A study on the thickness of radicular dentine and cementum in anterior and premolar teeth
http://endodonticsjournal.com/articles/73/1/A-study-on-the-thickness-of-radicular-dentine-and-cementum-in-anterior-and-premolar-teeth/Page1.html
By JofER editor
Published on 07/8/2002
C. Bellucci & N. Perrini
Private practice, Rome, Italy.
Accademia Italiana Endodonzia, Pistoia, Italy.
Aim.
This study aimed to measure the thickness of radicular dentine and cementum in incisors, canines and premolars, and to develop geometric average models.
Conclusions.
The aim of the study was to calculate an average thickness of root dentine and cementum for anterior and premolar teeth. The results obtained and the analysis conducted allowed the formulation of a hypothesis of a ‘standard average’ form for each group of teeth. Based on the results of this study, the following conclusions were drawn:
Private practice, Rome, Italy.
Accademia Italiana Endodonzia, Pistoia, Italy.
Aim.
This study aimed to measure the thickness of radicular dentine and cementum in incisors, canines and premolars, and to develop geometric average models.
Conclusions.
The aim of the study was to calculate an average thickness of root dentine and cementum for anterior and premolar teeth. The results obtained and the analysis conducted allowed the formulation of a hypothesis of a ‘standard average’ form for each group of teeth. Based on the results of this study, the following conclusions were drawn:
- Wall thicknesses varied greatly.
- Generally, thicknesses were greater on the lingual surfaces of the roots.
- Statistically significant differences between thicknesses in the mesial and distal surfaces of the roots were observed only in one case. Nevertheless, many roots were flattened mesio-distally.
- Wall thickness was thin in the apical third.
Introduction - Materials and methods.
C. Bellucci & N. Perrini
Private practice, Rome, Italy.
Accademia Italiana Endodonzia, Pistoia, Italy.
Introduction.
The survival of root filled teeth may depend on the amount of residual dentine (Hess & Keller 1928,Weeler 1965, Lloyd DuBrul 1980).M any studies demonstrate a direct relationship between the loss of tooth structure and the possibility of fracture of the tooth crown or root (Trabert et al.1978, Guzy & Nicholls1979, Mondelli et al. 1980, Sorensen & Martinoff 1984, Morfis 1990, Felton et al.1991,Testori et al.1993,Assif&Gorfil1994).However, little information about the thickness of canal walls is available.
There is an appreciable loss of dentine whilst preparing the access cavity and during canal preparation. The root thickness may be thin especially where grooves are present or between two fused roots. Attention must be paid when selecting endodontic instrumentation, with regard to their diameter and flexibility so that they are compatible with the anatomic shape of the root canal.
It is generally recommended to prepare the longest possible post whilst leaving at least 4 mm of intact filling. However, although roots often appear straight in standard radiographic observations, one study reported straight roots in only 2.7% of cases (Zillich & Yaman 1986).The purpose of this study was to measure the root wall, including both dentine and cementum, in extracted human incisors, canines, and premolars to develop geometric average models. The average dimension of the radicular wall for each cut surface indicated the areas at risk of stripping, perforation and radicular fracturing during endodontic treatment and during post-preparation.
Materials and methods.
A total of 220 human teeth extracted primarily for periodontal reasons from adult subjects aged between 35 and 55 years and not previously root treated were collected. T he following teeth were included: 40 maxillary incisors, made up of 15 lateral incisors and 25 central incisors; 20 maxillary canines; 45 maxillary premolars; 50 mandibular incisors; 30 mandibular canines; and 35mandibular premolars. Teeth were stored in a buffered formalin solution or a 2%sodiumhypochlorite solution. The teeth were then cleaned with an ultrasonic instrument to remove calculus and placed in 2%sodiumhypochlorite solution to remove remnants of the periodontal ligament. The teeth were dried and submitted for sectioning and measuring.
The buccal surface of each sample was used to measure the entire length of the tooth and the length of the root alone; all measurements were repeated. Three reference points were established and three horizontal parallel planes for sectioning the root were designated:
The teeth were sectioned by the means of an ultra thin, silicon-carbide separating disk (Dedeco International Inc., Long Eddy, NY, USA), with a thickness of 0.2mm. Measurements of the dentinal width were made using anOPMI1-FC optical microscope (Carl Zeiss, Oberkochen, Germany) with focal lense of 220 mm and with the aid of an object micrometer. All of the measurements were made to an accuracy of 0.01mm. For each cut surface, the following were recorded: maximal bucco-lingual (B-L) diameter, and maximal mesio-distal (M-D) diameter; buccal root thickness, measured from the external buccal limit of the root canal to the buccal surface of the root; lingual root thickness, measured from the external lingual limit of the root canal to the lingual surface of the root; mesial root thickness, measured from the external mesial limit of the root canal to the mesial surface of the root; and distal root thickness, measured from the external distal limit of the root canal to the distal surface of the root.
No distinction was made between mandibular central or lateral incisors. All mandibular premolars were included in a single group. The presence of two canals in one root was rare. In these cases, analysis was carried out in the following manner: the buccal wall measurement was made in relation to the buccal root canal and the measurement of the thickness of lingual wall was made in relation to the lingual root canal; in the mesial and distal zones, respectively, two measurements were made corresponding to the two canals. Therefore, for sections with two canals there were six measurements of wall thickness rather than four; anarithmetic average was made between the two mesial measurements and two distal measurements. For this reason, only one canal roots appear in the graphic model. Maxillary premolars were placed in two groups depending whether they had one single root or two distinct roots.
The data obtained were processed using SPSS software (Statistical Package for the Social Sciences).Mea ns and standard deviations of wall thicknesses were calculated for each position (buccal, lingual, mesial, and distal), each cut surface and each group of teeth. A Matlab software graphic tool (The Mathworks, Natick, MA, USA) was used to obtain the representation of the average thicknesses. Effects, and interactions of tooth type (mandibular or maxillary incisor, canine or premolar), location (buccal, lingual, mesial or distal), and section (surfaces 1-3) on the variation of wall thickness were examined by subjecting the data to a three-way analysis of variance (anova). For the statistical analysis, we considered the thickness as the dependent variable and the tooth type, section and location as independent variables. A mixed, three-way anova model was applied to analyze one single independent factor (tooth type) and two repeated factors (section and location).We considered all the differences tested as significant when the experimental F had a significance equal to P < 0.05. From this analysis, the group of maxillary premolars with two roots was excluded since it was not homogeneous with respect to the other groups of teeth. A separate analysis was conducted for this group. More over data were subjected to one-way anova to determine which group of teeth presented the greatest wall thickness and whether the difference was significant with respect to the other groups, the Duncan post hoc test was performed with significance level of 0.01. Furthermore, the wall thicknesses were compared, to determine whether the canals were central; the means of the buccal and lingual thicknesses, and the mesial and distal thicknesses for each of the three cut surfaces were subjected to paired t-test. The test was considered statistically significant if the two-tailed significance level was less than 0.01.
Private practice, Rome, Italy.
Accademia Italiana Endodonzia, Pistoia, Italy.
Introduction.
The survival of root filled teeth may depend on the amount of residual dentine (Hess & Keller 1928,Weeler 1965, Lloyd DuBrul 1980).M any studies demonstrate a direct relationship between the loss of tooth structure and the possibility of fracture of the tooth crown or root (Trabert et al.1978, Guzy & Nicholls1979, Mondelli et al. 1980, Sorensen & Martinoff 1984, Morfis 1990, Felton et al.1991,Testori et al.1993,Assif&Gorfil1994).However, little information about the thickness of canal walls is available.
There is an appreciable loss of dentine whilst preparing the access cavity and during canal preparation. The root thickness may be thin especially where grooves are present or between two fused roots. Attention must be paid when selecting endodontic instrumentation, with regard to their diameter and flexibility so that they are compatible with the anatomic shape of the root canal.
It is generally recommended to prepare the longest possible post whilst leaving at least 4 mm of intact filling. However, although roots often appear straight in standard radiographic observations, one study reported straight roots in only 2.7% of cases (Zillich & Yaman 1986).The purpose of this study was to measure the root wall, including both dentine and cementum, in extracted human incisors, canines, and premolars to develop geometric average models. The average dimension of the radicular wall for each cut surface indicated the areas at risk of stripping, perforation and radicular fracturing during endodontic treatment and during post-preparation.
Materials and methods.
A total of 220 human teeth extracted primarily for periodontal reasons from adult subjects aged between 35 and 55 years and not previously root treated were collected. T he following teeth were included: 40 maxillary incisors, made up of 15 lateral incisors and 25 central incisors; 20 maxillary canines; 45 maxillary premolars; 50 mandibular incisors; 30 mandibular canines; and 35mandibular premolars. Teeth were stored in a buffered formalin solution or a 2%sodiumhypochlorite solution. The teeth were then cleaned with an ultrasonic instrument to remove calculus and placed in 2%sodiumhypochlorite solution to remove remnants of the periodontal ligament. The teeth were dried and submitted for sectioning and measuring.
The buccal surface of each sample was used to measure the entire length of the tooth and the length of the root alone; all measurements were repeated. Three reference points were established and three horizontal parallel planes for sectioning the root were designated:
- through the buccal cemento-enamel junction
- 4 mm coronal to the anatomic apex, and
- half-way between the other two planes.
The teeth were sectioned by the means of an ultra thin, silicon-carbide separating disk (Dedeco International Inc., Long Eddy, NY, USA), with a thickness of 0.2mm. Measurements of the dentinal width were made using anOPMI1-FC optical microscope (Carl Zeiss, Oberkochen, Germany) with focal lense of 220 mm and with the aid of an object micrometer. All of the measurements were made to an accuracy of 0.01mm. For each cut surface, the following were recorded: maximal bucco-lingual (B-L) diameter, and maximal mesio-distal (M-D) diameter; buccal root thickness, measured from the external buccal limit of the root canal to the buccal surface of the root; lingual root thickness, measured from the external lingual limit of the root canal to the lingual surface of the root; mesial root thickness, measured from the external mesial limit of the root canal to the mesial surface of the root; and distal root thickness, measured from the external distal limit of the root canal to the distal surface of the root.
No distinction was made between mandibular central or lateral incisors. All mandibular premolars were included in a single group. The presence of two canals in one root was rare. In these cases, analysis was carried out in the following manner: the buccal wall measurement was made in relation to the buccal root canal and the measurement of the thickness of lingual wall was made in relation to the lingual root canal; in the mesial and distal zones, respectively, two measurements were made corresponding to the two canals. Therefore, for sections with two canals there were six measurements of wall thickness rather than four; anarithmetic average was made between the two mesial measurements and two distal measurements. For this reason, only one canal roots appear in the graphic model. Maxillary premolars were placed in two groups depending whether they had one single root or two distinct roots.
The data obtained were processed using SPSS software (Statistical Package for the Social Sciences).Mea ns and standard deviations of wall thicknesses were calculated for each position (buccal, lingual, mesial, and distal), each cut surface and each group of teeth. A Matlab software graphic tool (The Mathworks, Natick, MA, USA) was used to obtain the representation of the average thicknesses. Effects, and interactions of tooth type (mandibular or maxillary incisor, canine or premolar), location (buccal, lingual, mesial or distal), and section (surfaces 1-3) on the variation of wall thickness were examined by subjecting the data to a three-way analysis of variance (anova). For the statistical analysis, we considered the thickness as the dependent variable and the tooth type, section and location as independent variables. A mixed, three-way anova model was applied to analyze one single independent factor (tooth type) and two repeated factors (section and location).We considered all the differences tested as significant when the experimental F had a significance equal to P < 0.05. From this analysis, the group of maxillary premolars with two roots was excluded since it was not homogeneous with respect to the other groups of teeth. A separate analysis was conducted for this group. More over data were subjected to one-way anova to determine which group of teeth presented the greatest wall thickness and whether the difference was significant with respect to the other groups, the Duncan post hoc test was performed with significance level of 0.01. Furthermore, the wall thicknesses were compared, to determine whether the canals were central; the means of the buccal and lingual thicknesses, and the mesial and distal thicknesses for each of the three cut surfaces were subjected to paired t-test. The test was considered statistically significant if the two-tailed significance level was less than 0.01.
Results.
Sections of the roots of the maxillary central incisors were mainly circular in shape or slightly triangular; this shape was generally maintained in the middle third of the root. The roots of the maxillary lateral incisors were flattened lengthwise in the mesio-distal direction and the radicular canal was slightly oval in shape. The sections of the maxillary canines displayed roots with a bucco-lingual major diameter; the radicular canals were oval in shape. Most of the roots of the maxillary premolars were flattened in the mesio-distal direction with a deep sulcus along the root. The maxillary premolars with two roots showed only one large chamber canal in the first section in correspondence with the cemento-enamel junction, the two roots in the remaining part were circular. The roots of the mandibular incisors were thin and flattened lengthwise in the mesio-distal direction and the radicular canals were ribbon-like. The roots of the mandibular canines were oval-shaped and the radicular canals were circular. The roots and canals of the mandibular premolars were mostly circular in shape.
The average and standard deviation of the values obtained for each group of teeth are listed in Tables 1-3. The average thicknesses of the radicular wall for each group of teeth are graphically illustrated in Figs 1-8. With the assumption that the centre of the canal is the centre of each drawing, profiles of the sections are drawn into a grid of known dimensions with values expressed in millimetres. The actual measurements are superimposed on one another for each of the three horizontal sections and displayed on the left side of the figures. In the right column of the figures, a schematic representation of the mean values of the measurements for each of the three sections is illustrated. The graphic images represent the average of the measurements obtained.
In the one-way anova results, the post hoc analysis with the Duncan tests, revealed that the mean wall thickness in the buccal position of the first cut surface %
The average and standard deviation of the values obtained for each group of teeth are listed in Tables 1-3. The average thicknesses of the radicular wall for each group of teeth are graphically illustrated in Figs 1-8. With the assumption that the centre of the canal is the centre of each drawing, profiles of the sections are drawn into a grid of known dimensions with values expressed in millimetres. The actual measurements are superimposed on one another for each of the three horizontal sections and displayed on the left side of the figures. In the right column of the figures, a schematic representation of the mean values of the measurements for each of the three sections is illustrated. The graphic images represent the average of the measurements obtained.
Table 2. Mean thickness and standard deviation (+-SD), in millimetres, for each cut surface of upper canines and lower canines and premolars.
Table 3. Mean thickness and standard deviation (+-SD), in millimetres, for each cut surface of upper premolars. In correspondence, the cementoenamel junction of premolars with two roots, surface1, the two canals are still fused together.
Figure 1. Maxillary central incisors (MCI): on the left is a superimposition of the graphic representation of actual measurements of all samples of the three horizontal sections. On the right is the average shape with the average wall thickness in millimetres.
In the one-way anova results, the post hoc analysis with the Duncan tests, revealed that the mean wall thickness in the buccal position of the first cut surface %
Discussion - References.
Discussion.
There is little information in the literature concerning the thickness of radicular dentine. This study was carried out with the intention of providing important data on this relevant topic.
The pulp of a tooth decreases in volume with the passage of time. The teeth examined in this study were from adult subjects aged between 35 and 55 years. The teeth were extracted primarily because of periodontal disease and the canals were often narrow.
Amongst the specimens examined the presence of two canals in a single root was rare. Only one main canal was found in each of the40maxillary incisors examined. In the group of maxillary canines only one specimen was divided in the coronal third due to the presence of a dentinal island. No distinction was made between mandibular central or lateral incisors because there were no remarkable differences between the two groups. Sometimes dentine islands forming two canals were noted in the second and third sections with in a longitudinally flattened canal, however, the canals always had a single apical foramen. For the group of mandibular canines, only in one case out of the 30 teeth examined were there two roots and two canals, in all the other cases there was one single, generally wide, canal. All mandibular premolars were included in a single group because none were found with two canals and also because roots of first and second premolars were similar in shape.
The results of the anova, with the computation of the ETAsqd, show that the thickness of radicular dentine mainly varies depending on location and section factors rather than tooth type. In other words, independent of the tooth type, a similar variation of dentine thickness can be observed in all of the teeth studied.
Larger values of dentine thickness were detected near the lingual and buccal surfaces with reduced thicknesses near the mesial and distal surfaces. In many sections, the dentine was very thin. Thus, it follows that the knowledge of the radicular dentine thickness must serve as a guide to all treatment that includes the root of the tooth. Clearly, one must use the utmost caution when introducing rotating, rigid or large-diameter instruments into the canal.
Biomechanical studies suggest that at least 1mm of root dentine should remain around the post (Caputo & Standlee 1988) to avoid the risk of root fracture. There fore, during canal preparation it is advisable to remove as little dentine as possible and during post-preparation, it is advisable to follow the anatomy of the radicular canal by designing flattened posts in a mesio-distal direction, with tapered vertical walls. The dentine should mainly be removed, if necessary, in the lingual area where the thickness is greater. In the apical part, there is very little dentine available therefore in this area it is preferable not to remove any dentine but only to clean the canals of filling material.
This study has been limited to the observation of radicular dentine thickness in anterior teeth and premolars. The teeth examined belonged to adult subjects between the ages of 35 and 55 years that were extracted because of periodontal disease.
As a result, data on the dentine thickness of teeth from younger subjects is missing. This would be expected to show a smaller radicular dentine thickness due to larger dimensions of the pulp. In the future it would be desirable to conduct studies on posterior teeth and other age groups.
There is little information in the literature concerning the thickness of radicular dentine. This study was carried out with the intention of providing important data on this relevant topic.
The pulp of a tooth decreases in volume with the passage of time. The teeth examined in this study were from adult subjects aged between 35 and 55 years. The teeth were extracted primarily because of periodontal disease and the canals were often narrow.
Amongst the specimens examined the presence of two canals in a single root was rare. Only one main canal was found in each of the40maxillary incisors examined. In the group of maxillary canines only one specimen was divided in the coronal third due to the presence of a dentinal island. No distinction was made between mandibular central or lateral incisors because there were no remarkable differences between the two groups. Sometimes dentine islands forming two canals were noted in the second and third sections with in a longitudinally flattened canal, however, the canals always had a single apical foramen. For the group of mandibular canines, only in one case out of the 30 teeth examined were there two roots and two canals, in all the other cases there was one single, generally wide, canal. All mandibular premolars were included in a single group because none were found with two canals and also because roots of first and second premolars were similar in shape.
The results of the anova, with the computation of the ETAsqd, show that the thickness of radicular dentine mainly varies depending on location and section factors rather than tooth type. In other words, independent of the tooth type, a similar variation of dentine thickness can be observed in all of the teeth studied.
Larger values of dentine thickness were detected near the lingual and buccal surfaces with reduced thicknesses near the mesial and distal surfaces. In many sections, the dentine was very thin. Thus, it follows that the knowledge of the radicular dentine thickness must serve as a guide to all treatment that includes the root of the tooth. Clearly, one must use the utmost caution when introducing rotating, rigid or large-diameter instruments into the canal.
Biomechanical studies suggest that at least 1mm of root dentine should remain around the post (Caputo & Standlee 1988) to avoid the risk of root fracture. There fore, during canal preparation it is advisable to remove as little dentine as possible and during post-preparation, it is advisable to follow the anatomy of the radicular canal by designing flattened posts in a mesio-distal direction, with tapered vertical walls. The dentine should mainly be removed, if necessary, in the lingual area where the thickness is greater. In the apical part, there is very little dentine available therefore in this area it is preferable not to remove any dentine but only to clean the canals of filling material.
This study has been limited to the observation of radicular dentine thickness in anterior teeth and premolars. The teeth examined belonged to adult subjects between the ages of 35 and 55 years that were extracted because of periodontal disease.
As a result, data on the dentine thickness of teeth from younger subjects is missing. This would be expected to show a smaller radicular dentine thickness due to larger dimensions of the pulp. In the future it would be desirable to conduct studies on posterior teeth and other age groups.
References.
Assif D, Gorfil C (1994) Biomechanical considerations in restoring endodontically treated teeth. Journal of Prosthetic Dentistry 71,565-7.
Caputo AA, Standlee JP (1988) Basic principles of posts: a foundation for the future. Journal of Clinical Dentistry 1, 45-9.
Felton DA, Webb EL, Kanoy MA, Dugoni J (1991) Threaded endodontic posts: effects of their morphology on the incidence of radicular fractures. Journal of Prosthetic Dentistry 65, 179-84.
Guzy GE, Nicholls JI (1979) In vitro comparison of intact endodontically treated teeth with and without endopost-reinforcement. Journal of Prosthetic Dentistry 42, 39-42.
HessW, Keller O (1928) Anatomical Plates.Zurich, CH:University of Zurich. Lloyd DuBrul E (1980) Sicher's Oral Anathomy,1st edn. St . Louis, MO, USA: C.V. Mosby Company.
Mondelli J, Steagal IL, Ishikiriama A, Navarro M, Soares FB (1980) Fracture strength of human teeth with cavity preparation. Journal of Prosthetic Dentistry 43, 419-22.
MorfisAS (1990) Vertical root fractures. Oral Surgery, Oral Medicine and Oral Pathology 69, 631-5.
Sorensen JA, Martinoff MD (1984) Intracoronal reinforcement and coronal coverage: a study of endodontically treated teeth. Journal of Prosthetic Dentistry 51, 780-7.
Testori T, Badino M, Castagnola M (1993) Vertical root fractures in endodontically treated teeth: a clinical survey of 36 cases. Journal of Endodontics19, 87-90.
Trabert K, Caputo AA, Abou-Rass M (1978) Tooth fracture: a comparison of endodontic and restorative treatments. Journal of Endodontics 4, 341-4.
Weeler RC (1965) A Textbook of Dental Anatomy and Physiology, 4th edn. Philadelphia, USA: W.B.Saunders Company.
Zillich R, Yaman P (1986) Root curvature localizations as indicators of post-length in various tooth groups. Endodontics and Dental Traumatology 2, 58-61.