The basics of orthodontic mechanics

The biologic cascade of events that ultimately results in bone remodeling and orthodontic tooth movement begins with the mechanical activation of an orthodontic appliance. The force systems produced by orthodontic appliances, consisting of both forces and moments, displace teeth in a manner that is both predictable and controllable. By varying the ratio of moment to force applied to teeth, the type of tooth movement experienced can be regulated by the orthodontist. Orthodontic appliances obey the laws of physics and can be activated to generate the desired force systems to achieve predetermined treatment goals for individual patients. Likewise, any orthodontic appliance can be analyzed to define the mechanical force systems it produces. Understanding the biomechanical principles underlying orthodontic appliance activations is essential for executing efficient and successful orthodontic treatment.     

The side effects of orthodontic mechanics in orthodontic treatments

The side effects of orthodontic mechanics at each tissue level (alveolar bone, periodontal ligament, gingiva, pulp, cementum, and enamel) are addressed, along with the issue of pain following orthodontic appointments, and psychobehavioral alterations observed in orthodontic patients. It is necessary to know how orthodontic treatment affects enamel health, including methods to manage these side effects, which are still a dilemma for orthodontic clinicians. It is interesting to note that the dental pulp, which lies deep in the tooth core, also reacts to orthodontic force. The way the periodontal ligament responds to light and heavy forces, in young and adult patients, with or without periodontal disease, should be considered. Root resorption is a well-recognized phenomenon following orthodontic treatment. Advances made in this area of research to identify the parameters and genes associated with this process are developing.     

The design of custom orthodontic mechanics

The straightwire appliance promises prescribed tooth positions within the arches. Unfortunately, such an outcome is not necessarily achieved, especially in the adult patient. Teeth do not always move according to a template. Continuous archwires do not allow for differentiation between active and reactive units; consequently, the correct force system is never developed. These shortcomings could be overcome by custom-designed mechanics. Here we report on the use of Dental Movement Analysis (DMA) software supported by two clinical examples. On the computerized occlusogram, DMA stimulates the desired tooth movements and computes the force vectors and moments necessary to achieve the planned result. These images enable the clinician to fabricate a custom appliance for maximum efficiency. Maximum efficiency results in minimal treatment time.     

正畸牵引治疗埋伏倒置阻生的上中切牙的受力分析

目的:通过对无萌出能力的埋伏倒置阻生上中切牙正畸牵引治疗的受力分析,探讨倒置阻生上中切牙正畸牵引治疗的最佳方法.方法:对19颗无萌出能力上颌埋伏倒置阻生牙作牵引治疗前的受力分析,进行摄片定位、拓展间隙后.行外科开窗术 正畸牵引治疗.结果:19颗埋伏牙中,治疗成功13颗(占68.4%),一般4颗(占21.1%),失败2颗(占10.5%);19颗埋伏牙平均破龈时间为6.5个月,最长12个月,最短3个月;19颗埋伏牙牙髓活力测验全部正常,未见根吸收、黏连.2颗唇侧出现2mm和3mm的牙龈退缩,1颗出现1mm的边缘骨丧失,1颗未能完全进入相应的牙位,需以后配合光固化或烤瓷再度修复.1例因牙根严重弯曲,不能进入相应的牙位,被迫拔除,1例牵引3个月后萌出,因无时间复诊而放弃治疗,未排齐,其余均牵引入列.结论:准确的定位、恰当的牵引方向和位置、适当的牵引力将直接决定埋伏倒置阻生牙的移动状况.     

An assessment of orthodontic treatment using occlusal indices.

This retrospective study was carried out to assess the need for orthodontic treatment and the standard of treatment provided by the Government Dental Clinic in Singapore. The materials for this study comprised the pre-treatment and post-treatment study models as well as the clinical notes of 194 patients who were consecutively debanded over a three-month period in 1996. The pre- and post-treatment models were assessed using the Index of Orthodontic Treatment Need (IOTN) and the Peer Assessment Rating (PAR) index. The results indicated that a large proportion (81.4%) of the cases were treated with extractions. The majority of the cases were treated by upper and lower fixed appliances. Treatment was completed, on average, in 21 visits spread over 2.1 years. The result also demonstrated that the majority of the patients had genuine need for treatment for both dental and aesthetic reasons. Eighty-two percent of patients fell into the category of "need" for treatment based on dental health grounds. The mean PAR score reduction was 77%, indicating a high standard of treatment.     

Principles of orthodontic mechanics in orthognathic surgery cases

In orthognathic surgery cases the treatment objectives, extraction patterns, and types of mechanics used are frequently the reverse of those used in conventional orthodontics. Thus, starting cases orthodontically and then, if unsuccessful, referring them for surgery often produces compromised results. Presurgical intra-arch objectives include positioning of the incisors in "ideal" positions, establishment of correct torque, and elimination of tooth-size discrepancies so as to permit the establishment of Class I canine and molar relationships after surgery. Presurgical objectives in the sagittal plane focus on removal of dental compensations. This may require the use of Class III elastics in Class II cases (and vice versa), thus allowing for maximal surgical correction of the underlying skeletal deformity. In the transverse plane, differentiation of skeletal from dental problems as well as identification of relative and absolute discrepancies should be carried out presurgically. Lateral corticotomies or segmental maxillary procedures should be used, depending on individual circumstances. Presurgical objectives in the vertical plane include maximizing the amount of presurgical orthodontic treatment carried out in open bites and minimizing the presurgical mechanics in deep bites. Encouragement of opening mandibular rotation at surgery while avoiding an increase in posterior face height contributes to stability. Orthodontic mechanics should not always include presurgical leveling of the curve of Spee and should actively avoid movements that may cause relapse tendencies. Careful attention to the use of surgical arch wires and splints during surgery and fixation, along with controlled elastic therapy and exercise programs after fixation, can greatly facilitate treatment.     

Longitudinal measurements of tooth mobility during orthodontic treatment using a periotest

The present study was designed to investigate the alteration of tooth mobility through orthodontic treatment using a Periotest. Eighty-three crowding cases without severe skeletal discrepancies were used as subjects. For each subject, the mobility of the central and lateral incisors on both arches (U1, U2, L1, and L2) was measured immediately before and after orthodontic treatment (T1 and T2 stages) and after retention (T3 stage) by use of a Periotest. No significant differences of all the measurements were found between the left and right sides. At T1 stage, the mean values were 10.8, 10.4, 9.3, and 7.4 for U1, U2, L1, and L2, respectively. At T2 stage, the Periotest values for all the teeth increased in comparison with those at T1 stage, and significantly decreased at T3 stage compared with those at T2 stage. Negative correlations were found between the Periotest value and age, which imply that tooth mobility decreases with age. The durations of treatment and retention had low correlation with the change of tooth mobility for all the teeth. It is suggested that the tooth mobility before treatment and after retention may be one of the useful indicators for determination of the retention period.     

Index of orthodontic treatment need as a predictor of orthodontic treatment uptake

INTRODUCTION: The aim of this study was to evaluate whether the index of orthodontic treatment need (IOTN) could be weighted by using consumer-based sociodental measures to predict the uptake of orthodontic services. METHODS: The sample consisted of 525 schoolchildren, 11 to 12 years old, from Greater Manchester, United Kingdom. Child-perceived IOTN aesthetic component (AC), examiner IOTN AC and dental health component, and child socioeconomic status (Townsend score) were recorded. Two consumer sociodental measures (utility and oral aesthetic subjective impact scale values) were recorded. Three years later, the proportion of the subjects who had received orthodontic treatment or were on a waiting list for orthodontic treatment was recorded, and the rate of service uptake was determined. RESULTS: Sociodental indicators did not predict uptake of orthodontic services. A child with higher normative clinical treatment need was 3 times more likely to receive orthodontic treatment than a child with low clinical need (P < .05). CONCLUSIONS: Consumer-based sociodental information does not predict future use of orthodontic services. Factors such as clinical IOTN and child-perceived IOTN AC will adequately predict use of orthodontic services.