day of wear recorded using the Theramon® sensors was 13.77 (interquartile range [IQR] = 10.19) for the CG and 17.72 (IQR = 5.62) for the TG. The difference in wear time recorded was not statistically significant (P = 0.16). The study concluded that text message reminders had no statistically significant influence on patient compliance with Twin Block appliances.

The use of the Hanks Herbst vs Twin-block in Class II malocclusion: A randomized controlled trial

This 2-arm parallel study aimed to compare and evaluate the efficiency of Hanks Herbst (HH) and Twin-block (TB) functional appliances in treating adolescents with Class II malocclusion. A parallel-group randomized controlled trial was undertaken in a single United Kingdom hospital. Eighty participants were recruited and randomized in a 1:1 ratio to receive either the HH or TB appliance. Eligibility criteria included children aged 10-14 years with an overjet of ≥7 mm without dental anomalies. The primary outcome was the time (in months) required to reduce overjet to normal limits (<4 mm). Secondary outcomes included treatment failure rates, complications and their impact on oral health-related quality of life (OHRQOL). Randomization was accomplished using electronic software with allocation concealed using sequentially numbered, opaque, and sealed envelopes. Blinding was only applicable for outcome assessment. Data were analyzed using descriptive statistics and regression analyses to detect between-group differences, including Cox regression for time to treatment success. HH was significantly faster than TB in reducing the overjet to within normal limits (95% confidence interval [CI], -3.00 to -0.03; P= 0.046). Mean overjet reduction was more efficient with the HH than the TB appliance (ß= 1.3; 95% CI, 0.04-2.40; P= 0.04). Fifteen (37.5%) of the participants in the TB group and 7 (17.5%) in the HH group failed to complete the treatment (hazard ratio= 0.54; 95% CI, 0.32-0.91, P= 0.02). However, TB was associated with fewer routine (incidence rate ratio= 0.81; 95% CI, 0.7-0.9; P= 0.004) and emergency (incidence rate ratio= 0.1; 95% CI, 0.1-0.3; P= 0.001) visits. Chairside time was greater with the HH (ß= 2.7; 95% CI, 1.8-3.6, P= 0.001). Participants in both groups experienced complications with similar frequency. A greater deterioration in OHRQOL was found during treatment with the TB. Treatment with HH resulted in more efficient and predictable overjet reduction than TB. More treatment discontinuation and greater deterioration in OHRQOL were observed with the TB. However, HH was associated with more routine and emergency visits. ISRCTN11717011. The protocol was not published before trial commencement. No specific external or internal funding was provided. Treatment for participants was provided as part of routine orthodontic treatment in the hospital.

Does the timing of treatment affect the clinical and psychological outcomes of Twin-block therapy?

This study is a multicenter, two-arm parallel randomized control trial carried out across 3 hospital orthodontic units. A total of 75 patients participated in the study, with 41 randomly allocated in an Immediate Treatment Group (ITG) and 34 randomly allocated into an 18-month delayed Later Treatment Group (LTG). The patients were aware as to which group they were being allocated, as were the clinicians. Both patient groups received the same twin block appliance for use during the study. The appliance was to be worn full time, including eating, but to be removed while participating in contact sports or swimming. Achieving an overjet reduction between 2-4 mm was defined as being the clinical endpoint. After this, the appliance was only worn at night up until the next data collection point, allowing an 18-month window to finish treatment. Blinded clinicians measured skeletal changes using lateral cephalograms and overjet change via study models. Psychological impact was measured using two questionnaires: Oral Aesthetic Subjective Impact Scale (OASIS) and the Oral Health Quality of Life (OHQL). Data was collected from when the patient first registered in the study (DC1), 18 months after registration (DC2) and 3 years after registration (DC3). In total, 41 boys and 34 girls were included in the study. Ages for the boys ranged from within 1 month of their 12th birthday to 13.5 years old. For the girls, the range was from within 1 month of their 11th birthday to 12.5 years old. Further inclusion criteria included a class II skeletal pattern and having an overjet of 7 mm+. Exclusion criteria included patients of non-white Caucasian origin, girls aged 12.5 years+ and boys aged 13.5 years+. Furthermore, patients with a history of cleft lip or palate, mandibular asymmetry, muscular dystrophy, general health precluding compliance with treatment, a medically diagnosed growth excess or deficiency, not dentally fit or having previously received orthodontic treatment were not included in the study. SPSS Version 25 software was used to undertake the data analysis. No formal statistical testing was undertaken. To analyze and compare the scores between the two groups, independent t-tests were used. All analysis was carried out at 0.05 level of significance. The reliability of the examining clinicians was assessed using Bland-Altman limits of agreement. As only the ITG were in treatment over the periods of DC1-DC2 a comparison of the clinical outcomes cannot be made. With regards to the psychological outcome, no statically significant impact was noted for the ITG when compared with the LTG, who had not started treatment (OASIS P = 0.53, OHQL P = 0.92). When comparing the treatment effects of twin block therapy for the ITG (DC1-DC2) and the LTG (DC2-DC3), study model overjet and cephalometric changes were not statistically significant with the exception of % lower facial height (which was deemed not to be clinically significant) and mandibular unit length. There was no statistical significance with regards to the psychological outcomes post treatment when comparing the groups (OASIS P = 0.30, OHQL P = 0.85) CONCLUSIONS: The findings of this study suggest that adolescents (with a mean age of 12 years 8 months for boys and 11 years 8 months for girls) will not be disadvantaged, either clinically or psychologically, by waiting 18 months for twin block therapy.

Comparative study of changes in the airway dimensions following the treatment of Class II malocclusion patients with the twin-block and Seifi appliances.

Functional appliances are frequently used to stimulate mandibular growth in cases of Class II malocclusion with mandibular deficiency. Many studies have reported improved pharyngeal airway passage (PAP) dimensions following functional appliance therapy in children. The present study aimed to assess changes in the airway dimensions following the treatment of Class II malocclusion patients with the twin-block and Seifi appliances. Lateral cephalograms of 37 patients with Class II malocclusion and mandibular deficiency treated with the twin-block appliance (n = 20) or the Seifi appliance (n = 17) were assessed in this before-and-after study. The preoperative and postoperative lateral cephalograms were compared to determine changes in the airway dimensions at the level of the palatal plane (PP), the occlusal plane (OP) and the 2nd-4th cervical vertebrae (C2-C4) in the 2 groups. The results were analyzed with the t test and the one-way analysis of covariance (ANCOVA). After treatment, significant changes occurred in the point A-nasion-point B (ANB) and sellanasion-point B (SNB) skeletal cephalometric indices in the twin-block appliance group, and in ANB, SNB and incisor-mandibular plane angle (IMPA) in the Seifi appliance group. The airway dimensions at the level of PP, OP and the 3rd cervical vertebra (C3) significantly increased postoperatively as compared to the baseline in the twin-block appliance group (p < 0.05). The increases in the airway dimensions at the level of PP and C3 in the twin-block appliance group were significantly greater than in the Seifi appliance group (p < 0.05). The treatment of Class II Division I malocclusion with the twin-block appliance significantly increased the airway dimensions at the level of PP, OP and C3, whereas the Seifi appliance did not cause any significant changes in the airway dimensions.

3D printed twin block: A feasibility study

AimsTwin blocks are appliances used for Class II skeletal discrepancies, where the lower jaw is positioned more posteriorly compared to the upper. The conventional method of fabrication of this appliance is tedious and labour-intensive; hence this study intends to explore the feasibility of a digital workflow to three-dimensionally (3D) print them. MethodsThree sets of twin blocks, identical except for amount of offset (0.0 mm, 0.1 mm and 0.2 mm), were designed and 3D printed for 5 anonymized scans of patients with Class II skeletal discrepancies. The intaglio surfaces of the 0.0 mm offset twin blocks were scanned and superimposed onto their original computer-aided-design files. The resultant colour maps, root mean square (RMS) deviations, and percentage in-tolerance values at thresholds of 0.1 mm and 0.2 mm were assessed. The fit and retention of all twin blocks were assessed on their 3D printed models via a fit and retention score (FRS). ResultsThe median RMS deviation was 0.10 mm; percentage in-tolerance values at thresholds of 0.1 mm and 0.2 mm were 79.90%, and 94.51%. Printing deviations occurred most often at labial and incisal edges anteriorly, and buccal and occlusal surfaces posteriorly. There was no significant difference between the total FRS for the three groups (p = 0.076). However, the frequency of satisfactory scores for upper fit (p = 0.049), lower fit (p = 0.018), upper retention (p = 0.038) and lower retention (p = 0.015) differed significantly between the three groups. ConclusionThis study demonstrated the viability of a digital workflow to 3D print twin blocks. Print accuracy was satisfactory, with 0.1 mm offset providing the best fit and retention.