Introduction
This study aimed to investigate dentofacial changes in patients treated with maxillary molar intrusion with zygomatic anchors.
Methods
The study group was composed of 19 patients with anterior open bite who had intrusion of the posterior dentoalveolar segment using an acrylic appliance supported by bilateral zygomatic miniplates. The study was carried out on lateral cephalograms of the subjects taken before treatment and after intrusion.
Results
Cephalometric changes obtained with maxillary molar intrusion were statistically significant. ANB, Wits, SN-GoGn, PP-MP, ANS-Me, NA-APo, SN-OP, U1-OP, U6-NF, overjet, and overbite values were also statistically significant.
Conclusions
Posterior dentoalveolar intrusion by zygomatic anchorage was an effective method for anterior open bite treatment. Although overbite and vertical skeletal measurements changed because of posterior dentoalveolar intrusion, the soft tissue was not significantly affected.
Highlights
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Miniplates in the zygomatic buttress area intruded maxillary molars and buccal segments.
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Changes in the dentofacial structures resulted from intrusion.
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Posterior dentoalveolar intrusion by zygomatic anchorage had no effects on soft tissue.
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This method was an effective treatment for anterior open bite.
Genetic and environmental factors play a role in the etiology of anterior open bite. Skeletal morphologic features of an anterior open bite include increase in the vertical dimension and mandibular plane angle, excessive growth of maxillary posterior dentoalveolar structures, clockwise rotation of the mandible, and a large gonial angle. Multiple factors such as genetic traits, differences in growth pattern, abnormal pressure habits, lingual and orofacial muscle activities, and respiratory tract obstruction play a role in its etiology.
The etiology of open bite must be well investigated to ensure the successful treatment of these patients. Etiology oriented treatment methods are divided into 2 categories: early- and late-term.
Early term treatment options include orthopedic treatment with a preventive approach such as the following: (1) myofunctional therapy, (2) habit-breaking appliances, (3) molar intrusion using high-pull headgear, (4) vertical pull chincup, (5) functional appliances and posterior bite-blocks, and (6) molar intrusion with rapid molar intruder appliance.
Late-term treatment options include the following: (1) molar intrusion with fixed appliances, (2) extraction orthodontic treatments, (3) molar intrusion with miniplate and miniscrews or rapid molar intruder, (4) corticotomy-assisted molar intrusion, and (5) orthognathic surgery.
Treatment of open bite is very difficult in nongrowing patients. One of the treatment objectives in these patients was reducing the vertical height of the buccal segments. This approach was possible only with skeletal anchorage systems such as mini-implants, miniscrews, and miniplates. These systems meet the anchorage requirements avoiding the need for patient cooperation. ,
Infrazygomatic crest region, vestibular and palatal regions of alveolar bone, and the median and paramedian palatal regions were used as anchorage sites for maxillary posterior molar intrusion in patients in which there was sufficient bone thickness. The teeth to be intruded, the mechanics, and the anatomical structures planned to be used are decisive in the choice of the anchorage region and device.
Changes in the dentofacial structures resulting from the maxillary molar and buccal segment intrusion with miniplates placed on zygoma are presented in multiple studies and case reports. , ,
The purpose of this retrospective study was to examine the early dentofacial changes in patients undergoing maxillary molar intrusion with zygomatic anchorage.
Material and methods
The effect size in the study of Erverdi et al was calculated according to the average of the differences of the 2 dependent variables by using G∗Power software (version 3.1.3; Franz Faul University, Kiel, Germany). The effect size was 1.09, and the required number of samples that provided at least 95% power at α = 0.05 significance level was calculated as 14 (critical t = 2.1604; noncentrality parameter λ = 4.073). According to inclusion criteria, the pretreatment (T0) and postintrusion (ie, the day of removal of the intraoral appliance) (T1) records for 19 patients were completely available in archives. Therefore, a total of 19 patients were included in this study.
The records of 19 patients (5 boys, 14 girls) (mean age 16.5 years) that were used in this study were obtained from the archive of the Department of Orthodontics at İzmir Katip Celebi University, İzmir, Turkey. Cephalometric radiographs that were taken at T0 and T1 were evaluated. The mean intrusion period was 9.4 ± 0.7 months in the treatment group. Inclusion criteria were as follows: (1) appearance of incisor in the smile and rest position was normal, (2) overbite <0 mm, (3) patients at cervical vertebral maturation index 5 and 6 periods as defined by Baccetti (ie, at postpeak period) were investigated, (4) radiography image quality was good, and (5) records of patients indicated intrusion of maxillary posterior teeth was used after clinical and cephalometric evaluation.
The cephalometric analysis was performed on the Dolphin Imaging & Management Solutions software (Dolphin Imaging and Management Solutions, Chatsworth, Calif) by 1 examiner (O.Ş.). The landmarks used in the analysis of skeletal, dental, and soft-tissue measurements are shown in Figure 1 .
The main part of the zygomatic anchorage unit was a titanium miniplate with 3 screw holes (Tasarim Med, Istanbul, Turkey) ( Fig 2 ). The 1.5 mm bar, which was an extension of the miniplate, was connected to the intraoral part. The plate was adapted to the bone in the zygomatic buttress zone with 3 titanium screws, with a diameter of 2 mm and a length of 5-7 mm. A schematic view of the zygomatic miniplates is shown in Figure 2 . The placement of plates was carried out under local anesthesia in the Department of Oral and Maxillofacial Surgery at the Izmir Katip Celebi University Faculty of Dentistry.
A vertical incision approximately 1 cm in length was made in the line of the first molar, below the zygomaticomaxillary buttress region, and the mucoperiosteal flap was elevated, and the cortical bone left bare. The zygomatic anchor plates are adjusted to fit the bone surface in the buttress area, and the hook-shaped tip was set to be exposed to the oral cavity in the vestibule. The plates were fixed with the aid of titanium monocortical 5 mm and 7 mm long screws. Then the incision area was closed with 4.0 silk suture.
The expansion screw (G&H Orthodontics, Franklin, Ind) was activated 10 turns and then set on the maxillary jaw plaster models. The 1.1-in full round stainless steel tilted balcony-like extension was bent at the vestibule level of posterior teeth and 6-9 mm and 12 mm nickel-titanium close coil springs (Masel, Bristol, Pa) were attached to it. These attachments were waxed on the model, and cold-cure acrylic (Vertex Dental, Zeist, Holland) bite-blocks completely covering the posterior teeth were fabricated and adjusted in mouth correctly. The appliance design is shown in Figure 3 . The appliance was fixed to maxillary posterior teeth with glass ionomer cement (Ketac Cem; 3M ESPE, Seefeld, Germany). Approximately 400 g of intrusive force was applied to each posterior segment via nickel-titanium close coil springs. The hyrax screw was closed step by step to counteract the buccal tipping effect of the coil spring. When the overbite value was at least 2 mm, the intrusion was stopped, and the intraoral appliance was taken out. After completion of the impaction, orthodontic therapy was started. For stability, the maxillary first molar was connected to the zygoma plate on the buccal surface and to the transpalatal arch (TPA) from the palatal surface with wire ligature. These precautions were continued throughout the treatment.
Initial and progress photographic and cephalometric recordings of 1 of the patients are shown in Figures 4 , A and B, and 5 . The treatment results were examined on 38 lateral cephalometric radiographs obtained from 19 patients at T0 and T1.
Statistical analysis
The study variables were analyzed with SPSS statistical software (version 22; SPSS, Chicago, Ill). The measurements were performed again on randomly selected 15 cephalograms by the same examiner after 2 weeks.
The Shapiro-Wilk test was used to confirm the normal distribution of data. A paired t test was used to evaluate pre- and postintrusion differences, with a significance level of 0.05. Parametric variables were defined as mean and standard deviation.
Pearson correlation test was performed to evaluate the relationships of the data with each other. A value of P <0.05 was considered statistically significant.
Results
Intraclass correlation coefficients ranged from 0.9 to 1.00. The results of the intraclass correlation analysis related to the methodological errors showed the measurements not to affect the results and to be repeated with a nonsignificant error.
The data from skeletal, dental, and soft-tissue measurements of the T0 and T1 lateral cephalograms are summarized in Table I . Statistically significant cephalometric changes given below were observed, and the null hypothesis was thus rejected.
| Parameter | T0 | T1 | P | ||
|---|---|---|---|---|---|
| Mean | SD | Mean | SD | ||
| Sagittal skeletal measurements | |||||
| SNA, ° | 80.16 | 4.54 | 80.12 | 4.39 | 0.952 |
| SNB, ° | 75.75 | 4.55 | 76.44 | 4.14 | 0.324 |
| ANB, ° | 4.05 | 2.00 | 2.87 | 2.18 | 0.008∗∗ |
| Maxillary skeletal (A-Na Perp), mm | 0.14 | 4.58 | −0.16 | 4.61 | 0.762 |
| Mandibular skeletal (Pg-Na Perp), mm | −7.10 | 10.33 | −5.29 | 10.13 | 0.404 |
| Wits appraisal, mm | 1.64 | 3.40 | −1.91 | 2.76 | <0.001∗∗∗ |
| Vertical skeletal measurements | |||||
| Y-axis-downs (SGn-FH), ° | 62.71 | 6.00 | 61.67 | 5.46 | 0.372 |
| SN-GoGn, ° | 40.90 | 4.43 | 39.22 | 4.30 | 0.020∗ |
| SN-palatal plane, ° | 7.14 | 3.68 | 7.68 | 3.59 | 0.358 |
| Palatal-mandibular angle (PP-MP), ° | 36.37 | 3.94 | 34.43 | 5.07 | 0.050∗ |
| Sum total: N-S-Art + S-Art-Go + Art-Go-Me, ° | 403.51 | 4.29 | 402.11 | 4.11 | 0.081 |
| Anterior facial height (ANS-Me), mm | 70.52 | 5.37 | 68.71 | 5.62 | 0.037∗ |
| Convexity (NA-APo), ° | 7.76 | 4.97 | 5.31 | 5.69 | 0.038∗ |
| PFH/AFH, % | 60.64 | 3.80 | 61.15 | 3.69 | 0.415 |
| SN-maxillary occlusal plane (Max.OP) | 17.45 | 4.56 | 20.22 | 4.97 | 0.004∗∗ |
| Dental measurements | |||||
| U1-SN, ° | 109.02 | 5.11 | 108.48 | 5.65 | 0.557 |
| U1-Max.OP, ° | 126.57 | 4.85 | 128.94 | 5.26 | 0.025∗ |
| U1-NA, ° | 29.22 | 3.91 | 29.16 | 5.52 | 0.963 |
| U1-NA, mm | 5.52 | 1.46 | 5.69 | 2.09 | 0.661 |
| IMPA (L1-MP), ° | 89.62 | 6.51 | 89.92 | 6.21 | 0.778 |
| L1-NB, ° | 28.86 | 5.33 | 28.47 | 5.28 | 0.686 |
| L1-NB, mm | 6.28 | 1.81 | 6.28 | 1.51 | 0.984 |
| Interincisal angle (U1-L1), ° | 118.09 | 6.62 | 119.52 | 7.27 | 0.034∗ |
| U1-NF (perp NF), mm | 28.19 | 2.62 | 28.54 | 3.01 | 0.321 |
| U6-NF (perp NF), mm | 23.69 | 2.52 | 21.37 | 2.53 | <0.001∗∗∗ |
| L1-MP (perp MP), mm | 36.80 | 2.80 | 37.36 | 2.48 | 0.310 |
| L6-MP (perp MP), mm | 28.01 | 2.49 | 28.99 | 2.22 | 0.146 |
| Overjet | 4.74 | 1.59 | 3.43 | 1.97 | 0.015∗ |
| Overbite | −3.20 | 1.75 | −0.72 | 1.55 | <0.001∗∗∗ |
| Soft tissue measurements | |||||
| Nasolabial angle (Col-Sn-UL), ° | 108.75 | 9.57 | 104.70 | 11.58 | 0.078 |
| Lower lip to E-plane, mm | −0.14 | 2.11 | −0.78 | 2.55 | 0.147 |
| Upper lip to E-plane, mm | −3.34 | 2.13 | −3.90 | 2.64 | 0.246 |
| Nasal projection, mm | 14.30 | 1.71 | 14.95 | 2.50 | 0.207 |
| Soft tissue A point (A′), mm | 3.13 | 8.62 | 2.53 | 7.68 | 0.474 |
| Soft tissue B point (B′), mm | −10.04 | 4.69 | −8.93 | 4.22 | 0.172 |
| Soft tissue Pogonion (Pog′-Sn), mm | −9.74 | 4.90 | −8.13 | 5.80 | 0.152 |
| Soft tissue convexity, ° | 127.47 | 4.45 | 128.48 | 5.15 | 0.248 |
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