Influence of Connection Type and Platform Diameter on Titanium Dental Implants Fatigue: Non-Axial Loading Cyclic Test Analysis

In e na ional Jou nal o En i onmen al Resea ch and Public Heal h A icle In luence o Connec ion Type and Pla o m Diame e on Ti anium Den al Implan s Fa igue: Non-Axial Loading Cyclic Tes Analysis Ana I. Nicolas-Sil en e 1, Eugenio Velasco-O ega 2,*, I an O iz-Ga cia 2, Al a o Jimenez-Gue a 2, Lo e o Monsal e-Guil 2, Raul Ayuso-Mon e o 3, Ja ie Gil 4 and Jose Lopez-Lopez 5 1Pe iodon al and Implan Su ge y, CEIR Campus Ma e Nos um, School o Den is y, Uni e si y o Mu cia, 30008 Mu cia, Spain; [email p o ec ed] 2Comp ehensi e Den is y o Adul s and Ge odon ology, Facul y o Den is y, Uni e si y o Se ille, 41009 Se ille, Spain; [email p o ec ed] (I.O.-G.); [email p o ec ed] (A.J.-G.); [email p o ec ed] (L.M.-G.) 3Facul y o Den is y, Uni e si y o Ba celona, 08007 Ba celona, Spain; [email p o ec ed] 4Chai man o Bioenginee ing Ins i u e o Technology, Uni e si a In e nacional de Ca alunya, 08017 Ba celona, Spain; xa ie [email p o ec ed] 5Facul y o Den is y, Se ice o he Medical-Su gical A ea o Den is y Hospi al, Uni e si y o Ba celona, 08007 Ba celona, Spain; [email p o ec ed] *Co espondence: [email p o ec ed] Recei ed: 1 No embe 2020; Accep ed: 30 No embe 2020; Published: 2 Decembe 2020   Abs ac : Two-pieces den al implan s mus p o ide s abili y o he implan -abu men -in e ace. The connec ion ype and pla o m diame e could in luence he biomechanical esis ance and s ess dis ibu ion. This s udy aims o e alua e he a igue o di e en ypes o connec ions, ex e nal and in e nal, and di e en pla o m diame e s. Th ee implan designs wi h he same leng h we e used: (a) ex e nal hexagon/na ow pla o m; (b) in e nal double hexagon/na ow pla o m; (c) in e nal oc agon/ egula pla o m. A a igue es was de eloped o es ablish he numbe o cycles needed be o e ac u e. A 30 º oblique load wi h a sinusoidal unc ion o a igue a a equency o 15 Hz and 10% s ess a ia ion was applied o each sys em. The a igue load limi (FLL) o design (a) was 190 N, being he nominal-cu a u e-momen (NCM) =1.045; FLL =150 N, wi h a NCM =0.825 o (b), and FLL =325 N, wi h a NCM =1.788 o (c). The pla o m diame e a ec s he FLL, ob aining lowe FLL on a na ow pla o m. The connec ion ype in e e es wi h he implan walls’ wid h, especially in na ow implan s, making in e nal connec ions mo e uns able a his le el. Long- e m clinical s udies o assess he es o a ion’s success a e and su i al a e manda o y. Keywo ds: connec ion ype; den al implan s; design; a igue es ; pla o m diame e 1. In oduc ion Two-piece den al i anium implan s ha e been widely used o single- oo h eplacemen s up o ull-a ch ehabili a ion [ 1 ]. The implan -abu men -in e ace (IAI) [ 2 ] has o esis dynamic o ces and be s able o wi hs and unc ional loads and o educe sc ew loosing [ 3 ]. To main ain he s abili y o he IAI, di e en implan connec ion geome ies ha e been de eloped, which can be summa ized in wo b oad g oups: ex e nal and in e nal connec ions. In e ms o design, in he ex e nal connec ions, bo h he implan index and he p os he ic abu men index a e loca ed abo e he le el o he implan pla o m. In con as , in he in e nal connec ions, bo h s uc u es a e loca ed inside he implan ’s body, below he le el o he implan pla o m [4]. In . J. En i on. Res. Public Heal h 2020,17, 8988; doi:10.3390/ije ph17238988 www.mdpi.com/jou nal/ije ph In . J. En i on. Res. Public Heal h 2020,17, 8988 2 o 12 The ex e nal connec ions a e usually p o ided o an ou e hexagon whose unc ion is o p o ide o a ional o que con ol du ing implan placemen [ 5 ] and an i- o a ional con ol be ween he implan index and he p os he ic abu men index. Se e al s udies indica e ha his ype o connec ion is less a o able o s ess dis ibu ion and has lowe s abili y when compa ed o he in e nal connec ion [ 6 ]. The in e nal connec ion can p esen di e en designs depending on i s geome ic ea u es and can be di ided in o an in e nal hexagon, in e nal oc agon, ilobed sys em, o mo se ape connec ion be ween o he s [ 7 , 8 ]. This ype o design inc eases he implan -abu men con ac a ea and imp o es he dis ibu ion and dissipa ion o o ces, p o iding be e s abili y [ 9 ], bu is he in e nal conical connec ion ( ape Mo se connec ion) he one ha shows he mos in ima e ela ion be ween he implan and he abu men , p o iding he mos excellen s abili y and bac e ial seal [10,11]. The p esence o di e en design ea u es (angles, channels, s aigh walls, cones, ubes) in he di e se connec ions ypes p e en s o a ion be ween he componen s o he sys em [ 12 ]. I s s uc u al in eg i y is c ucial o long- e m s abili y [ 13 ], and some ac o s could induce de o ma ion when he sys em is o e loaded, o e - o quing o non-axial o ces a e p esen ed [ 14 ]. The hickness o he implan walls is a ele an ac o since, some imes, he design o he an i- o a ional componen s inside he connec ion o ces o lea e walls excessi ely hin, especially in na ow implan s [15,16]. The use o na ow implan s is widely documen ed in pa ien s wi h de icien bone c es al wid h in which, o some eason (inc eased healing ime, cos , o pa ien mo bidi y), he applica ion o ho izon al bone egene a i e echniques is no indica ed [ 17 – 19 ]. The mechanical s eng h o i anium na ow implan s is some imes no enough o suppo he dynamic o ces. The implan sys em does no o e long- e m in eg i y o he connec ion complex, ep esen ing a signi ican isk o ac u es [ 20 , 21 ]. Some aspec s o he di e en connec ion con igu a ions, such as biomechanical esis ance and s ess dis ibu ion, a e c ucial [ 22 ]. No much is known abou implan a igue de ailed by he ype o connec ion. Hence, he objec i e o he p esen s udy was o e alua e he a igue o di e en kinds o connec ions, ex e nal and in e nal, and di e en pla o m diame e s, o es ablish which ype o design suppo ed highe alues. Ou null hypo hesis was ha indexa ion design and pla o m diame e in luences i anium implan a igue in he long- e m. 2. Ma e ials and Me hods 2.1. Den al Implan s Fi y- ou i anium den al implan s om h ee di e en implan sys ems we e compa ed in his s udy. The cha ac e is ics o each implan g oup a e summa ized in Table 1and each implan design is exposed in Figu e 1: - G oup I (n =19): Su gimplan CE: i anium g ade 5 den al implan wi h hexagon ex e nal connec ion (pla o m: 3.5 mm, leng h: 12 mm) (Galimplan SLU, Sa ia, Lugo, Spain) - G oup II (n =18): Su gimplan CI Double Hexagon: i anium g ade 5 den al implan wi h double hexagon in e nal connec ion (pla o m: 3.5 mm, leng h: 12 mm) (Galimplan SLU, Sa ia, Lugo, Spain) - G oup III (n =17): Su gimplan CI Oc agonal: i anium g ade 5 den al implan wi h oc agonal in e nal connec ion (pla o m: 4.0 mm, leng h: 12 mm) (Galimplan SLU, Sa ia, Lugo, Spain). In . J. En i on. Res. Public Heal h 2020,17, 8988 3 o 12 Table 1. Implan cha ac e is ics dis ibu ed by g oups. G oup G oup I G oup II G oup III n 19 18 17 Connec ion Type Hexagon Ex e nal Connec ion Double Hexagon In e nal Connec ion Oc agonal In e nal Connec ion Diame e 3.5 3.5 4.0 Leng h 12 12 12 Ma e ial Ti anium G ade 5 Ti anium G ade 5 Ti anium G ade 5 Figu e 1. Implan design o each expe imen al g oup. 2.2. Fa igue Tes A a igue es was pe o med o ob ain he numbe o cycles be o e ac u e. The maximum and minimum o ce applied was eco ded o each sample. The assays we e pe o med wi h a se o-hyd aulic es ing machine (MTS 858 Mini Bionix II, MTS, Minneapolis, MN, USA) equipped wi h a load cell MTS 661.19F-01 o 5 kN. The sphe ical membe o he load applica ion was made o i anium g ade 5 (Figu e 2). In . J. En i on. Res. Public Heal h 2020,17, 8988 4 o 12 Figu e 2. Sphe ical membe o he load applica ion design de ails. The implan s we e ixed 30 ◦ angula ed wi h he axis z o he load cell (Figu e 3). They we e loaded wi h a sinusoidal unc ion o a igue a a equency o 15 Hz and 10% s ess a ia ion. The e o du ing loading measu emen s was less han 5 N, and he maximum loading applied o he implan was a ound 80% o he alue o he implan ailu e load, ob ained by a s a ic es unde he same geome ic condi ions as a igue es s, ollowing ISO 14801:2008 ecommenda ions [ 23 ]. All es s we e ca ied ou unde s able en i onmen al condi ions wi h a empe a u e o 25 ◦C and ela i e humidi y o 60%. Figu e 3. Load cell o e he sample in he es ing machine. In . J. En i on. Res. Public Heal h 2020,17, 8988 5 o 12 2.3. Scanning Elec on Mic oscopy (SEM) Analysis The ac u e samples we e obse ed by SEM a 10 kV using a Neon 40 Focused Ion Beam Scanning Elec on (FIB-SEM) mic oscope (Ca l Zeiss NTS GmbH, Obe kochen, Ge many). 2.4. S a is ical Analysis S a is ically signi ican di e ences among he h ee g oups we e assessed using SPSS 18.0 so wa e (SPSS Inc., Chicago, IL, USA). Di e ences be ween g oups we e analyzed by Analysis o Va iance (ANOVA), and a mul iple compa ison Fishe es was applied. The le el o signi icance was es ablished a a p- alue o 0.05. 3. Resul s The ailu e mode was simila in all expe imen al g oups, including la ge de o ma ions a he implan neck a ea. The implan neck ac u e ook place mos o he cases be ween he i s and second h eads. 3.1. Hexagon Ex e nal Connec ion The minimum and maximum load exp essed in New ons (N) applied o all he samples o he hexagon ex e nal connec ion g oup was 190 N and 400 N, espec i ely. The cycles applied be o e ac u e we e be ween 3074 and 5,000,000. The cyclic load diag am ob ained om he esul s o he es is shown in Figu e 4. Figu e 4. Cyclic load diag am o hexagon ex e nal connec ion ob ained om he esul s o he es showed in Table 2. In . J. En i on. Res. Public Heal h 2020,17, 8988 6 o 12 Table 2. Summa y o he esul s ob ained in each expe imen al g oup. Implan Type Minimum Load (N) Maximum Load (L) Minimum Cycles Maximum Cycles Fa igue Load Limi (FFL) (N) Nominal Cu a u e Momen (N.m) Hexagon ex e nal connec ion 190 400 3074 5,000,000 190 1.045 Double hexagon in e nal connec ion 150 400 1583 5,000,000 150 0.825 Oc agonal in e nal connec ion 325 550 3555 5,000,000 325 1.788 The a igue load limi (F FL , acco ding o ISO 14801:2008) was F FL =190 N, being he nominal cu a u e momen (N.m) =1.045. 3.2. Double Hexagon In e nal Connec ion The minimum and maximum load exp essed in New ons (N) applied o all he samples o he double hexagon in e nal connec ion g oup was 150 N and 400 N, espec i ely. The cycles applied be o e ac u e we e be ween 1583 and 5,000,000. The cyclic load diag am ob ained om he esul s o he es is shown in Figu e 5. Figu e 5. Cyclic load diag am o double hexagon in e nal connec ion g oup ob ained om he esul s o he es . The a igue load limi (F FL , acco ding o ISO 14801:2008) was F FL =150 N, being he nominal cu a u e momen (N.m) =0.825. 3.3. Oc agonal In e nal Connec ion The minimum and maximum load exp essed in New ons (N) applied o all he samples o he oc agonal in e nal connec ion g oup and he cycles applied be o e ac u e we e 325 N and 550 N In . J. En i on. Res. Public Heal h 2020,17, 8988 7 o 12 espec i ely. The cycles applied be o e ac u e we e be ween 3555 and 5,000,000. The cyclic load diag am ob ained om he esul s o he es is shown in Figu e 6. Figu e 6. Cyclic load diag am o he oc agonal in e nal connec ion g oup ob ained om he esul s o he es . The a igue load limi (F FL , acco ding o ISO 14801:2008) was F FL =325 N, being he nominal cu a u e momen (N.m) =1.788. A summa y o he esul s o he h ee expe imen al g oups is shown in Table 2. The lack o e en ion be ween he abu men and den al implan was assessed as a ailu e. The ac u e mechanism s a s by abu men sc ew loosening p oducing c acks on he su ace ha g ow wi h he load cycles and la e ac u e, bu no due o des uc ion o he implan neck o shoulde . Analysis o ac u ed sc ews by SEM e ealed ha he mode and he egion o ac u e we e he same o he di e en sys ems s udied. The ac u e su aces we e simila o all implan s co esponding o he connec ion zone and ac u ed he body o he implan , acco ding o he indica ions o he in e na ional s anda ds o ac u e a igue beha io [24] o he den al implan s wi h good mechanical beha io . S a is ically, he hexagonal ex e nal connec ion p esen ed a lowe a igue limi load wi h s a is ical di e ences signi icance han he double hexagonal in e nal connec ion (p<0.012) and also in ela ion o he oc agonal in e nal connec ion (p<0.003). When bo h in e nal connec ions a e compa ed, he oc agonal connec ion p esen s a highe limi a igue load han he double hexagonal connec ion wi h s a is ical di e ences signi icance (p<0.004). The s ia ions om he ac og aphy can be obse ed in Figu e 7, whe e he c ack g ows om he su ace specimens and om 10-mm benea h he su ace. In all cases, we obse ed he same mo phology o ac u e. The equiaxed g ains can be obse ed, and in hei aces, he ma ks o he c ack in he p opaga ion p ocess o ac u e. In . J. En i on. Res. Public Heal h 2020,17, 8988 8 o 12 Figu e 7. SEM images a a magni ica ion o × 500 and × 1500 showing he s ia ions om he ac og aphy. 4. Discussion This expe imen al s udy aimed o e alua e he in luence o he connec ion ea u es and pla o m diame e in he a igue esponse o i anium g ade 5 den al implan s. Th ee di e en implan sys ems we e assessed, one na ow implan sys em (3.5 mm pla o m) wi h an ex e nal hexagonal connec ion, one na ow implan sys em (3.5 mm pla o m) wi h double hexagon in e nal connec ion, and one egula pla o m (4.0 mm) implan sys em wi h an oc agonal in e nal connec ion. The implan -abu men in e ace geome y is an in luencing ac o o he ansmission o s ess a ound he implan [25]. This expe imen al es is a eliable me hod o de e mine he e ec o di e en pa ame e s, such as connec ion design o pla o m diame e , on implan dynamic ailu e s eng h. The same company manu ac u ed he h ee expe imen al g oups and he h ee sphe ical membe s a ached o he connec ion, using he same i anium g ade 5. This ac is one o he s eng hs o he p esen s udy. In mos s udies, au ho s compa e ailu e s eng h be ween di e en implan s and di e en abu men in e aces, wi h di e en shapes, su ace cha ac e is ics, and ma e ial p ope ies, and he compa abili y is comp omised [26]. In addi ion o he ac o s men ioned abo e, some ac o s inhe en in he hos may a ec he dis ibu ion o s ain and s ess in bone and implan s. A s udy de eloped by Oli ei a e al. concluded ha he densi y o he medulla bone and he hickness o he co ical bone also a ec he dis ibu ion o s ain and s ess, nega i ely a ec ing he dec ease in medulla bone densi y [27]. Lo Giudice e al. demons a ed ha he bone p epa a ion could also a ec he bone quali y showing be e esul s in os eo omies pe o med wi h ul asonic ips and concluding ha he use o he piezosu ge y p ese es he bone mo phology and dec eases he p esence o mic o ac u es [ 28 ]. The ma ginal bone loss a ound implan s is also in luenced by he ac he implan is placed in na i e bone o placed in g a ed issues. Galindo-Mo eno e al. ound in a e ospec i e coho s udy ha implan s placed in g a ed issues showed mo e ma ginal bone loss han implan s placed in p is ine bone [ 29 ]. The ype o connec ion also a ec s he ma ginal bone s abili y, being he ex e nal connec ions s ongly associa ed wi h an inc eased ma ginal bone loss, no only in he i s wel e mon hs bu o e ime [29]. Also, bone quali y and c es al bone loss can be in luenced by o he ac o s. No only does he neck shape, mic o h eads, o su ace ex u e a ec c es al bone s abili y, bu he implan -abu men connec ion appea s o be a signi ican ac o on pe i-implan c es al bone le el [ 30 ]. The abu men heigh also has an impo an ole, as demons a ed in an in i o s udy de eloped by Spina o e al. They sugges ed ha he sho e he abu men heigh , he g ea e he ma ginal bone loss, especially in cemen - e ained p os hesis [31]. In . J. En i on. Res. Public Heal h 2020,17, 8988 9 o 12 Se e al s udies ha e es ed den al implan s using s a ic loading, while o he s use cyclic loads [ 32 ]. Mos o he e iews ocus on implan design bu does no men ion a igue as a complex ailu e mode [ 22 ]. A ew s udies ha e conside ed he e ec o he implan diame e on a igue pe o mance, concluding ha na ow implan s ailed o show ypical a igue beha io , which migh be a ibu ed o he implan design [ 33 ]. The inconsis en a igue beha io obse ed o na ow implan s could esul om ac o s like no ches, den s, o machining ma kings. To da e, no s udies ha e been published abou a ac u e mode analysis o suppo his assump ion [33]. Ca nei o e al. [34] de eloped an in i o s udy e alua ing he ac u e esis ance o in e nal and ex e nal hexagon in egula and na ow implan s, concluding ha i anium is a ma e ial ha p esen s no clea e idence o he exac poin be ween he plas ic and elas ic limi s. No signi ican educ ion o he blending elas ic limi was ound be ween na ow and egula in e nal connec ions. In ou s udy, he ailu e due o he bending elas ic limi was obse ed a 190 N wi h ex e nal hexagon na ow implan s e sus he 150 N esul ed in he in e nal hexagon na ow implan s. This esul could be because, in he in e nal connec ion, he indexa ion ea u es a e ubica ed inside he implan ’s body, lea ing hinne walls han ex e nal connec ions. Besides, an impo an cause o he high a igue li e o he oc agonal in e nal connec ion is he size o he esis an sec ion. The double hexagonal in e nal connec ion and ex e nal sys em p esen a highe alue o he a ea han he in e nal. Ou es simula ed he clinical si ua ion when he s ess concen a ion esul ing om occlusal o ces leads o mic o ac u es and bone loss a ound he implan , leading o mobili y and ac u e o he implan [35,36]. On he o he hand, ou esul s showed an inc ease om 150 N o 325 N in he elas ic limi by inc easing he pla o m diame e in he in e nal connec ion om 3.5 o 4 mm. This di e ence be ween he pla o m diame e was no signi ican in he esul s showed by Ca nei o e al., al hough hey ound a mo e subs an ial numbe o c acks in he na ow implan s han he egula . Tole ances o manu ac u ing a e he main eason o he loose- i o he componen s and equi ed he manu ac u e o imp o e he i . In hese si ua ions (loose- i ), he possibili y o ho izon al mo emen and o a ion be ween sc ew and implan and lowe han he o ces o igh en i , mic omo emen s could ha e led o a p og essi e unsc ewing o he abu men sc ew unde condi ions dynamic loading. The mos cause o he high a igue li e o he ex e nal connec ion is he size o he esis an sec ion. The ex e nal sys em p esen s a lowe alue o he su ace han he in e nal. This ac p oduces a wo se load dis ibu ion. This eason explains he di e ences in mechanical p ope ies. Besides, he ole ances in he in e nal connec ions a e be e , and his good inishing p o okes a highe a igue limi o he in e nal connec ion sys em [37–39]. Each implan -abu men in e ace has i s ad an ages and disad an ages. Acco ding o Maeda e al. [40], he ex e nal hexagon in e ace has bene i s such as sui abili y o he wo-s age me hod, p o ision o an an i- o a ion mechanism, e ie abili y, and compa ibili y among di e en sys ems. Howe e , inc eased sc ew loosening, componen ac u e, and di icul y in sea ing abu men s in deep subgingi al issues a e p oblems commonly expe ienced wi h ex e nal hexagon connec o s [ 41 ]. The ad an ages o he in e nal hexagon ollowing Maeda a e ease in abu men connec ion, sui abili y o one s age implan ins alla ion, highe s abili y and sui abili y o single- oo h es o a ion, highe esis ance o la e al loads due o he lowe cen e o o a ion, and be e o ce dis ibu ion. The mas ica o y loading a an e io egions is a iable wi h a mean alue o 286 N, s.d. 164 N, while he pos e io a ea shows a mean alue o 579 N, s.d. 235 N [ 42 ]. Those da a showed a high subjec a iabili y so ha he use o na ow implan s is ecommended jus o he an e io egion. In he pos e io a ea, i is manda o y o use a wide pla o m. The p esen s udy esul s suppo he accep ance o he null hypo hesis es ed since he e was a di e ence in he maximum o ce suppo ed in na ow implan s (in e nal o ex e nal connec ions) and egula pla o m implan s. Di e en ypes o connec ions also p esen ed di e ences in he a igue load limi . Clinical s udies a e manda o y o es he s abili y o he di e en connec ions e alua ed, assessing he success a e and su i al o he p os hesis in an e io and pos e io ee h.