STATISTICAL ANALYSIS OF ACOUSTIC EMISSIONS DURING SHRINKAGE OF - PDF document

18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS STATISTICAL ANALYSIS OF ACOUSTIC EMISSIONS DURING SHRINKAGE OF RESTORATION IN DENTAL SUBSTRATE J. U. Gu 1, N. S Choi 1 *, K. Arakawa 2 1 Department of Mech. Eng., Hanyang Univ., Gyunggi-do 426-791, Korea 2 Research Institute for Applied Mechanics, Kyushu Univ., Kasuga city, Fukuoka, Japan * Corresponding author (nschoi@hanyang.ac.kr) Keywords : Composite restoration, Acoustic emission, Non-parametric statistics 1 Introduction (significance probability) is calculated by Eqs.(1) Evaluation of marginal integrity at the composite and (2). � � �N��� resin-tooth interface is required for clinically E�W� � (1) � successful restorations. Polymerization contraction � � � � �N��� V�W� � (2) of the composite resin that fills in a cavity occurs �� during light curing. This contraction competes with W�E�W���.� p � value � 2Φ � � (3) �V�W� the bond strength and may cause marginal disintegration. There can be some unbonded state and/or cleavage formation around the margin of the where, n 1 : the number of sample 1, n 2 : the number of sample 2, N=n 1 +n 2 . composite resin part, leading to insufficient sealing of open dentinal tubules[1]. Various experiments 2.2 Kruskal-Wallis test such as SEM and dye penetration test[2] have been Kruskal-Wallis test[5] is a non-parametric performed for observing the marginal gap along the statistical test for testing the equality of population composite resin-tooth interface. These studies did medians among three or more groups. The test not show any temporal analysis of debonding statistic H is calculated by equation (4) with the rank mechanisms. The present authors investigated the of each data ( R i ). fracture process of composite/tooth by an acoustic emission (AE) monitoring in real-time[3]. The AE � �� � � � data that was newly obtained needs to be ������ ∑ � � � � � 3�� � 1� (4) ��� differentiated according to various test conditions. In this study, a non-parametric statistic is applied to where, n i : the number of sample in i th population, N: verify the difference of AE amplitudes and AE hits sum of total samples, R i : the rank of sample in i th depending on substrate kinds and adhesive population. conditions. p � value � 1 � χ � �k � 1, H� (5) 2 Non-parametric statistical tests The p-value is approximated by equation (5). 2.1 Mann-Whitney test The Mann-Whitney test[4] is a non-parametric 3 Experimental statistical hypothesis test for assessing whether two independent samples for observations show equality 3.1 Acoustic emission measurement values. First, the null hypothesis that the medians of Non-penetration ring type substrates(inner the first population and the second population are diameter 6mm, outer diameter 8mm, depth 2mm, equal is established. Each data rank is sought height 3mm) were prepared. Three substrate through a sum of two population samples. Equations materials of stainless steel, PMMA and human tooth (1) and (2) indicate the mean value(E) and the were adopted. The human tooth specimen was made variation(V) of the test statistic W. The p-value as shown Fig.1.

sig gnificance a among more e than two groups. A All sta atistical tests s were perfo ormed at a 95% level o of con nfidence. 3 .3 Microsco opic examina ation of the marginal dis sintegration n After the s train measu urement and the acoust tic em mission det tection of the com mposite resi in res storations, th he ring and human mol lar specimen ns we ere consolida ated into a p plastic mold. The top par rts of the specime ens were sli ightly section ned, and the en F Fig. 1 Prepara ation of the h human tooth specimen we ere ground a and polished d with buff and abrasiv ve alu umina pow wder. The polished su urfaces wer re ob served by optical and d SEM to examine th he ma arginal disin ntegration a and gap for rmation state es aro ound the mar rgin of the co omposite res storations. Th he gap p thickness and the gap percentage at the margi in of the compo osite resin w were measur red. The ga ap per rcentage wa s obtained fr from the sum mmation of th he gap p lengths for rmed along the margin o over the inn er per riphery of th he ring substr rate. 4 R Results and Discussion F Fig. 2 Schem matic of speci men fixture for acoustic e emission mea asurement 4 .1 Detection n of AE para ameter Table 1 sho ows the num mber of AE hits, the pea ak The extrac cted tooth w as mounted on the botto om. am mplitude and initial gene ration time of AE for th he The liquid po T olymer was f filled in a sh hort plastic p pipe go od bonding state. The q quantity of A AE hits for th he and then fixe a d by curing. For compari ison of bond ding hu uman tooth s substrate wa s much less than that fo for q quality, rings s without ad dhesive coat ting as well l as the e steel substr rate but more e than that fo for the PMM A ri ings with ad dhesive coati ing, but not exposed by the sub bstrate. The amplitude a and initial ge eneration tim me LED light, w L were also pr repared. The e specimen w was of AE, howeve er, was diffi icult to distin nguish clearl ly m mounted on the wave guide stee el plate us sing acc cording to s substrate ma aterials. Fig. 4 shows th he s pecially desi igned mecha anical fixture e(Fig.2). An AE nu umber of AE E hits and a amplitude fo or the huma an s ensor (micro o30, Physica al Acoustic C Corp.) havin ng a too oth substrate e according t to the bondin ng condition ns. detectable fre d equency ran ge of 100–6 600 kHz wit th a Th he number o f AE hits fo or good bond ding state wa as peak sensitiv p vity at 250 k kHz was al so mounted on les ss than for b bad bonding state. Howe ever, based o on th he steel plat te with a clo ose distance of 15mm fr rom the e mean valu ues of AE h hits and the amplitudes, it th he ring spec cimen. The v vacuum grea ase coupled the wa as hard to dif fferentiate th he bonding c conditions du ue s ensor and t the plate. A E measurem ment conditio ons to large deviati ions in AE d data. For the classification n, were a pre-am w mp of 40 dB , a threshold d level of 25 dB a s statistic comp parison of m measured AE parameters is and a samplin a ng rate of 4 M MHz. From t this AE test, the ne eded on vari ious experim mental conditi ions. A AE hits and th he amplitude es were meas sured. 3.2 Statistic cal analysis T Table 1 AE hit events a and amplitud de for variou us sub bstrate ring s specimens The AE h hits and AE amplitudes were analyz zed Amplitude t ini s tatistically b by the Krus kal-Wallis t test and Ma ann- Materials AE hits (dB) (sec) W Whitney test . The Mann -Whitney te st is conduc cted PMMA 1.89±1.17 36.08±5.73 19.23±16.88 to o investigate e the signific cance betwe een two grou ups. Human tooth 6.75±1.50 31.94±3.92 43.18±48.78 T The Kruskal- -Wallis test is conducted d to investig gate Stainless steel 12.00±3.39 34.83±10.53 25.00±23.60

STATISTICAL ANALYSIS OF ACOUSTIC EMISSIONS DURING SHRINKAGE OF RESTORATION IN DENTAL SUBSTRATE Table 2 AE hits and statistical result according to different substrate Table 3 AE hits and statistical results according to different adhesive conditions Fig. 3 Results of AE hit events and amplitude for the human molar dentin specimens 4.2 Significance analysis for AE hit data Table 2 shows the AE hits and their statistical results according to ring substrate in the good bonding state with adhesive and LED. The number of AE hits revealed statistically significant differences from both Mann-Whitney and Kruskal- Table 4 AE amplitude and statistical results Wallis tests (p<0.05). Table 3 shows the AE hits and according to different adhesive conditions statistical results according to different adhesive conditions. Statistical difference was observed between good bonding state and bad bonding state for PMMA substrate (p<0.05; Mann- Whitney test). Similarly for human tooth substrate, statistical difference was observed between good bonding state and bad bonding state (p<0.05; Mann-Whitney test). The AE hits were not statistically significant for bad states of PMMA and human tooth substrate. Meanwhile, statistical difference was not observed between good bonding state and bad bonding state for stainless steel substrate (p>0.05; Mann-Whitney test). On Kruskal-Wallis test, the number of AE hits showed significant results in all substrate (p<0.05). with a composite resin restoration. Because the PMMA had high bond strength with the adhesive human tooth substrate has higher stiffness than for a good restoration. PMMA ring was PMMA, AE events were more detected than PMMA. compressible due to its low stiffness. These advantages brought about little cracking, and led to 4.3 Significance analysis for AE amplitude less detection of AE events for PMMA substrate. Table 4 shows the AE amplitude and statistical Many AE events, meanwhile, were detected for results according to various adhesive conditions. For stainless steel substrate since stainless steel had high PMMA and human tooth substrate, since most of stiffness and poor bonding state. Human tooth hits corresponded to the low amplitudes 25-40dB substrate etched by a bonding agent combined well 3