| [Objectives]The aim of this in vivo study was to investigate the thickness of hard tissues of maxillary incisors, and to provide some anatomic basis for crown and post space preparation of Chinese maxillary incisors.[Materials and Methods]CBCT (NewTom 3G QR-DVT9000, Italy) data were obtained from Department of Radiology, Hospital of Stomatology affiliated to Zhejiang University School of Medicine, from August 2014～January 2015. One hundred fifty maxillary central and lateral incisors from the CBCT data were selected for this study, age from 20 to 50 years old. The cross-sections of incisors at 0.5mm interval were used to measure the thicknesses of hard tissues and the diameters of the root. The crown and root lengths were calculated by the cross-section numbers from the incisal margin(IM) to the cemento-enamel junction(CEJ), and from the CEJ to the apex. The probability that the residual dentine thickness(RDT) remaining not less than 0.5mm or 1.0mm after crown preparation was analyzed. The rotary instruments (peeso reamers, Mani, Japanese; 3M RelyXTM Fiber Post, USA) were used for theoretical calculatiom. Diameters from 1#-6# peeso reamers (Mani) are 0.7,0.9,1.1,1.3,1.5,1.7mm, and the top end of the fiber post (3M, ESPE) are 0.7,0.8,0.9mm. The probability of the residual root wall thickness(RRT) remaining 1.0mm after post space preparation by 1#-6# peeso reamers (Mani) and use fiber post (3M, ESPE) were analyzed. Use the single sample K-S test to check the date is obey normal distribution or not, then use Wilcoxon signed rank test or Paired Sample T test to check the significant difference between the test groups.[Results]The ratios of crown to root of maxillary central and lateral incisors are 1:1.20,1:1.23 respectibely. The low percentile (P25) of pulp cavity walls thickness was greater than 1.4mm. The mesial thickness of crown was slightly thinner than the distal.When ceramic crown preparation at maxillary central incisors, the probability that residual dentin thickness(RDT) remaining not less than 1.0mm(RDT≥1.0mm):incisal third, center third and neck third at the labial side (49%,30%,73%), palatal side (18%, 32%,96%), mesial side (23%,25%,81%), distal side (62%,60%,92%), respectively. The least all close to 100%.And their probabilities that RDT≥0.5mm were incisal third and center third at palatal side (63%,80%), mesial side (79%,84%), center third at labial side(89%), respectively. The least all close to 100%.The metal-ceramic crown preparation is similar to ceramic crown, the probabilities that mesial and distal of the crown are same as ceramic crown. The probabilities that RDT≥1.0mm:incisal third and center third at labial side (49%,70%), palatal side (34%,52%), respectively. The least all close to 100%. And their probabilities that RDT≥0.5mm:incisal third at palatal side (80%), the least all close to 100%. When ceramic crown preparation at maxillary lateral incisors, the probabilities that RDT≥0.5mm:incisal third and center third at labial side (78%,89%), palatal side(64%,77%), mesial side (78%,80%), respectively. The least all larger than 90%. The metal-ceramic crown preparation is similar to ceramic crown, the probabilities that mesial and distal of the crown are same as ceramic crown. The probabilities that RDT≥0.5mm:incisal third and center third at palatal side (78%,86%),respectively. The least all larger than 90%.If the shoulder width was set at 1.0mm, at the mesial and distal of the cross-sections at enamelo-cemental junction(CEJ), the thickness of pulp chamber of central incisors were 2.1±1.9/2.3mm(Median±P25/P75,the same below)and 2.1±2.0/2.3mm,their probabilities that RDT≥1.0mm were less than 70%, RDT≥0.5mm were about 100%; at the same position of lateral incisors, the thickness were 1.7±1.6/1.9mm, while the probabilities that RDT≥1.0mm were less than 20%, RDT≥0.5mm were about 85%. When the shoulder width was set at more than 0.8mm, the probabilities that RDT≥0.5(1.0)mm decreased dramatically at central incisors. At lateral incisors the shoulder width was set at more than 0.5mm, the probability of RDT≥1.0mm decreased dramatically; and when more than 0.8mm, the probability of RDT≥0.5mm decreased dramatically. There is 0.67% teeth of maxillary lateral incisors that the thickness of incisal margin(IM) are less than 2.5mm. When prepared for 2mm, the probabilities that not RDT≥1.0(0.5)mm are 95%(99%) (central),96%(99%)(lateral). The thickness of IM increased with age over 30 years old. If the preparation reduction was greater than 1.4mm at the mesial and distal sides of maxillary incisors, the RDT decreased dramatically.The root walls thicknesses(P25) were not less than 1.2 mm at 4-6 mm distant from the apex in maxillary centeral incisors, and not less than 0.9mm in lateral incisors.In maxillary central incisors:The palatal root walls thickness of the maxillary central incisors was greater than the labial, while the mesial root wall thickness was similar to the distal. The probabilities that the residual root thickness(RRT)≥1.0mm of the labial root walls in central incisors at 4mm distance from the apex were 96%,92%,88%,81%,respectively, after post preparation by 1～4# peeso reamer (Mani); at the palatal side were up to 100%. The probabilities of the labial and palatal side at 5mm distance from the apex were up to 100%.The thickness of the mesial and distal root walls in central incisors at 4mm distance from the apex was 1.4±1.2/1.5mm, and their probabilities that RRT≥1.0mm were 87%,82% 77%, respectively, after post space preparation by 1-3# peeso reamer (Mani), and 88%,81%,72% after use yellow, red, blue-marker fiber post (3M ESPE). The probability approach 100% when RRT≥0.8mm,0.7mm,0.6mm after use 1～3# peeso reamer. The thickness of the mesial and distal root walls in central incisors at 5mm distance from the apex was 1.5±1.4/1.7mm, and the probability that RRT≥1.0mm was 95%,91%,86%, after post space preparation by 2-4# peeso reamer, and approach 100% after use yellow, red and blue-marker fiber post.The probability that RRT≥1.0mm approach 100% at 6mm distance from the apex when 6# peeso reamer used.In maxillary lateral incisors:The palatal root walls thickness of the maxillary central incisors was similar to the labial, while the mesial root wall thickness was similar to the distal. The probabilities that the RRT≥1.0mm of the labial and palatal root walls at 4-9mm distance from the apex all approach 100%. The thickness of the mesial and distal root walls in central incisors at 4mm distance from the apex was 1.0±0.9/1.2mm, and the probabilities that the RRT≥1.0mm were less than 40%, after post space preparation by 1# peeso reamer (Mani) and yellow-marker fiber post (3M ESPE). The probability approach 100% when RRT≥0.5mm after use 1# peeso reamer. The thickness of the mesial and distal root walls in central incisors at 5mm distance from the apex was 1.2±1.0/1.3mm, and the probability that RRT≥1.0mm was 75% and 61%, respectively, after post space preparation by 1～2# peeso reamer (Mani) and 70% after use yellow-marker fiber post (3M ESPE). The probability approach 100% when RRT≥0.7, 0.6mm after use 1-2# peeso reamer.The thickness of the mesial and distal root walls in central incisors at 6mm distance from the apex was 1.3±1.2/1.4mm, and the probabilities that RRT≥1.0mm was 92%,85%, after post space preparation by 1-2# peeso reamer, and the probabilities were 92%,87% after use the yellow, red-marker fiber post.[Conclusions]1.It’s applicable to prepare no more than 0.8mm shoulder at mesial and distal of centeral incisors,0.5mm at lateral incisors, and maximum no more than 0.8mm. And it’s inapplicable to prepare more than 1.4mm at mesial and distal of maxillary incisor’s crown.2.1t’s inapplicable to use lager than 2# peeso reamers and blue fiber post at 4mm distance from the apex, and use larger than 3# peeso reamer at 5mm distance from the apex of maxillary central incisors.3.It’s applicable to only use 1# peeso reamers and yellow fiber posts at 4,5mm distance from the apex of maxillary lateral incisors. |
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