A study on the thickness of radicular dentine and cementum in anterior and premolar teeth

AIM: This study aimed to measure the thickness of radicular dentine and cementum in incisors, canines and premolars, and to develop geometric average models. METHODOLOGY: The roots of 220 extracted human teeth were sectioned in three horizontal parallel planes and measured using an optical microscope. For each cut surface buccal, lingual, mesial, and distal thickness of the root wall was measured. Mean values of the thickness at each location of each cut surface were calculated. The observed differences in thickness by tooth type, location, and section were compared by ANOVA and Student's t-test. RESULTS: Maxillary central incisors and maxillary canines had the greatest widths. In all teeth with a single root, the wall thickness were greater on the lingual side than the buccal side. Although differences between mesial and distal thicknesses were not statistically significant. CONCLUSIONS: Wall thickness varied greatly. The lingual surfaces of roots were larger. All roots had thin walls in the apical third.     

无托槽隐形矫治拔牙病例的后牙不同轴倾度对牙齿三维力学影响

目的 研究无托槽隐形矫治技术拔除双侧上颌第一前磨牙病例整体内收前牙，后牙不同轴倾度时，各个牙齿的瞬时受力情况。方法 设置4组后牙不同轴倾度的上颌牙列，T1组后牙为正常牙合轴倾度，T2组后牙在T1组基础上后倾5°,T3组后牙在T1组基础上前倾5°,T4组后牙在T1组基础上前倾10°。拔除双侧第一前磨牙，整体内收前牙0.25 mm,在矫治器六轴力传感器测试平台上测量4组牙列中各个牙齿在三维方向的瞬时力。每组牙列设计12副隐形矫治器。结果 与T1组相比，T2组切牙伸长力减小，尖牙远中向力增加，后牙近中向力减小，磨牙颊向和伸长力增大，差异均有统计学意义(P<0.05)。与T1组相比，T3和T4组切牙舌向力和伸长力增大，尖牙远中向力增大，后牙近中向力也增大，磨牙颊向和伸长力增大，差异均有统计学意义(P<0.05)。结论 后牙后倾时利于前牙转矩的表达，有助于保护后牙支抗，但增加了磨牙的颊向力和伸长力。后牙前倾时，前牙更容易出现转矩丢失，覆牙合加深的现象。后牙越前倾，覆牙合越容易加深，后牙支抗容易丢失。     

滑动法关闭下颌拔牙间隙的力学行为有限元分析

目的模拟临床加载力系统,研究滑动法内收下前牙过程中,不同方向载荷作用下,牙及弓丝力学行为的变化。方法建立含有托槽、弓丝、前后牙牵引钩的下牙列及下颌骨有限元模型。连接前后牵引钩上的点来确定矫治力的方向。并通过改变牵引钩高度来改变矫治力的作用点和方向。分析计算每一组加载力对牙的三维瞬间移动趋势、牙周膜的单元应力、弓丝的节点最大位移。结果前后牵引钩高度的变化与各牙角位移及牙周膜应力间均有相关性(P<0.01),各牙在不同后牙牵引钩高度,均随着前牙牵引钩高度变化而产生不同的移动。①随着前牙牵引钩高度的增加,中切牙、侧切牙的移动趋势逐渐由近中舌侧倾斜变为近中唇侧倾斜;而尖牙则向远中舌侧倾斜;第二前磨牙由近中颊侧倾斜变为近中舌侧倾斜;第一磨牙则由近中舌侧倾斜变为远中舌侧倾斜,且近中根比远中根舌向倾斜角度要大。②全牙弓牙周膜的最大应力始终出现在侧切牙的唇侧根尖1/3处;而尖牙、第一磨牙的牙周膜最大应力分别集中在牙槽嵴顶、根分叉处。结论在临床治疗中,可通过改变牵引钩的高度来实现前后牙的不同移动趋势,在弓丝上弯制不同的序列以更好地控制支抗牙。     

A comparative study of dentin thickness of primary human molars

The aim of the present survey was to evaluate the dentin thickness of buccal, lingual, mesial and distal surfaces of first and second primary molars. These evaluations were done at the middle third of the crowns of twenty extracted non-carious primary teeth separated in two groups (first molars and second molars). Comparisons were performed within-groups and between-groups. The mean values of dentin thickness observed for first molars were 2430 mm (buccal), 1.869 mm (lingual), 1.655 mm (mesial) and 1.664 mm (distal). For second molars the dentin thickness presented 3.006 mm (buccal), 2730 mm (lingual), 2130 mm (mesial) and 2192 mm (distal). The dentin thickness was higher in the buccal surface in both groups (P<0.05; Wilcoxon Test), except for the lingual surface of second molars (P>0.05). No differences were observed between mesial and distal surfaces in both groups (P>0.05). Comparisons between-groups showed that the dentin thickness was higher in all surfaces of second molars (P<0.01; Mann-Whitney Test). It was concluded that there are differences in the dentin thickness between first and second primary human molars and within the different surfaces of such teeth.     

第一磨牙的生理性磨耗

目的：通过对上、下颌第一磨牙不同部位生理性磨耗的观察，探讨磨耗特征及其生理意义。方法：５５１ 个上颌第一磨牙和６８６ 个下颌第一磨牙，根据磨耗程度分为轻、中、重度（ 绝对磨耗程度），根据单个牙上不同部位磨耗程度排序（ 相对磨耗程度），比较各部差别。结果： 上颌第一磨牙磨耗程度由重到轻排序：近、远舌尖＞ 近、远中边缘嵴＞ 近、远颊尖；下颌第一磨牙排序：远中尖、远中边缘嵴＞ 近、远颊尖＞ 远舌尖＞ 近舌尖、近中边缘嵴。结论：上颌第一磨牙以舌尖磨耗最重，而下颌第一磨牙则为远中部磨耗最重，可能与局部咬合力作用时间及作用强度有关。     

Cross-sectional morphology and minimum canal wall widths in C-shaped roots of mandibular molars

The cross-sectional canal morphology and minimum widths of buccal and lingual canal walls were studied in 20 mandibular molars with C-shaped roots and canal orifices. The roots were mounted in clear resin blocks and sectioned transversely at 1-mm intervals. A total of 154 cross-sections were evaluated with an image analyzer. Twelve different longitudinal canal configurations were identified. The most prevalent were types 1-2 and 1-2-1 with each type occurring in four roots. Evaluation of the cross-sectional morphology showed that the configurations were complete "C" (27%), incomplete C (64%), and non-C (9%). The mean value for the minimum width of the lingual canal wall was 0.58 +/- 0.21 mm and the buccal wall was 0.96 +/- 0.26 mm. This suggests that there is a higher risk of root perforation at the thinner lingual walls of C-shaped canals during shaping and post canal preparation procedures. Both buccal and lingual canal walls were frequently narrower at mesial locations.     

The effect of axial grooves on the resistance form of cast restorations.

Fifteen sets of castings were fabricated to machined stainless steel dies of 5 degrees, 10 degrees, and 15 degrees of taper and 3, 4, 6, 8, and 10 mm of preparation length. Each casting was loaded vertically on its sloped surface in an attempt to unseat the casting. Only the castings of 3 and 4 mm of preparation length and 10 degrees and 15 degrees taper were unseated. Two experiments were performed on these four sets of dies to test parallel proximal and parallel buccolingual grooves. Dies with grooves oriented on the proximal surfaces provided complete resistance to horizontal dislodgement, whereas dies with grooves oriented on the buccal and lingual surfaces provided only partial resistance to horizontal displacement and potential failure of the castings.     

Effect of groove placement on the retention/resistance of resin-bonded retainers for maxillary and mandibular second molars

STATEMENT OF PROBLEM: Lack of retention/resistance form in the clinical preparation of teeth for resin-bonded retainers may lead to clinical failure. PURPOSE: This study investigated the effect of proximal grooves on the retention/resistance of cast resin-bonded retainers for maxillary and mandibular second molar teeth. MATERIAL AND METHODS: Two ivorine teeth (a maxillary and a mandibular second molar) were prepared for resin-bonded retainers. Twenty metal replicas of the prepared teeth were made (10 for each tooth morphotype). Resin-bonded retainers 0.5 mm thick were made for the 40 replicas and luted with Panavia EX cement. Forces for dislodgment of the retainers were applied along the long axes of the teeth. Forces recorded at the time of dislodgment were analyzed with 2-way analysis of variance and the post hoc Scheffé test. RESULTS: Grooves resulted in substantial increases in debonding forces for maxillary molars (P<.001). The effect of grooves on mandibular second molars was not significant (P=.13). CONCLUSION: Grooves placed in tooth preparations of maxillary molar teeth for resin-bonded retainers had a significant effect on retention/resistance. The effect of grooves on mandibular second molars was less pronounced.     

In vitro study of the incidence of radicular grooves in maxillary incisors.

The purpose of this investigation was to determine the prevalence of radicular grooves in 500 central and 421 lateral extracted maxillary incisors. Radicular grooves were present in 2.0% of the central and 2.6% of the lateral maxillary incisors. The majority of radicular grooves in central maxillary incisors were detected on the buccal root surface (1.6%), and fewer on the lingual root surface (0.4%). In lateral maxillary incisors, the radicular grooves were always observed on the lingual surface.     

The topography of the furcation entrance in Chinese molars

Abstract The purpose of the present study was to document the furcation entrance dimensions (FEDs) of the maxillary and mandibular 1st and 2nd molars and relate them to the choice of periodontal therapy. Study samples consisted of 89 maxillary molars (49 1st and 40 2nd molars) and 93 mandibular molars (50 1st and 43 2nd molars). All the FEDs of the molars were examined and measured under a stereomicroscope at 2.5 × equipped with a Bioscan OPTIMAS Image Analyzer (BOIA). The results may be summarized as follows. (1) The mean FEDs in the buccal, distal and mesial furcations of maxillary 1 st and 2nd molars were 0.74 mm, 0.99 mm and 1.04 mm in the 1st molars, and 0.63 mm, 0.67 mm, 0.90 mm in the 2nd molars, respectively. In the buccal and lingual furcations of mandibular 1st and 2nd molars, they measured 0.88 mm and 0.81 mm, and 0.73 mm and 0.71 mm, respectively. (2) The %s of FEDs of 0.56 mm or less (the tip width of a Cavitron tip being 0.56 mm) in the buccal, distal and mesial furcations of maxillary 1st and 2nd molars, accounted for 32%, 8% and 6% of 1st molars, and 40%, 40% and 18% of 2nd molars. In the buccal and lingual areas of mandibular 1st and 2nd molars, they accounted for 16% and 26%, and 35% and 33% of the furcations, respectively. (3) The %s of FEDs of 0.75 mm or less (the width of curettes being 0.75–1.0 mm) in the buccal, mesial and distal furcations of maxillary 1st and 2nd molars accounted for 57%, 18% and 43% of 1st molar furcations, and 83%, 43% and 65% of 2nd molar furcations, respectively. In the buccal and lingual areas of mandibular 1st and 2nd molars, they accounted for 36% and 52%, and 63% and 61% of the furcations, respectively. (4) The majority of mean FEDs in 2nd molars were less than the blade width of new Gracey curettes, whereas in 1st molars they were similar to the blade width of unused Gracey curettes. (5) Most mean FEDs in 1st and 2nd molars were greater than the width of unused Cavitron tips. (6) To achieve complete debridement of root surfaces within furcations, an appropriate selection and combination of Cavitron tips and periodontal curettes should be considered.     

Effects of resistance form on attachment strength of resin-retained castings

This study evaluated the effects of tooth preparation design on resistance to dislodgment of a resin-bonded fixed partial denture (RBFPD). The variations of tooth preparation tested included axial coverage, retentive grooves, and an occlusal rest. Patterns of the tooth preparation designs were prepared and cast in a base metal alloy. Retainer patterns were waxed to refractory casts of metal dies, cast, finished and then bonded to the dies. The complete assemblies were loaded to failure on an Instron mechanical testing machine, and analysis indicated that retainers with occlusal rests were the most resistant. Grooves provided no statistically significant increase in resistance to failure of the cement. Increased axial coverage did not increase resistance to dislodgment. Successful fixed partial dentures (FPDs) depend on cast retainers to resist displacement of the restoration during function. Introduction of resin-bonded restorations opened the possibility of FPDs with minimal reduction of abutments. Specific questions concerning long term success and tooth preparation designs were prominent concerns. The influence of resistance form on overall stability of a restoration was also of particular interest. Buonocore established the foundation for retention of composite resins to acid-pitted enamel. Rochette used this technology to bond perforated cast metal splints to periodontally compromised teeth. A mechanical interlock was created as composite resin engaged these perforations and sustained the cast splint to acid-etched enamel. Howe adapted this design for replacement of anterior teeth by adding porcelain to a metal ceramic framework and then bonding the framework to abutments without tooth preparations. The advantages of these procedures were their conservative nature, esthetics, and ease of rebonding after dislodgment. Livaditis and Thompson adapted the procedure proposed by Tanaka of corrosion-pitting the bonding surface of a base metal alloy. They increased the surface area to be bonded, eliminated the perforations to improve rigidity of the framework, and described tooth preparation modifications of the abutments. They suggested an occlusal rest, establishment of guide planes through axial reduction, and a proximal extension to the facial surface to resist lingual displacement. Simonson, et al., based their anterior tooth preparation design on the configuration suggested by Livaditis which included a slight chamfer finish line plus reduction of the lingual surface to provide a thicker metal framework. Barrack introduced an inlay type tooth preparation for the occlusal rest plus shallow vertical proximal grooves, and Meiers used grooves as an esthetic alternative to proximal extensions. Clinical studies and surveys have identified specific variables involved with success and failure, while in vitro studies have evaluated framework designs, bonding agents, and methods for pitting the metal surface. This study evaluated resistance of RBFPDs to dislodgment of different tooth preparation designs.     

The morphological studies of root resorption of maxillary primary canines and their relation with the position of successive permanent teeth using Micro-CT

The purpose of this study is to clarify the root resorption of maxillary primary canines in relation to the development of successive permanent teeth. It was observed the maxilla of dry skulls of Indian children, using Micro-CT, and measured shortest distance between the root surface of maxillary primary canine and the bony crypt of maxillary canine. The bony crypt including successive canine was positioned almost directly above the root of primary canine and located superior to another bony crypts in the primary dentition stage. When the first molars reached the alveolar crest in addition to the primary dentition stage, the bony crypt of canine grew, showing the distal inclination of the superior margin and mesial inclination of the inferior margin. After the stage which is central incisors reached the alveolar crest, root resorption of primary canines was observed on the lingual side nearby the root apex and the bony crypt of canine was adjacent to the nasal cavity. It was quantitatively shown that the distance between the roots of primary maxillary canine and canine bony crypts reduced from central incisors reached the alveolar crest to lateral incisors reached that.     

Morphometric study of length and grooves of maxillary lateral incisor roots

OBJECTIVE: Root grooves are considered a risk factor for periodontal disease. The purpose of this study was to measure the length of the root of maxillary lateral incisors (MLI), as well as the width and depth of the concavities of their proximal surfaces, and also to determine the prevalence of palato-gingival grooves. METHODS: the width and depth of root concavities, as well as root length were evaluated in 73 MLI. All teeth were measured using a digital contour measuring instrument for the root grooves and a caliper for evaluating root length. RESULTS: After statistical analysis (p<0.05) it was possible to confirm: the mean root length on its mesial surface was (15.47+/-1.72 mm), on its distal surface (14.99+/-1.70 mm), on its buccal surface (13.10+/-1.69 mm) and on its lingual surface (12.71+/-1.53 mm); concavities were present in 100% of the samples; concavities were found 2mm, coronally from the CEJ, at the CEJ, and apically up to 8mm; the concavities were wider than deeper; on the mesial surface, the greatest width was (1.05 mm) and the greatest depth was (0.06 mm) both at the CEJ; 5) on the distal surface the greatest width was (0.73 mm) at 6mm apically from the CEJ and the greatest depth was (0.003 mm); the palato-gingival groove was observed in 9.58% of the samples. CONCLUSIONS: The mesial surface of the maxillary lateral incisor is the longest. The root concavities on the proximal surfaces are present in 100%. One must get acquainted to the morphological variations of roots to enhance diagnosis and treatment.     

Effect of die spacer on the seating of complete cast gold crowns with grooves

Fifty crowns were constructed with an indirect technique for a standardized Ivorine tooth preparation to determine whether casting relief would improve the seating of complete cast crowns with zinc phosphate cement. The variables were two grooves in the preparations and die spacer casting relief of approximately 20 to 40 micron. The tooth preparations of two groups had no grooves, but castings were made with internal relief for only one group. Three groups had buccal and lingual grooves in the preparation. One group had no relief, a second group had complete relief, and a third group had relief but not in the grooves. The discrepancies noted before and after cementation of the castings were measured. The average discrepancy for each group and the significance between groups was determined. Results of this study demonstrated the following. Die relief significantly improved the seating of complete cast-gold crowns with or without grooves. Omitting die spacer from grooves did not reduce the benefits of relieving the remainder of the die. Partial internal relief was better than no relief. The grooves did not disrupt seating when die spacer application was complete or specifically omitted from the grooves alone.     

Three-dimensional inclination of the dental axes in healthy permanent dentitions--A cross-sectional study in a normal population

The 3-dimensional (3-D) inclination of the facial axis of the clinical crown (FACC) and the size of the clinical crowns were measured in 100 white northern Italians. The subjects consisted of 22 girls and 21 boys, ages 13-15 years (adolescents), and 31 women and 26 men, ages 16-26 years (adults), all with a complete permanent dentition and Class I dental relationships. The 3-D coordinates of dental landmarks were obtained with a computerized electromagnetic digitizer. Clinical crowns heights and FACC inclinations in the anatomical frontal and sagittal planes relative to 2 reference planes, maxillary and mandibular (between the incisive papilla and the intersection of the palatal/lingual sulci of the first permanent molars with the gingival margin), were calculated. Ages and sexes were compared by ANOVA. On average, the frontal plane FACCs of most teeth converged toward the midline plane of symmetry. In contrast, the incisors diverged from the midline plane or were nearly vertical. Within each quadrant, the inclinations of the postincisor teeth progressively increased. In the sagittal plane, most teeth had a nearly vertical FACC. FACC inclinations showed sex- and age-related differences (P < .05). In the frontal plane, the canines, premolars, and molars were more inclined in adolescents than in adults. In the sagittal plane, a large within-group variability was observed. Clinical crown height was significantly larger in males than in females in all maxillary and mandibular canines, premolars, second molars, maxillary central incisors, and first molars. With age, some degree of dental eruption was found in maxillary and mandibular canines, maxillary second premolars, and molars. The age-related decrease in FACC inclination may be the effect of a progressive buccal and mesial drift.     

广州市991名老年人根面龋RCI值调查分析

目的：调查广州市老年人根面龋的患病状况。方法：采用分层多阶段抽样方法,选取广州市城区的3个区和郊区的2个县级市作为调查点,共调查广州市65-74岁组老年人991名。以根面龋指数（Rootcariesindex,RCI）分析其患病状况。结果：上颌第一磨牙发生根面龋的RCI值最高,其次是下颌第三磨牙和上颌尖牙。上颌近中面RCI值最高（3.99%）,其次为远中面（3.67%）;下颌唇颊面最高（2.33%）;全口远中面最高（2.89%）,其次是近中面（2.87%）。舌腭面RCI值均为最低。上颌各牙面RCI值高于下颌。大部分患根面龋的老年人仅累及1个根面（84.6%）,累及2个根面的占12.0%,累及3个及以上根面的发生率很低。就患牙数目而言,根面龋牙数1颗者占24.8%,2-7颗者占24.7%,8颗及以上者仅有0.6%。结论：在根面暴露的情况下,受根面龋侵袭比例最高的是上颌第一磨牙,其次是下颌第三磨牙和上颌尖牙;易感牙面为上颌邻面和下颌唇颊面;上颌牙患龋危险性高于下颌。     

Study of the incidence of radicular grooves in maxillary incisors.

The purpose of this investigation was to determine the incidence of radicular grooves in the upper incisors of 642 patients from the region of Ribeir?o Preto, SP, Brazil. Radicular grooves, present in 3.9% of the patients, were found mainly on the lingual surface of the maxillary lateral incisor (3.0%). The maxillary central incisors showed radicular grooves on both the buccal and lingual surfaces with an incidence of 0.9%. It was not possible to relate the incidence of these grooves with race (white and negro) or with sex.     

The effectiveness of auxiliary features on a tooth preparation with inadequate resistance form

STATEMENT OF PROBLEM: No study has evaluated the efficacy of auxiliary tooth preparation elements for crowns with originally reduced resistance form. PURPOSE: This study evaluated the effects of different auxiliary preparation features on the resistance form of crowns with reduced axial wall and total occlusal convergence. MATERIAL AND METHODS: An Ivorine tooth was prepared on a milling machine with 20-degree total occlusal convergence (TOC), 2.5 mm of occlusocervical dimension, and a shoulder finish line. This design lacked geometric resistance form. The crown preparation was subsequently modified to include mesiodistal grooves, mesiodistal boxes, buccolingual grooves, occlusal inclined planes, an occlusal isthmus, and reduced TOC in the axial wall from 20 to 8 degrees TOC in the cervical 1.5 mm of the axial wall. The grooves and boxes were placed into the tooth with the same 20-degree TOC as the initial axial walls. Ten standardized metal dies were used for each preparation design. Standardized complete metal crowns were fabricated for all specimens. The metal crowns were cemented on metal dies with resin-modified glass ionomer cement. A strain gauge was placed at the mid-lingual cervical area of each crown preparation margin. The resistance of each specimen was evaluated when force was applied at a 45-degree angulation to the long axis of the die in a lingual to buccal direction. The peak loads during crown dislodgment, as well as the tensile stress at the mid-lingual cervical area, were measured using a universal testing machine (Kgs) for each specimen. The control group consisted of 10 dies, with the original crown preparation having no geometric resistance form and no auxiliary preparation features. Strain gauges provided the force (Kgs) that resulted in electric currency disrupt at the crown/die interface, thus providing data regarding the force required for slight crown micromovement (2 microm). Data between control and experimental groups were compared using the Mann-Whitney U test (alpha=.05). RESULTS: Proximal grooves, proximal boxes, buccolingual grooves, occlusal inclined planes, and occlusal isthmuses were not effective at increasing a crown's resistance to dislodgement when the tooth preparation lacked resistance. The only crown modification that offered enhanced resistance form when compared with the control group was the reduced TOC in the cervical half of the axial wall. CONCLUSION: Within the limitations of this in vitro study the crown preparation modification that significantly enhanced the resistance form of a compromised tooth preparation was reducing the TOC at the cervical aspect of the axial wall. Placing auxiliary retentive features such as grooves and boxes into a compromised tooth preparation (2.5 mm occlusocervical dimension and 20-degree TOC) was not effective when these retentive features possessed the same 20-degree TOC as the prepared axial walls.     

Cone beam computed tomography evaluations of marginal alveolar bone before and after orthodontic treatment combined with premolar extractions

Using cone beam computed tomography (CBCT) we investigated the distance between the cemento-enamel junction (CEJ) and the marginal bone crest (MBC) at buccal, lingual, mesial, and distal surfaces of incisors to first molars in adolescents before (baseline) and after extractive orthodontic treatment (study end point). Patients with Class I malocclusion, crowding and an overjet of ≤ 5 mm were examined with a CBCT unit using a 60 × 60-mm field of view and a 0.125-mm voxel size. Large differences in marginal bone height were found at baseline, particularly between tooth surfaces. There was a slight correlation between age and CEJ-MBC distance. From baseline to the study end point, large bone-height changes among teeth and tooth surfaces could be seen. Lingual surfaces, followed by buccal surfaces, showed the largest changes. Eighty-four per cent of lingual surfaces of mandibular central incisors exhibited a bone-height decrease of > 2 mm. The bone-height decrease was larger at lingual surfaces in the mandible than in the maxilla, and larger in girls (mean=1.8 mm) than in boys (mean=1.5 mm). Fewer than 1% of proximal surfaces exhibited changes of > 2 mm. It is unknown whether the changes in marginal bone height are transitory. A high-quality CBCT technique may help to determine this by providing a deeper insight into the long-term side effects of orthodontic treatment.     

New Guidelines for Preparation Taper

The purpose of this article is to provide new guidelines for minimally acceptable preparation taper by developing a theoretical mathematical foundation based on principles of resistance form. Yes and no are the possible answers to the question, “Does a preparation have resistance form?” This dual nature is useful because in graphing resistance form as a function of taper, potential tapers on the x axis are divided into two groups with an exact dividing point. Tapers less than this dividing point provide resistance form; tapers larger or equal do not provide resistance form. This dividing point makes a reasonable standard for minimally acceptable taper. Average tapers are defined as the limiting average taper and are mathematically determined to equal 1/2 arcsin (H/B), where H is the height of the preparation and B is the base. From this equation, the taper required to provide resistance form for an individual preparation can be calculated by using the preparation's height to base ratio. The equation can also be used to provide guidelines by tooth group. Dies of a prosthodontist were saved and sorted by group (incisors, canines, premolars, and molars). Measurements of 30 dies from each of these groups were used to calculate the average (H/B) ratios and standard deviations. Calculating the limiting average taper by using the average height-to-base ratio minus two standard deviations provides the dividing point taper that is acceptable for over 97% of the preparations. The values calculated are: 29° for incisors, 33° for canines, 10° for premolars, and 8.4° for molars. These values are recommended as guidelines for minimally acceptable taper. They are not ideals for which to strive, but the boundary of unacceptable tapers to avoid. Evaluating reported clinical average tapers based on these guidelines shows that anterior preparations easily exceed the standard, and premolars are acceptable, whereas the average taper reported for molars is unacceptable.