Journal of Dental Sciences
Volume 7, Issue 1 , Pages 72-76, March 2012

The Collum angle of the maxillary central incisors in patients with different types of malocclusion

  • Yen-Wen Shen

      Affiliations

    • School of Dentistry, College of Medicine, China Medical University, Taichung, Taiwan
    • Department of Dentistry, China Medical University Hospital, Taichung, Taiwan
    • These authors contributed equally to this work.
    • ,
  • Jui-Ting Hsu

      Affiliations

    • School of Dentistry, College of Medicine, China Medical University, Taichung, Taiwan
    • These authors contributed equally to this work.
    • ,
  • Yi-Hui Wang

      Affiliations

    • Department of Dentistry, China Medical University Hospital, Taichung, Taiwan
    • ,
  • Heng-Li Huang

      Affiliations

    • School of Dentistry, College of Medicine, China Medical University, Taichung, Taiwan
    • ,
  • Lih-Jyh Fuh

      Affiliations

    • School of Dentistry, College of Medicine, China Medical University, Taichung, Taiwan
    • Department of Dentistry, China Medical University Hospital, Taichung, Taiwan
    • Corresponding Author InformationCorresponding author. School of Dentistry, College of Medicine, China Medical University, 91 Hsueh-Shih Road, Taichung 404, Taiwan.

Received 23 August 2011; accepted 16 December 2011. published online 22 February 2012.

Article Outline

Abstract 

Background/purpose

The Collum angle (the supplementary angle of the crown-root angle) of the maxillary central incisors is extremely important for patients who are undergoing orthodontic treatment and who are to receive an implant restoration. However, there is no report on the Collum angle in Taiwanese. Therefore, the purpose of this study was to evaluate the Collum angle of the maxillary central incisors in Taiwanese patients with different types of malocclusion.

Materials and methods

This study collected 124 samples of lateral cephalometric radiographs (38 radiographs from male patients and 86 from female patients). The age of sampled patients ranged 8–58 (mean, 19.9) years. Samples were divided into four groups according to the malocclusion type, and the Collum angle of the maxillary central incisors in each group was measured. A one-way ANOVA and the Scheffe test were used to compare whether or not the angle differed among the groups.

Results

The average value of the Collum angle was 6.1° ± 5.2° for class-I malocclusions, 5.3° ± 4.2° for class-II division-I malocclusions, 10.6° ± 4.4° for class-II division-2 malocclusions, and 5.6° ± 5.1° for class-III malocclusions. A statistical analysis showed that the Collum angle of the maxillary central incisors for patients with class-II division-2 malocclusions significantly exceeded values in the other three groups.

Conclusion

Compared to groups with other malocclusion types, the Collum angle of natural teeth for patients with class-II division-2 malocclusions was the greatest.

Keywords: cephalometry, Collum angle, crown-root angle, malocclusion, maxillary central incisors

 

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Introduction 

In recent years, dental implant surgery has been widely applied as a method for treating missing teeth. Normally, the survival rate of dental fixtures in the maxillary anterior zone is quite high.1 However, in the maxillary anterior zone, special malocclusion conditions in patients may cause the angle between the fixture implanted into the maxillary alveolar bone and the externally connecting abutment to be excessive, necessitating the use of an angled abutment.2, 3 Previous studies indicated that when using an angled abutment in the anterior zone, stresses are concentrated on the turning point between the buccal side of the fixture and the abutment, causing the gum at this point (the turning point) to experience postsurgery tension, thereby creating the possibility of gingival recession.4, 5, 6, 7 Gingival recession may lead to cosmetic defects. Additionally, if soft tissue graft is used in an attempt to repair exposed fixtures, the persistence of tension will cause the repaired gums to recede again. Studies indicated that the extent of recession is related to the bending angle.4, 5, 6 Otherwise, using an angled abutment may also cause nonaxial occlusal forces, leading to sequelae of abutment screw fracture, abutment screw loosening, or a reduction in osseointegration.8 Therefore, understanding the crown-root angle (the angle formed by the intersection of the long axes of the crown and root) in patients with different types of malocclusion is a critical issue.

Using lateral cephalometric radiographs is the most common method for investigating the crown-root angle, also known as the Collum angle (the supplementary angle of the crown-root angle).9, 10, 11, 12, 13, 14 Although computed tomography (CT)15 and cone-beam CT (CBCT)16, 17 can supply three-dimensional spatial structural information, using cephalometric radiographs provides sufficient information about the central incisors. Additionally, in dental clinics, CT and CBCT are not as easy to obtain as cephalometric radiographs, reducing their applicability.

Previous studies indicated that the Collum angle differs among groups with different types of malocclusion.9, 10, 11, 13, 14 However, previous research largely investigated the crown-root angle or Collum angle from the perception of orthodontic treatment, mainly because dental implant surgery was not common 20–30 years ago. To the present, no related research reports (research on the crown-root angle or Collum angle) regarding Taiwanese patients exist. The aim of this study was therefore to determine the Collum angle of the maxillary central incisors in Taiwanese patients with different types of malocclusion using cephalometric radiographs.

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Materials and methods 

Subjects 

Subjects of this study were patients in the Department of Orthodontics at the Dental Department of China Medical University Hospital (Taichung, Taiwan). The research studied radiographs from 124 patients, including 38 male and 86 female patients. The ages ranged 8–58 (mean, 19.9) years. The orthodontists categorized patients into four groups according to the malocclusion type using Angle's classification by a model analysis: class-I, class-II division-I, class-II division-II, and class-III malocclusions. Moreover, in order to clearly measure the Collum angle of the maxillary central incisors on lateral cephalometric radiographs of all patients, researchers had to be able to identify the natural tooth axis of the maxillary central incisors; therefore, no prostheses (posts, dental implants, or fixed partial dentures) could be present in the anterior zone. Additionally, lateral cephalometric radiographs showing severe crowding or mixed dentition in the anterior zone were excluded from the analysis.

Collum angle measurements 

After sketching the maxillary central incisor type from the lateral cephalometric radiographs, the single observer in this study (Dr. Y-H Wang) joined the superius point of the incisal edge and the middle point of the cementoenamel junction to depict the crown axis, and then joined the middle point of the cementoenamel junction with the root apex to depict the longitudinal axis. The Collum angle was then measured, as shown in Fig. 1.

The accuracies of the measurements were validated before analyzing the Collum angle of the maxillary central incisors. Two statistical analyses were used to assess the reliabilities of intraexaminer and interexaminer measurements. The interexaminer error was determined by measuring the Collum angle of maxillary central incisors once by each of two examiners, and the intraclass correlation coefficient (ICC) and P value of the repeated-measures analysis of variance (ANOVA) were 0.951 and 0.832, respectively. The intraexaminer error was determined by measuring the Collum angle of the maxillary central incisors in a certain lateral cephalometric radiograph five times by a single examiner. The ICC and P value of the repeated-measures ANOVA tests were 0.983 and 0.996, respectively. These values indicated that the intraexaminer and interexaminer errors of this method could be neglected in this study.

Statistical analysis 

SPSS 13.0 for Windows (SPSS, Chicago, IL, USA) was used for the statistical analysis. Values of the malocclusion types measured in the four groups were entered into the software, and the critical point was established at α = 0.05. The Scheffe test was used to examine whether or not any statistically significant differences existed among the four groups.

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Results 

The class-I malocclusion group had 33 samples; the class-II division-1 malocclusion group had 32 samples; the class-II division-2 malocclusion group had 28 samples; and the class-III malocclusion group had 31 samples. The distribution is shown in Table 1.9, 10, 14 Multiple comparisons of samples among the four groups showed that the mean of the class-II division-2 malocclusion group significantly exceeded that of the other three groups (Table 2).

Table 1. Reference Collum angles (or crown-root angle) in different malocclusion types (expressed in degree).
Malocclusion typeThis studyDelivanis10Bryant9bWilliams14
Sample numberMean ± SD95% Confidence intervalMinimumMaximumMean ± SDMean ± SDbMean ± SD
Lower boundUpper bound
Class I336.1 ± 5.24.27.90.019.01.5±4.4a177.5 ± 4.5b−0.7 ± 4.9
Class II-1325.3 ± 4.23.86.8−1.513.5179.4 ± 4.0b−1.7 ± 6.3
Class II-22810.6 ± 4.48.912.3318.06.1±5.9175.2 ± 5.1b1.2 ± 5.9
Class III315.6 ± 5.13.77.42.516.01.5±4.4a178.6 ± 4.7b0.0 ± 5.3

aClass I, Class II-1, and Class III in the same pool.

bin crown-root angle.

Table 2. Multiple comparisons.
Malocclusion typeMean differenceStandard deviationSignificant95% Confidence interval
Lower boundUpper bound
Class IClass II-10.781.180.932−2.564.12
Class II-2−4.55∗1.220.004−8.00−1.09
Class III0.511.190.980−2.863.87
Class II-1Class I−0.781.180.932−4.122.56
Class II-2−5.33∗1.230.001−8.81−1.85
Class III−2.741.200.997−3.663.12
Class II-2Class I4.55∗1.220.0041.098.00
Class II-15.32∗1.230.0011.858.81
Class III5.05∗1.240.0011.558.56
Class IIIClass I−5.061.190.980−3.872.86
Class II-10.271.200.997−3.123.66
Class II-2−5.05∗1.240.001−8.56−1.55

* The mean difference is significant at the 0.05 level.

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Discussion 

Currently, dental implants are a commonly used method for treating missing teeth. In the maxillary anterior zone, the phenomenon of bending to various extents exists between the crown axis and root axis. The probability of applying an angled abutment in the maxillary anterior zone is quite high. Although previous research investigated the Collum angle (or crown-root angle),9, 10, 13, 14 such studies focused on the domain of orthodontic treatment, and more importantly, did not study Taiwanese patients. Under a classification model of the four malocclusion types, this study measured the Collum angle of maxillary central incisors in Taiwanese patients.

When substances with properties of radiation and higher impermeability (e.g., a post or fixed partial dentures) are located near the site to be observed, the influence of such substances may result in artifacts18 or distortion.19, 20 Additionally, if the teeth alignment shows severe crowding or higher alveolar bone density, or if mixed dentition causes an overly complicated image overlay in the alveolar bone, these phenomena will all cause difficulty in distinguishing the maxillary central incisor types. Radiographs that showed fixed partial denture prostheses on the maxillary central incisors were not included in the samples of this study, as natural tooth axes in such cases may have already been altered. Therefore, during sample collection, care must be taken to exclude lateral cephalometric radiographs, such as those described above that negatively influence the degree of identification, to reduce measurement errors.

There are several explanations for the formation of the Collum angle. Backlund indicated that research relating to tooth morphology and overbite proposed that the force of the lower lip influences the growth of the maxillary central incisors, causing the phenomenon of bending,21 leading to formation of the Collum angle. Other scholars indicated that heredity is also a primary cause of maxillary central incisor bending.22

The age range of the 124 subjects was 8–58 years, with some of the young patients having mixed dentition. However, the maxillary anterior zone of all patients where the research focused on contained permanent dentition. Therefore, the research results were not influenced by age differences.

The results of this study showed that the Collum angle of the class-II division-2 malocclusion group significantly differed from the other three malocclusion group types. These results showed a trend (Table 1) similar to those of other researchers such as Delivanis,10 Bryant,9 and Williams.14 Compared to research references, the results of this study showed greater Collum angles (Table 1). We inferred that this may have been due to the influence of differences in hereditary genes between Western and Oriental races. Bone development in Oriental races tends towards bimaxillary protrusion; therefore, Oriental races have greater tooth axis bending to compensate for bony protrusion.

The results of this study imply that if dental implants are used in patients with a class-II division-2 malocclusion, the probability of using an angled abutment is also greater. However, using an angled abutment can cause stress to concentrate in the cortical bone zone contralateral to the abutment turning point.4, 5, 6 In other words, if an angled abutment is used in the maxillary anterior zone, stresses will concentrate on the facial cortical bone zone; i.e., the alveolar ridge under the free gingival margin. When stress is concentrated on the alveolar ridge of the facial profile in the maxillary anterior zone, the covering gingival tissue in this zone experiences considerable tension. If an undue external force (such as damage caused by excessive force during gingival retraction) or eccentric occlusal overload is imposed in addition to this tension, gingival recession may occur with adverse cosmetic effects.

Additionally, the alveolar ridge of the facial profile in the maxillary anterior zone is usually thin, and when implant-supported prostheses begin to experience occlusal forces, the phenomenon of microvertical bone loss is highly likely to occur. According to the theory of the biological width constant, health gingival tissues also recede along with resorption of the alveolar ridge, causing uneven edges of the free gingiva in the anterior cosmetic region and a discordant cervicoincisal length of the teeth.

Lapatki researched differences in the level of the lip line and resting lip pressure between patients with a class-II division-2 malocclusion and a class-I malocclusion.23 Results showed that patients with a class-II division-2 malocclusion had a higher lip line, and the resting lip pressure had a positive value on the side margin of the maxillary central incisors but a negative value in the cervical tooth zone. Patients with a class-I malocclusion showed opposite phenomena regarding the lip line and resting lip pressure. Therefore, Lapatki proposed that the levels of the lip line and lip pressure are external causal factors of bending between the crown and root long axes in maxillary anterior teeth.

This study has several limitations. The first is because the main purpose of this study was to measure the Collum angle, researchers did not measure the incisor shape. Second, although 124 samples of patient data were gathered in total, after categorization into the four malocclusion type groups, the number of samples in the class-II division-2 malocclusion group was less than 30. In the future, the sample sizes should be increased to ensure a more complete analysis.

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Conclusion 

In regards to the Collum angle between the crown axis and root axis in maxillary central incisors, among patients with different types of malocclusion, the class-II division-2 malocclusion group showed a significantly greater Collum angle.

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References 

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PII: S1991-7902(12)00011-6

doi:10.1016/j.jds.2012.01.010

Journal of Dental Sciences
Volume 7, Issue 1 , Pages 72-76, March 2012

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