Vertical Teeth Preparation: A Comprehensive Systematic Review of Patient Outcomes and Clinical Complications

1. INTRODUCTION

Tooth preparation involves the mechanical modification of diseased and/or healthy tooth structures (enamel, dentin, and cementum) to restore aesthetics, function, and structural integrity [1]. The primary challenge during tooth preparation is balancing aesthetic outcomes with minimally invasive procedures that preserve tooth structure, which enhances crack resistance, stress distribution, and long-term durability [2]. Traditional methods for preparing teeth for fixed dental prostheses, such as horizontal designs (e.g., chamfer or shoulder margins), often necessitate substantial tissue removal. These risks weaken tooth integrity, may trigger gingival margin displacement, and potentially compromise long-term outcomes due to various factors, such as insufficient keratinized tissue, procedural trauma, or chronic inflammation from prosthetic inaccuracies [3]. The designs of preparations as vertical (red bur) and horizontal (blue bur) for anterior teeth are shown in Fig. (1A), while those for posterior teeth are presented in Fig. (1B).

By contrast, vertical preparation techniques, including feather-edge designs and the BOPT, have emerged as conservative alternatives [4]. These methods minimize structural reduction while addressing aesthetic and biological challenges [5]. Vertical preparations are particularly advantageous for patients with thick or medium periodontal biotypes, periodontal attachment loss, or probing depths exceeding 2 mm, where horizontal approaches could exacerbate tissue loss [5, 6]. Vertical preparations are also effective for managing subgingival caries and adjusting gingival morphology by situating crown margins beneath the gingival level [7]. This strategy is especially beneficial for teeth with insufficient clinical crowns, such as lower anterior incisors, where conventional horizontal reduction could lead to excessive tissue removal [8].

BOPT, a subset of vertical techniques, eliminates defined finish lines through vertical milling and replaces the natural crown emergence profile at the cementoenamel junction with a prosthetic-defined contour [9]. This process is complemented by rotary curettage of the gingival sulcus, adapted from periodontal protocols [10]. In periodontally healthy patients, this technique removes sulcular epithelium and prompts localized bleeding and subsequent connective tissue reorganization under provisional restorations [9]. The resulting prosthetic cementoenamel junction mimics natural anatomy and aligns crown margins 0.5–1 mm from the gingival margin to prioritize tissue stability and aesthetic integration [11, 12].

Studies comparing vertical and horizontal techniques have revealed vertical preparation to achieve similar or superior outcomes in periodontal health and clinical performance [13]. Vertical preparation of maxillary and mandibular incisor teeth for full-coverage restorations exhibited impressive longevity with survival rates exceeding 48–72 months, alongside optimal periodontal outcomes, such as stable gingival margins, enhanced tissue thickness, and minimal inflammation [14, 15]. A research study on posterior vertical preparation restorations also demonstrated enhanced marginal stability, reduced plaque accumulation, lower gingival scores, and fewer deep periodontal pockets over 60 months compared to horizontal methods [11]. While complication rates are comparable, vertical preparation cases often show better clinical responses, which positions it as another choice [11].

In addition to the type of preparation, the material used influences the behavior of the surrounding soft tissues. Long-term evaluations of minimally invasive zirconia crowns prepared with vertical preparation demonstrated reliability, no failures or complications over 36 months, and a high survival rate and patient satisfaction [4]. Other studies have exhibited ceramic restorations to achieve vertical marginal gaps falling within the clinically acceptable range [16, 17]. Vertical preparation techniques effectively balance aesthetic and structural preservation, and 84 months of studies have shown stable marginal integrity and favorable esthetic outcomes, minimizing tooth structure removal while delivering durable results [18].

Despite promising evidence, systematic reviews evaluating the vertical preparation efficacy and its influence on periodontal health remain limited. A recent meta-analysis revealed no remarkable differences in periodontal outcomes (e.g., plaque, recession, and restoration success) between BOPT and horizontal techniques [1]. This study aimed to provide a systematic review and evaluation of the clinical performance, periodontal outcomes, patient satisfaction, and clinical complications of vertical preparation as a routine alternative to conventional horizontal preparations in clinical practice, particularly in cases requiring structural preservation, aesthetic integration, and periodontal stability.

2. MATERIALS AND METHODS

3. RESULT

3.2. Characteristics of Included Studies

Table 2 presents the characteristics of the included studies, including the author (s), publication year, study design, finish line type, material used, and follow-up periods in months. The results covered periodontal outcome (PI, GI, PD, and BoP), patient-related variables (as percentage of survival rate, success rate, and patient satisfaction), and complications (mechanical and biological).

Only 12 papers were included in the current systematic review. The first paper was published in 2012 [30], whereas the last one was published in 2024 [18] with 7 prospective clinical trials [4, 10-12, 14, 15, 26, 28], 3 randomized clinical trials [27, 29], and 2 retrospective cohort studies [18, 30]. In relation to the finish line assessed, the highest type was BOPT, assessed in 6 studies [10, 11, 14, 15, 26, 28], followed by the feather or knife-edge, as well as chamfer finish lines types that were assessed in 4 studies each [12, 26, 27, 29, 30]. Vertical preparation was mentioned in 2 studies only [4, 18]. Most of the studies used monolithic zirconia as a prosthetic material or zirconia core covered by feldspathic ceramic, and one study used PFM [18].

A total of 1,033 cemented prostheses, as a single crown or as a part of fixed prosthodontics (FPD), were observed, and the highest numbers per study were 198 and 196, cemented on all types of teeth (incisors, premolars, and molars) [12, 29]. The minimum follow-up period was 6 months [12], whereas the longest follow-up period was 84 months [18].

Table 2.

Author, Year, Type of Study/Refs.	Finish Line Type	Tooth (restoration and material type)	Follow-up Period	Survival/success Rate	Periodontal Outcome	Patient Satisfaction	Mechanical/biological Complications
Gonzalez-Bonilla et al., 2024/retrospective cohort study [18]	Vertical preparation	50 molars and premolars (25 zirconia crowns and 25 PFM crowns)	60 and 84 months	NM/zirconia 100% and PFM 86%	PI: 82% score 0, 6% score 1, and 12% having 2	NM	4% chipping of the PFM/NM
					GI: 50% index of 0; 28% index of 1; 20% index of 2
					PD: 80% ≤ 3mm - 20% ↔3 and 5 mm
Serra-Pastor et al., 2023/prospective clinical trial [15]	BOPT	70 teeth (25 FPDs)	12, 24, 36, 48, 60, and 72 months	100%/NM	A 100% significant increase in gingival thickness and a stable gingival margin	NM	NM
Kasem et al., 2022/clinical study [4]	Vertical preparation	40 premolars/20 zirconia and 20 ZL crowns	6, 12, 18, 24, and 36 months	100%/NM	40% scored as 1 and 60% scored as 2	100%	No mechanical complications/NM
Talaat et al., 2022/clinical study [26]	Chamfer	44 teeth/zirconia crowns	6, 9, and 12 months	NM/NM	40.9% score 0 and 59.1% score 1 in gingival inflammation	NM	NM/NM
	BOPT				36.4% score 0 and 63.6% score 1 in gingival inflammation
Serra-Pastor et al., 2021/prospective clinical study [10]	BOPT	74 incisors, canines, and premolars/zirconia core and feldspathic ceramic covering	12, 24, 36, 48, 60, and 72 months	97%/93%	PI: 78.6% score 0; 14.3% score 1; 7.1% score 2	90%	4.1% decementation and complete crown fracture/2.7% pulpitis and vertical fracture
					PD of 4–6 mm in 1.7% of cases
					GR: 2.9% of cases
Agustin-Panadero et al., 2021/prospective observational study [11]	BOPT	65 posterior teeth in both arches/zirconia FPD	12, 36, and 60 months	100%/95%	PI: 35% of 1	NM	10% chipping of ceramic veneer/2.5% irreversible pulpitis
					GI: 30% of 1
					PD: 10% of 3 mm
	Chamfer				PI: 57.9% of 1
					GI: 68.4% of 1,		15% chipping of veneer/2.5% vertical root fracture
					PD: 26.3% of 3mm
Cagidiaco et al., 2019/randomized clinical trial [27]	Feather-edge	25 premolars and molars/zirconia crowns	6, 12, 24, 36, and 48 months	96%/80%	BoP: 48% of cases	NM	15% crowns chipped and 5% irreparable fractures/NM
	Chamfer	25 premolars and molars/zirconia crowns		100%/76%	BoP: 55.5% of cases		5 crowns chipped/NM
Serra-Pastor et al., 2019/prospective study [14]	BOPT	144 all types of teeth (74 crowns and 75 FPDs)/zirconia core and feldspathic ceramic covering	Every 12 months for 48 months	Zirconia crowns 97%; FPDs 96%/97%	Plaque affecting 20% of teeth after 24 months	90%	1.4% porcelain veneer chipping and connector fracture in one FPD/2% pulpitis and vertical fracture
					GR: 1.4% after 24 months
					GI: 12% after 24 months
					PD: 97.9% 0 to 3 mm; 2.1% 3–6 mm after 24 months
Agustin-Panadero, 2018/prospective study [28]	BOPT	149 incisors, canines, premolars (74 crowns and 27 FPDs)/zirconia core and feldspathic ceramic covering	6, 12, and 24 months	100%/NM	80.5% remained without gingival inflammation or bleeding, while 29 (19.5%) showed inflammation and/or bleeding	80%	2% porcelain veneer chipping; 0%
Paniz et al., 2017/prospective randomized clinical study [12]	Chamfer	198 incisors, canines, premolars/zirconia crowns	6 months	NM/ NM	GI: 33.3% score 1; 10.5% score 2; 1.9% score 3	91%	NM/NM
					PI: 15.2% score 1
					BoP: 30.5% score 1
	Feather-edge				GI: 33.3% score 1; 7.5% score 2; 0% score 3
					PI: 9.7% score 1
					BoP: 8.4% score 1
Paniz et al., 2016/prospective randomized controlled double-blind clinical trial [29]	Feather-edge	196 incisors, canines, premolars/zirconia crowns	12 months	NM/NM	GI: 31.5% score 1 and 9.8% score 2	NM	1.88% restoration fracture/NM
					PI: 17.4% score 1 and none score 2
					BoP: 52.2%
					GR: 3.3%
	Chamfer				GI: 33.7% score 1; 11.5% score 2; 1.9% score 3
					PI: 14.4% score1; 3.8% score 2
					BoP: 36.5%
					GR: 11.5%
Poggio et al., 2012/retrospective study [30]	Knife-edge	102 (38 incisors, 13 canines, 29 premolars, 22 molars)/zirconia core and feldspathic ceramic covering	72 months	100%/NM	NM	NM	1.02% porcelain chipping/NM

Note: BOPT - Biologically oriented preparation technique; FPD - Fixed partial denture; ZLS - Zirconia-reinforced lithium silicate; PFM - Porcelain fused to metal; PI - Plaque index; NM - Not mentioned; GI - Gingival index; GR - Gingival recession; PD - Pocket depth; BoP - Bleeding on probing; ↔ -between .

Patient satisfaction was recorded in 5 studies only, with 90% overall satisfaction; the lowest percentage was 80% [28], and the highest was 100% [4]. Only 7 studies documented the survival rate and determined it as 100% [4, 11, 15, 28, 30] and an average of 98% (Cagidiaco et al., 2019) and 96.5% (Serra-Pastor et al., 2019) [14, 27]. Similarly, only five studies reported on the success rate, with findings indicating a 100% success rate for zirconia crowns and 86% for FPD [18]. The reported success rates were 93%, 95%, an average of 78%, and 97% in the studies by Serra-Pastor et al. (2021), Cagidiaco et al. (2019), and Serra-Pastor et al. (2019), respectively [10, 11, 14, 27].

4. DISCUSSION

Establishing an optimal relationship between prosthetic restorations and the periodontium is essential for achieving long-term functional and aesthetic success in FPDs [31]. Historically, horizontal finishing lines have led to issues, such as marginal discrepancies, biological complications, and affected aesthetics due to crown adaptation difficulties [3]. Vertical preparation designs have been proposed to enhance precision at the restoration–tooth interface [5]. These preparations, which lack a defined finishing line, may improve marginal seal and soft tissue stability compared to traditional horizontal designs [27].

The majority of systematic reviews and meta-analyses of existing literature have examined the effect of cemented fixed maxillary and mandibular prostheses on the status of gingival and periodontal health as GI and PI, and concentrated on the category and form of the cemented prosthesis, finishing line location, and prosthesis materials [31-33]. One published meta-analysis study focused on the effect of horizontal, traditional, or conventional preparation on soft tissue surrounding associated with natural, unprepared sound teeth [34]. The impact of vertical preparation designs on patient outcomes and clinical complications in fixed prosthodontics remains inconsistent across the literature, making it difficult to draw definitive conclusions.

Previous studies have characterized survival rate as the duration of the fixed prosthesis in situ, regardless of adjustments made during follow-up, whereas success rate has been referred to as prostheses remaining intact without any clinical intervention [19]. In this review, the average survival rate was 98%. These results have been found to align with prior reviews and meta-analyses that have indicated vertical techniques to demonstrate excellent long-term survival potential when performed correctly [13, 19]. Success rates have been found to exhibit more variability, especially for horizontal preparations. Cagidiaco et al. (2019) reported a success rate of 76%, influenced by factors, such as material selection (zirconia versus metal-ceramic), biomechanical challenges, and occlusal loading variations [27]. These discrepancies highlight the importance of evaluating case-specific factors, such as masticatory forces and parafunctional habits, in the choice of preparation design [33].

In this review, six studies [10-13, 26, 27, 29] compared BOPT with chamfer finishing lines. Agustín-Panadero et al. (2021) and Paniz et al. (2017) reported lower PI and GI for BOPT than chamfer with 60 months of follow-up [11, 12]. Talaat et al. (2022) found comparable gingival inflammation outcomes between BOPT (63.6%; score 1) and chamfer (59.1%; score 1) [26]. For BoP, Cagidiaco et al. (2019) reported 48% BoP with feather-edge versus 55.5% with chamfer, suggesting the superiority of BOPT [27]. Moreover, Paniz et al. (2017) observed lower BoP (8.4%) with the feather-edge technique than with chamfer (30.5%) at 6 months [12]. However, Paniz et al. (2016) observed higher BoP (52.2%%) with the feather-edge technique than with chamfer (36.5%) at 12 months [29]. GR outcomes also varied; Serra-Pastor et al. (2021) [10] reported 2.9% GR with BOPT, whereas Paniz et al. (2016) noted 11.5% GR with chamfer [29].

Throughout the follow-up intervals, both groups showed a trend of increasing PD while remaining within clinically acceptable ranges (≤3 mm), particularly with BOPT. Over 80% of cases in the studies carried out by Gonzalez-Bonilla et al. (2024) and Serra-Pastor et al. (2019) had PD ≤3 mm, which indicated stable periodontal health [14, 18]. Deeper pockets (4–6 mm) were rare but more common in chamfer cases [11]. This outcome has been found to be in accordance with other studies that have demonstrated that the placement of margins within the supracrestal tissue can lead to gingival inflammation and possible recession or pocket formation [3, 32]. Despite various clinical factors influencing periodontal health, effective assessment, treatment, self-care instructions, and adherence to maintenance protocols are crucial to mitigating the negative effects of fixed restorations.

The reviewed studies have indicated a high overall patient satisfaction rate of 90%, though mechanical complications, such as ceramic veneer chipping, have remained a concern, with reported incidence rates ranging from 1.4% (14) to 15% [11, 27]. BOPT demonstrated lower mechanical failures of 10% for ceramic chipping and 15% for chamfer [11], whereas feather-edge demonstrated higher mechanical failures of 15% for ceramic chipping and 5% for chamfer [27]. Other studies focused on vertical preparations have reported a 4% PFM chipping rate over 60–84 months as the most common complication (Gonzáles-Bonilla et al., 2024). Serra-Pastor et al. (2021) have found 4.1% crown fractures to be associated with teeth prepared using BOPT [10]. Knife-edge preparations have shown lower complication rates, with Poggio et al. (2012) reporting 1.02% porcelain chipping over 72 months [30]. Biological failures, though less frequent, have included irreversible pulpitis and vertical root fractures associated with chamfer and BOPT [10, 11, 14].

In addition to the clinical trials and cohort studies included in this systematic review, numerous case reports and observational studies have further underscored the promising efficacy of vertical tooth preparation techniques [35]. Agustín-Panadero and Solá-Ruiz (2015) have highlighted the biological advantages of BOPT in maintaining gingival health and stability through controlled tissue remodeling, particularly in aesthetic zones [36]. Recent case reports have further illustrated the efficacy of vertical techniques in achieving optimal aesthetic and functional outcomes for patients with limited clinical crown height, underscoring them as a minimally invasive approach and their adaptability to advanced materials, such as zirconia [37, 38]. These findings have been found to align with the broader literature, which frequently associates vertical preparation with reduced procedural trauma, enhanced marginal adaptation, and improved soft tissue integration [39-41].

The collective evidence reinforces the clinical potential of BOPT techniques, particularly in complex cases requiring structural preservation or periodontal rehabilitation [3, 7]. This growing body of evidence supports the paradigm shift toward vertical preparation as a viable alternative to conventional methods, though its broader adoption necessitates further high-quality, long-term investigations.

5. LIMITATIONS

Only literature published in the English language was included in this study, which represents a limitation. This language restriction may have excluded relevant data and limited the exchange of knowledge from studies published in other languages. The small sample size and limited number of studies on certain outcomes, such as success rates and level of patient satisfaction, may further limit the generalizability of the results. The evidence obtained from the current analysis has supported the usage of vertical preparation, especially BOPT, because it is associated with better periodontal health status, increased patient satisfaction, and lower complications. Future research should focus on periodontal health parameters with similar case selection criteria, larger sample sizes, and long-term follow-ups, and should compare various vertical preparation techniques. This approach could enhance the evidence base for promoting vertical preparation as a standard practice or maintaining it as a specialized approach.

CONCLUSION

This systematic review has demonstrated vertical preparation techniques, such as BOPT and feather-edge designs, to be associated with favorable periodontal outcomes, including reduced plaque accumulation, gingival inflammation, and recession. Survival rates (≥95%) and patient satisfaction (≥90%) have also been found to be high. Mechanical complications, primarily ceramic chipping (1.4%–15%), and rare biological issues (2%–2.7%) have underscored their reliability. While longer-term studies are needed, vertical preparation emerges as a promising approach for tooth-supported fixed prostheses and for balancing periodontal health and prosthetic success.

REFERENCES