Effect of the length of orthodontic mini-screw implants on their
long-term stability:
A prospective study
Michał Sarula
; Liwia Mincha
; Hyo-Sang Parkb
; Joanna Antoszewska-Smith. Angle Orthodontist, Vol 85, No 1, 2015
Though the conclusion of the study is very logical and obvious, what is important here is the way the study has been designed to isolate the variable to be tested (length of microimplant).
Being a prospective study in design, the authors have devised a well though of study to try and isolate "length of microimplant' as a variable to be tested.
LEARNING POINT
What is interesting here is that despite various factors that may affect Microimplant stability viz patient related (systemic diseases, smoking, habits, hygiene, the level of immunity, etc), orthodontist related (treatment methodology, experience), and TISAD/TAD related (size, surface coating, and shape), The authors have tried to standardize these complex variables so that the study becomes homogeneous and the only variable that remains is the length of implant (6 mm and 8 mm)
METHODS BY WHICH STANDARDIZATION WAS DONE
1. The study included a group of generally healthy patients of the same gender (female) and age (20– 29 years), who reported toothbrushing three times per day (after each meal) and no symptoms of any oral disease. Since it is known that a patient’s right- or lefthandedness may affect the long-term result,14 this aspect was also taken into account. All of the lefthanded patients were rejected from the study group.
2. All patients presented a Class I skeletal pattern with the hyperdivergent (in the range of 1 standard deviation) angle between the maxillary and mandibular planes. Only patients with planned extraction of the lower first or second premolar were included in the study group
3. Morphology of the oral mucosa (ie, frenula) in the area of implantation was also considered: only patients without frenula potentially loading the TISAD/ TAD head while chewing or facial movement were considered
4. To provide the highest homogeneity of the study material, the optical bone density (OPD) was evaluated in each individual, applying Østravik’s protocol (Useful method of standardization)
5. To obtain the same force characteristics, the maximum anchorage was introduced only in extraction cases (first or second premolar), for the purpose of the group retraction of the lower incisors and canines
6. All mini-screw implants were screwed by the same orthodontist and always according to the same Wroclaw protocol: N Working on both sides of a dental unit N Mandatory stab incision and predrilling mode N Placing the TISAD/TAD perpendicularly to the alveolar bone, which was allowed since the TISAD/ TAD were located 3 mm beneath the mucogingival junction, and therefore the roots were not jeopardized N Placing the TISAD/TAD between the first and second molars N Loading mini-screw implants after 2 weeks with a 13-mm NiTi spring (Dentos, Daegu, South Korea) with 100–150 g of force
8.All TISAD/TAD were evaluated considering the root proximity by taking periapical radiograms. If there was no contact or overlapping of the roots adjacent to TISAD/TAD, the case was included in the study. Only TISAD/TAD with no initial mobility or perfect initial stability were included. All patients were instructed to maintain a perfect oral hygiene regimen and to use gel with chlorhexidine
8. All individuals were asked to avoid any recurrent hit against TISAD/TAD and any hard contact with the toothbrush body.
THE DISCUSSION FURTHER ANALYZES THE STUDY DESIGN
1. One method of study design might be to establish a group with a large sample size that provides many different variables and to further analyze the impact of the variables on TISAD/TAD stability.Another approach is to analyze only one variable, on the assumption that the influence of other factors on the results is eliminated to the maximum(which was attempted in this study)
2. The strategy of analyzing only one variable also has a weak point: selection of a study group of patients, in whom the effects of all known factors are eliminated—except for the effect undergoing planned analysis—is technically very difficult. However, this difficulty may be overcome if a certain degree of homogeneity (deciding on the significance results) is strictly obeyed.(this was attempted by the methods mentioned above)
3. On the other hand, high homogeneity has a kind of quid pro quo (something that comes along) limitation: it reduces the external validity of the obtained results, making them likely to match only the individuals strictly corresponding to the characteristics of the study group. Nonetheless, high homogeneity allows control of variables and facilitates the determination of the objective of further research. Therefore, it seems to be a good option for the purpose of clinical trial
STUDY DURATION - 9-12 months
Interesting studies mentioned in the article
1. META ANALYSIS Papageorgiou SN, Zogakis IP, Papadopoulos MA. Failure rates and associated risk factors of orthodontic miniscrew implants: a meta-analysis. Am J Orthod Dentofacial Orthop. 2012;142:577–595 revealed that the length of the mini-screw implant was unimportant. However, according to these authors, both the close proximity to the root and too high torque during the TISAD/TAD insertion may increase the risk of their loss.
QUESTIONS THAT ARISE
1. Is 100-150 gms per side good enough for enmasse retraction?
2. Implants were loaded 2 weeks after placement. Why? Was it to improve the initial stability of the microimplant?
Though the conclusion of the study is very logical and obvious, what is important here is the way the study has been designed to isolate the variable to be tested (length of microimplant).
Being a prospective study in design, the authors have devised a well though of study to try and isolate "length of microimplant' as a variable to be tested.
LEARNING POINT
What is interesting here is that despite various factors that may affect Microimplant stability viz patient related (systemic diseases, smoking, habits, hygiene, the level of immunity, etc), orthodontist related (treatment methodology, experience), and TISAD/TAD related (size, surface coating, and shape), The authors have tried to standardize these complex variables so that the study becomes homogeneous and the only variable that remains is the length of implant (6 mm and 8 mm)
METHODS BY WHICH STANDARDIZATION WAS DONE
1. The study included a group of generally healthy patients of the same gender (female) and age (20– 29 years), who reported toothbrushing three times per day (after each meal) and no symptoms of any oral disease. Since it is known that a patient’s right- or lefthandedness may affect the long-term result,14 this aspect was also taken into account. All of the lefthanded patients were rejected from the study group.
2. All patients presented a Class I skeletal pattern with the hyperdivergent (in the range of 1 standard deviation) angle between the maxillary and mandibular planes. Only patients with planned extraction of the lower first or second premolar were included in the study group
3. Morphology of the oral mucosa (ie, frenula) in the area of implantation was also considered: only patients without frenula potentially loading the TISAD/ TAD head while chewing or facial movement were considered
4. To provide the highest homogeneity of the study material, the optical bone density (OPD) was evaluated in each individual, applying Østravik’s protocol (Useful method of standardization)
5. To obtain the same force characteristics, the maximum anchorage was introduced only in extraction cases (first or second premolar), for the purpose of the group retraction of the lower incisors and canines
6. All mini-screw implants were screwed by the same orthodontist and always according to the same Wroclaw protocol: N Working on both sides of a dental unit N Mandatory stab incision and predrilling mode N Placing the TISAD/TAD perpendicularly to the alveolar bone, which was allowed since the TISAD/ TAD were located 3 mm beneath the mucogingival junction, and therefore the roots were not jeopardized N Placing the TISAD/TAD between the first and second molars N Loading mini-screw implants after 2 weeks with a 13-mm NiTi spring (Dentos, Daegu, South Korea) with 100–150 g of force
8.All TISAD/TAD were evaluated considering the root proximity by taking periapical radiograms. If there was no contact or overlapping of the roots adjacent to TISAD/TAD, the case was included in the study. Only TISAD/TAD with no initial mobility or perfect initial stability were included. All patients were instructed to maintain a perfect oral hygiene regimen and to use gel with chlorhexidine
8. All individuals were asked to avoid any recurrent hit against TISAD/TAD and any hard contact with the toothbrush body.
THE DISCUSSION FURTHER ANALYZES THE STUDY DESIGN
1. One method of study design might be to establish a group with a large sample size that provides many different variables and to further analyze the impact of the variables on TISAD/TAD stability.Another approach is to analyze only one variable, on the assumption that the influence of other factors on the results is eliminated to the maximum(which was attempted in this study)
2. The strategy of analyzing only one variable also has a weak point: selection of a study group of patients, in whom the effects of all known factors are eliminated—except for the effect undergoing planned analysis—is technically very difficult. However, this difficulty may be overcome if a certain degree of homogeneity (deciding on the significance results) is strictly obeyed.(this was attempted by the methods mentioned above)
3. On the other hand, high homogeneity has a kind of quid pro quo (something that comes along) limitation: it reduces the external validity of the obtained results, making them likely to match only the individuals strictly corresponding to the characteristics of the study group. Nonetheless, high homogeneity allows control of variables and facilitates the determination of the objective of further research. Therefore, it seems to be a good option for the purpose of clinical trial
STUDY DURATION - 9-12 months
Interesting studies mentioned in the article
1. META ANALYSIS Papageorgiou SN, Zogakis IP, Papadopoulos MA. Failure rates and associated risk factors of orthodontic miniscrew implants: a meta-analysis. Am J Orthod Dentofacial Orthop. 2012;142:577–595 revealed that the length of the mini-screw implant was unimportant. However, according to these authors, both the close proximity to the root and too high torque during the TISAD/TAD insertion may increase the risk of their loss.
QUESTIONS THAT ARISE
1. Is 100-150 gms per side good enough for enmasse retraction?
2. Implants were loaded 2 weeks after placement. Why? Was it to improve the initial stability of the microimplant?
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