| Restoration of endodontically treated tooth commonly requires use of a post for coronoradicular stabilization.The main reason for this post is to retain the core that substitutes for the missing coronal portion of a tooth, and provides retention for a permanent restoration. Research has confirmed that posts do not reinforce teeth, but actually have the potential to weaken teeth. The main factors that determine the prognosis of restored pulpless teeth have been the preservation of healthy dentin. The main factor that determines the prognosis of restored pulpless teeth is preservation of sound dentin.Purpose:This study evaluated the mesio-distal distance of first maxillary premolars and the residual dentinal thickness (RDT) of maxillary and mandibular first premolars before and after root canal therapy and conservative post space preparation with 1#,2#,3#Peeso drills.Material and methods:1.30 first maxillary premolars, divided into three groups(A:bifurcation is within 5mm from CEJ B:bifurcation is over 5mm from CEJ or fused C:single root canal), were embedded in Silicone rubber and gypsum to the cemento-enamel junction. Five horizontal sections were made 2,4,6,8 and 10 mm apical to the CEJ. Mesio-distal (MD) and faciolingual (FL) axes were carefully marked, mesio-distal distance and the dentine thickness of buccal, lingual,medial and distal wall,was measured for each slice. Each tooth slice was reassembled in the muffle device.This procedure was repeated after root canal preparation to K-40 file and conservative post space preparation with 1#,2#,3# Peeso drills. 2.30 extracted single canal mandibular premolars were embedded in Silicone rubber and gypsum to the cemento-enamel junction (CEJ). Five horizontal sections were made 2,4,6,8 and 10 mm apical to the CEJ. Mesiodistal (MD) and faciolingual (FL) axes were carefully marked and the dentine thickness of buccal, lingual,medial and distal wall was measured for each slice. Each tooth slice was reassembled in the muffle device. This procedure was repeated after root canal preparation to K-40 file and conservative post space preparation with 1#,2#,3# Peeso drills.3. statistical analysisResults:1 Mesio-distal distance of first maxillary premolars (A:bifurcation is within 5mm from CEJ B:bifurcation is over 5mm from CEJ or fused C:single root canal)1.1 For first maxillary premolars, in each root level, the mesio-distal distance of buccal root or buccal side is more than palatal root or palatal side.1.2 Group A:the average mesio-distal distance of buccal and palatal root of 8mm apical to CEJ, and buccal root of 10mm apical to CEJ are over 3mm, and with significance (P<0.05). Group B:the average mesio-distal distance of buccal and palatal root of 6mm,8mm apical to CEJ is less than 3mm, in which no significance (P>0.05) of buccal root of 6mm apical to CEJ. Group C:the average mesio-distal distance of buccal and palatal root of 6mm,8mm, and buccal root of 10mm are less than 3mm, and with significance (P<0.05)2 RDT of maxillary first premolars (A:bifurcation is within 5mm from CEJ B: bifurcation is over 5mm from CEJ or fused C:single root canal)Group A:average primary dentinal thickness of each wall within 10mm apical to CEJ is over 1mm, in which no significance in dentinal thickness of buccal and palatal wall of buccal root (P>0.05); Group B:average primary dentinal thickness of each wall within 8mm apical to CEJ is over 1mm, in which no significance in dentinal thickness of medial and distal walls of 6mm and 8mm, and average primary dentinal thickness of medial and distal walls of 10mm is below 1mm, in which no significance exist (P>0.05); Group C:average primary dentinal thickness of medial and distal walls of 4mm and medial wall of 6mm are over 1mm, but with no significance, average primary dentinal thickness of medial and distal walls of 6mm and distal wall of 8mm is below lmm, with significance (P<0.05);3 RDT of mandibular first premolars3.1 For first mandibular premolars,8mm apical to CEJ, average primary dentinal thickness of medial and distal walls is over 1mm, in which no significance in dentinal thickness of medial wall (P>0.05); 10mm apical to CEJ, average primary dentinal thickness of medial and distal walls is below lmm, with no significance (P>0.05);3.2 For first mandibular premolars, average RDT of medial wall 8mm apical to CEJ is below 1 mm after RCT, with no significance (P>0.05); average RDT of medial wall 8mm apical to CEJ is below 1mm after being prepared by 1#P drill,, with significance(P<0.05); average RDT of medial and distal walls 6mm apical to CEJ is over 1mm, after being prepared by 2#P drill, with no significance (P>0.05); average RDT of medial and distal walls 6mm apical to CEJ, is below 1mm, after being prepared by 3#P drill, also with no significance (P>0.05);Conclusions:1 For maxillary first premolars,8mm, even 10mm length post can be used in bifurcated first maxillary premolars with bifurcation within 5mm to CEJ(the length of root is long enough to make sure of 4mm apical closure),others should use posts shorter than 6mm or with no post.2 For first mandibular premolars, on the basis that the the RDT of of each wall after post space preparation should be more than 1mm when post-core prosthesis be used, the size of peeso drill to prepare post is 1# for 8mm to CEJ,2# and 3# for 6mm to CEJ... |
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