DT Middle East and Africa

Media CME DENTALTRIBUNE Middle East & Africa Edition 6 2 Hours (mCME articles in Dental Tribune (always page 6) has been approved by HAAD as having educational content acceptable for (Cate- gory 1) CME credit hours. Term of approval covers issues published within one year from the distribution date (September, 2010). This (Volume/Issue) has been approved by HAAD for 2 CME credit hours. Young Guk Park & Ze’ev Davidovitch Korea & USA Orthodontic tooth movement results from forces applied to teeth that evoke cellular re- sponses in the teeth and their surrounding tissues, including the periodontal ligament (PDL), alveolar bone and gin- giva. It is advantageous for the orthodontist to know the de- tails of the biological events that unfold during tooth move- mentbecausesomeofthesede- tails may differ from one per- son to another, owing to vari- ables such as gender, age, psy- chological status, nutritional habits and drug consumption. Thepurposeofthisarticleisto emphasise that orthodontics is a field of endeavour in which me- chanics and biology are inte- grated, and to stress the reality thattoothmovementisconducted in individual human beings, each with a unique and intricate physi- ological system. Biological varia- tionsmaybethefoundationofthe differencesthatarefrequentlyob- served in the outcomes of ortho- dontic treatment between pa- tients with similar malocclusions treated identically. Principles of orthodontic bio- mechanics are usually taught with the help of a typodont, con- sisting of artificial teeth embed- ded in wax. This set-up ignores entirely the biological aspect of tooth movement. In the clinical setting, living patients are en- countered, and mechanical forces mobilise their teeth. These movements result from the development of strains in dental and para-dental tissues, followed by modelling and re- modelling of these tissues. In some patients, systemic conditions may exist, causing complications such as root re- sorption, dehiscences and fenes- trations of the alveolar bone. Hence, clinical orthodontics must be viewed as a specialty staunchly entrenched in biology, allthewaytothemolecularlevel. Asaclinicalprofession,itmustbe based on a commanding knowl- edge of mechanics, biology, physiology, and pathology. The goal of this article is to enhance the biological awareness of the orthodontic practitioner in order to minimise or avoid tissue dam- age during orthodontic treat- ment. It will demonstrate that thisobjectivemaybeachievedby closely focusing on the nature of root movements, and avoiding the dogmatic following of “pre- scription” methods that promise “automatic” correction of all malocclusions. Tissueremodellingand orthodontictoothmovement Theactualrateoftoothmove- ment may depend on the rate of bone turnover. The latter was modified pharmacologically in rats undergoing maxillary molar mesial movement, by inducing either hypothyroidism or hyper- thyroidism(Vernaetal.,2000).In rats with high bone turnover, the rate of tooth movement was in- creased, while it was reduced in animals with a low turnover. Al- though all teeth had been moved in the same manner (controlled tipping), the location of the cen- tre of rotation differed, depend- ing on the metabolic state of the bone. Examination of histologi- cal sections from the jaws of these rats (Verna et al., 2003) showed that root resorption had occurred in both groups, as well as in the control group, but that it was more pronounced in the low bone turnover group. However, bone metabolism normally demonstrates measurable diur- nal fluctuations that may affect the rate of tooth movement. Rats that were exposed to light for 24 or 12 hours per day for 21 days, and were subjected to orthodon- tic force only during the light pe- riod, presented doubling of the rate of tooth movement and bone remodelling, as compared with animals that received the force during the 12 hours of daily dark- ness (Miyoshi et al., 2001). The realisation that tissue re- modelling in orthodontics is me- diatedbyavarietyofcells,includ- ingfibroblasts,rootandbonesur- face lining cells; endothelial, ep- ithelial,andnervecells;aswellas different leukocytes, prompted clinical investigators to apply physical and chemical agents, concomitant with orthodontic forces in order to augment the ef- fect of the mechanical forces. In thisvein,Tweedle(1965)usedlo- cal application of heat to para- dentaltissuessurroundingortho- dontically treated teeth in dogs, Davidovitch et al. (1980) used minute electric currents, and Blechman (1998) advocated the use of static magnetic fields. Davidovitchetal.placedtheelec- trodesmuchclosertothecat’sca- nine,resultinginasignificanten- hancement of movement. Blech- man hypothesised that magnets generate mechanical forces, as well as magnetic fields, and that this combination acts synergisti- cally, causing the teeth to move faster. However, an experiment in rats (Tengku et al., 2000) re- vealed that magnets do not speed up the mesial movement of max- illary molars, and actually in- creaserootresorptionintheearly phases of treatment. Utilisation of chemical agents inattemptstoincreasethepaceof tissue remodelling and tooth movementhasbeentestedinvar- ious laboratories and clinics. Ya- masaki et al. (1984) injected prostaglandin (PG) E1 into the gingivaofmovingteethinhuman subjects,resultinginrapidmove- ment. Systemic application of misoprostol, a PGE1 analogue, to rats undergoing tooth movement fortwoweeks,increasedthepace of movement significantly with- out enhancing root resorption (Sekhavatetal.,2002).Similarre- sults were reported following in- traperitoneal injections of PGE2 in rats (Seifi et al., 2003). Chumb- ley and Tuncay (1986) adminis- teredindomethacinsystemically, a PG synthetase inhibitor. Collins and Sinclair (1988) used local ap- plications of vitamin D, while Engstrom, Granstrom and Thilander (1988) moved teeth in hypocalcaemic, vitamin-D-defi- cient, lactating rats. The bone matrix component osteocalcin was injected in rats into the palatal bifurcation of a tipping molar, causing rapid tooth move- ment owing to the attraction of numerous osteoclasts to this site (Hashimoto et al., 2001). The reports cited above sug- gest that the extent of tissue re- modelling and the rate of tooth movement can be significantly influenced by numerous factors capable of interacting with para- dental cells. However, if our goal is to complete orthodontic treat- ment successfully and in the shortestpossibleamountoftime, then we should avoid moving roots into areas from which they will have to be retrieved later. When mechanical loads are applied to intact tissues in vivo or in vitro, the tissues usually be- come distorted (strained). In the case of the skeleton, loads like gravity prompt cells to arrange thearchitectureofthebonystruc- turalfeaturesinawaythatwillre- sist redundant loads. This phe- nomenon is known as Wolff’s Law, defined by Julius Wolff in 1892. However, when bone cells are subjected to non-redundant loads, such as orthodontic forces, the cells are activated, and re- modelling of the alveolar process ensues, which facilitates tooth movement.Invivoapplicationsof compressive loads to ulnae in turkeys and roosters by Lanyon and Rubin (1984) revealed that extensive osteogenesis can be evoked by short-term dynamic (intermittent) forces. In those ex- periments, the optimal load mag- nitude was 2,000 to 4,000 micro- strain, and its daily duration was ten to 20 minutes. These findings suggest that orthodontic forces will be most effective when ap- pliedforbriefperiods,ratherthan continuously. This assumption was found to be correct in an ex- periment in rats by Gibson, King, and Keeling (1992). In that exper- iment, maxillary molars were subjected to mesially moving forces for one hour, one day, or 14 days. Teeth exposed to only one hour of force application contin- ued to move mesially for 14 days, and achieved 75% of the move- ment reached by the teeth that hadbeensubjectedtoorthodontic forces continuously for 14 days. The age factor The effect of age on the tissue responsetoorthodonticforcehas occupied the minds of orthodon- tists since Hunter, in the 18th cen- tury,andprobablyearlier.Hunter observed that orthodontic treat- ment takes longer in adults than in children. Studying histological sectionsofhumanteethandtheir surrounding tissues, Reitan con- cluded that the PDL is less cellu- lar in adults than in children. Therefore, he recommended, when treating adults, to subject their teeth to light forces initially, in order to stimulate cellular pro- liferation, then to increase the forcemagnitude,inordertostim- ulate these cells to remodel the para-dental tissues. This obser- vation implies that, in essence, the nature of the biological re- sponse to orthodontic forces is similar in young and adult sub- jects. This hypothesis was con- firmed by Shimpo et al. (2003). These investigators moved mo- lars bilingually in young (13- week-old) and old (60-week-old) rats, then studied their compen- satory alveolar bone apposition under the lingual periosteum. They reported that in both age groups there had been vigorous compensatory alveolar bone growth. Thus, alveolar bone is successfully maintained, even in agedrats.Agecanalsorefertothe duration of healing of a post-op- erative regenerate following dis- traction osteogenesis (Nakamoto et al., 2002). In an experiment on 15-month-old beagles, mandibu- lar premolars were moved into a two-week or a 12-week regener- ation period. The former con- sisted of immature, fibrous, and poorly mineralised bone, while the latter was composed of ma- ture, well-organised and miner- alised bone. Tooth movement was significantly faster in the “young”, immature regenerate, butthismovementwasaccompa- nied by extensive root resorption that extended from the cemento- enamel junction to the root apex. Theeffectsofpre-existing medicalconditionsandthe developmentofcomplications It is estimated that 10 to 15% of all children under the age of 16 are affected by chronic, long- term medical problems. These problemsmayaffecttheoutcome of orthodontic treatment (Bur- den et al., 2001). Common med- The role of biology in the orthodontic practice (Part 1) Dental Tribune Middle East & Africa in collaboration with CAPP introduce to the market the new project mCME - Self Instruction Program. mCME gives you the opportunity to have a quick and easy way to meet your continuing education needs. mCME offers you the flexibility to work at your own pace through the material from any location at any time. The con- tent is international, drawn from the upper echelon of den- tal medicine, but also presents a regional outlook in terms of perspective and subject matter. How can professionals enroll? They can either sign up for a one-year (10 exercises) by sub- scription for the magazine for one year ($65) or pay ($20) per article. After the payment, participants will receive their membership number and will be able to attend to the pro- gram. How to earn CME credits? Once the reader attends the distance-learning program, he/she can earn credits in three easy steps: 1. Read the articles. 2. Take the exercises 3. Fill in the Questionnaire and Submit the answers by Fax (+971 4 36868883) or Email :info@cappmea.com After submission of the answers, (name and membership number must be included for processing) they will receive the Certificate with unique ID Number within 48 to 72hours. 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