-Subjects
This study was performed using pre and post-treatment study casts of consecutive subjects from the archives of the Department of Orthodontics between 2000 and 2014. The study design was in accordance with Helsinki Declaration on Ethical Principles for Medical Research Involving Human Subjects. The approval for the study was obtained from the IRB and research ethics committee of the university (Ref No. TBZMED.REC.1393.6).
Based on 80% power and significance level of 5% (14 (link)), and considering 1.5 as maximum tolerable error rate and based on standard deviation of 2.5, 45 samples were needed in each group. Patients who were treated either with or without bilateral maxillary first premolars extraction were included in this study considering the following criteria:
1. All cases were originally diagnosed as having mild to moderate skeletal Class II division 1 malocclusion.
2. None of the cases had congenital anomalies, significant facial asymmetries, or congenitally missing teeth.
3. All cases were above 16 years of age and all were in the permanent dentition.
4. All cases received no palatal expansion, functional appliance, orthognathic surgery or fixed prosthodontic therapy
5. All cases had overbite of 5% to 40% and mandibular arch crowding of ≤4 mm.
6. All cases were treated with fixed preadjusted (0.022-inch bracket slot) technique with class II elastics for non-extraction and space closure with sliding for extraction cases.
7. A clinically acceptable occlusion was established after active treatment i.e., a Class I canine relationship, an overbite between 10% and 25%, and well-aligned and inter-digitated arches.
8. Plaster dental casts were taken before and after orthodontic treatment.
These criteria were adopted to insure that post-treatment changes were not caused by poor treatment results.
-Study casts analysis
Four arch width measurements were recorded from each subject’s dental casts using a digital calliper and recording the data to the nearest 0.1 mm. These measurements included: (A) maxillary inter-canine width between the height of contour points on the main buccal ridge located at the cervical third of the canines, (B) maxillary inter-molar width between the height of contour points located gingival to buccal grooves of the first molars, (C) mandibular inter-molar width between the height of contour points located gingival to main buccal pits of the first molars and (D) mandibular inter-canine width between the height of contour points on the buccal ridge located at the cervical third of the canines (Fig.1 A).
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Landmarks on the maxillary and mandibular dental casts were located and marked with a black 0.5 mm thick pencil. Each distance was measured by two examiners, on two occasions with a 2.5-month interval between the two measurements (Fig.1 B). Intra- and inter-examiner reliability was determined using intra-class correlation coefficients (ICCs).
-Statistical methods
Statistical analysis of the data was performed with SPSS for Windows version16 (IBM, Chicago, USA). A paired sample t-test was used to evaluate the treatment changes within each group. To compare the changes in the extraction and non-extraction groups for both males and females, independent student t-test was used. Statistical significance level was established at P<0.05.
This study was performed using pre and post-treatment study casts of consecutive subjects from the archives of the Department of Orthodontics between 2000 and 2014. The study design was in accordance with Helsinki Declaration on Ethical Principles for Medical Research Involving Human Subjects. The approval for the study was obtained from the IRB and research ethics committee of the university (Ref No. TBZMED.REC.1393.6).
Based on 80% power and significance level of 5% (14 (link)), and considering 1.5 as maximum tolerable error rate and based on standard deviation of 2.5, 45 samples were needed in each group. Patients who were treated either with or without bilateral maxillary first premolars extraction were included in this study considering the following criteria:
1. All cases were originally diagnosed as having mild to moderate skeletal Class II division 1 malocclusion.
2. None of the cases had congenital anomalies, significant facial asymmetries, or congenitally missing teeth.
3. All cases were above 16 years of age and all were in the permanent dentition.
4. All cases received no palatal expansion, functional appliance, orthognathic surgery or fixed prosthodontic therapy
5. All cases had overbite of 5% to 40% and mandibular arch crowding of ≤4 mm.
6. All cases were treated with fixed preadjusted (0.022-inch bracket slot) technique with class II elastics for non-extraction and space closure with sliding for extraction cases.
7. A clinically acceptable occlusion was established after active treatment i.e., a Class I canine relationship, an overbite between 10% and 25%, and well-aligned and inter-digitated arches.
8. Plaster dental casts were taken before and after orthodontic treatment.
These criteria were adopted to insure that post-treatment changes were not caused by poor treatment results.
-Study casts analysis
Four arch width measurements were recorded from each subject’s dental casts using a digital calliper and recording the data to the nearest 0.1 mm. These measurements included: (A) maxillary inter-canine width between the height of contour points on the main buccal ridge located at the cervical third of the canines, (B) maxillary inter-molar width between the height of contour points located gingival to buccal grooves of the first molars, (C) mandibular inter-molar width between the height of contour points located gingival to main buccal pits of the first molars and (D) mandibular inter-canine width between the height of contour points on the buccal ridge located at the cervical third of the canines (Fig.
A) Maxillary and mandibular inter-arch measurements. B) Landmarks on the maxillary and mandibular dental cast.
Landmarks on the maxillary and mandibular dental casts were located and marked with a black 0.5 mm thick pencil. Each distance was measured by two examiners, on two occasions with a 2.5-month interval between the two measurements (Fig.
-Statistical methods
Statistical analysis of the data was performed with SPSS for Windows version16 (IBM, Chicago, USA). A paired sample t-test was used to evaluate the treatment changes within each group. To compare the changes in the extraction and non-extraction groups for both males and females, independent student t-test was used. Statistical significance level was established at P<0.05.
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