ABSTRACT
Evaluat ion of t em perat ur e incr ease dur ing
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Rafael Francisco Lia MONDELLI, Ana Flávia SOARES, Eugenio Gabriel Kegler PANGRAZIO, Linda WANG, Sergio Kiyoshi ISHIKIRIAMA, Juliana Fraga Soares BOMBONATTI
Universidade de São Paulo, Faculdade de Odontologia de Bauru, Departamento de Dentística, Endodontia e Materiais Odontológicos, Bauru, SP, Brasil,
Corresponding address: Rafael Francisco Lia Mondelli - Departamento de Dentística, Endodontia e Materiais Odontológicos - Faculdade de Odontologia de Bauru - Universidade de São Paulo - Alameda Doutor Octávio Pinheiro Brisolla, 9-75 - Bauru - SP - Brazil - 17012-901 - Phone: 55 - 14 -32358265 / 55-14-81564686 - e-mail: rafamond@fob.usp.br
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he use of light sources in t he bleaching process reduces t he t im e required and prom ot es sat isfact ory result s. How ever, t hese light sources can cause an increase in t he pulp t em perat ure. Obj ect ive: The purpose of t he present st udy was t o m easure t he increase in int rapulpal t em perat ure induced by different light - act ivat ed bleaching procedures w it h and wit hout t he use of a bleaching gel. Mat erial and Met hods: A hum an m axillary cent ral incisor was sect ioned 2 m m below t he cem ent oenam el j unct ion. A K- t ype t herm ocouple probe was int roduced int o t he pulp cham ber. A 35% hydrogen peroxide bleaching gel was applied t o t he vest ibular t oot h surface. The light unit s used w ere a convent ional halogen, a hybrid light ( only LED and LED/ Laser) , a high int ensit y LED, and a green LED light . Tem perat ure increase values w ere com pared by t w o- way ANOVA and Tukey´ s t est sS5HVXOWV7KHUHZHUHVWDWLVWLFDOO\VLJQL¿FDQWGLIIHUHQFHVLQWHPSHUDWXUHLQFUHDVHV
bet w een t he different light sources used and bet w een t he sam e light sources w it h and w it hout t he use of a bleaching gel. The presence of a bleaching gel generat ed an increase in int ra- pulpal t em perat ure in groups act ivat ed w it h halogen light , hybrid light , and high int ensit y LED. Com pared t o t he ot her light sources, t he convent ional halogen lam p applied
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t em perat ure variat ions. Conclusion: I n t he present st udy, t he convent ional halogen lam p caused t he highest increase in int rapulpal t em perat ure, and t he green LED caused t he least . There was an increase in t em perat ure w it h all light s t est ed and t he m axim um t em perat ure rem ained below t he crit ical level ( 5.5° C) . The addit ion of a bleaching gel led t o a higher increase in int rapulpal t em perat ures.
Ke yw or ds: Toot h bleaching. Light . Tem perat ure.
I N TROD UCTI ON
Wh it en in g p r ocess h as b een r ein f or ced b y t h e dev elopm en t of n ew t ech n ologies allow in g pat ient s t o get fast er and bet t er result s16,22. This
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usually perform ed using bleaching agent s wit h high concent rat ions of hydrogen peroxide ( 15- 38% ) . An ext ernal source of hybrid light ( LED/ Diode Laser) can be applied t o act ivat e t he bleaching gel agent in less t im e wit h good result s, wit h a sm all increase in t he int rapulpal t em perat ure, and less sensit ivit y21.
These ext ernal light sources have t he abilit y t o heat t he hydrogen peroxide gel, t hus increasing t he rat e of oxygen decom posit ion, w hich prom ot es bleaching6,9.
Alt hough t he use of hybrid light sources in t he bleaching process reduces t he t im e required for perform ing t he process and prom ot es sat isfact ory result s21, som e of t hese light sources can cause an
increase in t he int rapulpal t em perat ure, w hich can increase t he incidence of post - operat ive sensit ivit y ( 55% - 100% )14,20.
infrared lasers, and high power LEDs, am ong ot hers.
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only a sm all fract ion of light is absorbed by t he bleaching gel, and it s ener gy is conv er t ed int o heat17,19. The light , how ever, can accelerat e t he
degradat ion of hydrogen peroxide w it h less t im e required for bleaching and increase t he t em perat ure of t he bleaching agent and t he dent al pulp21.
Many dif f er en t t y pes of ligh t s ar e cu r r en t ly used in dent ist ry for bleaching, including halogen, plasm a ar c, ligh t em it t in g diodes ( LED) , diode
lasers, carbon dioxide lasers ( CO2) , argon lasers,
and non- t her m al at m ospher ic pr essur e plasm as ( NAPP) . Most of t he light s em it t ed by t hese lam ps are w it hin t he visible spect rum , but som e lam ps also em it t he light near an infrared or an ult raviolet spect rum . Som e syst em s are designed solely t o be used for t oot h whit ening, while ot hers have several addit ional funct ions ( bleaching and polym erizat ion of rest orat ive m at erials) . When t hese lam ps are used, an increase in gel t em perat ure and int rapulpal t em perat ure can be observed.
Ext er nal heat applied t o t he t eet h can cause pulp dam age in var y ing degr ees, depending on t h e m agn it u de an d du rat ion of t h e in cr ease in t em perat ure17. I n an in v iv o st udy w it h m onkeys,
an in cr ease in t em p er at u r e in sid e of t h e p u lp cham ber of 5 . 5 ° C caused ir r ev er sible pulpit s2 9.
Tem perat ur es in t he pulp cham ber abov e 46° C can cause irreversible changes, such as st asis and
t hrom bosis in t he blood vessels25. Som e aut hors
claim t hat t he highest t em perat ur e t olerat ed by hum an pulp2, 5.5° C, is considered t he crit ical point
of t olerance for int rapulpal t em perat ure.
Mainly due t o aggr essive m ar ket ing of som e com pan ies, w h it en in g is becom in g in cr easin gly popu lar an d m an y pr odu ct s t h at u se dif f er en t energy sources and prot ocols are available on t he m arket . How ever, t hey should be t est ed in such a way t hat safet y param et ers are m aint ained.
The aim of t he present in v it r o st udy was t o evalu at e t h e in t r apu lpal t em per at u r e in cr eases generat ed by a select ion of light s used as part of t he bleaching process, alone or in com binat ion wit h a bleaching gel.
M ATERI AL AN D M ETH OD S
This is an in v it r o st udy, and t he experim ent al design for analysis of t em perat ure variat ion was divided int o t w o st udy fact or s: light sour ces ( in
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LED light , a LED/ Laser hy br id light , t est ed w it h and w it hout laser act ivat ion, and a convent ional halogen lam p) and t reat m ent ( in t w o levels: w it h or w it hout bleaching gel) , t he design det erm ined
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in Table 1.
M a t e r ia l
The m anufact urer ’s nam e and ot her inform at ion of t he light sour ces used ar e list ed in Figur e 1.
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peroxide gel ( Lase Peroxide, DMC Equipam ent os Lt da., São Carlos, SP, Brazil) . This product has a red color due t o t he addit ion of phot oact ive colorant s ( Urucum and Juá, Brazil) . Ot her com ponent s include am ide, glycol and wat er.
Toot h pr e pa r a t ion
A single, hum an cent ral upper incisor was used t hroughout t he t est . This t oot h was donat ed from an organ bank of t he Bauru School of Dent ist ry ( FOB- USP) , having obt ained approval by t he et hics com m it t ee of t he inst it ut ion t hrough process no. 002/ 2008. The r oot of t he t oot h w as sect ioned 2 m m b e l o w t h e c e m e n t o e n a m e l j u n c t i o n , perpendicular t o t he long axis of t he t oot h, using a slow speed diam ond disc ( I som et , Buehler Lt d., Lake Bluff, I L, USA) . The apical foram en of t he root canal was enlarged using a # 2135 diam ond bur
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rem nant s w ere rem oved from t he pulp cham ber.
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absor pt ion com pound ( Ter m al Past e, I m plast ec, Vo t o r a n t i m , SP, Br a zi l ; 5 5 . 1 5 . 3 2 4 3 . 3 7 8 8 ) t o sim u lat e t h e pu lp t issu e as a h eat con du ct in g m edium . A t hin K- t ype t herm ocouple probe ( MT 4 0 1 A, Min ilpa I n d. Com . Lt da., São Pau lo, SP, Brazil) was insert ed int o t he pulp cham ber t hrough t he apical foram en and placed at it s m ost coronal level. I t s posit ion was radiographically checked. During t he t est ing procedure, t he root surface of t he t oot h was part ially subm erged int o a wat er bat h at 37± 1° C ( Figure 2) .
Ble a ch in g m e t h od
Te m pe r a t u r e m e a su r e m e n t
Th e r o o m t e m p e r a t u r e w a s co n t r o l l e d a t 24+ 1° C. Each of t he light sources were applied wit h and w it hout t he bleaching gel on t he t oot h surface, for a t ot al of 10 experim ent al groups. The gel was rem oved and a new layer was applied every t im e t hat a light source was applied t o t he t oot h. At least 15 m in w ere allow ed in bet w een t he applicat ions of all light sources in order t o allow t he t em perat ure t o ret urn t o baseline. Each m easurem ent for all groups was repeat ed six t im es, and t he t em perat ure was recorded every 30 s during t he t est . The m ean values of t he differences bet w een t he init ial and
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calculat ed.
This prot ocol was used based on t he result s of a pilot st udy perform ed prior t o t his st udy.
St a t ist ica l a n a lysis
Two- way analysis of variance ( ANOVA) was used
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t he Tuk ey ´ s t est w as used for all com par isons
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st at ist ical analysis was t he St at ist ica for Window s ( version 6.0 St at Soft , Tulsa, Oklahom a, USA) .
RESULTS
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in t he t em perat ure increases am ong t he different light sour ces and t he sam e light sour ces, w it h and w it hout t he presence of a bleaching gel. The int eract ion bet w een t he light source and t he gel
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Co m p a r ed t o t h e o t h er l i g h t so u r ces, t h e conventional halogen lam p applied over the bleaching gel induced t he great est increase in t em perat ure ( 3.83± 0.41° C) ( Table 1, Figure 3) . The green LED light unit , w it h and w it hout gel applicat ion, did
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pr om ot ed t h e t em per at u r e in cr eases in all t h e ot her unit s.
Figure 2- Schematic drawing of experimental set up showing the starting temperature before light activation Light sources Type and number of light Power density (mW/cm²) Manufacturers
D-Light Green Green LED (3) 180 Kondortech, São Carlos, SP,
Brazil
Smart Lite OS High intensity LED (1) 900 Dentsply Int.
UltraBlue IV LED (19)
Diode laser (1)
1387 200
DMC Equipment Ltda., São Carlos, SP, Brazil
Spectrum Conventional Halogen (1) 500 Dentsply Int.
D I SCUSSI ON
Pr o ced u r es w i t h b l ea ch i n g a g en t s i n h i g h concent rat ions, coupled w it h a longer ex posur e t im e, can dam age t he pulp t issue8,28. I n addit ion, t he
t em perat ure variat ions of t he int ra- pulpal cham ber
has been a reason for concern27.
An incr ease in r eal t em perat ur e in t he int ra-p u l ra-p a l ch a m b er w a s o b ser v ed f o r a l l g r o u ra-p s evaluat ed, w it h t he except ion of t he groups w ho used t he green LED light source, possibly due t o t he low power densit y10. The higher t em perat ure of t he
int ra- pulpal cham ber was achieved wit h t he use of a convent ional halogen lam p coupled wit h a bleaching gel, w hich corroborat es previous st udies15,30. This
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bleaching w it h t he use of a light source, but it s unst able t em perat ure increases and, consequent ly, t oot h sensit ivit y has caused it t o fall int o disuse.
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regarding t he increase in t em perat ure w hen t he hybrid light source was also used, probably due t o t he low pow er densit y of t he diode laser. This
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diode lasers are harm ful t o t he pulp, but when used wit h a low pow er densit y, m ay have t herapeut ic
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Alt hough t he present st udy did not evaluat e t he sensit ivit y, t he clinical use of t his t herapeut ic laser during bleaching m ay lead t o a reduct ion in post -operat ive sensit ivit y3.
I n order t o increase t he absorpt ion of light , and con sequ en t ly t h e t em perat u r e, t h u s opt im izin g
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ar e added t o t he bleaching agent s such as r ed dye ( Urucum and Juá, present ed in Lase Peroxide, DMC Equipam ent os Lt da., São Carlos, SP, Brazil) . Th e gr ou ps w h ich u sed t h e gel ex per ien ced a
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Groups Light sources Mean±SD
G1 D-Light Green 0.00±0A
G2 D-Light Green + gel 0.17±0.41A
G3 Smart Lite 2.17±0.41C
G4 Smart Lite + gel 3.00±0D
G5 UltraBlue IV 1.00±0B
G6 UltraBlue IV + gel 2.17±0.41C
G7 UltraBlue IV laser 1.17±0.41B
G8 UltraBlue IV laser + gel 2.33±0.52CD
G9 Spectrum 2.70±0.41C
G10 Spectrum + gel 3.83±0.41E
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sh ow n in p r ev iou s st u d ies5 , 1 1. I n con t r ast , t h e
ap p licat ion of a b leach in g g el or v aselin e h as been show n t o act as a physical barrier, causing a decrease in t he int rapulpal cham ber t em perat ure17.
A n i n c r e a s e o f 5 . 5 ° C i n t h e i n t r a p u l p a l t em perat ure has been show n t o cause irreversible pu lpit is in 1 5 % of t h e m on k ey t eet h t est ed2 9.
How ever, ex t rapolat ion of values obt ained fr om hum ans t o m onkeys is highly quest ionable7. I n t he
present st udy, an increase of 5.5° C in t he int ra-pulpal t em perat ure is regarded as t he t hreshold, w hich should not increase t o prevent irreversible dam age t o t he pulp.
S o m e s t u d i e s h a v e m e a s u r e d t h e p u l p t em perat ur e incr eases induced by t he bleaching gel w hen t he t oot h is exposed t o different energy sources. The CO2 lasers, diode lasers30, convent ional
h alog en lam p s, an d LED1 1 w it h h ig h d en sit ies
r epor t ed t em per at u r e valu es abov e t h e cr it ical t em perat ure. How ever, anot her st udy report ed a low er t em perat ure increase w it h halogen lam ps, Plasm a ar cs, LED, and LED/ Laser s1 1. I t is v er y
d if f icu lt t o com p ar e t h e d if f er en t st u d ies an d evaluat e t heir result s because of t he num ber of v ar iables pr esen t su ch as t im e, en er gy, in it ial t em perat ure of t he pulp cham ber, and dist ance from t he phot oact ivat or t ip9.
Alt h ou g h an at t em p t i n v i t r o w as m ad e t o sim ulat e t he t em perat ur e of t he pulp cham ber, t hese result s should be int erpret ed w it h a cert ain
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heat diffuser, w it h t he pulp circulat ion capable of dissipat ing som e heat prior t o dam aging t he pulp cells18,24. The current in v it r o m odel was unable t o
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t he increase in t em perat ure was lower. The heat ing of t he bleaching agent not only leads t o an increase in t em perat ur e in t he int ra- pulpal cham ber, but also a great er penet rat ion of peroxide in t he pulp cham ber4.
The diffusion of hydrogen peroxide in t he pulp leads t o ox idat ive st r ess, w hich could adver sely affect t he cell m et abolism of t he pulp6. Hist ological
evaluat ions of ext ract ed hum an t eet h have show n
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I n som e cases, how ever, it could also be caused by t he use of 35% H2O21.
Cl i n i ca l l y, p a t i en t s t r ea t ed w i t h b l ea ch i n g agent s act ivat ed wit h heat oft en com plain of dent al hy per sensit iv it y up t o 48 h aft er t he bleaching procedure12.
Li g h t so u r ce s h a v e b e e n w i d e l y u se d t o accelerat e t he w hit ening process, w it h advant ages such as an im m ediat e low er t oot h sensit ivit y23,26,28,
besides decr easing t he clinical t im e21. How ever,
m ore st udies are needed t o est ablish t he precise cor r elat ions bet w een t he new light sour ces and
bleach in g gels av ailable in t h e m ar k et an d it s im plicat ion t o t he pulp organ.
CON CLUSI ON
Wit hin t he lim it at ions of t he pr esent in v it r o st udy, t he r esult s show ed t hat t he convent ional halogen lam p caused t he great est increase in int ra-pulpal t em perat ure and t he green LED t he low est . There was an increase in intra- pulpal tem perature w it h all light sour ces t est ed, and t he m ax im um t em p er at u r e r em ain ed b elow t h e cr it ical lev el ( 5.5° C) .The addit ion of bleaching gel led t o a higher increase in int ra- pulpal t em perat ures.
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