Fracture Resistance of Titanium and Fiber Dental Posts: A Systematic Review and Meta-Analysis.

PURPOSE: The fracture resistance of dental post systems is influenced by the material of the post. The purpose of this systematic review and meta-analysis was to assess if there is a difference in fracture resistance between prefabricated dental titanium posts and fiber posts. METHODS: An online electronic search was performed using the PubMed, Scopus, and Web of Science databases for in vitro studies published from 2010 to 2020 in English. The retrieved eligible studies that compared the fracture resistance of titanium and fiber posts on human teeth were selected. The pooled standardized mean difference (SMD) with a 95% confidence interval was calculated. In addition, the trial sequential analysis (TSA) was performed to test if the available studies are sufficient to make conclusive evidence. RESULTS: Of the 1165 retrieved studies, 17 studies were included in the qualitative analysis, while 16 studies were included in the quantitative analysis. Because of the high heterogeneity among studies, data from 10 studies were pooled and submitted to TSA. A total of 852 teeth were evaluated for fracture of the posts in 27 independent comparison groups. The pooled effect of the residual studies revealed no significant difference between titanium and fiber posts (SMD = -0.12; 95% CI = -0.30, 0.06; p = 0.20). Results of the TSA revealed no conclusive evidence. CONCLUSIONS: The results of the current evidence revealed no significant difference between fiber and titanium posts. The evidence is insufficient, and more standardized in vitro studies are required.

Clinical Characteristics of Abutment Teeth with Gingival Discoloration.

PURPOSE: The grey-bluish discoloration of gingiva (known as "amalgam tattoo") does not appear only in the presence of amalgam restorations. It may also be seen in cases of teeth restored with cast dowels and porcelain-fused-to-metal (PFM) restorations. The aim of this article was to determine the clinical characteristics of abutment teeth with gingival discoloration. MATERIALS AND METHODS: This research was conducted on 25 patients referred for cast dowel and PFM restorations. These restorations were manufactured from Ni-Cr alloys. Ninety days after cementing the fixed prosthodontic restorations, the abutment teeth (n = 61) were divided into a group with gingival discoloration (GD) (n = 25) and without gingival discoloration (NGD) (n = 36). The control group (CG) comprised the contralateral teeth (n = 61). Plaque index, gingival index, clinical attachment level, and probing depth were assessed before fabrication and also 90 days after cementation of the PFM restorations. RESULTS: The gingival index, clinical attachment level, and probing depths of the abutment teeth that had GD were statistically higher before restoration, in comparison with the abutment teeth in the NGD and control groups. Ninety days after cementation, the abutment teeth with GD had significantly lower gingival indexes and probing depths, compared to the abutment teeth in the NGD group. Both abutment teeth groups (GD and NGD) had significantly higher values of clinical attachment levels when compared to the control group. There were no statistically significant differences in plaque index values between the study groups. CONCLUSIONS: The results of this study indicated that impairment of periodontal status of abutment teeth seemed to be related to the presence of gingival discolorations. Therefore, fabrication of fixed prosthodontic restorations requires careful planning and abutment teeth preparation to minimize the occurrence of gingival discolorations. CLINICAL RELEVANCE: With careful preparation of abutment teeth for cast dowels and crown restorations it may be possible to decrease the frequency of gingival discolorations adjacent to abutment teeth.

The Influence of Post System Design and Material on the Biomechanical Behavior of Teeth with Little Remaining Coronal Structure.

PURPOSE: To evaluate the influence of different post systems on the biomechanical behavior of teeth with a severe loss of remaining coronal structure. MATERIALS AND METHODS: Fifty standardized bovine teeth (n = 10 per group) were restored with: cast post-and-core (CPC), prefabricated metallic post (PFM), parallel glass-fiber post (P-FP), conical glass-fiber post (C-FP), or composite core (no post, CC). The survival rate during thermomechanical challenging (TC), the fracture strength (FS), and failure patterns (FP) were evaluated. Finite element models evaluated the stress distribution after the application of 100 N. RESULTS: All specimens survived TC. Similar FS was observed among post-containing groups. Groups P-FP and CC presented 100% repairable fractures. The von Mises analysis showed the maximum stresses into the root canal in groups restored with metallic posts. Glass-fiber posts and CC presented the maximum stresses at the load contact point. Glass-fiber groups showed lower stresses in the analysis of maximal contact pressure; CPC led to the highest values of contact pressure. The modified von Mises (mvM) stress in dentin did not show differences among groups. Moreover, mvM values did not reach the dentin fracture limit for any group. CONCLUSIONS: The type of intracanal post had a relevant influence on the biomechanical behavior of teeth with little remaining coronal structure.

Coronal Microleakage of Teeth Restored with Cast Posts and Cores Cemented with Four Different Luting Agents after Thermocycling.

PURPOSE: The apical seal provided by a root canal filling may be breached via coronal leakage. This study aimed to compare the teeth restored with custom-made cast metal posts and cores cemented with different luting agents in terms of coronal microleakage after thermocycling. MATERIALS AND METHODS: This in vitro study was conducted on 32 extracted single-canal teeth. Root canals were prepared by step-back technique and filled with gutta percha and sealer. The coronal 7 mm of gutta percha was removed, and post space was prepared using peeso reamers #2 and #3 consecutively. After fabricating the acrylic resin patterns of the posts and cores, they were cast using Ni-Cr metal alloy. The specimens were divided into 4 groups in which the castings were cemented using one of the following luting agents: zinc phosphate (ZP), glass ionomer (GI), Panavia F 2.0, and Speed CEM. After cementation, the teeth were immersed in distilled water and incubated for 7 days. Then, the teeth were subjected to thermocycling, immersed in silver nitrate for 6 hours, and finally sectioned. The degree of dye penetration into the coronal part of the specimens was measured using a stereomicroscope. Data were analyzed using Kruskal-Wallis and Mann-Whitey U tests with significance level of 0.05. RESULTS: The median microleakage in ZP, Speed CEM, GI, and Panavia were 171.89, 114.76, 26.51, and 20.02 µm, respectively. Pairwise comparisons among GI and ZP, GI, and Speed CEM, ZP and Panavia, ZP and Speed CEM, and Panavia and Speed CEM groups yielded significant differences (p < 0.05). CONCLUSION: Complete coronal seal was not achieved with any of the luting agents. The highest and the lowest degree of microleakage was yielded by ZP and Panavia luting agents, respectively.

Failure loads of all-ceramic cantilever fixed dental prostheses on post-restored abutment teeth: influence of the post presence and post position.

The influence of a fiber post-restored abutment tooth on the load capability of a three-unit zirconia framework cantilever fixed dental prosthesis (cFDP) was evaluated after simulated clinical function. Human lower sound premolars (n = 64) were distributed, in equal numbers, to four experimental groups: two vital abutment teeth (group I; control); mesial abutment tooth post-restored (group II); distal abutment tooth post-restored (group III); and mesial and distal abutment teeth post-restored (group IV). All specimens received an adhesively luted three-unit cFDP of veneered zirconia. Simulated clinical function was performed by two subsequent sequences of thermal-cycling (2 × 3,000 cycles) and mechanical loading (1.2 × 106 load cycles from 0 to 50 N) (TCML). Four specimens failed during TCML (one in each of groups I and IV and two in group II). The maximum load capability ranged from 365 to 538 N and was not significantly different between groups. Specimens with post-restored abutments failed mainly because of abutment tooth fracture of the distal abutment. The presence or position of post-restored abutment teeth has no significant impact on load capability of all-ceramic three-unit cFDPs. The risk of tooth fracture of the distal abutment teeth of a cFDP was significantly increased when one abutment tooth, irrespective of its position, was post-and-core restored.

Comparative Clinical Evaluation of Composite Overcast Gold Post and Core Buildups in Endodontically Treated Teeth.

BACKGROUND: The management of non-vital teeth includes endodontic treatment and restoration followed by post and core restoration in selected cases. The present study was conducted to compare the indirect cast post, and core buildup with direct composite post build up in patients. MATERIALS AND METHODS: The present study was conducted on 128 teeth of 82 patients. The success rate over 3 years was evaluated clinically and radiographically by observing caries, tooth mobility, probing depth, periapical pathology, and root fractures. RESULTS: Group I consisted of 16 incisors, 20 canines, 22 premolars, and six molars while group II had 17 incisors, 14 canines, 25 premolars, and eight molars. The difference was statistical non-significant (p-0.1). Forty-four teeth in group I and 42 teeth in group II utilized composite cement, whereas 18 teeth in group I and 16 teeth in group II used GIC and zinc phosphate was used in two teeth in group I and six teeth in group II. The difference was statistical ly significant (p< 0.05). Four teeth in group I and 8 in group II were lost. One tooth in group I and two teeth in group II showed root fracture and three teeth in group I and six teeth in group II showed periapical pathology. The difference was statistically significant (p-0.01). Most common type of complication was probing depth > 4 mm, caries, tooth mobility, and root fracture. The difference was non- significant (p-0.31). CONCLUSION: Both composite post buildup and cast gold post and core build-up exhibited similar properties. CLINICAL SIGNIFICANCE: Both composite post buildup and cast gold post and core build-up exhibited similar properties hence either of the methods can be used in post core build up.

Are fibre posts associated with the occurrence of prosthetic complications?

Data sourcesThe Pubmed, Evidence-Based Dentistry, BMJ Clinical Evidence, EmbaseDynamed, and www.opengrey.eu databases and manual search of reference lists.Study selectionRandomised clinical trials (RCTs) were accepted if they had: participants with no periodontal disease and teeth restored with SCs or FDPs and compared fibre posts and other prosthetic systems and evaluated the prosthetic complications with a minimum observational period of 36 months.Data extraction and synthesisTitles and abstracts were evaluated independently by two reviewers, any disagreement was discussed with a third reviewer. The agreement for the two reviewers was 97%. The quality and the risk of bias of the studies included was assessed following the Cochrane Handbook considering the domains of randomisation, sample size, inclusion and exclusion criteria, follow-up achieved, blinding, withdrawing and groups' compatibility for quality assessment, and for the risk of bias the domains evaluated were allocation concealment, blinding of outcome assessor and follow-up.ResultsThe database search yielded 4,230 records; after duplications removal, 3,670 records were reviewed independently by the authors, and four articles were chosen to include in the systematic review.The most frequently reported failures in the available studies were as follows: fibre post debonding, loss of retention of single crowns and marginal gaps. Less frequently, chippings and fractures were recorded in SCs. No studies about complications related to FDPs were found.The failure rate ranged from 0 to 28.2%.ConclusionsA correlation between the failure rates of fibre posts and the type of prosthetic restoration (SCs or FDPs ) cannot be found. Further RCTs are required to achieve evidence-based conclusions, particularly about the use of fibre posts with FDPs.

Influence of glass fibre post length and remaining dentine thickness on the fracture resistance of root filled teeth.

AIM: To evaluate, ex vivo, the influence of glass fibre post length and remaining thickness of dentine on the fracture resistance of bovine roots, after thermomechanical ageing. METHODOLOGY: Ninety bovine roots of the same size were root filled and randomly distributed into nine groups (n = 10), according to the root weakening protocol (NW - nonweakened; MW - medium weakened; HW - highly weakened) and post length (7 mm; 9 mm and 12 mm). The weakening of roots was performed using diamond burs, resulting in different thicknesses of remaining dentine. The post spaces were prepared, and in the weakened roots, the glass fibre posts were customized with composite resin, to create posts matching the canal size. Chemically activated resin cement was used to lute the posts. After luting, full crowns made of composite resin were attached to a silicon matrix. To reproduce physiological mobility, the roots were covered with polyether and embedded in polyurethane. The thermomechanical cycling was performed (1 200 000 cycles; 88N; 3,8 Hz; 5 ± 1 °C to 55 ± 1 °C). Then, the specimens were subjected to compressive force in a universal testing machine (1 mm min-1 ; 100 kgf) to analyse the fracture resistance. The specimens were analysed through a stereomicroscope to classify the failure mode (repairable/catastrophic). The values were subjected to statistical analysis (two-way anova and Tukey's test at 5%). The frequencies of failure mode were compared using chi-square test. RESULTS: The association between length and dentine thickness was significant (P > 0.05). The difference was between NW and HW roots for posts of 12 mm in length. There was an association between failure mode and the length and remaining dentine thickness. CONCLUSIONS: Reduced dentine thickness in roots with longer posts had lower fracture resistance values, as catastrophic failure was more predominant.

Changing the gingival color discrepancy induced by pigmented root using subepithelial connective tissue graft: a case report.

Metallic alloys can suffer corrosion, and metallic posts and cores used for restorative procedures may develop a blue-gray pigmentation in root dentin, which in turn changes the color of gingival tissues. Removing posts and cores may lead to root fracture, and bleaching agents have a limited effect on staining from alloy corrosion. Surgical techniques for correcting undesirable esthetic deficiencies have been investigated in the literature. This article describes the case of a patient with gingival discoloration caused by root pigmentation in the maxillary area. A subepithelial connective graft harvested from the palate was used to treat the gingival color discrepancy.

The effect of ultrasonic vibration protocols for cast post removal on the incidence of root dentin defects.

PURPOSE: To investigate the effects of two ultrasonic vibration protocols for cast post removal (single or double ultrasound units) on the development of defects in root dentin. METHODS: Sixty bovine incisors were selected. Fifteen roots were left unprepared (control). Forty-five roots were instrumented and filled. A 10-mm post space was prepared using #1-4 Largo drills. Fifteen teeth were prepared for post space and received no further procedure. Thirty roots had cast posts cemented and were submitted to ultrasonic vibration protocols for removal. The time necessary to remove each post was recorded. Roots were sectioned 3, 6, 9, and 12 mm from the coronal portion and viewed through a 25× magnification in a stereomicroscope. The presence of root fractures, partial cracks, and craze lines was registered. Chi-square and Fisher's exact tests were performed to compare the incidence of dentin defects. The Kruskal-Wallis test was performed to explore the difference between the time needed for post removal. The significance level was set at P = 0.05. RESULTS: Root defects were observed in all experimental groups. There were no statistical differences comparing previous root canal treatment and post removal steps, either with 1 or 2 ultrasonic units, in the formation of defects (P = 0.544) or fractures (P = 0.679). CONCLUSION: Ultrasonic vibration protocols for removing cast posts did not increase the number of dentin defects compared to root canal preparation and obturation and post space preparation steps.

Discolouration potential of endodontic procedures and materials: a review.

Advances in endodontic materials and techniques are at the forefront of endodontic research. Despite continuous improvements, tooth discolouration, especially in anterior teeth, is considered an undesirable consequence following endodontic treatment as it creates a range of aesthetic problems. This article aims to discuss the intrinsic and internalized tooth discolouration caused by endodontic procedures, and to address the discolouration potential of materials used during root canal treatment, including root canal irrigants, intra-canal medicaments, endodontic and post-endodontic filling materials. In addition, the discolouration patterns caused by combined endodontic and nonendodontic aetiological factors are discussed. The recommended guidelines that should be followed by dental practitioners to prevent and manage tooth discolouration are also outlined.

Medico-legal aspects of vertical root fractures in root filled teeth.

AIM: To analyse the medico-legal aspects of vertical root fracture (VRF) following root canal treatment (RCT). METHODOLOGY: A comprehensive search in a professional liability insurance database was conducted to retrospectively identify cases of VRF following RCT. The complaints were categorized as either financial risk bearing or financial nonrisk bearing, and related demographic, prosthetic and endodontic variables were analysed. RESULTS: Seventy-seven legal cases of patients with VRFs following RCT were identified. Most of the cases were either in premolars or in mandibular molar teeth (P<0.05). Poor-quality root filling was associated with an extended delay of diagnosis (P<0.05). The presence of a post significantly increased the financial risk assessment (P<0.05). CONCLUSIONS: Poor quality root fillings complicate the diagnosis of VRF, which in turn extends the time for achieving an accurate diagnosis and increasing the medico-legal risk. Premolar and mandibular molar teeth were more prone to medico-legal claims related to VRF following RCT. Post should be placed only when essential for additional core support to avoid medico-legal risk.

The impact of post preparation on the residual dentin thickness of maxillary molars.

STATEMENT OF PROBLEM: The oval-shaped palatal roots of maxillary molars usually have smaller cross-sectional diameter in the buccolingual direction. However, the effect of parallel-sided post preparation on the remaining dentin thickness of root canal walls is unknown. PURPOSE: The purpose of this study was to investigate, in vitro, the residual dentin thickness (RDT) of palatal roots in maxillary molars after various intracanal procedures for post placement, and to determine the risk of root canal perforation or weakening on different root canal walls at 2 levels, coronal and apical. MATERIAL AND METHODS: Fifteen extracted first maxillary molars exhibiting radiographic mesiodistal root canal widths ranging from 3.8 to 4.2 mm, measured at 5 mm from the apex, were selected from a pool of teeth. The teeth were horizontally sectioned at 2 levels, coronal and apical, after being embedded in acrylic resin with the aid of a metal index, allowing identical repositioning of the sectioned parts throughout the study. Each sectioned surface was photographed with a digital camera coupled to a microscope. The palatal roots were subsequently prepared for post placement as follows: endodontic preparation up to file K50, Largo 3 and 4 drills, and ParaPost 4.5 and 5.0. Cross-sections were rephotographed after each step. Image J software was used to measure the RDT of each root wall at both levels, and data were further analyzed with a 3-way ANOVA/General Linear Model (GLM) for repeated measures. The post-hoc Tukey's range test was used to calculate differences in RDT among the 4 root walls at each root level (α=.05). RESULTS: A significant difference was observed among the intracanal procedures (P<.001). At the apical level, RDT was significantly lower after ParaPost preparation than at the coronal level (P=.009). Buccal and palatal walls displayed significantly lower RDT than the mesial and distal walls at both levels (P=.004). CONCLUSIONS: Intracanal preparation up to ParaPost 5.0 increased the risk of perforation or weakening of the buccal and palatal walls, especially at the apical level.

[Evaluation of crown-root restorations in non-vital teeth. Survey of dentists in the city of Abidjan]. / Evaluation de l'utilisation des restaurations corono- radiculaires foulées: enquête réalisée auprès des praticiens de la ville d'Abidjan.

Coronal-radicular restoration is the coronal reconstruction of an endodontically treated tooth, with a support on and in the root. The objective of this study is to assess the importance of the carried coronal-radicular restorations in the dental practice in Abidjan. It is about a prospective survey of 100 dental surgeons practicing in the city of Abidjan, pulled at random. The information was collected through a self-interview. As results, 79% of our population knows and performs coronal-radicular restorations especially in the absence of 3 dental walls but at a very low, less of 5/month for 90% of this population. The protocol of realization seems well known and followed for the majority of the pooled practitioners. However, we deplored often absence of radiography in the protocol and also the exclusive use of metal posts. In conclusion, the coronal-radicular restorations are much used in the daily practice in Côte d'Ivoire. The protocol for achieving this type of restoration seems well known and followed by the practitioners according to our study. However, as material all the dentists are still in the screw post (metal post). The adhesive technologies using fiber posts don't seem accessible to our people.

Complication and failure rates in patients treated for chronic periodontitis and restored with single crowns on teeth and/or implants.

OBJECTIVES: To assess the biological and technical complication rates of single crowns on vital teeth (SC-V), endodontically treated teeth without post and core (SC-E), with a cast post and core (SC-PC) and on implants (SC-I). MATERIAL AND METHODS: From 392 patients with chronic periodontitis treated and documented by graduate students during the period from 1978 to 2002, 199 were reexamined during 2005 for this retrospective cohort study, and 64 of these patients were treated with SCs. Statistical analysis included Kaplan-Meier survival functions and event rates per 100 years of object-time. Poisson regression was used to compare the four groups of crowns with respect to the incidence rate ratio of failures, and failures and complications combined over 10 years and the entire observation period. RESULTS: Forty-one (64%) female and 23 (36%) male patients participated in the reexamination. At the time of seating the crowns, the mean patient age was 46.8 (range 24-66.3) years. One hundred and sixty-eight single unit crowns were incorporated. Their mean follow-up time was 11.8 (range 0.8-26.4) years. During the time of observation, 22 biological and 11 technical complications occurred; 19 SC were lost. The chance for SC-V (56) to remain free of any failure or complication was 89.3% (95% confidence interval [CI] 76.1-95.4) after 10 years, 85.8% (95% CI 66-94.5) for SC-E (34), 75.9% for SC-PC (39), (95% CI 58.8-86.7) and 66.2% (95% CI 45.1-80.7) for SC-I (39). Over 10 years, 95% of SC-I remained free of failure and demonstrated a cumulative incidence of failure or complication of 34%. Compared with SC-E, SC-I were 3.5 times more likely to yield failures or complications and SC-PC failed 1.7 times more frequently than did SC-E. SC-V had the lowest rate of failures or complications over the 10 years. CONCLUSIONS: While SCs on vital teeth have the best prognosis, those on endodontically treated teeth have a slightly poorer prognosis over 10 years. Crowns on teeth with post and cores and implant-supported SCs displayed the highest incidence of failures and complications.

Vertical fracture of root filled teeth restored with posts: the effects of patient age and dentine thickness.

AIM: To determine whether patient age contributed to the fracture resistance of teeth subjected to root canal treatment and post placement. METHODOLOGY: Forty-five single-rooted, single-canal human teeth were mounted, instrumented, obturated and prepared for a post. The teeth were divided into young (18 < or = age < or = 35) and old (60 < or = age) groups and subjected to cyclic loading until fracture; those reaching 200,000 cycles without undergoing failure were then subjected to static loading to fracture. Statistical differences between groups were examined using one-way anovas, and correlations were identified using Pearson's r; significance was established at P < or = 0.05. RESULTS: There was no significant difference between the two age groups in terms of the number of cycles to fracture (P > 0.05) or the load to fracture (P > 0.05). However, there was a significant correlation (P < or = 0.05) between the root fracture resistance and individual age, indicating that the susceptibility to root fracture increases significantly with increasing patient age. Also, the dentine thickness of roots that fractured was significantly less than those that did not (P = 0.04). CONCLUSION: Vertical root fracture of teeth receiving root canal treatment with posts is more likely to occur in the teeth of older patients (60+) and particularly in those with low dentine thickness.

The mechanism of gingiva metallic pigmentations formation.

The occurrence of blue-grey areas in the soft tissue represents one of the problems affecting patients whose teeth have been restored using metallic materials. It is generally accepted that it is caused by mechanical penetration of a metallic material into the soft tissue. Several facts indicate that this mechanism is not general. The aim of the study was to determine an alternative mechanism of the origin of pigmentations, based on the corrosion interaction of metallic materials used in prosthodontics with the oral environment. The study was comprised of an analysis of pigment particles, determination of exposure conditions of metallic materials in vivo and laboratory evaluation of corrosion properties of the studied materials. Particles containing silver, sulphur and/or selenium could be seen in ultra-thin sections in the lamina propria gingivae. Comparison of the corrosion laboratory results with the results of in vivo measurements indicated the intensification of corrosion under these conditions. Amalgams and silver-containing alloys used for teeth restorations may release silver under the conditions of the oral cavity. The formation of soluble silver compounds in the sulcular area or in a crevice between the crown and the cast post-and-core reconstruction facilitates their transport to the soft tissue and subsequent deposition.

Effects of post materials and length on the stress distribution of endodontically treated maxillary central incisors: a 3D finite element analysis.

Traditionally, using a long post can cause progressive removal of the root structure, complicate the ability to re-treat the tooth if necessary and make it difficult to apply an adhesive bonding agent into the root canal. It is unclear if a shorter post length can be applied when a light translucent glass fibre post and adhesive resin cement are used. The aim of this study was to evaluate the biomechanical performance of endodontically treated teeth restored with three post materials, glass-fibre, stainless steel and cast-nickel chromium posts and cores of different lengths of 7, 10 and 13 mm. A 3D finite element analysis model of the maxillary central incisor was constructed. An occlusal load of 300 N was applied to a node at the palatal surface of the crown at 45 degrees to the long axis of the tooth. von Mises stress analyses were carried out in three regions. Simulated data were collected for plotting various pattern graphics and conducting statistical tests. The pattern graphics showed that when the post length changed from 13 to 7 mm, the stress patterns were even and flat in all fibre-post groups, while the stress patterns of the metal-post groups showed an M-shaped peak and trough. Statistical tests showed that the shorter fibre post was superior to the longer metal post in some situations. Within the limitations of this study, it was concluded that when a metal post is used, the post should be as long as possible, while the biomechanical performance of a glass-fibre post combined with a composite resin core was less sensitive to post length.

Restoration of endodontically treated teeth: the seven keys to success.

Preservation of tooth integrity and strength is important for the long-term survival of endodontically treated teeth. Endodontic treatment and post space preparation requires reduction of the remaining supportive tooth structure. Restorative modalities following root canal therapy must provide sufficient strength for the prosthetic material and tooth structures. This article presents seven key factors that should be taken into consideration to ensure clinical success when restoring an endodontically treated tooth.