advances in orthodontic treatment
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8/12/2019 Advances in Orthodontic Treatment
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8/12/2019 Advances in Orthodontic Treatment
Educational ObjectivesThe overall goal of this article is to provide dental profession-als with information on orthodontic treatment options.
Upon completion of this course, the participant will beable to do the following:1. Know the reasons patients request orthodontic treatment,
as well as the reasons they may reject orthodontic treatment
2. Know the biomechanics involved in orthodontic toothmovement
3. Know the factors that can increase the duration oforthodontic treatment
4. Understand the role static and cyclic forces play inbiomechanics and the potential duration of orthodontictreatment
AbstractFunctionality and aesthetics are key considerations in patientsrequesting, and orthodontists recommending, orthodontic
treatment. However, patients may elect to forego orthodontictreatment due to the cost and the duration of treatment. Orth-odontic treatment can be provided using removable or xedorthodontic appliances (FOAs), and current options offerimproved aesthetics compared to earlier generation appliances.Many methods have been explored and developed to reducethe duration of treatment. Most recently, a device has beendeveloped that utilizes the concept of cyclic force applicationto reduce the duration of orthodontic treatment.
IntroductionOrthodontic treatment is requested and recommended forfunctionality and aesthetics. Patients seek orthodontic treat-ment primarily for aesthetic reasons. Orthodontists typicallyrecommend orthodontic treatment to patients for function.The number of orthodontic cases has continued to grow overtime. Between 1990 and 1999, the number of orthodonticcases annually more than doubled, from approximately 25.8million cases to more than 61 million cases. The majority ofcases in 1999 were for comprehensive therapy around 48million, with 81.5% of these in the 1019 age group and justover 14% in adults age 20 and over.1 The number of adult caseshas increased in the last decade as the importance of aestheticshas increased and afuence has led to an increased demand.Treated cases by age and type can be found in Table 1.
Table 1. Orthodontic casesTotal Under
10 - 19Age 20
and aboveComprehensiveorthdontics 48,184,000 4.40% 81.50% 14.10%
Interceptiveorthdontics 6,412,200 53% 46.60% 0.40%
Limitedorthodontics 7,118,200 19.40% 56.90% 23.70%
Adapted from: American Dental Association. 1999 Survey of dental services rendered
Patients may elect to forego orthodontic treatment dueto the cost of treatment, the duration of treatment mostcases traditionally take 1.52.5 years to complete or due tothe appearance of orthodontic appliances (depending on thetype used). In addition, some patients have difculty wearingorthodontic appliances, which can result in patients startingbut not completing orthodontic treatment. Dental profes-
sionals may reject patients for orthodontic treatment dueto an assessment that the patient will be noncompliant withtreatment or noncompliant with oral hygiene requirementsduring orthodontic treatment. The patients treatment mayalso be discontinued due to noncompliance. The duration oftreatment, oral hygiene requirements and appearance duringtreatment vary depending on the type of orthodontic treat-ment and appliances used.
Table 2. Rejection of t reatment
PatientsDuration of treatmentPoor aesthetics during treatmentDifficulty wearing an applianceCostDental ProfessionalPoor compliance with use (removable)Poor compliance with adjustment appointmentsPoor oral hygieneUnrealistic patient expectations
Orthodontic AppliancesOrthodontic treatment can be provided using removable orxed orthodontic appliances (FOAs). Removable appliancesinclude acrylic plates with clasps and springs variously posi-tioned depending on the treatment needs. Simple orthodonticcases can be successfully treated using this type of appliance,which also relies on the patient wearing the appliance as in-structed. Since the appliance is removable, patients may benoncompliant and leave the appliance out for extended periodsof time, which can result in slower treatment or reversal oftooth movements. Other removable appliances include thosedesigned for specic tooth movements, such as the Schwartzappliance. Removable appliances offer the advantage of beingable to be removed for oral hygiene procedures, simplifyingoral home care, but are subject to noncompliance and lack ofuse by patients.
A more recent removable option is the use of clear resinfull coverage invisible orthodontic appliances (Invisalign,Align Technology). These have increased adult orthodonticcase acceptance and adult requests for orthodontia due totheir acceptable aesthetics. Clear, full-coverage, removable
resin appliances are not indicated for all types of cases, andthree-axis tooth movement is better controlled using standardxed appliances; they can be used stand-alone or after use ofa xed orthodontic appliance. Clear aligners have been found
8/12/2019 Advances in Orthodontic Treatment
to be more comfortable for the patient and to result in lessperiodontal inammation than xed appliances (noting thatsuch periodontal inammation has been found to resolve fol-lowing removal of xed appliances). 2 , 3 However, Invisalignand similar products only address crowding up to a few mil-limeters and cannot address most cases with bicuspid extrac-tions. Accordingly, Invisalign and similar products only serve
a fraction of the orthodontic patient population.
Figure 1. Clear, full-coverage aligner
Functional appliances are used to inuence and alter the po-sitioning of the patients hard tissues (teeth, alveolar bone and jaw positions) by altering the patients function. These maybe xed or removable. Examples of functional appliancesinclude the Herbst, which is xed and therefore does notrequire patient compliance for wear; the bionator and Frankelappliances, which are removable.
Figure 2. Functional appliance (Herbst)
Fixed orthodontic appliances are used for the majority oforthodontic cases. Modern xed orthodontic applianceshave their genesis in Angles ribbon arch technique, whichwas introduced in the early 20th century. The ribbon archtechnique utilized a curved archwire with friction sleevenuts and threaded ends, and bands with lockpins cementedon the teeth. This appliance was the rst that could achieve
controlled three-axis tooth movement.4
The ribbon arch tech-nique was subsequently replaced by the Edgewise techniquein the 1920s. Over time, nickel-silver bands and archwires su-perseded gold-platinum, and were later replaced by stainless
steel bands and archwires. The latest-generation xed orth-odontic appliances utilize either clear or metal brackets thatare bonded onto the buccal/facial surfaces of the teeth withthe archwire threaded through attachments on the brackets.The ability to successfully bond orthodontic brackets to teethhas removed the need to utilize banding encircling the teeth,thereby improving aesthetics and reducing discomfort, as
well as reducing the impact of orthodontic treatment on oralhygiene requirements and difculties. In addition, the use ofclear resin bonded brackets has substantially improved theaesthetics during treatment with FOAs. Currently availableappliances frequently incorporate the use of elastics intoforces applied during therapy, and nickel-titanium is utilizedfor the archwires and other wire/spring components. Varia-tions include lingual/palatal appliances designed to achievetooth movement with improved aesthetics during treatment,and the use of self-ligating brackets, which have simpliedthe process of attaching archwires to brackets.
Regardless of the design, each generation of orthodonticappliance to date has utilized static force to move the teeth,i.e., force that is applied continually between visits and isonly altered as a result of adjustments during orthodonticrecall visits.
Mechanism of Action of Orthodontic Appli-ances (Biomechanics)Bone is known to adapt to mechanical forces, including weight-bearing loads and orthodontic (therapeutic) forces, therebybiologically balancing the load-bearing capacity of bone withthe mechanical stress to which it is subjected. 5,6,7 The oppositeis also seen with disuse atrophy, when loss of bone or musclemass occurs with disuse, such as during immobilization. 8 Theapplication of mechanical force is the premise for orthodontictooth movement. When a mesial force is placed on a tooth,bone is resorbed on the mesial surface (compression side) andlaid down on its distal (tension side) surface.
Orthodontic appliances have relied on static force to inducebone remodeling and tooth movement, with the duration oftreatment depending on the rate of bone remodeling. As forceis applied to the tooth, micromovement results in it exing,and the periodontal ligament and bone on that aspect of theroot undergo remodeling, with resorption of the bone. Thealveolar bone on the opposite side undergoes bone formation.This combination represents the bone remodeling processduring orthodontic treatment. The osteoclasts are respon-sible for bone resorption, which begins with the attachmentof these cells to the bone surface, after which acid dissolutionof the hydroxyapatite occurs and is followed by destructionof the bones organic matrix. The osteoblasts are the cellsthat develop bone matrix and maintain the bones stru